Mixed Matrix Membranes for Natural Gas Upgrading: Current Status and Opportunities

In the past few decades, natural gas has attracted worldwide attention as one of the most desired energy sources owing to its more efficient and cleaner combustion process compared to that of coal and crude oil. Due to the presence of impurities, raw natural gas needs to be upgraded to meet the pipeline specifications. Membrane-based separation is a promising alternative to conventional processes such as cryogenic distillation and pressure swing adsorption. Among the existing membranes for natural gas upgrading, polymeric membranes and inorganic membranes have been extensively explored, but each type has its own pros and cons. The development of mixed matrix membranes (MMMs) by incorporating organic/inorganic fillers into the polymer matrix provides a good strategy to combine the merits of each material and fabricate novel membranes with superior gas separation performance. In this review, we first discuss the recent advances in MMMs showing potentials in natural gas upgrading. Special attention is paid to a detailed evaluation on the polymer and filler choices for acidic gas removal. After that, we analyze factors that influence the membrane separation performance and summarize effective strategies reported in the open literature for the fabrication of high-performance MMMs. Finally, a perspective on future research directions in this field is presented

Computational intelligence

Covalent organic frameworks (COFs) have recently emerged as a new class of crystalline porous materials with many potential applications. The development of facile and effective synthetic methods of COFs is highly desirable for their large-scale applications. Herein, we demonstrate the room temperature batch synthesis of three classical two-dimensional (2D) COFs with various types of linkage, namely, COF-LZU1 (imine-linked), TpPa-1 (enamine-linked), and N₃-COF (azine-linked). These obtained COFs exhibit good crystallinity and high porosity comparable to their counterparts synthesized solvothermally at higher temperatures. The facile formation of these COFs under such mild synthetic conditions can be attributed to (1) high solubility of monomers and (2) the strong π–π stacking interactions between monomers and π-systems of oligomers during the initial and the subsequent error-correction crystallization process. Based on this conclusion, two new imine-linked COFs named NUS-14 and NUS-15 were successfully synthesized with good crystallinity under ambient conditions. Moreover, continuous flow synthesis has been demonstrated in COF-LZU1 with a production rate of 41 mg h^–1 at an extremely high space-time yield (STY) of 703 kg m^–3 day^–1. This study represents the first example of synthesizing COFs by continuous processes, which sheds light on the scaled-up synthesis of these promising materials

Process-Tracing Study on the Postassembly Modification of Highly Stable Zirconium Metal–Organic Cages

Metal–organic cages (MOCs) are discrete molecular assemblies formed by coordination bonds between metal nodes and organic ligands. The application of MOCs has been greatly limited due to their poor stability, especially in aqueous solutions. In this work, we thoroughly investigate the stability of several Zr-MOCs and reveal their excellent stability in aqueous solutions with acidic, neutral, and weak basic conditions. In addition, we present for the first time a process-tracing study on the postassembly modification of one MOC, ZrT-1-NH₂, highlighting the excellent stability and versatility of Zr-MOCs as a new type of molecular platform for various applications