Process for the selective preparation of acetic acid using a mol

Details Process for the selective preparation of acetic acid using a mol Process for the selective preparation of acetic acid using a mol

1998-11-19

2000-03-07

Geist, Gary

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

Organic compounds

Carboxylic acids and salts thereof

502313, 502321, 502333, 562549, C07C 5116, B01J 2303

Patent

active

060342706

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the selective preparation of acetic acid by catalytic gas-phase oxidation of ethane and/or ethylene in the presence of a palladium-containing catalyst.
The oxidative dehydrogenation of ethane to ethylene in the gas phase at temperatures of >500.degree. C. is known, for example from U.S. Pat. Nos. 4,250,346, 4,524,236 and 4,568,790.
Thus, U.S. Pat. No. 4,250,346 describes the use of a catalyst composition comprising the elements molybdenum, X and Y in the ratio a:b:c for converting ethane into ethylene, where X is Cr, Mn, Nb, Ta, Ti, V, and/or W and Y is Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Tl and/or U and a is 1, b is from 0.05 to 1 and c is from 0 to 2. The total value of c for Co, Ni and/or Fe must here by less than 0.5.
The reaction is preferably carried out in the presence of added water. The disclosed catalysts can likewise be used for the oxidation of ethane to give acetic acid, with the efficiency of the conversion to acetic acid being about 18%, at an ethane conversion of 7.5%.
The abovementioned documents are concerned mainly with the preparation of ethylene, less with the target preparation of acetic acid.
In contrast, EP-B-0 294 845 describes a process for the selective preparation of acetic acid from ethane, ethylene or mixtures thereof using oxygen in the presence of a catalyst mixture comprising at least A.) a calcined catalyst of the formula Mo.sub.x V.sub.y or Mo.sub.x V.sub.y Z.sub.y, where Z is one or more of the metals Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Sc, Y, La, Ce, Al, Tl, Ti, Zr, Hf, Pb, Nb, Ta, As, Sb, Bi, Cr, W, U, Te, Fe, Co and Ni, and x is from 0.5 to 0.9, y is from 0.1 to 0.4 and z is from 0.001 to 1, and B.) an ethylene hydration catalyst and/or ethylene oxidation catalyst. The second catalyst component B is, in particular, a molecular sieve catalyst or a palladium-containing oxidation catalyst. When the catalyst mixture described is used and a gas mixture comprising ethane, oxygen, nitrogen and water vapor is passed through the catalyst-containing reactor, the maximum selectivity is 27% at an ethane conversion of 7%.
A further process for preparing a product comprising ethylene and/or acetic acid is described in EP-B-0 407 091. Here, ethane and/or ethylene and a gas comprising molecular oxygen is brought into contact at elevated temperature with a catalyst composition comprising the elements A, X and Y. A is here Mo.sub.d Re.sub.e W.sub.f, X is Cr, Mn, Nb, Ta, Ti, V and/or W and Y is Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Tl and/or U. The maximum selectivities which were able to be achieved when using the catalyst described in the oxidation of ethane to acetic acid are 78%. Further by-products formed are carbon dioxide, carbon monoxide and ethylene.
However, none of the publications listed above describes the use of a catalyst comprising the elements rhenium, palladium and molybdenum for the selective oxidation of ethane and/or ethylene to give acetic acid. Furthermore, the selectivities achieved up to now in the prior art for the oxidation to acetic acid are still not satisfactory.
It is therefore an object of the invention to provide a process which allows ethane and/or ethylene to be oxidized in a simple and targeted manner and with high selectivity to give acetic acid.
It has now surprisingly been found that use of a catalyst comprising the elements molybdenum, rhenium and palladium and one or more elements selected from the group consisting of chromium, manganese, niobium, tantalum, titanium, vanadium and/or tungsten makes it possible to oxidize ethane and/or ethylene under relatively mild conditions, in a simple manner with high selectivity to give acetic acid.
The present invention accordingly provides a process for the selective preparation of acetic acid from a gaseous feed comprising ethane, ethylene or mixtures thereof plus oxygen at elevated temperature, which comprises bringing the gaseous feed into contact with a catalyst comprising the elements Mo, Pd, Re, X and Y in gram atom ratios

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