Krishna Rajamani
Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
ACS Omega. 2020 Jul 10;5(28):16987-17004. doi: 10.1021/acsomega.0c02218. eCollection 2020 Jul 21.
For mixture separations, metal-organic frameworks (MOFs) are of practical interest. Such separations are carried out in fixed bed adsorption devices that are commonly operated in a transient mode, utilizing the pressure swing adsorption (PSA) technology, consisting of adsorption and desorption cycles. The primary objective of this article is to provide an assessment of the variety of metrics that are appropriate for screening and ranking MOFs for use in fixed bed adsorbers. By detailed analysis of several mixture separations of industrial significance, it is demonstrated that besides the adsorption selectivity, the performance of a specific MOF in PSA separation technologies is also dictated by a number of factors that include uptake capacities, intracrystalline diffusion influences, and regenerability. Low uptake capacities often reduce the efficacy of separations of MOFs with high selectivities. A combined selectivity-capacity metric, Δ, termed as the separation potential and calculable from ideal adsorbed solution theory, quantifies the maximum productivity of a component that can be recovered in either the adsorption or desorption cycle of transient fixed bed operations. As a result of intracrystalline diffusion limitations, the transient breakthroughs have distended characteristics, leading to diminished productivities in a number of cases. This article also highlights the possibility of harnessing intracrystalline diffusion limitations to reverse the adsorption selectivity; this strategy is useful for selective capture of nitrogen from natural gas.
对于混合物分离而言，金属有机框架材料（MOFs）具有实际应用价值。此类分离在固定床吸附装置中进行，这些装置通常以瞬态模式运行，采用变压吸附（PSA）技术，该技术由吸附和解吸循环组成。本文的主要目的是评估适用于筛选和排名用于固定床吸附器的MOFs的各种指标。通过对几种具有工业意义的混合物分离进行详细分析，结果表明，除了吸附选择性外，特定MOF在PSA分离技术中的性能还受许多因素影响，这些因素包括吸附容量、晶内扩散影响和再生能力。低吸附容量通常会降低具有高选择性的MOFs的分离效率。一种结合了选择性和容量的指标Δ，称为分离潜力，可根据理想吸附溶液理论计算得出，它量化了在瞬态固定床操作的吸附或解吸循环中可以回收的某一组分的最大生产率。由于晶内扩散限制，瞬态突破具有扩展特征，在许多情况下会导致生产率降低。本文还强调了利用晶内扩散限制来逆转吸附选择性的可能性；这种策略对于从天然气中选择性捕获氮气很有用。
