SUPERCRITICAL-FLUID EXTRACTION OF PENTACHLOROPHENOL FROM PRESSURE-TREATED WOOD

The extraction of pentachlorophenol (PCP) from pressure-treated wood w afers with supercritical carbon dioxide (SC-CO2) was studied in a cont inuous-flow extractor. PCP extraction rates were determined as a funct ion of pressure (17.5-25 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 PCP concentrations in the extracto r effluent intermittently. The rate of extraction increased with an in crease in solvent pressure and a decrease in particle size. A fundamen tal model was developed which includes rates of intraparticle diffusio n, external film mass transfer, linear desorption isotherms, and initi al distribution of PCP between pore volume (cell lumen) and pore surfa ces (cell wall) of wood wafers. The overall mass transfer coefficient and the rate of extraction increased with an increase in solvent press ure, temperature, and flow rate. The adsorption equilibrium coefficien ts of PCP with wood substance were very small, and more than 80% of th e PCP was found to be in the cell lumen initially.