Browsing by Author "Dry, Mark"

Now showing 1 - 9 of 9
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    Aromatization of alkenes by gallium/H-ZSM-5 zeolite catalysts
    (1994) Nash, Robin John; Dry, Mark
    Gallium/H-ZSM-5 zeolite catalysts have been extensively researched for the aromatization of liquified petroleum gas (LPG). In 1989 BP and UOP collaborated to commission a pilot plant in Grangemouth, Scotland, for the aromatization of propane and butane. This plant, based on a technology called the Cyclar process, used continuous catalyst regeneration (CCR) and a gallium impregnated ZSM-5 zeolite catalyst to achieve yields of ca. 65% aromatics, mainly benzene, toluene and xylenes (BTX) [Guisnet and Gnep, 1992]. As a result of the Fischer-Tropsch process used by SASOL Ltd., South Africa is in an internationally unique position, in that it has a surplus of long chain linear alkenes with carbon numbers in the range C6-C8 . There could be large economic incentives to convert these alkenes into more valuable products, like alcohols or aromatics. Thus the purpose of this project was to determine if gallium/H-ZSM-5 catalysts, similar to those used in the Cyclar process, would be suitable for the aromatization of long chain alkenes. Three methods were investigated for the introduction of gallium into ZSM-5: (i) physical mixing with gallium oxide; (ii) impregnation by incipient wetness with gallium nitrate; (iii) ion-exchange with gallium nitrate. The catalysts were. tested with regard to their catalytic activity for the aromatization of 1-hexene and 1-octene.
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    Aromatization over platinum/zeolite L catalysts : the effect of oxygenates
    (1997) Nash, Robin John; Dry, Mark
    In 1980, Bernard reported that platinum dispersed on zeolite LTL (Pt/KU had exceptionally high selectivity for the aromatization of n-hexane to benzene. The selectivity was ca. 95 at 99 conversion of n-hexane. This Pt/KL catalyst has been extensively studied to determine the reasons for the exceptional stability and benzene yields relative to platinum supported on silica (Pt/Si0₂ ) and alumina (Pt/Al₂0₃). The Pt/KL catalyst was found to be monofunctional with all the activity occurring on platinum metal clusters inside the pores of zeolite L. The catalyst exhibits excellent stability and the Aromax Process developed by Chevron Ltd., using I a barium doped Pt/KL catalyst, PtBa/KL, has been reported to operate continually for the equivalent of one year during accelerated deactivation testing at 450°C and a hydrogen partial pressure of 6 bar. However, sulphur-containing I compounds such as thiophene, result in rapid and irreversible deactivation of the catalyist due to sintering of platinum clusters. Thus the level of sulphur-containing I compounds, especially thiophene, must be kept below 50 ppb of the feed to avoid deactivation by sintering. SASOL Ltd. may be in a unique position to use Pt/KL as a catalyst for the aromatization of hexanes and heptanes to benzene and toluene respectively, as their products which are produced by the Fischer-Tropsch process are sulphur free. However, a substantial amount of oxygenates are formed in the Fischdr-Tropsch process and as yet no study has been undertaken to determine the effect of these compounds on the activity and selectivity of the catalyst.
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    Dehydrogenation of N-Propanol to Propionaldehyde over a copper chromite catalyst
    (1998) Hop, Marina; Dry, Mark
    Methyl methacrylate (MMA) is widely used for a range of polymer products. MMA can be produced from propionaldehyde via the BASF process. n-Propanol is readily available 'in South Africa as a byproduct of Fischer-Tropsch synthesis. This prompted an investigation into the production of propionaldehyde by the dehydrogenation of n-propanol. There is presently no established technology for the dehydrogenation of n-propanol to propionaldehyde and there has been very little work carried out on the effect of process variables on propionaldehyde yield. The emphasis of the current work was optimising propionaldehyde production. A commercial copper-chromite catalyst (G-13), for the dehydrogenation of ethanol to acetaldehyde, was used for the purposes of this study.
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    The effect of copper as a chemical promoter on the performance of a cobalt based Fischer-Tropsch synthesis catalyst
    (2000) Van Wyk, Gert Stefanus; Dry, Mark; Van Steen, Eric
    In the light of the fact that copper is used as a promoter for the iron catalyst and that the industry is looking at a commercial FT synthesis cobalt catalyst, it is essential to reinvestigate the effect of copper on a cobalt catalyst. Copper has an effect on the overall activity of iron and cobalt [Kolbel, 1951, J. Schwank, 1991], but the reasons are not clearly understood. In the present study the role of copper as a promoter on the performance of 16.67% (wt) Co/Si02 is investigated with TPR, CO chemisorption, TEM and FT synthesis.
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    Encapsulation of cobalt complexes in zeolite Y for use as hydroformylation catalysts
    (1997) Galatolo, Paul Joseph Victor; Moss, John; Dry, Mark; O'Connor, Cyril
    In industry, the hydroformylation reaction is predominantly homogeneously catalysed using carbonyl complexes of cobalt and rhodium (1-3,45). The main disadvantage of homogeneous catalysts is that, especially for the longer chain hydrocarbon systems, very energy-intensive methods (such as distillation) are required to remove them from the reaction products. These separation techniques usually lead to losses of the catalyst. From an economic viewpoint, this is highly undesirable since the catalysts (especially rhodium) are expensive. Research has been carried out on encapsulating the catalysts within the cages of a zeolite, maintaining the activity of the catalyst while allowing it to be easily removed from the reaction medium ( eg. by filtration). However, all research reported so far has only considered rhodium catalysts (1,66-71,87). Furthermore, in most cases, leaching of the rhodium from the zeolite was significant enough to be undesirable. No successful research has been reported on encapsulating cobalt in zeolites for use as a hydroformylation catalyst. In this study, the synthesis of cobalt complexes encapsulated in the supercages of zeolite Y was attempted. The species initially present on the zeolites were analysed by Fourier-Transform Infrared Spectroscopy (FT-IR) and identified by comparison with the IR spectra of pure cobalt complexes synthesised independently in the laboratory. The impregnated catalysts were washed with various solvents to see if the cobalt complex remained in the zeolite. The impregnated zeolites were also tested as hydroformylation catalysts and compared with homogeneous catalysts.
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    Hydroformylation of high temperature Fischer-Tropsch synthol products for the production of detergent alcohols
    (1996) Betts, Mark Justin; Dry, Mark
    The use of Synthol High Temperature Fischer-Tropsch (HTF-T) products as an inexpensive and alternative hydroformylation feedstock for producing Oxo alcohols has been investigated. These alcohols are precursors for biodegradable detergents. The HTF-T product targeted as a feedstock source was Synthol Light Oil (SLO), in the C₈ to C₁₂ range. The aim of the work was to identify a suitable hydroformylation catalyst system for use with SLO feeds. Process variables such as feed composition, temperature, pressure and contact time were investigated. Emphasis was placed on the determination of feed-catalyst compatibility; the development of a "working" kinetic model on a batch micro-reactor scale; and extrapolation of the results to a continuous catalyst testing unit. An integral part of the work therefore involved characterization and quantification of these complex hydroformylation systems, as well as the development of methods to achieve this goal.
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    Incorporation of Platinum onto Zeolite KL for aromatisation reactions
    (1994) M'kombe,Chamu Mark; Dry, Mark
    The main objectives of the work presented in this thesis were two fold - i) to determine the effect of varying various parameters on the platinum dispersion and ii) to determine the conditions that would yield the highest platinum dispersion on the zeolite KL. Loading of platinum onto the zeolite KL was mainly via liquid state ion exchange. Loading via impregnation and solid state ion exchange were also briefly investigated in order to compare these techniques with liquid ion exchange. After loading the platinum onto the zeolite KL the Pt/KL samples obtained were then calcined under different conditions in order to see the effect of calcination temperature, calcination medium, and calcination time on the dispersion of the platinum. After obtaining the optimum calcination conditions, a set of samples were then prepared under these calcination conditions and used to investigate the different reduction parameters. It was important to observe the effect of varying the different reduction parameters on the dispersion of the platinum. The parameters investigated during reduction were the reduction medium, the reduction temperature and the reduction time.
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    The oxidative reforming of methane to synthesis gas on a commercial steam reforming catalyst
    (1997) Theron, Johannes Nicolaas; Fletcher, Jack; O'Connor, Cyril; Dry, Mark; van Steen, Eric
    The oxidative reforming of methane to predominantly carbon monoxide and hydrogen was studied over a commercial steam reforming catalyst. The said reaction was performed in an integral fixed-bed reactor at temperatures between 575°C and 650°C at a total pressure of 200 kPa(a). The primary objective of the study was the design and construction of equipment to facilitate firstly, the measurement of axial bed temperature profiles, and secondly, the investigation of transport effects during the oxidative reforming of methane. The absence of internal or external temperature- and concentration gradients were tested by subjecting the experimental results to theoretical criteria that had previously been derived to check for transport limitations. In all cases the correlations confirmed that the experimental system was free of transport resistances. Having obtained differential reaction rates from the integral data, two LangmuirHinshelwood models were developed and fitted to the data. The model which was derived from the assumption that methane adsorption on a single active site was the rate-determining step, gave the best fit to the experimental data. Adsorption constants correlated in broad terms with the reaction orders of the species which were previously determined by the method of initial rates. The differential kinetic data that were obtained from the fitting of exponential curves to the integral data gave the best correlation between predicted and measured reaction rates. Subsequent to the differential treatment of the data, an attempt was made to correlate the integral data by means of an integral reaction model. A combination of the total oxidation-, oxidative reforming- and steam reforming of methane, as well as the water-gas shift reaction, resulted in the best fit between measured- and predicted data. The predicted methane, carbon monoxide- and hydrogen partial pressures correlated well with experimental data, but that of oxygen, carbon dioxide and water were less accurately predicted by the model. The lack of any comparable study in the literature made it impossible to compare adsorption- and rate constants to other work. X-ray diffraction results showed that the active catalyst bed consisted of a top layer of nickel oxide on alumina and zero-valent nickel on alumina deeper into the bed. Evidence from thermogravimetric experiments revealed that carbon formation was inhibited by H2 cofeeding and high 0 2 inlet partial pressures, but that it was enhanced by CO co-feeding.
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    The thermodynamics, mechanism and kinetics of the catalytic conversion of propylene and water to diisopropyl ether over amberlyst 15
    (1998) Heese, Frank Patrick; Dry, Mark; Möller, Klaus
    Diisopropyl ether (DIPE) was synthesised in a single step from a feed of propylene and water over Amberlyst 15 ion exchange resin catalyst. It was produced in a trickle bed reactor at pressures between 1 bar and 60 bar, at temperatures between 70°C and 160°C and at overall propylene to water ratios between 1:5 and 10:1. Reaction proceeded in the liquid phase within the catalyst particles. The only reactions that occurred in the system were the hydration of propylene to form isopropanol (IPA) , the alkylation of IPA with propylene to form DIPE and the bimolecular dehydration of IP A to form DIPE and water. No side reactions such as propylene oligomerisation were observed. Starting from a feed of propylene and water the primary reaction product was IPA. IPA was subsequently consumed in two secondary reactions which produced DIPE. DIPE was produced either by the alkylation of IPA with propylene or by the bimolecular dehydration of IPA. It was generally not possible to study the two DIPE formation reactions separately as they are linked via the propylene hydration reaction. All experimental data was thus reported in terms of a hydration rate and an etherification rate, the latter being the sum of the IPA alkylation and the bimolecular IPA dehydration rates.