Dewatering green sapwood using carbon dioxide cycled between supercritical fluid and gas phase

Abstract

Green radiata pine sapwood was dewatered through exposure to CO2, cyclically alternated between supercritical fluid and gas phase. Plots of moisture content against cycle number showed sigmoidal shapes, with the maximum slope showing a linear dependence on the maximum pressure applied in each cycle, over the range 8–20MPa. The initial slope varied as the square root of the hold time at 40MPa, as expected for diffusion of CO2 through water into the wood. The temperature of the vessel showed no influence on the dewatering rate over the range 38–58°C. Dissection of partly-dewatered specimens showed strong moisture gradients in green wood, changing to a relatively uniform distribution through a cross-section as the moisture content decreased to an end-point of 40% of the oven-dry weight. This end-point was attributed to moisture remaining in cell walls, after the lumens had been emptied.