Membrane contactors dramatically increase the specific surface area between gas and liquid compared to conventional packed towers, which can reduce the volume by up to a tenth. The small process volume, low weight and ease of scale-up of the membrane contactor-based CO₂ capture process make it suitable for small-scale applications such as biogas plants and CO₂ capture from ships. Hollow fiber membrane modules made of polypropylene are suitable for economical membrane contactor based CO₂ capture processes due to their low cost and hydrophobic nature. The CO₂ absorbent solution used in this technology must be able to reduce pore wetting of the membrane during long-term use. It should also have a good combination of properties such as fast CO₂ uptake, high CO₂ removal capacity and low regeneration heat of the absorbent solution.

In this study, experiments were carried out to select the optimum CO₂ absorbent solution using a 2 Nm³/hr bench scale membrane contactor system and proprietary CO₂ absorbent solutions. The circulating flow rate of the CO₂ absorbent solution was controlled, and the CO₂ removal efficiency and regeneration heat of the absorbent were measured and compared according to the liquid-to-gas (L/G) ratio. In addition, to verify the membrane pore wetting characteristics of each CO₂ absorbent solution, the condensed absorbent solution in the knock-out drum was measured and compared. The surface tension and vapor pressure data of the CO₂ absorbent solution were further evaluated. In conclusion, it was found that the developed CO₂ absorbent solution has about 40 % lower regeneration heat and half the membrane pore wetting properties compared to the 30 wt% monoethanolamine (MEA) solution. Key factors for future scale-up were also discussed.

Keywords: Carbon Dioxide, Absorbent Solution, Membrane Contactor, Membrane Pore Wetting, Regeneration Heat of CO₂ Absorbent

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