Purifying di:methyl terephthalate by recrystallisation from methanol - washing moist crystals, drying by melting and evapn. of methanol and recycling wash liq. and part of mother liquor

摘要

In purifying dimethyl terephthalate (DMT) by recrystallisation from methanol soln., the mother liquor, contg. the impurities, is sepd. by filtration and the moist crystals are washed, and dried by melting and evapm. of the methanol. The wash liq. and parts of the sepd. mother liquor are recycled to the recrystallisation. The crystals are washed with methanol. The washed crystals are recrystallised from methanol in a 2nd stage, the mother liquor is sepd., and one part is fed to the 2nd stage recrystallisation, and the other part is used as solvent in the 1st stage recrystallisation, and as wash liq. in the 1st stage. The crystals from the 2nd stage recrystallisation are washed with methanol, after sepn. of the mother liquor, and the wash liq. is fed to the 2nd stage recrystallisation. The crystals from the 1st stage recrystallisation are washed with mother liquor sepd. after the 2nd recrystallisation. ADVANTAGE - The amt. of methanol used is about halved, and the quality of the DMT is at least as good.