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  Selective preparation of tetrahydrofuran by hydrogenation of maleic anhydrideUSPTO Application #: 20080097112Title: Selective preparation of tetrahydrofuran by hydrogenation of maleic anhydride Abstract: c) 2-79.995% by weight, preferably 5-59.99% by weight, in particular 8-39.95% by weight, of an oxidic support selected from the group consisting of the oxides of Al, Si, Zn, La, Ce, the elements of groups IIIA to VIIIA and of groups IA and IIA of the Periodic Table of the Elements. b) 0.005-5% by weight, preferably 0.01-3% by weight, in particular 0.05-2% by weight, palladium and/or a palladium compound (calculated as metallic palladium) and a) 20-94% by weight of copper oxide (CuO), preferably 40-92% by weight of CuO, in particular 60-90% by weight of CuO, and A catalyst for the hydrogenation of C4-dicarboxylic acids and/or derivatives thereof, preferably maleic anhydride, in the gas phase comprises (end of abstract) Agent: Novak Druce Deluca + Quigg LLP - Washington, DC, US Inventors: Stephan Schlitter, Holger Borchert, Michael Hesse, Markus Schubert, Nils Bottke, Rolf-Hartmuth Fischer, Markus Rösch, Gunnar Heydrich, Alexander Week USPTO Applicaton #: 20080097112 - Class: 549313 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080097112. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001]The present invention relates to a process for preparing unsubstituted or alkyl-substituted y-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, these derivatives are esters and anhydrides which, like the acids, may bear one or more alkyl substituents. The catalyst used is an all-active catalyst (i.e. a catalyst having the same composition throughout, as distinct from a coated catalyst) comprising copper oxide, palladium and/or a palladium compound and at least one further metal oxide. [0002]The preparation of v-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 chosen, different product distributions are achieved using such catalysts. [0003]Apart from MA, further possible starting materials for preparing GBL and THF are maleic acid itself, succinic acid and its anhydride and the esters of these acids. If alkyl-substituted GBL and THF are to be prepared, it is possible to use the correspondingly alkyl-substituted species derived from the abovementioned acids, esters and anhydrides. [0004]U.S. Pat. No. 3,065,243 discloses a process in which copper chromite serves as catalyst. According to the description and examples, appreciable amounts of succinic anhydride (SA) are formed in this process and have to be circulated. As is known, this frequently results in process engineering problems caused by crystallization of the SA or succinic acid formed therefrom with subsequent blockage of pipes. [0005]Further copper chromite catalysts for the hydrogenation of MA are disclosed, for example, in U.S. Pat. No. 3,580,930, U.S. Pat. No. 4,006,165, EP-A 638 565 and WO 99138856. 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, it is often the case that relatively large amounts of THF are desired for a number of reasons. [0006]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 CulZnbAlcMdOx, where M is at least one element selected from the group consisting of groups IIA and IIIA, VA, VIII, Ag, Au, the groups IITB 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 to meet the valence criteria. [0007]Although it is stated that no chromium needs to be present in the catalysts disclosed in this patent, chromium-containing catalysts are described in all examples. According to these examples, a maximum THF yield of 96% is obtained, and the hydrogenation is carried out at pressures of from 20 to 40 bar. [0008]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 free of chromium while the catalyst for the second stage is based on Cu--Zn--Cr oxides. [0009]An in-principle disadvantage of all the above-described catalyst systems is the presence of chromium oxide, whose use should be avoided because of its acute toxicity. Such 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 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 obtain high yields of GBL, up to 98%, but THF is formed only in traces) if at all. Although the formation of TEF can, as is known, be promoted by an increase in the reaction temperature or relatively long residence times in the reactor, the proportion of undesirable by-products, for example butanol, butane, ethanol or ethane, increases at the same time. [0010]A catalyst for the gas-phase hydrogenation of MA to GEL which is made up exclusively of Cu and Al oxides is disclosed in WO 97/24346. This, too, suffers from the same disadvantages as the processes disclosed in the documents described in the previous paragraph, namely only minor formation of THE which can be increased only by means of extreme reaction conditions. [0011]The use of a catalyst having in principle the same composition as that described in WO 97/24346, namely based on Cu--Al oxides, is also disclosed in JP 2 233 631. The aim of this invention is to carry out the hydrogenation of MA in such a way that THF and 1,4-butanediol are formed as main products together with only small amounts, if any, of GBIS. This is achieved by the use of the catalysts based on mixed Cu-Al oxides and by adherence to particular reaction conditions. Typical mixtures obtained using 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 above 99 mol% according to one example. [0012]This is achieved by using a large excess of GBL as solvent. In contrast, if no solvent is employed, the yields drop considerably to values in the region of 75%. [0013]U.S. Pat. No. 4,105,674 discloses a process for the hydrogenation of maleic acid, succinic acid or their anhydrides over supported or unsupported Cu-Pd or Cu-Pt catalysts. The aim of that invention is to produce GBL in high yields and with formation of very small amounts of by-products such as THF and butanol. For this purpose, a nonacidic material in the examples always magnesium silicate, is preferably used as support. The catalysts according to that invention achieves selectivities to GBL of over 90%; the selectivity to THF is generally reported as 2-10%. [0014]All the types of catalyst described in the abovementioned documents have the disadvantage that they produce a large amount of undesirable by-product or satisfactory activities can be achieved only for the preparation of GEL. In addition, Cr is frequently present in the catalyst. [0015]It is an object of the present invention to provide a catalyst for the gas-phase hydrogenation of maleic acid and/or succinic acid and/or their above-mentioned derivatives which gives high selectivities to substituted or unsubstituted THF. This catalyst should, under appropriate reaction conditions, make it possible to obtain high yields of THF with at the same time formation of only small amounts of undesirable by-product. The catalyst should be free of Cr. [0016]We have found that this-object is achieved by a catalyst for the hydrogenation of C.sub.4-dicarboxylic acids and/or derivatives thereof in the gas phase, which catalyst comprises [0017]a) 20-94% by weight of copper oxide (Cuo), preferably 40-92% by weight of CuO, in particular 60-90% by weight of CUO, and [0018]b) 0.005-5% by weight, preferably 0.01-3% by weight, in particular 0.05-2% by weight, palladium and/or a palladium compound (calculated as metallic palladium) and [0019]c) 2-79.995% by weight, preferably 5-59.99% by weight, in particular 8-39.95% by weight, of an oxidic support selected from the group consisting of the oxides of Al, Si, Zn, La, Ce, the elements of groups IIIA to VIIIA and of groups IA and hIA of the Periodic Table of the Elements. [0020]The catalysts of the present invention allow the hydrogenation of C.sub.4-dicarboxylic acids and/or derivatives thereof in the gas phase to be carried out so that an unsubstituted or alkyl-substituted tetrahydrofuran is formed as main product in yields of significantly above 90%. It has surprisingly been found that the addition of palladium as active metal has a significant influence on the selectivity to THF. [0021]For the purposes of the present invention, the groups of the Periodic Table of the Elements are designated according to the old IUPAC nomenclature. [0022]For the purposes of the present patent application, the term C.sub.4-dicarboxylic acids and derivatives thereof refers to maleic acid and succinic acid, which may each bear one or more C.sub.1-C.sub.6-alkyl substituents, and the anhydrides and esters of these unsubstituted or alkyl-substituted acids. An example of such an acid is citraconic acid. Preference is given to using MA. The THF produced can, depending on the starting material used, also bear one or more alkyl substituents. [0023]The catalysts of the present invention comprise copper oxide which is known per se, palladium and/or a palladium compound, preferably palladium oxide and/or palladium nitrate, and an oxidic support having acid centers. It is preferred that no Cr is present in the catalyst. The catalysts can be used as shaped bodies, for example as rod extrudates, ribbed extrudates, other extrudate sharpest pellets, rings, spheres and granules. [0024]The support material can be made up of one or more of the oxides of elements from the group consisting of Al, Si, Zn, La, Ce, the elements of groups IIIA to VIIIA and of groups IA and IIA. The support preferably has an appropriate number of acid centers. Preference is given to using an oxide of elements selected from the group consisting of Al, Si, Ti, Zn, Zr and/or Ce. Al is particularly useful. The support is used in an amount of <80% by weight, based on the total catalyst. The amount of copper oxide is >20% by weight and the amount of palladium and/or palladium compound is <5% by weight. [0025]The catalyst of the present invention preferably consists exclusively of copper oxide, palladium and/or a palladium compound and aluminum oxide, apart from the usual impurities known to those skilled in the art. [0026]The catalysts of the present invention can further comprise auxiliaries in an amount of from 0 to 10% by weight. For the purposes of the present invention, auxiliaries are organic and inorganic materials which contribute to improved processing during catalyst production and/or to an increase in the mechanical strength of the shaped catalyst bodies. Such auxiliaries are known to those skilled in the art and include graphite, stearic acid, silica gel and copper powder. [0027]The catalysts of the present invention are produced by methods known per se to those skilled in the art, for example by coprecipitation of all or at least two components, precipitation of the individual components with subsequent intimate mixing, for example by kneading or processing in a pan mill, impregnation of the oxidic support with the other components a) and b) in one or more steps. Furthermore, the catalysts of the present invention can be obtained by shaping a heterogeneous mixture of the components a), b) and c). Continue reading... Full patent description for Selective preparation of tetrahydrofuran by hydrogenation of maleic anhydride Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Selective preparation of tetrahydrofuran by hydrogenation of maleic anhydride patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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