Basf Se Corporation

Bernd Schall

Claus Hechler

Catharina Horstmann

Gregor Grackiewicz

A process for continuously preparing the tert-butyl ester of an ethylenically unsaturated carboxylic acid, by a) reacting an ethylenically unsaturated carboxylic acid with isobutene in the presence of an acidic catalyst to give an esterification mixture; b) removing the acidic catalyst; c) removing low-boiling components; and d) supplying a tert-butyl ester-comprising liquid to a distillation apparatus and subjecting it to purifying distillation in the distillation apparatus, where d1) in the distillation apparatus the tert-butyl ester-comprising liquid is separated into a tert-butyl ester-comprising gaseous top product and a carboxylic acid-comprising liquid bottom product; d2) the tert-butyl ester-comprising gaseous top product is at least partly condensed and the condensate is recycled partly as reflux to the distillation apparatus; d3) the carboxylic acid-comprising liquid bottom product is recycled at least partly to step a); d4) carboxylic acid-comprising liquid bottom product is drawn off and passed to a heater; a superheated, liquid recycle stream is taken from the heater; and the superheated recycle stream is let down into the distillation apparatus; and d5) at least in the top region of the distillation apparatus, the distillation apparatus walls in contact with the vapor, at least in sub-regions, are heated and/or thermally insulated. In the course of the process, the separation of the tert-butyl ester from unreacted carboxylic acid is carried on with a particularly low level of accompanying polymerization both of the tert-butyl ester and of the carboxylic acid.

Production of tert-butyl esters of ethylenically unsaturated carboxylic acids

A process for continuously preparing the tert-butyl ester of an aliphatic C-Ccarboxylic acid comprises: a) the reaction of an aliphatic C-Ccarboxylic acid with isobutene in the presence of an acidic catalyst to give an esterification mixture (G); b) the partial evaporation of the esterification mixture (G), giving a liquid first high boiler phase (SPh) comprising the acidic catalyst, and a first vapor (B) comprising tert-butyl ester; c) the fractional condensation of the first vapor (B) by partially condensing the first vapor (B) at a first pressure and a first temperature and obtaining a first condensate (K), partially condensing the uncondensed second vapor (B) at a second pressure and a second temperature and obtaining a second condensate (K), the first temperature being 0 to 45&#xb0; C. below the condensation temperature of the tert-butyl ester at the first pressure and the second temperature being 45 to 80&#xb0; C. below the condensation temperature of the tert-butyl ester at the second pressure, with the proviso that the second temperature is at least 5&#xb0; C. below the first temperature; and d) the combination of the first condensate (K) and the second condensate (K) and the feeding to a combined workup, and recycling of the third vapor (B) not condensed at the second temperature into step a). The process allows the preparation of the tert-butyl ester of an aliphatic C-Ccarboxylic acid by reaction of the carboxylic acid with isobutene, with isolation of unconverted isobutene from the esterification mixture in an energetically favorable manner and with an improved degree of removal.

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Ludwigshafen, Germany

Bernd Schall