The Effect Of Porosity On Mass Transfer Behavior In Membrane Gas Absorption Process

Unlike traditional absorption process, which is dispersive contact between gas phase and liquild phase, membrane gas absorption process is non-dispersive contact due to the presence of membrane. It can effectively eliminate operational problems associated with the conventional equipments, for instance, flooding, foaming, channeling and entrainment. So, the membrane plays an important role in membrane gas absorption process. The solute can only diffuse from membrane pore to bulk liquid, rather than the entire surface of the membrane. Therefore, deeply studying the effect of membrane pore structure on the solute diffusion in liquid side will be beneficial to reveal microscopic mass behavior of the solute on membrane surface.The previous studies about membrane gas absorption process have shown the effect of the membrane porosity on membrane gas absorption process. The presence of membrane pores and membrane walls cause uneven distribution of solute concentration on membrane surface. The solute diffusion from non-uniform liquid layer to the bulk liquid results in the change of the effective mass transfer area. The uneven distribution of solute concentration on membrane surface is related with membrane porosity, two-phase flow state, physical and chemical properties of the system and chemical reaction. Since most researchers do not consider the effect of membrane pore structure on mass transfer, the mass transfer model established is greatly constrained in application. On basis of summarizing experimental data of the predecessor in membrane gas absorption process, the mass transfer model is built by analyzing the influence of dimensionless number on mass transfer including Re, rp/a, μ/μo, Ha, E. The interaction of these parameters has to be considered. The results of the model are in good agreement with the experimental results.Further, the effect of membrane structure parameters on mass transfer in hollow fiber membrane absorption process is researched. The hollow fiber membrane materials including polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypropylene (PP) are used in experiments. The absorbents include NaOH solution and deionized water. The absorbent viscosity is adjusted by adding an appropriate amount of thickener. Studying the effect of membrane pore structure on mass transfer performance especially membrane porosity can further reveal the microscopic mechanism of mass transfer in membrane gas absorption process. Mass transfer distance which is perpendicular to the membrane surface is changed by liquid flow rate, the absorbent viscosity and concentration. Mass transfer distance which is parallel to the membrane surface is changed by the membrane porosity. Mass transfer behavior of the solute on membrane surface is discussed. When absorbent viscosity increase, the effect of the membrane porosity on the mass transfer will weaken and the uneven distribution of solute concentration on membrane surface can be improved. When absorbent absorbents concentration and liquid flow rate increase, the effect of the membrane structure on the mass will enhance and the uneven distribution of solute concentration on membrane surface can be aggravated.