| 摘要 |
<p>The invention relates to a method for producing hexanediol-1,6 from a carboxylic acid mixture containing adipic acid, 6-hydroxycaproic acid and small amounts of 1,4-cyclohexanediols, said mixture being obtained as a by-product of the oxidation of cyclohexane to form cyclohexanon/cyclohexanol with oxygen or gases containing oxygen and through the water-extraction of the reaction mixture, by means of esterification of the acids and hydrogenation. The method comprises the following steps: a) converting the mono- and dicarboxylic acids contained in the aqueous dicarboxylic acid mixture to the corresponding carboxylic acid esters with a low-molecular alcohol; b) liberating the resulting esterification mixture from excess alcohol and light-boiling substances in a first distillation stage; c) separating the bottom product into an ester fraction which is essentially free of 1,4-cyclohexanediols and a fraction containing at least the majority of the 1,4-cyclohexanediols; d) hydrogenating the ester fraction which is essentially free of 1,4-cyclohexanediols with a catalyst; and e) extracting hexanediol-1,6 from the discharge from the hydrogenation using a method known per se, in a pure distillation step. According to the invention, an aqueous dicarboxylic acid containing more than 20 ppm cobalt and more than 40 ppm phosphorus is used in the form of phosphate and this aqueous dicarboxylic acid mixture is passed over a cation exchanger and after the esterification in accordance with step (a), over an anion exchanger.</p> |
