Thesis (Ph. D.)--Lehigh University, 1998. / Includes vita. Bibliography: leaves 157-165.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

The effect of supercritical water treatment on the composition of bio-oil was investigated. Preliminary studies were carried in batch mode using a bio-oil simulant. This bio-oil simulant was designed to mimic crude bio-oil by possessing the same functional groups as are found in crude bio-oil, but with reduced complexity. Experiments of this type allow to be gained of the reaction chemistry involved. These were then followed up by experiments using crude bio-oil. Critical process parameters for all these experiments were reaction time, bio-oil/water ratio, reaction temperature and pressure. One of the objectives of this work was to identify processing conditions that would either suppress formation of, or elimination of the coke precursors. This would then result in a bio-oil with improved storage characteristics and a reduced tendency towards coke formation during catalytic upgrading. The results suggest that supercritical water treatment can effectively eliminate the coke pre-cursors resulting from bio-oil, resulting in a bio-oil with improved properties.

The thesis outlines an investigative study of the supercritical fluid extraction (SFE) of organic natural products from two Meliaceae species. Extractions from ground wood, bark and seeds of the selected species were studied. Qualitative and quantitative studies were performed using a number of techniques. In the qualitative study, both off-line and on-line combination of micro-SFE with capillary gas chromatography (SFE-GC) were performed on the wood and bark of Cedrela toona to show the applicability of the technique in the analysis of semi-volatile components from plant matrices. Results for the on-line and off-line SFE-GC were comparable and indicated that the on-line studies could be used to predict results obtainable from large scale SFE. Dynamic SFE of the limonoid (cedrelone) from the wood of Cedrela toona using pure and modified carbon dioxide was studied on the basis of a theoretically-derived dynamic extraction model. Extracts were collected for different lengths of time in order to investigate the extraction kinetics of this compound. The theoretically-derived model which involved extrapolating data obtained from shorter extraction times was used to estimate the amount of the compound present in the wood. The estimated quantitative results were found to be comparable to exhaustive extractions using liquid hexane as well as methanol-modified carbon dioxide. Further, data from the SFE extractions were fitted into the model to produce a characteristic kinetic curve from which factors controlling the extraction of the specific compound could be predicted. Following the dynamic extraction study, a statistical optimisation strategy was used to propose a model equation for the extraction of cedrelone from the wood of Cedrela toona. As the preliminary step, a screening design utilising a two level, three-factor full factorial analysis was used to study the effects of the variables pressure, temperature and the length of extraction time on the yields of cedrelone from the wood of Cedrela toona. By a statistical analysis of variance (ANOVA) at the 95% confidence level on the preliminary data collected, pressure and temperature were found to be the significant variables influencing the yields of the compound. Finally response surface methodology using the central composite design was used in an attempt to determine the maximum response space for the pressure and temperature effects by plotting a 3-dimensional response surface graph. An ANOVA study at the 99% confidence level was then employed to establish the true model equation for the extraction. / Thesis (M.Sc.)-University of Natal, 1995.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 167-170). Also available via the Internet.

No description available.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 151-154). Also available via the Internet.

Supercritical fluids were introduced as mobile phases for chromatography and extractions in the early sixties. Over the past decade the technique has received increased attention, largely owing to the introduction of several commercial instruments and to the ease of adapting available commercial equipment for use in sfe and sfc. This dissertation examines the use of supercritical CO₂ as a mobile phase for chromatography and extraction. The first chapter explores the problems and provides background for the research. The physical properties of supercritical fluids are described and pertinent recent research is identified and summarized. The following chapter presents the design of three interrelated studies that investigate in-situ concentration, quantitative aspects of sfc, and quantitative aspects of sfe. The first of the three studies examined the exploitation of the innate properties of a supercritical fluid. Because the mechanism of elution with supercritical fluid mobile phases is based on solvation, it was possible in this study to concentrate analytes at the head of the supercritical zone. Concentration was followed by supercritical fluid chromatography. This allowed the analysis of sample components at part per billion levels. The use of supercritical fluids as mobile phases for chromatography and the quantitative nature of sfc with flame ionization detection was examined in the second study. Under numerous detector and injector configurations, a distinct decrease in response factors with an increase in carbon number was evident. Results showed that the decrease in response factors was related to an increase in CO₂ flow through the detector. The magnitude of the decrease was multivariably dependent. The third study dealt with the quantitative aspects of using a supercritical Oobile phase for the extraction of PNAs and pesticides from several matrices including contaminated soil. Results showed that sfe is a reliable, easy, and efficient (> 85% recovery) method of removing trace materials from contaminated soil. Implementation of a simple resistively heated collector was used to circumvent the problems of extracting damp matrices such as soil. The results and conclusions are presented in the final two chapters. / Ph. D.

Phospholipids are commonly found in biological membranes. They have a polar head group and two ester linked fatty acids tails. Different methods such as thin layer chromatography and high performance liquid chromatography coupled with ultraviolet, refractive index, flame ionization detector, and mass spectrometry (MS) detection have long been used in the study of phospholipids. These methods were time-consuming and lacked quantitative accuracy. In this work, phosphatidylcholine, phosphatidyl-ethanolamine, phosphatidylinositol and phosphatidylserine have been studied by supercritical fluid chromatography (SFC) coupled with evaporative light scattering detection (ELSD) and mass spectrometry (MS). Four different silica-based stationary phases were studied: 2-ethylpyridine, 4-ethylpyridine, diol and conventional cyanopropyl. The influence of different mobile phase additives on the elution of phospholipids has been studied. The results have shown that isopropylamine is a better additive compared with ammonium acetate, tetrabutyl-ammonium acetate, and trifluoroacetic acid for the elution of phospholipids. All phospholipids have been eluted with baseline separation in less than 15 minutes although there is some partial overlap on the pyridine columns. The second goal for this work was fractionation of phospholipids from lecithin (a by-product from soybean) by using supercritical fluid extraction (SFE) with methanol-modified CO2. Neutral lipids were first removed from the crude sample using pure CO2. Partrial fractionation of PE and nearly pure fractionated PC were obtained by varying the modifier concentration in the extraction fluid at 460 atm and 40oC with silica gel inside the extraction vessel. A total of six components were isolated from crude soybean lecithin. / Master of Science