Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-09-15
2001-11-13
Rotman, Alan L. (Department: 1612)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S505000, C549S508000
Reexamination Certificate
active
06316640
ABSTRACT:
The present invention relates to a process for preparing tetrahydrofuran (THF) by reaction of a 1,4-butanediol-containing reaction mixture over an acid catalyst.
Processes for preparing THF from 1,4-butanediol have been known for a long time. K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie, VCH Verlagsgesellschaft, D 69451 Weinheim, 1994, page 111, describes the conversion of 1,4-butanediol into THF by elimination of water with addition of phosphoric acid, sulfuric acid or acid ion exchangers. In this process, the 1,4-butanediol admixed with acid is heated and further 1,4-butanediol is added at the rate at which THF/water distills out.
A disadvantage of this process for preparing THF is that the 1,4-butanediol which is usually used has to be purified before use. The purification is usually carried out by a complicated multistage distillation in which undesired low- and/or high-boiling constituents, including water, are removed. Subsequently, this water-free pure butanediol is converted into THF, with water and undesirable byproducts being formed. For this reason, the THF obtained as product again has to be purified by a multistage distillation after the reaction. Thus, comparable, complicated purification and separation steps have to be carried out twice.
In DE-A-196 01 375, this problem is solved by first removing the volatile organic compounds present in an aqueous butanediol solution by distillation. The aqueous butanediol solution which has been prepurified in this way is dehydrated over an acid aluminum oxide catalyst and the THF-rich fraction obtained is distilled to obtain pure THF. Here, the presence of water in the butanediol solution increases the selectivity of the catalyst. Such aqueous butanediol solutions used as starting material are usually obtained industrially in the preparation of butanediol from acetylene and formaldehyde and subsequent hydrogenation of the butynediol formed. These hydrogenation products comprise water and butanediol together with low boilers such as methanol, propanol and butanol.
It has been proposed already in WO 99/35136 and WO 99/35113, both being non pre-published but having the earlier priority, to produce THF together with &ggr;-butyrolactone and optionally additionally 1,4-butanediol in a multistage process, wherein starting from e.g. dimethyl maleate hydrogenation and cyclization is conducted in two or three partial stages at different catalysts. A typical composition comprises, leaving the said partial stages, 53% &ggr;-butyrolactone, 34% THF, 7% 1,4-butanediol and 3% byproducts (based on an overall conversion rate of 97%. A removal of water, resulting from the synthesis of THF, is only mentioned in relation to the recycling of the gaseous parts. The liquid parts of the reaction effluent are (note FIG. 1 of both WO's), after distillation fraction, THF, methanol, &ggr;-butyrolactone, a recyclable fraction of 1,4-butanediol and the educt dimethyl maleate, heavy boiling organic byproducts and a fraction of water and light boiling organic byproducts. It is expressely mentioned, that the said multistage processes are preferred compared with a process starting with 1,4-butanediol as educt.
There is particular interest in the efficient preparation of THF from essentially nonaqueous butanediol solutions obtained, for example, by hydrogenation of maleic acid or its derivatives, without prior removal of the low boilers such as methanol, propanol, etc. and other by-products present in the hydrogenation product. A problem is that under the reaction conditions of the cyclization of 1,4-butanediol to THF (intramolecular etherification) the other alcohols present in the reaction mixture can also be etherified (intermolecular etherification). Furthermore, the formation of olefins from alcohols, e.g. of butene from butanol, is possible. These by-products would reduce both the yield of THF and the operating lives of the catalyst.
It is an object of the present invention to provide a process for preparing THF from largely water-free 1,4-butanediol in which the butanediol-containing reaction mixture used does not have to be prepurified and the formation of significant amounts of by-products is avoided.
We have found that this object is achieved by using a process for preparing THF by reaction of a 1,4-butanediol-containing reaction mixture over an acid catalyst as the starting point. In the process of the present invention, the reaction mixture comprises further alcohols different from 1,4-butanediol and is essentially free of water.
For the purposes of the present invention, “essentially free of water” means a water content of the reaction mixture of generally less than 5% by weight, preferably less than 2% by weight, particularly preferably less than 1% by weight.
The process of the present invention has the advantage that the 1,4-butanediol-containing reaction mixtures used do not have to be prepurified prior to being converted into THF over an acid catalyst. 1,4-Butanediol is cyclized to THF in the presence of further alcohols without appreciable amounts of by-products being formed. This eliminates the complicated prepurification, thus saving money.
The conversion of 1,4-butanediol-containing reaction mixtures—preferably containing it as the main component, especially containing more than 50% by weight—into THF can be carried out preferably in the liquid phase or also in the gas phase.
The 1,4-butanediol-containing reaction mixtures used as feed in the reaction can be obtained by known methods.
Thus, for example, it is possible to use a 1,4-butanediol-containing reaction mixture which is obtained by the Reppe process from acetylene and formaldehyde and subsequent hydrogenation of the 1,4-butynediol formed, or by acetoxylation or chlorination of butadiene.
Preference is given to using the hydrogenation product from the hydrogenation of a compound selected from the group consisting of maleic acid, maleic monoesters, maleic diesters, maleic anhydride and intermediates formed in the hydrogenation as feed. Examples of such intermediates are succinic anhydride, &ggr;-butyrolactone, succinic acid and succinic diesters. Particular preference is given to using the hydrogenation product of the hydrogenation of maleic diesters as feed in the conversion into THF.
The hydrogenation can be carried out in a known manner in the gas or liquid phase. For example, dimethyl maleate can be hydrogenated in the gas phase over a catalyst, e.g. copper chromite, at superatmospheric pressure and elevated temperature. The hydrogenation product obtained, which is used as feed in the process of the present invention, generally comprises 5-85% by weight of butanediol and 15-95% by weight of alcohol, preferably from 10 to 70% by weight of butanediol and from 15 to 70% by weight of alcohol, particularly preferably from 15 to 60% by weight of butanediol and from 15 to 50% by weight of alcohol. In addition, products such as &ggr;-butyrolactone or succinic diesters can be present in concentrations up to, for example, 30% by weight. The contents of &ggr;-butyrolactone or succinic diesters are generally not critical in the process, but preferably the said contents are not higher than half of the weight content of butanediol. Furthermore, water may be present in a proportion of generally less than 5% by weight, preferably less than 2% by weight, particularly preferably less than 1% by weight, and small amounts of further compounds may also be present. It is possible for THF to be present in the hydrogenation product before it is used in the process of the present invention; the THF content is not critical in the process and can be, for example, from 10 to 30% by weight.
In a preferred embodiment of the invention the feed contains 15 to 60% by weight of butanediol, 15 to 50% by weight of (further) alcohol(s), up to 30% by weight of &ggr;-butyrolactone and/or succinic diester, the content thereof is not higher than half of the weight content of butanediol, and up to 30% by weight of THF, and furthermore, based on the total of all other components being 100% by weight, l
Fischer Rolf
Liang Shelue
Pinkos Rolf
BASF - Aktiengesellschaft
Desai Rita
Keil & Weinkauf
Rotman Alan L.
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