Procédé pour l'obtention de téréphtalate de diméthyle pur

摘要

Dimethyl terephthalate is purified by continuously distilling the crude ester under reduced pressure, condensing the vapour in a condenser and cooling it down to a temperature which lies above the melting point of the ester, withdrawing the ester in the liquid phase and solidifying it, and precipitating the dimethyl terephthalate entrained by the gases or vaporized liquid from the waste gases before they are allowed to escape through the suction apparatus onto the free atmosphere, by injecting water, withdrawing the resultant suspension and separating the ester. In a preferred embodiment, crude dimethyl terephthalate is heated in a vessel 1 by internal or external steam heating coils 2. The vaporous dimethyl terephthalate passes through a column 4 and a dephlegmator 5 and into a condenser 7 in which the ester is condensed to a temperature such as 145-155 DEG C. which is above the melting-point of the ester. The liquid ester without further cooling passes into a separating vessel 8 and a down pipe 9. The ester is crystallized on rollers 10 and passes through a pipe 11 to storage. The waste gas leaves the condenser 7 at a temperature above the melting-point of the ester and passes through a heated tube 12 into an injection condenser 13 and then through a suction apparatus attached to the pipe 14. By injecting water at a temperature of 0 DEG to 25 DEG C. through pipe 15 into the condenser 13 the dimethyl terephthalate entrained by the waste gases is precipitated in solid form and flows down through pipe 16 as a milky aqueous suspension. After contrifuging and drying this fraction is extremely pure.ALSO:Dimethyl terephthalate is purified by continuously distilling the crude ester under reduced pressure, condensing the vapour in a condenser and cooling it down to a temperature which lies above the melting point of the ester, withdrawing the ester in the liquid phase and solidifying it, and precipitating the dimethyl terephthalate entrained by the gases or vaporized liquid from the waste gases before they are allowed to escape through the suction apparatus into the free atmosphere, by injecting water, withdrawing the resultant suspension and separating the ester. After centrifuging and drying this fraction is extremely pure.