Browsing by Subject "Supercritical fluid extraction"
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Item Extraction of post-tanning chemicals from leather wastes(Texas Tech University, 2000-12) Arcot, G. SenthilkumarThe disposal of leather scraps produced by the footwear industry is a difficult and expensive task due to their undesirable and adverse effects on the environment. It will be profitable for the shoe industry to convert this waste into value added products. This thesis investigated the feasibility of employing supercritical fluid extraction (SFE) technique in the pre treatment phase of gelatin extraction process (Taylors' Process). The current study had three experimental phases namely sample preparation, extraction of components from the sample and quantification of the extracted components. Three methods (one-step process, two-step process and modifier-assisted SFE process) were used in the extraction of components from leather samples. In the one-step process, the post-tanning chemicals were extracted using SFE. In the two-step process, Soxhlet extraction followed by SFE was employed in extracting the post-tanning chemicals. Preliminary SFE experiments were conducted to determine optimum extracting conditions for the extraction of post-tanning chemicals from leather scraps. The third method was similar to one-step process, except that instead of using carbon dioxide as extracting solvent modified carbon dioxide was used. The modifiers used were methanol and phenol. This research was able to introduce SFE as an option for extracting post-tanning chemicals from leather scraps by optimizing the extraction conditions and comparing the results with conventional Soxhlet extraction technique.Item Structure and interaction of polymer thin films with supercritical carbon dioxide(2003) Sirard, Stephen Michael, 1975-; Johnston, Keith P., 1955-; Green, Peter F. (Peter Fitzroy)An understanding of colloid stability in CO2 as well as the interaction of CO2 with polymer thin films is necessary for the intelligent design of CO2-based processes for future materials applications. In-situ spectroscopic ellipsometry (SE) was used to measure the thickness and optical properties of nanoscale poly(dimethylsiloxane) (PDMS) and poly(methyl methacrylate) films exposed to compressed CO2. Both the sorption and CO2-induced dilation of the thin films were measured simultaneously with SE and deviations between the thin films and the corresponding bulk films may be attributed to excess CO2 at the free interface as well as the influence of film confinement and the compressible nature of CO2 on the orientation and mobility of the polymers. SE was also used to measure sorption equilibrium and kinetics and CO2-induced dilation of polyimide (6FDADAM:DABA 2:1) thin films to determine how a gas separation membrane’s structure affects its susceptibility to CO2-induced plasticization. Both thermal annealing and chemical crosslinking reduced the polymer dilation to prevent large increases in the CO2 diffusion coefficient at high CO2 pressures. The CO2 permeability and polymer free volume strongly depend on the annealing temperature, and different effects are observed for the crosslinked and uncrosslinked membranes and for the thick and thin membranes. Neutron reflectivity (NR) and SE were used to characterize the structure of end-grafted dPDMS brushes on SiOx wafers exposed to compressed CO2. NR revealed two distinct regions in the segment density profile as a function of distance from the surface. The thickness and volume fraction profiles for the brush change much more with solvent quality than has been seen in previous studies with incompressible solvents, due to the high asymmetry in the intermolecular interactions, as well as the large compressibility and free volume differences between the polymer segments and the solvent. Turbidity versus time measurements were used to determine the critical flocculation densities (CFDs) of silica collids in CO2 that were sterically stabilized with end-grafted poly(1H, 1Hdihydroperfluorooctyl methacrylate) (PFOMA). The CFDs occurred above the UCSD for the corresponding finite molecular weight stabilizer in bulk CO2 and corresponded more closely with the Θ-density. The CFDs decreased (greater stability) when temperature was increased or the PFOMA molecular weight was decreased.Item Supercritical fluid extraction of capsaicin from peppers(Texas Tech University, 1997-05) Sethuraman, RavishankarSupercritical Fluid Technology utilizes the unique physico-chemical properties of solvents in numerous applications. Supercritical Fluid (SF) Technology has become an interdisciplinary field, utilized by chemical engineers, chemists, food scientists, materials scientists, agronomists, and researchers in biotechnology and environmental control. The last ten years have seen the importance in SF applications expand from commodity chemicals and synthetic fuels toward more complex, highly specialized, and more valuable substances. Substantial efforts have also been directed at gaining a better fundamental understanding of phase behavior and transport properties of SFs. Development of the technique of separating substances using SFs commenced in the early '60s, though certain fundamental principles had already been understood for more than 80 years. Every pure component has a particular temperature and pressure that is defined as the critical point. Above this temperature and pressure, the substance exists strictly as a gas. Below the critical point, it can exist as both a liquid and a vapor. For water, the critical point is 375 C and 3226 psia pressure. SFs have density and diffusivity like a liquid and viscosity like that of a gas, thus making it an attractive solvent for extraction processes. The solvating strength and the transport properties of a SF can be conveniently varied by changing the temperature and pressure (or the density) of the fluid. Depending on the conditions and the application of interest, SFs can diffuse and penetrate rapidly into the sample matrix from which the product of interest is to be separated.