Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-09-10
2002-05-28
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S476000, C568S449000, C568S491000, C568S480000, C562S532000, C562S534000
Reexamination Certificate
active
06395936
ABSTRACT:
The present invention relates to a process for the catalytic gas-phase oxidation of propene to acrolein, in which a reaction gas starting mixture comprising propene, molecular oxygen and at least one inert gas, at least 20% by volume of which consists of molecular nitrogen, and containing the molecular oxygen and the propene in a molar ratio O
2
:C
3
H
6
of ≧l is passed over a fixed-bed catalyst, whose active material is at least one molybdenum- and/or tungsten- and bismuth-, tellurium-, antimony-, tin- and/or copper-containing multimetal oxide, in such a way that the propene conversion in a single pass is ≧90 mol % and the associated selectivity of the acrolein formation and of the acrylic acid byproduct formation together is ≧90 mol %.
The abovementioned process for the catalytic gas-phase oxidation of propene to acrolein is generally known (cf. for example EP-A 15565, EP-A 700714, DE-C 2830765, DE-C 3338380, JP-A 91/294239, EP-A 807 465, WO 98/24746, EP-B 279374, DE-C 2513405, DE-A 3300044, EP-A 575897 and DE-A 19855913) and is important in particular as the first oxidation stage in the preparation of acrylic acid by two-stage catalytic gas-phase oxidation of propene in two reaction stages in series (cf. for example DE A 3002829). Acrylic acid is an important monomer which is used as such or in the form of its alkyl esters for the production of polymers suitable, for example, as adhesives.
Since a small amount of acrylic acid byproduct is usually formed in the abovementioned catalytic gas-phase oxidation of propene to acrolein and, according to the above, acrylic acid is as a rule the desired natural secondary product of acrolein, the molar sum of acrolein formed and acrylic acid formed as byproduct is usually considered as desired product in a catalytic gas-phase oxidation of propene to acrolein. This approach is also to be applicable in the present patent application.
The object of any catalytic fixed-bed gas-phase oxidation of propene to acrolein is in principle to obtain a very high space-time yield (STY) of desired product (in a continuous procedure, this is the amount of desired product produced in grams per hour and unit volume of the catalyst bed used in liters).
There is therefore general interest in carrying out the gas-phase oxidation with a very high loading of the catalyst bed with propene (this is understood as meaning the amount of propene in liters under standard temperature and pressure conditions (=l(S.T.P.); the volume in liters which the corresponding amount of propene would assume under standard temperature and pressure conditions, i.e. at 25° C. and 1 bar) which is passed as a component of the reaction gas mixture, per hour, through one liter of catalyst bed), without significantly impairing the propene conversion taking place in a single pass of the reaction gas starting mixture through the catalyst bed and the selectivity of the associated formation of desired product.
The implementation of the abovementioned is impaired by the fact that gas-phase oxidation of propene to acrolein on the one hand is highly exothermic and on the other hand is accompanied by a multiplicity of possible parallel and subsequent reactions.
With increasing loading of the catalyst bed with propene, and with realization of the desired boundary condition of an essentially constant propene conversion, it must therefore be assumed that the selectivity of the formation of desired product decreases as a result of the greater heat production (cf. EP-B 450596, Example 1 and 2).
The conventional processes for the catalytic gas-phase oxidation of propene to acrolein, wherein nitrogen is used as a main component of the inert diluent gas and in addition a fixed-fed catalyst present in a reaction zone and homogeneous along this reaction zone, i.e. having a chemically uniform composition over the catalyst bed, is employed and the temperature of the reaction zone is kept at a value standard over the reaction zone (temperature of the reaction zone here is understood as meaning the temperature of the catalyst bed present in the reaction zone when the process is carried out in the absence of a chemical reaction; if this temperature in such reaction zone is not constant, the term temperature of the reaction zone means here the numerical average of the temperature of the catalyst bed along the reaction zone), therefore limit the applicable value of the propene loading of the catalyst bed to ≦155 l(S.T.P.) of propene per l of catalyst bed per h (cf. for example EP-A 15565 (maximum propene load=120 l(S.T.P.) of propene/l·h), DE-C 2830765 (maximum propene load=94.5 l(S.T.P.) of propene/l·h), EP-A 804465 (maximum propene load=128 l(S.T.P.) of propene/l·h), EP-B 279374 (maximum propene load=112 l(S.T.P.) of propene/l·h), DE-C 2513405 (maximum propene load=110 l(S.T.P.) of propene/l·h), DE-A 3300044 (maximum propene load=112 l(S.T.P.) of propene/l·h), EP-A 575897 (maximum propene load=120 l(S.T.P.) of propene/l·h), DE-C 3338380 (in essentially all examples, the maximum propene load is 126 l(S.T.P.) of propene/l·h; only in the case of a special catalyst composition was a propene load of 162 l(S.T.P.)/l·h realized) and DE-A 19855913 (maximum propene load=155 l(S.T.P.) of propene/l·h)).
WO 98/24746 considers it necessary, even at a propene loading of up to 148.8 l(S.T.P.) of propene/l·h, to structure the catalyst bed in such a way that its volume-specific activity increases gradually in the direction of flow of the reaction gas mixture.
Although JP-A 91/294239 discloses, in an exemplary embodiment, that a propene load of the catalyst bed with 160 l(S.T.P.) of propene/l·h is possible in an essentially conventional procedure for a catalytic gas-phase oxidation of propene to acrolein, this is likewise only at the expense of a volume-specific activity gradually increasing in the direction of flow of the reaction gas mixture. However, such a procedure is not very practicable on an industrial scale, the gas-phase catalytic oxidation of propene to acrolein usually being carried in tube-bundle reactors comprising a few thousand catalyst tubes, each individual one of which has to be loaded with a gradated catalyst bed.
EP-B 253409 and the associated equivalent, EP-B 257565, disclose that, with the use of an inert diluent gas which has a higher molar heat capacity than molecular nitrogen, the propene content of the reaction gas starting mixture can be increased. Nevertheless, in the two abovementioned publications, the maximum realized propene loading of the catalyst bed is 140 l(S.T.P.) of propene/l·h.
Only in EP-A 293224 have propene loadings above 160 l(S.T.P.) of propene/l·h been realized to date. However, this has been achieved at the expense of a special inert diluent gas to be used, which is completely free of molecular nitrogen. The disadvantage of this diluent gas is in particular the fact that, in contrast to molecular nitrogen, all its components are desired products which, when the process is carried out continuously, have to be recycled at least partially to the gas-phase oxidation in an expensive manner for cost-efficiency reasons.
EP-B 450596 used a structured bed of catalyst and obtained a propene loading of 202.5 l(S.T.P)/l·h, but at the cost of reduced selectivity to desired product.
It is an object of the present invention to provide a process, as defined at the outset, for the catalytic gas-phase oxidation of propene to acrolein, which process ensures a higher space-time yield with respect to desired product without having the disadvantages of the high-load procedures of the prior art.
We have found that this object is achieved by a process for the catalytic gas-phase oxidation of propene to acrolein, in which a reaction gas starting mixture comprising propene, molecular oxygen and at least one inert gas, at least 20% by volume of which consists of molecular nitrogen, and containing the molecular oxygen and the propene in a molar ratio O
2
:C
3
H
6
of ≧1 is passed, at elevated temperatures, over a fixed-bed catalys
Arnold Heiko
Hammon Ulrich
Harth Klaus
Neumann Hans-Peter
Tenten Andreas
BASF - Aktiengesellschaft
Forohar Farhad
Geist Gary
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