Preparation of alcohols

Details Preparation of alcohols Preparation of alcohols

1996-11-19

2001-03-13

Shippen, Michael L. (Department: 1621)

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

Organic compounds

Oxygen containing

C502S305000, C502S318000, C502S345000, C568S727000, C568S799000, C568S891000

Reexamination Certificate

active

06201160

ABSTRACT:

The present invention relates to the preparation of alcohols by catalytic hydrogenation of the corresponding carbonyl compounds. The present invention relates in particular to the use of novel catalysts for this hydrogenation.
The present invention provides in particular a novel process for the preparation of diols from the corresponding aldehydes. A particular application is the preparation of propanediols.
Propanediols and their industrially most important member, neopentylglycol, are intermediates having a broad range of applications in the plastics industry, especially for manmade fibers, polyurethanes and plasticizers.
Neopentylglycol is prepared by condensation of isobutyraldehyde with formaldehyde and subsequent catalytic hydrogenation of the resulting hydroxypivalaldehyde. This hydrogenation has been described in many publications.
Known catalytically active elements for the hydrogenation of alcohols are Ni, Ru, Pt, Re and Cu.
Ni-containing catalysts are mentioned in the patents DE 19 57 592 (1971), DE 20 54 601 (1972) and SE 454 171 (1988). DE 16 43 856 describes the hydrogenation of saturated and unsaturated aldehydes to give alcohols or combined Cu/Ni supported catalysts in the gas phase. However, a disadvantage of Ni-containing catalysts is their considerable tendency to form byproducts, as described in EP 0 044 412.
Noble metal-containing catalysts are described in EP 0 343 475 (Pt-Ru-W), EP 0 373 938 (Re) and SU 361998 (Ru-Ni-Cr). Owing to their high price, these catalysts are however not very suitable for large scale industrial use.
Owing to their wide range of advantages over catalysts containing nickel and noble metal, copper-catalysts form containing the most important group of hydrogenation catalysts for the preparation of alcohol in practice. In particular, Cu—Cr catalysts have a wide range of applications. However, they have the disadvantage that high space-time yields can be achieved only by means of relatively high pressures and temperatures during the hydrogenation. Catalysts of this type are described in U.S. Pat. No. 4,855,515, DE 18 04 984 and JP 49 011 684.
However, these catalysts, too, have been found to have a high tendency to form byproducts, which is described in DE 40 37 729 and U.S. Pat. No. 4,666,879.
However, the properties of the catalyst depend not only on the choice of the catalytically active component but also decisively on the choice of the carrier.
Thus, copper catalysts having carriers containing Al
2
O
3
or ZnO are described in EP 0 044 444 (CuO/Al
2
O
3
), EP 0 044 412 (CuO/ZnO) and EP 0 484 800 (CuO/ZnO/ZrO
2
). The CuO/Al
2
O
3
catalysts and CuO/ZnO catalysts initially have high activity and selectivity but also exhibit pronounced aging. A further problem in the case of Al
2
O
3
-containing catalysts is the rehydration which occurs at relatively high temperatures and is caused by the use of the starting material in aqueous solution and may lead to disintegration of the catalysts.
The use of ZrO
2
-containing carrier gives stable catalysts which, however, owing to the high content of ZrO
2
, have virtually twice as high a bulk density as the Al
2
O
3
-containing catalysts.
However, the properties of the copper catalysts used depend not only on the choice of the active component and of the total composition but also decisively on the conditions of the preparation process. A number of processes for the preparation of copper catalysts for the hydrogenation of carbonyl compounds are known.
Thus, DE 41 42 897 describes the preparation of copper catalysts having small copper particles and a correspondingly large effective surface area of the catalyst material by precipitation of the copper-containing component. However, this process generally leads to unsatisfactory results in spite of considerable expense.
According to EP 0 006 313, small copper crystallites can also be obtained by precipitation of a copper compound at elevated temperatures onto an inert carrier.
The preparation of catalysts having high copper contents by precipitation is furthermore described in FR 1520584.
U.S. Pat. No. 3,701,739 describes a process for the preparation of Cu/Zn catalysts by agglomeration of copper-containing particles in a fluidized bed and subsequent decomposition of the agglomerated components. However, the disadvantage of catalysts prepared in this manner is their relatively low mechanical hardness.
Important criteria for the suitability of the catalysts which can be used in these processes are not only their activity and selectivity for the catalyzed reaction but also their mechanical properties, such as hardness and abrasion resistance. The mechanical properties of the catalysts used are therefore of particular importance for the cost-effectiveness of the process, because insufficient mechanical stability of the catalyst may lead in a relatively short time to blockage of the plant owing to pronounced catalyst abrasion, resulting in long downtimes.
It is an object of the present invention to provide a process which permits the preparation of alcohols from the corresponding carbonyl compounds in an economical manner and with good yield and selectivity. For this purpose, it was intended to provide catalysts which permit this reaction with high activity and selectivity and which possess good mechanical properties, in particular great hardness and abrasion resistance, and, advantageously, a low bulk density. These catalysts should also be capable of being prepared in an economical manner.
We have found that this object is achieved by the process, described in the claims, for the preparation of alcohols by catalytic hydrogenation of the corresponding carbonyl compounds at elevated temperatures and at superatmospheric pressure in the liquid phase. According to the invention, the catalyst used is one which contains copper on an SiO
2
-containing carrier in the presence or absence of one or more of the elements magnesium, barium, zinc and chromium.
The catalyst used in the novel process for the preparation of alcohols is distinguished by the fact that the active component copper is applied to an SiO
2
-containing carrier.
The carrier used for a catalyst is referred to as SiO
2
-containing if it contains SiO
2
or a silicate, such as magnesium silicate. Since the anionic silicate groups are present in monomeric, oligomeric and polymeric form side by side in the catalyst, they are detected analytically and calculated as SiO
2
.
The copper catalyst used for the novel process and having an SiO
2
-containing carrier contains preferably from 5 to 75% by weight, calculated as CuO, of copper and from 95 to 25% by weight, calculated as SiO
2
, of Si, based in each case on the total weight of the calcined catalyst.
Other catalysts which may be advantageously used in the novel process are those which, in addition to copper and silicon, contain one or more of the elements magnesium, barium, zinc and chromium. Magnesium is present in an amount of from 0 to 20% by weight, calculated as MgO, barium in an amount of from 0 to 5% by weight, calculated as BaO, zinc in an amount of from 0 to 5% by weight, calculated as ZnO, and chromium in an amount from 0 to 5% by weight, calculated as Cr
2
O
3
, based in each case on the total weight of the calcined catalyst, with the proviso that the sum of the catalyst components copper, silicon and, if present, magnesium, barium, zinc and chromium is 100% by weight.
The copper catalysts described, which have an SiO
2
-containing carrier, can be prepared by the known and abovementioned processes.
In particular, the following preparation processes are suitable: Application of an aqueous copper salt solution in one or more impregnation stages to a prepared carrier consisting of SiO
2
, magnesium silicate or another sparingly soluble silicate. A preferred carrier is SiO
2
. The impregnated carrier is then dried and calcined.
The impregnation can be carried out by the incipient wetness method, in which the carrier is moistened according to its water absorptivity with the impregnating solution up to saturation. However, impregnation may

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