Process for production of dimethyl terephthalate

Claim 1

A CONTINUOUS PROCESS FOR PRODUCING DIMETHYL TEREPHTHALATE CONTAINING NO MORE THAN 0.01 MOL PERCENT IMPURITY COMPRISING CONTINUOUSLY PREHEATING METHANOL FEED CONTAINING NO MORE THAN 2 PERCENT WATER BY WEIGHT TO A TEMPERATURE OF 260*C. AND 1900 P.S.I.G., CONTINUOUSLY CHARGING 5 PARTS OF PREHEATED METHANOL PER PART OF SAID TEREPHTHALIC ACID AT 150*C. TO AN ESTERIFICATION ZONE CONTAINING AN ESTERIFICATION REACTION MIXTURE RESULTING FROM THE REACTION OF SAID PROPORTIONS OF METHANOL AND TEREPHTHALIC ACID AT 260*C. AND 1900 P.S.I.G., CONTINUOUSLY WITHDRAWING A PORTION OF THE ESTERIFICATION REACTION MIXTURE AT A RATE TO PROVIDE ABOUT 30 MINUTES RESIDENCE IN SAID ESTERIFICATION ZONE, CONTINUOUSLY CONTACTING SAID WITHDRAWN PORTION OF THE ESTERIFICATION REACTION MIXTURE IN INDIRECT HEAT EXCHANGE RELATIONSHIP WITH SAID FEED METHANOL TO COOL SAID PORTION OF THE ESTERIFICATION REACTION MIXTURE TO 120*C. AND A ACCOMPLISH SAID PREHEATING OF FEED METHANOL, CONTINUOUSLY FLASH COOLING THE 120*C PORTION OF SAID ESTERIFICATION REACTION MIXTURE TO 65 TO 105*C. AT 0 TO 50 P.S.I.G. WHILE REMOVING A FIRST WEB METHANOL AND NUCLEATING SEED CRYSTALS OF CRUDE DIMETHYL TEREPHTHALATE, CONTINUOUSLY COOLING SAID MIXTURE IN A FIRST CRYSTALLIZATION ZONE RAPIDLY AT 100 TO 400 MM. HG AND 25 TO 35*C. TO GROWTH LARGE CRYSTALS OF CRUDE DIMETHYL TEREPHTHALATE WHILE REMOVING A SECOND WET METHANOL, CONTINUOUSLY SEPARATING SAID CRUDE DIMETHYL TEREPHTHALATE CRYSTALS FROM THE MOTHER LIQUOR, CONTINUOUSLY WASHING SAID CRUDE DIMETHYL TEREPHTHALATE CRYSTALS WITH A METHANOL WASH HEREINAFTER PROVIDED BY THE WASHING OF RECRYSTALLIZED DIMETHYL TEREPHITHALATE, REDISSOLVING SAID WASHING CRUDE DIMETHYL TEREPHTHALATE AT 65 TO 105*C. AND 0 TO 50 P.S.I.G. IN METHANOL COMPRISING (A) SAID FIRST AND SECOND PORTIONS OF WET METHANOL REMOVED IN THE PRIOR COOLING STEPS, (B) A THIRD PORTION OF WET METHANOL HEREINAFTER OBTAINED IN A SECOND CRYSTALLIZATION ZONE AND (C) DEHYDRATED RECYCLE METHANOL TO PROVIDE A TOTAL OF 5 PARTS OF METHANOL PER PART OF CRUDE DIMETHYL TEREPHTHALATE BY'' WEIGHT, CONTINUOUSLY COOLING SAID SOLUTION IN A SECOND RECRYSTALLIZATION ZONE AT 100 TO 400 MM. HG AND 25 TO 35*C. TO RECRYSTALLIZE DIMETHYL TEREPHTHALATE, CONTINUOUSLY SEPARATING RECRYSTALLIZED DIMETHYL TEREPHTHALATE FROM ITS MOTHER LIQUOR, CONTINUOUSLY WASHING THE RECRYSTALLIZED DIMETHYL TEREPHTHALATE WITH EQUAL PARTS BY WEIGHT OF DEHYDRATED METHANOL AND CHARGING THE WASH LIQUOR TO WASH THE CRUDE DIMETHYL TEREPHTHALATE CRYSTALS, CONTINUOUSLY DRYING SAID WASHED RECRYSTALLIZED DIMETHYL TEREPHTHALATE.