Novel Nonaqueous PD/PZ/NMP Absorbent for Energy-Efficient CO<sub>2</sub> Capture: Insights into the Crystal-Phase Regulation Mechanism of the Powdery Product
Feng Xie, Guanghuan Li, Feng Yan, Xiao Chengbin, Pengju Wang, Xuehua Shen, Biao Yang, Lin Han, Huarong Luo, Zuotai Zhang
Abstract
Solid–liquid biphasic absorbents are a promising solution for overcoming the high-energy consumption challenge faced by liquid amine-based CO 2 capture technologies. However, their practical applications are often hindered by difficulties in separating viscous solid-phase products. This study introduces a novel nonaqueous absorbent system (PD/PZ/NMP) composed of 4-amino-1-methylpiperidine (PD), piperazine (PZ), and N -methyl-2-pyrrolidone (NMP), engineered to produce easily separable powdery products. The PD/PZ/NMP absorbent achieves a CO 2 loading of 0.86 mol-CO 2 /mol-amine, with 91% of CO 2 concentrated in the solid phase. It demonstrates excellent cyclic stability, maintaining a regeneration efficiency of 91% after five regeneration cycles, and reduces energy consumption by 52% compared with the conventional monoethanolamine absorbent. Remarkably, PZ plays a crucial role in regulating the crystal composition of solid-phase products, transforming them from a viscous state to a crystalline powder. Characterization and density functional theory analysis explain the crystal-phase regulation mechanism: PD absorbs CO 2 to form zwitterions (PDH + COO – ), affording viscous products, and PZ forms protonated amines (PZH + ) and monocarbamates (PZCOO – ), which interact with PDH + COO – via hydrogen bonding to form a crystalline powder. These findings demonstrate the CO 2 capture efficacy of the PD/PZ/NMP absorbent and provide a robust theoretical framework for fabricating solid–liquid biphasic absorbents tailored for practical applications.