Patent GB-601313-A (GB)
Title: Methods of improving the drying properties of oils
Filed: 1945-01-30
Abstract: Non-drying constituents are removed from drying or semi-drying oils to improve their drying properties, by treating the oil at an elevated temperature with an aliphatic diboric acid which displaces non-drying constituents from the oil and which has a vapour pressure at ordinary temperatures lower than the vapour pressure of the displaced constituents, and then removing the non-drying constituents by distilling them from the oil.  The di-basic acid may be azelaic, sebacic, or adipic acid or a mixture of di-basic acids obtained by oxidation of a fatty acid such as oleic or of a part of the oil to be treated, e.g. with a chromium trioxide-sulphuric acid oxidizing agent.  The proportion of di-basic acid employed may be about 10 to 20 per cent by weight of the oil to be treated therewith and the treatment may be carried out at 300-340 DEG  C.  The drying or semi-drying oil treated may be linseed oil, soya bean oil, perilla oil, or a fish oil, the treatment may be carried out in an atmosphere of an inert gas, and the displaced constituents may be removed by distillation under reduced pressure.  The displaced non-drying constituents are believed to be saturated and/or mono-unsaturated components of the oil such as stearic acid and oleic acid which are displaced from the glyceride compounds in which they were originally present.  In an example, 600 parts of linseed oil are heated for one hour at approximately 300 DEG  C. at atmospheric pressure in an atmosphere of carbon dioxide with 60 parts of azelaic acid.  The free fatty acids liberated are removed by vacuum distillation for about 1 1/2 hours, or until the acid value of the still contents is reduced to about 8.0, about 20.4 per cent of distillate being obtained.  The residue of modified linseed oil has a viscosity of 34 poises at 25 DEG  C.  In another example, 600 parts of linseed oil and 150 parts of mixed oxidation products of oleic acid are heated in a vacuum still for an hour at 300 DEG  C. in an atmosphere of carbon dioxide. The pressure is then gradually reduced in 2 1/2 hours to 5 mm. and the temperature raised to 318 DEG  C.  259 parts of distillate are collected and the residue of modified linseed oil has an acid value of 1.6 and a viscosity of 45 poises at 25 DEG  C.  The mixed oxidation product of oleic acid contains a mixture of approximately 33 to 35 per cent of aliphatic di-basic acids and is prepared by treating 50 parts of oleic acid with 472 parts of a mixture of one part of chromium trioxide, 2 1/2 parts of concentrated sulphuric acid and 4 parts of water at a temperature not exceeding 90 DEG  C.  When the reaction is complete the spent solution is drawn-off and the oxidised oleic acid washed with acid until its green colour is removed.  In a third example, 400 parts of soya bean oil is treated with 1295 parts of the chromic acid solution at 80 to 90 DEG  C., until the chromic acid is completely reduced.  The mixture is allowed to separate into two layers, the upper oily layer drawn-off and washed with 10 parts of concentrated hydrochloric acid and then with water until free from mineral acidity.  The partially oxidised washed oil is heated to 300 DEG  C. for 1 hour in an atmosphere of carbon dioxide and the still then gradually evacuated to 2 mm. pressure. Simultaneously, the temperature is raised slowly to 325 DEG  C. After about 3 1/2 hours the viscosity of the oil remaining in the still has increased to 29 poises at 25 DEG  C. and its acid number decreased to 1.0.