The Influence Of CO₂ Gas On Hydrophobic PVDF Hollow Fiber Membrane Wetting By Ethanolamine Solution

Nowdays,the greenhouse effect caused by CO₂ is being increasingly serious,and membrane contactor technology is considered as one of the most promising CO₂ absorption technologies.However,in membrane contactor operation process,the membrane pores wetted phenomenon could be taken place.And this phenomenon would lead to a significant decrease of CO₂ absorption efficiency,which is a major obstacle for CO₂ absorption membrane contactor commercialization.Therefore,how to alleviate membrane wetting and explore the mechanism of membrane wetting have drown great attention of researchers,which are also the main contents of this paper.Conventionally,the previous researchers focused on the relationship between absorbents and membrane wetting.Nevertheless,the influence of gas phase on membrane wetting in a hydrophobic PVDF hollow fiber membrane contactor was studied in this paper by two research views,including?1?the effects of gas pressure on the rate of membrane wetting,and?2?the effect of membrane wetting by CO₂ as a component of gas.For this purpose,CO₂ flux,membrane mass transfer coefficient and drag reduction parameters were measured under different experimental conditions to evaluate the extent of membrane wetting.The results of experiments are listed as follows:1.As gas pressure increasing,the membrane wetting rate can be effectively reduced and the CO2 adsorption can be accelerated.Since the membrane contactor operation begins,the pressure of the gas phase is intermittently increased,and the gas phase pressure at the entrance of the membrane contactor increases to 13.84 kPa,and the pressure returned to the original state after 10 min,then results that the value of F could reach 0.74 and the CO₂ flux could be increased by about 23.31%.According to the concentration of CO2 in DEA solution,the amount of CO₂ absorption increase by 38%after 600min.In addition,the gas phase exit pressure is reduced by 0.34 kPa in the 10min.And as the inlet gas phase pressure is adjusted to 0.67 kPa,the gas phase exit pressure decreases by 0.050 kPa.It is proved that when the transmembrane pressure difference ? PL-G<0,the liquid could be compressed into the bulk motion of liquid phase and the degree of the membrane wetting could be reduced.2.Compared with the CO2 and N2 enters the shell of the membrane contactor under the same experi mental conditions,the mass transfer coefficient of membrane in contactor which CO2 entering decreased by two times than membrane in contactor which N2 entering,which proves that CO₂ can accelerate the rate of membrane wetting.Under the experimental conditions that liquid velocity uL is 0.26 m/s,gas speed us is 0.029 m/s,temperature of absorbents is 25?,liquid phase inlet pressure 20 kPa and gas phase inlet pressure is 0.406 kPa.The decrease of mass transfer coefficient caused by DEA solution is about 39%,the decrease of mass transfer coefficient caused by CO₂ itself is about 12%,and the decrease of mass transfer coefficient caused by the interaction of DEA and CO₂ is about 49%.3.Infrared characterization results showed that there is no substance reacting with the surface of the membrane,which changing the hydroph-obicity of the membrane surface and affecting the membrane wetting.The results of EDX scanning and SEM scanning showed that CO₂ could accelerate the membrane wetting rate,and the reaction products of DEA and CO₂ have no effect on membrane wetting.In addition,the pore structure would change when the PVDF hollow fiber membrane pores are wetted,and the radius of membrane pores get larger.