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

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

Graphite has important applications in several key industries, which has been listed as a “criticalraw material” considered to be supply-risk by European since 2020. Purification of engineered graphite is one of the essential processes for the manufacturing of high-quality graphite. In this work, the production process and the existing methods to purify the three major types of graphite are evaluated and compared. Then purification method focusing on acid washing to remove iron from bio-graphite is investigated. The results showed that the impurity removalefficiency of acid washing increases with the increase of temperature, but efficiency decreased because of HCl volatilization when the temperature reaches 100 ℃. High concentrations of hydrochloric acid and other strong acids can improve the ability of acid washing. The smaller the graphite particle size, the more iron impurities are removed. Finally, through multi-steps acid washing with hydrochloric acid and aqua regia at 80 °C, bio-graphite with a purity of 99.67 % was obtained. This meets the requirements of metallurgical electrodes and other applications. The acquisition of ultra-high-purity graphite still needs more further work. / Grafit har viktiga tillämpningar i flera nyckelindustrier, som har listats som en "kritisk råvara" som anses vara en försörjningsrisk av Europa sedan 2020. Rening av teknisk grafit är en av de väsentliga processerna för tillverkning av högkvalitativ grafit. I detta arbete utvärderas och jämförs produktionsprocessen och de befintliga metoderna för att rena de tre huvudtyperna av grafit. Därefter undersöks reningsmetod med fokus på syratvätt för att avlägsna järn från biografit. Resultaten visade att effektiviteten för avlägsnande av föroreningar vid syratvätt ökar med ökningen av temperaturen, men effektiviteten minskade på grund av HCl-förångning när temperaturen når 100 ℃. Höga koncentrationer av saltsyra och andra starka syror kan förbättra förmågan till syratvätt. Ju mindre grafitpartikelstorlek, desto mer järnföroreningar avlägsnas. Slutligen erhölls biografit med en renhet på 99,67 % genom syratvätt i flera steg med saltsyra och aqua regia vid 80 °C. Detta uppfyller kraven för metallurgiska elektroder och andra applikationer. Förvärvet av grafit med ultrahög renhet kräver fortfarande mer arbete.

This thesis pertains to the processing of ultra-fine mineral particles and low rank coal using the hydrophobic--hydrophilic separation (HHS) method. Several explorative experimental tests have been carried out to study the effect of the various physical and chemical parameters on the HHS process. In this study, the HHS process has been employed to upgrade a chalcopyrite ore. A systematic experimental study on the effects of various physical and chemical parameters such as particle size, reagent dosage and reaction time on the separation efficiencies have been performed. For this, a copper rougher concentrate (assaying 15.9 %Cu) was wet ground and treated with a reagent to selectively hydrophobize the copper-bearing mineral (chalcopyrite), leaving the siliceous gangue minerals hydrophilic. The slurry was subjected to a high-shear agitation to selectively agglomerate the chalcopyrite and to leave the siliceous gangue dispersed in aqueous phase. The agglomerates were then separated from dispersed gangue minerals by screening and the agglomerates dispersed in a hydrophobic liquid (n-pentane) to liberate the water trapped in the agglomerates. The chalcopyrite dispersed in the hydrophobic liquid was separated from the medium to obtain a concentrate substantially free of gangue minerals and moisture. The copper recoveries were substantially higher than those obtained by flotation. The HHS process was also tested on ultrafine mono-sized silica beads. The results were superior to those obtained by flotation, particularly with ultrafine particles. The HHS process has also been tested successfully for upgrading subbituminous coals. Low-rank coals are not as hydrophobic as high-rank coals such as bituminous and anthracite coals. In the present work, a low-rank coal from Wyoming was hydrophobized with appropriate reagents and subjected to the HHS in a similar manner as described for processing copper. The results showed that the HHS process reduced the moisture substantially and increased the heating value up to 50% without heating the coal. Laboratory-scale tests conducted under different conditions, e.g., particle size, reagent type, reaction time, and pretreatments, showed promising results. Implementation for the HHS process for upgrading low-rank coals should help reduce CO2 emissions by improving combustion efficiencies. / Master of Science

Biomass liquefaction by fast pyrolysis is considered to be a key technology in future biorefineries for the production of low-carbon renewable liquids. These liquids may be used as a fuel for heat and power, as an intermediate for catalytic upgrading to distillate transportation fuels (such as renewable diesel or biojet) and as a raw material for advanced bioproducts. With the estimated supply of bioenergy required to meet international GHG reduction targets, the use of high ash (mineral-containing) biomass sources, such as harvest residues, hog fuels, and other unmerchantable wood sources is also expected to increase. However, the elevated presence of suspended char particulate (solids), as well as minerals and other ash components contained in pyrolytic liquids resulting from the conversion of these lower quality biomass residues may create new challenges for end-users. In light of this, two treatment pathways were investigated in this work: biomass pretreatment through sieving and acid washing, and post-condensation microfiltration of fast pyrolysis bio-oils. Selection of these two pathways was prioritized based on scarcity of published data, as well as the technical potential of both approaches for suspended char particulate and ash reduction in fast pyrolysis bio-oils. For biomass sieving and acid washing carried out at pilot scale, it was found that removing up to 80% of the ash contained in a hog fuel feedstock was possible by sieving out a fraction of the fines and subsequently washing with 0.1M nitric acid provided up to 40% increase in organic liquid yield after fast pyrolysis. Reaction water in the product was minimized when acid leaching was performed, while the solids content and ash content of the produced liquids were reduced by up to 80% and 87%, respectively. Cross-flow microfiltration of fast pyrolysis bio-oils produced principally from non-pretreated mill and harvest residues in the 1-40 µm range was performed. Microfiltration was found to remove between 80-95% of suspended solid particles, while only removing 4-45% of ash, presumably in the solid phase. To achieve high ash removal (>90%), microfiltration was combined with use of solid-phase adsorbents, such as Amberlyst 15, to remove cationic ash elements such as magnesium, calcium, iron, etc. The flux profiles from bio-oil cross-flow microfiltration were analyzed and consistently demonstrated a transient rapid and intermediate decline operating region, followed by a pseudo steady-state operating region. It was found that the initial flux of permeate in the transient operating region ranged from 100-1000 L m-2 h-1, while the pseudo steady-state flux ranged from 20-50 L m-2 h-1 for the experimental trials included in this study. It was determined that bio-oil temperatures of 50-60 ˚C, transmembrane pressures less than 1 bar and the addition of diluent solvents provided the highest pseudo steady-state fluxes of such a process. To improve the throughput of the process, different fouling remediation strategies were experimentally evaluated. The use of permeate, solvent and air backflushing confirmed that on-line cleaning strategies are suitable for active flux remediation, as fouling was found to be reversible over continuous operating periods up to 10 hours. Furthermore, it was found that the use of non-optimized on-line air backflushing resulted in increased throughput of low solids fast pyrolysis bio-oil from cross-flow microfiltration by 100%. Ultimately, the data produced from this work is intended to be used to generate design parameters and associated cost estimates for biomass washing and post-condensation microfiltration as processing strategies to generate high quality bio-oils from low cost biomass feedstocks.