Browsing Chemistry by Title
Now showing items 1-9 of 9
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Muriithi, Grace; Gitari, Wilson; Petrik, Leslie; Ndungu, Patrick (Elsevier, 2011)[more][less]
Abstract: Coal combustion by-products such as fly ash (FA), brine and CO2 from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface and ground water through leaching of toxic elements present in their matrices while CO2 has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO2 with FA/brine slurry can potentially provide a viable route for CO2 sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20–150 μm size fraction was observed to have the highest CO2 sequestration potential of 71.84 kg of CO2 per ton of FA while the >150 μm particles had the lowest potential of 36.47 kg of CO2 per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues. URI: http://hdl.handle.net/10566/757 Files in this item: 1
MuriithiFlyAsh2011.pdf (5.073Mb) -
Motswainyana, William M.; Onani, Martin O.; Jacobs, Jeroen; van Meervelt, Luc (International Union of Crystallography, 2012)[more][less]
Abstract: The title complex, [PdCl2(C20H20N2)] CH3CN, was synthesized by the reaction of 2-[(2,6-diethylphenyl)iminomethyl]quinoline with dichlorido(cycloocta-1,5-diene)palladium(II) in dry CH2Cl2. The PdII ion is coordinated by two N atoms of the bidentate quinoline ligand and by two chloride anions, generating a distorted square-planar coordination geometry around the metal centre. There is a detectable trans influence for the chloride ligands. The crystal packing is characterized by – stacking between the quinoline rings. The use of acetonitrile as the crystallization solvent was essential for obtaining good-quality crystals. URI: http://hdl.handle.net/10566/751 Files in this item: 1
MotswainyanaDichlorido2012.pdf (481.6Kb) -
Motswainyana, William M.; Onani, Martin O.; Jacobs, Jeroen; van Meervelt, Luc (International Union of Crystallography, 2013)[more][less]
Abstract: The title imino–phosphine compound, [PdCl2(C26H22NP)] - CH3CN, was prepared by reaction of N-[2-(diphenylphosphanyl) benzylidene]-2-methylaniline with dichlorido(cycloocta- 1,5-diene)palladium(II) in dry CH2Cl2. The PdII cation is coordinated by the P and N atoms of the bidentate chelating ligand and by two chloride anions, generating a distorted square-planar coordination geometry. There is a detectable trans influence for the chloride ligands. The methyl group present in this structure has an influence on the crystal packing. URI: http://hdl.handle.net/10566/752 Files in this item: 1
MotswainyanaDichlorido2013.pdf (594.0Kb) -
Madzivire, Godfrey; Gitari, Wilson, M.; Vadapalli, V.R. Kumar.; Ojumu, Tunde V.; Petrik, Leslie, F. (Elsevier, 2011)[more][less]
Abstract: The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca2+. This resulted in increased removal of sulphate as CaSO4·2H2O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO4·2H2O. The results of this study would have implications on the design of treatment methods relevant for different mine waters. URI: http://hdl.handle.net/10566/763 Files in this item: 1
MadzivireSulphate2011.pdf (4.952Mb) -
Musyoka, Nicholas; Petrik, Leslie; Hums, Eric; Baser, Hasan; Schwieger, Wilhelm (Elsevier, 2012)[more][less]
Abstract: In this study, high phase purity of zeolite A was prepared from coal fly ash precursors. The molar regime of both the clear solution extract and unseparated fly ash slurry was adjusted to achieve the right composition for zeolite A crystallization. The formation process for zeolite A from coal fly ash precursors was monitored in detail using an in situ ultrasonic system and was complemented by use of ex situ techniques such as XRD, FTIR, SEM and FTIR. The findings from both the in situ ultrasonic monitoring process and ex situ techniques clearly contributed significantly in unmasking the formation process of zeolite A from coal fly ash compared to previous studies reported in the literature. The study also enriches the existing body of literature by deeply investigating the gel–solution–crystal interactions starting from this complex feedstock. Comparable ultrasonic signals were generated when both clear and unseparated fly ash based precursor solutions were used during the zeolite synthesis process. URI: http://hdl.handle.net/10566/708 Files in this item: 1
MusyokaCoalFlyAsh2012.pdf (9.057Mb) -
Babajide, Omotola; Leslie, Petrik; Amigun, Bamikole; Ameer, Farouk (MDPI, 2009)[more][less]
Abstract: Biodiesel has attracted increasing interest and has proved to be a good substitute for fossil-based fuels due to its environmental advantages and availability from renewable resources such as refined and waste vegetable oils. Several studies have shown that biodiesel is a better fuel than the fossil-derived diesel in terms of engine performance, emissions reduction, lubricity and environmental benefits. The increasing popularity of biodiesel has generated great demand for its commercial production methods, which in turn calls for the development of technically and economically sound process technologies. This paper explores the applicability of ultrasound in the optimization of low-cost feedstock – in this case waste cooking oil – in the transesterification conversion to biodiesel. It was found that the conversion efficiency of the waste oil using ultrasound was higher than with the mechanical stirring method. The optimized variables of 6:1 methanol/oil ratio at a reaction temperature of 30 °C and a reaction time of 30 min and 0.75% KOH (wt/wt) catalyst concentration was obtained for the transesterification of the waste oil via the use of ultrasound. URI: http://hdl.handle.net/10566/573 Files in this item: 1
BabajideBiodiesel2009.pdf (248.8Kb) -
Babajide, Omotola; Petrik, Leslie; Musyoka, Nicholas; Ameer, Farouk (Elsevier, 2012)[more][less]
Abstract: Several studies have been carried out on the production of biodiesel using different heterogeneous catalysts but this study has been able to demonstrate the prospect of utilizing South African class F fly ash as a raw material for zeolite synthesis subsequently applied as a solid base catalyst in the production of biodiesel. A novel faujasite zeolite material synthesized from South African class F fly ash and denoted as FA/Na-X was ion exchanged with potassium to obtain the South African class F fly ash based zeolite FA/K-X. This heterogeneous catalyst was used in the conversion of sunflower oil with methanol to yield fatty acid methyl esters. Different characterization techniques were employed to give more information about this zeolite material. The FA/Na-X and the ion exchanged FA/K-X were applied as catalysts in biodiesel synthesis via transesterification reactions. A high quality biodiesel with a yield of 83.53% was obtained at reaction conditions of methanol:oil ratio of 6:1, catalyst amount of 3% (w/w) of oil and reaction temperature of 65 ◦C after 8 h. URI: http://hdl.handle.net/10566/679 Files in this item: 2
Babajide Omotola.pdf (1.441Mb)BabjideBiodieselProduction2012.pdf (4.254Mb) -
Muriithi, Grace; Gitari, Wilson; Petrik, Leslie (Taylor & Francis, 2012)[more][less]
Abstract: A D-optimal design was applied in the study of input factors: temperature, pressure, solid/liquid (S/L) ratio and particle size and their influence on the carbonation of brine impacted fly ash (FA) determined. Both temperature and pressure were at two levels (30◦C and 90◦C; 1 Mpa and 4 Mpa), S/L ratio was at three levels (0.1, 0.5 and 1) while particle size was at 4 levels (bulk ash, <20 μm, 20 μm −150 μmand >150 μm). Pressure was observed to have a slight influence on the % CaCO3 yield while higher temperatures led to higher percentage CaCO3 yield. The particle size range of 20 μm – 150 μm enhanced the degree of carbonation of the fly ash/brine slurries. This was closely followed by the bulk ash while the >150 μm particle fraction had the least influence on the % CaCO3. The effect of S/L ratio was temperature dependent. At low temperature, the S/L ratio of 1 resulted in the highest % CaCO3 formation while at high temperature, the ratio of 0.5 resulted in the highest percentage CaCO3 formation. Overall the two most important factors in the carbonation of FA and brine were found to be particle size and temperature. URI: http://hdl.handle.net/10566/764 Files in this item: 1
MuriithiCarbonationBrine2012.pdf (861.1Kb) -
Babajide, Omotola; Petrik, Leslie; Musyoka, Nicholas; Amigun, Bamikole; Ameer, Farouk (Slovnaft VÚRUP, 2010)[more][less]
Abstract: South Africa is largely dependent on the combustion of coal for electricity production; Eskom’s coalfired power stations consume approximately 109 million tons of coal per annum, producing around 25 million tons of ash, to supply the bulk (93%) of South Africa’s electricity. The management of this fly ash has been a concern with various approaches for its beneficial use being investigated. This work presents the results of transesterification reaction using sunflower oil as feedstock with methanol and class F fly ash catalyst derived from a coal fly ash dump in South Africa to produce methyl esters (biodiesel). The fly ash based catalyst was prepared using the wet impregnation procedure with different loadings of potassium. This was characterized by powder X-ray diffraction (XRD), FTIR spectroscopy. The XRD patterns obtained indicated that the structure of the support gradually deformed with an increase in the loading and the extent of decomposition of KNO3 varied with the amount of loading. The influence of various reactions parameters such as loading amount of active components, methanol: oil ratio, reaction time, temperature and catalyst deactivation was investigated. The fly ash based catalyst loaded with 5% wt KNO3 at a reaction temperature of 160ºC exhibited maximum oil conversion (86.13%). The biodiesel synthesized was tested and important fuel properties of the methyl esters (Biodiesel) compared well with ASTM biodiesel standard URI: http://hdl.handle.net/10566/574 Files in this item: 1
BabajideBiodieselProduction2010.pdf (597.5Kb)
Now showing items 1-9 of 9