Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-08-30
2003-02-25
Davis, Brian J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S545000, C562S518000, C562S531000, C562S532000, C568S476000, C568S449000, C568S491000
Reexamination Certificate
active
06525217
ABSTRACT:
The present invention relates to a process for the catalytic gas-phase oxidation of propene to acrylic acid, in which a reaction gas starting mixture 1 which comprises propene, molecular oxygen and at least one inert gas and contains the molecular oxygen and the propene in a molar O
2
:C
3
H
6
ratio of ≧1 is first passed, in a first reaction stage at elevated temperatures, over a first fixed-bed catalyst whose active material is at least one multimetal oxide containing molybdenum and/or tungsten and bismuth, tellurium, antimony, tin and/or copper, 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 temperature of the product gas mixture leaving the first reaction stage is, if required, reduced by direct and/or indirect cooling and, if required, molecular oxygen and/or inert gas are added to the product gas mixture, and the product gas mixture, as reaction gas starting mixture 2 which comprises acrolein, molecular oxygen and at least one inert gas and contains the molecular oxygen and the acrolein in a molar O
2
:C
3
H
4
O ratio of ≧0.5, is then passed, in a second reaction stage at elevated temperatures, over a second fixed-bed catalyst whose active material is at least one multimetal oxide containing molybdenum and vanadium, in such a way that the acrolein conversion in a single pass is ≧90 mol % and the selectivity of the acrylic acid formation balanced over both reaction stages is ≧80 mol %, based on propene converted.
The abovementioned process for the catalytic gas-phase oxidation of propene to acrylic acid is generally known (cf. for example DE-A 3002829). In particular, the two reaction stages are known per se (cf. for example EP-A 714700, EP-A 700893, EP-A 15565, DE-C 2830765, DE-C 3338380, JP-A 91/294239, EP-A 807465, WO 98/24746, EP-B 279374, DE-C 2513405, DE-A 3300044, EP-A 575897 and DE-A 19855913).
Acrylic acid is an important monomer which is used as such on its own or with alkyl esters for producing, for example, polymers suitable as adhesives.
The object of every two-stage fixed-bed gas-phase oxidation of propene to acrylic acid is in principle to achieve a very high space-time yield of acrylic acid (STY
AA
) (in a continuous procedure, this is the total amount of acrylic acid, in liters, produced per hour and total volume of the catalyst bed used).
There is therefore general interest in carrying out such as two-stage fixed-bed gas-phase oxidation of propene to acrylic acid on the one hand with a very high loading of the first fixed catalyst bed with propene (which is understood as meaning the amount of propene in liters (S.T.P.) (=l (S.T.P.), the volume in liters which the corresponding amount of propene would occupy under standard temperature and pressure conditions, i.e. at 250° C. and 1 bar) which is passed as a component of the reaction gas starting mixture 1 per hour through 1 liter of catalyst bed 1) and, on the other hand, with a very high loading of the second fixed catalyst bed with acrolein (this is understood as meaning the amount of acrolein in liters (S.T.P.) (=l(S.T.P.), the volume in liters which the corresponding amount of acrolein would occupy under standard temperature and pressure conditions, i.e. at 25° C. and 1 bar) which is passed as a component of reaction mixture 2 per hour through 1 liter of catalyst bed 2) without significantly impairing the propene and acrolein conversion taking place during a single pass of the two reaction gas starting mixtures 1, 2 through the two fixed catalyst beds and the selectivity, balanced over both reaction stages, of the associated acrylic acid formation (based on propene converted).
The realization of the abovementioned is adversely affected by the fact that both the fixed-bed gas-phase oxidation of propene to acrolein and the fixed-bed gas-phase oxidation of acrole into acrylic acid are highly exothermic on the one hand and, on the other hand, are accompanied by a variety of possible simultaneous and subsequent reactions.
In principle, the multimetal oxides suitable as catalytic active materials can be used in powder form in the fixed-bed gas-phase oxidation of propene to acrylic acid described at the outset. Usually, however, they are shaped into specific catalyst geometries before being used, since active material powder is unsuitable for industrial use owing to the poor gas permeation.
It is an object of the present invention to select the geometry of the catalyst moldings to be used in the two fixed catalyst beds of the catalytic fixed-bed gas-phase oxidation described at the outset so that, with high loading of the fixed catalyst beds with starting material and a given conversion of starting material, a very high selectivity of the desired compound acrylic acid results in a single pass through the fixed catalyst beds.
The following prior art may be used as a basis.
The conventional processes for the catalytic fixed-bed gas-phase oxidation of propene to acrolein or of acrolein to acrylic acid, wherein nitrogen is used as a main component of the inert diluent gas and moreover a fixed-bed catalyst present in the reaction zone and homogeneous along this reaction zone, i.e. having a chemically uniform composition over the fixed catalyst bed, is used and the temperature of the reaction zone is kept at a value uniform over the reaction zone (temperature of a reaction zone is understood here as meaning the temperature of the fixed catalyst bed present in the reaction zone when the process is carried out in the absence of a chemical reaction; if this temperature is not constant within the reaction zone, the term temperature of the reaction zone in this case means the number average of the (temperature of the catalyst bed along the reaction zone), limit the applicable propene or acrolein loading of the fixed catalyst bed to comparatively low values.
Thus, the propene loading used in the fixed catalyst bed is usually ≦155 l (S.T.P.) of propene/l of catalyst bed·h (cf. for example EP-A 15565 (maximum propene loading=120 l (S.T.P.) of propene/l·h), DE-C 2830765 (maximum propene loading =94.5 l (S.T.P.) of propene/l·h), EP-A 804465 (maximum propene loading=128 l (S.T.P.) of propene/l·h), EP-B 279374 (maximum propene loading=112 l (S.T.P.) of propene/l·h), DE-C 2513405 (maximum propene loading=110 l (S.T.P.) of propene/l·h), DE-A 3300044 (maximum propene loading=112 l (S.T.P.) of propene/l·h):and EP-A 575897 (maximum propene loading=120 l (S.T.P.) of propene/l·h).
Furthermore, in essentially all examples of DE-C 3338380, the maximum propene loading is 126 l (S.T.P.) of propene/l·h; only in Example 3 of this publication is a propene loading of 162 l (S.T.P.)/l·h realized, the catalyst moldings used being exclusively solid cylinders consisting of active material and having a length of 7 mm and a diameter of 5 mm.
EP-B 450596 discloses a propene loading of the catalyst bed of 202.5 l (S.T.P.) of propene/l·h, with the use of a structured catalyst bed in an otherwise conventional procedure. The catalyst moldings used are spherical coated catalysts.
EP-A 293224 likewise discloses propene loadings above 160 l (S.T.P.) of propene/l·h, an inert diluent gas completely free of molecular nitrogen being used. The catalyst geometry used is not stated.
EP-A 253409 and the associated equivalent, EP-A 257565, disclose that, when an inert diluent gas which has a higher molar heat capacity than molecular nitrogen is used, the proportion of propene in the reaction gas starting mixture can be increased. Nevertheless, in the two abovementioned publications too, the maximum realized propene loading of the catalyst bed is 140 l (S.T.P.) of propene/l·h. Neither of the two publications provides any information regarding the catalyst geometry to be used.
In a manner corresponding to the conventional processes for the catalytic fixed-bed gas-phase oxidation of propene to acrolein, the conventional processes for
Arnold Heiko
Hammon Ulrich
Harth Klaus
Neumann Hans-Peter
Tenten Andreas
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