Pitch material is an important precursor in the production of carbon bre, carbon composites and synthetic graphite. It has a complex transformation during pyrolysis which incorporates the separation of a liquid crystalline phase, known as mesophase. This thesis attempts to enhance the understanding of this change in composition, structure and its resultant behaviour. In this study, two pitches, a coal-tar pitch (MP110) and a (SASOL) Lurgi-gasi er pitch, are pyrolised to produce material at di erent stages of mesophase development. These pitches produce mesophase of di erent mosaic type and therefore also resultant coke. The MP110 was thermally treated up to a temperature of 437 and produced anisotropic pitch (which still contains signi cant particulate matter). The nucleated mesophase spheres did not coalesce to produce domains; this behaviour being attributed to the particulate material. The SASOL pitch produced a di erent type of mesophase material. The mesophase produced was of ne mosaic domains; a sample with continuous mesophase regions was also produced with a mesophase content of approximately 60% (by volume). The aromatic starting material of MP110 produced higher quinolone and toluene insoluble (QI and TI) compounds after pyrolysis. This was also observed in the increase of C/H (molar ratio of carbon to hydrogen). The more aliphatic SASOL starting pitch showed similar trends to its MP110 counterparts with respect to QI (quinoline insolubles), TI (toluene insolubles) and C/H. The glass transition and associated temperatures of the pitches were analysed via thermal mechanical analysis (TMA), dynamic scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The techniques showed consistency between instruments, with TMA providing the likeliest re ection of the true thermodynamic glass transition temperature. The loss of volatile components was accompanied by an increase in glass transition temperature (observed in conjunction with C/H and mesophase content). For anisotropic MP110 pitches, two relaxations were observed, one for the isotropic fraction, the other for the mesophase. No such behaviour was easily observed for the SASOL pitches. Rheological measurements were obtained to understand the behaviour of the pitches. Measurements were limited to a speci c viscosity range. The measurements of the samples were therefore made at di erent temperatures. The relation of the measurement temperature to the glass transition temperature is thus of extreme importance. The temperature governs the state of the structure; whether it be suspension, emulsion or gel. Oscillatory shear experiments were undertaken for the pitch material. Predominantly isotropic material showed transition from viscoelastic solid to viscoelastic liquid as previously observed in pitch material. The anisotropic MP110 pitches did not allow for the production of mastercurves due to non-linear viscoelastic e ects caused by the softening of mesophase. This being the transition from a suspension of hard spheres to an emulsion of deformable droplets (depending on temperature). For the higher mesophase content anisotropic SASOL pitches, mastercurves were produced; it had a similar shape to the isotropic pitches (at temperatures closer to the glass transition), but signi cantly increased elasticity was observed at higher temperatures. This phenomenon supported the hypothesis of a strong interaction between the components and phases of the pitch, and thus the possibility of gelled systems. Rotational shear-rheometry was also utilised and showed that isotropic pitch material behaves as a predominantly isoviscous uid. The anisotropic MP110 pitches of approximately 30% mesophase showed high- and low-shear viscosity plateau uid behaviour. This being caused by the breakup of agglomerated mesophase spheres. This was tested by the implementation of the Krieger- Dougherty suspension model. The possibility of droplet deformation was investigated for these samples by utilising a Krieger-Douherty based emulsion analogue, which con- rmed suspension like behaviour (at the measured temperatures). MP110 samples with more mesophase were measured at higher temperatures. Their behaviour is more akin to Power-law shear-thinning behaviour. Being further away from the continuous isotropic phase glass transition temperature, the behaviour observed is similar to that of emulsions. SASOL anisotropic pitches showed signi cant yielding upon shear, which is attributed to structure breakdown. This behaviour is appropriately described by a yield stress, shearthinning model such as Herschel-Bulkley. Measurements of viscosity for these samples were made at temperatures signi cantly further from the glass transition temperature as compared to that of the MP110 pitches. This corroborates strong interaction between its components. The observed shapes of the curve, at temperatures of measurement, support the notion of a gel structure. This behaviour is rst proposed via the complex structure observed (clusters of ne mosaic mesophase domains) and supported by strong interaction of the components inferred from obtained rheological properties. / Thesis (PhD)--University of Pretoria, 2015. / tm2015 / Chemical Engineering / PhD / Unrestricted

Automated start–up and shutdown procedures increase the profitability and safety of a process, but are difficult to implement due to the complex nature of the concepts that must be incorporated. Generic components used specifically for the implementation of automated startup and shutdown procedures were defined to streamline the implementation process. The generic components developed are based on Sequential Function Charts and were applied to the startup of a fixed–bed gasification unit, for which a dynamic simulation model was developed. The application showed that the automated startup can be defined by a few generic components and that the flexibility of the startup procedure is increased through the incorporation of a fault accommodation module. The use of a visual–based definition of sequential processes increases the understanding of the complex scheduling procedures as well as the efficiency of the development of these automated procedures. In addition, iterative learning was incorporated into the generic definition to optimise controller performance during the non–linear phases of operation. / Dissertation (MEng (Control Engineering))--University of Pretoria, 2006. / Chemical Engineering / MEng / Unrestricted

Coals, from mines in the Highveld coalfield, as well as gasification ash samples were characterised, in order to understand the mineralogical and chemical properties of the individual components in the gasification feedstocks. X-ray diffraction of low temperature oxygen-plasma ash indicates that the coals contain significant proportions of kaolinite, quartz and a fluxing elements-bearing mineral (dolomite), plus minor concentrations of illite and other fluxing elements-bearing minerals namely calcite, pyrite and siderite. Of the feed coal, the -75+53 mm size fraction has a high pyrite, and to a lesser extent a high calcite and dolomite content. However, the small proportion of iron-bearing phases (from the reaction between kaolinite and pyrite) in samples taken from the gasifier implies that pyrite contributes minimally to sintering or slagging in this case. Calcite is mainly present in the >1.8 g/cm3 density fraction of the feed coal, whereas dolomite is mainly present in the 1.5-1.8 g/cm3 density fraction, as inclusions or fine cleats in the coal matrix. Electron microprobe analyses of coals from the six different South African mines confirmed that some Ca, Mg, Al, Si, Na, K, Ti and Fe are present in the organic matrix in the coal samples tested in this study, but the amounts of these are small compared with the fluxing elements in minerals. XRD and microprobe analyses indicate that the ash clinker samples taken from the gasifiers contain a number of crystalline high temperature phases, including anorthite, mullite, cristobalite, quartz and diopside. FactSage confirmed that anorthite and mullite are equilibrium phases at elevated temperatures in the ash clinkers and heated rock fragments. Limited reaction takes place between the included coal minerals and the extraneous rock fragments. / Thesis (PhD)--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted