The Mechanism Of Supercritical Carbon Dioxide Mass Transfer Through Membrane And The Investigation Of Coupling Supercritical Technique With Membrane Separation

Supercritical fluid extraction technology and membrane separation technology are highly concerned new technologies in the modern chemical separation techniques. A combination of these two technologies is beneficial for recycling the high-pressure supercritical fluid, strengthen the membrane separation process, as well as expand application in supercritical membrane reactor. Currently, few researches are reported on the diffusion and permeation mechanism of supercritical fluids in the porous membrane penetration. Thus, further studies using experiment method and model calculations are necessary.(1) In order to avoid large crack defects of the traditional method of calcinations, the method of supercritical fluid extraction are used to remove the template to obtain MCM48composite membrane. The mechanism of diffusion and permeation of CO2in mesoporous membrane (MCM48composite membrane with theoretical aperture of2.6nm in effective separation layer) and macroporous membrane (commercial ceramic membrane with average pore diameter of50nm) are investigated at40-100℃and1-12MPa. The results show that the effects of temperature and pressure on the diffusion and penetration behaviors of CO2in these two membranes are significant and almost the same. At low pressure range, the penetration rate increases linearly with the increase of pressure and increases sharply near the critical point. But at high pressure range, no significant changes of penetration rate are observed with an increase of pressure and even a downward trend appears at low temperature.(2) On the basis of experiment, theoretical model is established to predict and fit the effect of Knudsen diffusion and Viscous flow on the diffusion and permeation of CO2in membrane. The prediction results with P-R equation but not the ideal gas status equation show good agreement with the experimental results, though a little higher than experimental results at high pressure range. This may be result from only membrane parameters and diameters at low pressure range are used in the process of prediction or the change of diffusion and permeation mechanism at supercritical region of CO2.(3) Based on the research background of extracting polyalcohol from fermentation broth, extracting ethanol from ethanol dilute aqueous solution using the method of supercritical fluid extraction is studied in this article. In addition, the feasibility of recovering carbon dioxide at high pressure using the method of supercritical fluid extraction combining with NaA membrane is discussed. The results show that the extraction rate increases significantly with the increase of temperature under steady state continuous operating conditions. The extraction rate increases from10.27%at35℃to19.99%at55℃when the extracting time is120minutes. After membrane separation, the separation factor gradually decreases as the operation time increases but gradually increases as the temperature increases.