Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-06-05
2002-06-04
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S536000, C562S547000, C562S548000
Reexamination Certificate
active
06399816
ABSTRACT:
This application is a 371 of PCT/EP98/06414 filed Oct. 9, 1998.
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 a ratio of 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, TI 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 has to be 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 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 targeted 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 may be one or more of the metals Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Sc, Y, La, Ce, Al, TI, 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 using the catalyst mixture described and passing a gas mixture comprising ethane, oxygen, nitrogen and water vapor through the reactor containing the catalyst, the maximum selectivity is 27% at an ethane conversion of 7%. According to EP 0 294 845, the high conversions of ethane are achieved only using the catalyst mixture described, but not using a single catalyst comprising 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 with a catalyst composition comprising the elements A, X and Y at elevated temperature. A is 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, TI and/or U. The maximum selectivities which can 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.
The German Patent Application P 19630832.1, which is not a prior publication, describes a process for the selective preparation of acetic acid from a gaseous feed comprising ethane, ethylene or mixtures thereof plus oxygen at elevated temperature. The feed is brought into contact with a catalyst comprising the elements Mo, Pd, X and Y in combination with oxygen.
Here, X is one or more elements selected from the group consisting of Cr, Mn, Nb, Ta, Ti, V, Te and W and Y is one or more elements selected from the group consisting of B, Al, Ga, In Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, TI and U.
The gram atom ratios of the corresponding elements are given as follows:
a(Mo)=1; b(Pd)>0; c(X)>0; and d(Y)=0-2.
The catalysts described in the abovementioned application give a maximum space-time yield of 149 kg/hm
3
at an acetic acid selectivity of >60 mol %. Space-time yields characterize the amount of acetic acid produced per unit time and catalyst volume. Higher space-time yields are desirable since the size of the reactors and the amount of circulated gas can be reduced thereby.
It is therefore an object of the invention to provide a process which allows ethane and/or ethylene to be oxidized to acetic acid in a simple and targeted manner and at high selectivity and space-time yield under reaction conditions which are as mild as possible.
It has surprisingly been found that it is possible to oxidize ethane and/or ethylene to acetic acid under relatively mild conditions in a simple manner at high selectivity and excellent space-time yields when using 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.
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, wherein the gaseous feed is brought into contact with a catalyst comprising the elements Mo, Pd, X and Y in the gram atom ratios a:b:c:d in combination with oxygen
MO
a
Pd
b
X
c
Y
d
(I)
where the symbols X and Y have the following meanings:
X is one or more elements selected from the group consisting of: Cr, Mn, Ta, Ti, V, Te and W, in particular 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, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, TI and U, in particular Nb, Ca, Sb and Li.
The indices a, b, c and d are the gram atom ratios of the corresponding elements, where
a=1,
b=0.0001-0.01,
c=0.4-1 and
d=0.005-1.
If X and Y represent a plurality of different elements, the indices c and d can likewise assume a plurality of different values.
Furthermore, the present invention 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=0.0001-0.005;
c=0.5-0.8 and
d=0.01-0.3.
Palladium contents in the catalyst which are above the upper limit indicated promote carbon dioxide formation 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 limit indicated favor formation of ethylene.
Apart from the elements molybdenum and palladium, the catalyst used according to the invention preferably further comprises vanadium, niobium, antimony and calcium in combination with oxygen. The gram atom ratios a:b:c
1
:d
1
:d
2
:d
3
of the elements Mo:Pd:V:Nb:Sb:Ca are preferably as follows:
a (Mo)=1;
b (Pd)=0.0001-0.005, in particular 0.0001-0.001;
c
1
(V)=0.4-1.0;
d
1
(Nb)=0.01-0.2;
d
2
(Sb)=0.01-0.3;
d
3
(Ca)=0.01-0.3.
Examples of such catalyst compositions which are preferably used in the process of the invention are:
Mo
1.00
Pd
0.0005
V
0.45
Nb
0.03
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.0005
V
0.45
Nb
0.03
Sb
0.01
Ca
0.01
K
0.015
Mo
1.00
Pd
0.00075
V
0.45
Nb
0.03
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.00075
V
0.55
Nb
0.03
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.00075
V
0.45
Nb
0.06
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.0008
V
0.55
Nb
0.06
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.00085
V
0.55
Nb
0.06
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.00075
V
0.55
Nb
0.09
Sb
0.01
Ca
0.01
Mo
1.00
Pd
0.0008
V
0.50
Nb
0.15
Te
0.01
Ca
0.01
Mo
1.00
Pd
0.00075
V
0.50
Nb
0.09
W
0.01
Pd
0.0003
The catalysts used according to the invention can be prepared by conventional methods. These start from a slurry, in particular an aqueous solution, comprising the individual starting components of the elements in the appropriate proportions.
The starting materials of the individual components for preparing the catalyst of t
Borchert Holger
Dingerdissen Uwe
Bierman, Muserlian and Lucas
Celanese Chemicals Europe GmbH
Padmanabhan Sreeni
Witherspoon Sikarl A.
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