Theses and dissertations (Engineering and Built Environment)
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Item Product development and processing of sugarcane wax from dissolved air flotation (DAF) mud(2023-05) Mtolo, Sandile; Kiambi, Sammy Lewis; Stark, AnneThe South African sugar industry is one of the world’s leading cost competitive producers of high-quality sugar. However, this industry is currently experiencing a gradual decline due to numerous challenges such as unfavourable climate conditions, economic decline, cheap sugar imports, the Health Promotion Levy (“sugar tax”), and lack of required capital for innovation (SASA, 2022). This crisis threatens tens of thousands of jobs and hundreds of thousands of livelihoods. As a result, this study seeks to contribute to the mitigation of the crisis faced by this industry. Recently, the Illovo’s Sezela furfural production plant downstream to the sugar mill was commissioned. This plant produces a waste with a sugarcane wax content of about 30% (R.D Gent, 2012), which is higher than the wax (8.3%) extracted from press mud reported by (Paturau, 1982). The aims of this study were to assess methods of separating the wax from DAF mud, as well as a method to refine the crude wax. Furthermore, the resulting waxes were to be characterised to allow for comparison with conventional sugarcane wax as well as other plant-based waxes such as carnauba wax. Finally, a preliminary process layout was proposed, and a mass balance of the overall process presented. This serves as a basis for future equipment sizing and costing exercises. Two methods of producing crude wax from DAF mud were compared in this study, namely a solvent extraction method and the, heating and melting method. The solvent extraction method involved dissolving DAF mud in five different solvents namely, turpentine oil, toluene, butanol, 2-butanone or ethanol. The heating and melting method involved heating the DAF mud to a melting point of crude wax and collecting the resulting wax by decanting. The crude wax yield obtainable via solvent extraction was in a range of 80 - 87.3 %, while the crude wax yield obtained via heating and melting was approximately 56%. Despite the relatively low attainable yield of crude wax via this latter method it was preferred over solvent extraction because eco-friendliness, and being more cost effective, simpler, and faster. The crude wax obtained via this method was a solid at room temperature, whilst the crude wax produced via the solvent extraction method was not in a solid at room temperature. Therefore, crude wax in a solid form is suitable for refined wax production as it can be directly treated with charcoal and a green solvent to obtain refined wax. Crude wax from the heating and melting method was used in the refining step. Both the crude and refined wax were characterized for their physico-chemical properties. Results show that crude wax produced by heating and melting method has an acid value of 155 ± 2.2 (mg KOH/g wax), saponification value of 227 ± 10 (mg KOH/g wax), % FFA of 78 ± 1, ester value of 72 ± 10 (mg KOH/g wax), Iodine number of 53 ± 5 (g I2/100 g), unsaponifiable matter (%) of 21.5 ± 2, melting point (°C) of 76 ± 2, density (g/cm3 ) of 0.850 – 0.882 (at temperatures between 25 and 80 °C) and refractive index (26°C) of 1.4923. Crude wax was further treated with activated charcoal and ethanol to obtain refined wax, at a crude wax: ethanol: activated charcoal ratio of 1:04:02. After crude wax was refined, it was then characterised for its physical and chemical properties. Refined wax characterization results showed that it has an acid value of 23 ± 3 (mg KOH/g wax), saponification value of 59 ± 7 (mg KOH/g wax), % FFA of 12 ± 1, ester value of 35 ± 7 (mg KOH/g wax), Iodine number of 44 ± 8 (g I2/100 g), melting point (°C) of 75 ± 2, density (g/cm3 ) of 0.787 – 0.814 (at temperatures between 25 and 80 °C) and refractive index (26°C) of 1.4867. The GC-MS analysis revealed that, similar to crude wax, refined wax predominantly consists of five main classes of compounds namely, fatty acids, alkanes, alcohols, aldehydes, and esters. Fatty acids contributed about 50% to the total composition for both crude and refined wax samples. Furthermore, both crude and refined wax samples were found to contain policosanol, which can be used to support the evidence of the applicability of sugarcane wax derived from Illovo’s Sezela DAF mud in various applications such as pharmaceuticals industry. In preparation for the scale up of the process a process layout was proposed and a process flow sheet for the whole process and subsequent mass balances derived. Mass balances will be useful in equipment sizing and overall project costing which is part of the future work and beyond the scope of this study. It was concluded that the crude sugarcane wax obtained from DAF mud is quite different from that obtained from filter mud. However, the ester number is in the range given in the literature for filter mud-derived sugarcane wax. The iodine number of the DAF mud-derived raw wax is much higher than that of the conventional filter mud-derived wax. The unsaponifiable matter was lower and the melting point is in the range reported for filter mud-based crude wax. The DAF mudderived refined wax of this study is compared to different wax fractions derived from conventional filter mud-based waxes. The saponification value lies within the ranges of “hard wax” and “refined wax”. The iodine number and the melting point of the refined wax from DAF mud lie within the ranges of “soft wax” and “hard wax”, respectively. Furthermore, the DAF mud-derived refined wax’ properties was found to resemble those of candelilla wax rather than carnauba wax, with the acid and saponification values as well as iodine number being in the same ranges. The melting point is 2-4°C higher than that specified for candelilla wax. Future studies should evaluate the economic feasibility of the process by costing the overall project, investing in the equipment to produce a completely eco-friendly refined sugarcane wax.Item Infinite dilution activity coefficient measurements for limonene as a green solvent for separation(2021-12-01) Mbatha, Banzi Patrick; Ramsuroop, Suresh; Ngema, Peterson ThokozaniThere is an increasing call from the international communities for the replacement of traditional petrochemical solvents used by the chemical and allied industries in the separation processes. This has led to the new interest in finding alternative “green” solvents, which can be used to optimize the separation processes of non-ideal or close boiling mixtures for better separation. This study focuses on investigating limonene as a “green” solvent to be utilized as a separating agent for separation processes. Limonene is a non-polar monoterpene solvent extracted from essential oils of the citrus peels. The extraction and distillation of this biomass extracted solvent releases fewer toxic pollutants and volatile gases, and as a result it has minimal impact to the environment. The infinite dilution activity coefficients (IDACs) for various solutes, which include alkanes, alkenes, alkynes, cycloalkanes, heterocycles, alcohol, aromatics, ketones, ethers, nitrile and water in the limonene solvent were measured using gas-liquid chromatography at (303.15, 313.15, 323.15 and 333.15) K. Through the experimental infinite dilution activity coefficients (IDACs), the values of partial molar excess enthalpy at infinite were obtained using the Gibbs-Helmholtz equation. To evaluate its potential of limonene as a mass transfer separation agent, its selectivity and capacity were calculated from the experimental limiting activity coefficients and were compared with ionic liquids and conventional solvents. From the results of this study, it was generally observed that for all solutes the activity coefficient at infinite dilution decreased with the increase of temperature and increased with the increase of alkyl chain length of the solute. The triple bond alkyl solutes had a strong interaction with the limonene, due to their low values of activity coefficients at infinite dilution. In some selective test cases, the selectivity and capacity for the separation of hexane/hex-1-ene and ethanol/water showing promising results when compared with ILs. The selectivity and capacity for the separation mixture of heptane/benzene, octane/ethylactetate, heptane/pyridine, octane/pyridine, and octane/thiophene indicated that the limonene was not suitable as the extraction solvent when compared with other ILs and conventional solvents. However, more investigation of limonene must be conducted through measurements liquid-liquid equilibrium and vapour-liquid equilibrium. Such data would provide useful information and understanding into the separation of hexane/hex-1-ene and ethanol/water mixtures. Green solvents extracted from biomass which have high boiling temperatures also be studied and compared with limonene solvent.Item Infinite dilution activity coefficient measurements of organic solutes in selected deep eutectic solvents by gas-liquid chromatography(2018) Nkosi, Nkululeko; Ramsuroop, Suresh; Tumba, Kaniki Armel; Osman, KhalidMany separation processes in the chemical and petrochemical industries are energy intensive, and unfortunately, involve a range of solvents that are environmentally harmful and destructive. Alternative, sustainable separation techniques are desired to replace these conventional methods used in the separation of azeotropic as well as close-boiling mixtures, with the intention of reducing energy costs and adverse impact on the environment. In the present study, a new class of solvents called deep eutectic solvents (DESs) of Type III were investigated as alternatives to conventional solvents currently employed in separation processes. DESs are classified as ‘green’ solvents because of a range of favourable properties including lower cost, desirable solubility properties and reduced environmental impact (Abbott et al., 2003b; Smith et al., 2014). The infinite dilution activity coefficients (IDACs) values of 24 solutes – including alk-1-anes, alk-1-enes, alk-1-ynes, cycloalkanes, alkanols, alkylbenzenes, heterocyclics, esters, and ketones – were measured at 313.15, 323.15, 333.15 and 343.15 K by gas-liquid chromatography (GLC) in DESs. The four investigated DESs were as follows: 1) Tetramethylammonium chloride + Glycerol (DES1); 2) Tetramethylammonium chloride + Ethylene Glycerol (DES2); 3) Tetramethylammonium chloride + 1,6 Hexanediol (DES3); and 4) Tetrapropylammonium bromide + 1,6 Hexanediol (DES4). This work focused on the performance of DESs as extractive solvents for selected azeotropic and close-boiling binary mixtures. The two key performance criteria for these extractive solvents – selectivity and capacity – were determined from experimental infinite dilution activity coefficients (IDACs) of various solutes. The effect of solute molecular structure on IDAC values was investigated. Moreover, the effect of varying the hydrogen bond donors (HBDs) in DESs on IDAC values was examined. Partial excess molar enthalpies at infinite dilution were determined from the experimental IDAC data. Moreover, common industrial separation problems were selected to investigate DES potential to separate various mixtures by determining selectivity and capacity at infinite dilution. The results obtained in this study indicate that the use of a long carbon chain HBDs greatly decreases miscibility of DESs with organic solutes. For systems such as n-heptane - toluene, acetone - ethanol, cyclohexane - benzene and n-hexane - benzene systems, DES4 was the best solvent regarding the separation performance index. However, further investigation for DES4 by measurements of vapour-liquid equilibria (VLE) and liquid-liquid equilibria (LLE) data is suggested, as these data would provide additional pertinent information regarding the separation of such mixtures using DES4. The data produced from this study can be used to extend the applicability range of predictive models such as Universal Quasi- Chemical Functional Group Activity Coefficients (UNIFAC) and modified UNIFAC (Do) which are already incorporated in some chemical engineering process simulators.Item VLE measurements of ether alcohol blends for investigation on reformulated gasoline(2016) Benecke, Travis Pio; Ramjugernath, Deresh; Ramsuroop, SureshSeparation processes in the chemical process industries is dependent on the science of chemical thermodynamics. In the field of chemical separation process engineering, phase equilibrium is a primary area of interest. This is due to separation processes such as distillation and extraction which involves the contacting of different phases for effective separation. The focal point of this research project is the measurement and modeling of binary vapour-liquid equilibrium (VLE) phase data of systems containing ether-alcohol organic compounds. The VLE data were measured with the use of the modified apparatus of Raal and Mühlbauer, (1998). The systems of interest for this research arose from an industrial demand for VLE data for systems containing ether-alcohol organic compounds. This gave rise to the experimental VLE data isotherms being measured for the following binary systems: a) Methyl tert-butyl ether (1) + 1-pentanol (2) at 317.15 and 327.15 K b) Methyl tert-butyl ether (1) + 2, 2, 4-trimethylpentane (2) at 307.15, 317.15 and 327.15K c) 2, 2, 4-Trimethylpentane (1) + 1-pentanol (2) at 350.15, 360.15 and 370.15K d) Diisopropyl ether (1) + 2,2,4-trimethylpentane (2) at 320.15, 330.15 and 340.15K e) Diisopropyl ether (1) + 1-propanol (2) at 320.15, 330.15 and 340.15K f) Diisopropyl ether (1) + 2-butanol (2) at 320.15, 330.15 and 340.15K The data for all the measured binary systems investigated at these temperatures are currently not available in the open source literature found on the internet and in library text resources. The systems were not measured at the same temperatures because certain system isotherm temperatures correlate to a pressures above 1 bar. This pressure of 1 bar is the maximum operating pressure specification of the VLE apparatus used in this project. The experimental VLE data were correlated for model parameters for both the and methods. For the method, the fugacity coefficients (vapour-phase non-idealities) were tabulated using the virial equation of state and the Hayden-O’Connell correlation (1975); chemical theory and the Nothnagel et al. (1973) correlation method. The activity coefficients (liquid phase non-idealities) were calculated using three local-composition based activity coefficients models: the Wilson (1964) model, the NRTL model (Renon and Prausnitz, 1968); and the UNIQUAC model (Abrams and Prausnitz, 1975). Regarding the direct method, the Soave-Redlich-Kwong (Redlich and Kwong, 1949) and Peng-Robinson (1976) equations of state ii were used with the temperature dependent alpha-function (α) of Mathias and Copeman (1983) with the Wong-Sandler (1992) mixing rule. Thermodynamic consistency testing, which presents an indication of the quality and reliability of the data, was also performed for all the experimental VLE data. All the systems measured showed good thermodynamic consistency for the point test of Van Ness et al. (1973) - the consistency test of choice for this research. This however, was based on the model chosen for the data regression of a particular system. Therefore, the combined method of VLE reduction produced the most favourable results for the NRTL and Wilson models.Item Effect of tray design on the performance of a vibrating plate extraction column(2015) Sincuba, Nomakhosi Dorothy; Rathilal, Sudesh; Carsky, MilanThere are various types of separation processes used in industries, such as, distillation, liquid-liquid extraction and gas absorption. Liquid-liquid extraction (LLE) is a separation process that involves mass transfer from a liquid mixture to an immiscible extraction solvent. This process is generally used where the mixture cannot be separated by fractional distillation due to close relative volatilities of the mixture components or for heat sensitive components. LLE is rated as the second most important separation process after distillation and it is widely used in chemical engineering industries. Different types of columns are available for LLE. Reciprocating and vibrating plate extraction columns are mechanically agitated extraction columns. In this research a vibrating plate extraction column was utilised. It uses perforated plates with down-comers. The perforations provide passage for the dispersed phase, while down-comers provide passage for the continuous phase. The effectiveness of a vibrating plate extractor was previously investigated but limited research was conducted on the effect of the different tray designs and agitation levels (as the product of amplitude and frequency of vibration). These variables affect the hydrodynamics and mass transfer in the column. The determination of the optimum process parameters is important in achieving the highest separation efficiency of the vibrating extraction column. The focus of this research is to test the effect of different tray designs in order to enhance the separation process efficiency. All tests were conducted using the toluene-acetone-water system as a standard test system proposed by the European Federation for Chemical Engineering, (1985). The experiments were conducted to test the effect of mass transfer on the hydrodynamics of the system while changing the agitation levels, downcomers and hole diameters. A comparative investigation was conducted on straight segment and circular downcomers, then hole diameters analysis was performed on the effective downcomer Comparison of the effect of the tray design types on the amount of acetone extracted was utilised to select the effective tray. Tray with the circular downcomer and 3.0 mm hole diameter had high dispersed phase holdup values and with the highest percentage amount of acetone extracted (95.05%) was obtained compared to other tray designs investigated.Item Separation processes for high purity ethanol production(2010) Ngema, Peterson Thokozani; Ramsuroop, Suresh; Pillay, Visvanathan Lingamurti; Ramjugernath, DereshGlobally there is renewed interest in the production of alternate fuels in the form of bioethanol and biodiesel. This is mainly due to the realization that crude oil stocks are limited hence the swing towards more renewable sources of energy. Bioethanol and biodiesel have received increasing attention as excellent alternative fuels and have virtually limitless potential for growth. One of the key processing challenges in the manufacturing of biofuels is the production of high purity products. As bioethanol is the part of biofuels, the main challenge facing bioethanol production is the separation of high purity ethanol. The separation of ethanol from water is difficult because of the existence of an azeotrope in the mixture. However, the separation of the ethanol/water azeotropic system could be achieved by the addition of a suitable solvent, which influences the activity coefficient, relative volatility, flux and the separation factor or by physical separation based on molecular size. In this study, two methods of high purity ethanol separation are investigated: extractive distillation and pervaporation. The objective of this project was to optimize and compare the performance of pervaporation and extraction distillation in order to produce high purity ethanol. The scopes of the investigation include: Study of effect of various parameters (i) operating pressure, (ii) operating temperature, and (iii) feed composition on the separation of ethanol-water system using pervaporation. Study the effect of using salt as a separating agent and the operating pressure in the extractive distillation process. The pervaporation unit using a composite flat sheet membrane (hydrophilic membrane) produced a high purity ethanol, and also achieved an increase in water flux with increasing pressure and feed temperature. The pervaporation unit facilitated separation beyond the ethanol – water system azeotropic point. It is concluded that varying the feed temperature and the operating pressure, the performance of the pervaporation membrane can be optimised. v The extractive distillation study using salt as an extractive agent was performed using the low pressure vapour-liquid equilibrium (LPVLE) still, which was developed by (Raal and Mühlbauer, 1998) and later modified by (Joseph et al. 2001). The VLE study indicated an increase in relative volatility with increase in salt concentration and increase in pressure operating pressure. Salt concentration at 0.2 g/ml and 0.3 g/ml showed complete elimination of the azeotrope in ethanol-water system. The experimental VLE data were regressed using the combined method and Gibbs excess energy models, particular Wilson and NRTL. Both models have shown the best fit for the ethanol/water system with average absolute deviation (AAD) below 0.005. The VLE data were subjected to consistency test and according to the Point test, were of high consistency with average absolute deviations between experimental and calculated vapour composition below 0.005. Both extractive distillation using salt as an extractive agent and pervaporation are potential technologies that could be utilized for the production of high purity ethanol in boiethanol-production.