Isomerization of 1-pentene over SAPO, CoAPO (AEL, AFI) molecular sieves and HZSM-5

Skeletal isomerization of I-pentene was carried out over SAPO and CoAPO mol ecular sieves with AEL and AFI type structure and for comparison over AlPO- 11 and HZSM-5. The equilibrium distribution within the linear pentenes and iso-pentenes was established over all catalysts except at very low temperat ures or conversions. The approach to the equilibrium distribution between t he Linear pentenes and iso-pentenes depends on the strength of the acid sit es, the pore dimensions and the structure of the catalyst. Over AlPO4-11, a material with very weak acid sites, the selectivity to skeletal isomerizat ion was only 5%, while the double bond isomerization and the isomerization via methyl shift were in equilibrium. Over SAPO-11 and CoAPO-11, having med ium strong acid sites and one-dimensional pores with a 10-membered ring-sys tem, the distribution of linear and iso-pentenes was near the equilibrium. On SAPO-5 and CoAPO-5, materials with sites of similar strength and one-dim ensional pores with a 12-membered ring-system, the equilibrium distribution was not achieved because of the rapid deactivation that diminished the acc essibility of the acid sites inside the pores. Due to the presence of stron g acid sites and a two-dimensional pore system with a 10-membered ring-syst em, the equilibrium distribution is achieved on HZSM-5, but this 'pentene p ool' react further by dimerization and cracking. (C) 2001 Elsevier Science B.V. All rights reserved.