GB1010480A - Separating trimethyl phosphate - Google Patents

Abstract

Trimethyl phosphate is purified by continuously feeding a charge including methanol, trimethyl phosphate and 10 to 35 mole per cent hydrogen chloride into a first zone maintained at -10 DEG to 125 DEG F. while providing a residence time of 1 to 7 minutes, thereby separating from the reaction mixture a hydrogen chloride-methanol rich fraction, and then passing the residual mixture into a second zone maintain-tained at 180 DEG to 290 DEG F. and therein substantially removing the remaining hydrogen chloride. Higher purity trimethyl phosphate may the be obtained by the distillation of the residual mixture from the second zone by maintaining an overhead temperature of approximately 190 DEG F. and a bottom temperature of 380 DEG to 430 DEG F. In a preferred embodiment chloride impurities are further removed by passing the residual mixture from the second zone into an intermediate zone prior to the third (distillation) zone, said intermediate zone being maintained at substantially the same temperature as the second zone while providing a residence time of 10 to 50 minutes. In another preferred embodiment a stripping agent is introduced into any one or more of the three zones, i.e. the first (separation), second (separation) or third (distillation) zone. More preferably the stripping agent is introduced into the third zone and recycled to the first zone together with any hydrogen chloride remaining after the second zone or the intermediate zone. The stripping agent is a liquid non-reactive with trimethyl phosphate and preferably has a boiling point between that of methanol and the phosphate and undergoes a phase separation with methanol and hydrogen chloride, e.g. acyclic, cyclic and aromatic hydrocarbons. Pressures of 0.1 to 0.6 p.s.i.a. and 0.1 to 3 p.s.i.a. are preferred in the first and second zones respectively and a residence time of 0.75 to 2 hours is preferably provided in the second zone. In the examples, a vertical column packed with Raschig rings provides the first zone, reboiler associated therewith provides the second zone and a distillation column adjacent thereto provides the third zone. The intermediate zone, where used, comprises a tubular member from the reboiler to the distillation column.