Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2001. / Current methods for wax fractionation result in products with large polydispersity, and due to the high temperatures required, thermal degradation of the wax is often incurred. The need for an alternative process thus exists. The purpose of this project is to investigate the technical viability of supercritical fluid processing as an alternative wax fractionation technology. The main aims of this project are to select a suitable supercritical solvent, to conduct binary phase equilibrium experiments, to determine if the process is technically viable and to investigate the ability of various equations of state to correlate the phase equilibrium data. Based on limited data from the literature, propane and a propane rich LPG (Liquefied Petroleum Gas) were selected as suitable solvents. Literature data for propane and high molecular weight alkanes is scares and incomplete, thus necessitating experimental measurements. A phase equilibrium cell was designed, constructed and commissioned. The cell was designed for pressures up to 500 bar and temperatures to 200 oC, and with the aid of an endoscope, the phase transitions were detected visually. The measurements correspond well to literature values from reliable research groups. Phase equilibrium data sets for propane with nC32, nC36, nC38, nC40, nC44, nC46, nC54 and nC60 as well as LP Gas with nC36 were measured. At temperatures just above the melting point of the alkanes, the phase transition pressures can be considered to be moderate, which will positively impact the economics of the process. The phase transition pressure increases with increasing carbon number, the relationship being found to be linear when the pressure is plotted as a function of carbon number at constant mass fractions and temperature. The increase in phase transition pressure with increasing carbon number indicates that the solvent will be able to selectively fractionate the wax. At higher temperatures the gradient of the line is larger and may thus lead to improved selectivity. The higher temperatures will also lead to better mass transfer. The linear relationship indicates that limited extrapolation to higher carbon numbers may be possible. However, this needs to be verified experimentally. The inability to measure the critical point and vapour pressure curves of the higher molecular weight normal alkanes, as well as the inability of cubic equations of state to predict liquid volumes and to capture the chain specific effects such as internal rotations, results in cubic equations of state requiring large interaction parameters to fit the data. The alternative, statistical mechanical equations of state, have difficulty in predicting the critical point of the solvent correctly and thus overpredicts the mixture critical point, yet require smaller interaction parameters to fit the data. Further work is required to improve the predictability of these non-cubic equations of state. This project has proven that wax fractionation by supercritical extraction with propane is technically feasible.

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Supercritical extraction is being investigated as a possible alternative to the processes currently used in the fractionation of paraffinic waxes. By removing the lighter carbon fractions from the wax, the wax hardness will be improved and its melting temperature range reduced, hence improving the performance of the wax product in certain applications. In order to evaluate and operate such an extraction process optimally, it is necessary to have a thermodynamic model that accurately represents the process system. There are, however, currently no predictive models available for these systems. In order to fit present models to the systems, accurate phase equilibrium data of the supercritical solvent - n-alkane systems are needed. Unfortunately, the amount of reliable published data on these systems in the required operating range is very limited. A view cell was designed and developed with which these high pressure equilibria could be studied. The binary phase equilibria of supercritical CO2 with n-CI2, n-CI6, n-C20, n-C24, n-C28 and n-C36 and of supercritical ethane with n-CI6, n-C24 and n-C28 were measured in the temperature range 313 - 367 K. It was found that the systems with these two solvents have very different types of phase behaviour. The n-alkane solubility is much higher in ethane, but supercritical CO2 will provide a much better degree of control over the selectivity achieved in an extraction process. Of the various equations of state investigated, it was found that the Patel Teja equation of state provided the best fit of the CO2 - n-alkane systems and that the Soave-Redlich- Kwong equation fitted the ethane - n-alkane systems the best. The interaction parameters of both these equations of state display a functional relationship with temperature and nalkane acentric factor, making it possible to determine parameter values for application at other operating temperatures and with other n-alkane systems. It was found that the current equations of state were not able to represent the phase equilibria accurately over the entire range of operating conditions. The poor performance of the equations of state can be attributed to inherent flaws in the existing equations of state. / AFRIKAANSE OPSOMMING: Superkritiese ekstraksie word tans ondersoek as 'n moontlike altematief vir die prosesse wat huidiglik gebruik word om paraffiese wasse te fraksioneer. Die Iigter koolstofwasse word verwyder om die washardheid te verhoog en die temperatuurgebied waaroor die was smelt te verklein. Dit verbeter dan die was se kwaliteit en werkverrigting. Modelle wat die superkritiese ekstraksie proses akkuraat kan voorstel word egter benodig om die ekstraksie proses te kan evalueer en optimaal te bedryf. Daar is tans geen modelle beskikbaar wat die proses direk kan voorstel nie. Akkurate fase-ewewigsdata word benodig om bestaande modelle aan te pas vir gebruik in hierdie sisteme. Daar is egter baie min betroubare faseewewigsdata vir die superkritiese oplosmiddel - n-alkaan sisteme beskikbaar in die literatuur. 'n Sig-sel, waarrnee hierdie hoe druk data gemeet kan word, is ontwerp en ontwikkel. Die volgende binere fase ewewigte is in die temperatuur gebied 313 - 367 K gemeet: superkritiese CO2 met n-CI2, n-CI6, n-C20, n-C24, n-C28 en n-C36, en superkritiese Etaan met n-CI6, n-C24 en n-C28. Daar is gevind dat hierdie twee superkritiese oplosmiddelsisteme verskillende tipes fase-ewewigsgedragte openbaar. Die n-alkane het 'n baie boer oplosbaarheid in Etaan, maar deur superkritiese C02 in 'n ekstraksie kolom te gebruik, sal tot beheer oor die selektiwiteit van die ekstraksieproses lei. Uit die verskillende toestandsvergelykings wat ondersoek is, is daar gevind dat die Patel- Teja vergelyking die CO2 sisteme die beste kon beskryf en dat die Soave-Redlich-Kwong vergelyking die beste vergelyking was om die Etaan sisteme mee te modelleer. Beide die toestandsvergelykings se interaksie parameters het 'n funksionele verband met temperatuur en die n-alkaan asentrise faktor getoon. Dit is dus moontlik om waardes vir die parameters vir sisteme by ander temperature en met ander n-alkaan tipes te bepaal. Daar was gevind dat die bestaande toestandsvergelykings nie die die fase-ewewigte oor die hele eksperimenele gebied akkuraat kon voorstel nie. Dit kan toegeskryf word aan foute wat inherent is aan die vergelykings.

Ionic liquid/scCO₂ biphasic systems have been studied as a possible solution to the main problems concerning homogeneous catalysis reactions such as, the product/catalyst separation, the catalyst retention in the reaction medium and the use of organic solvents. The hydroformylation of long chain alkenes (1-octene) has been carried out as a continuous flow reaction using [OctMIM]Tf₂N (OctMIM = 1-octyl-3-methylimidazolium, Tf = CF₃SO₂) as the reaction solvent and scCO₂as the mobile phase to extract the products. The performance of the rhodium complexes formed with the ionic ligands [PentMIM][TPPTS] (1-pentyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) and [OctMIM][TPPTS] (1-octyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) is described under different sets of experimental conditions. Continuous flow hydroformylation of 1-octene was also carried out using a SILP (Supported Ionic Liquid Phase) catalyst formed with the TPPTS-based ionic ligands named above. The SILP system described in this work has the peculiarity of introducing the “without gases” approach: syn gas was synthesised in situ by the decomposition of formaldehyde. The performance of both systems is compared in the end. The extension of the continuous flow ionic liquid/scCO₂ biphasic system is shown with the optimisation of the silver-catalysed heterocyclisation of furans. A comparison is carried out with a previously developed and optimised continuous flow heterogeneous system.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The Supercritical Fluid Extraction (SFE) technique was used to fractionate Suwannee River reference fulvic acid (FA). The fractions were characterized by gas chromatography (GC) and reversed-phase high performance liquid chromatography (RP-HPLC). A SFE fractionation method was developed using stepwise gradient of supercritical CO₂ and methanol. Three FA fractions were separated. The average mass recovery was 102% with the coefficient of variation of 2.8%. The fractionation dynamics and the difference in the ratios of UV absorption to fluorescence emission indicate the real fractionation of the FA. The HPLC chromatographic peak patterns and the spectra of the corresponding peaks were almost indistinguishable. The overall results of this research support the argument that FA exhibits polymer-like molecular structure.

Bifenilas Policloradas (PCB) são compostos orgânicos clorados altamente tóxicos e também são considerados poluentes orgânicos persistentes. Sua alta estabilidade térmica e química é responsável pela sua difícil degradação, e quando estas substâncias são liberadas no meio ambiente, sua acumulação nos ecossistemas incorpora-se na cadeia alimentar, exibindo biomagnificação. Deve-se ressaltar a importância para o meio ambiente do tratamento de resíduos com PCB. Considerando que a Convenção de Estocolmo sobre poluentes orgânicos persistentes (POP) estabeleceu a eliminação do uso de PCB em equipamentos, por exemplo, transformadores e capacitores elétricos, até 2025. O objetivo deste trabalho foi estudar a remoção de PCB pelos processos de extração usando fluido supercrítico e a extração convencional (Soxhlet) no tratamento de materiais contaminados com PCB. Assim foi desenvolvida uma ferramenta computacional para correlacionar os dados de solubilidade de PCB em CO₂ supercrítico, usando a equação de estado de Peng-Robinson com parâmetros ajustados. O procedimento de cálculo foi inicialmente usado para uma série de compostos aromáticos (naftaleno, antraceno, fenantreno e bifenil), a fim de testar a abordagem. Os parâmetros binários para a regra de mistura quadrática clássica (vdW2) foram sistematicamente estimados, juntamente com um novo conjunto de dados de pressão de vapor, a fim de descrever a dependência da temperatura e alcançar incertezas experimentais. Finalmente, foram utilizados os parâmetros estimados para simular valores de solubilidade dos principais congêneres constituintes das misturas comerciais reais de PCB, como função das condições de operação de extração com uma solução simultânea das equações de equilíbrio para cada composto. A modelagem termodinâmica demonstrou ser viável para a análise de processos. / Polychlorinated Biphenyls (PCB) are chlorinated organic compounds which are highly toxic and are also considered persistent organic pollutants. The high thermal and chemical stability of PCB are responsible for their hard degradation, and when these substances are liberated in the environment, their accumulation in ecosystems leads to their incorporation in the food chain, exhibiting biomagnification. It should be emphasized the environmental importance for treating wastes with PCB. Considering that, Stockholm Convention on persistent organic pollutants (POP) established the elimination of the use of PCB in equipments, e.g. electrical transformers and capacitors, by 2025. The objective of this work was to study the removal of PCB by the processes of extractions using supercritical fluid and conventional (Soxhlet) extraction method in the treatment of contaminated materials with PCB. As well was the formulation of a computational tool to correlate solubility data of PCB in supercritical CO₂, using Peng-Robinson equation of state with fitted parameters. The calculation procedure was initially used for a series of aromatic compounds (naphthalene, anthracene, phenanthrene and biphenyl) in order to test the approach. The binary parameters for the classical quadratic mixing rule (vdW2) were systematically estimated, together with a new set of vapor pressure in order to describe the temperature dependence and achieve experimental uncertainties. Finally, the estimated parameters were used to simulate solubility values of the major constituent congeners of commercial and real mixtures of PCB, as function of the operational conditions of extraction by a simultaneous solution of the equilibrium equations for each compound. The thermodynamic modeling demonstrated to be feasible for process analysis and design.

Drug re-engineering is an effective method for engineering existing products in alternative dosage forms and with enhanced pharmacokinetics. Insulin for the management of diabetic symptoms is an ideal candidate for re-engineering. Current subcutaneous therapy results in low patient compliance and is ineffective in meeting the physiological need for post-prandial insulin. Implementation of dose titration for more efficient blood-glucose management is also inconvenient and uncomfortable. Inhaled insulin is presented as a superior alternative to current therapy. The lungs offer excellent access to the circulatory system. Aerosols suspended in inspired air may deposit on lung epithelia and be available for systemic absorption. To evade the defense mechanism of the human respiratory tract, particle sizes have traditionally been minimized to achieve necessary aerosol performance. Recent developments indicate that more efficient performance augmentation may also be achieved by decreasing the bulk density of powders and modifying surface characteristics. Light and fluffy powders with rough surfaces experience much higher drag forces within an airstream. The Atomized Rapid Injection for Solvent Extraction (ARISE) process is a unique precipitation platform devised by incorporating a rapid injection technique for energetic solution delivery into supercritical fluid (SCF) media to effect recovery of previously dissolved pharmaceutical compounds. The quasi-instantaneous delivery of solutions alleviates the drawbacks of the use of capillary nozzles or micro-orifices, gradual elution and mixing controlled precipitation kinetics in existing SCF precipitation techniques. Most importantly, the energetic release of solution into SCF media effects supersaturation over a much larger spatial volume and promotes the homogeneous precipitation of low bulk density powders. ARISE processed insulin powders displayed characteristics that were highly influenced by anti-solvent conditions and powders of different qualities were obtained as a function of anti-solvent pressures. At lower anti-solvent pressures, powders of narrow particle size distribution were achieved, an indication of homogeneous supersaturation levels within processing. Span, the index of size distribution was as low as 0.991. At higher anti-solvent pressures, supersaturation rates were increased while mixing efficiencies decreased, resulting in powders of wider size distribution, and powder bulk densities as low as 0.01 g/ml. Low bulk density insulin displayed in-vitro respirable fractions as high as 78%.

Due to high consumption rates of petroleum derived fuels and environmental regulations, significant search has been initiated for the development of environmental friendly and efficient fuels, which were derived from more abundant feedstocks. Dimethyl ether (DME), as having a good combustion quality and high cetane number, is an efficient alternative for diesel fuel. With improved combustion quality, the emissions from DME used engines are greatly decreased. DME synthesis can be carried out via two different methods / methanol dehydration on acidic catalysis and syn-gas conversion on bifunctional catalysis. In this study, the aim is to synthesize acidic catalysts using direct hydrothermal synthesis method for DME synthesis as using methanol as feed stock via dehydration and to characterize these materials. The support of the synthesized materials comprises of MCM-41 structure and silicotungstic acid (STA) and metals (Zr / Ni / Cu) were incorporated into the MCM-41 structure during synthesis. Two different techniques were used to extract the surfactant (CTMABr) from catalyst matrix. First one is the conventional calcination technique (at 350&deg / C) and the second is supercritical fluid extraction (at various operating conditions) with methanol modified CO2. The effect of metal loading on extraction performance is analyzed through characterizations of Ni and Cu incorporated materials. In addition, The effect of operation parameters on catalyst properties are also investigated with performing extraction at different pressures for different durations. By changing the type of metal incorporated into the catalyst, the extraction performance is also monitored. The characterization results indicated that, SFE process is also a promising method for surfactant removal. The activities of zirconium added catalysts are tested in methanol dehydration reaction towards DME. It is concluded that the conversion of methanol and selectivity of DME in presence of extracted samples are lower (maximum yield -0.54- obtained at 450&deg / C with sceSZ1) compared to the calcined materials (maximum yield -0.80- obtained at 300&deg / C with cSZ6). This result can also be foreseen by DRIFTS analysis of pyridine adsorbed samples. The acid sites of extracted materials are not as strong as in the calcined catalysts.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (Ph. D.)(Chemistry)--University of Pretoria, 2003. / Includes bibliographical references.