Acetylpropionyl (2,3-pentanedione) and diacetyl (2,3-butanedione) are by-products of sugar manufacture. Both diketones have many uses, mainly food related. Vapour-liquid equilibrium data and infinite dilution activity coefficients are required to design purification processes for these chemicals. A review of available experimental methods revealed that the vapour and liquid recirculating still is most appropriate when both isobaric and isothermal VLE are required. The low-pressure dynamic still of Raal and Muhlbauer (1998) used in this study incorporates many features to ensure that measurements are of excellent quality (as demonstrated by Joseph et al., 2001). VLE measurements were made for the following systems: • Acetone with diacetyl at 30 C, 40 C, 50 C and 40 kPa • Methanol with diacetyl at 40 C, 50 C, 60 C and 40 kPa • Diacetyl with 2,3-pentanedione at 60 C, 70 C, 80 C and 40 kPa • Acetone with 2,3-pentanedione at 50 C, 30 kPa and 40 kPa. All the systems, except for methanol with diacetyl, displayed close to ideal behaviour. This was expected as they are mixtures of ketones. Solution thermodynamics allows one to perform data reduction of the measured VLE data to ensure accurate extrapolation and interpolation of the measurements. Furthermore, the quality of the data can be judged using thermodynamic consistency tests. The data were represented by the Gamma-Phi approach to VLE (the preferred method for low-pressure VLE computations). The two-term virial equation of state was used to account for vapour phase non-ideality. Second virial coefficients were calculated by the method of Hayden and 0'Connell (1975). The liquid phase non-ideality was accounted for by the Wilson, NRTL or UNIQUAC models. The best fit models are proposed for each system, as are parameters as functions of temperature for the isobaric data. The data were judged to be of high thermodynamic consistency by the stringent point test (Van Ness and Abbott, 1982) and the direct test (Van Ness, 1995) for thermodynamic consistency. The data sets were rated, at worst, "3" on the consistency index proposed by Van Ness (1995). A rating of "I" is given for a perfectly consistent data set and "10" for an unacceptable data set. For the system acetone with 2,3-pentanedione, isobars at 30 kPa and 40 kPa were measured. The results from the reduction of the 30 kPa set were used to accurately predict the 40 kPa data set. Infinite dilution activity coefficients were measured by the inert gas stripping method (based on the principle of exponential dilution). In order to specify the appropriate dilutor flask height (to ensure equilibrium is achieved), mass transfer considerations were made. These computations ensured that the gas phase was in equilibrium with the liquid phase at the gas exit point. The following infinite dilution activity coefficients were measured: • Acetone in diacetyl at 30 C • Methanol in diacetyl at 40 C • Diacetyl in 2,3-pentanedione at 60°C • Acetone in 2,3-pentanedione at 50 C. The ketone mixtures, once again, displayed close to ideal behaviour. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Separation processes are fundamental to all chemical engineering industries. Solvent separation, either liquid-liquid extraction or extractive distillation, is a specialised segment of separation processes. Solvents can be used either to optimise conventional distillation processes or for azeotropic systems, which can not be separated by conventional means. This work focuses on the performance of monoethanolamine (MEA) as a solvent in extractive distillation. Furthermore, the methodology of solvent evaluation is also studied. The preliminary assessment of solvent selection requires the determination of selectivity factors. The selectivity factor is defined as follows: P• = y,." . y, where y" is the activity coefficient at infinite dilution of the solute in the solvent. Subscript 1 and 2 refer to solute 1 and 2. A large selectivity factor implies enhanced separation of component 1 from 2 due to the solvent. Activity coefficients at infinite dilution were determined experimentally (gas-liquid chromatography) and predicted theoretically (UNIFAC group contribution method) for twenty-four solutes at three temperatures. Solutes used were alkanes, alkenes, alkynes, cyclo-alkanes, aromatics, ketones and alcohols. Most of this experimental work comprises data for systems which have not been measured before. Predicted and experimental values for y' were compared. For systems such as these (with polar solvents and non-polar solutes), UNIFAC results are not accurate and experimentation is vital. The experimental selectivity factors indicated tihat MEA could be an excellent solvent for hydrocarbon separation. Three binary azeotropic systems were chosen for further experimentation with MEA n-hexane (1) - benzene (2): fJ,~ = 31. Compared to other industrial solvents this is one of the largest values and MEA could serve as an excellent solvent. cyclohexane (1) - ethanol (2): fJ,~ = 148. This high value indicates an excellent solvent for this system. Acetone (1) - methanol (2): fJ,~ = 7.7. Further work involved vapour-liquid equilibrium experimentation at sub-atmospheric pressures in a dynamic recirculating stil l. The binary components with a certain amount of MEA were added to the still. The vapour and liquid mole fractions for the binary azeotropic components were measured and plotted on a solvent-free basis. The results are summarised below: n-hexane - benzene: Amount MEA added to still feed: 2%. MEA improved separability slightly. Further addition of MEA resulted in two liquid phases forming. cyclohexane - ethanol: Amount MEA added to still feed: 5% and 10%. Two liquid phases were formed for cyclohexane rich mixtures. Addition of MEA improved separability but did not remove the azeotrope. acetone - methanol: Amount MEA added to still feed : 5%, 10% and 20%. The ternary mixture remained homogenous and separability improved with addition of MEA. The binary azeotrope was eliminated. Due to the hetrogenous nature of the cyclohexane - ethanol system liquid-liquid equilibrium experimentation was performed to complete the analysis. Viable separation processes are possible for (a) cyclohexane - ethanol mixtures and for (b) acetone - methanol mixtures using MEA as the solvent. Comparison of various solvents used for the separation of acetone from methanol was possible by constructing equivolatility curves for the ternary systems. Results showed that MEA may possibly be the best solvent for this extractive distillation process. This study provides the following results and conclusions: • New thermodynamic data, important for the understanding of MEA in the field of solvent separations, was obtained. • Results show that the UNIFAC contribution method cannot be used to accurately predict polar solvent - non-polar solute y«> values. Experimentation is essential. • Selectivity factors indicate that MEA could be an excellent solvent for hydrocarbon separation. • The separation of the azeotropic cyclohexane - ethanol mixture is possible with a combination of extractive distillation and liquid-liquid extraction or simply liquid-liquid extraction using MEA as the solvent. • The separation of the azeotropic acetone methanol mixture is possible with extractive distillation using MEA as the solvent. The solvent MEA is possibly the best solvent for this separation. / Thesis (M.Sc.Eng.)-Univeristy of Natal, Durban, 2000.

A typical petro-chemical or oil-refining plant is known to operate with hundreds if not thousands of control loops. All critical loops are primarily required to operate at their respective optimal levels in order for the plant to run efficiently. With such a large number of vital loops, it is difficult for engineers to monitor and maintain these loops with the intention that they are operating under optimum conditions at all times. Parts of processes are interactive, more so nowadays with increasing integration, requiring the use of a more advanced protocol of control systems. The most widely applied advanced process control system is the Model Predictive Controller (MPC). The success of these controllers is noted in the large number of applications worldwide. These controllers rely on a process model in order to predict future plant responses. Naturally, the performance of model-based controllers is intimately linked to the quality of the process models. Industrial project experience has shown that the most difficult and time-consuming work in an MPC project is modeling and identification. With time, the performance of these controllers degrades due to changes in feed, working regime as well as plant configuration. One of the causes of controller degradation is this degradation of process models. If a discrepancy between the controller’s plant model and the plant itself exists, controller performance may be adversely affected. It is important to detect these changes and re-identify the plant model to maintain control performance over time. In order to avoid the time-consuming process of complete model identification, a model validation tool is developed which provides a model quality indication based on real-time plant data. The focus has been on developing a method that is simple to implement but still robust. The techniques and algorithms presented are developed as far as possible to resemble an on-line software environment and are capable of running parallel to the process in real time. These techniques are based on parametric (regression) and nonparametric (correlation) analyses which complement each other in identifying problems -iiwithin on-line models. These methods pinpoint the precise location of a mismatch. This implies that only a few inputs have to be perturbed in the re-identification process and only the degraded portion of the model is to be updated. This work is carried out for the benefit of SASOL, exclusively focused on the Secunda plant which has a large number of model predictive controllers that are required to be maintained for optimal economic benefit. The efficacy of the methodology developed is illustrated in several simulation studies with the key intention to mirror occurrences present in industrial processes. The methods were also tested on an industrial application. The key results and shortfalls of the methodology are documented. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

The work described in this thesis was aimed at obtaining a better understanding of the neutral sulphite semichemical pulping process employed by Mondi Kraft's Piet Retief mill, and to investigate ways to improve this process. The unique feature of the process in this mill is that hardwood and softwood species are pulped simultaneously in a continuous digester. The pulping trials described were carried out in a laboratory batch digester which was build as a part of this project. Pulps were evaluated for yield, Hypo number as an indication of the residual lignin content and strength properties. The first part of the experimental work focused on the effect that different pulping variables have on the process and the resulting pulp. Variables investigated were the chemical charge, pulping temperature, chip composition and anthraquinone dosage. The second part of the work was to investigate ways in which the process can be improved. In particular it was investigated whether it would be advantageous to pulp hardwood and softwood separately and mix the two pulps together after pulping. The effect of changing to an alkaline sulphite process was also briefly investigated. It was found that the current process is optimized as far as the chemical charge and pulping temperature is concerned. Increasing the softwood percentage used to 50 % (from current value of 41 %) increases the tear strength, whilst decreasing it to 30 % increases the tensile strength of the resulting pulp. It was also determined that increasing the AQ dosage from 0.1 % to 0.5 % might bring savings in chemical costs. It is suggested that this is investigated in a mill trial. It was further found that pulping the two species separately improves the tear strength of the pulp by about 20 % compared with that which was pulped simultaneously. The results indicate that no benefits concerning the chemical costs, pulping temperature, pulp yield, burst strength or tensile strength are to be gained from separate pulping. Preliminary results indicated that significant strength increases and possible chemical cost savings are to be gained by changing from a neutral sulphite to an alkaline sulphite process. Further work to determine the reproducibility of these results, as well as the effect of different chemical charge and ratios is suggested. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

The desire for precise polymer property control, minimum wastage through grade transitions, and early instrument fault detection, has led to a significant effort in the modelling and control of ethylene polymerisation world-wide. Control is difficult due to complex inter-relationships between variables and long response times from gas to solid phase. The approach in this study involves modelling using the kinetic equations. This forms the basis of a scheme for real-time kinetic parameter identification and Kalman filtering of the reactor gas composition. The scheme was constructed off-line and tested on several industrial polymer grades using historical plant data. The scheme was also converted into a form for use on the linear low-density polyethylene plant, Poly 2, at POLlFIN Limited. There proved to be no difficulty in the identification step, but the Kalman filter requires more tuning for reliable fault detection. The software has been commissioned on-line and results from the POLlFIN plant match the off-line model exactly. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Climbing film evaporators are in widespread use in the South African sugar industry, with the vast majority of the local sugar mills currently utilising these evaporators as first effect vessels in multiple effect evaporator sets. However, it is generally considered that the performance of these evaporators has not been maximised, and that improvements could be achieved by proper optimisation of the operating parameters. Unfortunately, very little comprehensive design information has been published in the literature. owing to the complexity of the heat transfer and hydrodynamic interactions in the evaporator tube. Attempts at performance improvement have been hampered by the lack of any theory to explain fully the effects of the operating parameters and physical properties of the feed liquor on the performance of the evaporator. In this study. a mathematical model of the climbing film evaporator system was developed in order to assess the effects of changing operating conditions on evaporator performance, based on as solid a theoretical foundation as cunendy possible. The model was tested against experimental data from a pilot plant climbing film evaporator and this experimental data was used to enhance the accuracy of the model by means of process identification. Because of the complexity of the model and the extensive computational time required for its solution, a simplified evaporator model was also developed, based on Iinearisation of the system of ordinary differential equations describing the climbing film evaporator system. This simplified model was used to predict trends in evaporator behaviour under various operating conditions. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.

The objective of this project is to optimize the SAPREF oil refinery steam distribution in which imbalances between the various levels presently require the venting of steam from the lowest level. The overall steam balance shows that the problem originates from an excess of high·pressure (HP) steam production for too few medium pressure steam users and turbines. We proposed to solve this problem by considering the replacement of selected steam turbines with electrical drives. Given a set of demands of electricity, mechanical power and steam at various pressure levels, the objective is to recommend configuration changes to minimize overall cost. This is not a trivial problem, as steam not passed down through turbines to lower levels can create a shortage there, so a combination of replacements is required. The variables of the problem are both decision variables on every steam turbine and continuous variables, such as flows and enthalpies. These decision variables are integer variables, 0 or 1 for every steam turbine. Depending on whether it is kept on steam use or replaced with an electrical drive, these variables are as follows: E = 0: keep the existing steam turbine E - 1: switch it to an electrical drive. A complete and realistic model of this utility section must be constructed in order to represent the actual distribution accurately. This model will include an objective function to minimize, some equality and inequality constraints, and some cost functions. If we want this model to be accurate, we shall have to deal with nonlinearities to avoid simplifications, and these non-linearities could lead to infeasabilities or sub-optimal solutions. So we are facing a typical MTNLP (Mixed Integer Non-Linear Programming) problem to find optimal configuration changes which will maximize the return on investment, meeting the electrical, mechanical and steam demands of the refinery. In order to solve this difficult optimization problem we shall use the user-friendly package GAMS (General Algebraic Modeling System). / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.

Experimental vapour-liquid equilibria (VLE) data is required for the design of separation / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

Environmental and safety concerns have prompted an active quest for ―green‖ alternatives to / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

The mining of coal in arid regions has led to calls for research in to the field of dry beneficiation, / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.