GB1257558A - - Google Patents

Abstract

1,257,558. Glycols, purification by distillation. UNION CARBIDE CORP. 21 Aug., 1969 [22 Aug., 1968], No. 41755/69. Heading BIB. [Also in Division C2] A glycol of the formula: in which R is H, CH 3 or C 2 H 5 and n is 1, 2, 3, or 4, is purified by feeding the impure glycol into a fractionating column wherein it is distilled under reflux in the presence of water so that there is at least 40% by weight of water at the glycol feed point and in part of the lower section of the column, the pressure being maintained at a value from 50 to 760mm Hg absolute, whereby the impurities distil off with water, and recovering the purified glycol from the bottoms fraction by distillation in a further column. If the impure glycol contains hydrolyzable impurities, a mineral acid is added to the first column in order to maintain the liquid in the lower section at a pH between 2 and 5; but the pH of the bottoms fraction is adjusted to a pH greater than 7 prior to further distillation. An example relates to the purification of spent monoethylene glycol containing terephthalic acid, terephthalic ester and carbonyl compounds. The spent glycol was mixed with an equal amount of ion-exchanged water and introduced as hot feed (75‹C) to the 10th tray (above the kettle) of a 20-tray oldershaw column. The bottoms fraction, consisting essentially of dry monoethylene glycol and minor amounts of diethylene glycol and triethylene glycol, was introduced to the 5th tray of a 15-tray oldershaw column. Purified monoethylene glycol was withdrawn as a liquid sidestream from the 10th tray. Other examples relate to the purification of diethylene glycol containing typical impurities generated during the manufacture of the glycol.