GB694362A - Manufacture of unsaturated aldehydes - Google Patents

Abstract

Unsaturated aldehydes R(CHO).C=CHR1 are made by reacting an olefine R.(CH3)C= CHR1 in the vapour phase with molecular oxygen at elevated temperatures in the presence in the reaction zone of elementary selenium and a solid contact material comprising reformed copper silicate. In the formul R and R1 are hydrogen atoms or straight or branched chain alkyl groups. Specified olefines include propylene, 2-methylbut-2-ene, 2 : 4 : 4-trimethylpent-2-ene and codimers of n-butene with isobutene and 2-methylpent-1-ene. The copper silicate may be made in known fashion and applied on conventional carriers although preferably no carriers are used. Preferably the silicate is heated at 200-1000 DEG C. before use. Silicate which has been in contact with an acid aqueous medium of pH7-4.5 before drying but after precipitation is especially useful as is a silicate which contains excess copper, e.g. that made when 20-100 per cent above the stoicheometrical quantity of copper salt is added to an alkali metal silicate. Reaction temperatures are 200-400 DEG C., preferably 280-350 DEG C. Selenium may be added as vapour or generated in situ from selenides, e.g. those of silver, antimony and cobalt. Quantities of selenium indicated per 100 litres of gas vary from 0.02 to 0.2 gms. according to the olefine used. Oxygen may be present as such or as air and the quantity of olefine should be less than that corresponding to the lower explosion limit. This limit is given for propylene and isobutene. Inert gases may be present. Reaction gas mixture is preferably recycled after removal of aldehydes which may be effected by scrubbing with a solvent or by cooling. In examples (1) and (2) propylene and isobutene yield respectively acrolein and methacrolein, (3) and (4) isobutene yields methacrolein, and (5) diisobutene yields C8 unsaturated aldehydes (in these three examples acid washed silicate is used), (6), (7) and (8) isobutene yields methacrolein, (9) diisobutene yields alpha-neopentylacrolein and alpha-methyl-beta-tertiary butyl acrolein, and (10) n-butenes yield crotonic aldehyde (in these five examples silicate containing excess copper is used). Specifications 625,330, 648,386, 655,210 and 658,179 are referred to.ALSO:Unsaturated aldehydes R(CHO)C=CHR1 are made by reacting an olefine of formula R(CH3)C=CHR1 where R and R1 are hydrogen atoms or straight or branched chain alkyl groups in the gaseous phase with molecular oxygen at elevated temperatures in the presence of elementary selenium and a solid contact material comprising preformed copper silicate. The copper silicate may be on conventional carriers and may be prepared by known methods and is preferably pre-treated by heating at 200-1000 DEG C. Elementary selenium may be added as such or formed in situ from selenides such as those of silver, antimony and cobalt. In a modification the silicate is after precipitation but before drying contacted with an aqueous acid medium of pH 7-4.5. Thus equimolar quantities of a copper salt may be reacted p with an alkali metal metasilicate, e.g. commercial sodium silicate in aqueous solution; and acid added to the required pH. Copper salts specified are the nitrate, sulphate, acetate and chloride and acids are nitric and phosphoric. The acid may be added to the copper salt solution before the addition of the alkali metal silicate or after precipitation of the copper silicate. Copper silicate may be separated and washed with acid until the washings have the desired pH. Preferably the copper salt solution does not considerably exceed 25 per cent conc. and likewise the silicate does not exceed per 5 cent. The copper silicate is not washed free of acid before drying. In a further modification copper silicates are made in which the copper exceeds that stoichiometrically required for the replacement of the metal in the alkali metal silicate by divalent copper. Preferably an excess of 20-100 per cent is obtained. In the preparation of such silicates an excess of copper salt, e.g. nitrate, chloride or sulphate, solution is reacted with the alkali metal silicate. Preferably a dilute aqueous solution of the salt is added to a cold solution of the alkali metal silicate in concentrations similar to those of the previous modification. The copper silicate is dried and used without any substantial washing. In examples (1) copper silicate is made from copper nitrate and sodium metasilicate, (3), (4) and (5) nitric acid treated copper silicate are made from the reactants of (1) and in (6) and (8) copper silicates containing excess copper are made. Specifications 625,330, 648,386, 655,210 and 658,179, [Group IV(b)], are referred to.