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Methods of distillative purification of mixtures comprising hexanediol and pentanediol

IP.com Disclosure Number: IPCOM000235808D
Publication Date: 2014-Mar-25

Publishing Venue

The IP.com Prior Art Database

Abstract

1,6-Hexanediol (1,6-HDO) and/or 1,5-pentanediol (1,5-PDO) obtained in the hydrogenation of dicarboxylic acid solutions are continuously removed from the hydrogenation effluent in an arrangement of two or more distillation columns.

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Methods of distillative purification of mixtures comprising hexanediol and pentanediol

There follows a description of the methods for continuous removal of 1,6-hexanediol (1,6- HDO) and/or 1,5-pentanediol (1,5-PDO) which are obtained in the hydrogenation of dicarboxylic acid solutions in an arrangement of two or more distillation columns. This hydrogenation is effected as described, for example, in WO 2011/064182 from page 2 line 16 to page 6 line 22. The hydrogenation output thus obtained consists predominantly of 1,6- HDO and water.

First of all, it is advisable to remove from the hydrogenation output in one or more distillation columns, water or a mixture of water and low-boiling by-products overhead. The hydrogenation output, at the pressure which exists in the synthesis, is brought to a lower pressure, typically between 1 and 10 bar abs, in a vessel or in a column. In this flash operation, 20 to 90% by weight of the water present in the hydrogenation output is removed. According to the composition of the hydrogenation output, the gaseous top stream comprises, as well as water, also between 1-90% by weight of low boilers, for example various monoalcohols. The temperature of the top stream is between 100 and 180°C according to the pressure level selected. The vessel or the column advantageously has between 1 and 30 theoretical plates, preferably between 1 and 15, more preferably between 2 and 8 theoretical plates, and can be operated with or without an evaporator. In the case of a column, suitable separating internals are all known column internals, such as random packings, structured packings or trays in all known designs. The reflux ratio should advantageously be between 0 and 3. The liquid bottoms discharge comprises, inter alia, between 10-90% by weight of 1,6-HDO, 1-80% by weight of water and 0.5-9% by weight of 1,5-PDO. The gaseous top stream is condensed in one or more series-connected heat exchangers, where it is also possible for dissolved hydrogen to be released. The reflux ratio is advantageously between 0.1 and 2, preferably between 0.2 and 0.4, more preferably 0.35.

If the bottoms discharge contains even greater amounts of water, it can be passed into a further column which is operated at a lower pressure than the first stage, for example between 0.1 and 5 bar abs, preferably between 0.5 and 3 bar abs, more preferably between
0.75 and 1.5 bar abs. In order to avoid possible solids deposits in the downstream heat exchangers, columns and other components, it is advantageous to meter between 1 ppm by volume and 1% by volume of a water-soluble polymer which may also be diluted with water, advantageously with condensate from the process, into the feed line of the column.

In addition, it is advantageous to equip the column with sufficient theoretical plates, advantageously between 5 and 40, preferably between 10 and 30, more preferably between 10 and 20, theoretical plates. Suitable separating internals here are all kn...