Comparison of large pore zeolites for n-octane hydroisomerization: Activity, selectivity and kinetic features

The hydroisomerization of n-octane has been catalyzed by different zeolitic structures with large pore size (12 MR). It has been seen that channel topology, chemical composition, crystal size, and adsorption proper-ties are of paramount importance for improving the isomerization activity and selectivity. Nanocrystalline beta zeolite (30 nm) with large pore size (0.66 x 0.67 and 0.56 x 0.56 nm), and high aluminum content (Si/Al= 16), was the best catalyst to produce multibranched isomers. Cracking reactions also occur together with isomerization and the product distribution will depend on the rate constant and relative activation energies of isomerization, desorption, and cracking. Furthermore, a complete kinetic study of n-octane isomerization has been carried out with beta zeolite, and kinetic rate constants, heats of adsorption, and activation energies have been determined for each individual isomerization step. The rate of isomerization of n-octane to monobranched products was found to be faster than the rate of cracking of dibranched products and the rate of isomerization of mono- to dibranched products. It should be possible to obtain high yields of dibranched alkanes by distillation and recycling units, or by using membrane reactors.