Gegenstand der vorliegenden Arbeit ist die Herstellung und Charakterisierung neuer sternförmiger Mesogene. Bei den aufgeführten Sternverbindungen, handelt es sich um Oligobenzoate, bestehend aus aromatischen Hydroxy- oder Aminocarbonsäuren, die durch Kupplungsreaktionen mit Dicylohexycarbodiimid, in einer konvergenten Synthesestrategie verknüpft wurden. Das besondere Augenmerk der Arbeit richtete sich auf die Charakterisierung der von den neuen Substanzen gebildeten Mesophasen, die mit Hilfe von Polarisationsmikrokopie, dynamischer Differenzialkalorimetrie und Röntgenstreuung erfolgte. Zur Aufklärung spezieller dreidimensionaler Strukturen wurden als zusätzliche Methoden die Rasterkraftmikroskopie angewandt und der Zirkulardichroismus untersucht.

The formation and development of mesophase from different pitches under carbonisation conditions was investigated. Members of the pyrolysis series were prepared from four pitches. A temperature range between 380 and 500°C was used to follow mesophase development for each pitch. As-received pitches and their green cokes were characterised by thermomechanical analysis (glass transition temperature and softening point temperature), elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry or differential thermogravimetry, and optical microscopy (mesophase content). Additional data about the evolution of different volatile products and about possible chemical reactions occurring during thermal decomposition were obtained from thermogravimetric mass spectrometric analysis. The effect of heating rate on the behaviour and carbon yield was also studied. The results showed that the two anthracene oil pitches do not develop mesophase, whereas the medium-temperature and high-temperature pitches do. However, their textures are completely different. The medium-temperature pitch shows an improvement in texture from the mosaic to the coarse domain at 500°C, whereas the high-temperature pitch shows flow domains. It was further shown that the process of preparing mesophase, i.e. the heat-treatment process, increases the aromaticity and carbon yield. Thermogravimetric mass spectrometric analysis showed that the dominant reaction for all the pitches is the condensation reaction, which is accompanied by the evolution of H2 and CO. The heating rate affects the behaviour of the pyrolysing pitches in that a lower heating rate lowers the carbon yield. This study gave insight into the influence of the nature and composition of the precursor on the formation of mesophase. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

Commercial ebullated bed hydroprocessors, such as the LC-Finer, are used for the production of synthetic crude oil by upgrading bitumen extracted from the Alberta oil sands. The objective of this thesis was to investigate the impact of an increased vacuum distillation tower bottoms feed fraction on the reactor fluid dynamics (e.g., bed and freeboard phase holdups, bubble characteristics and local fluidization behaviour). Industrial conditions were simulated in a high pressure gas-liquid-solid fluidization system based on dimensional and geometric similitude. Considering important geometric characteristics and matching dimensionless groups, base-case conditions resulted in an ebullated bed of nitrogen, 0.5 wt.% aqueous ethanol, and aluminum cylinders (average lengths and diameters of 7.5 and 3.2 mm, respectively) operating at 6.5 MPa and a gas-to-liquid superficial velocity ratio of 0.78. The proposed scale-down method resulted in high gas holdup conditions similar to industrial measurements. The use of the Sauter mean diameter to account for particle size and shape at the simulation conditions was investigated by comparing glass spheres with diameters of 4 and 1.5 mm to aluminum cylinders with equivalent volume-to-surface area ratios. Local bubble characteristics, including gas holdups, bubble rise velocities, and chord lengths, were then investigated under various operating conditions using a monofibre optical probe. Overall fluid dynamics were studied when increasing the liquid viscosity and varying the gas and liquid superficial velocities due to their relevance for industrial ebullated bed hydroprocessors. Freeboard and bed region gas holdup relations were studied and correlations were developed for gas and solid holdups at the simulation conditions based on the dimensionless groups. Mesophase generation in hydroprocessors due to undesired secondary reactions was also considered for an increased vacuum residue feed fraction. Adding a dispersed immiscible liquid phase which preferentially wetted the particles was therefore experimentally studied at non-simulating conditions using nitrogen, biodiesel, glycerol and various particles, where fluidization behaviour and phase holdups were considerably affected due to particle clustering. A study on the impacts of particle size, shape and material demonstrated the influences of fluid and particle properties, specifically the relative surface energies and viscous forces, on agglomeration due to interparticle liquid bridging.

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

This research study determines the potential to increase substantially the anisotropy of a coke from an aliphatic Waxy Oil produced by Sasol Synfuels at Secunda, South Africa. Experimental modifications included filtration, distillation and thermal treatment, followed by distillation with the aim of producing a carbonised product similar to needle coke. The substantial concentration of an iron oxide catalyst (up to 2%) in Waxy Oil is increased by an order of magnitude upon carbonisation and calcination due to low coke yield and reactivity factors. The catalyst also promotes oxidative polymerisation of the residue, acts as a barrier to mesophase formation and promotes multi-phase graphitisation. Filtration of Waxy Oil using a 0.5 ìm sintered metal filter reduces the ash content to 0.006% and increases the anisotropy of the carbonised product to 54% flow domains compared with 22% for the carbonised product of virgin Waxy Oil. Thermal treatment followed by distillation of Waxy Oil reduces the effect of organic reactivity promoters (mainly multi-alkylated aliphatics/aromatics and oxygenates), while increasing the concentration of thermally stable (C18 to C30) normal alkanes to 85% compared with 38% in the filtered Waxy Oil. Compared with the filtered Waxy Oil, thermally stabilised Waxy Oil reduces the amount of the pre-carbonisation residue (from 98.7 to 43.0%), while “static” carbonisation thereof increases the green coke yield (from 19.8 to 36.3%) and increases the anisotropicity (from 54 to 100% flow domains). The carbonisation mechanism of filtered and thermally treated Waxy Oil involves initial cracking of high molecular weight normal alkanes (C18 to C30), thus concentrating the molecular weight of normal alkanes (C18 to C22). This is followed by a slow cyclisation step involving both self condensation and cyclo addition reactions to form two- to six-ring cyclo-alkanes or hydro-aromatics. The hydro-aromatics are dehydrogenated rapidly to form methyl and di-methyl three- to six-ring substituted aromatics. Further thermal degradation dealkylates these molecules to form stable four- to six-ring “pre-mesogens”. The mesospheres are nucleated from the isotropic matrix and grow to more than 0.050 mm in diameter, with a volume of 2.61 x 10-3 mm3. Subsequent coalescence of the mesospheres produces mesospheres with diameters of over 0.200 mm and volumes of 41.82 x 10-3 mm3. The resultant microstructure of the solid carbon is composed of flow domains more than 400 ìm in length. Although needle cokes have historically been produced from aromatic residues, this research is the first to show that a coke with a similar microstructure can be produced from a totally aliphatic residue. The research thus provides potential for the development of a needle coke from a totally unique Waxy Oil residue with negligible sulphur (< 0.008%) and nitrogen (< 0.09%) contents. This is the first academic study of the chemistry of Waxy Oil. / Thesis (PhD)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

No description available.

The efficacy of dispersed reduced graphene oxide (rGO) as a nucleation site for the growth of mesophase in an isotropic pitch was investigated and quantified in this study. Concentrations of rGO were systematically tested in an isotropic petroleum and coal-tar pitch during thermal treatments and compared to pitch without rGO. The mesophase content of each thermally treated pitch was quantified by polarized light point counting. Further characterization of softening temperature and insolubles were quantified. Additionally, the pitches with and without rGO were melt spun, graphitized, and tensile tested to determine the effects of rGO on graphitized fiber mechanical properties and fiber morphology.

Azobenzene upon photochemical E/Z isomerization changes both its shape and size. The E-azobenzene moiety falls in the class of calamitic liquid crystalline mesogens, producing a wide variety of mesophases. Two series of linear bis(azobenzene) compounds, one with phenyl benzoate linkage and the other with benzyl benzoate linkage were synthesized. The termini of these molecules ranged from a dodecyloxy chain to hydrophobic amphiphilic dendrons up to first generation. We determined the effects of both the linkages and generation number on the mesogenic properties of these compounds. Our results show that the mesogenic behavior of these bis(azobenzene) compounds are highly dependent on the linkages between individual azobenzenes and that for the bis(azobenzene) compounds of the phenyl benzoate series, generation number had an effect on the liquid crystalline mesophase of the compounds

Gegenstand der vorliegenden Arbeit ist die Herstellung und Charakterisierung neuer sternförmiger Mesogene. Bei den aufgeführten Sternverbindungen, handelt es sich um Oligobenzoate, bestehend aus aromatischen Hydroxy- oder Aminocarbonsäuren, die durch Kupplungsreaktionen mit Dicylohexycarbodiimid, in einer konvergenten Synthesestrategie verknüpft wurden. Das besondere Augenmerk der Arbeit richtete sich auf die Charakterisierung der von den neuen Substanzen gebildeten Mesophasen, die mit Hilfe von Polarisationsmikrokopie, dynamischer Differenzialkalorimetrie und Röntgenstreuung erfolgte. Zur Aufklärung spezieller dreidimensionaler Strukturen wurden als zusätzliche Methoden die Rasterkraftmikroskopie angewandt und der Zirkulardichroismus untersucht.

No description available.