GB727318A - Manufacture of an unsaturated aldehyde - Google Patents

Abstract

A process for the manufacture of acrolein by passing propylene with gases containing molecular oxygen at elevated temperatures in the presence of elementary selenium in the reaction zone over a contact material comprising initially copper oxide distributed upon activated alumina comprises preheating the contact material at temperatures between 750 DEG and 1000 DEG C., passing the gaseous reaction mixture over the contact material at a temperature between 210 DEG and 350 DEG C. and providing for the presence in the mixture of reacting gases of selenium vapour in an amount within the range of 0.008 to 0.12 milligram per litre of gas mixture. Two reactors in series may be used, the first containing solid contact material which has been previously heat-treated, the second reactor containing solid contact material previously heat-treated at a lower temperature which is maintained at an elevated temperature whilst the first reactor is kept at a slightly higher temperature than the second reactor. Alternatively a mixture of the more and less active contact materials in a single reactor may be employed. A high selenium content may be employed initially in the gaseous mixture to bring the selenium content of the contact material to the normal equilibrium content. Selenium is recovered by cooling the mixture issuing from the reaction zone and acrolein is recovered by scrubbing the reaction products with water followed by fractional distillation. Residual volatile selenium compounds may be recovered by adsorption on active charcoal. Part only of the aldehyde may be removed from the reacted mixture and the remainder of the gas mixture may be recycled with fresh olefine, oxygen containing gases and selenium. In examples: acrolein is prepared by passing propylene mixed with air over heated selenium and a contact material prepared by evaporating a mixture of copper nitrate solution and activated alumina to dryness and heating, a high selenium content being first employed in the reactant gases which is subsequently reduced to within the specified range (1); a similar process is carried out using a tubular steel reactor (2); and a similar process is carried out using a contactmaterial which has been heat-treated at a higher temperature than that employed in (1). Specification 706,552 is referred to.