Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1998-09-03
2000-12-19
Padmanabhan, Sreeni
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502307, 568338, 568361, 568366, 585379, B01J 2302, C07C 4565
Patent
active
061627585
DESCRIPTION:
BRIEF SUMMARY
This is the U.S. National stage application of PCT/EP97/01124 filed Mar. 6, 1997.
The present invention relates to a process for dehydrogenating secondary alcohols in the presence of a catalyst comprising zinc oxide and calcium carbonate at elevated temperature in the gas phase.
DE-A 1,443,462 discloses a process for dehydrogenating primary and secondary alcohols in which the alcohol used is dehydrogenated at elevated temperature in the gas phase over catalysts consisting predominantly of zinc oxide to give the corresponding aldehyde or ketone. The catalyst can contain both copper compounds and alkaline earth metals. During the dehydrogenation, ie. after hydrogen elimination has commenced, the hydrogen feed in the process described is discontinued. In particular, the dehydrogenation of cyclohexanol to cyclohexanone is described, but the yield of cyclohexanone is only 81.5%. Apart from 17% of unreacted cyclohexanol, the reaction mixture contains from 0.1 to 0.5% of hydrocarbons and 1% of higher-boiling condensation products.
DE-B 1,296,625 describes a process for preparing cyclohexanone from cyclohexanol contaminated with organic acids and esters at elevated temperatures in the presence of a zinc-containing catalyst comprising zinc oxide-zinc carbonate or mixtures of zinc oxide-zinc carbonate with calcium oxide-calcium carbonate or with magnesium oxide-magnesium carbonate. A disadvantage of this process is the excessive decrease in the pellet hardness in long-term operation which leads to frequent replacement of the catalyst and corresponding down times. The decrease in the pellet hardness in long-term operation results from the massive decomposition of the carbonates by organic acids or from phase transformations.
Acta Chim. Acad. Sci. Hung 107 (1981) 343-360, Acta Chim. Acad. Sci. Hung 97 (1978) 439-449 disclose that in the dehydrogenation of cyclohexanol in the presence of hydrogen and catalysts comprising elements of the eighth transition group, e.g. rhodium, nickel and platinum, increased amounts of cracking products and formation of phenol and benzene are observed in comparison with processes not using hydrogen. This is not observed in the dehydrogenation of aliphatic alcohols: thus DE-A 2,028,350 describes a process for dehydrogenating aldehydes and ketones, in particular for preparing acetone and methyl isobutyl ketone, over a copper-containing catalyst in the presence of hydrogen. It may be remarked that although this reference mentions cyclohexanol as starting material among many others, there are no experimental data on the dehydrogenation of cyclohexanol. In all probability it would also be possible to prepare cyclohexanone by the process described in DE-A 2,028,350, but in the light of the abovementioned Acta Chim. Acad. Sci. Hung 107 (1981) 343-360 and also Acta Chim. Acad. Sci. Hung 97 (1978) 439-449 one would have to expect by-products which prohibit economical use.
It is an object of the present invention to provide a process in which cyclic ketones, in particular cyclohexanone, can be obtained in higher selectivities and yields than hitherto possible and in which the formation of cracking products and aromatic by-products is minimized. The present invention is also to make available a catalyst which in long-term operation has a good pellet hardness, particularly in respect of compressive strength on the end face and lateral compressive strength, so that the catalyst has to be replaced less often than hitherto.
We have found that this object is achieved by a process for dehydrogenating secondary alcohols in the presence of a catalyst comprising zinc oxide and calcium carbonate at elevated temperature in the gas phase, wherein secondary cyclic alcohols are used and the dehydrogenation is carried out in the presence of hydrogen and a catalyst whose active components comprise from 30 to 60% by weight of zinc oxide and from 40 to 70% by weight of calcium carbonate in the calcite form.
In addition, a dehydrogenation catalyst and a process for its preparation and its use have been found.
Secondar
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Chem. Abstracts, vol 121, 1994.
Chem. Abstracts, vol 111, No. 14, 1989.
Acta. Chim. Acad. Sci. Hung, 97, 1978, pp. 439-449.
Acta. Chim. Acad. Sci. Hung, 107, pp. 343-360 (1981).
Brocker Franz Josef
Hesse Michael
Markl Robert
BASF - Aktiengesellschaft
Padmanabhan Sreeni
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