Patent ID: 8629306

Claim:
A process for preparing 1,6-hexanediol from a first carboxylic acid mixture the process comprising (a) hydrogenating only any aldehyde or ketone present in an aqueous carboxylic acid mixture catalytically to a corresponding alcohol at a hydrogenation temperature of from 50 to 200° C. and a reaction pressure of from 5 to 35 bar absolute and degrading more than 50% of formic acid present in the mixture; to obtain a second aqueous mixture, (b) reacting any monocarboxylic acid or dicarboxylic acid present in the second aqueous reaction mixture, after dewatering, with a low molecular weight alcohol to give a corresponding carboxylic ester, in an esterification mixture; (c) freeing the esterification mixture of excess alcohol and low boilers in a first distillation stage, to obtain a bottom product; (d) in a second distillation stage, performing a separation of the bottom product into an ester fraction depleted of at least one 1,4-cyclohexanediol and a second fraction comprising at least one 1,4-cyclohexanediol; (e) catalytically hydrogenating the ester fraction from (d), and obtaining 1,6 hexanediol by distilling the hydrogenation product, wherein the first carboxylic acid mixture comprises: adipic acid; 6-hydroxycaproic acid; 6 oxocaproic acid:, 4 hydroxycyclohexanone; formic acid; and, based on a sum of adipic acid and hydroxycaproic acid, between 0.5 and 5% by weight of at least one 1,4-cyclohexanediol, and wherein the first carboxylic acid mixture is obtained as a by-product of a catalytic oxidation of cyclohexane to cyclohexanone/cyclohexanol with oxygen or at least one oxygen-comprising gas by water extraction of a reaction mixture from the oxidation.