Abstract
The bidisperse pore diffusion model applied to the pulse gas chromatography (PGC) technique was used to determine the effect of coke formation on the diffusion and adsorption of propane, n-butane and isobutane in the pores of zeolite Y (HY) and mordenite (HM) before and after deactivation during hexane cracking and propene oligomerization. The catalysts were characterized using TPD, TG/DTA, BET and pore volume measurements. Tracer diffusion measurements taken before and after reaction showed that in the case of hexane cracking over HY the diffusivity decreased by more than three orders of magnitude while the tracer adsorption 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 propene oligomerization, the diffusion was an order of magnitude faster than in the case of the catalyst deactivated by hexane cracking, while the adsorption equilibrium constant decreased. HM deactivated by oligomerization showed macropore behaviour. Proposals are made to explain the above observations.
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