Masters Degrees (Chemical Engineering)

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A vapour-liquid equilibrium study on sub-critical systems using a static apparatus.
(2009) Wilson, Etienne P.; Ramjugernath, Deresh.; Naidoo, Paramespri.
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.
Production of activated carbon from South African sugarcane bagasse.
(2005) Mwasiswebe, Denny.; Arnold, David R.
South Africa has an annual sugarcane milling capacity of about 22 million tonnes on average producing about 3.3 million tonnes of dry bagasse, of which one third is surplus to factory requirements. Currently surplus bagasse is used for furfural, pulp and paper and cogeneration but significant amounts still remain . This prompted the need to find viable alternative and appropriate technology to utilize the surplus. A laboratory pilot plant was used to investigate the production of activated carbon from bagasse. Experiments were carried out to investigate conditions for making the best activated carbon in a rotary batch kiln, and also to examine potential ene rgy recovery from process gases using Gas Chromatography. Derived results from the laboratory experiments were used to develop a conceptual design for a demonstration plant sited within a sugar mill. The conceptual design was evaluated for economic and environmental impacts using a robust Excel spreadsheet and GABI-3 modelling software respectively. Excellent activated carbon was produced from sugarcane bagasse by a two-stage physical process involving pyrolysis and gasification with steam. The best operating conditions were pyrolysis at 700°C for 1 hr and activation at 850°C for 1hr, a heating rate of 10°C/min and a steam flow of 15g/g of char per hour. The active carbon yield was 7% on dry bagasse basis with a Methylene Blue Number of 257mglg of carbon. The active carbon had a sugar decolourisation capacity of 20% at a carbon dosage rate of 0.7 wt% on Brix using clear juice (l2°Brix) and 70% at 0.5 wt% on Brix using brown liquor (65°Brix) . The Freundlich isotherm showed that the bagasse-based activated carbon was a suitable adsorbent for sugar colour bodies. Gas analysis results revealed that the off gases from the pyrolysis and activation stages had calorific values of about 63MJ and 31MJ per kg of activated carbon respectively . The total combustion energy of 94 MJ/kg of active carbon was enough to satisfy the process energy requirements for drying, pyrolysis and activation. By burning combustibles like tar, methane, carbon monoxide, ethylene and hydrogen for process thermal energy needs, the environmental impact of the manufacturing process was reduced to a Global Warming Potential of llkg CO2 Equiv per kg of carbon produced. The demonstration plant requires a capital investment of US$lOA million to give a competitive bagasse-based activated carbon (BPAC) selling price of US$1.80 per kg and IRR, ROI and Investment payback time of 17.93%, 23.93% and 3.80 years respectively. A sensitivity analysis was also carried out to investigate the effect of possible variation in the main project forecasts which are BPAe selling price , bagasse buying price, capital investment and production costs on IRR, ROI and payback time . The benefits of process integration within a sugar mill would be expected to improve the business feasibility ; If bagasse was free the IRR would increase to 28.59% and even better to 32.12% if extra boiler and electricity capacity was also available at the mill.
Development and modelling of a semi-batch flotation apparatus.
(2008) Ramlall, Nigel Valentino.
When designing or optimizing flotation circuits in mineral processing plants, it is necessary to have accurate values of the flotation kinetics to ensure the correct mass pulls and material balances on the plant. Previous studies have shown that rate constants measured by single cell batch testing can cause a shift in the recovery—grade curve. The shift in the recovery—grade curve is the result of poor separation in conventional laboratory flotation devices. This project involved the development and modelling of a flotation device that provides a better separation than a conventional batch flotation cell. The device is called a semi—batch flotation apparatus (SBFA) because it simulates the operations of a pilot plant in a laboratory environment. It also provides dynamic data which facilitates the evaluation of model parameters. The SBFA tested a synthetic ore made from limestone, talc and silica. The synthetic ore was used as it was economical and easy to analyze. The results from the SBFA were compared to results obtained from conventional batch flotation tests; by using recovery—grade curves to assess the degree of separation achieved from both devices. The SBFA separated the limestone from the gangue (silica and talc) much better than the batch tests. For instance the final grade for a concentrate obtained from a single cell batch test was 20 % limestone while the final grade for a concentrate obtained from the SBFA was between 40 % and 70 % limestone. The improvements in separation can be attributed to the multistage design of the SBFA which has a pulp recycle between the stages. A model has been developed for the SBFA. The model fitted the experimental data well with a correlation coefficient close to unity. The cumulative recoveries predicted from the SBFA model was compared to the actual cumulative recoveries, by using a global set of parameters (&2 and RMAX)- The investigation showed that the model had problems in fitting the data for the early periods of the experiments because of the complex interaction between the stages in the SBFA.
Application of water pinch to an integrated pulp and paper Kraft mill with an already highly closed water system.
(2009) Slabbert, Eric.
Sappi's Ngodwana integrated Kraft pulp and paper mill was used as case study for the application and evaluation of the water pinch technique. The technique of water pinch originates from energy pinch, but uses mass flow and contaminant concentration to identify water and effluent reduction opportunities. The classical meaning of pinch, as defmed by energy pinch has however been changed to a more modem meaning. Historically the terms water or energy pinch was used to refer to the points where two composite curves touched on energy or water graphs. This graphical meaning of pinch is gradually being replaced to refer to the optimal po int proposed by a numerical solver beyond which improvement of the water network is no longer possible for the given inputs. The water pinch technique was applied by means of a numerical solver that used mixed integer non-linear programming to optimise to the minimum cost for running the water network under investigation. The problem defmition was defined in terms of costs associated with the use of utilities, raw material, treatment facilities and process units. It was also possible to define factors such as environmental impact, corrosion, fouling, scaling, cooling tower treatment cost, legal risk etc in terms of a penalty cost. The water pinch technique has been refined in software packages that are user friendly, ca~ble of handling multi-contaminants and suitable for varying flows. The software package WaterPinch by Linnhoff March was used. The case study was applied on Ngodwana mill that has an already highly closed water system with effluent generation rates as low 20 kL per ton of pulp and paper. The pinch study included sodium, chloride, calcium, suspended solids and COD as contaminants. The study investigated different applications of the pinch technique. The following was concluded: • The mill's understanding of its current restrictions, ()l pinch points, of its water network was confirmed. No new pinch points have been identified of which the mill was not aware. This indicates that the mill was already highly knowledgeable about its water system. This was expected of a mill that has a very low specific-effluent-generation rate. Water pinch was unable to significantly improve on the effluent generation rate of the mill. • The pinch analysis has identified opportunities of mixing small quantities of waste streams into process water streams to replace fresh water. These changes can introduce minor water savings and new risks to the process that have to be understood better before implementation. • The mill has progressed far with the design and costing of a proposed effluent treatment plant (ERPl). The integration of this treatment plant into the water network was investigated using the pinch technique. The pinch solver suggested a totally different approach to the integration of the ERPI plant compared to design of the mill. The mill's design revolves around the treatment of low chloride streams in the ERPl plant and using of the treated water as make-up to the cooling towers. Sodium was recovered as raw material from the cooling towers' blow-down. Pinch proposed treatment of the high cWoride containing streams and returning the streams to users suitable of using high chloride water. The network proposed by mill's design generates 8.2 MLlday effluent less than the pinch proposal, and recovers sodium as raw material. The proposal presented by pinch is not recommended and points to the difficulty in simulating factors, such as raw material recovery, in a pinch analysis. • Users for the excess storm water were identified using water pinch and will be suitable for implementation. The mill has mwever decided on alternative sinks for the storm water based on considerations such as process inter-dependency, risks associated with contamination and general management philosophy for the different systems in the mill. These considerations could have been included into the pinch solver, but were not because it was of interest what the second best option would be. • The pinch investigation proved useful to confirm certain understandings of the mill. The investigation confirmed the difficulty of improving the water systems of the mill due to the fact that Ngodwana is already a highly closed and integrated mill. Numerous smaller process changes have been identified by the pinch solver and could be investigated further for smaller process improvements. • It i; recommended that pinch technology be applied again when the mill plans to make major process changes or expansions. It is also recommended to use water pinch on a more frequent basis in smaller sections of the mill or for other evaluations in the mill. As a group Sappi could benefit from the use of water pinch, especially in situations where the water network of the mill is not already water efficient. • The recommendations and conclusions in this report have not been subjected to technical and economical feasibility studies. Extensive further studies must be conducted before implementation of any of the results. Further studies must include impacts from process dynamics, long term effects, impacts from other contaminants that have not been simulated, etc.
Vapour-liquid equilibria studies for binary systems containing 1-hexene and n-hexane
(2009) Moodley, Prebantha
Experimental vapour-liquid equilibria (VLE) data is required for the design of separation
Infinite dilution activity coefficient measurements of organic solutes in fluorinated ionic liquids by gas-liquid chromatography and the inert gas stripping method
(2009) Tumba, Armel Kaniki.
Environmental and safety concerns have prompted an active quest for ―green‖ alternatives to
The development of a three-phase filtration cell
(2010) Naidu, Charvinia.
The chemical and process industries rely largely on filtration processes to separate solid-liquid process
Dry beneficiation of coal using an air dense-medium fluidised bed separator
(2010) Kretzschmar, Simon.
The mining of coal in arid regions has led to calls for research in to the field of dry beneficiation,
Measurement of phase equilibria for oxygenated hydrocarbon systems
(2010) Iwarere, Samuel Ayodele.; Ramjugernath, Deresh.; Naidoo, P.
A number of industrially relevant separation processes involve carboxylic acids. Carboxylic acids are also amongst the various oxygenated products found in aqueous waste streams or as by-products of industrial operations in Sasol’s Fischer Tropsch processes. Other by-products include alcohols and ketones. Accurate vapour-liquid-equilibrium (VLE) data are required for the efficient and optimal modeling and simulation of these processes. In addition, removing and separating these components will help to prevent their pollution and the associated impact on the environment.
Modelling biological sulphate reduction in anaerobic digestion using WEST.
(2010-09-03) Rajkumar, Shailendra.
Researchers at Rhodes University conducted investigations into the anaerobic co-disposal of primary sewage sludge (PSS) and high sulphate acid mine drainage (AMD) resulting in the development of the Rhodes BioSURE Process® which forms the basis for the operation of a pilot recycling sludge bed reactor (RSBR). Further research has been conducted by researchers at the University of Cape Town (UCT), with the principle aim of determining the rate of hydrolysis of PSS under rnethanogenic, acidogenic and sulphate reducing conditions in laboratory-scale anaerobic digesters. The University of Cape Town's Anaerobic Digestion Model No.1 (UCTADMI) which integrates various biological anaerobic processes for the production of methane was extended with the development of a mathematical model incorporating the processes of biosulphidogenic reduction and the biology of sulphate reducing bacteria (SRB). Kinetic parameters used in the model were obtained from SOtemann et al. (2005b) and Kalyuzhnyi et al. (1998). The WEST® software was used as a platform in translation of the basic UCTADMI from AQUASIM, and subsequently applied to data sets from UCT laboratory experiments. Incomplete closure of mass balances was attributed to incorrect reaction stoichiometry inherited through translation of the AQUASIM model into WEST®. The WEST® implementation of the model to the experimental methanogenic systems gave fairly close correlations between predicted and measured data for a single set of stoichiometric and kinetic constants, with regressed hydrolysis rate constants. Application of the extended UCTADMI to experimental sulphidogenic systems demonstrated simulation results reasonably close to measured data, with the exception of effluent soluble COD and sulphate concentrations. Except for a single system with a high COD:Sat ratio, sulphidogens are out competed for substrate by methanogens within the model. Therefore the model does not properly represent the competition between methanogenic and sulphidogenic organism groups. Trends observed in application of the model to available pilot plant RSBR data were similar to those observed in sulphidogenic systems, resulting in methanogens out-competing sulphidogens. The model was used as a tool to explore various scenarios regarding operation of the pilot plant. Based on the work conducted in this study, various areas for further information and research were highlighted and recommended.
The separation of hexafluoropropylene and hexafluoropropylene oxide using toluene and a novel solvent.
(2010-09-10) Subramoney, Shalendra Clinton.
ABSTRACT PELCHEM, the chemical division of NECSA, produces the fluorocarbon hexafluoropropylene (HFP) onsite. In 2005 PELCHEM initiated research into the wet oxidation of HFP to produce the higher value fluorocarbon hexafluoropropylene oxide (HFPO). Although successful in the conversion of HFP to HFPO, the product stream contained both the product and the unreacted HFP. As a result, PELCHEM contracted the Thermodynamics Research Unit at the University of KwaZulu-Natal to investigate the separation of HFP and HFPO. A solvent selection procedure was used to identifY potential solvents and an initial list of two hundred and seven candidate solvents compiled. Utilising the UNIFAC group contribution method, the initial list was narrowed down to thirty solvents using the criterion of selectivity at infinite dilution. Through the comparison of specific solvent properties such as recoverability, safety, environmental factors and economic considerations, a final list of ten solvents was generated. The list of ten solvents was proposed to PELCHEM who identified four solvents for further studies. The work involving the two solvents, toluene and hexafluoroethane (RI 16), is presented in this dissertation. The solvent toluene has been previously used by the du Pont company for the separation of HFP and HFPO, while R116 is a novel solvent for this application. The solvent selection procedure was performed in collaboration with a member of the Thermodynamics Research Unit, and the work on the remaining two solvents is presented in the dissertation of (Nelson 2008). Experimental binary high pressure vapour liquid equilibrium data were measured for the HFP + toluene, HFPO + toluene, R116 + HFP, and R116 + HFPO systems at two temperatures: 273.15 and 3 13.15 K. Pure component vapour pressure data for HFPO in the temperature range of 271.90 to 318.20 K were also measured. The HPVLE measurements were performed at the Thermodynamics Energy and Phase Equilibria laboratories at Ecoles des Mines de Paris using two experimental techniques and equipment. The binary systems involving toluene were measured on a static synthetic Pressure Volume Temperature apparatus equipped with a variable volume cell. The binary systems involving RI16 were measured on a static analytic apparatus equipped with a Rapid On-line Sampler Injector. None of the systems measured for this project have been reported in the literature. The four binary systems and the pure component vapour pressure measurements thus constitute new data sets. All experimental data were modelled via the direct method using the computer software Thermopack. Three model combinations were used to represent the data: the Peng-Robinson equation of state with the Wong-Sandler mixing rules, the Peng-Robinson equation of state with the Modified-Huron-Vidal first order mixing rules, and the Soave-Redlich-Kwong equation of state with the Wong-Sandler mixing rules. The Mathias-Copeman alpha function was used in conjunction with the equation of state models, and the NRTL activity coefficient model was incorporated into the mixing rules. Due to time constraints, experimental data for the binary system HFP + HFPO were not measured. Data for this system was predicted at two temperatures, 273.15 and 313.15 K, via the PSRK-UNIFAC method. The critical line for the supercritical systems R116 + HFP and R116 + HFPO were calculated in Thermopack. PELCHEM required a commercial grade HFPO product stream of purity greater than 99 % (mole), and a purified HFP product stream of purity greater than 95 % for the recycle and conversion of HFP into HFPO. Using the regressed experimental high pressure vapour liquid equilibrium data, two preliminary separation processes were designed in Aspen Plus to achieve these objectives. The first scheme involved toluene and utilised the process of extractive distillation with toluene introduced as a liquid solvent. The toluene bonded to the HFP and was removed as a bottoms product which allowed a purified HFPO stream to be recovered as a distillate. The second scheme involved RI16 and utilised the process of gas stripping, with a liquid mixture of HFP and HFPO contacted with a gaseous stream of R116. The R116 removed the HFP from the liquid mixture, resulting in a purified HFPO stream. The toluene process resulted in an overall HFPO product recovery of 98.46 % and HFPO product purity of99.88 % (mole). The RI16 process resulted in an overall HFPO product recovery of96.57 % and HFPO product purity of99.71 %. For the component HFP, the toluene process resulted in an overall HFP product recovery of 99.42 % and product purity of96.41 %. The RI16 process resulted in an overall product recovery of99.36 % and product purity of93.45 %. From a comparison of the preliminary design of the separation processes on the basis of patent issues, performance, and other miscellaneous factors, it was concluded that the RI16 process compared favourably to the process involving the solvent toluene. The preliminary process designs were presented to PELCHEM in 2007, and pending further experimental work PELCHEM plans to patent the RI16 separation process.
The study of the extraction of pectin from dried lemon peels.
(2010-09-14) Lerotholi, Letsabisa.
Pectin is a polysaccharide found in plant cell walls. It is a linear molecular chain of D-galacturonic acid units linked by a 1—»4 glycosidic bonds. Pectin is widely used in the food industry. The main sources of pectin are citrus fruits and apple. In South Africa, pectin is still imported whereas it can be produced from waste peels that result from citrus processing. A consortium was formed by CSIRBio/Chemtek, Chemin, Kat River Co-op and University of KwaZulu Natal (UKZN) to investigate pectin production. UKZN was to develop the drying (for off-season purposes) and extraction technology required for pectin production. The project was categorized into two phases; the drying and the extraction phases.
The modelling and control of a 1-octene dividing wall distillation column.
(2010-09-14) Kader, Muhammad Abdul.
Partitioned or Dividing Wall Columns (DWC) for distillation are currently receiving a lot more
The use of n-dodecane as a solvent in the extraction of light alcohols from water.
(2008) Bhownath, Rinay.
Phase equilibrium data is essential in the operation, design and development of industrial
Impact of hexenuronic acid on the physical and chemical properties of eucalyptus clonal pulps during ECF bleaching .
(2007) Andrew, Jerome Edward.
The work described in this dissertation was aimed at obtaining an understanding of
Investigation of the potential to develop high pulp strength from high yield Kraft pulp made from Pinus patula.
(2007) Johakimu, Jonas Kalebe.
The major focus of this study was to provide better understanding of the potential of
Gas-phase ethylene polymerization studies using a magnesium chloride-supported Ziegler-Natta catalyst.
(2006) Naicker, Omasha.
The gas phase polyethylene production process is the most recently developed and boasts many
Development of an improved group contribution method for the prediction of vapour pressures of organic compounds.
(2007) Moller, Bruce.
Vapour pressure is an important property in the chemical and engineering industries. There are
Removal of reactive dyes from dye liquor using activated carbon for the reuse of water, salt and energy.
(2007) Mbolekwa, Z.; Buckley, Christopher Andrew.
The removal of colour from effluent after dyeing of cellulosic fibres is a major problem due to the difficulty in treating such effluents by conventional treatment methods. Cellulosic fibres of a specific shade (colour) are produced by reacting the fibres with a mixture of reactive dyestuffs, salt and auxiliary chemicals. Reactive dye exhaustion to the fibre is about 80% i.e. 20% remains in the effluent; this is hydrolysed dye which cannot be reused for dyeing. The exhausted reactive dye bath together with first rinse represents 6 to 30 L effluent/kg of fabric and most of the colour and salt. The total water consumption for reactive dyeing ranges from 25 to 100 L effluent/kg fabric while the water consumption from total textile finishing ranges from 30 to 150 L effluent/kg fabric. Thus the concentration of the dye and salts are 5 times more concentrated when obtained at source. The use of activated carbon adsorption for the removal of colour from exhausted dyebath for the re-use of water, salt and energy has been studied. Four different commercial reactive dye chemistries and associated auxiliaries were tested and commercial activated carbon was used as an adsorbent. Different temperatures (20°C to 100°C), pH values (acidic, neutral, basic) and salt concentrations (50 g/L to 100 g/L) were evaluated and the high adsorption results were achieved when using high temperature, low pH (acidic) and high salt concentrations. The Freundlich adsorption parameters were obtained for activated carbon adsorption capacity and adsorption bond strength between reactive dyes and activated carbon. The overall removal of the reactive dye shades was 36% to 53% (based on colour in the effluent), salt recovery was about 94% to 97%, the water recovery ranged from 14% to 25% and energy savings of 17% to 32% could be achieved. Column adsorption test were performed at different temperatures and flowrates. The saturated activated carbon was regenerated and repeatedly used by elution with 1.0 M NaOH. The regenerated carbon was found to be effective up to 3 cycles of operations. A column system for treatment of reactive dyes using activated carbon was designed. The outcome of this study showed that treatment of reactive dyebath with activated carbon adsorption technique can allow re-use of water, salt and energy, thus enabling environmental improvements with a savings in salt, energy, water and treatment costs.
Phase equilibrium investigation of the water and acetonitrile solvent with heavy hydrocarbons.
(2006) Narasigadu, Caleb.; Ramjugernath, Deresh.; Naidoo, Paramespri.; Raal, Johan David.
Thermodynamics plays an important role for separation processes in chemical industries. Phase equilibrium is of special interest in chemical engineering as separation processes such as distillation and extraction involve phase contacting. The main focus of this research was the measurement of new phase equilibrium data for acetonitrile and water with heavy hydrocarbons that included: heptanoic acid, 1-nonanol, dodecane and 1-dodecene. Hence, binary vapour-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE) and vapour-liquid-liquid equilibrium (VLLE) data were investigated. The VLE and VLLE data were measured with the modified apparatus of Raal (Raal and Miihlbauer, 1998). The modification, undertaken by Ndlovu (2005), enabled measurement for VLLE systems. Isothermal binary VLE data for the (nonanol + 1-dodecene) system at 403.15 K was measured and VLLE data for the systems (acetonitrile + 1-dodecene) at 343.15 K, and (nonanol + water) at 353.15 K were investigated. The LLE data were measured with the modified apparatus of Raal and Brouckaert (1992). The modification, introduced by Ndlovu (2005), improved thermal insulation and the sampling procedures. Binary LLE data for the systems (acetonitrile + 1-dodecene) at 1 atm and (water + 1-nonanol) at 1 atm were measured. Furthermore, ternary data at 323.15 K and 1 atm were also measured for the systems containing water + acetonitrile with the each of the following components: heptanoic acid, 1-nonanol, dodecane and 1-dodecene. The experimental VLE data were regressed using two different methods: the combined method and the direct method. For the combined method, the second virial coefficients were calculated from the methods of Pitzer and Curl (1957) and Tsonopoulos (1974). The activity coefficients were calculated using three local-composition based activity coefficients models: the model of Wilson (1964), the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Anderson and Prausnitz (1978). For the direct method, the equation of state of Stryjek and Vera (1986) and the alpha function of Twu et al. (1991) in the equation of state of Peng and Robinson (1976) were employed. In addition, the mixing rules of Wong and Sandler (1992) and Twu and Coon (1996) were utilised. Furthermore, the point test of Van Ness et al. (1973) and the direct test of Van Ness (1995) were employed to test the thermodynamic consistency of the experimental VLE data measured in this work. The experimental binary LLE data were regressed using the three-suffix Margules model, Van Laar (1910) model and the NRTL model of Renon and Prausnitz (1968) to obtain the temperature dependence of the model parameters. The experimental ternary LLE data were subjected to a two part correlation: the tie-line correlation and the binodal curve correlation. The tie-lines were correlated with the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Anderson and Prausnitz (1978). The binodal curves were correlated with the Hlavaty (1972) equation, B-density function equation of Letcher et al. (1989) and the log y equation of Letcher et al. (1986).

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