The cracking of cyclo pentane and n -pentane on a silica-alumina catalyst

Abstract

The cracking of cyclo pentane on silica-alumina was studied in a flow system over the temperature range 493 to 603 °C with the use of the same catalyst and experimental methods as previously described by Kemball & Rooney (1960). The partial pressures of the gaseous products were estimated at a series of points along the catalyst bed and an analysis of the end-liquids was also made in some of the experiments. Similar studies were carried out on the cracking of n -pentane at 548 and 585 °C. Many differences were noted between the amounts and the nature of the products from these saturated reactants and those observed previously from cyclo pentane. These are ascribed to the relatively small amounts of polymerization which occurred slowly and autocatalytically from the saturated reactants compared with the rapid and extensive polymerization with the olefin. Minor differences between the results for n -pentane and cyclo pentane are attributed to the difficulty of cyclization of the adsorbed species from the former reactant. The mechanisms of the reactions are discussed and it is suggested that the formation of olefins and carbonium ions occurs reversibly from saturated compounds at Lewis acid sites. The removal of hydrogen from the surface phase is a key factor governing the extent of polymerization which can occur. While C 2 -, C 3 - and C 5 -products are formed from C5-carbonium ions, all other products including hydrogen, methane, C 4 -hydrocarbons and aromatic compounds originate mainly from polymeric species on the surface.