GB604281A - Improvements in or relating to methods of oxidizing relatively long chain unsaturated fatty bodies - Google Patents

Abstract

Relatively long chain unsaturated fatty bodies are oxidized to relatively short chain saturated fatty bodies by treating with a solution made by electrolyzing an aqueous solution containing at least 7 per cent sulphuric acid, and 15-35 per cent chromium sulphate to liberate hydrogen and convert 40-75 per cent of the chromium sulphate to chromic and sulphuric acids. Animal or vegetable oils having substantial unsaturated components, fatty materials having lower unsaturated content, fatty acids obtained from such materials, esters of unsaturated fatty acids, and unsaturated synthetic fatty products may be treated. A preferred oxidizing solution is a 50-60 per cent regenerated solution derived from an original solution containing 1 part chromic anhydride, 2 parts sulphuric acid, and 4 parts water. After use it is again regenerated by electrolysis for re-use. The hydrogen produced may be used to harden other unsaturated fats. The sulphuric acid concentration in the spent solution should not exceed 20 per cent and is 10-15, preferably 12-13 per cent for highest yields and minimum voltage for regeneration. Reaction temperature is usually 5-100 DEG , preferably 75-90 DEG C. The reactants are mixed by stirring and separated by gravity settling or centrifuging, preferably below 40 DEG C. or the separated spent solution is cooled below 40 DEG C. to remove organic material. The oxidizing solution may be added in portions, withdrawal of separated spent solution being effected before addition of the next portion. Oleic acid gives azelaic and pelargonic as well as other shorter chain fatty acids, triolein yields pelargonic acid and mixed glycerides, rape seed oil fatty acids give pelargonic, brassylic and shorter chain acids, while methyl, ethyl, propyl or like esters of oleic acid yield pelargonic acid, the half esters of azelaic acid, and shorter chain fatty acids. The products are treated with sulphuric acid to remove chromium, washed free from acid, and pelargonic acid separated by distillation. The azelaic acid can then be separated from other acids by washing with hot water in such amount that the azelaic content is not above about 10 per cent, and the solution crystallized or evaporated. In examples, a spent solution of percentage composition chromium sulphate 26.9, sulphuric acid 12.2, and water 60.9 is fed to the cathode chambers of a series of continuous cells with lead electrodes and ceramic diaphragms and electrolysed at 24 amps./sq. ft. anode current density to 50 per cent conversion, the solution leaving the anode chambers having the composition: chromic anhydride 6.77, chromium sulphate 13.2, sulphuric acid 21.9, and water 58.1 per cent. This is used for oxidizing: (1) oleic acid, yielding chiefly azelaic and pelargonic acids; (2) cottonseed fatty acids, giving chiefly pelargonic, palmitic and dibasic acids; (3) methyl oleate to pelargonic and azelaic acids and a neutral ester; (4) teaseed oil to pelargonic acid and azelaic acid triglyceride.