The extraction of pentachlorophenol (PCP) from pressure treated wood wafers with supercritical carbon dioxide has been studied. Experimental data were obtained for the effects of pressure (17.5 - 25.0 MPa), temperature (313 - 353 K), flow rate (1 - 3 ml/min at supercritical conditions), and sample size (0.8 x 10 x 50 mm and 2.2 x 10 x 50 mm) by measuring the effluent concentration versus time. A fundamental model was developed which includes rates of intraparticle diffusion, external film mass transfer, desorption and the initial distribution of PCP between the pore volume (cell lumen) and pore surface (cell wall) of wood wafers. The intraparticle diffusion and external mass transfer rates are combined in terms of an overall mass transfer coefficient derived from the assumption of a parabolic concentration profile of PCP inside the wafer pores. The initial distribution of PCP between cell lumen and cell wall was determined by fitting the mathematical model to dynamic extraction rate data. The desorption rate was very small for all the extraction conditions, and extraction rate increased with the pressure, temperature, and flow rate because the combined mass transfer increased. Similar values of mass transfer coefficient were achieved for two different sample sizes: 0.8 x 10 x 50 mm and 2.2 x 10 x 50 mm. / Graduation date: 1994

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Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 106-113). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 106-113). Also available on the Internet.

The technique of extraction with supercritical carbon dioxide (SC-CO$ sb2$), which is now used routinely for the recovery of non-polar analytes from a variety of liquid and semipermeable solid media, was extended to the efficient extraction of metal ions. Measurements of the solubilities in SC-CO$ sb2$ corroborated the hypothesis that the non-polar character of a series of tetraalkylammoniun dialkyldithiocarbamates ion pairs was influenced (i) primarily by the chain length of the alkyl substituent(s) on the carbamate nitrogen and (ii) to a lesser extent, by the chain length of the alkyl substituent(s) on the ammonium counter ion. In operation, analyte metal(s) in aqueous medium was derivatized by in situ complexation with the dithiocarbamate complexing reagent and the product complex(es) was partitioned into the SC-CO$ sb2$ mobile phase then purged from the extractor by replacing the headspace with fresh solvent. A novel silica flame-in-tube interface was developed for the sensitive detection, by atomic absorption spectrometry (AAS), of As, Cd, Cu, Mn, Pb, Se, or Zn in SC-CO$ sb2$ extractor eluate. For different analyte elements, the limits of detection (LODs) ranged from sub-nanogram to low picogram if standard was flow injected into the mobile phase. These sensitivities permitted differences in the rates of mobilization of different forms of the analyte metal from various media to be explored as a technique for probing the interaction of the analyte metal with the matrix. A portion of the Zn burden in fresh bovine liver was mobilized rapidly in the absence of complexing agent and the remainder was solubilized more rapidly than the Zn in a freeze-dried reference material of this tissue. The nebulizer assembly of a conventional flame-AAS was modified to extend the range of metals amenable to on-line detection. Supplemental heating of the inlet air to 200$ sp circ$C resulted in an on line detector which provided approximately a ten-fold improvement over convention

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

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