Influence Of Porosity On Solute Mass Transfer Behavior Near The Membrane Surface Under Different Absorbent Viscosity In Gas Membrane Absorption Process

The early experimental and theoretical research showed that theporosity of the porous membrane result in different behaviors of solutemass transfer near membrane surface side, while the influence of porosityon solute mass transfer behavior near membrane surface related to notonly mass transfer system, the fluid flow conditions and other factors butalso the physical properties of system. In the physical properties affectingthe membrane mass transfer process, the viscosity of the fluid plays animportant role on the fluid dynamics and the diffusion behavior of solutein the liquid phase, but the influence of viscosity on the mass transferperformance of membrane absorption process is not yet clear. Therefore,on the basis of the laboratory preliminary study, we have done someexperimental and theoretical studies about the influence of viscosity onsolute mass transfer behavior near the membrane surface, which will help to further reveal the mechanism of mass transfer of membrane absorptionprocess.In this paper, with adding sodium carboxymethyl cellulose (CMC) tochange the viscosity of the absorbents, selecting six different porosityboard style membranes to absorb pure CO2by water and NaOH solutionwith different pH, to investigate the influence of porosity on solutionconcentration distribution near the membrane surface in membraneabsorption process with different absorbent viscosity in the unsteady-stateconditions and steady state conditions, respectively. In this study, therelationship among the absorbent flow rate, membrane porosity, pH andother factors under different absorbent viscosity has beencomprehensively studied. The experimental results show that, asabsorbent viscosity increases, the rate of the solute diffusion in the liquidside decreases, while the liquid boundary layer thickness increases. Bothof the changing increase the liquid phase mass transfer resistance,resulting in significant downward trend in the liquid phase mass transfercoefficient. In the unsteady experiments, the diffusion rate of solute innormal and tangential direction decreased with the increase of theabsorbent viscosity, which making the membrane surface concentrationprofile decreases, leading to the influence of porosity on mass transferperformance increased with the absorbent viscosity. In the steady-stateexperiments, the diffusion distance of solute in the normal direction is affected by the liquid boundary layer thickness which thickened withviscosity of absorbent increases, thereby improving the concentrationdistribution inhomogeneity of the solute near the membrane surface, andreducing the influence of porosity on the mass transfer performance.Especially in the fast mass transfer system and the conditions of highabsorbent flow rate, along with the increase of the absorbent viscosity, thehigher porosity, the stronger decreasing trend of mass transfer coefficient.At the same time, with the relationship between the solute diffusionbehavior and absorbent viscosity was described by Stokes-EinsteinEquation, we have changed the solute diffusion coefficient in thepreliminary model, and compared the experimental and simulation datasin the steady-state situation, the results showed that although the masstransfer performance model which did not include the influence ofphysical properties is predictable, its accuracy was restricted by theinfluence of absorbent viscosity on the fluid dynamics. Therefore, inorder to establish a mass transfer model which has more accurate andextensive application, the influence of the system physical properties onmass transfer process has to be considered, and the application ofmembrane absorption technology can be advanced in the related fields.