Browsing by Author "Ntalikwa, J. W."
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Item Electrophoresis of colloidal α-alumina(2001) Ntalikwa, J. W.; Bryant, R.; Zunzu, J. S. M.Measurements of the electrophoretic mobility (u E) of particles of colloidal α-alumina were made as a function of pH, electrolyte concentration and electrolyte type (NaCl, NaNO3 and KCl) using two similar instrumental techniques. Significant differences (50% or less) in the values of u E of particles in NaCl were obtained from the two instruments; however, the isoelectric points (IEPs) (the pH at which u E=0), estimated from the two sets of measurements, occurred at 7.5 ± 0.3 and 7.8 ± 0.05 and were not significantly different. The latter estimate corresponds with those for particles in KCl and NaNO3 of 8.05 ± 0.11 and 7.95 ± 0.18, respectively, made using the same instrument and indicate that the IEP was a weak function of electrolyte type. When cations acted as counterions (pH > IEP), the absolute magnitudes and the ranges of u E with electrolyte concentration were found to be significantly less than when anions acted as counterions (IEP > pH). Estimates of the zeta potential (ζ), made using various procedures, showed variations of up to 25% at low ratios of electrical-double-layer thickness (κ −1) to particle radius (a) (κa∼10) and were of a similar scale to differences in u E, but no significant variations (95% confidence) in ζ were obtained at high values (κa∼200).Item Physico-chemical properties of biodiesel from jatropha and castor oils(Gazi University, 2012) Okullo, Aldo; Temu, A. K.; Ogwok, P.; Ntalikwa, J. W.Biodiesel is becoming prominent among the alternatives to conventional petro-diesel due to economic, environmental and social factors. The quality of biodiesel is influenced by the nature of feedstock and the production processes employed. High amounts of free fatty acids (FFA) in the feedstock are known to be detrimental to the quality of biodiesel. In addition, oils with compounds containing hydroxyl groups possess high viscosity due to hydrogen bonding. American Standards and Testing Materials, (ASTM D 6751) recommends FFA content of not more than 0.5% in biodiesel and a viscosity of less than 6 mm2/s. The physico-chemical properties of jatropha and castor oils were assessed for their potential in biodiesel. The properties of jatropha and castor oils were compared with those of palm from literature while that of biodiesel were compared with petro-diesel, ASTM and European Standards (EN14214). Results showed that high amounts of FFA in oils produced low quality biodiesel while neutralized oils with low amounts of FFA produced high quality biodiesel. The quality of biodiesel from jatropha and castor oils was improved greatly by neutralising the crude oilsItem Roasting kinetics of crude pyrite as acid mine drainage remediation option: A case study of Merelani(2018) Hiji, M. F.; Vuai, S. A.; Ntalikwa, J. W.Large-scale production of mine wastes and their secure disposal has been a problem of global concern. In this work, the chemical kinetics of roasting of crude pyrite, a mine waste from Merelani to form sulphur dioxide, a key precursor in the production of sulphuric acid was studied. Conversion of pyrite into sulphur dioxide revealed pseudo first order kinetic with respect of solid reactant in gas-solid system. The activation energy (Ea) value of 15kJ/mol was deduced from Arrhenius equation suggesting that the roasting reaction was controlled by diffusion of oxygen through the ash layer to the reacting surface. The utilisation of crude pyrite overburden will provide not only social economic development but also proper environmental mitigation of acid mine drainage.Item Transesterification reaction kinetics of jatropha oil for biodiesel production(2011) Okullo, A.; Temu, A. K.; Ntalikwa, J. W.Biodiesel, defined as the monoalkyl esters of vegetable oils and animal fats, is becoming prominent among alternatives to conventional petro-diesel due to economic, environmental and social factors. Transesterification is the most preferred method of biodiesel production. Knowledge of transesterification reaction kinetic enables prediction of the extent of the chemical reaction (or the conversion) at any time under particular conditions. It is also essential in the optimization of operating conditions in industrial applications and in the design of reactors for biodiesel production. In this study, transesterification of jatropha oil with methanol was carried out in a well mixed reactor at different agitation speeds (600-900 rpm) and temperatures (35-65 oC) using sodium hydroxide as a catalyst. The methanol to oil molar ratio of 6:1 was used and catalyst loading was 0.5% weight of oil. Mass transfer controlled state was assumed to be minimal using the above agitation speeds. A second order kinetic model was used to determine the reaction rate constants. The goodness of fit predicting the moles of methyl ester in the reaction products was determined by correlation coefficient (R2) and least square curve fit. The forward reactions were the most important as revealed by the rate constants.