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The membrane wetting by amine absorbents is a big concern and may result in performance deterioration of membrane gas absorption technology for CO₂ post-combustion capture. In this paper, the polypropylene membrane was modified by depositing a rough layer on the membrane surface so as to improve the membrane non-wettability. Characterization results showed that the contact angle increases dramatically from 122˚ to 162˚ by the modification, thereby improving the hydrophobicity of the membrane. The modified membrane characteristics were also studied by the correlation of scanning electron microscope and atomic force microscopy results. In addition, CO₂ absorption in the polypropylene hollow fiber membrane contactors with and without surface modification was investigated in a continuous experiment for 20 days using an aqueous MEA solution as the absorbent. The long-term system operation results showed that the modified PP hollow fiber membrane contactor is feasible for CO₂ capture from the flue gas of large-scale power plants.

Post combustion CO₂ capture is corresponding to the most widely applicable option in terms of industrial sectors and is compatible to a retrofit strategy. In addition to the conventional chemical absorption process, membrane gas absorption is considered as one of the promising alternatives to conventional techniques for the CO₂ separation from the flue gas of fossil fuels combustion. As a hybrid approach of chemical absorption and membrane separation, it may offer a number of important features, e.g., economical viability due to its larger interfacial area, no flooding at high flow rates, no foaming and channeling, linear scale-up with predictable performance. This paper is to describe and present the state-of-the-art of the R&D efforts on membrane contactors focused on the microporous hallow fiber structure. The operating principles, liquid absorbents selection, influence of membrane wetting phenomenon, membrane materials and module types have been intensively reviewed. Model parameters including economic performance has been evaluated with comparison of other technologies. Technical obstacles of applying membrane contactors in CO₂ capture process have also been discussed. The knowledge and application gaps have been examined and identified, thus providing a recommendation for the future studies.

The membrane wetting by amine absorbents results in performance deterioration of membrane gas absorption system for CO2 post-combustion capture. To solve this problem, in this study, the polypropylene membrane fiber was modified by depositing a rough layer on the surface to improve its hydrophobicity. Weighing the coating homogeneity, hydrophobicity and modification process efficiency, the mixture of cyclohexanone and MEK system was considered as the best non-solvent. The contact angle increased dramatically from 122_ to 158_ by the modification, thereby obtaining superhydrophobic membrane surface. The membrane–absorbent interaction results demonstrated that the modification treatment effectively enhanced the stability and maintained the superhydrophobicity of fibers contacting with the absorbent. In addition, continuous CO2 absorption experiments for up to 20 days were carried out in untreated and modified polypropylene hollow fiber membrane contactors, using 1 mol L_1 MEA solution as the absorbent. The long-term system operation results indicated that, even though additional mass transfer resistance was introduced by the surface coating, the modified polypropylene hollow fiber

membrane contactor was still technically feasible for CO2 capture from the power stations.

Membrane gas absorption technology is a promising alternative to conventional technologies for the mitigation of acid gases. In this study, simultaneous removal of SO₂ and CO₂ from coal-fired flue gas was studied in a polypropylene hollow fiber membrane contactor using aqueous monoethanolamine as the absorbent. The influences of liquid and gas flow rates on the simultaneous absorption performance of CO₂ and SO₂ were investigated. The experimental results indicated that the membrane contactor could eliminate these two sour gases simultaneously and effectively. Absorption of SO₂ and CO₂ was enhanced by the increase in liquid flow rate and decrease in gas flow rate. It was observed that a small amount of SO₂ in the flue gas had a slight influence on the absorption of CO₂. In addition, the membrane contactor was continuously operated for two weeks to evaluate its duration performance. The results showed that the CO₂ mass transfer rate was decreased significantly with the operating time due to partial wetting of membrane pores. After 14 days of continuous operation, the CO₂ mass transfer rate of the wetted membrane contactor was decreased by 41% but could be retrieved to 86% of the fresh one by increasing the gas phase pressure.

The membrane wetting by the absorbent leads to the increase of mass transfer resistance and deterioration of CO₂ absorption performance during membrane gas absorption process. In this paper, polypropylene (PP) fibers were immersed in monoethanolamine (MEA), methyldiethanolamine (MDEA) and deionized (DI) water, respectively, assuming that the immersed PP fibers would undergo similar exposure conditions as those used in hollow fiber membrane contactor. The wetting evolution of PP fibers was investigated as a function of immersion time. The characterization results confirmed that the absorbent molecules diffused into the PP polymer during the exposure process, resulting in the swelling of the membrane. The absorption-swelling wetting mechanism was proposed to explain what happened during the wetting process. A 30.8° reduction in the contact angle was observed, indicating that the membrane surface hydrophobicity decreased significantly following the immersion time. Experimental results showed that the membrane surface morphology and surface roughness suffered significant and complicated changes after being immersed in the absorbents for a certain period. It was found that the absorbent with higher surface tension is in favor of fewer changes of the membrane surface morphologies. Based on the experimental results, improving the membrane surface hydrophobicity was suggested as an effective way to overcome the wetting problem.

Membrane has a potential to improve the CO2 capture process. In this paper, experimentswere carried out to investigate the impact of amine absorbents on membrane surfaceproperties with polypropylene (PP) fibers immersed in monoethanolamine (MEA) andmethyldiethanolamine (MDEA) aqueous solutions with and without CO2 loading. The surfacemorphological changes of the membrane were examined by using scanning electronmicroscopy (SEM). The experimental results showed that the fibers immersed in the aqueoussolutions without CO2 loading underwent significant deformation than those with CO2 loading,which is mostly linked to the decrease of absorbent concentration with the reaction betweenCO2 and aqueous solutions. It was also found that the morphological changes of membraneimmersed in MDEA were severer than that in MEA due to the lower surface tension of theformer.

Membrane has a potential to improve the CO2 capture process. In this paper, experimentswere carried out to investigate the impact of amine absorbents on membrane surfaceproperties with polypropylene (PP) fibers immersed in monoethanolamine (MEA) andmethyldiethanolamine (MDEA) aqueous solutions with and without CO2 loading. The surfacemorphological changes of the membrane were examined by using scanning electronmicroscopy (SEM). The experimental results showed that the fibers immersed in the aqueoussolutions without CO2 loading underwent significant deformation than those with CO2 loading,which is mostly linked to the decrease of absorbent concentration with the reaction betweenCO2 and aqueous solutions. It was also found that the morphological changes of membraneimmersed in MDEA were severer than that in MEA due to the lower surface tension of theformer.