Oilseed processing - Aligarh Muslim University

Oilseed Processing, Processing Operation, Oil Extraction Methods (Ghani, Hydraulic Press,

Solvent Extraction)

Faizan AhmadAssistant Professor

Post Harvest Engineering & TechnologyFaculty of Agricultural Sciences

Aligarh Muslim University

Oilseed Processing

• Vegetable oils constitute an important part of our diet. They are

mainly used as cooking (frying) medium.

• The oils and fats are composed of different mixtures of glycerides

of various fatty acids.

• The waxes are mixtures of higher polyhydric alcohols with fatty

acids.

• The main constituents of the vegetable oils are 16 and 18 carbon

acid. Esters containing more unsaturated acids and having lower

melting points are oils.

Oilseed/oil bearing materials Oil content (%)

Cottonseed 18-20

Shelled groundnut 45-50

Rapeseed 40-43

Soybean 18-20

Palm kernel 45-50

Safflower 30-35

Sesame 50

Flaxseed 35-42

Sunflower 35-45

Rice bran (from various mills) 5-18

Oil content of major oilseeds and oil bearing materials

Processing OperationsPre-cleaning and cleaning:

• Pre-cleaning is to remove wastes, stones and extraneous materials.

• It is essential that seed delivered to the press be clean and free from the impurities.

• If these operations are neglected, oil of poor quality will result.

Storage:

• Deterioration of oilseed occur in storage.

• The effect on seed oil and its constituent is important, since it will affect a plant's

profitability.

• In India experience has shown a major loss of oil quality in terms of colour, free fatty

acids, iodine and other values in oil from seed kept in unsuitable or prolonged storage.

• High moisture, relative humidity and temperature and

fungal infection are the main reasons for this deterioration.

• If full benefit is to be obtained from oil seed production, rapid movement from

producer to processing plant is essential.

Hulling:• Hulling is recommended to produce high quality of edible oil and

this also reduces the fibre content of the meal, increasing itsmarketability on stock feed.

• Hulling also increases the cost of production.• Hulling may be omitted if the meal is to be used solely for

fertilizer, but extraction rate of unhulled seed will be lower unlesshigher pressure is used.

• This will increase the extraction cost and the merits of hulling andlower pressure or not hulling and higher pressure must bedetermined.

• Some oils are possibly hulled partially and consist of cracking theseeds and pressing them through an air blast adjusted to removeonly higher hull particles.

• The mixture is less liable to mash during screw pressing andrequires only a moderate increase in operating pressures.

• Disc or roller huller may be used.

• In case of the delivery of pressed cake with a residual oil content of 10 to 15% tothe extractor directly takes place where a combination of press and solventextraction method is used. If the meal is too ground prior to pressing it tends todisintegrate in the solvent, the fine particles then remaining in suspension.

Cooking and Drying:• Prior to pressing material with a high protein content must usually be cooked.• This not only coagulates the protein but frees the oil for efficient pressing.• Following cooking, which is normally carried out at a moisture content of 10-12

% the raw material must be dried to approximately 2-3 % before entering thescrew press.

• Low protein materials with a high oil, high fibre, for example, copra, usuallyrequire drying only.

• The art of commercially cooking vegetable oil seeds which contain a highproportion of protein is almost as old as vegetable oil milling itself.

• When hydraulic presses predominated, cookers are invariably considered anecessary part of the mill.

• Duration of the cooking period was originally determinedempirically by touch and visual inspection of a drawn sample.

• A modern automatic circular cooker with a diameter of 90 cmshould be capable of handling 40,000-50,000 kg per day of meal.

• A cooker must be large enough to hold material upto 20 minutesunder air tight conditions at a temperature of 88-93 oC butdrying is carried out approximately higher temperatures,between 110 to 115 oC .

• The higher temperatures are critical when processing oil seedswhose oil is heat sensitive.

• The temperature during drying of vegetable oil seeds must becontrolled to avoid burning because of its composition.

• Retention time must be as short as possible as over longretention even at a controlled atmosphere and may have adeleterious effect on oil colour.

Oil Extraction MethodsGhani:

• Ghani is basically a large pestle-mortar. the mortar is an inverted cone, the pestleis a heavy bank of timber seated at the bottom of the cone and inclined at anangle so that meal is crushed against the mortar during rotation.

• The timber bank is pulled against the sideway mortar by weight and is rotatedby a pole inserted through it at right angle.

• One or two bullocks yoked to the pole provide power by walking blind foldedin a circle around the mortar.

• The traditional bullock ghanis fast disappearing and power ghanis have come up.

• The mustard oil expelling by ghanis is still preferred over screw pressed oil, asthe former preserves characteristic pungent smell of mustard oil more.

• Traditional ghais leave about 7-10 % oil in cake.

• Power ghains are two types, namely, stationary mortar type and stationary pestletype.

Bullock driven ghani

Stationary pestle Stationary mortar

Power ghanis

Hydraulic Press • Originally majority of presses were hydraulicbut most have been replaced by mechanicalscrew press, primarily because of saving oflabour and increased oil recovery.

• The cooked flakes are placed in the hydraulicpress and gradually pressure is applied.

• The pressure is raised to a maximum of 113-141 kg/cm2 till the oil begins to flow.

• The the pressure is maintained for 30-45 minand then cake is discharged.

• The capacity of a press may be as high as 7tons per day.

Screw Press:• The invention of continuous high pressure screw press,

commonly known as "expeller" by A.D. Anderson in 1990radically changed the structure of the oil expelling industry. Thishas greatly reduced the capital investment.

• Since the introduction of screw press, there had been somechange in design but the basic design remained the same andwhatsoever changed had occurred were not introduced in Indianexpellers.

• These expellers were introduced when energy was not a majorconsideration, the oil recovery was much higher and continuousoperation was available, when compared to oil ghanis andhydraulic press.

• As an estimate, Indian expellers require 15 times more energyand have residual oil in cake 2-4% higher compared to thoseavailable in developed countries (European models).

• Indian expellers consume about 53 kWh energy/t of oil.

• The screw press operating in a cage like perforated cylinder throughwhich the oil diffuses has a major advantage over batch typehydraulic press is that it need not be stopped for recharging.

• A screw press operating at a greater pressure (1550-1860 kg/cm2)than in hydraulic press, with consequently higher oil extractionrate.

• The hot oil bearing material is forced through a cylindrical cage andthen through a tapered outlet by means of powerful rotating screw.

• An extremely high pressure is developed by this restricteddischarge, oil being expelled through narrow slits around the pressbarrel.

• The compressed cake is extruded the discharge outlet.• A modern type of screw press could be expected to process 13,000

and 26,000 kg/day of meal.• The improvement in mechanical extraction techniques through

proper preconditioning of oil seeds and control of pressure can raisethe average recovery in mechanical extraction from 73 to over 83%in ground and mustard, etc. and from 60 to 65% for cottonseed.

• The cost is the main obstacle in adoption of improvedmechanical extraction technology.

• The smaller capacity model are not efficient, however, twomodels of oil expellers namely (i) 6-bolt, 16 plate "Tiny-Tech"model and (ii) 4-bolt, 12 plate "Super " model of Rajkot used forextracting oil from groundnut and mustard have given thesuitability of these models.

• This is the most efficient method of oil extraction.• The soluble constituent in the process of extraction is removed

from solid or liquid by the use of solvent.• When the solid constituent is separated from the feed, the

process is called leaching or solid extraction and when theliquid constituent is separated then the process is called solventextraction or liquid extraction.

System of Leaching• Single stage: It represents the complete operation containing the

solids, feed and fresh solvent and subsequent mechanicaloperation.

• Multi stage Co-current: In this system fresh solvent and solidfeed are mixed in the first stage. Underflow from first stage issent to second stage where more fresh solvent is added forbetter separation.

• Multi stage counter-current: In this system the underflow andover How streams flow counter-currently to each other.

Solvent Extraction:

System for Solvent ExtractionA. Single contactB. Simple multistage contactC. Counter current multi stage• These systems utilize the difference in solubilities of the

components. Since the solubility depends on chemical propertiesthis type of extraction exploits chemical difference.

Leaching EquipmentStationary bed typei. Open tank, ii. Extraction Battery iii. Diffusion BatteryMoving bed typei. Bullman extractorii. Hilderbrandt extractor.• In stationary bed type the feed is stationary in any tank with

false bottom. Solvent is applied at the top until the feed is extracted.

• In moving bed type the feed is moving counter currently with solvent until the feed is extracted.

Solvent Extraction Process:• This process is most suitable for low oil bearing materials, such

as, soybean, rice bran or oil cakes obtained from hydraulic press.• After cooking the material, it is flaked/palletized to prevent

dispersion of fines.• Flaked material is charged in to the continuous extraction unit

where solvent (normal hexane) is sprayed in counter currentfashion.

• The solvent containing oil (called miscella) is passed through apreheater and sent to a flash evaporator utilizing steam forvaporization of solvent (being low in boiling point).

• The deoiled cake containing absorbed solvent is sent todesolventizer where the solvent is vaporized using steam.Deoiled and solvent free cake is discharges from desolventizer

• Oil containing trace of solvent is sent to a distillation columnand under low pressure and by the use of live steam, theremaining solvent is again vaporized and crude oil, almostcompletely solvent free, collected in the tank.

• Solvent vapour from flash evaporator, distillation column anddesolventizer are sent to condensers where solvent and water bothcondense and separated by virtue of difference in specific gravity.

• Recovered solvent is used repeatedly.