GB632291A - Improvements in methods of dehydrogenating aliphatic hydrocarbons - Google Patents

Abstract

Aliphatic hydrocarbons are dehydrogenated by flowing the vapour in the presence of steam over a catalyst comprising granules of naturally-occurring carbonate of calcium or magnesium partially calcined to form a minor portion of oxides as an outer layer integral with a major, inner core portion of undecarbonated carbonate maintained at a dehydrogenating temperature and maintaining the said major portion (by weight) of the catalyst particles in the form of carbonate throughout the dehydrogenation reaction. The partially calcined granules may be regenerated in situ by periodically temporarily increasing the flow rate of steam thereover and thereby decreasing the partial pressure of carbon dioxide to less than the partial pressure of the carbonate compound core-like inner portions. The dehydrogenating temperature is preferably between 600 DEG and 650 DEG C. Dolomite, limestone, dolomitic limestone, and marble are preferred since magnesite and ferruginous dolomite have too high a partial pressure of carbon dioxide for core stability at the operating temperatures. Carbon dioxide, e.g. combustion products, may however, be introduced to correct this. The material may contain oxides of iron, silicon and aluminium and may be sprayed with suspensions of oxides of iron or nickel in a non-hydrous medium to increase activity or impregnated with a silica salt to form a fibrous skeleton which resists erosion. The granules preferably have a size lying between the 4 and 10 mesh per inch sieves and show 30-45 per cent loss of weight on complete calcination. Examples describe the dehydrogenation of ethyl benzene to styrene using limestone marble, dolomitic limestone and "Red Flux" ferruginous limestone; diethyl benzene to styrene and divinyl benzene using dolomitic limestone; isopropyl benzene to styrene and methyl styrene using dolomite; monoethyl naphthalene to vinyl naphthalene using dolomite. isobutene to isobutylene and propylene using dolomite. Specification 632,350 is referred to.ALSO:Aliphatic hydrocarbons are dehydrogenated by flowing the vapour in the presence of steam over a catalyst comprising granules of naturally-occurring carbonate of calcium or magnesium partially calcined to form a minor portion of oxides as an outer layer integral with a major inner core portion of undecarbonated carbonate maintained at a dehydrogenating temperature, and maintaining the said major portion (by weight) of the catalyst particles in the form of carbonate throughout the dehydrogenation reaction. The partially-calcined granules may be regenerated in situ by periodically temporarily increasing the flow rate of steam thereover and thereby decreasing the partial pressure of carbon dioxide to less than the partial pressure of the carbonate compound core-like inner portions. The dehydrogenating temperature is preferably between 600 DEG and 650 DEG C. Dolomite, limestone, dolomitic limestone, and marble are preferred since magnesite and ferruginous dolomite have two high a partial pressure of carbon dioxide for core stability at the operating temperatures. Carbon dioxide, e.g. combustion products, may, however, be introduced to correct this. The material may contain oxides of iron, silicon, and aluminium, and may be sprayed with suspensions of oxides of iron or nickel in a non-hydrous medium to increase activity or impregnated with a silica salt to form a fibrous skeleton which resists erosion. The granules preferably have a size lying between the 4 and 10 mesh per inch sieves and show 30-45 per cent loss of weight on complete calcination. Examples describe the dehydrogenation of ethyl benzene to styrene using limestone marble, dolomitic limestone and "Red Flux" ferruginous limestone; diethyl benzene to styrene and divinyl benzene using dolomitic limestone; isopropyl benzene to styrene and methyl styrene using dolomite; monoethyl naphthalene to vinyl naphthalene using dolomite; isobutene to isobutylene and propylene using dolomite. Specification 632,350, [Group III], is referred to.