GB694356A - Improvements in or relating to the removal of selenium from unsaturated aldehydes obtained by selenium catalyzed oxidation of olefines - Google Patents

Abstract

In the manufacture of unsaturated aldehydes by the oxidation of olefines in the gaseous phase with molecular oxygen over heavy metal compounds containing contact materials in the presence in the reaction zone of elementary selenium, the gaseous reaction mixture issuing from the reactor is passed over gas adsorption charcoal for removal of selenium and selenium compounds from the reaction mixture before it is released to the atmosphere. Preferably, the unsaturated aldehyde is removed from the gaseous mixture before bringing the latter into contact with the charcoal. If desired, the selenium content of the gas mixture may be reduced by cooling the mixture, thereby depositing crystalline selenium prior to the charcoal treatment. Increased adsorption results when deposition of water on the charcoal is prevented by warming the charcoal. The adsorped selenium may be recovered by heating the charcoal to volatilize the selenium, by passing fresh gas reaction mixture over the charcoal at elevated temperature prior to the mixture entering the reactor, or by converting the selenium into a soluble compound and extracting with a suitable solvent, e.g. by treating with chlorine in presence of steam and then washing with water. In examples, a gaseous mixture of air, propylene and selenium is passed over copper-oxide/alumina at 320 DEG C., the issuing gaseous products washed free of acrolein and then passed through an adsorbent and data is given showing the superiority of activated coconut charcoal over silica gel and activated alumina in the retention of residual selenium. The oxidation of isobutene to methacrolein is also mentioned. Specifications 625,330, 648,386, 655,210, 658,179, 678,557, 694,353, 694,354 and 694,362 are referred to.