Abstract
Water condensation is a possible cause of membrane wetting in the operation of membrane contactors, especially under high-temperature conditions. In this study, water condensation in pores of polytetrafluoroethylene (PTFE) hollow fiber membranes was investigated during high-pressure CO2 absorption around 70 °C. It was found that the liquid accumulation rate in the treated gas knock-out drum was constant during continuous operation for 24 h when all experimental conditions were fixed, indicating a stable degree of membrane wetting. However, as the operating parameters were changed, the equilibrium vapor pressure of water within membrane pores could change, which may result in a condensation-conducive environment. Water condensation in membrane pores was detected and proven indirectly through the increase in liquid accumulation rate in the treated gas knock-out drum. The Hagen–Poiseuille equation was used to correlate the liquid accumulation rate with the degree of membrane wetting. The degree of membrane wetting increased significantly from 1.8 × 10−15 m3 to 3.9 × 10−15 m3 when the feed gas flow rate was reduced from 1.45 kg/h to 0.40 kg/h in this study due to water condensation in membrane pores. The results of this study provide insights into potential operational limitations of membrane contactor for CO2 absorption under high-temperature conditions.
Highlights
CO2 removal from gas streams is a common operation in the chemical industry
It can be seen that CO2 removal performance was stable under high pressure and high absorption temperature, seen that CO2 removal performance was stable under high pressure and high absorption showing no sign of performance deterioration
Liquid penetration or membrane wetting happened to a small number of membrane pores during the experiments, and the number of liquid-penetrated membrane pores was constant throughout the experiment, indicated by constant liquid accumulation rate in the treated gas knock-out drum
Summary
Many methods, including low-temperature distillation (cryogenic separation), membrane separation, adsorption, and absorption, have been used in CO2 removal. The advantages offered by this technology include a larger specific contact area, higher mass transfer coefficient, a smaller size, and less operational problems such as foaming, channeling, and flooding [4]. Membrane wetting, which can lead to partially or fully liquid-filled membrane pores, a condition where CO2 has to diffuse through a liquid phase instead of a gas phase, is a major challenge for this technology. This phenomenon will increase mass transfer resistance across the membrane, which is Membranes 2020, 10, 407; doi:10.3390/membranes10120407 www.mdpi.com/journal/membranes
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