Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1998-11-12
2000-03-21
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
564420, C07C20900
Patent
active
060404817
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the hydrogenation of aromatic nitro compounds using a catalyst in a fixed bed.
BRIEF DESCRIPTION OF DRAWING
Among the processes of this type, two categories can be listed, the first using a catalyst in the form of a stirred suspension, the second using a catalyst in a fixed bed.
Processes involving catalysts in the form of a stirred suspension have experienced considerable industrial developments. The reason for this is that, despite a large investment, they have the advantage of effectively controlling the exothermicity of the hydrogenation reaction, which is considerable for compounds of this type. Moreover, the hydrogenation of nitro compounds on a catalyst in a stirred suspension exhibits good performance, in terms of selectivity of desired compound, conversion of the nitro product and production efficiency. Lastly, the catalyst is relatively easy to replace for these processes, which contributes towards conserving their good performance.
The other category consisting in using catalysts in a fixed bed to hydrogenate aromatic nitro compounds has not experienced as extensive an industrial-scale development as the previous category. This is because the major difficulty with this process lies in the removal of the heat evolved during the reaction; if this removal of heat is not sufficient, it can lead to a runaway reaction, and also to a lowering in the performance of the process and degradation of the catalyst used.
One solution recommended to remove the heat of reaction has been to recycle a fraction of the reaction mixture, which has been cooled beforehand.
Thus, it has been proposed to hydrogenate aromatic nitro compounds in a tubular reactor with a fixed bed of flowing type (i.e. injection of the reactants co-currentwise downwards in the reactor) in which the supply flow comprises some of the recycled reaction mixture coming from the said reactor. However, the reactor dimensions are such that this reactor cannot be considered as operating adiabatically since 60 to 70% of the heat exchanges take place by means of losses through the walls of the said reactor. Consequently, extrapolation of this process to the industrial scale would result in having reactors whose height would be considerably greater than their cross-section, so as to conserve a reasonable level of heat exchange through the walls. However, such reactors would need to use very large amounts of catalyst, which would detract from one of the advantages of the process with a fixed bed compared with catalyst suspensions. Another possibility for the industrial-scale exploitation of this type of process would be to increase the heat exchanges with the recycled reaction flow. In other words, this would consist in increasing the rate of recycling of the reaction medium considerably. In this case, the production efficiency of such a process would be much too low, on account of the large dilution required for the compounds to be nitrated and the need to convert these compounds completely.
As may be observed, there is currently no process for the fixed-bed hydrogenation of aromatic nitro compounds which can be industrially exploited satisfactorily.
The subject of the present invention is thus to propose such a type of process, which does not have the abovementioned drawbacks of hydrogenation reactions using catalysts in a fixed bed.
Thus, the process according to the invention has all the advantages of processes using fixed beds when compared with processes using a stirred suspension of catalyst.
In particular, the process according to the invention is easy to carry out and incurs lower capital costs since it is no longer necessary to provide complex systems for separating out the catalyst once the reaction is complete, nor even to provide stirring systems, with all the problems of leaktightness inherent therein.
Furthermore, the process according to the invention allows the difficulties associated with carrying out the reaction in a fixed bed, i.e. the exothermicity of the reaction, to be solved.
Lastly, the perfo
REFERENCES:
patent: 3935264 (1976-01-01), Bhutani
patent: 5877350 (1999-03-01), Langer et al.
Chambost Bernard
Marion Philippe
Mathieu Corinne
Killos Paul J.
Parsa Jatar
Rhodia Chimie
Seugnet Jean-Louis
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