Vegetable Oil Processing as a critical step prior to biodiesel production

Vegetable oil processing involves the extraction and processing of oils and fats from vegetable and animal resources. The oils and fats are extracted from a variety of fruits, seeds, and nuts. Natural vegetable oils and animal fats are extracted or pressed to obtain crude oil or fat. These usually contain free fatty acids, phospholipids, sterols, water, odorants, and other impurities. Even refined oils and fats contain small amounts of free fatty acids and water.

The preparation of raw materials includes husking, cleaning, crushing, and conditioning. The extraction processes are generally mechanical (boiling for fruits, pressing for seeds and nuts) or involve the use of solvent such as hexane. After boiling, the liquid oil is skimmed; after pressing, the oil is filtered; and after solvent extraction, the crude oil is separated and the solvent is evaporated and recovered. Residues are conditioned (e.g., dried) and are reprocessed to yield byproducts such as animal feed. Crude oil refining includes degumming, neutralization, bleaching, deodorization, and further refining.

Corn, cottonseed, and peanut oil processing are similar to soybean processing, except for differences in the preparation of soybean for oil extraction. The process for soybeans typically consists of three main steps: oilseed handling/elevator operations, preparation of soybeans for solvent extraction, and oil refining.

Color-producing substances (i.e., carotenoids, chlorophyll) within oil are removed by a bleaching process, which employs the use of adsorbents such as acid-activated clays. Volatile components are removed by deodorization, which uses steam injection under a high vacuum and temperature. The refined oil is then filtered and stored until used or transported.

An important step in vegetable oil purification is physical refining by removing free fatty acids present in the vegetable. This separation is carried out at a low temperature to reduce the degradation of the final products at high vacuum. The free fatty acids can be removed using stripping steam at 525 K at 2 to 3 mm Hg column top pressure.