Browsing by Author "Kojima, M"

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    Diffusion and adsorption in zeolite Y and mordenite deactivated by propene oligomerization and hexane cracking.
    (Elsevier, 1994) Möller, K P; Kojima, M; O'Connor, C T
    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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    The oligomerization of propene over nickel synthetic mica-montmorillonite
    (1987) Jacobs, Lester Lance; O'Connor, Cyril; Kojima, M
    The catalytic oligomerization of propene to liquid fuels using synthetic mica montmorillonite (SMM) as well as the effect of incorporating nickel into the lattice and nickel, cobalt and zinc into the interlayer spaces was investigated. NiSMM is more active for propene oligomerization than SMM, although the product selectivity (60% of the oligomers boiled at above 453 K) is similar. The increase in activity of NiSMM is attributed to an increase in the surface acidity of the catalyst. The maximum activity over the nickel exchanged catalyst occurs at a nickel loading of 0.057 wt %. It is proposed that the bond strength of the acidic hydroxyl groups are perturbed by the polarizing effect of the divalent cation (Co, Zn or Ni) present in the interlayer spaces of SMM. The reduction of nickel, ion exchanged into SMM, removes the induction period associated with SMM and increases the catalyst lifetime. However, reduction of the lattice nickel results in a decrease in catalyst lifetime although the Bronsted acidity has increased. It is proposed that the metallic nickel present in reduced NiSMM may promote dehydrogenation of high molecular weight hydrocarbons thus causing rapid deactivation of the catalyst by increasing the formation of "graphitic" coke. The lifetime of NiSMM is greatly reduced by using a wet propene feed and reacting at higher temperatures (443 K) due to the generation of Bronsted sites and increased coke formation rates, respectively. Deactivation of the catalyst is associated with a "graphitic" coke build up. The RON of the petrol fraction is 94.5 and the hydrogenated diesel fraction has a cetane number less than 35.