Browsing by Author "O'Connor, Cyril T"

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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 catalytic conversion of low chain length hydrocarbons to liquid fuels using ion exchange resin
    (1984) Schumann, Werner Karl; O'Connor, Cyril T
    The use of ion exchange resins in the polymerization of a c 4 -mixture to liquid fuels has shown that the catalyst is highly active, deactivates at a slow rate and selectively produces mainly dimers. Macropore diffusion resistance strongly influences the overall rate of the reaction. An increase in liquid production rate is obtained with increasing macroporosity, increasing degree of functionalization and decreasing catalyst bead size. A minimum acid strength of pKA = -2.4 is required. The liquid production rate is increased by increasing the reaction temperature and weight hourly space velocity. Moreover, longer chain length product are obtained with increasing reaction temperature and at reaction conditions, which result in the complete conversion of monomers. Recycling liquid product reduces the liquid production and increases the production of trimer at the expense of dimer. At moderate reaction temperatures ion exchange resins are regenerable but the activity of the catalyst is destroyed at reaction temperatures greater than approximately 130°C. Deactivation occurs parallel to the main reaction and is due to cationic fouling. The liquid product obtained is highly branched. The R.O.N. of the -180°C fraction is approximately 97 and the cetane number of the +180°C fraction approximately 35.
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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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    The determination of the effects of physical and chemical parameters on the column flotation cell, performance in the flotation of pyrite
    (1991) Schommarz, Klaus Helmuth; O'Connor, Cyril T
    This masters dissertation an column flotation is to determine the effects of physical and chemical parameters on the column flotation cell performance in the flotation of pyrite. Hypotheses are also proposed to explain observed changes. Chapter one gives a brief description of flotation columns, some applications of flotation columns and a literature survey that covers the effects of various physical and chemical parameters. Chapter two states the objective of this research and the plan of action used to achieve this objective. Chapter three describes the first part of the plan of action, namely to design a laboratory flotation column and to draw up an experimental procedure. A flotation column rig with an adequately repeatable experimental procedure is the result. The repeatability and sensitivity of the experimental procedure is given in chapter four. This chapter also includes the results obtained when the physical and chemical parameters are varied. The effects on the flotation cell performance by varying parameters are summarised. The biggest changes observed in the flotation column cell performance are as follows: 1) An increased air rate yields an optimum sulphur recovery. 2) Concentrate sulphur grades decrease when the air rate is increased. 3) The concentrate grades increase when the froth depth is increased. 4) Increasing the feed solids percent to the flotation column has no effect on the concentrate grades and recoveries as long as the column is operated below its maximum carrying capacity. 5) The concentrate grades are improved by adding wash water. Chapter five then discusses the changes observed in the flotation column cell performance. Chapter six covers the design of a pilot plant flotation column rig, the results obtained on plant and the discussion of these results. It is found that the pilot plant rig can be effectively used for on site test work. The flotation column cell performed better than the conventional cells. The pilot plant test work showed that: 1) Increasing the air rate increases the recovery. 2) Increasing the wash water rate improves the concentrate grades. Finally, in chapter seven, conclusions are drawn regarding the results and discussions. Some of these conclusions are: 1) The flotation column cell performes better than conventional flotation cells due to the column's deep water washed froth and counter-current contact mechanism. 2) Increasing the air rate decreases the grades of the concentrate due to increased entrainment, while the recovery moves through an optimum. 3) Increasing the froth depth increases the concentrate grades due to a longer cleaning action. For the same reason the recovery decreases. 4) The feed solids percentage has no effect on the grade or recovery. Should the maximum carrying capacity however be reached the recovery will drop. 5) Froth stability is essential for good concentrate grades and recoveries. 6) Increased wash water rates increase the concentrate grades due to a stronger washing action and more stable froths. 7) The chemical parameters which are varied show the same trends as was observed in conventional flotation. All data obtained during the test work is attached in the appendices.
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    The effect of electrolytes on the flotation of pyrite
    (1983) Barker, Louise Madeleine; O'Connor, Cyril T
    In the flotation of pyrite a minimum concentration of any ions is necessary to stabilize the froth and thus produce a reasonable recovery of pyrite. In the absence of ions a "dry froth" is formed which results in a decreased mass pull and thus a low pyrite recovery. The predominant effect of an .increased concentration of univalent ions was a decrease in ·the formation of "dry froth" during flotation which resulted in an increase in pyrite recovery. This was due to the increase in froth stability with the addition of ions and was verified in the two and three phase froth stability tests. The predominant effects of the divalent ions were: (i) an increase in froth stability resulting in increased pyrite recovery (ii) a sharp increase in grade due to a decrease in gangue recovery (iii) a decreased rate of flotation. The decrease in gangue recovery was possibly due to the effect of the ion on the compression of the electrical double layer resulting in coagulation of the quartz particles. The slow rate of flotation was ascribed to the slow rate of the ascent of the heavily mineralized bubbles. This increase in bubble mineralization could be due to coagulation of pyrite in the pulp phase. The adsorption of the collector, sodium ethyl xanthate, on pyrite was not affected by the univalent or divalent cations but decreased with the addition of the nitrate anion. However these variations in xanthate adsorption did not seem to have a significant effect on the flotation of pyrite. Flotation experiments using oxidised ore showed a reduced pyrite recovery compared with the leached ore. This was ascribed to the low xanthate adsorption and the low natural floatability of the ore.
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    The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite
    (1995) O'Donovan,Anthony William; O'Connor, Cyril T
    Although there have been a number of studies of the effect of hydrothermal and acid dealumination on the properties of Mordenite, there is a lack of clarity on many issues related to the changes which these treatments cause to the structure, acidity and catalytic activity of Mordenite. Both methods remove aluminium from the framework thus creating extra framework aluminium species. Although there are some reports that these species, particularly when created by mild steaming, increase the acidity and catalytic activity of the dealuminated sample, it has also been reported that these species have either a negative or no effect on thecatalyst's acidity and activity [Mirodatos and Barthomeuf, 1981; Chen eta/., 1992; Meyerseta/., 1988; Bamwenda eta/., 1994; Brunner eta/., 1994]. These conflicting reports are understandable when one considers that the dealumination conditions in the various studies are usually not equivalent to each other and consequently the resultant catalysts may differ. The use of Mordenite from different sources to compare acidity in one case and structure in another may also lead to different and conflicting results. This has affected the interpretation of observed trends in the structure, acidity and catalytic behaviour of dealuminated Mordenite. A systematic study of the effect of acid washing of sodium Mordenite and hydrogen exchanged Mordenite, both before and after steaming, has been carried out. The bulk removal of aluminium was monitored by elemental analysis of samples. The study investigated the effect of different conditions of acid washing, steaming and steaming followed by acid washing on the solid state properties of Mordenite by use of solid state ²⁷AI and ²⁹Si nuclear magnetic resonance, x-ray diffraction and infrared techniques. The effect of these changes on the number, type and strength of acid sites in Mordenite was then investigated by ammonia temperature programmed desorption, Fourier-Transform infrared analysis of pyridine adsorption and proton nuclear magnetic resonance studies. The changes caused by dealumination to the catalytic activity and shape selective properties of Mordenite as determined by studies of isobutane cracking, cyclohexanol dehydration and isopropylation of naphthalene, were then explained in terms of the acidic and structural properties of the dealuminated Mordenite samples.
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    Methanol amination over hydrothermally treated zeolites RHO and Modernite
    (2000) Van Steen, Linda Heather Callanan; O'Connor, Cyril T; Van Steen, Eric
    Methylamines are important chemicals in many industrial processes. They have use as intermediates for the production of many compounds containing amino groups as well as being used on their own. The acid catalysed amination of methanol generally yields a thermodynamically controlled product distribution. The equilibrium distribution for mono-, di-, and trimethylamine (MMA, DMA, and TMA), at 325°C and a molar methanol to ammonia ratio of 1, is 17, 21, and 62 mol % respectively. The market demand, on the other hand, is for about 33, 53, and 14 mol % MMA, DMA and TMA. Industrially, methylamines are formed by the reaction of methanol or dimethyl ether and ammonia over amorphous silica-alumina. This process involves large separation and recycle units which are both costly and energy intensive as the separation requires azeotropic distillation at 15 bar. Methylamines can be formed over other solid acid catalysts with definite crystal structures, namely zeolites. While being more active than amorphous silica-alumina, most zeolites do not show improved selectivity. Catalysts, which have, however, been reported to show improved selectivity to DMA, include zeolites Rho, ZK-5 and Chabazite. In addition, certain forms of hydrothermally treated Mordenite can produce nonequilibrium product distributions. The performance of Rho can also be improved with hydrothermal treatment. The objectives of this study were briefly as follows. Firstly, the question was asked as to which of the catalysts studied, viz. Rho and Mordenite, was the most suitable for the methanol amination reaction. The second objective was to find the optimal performance achievable from any catalyst using hydrothermal treatment. The third, and possibly most important, objective was to propose reasons for the changes caused to each catalyst by hydrothermal treatment.
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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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    Modelling of the mixing characteristics and flotation kinetics of the collection zone in flotation columns
    (1992) Mills, Peter John Temple; O'Connor, Cyril T
    Column flotation has gained worldwide acceptance in the minerals processing industry in the past decade. This has been due the operating characteristics of flotation columns which can produce improved grades and recoveries over conventional cells. Added to this, flotation columns are both simple to operate and generally less expensive than the equivalent requirement of conventional cells. Flotation columns are able to produce improved results due to a deep washed froth phase and a quiescent pulp phase in which the pulp interacts countercurrently with the air bubbles. Models describing the behaviour of particles in both of these phases have been developed over the past decade. The present study focusses specifically on the pulp phase and models presently used to describe the pulp zone hydrodynamics and kinetics are evaluated and improved. The hydrodynamics of the pulp or collection zone are evaluated using data obtained from three residence time distribution (RTD) studies performed on two pilot columns (5.4cm and 5.8cm diameter) and an industrial column (120cm diameter). Sodium chloride liquid tracers as well as radioactively labelled solid and liquid tracers were used in the RTD studies. In the study performed on a pilot column using the salt tracer the degree of mixing was found to increase both with increasing gas rate at constant bubble size and decreasing bubble size at a constant gas rate. This increase in mixing is attributed to the increase in the number of bubble$ and the subsequent increase in the tracer-bubble interactions. By extrapolating this result to industrial columns it is clear that flotation columns, which have smaller and substantially more bubbles, will be more mixed than bubble columns.
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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.
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    Synthesis, characterization and high pressure propene oligomerization over heteropoly acids, SAPO-11 molecular sieves and MeAPSO-11 molecular sieves
    (1993) Vaughan, James Stuart; O'Connor, Cyril T; Fletcher, Jack C Q
    Heteropoly acids, HPAs, and SAPO-11 and MeAPSO-11 molecular sieves have been proposed to be active for the oligomerization of propene to high quality distillate fuels. In this study these catalysts have been synthesized, characterized, modified and screened for the oligomerization of propene to distillate fuels. Heteropoly acids consist of high molecular weight poly-oxoanions, counter cations and water of hydration and are strongly acidic. The following salts of 12-tungstophosphoric acid, a 12-type HPA with the Keggin anion structure, were synthesized: AI, Fe, Ce, Ni, Co, Cu, K and NH₄, as well as the AI and NH₄ salts of 12-tungstosilicic acid. Physicochemical characterization of the HPA salts revealed that, depending on the counter cation, these salts exhibited different thermal characteristics and surface areas. The salts were classified into two types, viz.: Type A:- low surface area salts, typically less than 15m²/g, with multiple endothermic mass losses (e.g. AI, Fe, Ce, Ni, Co, Cu) and; Type 8:- high surface area salts, typically 35-150 m²/g, with a single endothermic mass loss (e.g. K and NH₄). The Type A salts were multi-crystalline, consisting of more than one phase, and exhibited a non-uniform morphology. The Type B salts, on the other hand, were uniformly crystalline and consisted of small rounded cubic crystallites. Ammonia desorption, monitored by both TCD and FT-IR, revealed that both the Type A and B salts were strongly acidic with the majority of the ammonia being released only upon decomposition of the salt. However, as ammonia and other polar molecules are known to readily absorb into the bulk of HPAs, the ammonia TPD results did not correlate with catalytic activity for surface type reactions such as alkene isomerization and oligomerization. The Type B salts were active for cracking and skeletal isomerization reactions which suggested strong acid sites were present on their surface. The Type A salts only exhibited double bond shift isomerization activity, suggesting sites of only weak to medium acid strength.