Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2003-06-04
2004-12-14
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S325000, C549S326000, C549S429000
Reexamination Certificate
active
06831182
ABSTRACT:
The present invention relates to a process for preparing unsubstituted or alkyl-substituted &ggr;-butyrolactone and tetrahydrofuran by catalytic hydrogenation in the gas phase of substrates selected from the group consisting of maleic acid and succinic acid and derivatives of these acids. For the purposes of the present invention, such derivatives are esters and anhydrides which, like the acids themselves, may bear one or more alkyl substituents. The process makes it possible to achieve high yields and the ratio of the two products can be set over a wide range. The process of the present invention is carried out in two reaction zones connected in series.
The preparation of &ggr;-butyrolactone (GBL) and tetrahydrofuran THF) by gas-phase hydrogenation of maleic anhydride (MA) is a reaction which has been known for many years. Numerous catalyst systems for carrying out this catalytic reaction are described in the literature. These are mostly Cr-containing. Depending on the composition of the catalyst and the reaction parameters selected, such catalysts give different product distributions.
Apart from MA, further possible starting materials for preparing GBL and THF are maleic acid itself, succinic acid and its anhydride and also esters of these acids. If GBL and THF bearing alkyl substituents are to be prepared, the appropriately alkyl-substituted derivatives of the abovementioned acids, esters and anhydrides can be used.
U.S. Pat. No. 3,065,243 discloses a process in which copper chromite is used as catalyst. According to the description and examples, this process forms considerable amounts of succinic anhydride (SA) which has to be circulated. As is well known, this frequently results in process engineering problems due to crystallization of SA or succinic acid formed therefrom followed by blockage of pipes.
Further copper chromite catalysts for the hydrogenation of MA are disclosed, for example, in the publications U.S. Pat. Nos. 3,580,930, 4,006,165, EP-A 638 565 and WO 99/38856. According to these disclosures, high yields of GBL can be achieved using the catalysts described there. THF is in each case formed only in traces. However, larger amounts of THF are often desired for a number of reasons.
A process which allows this is disclosed in U.S. Pat. No. 5,072,009. The catalysts used according to this patent have the formula Cu
1
Zn
b
Al
c
M
d
O
x
, where M is at least one element selected from the group consisting of the elements of groups IIA and IIIA, VA, VIII, Ag, Au, groups IIIB to VIIB and the lanthanides and actinides of the Periodic Table of the Elements, b is from 0.001 to 500, c is from 0.001 to 500 and d is from 0 to <200 and x corresponds to the number of oxygen atoms required according to the valence criteria. Although it is stated that it is not necessary for chromium to be present in the catalysts disclosed in this patent, all examples describe chromium-containing catalysts. According to these examples, the maximum THF yield is 96%, and the hydrogenation is carried out at pressures of from 20 to 40 bar.
An in-principle disadvantage of all the above-described catalyst systems is the presence of chromium oxide whose use should be avoided because of the high toxicity. Cr-free catalyst systems for preparing GBL by hydrogenation of MA have also been described in the prior art. Examples of such catalyst systems may be found in the publications WO 99/35139 (Cu—Zn oxide), WO 95/22539 (Cu—Zn—Zr) and U.S. Pat. No. 5,122,495 (Cu—Zn—Al oxide). All these catalyst systems make it possible to achieve high yields of GBL, up to 98%, but the formation of THF is not observed or only traces are formed. Although the formation of THF can, as is known, be promoted by increasing the reaction temperature or having a longer residence time in the reactor, this at the same time also increases the proportion of undesirable by-products, for example butanol, butane, ethanol or ethane.
A catalyst made up exclusively of copper and aluminum oxides for the gas-phase hydrogenation of MA to GBL is disclosed in WO 97/24346. Here too, the same disadvantages as in the publications described in the previous paragraph, namely formation of THF in only minor amounts or traces, are encountered.
The use of a catalyst having essentially the same composition as described in WO 97/24346, namely based on Cu—Al oxides, is also disclosed in JP 2 233 631. The object of that invention is to carry out the hydrogenation of MA in such a way that THF and 1,4-butanediol are formed as main products and only small amounts, if any, of GBL are formed. This is achieved by the use of the catalysts based on mixed Cu—Al oxides and by adhering to particular reaction conditions. Typical mixtures obtained by means of this process comprise from about 15 to 20 mol % of 1,4-butanediol and from 60 to 80 mol % of THF, with the amount of THF even being able to be increased to over 99 mol % according to one example. This is achieved by using GBL as solvent in a large excess. If, on the other hand, no solvent is employed, the yields drop significantly to values of 75%.
In contrast, EP-A 0 404 408 discloses a catalyst for the hydrogenation of MA whose structure is different in principle from that of the catalysts in the above-mentioned references. Here, the catalytically active material corresponds essentially to the material disclosed in the above-cited U.S. Pat. No. 5,072,009. The material is then applied to an essentially inert, at least partly porous support having an external surface. The catalytically active material adheres to the outer surface of the support. In contrast to the corresponding, unsupported catalyst, which gives THF as main product, this catalyst forms GBL as preferred product. Here too, Cr is present in all catalysts used in the examples. Another disadvantage is the large amount of SA formed.
All the types of catalyst described in the abovementioned publications have the disadvantage that they still produce a large amount of undesired by-product or can be used only for the preparation of one of the main products THF and GBL which may be desired in principle. In addition, Cr is frequently present in the catalysts.
A two-stage process for the hydrogenation of MA is described in U.S. Pat. No. 5,149,836. This process enables GBL and THF to be produced in an adjustable selectivity ratio of from 15 to 92% of GBL or from 7 to 83% of THF. The process comprises a first step in which MA is hydrogenated over a first catalyst bed comprising from 30 to 65% by weight of CuO, from 18 to 50% by weight of ZnO and from 8 to 22% by weight of Al
2
O
3
to give a gas mixture comprising predominantly GBL. The GBL obtained in the first step is hydrogenated to THF over a second catalyst bed comprising from 10 to 50% by weight of CuO, from 30 to 65% by weight of ZnO and from 3 to 20% by weight of Cr
2
O
3
. The first hydrogenation is carried out at from 200 to 400° C., while the second is carried out at from 200 to 350° C., preferably from 250 to 280° C. According to the examples, the reaction temperature in the first step is from 245 to 275° C. while that in the second step is from 250 to 280° C. At a temperature of 250° C., mainly butanediol is formed in the second hydrogenation step, while mainly THF is formed at 280° C.
WO 99/35136 describes a further process for preparing THF and GBL in variable relative amounts. Starting materials used are maleic anhydride or succinic anhydride or fumaric esters. In a first step, these are reacted with hydrogen over a copper-based heterogeneous catalyst, preferably a copper-zinc oxide or stabilized copper chromite catalyst. In a second reaction step, an acidic silicon-aluminum oxide is used. Disadvantages of this process are the use of two entirely different catalysts and also the limited flexibility in respect of the product mix, since the GBL:THF ratio can be varied only in the range from 70:30 to 40:60.
It is an object of the present invention to provide a process for the gas-phase hydrogenation of maleic acid and/or succinic acid and/or the abovementioned derivatives by means of which substitut
Borchert Holger
Fischer Rolf-Hartmuth
Kaibel Gerd
Rahn Ralf-Thomas
Rösch Markus
BASF - Aktiengesellschaft
Keil & Weinkauf
Trinh Ba K.
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