Mixed matrix membrane-based transport membrane condenser for improving the waste heat recovery performance in carbon capture process

Abstract

Applying a transport membrane condenser (TMC) based on the hydrophilic ceramic membrane to recover the waste heat from the hot stripped gas could effectively reduce the heat consumption of CO₂ regeneration in the carbon capture process. However, the high cost of ceramic membrane hindered the development of this technology. So in this study, a novel mixed matrix membrane (MMM) was proposed to replace the conventional ceramic membrane. MMMs were prepared by mixing carbon nanotube (CNT) into polyvinylidene fluoride (PVDF) casting solution through non-solvent phase separation method, and then were adopted for the waste heat recovery from the stripped gas featured with the molar ratio of CO₂ to H₂O(g) of 1:1∼1:2. Furthermore, the heat transfer resistance between the stripped gas and bypassed CO₂-rich solvent when adopting MMMs was also analyzed through computational fluid dynamics (CFD). Results indicated that the addition of CNT or hydroxylated CNT (CNT-OH) effectively enhanced the heat recovery performance of MMMs. Moreover, MMMs prepared by mixing CNT-OH and hydroxylated boron nitride (BN–OH) further boosted the heat flux, achieving a maximum value of 23.72 MJ/(m²·h), representing an increase of up to 8.41 % compared to the original PVDF membrane without adding any additives. At the experimental conditions in this study, the gas-side individual thermal resistance dominated the overall thermal resistance and consequently the heat transfer performance. With an increase in the stripped gas flow rate, the ratio of individual heat transfer resistance of membrane to the overall resistance increased. Notably, the installation of baffles on the gas side of TMC reduced the gas-side thermal resistance. In this study, the optimum thermal conductivity of the organic membrane increased with the waste heat recovery scale from stripped gas. In addition, when the thermal conductivity of membrane exceeded 4 W/(m·°C), the increase in thermal conductivity on the waste heat recovery was not significant. This study confirmed the application potential of MMMs in the waste heat recovery.