Study Of Membrane Wetting In The Process Of CO₂Absorption By Using Hollow Fiber Menbranes

Carbon dioxide (CO2) has been known to contribute significantly to global warming, many countries around the world have paid attention to it. Several techniques are available for the absorption of CO2at present, membrane contactors using microporous hollow fiber membrane modules have been attracting attention as an alternative technology for its advantages such as operational flexibility, more economic, scale-up easy. Well, in the process of operation, the membrane was wetted by the alkanolamine solution, leading to the membrane resistance increased with time. Finally the mass transfer in the wetted membrane phase became the controlling step and resulted in the decline of CO2flux. So it’s important to study the factors that influence the membrane wetting.In this work, we studied the membrane wetting on the CO2capture in PVDF hollow fiber membrane contactors. In the absorption process, the gas (in the shell-side) and liquid (in the tube side) phase flow on opposite sides of the membrane in a countercurrent fashion. From the experimental results, we found that the membrane was partially wetted by the DEA solution, the membrane resistance increases to68%of the overall mass transfer resistance at most. We could conclude that even the relative wetting depth increases very slowly with time, the membrane mass transfer coefficient decreases obviously. We also studied the effect of the absorbent concentration, temperature, liquid flow rate and gas flow rate on membrane wetting. When the concentration of DEA increased from lmol/L to2mol/L, the relative wetting depth η decreased by7.7%; the rising concentration led to the increment of viscosity, making it difficult for the absorbents to penetrate into micropores of the membrane; With the temperature increased from15℃to25℃, the η increased by11.4%, When the liquid flow rate increased from u=0.113m/s to u=0.183m/s, the η increased by5.8%,; both rising the temperature and speeding up the liquid velocity could increase the membrane wetting, but the temperature influence is more obvious; however, the changing of gas flow rate had no effect on the membrane wetting.Additionally, Investigation of the absorbent regeneration has been done to study its influence on membrane wetting. We found that the wetting degree of membrane by using regenerated absorbent is more significant and almost1.38times than the original one, this phenomenon may be caused by the impurities generated in the regeneration process, and also leading to the decline of the CO2flux and the overall mass transfer coefficient.At last, a static membrane wetting experiment based on the method of Washburn was done to get the connection between the wetting depth and time, combined with the membrane structure, a semi empirical theory model was established and the change of overall mass transfer coefficient with time was estimated.