GB625330A - Improvements in and process for the manufacture of acrolein - Google Patents

Abstract

Acrolein is prepared by oxidising propylene with gases containing molecular oxygen in the presence of a catalyst comprising elementary selenium and one or more of copper, copper oxides and copper compounds which are reducible to the metal under the reaction conditions or by a pretreatment with hydrogen or the reactants. In the latter modification an increase in the activity of the catalystis obtained. The preferred catalyst is selenium and copper oxide supported on e.g. asbestos or pumice. The selenium may be present initially, introduced as vapour or generated by the dissociation of selenides during the reaction. Selenides instanced are those of silver, antimony and cobalt. 10 volumes of propylene are preferably reacted with 90 volumes of air at 200-400 DEG C., favourably 300-350 DEG C. Inert diluents, e.g. nitrogen, steam and carbon dioxide may be present to minimise explosion hazards. Vaporised selenium may be condensed on the exit side of the apparatus and re-introduced to the reacting zone by reversing the flow of gases. In examples: acrolein is obtained by passing propylene and air over mixed (1) silver selenide and (2) selenium with copper oxide (obtained by heating copper nitrate to 450 DEG C.) supported on asbestos, selenium deposited on copper oxide supported on pumice by (3) vaporising selenium in a stream of nitrogen and by (4) dusting on selenium powder fresh selenium vapour being introduced when the catalyst had lost its activity, and (5) illustrates the increase in activity of the copper oxide catalyst used in (4) when pre-treated with the reacting gases. The Provisional Specification states that lead selenide may be used as a source of selenium and in example (2) the catalyst used is a mixture of lead selenide and copper oxide deposited on asbestos.ALSO:Acrolein is prepared by oxidizing propylene with gases containing molecular oxygen in the presence of a catalyst comprising elementary selenium and one or more of copper, copper oxides and copper compounds which are reducible to the metal under the reaction conditions or by a pretreatment with hydrogen or the reactants. In the latter modification an increase in the activity of the catalyst is obtained. The preferred catalyst is selenium and copper oxide supported on e.g. asbestos or pumice. The selenium may be present initially, introduced as vapour or generated by the dissociation of selenides during the reaction. Selenides instanced are those of silver, antimony and cobalt. Ten volumes of propylene are preferably reacted with 90 volumes of air at 200-400 DEG C., favourably 300-350 DEG C. Inert diluents, e.g. nitrogen, steam and carbon dioxide may be present to minimize explosion hazards. Vaporized selenium may be condensed on the exit side of the apparatus and reintroduced to the reacting zone by reversing the flow of gases. In examples, acrolein is obtained by passing propylene and air over mixed (1) silver selenide and (2) selenium with copper oxide (obtained by heating copper nitrate to 450 DEG C.) supported on asbestos, selenium deposited on copper oxide supported on pumice by (3) vaporizing selenium in a stream of nitrogen and by (4) dusting on selenium powder fresh selenium vapour being introduced when the catalyst had lost its activity, and (5) illustrates the increase in activity of the copper oxide catalyst used in (4) when pretreated with the reacting gases. The Provisional Specification states that lead selenide may be used as a source of selenium and in example (2) the catalyst used is a mixture of lead selenide and copper oxide deposited on asbestos.