Deactivation of solid acid catalysts during isobutane alkylation with C4 olefins

Abstract

Coke formation on solid acid catalysts during isobutane alkylation with C4 olefins was studied. Y-zeolite, mordenite and L-zeolite were investigated, as well as sulfated zirconia catalysts. Zeolites were used in protonic form or after ion exchange with lanthanum nitrate. Studies were carried out in liquid phase in a fixed-bed reactor. It was found that Y-zeolite exchanged with lanthanum, being the catalyst with the best stability, is the catalyst that forms higher quantities of carbonaceous deposits. The amount of coke on this catalyst can be as high as 13–14%. This coke requires temperatures higher than 500°C to be completely eliminated. Temperature-programmed analyses indicated that the amount of coke eliminated from the catalyst during partial regeneration, strongly depends on the heating rate. This is due to a competition between coke gasification and its modification in structure leading to an aromatic type of coke, which then requires higher temperatures to be burnt. Pore and surface area measurements carried out on deactivated catalysts suggest that a pore plugging mechanism takes place during the reaction. Catalysts with too strong acidity (e.g. protonic form of Y-zeolite or sulfated zirconia) have no activity for trimethylpentane production at 80°C, most probably due to a very fast deactivation, even though the amount of coke is notably lower than in the lanthanum-exchanged zeolites.