The demand for a new solvent to treat oilsands was behind the purpose of this project; molecular dynamics simulation was used in this study. Supercritical water, supercritical carbon dioxide and other selected organic solvents in their supercritical state were studied. Meso-tetraphenyl porphyrin (H2TPP) and Octaethyl porphyrin (H2OEP) are the porphyrin model compounds and, 4-Bis-(2-pyren-1-yl-ethyl)-[2, 2] bipyridinyl (PBP) is the asphaltene model compound. A solubility parameter approach was used to infer the solubility of model compounds in the supercritical fluids. First, the solubility of water, carbon dioxide, 4 selected organic solvents, and the three model compounds were computed using molecular dynamics simulation and compared with experimental results. The computed solubility parameters showed that the model compounds would dissolve in supercritical water (22.5 MPa and 645-655 K) but exhibited no solubility in supercritical carbon dioxide. / Chemical Engineering

Thesis (doctoral) -- Helsinki University of Technology, 2000. / Includes bibliographical references. Also available on the World Wide Web.

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In this thesis, some fundamentals and possible applications of high-pressure microfluidics have been explored. Furthermore, handling fluids at high pressures has been addressed, specifically by creating and characterizing strong microvalves and pumps. A variety of microstructuring techniques was used to realize these microfluidic devices, e.g., etching, lithography, and bonding. To be able to handle high pressures, the valves and pumps need to be strong. This necessitates a strong actuator material. In this thesis, the material of choice is paraffin wax. A new way of latching paraffin-actuated microvalves into either closed or open position has been developed, using the low thermal conductivity of paraffin to create large thermal gradients within a microactuator. This allows for long open and closed times without power consumption. In addition, three types of paraffin-actuated pumps are presented: A peristaltic high-pressure pump with integrated temperature control, a microdispensing pump with high repeatability, and a pump system with two pumps working with an offset to reduce flow irregularities. Furthermore, the fundamental behavior of paraffin as a microactuator material has been explored by finite element modeling. One possibility that arises with high-pressure microfluidics, is the utilization of supercritical fluids for different applications. The unique combination of material properties found in supercritical fluids yields them interesting applications in, e.g., extraction and cleaning. In an attempt to understand the microfluidic behavior of supercritical carbon dioxide, the two-phase flow, with liquid water as the second phase, in a microchannel has been studied and mapped with respect to both flow regime and droplet behavior at a bi-furcating outlet.

Peripheral steroids and oxycholesterols are important lipid compounds controlling various functions in the human body. Steroid analysis of biological samples is routinely employed in the clinical environment as an essential source of information on endocrine and metabolic disorders. It has been reported that stress related neurosteroids have been implicated in the development and prognoses of neurodegenerative disorders such as Alzheimer’s disease (AD). These compounds have been identified as possible biomarkers in the diagnosis of AD and other neurodegenerative disorders. Therefore, methods for the simultaneous analysis of steroids from the four major classes (estrogens, androgens, progestogens and corticosteroids) are vital in providing useful and more comprehensive data. Homeostasis of cholesterol in the brain is maintained primarily by metabolism to oxysterols, including oxycholesterols. These oxycholesterols act as a transport form of cholesterol as it readily navigates the blood-brain barrier. Oxycholesterols are generally more bioactive than cholesterol and is of interest in pathophysiology. Moreover, if their production in cells and tissues and/or their introduction with dietary animal fat are excessive, oxycholesterols could indeed contribute to the pathogenesis of various disease processes. The first study in this thesis focuses on a novel supercritical fluid chromatography–tandem mass spectrometry method for targeted analysis of eighteen peripheral steroids. The method is simple and fast. It has sufficient sensitivity for quantification of 18 different steroids in small volume human plasma. Therefore, this novel method can be applied for screening many steroids within 5 minutes providing the possibility to use for routine healthcare practice. The second study involves the quantification of three adrenal steroids in plasma from domesticated White Leghorn (WL) chickens and Red Junglefowl (RJF) birds. The domestication effects on stress induced steroid secretion and adrenal gene expression in chickens are evaluated. The third study focuses on determination of more than ten oxycholesterols in biological samples with a gas chromatography–mass spectrometry method and a supercritical fluid–tandem mass spectrometry method.

Graduation date: 2000

Thesis (M. Sc.)(Chemistry)--University of Pretoria, 2006. / Summaries in English and Afrikaans. Includes bibliographical references. Available on the Internet via the World Wide Web.

Supercritical fluid technology is a well documented and emergent technology used in many industries today for the formation of micro- and nano- particles. The use of supercritical fluids allows synthesis of various types of particles since their properties can be varied with temperature or pressure, which sequentially can control the physical and chemical properties of the particles produced. Several different processes designed to generate powders and composites using supercritical fluids have been proposed in the past 20 years which can be used to synthesize materials with high performance specifications and unique functionality. In this research work, an extrusion micronization process using supercritical fluid has been proposed. This powder production technique could be a promising alternative to conventional techniques in terms of improvement in product quality as it provides a better control over particle size, morphology and particle size distribution, without degradation or contamination of the product. In addition, as extrusion is globally used for polymer production and processing, particle production by extrusion will allow production and processing in a single process step, eliminating the need for secondary particle production methods. The micronization process designed and described in this thesis involves a twin screw extruder equipped with a converging die and a high resistance spraying nozzle for particle production. A special CO2 injection device and polymer collection chamber was designed for CO2 supply and powder collection. To ensure complete dissolution of CO2 into the polymer matrix, stable injection of CO2, pressure generation and constant spray of micronized polymer particles, a special screw configuration was carefully designed for the extrusion process. The feasibility and the performance of this process have been demonstrated by experimental studies performed with low molecular weight polyethylene wax. Carbon dioxide at supercritical conditions was used as a solvent for processing the polymer. The generated polyethylene particles from the polyethylene wax/carbon dioxide solution system were analyzed and studied using an optical microscope, scanning electron microscope, capillary rheometer and differential scanning calorimeter. A detailed study on the effects of the processing parameters, such as temperature, pressure, flow rate and supercritical fluid on properties of polyethylene particle produced was carried out. The particle size data collected using an optical microscope indicate a significant impact of temperature and CO2 content on particle size. The obtained size data were utilized to generate particle size distribution plots and studied to analyze the effect of the processing variables. It was found that particle size distribution is affected by processing temperature and CO2 content. Studies of the SEM images reveal that the morphology of particles can be controlled by varying processing variables like temperature, polymer feed rate and CO2 content. The particles generated during this study indicate that particle production in an extrusion process using supercritical carbon dioxide is achievable and appears to be a promising alternative to conventional polymer particle production methods such as grinding, milling and other supercritical fluid-based precipitation methods. To validate and generalize the applicability of this process, micronization of other polymeric material should be performed. Commercialization of this technology will further require predictability and consistency of the characteristics of the product, for which a detailed understanding of the influence of all relevant process variables is necessary. In addition, development of theoretical models will further assist in the scale-up and commercialization of this supercritical fluid assisted micronization technology in the near future.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.