Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2002-04-22
2004-05-25
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06740779
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 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 passed, in a first reaction stage, using a propene loading of ≧160 l (S.T.P.) of propene/l of fixed catalyst bed 1 per h, over a fixed catalyst bed 1 which is arranged in two spatially successive reaction zones A, B, the temperature of the reaction zone A being from 300 to 370° C. and the temperature of the reaction zone B being from 305 to 380° C. and simultaneously at least 5° C. above the temperature of the reaction zone A and the active material of which being at least one multimetal oxide containing at least the elements Mo, Fe and Bi, in such a way that the reaction zone A extends to a propene conversion of from 40 to 80 mol % and the propene conversion during a single pass through the fixed catalyst bed 1 is ≧90 mol % and the associated selectivity of the acrolein formation and of the acrylic acid byproduct formation together are ≧90 mol %, and the resulting product gas mixture, which contains the molecular oxygen and the acrolein in a molar O
2
: C
3
H
4
O ratio of ≧0.5, is passed, in a second reaction stage, over a fixed catalyst bed 2 which is arranged either in a single reaction zone C or in two spatially successive reaction zones D, E, the temperature of the reaction zone C being from 230 to 300° C. and the temperature of the reaction zone D being from 230 to 280° C. and the temperature of the reaction zone E being from 250 to 300° C. and simultaneously at least 5° C. above the temperature of the reaction zone D and the active material of which being at least one multimetal oxide containing at least the elements Mo and V, in such a way that the acrolein conversion during a single pass through the reaction zone C or the reaction zones D and E is ≧90 mol % and the selectivity of the acrylic acid formation balanced over all reaction zones and based on propene converted is ≧80 mol %, the sequence in which the reaction gas starting mixture flows through the reaction zones corresponding to the alphabetic sequence of the reaction zones.
Acrylic acid is a key monomer which is used as such or in the form of its alkyl esters for producing, for example, polymers suitable as adhesives.
The preparation of acrylic acid can be carried out, for example, by two-stage catalytic gas-phase oxidation of propene to acrylic acid.
The process for the two-stage 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).
In particular, it has been proposed to realize the two reaction stages in two tube-bundle reactors which have a plurality of catalyst tubes and each of which has two temperature zones (cf. for example DE-A 19948241, DE-A 19948523, DE-A 19910506, DE-A 19910508 and DE-A 19948248), which is considered advantageous particularly in the case of high loading with starting materials.
In all abovementioned cases, it is advisable to use, for each reaction stage, one tube-bundle reactor comprising a plurality of catalyst tubes, i.e. to carry out the process as a whole in two tube-bundle reactors spatially separated from one another and arranged one behind the other.
The background of this recommendation is the fact that, for example, U.S. Pat. No. 4,029,636 discloses that MoO
3
volatilizes from the multimetal oxide catalyst of the first reaction stage operated at the higher temperature and is partially deposited again in the fixed catalyst bed 2 of the second reaction stage having the lower operating temperature.
Consequently, an increase in pressure drop of the reaction gas mixture flowing through the two fixed catalyst beds occurs over time (fixed catalyst bed 2 slowly becomes blocked).
According to EP-A 614 872, the pressure drop established over time is even further increased by the fact that organic materials, for example solid carbon, are additionally regularly deposited in the fixed catalyst bed 2.
According to U.S. Pat. No. 4,029,639, the problem described can be remedied when the two reaction stages are realized in two spatially separated tube-bundle reactors arranged one behind the other and the major part of the abovementioned deposit is effected in an intermediate condenser which is mounted between the two tube-bundle reactors and is equipped with inert solids.
For example, DE-A 2830765 and EP-A 911313 recommend carrying out two-stage catalytic gas-phase oxidation of propene to acrylic acid in a single tube-bundle reactor. However, the propene loading of the fixed catalyst bed 1 in all exemplary embodiments is ≧100 l (S.T.P.) of propene/l of fixed catalyst bed 1 per h. Lower propene loadings are however equivalent to lower MoO
3
volatilization since, for example, the amount of water of reaction formed within a specific period (assuming comparable conversions) at lower loading is smaller than at high loading. However, U.S. Pat. No. 4,029,636 discloses that the MoO
3
volatilization is promoted in particular by steam.
On the other hand, at a higher propene loading per hour, a larger amount of MoO
3
can volatilize since of course a larger saturation amount of MoO
3
corresponds to a larger amount of gas.
On the other hand, realizing the two-stage catalytic gas-phase fixed-bed oxidation of propene for the preparation of acrylic acid in two spatially separated tube-bundle reactors comprising a plurality of catalyst tubes entails particularly high capital costs.
It is an object of the present invention to provide a process for the two-stage catalytic gas-phase fixed-bed oxidation of propene to acrylic acid in a single tube-bundle reactor comprising a plurality of catalyst tubes, and to do so with a high propene loading of the fixed catalyst bed
1
, which process has the advantage of a pressure drop rapidly increasing over time along the catalyst tubes only in reduced form.
We have found, surprisingly, that this object is achieved if the first reaction stage is realized, as described at the outset, in two spatially successive temperature zones A, B.
The present invention therefore relates to a process for the catalytic gas-phase oxidation of propene to acrylic acid, in which a reaction gas starting mixture 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 passed, in a first reaction stage, using a propene loading of ≧160 l (S.T.P.) of propene/l of fixed catalyst bed 1 per h, over a fixed catalyst bed 1 which is arranged in two spatially successive reaction zones A, B, the temperature of the reaction zone A being from 300 to 370° C. and the temperature of the reaction zone B being from 305 to 380° C. and simultaneously at least 5° C. above the temperature of the reaction zone A and the active material of which being at least one multimetal oxide containing at least the elements Mo, Fe and Bi, in such a way that the reaction zone A extends to a propene conversion of from 40 to 80 mol % and the propene conversion during a single pass through the fixed catalyst bed 1 is ≧90 mol % and the associated selectivity of the acrolein formation and of the acrylic acid byproduct formation (overall selectivity of formation of desired product) together are ≧90 mol %, and the resulting product gas mixture, which contains the molecular oxygen and the acrolein in a molar O
2
: C
3
H
4
O ratio of ≧0.5, is passed, in a second reaction stage, over a fixed catalyst bed 2 which is arranged either in a single reaction zone C or in two spatially successive reaction zones D, E, the temperature of the reaction zone C being from 230 to 300° C. and the temper
Hechler Claus
Hibst Hartmut
Machhammer Otto
Müller-Engel Klaus Joachim
Tenten Andreas
BASF - Aktiengesellschaft
Kumar Shailendra
Oblon, Spivak, McCelland, Maier & Neustadt, P.C.
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