Process for the selective preparation of acetic acid using a...

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

1999-01-28

2001-02-27

Wilson, James O. (Department: 1623)

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

Organic compounds

Carboxylic acids and salts thereof

C562S546000, C562S547000, C502S209000, C502S210000, C502S211000, C502S212000, C502S213000, C502S214000, C502S215000, C502S248000, C502S257000, C502S305000, C502S313000

Reexamination Certificate

active

06194610

ABSTRACT:

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° C. is known, for example from U.S. Pat. No. 4,250,346, U.S. Pat. No. 4,524,236 and U.S. Pat. No. 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
x
V
y
or Mo
x
V
y
Z
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.) and 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%. The high conversion rates of ethane are, according to EP 0 294 845, achieved only using the catalyst mixture described, but not using a single catalyst containing the components A and B.
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
d
Re
e
W
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 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 under very mild reaction conditions to give acetic acid.
It has now surprisingly been found that use of a catalyst comprising the elements molybdenum and palladium and one or more elements selected from the group consisting of chromium, manganese, niobium, tantalum, titanium, vanadium, tellurium 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, X and Y in gram atom ratios a:b:c:d in combination with oxygen
Mo
a
Pd
b
X
c
Y
d
  (1)
where the symbols X and Y have the following meanings:
X is one or more elements selected from the group consisting of: Cr, Mn, Nb, Ta, Ti, V, Te and/or W, in particular Nb, V and W;
Y is one or more elements selected from the group consisting of: B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Cu, Rh, Ir, Au, Ag, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Tl and U, in particular Ca, Sb and Li.
The indices a, b, c and d are the gram atom ratios of the corresponding elements, where
a=1, b>0, c>0, and d=0-2.
If X and Y are a plurality of different elements, the indices c and d can likewise assume a plurality of different values.
The present invention further provides a catalyst for the selective preparation of acetic acid comprising the elements Mo, Pd, X and Y in the gram atom ratios a:b:c:d in combination with oxygen.
The gram atom ratios a:b:c:d are preferably within the following ranges:
a=1;
b=0.0001 to 0.5;
c=0.1-1.0 and
d=0-1.0.
Palladium contents in the catalyst which are above the upper limit specified promote the formation of carbon dioxide in the process of the invention. Furthermore, higher palladium contents are generally also avoided because they make the catalyst unnecessarily expensive. On the other hand, palladium contents below the limiting value specified favor ethylene formation.
The catalyst used according to the invention preferably comprises not only the elements molybdenum and palladium but also vanadium, niobium, antimony and calcium in combination with oxygen. The gram atom ratios a:b:c
1
:c
2
:d
1
:d
2
of the elements Mo:Pd:V:Nb:Sb:Ca are preferably as follows:
a(Mo)=1;
b (Pd)=0.0001-0.5, in particular 0.0001-0.05;
c
1
(V)=0.1-1.0;
c
2
(Nb)=0.1-0.5;
d
1
(Sb)=0-0.5;
d
2
(Ca)=0-0.2.
Examples of such catalyst compositions which are preferably used in the process of the invention are:
Mo
1.00
V
0.25
Nb
0.12
Pd
0.0005
Mo
1.00
V
0.25
Nb
0.12
Pd
0.0004
Mo
1.00
V
0.25
Nb
0.12
Pd
0.0003
Mo
1.00
V
0.36
Nb
0.03
Sb
0.01
Pd
0.0005
Mo
1.00
V
0.50
Nb
0.15
Te
0.2
Pd
0.0002
Mo
1.00
V
0.25
Nb
0.3
W
0.2
Pd
0.0003
Mo
1.00
V
0.25
Nb
0.3
Sb
0.1
Pd
0.0004
The catalysts used according to the invention can be prepared by conventional methods. These start out from a slurry, in particular an aqueous solution, comprising the individual starting components of the elements in accordance with their proportions.
The starting materials for the individual components in the preparation of the catalyst of the invention are, apart from the oxides, preferably water-soluble substances such as ammonium salts, nitrates, sulfates, halides, hydroxides and salts of organic acids which can be converted into the corresponding oxides by heating. To mix the components, aqueous solutions or suspensions of the metal salts are prepared and mixed.
In the case of molybdenum, it is advisable to use the corresponding molybdates e.g. ammonium molybdate, as starting compounds because of their commercial availability.
Suitable palladium compounds are, for example, palladium(II) chloride, palladium(II) sulfate, tetramminepalladium(II) nitrate, palladium(II) nitrate and also palladium(II) acetylacetonate.
The reaction mixture obtained is then stirred at from 50 to 100° C. for from 5 minutes to 5 hours. The water is subsequently removed and the remaining catalyst is dried at a temperature of from 50 to 150° C., in particular from 80 to 120° C.
If the catalyst obtained is subsequently subjected to a calcination process, it is advisable to calcine the dried and pulverized catalyst at a temperature in the range from 100° C. to 800° C., in particular from 200 to 500° C., in the presence of nitrogen, oxygen or an oxygen-containing g

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