Continuous extraction of oil-containing vegetable matter with

Abstract

The oil in comminuted oil-containing vegetable matter is extracted by passing the vegetable matter through a closed extraction zone in contact preferably in countercurrent flow relation with a liquid extraction medium, which is a normally gaseous hydrocarbon, preferably propane, under a pressure sufficient to liquify the same up to about 250 psi, a temperature from about room temperature up to about 40.degree.-50.degree. C. and in sufficient volume to extract substantially the oil from such matter, e.g., a solvent feed ratio of about 1-3:1 by weight, the vegetable matter being continuously introduced into the zone by the steps comprising: advancing said vegetable matter through an elongated tubular screw-feeding stage communicating at its discharge end with one end of said extraction zone, subjecting said vegetable matter while within said screw-feeding stage to compacting pressure to create a region of compacted matter, and introducing under pressure into the compacted region a discrete innocuous normally liquid sealing medium which if different from said oil is capable of being at least substantially separated from the extracted oil, in an amount up to about 10% by weight of such matter which is effective to form the matter when compacted into a generally plastic mass, the magnitude of said compacting pressure in the absence of said medium being insufficient either to express said oil directly from said matter or densify said matter to a solid density capable of containing the pressure in the extraction zone. The preferred sealing medium upstream of the extraction zone is a recycled fraction of the extracted oil, and preferably a similar compaction zone is created in a screw-feeding stage at the discharge end of the extraction zone. The solvent and extracted oil are separated and recovered, the solvent being recycled for further extraction. The solid residue is freed of solvent and is useful, e.g., as defatted bran or meal. Preferably, the solvent-oil mixture after removal from the zone is subjected to a phase separation by raising its temperature and pressure to recover a liquid solvent phase containing a small amount of oil which can be reused as a solvent and an oil-enriched phase that can be freed of solvent by controlled volatilization. The solid residue is preferably freed of solvent by reducing the pressure thereon in at least two stages with heating, the solvent vapors being removed separately and compressed for recycling and reuse.