Grossmann Quirin, Mazzotti Marco
Institute of Energy and Process Engineering, ETH Zurich, Sonneggstrasse 3, Zurich 8092, Switzerland.
Ind Eng Chem Res. 2025 Jan 13;64(4):2339-2353. doi: 10.1021/acs.iecr.4c04099. eCollection 2025 Jan 29.
Extracting CO from the atmosphere via direct air capture (DAC) provides a pathway to counteract the rising CO concentration in the atmosphere. Processes using amine functionalized solid sorbents have attracted considerable attention, as they exhibit high affinity toward CO at atmospheric concentrations. The process is significantly influenced by the mass transfer kinetics of adsorption, and accurate quantification is crucial for improving process models and DAC systems. In this study, we addressed this critical issue by quantifying the mass transfer kinetics of three amine functionalized structured sorbents: two alumina pellets with unimodal (TRI@unimodal) and bimodal (TRI@bimodal) pore size distributions, and a honeycomb mullite/alumina monolith (TRI@monolith). A modeling framework was developed to enable the use of a commercial volumetric sorption device to measure sorbent mass transfer kinetics, and to distinguish them from resistances within the device. The measurements revealed distinct mass transfer regimes, with pore diffusion playing a significant role in the bimodal pellets, whereas a surface resistance introduced by the functionalization procedure dominated in the unimodal pellets. The device was unable to capture the pore diffusion in the monolith due to instrument resistances limiting this regime. A self-limiting diffusion behavior previously reported in literature was identified in the amine layer, which decreased diffusion with increasing CO uptake. We estimate kinetic parameters for all three sorbent materials for use in a widely used linear driving force (LDF) model adapted for amine functionalized sorbents. The parameter describing the mass transfer in the gas phase is nearly five times larger for TRI@bimodal than for TRI@unimodal. For the mass transfer in the amine layer, the parameter increases progressively from TRI@monolith to TRI@unimodal to TRI@bimodal. The results highlight the importance of pore structure and functionalization procedure to improve DAC sorbents.
通过直接空气捕获（DAC）从大气中提取二氧化碳提供了一种应对大气中不断上升的二氧化碳浓度的途径。使用胺功能化固体吸附剂的过程引起了广泛关注，因为它们在大气浓度下对二氧化碳表现出高亲和力。该过程受到吸附传质动力学的显著影响，准确量化对于改进过程模型和DAC系统至关重要。在本研究中，我们通过量化三种胺功能化结构化吸附剂的传质动力学来解决这一关键问题：两种具有单峰（TRI@单峰）和双峰（TRI@双峰）孔径分布的氧化铝颗粒，以及一种蜂窝状莫来石/氧化铝整体材料（TRI@整体材料）。开发了一个建模框架，以便能够使用商业体积吸附装置测量吸附剂传质动力学，并将其与装置内的阻力区分开来。测量结果揭示了不同的传质机制，孔扩散在双峰颗粒中起重要作用，而功能化过程引入的表面阻力在单峰颗粒中占主导地位。由于仪器阻力限制了这一机制，该装置无法捕捉整体材料中的孔扩散。在胺层中发现了文献中先前报道的自限扩散行为，随着二氧化碳吸收量的增加，扩散降低。我们估计了所有三种吸附剂材料的动力学参数，以便用于适用于胺功能化吸附剂的广泛使用的线性驱动力（LDF）模型。描述气相中传质的参数，TRI@双峰比TRI@单峰大近五倍。对于胺层中的传质，该参数从TRI@整体材料到TRI@单峰再到TRI@双峰逐渐增加。结果突出了孔结构和功能化过程对改进DAC吸附剂的重要性。
