GB632304A - Improvements relating to the extraction of vegetable oil - Google Patents

Abstract

Oil is extracted from seeds, beans and nuts by a continuous solvent extraction process which is over-all on the counter-current principle and which consists of two or more stages, in each of which the flow of seeds &c. and solvent is concurrent. Each stage comprises the steps of dispersing oil-containing seeds or seed-solids in an extracting liquid of lower specific gravity than the seed solids to form a slurry, thickening and compacting the seed-solids in a solid bowl centrifuge to produce a substantially solid-free miscella, and to separate the substantially solid-free miscella from the thickened and compacted solids; and the further step of moving the seed-solids and miscellas countercurrent between the stages, whereby the miscella from one intermediate stage or from the final stage is employed as an extracting liquid in a preceding stage. The seeds &c. may be triturated before dispersion in the initial extraction stage and the solvent may be recovered from the miscella produced in the initial extraction stage to produce a substantially solid-free extracted oil. The recovered solvent may be recirculated to the final stage and used there as an extracting liquid. The amount of solvent introduced in the final stage and of seeds &c. introduced in the initial stage may be proportioned to produce a miscella in the initial stage containing from 15 to 30 per cent by weight of oil. The seeds may be flax seed and the solvent may be hexane, the rate of feed of these to the process being proportioned to produce a miscella in the initial stage containing 20 to 30 per cent by weight of linseed oil. Alternatively the seeds may be castor beans and the solvent heptane, the feed rates being proportioned to produce a miscella in the initial stage containing 15 to 25 per cent by weight of castor oil, the temperatures of the slurries being maintained at not substantially less than 50 DEG C. The process is said to be particularly applicable to seeds &c. which, unlike soya beans, disintegrate upon contact with an oil solvent after trituration to form slurries containing substantial quantities of gelatinous material which render continuous solvent extraction by the usual methods difficult. Thus, the process is said to be applicable to linseed, cottonseed, castor bean, perilla, sunflower seed, hemp seed, peanut, oiticica, tungnut and coconut. The number of stages used in the process may be sufficient to extract at least 98 per cent of the oil and to leave a residue of extracted solids containing less than 1 per cent of oil, and may vary from two to six or more, three usually sufficing. The final miscella from the initial stage may be clarified by means of a "polishing" filter and the seed to be extracted may have been given a prior treatment such as the removal of a portion of the oil by pressing. Any of the usual oil solvents may be used individually or mixed provided that the requirement regarding specific gravity is satisfied.