Influence Of Porosity On The Mass Transfer Performance And Modelling Of Non-Ideal Flow In Membrane Gas Absorption Process

Membrane absorption technology is a novel separation technology that combines membrane separation technology and traditional gas absorption technology. This novel technology make use of hydrophobic porous membrane to ensure the gas and liquid phase flowing on the opposite side of the membrane. Compared with the conventional absorption process in column type devices, membrane absorption process has the following advantages: larger mass transfer area per volume, higher mass transfer rate, gas and liquid phase flowrates can be manipulated independently. So, membrane absorption technology can avoid the problems like flooding, foaming and entrainment. Therefore, membrane absorption technology has promising applications in removing VOCs, waste water treatment and removing acid gas.Membrane absorption experiments were carried out in a flat-membrane contactor with eight different membranes. CO₂/H₂O or CO₂/NaOH solutions were chosen as experimental system. The influence of porosity on the mass transfer coefficient was investigated. For unsteady-state membrane absorption process, when the pH value of absorbent was at the range of 7 to 11, the effect porosity on the mass transfer coefficient can be ignored. When the pH value of absorbent increased to 12 or 13, the mass transfer coefficient was influenced by porosity, and with the pH value increasing the influence was more obvious. For steady-state membrane absorption process, when the pH value of absorbent was at the range of 7 to 11 and the liquid velocity was relative slow, the porosity had no influence on the mass transfer coefficient. However, when the liquid velocity was large, the mass transfer coefficient was increased with porosity. When the pH value of absorbent increased to 12 or 13, the mass transfer coefficient was affected by porosity even if the liquid velocity was relative slow. With the pH value and velocity of absorbent increasing, the effect of porosity on the mass transfer coefficient was more obvious. Based on the experimental data, the mass transfer correlation for steady-state membrane absorption process was obtained.Based on the experimental results, The preliminary theoretical analysis of porosity on the mass transfer coefficient was also presented. The key factors are the b and l, which is the half interval between the pores and thickness of boundary layer. In case of l