Process for preparing pentane-1,5-diol

Details Process for preparing pentane-1,5-diol Process for preparing pentane-1,5-diol

2000-04-19

2001-07-24

Owens, Amelia (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S854000

Reexamination Certificate

active

06265624

ABSTRACT:

This invention relates to a process for the production of pentane-1,5-diol.
Pentane-1,5-diol (or pentamethylenediol) has the formula:
It is a specialty chemical which has potential for use in the plastics industry as a monomer from which to make polyesters. Pentane-1,5-diol is commercially available at a purity of 96% with a quoted boiling point of 242° C.
One method of producing pentane-1,5-diol is by hydrogenation of a dialkyl glutarate, such as dimethyl glutarate, according to the following equation:
However, a byproduct of this reaction is &dgr;-valerolactone of the formula:
which is a reactive compound. Thus &dgr;-valerolactone can polymerise to form a polymer of the formula:
Such polymers cause difficulties in the purification of pentane-1,5-diol because they tend to break down during distillation, thereby reforming &dgr;-valerolactone. Another possible reaction is that between the alkanol, e.g. methanol, present in the crude hydrogenation product to form methyl 5-hydroxypentanoate according to the reaction:
These reaction products tend to form spontaneously even at ambient temperature and slowly decompose during distillation of the crude pentane-1,5-diol, thereby reforming &dgr;-valerolactone. In addition conditions in a distillation column can favour the formation of polyesters and other heavy byproducts, including methyl 5-hydroxypentanoate. According to the published literature &dgr;-valerolactone is commercially available at a purity of 99%. Such a commercial product has a quoted melting point of 38° C. to 40° C. and a boiling point of 256° C. Since the boiling point of &dgr;-valerolactone is close to that of pentane-1,5-diol, its separation from pentane-1,5-diol during distillation of the crude hydrogenation product is problematic because &dgr;-valerolactone behaves non-ideally during distillation and tends to report with pentane-1,5-diol in the distillation step. Hence it is difficult to avoid small amounts of &dgr;-valerolactone contaminating the pentane-1,5-diol distillation product.
It would accordingly be desirable to provide a process for the purification of crude pentane-1,5-diol from a crude hydrogenation product containing same, for example a crude hydrogenation product resulting from the hydrogenation of a dialkyl glutarate, such as diethyl glutarate or, preferably, dimethyl glutarate. It would further be desirable to provide such a process that can be operated continuously.
The present invention accordingly seeks to provide a process for the purification of a crude pentane-1,5-diol which contains minor amounts of &dgr;-valerolactone so as to produce a pentane-1,5-diol product that is substantially free from &dgr;-valerolactone. It further seeks to provide a process for the recovery from a crude product containing pentane-1,5-diol and &dgr;-valerolactone of substantially pure pentane-1,5-diol. Yet another objective of the invention is to provide a continuous process for the recovery of pentane-1,5-diol from a crude product containing both pentane-1,5-diol and &dgr;-valerolactone.
According to one aspect of the present invention there is provided a process for the continuous recovery of substantially pure pentane-1,5-diol from a crude product stream containing pentane-1,5-diol and &dgr;-valerolactone which comprises:
continuously supplying the feed stream to a vaporisation zone maintained under temperature and pressure conditions effective for the vaporisation of pentane-1,5-diol and conducive to the thermal decomposition of reaction products of &dgr;-valerolactone thereby to form a vaporous stream;
continuously supplying resulting vaporous stream to an intermediate section of a distillation zone, said intermediate section lying below an upper distillation section and above a lower distillation section;
continuously supplying to the upper section of the distillation zone a reflux stream of dimethyl glutarate;
continuously recovering from the upper section of the distillation zone an overhead vapour product stream comprising &dgr;-valerolactone and dimethyl glutarate;
continuously recovering from the distillation zone an intermediate stream comprising substantially pure pentane-1,5-diol; and
continuously recovering from the bottom section of the distillation zone a bottoms product.
In a preferred process the bottoms product is recycled to the vaporisation zone.
It will thus be appreciated that the process of the invention involves the use of a vaporisation zone which precedes and is separate from the distillation zone. By use of such an arrangement it can effectively be ensured that reaction products from &dgr;-valerolactone do not enter the distillation zone but remain in the sump section of the vaporisation zone. Thus, although the vapour stream supplied to the distillation zone contains &dgr;-valerolactone, it cannot reform undesirable products and thus does not behave in a non-ideal way. Hence the separation of traces of &dgr;-valerolactone from the pentane-1,5-diol product is facilitated.
The dimethyl glutarate used as reflux stream has a higher boiling point than &dgr;-valerolactone and hence helps to ensure that in the distillation zone &dgr;-valerolactone remains vaporous and hence cannot condense and form undesirable condensation products.
Dimethyl glutarate has a published boiling point of 93° C. to 95° C. at 13 mm Hg (1733.19 kpa), i.e. a boiling point lower than pentane-1,5-diol, and hence, when it is used as the material of the reflux stream, it reports in the vaporous overhead stream from the upper section of the distillation zone. This vaporous overhead stream can then be condensed. When the process used for the production of pentane-1,5-diol involves hydrogenation of dimethyl glutarate, then the resulting condensate can recycled to the hydrogenation zone to form the feed, or a part of the feed, thereto.
Hence according to another aspect of the present invention there is provided a process for the continuous production of pentane-1,5-diol which comprises:
supplying a feed stream comprising dimethyl glutarate in admixture with hydrogen to a hydrogenation zone containing a charge of an ester hydrogenation catalyst maintained under temperature and pressure conditions effective for the hydrogenation of dimethyl glutarate to pentane-1,5-diol;
recovering from the hydrogenation zone a hydrogenation product mixture comprising unreacted hydrogen, methanol, &dgr;-valerolactone and pentane-1,5-diol;
separating from the hydrogenation product mixture a crude reaction product stream comprising &dgr;-valerolactone and pentane-1,5-diol;
continuously supplying the crude reaction product stream to a vaporisation zone maintained under temperature and pressure conditions effective for the vaporisation of pentane-1,5-diol and conducive to the thermal decomposition of reaction products of &dgr;-valerolactone thereby to form a vaporous stream;
continuously supplying resulting vaporous stream to an intermediate section of a distillation zone, said intermediate section lying below an upper distillation section and above a lower distillation section;
continuously supplying to the upper section of the distillation zone a reflux stream of dimethyl glutarate;
continuously recovering from the upper section of the distillation zone an overhead vapour product stream comprising &dgr;-valerolactone and dimethyl glutarate;
continuously recovering from the distillation zone an intermediate stream comprising substantially pure pentane-1,5-diol;
continuously recovering from the bottom section of the distillation zone a bottoms product; and
recycling material of the overhead vaporous stream from the distillation zone to the hydrogenation zone.
In such a process the hydrogenation catalyst is preferably a reduced copper chromite catalyst, for example, that sold under the designation DRD92/89 by Kvaerner Process Technology Limited of P.O. Box P.O. Box 37, Bowesfield Lane, Stockton-on-Tees, Cleveland TS18 3HA. Typical reaction conditions include use in the hydrogenation zone of a hydrogen:dimethyl glutarate molar ratio of from about 200:1 to about 600:1, a temperature in the ran

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