Method for the hydrogenation of carbonyl compounds

Details Method for the hydrogenation of carbonyl compounds Method for the hydrogenation of carbonyl compounds

2000-01-11

2001-03-27

O'Sullivan, Peter (Department: 1621)

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

Organic compounds

Oxygen containing

C568S808000, C568S809000, C568S812000, C568S814000, C568S831000, C568S832000, C568S853000, C568S857000, C568S861000, C568S863000, C568S864000, C568S881000, C568S885000

Reexamination Certificate

active

06207865

ABSTRACT:

This application is a 371 of PCT/EP98/04402 filed Jul. 15, 1998.
The invention relates to a process for the catalytic hydrogenation of carbonyl compounds in the presence of a Raney copper catalyst.
Catalytic hydrogenation of carbonyl compounds, such as the hydrogenation of aldehydes to prepare simple and functionalized alcohols, occupies an important place in the production sequences in the basic chemicals industry. This is particularly true of the hydrogenation of aldehydes which can be obtained by the oxo synthesis or the aldol reaction.
Catalytic hydrogenation of aldehydes in a suspension or fixed bed procedure has been known for a long time. Industrial systems operate almost exclusively with fixed bed reactors.
The fixed bed catalysts used in particular are supported catalysts, for example Cu/Ni or Cu/Cr catalysts supported on SiO
2
or Al
2
O
3
.
Suitable alternatives to the supported catalysts are Raney-type catalysts. Raney catalysts show particularly high hydrogenation activity owing to the large surface area of metal. Suitable metals are nickel, cobalt, iron and copper.
SU 430 876 describes the hydrogenation of furfural on a Raney copper catalyst in a suspension procedure. Suspension processes have the disadvantage by comparison with fixed bed processes that the catalyst consumption is greater. It is furthermore necessary for the catalyst to be removed from the reaction mixture in an additional step.
RO 106 741 describes a process for the hydrogenation of furfural to furfuryl alcohol in a fixed bed reactor in a downflow procedure. Raney copper inter alia is employed as catalyst. The publication contains no information on the preparation of the catalyst and its properties.
JP-A-3 141 235 describes a process for the hydrogenation of acetone to isopropanole wherein a Raney nickel catalyst is employed. It is described that the Raney nickel catalyst is mixed with a Raney copper catalyst. At the same time, however, it is implicitly stated that when adding more than a certain amount of said catalyst, productivity will be decreased.
Raney catalysts which can be used in a fixed bed process are normally prepared by kneading an aluminum/copper alloy powder with binders and auxiliaries, producing moldings, for example tablets or extrudates, from the kneaded composition, calcining the moldings and activating the calcined moldings by treatment with an alkali metal hydroxide. Processes of this type for preparing Raney catalysts are described, for example, in DE-A 43 45 265, Ind. Eng. Chem. Res. 28 (1989) 1764-1767 and DE-A 44 46 907. Preparation of the catalyst by this process involves a plurality of steps.
It is an object of the present invention to provide a process for the catalytic hydrogenation of carbonyl compounds employing a catalyst which is easy to prepare industrially and has high activity and selectivity.
We have found that this object is achieved by employing Raney copper in the form of nuggets for the hydrogenation of carbonyl compounds to, for example, the corresponding alcohols with a high catalytic activity and selectivity exceeding the activity and selectivity of Raney copper catalysts prepared according to the prior art.
Accordingly the object has been achieved by a process for the catalytic hydrogenation of a carbonyl compound or of a mixture of two or more carbonyl compounds in the presence of a Raney copper catalyst, wherein the Raney copper catalyst is employed in the form of nuggets.
Nuggets mean that the metal is in the form of particles of irregular geometry with a size of from 0.5 to 10 mm. The Raney copper nuggets are produced from coarse-particle copper/aluminum alloy, without the intermediate steps of kneading the copper/aluminum alloy with a binder and/or auxiliary, shaping the kneaded composition to moldings and calcining the moldings, by treatment of the coarse-particle copper/aluminum alloy with alkali metal hydroxide.
The nuggets employed in the process according to the invention can be from 0.5 to 10 mm in size. They are preferably from 1 to 8 mm, particularly preferably from 2 to 7 mm, especially from 2 to 6 mm.
The Raney copper used in the process according to the invention is prepared starting from a copper/aluminum alloy. The copper/aluminum alloy is prepared in a manner known per se, for example by the process described in DE-A 21 59 736. The ratio by weight of aluminum to copper in the initial alloy is generally chosen in the range from 30:70 to 70:30% by weight, preferably from 40:60 to 60:40% by weight.
The Raney copper catalyst is prepared from the copper/aluminum alloy by dissolving out the catalytically inactive constituents with alkali metal hydroxide (activation). Preferred alkali metal hydroxides are sodium hydroxide or potassium hydroxide, and sodium hydroxide is particularly preferred. An aqueous solution of the alkali metal hydroxide is generally employed, preferably sodium or potassium hydroxide solution, particularly preferably sodium hydroxide solution, normally using a 5-30% by weight aqueous solution of the alkali metal hydroxide. The molar ratio of alkali metal hydroxide to aluminum is generally chosen in the range from 1:1 to 4:1, preferably from 1.5:1 to 2.5:1. The activation is normally carried out at from 25° C. to 95° C., preferably 45 to 90° C. The duration of the activation essentially depends on the required final aluminum content and is normally in the range from 10 to 30, preferably 15 to 25, h. The activation is expediently monitored by measuring the amount of hydrogen liberated during it. The activation process can also be carried out several times.
The starting material for the activation is normally the coarse-particle copper/aluminum alloy. The size of the copper/aluminum alloy particles can correspond to that of the Raney copper nuggets employed in the process according to the invention. However, it is also possible for the particles to be reduced to the required size after the activation.
The Raney copper catalysts employed in the process according to the invention preferably have a copper content of from 40 to 90% by weight, more preferably from 50 to 80% by weight, particularly preferably from 60 to 70% by weight.
The Langmuir specific surface area of the Raney copper catalysts employed in the process according to the invention is preferably from 5 to 50 m
2
/g, more preferably from 15 to 40 m
2
/g, particularly preferably from 20 to 40 m
2
/g. The Langmuir surface area is determined by nitrogen absorption using the DIN 66 132 method.
A variable characteristic of the Raney copper catalysts according to the invention is also their specific Cu surface area (S—Cu). It is calculated from the N
2
O consumption measured on oxidation of surface copper atoms with gaseous N
2
O in a heated sample of the catalyst.
This is done by initially treating the sample with 10 mbar of H
2
at 240° C. for 4 hours. The pressure over the sample is then reduced to less than 10
−3
mbar, and it is then treated with 30 mbar of H
2
for 3 hours, subsequently the pressure is again reduced to less than 10
−3
mbar, followed by treatment with 100 mbar of H
2
for 3 hours, the pressure is again reduced to less than 10
−3
mbar, followed by a final treatment with 200 mbar of H
2
for 3 hours, the hydrogen treatment in each case being carried out at 240° C.
In a second stage, the sample is exposed to N
2
O under a pressure of 266 mbar at 70° C. for 2 hours, the N
2
O being decomposed on the sample; the pressure over the sample is then reduced to less than 10
−3
mbar, after which the increase in weight of the catalyst as a result of the formation of copper oxide on the surface thereof is determined.
The specific Cu surface area of the Raney copper catalysts is preferably from 0.5 to 7 m
2
/g, more preferably from 1 to 4 m
2
/g.
The pore volume of the Raney copper catalyst determined by mercury porosimetry is preferably from 0.01 to 0.12 ml/g, more preferably from 0.03 to 0.08 ml/g. The average pore diameter determined by this method is preferably from 50 to 300 nm, more preferably from 60 to 100 nm. The mercury po

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