Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2003-06-04
2004-05-04
Owens, Amelia A. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S429000, C549S508000
Reexamination Certificate
active
06730800
ABSTRACT:
The present invention relates to a process for preparing unsubstituted or alkyl-substituted tetrahydrofuran by catalytic hydrogenation in the gas phase of substrates selected from the group consisting of derivatives of maleic acid and succinic acid and these acids themselves. For the purposes of the present invention, derivatives are anhydrides which, like the acids, may bear one or more alkyl substituents.
The preparation of 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. Depending on the composition of the catalyst and the reaction parameters chosen, different product distributions are obtained using such catalysts.
It has been able to be shown that the hydrogenation of MA to THF forms firstly succinic anhydride (SA) and subsequently &ggr;-butyrolactone (GBL) as intermediates and the latter can be hydrogenated further to form 1,4-butanediol (BDO). All the abovementioned intermediates can themselves be used as starting materials for preparing THF.
If GBL and THF bearing alkyl substituents are to be prepared, the alkyl-substituted species corresponding to the abovementioned starting materials can be used.
The catalysts used in the hydrogenation frequently comprise chromium, particularly in older processes. This is reflected in the patent literature in which there are a large number of patents and patent applications which disclose chromium-containing catalysts for the above-described hydrogenation reaction, with the hydrogenation in most cases being restricted to MA as starting material. U.S. Pat. No. 3,065,243 discloses a process in which copper chromite is employed as catalyst. According to the description and examples, this reaction results in formation of considerable amounts of SA which has to be circulated. As is known, process engineering problems due to crystallization of SA or succinic acid formed therefrom with subsequent blocking of pipes frequently occur.
Further copper chromite catalysts for the hydrogenation of MA are disclosed, for example, in U.S. Pat. Nos. 3,580,930, 4,006,165, EP-A 638 565 and WO 99/38856.
The catalysts used in U.S. Pat. No. 5,072,009 have the formula Cu
l
Zn
b
Al
c
M
d
O
x
in which M is at least one element selected from the group consisting of the elements of groups IIA and IIIA, VA, VIII, Ag, Au, the elements of 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 necessary according to valence criteria. In the examples, where only chromium-containing catalysts are used, the hydrogenation of MA using the catalysts of that invention forms THF in yields of over 90%.
EP-A 0 404 408 discloses a catalyst whose catalytically active material corresponds essentially to the material disclosed in the above-cited U.S. Pat. No. 5,072,009 for hydrogenation of MA. The catalytically active material is used in immobilized form on a support as coated catalyst and not as all-active catalyst. In contrast to the material present as all-active catalyst, mainly GBL is formed according to the examples reported, in which once again only chromium-containing catalysts are used.
A two-stage catalyst system for the hydrogenation of MA is described in U.S. Pat. No. 5,149,836. The catalyst for the first stage is chromium-free while the catalyst for the second stage is based on Cu—Zn—Cr oxides.
Owing to the toxicity of chromium, more modem technologies are increasing moving away from the use of chromium-containing catalysts. Examples of chromium-free catalyst systems may be found in WO 99/35139 (Cu—Zn oxide), WO 95/22539 (Cu—Zn—Zr) and U.S. Pat. No. 5,122,495 (Cu—Zn—Al oxide).
A catalyst made up exclusively of copper oxide and aluminum oxide for the gas-phase hydrogenation of MA to form GBL is disclosed in WO 97/24346. This catalyst comprises from 50 to 95% by weight, preferably from 80 to 90% by weight, of copper oxide, from 3 to 30% by weight, preferably from 5 to 15% by weight, of aluminum oxide and optionally a binder. Selectivities to GBL of up to about 98% are achieved in the hydrogenation of MA using such a catalyst.
WO 91/16132 discloses a chromium-free catalyst for the hydrogenation of MA. The catalyst comprises 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
. Before use in the hydrogenation reaction, the catalyst is reduced in a hydrogen atmosphere and subsequently activated in a hydrogen atmosphere at not less than 400° C. for at least 8 hours. Such a catalyst gives GBL selectivities of about 90%.
In Catalysis Today 27 (1996), pp. 181 to 186, Castiglioni et al. disclose CuO/ZnO/Al
2
O
3
catalysts which give mainly GBL in the hydrogenation of MA; a maximum THF selectivity of 17% is observed.
The use of a catalyst having a similar composition as in WO 97/24346 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 BDO are formed as main products and only small amounts, if any, of GBL, are formed. This is achieved by use of catalysts based on mixed Cu—Al oxides and by adherence to particular reaction conditions. General indications of amounts of the Cu—Al oxide are not given; the examples disclose two catalyst compositions, one comprising about 46% by weight of CuO and 33% by weight of Al
2
O
3
and the other comprising about 36% by weight of CuO and 47.% by weight of Al
2
O
3
. Use of this catalyst is said to give a THF selectivity of up to 99%, but only when an excess of GBL is employed as solvent. If the hydrogenation is carried out using the same catalyst in the absence of GBL, the selectivity drops to 76%. According to the examples, the hydrogenation is carried out at from about 210 to 230° C. and GHSVs of from about 3200 to 9600. The hydrogen/MA ratios are at values which are rather unfavorably high for industrial processes, namely from 200 to 800 in the examples.
The hydrogenation of MA under conditions corresponding to those of JP 2 233 631 but using a different catalyst is disclosed in JP 2 639 463. The use of the catalyst is said to make it possible to prepare BDO and THF by hydrogenation of MA. Use is made here of a copper oxide/zinc oxide/aluminum oxide catalyst whose composition is not disclosed quantitatively in the description. The catalysts used according to the examples have a composition of 20% by weight of CuO, 43.6% by weight of ZnO and 18.1% by weight of Al
2
O
3
, 32.6% by weight of CuO, 38.1% by weight of ZnO and 9.5% by weight of Al
2
O
3
, 24.2% by weight of CuO, 36.4% by weight of ZnO and 17.2% by weight of Al
2
O
3
, 26.4% by weight of CuO, 52.9% by weight of ZnO, 7.6% by weight of Al
2
O
3
and 1.4% by weight of CaO or 22.9% by weight of CuO, 44.8% by weight of ZnO and 16.3% by weight of Al
2
O
3
. The hydrogenation is generally carried out using a solvent such as GBL or dioxane, giving a maximum THF selectivity of 94%. When the reaction is carried out without a solvent, the THF selectivity is no more than 83%.
The technologies on which the above-cited publications are based use prepurified MA which has, after its preparation, generally been freed of impurities by distillation as starting material for the hydrogenation reactions. MA is prepared by partial oxidation of particular hydrocarbons, namely benzene, butene mixtures and n-butane, with preference being given to using the latter. The crude product of the oxidation comprises not only the desired MA but also, in particular, by-products such as water, carbon monoxide, carbon dioxide, unreacted starting hydrocarbons and acetic and acrylic acids, with these by-products being independent of the hydrocarbons used in the oxidation. The by-products are usually separated off by complicated methods, for example by distillation as mentioned above. The purification is necessary because, in particular, the catalysts used in t
Borchert Holger
Fischer Rolf-Hartmuth
Hesse Michael
Pinkos Rolf
Rahn Ralf-Thomas
LandOfFree
Method for the production of tetrahydrofuran does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the production of tetrahydrofuran, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the production of tetrahydrofuran will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3204613