Economical production of pure 1,6-hexane-diol and epsilon-capro-lactone from by-product of oxidation of cyclohexane

Verfahren zur Herstellung von 1,6-Hexandiol und Caprolacton


A process for the production of 1,6-hexandiol (I) and iota -caprolactone (II) from a carboxylic acid mixture (III) of adipic acid, 6-hydroxycaproic acid and small amounts of cyclohexan-1,4-diol(s) is obtained as by-product of the oxidation of cyclohexane to cyclohexanone/cyclohexanol with (gas containing) oxygen by extraction of the reaction mixture with water. The process involves esterification, hydrogenation of a side stream to (I) and cyclisation of 6-hydroxycaproic ester to (II) by the following stages. First, (a) the mono- and dicarboxylic acids in the aqueous (III) are esterified with a low molecular alcohol. This is followed by 3 distillation stages, in which (b) excess alcohol and low-boiling compounds are removed, (c) the sump is separated into an ester fraction free from cyclohexan-1,4-diol(s) and a fraction of (mainly) cyclohexan-1,4-diol(s), and (d) a stream of (mainly) 6-hydroxycaproic ester is separated from the ester fraction. Then (e) the remaining ester fraction from (d) is hydrogenated catalytically and (I) is recovered from the hydrogenation product by distillation and (f) the 6-hydroxycaproic ester stream is heated to > 200 deg C at low pressure to cyclise the ester to (II), and pure (II) is recovered from the cyclisation product by distillation.




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Cited By (19)

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