Abstract:

The reduction of the number of water molecules in a nano-system actively promotes the hydrolysis of CO₃^2- to HCO₃^- and OH^-, leading to a moisture-swing nano-structured CO₂ sorbent that spontaneously binds CO₂ in ambient air when dry, while releasing it when wet. As it trades the input of heat in a thermal swing or the mechanical energy in a pressure swing of the traditional sorbents, against the consumption of water, the energy input for CO₂ capture is very low. This brings about an inexpensive and efficient direct air capture technology for mitigating the greenhouse problem. The sorbents are usually heterogeneous sheets composed of amine-based anion exchange resins and a matrix polymer. In order to obtain a hierarchical microporous structure to allow sufficient access of the air to the ion-exchange resins buried inside the matrix, previously, hydrothermal pretreatment of the resin sheets was employed before put into operation. In addition, the desorption ratio (desorption quantity/adsorption quantity) of the material is only ~30% when desorption is activated by exposing to bulk water. The present work aims to reduce the energy consumption for pretreatment and improve the desorption performance. The hydrothermal pretreatment time and temperature are studied systematically. It was found that the room-temperature soaking pretreatment instead of hydrothermal pretreatment of the resin sheets, can also lead to excellent microporous structures and carbon capture performances, concerning both the capture capacity and kinetics. More importantly, based on the infiltration mechanism of gas and liquid into nanopores, we found that the micron-sized water particles produced by ultrasonic atomization could greatly promote the desorption ratio, from ~30% to ~60%, compared to that by exposing the sorbent to bulk water. The mechanism is analyzed from the perspectives of the water quantity, water particle size and its diffusion/infiltration ability. The optimization of these pretreatment energy consumption and desorption performance provides favorable conditions for the engineering implementation of large-scale air capture.

Key words: carbon dioxide, adsorption, desorption, direct air capture, ion exchange resin, moisture-swing

摘要：

湿法再生阴离子交换树脂膜材料，可通过调控湿度驱动CO₂的吸附与脱附，材料再生成本极低。该材料需经过高温水热预处理张开孔结构，增强气体扩散速率，能耗较高；此外，利用液态水润湿材料以驱动脱附时，材料的解吸比（脱附量/吸附量）只有~30%。通过系统研究不同预处理水温及时间下膜材料的CO₂吸附/脱附性能，发现采用常温水浸泡预处理亦可获得良好的材料微观孔结构以及碳捕集性能，显著降低预处理能耗；更重要的是，基于微观尺度的气体吸附和液体浸润相关理论，实验发现超声雾化所获得的微米级水颗粒，由于更易扩散进入孔隙，可将解吸比从~30%提升到~60%，极大提升了树脂膜材料的再生性能。这些预处理能耗与脱附性能的优化，为大规模空气捕集的工程化实施提供了有利条件。

关键词: 二氧化碳, 吸附, 脱附, 空气捕集, 离子交换树脂, 湿法再生