3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Development of a Non-Derivatizing Solvent System for the Pretreatment of South AfricanCorn Cob(2019) Ejekwu, OlayileDepleting fossil fuels and the increasing energy demand has necessitated the move to alternative renewable forms of energy. Lignocellulosic biomass is a renewable and sustainable source for highly valuable bio-based chemicals and material production in a biorefinery system. The effective fractionation of the main components of lignocellulosic biomass (cellulose, hemicellulose and lignin) into usable forms is a crucial step in unlocking an economically viable, high-value product producing biorefinery. The main concern associated with the conversion of lignocellulose is overcoming biomass recalcitrance using pretreatment while still maintaining a green, cost-effective and energy efficient process. Over the last decade, molten hydrate salts have been used for isolated cellulose dissolution, however very few studies have been done to check their ability in lignocellulosic biomass pretreatment. The aim of the study was to compare seven molten hydrate salt solvent systems including unary, binary and ternary mixtures of ZnCl2.4H2O, LiClO4.3H2O and Urea for the effective pretreatment of corncob in terms of physicochemical properties and pretreatment efficiencies and to optimise these efficiencies. The molten salt hydrate pretreatment systems used in this study are aimed at fractionating the corn cobs biomass into a solid fraction which mostly contains cellulose and lignin as the major components, while the liquid fraction contains hemicellulose as the main component. The pretreatment experiments were carried out at 70 for 60 minutes at a biomass: solvent ratio of 1:10. Physicochemical change after pretreatment was checked by FTIR, XRD and SEM. The most efficient solvent mixture was identified by gravimetric analysis for its ability to fractionate the biomass into a cellulose and lignin rich solid fraction and a hemicelluloserich liquid fraction. The effect of solvent pretreatment operating variables (temperature, time and solvent concentration) was investigated to maximize cellulose recovery, hemicellulose recovery in the liquid fraction and lignin recovery from the biomass by response surface methodology (RSM) approach using a central composite design (CCD). Physicochemical analysis showed a decrease in crystallinity and an increase in surface area after the pretreatment in all the MHS solvents tested. This work has successfully shown the use of ZnCl2.4H2O/ Urea, to pre-treat and fractionate corn cob with high recovery of cellulose (100%), low recovery of hemicellulose (42%) and lignin (44%) when compared to the other proposed systems. Through the RSM approach, optimum pretreatment conditions obtained Abstract were: 90 min, 120 oC and concentration of 71.32%/28.68 (w/w) ZnCl2.4H2O/ Urea. At these conditions, the predicted recovery for cellulose, hemicellulose and lignin 99.03%, 27.18% and 72.43% respectively with a desirability of 0.902. The actual recovery was 91%, 29% and 68% for cellulose, hemicellulose and lignin respectively at the same conditions. For a better understanding of the dissolution kinetics and thermodynamics of cellulose, hemicellulose and lignin dissolution in ZnCl2.4H2O/ Urea solvent system, a kinetic study was carried out. The results reveal the dissolution to be a 1st order kinetics and the obtained activation energy for cellulose, hemicellulose and lignin dissolution were 14.10 kJ.mol-1, 11.29 kJ.mol-1 and 7.606 kJ.mol-1 ,respectively. that the dissolution process for all three components are endothermic and endergonic. The -0.190; -0.195 kJ.mol-1) showed that the process of dissolution of hemicellulose occurred more rapidly and produced more stable products. It was concluded that ZnCl2.4H2O/ Urea pretreatment provided a potential way to fractionate lignocellulosic biomass which can improve the effective utilization of all feedstock fractions.Item Product carbon footprint analysis for the packaging process of returnable glass and pet containers for a South African carbonated soft drinks business(2016) Ivanov, IvanNon-renewable resources are becoming scarce and current Global Warming Potential (GWP) values are rising. In an effort to promote a successful shift towards a “greener’ planet, governments worldwide are developing policies, which enforce businesses to contribute to the effort. One such policy is the potential upcoming carbon tax (measured in weight of C02e) in South Africa. As a result, industries need to carefully analyse and understand their core processes and their impact on the environment to ensure that their operations have the lowest environmental cost possible. One such industry in South Africa is the fast growing Carbonated Soft Drinks (CSD) beverage packaging industry. CSD are packaged in both Returnable Glass Bottles/Glass (RGB) and PET containers. The Product Carbon Footprint (PCF) of the CSD packaging process for 300ml Glass and 500ml PET containers was of particular interest. Review of academic literature revealed that no similar research has been conducted previously in South Africa. International studies on PCF, which vastly use the (ISO 14040/14044, 2006) for their method, were found to have conflicting results and conclusions regarding the “greenness” of the two types of containers both with respect to the overall GWP of each and the percentage contribution of the packaging process life cycle stage to the total environmental impact. This is mainly because such studies are region and technology specific. A study was therefore required to understand the implications the business' Glass and PET CSD packaging process has on its GWP and hence carbon tax. The GHG (Green House Gas) Protocol PCF guideline (World Resource Institute, 2013) was used to construct the method for this research to ensure best practice, which would allow the study to be expanded into a full blown Fife Cycle Assessment (FCA) as future work. It was found that the 500ml PET packaging process draws 100% of its Cumulative Energy Demand (CED) from purchased electricity (generated by burning coal) and has a GWP of 65 147 gCCTe/hl (hectolitre), which is 4.5 times less than that for 300ml Glass (294 173 gCCEe/hl) which has 71% of its emissions resulting directly from coal fired boilers on site. A dynamic model analysis revealed that packaging in larger containers results in a significant GWP reduction per volume for both Glass and PET containers. It was recommended that short term the business needs to focus on optimising its packaging lines’ equipment, work with suppliers on reducing the weight of the raw materials used for the packaging containers manufacture and promote rate of return of its Glass.Item Optimization and kinetics study of solvent pretreatment of South African corn cob for succinic acid production(2018) Mudzanani, Khuthadzo EdnaIncreasing concerns over environmental and geo-political issues on resources’ sustainability have driven the industries to shift their efforts to produce chemicals from renewable biomass. Amongst the lignocellulosic biomass, corncob contains cellulose, hemicellulose and lignin that are built in a compact structure which makes it difficult to access. Pre-treatment is then applied to make the content to be accessible to enzymatic hydrolysis which breaks down the polysaccharides to monomers. The sugar monomers can be converted to a wide range of bioproducts such as biofuels and bio-chemicals. The objective of the study was to determine, evaluate and optimize the best solvent system to pre-treat corn cob. In addition, the study evaluated the effect of pre-treatment parameters on the yield of cellulose and hemicellulose and attempt to develop a kinetic model to explain the dissolution. Lithium perchlorate, zinc chloride, phosphoric acid, sulphuric acid and sodium hydroxide were used during the pre-treatment, which was carried out at 70-80 ° C for 6 hours. Characterization of pre-treated samples showed a significant change in structure after pretreatment indicating disruption in cell wall of the lignocellulosic material. FTIR revealed a reduction in phenolic group; indicating that the lignin content has been reduced. The XRD patterns show that crystallinity was considerably reduced; this was shown by an increase in calculated crystallinity index (CrI) after LiClO4, ZnCl2, H3PO4 and NaOH pre-treatment. The CrI of raw corncob (CrI= 32.7%) increased to 46.2 %, 42.3 %, 55.6 % and 53.4 % of LiClO4, ZnCl2, H3PO4 and NaOH, respectively. The crystallinity index increased for pre-treated material, indicating that the amorphous cellulose is dissolved in the liquor, as well as lignin and hemicellulose removal This study has shown that LiClO4.2H2O pretreatment agent is an efficient solvent system to pretreat corncob which consecutively increase the accessibility of cellulose and hemicellulose from the solid fractions. The accessibility was confirmed by an ease hydrolysis of cellulose & hemicellulose to glucose & xylose respectively. An increase of nearly four times compared to the untreated corncob. The effect of reaction operating parameters i.e. Reaction time, temperature and solvent concentration was carried out and then optimized by response surface methodology (RSM) using Minitab 16. The target was to maximize the yield of cellulose and hemicellulose. It was discovered that the increase in temperature and reaction time increase the accessibility of cellulose and hemicellulose until an equilibrium is reached at 3 & half hours and 176 °c. The pretreatment solvent concentration was discovered to have an effect on the accessibility but not as much as temperature and time. The best pretreatment conditions to obtain high polysaccharides conversions to monomers were at 176°c for 3.5 hours using LiClO4.2H2O for 10 g of corncob. The results obtained from RSM were used to evaluate the temperatures profile, kinetic model for the corncob pretreatment as a function of temperature. The kinetics of pretreatment were studied by the amount of glucose, xylose and the lignin removed from the pretreated solids. The kinetic model of lignin removal and sugars accessibility was identified as a first-order reaction corresponding to the bulk phase for pretreatment time up to 24 hours. The rate constant results show that the kinetic rate increased with temperature. The activation energy for glucose, xylose and lignin were calculated to be 15.0 kJ/mol, 14.2 kJ/mol and 36.54 kJ/mol, respectively.