Solvent Extraction
Solvent Extraction, in principle is a process to extract oil from oil bearing materials by treatment with a low boiling point solvent, which has more affinity to extract.
The oil bearing materials or parent materials consist of oil cakes namely Sun flower, soy bean, canola, rape seed, cotton seed, mustard seed, rice bran, copra, lin seed, kardi seed (safflower) neem, caster seed, Mowha, salseed, and karinja.
The solvent involved is a normal hexane which is a petroleum product having low boiling range of 65 degree to 67 degrees celsius. The solvent, which has good affinity for the vegetable oils, when bought in contact with oils bearing materials absorbs the oils, which is then separated form solvent by distillation.
Solvent Extraction Process
Solvent Extraction is a process of diffusion of solvent into the oil bearing cells of the raw material resulting a solution of the oil in the solvent "Hexane" is chosen to be appropriate and the best for the use considering its viability with reference to commercial economics, edibility of various products being obtained after extraction, characteristics mainly its low boiling point and other factors.
The entire process is largely divided into three main sections as follows:
- Preparatory Section
- Main Extraction Section
- Meal Bagging Section
The Main Extraction Section is again divided into the following subsections:
- Extraction of oil from prepared raw materials
- Desolventisation
- Distillation to recover oil from miscella
- Condensation
- Final Solvent Recovery Section
Preparatory Section
An efficient Extraction would need that every oil bearing cell of the material is in contact with solvent. In other words, the smooth preparation prior to main extraction is very vital to comply with this contact. Smaller the material size, better the penetration of the solvent into the oil bearing cells, but too fine a size will prevent the solvent from percolation through the mass. Hence an optimum size is absolutely essential for efficient extraction.
The method of material preparation does vary from material to material depending upon its oil content and physical properties. We group them as follows:
- Oil Cakes
- High Oil Content Material (soybean, sunflower, rape seed, canola)
- Floury Materials (rice bran)
In the case of oil cakes being big in pieces, they have to be reduced to proper size without failing, ensuring that there are no "fines". Oiltek Cake Sizer and Cake Cracker are the finest to this process.
In case of high oil content seeds like soybean, sunflower, rapeseed, and canola it passes through.
The well proven Oiltek expanders after cracking, cooking & flaking, seeds like sunflower, rapeseed, and canola will pass through squeezomatic attachment for squeezing the oil before the collects goes to extraction. Passing through updated Oiltek Drier Cooler.
In case of Floury materials like rice bran, etc. any of the above equipment are not workable. Hence an Oiltek Palletize or Expander with conditioning arrangement was used to from pellets before extraction. The prepared material is transported to the Main Extraction Section via the Oiltek Conveyor.
Main Extraction
The prepared material as above is received into Extraction plant by an Oiltek Conveyor via an Oiltek Air seal in the raw material receiver with an arrangement for controlling the level of material receiver of the Oiltek Extractor.
The design of Oiltek Extractors is such that it can transport the material through the Solvent Spraying Chamber and the speed of transportation can be varied easily.
This chamber consists of a number of solvent sprayers which in uniform sprays the solvent over the entire bed of raw material. The length and breadth is designed to give sufficient time for intimate contact penetration and percolation of solvent into raw material, to view the distribution of spray, provided on the OILTEK Extractor are light and sight viewing glasses.
The material coming out of the spraying chamber is deoiled material with solvent which is to be recovered in the desolventing section. While the mixture of the oil and solvent called "Miscella" is pumped into the miscella tank, from where it will be transported by means of a special Oiltek Conveyor to the Desolventizer.
Desolventisation
The extracted material usually has a tendency for retaining the solvent with it, and this solvent has to be recovered. The retention varies from 20% to 35% weight of the material extracted. The basic principal involved in desolventization is direct and indirect heating of material with steam to a temperature well above boiling point on solvent and thus entrusting no solvent vapors are sent to Oiltek Condensers via Oiltek Scrubber where the solvent to trace vapor is washed any particulars of fines being carried to condenser. The Oiltek Air Seals are provided at inlet and outlet of Oiltek Desolventizers to ensure an air tight arrangement. This is essential to keep the solvent loss figure down. The deoiled and desolventised meal thus obtained is then transported to bagging section with the help of an Oiltek Conveyor. A cooling arrangements consisting of Meal Cooler is provided thus ensuring proper cooling of the material for easy bagging and to hold moisture 10 to 12%.
Distillation
Mixture of oil and solvent obtained in the OILTEK Extractor is known as "miscella" and it normally contains 12% to 18% of oil in the solvent incase of oil cakes / rice bran and 25% to 35% in case of sunflower seed / rapeseed. During distillation, solvent evaporates first due to its low boiling point (65 to 67 deg C) thus leaving clean oil behind.
Distillation is performed in three stages under vacuum to ensure that no oxygen is present when the oil is heated to a high temperature.
Presence of oxygen will exercise the oil making it unsuitable. First Evaporation takes place in Economizer and concentrates in the first and second, flasher leaving practically only oil behind. This oil is further treated with open steam to ensure that no solvent finds its way along with the oil.
The solvent vapors thus produced passes through OILTEK oil vapor separator to separate out any oil particles trapped with solvent vapors and are then passed on to Oiltek Condenser for condensation. Vacuum, in distillation is maintained with the help of Oiltek Evacuators.
Condensation
Solvent vapors are formed both in desolventisation section as well as in distillation section and these are to be condensed. Special floating head type Oiltek Condenser is provided. The floating head type Oiltek Condensers help quick and easy removal of tubular bundles for periodical cleaning. Adequate surface have been provided for OILTEK condensers for complete condensation of solvent vapor.
Final Solvent Recovery
In spite of providing adequate condensers, the air that is being injected out of the system contains traces of solvent. In order to recover the traces, a special final vent air stripping column has been provided. It comprises of a main Oiltek Absorber to give a large surface of contact. It is partly filled with groundnut oil / mineral oil being suitable absorbing media which absorbs the solvent vapors from the air. The oil and solvent mixture is distilled to recover the solvent.
Bagging Section
The extracted and desolventised meal is transported to bagging section by means of an Oiltek Conveyor fitted with cooling arrangements.