Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-05-24
2002-10-01
Dentz, Bernard (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S258000
Reexamination Certificate
active
06458971
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of maleic anhydride. More particularly, the present invention relates to a process for the production of maleic anhydride which comprises subjecting an aliphatic hydrocarbon having four or more carbon atoms as a raw material to gas phase oxidation reaction in the presence of a catalyst to produce maleic anhydride efficiently in assured safety.
BACKGROUND OF THE INVENTION
In a process for the production of maleic anhydride which comprises subjecting a hydrocarbon as a raw material to gas phase oxidation reaction in the presence of a catalyst in a fluidized bed reactor, a gaseous raw material hydrocarbon previously mixed with an oxygen-containing gas such as air is introduced into a catalyst fluidized bed, or a gaseous raw material hydrocarbon is introduced into a catalyst fluidized bed which has become fluidization by an oxygen-containing gas such as air, thereby causing catalytic reaction. During this procedure, the catalyst is carried above the fluidized bed while being entrained by the reaction product gas. Thus, a dense-phase fluidized bed in which the majority of the catalyst exists is formed and a dilute-phase fluidized bed (freeboard) having a low catalyst density is formed above the dense-phase fluidized bed in the fluidized bed reactor.
In a process for the production of maleic anhydride which comprises subjecting an aliphatic hydrocarbon having four or more carbon atoms to gas phase oxidation reaction in the presence of a catalyst in a fluidized bed reactor, it is usual for the purpose of enhancing the productivity to keep the hydrocarbon concentration in the reactor feed gas higher than that of the reaction using a fixed bed reactor, that is, to supply a hydrocarbon and air as raw material with the concentration of the hydrocarbon, i.e., raw material hydrocarbon in all the feed gases to the reactor being predetermined to a range of from not less than 3.7 vol % to not more than 7.0 vol %. In this case, since the concentration of flammable components in the reaction product gas (sum of the concentration of hydrocarbon, maleic anhydride and carbon monoxide) exceeds so-called lower flammability limit, it is likely that the reaction product gas can further undergo non-catalytic oxidation reaction.
In the reaction using a fluidized bed reactor, this non-catalytic oxidation reaction can be inhibited by the presence of catalyst particles. However, since the dilute-phase fluidized bed has a low catalyst density, it is very likely that the non-catalytic oxidation reaction of maleic anhydride which is a reaction product and the hydrocarbon which is a raw material can proceed. In other words, in an oxygen-containing gas atmosphere such as high temperature air, maleic anhydride and unreacted raw material hydrocarbons which are contained in the reaction product gas in a substantial concentration are liable to non-catalytic oxidation that causes the drop of yield of maleic anhydride as a product. In some cases, abnormal heat generation causes runaway reaction. In extreme cases, explosion can occur.
In order to prevent non-catalytic oxidation reaction in a dilute-phase fluidized bed when the concentration of flammable components in the reaction product gas exceeds the lower flammability limit, a method may be used which comprises keeping the oxygen concentration lower than the minimum oxygen concentration or keeping the flammable component concentration higher than the upper flammability limit.
As a means for inhibiting non-catalytic oxidation there is proposed in JP-B-8-9606 (The term “JP-B” as used herein means an “examined Japanese patent publication”) a method which comprises cooling the reaction product gas to a temperature of from 330° C. to 450° C., preferably from 350° C. to 400° C., by means of an indirect heat exchanger provided in the dilute-phase fluidized bed. However, excessive cooling rather raises the possibility of suppression of reaction or deterioration of catalyst. Further, the studies made by the present inventors show that a stable and safe operation is not always sufficient.
The method which comprises reducing the oxygen concentration at the outlet of the reactor to not more than the minimum oxygen concentration of a flammable component having the smallest minimum oxygen concentration among those contained in the reaction product gas, e.g., carbon monoxide, is disadvantageous in that the concentration of oxygen in the reaction product gas is excessively lowered, resulting in an undesirable drop of yield of maleic anhydride, and the resulting low oxygen concentration atmosphere causes excessive reduction that deteriorates the catalyst.
On the other hand, no method for accurately estimating the upper flammability limit of the reaction product gas has been known, making it impossible to employ a method which comprises keeping the flammable component concentration higher than the upper flammability limit in a relatively high oxygen concentration range.
While in the case of a reaction executed in a fixed bed reactor, since the concentration of flammable components in the reaction product gas is normally lower than the lower flammability limit, there does not cause such problems. However, methods of increasing the raw materials concentration or recycling the unreacted hydrocarbon are proposed recently in order to enhance the productivity, there is a possibility of causing non-catalytic oxidation even in the case of the fixed bed reactor.
SUMMARY OF THE INVENTION
The present invention has been worked out on the basis of the conventional techniques for the purpose of providing a process for the production of maleic anhydride which comprises subjecting an aliphatic hydrocarbon having four or more carbon atoms to gas phase oxidation reaction in the presence of a catalyst, characterized in that the loss of unreacted hydrocarbon and maleic anhydride as reaction product due to non-catalytic oxidation of the reaction product gas is prevented, the yield of maleic anhydride is kept high as much as possible while assuring safety, and the reduction deterioration of the catalyst is prevented, making it possible to produce maleic anhydride in safety and in an economical manner. In other words, the provision of a means for confirming that the reaction product gas always lies in a flammable component concentration range above the upper flammability limit allows economic operation with assured safety.
The inventors made extensive studies of the foregoing problems. As a result, it was found that when the temperature, the pressure and the composition of the reaction product gas satisfy the predetermined relationships, no oxidation reaction takes place even in the absence of catalyst, making it possible to produce maleic anhydride efficiently in safety. Thus, the present invention has been worked out.
The present invention provides a process for the preparation of maleic anhydride which comprises subjecting an aliphatic hydrocarbon having four or more carbon atoms to gas phase oxidation reaction in the presence of a catalyst, wherein supposing that the function of reaction product gas composition is F
L
and the function of temperature and pressure of reaction product gas is F
R
, the safety index F satisfies the following relationship (1)
F=F
L
−F
R
>0 (1)
wherein
F
L
represents the value calculated by the following equation (2):
F
L
=C/C
T
/C
O
(2)
wherein
C represents the concentration (vol %) of flammable gas in the reaction product gas;
C
O
represents the concentration (vol %) of oxygen gas in the atmosphere; and
C
T
represents the stoichiometric flammable gas concentration (vol %): and
F
R
represents the value calculated by the following equation (3):
F
R
=2.319×10
−5
×T
2
−1.688×10
−2
×T
+3.288+(
P
−0.15)×0.3 (3)
wherein
T represents the temperature (°C.) of reaction product gas; and
P represents the reaction pressure (MPaG).
In accordance with another embodi
Ihara Tatsuya
Iizuka Yoshiaki
Sawaki Itaru
Sawano Mamoru
Yamauchi Yasuyuki
Dentz Bernard
Mitsubishi Chemical Coporation
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