With increasing energy demand globally and, in particular, in South Africa coupled with depletion of the earth’s fossil energy resources and growing problem of disposal of nonbiodegradable waste such as waste tyres, there is a need and effort globally to find alternative energy from waste material including waste tyres. One possible way of exploiting waste tyre for energy or chemicals recovery is through gasification for the production of syngas, and this is what was investigated in this study. The possibility of gasification of waste tyre blended with coal after pyrolysis was investigated and two Bituminous coals were selected for blending with the waste tyre in co-gasification. A sample of ground waste tyre / waste tire, WT, a high vitrinite coal from the Waterberg coalfield (GG coal) and a high inertinite coal from the Highveld coalfield (SF coal) were used in this investigation. The waste tyre sample had the highest volatile matter content of 63.8%, followed by GG coal with 27% and SF coal with 23.8%. SF coal had the highest ash content of 21.6%, GG coal had 12.6% and waste tyre had the lowest of 6.6%. For the chars, SF char still had the highest ash of 24.8%, but WT char had higher ash, 14.7%, when compared to GG char with 13.9% ash. The vitrinite content in GG coal was 86.3%, whilst in SF coal it was 25% and SF coal had a higher inertinite content of 71% when compared to GG coal with 7.7%. SF char had the highest BET surface area of 126m2/g, followed by GG char with 113m2/g, and WT had the lowest value of 35.09m2/g. The alkali indices of the SF, WT and GG chars were calculated to be 8.2, 4.2 and 1.7 respectively. Coal samples were prepared by crushing and milling to particle sizes less than 75μm before charring in a packed bed balance reactor at temperatures up to 1000oC.Waste tyre samples were charred at the same conditions before milling to < 75μm particle size. Coal and WT chars were blended in ratios of 75:25, 50:50 and 25:75 before gasification experimentation. Carbon dioxide gasification was conducted on the blends and the pure coal and WT chars in a Thermogravimetric analyser (TGA) at 900oC, 925oC, 950oC and 975oC and ambient pressure. 100% CO2 was used at a flow rate of 2L/min. Reactivity of the pure char samples was found to be in the order SF > GG > WT, and the relationship between the coal chars’ reactivities could be explained by the high ash content of the SF char and low reactivity of the WT char corresponds to its low BET surface area. In general, the coal/WT char mixtures were less reactive than the respective coal, but more reactive than the pure WT char, the only exception being the 75% GG char blend which was initially more reactive than the GG char, and reactivity decreased with increasing WT content. For all samples reactivity increased with increasing temperature. The relationship between the reactivities of the GG char and its blends and that of the SF char and its blends was found to be affected by the amount of WT char added, especially at the lower temperatures 900oC and 925oC. SF coal is more reactive than GG coal, but at 900oC and 925oC, the reactivity of GG/WT blends improves in relation to the SF/WT blends with an increase in the ratio of WT in the blends, i.e. the 25% GG char blend is more reactive than the 25% SF char blend. The reactivity of the coal/WT blends was also checked against predicted conversion rates based on the conversion rates of the pure WT and coal samples. At 900oC and 925oC, the reactivities of the blends of both coal chars with WT char were found to be greater than the predicted conversion rates, and for the GG/WT blends the deviation increased with increasing WT ratios, while for the SF/WT blends the deviation increased with increasing SF ratios. These findings suggest the presence of synergism or enhancement between the coal chars and WT char in gasification reactions. The random pore model (RPM) was used to model the gasification results and it was found to adequately describe the experimental data. Activation energies determined with the RPM were found to be 205.4kJ/mol, 189.9kJ/mol and 173.9kJ/mol for SF char, WT char and GG char respectively. The activation energies of the coal/WT blends were found to be lower than those of both the pure coal and the pure WT chars. For the GG/WT blends the activation energy decreased with increasing WT char ratio, while for the SF/WT blends the activation energy decreased with increasing SF char ratio. The trends of the activation energies and conversion rates of the blends point to synergism or enhancement between the coal and WT chars in CO2 gasification reactions, and in the GG/WT blends this enhancement is driven more by the WT char, while in SF/WT blends it is driven by SF chars. It is possible that enhancement of the reactions is caused by mineral matter catalysis of the gasification reactions. The ash contents and alkali indices of the pure samples follow the order SF > WT > GG. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

An investigation was undertaken to compare the kinetics of combustion and gasification reactions of chars prepared from two South African coals in different reaction atmospheres: air, steam, and carbon dioxide. The two original coals were characterised as vitrinite-rich (Greenside) and inertinite-rich (Inyanda) coals with relatively low ash content (12.5-16.7 wt. %, adb). Chars were prepared from the parent coals under nitrogen atmosphere at 900 °C. Characterisation results show that the volatiles and moisture were almost completely driven off from the parent coals, indicating that the pyrolysis process was efficient. Physicalstructural properties such as porosity and surface area generally increased from the parent coals to the subsequent chars. The heterogeneous char-gas reactions were conducted isothermally in a TGA on ~1 mm size particles. To ensure that the reactions are under chemical reaction kinetic control regime, different temperatures zones were selected for the three different reaction atmospheres. Combustion reactivity experiments were carried out with air in the temperature range of 387 °C to 425 °C; gasification reactivity with pure steam were conducted at higher temperatures (775 °C - 850 °C) and within 825 °C to 900 °C with carbon dioxide. Experimental results show differences in the specific reaction rate with carbon conversion in different reaction atmospheres and char types. Reaction rates in all three reaction atmospheres were strongly dependent on temperature, and follow the Arrhenius type kinetics. All the investigated reactions (combustion with air and gasification with CO2 and steam) were found to be under chemical reaction control regime (Regime I) for both chars. The inertinite-rich coals exhibit longer burn-out time than chars produced from vitrinite-rich coals, as higher specific reaction rate were observed for the vitrinite-rich coals in the three different reaction atmospheres. The determined random pore model (RPM) structural parameters did not show any significant difference during steam gasification of Greenside and Inyanda chars, whereas higher structural parameter values were observed for Greenside chars during air combustion and CO2 gasification (ψ > 2). However a negative ψ value was determined during CO2 gasification and air combustion of Inyanda chars. The RPM predictions was validated with the experimental data and exhibited adequate fitting to the specific rate of reaction versus carbon conversion plots of the char samples at the different reaction conditions chosen for this study. The activation energy determined was minimal for air and maximum for CO2 for both coals; and ranged from 127-175 kJ·mol-1 for combustion, 214-228 kJ·mol-1 and 210-240 kJ·mol-1 for steam and CO2 gasification respectively. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

With increasing energy demand globally and, in particular, in South Africa coupled with depletion of the earth’s fossil energy resources and growing problem of disposal of nonbiodegradable waste such as waste tyres, there is a need and effort globally to find alternative energy from waste material including waste tyres. One possible way of exploiting waste tyre for energy or chemicals recovery is through gasification for the production of syngas, and this is what was investigated in this study. The possibility of gasification of waste tyre blended with coal after pyrolysis was investigated and two Bituminous coals were selected for blending with the waste tyre in co-gasification. A sample of ground waste tyre / waste tire, WT, a high vitrinite coal from the Waterberg coalfield (GG coal) and a high inertinite coal from the Highveld coalfield (SF coal) were used in this investigation. The waste tyre sample had the highest volatile matter content of 63.8%, followed by GG coal with 27% and SF coal with 23.8%. SF coal had the highest ash content of 21.6%, GG coal had 12.6% and waste tyre had the lowest of 6.6%. For the chars, SF char still had the highest ash of 24.8%, but WT char had higher ash, 14.7%, when compared to GG char with 13.9% ash. The vitrinite content in GG coal was 86.3%, whilst in SF coal it was 25% and SF coal had a higher inertinite content of 71% when compared to GG coal with 7.7%. SF char had the highest BET surface area of 126m2/g, followed by GG char with 113m2/g, and WT had the lowest value of 35.09m2/g. The alkali indices of the SF, WT and GG chars were calculated to be 8.2, 4.2 and 1.7 respectively. Coal samples were prepared by crushing and milling to particle sizes less than 75μm before charring in a packed bed balance reactor at temperatures up to 1000oC.Waste tyre samples were charred at the same conditions before milling to < 75μm particle size. Coal and WT chars were blended in ratios of 75:25, 50:50 and 25:75 before gasification experimentation. Carbon dioxide gasification was conducted on the blends and the pure coal and WT chars in a Thermogravimetric analyser (TGA) at 900oC, 925oC, 950oC and 975oC and ambient pressure. 100% CO2 was used at a flow rate of 2L/min. Reactivity of the pure char samples was found to be in the order SF > GG > WT, and the relationship between the coal chars’ reactivities could be explained by the high ash content of the SF char and low reactivity of the WT char corresponds to its low BET surface area. In general, the coal/WT char mixtures were less reactive than the respective coal, but more reactive than the pure WT char, the only exception being the 75% GG char blend which was initially more reactive than the GG char, and reactivity decreased with increasing WT content. For all samples reactivity increased with increasing temperature. The relationship between the reactivities of the GG char and its blends and that of the SF char and its blends was found to be affected by the amount of WT char added, especially at the lower temperatures 900oC and 925oC. SF coal is more reactive than GG coal, but at 900oC and 925oC, the reactivity of GG/WT blends improves in relation to the SF/WT blends with an increase in the ratio of WT in the blends, i.e. the 25% GG char blend is more reactive than the 25% SF char blend. The reactivity of the coal/WT blends was also checked against predicted conversion rates based on the conversion rates of the pure WT and coal samples. At 900oC and 925oC, the reactivities of the blends of both coal chars with WT char were found to be greater than the predicted conversion rates, and for the GG/WT blends the deviation increased with increasing WT ratios, while for the SF/WT blends the deviation increased with increasing SF ratios. These findings suggest the presence of synergism or enhancement between the coal chars and WT char in gasification reactions. The random pore model (RPM) was used to model the gasification results and it was found to adequately describe the experimental data. Activation energies determined with the RPM were found to be 205.4kJ/mol, 189.9kJ/mol and 173.9kJ/mol for SF char, WT char and GG char respectively. The activation energies of the coal/WT blends were found to be lower than those of both the pure coal and the pure WT chars. For the GG/WT blends the activation energy decreased with increasing WT char ratio, while for the SF/WT blends the activation energy decreased with increasing SF char ratio. The trends of the activation energies and conversion rates of the blends point to synergism or enhancement between the coal and WT chars in CO2 gasification reactions, and in the GG/WT blends this enhancement is driven more by the WT char, while in SF/WT blends it is driven by SF chars. It is possible that enhancement of the reactions is caused by mineral matter catalysis of the gasification reactions. The ash contents and alkali indices of the pure samples follow the order SF > WT > GG. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

An investigation was undertaken to compare the kinetics of combustion and gasification reactions of chars prepared from two South African coals in different reaction atmospheres: air, steam, and carbon dioxide. The two original coals were characterised as vitrinite-rich (Greenside) and inertinite-rich (Inyanda) coals with relatively low ash content (12.5-16.7 wt. %, adb). Chars were prepared from the parent coals under nitrogen atmosphere at 900 °C. Characterisation results show that the volatiles and moisture were almost completely driven off from the parent coals, indicating that the pyrolysis process was efficient. Physicalstructural properties such as porosity and surface area generally increased from the parent coals to the subsequent chars. The heterogeneous char-gas reactions were conducted isothermally in a TGA on ~1 mm size particles. To ensure that the reactions are under chemical reaction kinetic control regime, different temperatures zones were selected for the three different reaction atmospheres. Combustion reactivity experiments were carried out with air in the temperature range of 387 °C to 425 °C; gasification reactivity with pure steam were conducted at higher temperatures (775 °C - 850 °C) and within 825 °C to 900 °C with carbon dioxide. Experimental results show differences in the specific reaction rate with carbon conversion in different reaction atmospheres and char types. Reaction rates in all three reaction atmospheres were strongly dependent on temperature, and follow the Arrhenius type kinetics. All the investigated reactions (combustion with air and gasification with CO2 and steam) were found to be under chemical reaction control regime (Regime I) for both chars. The inertinite-rich coals exhibit longer burn-out time than chars produced from vitrinite-rich coals, as higher specific reaction rate were observed for the vitrinite-rich coals in the three different reaction atmospheres. The determined random pore model (RPM) structural parameters did not show any significant difference during steam gasification of Greenside and Inyanda chars, whereas higher structural parameter values were observed for Greenside chars during air combustion and CO2 gasification (ψ > 2). However a negative ψ value was determined during CO2 gasification and air combustion of Inyanda chars. The RPM predictions was validated with the experimental data and exhibited adequate fitting to the specific rate of reaction versus carbon conversion plots of the char samples at the different reaction conditions chosen for this study. The activation energy determined was minimal for air and maximum for CO2 for both coals; and ranged from 127-175 kJ·mol-1 for combustion, 214-228 kJ·mol-1 and 210-240 kJ·mol-1 for steam and CO2 gasification respectively. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

With the increasing global energy demand and the decreasing availability of good quality coals, a better understanding of the important properties that control the behaviour of low–grade coals and the subsequent chars in various utilisation processes, becomes pertinent. An investigation was therefore undertaken, to study the effects of chemical and physical properties imparted on chars during pyrolysis on the subsequent gasification reaction kinetics of typical South African inertinite–rich, high ash Highveld coals. An attempt was made at following these changes in the transition from coals to chars by a detailed characterisation of both the parent coals and the respective chars. These changes were determined using various conventional and advanced techniques, which included among others, carbon crystallite analysis using XRD and char carbon forms analysis using petrography. Three of the four original coals were characterised as Bituminous Medium rank C (coals B, C and C2), while coal D2 was found to be slightly lower in rank (Bituminous Medium rank D). The coals were rich in inertinites (> 54 vol. %, mmb with coal C2 having as high as 79 vol. %, mmb) and high in ash content (> 26.7 wt. %, db) and cabominerite and minerite contents (26 – 39 vol. %, mmb). The inertinitevitrinite ratios of the coals were found to range from 1.93 to 26.3. Characterization results show that both volatile matter and inherent moisture content decreased, while ash, fixed carbon and elemental carbon contents increased from coals to chars, indicating that the pyrolysis process was efficient. Elemental hydrogen, oxygen and nitrogen contents decreased, whereas total sulphur contents increased from coals to chars. This reveals that the total sulphur contained in the char samples was associated with the char carbon matrix and the minerals. Hydrogen–carbon and oxygen–carbon ratios decreased considerably from coals to chars showing that the chars are more aromatic and denser products than the original coals. Despite the fact that mineral matter increased from coals to chars, the relative abundance of the different mineral phases and ash components did not exhibit significant variation amongst the samples. The alkali index was, however, found to vary considerably among the subsequent chars. Petrographic analysis of the coals and char carbon forms analysis of the chars reveal that total reactive components (TRC) decrease while the total inert components (TIC) increase from coals to chars. The 0% gain in TIC observed in char C2 was attributed to its relatively high partially reacted maceral char carbon forms content. Total maceral reflectance shifted to higher values in the chars (4.43 – 5.28 Rsc%) relative to the coals (1.15 – 1.63 Rsc%) suggesting a higher structural ordering in the chars. Carbon crystallite analyses revealed that the chars were condensed (smaller in size) relative to the parent coals. Lattice parameters: interlayer spacing, d002, increased, while the average crystallite height, Lc, crystallite diameter, La, and number of aromatic layers per crystallite, Nave, decreased from coals to chars. Carbon aromaticity generally increased whereas the fraction of amorphous carbon and the degree of disorder index decreased from parent coals to the respective chars. Both micropore surface area and microporosity were observed to increase while the average micropore diameter decreased from coals to chars. This shows that blind and closed micropores were “opened up” during the charring process. Despite the original coal samples not showing much variation in their properties (except for their maceral content), it was generally observed that the subsequent chars exhibited substantial differences, both amongst themselves and from the parent coals. The increasing orders of magnitude of micropore surface area, microporosity, fraction of amorphous carbon and structural disorderliness were found to change in the transition, a good indication that the chars’ properties varied from that of the respective parent coals. Isothermal CO2 gasification experiments were conducted on the chars in a Thermax 500 thermogravimetric analyser in the temperature range of 900 – 950 °C with varying concentrations of CO2 (25 – 100 mol. %) in the CO2–N2 reaction gas mixture at ambient pressure (0.875 bar in Potchefstroom). The effects of temperature and CO2 concentration were observed to be in conformity with established trends. The initial reactivity of the chars was found to increase in the order: chars C2 < C < B < D2, with char D2 reactivity greater than the reactivity of the other chars by a factor > 4. Gasification reactivity results were correlated with properties of the parent coals and chars. Except for the rank parameter (the vitrinite reflectance), no significant trend was observed with any other coal petrographic property. Correlations with char properties gave more significant and systematic trends. Major factors affecting the gasification reactivity of the chars as it pertains to this investigation are: parent coal vitrinite reflectance, and: aromaticity, fraction of amorphous carbon, degree of disorder and alkali indices, micropore surface area, microporosity and average micropore diameter of the chars. The random pore model (chemical reaction controlling) was found to adequately describe the gasification reaction experimental data (both conversions and conversion rates). The determined activation energy ranged from 163.3 kJ·mol–1 for char D2 to 235.7 kJ·mol–1 for char B; while the order of reaction with respect to CO2 concentration ranged between 0.52 to 0.67 for the four chars. The lower activation energy of char D2 was possibly due to its lower rank, lower coal vitrinite reflectance and higher alkali index. The estimated kinetic parameters of the chars in this study correspond very well with published results in open literature. It was possible to express the intrinsic reactivity, rs, of the chars (rate of carbon conversion per unit total surface area) using kinetic results, in empirical Arrhenius forms. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2011.

With the increasing global energy demand and the decreasing availability of good quality coals, a better understanding of the important properties that control the behaviour of low–grade coals and the subsequent chars in various utilisation processes, becomes pertinent. An investigation was therefore undertaken, to study the effects of chemical and physical properties imparted on chars during pyrolysis on the subsequent gasification reaction kinetics of typical South African inertinite–rich, high ash Highveld coals. An attempt was made at following these changes in the transition from coals to chars by a detailed characterisation of both the parent coals and the respective chars. These changes were determined using various conventional and advanced techniques, which included among others, carbon crystallite analysis using XRD and char carbon forms analysis using petrography. Three of the four original coals were characterised as Bituminous Medium rank C (coals B, C and C2), while coal D2 was found to be slightly lower in rank (Bituminous Medium rank D). The coals were rich in inertinites (> 54 vol. %, mmb with coal C2 having as high as 79 vol. %, mmb) and high in ash content (> 26.7 wt. %, db) and cabominerite and minerite contents (26 – 39 vol. %, mmb). The inertinitevitrinite ratios of the coals were found to range from 1.93 to 26.3. Characterization results show that both volatile matter and inherent moisture content decreased, while ash, fixed carbon and elemental carbon contents increased from coals to chars, indicating that the pyrolysis process was efficient. Elemental hydrogen, oxygen and nitrogen contents decreased, whereas total sulphur contents increased from coals to chars. This reveals that the total sulphur contained in the char samples was associated with the char carbon matrix and the minerals. Hydrogen–carbon and oxygen–carbon ratios decreased considerably from coals to chars showing that the chars are more aromatic and denser products than the original coals. Despite the fact that mineral matter increased from coals to chars, the relative abundance of the different mineral phases and ash components did not exhibit significant variation amongst the samples. The alkali index was, however, found to vary considerably among the subsequent chars. Petrographic analysis of the coals and char carbon forms analysis of the chars reveal that total reactive components (TRC) decrease while the total inert components (TIC) increase from coals to chars. The 0% gain in TIC observed in char C2 was attributed to its relatively high partially reacted maceral char carbon forms content. Total maceral reflectance shifted to higher values in the chars (4.43 – 5.28 Rsc%) relative to the coals (1.15 – 1.63 Rsc%) suggesting a higher structural ordering in the chars. Carbon crystallite analyses revealed that the chars were condensed (smaller in size) relative to the parent coals. Lattice parameters: interlayer spacing, d002, increased, while the average crystallite height, Lc, crystallite diameter, La, and number of aromatic layers per crystallite, Nave, decreased from coals to chars. Carbon aromaticity generally increased whereas the fraction of amorphous carbon and the degree of disorder index decreased from parent coals to the respective chars. Both micropore surface area and microporosity were observed to increase while the average micropore diameter decreased from coals to chars. This shows that blind and closed micropores were “opened up” during the charring process. Despite the original coal samples not showing much variation in their properties (except for their maceral content), it was generally observed that the subsequent chars exhibited substantial differences, both amongst themselves and from the parent coals. The increasing orders of magnitude of micropore surface area, microporosity, fraction of amorphous carbon and structural disorderliness were found to change in the transition, a good indication that the chars’ properties varied from that of the respective parent coals. Isothermal CO2 gasification experiments were conducted on the chars in a Thermax 500 thermogravimetric analyser in the temperature range of 900 – 950 °C with varying concentrations of CO2 (25 – 100 mol. %) in the CO2–N2 reaction gas mixture at ambient pressure (0.875 bar in Potchefstroom). The effects of temperature and CO2 concentration were observed to be in conformity with established trends. The initial reactivity of the chars was found to increase in the order: chars C2 < C < B < D2, with char D2 reactivity greater than the reactivity of the other chars by a factor > 4. Gasification reactivity results were correlated with properties of the parent coals and chars. Except for the rank parameter (the vitrinite reflectance), no significant trend was observed with any other coal petrographic property. Correlations with char properties gave more significant and systematic trends. Major factors affecting the gasification reactivity of the chars as it pertains to this investigation are: parent coal vitrinite reflectance, and: aromaticity, fraction of amorphous carbon, degree of disorder and alkali indices, micropore surface area, microporosity and average micropore diameter of the chars. The random pore model (chemical reaction controlling) was found to adequately describe the gasification reaction experimental data (both conversions and conversion rates). The determined activation energy ranged from 163.3 kJ·mol–1 for char D2 to 235.7 kJ·mol–1 for char B; while the order of reaction with respect to CO2 concentration ranged between 0.52 to 0.67 for the four chars. The lower activation energy of char D2 was possibly due to its lower rank, lower coal vitrinite reflectance and higher alkali index. The estimated kinetic parameters of the chars in this study correspond very well with published results in open literature. It was possible to express the intrinsic reactivity, rs, of the chars (rate of carbon conversion per unit total surface area) using kinetic results, in empirical Arrhenius forms. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2011.