The plasticity of coal during pyrolysis is of significant importance, since it affects the reactivity, porosity, particle size and the density of the char and thus also the behaviour of the char during further utilisation processes. The main focus of this study was to characterize the chemical and physical changes which the thermally treated coal undergoes, in order to better understand the pyrolysis process of caking and non-caking South African coals. The pyrolysis behaviour of three South African coals with different caking indices was investigated. The coal samples included; (1) Highveld (TWD), a medium rank C coal with a free swelling index (FSI) of 0, (2) Grootegeluk (GG), also a medium rank C coal, with a FSI of 6.5, and (3) Tshikondeni (TSH), a medium rank B coal with the highest FSI of 9. The three coal samples were classified as vitrinite-rich coals consisting of mainly aliphatic structures. Thermogravimetric experiments were used to determine the different temperatures relating to specific percentages of mass loss using set conditions. The pyrolysis process was stopped at various percentages of mass loss (thus at various stages of the reactions) to characterize the chemical structural changes that occurred at the specific mass loss percentages. The results obtained from characterization analyses indicated that the three coals differ in chemical composition and thus were expected to behave differently during pyrolysis. The coal samples consist of different amounts of macerals and minerals according to X-ray Fluorescence (XRF) and X-ray Diffraction (XRD) analyses. The Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) results indicated that some of the functional groups within the coal samples evolved with the increase in temperature. The highly caking coal (TSH) exhibited the highest aromaticity and ring condensation. The surface areas were determined by CO2 adsorption and an increase in surface area was observed with an increase in temperature. The surface area of the GG and TSH coal-derived char samples decreased at some stage, which is an indication of thermoplastic behaviour and subsequent swelling of the coal samples. Scanning electron microscopy (SEM) images confirm the plastic stage of caking coals at specific temperatures and volatile matter release via the multiple bubble mechanism. All these results are given and discussed extensively in this dissertation. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

The plasticity of coal during pyrolysis is of significant importance, since it affects the reactivity, porosity, particle size and the density of the char and thus also the behaviour of the char during further utilisation processes. The main focus of this study was to characterize the chemical and physical changes which the thermally treated coal undergoes, in order to better understand the pyrolysis process of caking and non-caking South African coals. The pyrolysis behaviour of three South African coals with different caking indices was investigated. The coal samples included; (1) Highveld (TWD), a medium rank C coal with a free swelling index (FSI) of 0, (2) Grootegeluk (GG), also a medium rank C coal, with a FSI of 6.5, and (3) Tshikondeni (TSH), a medium rank B coal with the highest FSI of 9. The three coal samples were classified as vitrinite-rich coals consisting of mainly aliphatic structures. Thermogravimetric experiments were used to determine the different temperatures relating to specific percentages of mass loss using set conditions. The pyrolysis process was stopped at various percentages of mass loss (thus at various stages of the reactions) to characterize the chemical structural changes that occurred at the specific mass loss percentages. The results obtained from characterization analyses indicated that the three coals differ in chemical composition and thus were expected to behave differently during pyrolysis. The coal samples consist of different amounts of macerals and minerals according to X-ray Fluorescence (XRF) and X-ray Diffraction (XRD) analyses. The Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) results indicated that some of the functional groups within the coal samples evolved with the increase in temperature. The highly caking coal (TSH) exhibited the highest aromaticity and ring condensation. The surface areas were determined by CO2 adsorption and an increase in surface area was observed with an increase in temperature. The surface area of the GG and TSH coal-derived char samples decreased at some stage, which is an indication of thermoplastic behaviour and subsequent swelling of the coal samples. Scanning electron microscopy (SEM) images confirm the plastic stage of caking coals at specific temperatures and volatile matter release via the multiple bubble mechanism. All these results are given and discussed extensively in this dissertation. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

Thirty million tons of coal fly ash are produced each year in South Africa of which approximately 5% is utilised beneficially. With the growing concern about pollution and increasing landfill costs, the study of the utilisation and application of coal fly ash has increased worldwide. The morphology and particle size of fly ash make it suitable for application as filler in polymers, but its application is hindered by the lack of compatibility between the inorganic surface of the ash and the organic matrix of the polymer. Another concern is the agglomeration between fly ash particles. For this reasons, surface treatment is usually performed on mineral fillers to enhance workability and compatibility between the polymer and filler. This study involved the surface modification of South African coal fly ash with an anionic surfactant, sodium lauryl sulphate (SLS), under different treatment conditions. Surface and physical properties of the untreated and treated fly ash were studied systematically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in order to determine the extent of interaction between the SLS and the fly ash surface. Other analytical techniques applied include Thermogravimetric analysis (TGA-FTIR), Particle size distribution, X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), Raman spectroscopy and Fourier Transform Infrared spectroscopy FTIR). Although the overall chemical composition of the SLS modified coal fly ash investigated in this study was not altered extensively, significant changes could be observed in its physical properties. The hydrophilic surface of untreated fly ash was rendered hydrophobic after SLS treatment. SEM results indicated a decrease in agglomeration between fly ash spheres upon surfactant treatment, while results obtained from TEM have shown agglomerates on the surface of most of the fly ash spheres. There is a distinct difference between the morphology of agglomerates on the untreated and SLS modified fly ash, and also between samples treated under different conditions. Not all SLS modified fly ash particles were covered with agglomerates to the same degree. Results obtained from FTIR and TGA-FTIR studies were promising in the sense that hydrocarbon fractions could be observed in the TGA-FTIR decomposition products. The possibility of interactions between fly ash and SLS could be deduced from the FTIR results of the solid samples, due to a small shift in peak positions of the S-O stretch vibration, which may be indicative of electrostatic interactions rather than bonding interactions between SLS and fly ash. The presence of SLS could not be confirmed by Raman spectroscopy, but rendered information about the spatial distribution of the various phases in the fly ash. Feasibility tests were performed on the application of fly ash samples as filler in PVC. These results indicate that SLS treated fly ash can successfully replace CaCO3 as filler in PVC under conditions of low filler loadings / Dissertation (MSc)--University of Pretoria, 2013. / Chemistry / unrestricted

The swelling and caking propensity of coals may cause operational problems such as channelling and excessive pressure build-up in combustion, gasification and specifically in fluidised-bed and fixed-bed operations. As a result, the swelling and caking characteristics of certain coals make them less suitable for use as feedstock in applications where swelling and/or caking is undesired. Therefore, various studies have focused on the manipulation of the swelling and/or caking propensity of coals, and have proven the viability of using additives to reduce the swelling and caking of powdered coal (<500 μm). However, there is still a lack of research specifically focused on large coal particle devolatilisation behaviour, particularly swelling and caking, and the reduction thereof using additives. A comprehensive study was therefore proposed to investigate the swelling and caking behaviour of large coal particles (5, 10, and 20 mm) of typical South African coals, and the influence of the selected additive (potassium carbonate) thereon. Three different South African coals were selected based on their Free Swelling Index (FSI): coal TSH is a high swelling coal (FSI 9) from the Limpopo province, GG is a medium swelling coal (FSI 5.5-6.5) from the Waterberg region, and TWD is a non-swelling coal (FSI 0) from the Highveld region. Image analysis was used to semi-quantitatively describe the transient swelling and shrinkage behaviour of large coal particles (-20+16 mm) during lowtemperature devolatilisation (700 °C, N2 atmosphere, 7 K/min). X-ray computed tomography and mercury submersion were used to quantify the degree of swelling of large particles, and were compared to conventional swelling characteristics of powdered coals. The average swelling ratios obtained for TWD, GG, and TSH were respectively 1.9, 2.1 and 2.5 from image analysis and 1.8, 2.2 and 2.5 from mercury submersion. The results showed that coal swelling measurements such as FSI, and other conventional techniques used to describe the plastic behaviour of powdered coal, can in general not be used for the prediction of large coal particle swelling. The large coal particles were impregnated for 24 hours, using an excess 5.0 M K2CO3 impregnation solution. The influence of K2CO3-addition on the swelling behaviour of different coal particle sizes was compared, and results showed that the addition of K2CO3 resulted in a reduction in swelling for powdered coal (-212 μm), as well as large coal particles (5, 10, and 20 mm). For powdered coal, the addition of 10 wt.% K2CO3 decreased the free swelling index of GG and TSH coals from 6.5 to 0 and from 9.0 to 4.5, respectively. The volumetric swelling ratios (SRV) of the 20 mm particles were reduced from 3.0 to 1.8 for the GG coal, and from 5.7 to 1.4 for TSH. In contrast to the non-swelling (FSI 0) behaviour of the TWD powders, the large particles exhibited average SRV values of 1.7, and was found not be influenced by K2CO3-impregnation. It was found that the maximum swelling coefficient, kA, was reduced from 0.025 to 0.015 oC-1 for GG, and from 0.045 to 0.027 oC-1 for TSH, as a results of impregnation. From the results it was concluded that K2CO3-impregnation reduces the extent of swelling of coals such as GG (medium-swelling) and TSH (high-swelling), which exhibit significant plastic deformation. Results obtained from the caking experiments indicated that K2CO3-impregnation influenced the physical behaviour of the GG coal particles (5, 10, and 20 mm) the most. The extent of caking of GG was largely reduced due to impregnation, while the wall thickness and porosity also decreased. The coke from the impregnated GG samples had a less fluid-like appearance compared to coke from the raw coal. Bridging neck size measurements were performed, which quantitatively showed a 25-50% decrease in the caking propensity of GG particles. Coal TWD did not exhibit any caking behaviour. The K2CO3-impregnation did not influence the surface texture or porosity of the TWD char, but increased the overall brittleness of the devolatilised samples. Both the extent of caking and porosity of TSH coke were not influenced by impregnation. However, impregnation resulted in significantly less and smaller opened pores on the surface of the devolatilised samples, and also reduced the average wall thickness of the TSH coke. The overall conclusion made from this investigation is that K2CO3 (using solution impregnation) can be used to significantly reduce the caking and swelling tendency of large coal particles which exhibits a moderate degree of fluidity, such as GG (Waterberg region). The results obtained during this investigation show the viability of using additive addition to reduce the caking and swelling tendency of large coal particles. Together with further development, this may be a suitable method for modifying the swelling and caking behaviour of specific coals for use in fixed-bed and fluidised-bed gasification operations. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

Mineral matter affect various coal properties as well as the yield and composition of products released during thermal processes. This necessitates investigation of the effect of the inherent minerals on the products derived during pyrolysis, as pyrolysis forms the basis of most coal utilisation processes. A real challenge in this research has been quantifying the changes seen and attributing these effects to specific minerals. Thus far it has been deemed impossible to predict product yields based on the mineral composition of the parent coal. Limited research regarding these aspects has been done on South African coal and the characterisation of pyrolysis products in previous studies was usually limited to one product phase. A novel approach was followed in this study and the challenges stated were effectively addressed. A vitrinite-rich South African coal from the Highveld coal field, was prepared to an undersize of 75 μm and divided into two fractions. HCl/HF acid washing reduced the ash yield from 14.0 wt% d.b. to 2.0 wt% d.b. (proximate analysis). Pyrolysis was carried out with the North-West University (NWU) Fischer Assay setup at 520, 750 and 900°C under N2 atmosphere and atmospheric pressure. The effect of acid washing and the addition of minerals on the derived pyrolysis products were evaluated. Acid washing led to lower water and tar yields, whilst the gas yields increased, and the char yields were unaffected. The higher gas yield can be related to increased porosity after mineral removal as revealed by Brunauer-Emmett-Teller (BET) CO2 adsorption surface area analysis of the derived chars. Gas chromatography (GC) analyses of the derived pyrolysis gases indicated that the acid washed coal fraction (AW TWD) derived gas contained higher yields of H2, CH4, CO2, C2H4, C2H6, C3H4, C3H6 and C4s when compared to the gas derived from the raw coal fraction (TWD). The CO yield from the TWD coal was higher at all final pyrolysis temperatures. Differences in gas yields were related to increased tar cracking as well as lower hydrogen transfer and de-hydrogenation of the acid washed chars. Analyses of the tar fraction by means of simulated distillation (Simdis), gas chromatography mass spectrometry (GC-MS) –flame ionization detection (–FID) and size exclusion chromatography with ultraviolet (SEC-UV) analyses, indicated that the AW TWD derived tars were more aromatic in nature, containing more heavier boiling point components, which increased with increasing final pyrolysis temperature. The chars were characterised by proximate, ultimate, X-ray diffraction (XRD), X-ray fluorescence (XRF), diffuse reflectance infrared Fourier-transform (DRIFT) and BET CO2 analyses. Addition of either 5 wt% calcite, dolomite, kaolinite, pyrite or quartz to the acid washed fraction (AW TWD) was done in order to determine the effect of these minerals on the pyrolysis products. These minerals were identified as the most prominent mineral phases in the Highveld coal used in this study, by XRD and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) analyses. It was found that mineral activity decreased in the order calcite/dolomite>pyrite>kaolinite>>>quartz. Calcite and dolomite addition led to a decrease in tar yield, whilst the gas yields were increased. Markedly, increased water yields were also observed with the addition of calcite, dolomite and pyrite. Kaolinite addition led to increased tar, char and gas yields at 520°C, whilst the tar yield decreased at 750°C. Pyrite addition led to decreased tar and gas yields. Quartz addition had no noteworthy effect on pyrolysis yields and composition, except for a decrease in char yield at all final pyrolysis temperatures and an increased gas yield at 520°C. Regarding the composition of the pyrolysis products, the various minerals had adverse effects. Calcite and dolomite affected the composition of the gas, tar and char phases most significantly, showing definite catalytic activity. Tar producers should take note as presence of these minerals in the coal feedstock could have a significant effect on the tar yield and composition. Kaolinite and pyrite showed some catalytic activity under specific conditions. Model coal-mineral mixtures confirmed synergism between coal-mineral and mineral-mineral interactions. Although some correlation between the pyrolysis products derived from the model coal-mineral mixtures and that of TWD coal was observed, it was not possible to entirely mimic the behaviour of the coal prior to acid washing. Linear regression models were developed to predict the gas, tar and char yields (d.m.m.f.) with mineral composition and pyrolysis temperature as variables, resulting in R2 coefficients of 0.837, 0.785 and 0.846, respectively. Models for the prediction of H2, CO, CO2 and CH4 yields with mineral composition and pyrolysis temperature as variables resulting in R2 coefficients of 0.917, 0.702, 0.869 and 0.978, respectively. These models will serve as foundation for future work, and prove that it is feasible to develop models to predict pyrolysis yields based on mineral composition. Extending the study to coals of different rank can make the models universally applicable and deliver a valuable contribution in industry. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

The swelling and caking propensity of coals may cause operational problems such as channelling and excessive pressure build-up in combustion, gasification and specifically in fluidised-bed and fixed-bed operations. As a result, the swelling and caking characteristics of certain coals make them less suitable for use as feedstock in applications where swelling and/or caking is undesired. Therefore, various studies have focused on the manipulation of the swelling and/or caking propensity of coals, and have proven the viability of using additives to reduce the swelling and caking of powdered coal (<500 μm). However, there is still a lack of research specifically focused on large coal particle devolatilisation behaviour, particularly swelling and caking, and the reduction thereof using additives. A comprehensive study was therefore proposed to investigate the swelling and caking behaviour of large coal particles (5, 10, and 20 mm) of typical South African coals, and the influence of the selected additive (potassium carbonate) thereon. Three different South African coals were selected based on their Free Swelling Index (FSI): coal TSH is a high swelling coal (FSI 9) from the Limpopo province, GG is a medium swelling coal (FSI 5.5-6.5) from the Waterberg region, and TWD is a non-swelling coal (FSI 0) from the Highveld region. Image analysis was used to semi-quantitatively describe the transient swelling and shrinkage behaviour of large coal particles (-20+16 mm) during lowtemperature devolatilisation (700 °C, N2 atmosphere, 7 K/min). X-ray computed tomography and mercury submersion were used to quantify the degree of swelling of large particles, and were compared to conventional swelling characteristics of powdered coals. The average swelling ratios obtained for TWD, GG, and TSH were respectively 1.9, 2.1 and 2.5 from image analysis and 1.8, 2.2 and 2.5 from mercury submersion. The results showed that coal swelling measurements such as FSI, and other conventional techniques used to describe the plastic behaviour of powdered coal, can in general not be used for the prediction of large coal particle swelling. The large coal particles were impregnated for 24 hours, using an excess 5.0 M K2CO3 impregnation solution. The influence of K2CO3-addition on the swelling behaviour of different coal particle sizes was compared, and results showed that the addition of K2CO3 resulted in a reduction in swelling for powdered coal (-212 μm), as well as large coal particles (5, 10, and 20 mm). For powdered coal, the addition of 10 wt.% K2CO3 decreased the free swelling index of GG and TSH coals from 6.5 to 0 and from 9.0 to 4.5, respectively. The volumetric swelling ratios (SRV) of the 20 mm particles were reduced from 3.0 to 1.8 for the GG coal, and from 5.7 to 1.4 for TSH. In contrast to the non-swelling (FSI 0) behaviour of the TWD powders, the large particles exhibited average SRV values of 1.7, and was found not be influenced by K2CO3-impregnation. It was found that the maximum swelling coefficient, kA, was reduced from 0.025 to 0.015 oC-1 for GG, and from 0.045 to 0.027 oC-1 for TSH, as a results of impregnation. From the results it was concluded that K2CO3-impregnation reduces the extent of swelling of coals such as GG (medium-swelling) and TSH (high-swelling), which exhibit significant plastic deformation. Results obtained from the caking experiments indicated that K2CO3-impregnation influenced the physical behaviour of the GG coal particles (5, 10, and 20 mm) the most. The extent of caking of GG was largely reduced due to impregnation, while the wall thickness and porosity also decreased. The coke from the impregnated GG samples had a less fluid-like appearance compared to coke from the raw coal. Bridging neck size measurements were performed, which quantitatively showed a 25-50% decrease in the caking propensity of GG particles. Coal TWD did not exhibit any caking behaviour. The K2CO3-impregnation did not influence the surface texture or porosity of the TWD char, but increased the overall brittleness of the devolatilised samples. Both the extent of caking and porosity of TSH coke were not influenced by impregnation. However, impregnation resulted in significantly less and smaller opened pores on the surface of the devolatilised samples, and also reduced the average wall thickness of the TSH coke. The overall conclusion made from this investigation is that K2CO3 (using solution impregnation) can be used to significantly reduce the caking and swelling tendency of large coal particles which exhibits a moderate degree of fluidity, such as GG (Waterberg region). The results obtained during this investigation show the viability of using additive addition to reduce the caking and swelling tendency of large coal particles. Together with further development, this may be a suitable method for modifying the swelling and caking behaviour of specific coals for use in fixed-bed and fluidised-bed gasification operations. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

Mineral matter affect various coal properties as well as the yield and composition of products released during thermal processes. This necessitates investigation of the effect of the inherent minerals on the products derived during pyrolysis, as pyrolysis forms the basis of most coal utilisation processes. A real challenge in this research has been quantifying the changes seen and attributing these effects to specific minerals. Thus far it has been deemed impossible to predict product yields based on the mineral composition of the parent coal. Limited research regarding these aspects has been done on South African coal and the characterisation of pyrolysis products in previous studies was usually limited to one product phase. A novel approach was followed in this study and the challenges stated were effectively addressed. A vitrinite-rich South African coal from the Highveld coal field, was prepared to an undersize of 75 μm and divided into two fractions. HCl/HF acid washing reduced the ash yield from 14.0 wt% d.b. to 2.0 wt% d.b. (proximate analysis). Pyrolysis was carried out with the North-West University (NWU) Fischer Assay setup at 520, 750 and 900°C under N2 atmosphere and atmospheric pressure. The effect of acid washing and the addition of minerals on the derived pyrolysis products were evaluated. Acid washing led to lower water and tar yields, whilst the gas yields increased, and the char yields were unaffected. The higher gas yield can be related to increased porosity after mineral removal as revealed by Brunauer-Emmett-Teller (BET) CO2 adsorption surface area analysis of the derived chars. Gas chromatography (GC) analyses of the derived pyrolysis gases indicated that the acid washed coal fraction (AW TWD) derived gas contained higher yields of H2, CH4, CO2, C2H4, C2H6, C3H4, C3H6 and C4s when compared to the gas derived from the raw coal fraction (TWD). The CO yield from the TWD coal was higher at all final pyrolysis temperatures. Differences in gas yields were related to increased tar cracking as well as lower hydrogen transfer and de-hydrogenation of the acid washed chars. Analyses of the tar fraction by means of simulated distillation (Simdis), gas chromatography mass spectrometry (GC-MS) –flame ionization detection (–FID) and size exclusion chromatography with ultraviolet (SEC-UV) analyses, indicated that the AW TWD derived tars were more aromatic in nature, containing more heavier boiling point components, which increased with increasing final pyrolysis temperature. The chars were characterised by proximate, ultimate, X-ray diffraction (XRD), X-ray fluorescence (XRF), diffuse reflectance infrared Fourier-transform (DRIFT) and BET CO2 analyses. Addition of either 5 wt% calcite, dolomite, kaolinite, pyrite or quartz to the acid washed fraction (AW TWD) was done in order to determine the effect of these minerals on the pyrolysis products. These minerals were identified as the most prominent mineral phases in the Highveld coal used in this study, by XRD and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) analyses. It was found that mineral activity decreased in the order calcite/dolomite>pyrite>kaolinite>>>quartz. Calcite and dolomite addition led to a decrease in tar yield, whilst the gas yields were increased. Markedly, increased water yields were also observed with the addition of calcite, dolomite and pyrite. Kaolinite addition led to increased tar, char and gas yields at 520°C, whilst the tar yield decreased at 750°C. Pyrite addition led to decreased tar and gas yields. Quartz addition had no noteworthy effect on pyrolysis yields and composition, except for a decrease in char yield at all final pyrolysis temperatures and an increased gas yield at 520°C. Regarding the composition of the pyrolysis products, the various minerals had adverse effects. Calcite and dolomite affected the composition of the gas, tar and char phases most significantly, showing definite catalytic activity. Tar producers should take note as presence of these minerals in the coal feedstock could have a significant effect on the tar yield and composition. Kaolinite and pyrite showed some catalytic activity under specific conditions. Model coal-mineral mixtures confirmed synergism between coal-mineral and mineral-mineral interactions. Although some correlation between the pyrolysis products derived from the model coal-mineral mixtures and that of TWD coal was observed, it was not possible to entirely mimic the behaviour of the coal prior to acid washing. Linear regression models were developed to predict the gas, tar and char yields (d.m.m.f.) with mineral composition and pyrolysis temperature as variables, resulting in R2 coefficients of 0.837, 0.785 and 0.846, respectively. Models for the prediction of H2, CO, CO2 and CH4 yields with mineral composition and pyrolysis temperature as variables resulting in R2 coefficients of 0.917, 0.702, 0.869 and 0.978, respectively. These models will serve as foundation for future work, and prove that it is feasible to develop models to predict pyrolysis yields based on mineral composition. Extending the study to coals of different rank can make the models universally applicable and deliver a valuable contribution in industry. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

Alkali compounds were added to a South African coal with a high swelling propensity and the behaviour of the blends were investigated. A vitrinite-rich bituminous coal from the Tshikondeni coal mine in the Limpopo province of South Africa was used. To reduce the influence of the minerals in the coal, the coal was partially demineralized by leaching with HCl and HF. The ash content of the coal sample was successfully reduced from 17.7% to 0.6%. KOH, KCl, K2CO3 and KCH3CO2 were then added to the demineralized coal in mass percentages of 1%, 4%, 5% and 10%. The free swelling indices (FSI) of the blends were determined and the samples were subjected to acquisition of TMA and TG-MS data. Addition of these potassium compounds to the demineralized coal reduced the swelling of the vitrinite-rich coal. From the free swelling indices of the various mixtures, it was concluded that the potassium compounds reduce the swelling of the coal in the following order of decreasing impact: KCH3CO2 > KOH > K2CO3 > KCl. From dilatometry experiments done on the blends with the 10% addition of potassium compounds, it was seen that with the addition of potassium compounds to the demineralized coal, a reduction in dilatation volume was obtained. The influence of the potassium compound in decreasing order: K2CO3> KOH> KCH3CO2> KCl. An increase in the softening temperature was observed for the demineralized coal-alkali blends. Thermogravimetric analyses were performed on the demineralized coal-potassium blended samples (<75 μm). These samples were pyrolyzed under a nitrogen atmosphere to a maximum temperature of 1200 °C using a heating rate of 10 °C/min. The relative reactivity for each of the blends with the different wt% addition was determined. From these results it was seen that KCH3CO2 increased the relative reactivity, whereas the KOH, KCl and K2CO3 showed an inhibiting influence. The attached mass spectrometer provided information on the low molecular mass gaseous products formed in the various temperature ranges as the thermal treatment proceeded. From the mass spectroscopy results, it was found that the potassium compounds decreased the temperature at which maximum evolution of H2 takes place. Thermomechanical analyses were performed on the 10 wt% addition of the potassium compounds to the demineralized coal. During TMA analyses, the sample was heated to 1000 °C using a heating rate of 10 °C/min. From the TMA result obtained it was clear that the addition of KCl did not have an influence on the swelling of the demineralized coal. All results are discussed. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

A fundamental understanding of the process of devolatilization requires extensive knowledge of not only the intrinsic properties of the parent coal and its subsequent formed products (tars, gases and chars), but also its characteristic reaction rate behaviour. Devolatilization behaviour has been extensively addressed in literature with the use of powdered coal samples, which normally do not adhere to particle size constraints of coal conversion processes utilizing lump coal. The aim of this investigation was therefore to assess the devolatilization behaviour (with respect to product yield and -quality; and reaction rate modelling) of four typical South African coals (UMZ, INY, G#5 and TSH) confined to the large particle regime. All four coals were found to be bituminous in rank, with vitrinite contents ranging between 24.4 vol.% and 69.2 vol.% (mineral matter free basis). Two were inertinite-rich coals (UMZ and INY) and the other two were vitrinite-rich coals (G#5 and TSH). From thermoplasticity measurements it was evident that only coal TSH displayed extensive thermoplastic behaviour, while a comparison between molecular properties confirmed the higher abundance of poly-condensed aromatic structures (aromaticity of 81%) present in this coal. Product evolution was evaluated under atmospheric conditions in a self-constructed, large particle, fixed-bed reactor, on two particle sizes (5 mm and 20 mm) at two isothermal reactor temperatures (450°C and 750°C) using a combination of both GC and MS techniques for gas species measurement, while standard gravimetric methods were used to quantify tar- and char yield respectively. Elucidation of tar- and char structural features involved the use of both conventional- and advanced analytical techniques. From the results it could be concluded that temperature was the dominating factor controlling product yield- and quality, with significant increases in both volatile- and gas yield observed for an increase in temperature. Tar yields ranged between 3.6 wt.% and 10.1 wt.% and increased in the order UMZ < INY < TSH < G#5, with higher tar yields obtained for coal G#5, being ascribed to larger abundances of vitrinite and liptinite present in this coal. For coal TSH, lower tar yields could mainly be attributed to the higher aromaticity and extensive swelling nature of this coal. Evolved gases were found to be mainly composed of H2, CH4, CO and CO2, low molecular weight olefins and paraffins; and some C4 homologues. Advanced analytical techniques (NMR, SEC, GC-MS, XRD, etc.) revealed the progressive increase of the aromatic nature of both tars and chars with increasing temperature; as well as subsequent differences in tar composition between the different parent coals. In all cases, an increase in devolatilization temperature led to the evolution of larger amounts of aromatic compounds such as alkyl-naphthalenes and PAHs, while significant decreases in the amount of aliphatics and mixed compounds could be observed. From 13C NMR, HRTEM and XRD carbon crystallite results it was clear that an increase in temperature led to the formation of progressively larger, more aromatic and structurally orientated polycondensed carbon structures. Reaction rate studies involved the use of non-isothermal (5-40 K/min) and isothermal (350- 900°C) thermogravimetry of both powdered (-200 μm) and large particle samples (20 mm) in order to assess intrinsic kinetics and large particle rate behaviour, respectively. Evaluation of the intrinsic kinetic parameters of each coal involved the numerical regression of non-isothermal rate data in MATLAB® 7.1.1 according to a pseudo-component modelling philosophy. Modelling results indicated that the intrinsic devolatilization behaviour of each coal could be adequately described by using a total number of eight pseudo-components, while reported activation energies were found to range between 22.3 kJ/mol and 244.3 kJ/mol. Description of the rate of large particle devolatilization involved the evaluation of a novel, comprehensive rate model accounting for derived kinetics, heat and mass transport effects, as well as physical changes due to particle swelling/shrinkage. Evaluation of the proposed model with the aid of the COMSOL Multiphysics 4.3 simulation software provided a suitable fit to the experimental data of all four coals, while simulation studies highlighted the relevant importance of not only the effect of particle size, but also the importance of including terms affecting for heat losses due to particle swelling/shrinkage, transport of volatile products through the porous char structure, heat of reaction and heat of vaporization of water. / Thesis (PhD (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013

Alkali compounds were added to a South African coal with a high swelling propensity and the behaviour of the blends were investigated. A vitrinite-rich bituminous coal from the Tshikondeni coal mine in the Limpopo province of South Africa was used. To reduce the influence of the minerals in the coal, the coal was partially demineralized by leaching with HCl and HF. The ash content of the coal sample was successfully reduced from 17.7% to 0.6%. KOH, KCl, K2CO3 and KCH3CO2 were then added to the demineralized coal in mass percentages of 1%, 4%, 5% and 10%. The free swelling indices (FSI) of the blends were determined and the samples were subjected to acquisition of TMA and TG-MS data. Addition of these potassium compounds to the demineralized coal reduced the swelling of the vitrinite-rich coal. From the free swelling indices of the various mixtures, it was concluded that the potassium compounds reduce the swelling of the coal in the following order of decreasing impact: KCH3CO2 > KOH > K2CO3 > KCl. From dilatometry experiments done on the blends with the 10% addition of potassium compounds, it was seen that with the addition of potassium compounds to the demineralized coal, a reduction in dilatation volume was obtained. The influence of the potassium compound in decreasing order: K2CO3> KOH> KCH3CO2> KCl. An increase in the softening temperature was observed for the demineralized coal-alkali blends. Thermogravimetric analyses were performed on the demineralized coal-potassium blended samples (<75 μm). These samples were pyrolyzed under a nitrogen atmosphere to a maximum temperature of 1200 °C using a heating rate of 10 °C/min. The relative reactivity for each of the blends with the different wt% addition was determined. From these results it was seen that KCH3CO2 increased the relative reactivity, whereas the KOH, KCl and K2CO3 showed an inhibiting influence. The attached mass spectrometer provided information on the low molecular mass gaseous products formed in the various temperature ranges as the thermal treatment proceeded. From the mass spectroscopy results, it was found that the potassium compounds decreased the temperature at which maximum evolution of H2 takes place. Thermomechanical analyses were performed on the 10 wt% addition of the potassium compounds to the demineralized coal. During TMA analyses, the sample was heated to 1000 °C using a heating rate of 10 °C/min. From the TMA result obtained it was clear that the addition of KCl did not have an influence on the swelling of the demineralized coal. All results are discussed. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014