Material containing low amount of oil such as oilseed cake (meal) and rice bran are suitable for solvent extraction. Hexane is most widely used solvent and this process can extract oil form feed until oil present in feed is reduced to 0.5 % or less.
Perforated basket attached in conveyor belts holds the feed. Fresh warm solvent is sprayed from the top. Hexane is used as solvent whose boiling point is nearly 60°C. The basket moves up carrying the feed which is extracted through screen at the bottom of basket. The residue is treated with fresh solvent and finally defatted cake is obtained. The half miscella is recirculated through pump and again comes in contact with solvent. The full miscella is evaporated, refined, bleached and deodorized to obtain refined bleached and deodorized (RBD) oil.
For industrial process of solvent extraction, the feed is introduced in the feed tank. Imagining the different compartments in the tank, below are kept the miscella holding tanks. In the upper tank, the feed is mixed with warm fresh solvent. Then miscella is passed to miscella holding tank through spray nozzle. The solvent is then again mixed with the feed in previous compartments.
Here the amount of fresh solvent flow and speed of belt can be controlled. If the feed contain high amount of oil, speed of conveyor is slowed and amount of fresh solvent flow is increased. The imaginary secondary is supposed to contain maximum oil ready for leaching so the full miscella is obtained through it. The defatted cake is extracted as the belt proceeds from imaginary chamber ‘I’ to ‘V’ and collected from terminal point where the cake is further desolventized and used further. Such cake should contain oil less than 0.5 %.
Name : Pratiksha Shrestha
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.