No abstract available. / Thesis (Ph.D.)-University of Natal, Durban, 1973.

No abstract available. / Thesis (Ph.D.)-University of Natal, Durban,1975.

The shock tube was used to investigate the product spectrum of the initial stages of the Fischer-Tropsch synthesis carried out at elevated temperatures. Special attention was paid to the relationship between methane selectivity and temperature. The range of reaction environments studied are summarised below:- Reaction temperature 780 K - 1425 K. Reaction pressure 160 psia - 330 psia. Mean reaction time 628 u sec. - 727 u sec. Test gas composition - argon 81 - 87 mol. %. - hydrogen 6,5 - 9 mol. %. - carbon monoxide 6,5 - 9,5 mol.%. Catalyst type - fused iron, triply promoted. Catalyst loading - 0,12 - 0,14 mass catalyst / mass gas. The experiments were conducted in the incident shock region and quenching was achieved by the reflected rarefaction wave. Percentage conversion of hydrogen and carbon monoxide to useful products (hydrocarbons) varied between 0,1 and 2. Products detected in measurable quantities were methane, ethylene, ethane and propylene. The theory of shock tube wave propagations through heterogeneous medi a was studied in detail and unique theory developed for handling conditions of varying temperature and pressure. This enabled characterisation of the reaction environment so that multilinear regression could be used to find a correlation between H2 + CO consumption and system variables. Major information gleaned on the initial stages of the Fischer-Tropsch synthesis at elevated temperatures was; (i) contrary to observed trends under normal synthesis conditions, methane selectivity decreased and propylene selectivity increased with increasing temperature; (ii) the process appeared to be hydrogen adsorption, pate controlled; (iii ) molecular degradation processes played a negligible part in the format ion of final reaction products, and (iv) oxygen compounds, such as methanol, did not appear to be important intermediate products. It has been shown that the heterogeneous shock tube offers a possible means of obtaining initial reaction rate data for highly complex systems. / Thesis (Ph.D.)-University of Natal, 1973.

This work is concerned with the effect of vessel geometry on the hydrodynamics of fluidisation of a bed of milled iron oxide. The effect of going from a cold model representative of a typical pilot plant reactor to one simulating a semi-commercial unit is quantified, and various reactor internal configurations on the latter are evaluated. The experimental approach is one based on residence time testing and model fitting with parameter optimisation. A model screening aimed at identifying the most reasonable modelling approach is included, and altogether seven models in two categories are formulated and solved in the dynamic mode. Three of these models are considered novel at present, along with the dynamic solutions to two of the others. The residence time technique involves methane as an inert tracer in air, and continuous analysis of gas withdrawn from the bed via sample probes by a pair of flame ionisation detectors. The process stimulus is governed by a pseudo-random binary sequence, and correlation analysis is employed for noise reduction. A Fourier transform routine, developed from first principles, converts a pair of correlation functions to a process frequency response, and model predictions are compared with the experimental data in this form. Two parameters per model are fitted, and the residual error at the optimum parameter combination provides a means of identifying the best-fitting model. The optimised parameters of this model are regarded as estimates of those of the actual process. Five models compete in the first screening category. Four of these have appeared in the literature in one form or another, and the fifth is novel in that it accounts for axial mixing in the bubble phase by employing multiple plug flow units. This model, referred to as the multiple bubble-track or MBT model, is shown to fit the experimental data better than any of the other models in both bubbling and slugging systems. This suggests that employing multiple plug flow units in parallel for the bubble phase is mechanistically more correct than employing a single plug flow unit. The second screening category is related to the situation in which gas is sparged into an already fluidised bed at some height above the main distributor. The two models in this category are both considered novel, and describe opposite extremes of possible behaviour in one particular sense: one assumes rapid coalescence between grid and sparger bubbles, and the other none at all. The laterally segregated bubble phase or LSBP model emerges as the better process description.The formulation of this model suggests that physically, bubbles from the sparger tend to retain their identity as they pass through the bed. Crossflow ratios estimated on the basis of the best-fitting model in each category point to the existence of a very strong scale-up effect. From the shape of the crossflow profiles it appears that most of the interphase mass transfer occurs in the bottom meter or so of the bed, and it is suggested that grid design is the most significant controlling factor. The presence or otherwise of vertical coils in the bed is shown to have no significant effect on crossflow, and mass transfer between sparger bubbles and the dense phase is shown to be similar to that between grid bubbles and the dense phase. Finally, it is demonstrated that the axial crossflow profile in the bubbling bed is consistent with the concept of an axially invariant mass transfer coefficient based on bubble to dense phase interfacial area. / Thesis (Ph.D.)-University of Natal, Durban, 1984.

Four sphalerites (synthetic, high grade natural, moderately impure flotation concentrate and highly impure flotation concentrate) were leached in acid sulphate media without and with ferric ions present under the following conditions :- Case (i) [Fe3+]o : [H2S04]o = 0,0 Case ( ii) [Fe3+]o : [H2S04]o = 1,8 Case (iii) [Fe3+]o : [H2S04]o = 0,1 Extensive data for leaching under these conditions are tabulated. Kinetic mechanisms based on Langmuir-Hinschelwood adsorption theories were proposed, and leaching models were developed for different assumed rate limiting steps. The initial rate and overall forms of the models were tested using experimental data.Leaching under case (i) conditions Non-oxidative dissolution took place with Zn2+ and H2S the predominant reaction products. The H2S partial pressure was monitored continuously and solution samples were taken for analysis at discrete time intervals. Vibratory (i.e. attrition) milling eliminated very large differences observed in the leaching characteristics of course size fractions of the natural sphalerites. The initial rate form of a model based on a dual site reaction mechanism and on either H+ adsorption or reaction product desorption rate control was found to fit the data for the synthetic and vibratory milled forms of sphalerite. The most impure vibratory milled sphalerite adsorbed Zn2+ and H2S very strongly, and this resulted inproduct desorption rate control. Vibratory milled forms of the high grade natural sphalerite and the moderately impure flotation concentrate, exhibited virtually identical initial rate dissolution kinetics, despite large differences in their chemical compositions. Leaching under case (ii) conditions Oxidative dissolution took place with Zn2+ and elemental sulphur the predominant reaction products. Scanning electron microscope photographs of leached and unleached particles showed the sulphur present on the particle surface. These photographs, and optical microscope photographs of etched polished sections, showed that dissolution took place in a complex way. A model based on ferric ion adsorption as the rate limiting step was proposed and confirmed experimentally. The model demonstrated a proportional dependency of the rate on the area and ferricion concentration, and an inverse dependency on the hydrogen ion concentration. For a -90,0 + 63,0 um size fraction, the three natural sphalerites exhibited virtually identical dissolution rates per unit area. The effect of ball milling or vibratory milling the sphalerites fine, was to increase the rate per unit area for the most impure natural sphalerite but decrease the rate per unit area for the high grade natural sphalerite.It was shown that for course size fractions of sphalerite, the most impure sphalerite which leached slowest under case (i) conditions (i.e. adsorbed H+ poorly) leached fastest under case (ii) conditions (i.e. adsorbed Fe3+ strongly). The reverse was true for the high grade natural sphalerite. Except in the case of synthetic sphalerite leaching under case (i) conditions, no correlation was shown to exist between the way the B.E.T. measured area changed, and the way the calculated active area changed during leaching. Leaching under case (iii) conditions Oxidative and non-oxidative dissolution, as well as H2S oxidation by Fe3+ occured simultaneously. The extents to which oxidative or non-oxidative dissolution occured could be explained in terms of the hydrogen ion and ferric ion adsorption characteristics of the sphalerites.The ferric ion oxidation of H2S was studied in the absence and presence of solids, and the presence of sphalerite or activated charcoal catalysed this reaction. No advantage was gained by leaching in the presence of activated charcoal with or without Fe3+ present, unless conditions were such that H2S was formed as a product of reaction. / Thesis (Ph.D.)-University of Natal, Durban, 1977.

The initial phase of the project involved an investigation into the modeling of binary carboxylic acid vapour-liquid equilibrium (VLE) data. This stemmed from the Masters research that led into the current study, in which the conventional gamma-phi formulation of VLE was found to inadequately describe the complicated acid chemistry. In an effort to correctly describe the dimerization occurring in both the liquid and vapour phases, the chemical theory of vapour-phase imperfections was applied. The chemical theory technique allowed the experimental liquid-phase activity coefficients to be accurately calculated by taking the vapour phase dimerization into account. Once these activity coefficients had been determined, standard Gibbs excess energy models were fitted to permit analysis of the VLE data's thermodynamic consistency. In addition, the typical bubble-point iteration scheme used for VLE data regression was adapted to include the chemical theory expressions necessary for satisfactory modeling of the carboxylic acids. The primary focus of this study was to determine the ability of currently available computer simulation techniques and technology to correctly predict the phase equilibria of polar molecules. Thus, Monte Carlo simulations in the NVT- and NPT- Gibbs ensembles were used to predict pure component and binary phase equilibrium data (respectively), for a variety of polar compounds. The average standard deviations for these simulation results lay between 1 and 2 % for the saturated liquid densities, and varied between 5 and 10 % for the saturated vapour pressures and densities. Pure component data were simulated for alcohols, carboxylic acids, hydrogen sulfide (ELS), sulfur dioxide (SO2) and nitrogen dioxide (NO2). For H2S, S02 and NO2, a potential model parameterized as part of this project was used to describe the molecular interactions. All the other compounds were simulated using the TraPPE-UA force field. The simulation results for the alcohols and acids showed a consistent saturated vapour pressure over-prediction of 5 - 20 % depending on the species and the system temperature. The liquid density predictions were, in general, good and on average differed from experiment by 1 - 2 %. The critical temperatures and densities were estimated from the pure component data by fitting to the scaling law and the law of rectilinear diameters. They were found to lie within 1 and 2 % of the experimental values for the carboxylic acids and alcohols, respectively. Clausius-Clapeyron plots of the saturated vapour pressures allowed the critical pressure and normal boiling points to be determined. The critical pressures were, as expected, over-predicted for both compound classes and the normal boiling points were under-estimated somewhat for the acids, but deviated from experiment by less than 0.5 % for the alcohols. A Lennard-Jones 12-6 plus Coulombic potential energy surface was parameterized for H2S, SO2 and NO2. For FbS, the proposed force field offers improved saturated vapour pressure and vapour density predictions when compared to the existing NERD force field, and comparable accuracy with the recent models of Kamath and co workers. SO2 and NO2 had not previously been parameterized for a Lennard-Jones 12-6 based force field. For SO2, there was excellent agreement with experimental data. In the case of NO2, the saturated liquid density predictions were very good, but the vapour pressures and densities were over-predicted. Binary VLE simulations were carried out for systems consisting purely of carboxylic acids, and also for H2S and SO2 with a selection of alkanes and alcohols. The liquid and vapour composition predictions were good for the acid systems, but the anticipated pressure and temperature deviations were observed in the isothermal and isobaric simulations, respectively. The H2S + alkane systems were generally good, as were the SO2 + alkane systems. For both H2S and SO2, the systems involving an alcohol displayed a characteristic pressure over-estimation. The azeotropes were, in most cases, predicted fairly well; the exception was the SO2 + methane binary. A sensitivity analysis of the Lennard-Jones unlike interaction parameters was also conducted. It was demonstrated that even minor changes to these parameters can have a significant effect on the final simulation results. The considerable affect that these parameters have on the simulation outputs was emphasized by studying the influence of different combining rules on the H2S + methane and H2S + ethane binary systems. Analysis of the radial distribution functions indicated that hydrogen bonding and dimerization were occurring in the alcohol and carboxylic acid systems, respectively. The H2S, SO2 and NO2 distribution functions showed little sign of any association, except for a small plateau in that of SO2. A radial distribution function from one of the carboxylic acid binary simulations was also analysed, and supported the assumption made in the chemical theory modeling work of using a geometric mean (instead of twice the geometric mean, which is favoured by some researchers) to determine the heterodimerization constant, KAB- / Thesis (Ph.D.)-University of KwaZulu-Natal, 2006.

Partitioned or Dividing Wall Columns (DWC) for distillation are currently receiving a lot more / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

High pressure vapour-liquid equilibrium experiments were undertaken with a static high-pressure apparatus designed by Prof. J. D. Raal and commissioned by Prof. D. Ramjugernath. Isothermal VLE binary data data was measured at moderate temperatures and pressures ranging from atmospheric to 7.2 bar. The equipment had a combined operating pressure and temperature limit of approximately 150 bar and 215° C respectively. The apparatus was initially designed for the measurement of gas-liquid binary systems- where one of the components was supercritical at the operating conditions. Test data were measured for the pentane + ethanol system at 100.41°C. The 2-methyl-2-butene + TAME, hydrocarbon + olefin system, was observed at 70°C, 94.6°C and 104.5°C. The apparatus was modified for the measurement of binary systems containing sub-critical components at the operating conditions specified. An injection port was installed on the apparatus assembly such that the second component of the binary system could be introduced into the equilibrium cell. The binary VLE data was regressed using various thermodynamic models. The direct method or phi-phi approach was considered. The equations of state models used in the regression were the Peng-Robinson-Stryjek-Vera (PRSV) and Soave-Redlich-Kwong (SRK). The 1-fluid van der Waals, Wong and Sandler mixing rules were selected to estimate binary interactions. The excess Gibbs energy equations coupled with the Wong and Sandler mixing rules were the NRTL and WILSON equations. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

The work described in this dissertation was aimed at obtaining an understanding of / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007

The major focus of this study was to provide better understanding of the potential of / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007