Improvements in the separation and recovery of dimethyl terephthalate from vapour mixtures containing the same and methanol

摘要

Dimethyl terephthalate is recovered from a vapour mixture consisting mainly of dimethyl terephthalate and methanol by leading the mixture at a temperature between 150 DEG and 350 DEG C. into methanol boiling under reflux, which serves as a cooling medium, and withdrawing a suspension of dimethyl terephthalate in methanol from the system at a rate corresponding to the amount of methanol and ester introduced with the vapour mixture; the dimethyl terephthalate is then separated from the suspension in known manner, e.g. by filtration, centrifuging or decantation, if desired after the suspension has been cooled to between 40 DEG and -10 DEG C. The vapour mixture to be treated preferably contains at least 0,1 part by weight of dimethyl terephthalate per part of methanol and may be a mixture obtained by distilling crude dimethyl terephthalate by carrier-vapour distillation, methanol vapour being used as the carrier. The crude dimethyl terephthate may itself have been obtained from p-xylene by oxidation with nitric acid and the impurities in the vapour mixture may comprise methyl toluate, esters of nitrobenzoic acid, dimethyl nitroterephthate and monomethyl terephthalate. Specification 770,797 is referred to.ALSO:Dimethyl terephthalate is recovered from a vapour mixture consisting mainly of dimethyl terephthalate and methanol by leading the mixture at a temperature between 150 DEG C. and 350 DEG C. into methanol boiling under reflux, which serves as a cooling medium, and withdrawing a suspension of dimethyl terephthalate in methanol from the system at a rate corresponding to the amount of methanol and ester introduced with the vapour mixture; the dimethyl terephthalate is then separated from the suspension in known manner, e.g. by filtration, centrifuging or decantation, if desired after the suspension has been cooled to between 40 DEG C. and - 10 DEG C. The vapour mixture to be treated preferably contains at least 0.1 part by weight of dimethyl terephthalate per part of methanol and may be a mixture obtained by distilling crude dimethyl terephthalate by carrier-vapour distilling, methanol vapour being used as the carrier. The crude dimethyl terephthalate may itself have been obtained from p-xylene by oxidation with nitric acid and the impurities in the vapour mixture may comprise methyl toluate, esters of nitrobenzoic acid, dimethyl nitroterephthalate and monomethyl terephthalate. Specification 770,797 is referred to.