Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-05-18
2001-08-28
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S512200, C562S607000
Reexamination Certificate
active
06281385
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing acetic acid by gas-phase oxidation of saturated C
4
-hydrocarbons and their mixtures with unsaturated C
4
-hydrocarbons using a coated catalyst, and also to a coated catalyst for preparing acetic acid by gas-phase oxidation of saturated C
4
-hydrocarbons and their mixtures with unsaturated C
4
- hydrocarbons.
2. The Prior Art
It is known that acetic acid can be prepared by gas-phase oxidation of C
2
-, C
3
- and C
4
-molecules with the aid of a catalyst. However, no process which is fully satisfactory from economic and process engineering points of view has yet been found.
DE-B 1,279,011 describes a process for preparing acetic acid by catalytical gas-phase oxidation of butene by oxygen using catalysts comprising aluminum vanadate and titanium vanadate. These catalysts are prepared by precipitation of the mixed oxides from the corresponding solutions and the mixed oxides can, if desired, be mixed with inert materials such as silica. The catalyst is used in fluidized-bed reactors as a finely divided powder. A disadvantage of such catalysts is the high degree of total oxidation.
To improve the yield obtained by means of such catalysts, DE-A 2,016,681 proposes that the catalysts be pretreated with an oxidizing agent before calcination.
DE-A 2,354,425 (U.S. Pat. No. 3,954,857) proposes treating the calcined titanium-vanadium mixed catalyst with hydrochloric acid to improve the selectivity. The catalysts are used as fully active catalysts, if desired in admixture with inert support materials such as silica.
A further way known from the prior art of improving the activity of titanium-vanadium mixed catalysts in the gas-phase oxidation of butenes to acetic acid is the use of TiO
2
in a defined crystal form or with a defined surface area.
DE-A 2,026,744 (U.S. Pat. No. 3,917,682) describes Ti-V mixed catalysts whose TiO
2
component is predominantly in the form of rutile. The catalysts can be used in powder form or after being pressed to form shaped bodies.
U.S. Pat. No. 4,448,897 discloses Ti-V catalysts for butene oxidation which comprise TiO
2
having a BET surface area of more than 40 m
2
/g. The catalysts are likewise used in powder form or as compacts.
It is also known from the prior art that the selectivity of Ti-V catalysts in the oxidation of butene can be improved by completely or partly replacing the titanium dioxide by other metal oxides.
For example, DE-A 2,110,876 (GB-A 1,333,306) describes catalysts comprising oxides of molybdenum, tin and vanadium as active components. The catalysts are used in powder form and the mixed oxide catalyst can also, if desired, be applied to finely divided support materials such as silicon dioxide.
U.S. Pat. No. 4,146,734 discloses the use of vanadium mixed oxides which are doped with cerium and further transition metal oxides. The catalyst is used as finely divided powder, but can also be applied as precipitate to finely divided, inert supports.
DE-A 2,235,103 discloses Ti-V mixed oxide catalysts for the gas-phase oxidation of butenes in the form of supported catalysts in which a preformed porous support is impregnated with the mixed solution of the catalyst components.
In all these processes, use is made of catalysts in which the active components are employed as such as powder or compacts. Also the active components can be employed in the form of powder or compacts in which they are diluted with finely divided support materials. For the purposes of the present invention, bulk catalysts also include porous supports which have been impregnated right through with active component as described in DE-A 2,235,103. Also, in this case too, the entire catalyst volume is catalytically active. Disadvantages of fully active catalysts are the high degree of total oxidation and the difficulty of controlling the oxidation reaction at high conversions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process and a catalyst for preparing acetic acid by gas-phase oxidation of saturated C
4
-hydrocarbons and their mixtures with unsaturated C
4
-hydrocarbons, which process and catalyst lead to a better yield and a better operating behavior in the oxidation reaction.
The present invention achieves this object and provides a process for preparing acetic acid by gas-phase oxidation of saturated C
4
-hydrocarbons and their mixtures with unsaturated C
4
-hydrocarbons in a tube reactor using a coated catalyst comprising an inert nonporous support body and a catalytically active mixed oxide composition comprising
(a) one or more oxides selected from the group consisting of titanium dioxide, zirconium dioxide, tin dioxide and aluminum oxide and
(b) from 0.1% to 1.5% by weight, based on the weight of the component (a) and per m
2
/g of specific surface area of the component (a), of vanadium pentoxide applied to the outer surface of the support body, wherein a gas mixture comprising oxygen or oxygen-containing gas, one or more C
4
-hydrocarbons and water vapor and having a C
4
- hydrocarbon/air (oxygen) volume ratio of from 0.2/99.8 to 25/75 and a C
4
-hydrocarbon/water vapor volume ratio of from 1/1 to 1/60 is reacted over the coated catalyst at a temperature of from 100° C. to 400° C. and a gauge pressure of from 0.2 to 50 bar.
In the process of the present invention, a gas mixture comprising oxygen or an oxygen-containing gas, preferably air, one or more C
4
-hydrocarbons, preferably butane and its mixtures with butene, water vapor and, if desired, an inert gas is reacted over the coated catalyst at an elevated temperature.
The gas-phase oxidation is carried out in cooled tube reactors which are charged with the coated catalyst and through which the reaction mixture flows. Customary fixed-bed reactors are upright multitube reactors having tube lengths of from 1 m to 10 m, an internal tube diameter of from 10 to 35 mm and a wall thickness of from 1 to 4 mm.
Heat-exchange media which are suitable for cooling are, in particular, water, heat transfer oils and eutectic salt melts, for example mixtures of KNO
3
/NaNO
2
.
The reaction tubes can, if desired, be charged with coated catalysts having different shapes and dimensions and also different compositions of the active components or shells (coatings). In such a case, the coated catalysts can be introduced into the reaction tubes as a random mixture or in zones.
Suitable starting materials are saturated and/or unsaturated hydrocarbons having four carbon atoms or gas mixtures comprising hydrocarbons having four carbon atoms. Unbranched C
4
-hydrocarbons give higher yields than branched C
4
-hydrocarbons and butadienes. Particular preference is given to n-butane, 1-butene, 2-butenes and mixtures thereof.
An advantage of the process of the invention for the gas-phase oxidation of C
4
-hydrocarbons using the coated catalyst is that it is also possible to use gas mixtures comprising compounds which do not react to form acetic acid or react in this way only to a small extent or in poor yields. Thus, it is also possible to use cheap raw material mixtures from refineries, for example “C
4
fraction” (predominantly butadiene and i-butene), “raffinate 1” (predominantly i-butene), “raffinate 2” (predominantly 1-butene and 2-butenes) and mixtures which comprise not only C
4
-hydrocarbons but also linear and/or branched and/or cyclic hydrocarbons having more or less than four carbon atoms. Examples of these hydrocarbons include methane, ethane, ethene, propene, propane, pentanes, pentenes, pentadienes, cyclopentane, cyclopentene, cyclopentadiene, methylcyclopentane, etc., as starting material. Likewise, alcohols, aldehydes, ethers, ketones and esters having 1-8 carbon atoms may also be present. The raw material mixtures mentioned can, if appropriate, also be subjected to a hydrogenation or purification step before use.
The reaction temperature for the oxidation of the butane and/or butene/oxygen (air)/water vapor reaction mixtures is generally from 100° C. to 400° C., preferably from 150° C.
Eberle Hans-Juergen
Ruedinger Christoph
Collard & Roe P.C.
Consortium fur Elektrochemische Industrie GmbH
Deemie Robert W.
Killos Paul J.
LandOfFree
Process for preparing acetic acid by gas-phase oxidation of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparing acetic acid by gas-phase oxidation of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing acetic acid by gas-phase oxidation of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2435282