Experimental Study On Membrane Wetting During Membrane Absorption Of CO₂

At present,coal-fired power plants are the main source of CO₂ emissions.With the greenhouse effect becoming more and more serious,the capture of CO₂ in the tail flue gas of coal-fired power plants has attracted more and more attention.At present,membrane absorption is one of the most common capture methods.However,the long-term operation of membrane absorption affects the stability of membrane and membrane materials and their CO₂ absorption process.Therefore,in this paper,a comprehensive study was carried out on the absorption performance of CO₂ membrane and the wettability effect of membrane materials in the process of coal-fired flue gas film absorption and capture from the macro-performance and micro-mechanism.The main work includes the following aspects:The CO₂ absorption performance of hollow fiber membranes under different operating conditions and the stability of continuous operation of polypropylene hollow fiber membranes were investigated by using simulated gas prepared by CO₂/N₂ as feed gas and MEA,DEA and MDEA solutions as absorbent liquids,respectively.At the same time,a model was established to fit the change of mass transfer resistance.Field emission scanning electron microscopy（FSEM-EDX）,Fourier in situ infrared（FTIR）,contact angle and surface tensiometer were used to study the evolution of membrane and membrane material microstructures（surface properties,pore structure,etc.）and their effects on CO₂ absorption performance.Secondly,the effect of composite absorbent on CO₂ absorption was studied,and the long-term dynamic membrane wetting experiment was carried out.The interaction process between membrane and absorbent was simulated by immersing polymer membrane in absorbent solution for a long time,and the influencing factors of membrane wetting were systematically investigated.The results showed that:Under the same operating conditions,the absorption efficiency is:MEA>DEA>MDEA;increasing the concentration of the absorption liquid,the removal efficiency of CO₂ and the mass transfer rate are improved,but as the concentration of the absorption liquid increases,the wetting of the membrane module is more likely to occur during operation.As the gas flow rate increases or the CO₂ concentration in the gas phase increases,the removal efficiency decreases,but the mass transfer rate increases.In the long-term experiment,the MEA wets the membrane more than DEA,which is not conducive to the long-term operation of the membrane module.Using the first-order reaction kinetics equation,the theoretical equations of the total mass transfer resistance of the membrane module were established,and the experimental data were fitted.The results were good.Under the long-term solution immersion,the surface properties of the membrane and the pore structure of the membrane changed.The absorption liquid dissolves in the membrane filament,causing a lateral force on the membrane pore,causing the pore shape of the membrane to change from the original slender shape to an elliptical shape,the pore diameter of the membrane pore is enlarged,the internal fiber becomes thick,and the absorption liquid having a small surface tension is easier.The membrane is wetted,so the membrane structure change in the high surface tension MEA solution is greater than the membrane structure change under the action of MDEA;the soaking is indicated by infrared spectrum and thermogravimetric analysis.After the surface composition of the membrane has changed;for MDEA solution,only a little MEA,PZ and PG need to be added,the CO₂removal efficiency and mass transfer rate are greatly improved,and the mixed solution after adding PZ shows better.But when a certain compounding ratio is reached,the promoting effect is no longer obvious;adding a high surface tension amino acid solution can effectively prevent membrane wetting.