Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2003-01-10
2004-09-14
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S490000, C564S491000, C564S492000, C564S493000
Reexamination Certificate
active
06790994
ABSTRACT:
The present invention relates to a process for the hydrogenation of nitrile functional groups to amine functional groups.
It relates more particularly to a process for the complete or partial hydrogenation of dinitrile compounds to diamine or aminonitrile compounds.
Hydrogenation of dinitriles to the corresponding diamines is a process which has been used for a long time, in particular hydrogenation of adiponitrile to hexamethylenediamine, one of the base materials in the preparation of polyamide-6,6.
An increasing interest has become apparent in recent years in the hydrogenation (also sometimes known as hemihydrogenation) of aliphatic dinitriles to aminonitriles, in particular the hydrogenation of adiponitrile to 6-aminocapronitrile, resulting either directly or via caprolactam in polyamide-6.
Thus, U.S. Pat. No. 5,151,543 discloses a process for the selective hydrogenation of aliphatic dinitriles to the corresponding aminonitriles, at 25-150° C. and under a pressure of greater than atmospheric pressure, in the presence of a solvent in a molar excess of at least 2/1 with respect to the dinitrile, the solvent comprising liquid ammonia or an alcohol with 1 to 4 carbon atoms and an inorganic base which is soluble in the said alcohol, in the presence of a Raney catalyst, the aminonitrile obtained being recovered as main product.
Patent WO-A-93/16034 discloses a process for the preparation of 6-aminocapronitrile by hydrogenation of adiponitrile in the presence of an inorganic base, of a transition metal complex, the transition metal being of low valency and chosen from chromium, tungsten, cobalt and iron, and of Raney nickel as catalyst, under hydrogen pressure and at a temperature of 50° C. to 90° C.
Patent WO-A-96/18603 discloses the hemihydrogenation of aliphatic dinitriles to aminonitriles by hydrogen in the presence of a catalyst based on optionally doped Raney cobalt or nickel and of a strong inorganic base, the starting hydrogenation medium comprising water, aminonitrile and/or diamine which are capable of being formed and unconverted dinitrile.
All these hydrogenation processes result in the desired aminonitrile and are presented as being able to be employed continuously in an industrial plant.
However, the selectivities and the yields of these processes have to be improved to render them more competitive.
One of the aims of the present invention is to provide a process for the hydrogenation of nitrile functional groups in the presence of a catalyst exhibiting an improved yield and an improved selectivity.
To this end, the invention provides a process for the hydrogenation of nitrile functional groups to amine functional groups using hydrogen in the presence of a hydrogenation catalyst and of a strong inorganic base preferably deriving from an alkali metal or alkaline earth metal.
According to the invention, the process comprises a stage of conditioning the catalyst which consists in mixing the hydrogenation catalyst, a predetermined amount of strong inorganic base and a solvent in which the strong inorganic base is not very soluble. According to the invention, the medium comprising a catalyst thus conditioned is fed into the hydrogenation reactor, the hydrogenation reaction being carried out according to the usual conditions or procedures already disclosed in the literature.
The term “hydrogenation catalyst” is understood to mean, in particular and advantageously, Raney metals, such as Raney nickel or Raney cobalt, mixed oxides with a hydrotalcite structure, as disclosed in WO97/10052, but also supported metals, in particular metals from Group VIII of the Periodic Table of the Elements, such as nickel, cobalt, ruthenium or rhodium, deposited on a support, which is generally a metal oxide or active charcoal.
In the case of Raney metals, their instability on contact with the air requires the use of a liquid storage medium. This liquid medium is generally water.
According to the invention, the solvent used exhibits a good affinity for the storage liquid, generally water, thus making it possible to obtain phase separation and formation of a phase comprising the strong inorganic base at a high concentration.
According to a preferred embodiment, the strong inorganic base is added to the said storage medium before the addition of the solvent.
In the case of the other catalysts, which do not require the presence of a storage liquid, it may be worthwhile and advantageous to add water to the mixture.
The term “affinity between the solvent and the storage liquid or water” should be understood as meaning that these compounds are soluble in one another.
Likewise, the term “not very soluble” used to characterize the solubility of the strong inorganic base in the solvent should be interpreted as meaning a solubility of less than 3% by weight of the said base in the pure solvent.
According to the invention, the order of addition of the components or the mixture is immaterial.
According to the process of the invention, the presence of the solvent results in a phase separation of the strong inorganic base or of a concentrated solution of strong inorganic base, forming a second liquid phase comprising all or essentially all of the amount of base added to the mixture, this said phase comprising the strong base being and remaining in intimate contact with the catalyst, the first phase being formed by the solvent and the storage liquid and optionally the solvent of the base, if the latter is added in the form of a solution in a solvent, such as water.
Therefore, the catalyst particles come into contact with a concentrated solution of strong inorganic base, allowing the catalyst to be conditioned by attachment or adsorption of the molecules of strong base at the surface of the said catalyst.
The use of a catalyst comprising molecules of strong base at its surface makes it possible to carry out a hydrogenation with an improved yield and selectivity which are reflected in particular by a decrease in the impurities formed, as is illustrated in the examples given below.
The hydrogenation catalyst can advantageously comprise, in addition to the catalytic metal, a doping element chosen from the elements from Groups Ib, IIb, IVb, VIb, VIIb and VIII of the Periodic Table of the Elements, as published in the Handbook of Chemistry and Physics (Weast, 5th edition of 1970-1971), and aluminium, present in particular in Raney metals.
The term “Raney metal” is understood as meaning in particular Raney nickel or Raney cobalt.
The strong inorganic bases which are suitable for the invention are alkali metal or alkaline earth metal hydroxides, for example LiOH, NaOH, KOH, RbOH, CsOH, and their mixtures.
According to another characteristic of the invention, the liquid storage medium for the Raney metal is preferably water.
According to one characteristic of the invention, the amount of strong base added in the stage of conditioning the catalyst is between 0.1 mol and 50 mol per kg of catalyst. The ultimate amount of base is determined for each catalyst.
According to a preferred form of the invention, the strong base is added in the conditioning stage in the form of a concentrated solution or in the pure form.
Furthermore, the amount of solvent added depends on the degree of solubility of water or of the storage liquid in this solvent and on the desired level of concentration in the phase comprising the strong base. Advantageously, the ratio by weight of the solvent to the water (or storage liquid) will be at least equal to 1, preferably greater than or equal to 2.
According to the invention, the solvent is chosen from the compounds which have an affinity (solubilizing ability, for example) for water or the storage liquid for the Raney metal and which, in contrast, do not have an affinity (low solubilizing ability) for the strong inorganic base. The concept of insolubility of the strong base in the solvent or more specifically in the liquid phase formed by the solvent and the water or the storage liquid should be understood as meaning a low solubility of the base, for example of less than 1% by weight.
In a prefer
Boschat Vincent
Leconte Philippe
Davis Brian J.
Rhodia Polyamide Intermediates
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