GB619976A - Improvements in or relating to the dehydration of tetrahydropyran - Google Patents

Abstract

Water is removed from tetrahydropyran/water mixtures by submitting the mixture to a distillation which is continued until the vapours therefrom give a condensate which, on cooling and standing, ceases to separate into two layers; tetrahydropyran being added to the mixture if the latter contains more water than the azeotrope, in an amount sufficient to ensure that, in a batch process, the proportion of tetrahydropyran in the still increases as the distillation proceeds, or that, in a continuous process, dry tetrahydropyran can be withdrawn continuously from the base of the distillation column. In the example, 500 parts by weight of tetrahydropyran containing 15 parts of water were boiled in a still fitted with a fractionating column, condenser and decanter. The condensate was passed to the decanter and the top, tetrahydropyran-rich, layer which separated was returned to the top of the column. Fifteen parts of the lower aqueous layer were collected at a still-head temperature of 71-75 DEG C. The distillation was then continued at a reflux ratio of 5 : 1 and about 27 parts of a wet fraction removed at a temperature of 75-88 DEG C. The remainder of the tetrahydropyran was then distilled off in a dry condition. The aqueous layer was submitted to redistillation and approximately 1 part of wet tetrahydropyran obtained. This and the moist intermediate fraction may be recycled to the initial distillation process. Specification 592,919 is referred to. p