Separation of H₂ and CO₂ Containing Mixtures with Mixed Matrix Membranes Based on Layered Materials

Abstract

Some membrane separation processes are gradually taking over conventional processes such as distillation, evaporation or crystallization as the technology progresses from bench-scale tests to large-scale prototypes. However, membranes for H 2 and CO 2 separation constitute a daring technology still under development. This overview focuses on mixed matrix membranes (MMMs), a special type of membranes in which a filler is dispersed in a polymer matrix, as a successful strategy to improve their permeability-selectivity performance while keeping the polymer processability. In particular, among all the possible fillers for MMMs, layered materials (porous zeolites and titanosilicates and graphite derivatives) are discussed in detail due to the several advantages they offer regarding selective microporosity, crystallinity and, what is most important, high specific surface area and aspect ratio. In fact, a selective and as thin as possible, i.e. with high aspect ratio, filler would help to develop high performance MMMs.

Current Status and Future Prospect of Polymer‐Layered Silicate Mixed‐Matrix Membranes for CO2/CH4 Separation

“…PSf/Matrimid® hollow‐fiber membranes exhibited a 50 % increase in selectivity by adding zeolite to its selective skin layers 17, 32. In comparison to neat polymers, addition of CMS to Matrimid® and Ultem® improved the membrane selectivity by 45 % and 40 %, respectively, for CO 2 /CH 4 systems 25. Much of this is due to the pore structure of porous fillers which provides discrimination of gas penetrants, thus enhances selectivity.…”

“…Similar techniques which are used to manufacture polymer membranes can be applied to fabricate MMMs. For instance, melt compounding which may produce direct exfoliation without using organic solvents, is an environmentally friendly, practical, and stable process that could be applied to fabricate MMMs dispersed with layered silicate 25. Typically, the phase boundary defects between layered silicate and polymer phase results in poor membrane performance, nevertheless, these can be solved via crosslinking, thermal treatment, and priming protocol.…”

“…In addition, nano‐sized fillers not only enhance polymer‐filler interaction and assist in forming thin asymmetric MMMs, but also will interact with the penetrating molecules, resulting in increased permeation rate. Since the selection of an appropriate combination of polymer/inorganic filler is important in determining MMM performance, the next section will review the feasibility of using different inorganic sources, especially layered silicates as the filler 25.…”

Polyurethane‐mesoporous silica gas separation membranes

“…Mixed matrix membranes (MMMs) have been considered as an effective approach to enhance the gas transport properties . The influence of particles with a variety of size, type (inorganic and organic), shapes (cubic, spherical, sheet‐like, etc), and pore diameters has been extensively studied . Also, the interaction of particles with polymer chains greatly effects on the gas separation performance.…”

Origins and Evolution of Inorganic-Based and MOF-Based Mixed-Matrix Membranes for Gas Separations

“…Most common molecular sieving materials such as MOFs, ZIFs, Zeolites show low aspect ratios compared to layered materials such as silicates. Therefore, the incorporation of a small volume fraction of such layered materials can improve the performance of MMMs [161,162]. Defontaine, et al were able to improve the CO2/CH4 selectivity of PDMS by 145% with the incorporation of sepiolite [163].…”