Permeation Of Supercritical Fluids Through Porous Membranes

As a new reaction and/or separation technology, membrane and supercriticalfluid coupled processes have got substantial development in recent years. Theypossess broad amplifications potential in green chemical processing. Obviously, themechanism of supercritical fluids permeating through porous membranes and thepredictive model are of great importance. They can help analyze the effect ofseparation parameters and direct the process of membrane synthesis, the latter ofwhich can provide the basis to optimize those coupled process from the first step.However, there is little mechanism research in literature, almost no available modelhas appeared in public concerning the permeation of supercritical fluids throughporous membranes up to present. The objective of this work is to systematically studythe permeation mechanism of supercritical fluids through meso-porous membranes,which will be of great theoretical significance and practical value.In our investigations, we studied the permeation of three supercritical fluids, CO2,N2, and He through porous ceramic membranes. Based on the two-term dusty-gasmodel, considering the contribution of viscosity and its singular change atnear-critical region, a new modification method and the model equation wereproposed.The average pore size calculated by permeating curve of supercritical He is inagreement with that by mercury porosimetry with the average error less than 5 percent.This reveals that the permeation of supercritical He can be described by two termsdusty-gas model. By the permeation data of He, the membrane structure parameterswere evaluated. These parameters can help calculate the permeation flux of otherfluids. By comparison with experimental results, it can be concluded that thepermeation of low- and middle-pressure CO2 and supercritical N2 can be expressed bythe two-term dusty-gas model. But in near-critical and supercritical region, thepermeation of CO2 is better described by the new-established model equation. Thenew model is of significance to reveal the permeation mechanism of supercriticalfluids and clarify key influence factors.