OpenUCT :: Browsing by Author "O'Connor, Cyril"

Browsing by Author "O'Connor, Cyril"

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Open Access
The addition of HZSM-5 to the Fischer-Tropsch process for improved gasoline production
(2002) Botes, Frederick Gideon; O'Connor, Cyril; Böhringer, Walter
The Fischer-Tropsch process has two important disadvantages with regard to the production of gasoline. Firstly, the carbon number distribution of the product spectrum follows the statistical Schulz-Flory function. This means that principally hydrocarbons of all lengths are produced and that the gasoline selectivity is limited to a theoretical maximum value of about 48%.
Open Access
Alkylation of phenol with methanol over H-ZSM-5, H-Beta, H-Mordenite, H-USY and H-MCM-22
(2003) Moon, Gillian Catherine; O'Connor, Cyril; Möller, Klaus
Alkylphenols are intermediates used in the synthesis of many important substances. The most signiﬁcant of the commercially important lower alkylphenols are cresols (methyl phenols) and xylenols (dimethyl phenols). The main markets for alkylphenol products are nonionic detergents, phenolic resins, polymer additives and agrochemicals. Of the western world cresol market, 55% originates from synthetic cresols whereas 45% originates from so-called “natural” cresols obtained from coal tars and reﬁnery caustics. The methylation of phenol is the only process speciﬁcally developed to produce cresols and xylenols. There are three cresol isomers, namely ortho, para and meta. It is possible to produce a high selectivity to o-cresol by alkylation of phenol with methanol over a basic or a Al2O3 catalyst or a Fe/V catalyst. A mixture of the cresol isomers can be obtained over aluminium oxides with strong acid sites, silica alumina, zeolites, aluminium phosphates and phosphoric acid-Kieselguhr catalysts. However, direct synthesis of high purity m-cresol and p-cresol is desirable due to the high costs of separating these two isomers. Thus to synthesize p-cresol, a m-cresol free or very low m-cresol concentration in the product is desirable for puriﬁcation reasons and a high p/o-cresol ratio is also desirable in the product for yield reasons since separation of the p- and the o-cresols is economically possible.
Open Access
Application of the transformation of 1,2,4-Trimethylbenzene to monitor the chemical vapour deposition of Tetraethoxysilane over ZSM-5
(1998) Röger, Hans Peter; Möller, Klaus; O'Connor, Cyril
The present work reports an improved chemical vapour deposition (CVD) technique using low temperature, tetraethoxysilane (TEOS) and repeated CVD-calcination cycles. This results in a better control of the external surface activity and the pore mouth size of ZSM-5. In search for effective characterisation tools and a model reaction which involves molecules which are critical in size relative to the size of the ZSM-5 channels, the transformation of 1,2,4-trimethylbenzene (1,2,4-TMB) was investigated with respect to the reaction network, the role of the micropore space and the response to CVD treatments and Silicalite I coating. A generalised interpretation of the effect of modifications of the external surface activity and the pore mouth size on activity and shape selectivity of zeolites is proposed.
Open Access
Catalytic conversion of Ethylbenzene over acid zeolites
(2000) Mabaso, Evans Itai; Fletcher, Jack; O'Connor, Cyril
In this study, the performance of this test reaction was employed to compare the acidity of various zeolites, viz. lanthanum/sodium-exchanged zeolite Y (LaNaY-72), hygrogen/sodium-exchanged zeolote Y (LZY-52, LZY-62, LZY-82), hydrogen-exchanged zeolite Beta (H-BEA-15, H-BEA-25) and hydrogen-exchanged ZSM-5 (H-MFI-45).
Open Access
The characterisation and cetane number determination of synthetic diesel fuels
(1991) Forrester, Robert David; O'Connor, Cyril
South African synthetic fuel plants produce large quantities of lower alkenes which can be catalytically oligomerized to liquid transportation fuels. In the screening of experimental catalysts for the production of diesel-range fuels, it is important to measure the quality, as well as the quantity, of the fuel being produced. Cetane number is an important indicator of the quality of a diesel fuel ru1d is measured by a standard engine test (ASTM D 613) which requires l litre of fuel and is therefore not suitable for the routine testing of the small volumes of fuel produced by experimental catalysts. Alternative cetane number prediction methods exist but these have generally been developed to predict the cetane number of crude-oil based fuels and are therefore not suitable for use with synthetically derived fuels. This thesis details the development of a formula which accurately predicts the cetane number of a fuel from other, easily measured parameters. Several samples of fuel were produced under varying reaction conditions and were hydrogenated to ensure that they were virtually 100% alkane. Differences in cetane number should therefore be due to differences in the degree of branching. By measuring the cetane number on a. standard test engine and correlating the result with the amount of branching as measured by ¹Hnmr, a formula was developed which was found to accurately predict the cetane number of these types of synthetic fuels. The results obtained also show that for the conversion of ethene over a supported nickel catalyst, cetane number decreases as temperature increases. This decrease is probably caused by secondary butane oligomerization reactions.
Open Access
The characterisation of the lead flotation circuit at Black Mountain Mining (Pty) Ltd. using the floatability component model approach
(2015) Galant, Malikaah; O'Connor, Cyril; Sweet, Jenni
Black Mountain Mining (Pty) Ltd. (BMM) is a base metal operation that has been producing chalcopyrite-, galena- and sphalerite-bearing concentrates for over 30 years. Silver is recovered in the concentrates as a result of elemental substitution within the crystal lattice of chalcopyrite and galena minerals. The primary objective of this study was to adapt the Floatability Component Model (FCM) as a simplified proof-of-concept model for the Lead flotation circuit of the BMM Concentrator based on plant- and laboratory-scale data. The model obtained, using the FCM approach in conjunction with the Woodburn and Wallin (1984) methodology, should give insight to the metallurgical team regarding the performance of the circuit based on the data pertaining to the feed characteristics of the Lead flotation circuit. Additionally, as a result of the known association of silver with galena minerals, an objective of the study was to be able to predict the response of silver based on the response of galena minerals. The model for the Lead flotation circuit of BMM Concentrator was developed in a single MS Excel spreadsheet and it was important that the raw data used to develop the model could be obtained easily, inexpensively and in a manner that was not disruptive to the operation.
Open Access
The characterization and elimination of the external acidity of ZSM-5
(1993) Weber, Reinier Willem; Fletcher, Jack; O'Connor, Cyril
The zeolite ZSM-5 is well-known for its unique intersecting channel system. This channel system has a great bearing on the shape-selective properties and the long life-times of ZSM-5. In this study, ZSM-5 was modified in various ways to eliminate the external acidity of the catalyst to further improve these properties, and the success and effects of these modifications were investigated primarily using temperature programmed desorption techniques. The internal surface of ZSM-5, a medium pore zeolite, plays a major role in the shape selective properties of this catalyst, due to the diffusional restrictions imposed by the channel system on bulky molecules. Even though the number of acid sites on the external surface is small compared to the total number of acid sites, these easily accessible and non-shape selective acid sites may provide a high turnover rate for non-shape selective reactions. Furthermore, the main cause of deactivation of ZSM-5 is thought to be the formation of polyaromatic molecules on the external surface, which block access to the channels of the catalyst.
Open Access
The chemical vapour deposition of Tetraethoxysilane on Zeolite ZSM-5
(2001) Manstein, Heiko; Möller, Klaus; O'Connor, Cyril
This thesis reports on the investigation of a cyclic chemical vapour deposition (CVD) method eliminating unwanted surface reactions and enhancing shape selective properties by depositing inert silica onto the external surface of zeolite ZSM-5. A CVD treatment consists out of a deposition, flushing and heating step followed by calcination in flowing air. Modifications are carried out in up to 33 cycles on one and the same sample employing tetraethoxysilane (TEOS) as silica precursor at deposition temperatures ranging from 50 to 400°C. After each CVD treatment the catalyst is tested with appropriate test reactions in order to quantify the extent of modification. The gradual inertisation of the external surface is followed with the catalytic cracking of 1,3,5-triisopropylbenzene (1,3,5-TiPB) which is too bulky to enter the micro-pore structure of ZSM-5. The disproportination of toluene (TDP) is employed to monitor changes of the internal activity and alterations in the shape selective properties of the catalyst. The analysis of reactor effluent during the deposition, flushing and heating step of the modification cycle allows investingating the reaction pathway. The deposition reaction proceeds with the reaction of the alkoxy groups of TEOS with the terminal hydroxyls of the zeolite under the formation of ethanol.
Open Access
The development of a model for high pressure propene oligomerisation over H-ZSM-5
(1996) Sealy, Sarah Jane; O'Connor, Cyril; Fraser, Duncan
The primary aim of this thesis is to develop a fundamental, mathematical model for high pressure propene oligomerisation over H-ZSM-5. To this end, this introductory chapter first revises the characteristics and applications of catalysts which have been shown to be active for oligomerisation. This is further split into acid catalysts, heterogeneous nickel catalysts, other transition metal catalysts and finally homogeneous metal catalysts. The next section covers the various mechanisms of oligomerisation on different catalyst types since an understanding of these mechanisms is an important step in the modelling process. Following this, the modelling of oligomerisation reactions is reviewed with an additional section on other complex reaction models. Throughout this chapter heterogeneous acid catalysts are given the most emphasis, especially H-ZSM-5, since this thesis is concerned with modelling oligomerisation over acid catalysts. The final sections of this chapter cover the objectives of this study and the approach to studying this complex reaction in detail.
Open Access
The effect of mixing thiol collectors in the flotation of pure sulphide ores
(2012) Castelyn, Daniel Gregory; McFadzean, Belinda; O'Connor, Cyril
Using mixtures of xanthate with either dithiophosphate (DTP) or dithiocarbamate (DTC) has been reported to increase the flotation performance of several sulphide flotation operations. The increased flotation performance has often been termed synergistic. Synergism is defined as the effect exceeding the pro rata contribution of either constituent in the mixture. This thesis aims to investigate the effects that mixtures of either xanthate and di-alkyl DTP or xanthate and di-alkyl DTC have on the pulp phase floatability of pure galena and pyrite by means of microflotation. Both minerals were chosen because they have been widely studied in sulphide flotation, and to determine whether flotation results with mixtures were mineral specific.
Open Access
The effect of synthesis and post-synthesis modifications on the activity of zeolite beta for cumene synthesis
(1998) Hurgobin, Sooviraj; O'Connor, Cyril
The isopropylation of benzene to produce cumene is an important petrochemical process since cumene is used as a chemical intermediate for the production of phenol and acetone. In recent years, the good performance of zeolite Beta for this particular reaction has often been reported in the literature (Reddy et al., 1993, Bellussi et al., 1995 and Perego et al., 1996). It is known, from the numerous studies that have been carried out on other zeolite types, that post synthesis modifications such as dealumination of the zeolite framework tend to enhance the activity of these zeolites for catalytic reactions. Moreover, the effect of synthesis parameters on the catalytic activity of zeolite Beta is an important issue that has not been thoroughly investigated in the literature. In this study, a commercial parent zeolite Beta catalyst (sample A) was modified by post synthesis modifications such as steaming, acid washing or steaming followed by acid washing. A series of zeolite Beta catalysts were also synthesised by different techniques. The samples were characterised with respect to structure, morphology, particle size, number of acid sites, co-ordination state of aluminium and the environment of silicon atoms. The isopropylation of benzene to cumene was used as a test reaction to evaluate the effect of post-synthesis modifications and synthesis procedure on the catalytic activity of the zeolite Beta catalysts.
Open Access
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.
Open Access
The flotation of pyrite using xanthate collecters
(1986) Dimou, Anna; O'Connor, Cyril
The flotation properties of pyrite were found to be significantly influenced by variations in the pH. In acidic solutions the pyrite floatability is very high, and recoveries of 95% could be achieved using only a frother. A sharp decrease in floatability was observed in alkaline solutions, possibly due to the formation of hydrophilic ferric hydroxide. The addition of a xanthate collector improved the flotation properties of pyrite at all pHs. In acidic solutions the main effect observed was on the rate of pyrite recovery and on the grade of the concentrates. In alkaline solutions the addition of a xanthate collector improved the final recovery, the rate of flotation and the grades. Variations in the pH had no effect on the recovery of pyrite to which xanthate was added. There was, however, a continual decrease in the final grade of the concentrates with an increase in pH, due to the increase in the recovery of the gangue mineral.
Open Access
A hydrodynamic investigation of fine particle flotation in a batch flotation cell
(1998) Deglon, David Alan; O'Connor, Cyril
Open Access
A hydrodynamic investigation of platinum flotation in a pilot flotation plant
(2003) Lewis, Jonathan Stretton; Deglon, David; O'Connor, Cyril
The aim of this thesis was to determine the effect of impeller speed and air flowrate on the flotation of platinum in mechanical flotation cells.
Open Access
An investigation into the role of DTP as a co-collector in the flotation of a South African PGM ore
(2011) Bezuidenhout, Jacques; Corin, Kirsten; O'Connor, Cyril
The primary aim of this study was to investigate, using a combination of batch flotation and ToF-SIMS experimental techniques, whether a collector-collector synergistic interaction between SIBX and diethyl DTP will result in significantly enhanced copper, nickel, platinum and/or palladium recoveries and grades in a PGM containing ore from South Africa.
Open Access
An investigation of particle collection efficiency in different particle-bubble contacting environments in flotation
(1995) Breytenbach, Jacobus Nicolaas; Franzidis, Jean-Paul; Harris, Martin; O'Connor, Cyril
The collection efficiency of quartz particles in four different particle-bubble contacting environments was investigated during this thesis. Flotation experiments were carried out in a hybrid flotation column that could be modified into three different cell configurations (a quiescent column cell, an agitated column cell and a Jameson-type cell), while the fourth cell environment comprised a laboratory batch subaeration flotation cell. High purity quartz was used as a probe ore in conjunction with a cationic collector and a commercial frother blend. The quartz was initially contaminated with organic material and needed to be cleaned by calcination. The cleaned quartz was divided into four narrow particle size fractions to determine the effect of particle size on particle collection efficiency. The quartz was floated over a wide range of collector dosages and frother dosage was kept constant during experiments. The flotation was conducted using tap water at neutral pH. Froth depth was kept shallow during all experiments in the hybrid column cell configurations to enable the investigation to focus specifically on the collection zone. The effect of contacting environment (cell type) on particle collection efficiency was investigated by considering the effect of particle hydrophobicity, particle size and agitation speed (turbulence) on flotation recovery in the different cell types. The unique particle-bubble contacting environments resulted in different particle collection efficiencies and it was found that increased contacting intensity generally led to increased efficiency of collection. Increased particle hydrophobicity generally resulted in increased particle collection efficiency, although the overdosing of collector led to decreased flotation recovery which was probably caused by combined collector double layer and flocculation effects. The effect of particle size on flotation recovery exhibited classical n-curve behaviour at intermediate collector dosages and the optimum particle size range as reported in the literature was confirmed. Intense contacting between particles and bubbles followed by relatively quiescent disengagement (such as the mechanism employed in the Jameson cell configuration) proved to be beneficial to collection of both fine and coarse particles.
Open Access
Investigation of the flotation behaviour of ball mill and IsaMill products
(2012) Khonthu, Tsepang; O'Connor, Cyril; Wiese, Jenny; Mainza, Aubrey Njema
Valuable minerals that are used in various aspects of everyday life are buried in fossilised storages below the ground in the earth's crust. These minerals are mined as rocks which then have to be crushed in order to liberate these minerals of value. The liberated valuable minerals have to be winnowed from the rock powder. Flotation is the main process which is used in mineral processing to recover valuable minerals. This process uses the differences in surface properties of particles to separate hydrophobic particles from hydrophilic ones. The strong relationship between the method of crushing the rocks and the amount of valuable minerals which can be reclaimed from the crushed rock has long been realized in mineral processing. The type of mineral, the size to which the rock must be reduced to and the amount of energy needed for this size reduction are among the most important factors which guide the decision on the type of device to be used in pulverising mineral rocks. Physical properties, with the exception of particle size, of mill products have not been investigated as thoroughly as the chemical properties. Physical properties include surface roughness and particle shape. The differences in shape, between particles produced by different mills, with respect to these properties, have been attributed to differences in the breakage mechanisms in the mills used to grind the particles. There is contradicting literature on the breakage mechanisms that dominate in various mills. This confusion is exacerbated by the fact that different breakage mechanisms occur simultaneously in any one mill. The definition and determination of particle shape are also difficult. Subsequently, the effect of particle shape on flotation is a subject that is rife with contradictions which add to the complexity of the subject.
Open Access
Isomerisation of cresols over zeolites HZSM5, HBeta and HMordenite
(2005) Hunt, Raymond Cedrick; O'Connor, Cyril; Bezuidenhoudt, Ben; Böhringer, Walter
In the natural (phenolic material obtained from coal) phenolics industry two problems are experienced with regards to cresol isomers. Firstly, insufficient quantities are recovered from natural sources such as coal tar and refinery caustics and secondly the isomer distribution is inflexible and does not always meet market demand. Thus, having technology which provides alternative routes to certain cresol isomers is of utmost importance to natural cresol producers. The isomerisation of one cresol isomer into one or more of the others would enable a producer to swing (to a limited extent) the distribution of isomers to suite the demand of customers. For this study, the isomerisation and disproportionation of the three cresol isomers were investigated over three types of zeolites under liquid as well as vapour phase (only o-cresol isomer) reaction conditions. The best activity for o-cresol isomerisation, in the liquid phase, was initially HMordenite but because the catalyst deactivates so quickly, HZSM5 was thus regarded as the best catalyst. HZSM5 gave the best activity for both m-and p-cresol isomerisation in the liquid phase. The activity over HBeta was between that of HZSM5 and HMordenite for all the cresol isomer conversions. Expected from the shape selectivity of the zeolite, the best isomerisation selectivity (>86.0%) was obtained with HZSM5. HBeta gave both isomerisation and disproportionation but the favored pathway is disproportionation, while HMordenite, due to the deactivation, proved to be suitable for neither isomerisation nor disproportionation. It can thus be concluded that HZSM5 gave the best conversion for 0-, m-and p-cresol in terms of the desired isomerised products and that it is the preferred catalyst for isomerisation in the liquid phase. The average activity for o-cresol conversion in the vapour phase followed the order HZSM5 > HBeta = HMordenite. HZSM5 proved to be the best isomerisation catalyst for o-cresol and high selectivity (>95%) and stability was obtained over five days on stream, while HBeta showed a gradual decline in isomerisation selectivity and stability. A rapid decrease was noticeable over HMordenite in terms of selectivity and stability. The activity, stability and isomerisation selectivity data obtained, is therefore conclusive with regards to HZSM5 being the preferred zeolite for isomerisation of o-cresol. Further work could entail optimisation of the p-selectivity, from o-cresol and m-cresol transformation, and lifetime studies of the preferred zeolite HZSM5. It is thus recommended to investigate CVD (chemical vapour deposition) to deactivate the external surface of the catalyst as well as noble metal impregnation and/or the use of hydrogen as a carrier gas.
Open Access
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.