超临界CO2对溶解水透过PDMS膜的影响

Abstract(#br)Water vapor permeation under supercritical carbon dioxide (scCO 2 ) conditions through dense polydimethylsiloxane (PDMS) was investigated up to pressure of 185 bars to evaluate the regenerability of scCO 2 as desiccant to dehydrate fresh products that are prone to product deterioration during conventional drying. This study experimentally examined the impact of concentration polarization on the H 2 O vapor permeation through dense PDMS membranes in the presence of sub- and supercritical CO 2 . The results were compared to a system containing N 2 instead of CO 2 .(#br)For the CO 2 system, the residual mass transfer resistance, which excludes the membrane layer resistance, decreased down to zero with increasing feed pressure, at 90 bar. This is the result of the convergence of the H 2 O contents of the feed bulk and permeate, which leads to a change of the main H 2 O transport mechanism within the feed boundary layer from diffusion to convection. Here the H 2 O and CO 2 molecules are transported with comparable speed towards the membrane surface. For the system with N 2 , the opposite trend was found, due to the maintained significant difference in transport speed between H 2 O and N 2 even at elevated pressures. Consequently, the water vapor transport rate through the PDMS membrane is governed by the type of matrix fluid (CO 2 or N 2 ).