Edible Oil Refinery : Cooking Oil Refinery : Vegetable Oil Refinery      

Edible Oil Refinery 5 Tonnes per day.

1. Neturalizer

2. Neturalizer

3. Bleacher

4. Deodourizer

5. Cooler

6. Thermic Fluid Boiler

7. Filter Press

8. Filter Press

9. Raw Oil Tank

10. Bleach Oil Tank

11. Soap Pan

12. Soap Pan

   

Steam generator and vaccum pump are on the back side and so can not be seen. Berometric Condensor and catchalls with 40ft. tower not shown.

 

Process Description :

 

For refining the oil, there are three basic processes in the refinery. First process is neutralizing the oil in the neutralizer to remove the Free Fatty Acids (FFA) by adding caustic soda. Oil is heated upto about 60°C by thermic fluid coils and oil is stirred by stirrer. Then soap stock formed due to chemical reaction is allowed to settle at the bottom of the neutralizer from where it is taken out into soap pan.

Neutralized oil is drawn into the second vessel called bleacher where colour of oil is removed by bleaching process with aid of chemicals such as carbon black and bleaching earth. Oil is generally heated upto 110°C by thermic fluid coils. Stirring is also continued. Bleaching process is done under vacuum.

Bleached oil then goes to the filter press where bleaching earth and chemicals are separated and clean bleached oil is then drawn to deodourizer where oil is heated above 110°C through thermic fluid coils and then live steam is given to the oil from the bottom steam nozzles and temperature of oil is raised upto 200 to 220°C through thermic fluid coils. Entire process is done under high vacuum. Thus smell is removed from the oil in the deodourizer. Then it goes to cooler where water circulating coils take away heat and oil is cooled. Again it goes to second filter press where completely refined and transparent colour less oil is obtained.

Thermic Fluid Boiler, Vacuum Pump, Barometric Condenser, Catchalls, Steam Generator etc. play their role in the refining process. So these equipments are part of the refinery and connected with the vessels through pipelines.

 

Additional Process for palm oil refinery :

Specially for palm oil refinery, fractionation process is required in which palm olene and palm sterene are separated by scientifically cooling the refined palm oil by chilling plant and then filtering the oil. For this purpose crystalizing vessel is used in which chilling pipe coils cool the oil for fractionation. Palm sterene crystals are formed due to chilling which are separated in the filter press and pure liquid of palm olene is obtained and palm sterene cake is retained in the filter press.

 

Specifications of Edible Oil Refinery :

Capacity 5 tonnes per day i.e. 4 batches of 1250 kg. eachS

» All the main vessels i.e. two neutralizers, one bleacher and one deodourizer are properly arranged on the first floor of the steel structure. So all these vessels are hanging on the steel strucutre. Just below the two neutralizers, two soap pans are resting on the ground floor in which soap stock is collected. There is a steam pipe arrangement in the soap pans also.

» Steel structure has size of 14ft. x 14ft. (i.e. 4.25mtr. x 4.25mtr). First floor is 9ft. above the ground level. There are 8 coloumns of double chanel which supports the entire steel structure. It has proper staircase and railing on all the sides of steel structure at the first floor and also on staircase. Two filter presses are also accomodated on the first floor of the steel structure.

» Two oil tanks i.e. raw oil tank and bleached oil tank are accomodated under the strucutre on the ground floor. Then cooler, thermic fluid boiler, two steam generators, vacuum pump, water pumps, oil pumps and refined oil tank are arranged on the ground floor around the steel structure i.e. outside the square of 14ft. x 14ft. of the steel structure. So total space occupied is about 30ft. × 30ft. (9mtr. x 9mtr.)

» 40ft. tower is erected just near the deodourizer and its complete structure is supported from the ground floor and also it is attached with the refinery structure. Berometric condenser is arranged at 40ft. height to create proper vacuum.

» All types of piplines are interconnected as per the requirement of the refinery i.e. oil pipelines (yellow colour), vacuum pipelines (blue colour), steam pipelines (black colour), water pipelines (white colour), thermic fluid pipelines (red colour). At all appropriate places, proper valves are provided in the pipelines.

» Neutralizer is provided with thermic fluid coil for heating the oil.

» Bleacher is provided with double pipe coil. One is for thermic fluid and another is for cooling water.

» Deodorizer is provided with double pipe coil i.e. in both the coils, thermic fluid is circulated. Steam is ejected from the stainless nozzles provided on the steam pipe cross supported at the bottom.

» Cooler is provided with double pipe coil. Both for cooling water.

» In every vessel temperature gauge is provided. Vacuum gauge is provided on deodorizer, bleacher and cooler.

» Neutralizer is open on the top having conical bottom.

» Bleacher has dished ends on both the sides. Similarly deodorizer has dished ends on both the sides. Cooler has also dished ends on both the sides.

Specification of Edible Oil Refinery with fractionation Process :

» There will be chilling plant for fractionation process which will include shell and tube chiller, compressor, motor, pump, condenser, control panel box etc.

» Crystallizing unit which is similar to neutralizer complete with chilling coil.

» Filter press for separation of palm olein and palm stearin.

The CHEMPRO Upgrading Approach

When we come up with a plan to upgrade a plant, the first thing we try to do is preserve as much of original investment as possible. With no need to duplicate existing facilities, one can enjoy savings in capital outlay. One can count on the cost of upgrading being substantially less than the cost of procuring a completely new plant. In theory, most of the existing equipment will be expanded to higher capacity. But after careful study of the cost-benefit analysis we recommend upgrading for best overall results against the capital outlay. Ideally, state of the art equipment is incorporated to make the existing plant operate with efficiency similar to a totally new plant.

CHEMPRO's customized approach to an upgrade gives the greatest benefits in the following areas :

To increase existing plant production capacity when one needs to meet new commitments in sales increases.

To achieve economy of scale in production or to meet a lower break-even Production cost.

CHEMPRO started with replacing of obsolete filter presses with Pressure Leaf Filters and in a short span of 3 years we installed more than 40 Pressure Leaf Filters from 10 sq. m. to 40 sq. m. filtration area which gave our customers benefits in terms of expanded capacity, utility savings and ease of operation. Buoyed with the success of our pressure leaf filter installations we found the need to offer continuous bleaching systems as an upgrade so that our clients could achieve still higher production capacities, consistent quality , ease of operation and an automated dosing of chemicals. In a span of 2 years we installed 20 such continuous bleaching systems which was again widely acclaimed by the industry as better than the contemporary systems offered by multinationals at exorbitant prices.

We then found the need to upgrade the deodorization process by changing the Batch deodorizer into continuous by installing SS trays, augmenting the heat exchange system by installing interchangers, revamping of existing vacuum systems and thus enabling our customers achieve quality in comparison to that offered by the multinationals.

Again our customers rewarded us with orders varying from 25 TPD to 200 TPD complete grassroot vegetable oil refining plants. In a short span of 2 years again we installed 8 plants upgrading each time to meet the ever changing technology needs of the industry. The need of the hour in industry is plant which can cater to variety of oils like palm oil, palm kernel oil, soybean oil, cottonseed oil, corn oil, rapeseed oil, sunflower oil, etc. We were required to upgrade a 100 TPD tray column to a 200 TPD physical refiner with the same steam consumption which we did by installing a Packed Column Prestripper and a cascade-tray Deaerator. This was another milestone we achieved heralding a new era in the refining technology.

THE NEUTRALIZATION PROCESS

Oil phase free of hydratable gums flows to a Centrifugal mixer after heating in a plate heat exchanger, where it is added with phosphoric acid from acid storage tank by a metering pump. The mixture is further taken to a Centrifugal mixer where it is added with caustic lye from lye solution service tank by a metering pump. The caustic solution circuit is completed with storage tank and recirculation pump. The mixture is then taken to a centrifuge where the non-hydratable gums and soap stock are separated and are pumped out of the system by a pump via a soap collecting tank.

Washing:Oil free of gums and having traces of soapstock is pumped by a pump through a plate heat exchanger where it is heated by steam. Then it is sent to the Centrifugal mixer to be mixed with water and further centrifuged in a centrifuge for water washing. The washed water is then further sent to the slop oil tank for collection and recovery of escaped neutral oil which is then taken back to the system by a pump.

THE BLEACHING PROCESS

The unique CHEMPRO "SOFTBLEACH" bleaching system gently removes residual phosphatides, metals, soaps and oxidation products in addition to colouring matters. The feedstock is heated up in the Crude/Neutral Oil Economiser or Crude/Neutral Oil Heater to degumming or bleaching temperature. When there is a need for acid pretreatment, phosphoric acid is mixed vigorously with the oil in a Acid Mixer to ensure efficient mixing. The resultant mixture is than held in a Retention Tank to allow for the precipitation of gums before going to the Bleacher through the cascade vacuum dryer.

When acid pre-treatment is not required , the feed stock is fed directly to the Bleacher after heating through the cascade vacuum dryer. Bleaching Earth and Activated carbon is added to the oil through a dosing unit which is controlled by PLC. The Bleacher is proprietary designed with internal partitions and set of high efficiency turbine agitators to avoid short cycling and provide necessary retention time before filtration. The conjunction of vacuum dryer with a Bleacher is what is unique about "SOFTBLEACH" whereby oil going to the Bleacher is thoroughly dried and deaerated in the cascade vacuum dryer besides the fugitive particles from the Bleacher are countercurrently scrubbed by the downcoming oil and hence bleaching earth going to the hotwell is avoided. The bleached oil from the Pressure Leaf Filters is transferred to the Bleached oil tank for intermediate storage.

THE DEODORIZATION PROCESS

The CHEMPRO "COMPACK DEODORISER" is based on thin-film, counter-current distillation technology which drastically reduces steam consumption less than half of what one would use in a conventional tray deodorizer. The COMPACK DEODORISER handles the most demanding of processing needs for a variety of stocks, in the most efficient manner besides being gentle on the oil. This ensures an extremely high steam to-oil interfacial surface without buildups or stagnant zones. Fatty acid removal occurs instantaneously and hydrolysis is avoided. Lower temperatures and lower residence times result in lower trans-fatty acid formation.

The COMPACK DEODORISER is available in variants like single column and split column design whereby the packed column and tray column are in series or in parallel respectively. The advantage in the latter being flexibility to use only the tray column bypassing the packed column if need arises. Besides the other option available is final heating and cooling under vacuum . The superior scrubbing equipment featuring structured packing and strategically placed demisters ensures minimal carry-over of the fatty acid to the hot well.

THE DEWAXING PROCESS

Definition & OverviewDewaxing: Separation of waxes, esters of long chain fatty acids and long chain primary alcohols present in mainly sunflower and maize oil.

Winterisation: Separation of saturated triacylglycerols from e.g. cottonseed oil and partly hydrogenated oils.

Some oils are dewaxed before packing so as to remove waxes, which are dissolved in the oil. Most of the oils do not need dewaxing as they contain little or no waxes. Only sunflower oil & Rice Bran oil contain appreciable quantities of wax to give a hazy appearance during winter season due to precipitation of dissolved waxes and hence require to be dewaxed. Dewaxing is carried out by chilling the oil up to 10-15°C followed by filtration of precipitated solids. The oil thus treated gives a sparkling appearance even in winter temperatures.

Winterisation is another name to the process of dewaxing. The name winterization appears as during winter when the temperature is low, waxes present in the oil crystallizes, they give hazy appearance to the oil.

DescriptionDewaxing (also called winterization) of sunflower oil is essential when the oil is to be used as salad oil. The presence of wax makes the oil appear cloudy at room temperature. The oil normally becomes cloudy in 5–6h but with proper dewaxing the oil remains clear after 24h of storage at 0˚C.

The following steps are used to dewax sunflower oil:

Crude oil is refined and bleached to low phosphorus (<1ppm) and low moisture content (<0.1%). The oil is heated to 55˚C to make sure the oil is fully liquid. The oil is cooled slowly to 7–8˚C. Cooled oil is held in a specially insulated tank with a special slow-speed mechanical agitator. Preferably, the oil is held for 12–24h at this temperature. The oil is mixed with diatomaceous earth/filter aid through an in-line mixing system and filtered through

a pressure leaf filter pre-coated with diatomaceous earth/filter aid. The filtered oil is collected, checked for cold test and filterable impurities, and then deodorized. The deodorized oil is checked again for cold test along with the other analyses listed earlier.

Dry Fractionation

OverviewThe   widespread use of the   three   oil modification processes - hydrogenation, interesterification and fractionation - extended the range of applications of the triglyceride oils. These processes principally serve the  purpose of modifying the melting properties of oils and  fats in order  to  improve their functional properties in specific  applications,  but the  processes are  also  used to improve  the  stability  of the oils and fats thus processed.

In edible oil processing, a fractionation process consists of a controlled cooling of the oil, thereby inducing a partial, or ‘fractional’, crystallization. The remaining liquid (olein) is then separated from the solid fraction (stearin) by means of filtration or centrifugation.

Natural oils and fats have different characteristics due to the fact that they are composed of a great number of different triglycerides. These contain fatty acids with carbon chins of different lengths and with different degrees of unsaturation.

Triglycerides with a high degree of unsaturation, indicated by a high iodine value, have a lower melting point than those containing more saturated fatty acids. If oil is cooled to a certain temperature, the high melting triglyceride (Stearin) will crystallize while the low melting ones will remain fluid. The stearin can then be separated from oil (Olein) by different methods and the fat/oil is thus divided into two fractions: Stearin with a high melting point and olein with a low cloud and melting points.

This technique is called fractional crystallization and used to obtain oils or fats more suitable for example, as cooking oils or for margarine/shortening production.

Three palm oil fractionation processes which are in use:

Dry Fractionation: through batch crystallization of oil without using additives by controlled cooling and subsequent continuous filtration.

Solvent Fractionation: through continuous crystallization of the oil in a solvent followed by separation of the liquid and solid fractions through a continuous drum filter. Solvent fractionation, involves the use of hexane or acetone to let the high-melting components crystallize in a very low-viscous organic solvent. This can be helpful with respect to the selectivity of the reaction, but mainly offers advantages in the field of phase separation: much purer solid fractions can be obtained, even with a vacuum filtration. Being a more expensive process, it is less common than dry fractionation and only comes into the picture when a very high added value of (at least one of) the resulting fractions makes up for the high cost.

Detergent Fractionation: through batch or continuous crystallization of the oil by controlled cooling and separation of the fractions either by gravity or centrifugation after adding a surfactant.

Alternative Routes to Fractionate Palm Oil Key: CBE =cocoa butter equivalent, CBI = cocoa butter improver, PMF = palm mid- fraction

Description Dry fractionation of oils and fats is the separation of high-melting triglycerides from low-melting triglycerides by crystallization from the melt. Apart from blending, it is the cheapest process in oils and fats processing. It is a pure physical process compared to other chemical modification processes such as hydrogenation and interesterification which modify triglycerides. Its most important applications are: palm olein used extensively as frying oil, palm super olein as salad oil and frying oil, the palm-mid fraction as component of cocoa butter equivalent, palm kernel stearin as cocoa butter substitute. Dry fractionation, also known as crystallization from the melt, is fractional crystallization in its most simple form, and the economy of the technology allows it to be used for production of commodity fats. Dry fractionation has long been regarded as an unpredictable, tedious and labor-intensive process. However, the relatively cheap dry fractionation technique has evolved to the modification technology of the 21st century, as without additives, polluting effluents or post-refining involved, the sustainability and safety of the process is second to none.

It should be able to gently cool down a mass of oil and keep the resulting crystal suspension as homogeneous as possible. Note that such gentle cooling means in fact imposing very low supercooling conditions, and it will result in a formation of fewer and larger crystals, because the said conditions simply rule out the existence of a mass of tiny crystals. Fat crystallization is a fairly exothermic reaction (up to 180 kJ can be released for every kg of crystals formed), so the efficiency with which this energy can be removed is an important design feature. For most industrial crystallizers, this ranges between 120 and 200 W/m2.K. Although the triglyceride separation theoretically is already established during crystallization, it is clear that the separation stage itself effectively determines the product yields as well as the stearin quality. As more residual olein can be expelled from the solids cake, the final stearin will be more concentrated in crystals and will turn out ‘purer’ and will display higher and steeper melting. The olein quality is determined entirely by the amount and selectivity of crystallization in the preceding stage. In some applications, the formed crystals are often not sufficiently stress-resistant and get squeezed through the filter medium. Obviously, such contamination of crystals in the olein phase affects the efficiency of the fractionation process negatively and results in a liquid phase with inferior cold stable properties. Overall, the ‘permitted’ degree of olein dilution in the stearin cake determines the choice for the applied separation technology.

Figure: Pressure Leaf FilterThe development of membranes for use in pressure filtration had a widespread effect on fractionation technology, making both vacuum filtration in dry fractionation as well as LIPOFRAC  fractionation  almost  instantly redundant.  By  using  membrane filter presses, olein yields in palm oil fractionation could be  raised to close on 80%  when aiming for an  increase in Iodine Value of 5 units, and  two-stage fractionation, which could be  used to produce olein of higher Iodine Values or stearin containing less entrained olein, became an attractive proposition.

When   first  introduced,  pressure  filtration using  membranes  was  carried  out   at pressures of 6-8  bar,  but  in more  recent years higher pressures have been used. The  use of high squeeze pressure (30 bar)  in the filter makes it possible to produce a palm mid-

fraction that matches in its principal characteristics the mid-fraction obtained by solvent fractionation. Also by changing  the  sequence of the  fractionation  stages in  a  two- stage process, different qualities of the fractions may be obtained, thus enhancing the versatility of the process.

The first step of dry fractionation of palm oil yields olein fractions with a cloud point below 10°C. The olein fractions are used as a substitute for soft oils in frying, cooking and salad oils or are being further fractionated. Together with a further development of single-stage palm oil fractionation by technological improvements, there is an increased tendency to execute a double or triple fractionation of palm oil in order to produce fractions with specific characteristics such as high IV superoleins (IV>65) and hard palm-mid-fractions (hard PMF) (IV<36).

The latter fraction can serve as a feedstock for the production of typical cocoa butter equivalents (CBE), which are non-lauric fats similar in their physical and chemical properties to cocoa butter. They are often prepared by solvent fractionation, though the more contemporary developments within dry fractionation (better suited crystallizers, improved separation technologies) are closing the gap between the quality of solvent- and dry-fractionated hard PMF.

Economics of FractionationDry fractionation has the advantage of basically only requiring crystallisers and  filters, though  filter costs have risen considerably as the  separating performance of the filter has grown. Dry fractionation is also non-energy-intensive, which obviously is advantageous from the point of view of operating costs.

It must be  remembered, however, that  in the  case of fractionation the  value of the secondary fraction(s) can play a significant role in the economics of production., and  it is in this respect that fractionation is at a disadvantage when compared to the other  oil modification processes, i.e. hydrogenation and interesterification , as these processes produce no secondary products that require marketing.

Miscella Refining

What is Refining? The crude oil obtained either from expellers or solvent extraction plant contains impurities, which must be removed to make the oil edible, more palatable and stable against rancidity upon storage. The process of removing these impurities is called refining.

Impurities present in the Oil

Gums: Gums are phospholipids. There are two types of gums present, hydratable and non-hydratable. Hydratable gums are removed during degumming steps.

Hydrolysis Products Of Oils: Like Diglycerides and monoglycerides and free fatty acids. These are removed during neutralisation step.

Proteineous Matter, Carbohydrates, Resins: These are removed during neutralisation step. Colouring Matter: Pigments such as chlorophyll (green colour) carotene (red colour), anthophyll

(yellow colour) and gossypol (orange colour). These colour bodies which impart distinct colour to the oil are removed during neutralising and bleaching steps.

Odour-causing Chemicals: They are generally present in small quantities but their presence imparts strong, sometimes objectionable odour to the oil. These substances are volatile in nature and removed by deodorisation step.

Waxes: Some oils like sunflower contains appreciable amounts of waxes. Waxes are high melting esters of fatty alcohol with long chain fatty acids. These are removed by dewaxing step.

What is Miscella Refining? Miscella is defined as a mixture of oil and solvent that results from the extraction of flakes or extruded cottonseed kernels. Thus the refining of the oil in a solvent (usually Hexane) in which it was extracted is known as “miscella refining”. Refining is done to remove pigments, free fatty acids and other mucilaginous materials.

Process Description

The crude miscella feedstock from the extractor is first adjusted to the desired miscella concentration by evaporation in the first stage evaporator or economiser against the outgoing vapours from the deodorosed tank.

The crude miscella is pumped through a heat exchanger to bring the miscella upto the desired processing temperature.

The crude miscella proceeds through a flow measuring device enters the neutralization process. o This process is completed by a four step process: Conditioning, Neutralization, Washing, and

Drying. o The fats are heated between 40º and 85ºC and treated with an aqueous solution of sodium

hydroxide(Caustic Soda). o Conditioning transforms non-hydrate phospholipids into their hydrate form by breaking down

metal/phosphatide complexes with a strong acid(Phosphoric Acid). o In neutralization the removal of free fatty acids and residual gums takes place. o Washing is the removal of residual gums by hot water. o Drying is the removal of moisture under a vacuum.

The reacted mixture is then passed through a trim heat exchanger to ensure the proper temperature for the centrifugation in the Hermetic Self cleaning centrifuge. The light coloured, refined miscella is easily separted from the dark brown gelatinuous soapstock in the specially designed centrifuge with nitrogen

blanketing. The oil is dissolved in hexane in miscella refining, which is why the separators which separate the soapstock from the neutralization process are blanketed with inert gas.

The refined miscella then reenters the extraction plant stripping system for removal of remaining hexane.

The soapstock, with its low hexane content, is usually pumped directly to the desolventiser-toaster for the recovery of hexane.

The addition of soapstock to the meal in the deodorized tank helps prevent excessively dusty meal and gives it a more natural appearance and makes it easier to handle. The soapstock generally increases the weight and fat content of the meal by approximately 0.9% and adds to its nutrient and commercial value as an animal feed.

The soapstock also tends to decrease the free gossypol content remaining in the solvent extracted meal.

Advantages of Miscella Refining

Removal of colour bodies before the oil is heated to remove hexane. This gives a finished product with excellent colour properties.

A lower refining loss due to less occluded neutral oil in the soapstock. Elimination of the water washing and vacuum drying step which is necessary in conventional refining to

remove residual soap resulting in reduction in pollution problems. Reduction in energy requirements due to the physical properties of Miscella ie. Low specific gravity and

lower viscosity. Higher yields due the fact that the miscella does not easily emulsify and the soap tends not to entrain oil. Removal of gums, colour bodies and other impurities in miscella refining helps prevent loss of

efficiency in evaporators. The effluent is eliminated as the rerefining and washing step is eliminated. Increased flexibility of operation because refining, degumming, dewaxing and hydrogenation can be

performed continuously in the miscella. Allow adding purchased crude oil or off specification refined oil to current plant production of miscella

for refining or reprocessing. The miscella containing soapstock can be advantageously added to the meal for solvent recovery and to

utilize nutrients in the soapstock.

Batch Refining Plant

Refining of vegetable oils is essential to ensure removal of gums, waxes, phosphatides and free fatty acid (F. F.A.) from the oil; to impart uniform colour by removal of colouring pigments and to get rid of unpleasant smell from the oil by removal of odiferous matter.

Refining is carried out either on batch operation or as continuous operation. With certain oils even physical refining can be carried out instead of chemical.

For processing less than thirty tones of oil per 24 hours, and when oil has F.F .A. content of 1 % or less normally batch process is recommended. Batch process involves low capital investment, simplicity of operation and low maintenance, making refining economically a viable proposition even at capacity as low as 10 tonnes per 24 hours.

The equipment involved are Neutralizer, Bleacher, Deodorizer, Heat Exchanger, High & low vacuum equipment & Filters. Troika plant with batch process have been operating at number of places, processing varity of vegetable oils.

If you are looking out for a refining line batch or continuous, physical or chemical for conventional or nor conventional vegetable oil -Get in touch with Troika -The Technocrats to Oils & Fats Industry, In the service since 1971.

VEGEATABLE OIL REFINING PLANTBatch Refining Plant Refining of vegetable oils is essential to ensure removal of gums, waxes, phosphatides and free fatty acid (F. F.A.) from the oil; to impart uniform colour by removal of colouring pigments and to get rid of unpleasant smell from the oil by removal of odiferous matter.

Refining is carried out either on batch operation or as continuous operation. With certain oils even physical refining can be carried out instead of chemical.

For processing less than thirty tones of oil per 24 hours, and when oil has F.F .A. content of 1 % or less normally batch process is recommended. Batch process involves low capital investment, simplicity of operation and low maintenance, making refining economically a viable proposition even at capacity as low as 10 tonnes per 24 hours.

The equipment involved are Neutralizer, Bleacher, Deodorizer, Heat Exchanger, High & low vacuum equipment & Filters. Troika plant with batch process have been operating at number of places, processing varity of vegetable oils.

If you are looking out for a refining line batch or continuous, physical or chemical for conventional or nor conventional vegetable oil -Get in touch with Troika -The Technocrats to Oils & Fats Industry, In the service since 1971.

Continuous Refining Line Refining of vegetable oils is essential to ensure removal of Gums, Waxes, Phosphatides and Free Fatty Acids (F.F.A.) from the oils.

For capacities higher than 30T/24hours Continuous Refining Process is recommended against Batch Refining.

Continuous Refining will comprise of following steps:-

Pretreatment / Degumming Section:- Here the oils are given acidic treatment where by gums are precipitated and separated out by centrifugal separation or some times only gum conditioning is carried out (when gum content is low) and gums are separated in subsequent neutralising process.

Neutralising Section:-The pretreated oil is subjected to Alkali Refining. The caustic soda reacts with Free Fatty Acids (F.F.A.) present

in the oil and forms soap stock, the soap stock is separated out by centrifugal separator, oil is washed with water for complete removal of soap stock. The wash water is separated out by centrifugal separators.

Bleaching Section:-The neutralized oil is treated with bleaching earth/activated carbon for removal of colouring pigments. The bleaching agent is filtered out in vertical pressure leaf filters. Troika design ensures uniform consistency in colour with minimum requirement of bleaching agent. The bleaching line is versatile and adoptable for all varieties of vegetable oils.

Deodorization Process:- As the name suggest process is meant for removal of odour. Every vegetable oil has its own distinct natural odour. During neutralization and bleaching operation unpleasant odour is imparted to the oil, it is therefore essential to remove this odour. The deodorisation is essentially a process of removal of odiferous matter. The operation is carried out at high temperature by injecting open steam and maintaining high vacuum at which time all odoriferous matter is distilled off and carried away to barometric condensors through vacuum system. The resultant oil is odourless – deodorized oil.

Dewaxing Section :-Oils like sunflower oil or maize germ oil (corn oil) have waxes present in them. At low temperature these waxes gives hazy appearance to oil, which is not liked by consumers. It is therefore essential to remove these waxes prior to bottling and marketing of oil. Troika offers dewaxing units.

Physical Refining:-For oils like palm oil there is no necessity to go for alkali refining. After pretreatment of oil the oil is deodorized cum physically refined. The Free Fatty Acid (F.F.A.) present in the oil is distilled off at high temperature and high vacuum. Troika offers physical refining system also.

Thus for any of your refining requirement of vegetable oils, whether batch or continuous Alkali Refining or Physical Refining Troika is at your service for more information please contact.

DEGUMMING - INTRODUCTION

1.  The Nature of Gums and Phosphatides

Crude oil obtained by screw pressing and solvent extraction of oilseeds will throw a deposit of so-called gums on storage. The chemical nature of these gums has been difficult to determine. They contain nitrogen and sugar and can start fermenting so they were at one stage thought to consist of glycolipids and proteins. Now we know that these gums consist mainly of phosphatides but also contain entrained oil and meal particles. They are formed when the oil absorbs water that causes some of the phosphatides to become hydrated and thereby oil-insoluble. Accordingly, hydrating the gums and removing the hydrated gums from the oil before storing the oil can prevent the formation of a gum deposit. This treatment is called water degumming. It is never applied to fruit oils like olive oil and palm oil since these oils have already been in contact with water during their production.

Water degumming is the oldest degumming treatment and also forms the basis of the production of commercial lecithin. I use the term ‘commercial lecithin‘ here to make a distinction from the use of the word ‘lecithin’ as the trivial name for the compound phosphatidylcholine (PC). Similarly, phosphatidylethanolamine (PE) has the trivial name ‘kephalin’. Since the water degumming process involves more water than when crude oil is allowed to absorb moisture from the atmosphere, the gums resulting from the water degumming process also remove hydrophilic substances such as sugars from the oil.

Lecithin as obtained by drying the gums resulting from the water degumming process contains a mixture of different phosphatides. The structural formulae of the main phosphatides present in lecithin are shown in Figure 1 (further information on phosphatides is available here...).

Figure 1. Chemical structure of most common phosphatides and indication of bonds that are hydrolysed by various phospholipase enzymes.

Table 1 gives the phosphatide composition of the phosphatide fraction in lecithins obtained from different oils.

Table 1. Composition (wt %) of phosphatides of various lecithins, adapted from [1]

Phosphatide Soyabean Sunflower seed RapeseedPC 32 34 37PE 23 17 20PI 21 30 22PA 8 6 8Others 15 13 13

Please keep in mind that Table 1 refers to lecithins, the mixture of phosphatides that has been obtained by degumming crude oil with water. Since this water degumming process does not remove all phosphatides from the oil, Table 1 does not reflect the composition of the phosphatides present in the crude oil itself.

Just as a triglyceride oil is a mixture of triacylglycerols with different fatty acids, each phosphatide is also a mixture of different compounds. These compounds differ in their fatty acid composition and isomerically, in their location on the glycerol backbone. In general, the fatty acid composition of the phosphatides reflects the fatty acid composition of the oil in which these phosphatides occur but it tends to have a higher palmitic acid content and a lower oleic acid content than the oil as illustrated by Table 2.

Table 2 Fatty acid compositions of vegetable lecithins and oils. adapted from [1] and [2].

Fatty acidSoya bean Sunflower seed Rapeseed

Lecithin Oil Lecithin Oil Lecithin Oil16:0 16 11 11 7 7 418:0 4 4 4 5 1 218:1 17 23 18 29 56 6118:2 55 54 63 58 25 2218:3 7 8 0 0 6 10Others 1 0 4 1 5 1

The above table contains the data required for arriving at a conversion factor that permits the amount of phosphatides present in the oil to be calculated from its phosphorus content. For the oils represented in Table 2, this factor equals about 25 to 26 [3]. In other words, oil containing say 200 ppm of phosphorus contains about 0.5 wt% phosphatides.

On the other hand, the literature often uses a factor of 31.5 [3] or thereabouts to arrive at the acetone-insoluble component of the lecithin. This difference stems from the fact that the acetone-insoluble component of lecithin also comprises glycolipids and sugars. The factor of 31.5 is therefore very much an empirical value. It should only be used for oils that have not yet been water degummed since on water degumming, sugars are removed. For water degummed oils, which contain alkaline earth salts of PA and lysophosphatidic acid (LPA) and some PE and lysophosphatidylethanolamine (LPE) and do not contain any more sugars, a factor of 23 to 24 should be used to convert phosphorus to phosphatides.

2.  Hydratability of Phosphatides

The extent to which a phosphatide present in the crude oil is removed during water degumming depends on its hydrophilicity. Phosphatidylinositol has five free hydroxyl groups on the inositol moiety that make PI strongly hydrophilic. Consequently, PI present in crude oil will be hydrated during the water degumming treatment and the PI content of properly water-degummed oil is negligible. Similarly, the positive charge of the trimethylamino group in phosphatidylcholine makes this phosphatide hydrophilic. This hydrophilicity does not depend on the pH of the water used to degum the oil since even at pH > 5, when the phosphate group in the PC is dissociated and therefore carries a negative charge, it does not form an internal salt with the quaternary amino group for steric reasons. Consequently, the positive quaternary amino group remains isolated at all pH values and causes PC to be hydrophilic at all pH values.

Table 3 shows what charges the various phosphatides carry at which pH.

Table 3. Charges of phosphatides as a function of pH.

pH PC PE PI PA Ca-PA2 + + 0 0 03 (+) (+) (0) (0) 04 (±) (±) (-) (-) 05-7 ± ± - - 08-9 ± ± - (2-) 0>10 ± - - 2- 0

Some charges in Table 3 have been put between brackets. They indicate a transition between the value at lower pH and the value at higher pH. So according to Table 3, almost all phosphatidylethanolamine (PE) molecules have a positive charge at pH=2. This charge causes these molecules to be hydrophilic so at that pH, PE is hydratable. When the pH is increased, more and more phosphate groups dissociate and so a Zwitterion (indicated by ±) is formed in which the positive amino group forms an internal salt with the negative phosphate group. The positive and negative charges are so close together that the hydrophilicity of this Zwitterion is quite weak and on water degumming, the hydration of PE is incomplete. Accordingly, water degummed oil still contains some PE.

Now we come to phosphatidic acid (PA). In an acid environment, the hydroxyl groups of its phosphate moiety will not dissociate since the pKa value of the first hydroxyl group equals 2.7-3.8 [4]. Consequently, PA will be poorly hydratable and remain in the oil when this is brought into contact with acid water. When the pH of this water is raised to 5, most of the PA will be dissociated so that the molecule has a negative charge giving it a hydrophilicity that makes it hydratable. Accordingly lecithin contains some PA as illustrated by Table 1. When the pH of the water is raised even further, the second hydroxyl will also dissociate since its pKa is 7.9-8.6 [4], whereby the actual value depends on what other salts are present in the water.

But what about the calcium salt of PA? According to the column on the far right in Table 3, this remains without charge at all pH values because the divalent calcium forms a salt with the two dissociated hydroxyl groups of the phosphate moiety. That is the reason that alkaline earth salts of PA remain in the oil when it is degummed with water. They are the main constituents of the non-hydratable phosphatides (NHP). However, when the oil is alkali refined, these salts are removed. Two possible mechanisms have been shown in Figure 2:

Figure 2. Calcium phosphatidate at high pH.

In the left hand structure in Figure 2, a hydroxyl ion has been linked to the Ca2+ ion so that it only has a single positive charge and the salt itself has a negative charge making it hydratable. In the right hand structure, the hydroxyl ion has been linked to the phosphorus of the phosphate moiety so that the calcium retains its 2+ charge. Because of the addition of a negative hydroxyl group the salt itself becomes negatively charged and thus hydratable.

PA moieties present in crude oil are generally considered to originate from the hydrolysis of phosphatides such as PC, PE and PI. This hydrolysis is most likely catalysed by phospholipase D (See Figure1). Phospholipase A1 and A2 on the other hand lead to the formation of lysophosphatides by hydrolysing one of the ester bonds between a fatty acid and the glycerol moiety in the phosphatide. What about the hydratability of these lysophosphatides? Their free hydroxyl group is more hydrophilic than the original fatty acid ester, but does this make them hydratable when the parent compound is non-hydratable?

The answer to this question is not straightforward. According to [5], the non-hydratable phosphatides (NHP) comprise lysophosphatidic acid (LPA) and lysophosphatidylethanolamine (LPE), indicating that lysophosphatides are not completely hydratable. According to [6], enzymatic hydrolysis of the NHP present in the oil phase using phospholipase A1 and phospholipase A2 led to lyso-compounds that were only detected in the aqueous phase indicating the hydrolysis of NHP causes the resulting lyso-compounds to migrate to the aqueous phase.

In the case of partial glycerides, 1,3-diglycerides are more stable than 1,2-diglycerides. Similarly, 1-/3-(α)-monoglycerides are more stable than 2-(β) monoglycerides so there is a preference for the fatty acid to be bound to the 1- and 3-positions. It is therefore to be expected that 1-acyl lysophosphatides are more stable than 2-acyl lysophosphatides and that the 2-acyl lysophosphatides formed by the action of the phospholipase A1 will isomerise to 1-acyl lysophosphatides. These have a fatty acid linked to a terminal carbon atom of the glycerol moiety and will therefore be prone to phospholipase A1 catalysed hydrolysis. This will lead to formation of a glycerophosphate and indeed glycerophosphates have been observed in the aqueous phase of oils treated with phospholipase A1 [7]; their concentrations were about equal to those of the lysophospholipids. However, in [6], the use of Lecitase® 10L (a phospholipase A2) led to lower concentrations of lysophosphatides in the aqueous phase than when a phospholipase A1 was used. This might indicate a higher stability of the 2-acyl lysophosphatides in comparison with their 1-isomers.

3.  Kinetics of Degumming Processes

The discussion of the hydratability of phosphatides indicates that their molecular structure determines whether they remain in the oil phase or move to the water phase when the oil containing them is contacted with water. They do not divide themselves over the two phases like isopropanol would do when added to a mixture of hexane and water. PE may be an exception in that the literature [8] suggests that PE is only removed on water degumming if other phosphatides with which the PE can form mixed micelles are present. pc is hydratable so there should be no residual PC in water-degummed oil. However, the analyses of quite a few samples of water degummed oil show some PC to be present. How come?

The reason lies in the kinetics of the degumming process. The samples still containing some PC do not represent the equilibrium situation and have not been given enough time to reach equilibrium. So when the partially degummed samples are again subjected to a water degumming treatment, their PC content will drop to the low level commensurate with the hydratability of PC. However, time is not the only factor involved. The interface between the oil and the water and the diffusion distance towards this interface are other factors affecting the hydration kinetics.

In the literature [9], relative rates of hydration have been reported and the values are shown in Table 4.

Table 4. Relative rate of hydration of various phospholipids.

PhospholipidRelative rate of

hydrationPhospholipid

Relative rate of hydration

PC 100 PE (Calcium salt) 0.9PI 44 PA 8.5PI (Calcium salt)

24 PA (Calcium salt) 0.6

PE 16Phytosphingolipid (Calcium salt)

8.5

The values in this table have been quoted over and over again despite the fact that the article containing this table [9] and its table raise many questions. It mentions calcium salts of PI and PE but does not indicate their molecular structures. However, my main problem with Table 4 is that the article [9] does not indicate at all how these relative rates have been determined. Moreover, the fact that each phosphatide has a rate of hydration that is larger than zero implies that with some patience, water degumming should lead to complete removal of all phosphatides from the oil and that is not what is observed.

On the other hand, my doubts about the relative rates of hydration tabulated above do not mean that I do not recognise the existence of rate differences. When water is used as degumming agent, every phosphatide molecule reaching the oil/water-interface encounters this agent. Yet, when an acid that is dissolved in this water has to interact with the phosphatides reaching this interface, most phosphatides will encounter just water and only a few will meet with the acid and react. This has important practical consequences.

In the water degumming process, the water has to be dispersed in the oil but the degree of dispersion is not very critical. A reasonable dispersion will already provide such an oil/water-interface that hydratable phosphatides are hydrated and move into the water phase. For the acid to react with the non-hydratable phosphatides and decompose the NHP, a much finer dispersion is required because both reagents are diluted. A very fine dispersion is especially needed when the reaction has to be almost completed and a very low residual phosphatide content has to be reached. Moreover, the situation is aggravated because the water/oil dispersion is not stable. Aqueous acid droplets will coalesce, the interface will decrease, diffusion distances will increase and

all this will slow down the reaction. Accordingly, the dispersion has to be so fine that the reaction between the acid and the NHP is almost instantaneous or at least almost completed within a minute.

These requirements are well illustrated by comparing the SOFT degumming process [10] and the Complete degumming process [11]. Both processes employ a salt of ethylene diamine tetraacetic acid (EDTA) as chelating agent to remove metal ions such as calcium ions from the NHP but they differ in that the process according to [10] employs an emulsifier to retard coalescence of the aqueous phase droplets and thus prolongs the reaction between the EDTA and the NHP. The process according to [11] on the other hand, starts with a very fine dispersion of the aqueous solution of the chelating agent in the oil to be degummed and thereby achieves an almost complete reaction between the EDTA and the NHP before coalescence starts to slow down the rate of reaction. The importance of a fine dispersion in degumming had already been pointed out by Mag [12] and Dijkstra [13].

For the enzymatic degumming processes the dispersion of the aqueous phase is even more important since on a molar basis, the enzyme concentration is much lower than the concentrations of acid degumming agents and steric requirements lead to a lower Arrhenius factor for enzymatic reactions. In my recent review of enzymatic degumming [14], I referred to [15] which presentation shows that for a given degree of dispersion, the rate of the enzymatic reaction with NHP is an order of magnitude lower than the rate with highly diluted citric acid.

This degree of dispersion was maintained by circulating the contents of the laboratory reaction vessel three times per minute by means of a Silverson mixer. Doing something like that on industrial scale is impossible, which implies that in industrial degumming processes, enzymes do not interact with the NHP present in the oil phase. For the enzymatic degumming process to arrive at low residual phosphorus levels, it has to be preceded by a treatment with a finely dispersed acid that converts the NHP to PA. By raising the pH, this PA moves into the aqueous phase and once there it has become accessible to enzymes.

Abbreviations: PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; PA, phosphatidic acid; LPE, lysophosphatidylethanolamine; LPA, lysophosphatidic acid; NHP, non-hydratable phosphatide.