Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2000-09-19
2001-05-15
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
Reexamination Certificate
active
06232488
ABSTRACT:
The present invention relates to a process for the hydrogenation of aliphatic dinitriles at least partly into corresponding aminonitriles.
The hydrogenation of dinitriles into corresponding diamines is a technique which has been known for a long time, in particular the hydrogenation of adiponitrile into hexamethylenediamine, one of the starting materials in the preparation of polyamide 66.
Recent years have seen growing interest in the hydrogenation (also sometimes referred to as hemihydrogenation) of aliphatic dinitriles into aminonitriles, in particular the hydrogenation of adiponitrile into 6-aminocapronitrile, leading, either directly or via caprolactam, to polyamide 6.
Thus, U.S. Pat. No. 5,151,543 describes a process for the selective hydrogenation of aliphatic dinitriles into corresponding aminonitriles, at 25-150° C. and at a pressure greater than atmospheric pressure, in the presence of a solvent in a molar excess of at least 2/1 relative to the dinitrile, the solvent containing liquid ammonia or an alcohol of 1 to 4 carbon atoms containing an inorganic base which is soluble in the said alcohol and in the presence of a Raney catalyst, the aminonitrile obtained being recovered as the main product.
Patent WO-A-93/16034 describes a process for the preparation of 6-aminocapronitrile by hydrogenation of adiponitrile, in the presence of an inorganic base, of a complex of a low-valency transition metal chosen from chromium, tungsten, cobalt, iron and Raney nickel as catalyst, under hydrogen pressure and at a temperature of from 50° C. to 90° C.
Patent WO-A-96/18603 describes the hemihydrogenation of aliphatic dinitriles into aminonitriles, by hydrogen and in the presence of a catalyst based on optionally doped Raney cobalt or nickel and on a strong inorganic base, the initial hydrogenation medium containing water, the aminonitrile and/or the diamine which can be formed and the unconverted dinitrile.
All of these hydrogenation processes lead to the desired aminonitrile and are presented as being able to be carried out continuously in an industrial plant.
However, certain problems have not been revealed for an industrial application. Thus, in the course of research carried out in this field by the Applicant, it has been found that hydrogenation catalysts, and in particular Raney nickel, Raney cobalt, supported metals, in particular the metals from group VIII of the Periodic Table of the Elements, such as nickel, cobalt, ruthenium and rhodium, deposited on a support which is generally an oxide, have a pronounced tendency to become deactivated more rapidly when they are in the presence of nitrile functions and in the absence of hydrogen.
This problem hardly ever arises in the current industrial processes which lead to the diamine, whereas hydrogenation into aminonitrile results in a large amount of nitrile functions being permanently retained in the reaction medium. In such a process, the reaction products, aminonitrile and diamine, need to be recovered, as well as the unconverted dinitrile, while at the same time maintaining or recycling most of the catalyst while it is sufficiently active. Given the above observations, it is thus necessary both to separate the aminonitrile and the diamine formed and the unconverted dinitrile in order to recover them, and to maintain or recycle the catalyst without giving rise to additional deactivation. This therefore involves having operating conditions and apparatus which allow a relatively rapid separation, which is compatible with industrial exploitation, of the catalyst and of the liquid part of the reaction mixture, and also requires the said separation not to result in excessive deactivation of the said catalyst.
A separation, by filtration or centrifugation, of some of the reaction mixture containing the catalyst could be envisaged, but, according to the Applicant's observations, the catalyst thus manipulated in the absence of hydrogen and in the presence of nitrile functions partially loses its activity; the reduction in the lifetime of the catalyst thus weighs unfavourably on the cost-effectiveness of the process. On the other hand, filtration under hydrogen pressure, and thus in the presence of dissolved hydrogen, avoids the deactivation of the catalyst.
The present invention proposes a solution to these various problems. More specifically, it consists of a continuous process for the hydrogenation of dinitrile, at least partly into corresponding aminonitrile, in the presence of a hydrogenation catalyst which is not dissolved in the reaction medium, characterized in that it is carried out in apparatus comprising means for the continuous separation of the hydrogenate and of the catalyst in a zone in which the gas-liquid transfer is limited or zero, the said separation and the recycling of the catalyst being carried out in a period of time less than or equal to 30 minutes.
The apparatus which is suitable for carrying out the process of the invention achieves excellent gas/liquid contact, rapid and effective separation of these two phases after contact, continuous separation of the hydrogenate and of the catalyst and recycling of the latter, in a time which is compatible with the least possible deactivation of the said catalyst.
The said apparatus includes three main sections: a reaction section, a gas-liquid separation section and a catalyst-liquid separation section with recycling of the said catalyst and removal of the liquid (hydrogenate).
The reaction section generally includes one or more U-shaped tubes whose branches are vertical or slightly inclined relative to the vertical, one of the branches of each U allowing for the rise of the gas/liquid/solid catalyst dispersion, the other allowing for the return of the at least partially degassed liquid. It also includes four inlets at the base of the rising branch: the hydrogen inlet, the dinitrile inlet, the inlet for the fresh or regenerated catalyst, with or without co-catalyst, and the recycled catalyst inlet.
The gas-liquid separation section consists of a vertical cylinder including one or more tangential inlets (coming from the rising branch of the reactor), one or more tangential exits (towards the descending branch of the reactor), a gas outlet and an outlet for the reaction mixture towards the liquid-solid separation section. The gas/liquid/solid catalyst dispersion enters at a point below the exit point of the degassed liquid.
The liquid-solid separation section consists of a decanter and/or of a filter which separates the hydrogenate from the catalyst and recycles the said catalyst. The hydrogenate is removed continuously while the catalyst suspension separated out in the decanter and/or in the filter is returned into the reaction section. Flushing is carried out when it is considered necessary to replace some of the catalyst with fresh catalyst.
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patent: 5508465 (1996-04-01), Schnurr et al.
patent: 5675045 (1997-10-01), Bueschken et al.
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patent: 98 11060 (1998-03-01), None
Boschat Vincent
Leconte Philippe
Rochette Daniel
Sever Lionel
Burns Doane Swecker & Mathis L.L.P.
McKane Joseph K.
Murray Joseph
Rhodia Fiber and Resin Intermediates
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