Browsing by Author "Kojima, Masami"

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    A kinetic study of the oligomerization of propene, butene and various hexenes over solid phosphoric acid
    (1987) McClean, Deaghlan Martin; O'Connor, Cyril T; Kojima, Masami
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    The deactivation of Zeolite-Y and mordenite during hexane cracking and propene oligomerisation
    (1989) Möller, Klaus Peter; Kojima, Masami; O'Connor, Cyril T
    The objective of this study was to determine the effect that the type of catalyst and reaction would have on the rate of deactivation, properties of coke and transport properties of the catalyst. HY and HM were chosen because of their different pore structures and acid site distributions. Hexane cracking at 1 atmosphere and high pressure propene oligomerisation provided two different reaction types. The transport properties of the catalysts were compared by measuring adsorption and diffusion using the GC technique with ancillary information obtained from ammonia TPD, mercury porosimetry and BET surface area measurements. It was confirmed that a knowledge of the crystallite size distribution was necessary to predict the adsorption and diffusion of light hydrocarbons in HY and HM. The adsorption constants and heats of sorption were found to,be much greater in HM than in HY, in agreement with the presence of a greater number of strong acid sites detected in HM by ammonia TPD. The diffusivities of the Tight hydrocarbons were too large to measure in HY. In HM only methane diffusion was too fast to measure. Diffusivities decreased and adsorption constant increased with increasing molecular size. HY had greater activity and slower deactivation than HM towards hexane cracking. The reaction as well as coking took place in the micro-pores. The graphitic coke content of HY was much greater than in HM. The introduction of the macro-pore adsorption term was necessary to predict diffusion in coked samples, emphasizing the severity of the diffusional resistance. While hydrocarbon diffusivities decreased after cracking, adsorption constants were found to increase in the presence of graphitic coke in J-IY. In HM the deactivation took place primarily by pore blockage, with strong acid sites being preferentially removed. Both diffusivities and adsorption constants decreased in the presence of coke in HM. In HY and HM deactivated by oligomerisation, macro-pore adsorption had to be taken into account, again emphasizing the severe diffusional resistance. Reaction as well as graphitic coke occurred predominantly in the micro-pores in HY. High boiling point hydrocarbons were able to migrate into the mesopores where they closed the mouths of the micro-pores in HY. Strongly adsorbed high boiling point hydrocarbons which deactivated the catalyst presented far less diffusional resistance in HY than the equivalent mass of graphitic coke. These high boiling point hydrocarbons also markedly lowered the adsorption constants. Graphitic coke was responsible for the modification of the catalyst selectivity. Temperature runaway in HY caused severe coking and hence deactivation. The inactivity of HM below 200°C was caused by strong adsorption and high diffusional resistance of reactant and product. Pore blockage was the dominant deactivation mechanism in HM, while in HY it was partial pore blockage by graphitic coke and pore mouth closure by high boiling point hydrocarbons. It was possible to restore the activity of HY for oligomerisation by flushing the high boiling point hydrocarbons in flowing nitrogen.
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    Methanol conversion to olefins and propene oligomerization over modified SAPO-34 and dealuminated mordenite
    (1992) Van Niekerk, Miles; Fletcher, Jack; O'Connor, Cyril T; Kojima, Masami
    SAP0-34 and mordenite, catalysts with quite different pore structures, are known to be suitable for methanol conversion to light olefins and propene oligomerization to a distillate type product, respectively. In this study, these catalysts were modified in various ways and the effect of these modifications on the activity and selectivity of the above two reactions investigated. SAP0-34, a small-pore silicoaluminophosphate molecular sieve, is highly selective in the formation of ethene and propene from methanol, but deactivates rapidly due to coke formation. This catalyst was synthesized and modified in various ways in an attempt to increase the catalyst lifetime and selectivity to ethene. Mild hydrothermal conditions encountered during deep-bed calcination of SAP0-34 were found to increase the catalyst lifetime. A number of further modifications were made to this deep-bed calcined material in an attempt to increase further the lifetime of this material. These modifications were : (i) Silanization - in order to neutralize the acidity on the external surface of the crystallites and hence reduce pore-mouth blockage by coke species on the crystallite external surface; (ii) Steaming - to investigate the effect of more severe hydrothermal conditions than those encountered under deep-bed-calcination conditions; (iii) Acid site poisoning by ammonia - in an attempt to reduce the rate of coke formation which takes place readily on strong acid sites; (iv) Boron impregnation - in order to reduce the intercrystalline void volume and thereby sterically hinder the formation of bulky coke molecules within the SAP0-34 pores; (v) Acid and caustic treatments - in order to reduce the catalyst acidity and thereby limit the rate of the coke formation reaction.
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    The oligomerisation of propene over nickel oxide silica alumina
    (1987) Harms, Stefan Mathias; Kojima, Masami; O'Connor, Cyril T
    A synthesis techniQue was developed for the preparation of a nickel oxide sil ica alumina catalyst. The propene oligomerisation activity and the selectivity of the catalysts prepared by homogeneous decomposition deposition (HDD) were investigated and compared with nickel oxide silica alumina catalysts prepared by the techniQues of impregnation (IMP) and co-precipitation (SG). Amongst others. the effect of the nickel content. reacti6n temperature and pressure, and water content of the feed, on the activity and selectivity. were investigated. Also investigated were the lifetime of the various catalysts and, in the case of HDD type catalysts. the ability to oligomerise high molecular weight hydrocarbons (Cb). Nickel oxide silica alumina prepared by the HDD method is more active for the propene oligomerisation than catalysts prepared by the IMP and SG methods. The product spectrum in the case of IMP and HDD type catalysts are similar, with a propene dimer (Cb) being the main product. In the case of SG type catalysts. however. a shift to heavier products was observed, i.e., propene dimer (Cb) and trimer (Cq) were formed in eQual Quantities. It is proposed that the increase in activity of HDD type catalysts was due to a large extent of metal dispersion and distribution and a stronger interaction between the metal and the support. It is also proposed that the metal is readily accessible to the reactant molecules. The activity and selectivity of catalysts prepared by the HDD method were independent of the nickel content. This was not the case for IMP and SG type catalysts. both of which showed decreasing activity with increasing nickel content when the nickel content was increased beyond 5 wt%. The lifetimes of the various catalysts were also examined. From the results obtained. over the first 10 h. the lifetime of HOD type catalysts was superior to that of the other catalysts studied. The activity and selectivity of the various catalysts were sensitive to the reaction conditions. Thus moving into the vapour phase. by either increasing the temperature at a fixed pressure or decreasing the pressure at a fixed temperature. was in each case acCompanied by a shift to heavier products and a decrease in activity.
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    The oligomerization of propene over cobalt catalysts
    (1987) Dickens, Paul Michael; Kojima, Masami; O'Connor, Cyril T
    This thesis set out to investigate the activity of various supported cobalt catalysts for high pressure propene oligomerization. This work was carried out as part of a larger research effort to upgrade light olefins to liquid fuels in the distillate range. The supports investigated included activated carbon, alumina, silica alumina, synthetic mica montmorillonite, zeolite Y and NH₄⁺-ZSM-5. A cobaltmolybdenum hydrodesulphurization catalyst was also tested. The synthesis procedures used in this work included double ammoniation (Co-C), incipient wetness impregnation (Co-C, alumina, NH₄⁺-ZSM-5), ion-exchange (NaY, NH₄⁺-ZSM-5), chemisorption (cobalt complex on activated carbon) and homogeneous deposition-precipitation (Co-Silica alumina).
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    Propene oligomerization over steam dealuminated and boron and phospherous modified ZSM-5
    (1991) Andersen, Bo; O'Connor, Cyril T; Kojima, Masami; Fletcher, Jack
    ZSM-5 was modified with boron and phosphorus compounds in an attempt to improve the selectivity of the catalyst with respect to the linearity of the liquid product of propene oligomerization. Boron was incorporated into the zeolite framework by inclusion in the synthesis gel. Boralite catalysts made in this way and containing very low Al contents had only weak acidity as was evident from only one, low temperature NH3 desorption peak at ca. 190 °C. These catalysts showed poor propene oligomerization activity as a result of the weak acidity arising from the weak B(OH)Si site and reduced catalyst free volume. The latter was ascribed to occluded B₂O₃ species. Activity of these catalysts was proportional to Al, rather than B content. No appreciable selectivity changes were observed for any of these catalysts. In an attempt to enhance the acidity and hence the activity of the boralite catalysts, mild fluorination treatments were carried out. A boralite catalyst containing 550 ppm Al and 1.2 wt% boron was treated with mild HF at room temperature. The activity of the catalyst was significantly reduced. The activity of the catalyst was essentially restored to its former level upon subsequent NH₄F treatment. The catalyst then contained 120 ppm Al and 0.8 wt% boron. Although some activity enhancement was achieved through mild fluorination, the catalyst utilization values (CUV) remained an order of magnitude lower than the CUV of unmodified ZSM-5. Catalytic activity remained proportional to trace Al content.
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    Synthesis, characterisation and catalytic testing of pillared clays and lanthanum exchanged ZSM-5 for hydrocarbon conversion
    (1989) Hartford, Radleigh; O'Connor, Cyril T; Kojima, Masami
    Pillared clays present interesting possibilities for use as acid catalysts. The present research investigated the effect that pillaring has on the physical and catalytic properties of some smectite clays. The effect of using a hydroxy-Al solution to pillar a predominantly octahedrally ,substituted clay (montmorillonite) and a tetrahedrally substituted clay (beidellite) were compared. The effects of pillaring tetrahedrally substituted clays with different swellable properties (beidellite, SMM, and Ni-SMM) were investigated. In an attempt to enhance the acidic properties of the pillars, montmorillonite was pillared with a hydroxy-Al solution containing tetraethyl orthosilicate. Montmorillonite was also pillared with a hydroxy-Ni/Al solution in an effort to produce a clay with an increased pillar density. The pillared and unpillared clays were characterised using x-ray diffraction, surface area measurements, thermogravimetric analysis and ammonia TPD. The possible shape selective properties of the different clays for the conversion of trimethylbenzene were investigated, and the catalytic activities and product selectivities of these clays for high pressure propene oligomerisation were studied.