Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2001-01-25
2003-05-06
Padmanabhan, Sreeni (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C558S452000, C558S454000, C558S456000
Reexamination Certificate
active
06559333
ABSTRACT:
This application is a 371 PCT/FR 99/00862 filed Apr. 13, 1999.
The present invention relates to a process for the purification of aliphatic aminonitriles and more particularly of 6-aminocapronitrile.
6-Aminocapronitrile is generally prepared by hydrogenation of one of the two nitrile functional groups of adiponitrile. Thus, U.S. Pat. No. 5,151,543 discloses a process for the partial hydrogenation of dinitriles to aminonitriles, in a solvent in molar excess of at least 2/1 with respect to the dinitrile comprising liquid ammonia or an alkanol comprising an inorganic base soluble in the said alkanol, in the presence of a catalyst of Raney nickel or cobalt type.
Patent WO-A-96/18603 discloses a process for the hemihydrogenation of aliphatic dinitriles to the corresponding aminonitriles using hydrogen and in the presence of a catalyst chosen from Raney nickel and Raney cobalt, the said Raney nickel or cobalt optionally comprising a doping element chosen from the elements from Groups IVb, VIb, VIIb and VIII of the Periodic Classification of the Elements and zinc, and of a strong inorganic base deriving from an alkali metal or alkaline earth metal, the starting hydrogenation medium comprising water, in a proportion of at least 0.5% by weight with respect to the combined liquid compounds in the said medium, diamine and/or aminonitrile, which can be formed from the dinitrile to be hydrogenated, as well as unconverted dinitrile, in a proportion for these three combined compounds of 80% to 99.5% by weight with respect to the combined liquid compounds in the said medium, the said process making it possible to obtain a selectivity for the targeted aminonitriles of at least 60%.
One of the possible uses of 6-aminocapronitrile (also known as ACN for convenience in the present text) consists in reacting it with water and in cyclizing it (cyclizing hydrolysis) in order to obtain caprolactam, which is the starting material for polyamide 6.
This cyclizing hydrolysis can be carried out in the liquid phase, as disclosed in Patent WO-A-96/00722, or in the vapour phase, as disclosed in Patent EP-A-0,659,741 or Patent WO-A-96/22974.
6-Aminocapronitrile subjected to cyclizing hydrolysis can contain up to several per cent of impurities, such as hexamethylenediamine or various imines formed during the hydrogenation of adiponitrile, without this prohibiting the said cyclizing hydrolysis reaction. This is particularly the case when the hydrolysis is carried out in the vapour phase. However, a portion of these impurities, converted or otherwise during the hydrolysis, may be reencountered in the caprolactam obtained. Now, even if the amounts of impurities which can be found in the caprolactam are relatively low, for example of the order of 1 to 2%, the purity required during the subsequent polymerization of the caprolactam is such that the purification of the said caprolactam can prove to be complex and very expensive. The purification of the 6-aminocapronitrile makes it possible to simplify the purification treatments of the caprolactam obtained. Thus, for example, the treatment of the caprolactam disclosed in patent WO-A-98/05636 can be carried out by passing over an ion-exchange resin and distillation, when the 6-aminocapronitrile is purified, and can additionally comprise a hydrogenation operation, if the 6-aminocapronitrile has not been sufficiently purified before its hydrolysis.
A purification of 6-aminocapronitrile before its conversion into caprolactam can consequently be regarded as technically and economically highly useful.
The present invention consists of a relatively simple process for the purification of aminonitrile, such as the purification of the 6-aminocapronitrile obtained after separation of the unconverted adiponitrile or directly by treatment of the reaction mixture from the hemihydrogenation of adiponitrile.
Hexamethylenediamine is coproduced with 6-aminocapronitrile during the hydrogenation of adiponitrile.
It can either be separated, completely or partially, from the said 6-aminocapronitrile before the treatment of the latter or, preferably, be kept in the mixture for the said treatment. In the present text, unless otherwise specified, the term 6-aminocapronitrile (or ACN) will therefore cover 6-aminocapro-nitrile and its mixtures with hexamethylenediamine. More generally, the term aminonitrile denotes, in the present text, a medium comprising an aminonitrile to be purified and optionally one or more diamines.
It consists more specifically in subjecting an aminonitrile and preferably 6-aminocapronitrile to a hydrogenation with molecular hydrogen in the presence of a catalyst comprising at least one metal chosen from palladium, platinum, ruthenium, osmium, iridium or rhodium.
The process of the invention applies more specifically to the purification of 6-aminocapronitrile and in particular of that obtained by hemihydrogenation of adiponitrile, such as that described in the preceding paragraph.
This catalyst comprises either one or more promoter elements generally chosen from Groups Ib, IIIa, IVa, Va, VIa, VIb and VIIb of the Periodic Classification of the Elements, such as published in the Handbook of Chemistry and Physics, 51st Edition (1970-1971) by The Chemical Rubber Company, or is subjected to a preconditioning stage which consists in bringing it into contact with a selectivating agent before or at the beginning of the hydrogenation reaction.
This preconditioning stage is optional when the is catalyst comprises, as catalytic element, an element chosen from the group consisting of ruthenium, osmium, iridium and rhodium, in the presence or otherwise of promoter elements.
In contrast, this stage is necessary when the catalyst comprises an element chosen from the group comprising palladium and platinum, in the absence of promoter elements.
Mention may be made, as examples of promoter elements suitable for the invention, of elements such as gold, silver, copper, chromium, molybdenum, tungsten, germanium, tin, lead, boron, gallium, indium, thallium, phosphorus, arsenic, antimony, bismuth, sulphur, selenium, tellurium, manganese, rhenium, vanadium, titanium or zinc.
These promoter elements can be in the free form or in the combined form, for example in the form of oxides or of salts. They have the aim of improving the selectivity of the hydrogenation of the impurities, in particular of the imines, by inhibiting even more the hydrogenation of the nitrile functional group of the aminonitrile and in particular of ACN. They are preferably employed with palladium, platinum and ruthenium catalysts. The promoter element/catalyst metal ratio by weight varies according to the promoter. It is generally between 0% and 100%. This ratio is preferably between 5 and 60% by weight for some promoters, such as silver. For other promoters, this ratio by weight varies between 0.0001% and 10%.
According to another characteristic of the invention, the catalyst of the invention can be subjected or is subject, according to its composition, to a preconditioning stage which makes it possible to improve the selectivity of the hydrogenation, that is to say to improve the degree of hydrogenation of the impurities of the aminonitrile, such as imines, while keeping the degree of hydrogenation of the aminonitrile at a minimum value.
This preconditioning stage consists in subjecting the catalyst to a fluid comprising a selectivating agent. This treatment can be carried out on the catalyst before it is charged to the hydrogenation reactor, by treatment with a flow of hydrogen comprising a certain amount of selectivating agent.
However, in a preferred embodiment of the invention, the preconditioning of the catalyst is carried out directly in the hydrogenation reactor, at the beginning of hydrogenation, either by feeding a flow of hydrogen comprising the said selectivating agent for a predetermined period of time sufficient to feed the desired amount of selectivating agent or by feeding the said selectivating agent as a mixture with the flow of aminonitrile to be hydrogenated for a period of time corresponding to feed
Brunelle Jean-Pierre
Leconte Philippe
Marion Philippe
Burns Doane Swecker & Mathis L.L.P.
Padmanabhan Sreeni
Rhodia Fiber & Resin Intermediates
Sackey Ebenezer
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