Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-04-13
2003-04-01
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S542000, C562S577000, C568S470000, C568S475000
Reexamination Certificate
active
06541664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the heterogeneously catalyzed gas-phase oxidation of propane to acrolein and/or acrylic acid, in which a reaction gas starting mixture comprising propane, molecular oxygen and, if desired, inert gas is passed at from 300 to 500° C. over a fixed-bed catalyst.
2. Discussion of the Background
Acrolein and acrylic acid are important intermediates which are employed, for example, for producing active compounds and polymers.
At present, by far the most widely employed process for the industrial preparation of acrolein and/or acrylic acid is the gas-phase catalytic oxidation of propene (for example EP-A 575897), with the propene being mostly produced as a by-product of ethylene production by steam cracking of naphtha. Since the other application areas for propene, e.g. the production of polypropylene, continue to expand, it would be advantageous to have an industrially usable, competitive process for preparing acrolein and/or acrylic acid which uses as raw material not propene but propane which, for example, occurs naturally in large amounts as a constituent of natural gas.
EP-A 117146 proposes preparing acrylic acid from propane by converting propane into a propylene-containing product stream by means of heterogeneous catalytic dehydrogenation in the absence of molecular oxygen in a first stage and, in subsequent oxidation stages, passing this product stream together with molecular oxygen over suitable oxidation catalysts so as to oxidize the propene present therein to acrolein and/or acrylic acid.
A disadvantage of this procedure is that it necessarily requires a plurality of reaction stages, with the individual reaction stages having to be carried out under different reaction conditions.
Furthermore, the abovementioned procedure has the disadvantage that the catalyst required for the nonoxidative dehydrogenation of the propane is relatively quickly deactivated as a result of carbon deposits and has to be regenerated. Since the dehydrogenation product mixture also contains hydrogen, CN-A 1105352 casts doubt on the possibility of passing the dehydrogenation product mixture on directly to a subsequent oxidation stage.
Both CN-A 1105352 and Y. Moro-oka in Proceedings of the 10th International Congress on Catalysis, Jul. 19-24, 1992, Budapest, Hungary, 1993, Elsevier Science Publishers B. V., pp. 1982 to 1986, recommend first converting propane partially into propene in a homogeneous oxidative dehydrogenation and converting this propene, without separating it off beforehand, into acrolein and/or acrylic acid in subsequent heterogeneously catalyzed oxidation stages. Disadvantages of this procedure are, on the one hand, that carbon is also formed in a homogeneous oxidative dehydrogenation of propane to propene and, on the other hand, that the selectivity of the formation of the desired product (acrolein and/or acrylic acid) is not satisfactory in such a procedure. Thus, in the examples in CN-A 1105352, the selectivity of propene formation achieved by homogeneous oxidative dehydrogenation is only ≦40% by volume and Moro-oka is also restricted to selectivities of acrolein formation of 64 mol %, based on propane reacted.
It has also been proposed that a heterogeneously catalyzed oxidative dehydrogenation of propane (which is not necessarily accompanied by carbon formation) be coupled with a subsequent heterogeneously catalyzed oxidation of the propene thus produced to give acrolein and/or acrylic acid (e.g. 210th ACS National Meeting, Chicago, Aug. 20-24, 1995 or WO 97/36849). However, further details regarding the type and manner of the coupling (in general, both reaction steps require reaction conditions which cannot be reconciled) were not given. CN-A 1105352 even advises decidedly against such a coupling, since, at reasonable propane conversions, achievable selectivities of propene formation in a heterogeneously catalyzed oxidative dehydrogenation do not exceed those in a homogeneous oxidative dehydrogenation.
Topics in Catalysis 3(1996), pp. 265-275, reports the heterogeneously catalyzed oxidative dehydrogenation of propane to propene over cobalt molybdate and magnesium molybdate. A disadvantage of the procedure of the abovementioned reference is that it is, presumably to ensure a satisfactory selectivity of propene formation, carried out in high dilution, i.e. the reaction gas starting mixture comprising propane and molecular oxygen further comprises up to 75% by volume of molecular nitrogen (inert gas). Such a high proportion of inert gas does not encourage coupling with a subsequent propene oxidation, since it reduces the space-time yields of acrolein and/or acrylic acid achievable in a single pass. Furthermore, such a proportion of nitrogen makes it more difficult to recirculate unreacted propane and/or propene after having separated off acrolein and/acrylic acid, should this be intended subsequent to the propene oxidation.
Journal of Catalysis 167 (1997), 550-559 likewise reports the heterogeneously catalyzed oxidative dehydrogenation of propane to propene or molybdates. A disadvantage of the procedure in this reference is that it likewise recommends the use of a reaction gas starting mixture whose proportion of molecular nitrogen is 70% by volume. Furthermore, the abovementioned reference proposes a dehydrogenation temperature of 560° C. Such a high dehydrogenation temperature likewise does not suggest coupling to a downstream heterogeneously catalyzed propene oxidation, since it damages the multimetal oxide compositions customarily used for an oxidative conversion of propene into acrolein and/or acrylic acid.
Journal of Catalysis 167 (1997), 560-569 likewise recommends a dehydrogenation temperature of 560° C. for a heterogeneously catalyzed oxidative dehydrogenation. Similarly, DE-A 19530454 similarly recommends temperatures above 500° C. for a heterogeneously catalyzed oxidative dehydrogenation of propane to give propene.
Furthermore, experiments on a heterogeneously catalyzed direct oxidation of propane to acrolein and/or acrylic acid are reported in the literature (e.g. Proceedings, 210th ACS National Meeting, Chicago, Aug. 20-24, 1995, FR-A 2693384 and 3rd World Congress on Oxidation Catalysis, R. K. Grasselli, S. T. Oyama, A. M. Gaffney and J. E. Lyons (Editors), 1997 Elsevier Science B.V., pp. 375-382), although in these studies, too, either the reported selectivity of the acrolein and/or acrylic acid formation and/or the reported yield of acrolein and/or acrylic acid on a single pass are not satisfactory.
EP-B 608838 likewise relates to the heterogeneously catalyzed direct oxidation of propane to acrylic acid. However, a disadvantage of the method disclosed in EP-B 608838 is that the selectivities of the acrylic acid formation reported by way of example in this document cannot be reproduced. Thus, our attempts to repeat the work gave a vanishing selectivity for acrylic acid formation. Instead, formation of acrolein was found when repeating these examples, but the selectivity for the acrolein formation was only ≦30 mol %.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for the heterogeneously catalyzed gas-phase oxidation of propane to acrolein and/or acrylic acid, in which a reaction gas starting mixture comprising propane, molecular oxygen and, if desired, inert gas is passed at from 300 to 500° C. over a fixed-bed catalyst, which process does not have the disadvantages of the methods described and/or recommended in the prior art.
DETAILED DESCRIPTION OF THE INVENTION
We have found that this object is achieved by a process for the heterogeneously catalyzed gas-phase oxidation of propane to acrolein and/or acrylic acid, in which a reaction gas starting mixture comprising propane, molecular oxygen and, if desired, inert gas is passed at from 300 to 500° C. over a fixed-bed catalyst which comprises two catalyst beds A and B arranged spatially in succession, with the proviso that the active composition of bed A is at least one mul
Arnold Heiko
Jachow Harald
Tenten Andreas
Unverricht Signe
BASF - Aktiengesellschaft
Deemie Robert W.
Killos Paul J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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