GB744421A - A process for decolourising plasticisers and improving their thermal stability - Google Patents

Abstract

An ester of an aromatic or saturated aliphatic dicarboxylic acid with a saturated monohydric alcohol, said ester having plasticizing properties for polymers of high molecular weight, particularly for polyvinyl chloride, is decolourized and its thermal stability improved by treating the ester with hydrogen in the presence of a hydrogenation catalyst but without hydrogenating the ester to such an extent as substantially to modify its plasticizing properties. The monohydric alcohol is preferably one containing from 4 to 10 carbon atoms. The treatment with hydrogen may be effected at 20 DEG to 200 DEG C., preferably at 120-140 DEG C., and at a pressure of from atmospheric pressure to 30 atmospheres, preferably at from 5 to 10 atmospheres. The process may be carried out batchwise by passing hydrogen at the desired pressure through a vigorously stirred mixture of the plasticizer and catalyst, or it may be carried out continuously by passing the plasticizer through a bed or beds of the catalyst in a zone containing hydrogen at the desired pressure. Specified catalysts are nickel and copper catalysts, preferably Raney nickel or copper deposited on a carrier such as kieselguhr for batch operation whereas for continuous operation it is preferred to use nickel or copper deposited on a carrier such as kieselguhr and pelleted. In the case of phthalic esters it is found that on treatment with hydrogen in the presence of a nickel catalyst at above 100 DEG C. and above 10 atmospheres pressure some hydrogenation of the aromatic ring occurs so that the treated ester is a mixture of phthalic esters with a small proportion of hydrophthalic esters. Although the thus treated ester does not lose its plasticizing properties the hydrogenation of the aromatic ring may be avoided by carrying out the hydrogenation either in the presence of a copper catalyst or by using temperatures of from 20 DEG to 90 DEG C. under a pressure between atmospheric pressure and 10 atmospheres in the presence of a nickel catalyst. Any small amounts of water and alcohol which may be present in the treated ester may be removed, e.g. by stripping with steam and then drying. The treatment with hydrogen may be applied to an ester at an intermediate stage of its manufacture and which still contains excess alcohol and/or an auxiliary entrainer substance. The hydrogen treatment may be supplemented by a treatment with alumina, e.g. at a temperature of from 60 DEG to 80 DEG C. for 15 minutes or more, whereby the plasticizers acquire a high electric resistivity and their colour may be further improved. Examples describe the treatment of di-octyl phthalate with hydrogen in the presence of (1) a catalyst consisting of nickel deposited on pellets of kieselguhr at 140 DEG C. and under a hydrogen pressure of 23 kg. per sq. cm; (2) in the presence of Raney nickel at 130 DEG C. and a hydrogen pressure of 23 kg. per sq. cm.; (3) in the presence of the same catalyst as in (1) but with a hydrogen pressure of 10 kg. per square centimetre and a temperature of 80 DEG C., the product being then neutralized and stripped and finally passed through a bed of alumina. In other examples: (4) dioctyl phthalate taken during the course of its manufacture by esterification and which still contains some cyclohexane (used as entrainer in the esterification) and octyl alcohol is treated with hydrogen at 10 kg. per sq. cm. and at 140 DEG C.; (5) dioctyl sebacate is treated with hydrogen at 20 kg. per sq. cm. and at 140 DEG C. using the same catalyst as in (2); (6) di-octyl adipate is treated with hydrogen as in (5) except that less Raney nickel and a shorter contact time are used; (7) dioctyl succinate is treated as in (2) except that the temperature is 140 DEG C. and the contact time is shorter; (8) dibutyl phthalate is treated as in (2) except that the temperature is 135 DEG C., the pressure is 22 kg. per sq. cm. and the contact time is shorter; (9) dinonyl adipate is treated as in (5) using less Raney nickel and a shorter contact time; (10) dioctyl phthalate is treated with hydrogen at 24 kg. per sq. cm. pressure and 140 DEG C. in the presence of copper on kieselguhr; (11) dioctyl phthalate is passed through a catalyst consisting of copper on kiesleguhr in pellet form, the hydrogen pressure being 25 kg. per sq. cm. and the temperature 140 DEG C. Examples (1), (3), (4) and (11) are carried out in a continuous manner. In the other examples which are operated batchwise the contact times vary from 1 to 2 hours.