Report WR Marnel

8/10/2019 Report WR Marnel

1/32

PETROCHEMICALS

I. Introduction

II. Crude Oil Distillation

III. Hydrocarbon Steam CrackingIV. Petrochemicals Production from Hydrocarbon Intermediates

1. Petrochemicals from Methane

1.1. Direct Reaction of Methane

1.1.1. Carbon Disulfide

1.1.2. Hydrogen Cyanide

1.1.3. Chloromethanes

1.1.4. Synthesis Gas1.1.4.a. Ammonia

1.1.4.b. Methanol

2. Petrochemicals from Ethylene

2.2. Vinyl Chloride


2/32

INTRODUCTION

The crude oil which is pumped out of the worlds oil fields is the result of

the slow decomposition of plant material in the absence of oxygen. As a

consequence, the products are dominated by hydrocarbons: a complex mixtureof mainly alkanes and cycloalkanes, with small amounts of alkenes, aromatic

compounds, compounds containing sulfur or nitrogen, as well as various

inorganic substances. It contains literally thousands of compounds, ranging

from low molecular gases to very large compounds with very high melting

points.

More than 90% of the petroleum produced is used for fuels for heating

and transportation. However, petroleum is also an extremely valuable source ofpetrochemicals, which serve as raw materials for the manufacture of a wide

variety of plastics, synthetic fibers, paints and coatings, adhesives, piping, and

other products of modern society. 90% of the production of synthetic organic

chemicals comes from crude oil and natural gas sources.

After desalting to remove acids and salts, the crude oil is transferred to a

distillation tower where various fractions are separated by fractional

distillation.

CRUDE OIL DISTILLATION

Crude oil distillation is the front end of every refinery, regardless of size

or overall configuration. It has a unique function that affects all the refining

processes downstream of it.

Crude distillation separates raw crude oil feed (usually a mixture of

crude oils) into a number of intermediate refinery streams (known as crude

fractions or cuts), characterized by their boiling ranges (a measure of their

volatility , or propensity to evaporate). Each fraction leaving the crude

distillation unit is defined by a unique boiling point range and is made up of

hundreds or thousands of distinct hydrocarbon compounds, all of which have

boiling points within the cut range. These fractions include (in order of


3/32

increasing boiling range) light gases, naphthas, gasoline, kerosaene, Diesel oils,

lubricating oils, heavy oils and residual oil. Each goes to a different refinery

process for further processing.

Each crude oil fractions will undergone various processes to be convertedinto various petrochemicals as shown in the next figure.


4/32


5/32

HYDROCARBON STEAM CRACKING FOR PETROCHEMICALS

In industrial processes, hydrocarbons are contacted with H2O,

depending upon the desired effect. When hydrocarbon vapors at very high

pressures are contacted with water, water which has a very high latent heat ofvaporization quenches the hydrocarbon vapors and transforms into steam. In

such an operation, chemical transformations would not be dominant and

energy lost from the hydrocarbons would be gained by water to generate steam.

The quenching process refers to direct contact heat transfer operations

and therefore has maximum energy transfer efficiency. This is due to the fact

that no heat transfer medium is used that would accompany heat losses. The

steam cracking of hydrocarbons is an anti-quenching operation, and will

involve the participation of water molecule in reactions in addition to the

cracking of the hydrocarbon on their own.

Since steam and the hydrocarbons react in the vapor phase the reaction

products can be formed very fast. Therefore cracking of the hydrocarbons on

their own as well as by steam in principle is very effective. When steam

cracking is carried out, in addition to the energy supplied by the direct contact

of steam with the hydrocarbons, steam also takes part in the reaction to

produce wider choices of hydrocarbon distribution along with the generation of

H2 and CO.

Reaction:

C x H y + H 2 O + O 2 C2 H 4 + C 2 H 6 + C 2 H 2 + H 2 + CO + CO 2 + CH 4 + C 3 H 6 + C 3 H 8

+ C 4 H 10 + C 4 H 8 + C 6 H 6 + C+ Heavy oils


6/32

Steam Cracking of Naphtha

Naphtha is mixed with superheated steam and fed to a furnace fuel gas +

fuel oil as fuels to generate heat. The superheated steam is generated from the

furnace itself using heat recovery boiler concept. The C2-C4 saturates are fed

to a separate furnace fed with fuel gas + fuel oil as fuels to generate heat.

In the furnace, apart from the steam cracking, steam is also generated.

After pyrolysis reaction, the products from the furnace are sent toanother heat recovery steam boiler to cool the product streams (from about 700

800 C) and generate steam from water.

After this operation, the product vapors enter a scrubber that is fed with

gas oil as absorbent. The gas oil removes solids and heavy hydrocarbons.


7/32

Separate set of waste heat recovery boiler and scrubbers are used for the

LPG furnace and Naphtha steam cracking furnaces

After scrubbing, both product gases from the scrubbers are mixed and

fed to a compressor. The compressor increases the system pressure to 35 atm.

The compressed vapor is fed to a phase separation that separates the

feed into two stream namely the vapor phase stream and liquid phase stream.

The vapor phase stream consists of H2, CO, CO2 C1-C3+ components in

excess. The liquid phase stream consists of C3 and C4 compounds in excess.

Subsequently, the vapor phase and liquid phase streams are subjected to

separate processing.

Gas stream processing:

CO 2 in the vapor phase stream is removed using NaOH scrubber.

Subsequently gas is dried to consist of only H 2 , CO, C1-C3 components only.

This stream is then sent to a demethanizer which separates tail gas (CO + H 2 +

CH 4 ) from a mixture of C1-C3 components. The C2-C3 components enter a

dethanizer which separates C2 from C3 components.

Here C2 components refer to all kinds of C2s namely ethylene, acetylene

etc. Similarly, C3 the excess of propylene, and propane. The C2 components

then enter a C2 splitter which separates ethane from ethylene and acetylene. The ethylene and acetylene gas mixture is fed to absorption unit which is

fed with an extracting solvent (such as N-methylpyrrolidinone) to extract

Acetylene from a mixture of acetylene and ethylene.

The extractant then goes to a stripper that generates acetylene by

stripping. The regenerated solvent is fed back to the absorber.

The ethylene stream is fed to a topping and tailing still to obtain high

purity ethylene and a mixture of ethylene and acetylene as the top and bottomproducts. The mixture of ethylene and acetylene is sent back to the C2 splitter

unit as its composition matches to that of the C2 splitter feed.

Liquid stream processing:

The liquid stream consists of C3,C4, aromatics and other heavy oil

components is fed to a NaOH scrubber to remove CO2


8/32

Eventually it is fed to a pre-fractionator. The pre-fractionator separates

lighter components from the heavy components. The lighter components are

mixed with the vapor phase stream and sent to the NaOH vapor phase

scrubber unit.

The pre-fractionator bottom product is mixed with the deethanizer

bottom product. Eventually the liquid mixture enters a debutanizer that

separates C3, C4 components from aromatics and fuel oil mixture. The bottom

product eventually enters a distillation tower that separates aromatics and fuel

oil as top and bottom products respectively.

The top product then enters a depropanizer that separates C3s from C4

components. The C4 components then enter an extractive distillation unit that

separates butane + butylene from butadiene. The extractive distillation unit

consists of a distillation column coupled to a solvent stripper. The solvent

stripper produces butadiene and pure solvent which is sent to the distillation

column.

The C3 components enter a C3 splitter that separates propylene from

propane + butane mixture. The saturates mixture is recycled to the saturates

cracking furnace as a feed stream.

PETROCHEMICALS FROM METHANE

Methane is the first member of the alkane series. It is the main

component of natural gas and also a by-product in all gas streams from

processing crude oils. It is a colorless, odorless gas that is lighter than air.

As a chemical compound, methane is not very reactive. It does not react

with acids or bases under normal conditions. It reacts, however, with a limited

number of reagents such as oxygen and chlorine under specific conditions. For

example, it is partially oxidized with a limited amount of oxygen to a carbon

monoxide-hydrogen mixture at high temperatures in presence of a catalyst. The

mixture (synthesis gas) is an important building block for many chemicals.


9/32

As mentioned, methane is a one-carbon paraffinic hydrocarbon that is

not very reactive under normal conditions. Only a few chemicals can be

produced directly from methane under relatively severe conditions.

Chlorination of methane is only possible by thermal or photochemical

initiation. Methane can be partially oxidized with a limited amount of oxygen or

in presence of steam to a synthesis gas mixture.

Many chemicals can be produced from methane via the more reactive

synthesis gas mixture. Synthesis gas is the precursor for two major chemicals,

ammonia and methanol. Both compounds are the hosts for many important

petrochemical products.


10/32

Petrochemicals based on Direct Reactions of Methane

A few chemicals are based on the direct reaction of methane with other

reagents. These are carbon disulfide, hydrogen cyanide, chloromethanes, and

synthesis gas mixture.

CARBON DISULFIDE

Physical Properties

Molecular Formula CS 2

Molar Mass 76.14g/mol

Appearance Colorless liquid

Density 1.266g/cm 3

Melting Point -111.61C

Boiling Point 46.24C

Conversion Process

Methane reacts with sulfur at high

temperatures to produce carbon disulfide. The

reaction is endothermic, and an activation energy of

approximately 160 KJ is required. Activated alumina

or clay is used as the catalyst at approximately

675C and 2 atmospheres. The process starts by

vaporizing pure sulfur, mixing it with methane, and

passing the mixture over the alumina catalyst. The reaction could be

represented as:

CH 4 (g) + 2S 2 (g) CS 2 (g) + 2H 2 S(g) H298 = +150 KJ/mol

Hydrogen sulfide, a co-product, is used to recover sulfur by the Claus

reaction. A CS 2 yield of 85 90% based on methane is anticipated.

Uses of Carbon Disulfide


11/32

Carbon disulfide is primarily used to produce rayon and cellophane

(regenerated cellulose). CS 2 is also used to produce carbon tetrachloride.

HYDROGEN CYANIDE (HCN)

Hydrogen cyanide (hydrocyanic acid) is a

colorless liquid that is miscible with water,

producing a weakly acidic solution.

It is a highly toxic compound, but a very

useful chemical intermediate with high reactivity.

It is used in the synthesis of acrylonitrile and

adiponitrile, which are important monomers for

plastic and synthetic fiber production.

Physical Properties

Molecular Formula CHN


AppearanceVery pale, blue, transparent liquid or

colorless gas

Density 0.687g/mL

Melting Point -14 to -12 C

Boiling Point 25.6 to 26.6 C

Conversion Process

Hydrogen cyanide is produced via the Andrussaw process using

ammonia and methane in presence of air. The reaction is exothermic, and the

released heat is used to supplement the required catalyst-bed energy:

2CH 4 + 2NH 3 + 3O 2 2HCN + 6H 2 O

A platinum-rhodium alloy is used as a catalyst at 1100C. Approximately

equal amounts of ammonia and methane with 75 vol % air are introduced to

the preheated reactor. The catalyst has several layers of wire gauze with a

special mesh size (approximately 100 mesh).


12/32


13/32

Chloromethane Production

Methane and Cl2 are mixed and sent to a furnace The furnace has a jacket or shell and tube system to accommodate feed pre-heating to desired

furnace inlet temperature (about 280 300 C). To control temperature, N2 is

used as a diluent at times. Depending on the product distribution desired, the

CH4/Cl2 ratio is chosen. The product gases enter an integrated heat exchanger


14/32

that receives separated CH4 (or a mixture of CH4 + N2) and gets cooled from

the furnace exit temperature (about 400 C).

Eventually, the mixture enters an absorber where water is used as an

absorbent and water absorbs the HCl to produce 32 % HCl. The trace amounts

of HCl in the vapor phase are removed in a neutralizer fed with NaOH. The gas

eventually is compressed and sent to a partial condenser followed with a phase

separator. The phase separator produces two streams namely a liquid stream

consisting of the chlorides and the unreacted CH4/N2.

The gaseous product enters a dryer to remove H2O from the vapour

stream using 98% H2SO4 as the absorbent for water from the vapour. The

chloromethanes enter a distillation sequence. The distillation sequence

consists of columns that sequentially separate CH3Cl, CH2Cl2, CHCl3 and

CCl4.

Uses of Chloromethanes

The major use of methyl chloride is to produce silicon polymers. Other

uses include the synthesis of tetramethyl lead as a gasoline octane booster, a

methylating agent in methyl cellulose production, a solvent, and a refrigerant.

Methylene chloride has a wide variety of markets. One major use is apaint remover. It is also used as a degreasing solvent, a blowing agent for

polyurethane foams, and a solvent for cellulose acetate.

Chloroform is mainly used to produce chlorodifluoromethane

(Fluorocarbon 22) by the reaction with hydrogen fluoride:

CHCl 3 + 2HF CHClF 2 Cl + 2HCl

This compound is used as a refrigerant and as an aerosol propellent. It is

also used to synthesize tetrafluoroethylene, which is polymerized to a heatresistant polymer (Teflon):

2CHClF 2 CF 2 =CF 2 + 2HCl

Carbon tetrachloride is used to produce chlorofluorocarbons by the reaction

with hydrogen fluoride using an antimony pentachloride (SbCl 5 ) catalyst:


15/32

CCl4 + HF r CCl3F + HCl

CCl4 + 2HF r CCl2F2 + 2HCl

The formed mixture is composed of trichlorofluoromethane (Freon-11)

and dichlorodifluoromethane (Freon-12). These compounds are used asaerosols and as refrigerants.

SYNTHESIS GAS

Methane is almost as important as ethene, for not only is it the major

component of natural gas, but also as a feedstock for what is known as

synthesis gas , a mixture of hydrogen, carbon monoxide and carbon dioxide. It

is produced by the catalyzed, high-pressure, high temperature reaction ofsteam with methane, as shown:

The typical composition of synthesis gas from the process varies, but is

typically 50-60% hydrogen, 40-50% carbon monoxide and 2-4% carbondioxide. If pure CO or H 2 is required, then simple post-processing is used:

hydrogen the CO is oxidized with more steam to CO 2 , which is then

removed by absorption carbon monoxide the CO is absorbed into a solution of

copper/ammonia complex, then liberated by heat.

Many chemicals are produced from synthesis gas. This is a consequence

of the high reactivity associated with hydrogen and carbon monoxide gases, the

main constituents of synthesis gas.

Synthesis gas is also an important building block for aldehydes from

olefins. The catalytic hydroformylation reaction (Oxo reaction) is used with

many olefins to produce aldehydes and alcohols of commercial importance.


16/32

The two major chemicals based on synthesis gas are ammonia and

methanol . Each compound is a precursor for many other chemicals. From

ammonia, urea, nitric acid, hydrazine, acrylonitrile, methylamines and many

other minor chemicals are produced. Each of these chemicals is also a

precursor of more chemicals.

Methanol, the second major product from synthesis gas, is a unique

compound of high chemical reactivity as well as good fuel properties. It is a

building block for many reactive compounds such as formaldehyde, acetic acid,

and methylamine. It also offers an alternative way to produce hydrocarbons in

the gasoline range (Mobil to gasoline MTG process). It may prove to be a

competitive source for producing light olefins in the future.

Manufacturing of Synthesis Gas


17/32

Most of synthesis gas is produced from natural gas. However it can also

be produced using crude oil by means of the fractions of naphtha from crude

oil distillation.

The naphtha is heated to form a vapor, mixed with steam and passed

through tubes, heated at 750 K and packed with a catalyst, nickel supported

on a mixture of aluminium and magnesium oxides. The main product is

methane together with oxides of carbon.

Whichever way the methane is obtained, it will contain some organic

sulfur compounds and hydrogen sulfide, both of which must be removed.

Otherwise, they will poison the catalyst needed in the manufacture of synthesis

gas. In the desulfurisation unit , the organic sulfur compounds are often first

converted into hydrogen sulfide, prior to reaction with zinc oxide. The feedstock

is mixed with hydrogen and passed over a catalyst of mixed oxides of cobalt

and molybdenum on an inert support (a specially treated alumina) at 700 K.

Then the gases are passed over zinc oxide at ca 700 K and hydrogen

sulfide is removed:

Primary steam reforming converts methane and steam to synthesis

gas, a mixture of carbon monoxide and hydrogen

High temperatures and low pressures favor the formation of the products

(Le Chatelier's Principle). In practice, the reactants are passed over a catalyst of

nickel, finely divided on the surface of a calcium oxide/aluminium oxide

support


18/32


19/32

used in the low temperature stage is very sensitive to high temperatures, and

could not operate effectively in the high temperature stage.

The gas mixture now contains about 18% carbon dioxide which is

removed by scrubbing the gas with a solution of a base. The carbon dioxide is

released on heating the solution in the carbon dioxide stripper .

The last traces of oxides of carbon are removed by passing the gases over

a nickel catalyst at 600 K. This process is known as methanation . A gas is

obtained of typical composition: 74% hydrogen, 25% nitrogen, 1%methane,

together with some argon.

AMMONIA

Ammonia is one of the most important inorganic

chemicals, exceeded only by sulfuric acid and lime.

This colorless gas has an irritating od or, and is very

soluble in water, forming a weakly basic solution.

Ammonia could be easily liquefied under pressure

(liquid ammonia), and it is an important refrigerant.

Anhydrous ammonia is a fertilizer by directapplication to the soil. Ammonia is obtained by the

reaction of hydrogen and atmospheric nitrogen, the

synthesis gas for ammonia.

Physical Properties

Molecular Formula NH 3

Molar Mass 17.031g/molAppearance Colorless gas

Density 0.73kg.m 3 @15C


Boiling Point -33.34C


20/32

Ammonia Production

(1) Synthesis gas, air and steam are heated by a fired heater using

synthetic natural gas as a fuel. These heated gases are introduced into (2) the

reformer where the methane is converted to carbon monoxide, carbon dioxide

and hydrogen. The exit gases from the reformer enter (3) shift conversion where

the carbon monoxide and water react to form hydrogen and carbon dioxide. In

the (4) carbon dioxide removal vessel, an absorption process is used to remove

the carbon dioxide. The stream from the carbon dioxide removal system still

contains small amounts of carbon monoxide and carbon dioxide so it is sent

through (5) the methanator where they react with hydrogen to form methane. Agas is obtained of typical composition: 74% hydrogen, 25% nitrogen, 1%

methane, together with some argon. Before the stream can be introduced to the

ammonia synthesis loop, the (6) dryers and cold box remove water and

methane along with excess nitrogen so that the hydrogen and nitrogen ratio


21/32


22/32


23/32

The major reactions take place during methanol synthesis converter can

be described by following equilibrium reactions:

The first two reactions are exothermic and proceed with reduction in

volume. In order to achieve a maximum yield of methanol and a maximum

conversion of synthesis gas, the process must be effected at low temperature

and high pressure.

After cooling to ambient temperature, the synthesis gas is compressed to

5.0-10.0 MPa and is added to the synthesis loop which comprises of following

items circulator, converters, heat exchanger, heat recovery exchanger, cooler,

and separator. The catalyst used in methanol synthesis must be very selective

towards the methanol reaction, i.e. give a reaction rate for methanol production

which is faster. And lastly, the obtained methanol is dilled to obtain purer

methanol.

Applications


24/32

PETROCHEMICALS FROM ETHYLENE

Ethylene is sometimes known as the king of petrochemicals because more

commercial chemicals are produced from ethylene than from any other

intermediate. This unique position of ethylene among other hydrocarbonintermediates is due to some favorable properties inherent in the ethylene

molecule as well as to technical and economical factors. These could be

summarized in the following:

o Simple structure with high reactivity.

o Relatively inexpensive compound.

o Easily produced from any hydrocarbon source through steam cracking

and in high yields.o Less by-products generated from ethylene reactions with other

compounds than from other olefins.

Ethylene reacts by addition to many inexpensive reagents such as water,

chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. It can

be initiated by free radicals or by coordination catalysts to produce

polyethylene, the largest-volume thermoplastic polymer. It can also be

copolymerized with other olefins producing polymers with improved properties.Below is the summary the important derivatives of ethylene.


25/32


26/32


27/32

Applications

VINYL CHLORIDE

Vinyl chloride is produced in a two-step

process from ethylene:

Ethylene first reacts with Chlorine to

produce Ethylene dichloride The purified Ethylene dichloride

undergoes selecti ve cracking to form

vinyl chloride

Physical Properties

Molecular Formula C 2H 3Cl


Density 911.00 kg/m 3


Boiling Point -13.4C


28/32

Ethylene Dichloride

Reactions:

o C 2 H 4 + C l2 C 2 H 4 C l2 o

Undesired products: Propylene dichloride and Polychloroethaneso Reaction occurs in a liquid phase reactor with ethylene dichloride serving

as the liquid medium and reactants reacting the liquid phase

o Catalyst is FeCl3 or Ethylene dibromide

Ethylene Dichloride Production

C 2H 4 and Cl 2 are mixed and sent to the liquid phase reactor. Here, the

feed mixture bubbles through the ethylene dichloride product medium. Reactor

operating conditions are 50C and 1.5 2 atm.


29/32

The reaction is exothermic. Therefore, energy is removed using either

cooling jacket or external heat exchanger. To facilitate better conversion,

circulating reactor designs are used. FeCl 3 traces are also added to serve as

catalyst

The vapor products are cooled to produce two products namely a vapor

product and a liquid product. The liquid product is partially recycled back to

the reactor to maintain the liquid medium concentration.

The vapor product is sent to a refrigeration unit for further cooling which

will further extract ethylene dichloride to liquid phase and makes the vapor

phase bereft of the product.

The liquid product is crude ethylene dichloride with traces of HCl.

Therefore, acid wash is carried out first with dilute NaOH to obtain crude

ethylene dichloride. A settling tank is allowed to separate the spent NaOH

solution and crude C 2H 4Cl 2 (as well liquid). The crude ethylene dichloride

eventually enters a distillation column that separates the ethylene dichloride

from the other heavy end products.

The vapour phase stream is sent to a dilute NaOH solution to remove

HCl and produce the spent NaOH solution. The off gases consist of H 2 , CH 4 ,

C 2H 4 and C 2H 6 .

Vinyl Chloride Production

Reaction

o C 2 H 4 Cl 2 CH 2 CHCl + HCl o Charcoal is used as the catalyst

o The reaction is a reversible gas phase reaction


30/32

Ethylene dichloride is initially vaporized using a heat exchanger fed with

process steam. Ethylene vapors then enter a dryer that removes traces of water

molecules. After drying, the vapors enter a pyrolysis furnace operated at 4 atm

and 500 C. The furnace is similar to a shell and tube arrangement with the

gases entering the tube side and hot flue gas goes past the tubes in the shell

side.

The product vapors eventually enter a quenching tower in which cold

ethylene dichloride is used to quench the product gases and cool them. The

gases from the quench tower then enter a partial condenser which produces

HCl as a gas and the liquid stream consisting of vinyl chloride, unreacted

ethylene dichloride and polychlorides.

The liquid stream from the quench tower as well as the condenser is fed

to the vinyl still which produces the vinyl chloride product. The product is

stabilized using a stabilizer as vinyl chloride is highly reactive without

stabilizer.

The bottom product from the vinyl still is fed to a distillation column

which separates the ethylene dichloride from the polychlorides. The ethylene

dichloride vapors are recycled back to the cracking furnace and the ethylene


31/32

dichloride liquid is sent to the quenching tower to serve as the quenching

liquid.


32/32

REFERENCES

Boardman Energy Partners, LLC (2014). Facts About Natural Gas . DateRetrieved: July 17, 2014 from http://benergypartners.com/Facts_About

_Natural_Gas.html

Dakota Gasification Company. Ammonia Plant . Date Retrieved: July 17, 2014from http://www.dakotagas.com/Gasification/Ammonia_Plant/index.html

Ammonia . Date Retrieved: July 17, 2014 from http://www.essentialchemicalindustry.org/chemicals/ammonia.html

Tuna, P. (2013). Generation of Synthesis Gas for Fuels and Chemicals .Date Retrieved: July 19, 2014 from http://lup.lub.lu.se/luur/download?func= downloadFile&recordOId=3732069&fileOId=3732073

Methanol . Date Retrieved: July 17, 2014 from http://en.wikipedia.org/

wiki/MethanolLecture 13: Petrochemicals Overview. Date Retrieved: July 17, 2014
http://benergypartners.com/Facts_Abouthttp://www.dakotagas.com/Gasification/Ammonia_Plant/index.htmlhttp://www.essentialchemical/http://en.wikipedia.org/http://en.wikipedia.org/http://www.essentialchemical/http://www.dakotagas.com/Gasification/Ammonia_Plant/index.htmlhttp://benergypartners.com/Facts_About

Report WR Marnel

Documents

Transcript of Report WR Marnel