DIFFUSION AND ADSORPTION OF ZEOLITE-Y AND MORDENITE DEACTIVATED BY PROPENE OLIGOMERIZATION AND HEXANE CRACKING

The bidisperse pore diffusion model applied to the pulse gas chromatog raphy (PGC) technique was used to determine the effect of coke formati on on the diffusion and adsorption of propane, n-butane and isobutane in the pores of zeolite Y (HY) and mordenite (HM) before and after dea ctivation during hexane cracking and propene oligomerization. The cata lysts were characterized using TPD, TG/DTA, BET and pore volume measur ements. Tracer diffusion measurements taken before and after reaction showed that in the case of hexane cracking over HY the diffusivity dec reased by more than three orders of magnitude while the tracer adsorpt ion equilibrium constant increased. In the case of HM, the diffusivity decreased by five orders of magnitude and the adsorption equilibrium constant also decreased by a factor of 10. In HY, deactivated during p ropene oligomerization, the diffusion was an order of magnitude faster than in the case of the catalyst deactivated by hexane cracking, whil e the adsorption equilibrium constant decreased. HM deactivated by oli gomerization showed macropore behaviour. Proposals are made to explain the above observations.