Process for purifying ethylene glycol

摘要

1,139,282. Ethylene glycol, purification of the material recovered from the manufacture of polyesters. E. I. DU PONT DE NEMOURS & CO. 19 Jan., 1967 [1 Feb., 1966], No. 3066/67. Heading B1B. Ethylene glycol, recovered from the manu- facture of polyesters, is purified by evaporating part of the glycol until the solid impurities (e.g. sodium salts of terephthalic acid) are precipitated and form a slurry with the remaining liquid, and submitting the vapour, or condensate thereof, to fractionation under vacuum, the purified glycol being withdrawn from the fractionation column as an intermediate fraction. The "spent" glycol is fed through pipe 1 to evaporator 2 where it is partially evaporated, under vacuum and at a temperature below 175‹C., so that the solids are precipitated. The slurry and the vapour flow to separator 4, whence the separated slurry flows down to evaporator 6 (e.g. a drum drier) in which 90% of the glycol is vaporized. The vapour flows to condenser 9, and the condensate is recycled through pipe 10 to evaporator 2. The vapour flowing from separator 4 through pipe 11 is condensed in condenser 12, and the condensate is introduced into the upper section of column 47. Alternatively, the glycol can be introduced as vapour into column 47. Low-boiling impurities, e.g. water, methanol and acetaldehyde, are removed from the top of column 47, which is operated at a high reflux ratio under vacuum, e.g. 200 mm. Hg absolute; and the bottoms liquid withdrawn from the base of the column is fractionated in column 35, which is also operated under vacuum. Purified glycol vapour is taken off from the top of column 35 and condensed; the condensate being passed through a column 45 containing activated carbon, and collected in the product storage tank. The residual slurry purged through pipe 7 and the high-boiling impurities discharged through pipe 37 are burned in an incinerator. The solids-free glycol from separator 4 may, alternatively, be fractionated in a single column from which is removed a vapour sidestream comprising the purified glycol.