OIL Expression and Extraction.

Oil expression and extraction:                 

Introduction

 

Oil seeds and pulses are a staple food for many millions of poor people in developing countries and are

 these days developing an even more important role as cash crops. The most important crops in these 

categories are palm, bean, and ground nuts. 

Further can be mentioned cashew, shea nut, sesame, sunflower, coconut and olives. 

Oil seeds and pulses add important nutritive value to the diet by high-quality protein and for vegetable oil together with oil soluble vitamins like vitamin A. 

Post-harvest practices of oil seeds and beans consist of threshing, shelling for podding and drying, after which the product can be stored like grains. 

Oil palm fruits need to be processed into palm oil soon after harvest.

 India is the fourth oil seed-producing country. India is the largest producer of groundnut, sesame, 

linseeds, and castor seeds oil as are composed of a mixture of glycerides of various fatty acids. The fats 

and oils are broadly classified into edible and non-edible. Groundnut, soybean, and mustard are some of

 the sources of edible oil. The edible oil is the main source of fat taken in daily meals and is used for

 cooking purposes and salad dressings. Non-edible oil are also used in the soap industries, paint, varnishes, and plasticizer industries. The mechanical expression and solvent extraction methods are

 employed for the manufacture of oil from the oil seeds.

There are three methods of oil expression and extraction:

 

• 1.   Mechanical expression
• 2.   Chemical expression

 

 

Traditional mechanical methods of oil expression and extraction:

 

Mechanical expression of the oil seeds:

The wedge press:

The wedge press operated manually or by using either wind or water power, was widely 

used to press oilseeds during the late 18th and early 19th centuries in the West and in 

the Far East. The typical operating principle of a wedge press used during this period is 

shown This shows the design of a wedge press using trees as the end braces 

(Broadright, 1979). The wedges should be made of a very hard wood and are best driven in with a 

wooden mallet. Two wedges should be applied, one from each side, and these should be 

driven in simultaneously to avoid pushing both bags and wedges out of the press.

 

The plank press:

The plank press represents the simplest mechanical pressing device used in oilseed 

processing. It consists of two long pieces of wood hinged at one end. The prepared seed,

 in a suitable woven container, is placed between the planks and squeezed by the 

application of pressure at the unhinged ends. Plate IV shows a plank press being used in 

Nepal for the extraction of rapeseed oil.

Cage presses:

Cage presses have formed the basis of many small-scale processing operations in recent years and are 

sometimes called screw presses, but this name should be avoided as it can be confused with the 

continuous screw expeller. There are a number of cage press designs and four types are shown in 

Figures 6-9. In a variation of the version shown in Figure 9, the hydraulic jack is mounted above the 

pressing cage. This design is not recommended because of the risk that leaking hydraulic fluid could 

contaminate the oil and cake.

The curb press The press shown in Figure 6 was designed by the Technology Consultancy Centre 

(TCC) at Kumasi in Ghana. It is a development of the 'Duchscher' curb press which was manufactured 

in Luxembourg and which has been widely used in Nigeria for extracting palm oil. The cage on the 

TCC press is made of two halves hinged on one side and locked together with a pin on the other. This 

enables the cage to be opened easily for unloading the oil-cake after pressing. This makes the press 

particularly convenient for processing palm fruits, but the central position of the screw inside the cage 

makes the press unsuitable for pressing other oilseeds.

Some of the modern methods of oil expression:

During the process of expression the oil seeds are compressed in various types of compression devices

. The oil is stored in different places of the oilseed in form of oil globules. There are two steps of

 expulsion of oil through oil expeller, 

 

oil expeller.

1.       Disintegration

2.       Pressing

Under disintegration process, oil globules are separated. The tough membrane surrounding the oil

 droplet is exposed and burst under pressure and oil will ooze out.

Expression is a process of mechanically pressing liquid out of liquid containing solids. Screw pressses

, roll presses and will collapsible plate and frame filler presses, disk mill are some of the examples of 

wide range of equipment used for expression of liquids. The advantage of mechanical  expression over

 chemical extraction is that it gives the liquid free of dissolved chemicals and thus a safer process.

Mechanical expression Devices:

1)      Hydraulic press:

The hydraulic press is considered of a series of horizontal corrugated iron plates. These plates are 

separated by 4 to 14 pre moulded oil seed cakes. It is completed in 2 stages. The out put of the press 

is varied depending on the sizes and seeds being pressed. In recent times a commercial  level 

processing the hydraulic press has been replaced by screw type.

 

Screw press can be used for various types of oil seeds, such as rape seed, sunnflower seed, soy bean, 

lameline seed, linseed castor bean. The press is provided with adjustment plates having thickness of 

0.1mm and 0.8 mm. The pressing chamber is build for oil discharge. Inside the pressing chamber is the

 active element of the press which is a variable pitch screw, cpmposed of six- segments, with a constant 

rotational speed of 8.9 rpm. The cake is discharged through the end of the pressinbg chamber where six 

nozzles are provided. One of the variable parameters followed during the experiments was the feed rate 

to the press with oleaginous material, which was varied by adjusting the position of the flap from the 

bottom of the feeding hopper maximim opening half opening and fourth opening. Another process

 varialbe in the experiments was the diameter of the nozzles for cake evaluvation the diameter may be 

6.8, 5.8 and 5.2 mm will be used. During experiments for oil collections it is used to tray with five 

compartments to which collect the oil separated from five segments of process in order to determine the

 oil yield 138 mm length, and the four sections having length of 118mm . After each experiment the

 extracted oil is collected from each pressing section while the cake was collected and weighed from the 

who press.

Hydraulic press.

Conclusion:

The oil expression process from oil seeds using screw presses is influenced by no. of parameters

 in which the most important  are physio chemical properities of seeds and constructive 

functional characteristics of process. In the first section if pressing section with material no oil is

 obtained, 2^nd section lightest oil is obtained from this to the last section of the pressure oil has 

continuous arch. Thus it can be said that the process efficiency substainally increases with the 

decrease decreasing of the nozzle diatmeters, but also with the decreasing of the feed rate.

                

Oil Extraction methods

a) Mechanical expression

During the process of mechanical expression, the oil seeds are compressed in various types of 

compression devices/equipment. Expression is the process of mechanically pressing liquid out of liquid 

containing solids. Screw press, roll presses, collapsible plate are some examples of wide range of 

equipment used for expression of liquid.

i) Hydraulic press: The hydraulic press is considered of a series of horizontal corrugated iron plates.  

These plates are separated by 4 – 14 premoulded oil seed cakes. Pressing is completed in two stages. In

 first stage, the oil seeds are pressed at about 5 MPa for 15-20 min and then pressure of 28 MPa is 

applied for 5-10 min to complete the expression process. The recovery of the oil varied depending upon 

the sizes and seed being pressed. But, the at commercial level, the hydraulic press is replaced by screw type presses.

ii) Screw press: A screw press has a horizontal main shaft. The screw assembly is formed integrally 

with this shaft. The screw rotates within a cage or barrel. The barrel is made of case-hardened, tool

 steel bars or rings to allow drainage of the oil as the pressure on the feed material is increased. 

At the discharge end, a movable choke or cone controls the operating pressure. It is achieved by

 changing the width of the annular space through which the oil cake passes. The choke is adjusted by a

 hand wheel on the opposite end of the screw. The configuration of the screw is such that the 

volume displacement at the feed end of the press is considerably greater than at the discharge end.

 As a result of such configuration, as the material is conveyed from the feed end to the discharge end, 

it is subjected to increasing pressure. As pressure increases, the material is compressed and 

oil is extracted through the bar and cage spaces.

 

iii) Ram press: A long pivoted lever moves a piston backward and forewords inside a cylindrical cage

 constructed from a metal bar spaced to allow the passage of oil. At one end of the piston’s stroke, it 

opens an entry port from the seed hopper so that the seed enters the press cage. When the piston is moved 

forward, the entry post is closed and the oilseed is compressed in the cage. As a result, oil is expelled

 from the oilseed the emerges through the gaps in the cage. Compressed seed is pushed out through the 

gaps in the cage. Compressed seed is pushed out through a circular gap at the end of the cage.

 

Chemical methods:

Soxhlet extraction.

Soxhlet extraction is one of the most traditional techniques still being used for the separation of a wide 

range of volatile compounds to oils from solid samples. In the mid-19th century, Baron Von Soxhlet  

introduced this method, after whom the method is named. Soxhlet extraction is a popular method and is 

being considered as a reference for several existing modern extraction techniques.  The picture shows 

the setup of a typical Soxhlet apparatus, mainly consisting of a round bottom flask, a thimble holder, and a condenser.

 

 

Ultrasound-assisted extraction (UAE).

 As conventional solvent extraction methods have limitations of longer duration of extraction, toxic

 solvent usage and low efficiency, investigations have reported that a combination of mechanical waves 

with solvent extraction techniques can transcend these barricades. Lately, ultrasonics have received

 greater attention to use in the extraction processes from medicinal tinctures to industrial biodiesel 

production. Ultrasonic extraction can be brought about in a lab scale by using an ultrasonic cleaning bath 

(indirect) and ultrasonic probe or horn (direct) systems. Ultrasonic reactors are used for industrial 

applications.

 The equipment is used in the production of the herbal oil. 

Even though ultrasonic-assisted extraction is more rapid and efficient than conventional Soxhlet extraction, it also involves large quantities of hazardous and expensive organic solvents.

Process of Oil Refining:

In many local markets, further refining is not required as the complexes of unrefined oils are preferred.

 International markets tend to prefer lighter less intense oils for cooking which means further processing 

of the oil. There is a series of refining processes that can be carried out after the oil has been filtered.

i)   De-odorising

Volatile compounds that produce bad odors can eliminated through the process of sparging, i.e. 

bubbling steam through the oil, under a vacuum.

Deodorization process.

ii)  Wintering

Allowing the oil to stand for a time at low temperatures so that glycerides, which naturally occur in the 

oil, with higher melting points solidify and can then be removed from the oil by filtering. Over time

 glycerides can degrade releasing fatty acids into the oil increasing the acidity levels and reducing the

 quality.

iii)  Neutralisation

Fatty acids can be neutralized by adding a sodium hydroxide solution, also known as caustic soda, or by

 stripping, which is a similar process to de-odorizing.

iv)  Bleaching

Some oils have a very dark color to them that is unpopular with consumers. The appearance of the oil 

can be lightened by bleaching.

Bleaching process

v)  De-gumming

De-gumming is a way of treating seeds that have high phosphatide content. The phosphatide, which

 makes a gummy residue, is removed by mixing the oil with 2 to 3% water. This hydrated phosphatide

 can then be removed by settling, filtering, or centrifuge.

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