Process for the preparation of a catalyst for the hydrogenation

Details Process for the preparation of a catalyst for the hydrogenation Process for the preparation of a catalyst for the hydrogenation

1996-09-23

1998-09-01

Burn, Brian M.

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

564491, 564492, 564493, 502301, C07C20948

Patent

active

058012869

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to the field of the catalytic hydrogenation of nitrites to amines and, more particularly, of dinitriles such as adiponitrile (ADN) to diamines such as hexamethylenediamine (HMD) or to aminonitriles such as aminocapronitrile.
More precisely, the present invention relates to a process for the preparation of a catalyst for the hydrogenation of nitriles to amines of Raney nickel type doped with at least one additional metal element selected from columns IVb, Vb and VIb of the periodic classification.
It also relates to the catalysts obtained by implementation of this process and a final subject is an application of these catalysts in catalytic hydrogenation of nitriles to amines and, more precisely, but non-limitingly, of adiponitrile to hexamethylenediamine.
Catalytic hydrogenation has been carried out for a considerable time using Raney nickels, which are obtained by alkaline leaching of aluminium-rich Al/Ni precursor alloys, the leaching normally having the effect of causing the removal of most of the aluminium. The finished catalyst exists in the form of agglomerates of finely-divided nickel crystallites which are characterized by a high specific surface and a variable residual aluminium content.
Conventionally, the parameters which make it possible to assess the behaviour of a catalyst are the activity, the selectivity and the stability with time.
In an attempt to optimize these properties in Raney Ni hydrogenation catalysts, it has been proposed to add to them promoters or doping agents which are additional metal elements chosen from transition metals in the periodic classification (especially iron, cobalt, chromium, molybdenum, zirconium, tantalum or titanium).
According to a first, so-called "metallurgic" route, the doping or the incorporation of promoter in catalysts of Raney nickel type is carried out at the stage of the Ni/Al precursor alloy, before alkaline attack. Introduction of the doping agent into the alloy is carried out in the molten state.
The article by B. N. Tyutyunnikov, "The Soviet Chemical Industries, No. 6, June 1971, pages 380 to 382", as well as the written work by Freidling et al., "Russian Chemical Reviews, Vol. 33, No. 6, June 1964, pages 319 to 329", are prior bibliographic references which relate to Raney Ni catalysts doped with at least one transition metal by the metallurgic route. These known catalysts are not generally more satisfactory as regards activity, selectivity and stability with time. Thus, the catalysts disclosed in Tyutyunnikov et al. seem relatively specific for mononitriles derived from fatty acids containing 7 to 20 carbon atoms. However, this is not evidence of efficiency as regards, for example, dinitriles.
The Raney Ni catalysts doped and described by Freidling et al. are active on dinitriles but their selectivity with respect to the substrates remains low. Finally, the hydrogenation reaction conditions required for these catalysts (Ni/Al/Ti) are not ideal on an industrial scale: temperature of 140.degree. to 180.degree. C., hydrogen pressure of 140 bars and reaction medium consisting of n-butanol+ammonia.
Moreover, a second route for doping the hydrogenation catalyst of Raney nickel type is known, described especially by Takagi and Yamanaka in "Scientific Papers I.P.C.R. - Tokyo, 55 (1961), 105-108".
These writers propose to improve the activity and selectivity of catalysts of Raney nickel type by addition of various metal salts (copper, cobalt or chromium nitrates, ammonium molybdate, sodium tungstate or ferric chloride) during the stage of alkaline attack on the precursor alloy. The nitrile to be hydrogenated tested in these experiments is acetonitrile. According to this document, the doped catalysts used would have an increased activity with respect to their non-doped homologues. These reports are questionable because they are made solely on the basis of visual observation of curves of the change in hydrogen consumption.
It should additionally be known that the incorporation of these metal salts in the alkaline leaching med

REFERENCES:
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patent: 4429159 (1984-01-01), Cutchens et al.
patent: 5210271 (1993-05-01), Mizuno et al.
patent: 5527946 (1996-06-01), Flick et al.
Russian Chemical Reviews, Uspekhi Khimii, vol. 33, 1964.
Effect of Additives on the Activity of Hydrogenation Catalyst, (II), Yuzuru Takagi et al, vol. 55, No. 2, 1961.
Catalytic Hydrogenation of Raney Nickel Catalyst Modified by Chromium Hydroxide Deposition, T. Koscielski et al, Applied Catalysis, 49 (1989), pp. 91-99.

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