Enichem Elastomers Ltd.

Ian D Hudson

Graham John Hutchings

The invention relates to a process for the preparation of a conjugated diene from the corresponding carbonyl compound having the same number of carbon atoms by dehydration at a temperature of 300.degree. to 450.degree. C. using a catalyst comprising aluminium phosphate having the cristobalite structure. This catalyst is superior to aluminium phosphate having the tridymite structure in the dehydration of carbonyl compounds and has advantages over boron phosphate catalysts. Using the process, isoprene may be prepared from 2-methyl butanal and/or methyl isopropyl ketone in high yields. Unexpectedly aluminium phosphate having the cristobalite structure is markedly superior to boron phosphate in converting methyl isopropyl ketone, which is an intermediate product formed in appreciable amounts in the dehydration of 2-methyl butanal to isoprene. This superiority significantly improves the process economics of the conversion reaction of 2-methyl butanal to isoprene.

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Freckleton, United Kingdom

Ian D Hudson