Petroleum Waxes - University of Illinois at Chicago · annual production of the combined total of...

try as a gelling agent for organic solvents·and as a raw material used. in lipstick formulations for the cosmetic market. Carnauba wax is recognized generally as safe by the United States Food and Drug Administration.

Candelilla wax is harvested from the shrubs Eurplwrbiea antisiphilitica, E. cerifera, and Pedilanthus pavonis in Mexico and southwest Texas. The candelilla wax is recovered after the entire mature plant is uprooted and immersed in acidified boiling water. During the immersion, the candelilla wax floats to the surface and is skimmed off. The primary market for candelilla wax is cosmetics where it is a component in lipstick formulations. The chemical composition of carnauba and candelilla wax is listed in Table 2.

Synthetic waxes are derived from either the Fischer-Tropsch process [7] or by ethylene based polymerization processes [8]. The Fischer-Tropsch (F-T) process originated in Germany in the 1920s and is illustrated schematically in Eq I. The F-T process was developed to synthesize hydrocarbonsand oxygenated compounds from a mixture of hydrogen andcarbon monoxide. During World War II, the F-T process was

· used by Germany to produce fuels from coal-derived gas. Thefirst commercial plant in South Africa started in 1955 atSasolburg, using coal as a feedstock. The so-called Sasol process is illustrated in Fig. I [9]. This plant produces waxes, fuels, pipeline gases (i.e., ethylene, methane), and other products using a fixed bed catalyst F-T process. During the F-Tprocess, carbon monoxide, which is generated from coalgasification, is reacted under fixed-bed conditions usinghigh-pressure at approximately 220°C in the presence of aniron catalyst to produce synthetic hydrocarbon waxes, asshown in Eq 1. Typical reaction products that may be derivedfrom the F-T process are listed in Table 3.

2nH2 + nCO -> Cn H2n + nHzO (1)

Poly(ethylene) waxes may be prodticed by the industrial polymerization of ethylene using high or low pressure ethylene polymerization technology [10], or as thermal decomposition products of the polyethylene polymers. The molecular weights and melting points of the synthetic waxes as compared with the Fischer-Tropsch waxes are listed in Table 4.

The market stability of pricing and availability of insect and vegetable waxes is affected by climate conditions and natural disasters. With the advent of the petroleum industry, the waxes from mineral and synthetic sources surpassed the annual production of the combined total of the other two wax categories. Waxes from insect and vegetable sources are mixtures of long chain fatty acids, esters of aliphatic alcohols, and hydrocarbons. Waxes from mineral origins are chemi-

525

Petroleum Waxes G. Ali Mansoori 1, H. Lindsey Barnes 2, Glenn M. Webster3

Chapter 19, Pages 525-556, 2003Manual 37 - Fuels and Lubricants Handbook: Technology,

Properties, Performance, and TestingASTM Manual Series: MNL37WCD

___________________________________P.O. Box C700, ASTM International, West Conshohocken, PA 19428-2959

____________________________________WAXES ARE USUALLY SOLID AT ROOM TEMPERATURE because they contain linear paraffinic hydrocarbons with carbon chains of various lengths. Waxes can vary in consistency from easily kneadable to brittle. They exhibit relatively low viscosity at temperatures slightly above their melting point. The appearance of waxes Can vary from translucent. to opaque, but they are not glassy. The consistency (i.e., hardness) and solubility of waxes depends on the temperature at which they are observed.

The use of waxes dates back more than 5000 years. As early as 4200 B.C. the Egyptians extracted a waxy �ubstance from the honeycomb of bees and used it to satw:ite · linen wrappings of mummies [!]. The spulptured porittaffof the deceased decorating a coffin cover was often modeled in beeswax and painted with pigmented beeswax. Another use of wax was in the preparation of erasable writing tablets. Fastening together several tablets with fiber produced forerunners. of the modern book [2].

Waxes are classified by the matter from which they are derived: insect, vegetable, synthetic, and mineral [3]. Beeswax is an example of insect wax. The chemical composition of beeswax is. unique and its characteristics vary with the species of the honeybee. Apis mellifera is the most common cultured bee in the world and will provide a chemical generalization of composition of wax for this species [ 4 ]. Beeswax is secreted in eight glands on the underside of the worker bee. Bees are believed to secrete one pound of wax £Or every eight pounds of honey they produce. Since secreted beeswax readily absorbs color, the final color of the beeswax is influenced by the source of the pollen. A typical composition analysis of beeswax is provided in Table I. Beeswax is extracted by melting or boiling the honeycomb in water and has applications in pharmaceuticals and cosmetics, and is the primary component of religious candles.

Vegetable waxes are extracted from the leaves, bark, and berries (seeds) of plants and trees. Abnost all multi-cellular plants are covered by a layer of wax [5]. Only a few species grown in semiarid climates produce enough wax to be commercially viable for recovery. Carnauba and candelilla wax are two of the most common vegetable waxes that are commercially marketed [6]. Carnauba wax is removed from the dried leaves (fronds) of palm trees grown in the northeast region of Brazil. Carnauba is utilized in the polish paste indus-

1 University of Illinois at Chicago, Chicago, IL 60607-7052.

2 CITGO Petr. Corp., H.W. 108 S., P.O. Box 1578, Lake Charles, LA

70602. 3 63 Rocklege Rd., Hartsdale, NY 10530.

526

TABLE I-Compositional analysis of beeswax. Component

Monoesters, C1sli.31COOC3oH61; C2sHs1COOC30�1 Diesters, triesters, hydroxy diesters Free fatty acids, C23COOH-C31COOH Free fatty alcohols, C340H-C360H Hydroxy-monoesters, C14H29CH(OH)COOC26H61

Hydrocarbonsa, C2sHs2-C31H64Moisture and mineral impurities

Amount in wt. %

55-65 8-12

9.5-10.5 1-28-10

12-151-2

aHydrocarbons most commonly found in beeswax include nonacosane (C2�) and nentriacontane (C31H64).

¢-, TABLE 2--Chem.ical composition of camauba and candelilla wax.

Component Carnauba (wt.%) Candelilla (wt.%)

Monoesters Fatty alcohols Free fatty acids Hydrocarbonsa

Resins Moisture and inorganic residue

83-88%2-33-4

1.5-3.0 4--6

0.5-1

28-30%2-37-9

49-57

4--6 2-3

aHydrocarbons commonly found in camauba and candelilla wax are principally hentriacontane (C31l¼) and tritriacontane (C33f4s).

COAL P0WER PLANT

STEAM

NH, MWCAS TARACID PIJBI1'JCAIION

COz+lfiS

1lREGAS

C,

0 f---+CO,

C,IC,

WATER

AIR

w:

.-------,

C,,

OILS

FIG. 1-Generalized Sasol Plant for hydrocarbon synthesis . by the_ Fischer-Tropsch Process.

TABLE 3-Products derived from the Fischer-Tropsch process.

Product

Paraffins (i.e., methane, ethane, propane, and butane)

Olefins (i.e., methylene, ethylene, propylene, and butylene)

Gasoline (Cs-Cu) Diesel (C,2-C") C19 to C23 Medium Wax (C24-C3s) Hard Wax (>C,s) Water soluble non-acid chemicals Water soluble acids

Approx. Typical Yield (wt.%)

7.2

5.6

18.0 14.0 7.0

20.0 25.0 3.0 0.2

TABLE 4-Comparison of Fischer-TroJ)Sch waxes with other synthetic waxes.

Type of Wax Molecular Weight Melting �oints; °C

Fischer-Tropsch wax 500-1200 85-110Low Pressure polyethylene 900-3000 90-125

wax High Pressure polyethylene 500-4000 85-130

wax Pyrolysisa waxes 1000-3000 90-130

aPyrolysis waxes are derive<J from thermo-cracking of polyethylene.

cally inert and are primarily composed of straighfchain (paraffinic) hydrocarbons.

Petroleum wax may vary compositionally over a wide range of molecular weight, up to hydrocarbon chain lengths of approximately CS0-C60. It is typically a solid at room temperature and is derived from relatively high boiling petroleum fractions during the refining process. Petroleum waxes are a class of mineral waxes that are naturally occurring in various fractions of crude petroleum. They have a wide range of applications that include: coating of drinking cups; an adhesives additive; production of candles and rubber; as components of hot melts, inks, and coatings for paper; and they can be used in asphalt, caulks, and binders. This chapter will provide a review of petroleum waxes including history, production, types, chemical composition, molecular structure, and property testing.

DISCUSSION

Classification of Crude Oils and Chemical Structure of Ingredients

Petroleum crude oil, commonly referred to as crude oil, is a complex mixture of hundreds of compounds including solids, liquids, and gases that are separated by the refining process. Solid. components at room temperature iriclude asphalt / bitumen and inorganics. Liquids of increasing viscosity vary from gasoline, kerosene, diesel oil, and light and heavy lubricating stock oils. Also included are the major components of natural gas, which include methane, ethane, propane, and butane (11).

An elemental analysis of crude oil shows that it consists of primarily two elements: hydrogen (11-14%) and carbon

Petroleum Waxes G.Ali Mansoori, H. Lindsey Barnes, Glenn M. Webster

Chapter 19, Pages 525-556, 2003, Manual 37 - Fuels and Lubricants Handbook: Technology, Properties, Performance,

and Testing, ASTM Manual Series: MNL37WCD

____________________________________

CHAPTER 19: PETROLEUM WAXES 527

TABLE 5-Crude oil content.

Crude Type Solvent Neutral Oil Base Oil Wax.Content Sulfur and Nitrogen Asphalt API Gravity" ASTM Test Method

Paraffinic base Yes Yes <10% Low No >40 E-1519Naphthenic base No Yes No Low No <33 D-2864Intermediate base No Yes <6% Low Yes 33-40 D-8Asphaltic base No Yes 0% High Yes <10 D-1079

a American Petroleum Institute gravity is an arbitrary scale expressing the density of liquid petroleum products. The measuring scale is calibrated in terms of degree API (0API) and can be calculated in terms of the formula: 0 AP[= 141.5/(SGL[60°F)) - 131.5 where SGL stands for liquid specific gravity with respect to water. The higher the value of API gravity, the more fluid the liquid.

(83-87%). Crude oil hydrocarbons contain long hydrocarbon chains (saturated and unsaturated), branch structures, and ring structures, with each having specific physical and chemical properties. Small quantities of other compounds containing sulfur, oxygen, nitrogen, carbon, and hydrogen are frequently present in crude oils.

Crude oils are generally classified based on their predominant hydrocarbon structure type, as shown in Table 5. The types are :['.eferred to as paraffi.nic, naphthenic, intennediate (mixture of paraffinic and naphthenic crude), and asphaltic base crude (12].

Paraffinic hydrocarbon fractions are saturated linear or branched alkanes. Naphthenic fractions contain five and six carbon cyclic alkane (alicyclic) structures. Naphthenes are monocyclic in the lower-boiling fractions (i.e., gasoline) and polycyclic in the higher-boiling fractions (i.e., lubricating oils) (13]. The asphaltic crudes contain unsaturated aromatic structures containing rings of five and six member carbon atoms. Aromatics are defined as those classes of organic compounds that behave chemically like benzene. They are cyclic, unsaturated organic compounds that can sustain an induced electronic ring current due to delocalization of electrons around the ring. Aromatic base oils contain 20-25% aromatic compounds. A constituent of asphaltic crudes is asphaltene. Asphaltenes are defined as the high molecular weight nonhydrocarbon fraction of crude oil precipitated by a designated paraffinic naphtha solvent at a specified temperature and solvent-oil ratio (14]. Like the naphthenic crude, the aromatic rings are monocyclic in the lower boiling fractions and polycyclic in the higher boiling fractions. Various ASTM test methods listed in Table. 6 are used for sampling, separation, and characterization of petroleum fractions.

Petroleum waxes are derived from both paraffinic and intermediate crude oils and are composed of three basic carbon structures (i.e., linear, branched, and ring) that are characteristic of the crude oil.

Production, Transportation, and Refining of Waxy Petrolenm Crndes]

The majority of crude oils produced around the world contain substantial amounts of paraffin wax. These compounds, sparingly soluble in solution components of the crude oils, crystallize at lower temperatures and are the major contributors to petroleum wax deposits [IS]. The wax present in petroleum crudes primarily consists of paraffin hydrocarbons (C18-C36), known as paraffin wax, and naphtenic hydrocarbons (C30-C60). Hydrocarbon components of wax can exist in various states of matter (gas, liquid, or solid) depending on their temperature and pressure. When these hydrocarbons freeze, they form crystals, which are known as macrocrys-

TABLE 6-ASTM test methods used for sampling, separation, and classification of various oil samples and the procedures used.

Test Method

D4057

D270 D4007

D86 D2007

D2425

D2549

D2786

D2887

D3239

D3279

Procedure and Application

Practice for manual sampling of petroleum and petroleum products

Sampling of petroleum and petroleum products Centrifuge method for determination of water and

sediment in crude oil Distillation of petroleum products Clay-gel absorption chromatography for oil- samples

of initial boiling point of at least 260°C (500°F} into the hydrocarbon types of polar compounds, aromatics and saturates, and recovery of representative fractions of these types

Mass· spectrometry for classification of hydrocarbon typ'es-in middle-distillate

Elution chromatography for separation of representative aromatics and non-aromatics fractions of high-boiling oils, between 232 aod 538°C (450 aod 1000°F)

High ionizing voltage mass spectrometry for hydrocarbon types analysis of gas-oil saturate fractions

Gas chromatography for boiling range distribution ofpetroleum fractions

High ionizing voltage mass spectrometry for aromatic types analysis of gas-oil aromatic fractions

Titration for determination of the weight percent of asphaltenes as defined by insolubility in normal heptane solvent

talline wax. Those formed from naphtenes are known as microcrystalline wax. A hydrocarbon in pure state has definite boiling and freezing (or melting) points, which can be measured in the laboratory (16]. Knowing the intermolecular energy parameters or critical properties and acentric factor and/or refractive index of hydrocarbons, one can predict their boiling point using vapor pressure correlations or equations of state as discussed in Section I of this report. However, such methods are not capable· of predicting pure hydrocarbon freezing points. There are other methods that can be used to predict hydrocarbon and wax freezing (melting) point, which include but are not limited to variational statistical mechanical theory (17] and cell-lattice theories (18].

Waxy Crude Oil

A waxy crude usually consists of: (a) a variety of light and intermediate hydrocarbons (paraffins, aromatics, naphtenic, etc.); (b) wax as defined above; and (c) a variety of other heavy organic (non-hydrocarbon) compounds, even though at very low concentrations they include resins, asphaltenes, diamondoids, organometallics, etc. When the temperature of a waxy crude oil is lowered to its cloud point, first the heavier fractions of its wax content start to freeze out. ,Upon lowering of the temperature of a crude oil to its pour point al-

---;,_;:_ - -

528 MANUAL 37: FUEI.S AND LUBRICANTS HANDBOOK

most all the fractions of its wax content will freeze out. A waxy crude is characterized by its cloud point and pour point, which are measured according to ASTM Test Methods D 2500 and D 97, respectively, as they are dis.cussed later in this report.

A clean waxy crude is defined as a crude oil in which there exists only hydrocarbons and wax as its only heavy organic constituent. As the clean waxy crude flows through a cold

·pipe or conduit (with a wall temperature below the cloud· point of the crude) wax crystals may be formed on the wall,which could then grow until possibly the whole inner wall iscovered with the encapsulating oil �ide the wax layers. Asthe wax thickness increases, pressure drop across the pipeneeds to be increased to maintain a constant flow rate. As aresult, the power requirement for the crude transport will increase. The arterial blockage problems of clean waxy crudecan be efficiently controlled by insulation and heating of thepipe to a temperature above its cloud point. Most of the existing wax deposition problems of the clean waxy crudes aredue to the lack of proper insulation and heating systems. Asa result, application of chemical anti-foulants and frequentuse of pigging operations have become necessary [15]. Regular paraffinic or waxy crudes are widespread. The major complex systems problems related to the production, processing,and transportation of these medium-gravity fluids is not justcrystallization of their wax content at low temperatures, butthe formation of deposits that do not disappear upon heating,and will not be completely removed by pigging.

Regular waxy crudes are not clean and, in addition to wax,they contain other heavy organics such as asphaltene, resin,etc. [1 SJ. Asphaltenes do not generally crystallize upori coolingand, for the most part, they may not have definite freezingpoints. Depending on their natures, these other heavy organicswill have different interactions with wax, which could eitherprevent wax crystal formation or enhance it. Existence ofbranched paraffins, aromatics, naphtenes, and resins inpetroleum, however, contribute less to µtese deposits, but modify their crystallization behavior. However, asphaltene presence in the crude oil could prevent or erihance wax depositiondepending in the microscopic nature of asphaltene [19 ,20].

The precipitation of wax from petroleum fluids during production and transportation may give rise to a variety of problems [17]. One ofthe main problems observed is deposition ofsolid material on well and pipe walls as demonstrated in Fig.2. This happens if (a} the temperature of the wall is below thecloud point of the oil, {b) a negative radial temperature gradient is present in the flow, (c} the wall friction is high enoughfor wax crystals to stick to the wall, and (d} asphaltene presentin the crude oil has already deposited and has increased thefriction of the wall ( changed of wettability) and acting as mortar for the sticking together of wax crystals. Wax crystallization may cause three problems: (a} higher viscosity, whichleads to pressure losses, (b) high yield stress for restartabilityof flow, and (c} fouling of petroleum flow arteries [15].

To predict wax deposition tendency of a crude oil it is important to know its composition for paraffin wax and the other components present in, or added to, the crude oil; their composition distributions; and the pressure and temperature of the system. Thermodynamics and statistical mechanics of phase transitions in polydisperse mixtures can be utilized to develop predictive models for wax deposition in petroleum fluids [17].

FIG. 2-Pipeline petroleum transport plugging due to wax and other heavy organics depositions (Courtesy of Phillips Petroleum Company).

To predict the deposition as a function of time, principles of energy and mass conservation, the Jaws of diffusion, and the principles,of phase transitions need to be considered [21,22]. In order to prevent or remediate arterial blockage/fouling and facilitate the production of regular waxy crudes, many issues must be undertaken: (a} detailed fluid properties characterization, (b} production scheme alternatives, (c} retrograde condensation and deposition behavior prediction, ( d) onsets of deposition studies, (e) equipment and facility options, (f) design and use of chemical anti-foulants and/or pour-point depressants and blending alternatives, (g} performance specification and maintenance planning, and (h) transportation, storage, and blending studies [23,24].

Petroleum Refining . Crude oil is first desalted if salty, deasphalted if asphaltenic, and dewaxed if highly waxy, before it is distilled in an atmospheric distillation unit to separate light ends (gases}, naphtha, gasoline, jet, kerosene, gas oil distillate, and residuum (resid) (see Fig. 3). The residuum (resid) remaining after the atmospheric distillation is then further fractionated in a vacuum distillation unit into fractions that are distinguishable by viscosity for further processing into lubricating oil base stocks. Wax is concentrated in the distillate stream and the residuum fraction is used to produce the base oils for lubricant formulation. Both the distillate and residual lube fractions (stock) contain unde.sirable constituents such as aromatics that must be removed by extraction to yield base oils that are thermally stable with a sufficiently high viscosity index• product. The distillate fraction is extracted with a sol-

4 Viscosity Index is defined as V.I. = (µL - µx)/(µL - µH), where µL is the viscosity at 100°F of the zero-V.I. oil, µH is the viscosity at 100°F of thel00 V.I. oil, and µxis the viscosity at-100°F of the unknown (test) oil. See ASTM D 567 and D 2270 for further detail. A measure of the magnitude of viscosity changes in lubricating oils with changes in temperature. The higher the viscosity index number, the more resistant the oil is to change in viscosity.

vent (such as furlural) that has a greater solubility (selective solvent) for the components having a low viscosity index. The residuum fraction is extracted with propane to remove bitumen (asphalt) and resinous material. The desirable oil and wax component is solubilized for further processing.

The nonsoluble portion of the distillate extraction and the soluble portion of the residuum fraction are referred to as the raffinate phase and both contain the more paraffinic oil. Wax, which typically exhibits a hlgh viscosity index, remains in the raffinate phase for further processing. Because the raffinate produced from the extraction process contains wax, whlch crystallizes at relatively hlgh temperatures (> IS°F =-9.4°C), the fluidity of the base oil that exhibits a hlgh pour

Desaldng

Nater

Crude Storage Tank

v&ccum Dis�on


point (i.e., the temperature where the oil ceases to be fluid) is reduced.

Solvent Dewaxing Process

The solvent dewaxing process can be divided into three distinct sections: (a) crystallization of the wax components by dilution and chllling, (b) filtration of the wax from the solution of dewaxed oil and solvent, and (c) recovery of the solvent from the dewaxed oil and wax products [25]. To overcome the hlgh pour point, a solvent dewaxing process has been developed to remove the wax from lubricating oil basestocks, as shown in Fig. 4. The most widely used solvent dewaxing pro-

Water

Naplrta

Distillate

Gasoline, Jet, Kerosene

Dewaxed Oil

FIG. 3-Schematlc Illustration of various possible locations of wax production in petroleum refining.

Oily Wax Receiving

Oily Wax 1----..-C.,,stallization Storage

.Fliall Oil

S!an,p

Stop W.XIB' Faall 01

--

.......

Product Shipped

mended Product

..........

Wu: a

sai. .. t

Prailllc!Wu:

FIG. 4-Solvent dewaxing process for the removal of wax from lubricating oil slackwax basestocks.

530 MANUAL 37: FUELS AND LUBRICANTS HANDBOOK

90

80

70

00

- 50 � 40 -

'S 30 ·15 20""

1 10

s 0 u

•IO

-20

-30

-40

.50

30

Oil Phase Sepa�tion

40 50 00 W 80 90 �

% MEK Content In Dewu Solvent FIG. 5-lllustration of the effect of the ratio of MEK to the

petroleum fraction being dewaxed on the resulting cloud point of the mixture.

cesses are based on solvent mixtures of methyl ethyl ketone . and toluene, methyl ethyl ketone and methyl isobutyl ketone, or methyl isobutyl ketone itself. Figure 5 illustrates the effect of the ratio of MEK to the petroleum fraction being dewaxed on the resulting cloud point of the mixture. In the dewaxing process, the raffinate (feedstock) is diluted with solvent and heated 15-20°F (-8-11°C), above the cloud point of the raffinate/solvent mixture ( or slurry) and chilled at controlled rates in double-pipe scraped-surface heat exchangers and chillers. The slurry is chilled to 5-20°F ( -3-11 °C) below the desired pour point of the oil. When the wax/solvent solution is cooled, wax crystals precipitate from the solution, which are then removed by filtration using a rotary vacuum filter. The crys

tallized wax forms as a layer (cake) on the surface of the rotary vacuum filter. The wax cake (filtrate) is washed with a spray of a cold solvent to remove any residual oil before being discharged from the primary filters. At this point, the wax contains 10--40% oil and is referred to as "slack wax" if it is derived from the distillate lube fraction, or "petrolatum" if it is derived from the residual lube fraction. Figure 6 illustrates the effect of solvent dilution ratio on the amount of residual oil content in the slack wax.

To produce waxes with lower oil contents ( <5%), an additional dewaxing process is performed. The wax cake from the primary filter is diluted with additional solvent and filtered in a second (repulp) rotary vacuum filter using the same operating conditions as the primary filters to obtain the desired wax oil content.

The solvent is recovered from the dewaxed oil filtrate by flash vaporization and distillation. The solvent is recycled for future use in the dewaxing process. Residual solvent in the wax is recovered by flash vaporization and is recycled for future process use.

Dewaxing Process Variables

Wax production yield, oil content of the wax, and the pour point of base oil are directly affected by variables of the

dewaxing process. The major process variables include: 1) solvent composition, 2) feedstock composition, 3) solvent dilution procedure, 4) filtration temperature, 5) filtration procedure, and 6) solvent recovery method. 1. Ketone based solvents are excellent solvents for oils at low

temperatures necessary to remove the wax by filtering. Diluting the raffinate with too much ketone-based solvent cancause the oil to separate into a distinct layer. Oil phase separation will adversely affect the yield of wax and result inthe wax portion having an undesirable higher oil content.The likelihood of oil phase separation can be determinedexperimentally by maintaining a constant solvent dilutionratio and changing the percentage of ketone content.

2. If the raffinate feedstock contains a high proportion ofparaffinic content, it will have a high viscosity or viscosityindex. An oil phase separation can occur when a ketonebased dilution solvent is mixed with the raffinate.

3. The amount of dilution with the solvent can affect the oilcontent of the wax. Using a solvent dilution greater than 2parts solvent to 1 part raffinate will result in a re.duction ofthe oil content of the wax.

4. The cooling temperature used to crystallize the wax duringthe filtration process can affect the oil content of the waxand the desired physical properties such as melting pointand hardness. If the dilution solvent is too cold or low cooling temperatures are used, the crystal size of the wax formedon the surface of the rotary filter will be small and will retain more oil. As the dewaxing temperature is reduced,

, softer and lower melting point wax fractions will increasethe overall production yield. As illustrated in Table 7, as a

i 40. -

I 30

a

6 M '20

I

10

0

�· 2;I 3'I 4:1 5;1 6;1

--

FIG. 6-lllustration of the effect of solvent dilution ratio on the amount of residual oil content in the slack wax.

TABLE 7-Effect of dewax temperature on wax.

Dewax Temperature

("F) ("C)

60 15.6 55 12.8 so 10.0

Wax Yield (%)

62

67

72

Wax Melt.Point (ASTM D 127)

("F) ("C)

141 60.6 139 59.4

137 58.3

Wax Needle Penetration

@ 77°F (25°C) (ASTM D 1321)

11 13

16

lower dewaxing temperature is used, wax yield increases and the melting point and softness change.

5. The dewaxing process is performed to maximize the recovery of the wax with the desired oil content and physicalproperties such as melting point and hardness. This requires maintaining a uniform thickness (less than 2.5 cm)of the wax cake on the rotary filter by controlling the process temperatures and rotational speed of the filter. Applying wash solvents (for reducing oil content) uniformly prevents cracking of the wax cake. Diluting with adequaterepulp solvent is necessary to provide a sufficiently fluidraffinate.

The Wax Finishing Process

The last step in producing petroleum waxes is the finishing process. This process involves the removal of odor and questionable color. In addition, the finishing process may involve steps to reduce the polycyclic hydrocarbons to a level that meets the Food and Drug Administration regulations for food contact.5

Wax color removal may be performed by flowing wax through a static bed of activated clay or bauxite. There is a production loss in the amount of wax after completing the clay or bauxite contact process. ThiS loss is attributed tO absorption of the wax on the clay or bauxite medium and the production loss is greater for darker colored waxes. Newer finishing process technology is based on hydrofinishing (fixed bed catalytic process using hydrogen) and doesn't require any filtering medium. Hydrofinishing has the advantage of processing waxes with negligible product loss [26].

If the wax exhibits a questionable odor (such as extraction or dewaxing solvent odor), the wax may be steam stripped (distilled) to remove traces of processing solvent. Hydrofinishing may also be used to produce odor free waxes. After the wax has completed the finishing process step, it can be shipped to consumers; either in solid form (i.e., 22 kg cartons) or as a molten liquid (in specialized tanks with electrical heaters or steam coils).

Types of Petroleum Waxes

There are two general types of petroleum waxes that are produced during the dewaxing process. Wax that is obtained from the distillate lubricating oil fractions is known as macrocrystalline wax (paraffin wax), and wax derived from the residual distillate lubricating oil fraction is referred to as microcrystalline wax (microwax). This nomenclature is based on the crystal structure of the wax as seen through a microscope (microstructure). A paraffin wax can be distinguished from a microwax by its larger c:rystal structure. Paraffin waxes usually exhibit plate-like crystal structures while microwaxes exhibit needle-like crystal structures.

The composition, nomenclature, and physical properties of petroleum are related to the refinery process used in their production. Slack wax is a refinery term for distillate-derived waxes that have oil contents ranging from 3-40% by weight oil. Scale wax is a distillate wax that has an oil content be-

5 FDA regulations for waxes, 21 CFR 172.886 and 21 CFR 178.3710.


tween 1 and 3%. Petrolatums are derived from the residual lubricant fractions with oil contents between 10 and 30%

Compositional and Molecular Characteristics of Petroleum Wax

Paraffin waxes consist predominately of a mixture of straight chain saturated hydrocarbon molecules (normal-alkanes) with the chemical formula C,,H20+2 with n e: 16 [27,28]. In order to demonstrate the physical properties of straight chain saturated hydrocarbon molecules, Table 8 is reported as taken from Ref 28. In this table the molecular weights, melting points, latent heats of fusion, densities (at 20°C), specific heats in solid and liquid states, and boiling points of the normal alkanes from C1 to C100, all at atmospheric conditions, are reported. According to this table, the first four alkanes of the series, (from methane, CH., up to butane, C4H10) are gaseous at room temperature and atmospheric pressure. The alkanes between Cs and C17 are liquids and alkanes with more than 17 carbon atoms are waxy solids at room temperature. The melting points and heats of fusion of alkanes increase with their number of carbon atoms. In addition to the n-alkanes, paraffin waxes may contain varying amounts ofiso- and cyclo-alkanes (i.e., branched chains and aliphaticrings). Typically, paraffin waxes contain carbon atom chains_ __of C18 to C44. Their macrocrystalline structure is illustrated inFig. 7. Their plate-like crystal structures are illustrated by anatomic force microscope image given in Fig. 8. Their molecular weights are usually less than 450 and their kinematic viscosity at 100°C (212°F) will usually be less than six centistokes. Being derived from distillate fractions, paraffin waxeshave distinct boiling point curves that consist of a minimumand maximum value.

Microcrystalline waxes contain higher proportions of isoand cyclo-alkanes (naphthenic) than paraffin waxes. Microrystallline waxes exhibit molecular weights between 500 and 700 with carbon atom chains ranging typically from C23 to C85 in length. Their microcrystalline structure is illustrated in Fig. 9. Microcrystalline waxes (microwaxes) exhibit kinematic viscosities greater than 10 centistokes at 100°C (212°F). Because microcrystalline waxes are derived from residual fractions, they do not have a distinct boiling range. Physical properties of microcrystalline waxes vary with the type of crude oil and processing conditions used to produce the wax. Typically, m.icrocrystalline, naphthenic waxes exhibit needle-like microstructures.

Intermediate wax properties are intermediate between those exhibited by paraffin and microcrystalline waxes. They generally exhibit viscosities between 6 and 10 centistokes at 100°c (212°F) and a melting point between 155-165°F ( -68-7 4 °C). Intermediate waxes are derived from the highestboiling distillate lubricating oil fraction and like paraffinwaxes, they exhibit a distinct boiling point range.

Petrolatums are soft, unctuous products having a melting point between !00--149°F (-38-o5°C). The term "unctuous" means "smooth and greasy" in texture. Petrolatums are generally produced from the same residual oil fraction as microcrystalline waxes and can be prepared by controlled blending of microcrystalline wax with mineral oil. Petrolatums generally exhibit oil contents greater than 10% and are marketed with colors that vary from dark brown to white .. Table 9 lists the general physical properties of the different petroleum waxes.


TABLE 8---Physical properties of n-Alkanes (28].

Latent Heat Specific Heat (/mol K)

No.of Melting Pt of Fusion Density at 20°C Solid at Liquid at AlkaneS CAtoms Mol. Wt (K) (kJ/kg) (kg/m3) 298K 353K

Methane 1 16 90.68 58 0.658 (g) Ethane 2 30 90.38 95 0.124 (g) Propane 3 44 85.47 80 1.834 (g) Butane 4 58 134.79 105 2.455 (g) Pentane 5 72 143.45 117 621 (I) 0167.2 Hexane 6 86 177.83 152 655 (I) 195.4 Heptane 7 100 182.55 141 679 (I) 225.0 Octane 8 114 216.37 181 699 (I) 254.2 Nonane 9 128 219.65 170 714 (I) 284.5 Decane 10 142 243.50 202 726 (I) 314.5 Undecane 11 156 247.55 177 737 (I) 345.0 Dodecane 12 170 263.55 216 745 (I) 376.0 Tridecane 13 184 267.75 196 753 (!) 406.9 Tetradecane 14 198 278.95 227 759 (I) 438.5 Pentadecane 15 212 283.05 207 765 (!) 470.0 Hexadecane 16 226 291.25. 236 770 (!) ---,__ 501.5 Heptadecane 17. 240 295.05 214 775 (s) 534.3 Octadecane 18 254 301.25 244 779 (s) 485.4 564.4 Nonadecane 19 268 305.15 222 782 (s) • 514.6* 618* Eicosane 20 282 309.75 248 785 (s) 544.3 658* Heneicosane 21 296 313.35 213 788 (s) 570.7* 698* Docosane 22 310 317.15 252 791 (s) 598.1 * 739.0 Tricosane 23 324 320.65 234 793 (s) 625.0* 772.0 Tetracosane 24 338 323.75 255 796 (s) 651.4* 805.0 Pentacosane 25 352 326.65 238 798 (s) 670.4* 815.9 Hexacosane 26 366 329.45 250 800 (s) 677.8 870.0 Heptacosane 27 380 331.95 235 802 (s) 728.1* 928* Octacosane 28 394 334.35 254 803 (s) 752.8* 937.0 Nonacosane 29 408 336.35 239 805 (s) 777.2* 1001* Triacontane 30 422 338.55 252 806 (s) 801.2* 1037* Hentriacontane 31 436 341.05 242 808 (s) 824.5* 1073* Dotriacontane 32 450 342.85 266 809 (s) 867.4 1095 Tritriacontane 33 464 344.55 256 810 (s) 871.0* 1113 Tetratriacontane 34 478 346.25 268 811 (s) 887.4 1149 Pentatriacontane 35 492 347.85 257 812 (s) 916.0 1210* Hexatriacontane 36 506 349.35 269 814 (s) 937.5* 1206 Heptatriacontane 37 520 350.85 259 815 (s) 959.1 * 1276* Octatriacontane 38 534 352.15 271 815 (s) 980.4* 1305* Nonatriacontane 39 548 353.45 271* 816 (s) 1001* 1341* Tetracontane 40 562 354.65 272 817 (s) 1022* 1411 Dotetracontane 42 590 357.32 273 817 (s) 1062* 1435 Tritetracontane 43 604 358.65 273* 819* (s) 1085* 1465* Tetrateracontane 44 618 359.55 274 820* (s) 1102* 1495* Hextetracontane 46 646 361.45 276 822* (s) 1140* 1553* Octatetracontane 48 674 363.45 276 823 (s) 1177 1595 Pentacontane 50 702 365.15 276 825* (s) 1213* 1665* Hexacontane 60 842 372.15 279 831*(s) 1380* 1916* Heptacontane 70 982 378.65 281* 836* (s) 1526* 2131* Hectane 100 1402 388.40 285* 846* (s) 1869* 2598*

(*)Predicted value.

(a) X'200(b)

FIG. 7-A scanning electron microscopic illustration of a macrocrystalline structure wax (a= 200 X; b = 1000 X).

Boiling Pt (K)

116.6 184.6 231.1 272.7 309.0 341.9 371.6 398.8 424.0 447.3 469.1 489.5 508.6 526.7 543.8 560.0 575.2 589.5 603.1 617.0 629.7 641.8 653.4 664.5 675.1 685.4 695.3 704.8 714.0 722.9 731.2 740.2 748.2 755.2 763.2 770.2 777.2 784.2 791.2 795.2 804.2 813.2 818.2 829.2 838.2 848.2 888.2 919.2 935.2


FIG. 8-An atomic force microscope image of the spiral growth of paraffin crystal (measuring approximately 15 microns across). Inset shows orthorhombic arrangement (0A9 nm x 0.84 nm) of chain ends of one of the crystal terraces (courtesy of Professor M.J. Miles).

(a) X 200 X 1000 (b)

FIG. 9-A scanning electron microscopic illustration of a microstructural characterization of a refined paraffin wax (a. = 200 X; b = 1000 X).

TABLE 9-Physical properties of petroleum waxes. Property

Melt. Point (0F) Molecular Wt. Crystal Structure Color

Crystal Structure

Paraffin Wax

110-155320--450PlatesWhite

Intermediate

150-165450-550Needles

White-Yellow

Paraffin waxes exhibit several crystalline structures depending on their carbon chain length. Odd number carbon chains between C,9 and C29 exhibit an orthorhombic type crystal structure. Even numbered carbon chains between C18 and C26 exhibit a triclinic structure. Even numbered carbon chains between C28 and C36 exhibit a monoclinic structure. All paraffins with carbon chains between C20 and C3• have a distinct transition point ( change in crystal form) lower than the temperature at which they solidify. The transition point

Microcrystalline

14Q..a195 450-700Needles

White-Dark Brown

Petrolatum

110-180450-700Needles

White-Dark Brown

occurs when the wax crystal structure rotates from a hexagonal to orthorhombic form as the wax solidifies from a molten state. Paraffins with carbon atom chains above C37 do not exhibit a transition point due to the wax solidifying directly into an orthorhombic crystal structure. Microcrystalline and intermediate type waxes do not exhibit any transition pOiht because they contain higher amounts of branched alkanes.

Because of the steric effects caused by the arrangement of atoms in the molecule there is a difference between alkanes with odd and even numbers of carbon atoms. The even-num-


bered homologs have higher latent heat than the odd-numbered homologs. Humphries [29] showed that alkanes with an even number of carbon atoms (between 20 and 32) and alkanes with odd number of carbon atoms (higher than 7) exhibit a lattice transition in the solid state. The even-numbered carbon atom alkanes exhibit this transition closer to their melting point than the odd-numbered alkanes, as demonstrated in Fig. 10. The boiling point of normal-alkanes for the temperature range on the figure are also shown in Fig. 10.

The lattice transition in alkanes is accompanied by the release of heat of transition. Generally, lattice transition occurs

500

2" -450

I! 400 "&

� 350

300

250

- 200

150

100

5 10 15 20

in the solid state at about 2-S'K below the melting point. The difference between the transition temperature and melting temperature becomes smaller with increasing molecular weight and finally disappears for alkanes with more than 36 carbon atoms [25,28] as demonstrated in Fig. 10. The heat associated with this solid-solid transition is subtracted from the lattice heat of melting. Figures 11 and 12 show variations of the latent heat of melting, melting point, and density of normal alkanes versus increasing number of carbon atoms in their structure. According to these figures, while the melting point and density versus_ the number of carbon atoms have

25 30

MP

TrT

BP

35

Number of carbon atoins

40

FIG. 10-Variation of melting point (MP), transition temperature (TrT), and boiling point (BP) of normal alkanes with their number of carbon atoms [28].

-300

�

:250

�200

150

1000 20 40 60 . 80 100

Number of carbon atoms

FIG. 11-Variation of the latent heat of melting of normal alkanes with the number of carbon atoms in alkanes and exhibition of the steric effect [28].

l

Q' 40,n-r------------�1000

j a ..

:--------------7 "' 0 -� p.. 800 ,.Qo.0 300 ::I] -�- � ::E · 600 _e,

-�200 !

100-0-MP _._ DENSITY

400

200

0 00 20 40 60 80 .. 100Number of carbon atoms

FIG. 12-Variation of the melling point and densily (@ 20'C) of normal alkanes with the number of carbon atoms in alkanes [28].

smooth variations, the latent heat of melting goes throughfluctuations. Because of the steric effects (the solid-solidphase transitions mentioned above) the latent heats of melting of two consecutive alkanes do not always increase with increasing number of carbon atoms, as demonstrated in Fig. 11.Each even-numbered alkane (with eight carbon atoms ormore) exhibit a lower latent heat than the odd numberedalkane having one carbon atom less than it. This fluctuationof the latent heat of melting vanishes as the number of carbonatoms approaches 40, and after that the latent heat increasessmoothly with increase of the number of carbon atoms.

As an example, the composition and thermophysical dataof a paraffin wax sample (Suntech Pll6) [30], which containsalmost 100% normal alkanes, is reported in Table 1_0. According to this table, the hydrocarbons with 20--32 carbonatoms constitute 99% of the mixture and the ones with morethan 32 carbon atoms constitute the remaining 1 %. Paraffinwaxes are generally polydisperse compounds for which polydisperse solution (continuous ntixture) theories may be usedfor characterization [31]. Figure 13 is the graphic representation of the composition data of Suntech Pl16 paraffin waxreported in Table 10.

Wax can be crystallized out of a solution by lowering itstemperature. Varying the temperature gradient causes a transition between the growth of wax plates and growth of a treelike structure with regular branches as it is shown on Fig. 14.Also shown on Fig. 14 is the banded growth of wax due to addition of a crystallization inhibitor.

Equations of State

In order to characterize the petroleum wax and perform various operations on wax mixtures, such as.wax fractionation,


it is necessary to be able to predict thermodynamic properties of wax. In this section we present five equations of state,which are used for prediction of molar volumes, vapor pressures, and supercritical solubilities of alkanes [32].

The simplest and one of the most widely known equationsof state is that of van der Waals. However, this equation ofstate is not accurate enough to predict thermodynamic properties of most fluids. Inspired by the van der Waals model, investigators have proposed several equations of state throughthe years. Almost every equation of state has been claimed. to

� 0

Table 10-Chemical composition and thennophysical properties of Suntech P1!6Paraffin Wax (30]. Hydrocarbon

n-C-20 n-C-21n-C-22n-C-23n-C-24n-C-25n-C-26 n-C-27n-C-28n-C-29n-C-30n-C-31n-C-32Melting rangeHeat of fusion Liquid specific heatSolid specific heat Liquid thennal conductivitySolid thermal conductivity Liquid densitySolid density Liquid viscosity Molecular weight

2"

••

20

15 • •

10_

5 •

•

•

Weight�%

2.05.514.023.022.014.06.53.02.52.01.71.51.3 316-329K266 kJ/kg 2.51 kJ/kgK2.95 kJ/kgK0.24W/mK 0.24 W/mK760 kg/m3

818kg/m3

J.90kg/ms332 g/mol

• ••• •

•

• .

20 21 .22 23 24 25 26 27 28 29 30 31 32


FIG. 13-The distribution of n-alkanes in Suntech P116 paraffin wax as a function of the number of carbon-atoms (28].

$2'400------------1000

� a .s .... 0 -

p.. 800 ,.Q-01) 300 =

:E -�- � �- 600 _e,

....200 �

100 -0-- MP _._ DENSITY

400

200

0 00 20. 40 60 80 . .100 Number of carbon atoms

�

FIG. 12-Variation of the melting point and density (@ 20°C)of normal alkanes with the number of carbon atoms in alkanes (28].

smooth variations, the latent heat of melting goes through fluctuations. Because of the steric effects ( the solid-solid phase transitions mentioned above) the latent heats of melting of two consecutive alkanes do not always increase with in� creasing number of carbon atoms, as demonstrated in Fig. 11. Each even-numbered alkane (with eight carbon atoms or more) exhibit a lower latent heat than the odd numbered alkane having one carbon atom less than it. This fluctuation of the latent heat of melting vanishes as the number of carbon atoms approaches 40, and after that the latent heat increases smoothly with increase of the number of carbon atoms.

As an example, the composition and thermophysical data ofa paraffin wax sample (SuntechP116) [30], which contains almost 100% normal alkanes, is reported in Table 10. According to this table, the hydrocarbons with 20-32 carbon atoms constitute 99% of the mixture and the ones with more than 32 carbon atoms constitute the remaining I%. Paraffin waxes are generally polydisperse compounds for which polydisperse solution (continuous mixture) theories may be used for characterization [31]. Figure 13 is the graphic representation of the composition data of Suntech Pl 16 paraffin wax reported in Table 10.

Wax can be crystallized out of a solution by lowering its temperature. Varying the temperature gradient causes a transition between the growth of wax plates and growth of a treelike structure with regular branches as it is shown on Fig. 14. Also shown on Fig. 14 is the banded growth of wax due to addition of a crystallization inhibitor.

)

Equations of State

In order to characterize the petroleum wax and perform various operations on wax mixtures, such as wax fractionation,


it is necessary to be able to predict thermodynamic properties of wax. In this section we present five equations of state, which are used for prediction of mol:tr volumes, vapor pressures, and supercritical solubilities of alkanes [32].

The simplest and one of the most widely known equations of state is that of van der Waals. However, this equation of state is not accurate enough to predict thermodynamic properties of most fluids. Inspired by the van der Waals model, investigators have proposed several equations of state through the years. Almost every equation of state has been claimed to

�

'iii 3::

Table 10---Chemical composition and thermophysical properties of Suntech Pl 16

Paraffin Wax [30]. Hydrocarbon

n-C-20n-C-21n-C-22n-C-23n-C-24n-C-25n-C-26n-C-27n-C-28n-C-29n-C-30n-C-31n-C-32

Melting range Heat of fusion Liquid specific heat Solid specific heat Liquid thermal conductivity Solid thermal conductivity Liquid density Solid density Liquid viscosity Molecular weight

25

,, ••

20

15 • •

1C

5 •

•

•

Weight�%

2.0 5.5

14.0 23.0 22.0 14.0 6.5 3.0 2.5 2.0 1.7 1.5 1.3

• J .•

316-329 K 266 kJ/kg 2.51 kJ/kgK 2.95 kJ/kgK 0.24 W/rriK 0.24 W/rriK 760kg/m3

818 kg/m3

1.90 kg/ms 332 g/mol

• • • • •

20 21 .22 23 24 25 26 27 28 29 30 31 32


FIG. 13-The distribution of n-<>lkanes in Suntech P116 paraffin wax as a function of the number of carbon-atoms (28].


(a)

(b)

FIG. 14-(a) An atomic force microscope image of wax "trees" growth in a lowering temperature solidification of wax from solution. Varying the temperature gradient causes a transition between the growth of wax plates and growth of a tree-like structure with regular branches; (b) An atomic force microscope image of banded growth of wax due to addition of crystallization inhibitors (courtesy of Prof. J.L. Hutter).

be superior in some respects to the earlier ones. The RedlichKwong (RK) equation that is a modification of the van der Waals equation, was a considerable improvement over other equations of relatively simple forms at the time of its introduction. In the Soave-Redlich-Kwong (SRK) equation, the temperature-dependent term of aJT0·5 of the RK equation is replaced by a function denoted by a that depends on the acentric factor of the compound and temperature. The PengRobinson (PR) equation is another cubic equation of state involving acentric factor. Riazi and Mansoori [33] modified the parameter b of the RK equation by introducing a function, denoted by?, that depends on the refractive index of the compound. They showed that the resulting equation is quite accurate in the prediction of hydrocarbon densities. MohsenNia et al. [34] proposed that the 3M equation in which the repulsive part of the RK equation is modified based on the statistical mechanics improved the thermodynamic predictions appreciably. This equation is shown to be more accurate for heavy hydrocarbon phase behavior calculation than most of the other equations of state. RK and 3M equations are two-constant-parameter equations of state, while the RM,

PR, and SRK are three-constant-parameter equations. All the above-mentioned five equations of state can be written in the following generalized form [32]: Z = v+ -yb _ av/RT v-b T"(v+1JC)(v+Ac) (2)

where a = lJ,, a R2 T/2+•) IP, and b = c = 0,,, f3 RT, IP,. Parameters nw {Jb, 11 'l, and A are component-independent constants, while a and f3 are component-dependent constants, and their numerical values for various equations of states are given in Table I I. In extending the equations of state to mixtures, parameters a, b, and c are replaced with arm b= and Cm with the following expressions (mixing rules): RK, PR, SRK, RM-I: llm = LLYiY;ll;;

i j

bm = Cm = LYibii i

3M: llm = LLYiY;llij i i

bm = (3 LI,y,y;b.;; + iy,b,,)14� i J . i

Cm = L,yibii i

(3)

(4)

For the RM equation there is another alternative in extending it to mixtures by replacing T, and P, with Tern and Pcm as given below: RM-2: T cm = (:ff Yi)l;T;,; P cj) I( f't'Y;Y;Tcij P cj),

Pcm =_ (tfY;Y;T;;; Pc1;)i(tfYiY;T,,; Pc1;)2

(5)

R'/:i = LLYiY;Rij i j

These equations of state can be used to calculate properties of wax, its components, i.e., vapor pressure, and molar volumes of liquid at saturated-, sub--cooled and supercritical-conditions as well as the solubility of wax in supercritical solvents. To perform phase equilibrium and other saturated property calculations for wax in liquid and vapor states, we need to perform equality of pressures and fugacity calculations [32]. The fugacity coefficient of a component of the wax in a mixture (4>l')?derived from the generalized Eq I is in the fol-

TABLE It-Parameters of the generalized equation of state. Eq. of State-+P.µ-ameters -1. RK MMM RM PR SRK

1' 0 1.3191 0 0 0 1J 1 1 1 1 +../2 0 .\ 0 0 0 1-../2 0 e 0.5 0.5 0.5 0 0 n. 0.42748 0.487480 0.42748 0.45724 0.42748!ls 0.08664 0.064462 0.08664 0.07780 0.08664 " 1 1 1 "PR "SRK

{3 1 1 f3RM 1 1

apR = [1 + (0.37464 + 1.524226w - 0.26992w2)(1 - �·5)]2

aSRK = [1 + (0.48508 + 1.55171w - 0.15613.:J)(l - �-5)]2

(/3RM)-• - I+ [0.02(1 - 0.92 exp(-J,OOOIT0 - 11)] - 0.035 (Tc - l)}(R* - I)

lowing form [32): In ef>Y = (I + 'l'i[ a(:�t�n, - ln(v - bmlv)]

In z a,,, [ v ] a(nc,,,) - - CmRT(l+e) (v + 'f/Cm)(v + ACm) �

where for RK, PR, SRK, RM-1: 1 a(n2am)

for 3M:

To calculate liquid molar volume and vapor pressure using equations of state, the data of critical temperature and pressure, acentric factor, and molar refraction are needed. The experimental critical properties of n-alkanes up to.C2• are available in the literature [35,36), while those of n-alkanes higher than C24 can be estimated using correlations. The critical temperature (in degrees Rankine) can be written as [37): Tc

= T;[(l + 2fr)/(1 - 2fr)]2 (7) where fr = l!,.SGr [ -0.362456/Tt'2

· + (0.0398285 - 0.948125/I'612)<iSGrJ <iSGr = exp [5(SG0 - SG)] - 1

T;; = Tb(0.533272 + 0.191017 X 10-3 Tb + 0.77968X 10-1 rt -0.284376 X 10-10 rt + 0.959468 X 1028 T,;13)

SG0 = 0.843593 - 0.128624a - 3.3615a3 - 13749.5a12

and where subscript T refers to temperature, subscript crefers to the critical conditions, superscript o refers to the ref-

CHAP'I'ER 19: PETROLEUM WAXES 537

erence system, SG = specific gravity, Tb = normal boiling point, in degrees Rankine, a = 1 - Tb I Tg, <iSG = specific gravity correction and f = correction factor. The critical volume (in cubic feet per pound mole) is given by the following expressions [37) Ve = l/g [(1 + 2fv)f(1 - 2fv)J2 (8)

where fv = <iSGv [0.466590!Tt'2

+ (-0.182421 + 3.0172!Tt'2)<i5Gv]<iSGv = exp [ 4(SG02 - SG2)) - 1

vg = [(0.419869 - 0.505839a - 1.5643a3 - 9481.70a14)]-•

The critical pressure (in psia) is given by the following expression [37): Pc= Pg (TJT;;)(V"JVc)[(I + 2fp)!(1 - 2fp))2 (9)

where fp = <iSGp [(2.53262 - 46.1955/T,\'2 - 0.00127885 Tb)

+ (-11.4277 + 252.1401Tt'2 + 0.00230535 Tb),iSGp]

<iSGp = exp [0.S(SG0 - SG)] - 1 Pg = (3.83354 + 1.19629a112

+ 34.8888a + 36.1952a2 + 104.193a4)2

and where V = molar volume, in ft3 /lbmole, P = pressure, in psia and subscripts V and Prefer to the volume and pressure. The acentric factor can be estimated with the use of the generalized Edalat et al. vapor pressure equation [38): where

and

Jn PR = (aT + hT312 + CT3

+ d.f')/(1 - T) (10) T = 1-T!Tc, (11)

w = (-log PR)rR-0.1 - 1

a(w) = -6.1559 - 4.0855w b(w) = 1.5737 - 1.0540w - 4.4365x10-3 d(w) c(w) = -0.8747 - 7.8874w d(w) = (-0.4893 - 0.9912w + 3.1551w2)-1

The above equation is quite accurate for calculation of vapor pressure-provided the acentdc factor and critical properties of a fluid are available. The molar refractions of wax compounds needed in the RM equation of state are available in Ref. 36. The accuracy of molar volumes of saturated liquid wax components, molar volumes in sub-cooled and supercritical conditions and vapor pressures calculated using various equations of state are reported in Tables 12-14, respectively. According to these tables the three-constant RM equation of state is quite satisfactory for molar volume prediction while the SRK is accurate for vapor pressure prediction of wax. In Fig. 15 the solubility ofn-tritriacontane (n-C33H68) in supercritical carbon dioxide is depicted along with the predictions obtained from various equations of state. According to


TABLE 12-The average deviations of various equations of state in predicting saturated liquid molar volumes of pl.lre compounds compared with those calculated using the hankinson and thomson (1979) correlation.

AAD%

Compound T,. Range RK 3M RM PR SRK

co, 0.71-1.00 19.5 8.8 19.5 4.7 14.7 CR, 0.48-0.99 4.5 13.9 4.5 8.6 4.5 C2H6 0.33-0.99 10.3 11.8 6.4 6.0 9.2 C3Hs 0.35-0.98 11.2 10.8 3.9 5.3 9.2 n-C4H10 0.36-0.96 13.3 9.0 3.0 3.6 10.3 n-CsH12 0.47-0.99 16.8 7.5 2.4 3.4 12.5 n-C6H14 0.39-0.99 19.9 6.9 2.2 2.2 14.8 n-C1H16 0.41-0.99 22.3 7.4 1.4 2.7 16.0 n-CsH1s 0.41-0.99 24.7 6.9 1.2 4.2 17.7 n-C,,H,o 0.42-0.98 26.8 7.8 0.8 5.1 18.7 n-C10H22 0.43-0.98 29.9 10.5 0.7 7.0 20.8 n-C11H24 0.55-0.78 31.1 10.5 0.3 7.4 21.3 n-C12H26 0.54-0.89 35.3 14.7 0.4 10.1 24.3 n-C13H28 0.56-0.80 37.6 16.5 0.2 11.4 25.8 n-C1�30 0.54-0.85 42.8 21.4 1.2 15.0 29.9 n-C1sH32 0.58-0.82 45.8 24.1 1.2 16.7 31.8 n-C16H34 0.56-0.81 49.7 26.9 1.8 19.7 35.1 n-C11H36 0.59-0.83 56.2 32.9 3.9 24.3 40.3 n-C1sH3s 0.55-0.84 59.5 35.5 4.0 26.9 43.1 n-C19Rw 0.56-0.85 63.5 39.0 4.4 29.6 46,1 n-C20�2 0.57-0.85 67.9 42.9 4.8 32.2 49.0 n-C22Ri6 0.55-0.81 57.6 31.8 4.5 25.1 40.6 n-C24Hso 0.56-0.82 66.2 39.2 2.9 31.1 47.2 n-C2sHss 0.58-0.84 62.9 36.4 l!.2 27.7 43.1 Overall 36.5 19.7 3.6 13.8 26.1

TABLE 13-The average deviations of various equation of state in predicting molar volumes of liquids in sub-cooled and supercritical conditions compared with experimental data.

AAD% Experimental Data Compound T,. Range P,. Range RK 3M RM PR SRK No. of Data Pts. Ref co, 0.7-2.2 1.0-13.6 5.0 4.8 5.0 2.9 6.1 447 a

CR, 0.5-2.6 0.0-15.2 2.0 11.1 2.0 7.4 2.4 459 b C2H6 0.3-2.3 0.0-14.3 3.8 11.2 1.7 5.6 4.1 474 C

C3Hs 0.2-1.9 0.0-16.5 5.9 9.6 1.8 4.2 5.9 533 d n-C4H10 0.3-1.7 0.0-18.5 8.4 8.4 1.6 3.8 7.9 638 e

n-CsH12 0.4-0.7 0.0-71.3 11.2 7.6 0.8 2.5 9.4 880 f n-C6H14 0.4-0.7 0.0-332 14.7 5.8 2.0 2.5 12.6 510 f n-�H16 0.6-1.1 1.8-183 14.5 5.6 2.3 3.3 13.5 70 f,g n-C9H20 0.5-1.0 2.2-218 18.8 3.1 2.2 5.1 17.1 66 g n-C11H24 0.5-0.9 2.6-259 25.1 3.1 2.6 10.4 23.1 70 g n-CnH2s 0.4-0.9 3.0-303 32.3 7.9 3.2 16.7 30.1 70 g n-C11H36 0.4-0.8 4.1-410 48.5 19.8 7.2 31.0 45.9 60 g n-C2olf42 0.4-0.8 5.0-500 59.9 28.6 9.9 41.1 57.1 so g n-C3oH62 0.4-0.8 6.8-682 62.7 28.9 6.8 43.5 59.8 so g

· Overall 22.3 11.1 3.5 12.8 21.0 4377 a Angus et al., 197 6.1,Goodwin, 1974. c Goodwin and Roder, 1976. d Goodwin and Haynes, 1982. eHaynesandGoodwin, 1976. f Frenkel et al., 1997a. 8 Doolittle, 1964.


TABLE 14-The average deviations of various equations of state in predicting vapor pressures of pure compounds compared with the experimental data.

AAD% Experimental Data Compound Tr Range RK 3M

co, 0.71-1.00 19.1 4.0 CH, 0.48-0.99 17.2 50.0 C,H,; 0.33-0.99 11.5 36.3 C3Hs 0.35--0.98 19.8 39.5 n-C.JI10 0.36--0.96 43.2 32.4 n-CsH12 0.47--0.99 63.4 19.2 n-C6H14 0.39--0.99 >100 15.8 n-C1H16 0.41--0.99 >100 11.0 n-CsH1a 0.41--0.99 >100 18.5 n-CgH20 0.42--0.98 >100 33.2 n-C10H22 0.43--0.98 >100 51.4 n-C11H24 0.55--0.78 >100 81.7 n-C12H26 0.54--0.89 >100 89.9 n-C13H2s 0.56--0.80 >100 >100n-C1.µl30 0.54--0.85 >100 >100n-C1sH32 0.58-0.82 >100 >100n-C1�34 0.56--0.81 >100 >100n-C11H36 0.59--0.83 >100 >100n-C1sH3s 0.55--0.84 >100 >100n-C19llio 0.56--0.85 >100 >100n-C20H42 0.57--0.85 >100 >100n-C22l46 0.55--0.81 >100 >100n-Cz.µ!50 0.56--0.82 >100 >100n-CzsHss 0.58-0.84 >100 >100n-C29H60 0.54--0.84 >100 >100n-C3off62 0.54--0.84 >100 >100n-C32H66 0.55-0.85 >100 >100n-C3�6s 0.55--0.85 >100 >100Overall -2100 -650

a Angus et al., 1979. b Frenkel et al., 1997a. c Goodwin, 1974. d Goodwin and Roder, 1976. e Goodwin and Haynes, 1982. £Haynes and Goodwin, 1976. 8 Morgan and Kobayashi, 1994. h Salemo et al., 1986.

this figure, the 3M and RM equations are capable of predicting supercritical solubilities accurately. In all these cases the unlike-interaction parameter, kti, is best fitted to experimental data Table 15 shows the interaction parameters of various equations of state for a number of systems at various temperatures along with the AAD%. According to this table, the 3M equation of state gives the least value of AAD%.

Differential Scanning Calorimetry

When a solid is heated, it may absorb heat resulting in a temperature increase or a structural change (phase transition) such as a solid to liquid or a transition from one crystalline form to another. These transitions may be endothermic (absorb heat) or exothermic (emit heat) depending on the thermal process that is occurring. These thermal processes may be quantitatively measured by differential scanning calorimetry (DSC).

DSC analysis is performed by heating two small sample pans, one containing the material being analyzed and the other empty and used as a reference. The analysis concept is that the two sample pans are maintruned at a very small temperature difference(:!: 0.01°C). Each pan is heated with twoheaters; 3: main heater and an aUX11iary heater. After· begin-

RM PR SRK No. of Data Pts. Ref

19.1 0.8 0.5 47 a

17.2 0.7 2.9 84 b,c 11.9 3.0 2.6 114 b,d 8.3 3.0 1.9 101 b,e 7.0 5.6 1.9 130 b,f 9.9 0.8 1.5 91 b,h

16.5 3.1 1.9 88 b,h 20.7 2.4 1.2 80 b,h 28.9 2.7 1.2 87 b,h 33.3 2.1 1.5 82 c,h 37.4 3.1 1.2 86 b,g,h 37.7 6.6 4.4 27 b 31.7 2.9 0.4 40 b,g,h 28.8 3.3 0.5 27 b 30.3 5.8 2.5 42 b,g,h 23.4 4.0 0.6 27 b 29.3 5.6 0.9 45 b,g,h 23.9 6.2 1.6 43 b 30.2 9.2 3.0 44 b,g 30.4 10.4 3.6 42 b,g 33.0 8.8 2.4 42 b,g 69.1 18.6 1.2 21 b,g 79.4 24.7 1.5 22 b,g 57.9 33.9 1.7 23 b,g 82.5 42.S 2.7 12 b 75.8 44.5 2.7 12 b 61.5 48.9 3.2 12 b 56.9 51.8 3.9 12 b 35.4 12.7 2.0 1483

ning the experiment by supplying heat with the main heaters, while heating the temperature difference (<iT) between the sample and reference pans is sensed using a thermopile (set of thermocouples) which produces a small (0-SµV) off-setting voltage. The auxiliary heater is then used to heat the sample pan to keep the off-balance voltage close to zero. The instrument displays the differential power (<iP) between the two pans as a function of temperature. The area under the peak of differential power (<iP) versus temperature (T) provides an experimental measure of the energy or total enthalpy change (<iH) of the entire process [39,40].

As described in ASTM Test Method D 4419, the melting point can readily be determined by DSC analysis, as can heat of fusion, which is also an important characterization parameter for waxes. Heat of fusion is defined as the increase in enthalpy accompanying the conversion of one mole, or a unit mass, of a solid to a liquid at its melting point at constant pressure and temperature [ 43]. The heat of fusion (/JJi,) is obtained from the melting transition peak illustrated in Fig. 16, by measuring the total area under the peak that is proportional to the heat flow per mass of material. Heat flow is the heat emitted per second, therefore the area under the peak is given in units of (heat · temperature · time-1) for the mass ofthe sample used. As a result the area per unit mass (APUM)


-4 .---------'-----�

-5

-6

-7

S.a ·:&»..g

"!10 -11-12 RK

-13 ...... __ .,_ __ .,_ __ _,__..-.J 0 2

Pr 3 4

-4��C57 -st O O 0

-6

-7

Ss �9 ':lo ·11 -12 PR

-13 ,_ __ .,_ __ _,_ __ ..._ __ _,0 I 4

�r---;;:;;::o:e::e==o===i-6

-7

Ss J9 -10

-11 -12 �----' RM-1 -13 .__ _ __,.__ _ _,_ __ __._ __ _J

0 2 Pr 3 4

-<�----------� .5

-6 -7

�-9 -10-11 -12 SRK -13 ._ __ .,_ __ .,_ __ .,_ _ __,

. I 2 Pr 3 4

; r---=:;e::e�;::=o:::� -6 -7

-t -11 -12 MMM -13 ,_ __ .,_ __ ..._ __ _,_ __ _,

0 2 Pr

3 4

� r---�::o:e;:e==o===i -6

-7 S.a �-9 �10

-11:12 �-'--' RM-2 -13 ._ __ ,_ _ __, __ _,_ __ _,

0 2 Pr 3 4

FIG. 15-Solubility of n-tritriacontane (n-C.3H68) in supercritical carbon dioxide at 308 K as predicted by various equations of state and compared with the experimental solubility data [32].

of the sample will be

Heat x Temperature APUM = Ttime X Mass

Q.T

0.M (12)

Typically, the actual units of !J.Hr are (joules · Kelvin · seconds_, · grams-1). Typically, the APUM is divided by theheating rate (K/s) of the DCS experiment used to collect the data. This will simplify the expression to yield the specific heat.of melting:

Q.T

APUM 0.M QHeating Rate = T = M

e

(13)

Since the mass of the sample that was analyzed is known, it is then multiplied by the heat emitted/gram of sample to yield the amount of heat given off ( Q) during the melting process.

QXM=M (14) M

Figure 16 illustrates the DSC traces for three different petroleum waxes; one for each wax type - paraffin (Fig. 16a), intermediate (Fig. 16b), and microwax (Fig. 16c). The DSC

trace shown by Fig. 17 demonstrates the decrease in crystallinity as the melting point of the wax increases. The thermal analysis procedure for this work was started at -50°C foroptimum crystallization of the wax. The wax sample was heated at a controlled rate to + 150°C. The point at whichthere is a deflection in the base line is the temperature that the wax begins to melt. The point at which the peak scan returned to the base line is the temperature the wax sample is completely melted. The peak area represents the amount of energy used to melt the wax sample and is calculated as described above. In addition, an estimate on the expected melting point can be distinguished. The experienced technologist could tell by looking at the shape of a DSC trace if the wax is a paraffin, intermediate, or microwax. Paraffin waxes typically exhibit sharp peaks as shown in Fig. 16a, DSC peak shapes for intermediate waxes are less sharp as shown in Fig. 16b, and microwaxes exhibit even less sharp peaks, typically like the peak shown in Fig. 16c.

It should be noted that there is a characteristic small transition peak in the DSC trace for a macrocrystalline paraffinic wax as illustrated in Fig. 16a. The transition that is indicated is a solid-solid phase ch;mge ( orthorhombic to hexagonal

TABLE 15-Interaction parameter (k12) of some systems.

T System [K]

Cz� - n-C2sHss 308.2 C2� - n-C291¾0 308.2 C,H6 - n-C,oH.2 308.2

313.2 C2H6 - n-C32�6 308.2

313.2 318.2 319.2

C,H,; - n-C33H,;8 308.2 313.2 318.2

CO2 - n-CzsHss 307.2 308.2 313.2 318.2 318.6 323.4 325.2

CO2 - n-C29H60 308.2 318.2

CO2 - n-C3oH62 308.2 318.2

CO2 - n-C32H66 308.2 318.2 328.2

CO2 - n-C33H6s 308.2 318.2 328.2

Overall

a Kalaga and Trebble, 1997. b Moradinia and Teja, 1986. c Suleiman and Eckert, 1995. d Moradinia and Teja, 1988. "McHugh et al., 1984 fReverchonetal., 1993. 8 Chandler et al., 1996.

...

{ ...

j

p [bar]

56-240 65-24066-20066-13666-24066-20080-24080-13665-24065-20265-240

123-181 80-240 90-275

100-250 119-284125-327121-284100-240100-24090-250

105-250120-240140-240140-240120-240 140-240140-240

RK 3M

-0.4638 -0.2099-0.4146 -0.1618-0.4777 -0.2066-0.4738 -0.2137-0.5124 -0.2259-0.5011 -0.2264-0.5248 -0.2438-0.4872 -0.2241-0.4632 -0.1933-0.4459 -0.1845-0.4506 -0.1918-0.3458 -0.0936-0.3161 -0.0901-0.2910 -0.0835-0.2915 -0.0867-0.3067 -0.0859-0.2973 -0.0869-0.2946 -0.0867-0.2751 -0.0530-0.1961 -0.0540-0.3254 -0.1141-0.3125 -0.1197-0.4140 -0.1500-0.3913 -0.1462-0.3777 -0.1345-0.3461 -0.1051-0.3384 -0.1043-0.3057 -0.0990

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RM-2 PR SRK RM-1 RK

0.0807 -0.0553 -0.0189 -0.1283 46.2 0.1215 -0.0131 0.0260 -0.0701 53.1 0.1025 -0.0571 -0.0206 -0.1121 25.0 0.0901 -0.0517 -0.0139 -0.1233 13.9 0.1020 -0.0707 -0.0297 -0.1214 46. 0.1050 -0.0658 -0.0263 -0.1131 24.4 0.0966 -0.0762 -0.0347 -0.1142 45.2 0.1087 -0.0565 -0.0157 -0.1219 23.6 0.1100 -0.0286 0.0137 -0.0779 50.2 0.1433 -0.0240 0.0193 -0.0580 39.6 0.1433 -0.0203 0.0228 -0.0530 45.7 0.2487 0.0110 0.0507 0.0211 51.0 0.2477 0.0296 0.0708 0.0194 52.3 0.2532 0.0365 0.0765 0.0286 46.7 0.2504 0.0359 0.0746 0.0232 64.7 0.2531 0.0347 0.0736 0.0278 53.7 0.2552 0.0385 0.0764 0.0314 62.5 0.2540 0.0321 0.0690 0.0287 64.2 0.2782 0.0645 0.1075 0.0670 71.8 0.2789 0.0818 0.1451 0.0672 81.2 0.2481 0.0327 0.0779 0.0084 69.6 0.2439 0.0273 0.0700 -0.0005 67.5 0.2448 -0.0162 0.0316 c-0.0139 59.5 0.2483 -0.0035 0.0426 -0.0092 67.3 0.2596 0.0044 0.0477 0.0104 57.5 0.2825 0.0262 0.0754 0.0496 68.4 0.2832 0.0280 0.0872 0.0494 65.0 0.2878 0.0428 0.0876 0.0557 67.4

60.0

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-·--------------n=

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... ,-1----------------' 45.G 0.0 2!.G 50,0 .'1511 llU nu . WQ

FIG. 16-The heat of fusion (Mt,) calculation from the DSC melting transition peak by measuring the total area under the peak, (a) paraffin, (b) intermediate, (c) microwax.

AAD%

3M RM-2 PR

27.0 14.4 38. 29.9 23.9 48. 22.8 57.2 22. 30.8 29.7 18. 43.0 56.2 41. 34.5 40.2 20. 17.7 22.8 32. 37.4 39.3 28. 34.4 50.7 43. 21.5 28.9 25. 24.2 28.0 42. 7.5 34.4 45.

18.3 35.0 49. 25.0 44.5 39. 13.4 31.0 47. 8.2 33.2 45. 5.8 28.9 53. 7.3 22.6 45.

21.5 12.9 67. 22.2 6.9 76. 17.1 28.8 66. 8.3 28.7 57. 8.1 24.1 54. 6.7 22.3 55. 9.2 27.1 40.

25.0 11.3 64. 22.9 4.8 61. 18.5 3.5 60. 20.3 28.3 46.


85.0

80.0

75.0

70.0

{ 65.0

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so.o

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4M

35.0

30.0

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I

l

r' I" ! ,.,I1· I

I I f, �

0.0 25.0 SO.0 75.0 100.0 125.0 tso.0

Temperature ('CJ

FIG. 17-The heat of fusion (AH,) calculation from the DSC melting transition peak by measuring the total area under the peak of several paraffins demonstrating the decrease in crystallinity as the melting point of the wax increases.

crystal structure). As the wax crystal continues to absorb energy, a larger peak is recorded and then actual melting occurs with a return to the base line as the temperature continues to increase.

In addition, there is a bimodality indicated in the DSC trace peak shapes for intermediate (Fig. 16b) and microcrystalline (Fig. 16c) waxes. Bi-modal shape is related to the breadth of the wax composition. Bimodal peak shape is not related to transition. The apparent bimodality indicates that the wax has not been made as a narrow distillation cut. The melting point of wax is in the DSC area that the curve begins to return to the base line (downward slope) as the temperature increases. The squat DSC peak shape of the microwax shown in Fig. 16c indicates that it is less crystalline and has a broader melting. The apparent bimodality of the microwax is related to the different melting fractions that appear in this particular wax.

Determination of the heat of fusion of a wax is of practical significance for a number of reasons. For example, the changes of shape of a DSC trace to that of known waxes may indicate that a wax has been contaminated or altered. This may be confirmed by comparing the heat of fusion of a previously purchased paraffin wax with the suspect wax. For example, a historical value for heat of fusion of a wax may be 200 Jig and a newly purchased paraffin wax may have a heat of fusion of 180 Jig. This variation confirms that the two waxes exhibit different properties.

Another application of the heat of fusion could be for the comparison of properties of nominally similar waxes offered by two different suppliers. The higher the heat of fusion, the more crystalline the wax is. For some applications, like candles, high crystallinity is desirable to aid in the mold release properties due to shrinkage upon cooling. Low crystalline waxes do not shrink as much as high crystalline products.

ASTM Test Method D 4419 has been developed to characterize petroleum waxes and measurement of their transition temperatures by Differential Scanning Calorimetry (DSC). Figures 16a, 16b, and 16c are DSC endothermic scans of a paraffin, intermediate, and microcrystalline wax,

respectively. Referring again to Fig. 16a (paraffin wax), the endotherm is started at -50°C for optimum crystallization of the wax. The wax sample is heated at a controlled rate to + 1 S0'C. The point at which there is a deflection in the baseline is the temperature that the wax begins to melt. The point at which the peak scan returned to the base line is the temperature the wax sample is completely melted. The peak area represents the amount of energy used to melt the wax sample as discussed above. Figure 17 illustrates that as the melting point of paraffin wax increases, the heat of fusion decreases because of the higher content of less crystalline branched alkane structures. Microcrystalline waxes have a lower heat of fusion than paraffin wax that is directly related to the greater amount of branched alkanes (less crystalline microstrucfure). Listed in Table 16 are the typical heats of fusion data for both paraffin and microcrystalline waxes.

Effect of Additives

In the petroleum wax industry; it is often necessary to use additives to improve the processability of wax or wax mixtures by modifying their physical properties. This may be accomplished by the addition of additives that may include stearic acid, polyethylene, ethylene-vinyl acetate copolymer or a Fischer-Tropsch wax. For example, stearic acid may be added to a paraffin wax to increase firmness, reduce melting point, aid in mold release, prevent candles from losing their shape in warm weather, etc. Polyethylene is another additive that may be used. Polyethylene may be added to a paraffin wax to harden the wax structure, modify burning rate, and improve strength and gloss. In addition to physical property modification, additives also could alter the microstructure of waxes as demonstrated by Fig. 14.

Test Procedures for Petroleum Wax

Characterization

There are three properties used to characterize petroleum waxes: (I) physical properties, (2) chemical properties, and (3) functional properties.

Physical Property Determination

Melting Point - Test Methods ASTM D -87, D 3944, and D 127-Melting point is a wax property that is of interest to the consumer and can be an indication of the perlormance properties of the wax being tested. The melting point of a wax is defined as the temperature at which the melted petroleum wax first shows a minimum rate of temperature change when allowed to cool under prescribed conditions.

Test Method D 87 is one of the most commonly utilized tests for melting point determination for petroleum waxes. Paraffin waxes are often marketed based on melting point data produced by D 87. This test method is performed by placing a specimen of molten wax in a test tube equipped with a thermometer as illustrated in Fig. !Sa. The test tube is

TABLE 16--Typical heats of fusion (Jig).

Fully Refined Paraffin wax 180-210Microcrystalline wax 140-190

(b)


'c!!

(a)

..

I

. �·

1 51' ID d30)

.I Dimensions in inches (millimeters)

r

K. a �

.. .. -,.::

Time-+

FIG. 18-{a) Apparatus for ASTM Test Method D 87. Cooling curve for: (b) a paraffin wax, (c) for intermediate wax, microwax, petrolatum, or waxes containing a high percentage(>50%) of branched alkanes

(c)


then placed in an air bath that is immersed in a water bath and held at 16-28°C (-61-82°F). Temperature readings are taken periodically until the wax, solidifies under specified conditions. During solidification, the rate of temperature decreases and produces a plateau in the cooling CUIVe, which is obtained by plotting the temperature versus elapsed time as, illustrated in Fig. 18b. The temperature where the plateau occurs is defined as the melting point. (Note: The thermometer used for this work shall conform to ASTM Specification E-1.)

Test Method D 87 is not applicable for microcrystalline wax, intermediate wax, petrolatum, or waxes containing a high percentage (> 50%) of branched alkanes, because a temperature plateau will not occur with such type of waxes as illustrated in Fig. 18c and because these type of waxes have a much broader melting distribution ( characterized by DSC) than paraffin waxes. For non-paraffin type waxes, Test

'i'o Jli!:c:ordcr

Method D 3944, which is a "solidification point" method (Fig. 19a), can be used for melting point determination. The solidification point of a petroleum wax is: the temperature in the cooling curve of the wax where the slope of the curve first changes significantly as the wax sample changes from a liquid to a solid state. This is illustrated in Fig. 19b, which is a typical cooling curve for solidification point measurement of a petroleum wax.

Test Method D 3944 is performed by heating 50 mg of sample in a test tube above the solidification temperature. Once the wax is melted, Fig. 20a, a thermocouple (connected to a recorder) is placed in the sample, as illustrated in Fig. 20b,

and allowed to cool to ambient temperature. As the sample cools, a plot of temperature versus time (Fig. 18a) is obtained. This test method is based on the same methodology as D 87 with the exception that automated test equipment is

'I'B'E-nuorocarbon HoldOl" Adapter

6x50 111111. 'lest 'l'ube

A].uminUllll'BeatiAg Block

50x50x50 111111 (2x2x2 in) I

(a)

(b)

0.020 .in OD Metal Sheathed 'lheEmDCOuple Prabe

TFE-Fl.uorocarbon Disk CMt..ing ---+-...q, Guide

so mg wax sample

t · Temperatw:e

. I

Sol.idification Point

<:onnecti1;19' ;c.eaa

Heat turned ot.l

Autotransformer

TO 110 AC

out:let

FIG. 19-(a) Apparatus for determination of melting (solidification) point (cooling curve) of non-paraffin type waxes used in ASTM Test Method D 3944; (b) A typical cooling curve for melting (solidification) point measurement of non-paraffin type waxes.


(a)

Sample

Resistance Thermometer

Heater

Nitrogen��

Reference

AT-Signal

First-Order Transition:

Apex - TlA onset. - -r

20

.tnd - 'r2E

Second Order-Transition: l II II I

(b)

Apex - Tu Onset - T

10 End - TlE

� l '2A

FIG. 24-(a) Differential scanning calorimetry (DSC) experimental set up; {b) Schematic of petroleum wax DSC curve {heating cycle) sample determined to have solid-liquid and solid-solid transitions. This figure is similar to Fig. 16a.

method for petrolatum, which may also be used for softer waxes. The cone penetration value is more of a measure of finnness or consistency rather than hardness.)

Transition Temperatures by Differential Scanning Calorimetry (DSC )-Test Method D 4419-Test Method D 4419 is a rapid and convenient method for determining the temperature lim..: its governing the change a wax undergoes from solid to liquid or as a solid-solid transition. This test method measures the transition temperatures of petroleum waxes, including microcrystalline waxes, by differential scanning calorimetry (DSC) as shown in Fig. 24a. The normal operating temperature range extends from 1Sc-150°C. DSC is a technique that measures the difference in energy inputs into a substance and a reference material using a controlled-temperature pro-

gram. DSC can differentiate the type of petroleum wax being evaluated by its melting and crystallization property. Figure 24b (which is similar to Fig. 16a) is the schematic of a petroleum wax DSC curve exhibiting solid-liquid and solidsolid transitions (Heating Cycle) and the calculation of such temperatures. Paraffin waxes being derived from the distillation process have sharp peak shapes, while microcrystalline waxes being derived from residual fractions have broader peak shapes. This is shown in Fig. 16 (Note: Refer to Standard Terminology E 473 for additional information).

I

Chemical Property Detennination

Petroleum waxes being composed of hydrocarbons are relatively inert but they can undergo compositional chemical

changes when exposed to elevated temperatures in the presence of oxygen due to oxidation. Waxes can degrade in the presence of heat and oxygen. The degradation process involves breaking a bond between a carbon and a hydrogen atom to make a free radical. The free radicals quickly form peroxides initially and further react to form acids. The changes in composition can possibly be detected by testing for color and odor. Antioxidants are added to petroleum waxes to chemically stabilize them from the heat degradation process [ 41].

Color - Test Methods D 156 and D 1500-The color of petroleum waxes can indicate the degree of refinement or possible contamination. Color is not always a reliable parameter for determining quality and should be used judiciously as a specification. There are two methods for determining the color of petroleum waxes: Test Methods D 156 and D 1500, and both are subjective and measure the empirical value based on visual observation of the wax in the molten state.

Test Method D 156 is the Saybolt Chronometer Method for quantifying the color of petroleum products such as a petroleum wax. Saybolt color is an empirical definition of the color of a clear petroleum liquid based on a scale of -16 (darkest) to + 30 (lightest). The number is derived by finding the height of a column that visually matches the appropriate one of three glass standards and referring to Table 1 of Test Method D 156. Tiris is done using a Saybolt chronometer (see Fig. 25), which consists of a sample and standard tubes, optical system, light source, and ASTM color standards.

While Test Method D 156 is used to determine the degree of whiteness of a wax, Test Method D 1500 is used to measure the color of waxes that have a tint darker than off-white. Test Method D 1500 is conducted using a standard light source, with liquid sample placed into a standard glass container (sample jar) (see Fig. 26) and compared with colored glass disks ranging in value from 0.5--8.0 with 0.5 increments.

Carbonizable Substances - Test Method D 612-Test Method D 612 is applicaj,le to paraffin waxes for pharmaceutical use as defined in the United States National Formulary. Molten wax is treated with sulfuric acid and the acidic layer is compared visually with a colorimetric reference standard to determine if it passes the conformance criteria for refined wax using the color comparator shown in Fig. 27.

Peroxide Number - Test Method D 1832-Waxes are heat sensitive and they are susceptible to the action of the oxidation process. The detection of peroxides is the first indication that a wax has begun to deteriorate in terms of oxidation stability. Petroleum waxes should not have any measurable peroxide values. Deterioration of petroleum wax results in the formation of peroxides and other oxygen-carrying compounds that will oxidize potassium iodide. Peroxide content is reflected by the peroxide number that is defined as the milliequivalents of constituents per 1000 g of wax that will oxidize potassium iodide.

Odor - Test Method D 1833-In some end-use applications, such as food packaging, the intensity of the odor is an important characteristic. Odors can be an indication of the degree of refining, contamination, or oxidation. Test Method D 1833 describes how to rate the odor intensity based on a subjective evaluation using a multiple-member test panel. This test is conducted by preparing odor test specimens from petroleum


wax and placing approximately 10 g of thin shavings on odorfree paper or glassine. Individual test specimens are then evaluated for odor by each panel member and assigned a number according to the odor scale shown in Table 18 that best fits the intensity of the odor. As an alternative procedure, the wax shavings are placed in bottles with each panel member making an odor determination between 10 and 60 min after the shavings are placed into the bottles. The average of the panel ranking is reported as the odor rating of the sample.

Composition by Gas Chromatography-Test MethodD 5442-Test MethodD 5442 is applicable to petroleum derived waxes, including blends of waxes. This test method covers the quantitative determination of the carbon number distribution of petroleum waxes in the range of n-Cl 7 through n-C44 by gas chromatography using internal standardization. In addition, the content of normal and non-normal hydrocarbons for each carbon number is also determined. Material with a carbon number above n-C44 is determined by difference from 100 mass% and reported as C 45 +. (Note: Standard Practice E 260 provides further information on gas chromatography and Standard Practice E 355 provides information relating to gas chromatography terms and relationships.)

Test Method D 5442 is not applicable to oxygenated waxes, such as synthetic polyethylene glycols (i.e., Carbowax), or natural products such as beeswax or carnauba. This test method is not directly applicable to waxes with oil content greater than 10% as determined by Test Method D 721.

Functional Property Determination

The following methods are for the evaluation of wax base coatings intended for paper and paperboard. The methods were developed in concert with the Technical Association of Pulp and Paper Industries.

Specular Gloss - Test Method D 1834-Specular gloss is defined as the degree to which a swface simulates a mirror in its capacity to reflect incident light. Test Method D 1834 is a method designed to determine the capacity of a wax coated surface to simulate a mirror in its ability to reflect an incident light beam using a glossmeter such as that illustrated in Fig. 28. Surface gloss is desirable for some waxed paper applications. For determining the gloss of book paper, reference should be made to Test Method D 1223. For very high gloss paper refer to Wink et al. [ 42].

Gloss Retention - Test Method D 2895-This test is intended to correlate with the conditions that are likely to occur in the storage and handling of wax-coated paper and paperboard. Test Method D 2895 is intended primarily to measure the gloss retention, which is defined as the percent of original gloss retained by a test specimen after aging under specified conditions. It is calculated as the final gloss divided by the initial gloss multiplied by 100. The initial gloss of waxed paper or paperboard is measured in accordance with Test Method D 1834, then remeasured after aging the sample in an oven at 40°C (104°F) for 1 and 7 days. The !-day test is conducted to observe trends while the 7-day test is the standard test duration.

Surface Wax - Test Methods D 2423, D 3521, and D 3522-Wax coatings are applied to provide a better moisture barrier, appearance, and abrasion resistance. These perlormance features are influenced by the amount of wax present on the surface. Test Method D 2423 is used to determine the

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amount of wax present on the surface of the substrate, but not the absorbed wax. Test methods that determine the applied wax by solvent extraction (such as Test Method D 3344) do not clifferentiate between the wax present at the surface and to that which penetrated the substrate.

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Test Method D 3521 also determines the amount of wax that is present on the surface of corrugated paperboard. This method is applicable to a board on which wax has been applied by curtain coating, roll coating, or other methods. The substrate board may or may not contain impregnating (saturation) wax within its structure. If it is known that the specimen has coating wax only, with no internal saturating wax, then Test Method D 3344 may determine the total coating wax applied. Determination of the total amount of wax present by ASTM D 3521 involves delamination of the coated facing to obtain a ripple-free sheet, then scraping off the wax using a razor blade and calculating the amount of wax removed.

Test Method D 3522 is used to determine the amount of wax that has been applied to the inclividual layers of the corrugated paperboard and the amount of the impregnating (saturation) wax in the same facing. This is accomplished by peeling the coated facing from the meclium and then splitting it into two layers; one bearing the coating on waxed fibers only and the other containing waxed fibers only. The layers are extracted separately, collecting both fibers and wax. This will permit the calculation of the applied surface coating and the amount of impregnating wax.

TABLE 18-0dor intensity scale . Numerical Rating

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Odor Description

None Slight ModerateStrong Very strong

TEST TUBE

FIG. 27-Color comparator used in Standard Test Method D 612 for measurement of carbonizable substances in paraffin waxes for pharmaceutical use.


Specimen

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FIG. 28-Diagram of relative positions of essential elements of Glossmeter used in Standard Test Method D 1834.

Total Wax Content - Test Method D 3344--Many of the functional properties ofa wax-treated paperboard are dependent on the amount of wax that is present. Test Method D 3344 determines the total amount of wax in a sample of wax-treated corrugated paperboard by extraction. It is applicable to specimens that have been waxed by either impregnation (saturation) operations or coating operations, or combinations of the two.

Weight of Wax Applied During Coating - Test Method D 3708-Test Method D 3708 is used to determine the weight of a hot melt coating applied to corrugated board by curtain coating. This method is intended for use as a routine process control in the plant. The amount of wax applied is determined by attaching a folded sheet of paper to production corrugated board, running the combination through the curtain coater, and subsequently determining the applied weight of wax on the sheet of paper.

Blocking Point - Test Method D 1465-The blocking point of a wax is defined as the lowest temperature at which a film

disruption occurs across 50% of the waxed paper surface when the test strips are separated. The temperature at which the first film disruption occurs on the waxed paper when the test strips are separated is the wax picking point. Test Method D 1465 is used to determine the temperature at which two strips of wax-coated paper will adhere to each other. Surface disruption of wax coatings at relatively low ambient temperatures is a performance problem for low melting point waxes. If the surface of a waxed paper is blocked together, then surface gloss and barrier properties will be altered. Two strips of wax-coated paper are placed on a calibrated temperature gradient plate for 17 h and removed, cooled, and peeled apart to determine the block point temperature. Figure 29 illustrates a Type A and a Type B blocking plate used for these measurements.

Coefficient of Kinetic Friction - Test Method D 2534-A coated surface under load is pulled at a uniform rate over a second coated surface. This is done experimentally by preparing a "sled" with a weight and then pulling it over the surface to be tested using a horizontal plane and pulley assembly. The force required to move the load is measured, and the coefficient of kinetic friction (JL0 is calculated as follows:

(15)

Where A = the average scale reading from the electronic load cell-type tension tester for 1 SO mm ( 6 in) of uniform sliding and B = sled weight (g). The value obtained is related to the slip property of the wax coating. High slip property values may not be desirable for many commercial articles that have been coated with petroleum wax.

Abrasion Resistance - Test Method D 3234-This test method is designed to help predict the resistance in change of gloss that coatings may be subject to during the normal handling of coated paper and paperboard products. Abrasion resistance is the resistance to change in gloss when that coating has been subjected to an abrading action by an external object. Test Method D 3234 is conducted by dropping 60 g of sand on a very small area of a coating under fixed conditions. The abrasion resistance test apparatus is illustrated in Fig. 30. Gloss is measured with a 20° specular glossmeter illustrated in Fig. 28 before and after the abrading action by thefalling sand.

Hot Tack - Test Method D 3706-Hot tack is defined as the cohesive strength during the cooling stage before solidification of a heat seal bond formed by a wax-polymer blend. Flexible packaging materials are formed into finished packages by joining surfaces with heat sealed bonds. The bonding process is performed on high-speed packaging lines and the application pressure used to hold the surfaces together is released before the bond has completely solidified. The wax-polymer blend must have enough hot tack while still in a molten stage to hold the sealed areas together until the blend has cooled.

In Test Method D 3706, flexible packaging specimens are heat-sealed together over a series of temperatures and dwell times. Immediately after each seal is formed and before it has started to cool, a force tending to separate the specimens is applied by a calibrated spring. If the hot tack of the blend is strong enough, the seal remains closed until it has solidified; if not, the seal separates. Thus each spring force and test condition either passes or fails. The pattern of pass/fail results is plotted to the blend characteristics.

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Acknowledgments

The authors thank Dr. George Totten for his helpful advice and guidance in the preparation of this chapter and Dr. Sony Oyekan, Dr. Chen-Hwa Chiu, Dr. Sang J. Park. and Mr. Adrian D'Sousa for their technical assistance.

ASTM STANDARDS

No. Title

D87 Test Method for Melting Point of Petroleum Wax D97 Test Method for Pour Point of Petroleum Products D 127 Test Method for Drop Melting Point of Petroleum

Wax Including Petrolatum D 156 Test Method for Color, Saybolt, of Petroleum

Products D287 Test Method for Gravity, API, of Crude Petroleum

and Petroleum Products (Hydrometer Method) D445 Test Method for Kinematic Viscosity of Transpar-

ent and Opaque Liquids D 612 Test Method for Carbonizable Substances in

Paraffin Wax

D721 D937 D938

D 1168

D 1298

D 1223

D 1321

D 1465

D 1500

D 1832

D 1833 D 1834 D2423

Test Method for Oil Content of Petroleum Waxes Test Method for Cone Penetration of Petrolatum Test Method for Congealing Point of Petroleum Waxes, including Petrolatum Test Method for Hydrocarbon Waxes Used for Electrical Insulation Test Method for Density, Relative (Specific Gravity) or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method Test Method for Specular Gloss of Paper and Paperboard Test Method for Needle Penetration of Petroleum Waxes Test Method for Blocking and Picking Points of Petroleum Wax Test Method for Color, ASTM, of Petroleum Products (ASTM Color Scale) Test Method for Peroxide Number of Petroleum Wax Test Method for Odor of Petroleum Wax Test Method for 20 ° Specular Gloss of Wax Paper Test Method for Surface Wax on Waxed Coated Paper

D2500

D2534

D2669

D2895

D3234

D3235

D3236

D3344

D3451

D3521

D3522

D 3706

D 3708

D4419

D 5442

El E260

E355

E473

E537

Test Method for Cloud Point of Petroleum Products Test Method for Coefficient of Kinetic Friction for Wax Coating Test Method for Apparent Viscosity of Petroleum Waxes Compounded with Additives (Hot Melts) Test Method for Gloss Retention of Waxed Paper and Paperboard after Storage at 40 ° C (104 ° F) Test Method for Abrasion Resistance of Petroleum Wax Coatings Test Method for Solvent Extractables in Petroleum Waxes Test Method for Apparent Viscosity of Hot Melt Adhesives and Coatings Materials Test Method for Total Wax Content of Corrugated Paperboard Standard Practices for Testing Polymeric Powders and Powder Coatings Test Method for Surface Wax Coating on Corrugated Board Test Method for Applied Wax Coating and Impregnating (Saturating) Wax in Corrugated Board Facing Test Method for Hot Tack of Wax-Polymer Blends by Flat Spring Test Test Method for Weight of Wax Applied During Curtain Coating Operation Test Method for Transition Temperatures of Petroleum Waxes by Differential Scanning Calorimetry Test Method for Analysis of Petroleum Waxes by Gas Chromatography Specification for ASTM Thermometers Practice for Packed Column Gas Chromatography Practice for Gas Chromatography Terms and Relationships Standard Terminology Relating to Thermal Analysis Test Method for Assessing the Thermal Stability of Chemicals by Methods of Thermal Analysis

OTHER STANDARDS

No. BS 4633 & 4634

BS4695

DIN 53175

DIN 53181

Title

Method for the determination of crystallizing point. Method for the determination of melting point and/or melting range Method for determination of melting point of petroleum wax (cooling curve) Binders for paints, varnishes and similar coating materials; determination of the solidification point (titer) of fatty acids (method according to Dalican) Binders for paints, varnishes and similar coating materials; determination of the melting interval of resins by the capillary method

ISO 1392

ISO 2207

ISO 3016

ISO 3841

nsKo0-64

nsKo0-65

NFT60-114

NFT20-051

CHAPTER 19: PETROIEUM WAXES 555

Determination of crystallizing pointGeneral method Petroleum waxes-Determination of congealing point Petroleum products-Determination of pour point Method for determination of melting point of petroleum wax ( cooling curve) Testing methods for melting points of chemical products Test methods for freezing point of chemical products Petroleum products-Melting point of paraffins Chemical products for industrial use. Determination of melting point. Method for the determination of crystallizing point (freezing point).

REFERENCES

[1] Hackett, W. J., Maintenance Chemical Specialties, Chemical Pllblishing Co., Inc., NY, 1972.

[2) Warth, A.H., Chemistry and Technology of Waxes, Reinhold Publishing Corp., NY, 1956.

[3) Bennet, H., Industrial Waxes, Vol. 1, Chemical Publishing Company, Inc., NY, 1963.

[4] Puleo, S. L., "Beeswax," Cosmetics and Toiletries, Vol. 102, Al-lured Publishing Company, Inc., Chicago, 1987.

[5] Warth,A. H., Chemistry and Technology of Waxes, Reinhold Publishing Corp., NY, 1956.

[6) Letcher, C. S., 'Waxes," Kirk-Othmer: Encyclopedia of ChemicalTechnology, Vol. 24, 3"' ed., 1984, pp. 466-481.

[7] Dcy, M. E., "Sasol's Fischer-Tropsch_Experience," HydrocarbonProcessing, August, 1982, pp. 121-124.

[8] Erchak, Jr., M., "Process for the Oxidation of High MolecularWeight Aliphatic Waxes and Product 880kb, U. S. Patent2,504,400, Washington DC, April 18, 1950.

[9) Haggin, J., "Fischer-Tropsch: New Life for Old Technology," Chemical and Engineering News, October 1981, pp. 22-32.

[10] Caraculacu,A., Vasile, C., Caraculacu, G., "Polyethylene Waxes,Structure, and Thermal Characteristics," Acta Polymerica, Vol.35, No. 2, 1984, pp. 130-134.

[11) Brooks, B. T., Boord, C. E., Kurtz, S.S., and Schmerling, L., TheChemistry of Petroleum Hydrocarbons, Vol. 1, Reinhold Publishing Corp., NY, 1954.

[12) Gruse, W. A., Chemical Technology of Petroleum, 2nd ed., McGraw-Hill Company, NY, 1942.

[13] Mazee, w. M., "Petroleum Waxes," Modern Petroleum Technology, 4"' ed., 1973, pp. 782-803.

[14] Vasquez, D. and Mansoori, G. A., "Identification and Measurement of Petroleum Precipitates," Journal of Pe troleum &ienceand Engineering, Vol. 26, Nos. 1-4, 2000, pp. 49-56.

[15] Misra. S., Baruah, S., and Singh, K, Paraffin Problems in CrudeOil Production and Transportation: A Review, SPE Productionand Facilities, Society of Petroleum Engineers, Richardson, TX,Feb. 1995,pp.50-54.

[16) Holder, G. A. and Winkler, J., 'Wax Crystallization from Distillate Fuels," Journal of the Institute of Petroleum, Vol. 51, No. 499, 1965, pp. 228-243.

[17) Mansoori, G. A. and Canfield, F. B., "Variational Approach to Melting," Journal of Chemical Physics, Vol. 51, No. 11, 1969, pp. 4967-4972.


[18] Pourgheysar, P., Mansoori, G. A., and Modarress, H., "A SingleTheory Approach to the Prediction of Solid-Liquid and Liquid-Vapor Phase Transitions," Journal of Chemical Physics, Vol.105, No. 21, 1996, pp. 9580-9587.

[19] Park, S. J. and Mansoori, G. A., "Aggregation and Deposition ofHeavy Organics in Petroleum Crudes," International Jo urn.al ofEnergy Sources, Vol. 10, 1988, pp. 109--125.

[20] Branco, V. A. M., Mansoori, G. A., De Almeida Xavier, L. C.,Park, S. J., and Manafi, H., "Asphaltene Floccuiation and Collapse from Petroleum Fluids," Journal of Petroleum Science andEngineering, Vol. 32, 2001, pp. 217-230.

[21] Svendsen, J. A., "Mathematical Modeling of Wax Deposition inOil Pipeline Systems," AIChE Journal, Vol. 39, No. 8, 1993, pp.1377-1388.

[22] Brown, T. S., Nielsen, V. G., and Erickson, D. D., "Measurementand Prediction of the Kinetics of Paraffin Deposition," Journal

of Petroleum Technology, April 1995, pp. 328-329.[23] Noll, L., "Treating Paraffin Deposits in Producing Oil Wells,"

Topical Report NIPPER-551 (DE92001010), Bartelsville ProjectOffice, U.S. Department of Energy, Bartelsville, OK, 1992.

[24] Sanchez, J. H. P. and Mansoori, G. A., "In Situ Remediation ofHeavy Organic Deposits Using Aromatic Solvents," Paper #38966, Proceedings of the 68th Annual SPE Western RegionalMeeting, Bakersfield, CA, May 1998.

[25] Paraffin Products: Properties, Technology, Applications, G. Y.Mozes, Ed., Elsevier, NY, 1982.

[26] Murad, K. M., Lal, M., Agarwal, R. K., and Bhattacharyya, K. K.,"Improve Quality of Wax by Hydrofinishing," Petroleum Hydrocarbons, Vol. 7, No. 2, 1972, pp. 144--7.

[27] Ferris, S. W., "Characterization of Petroleum Waxes Tappi,"TAPPI Special Technical Association Publication No. 2, 1963,pp. 1-19.

[28] Himran, S., Suwono, A., and Mansoori, G. A., "Characterization ofAlkanes And Paraffin Waxes for Application as Phase Change Energy Storage Medium," EnugySources, Vol.16, 1994,pp.117-128.

[29] Humphries, W. F., Performance of Finned Thermal Capacitors,NASA TND-7690, Washington; D.C., 1974.

[30] Haji-Sheikh, A., Eftekhar, J. and Lou, D. Y. S., "Some Thermophysical Properties Of Paraffin Wax as a Thermal StorageMedium," Progress in Astronatics and Aeronautics 86, 1983, pp.241-253.

[31] Du, P. C. and Mansoori, G. A., "Phase Equilibrium of Multicomponent Mixtures: Continuous Mixture Gibbs Free Energy

Minimization and Phase Rule," Chemical Engin.eeri.ng Communication, Vol. 54, 1987, pp. 139-148.

[32] Hartono, R., Mansoori, G. A., and Suwono, A., "Prediction ofMolar Volumes, Vapor Pressures and Supercritical Solubilitiesof Alkanes by Equations of 5-tate," Chemical Engin.eeri.ng Communications, Vol. 173, 1999. pp. 23--42.

[33] Riazi, M. R. and Mansoori, G. A. "Simple Equation of State Accurately Predicts Hydrocarbon Densities," Oil & Gas Journal, 1993,pp. 108-111. J

[34] Mohsen-Nia, M., Modarress, H., and Ml\fisoori, G. A., "A SimpleCubic Equation of State for Hydrocarbons and Other Compounds," SPE Paper No. 26667, Proceedings of the 1993 AnnualSPE Meeting, Society of Petroleum Engineers, Ric/>ardson, TX,1��

[35] Nikitin E. D., Pavlov, P.A., and Bessanova, N. V., "Critical Constants of n-Alkanes with from 17 to 24 Carbon Atoms," Journalof Chemical Thennodynamics, Vol. 26, 1994, pp. 177-182.

[36] Frenkel, M., Gadalla, N. M., Hall, K. R., Hong, X., and Marsh, K.N., TRC Thermodynamic Tables-Hydrocarbon; Nim-Hydrocarbon, R. C. Wilhoit, Ed., ThermodYilamic Research Center, TheTexas A & M University System, College Station, TX, 1997.

[37] Twu, C.H., "An Internally Consistent Correlation for Predictingthe Critical Properties and Molecular Weights of Petroleum andCoal-Tar Liquids," Fluid Phase Equlibrium, Vol. 16, 1984, pp.137-150.

[38] Edalat, M., Mansoori, G. A., and Bozar-Jomehri, R. B., ''VaporPressure of Hydrocarbons, Generalized Equation," Encyclopedia of Chemical Processing and Design - 61, Marcel Dekker, Inc.,NY, 1997,pp.362-365.

[39] Letoffe, J. M., Claudy, P., Garcin, M., and Volle, J. L., ''Evaluation of Crystallized Fractions of Crude Oils by Differential Scanning Calorimetry, Correlation With Gas Chromatography,''Fuel, Vol. 74, No. 1, 1995, pp. 92-5.

[40] Braun, R., '!Limits in Differential Thermoanalysis of Waxes,"Fene SeifenAnstrichm, Vol. 82, No. 2, 1980, pp. 76-81.

[41] Handbook on Anti.oxidants and Anti.ozonants, Goodyear Chemicals, Akron, OH, 1977.

[42] Wink, W. A., Delevanti, C.H., and Van den Akker, J. A., Instrumentation Studies IXXVII, Study on Gloss I, A Goni.ophotometric Study of High Gloss Papers, TAPPI, Technical Association of the Pulp and Paper Industry, Vol. 35, December 1953, p. 163A.

[43] Tomsic, J., Dictionary of Materials and Testing, 2'"' ed., SAE International, Warrendale, PA, 2000, p. 205.

Petroleum Waxes

G.Ali Mansoori, H. Lindsey Barnes, Glenn M. WebsterChapter 19, Pages 525-556, 2003, Manual 37 - Fuels and Lubricants Handbook: Technology, Properties, Performance, and

Testing, ASTM Manual Series: MNL37WCD____________________________________

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