Browsing by Author "O'Connor, C T"

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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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    Effect of acid and steam treatment of Na- and H-mordenite on their structural, acidic and catalytic properties.
    (Elsevier, 1995) O'Donovan, A W; O'Connor, C T; Koch, K R
    A systematic study of the effect of acid washing of sodium mordenite (Na-MOR) and hydrogen-exchanged mordenite (H-MOR), both before and after steaming, has been carried out. The study investigated the formation and removal of extra-framework aluminium and the effect of dealumination on the acidity and isobutane cracking activity of the mordenite. Washing ammonia-exchanged mordenite (NH4-MOR), which has been calcined at 550°C, with deionised water resulted in an increase in extra-framework octahedral aluminium (EFAl-o). The corresponding decrease in tetrahedral aluminium and the sharp drop in catalytic activity is ascribed to the hydration of strong acid sites. Both acid washing and thermal treatment of Na- and NH4-MOR produced EFAl-o. A systematic study of the washing of Na- and H-MOR with nitric acid of increasing concentrations showed that a maximum occurrence of EFAl-o was reached by washing with 0.001 N acid in the case of H-MOR. Thereafter EFAl was removed with little accompanying framework dealumination up to an acid wash concentration of 1 N. Further washing up to 10 N removed large amounts of framework aluminium. A maximum in catalytic activity for isobutane conversion was observed for a sample washed with 1 N acid. Generally, however, catalytic activity increased with the number of framework acid sites. Extra-framework tetrahedral aluminium (EFAl-t) and penta-coordinated aluminium (Al-p), both produced by steaming, reduced both the catalytic activity and the number of framework acid sites. These aluminium species were progressively removed by increasing strength of acid washes. The number of Brönsted and strong Lewis acid sites as determined from ammonia temperature-programmed desorption (TPD) were found to be essentially equal to the amount of framework aluminium not charge-balanced by non-framework cations such as sodium and tetrahedral extra-framework aluminium.
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    Effect of activation procedure and support on the reductive amination of ethanol using supported cobalt catalysts.
    (Elsevier, 1997) Sewell, G; O'Connor, C T; van Steen, E
    The reductive amination of alcohols using ammonia catalyzed by supported cobalt catalysts has been studied. The catalytic activity for ethanol conversion is shown to be directly proportional to the exposed metal surface area, indicating that the activation of ethanol is metal-catalyzed and no metal-support effects were detected. The selectivity to the mono-, di-, and triethylamine varies with temperature, reactant partial pressures, and extent of reactant conversion generally as expected for a series-type reaction scheme. Both the activation procedure and the type of support also influence selectivity. Increasing the acidity of the support favors the formation of monoethylamine, probably due to disproportionation of diethylamine on the acid sites of the support indicating the bifunctionality of the catalyst.
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    A quality control model for the development of high-confidence flotation test data
    (1995) Lotter, Norman Owen; O'Connor, C T
    This thesis addresses the problem of obtaining reliable laboratory scale flotation test data for the Merensky ore type found in the Bushveld complex of South Africa. The complex nature of the platinum-group element (PGE) deportment in this ore renders the normally-practiced procedures inappropriate for this particular testwork. A more robust and thorough procedure is necessary because of the diverse mineralogical forms in which the PGE are found. The evaluation of the mass and value balances has accordingly to take these factors into account. The major features of the evaluation of input and output errors across the laboratory scale flotation test are analysed. It is found that unless size-by-size variance of PGE in a conventionally crushed mill feed is taken into account the mill feed sample size is underestimated by some 176%. Further the preparation of a reference distribution of assayed head material is necessary to provide the 95% confidence limits of grade estimate. The need for repeating flotation tests and compositing the adjudicated products is discussed, concluding that quintuplicates are suitable to achieve a desirable level of confidence in the built-up head grade. The sample preparation of the flotation products has a critical role in minimising evaluation errors, as is the case with fire assaying of samples where minimum numbers of replicate determinations have been calculated. An outlier rejection model for adjudication of the replicate built-up head grades is proposed, and a complete flowsheet of the quality control model is developed from first principles. The effect of this model on the PGE total balance is analysed. It is concluded that workable controls are defined, since a metal balance with < 1% error has been achieved.
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    The transformation of 1,2,4-trimethylbenzene A probe reaction to monitor external surface modifications of HZSM-5?
    (Elsevier, 1997) Röger, H P; Möller. K P; O'Connor, C T
    The transformation of 1,2,4-trimethylbenzene is proposed as a new probe reaction to monitor the catalytic effects of inertisation of the external surface of HZSM-5. The external surface has been modified by coating ZSM-5 crystallites with an inert silicalite shell. At 723 K and a WHSV of 0.6 h−1 it has been shown that the isomerisation products 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene reflect changes in external activity. The disproportionation products, 1,2,4,5-tetramethylbenzene and 1,2,3,5-tetramethylbenzene together are shown to indicate changes in overall activity and shape selective properties of the catalyst sample. The results correlate with those observed for the reaction of 1,3,5-triisopropylbenzene and n-hexane cracking.