Abstract
Membrane gas separation has attracted the attention of chemical engineers for the selective separation of gases. Among the different types of membranes used, ultrathin membranes are recognized to break the trade-off between selectivity and permeance to provide ultimate separation. Such success has been associated with the ultrathin nature of the selective layer as well as their defect-free structure. These membrane features can be obtained from specific membrane preparation procedures used, in which the intrinsic properties of different nanostructured materials (e.g., polymers, zeolites, covalent–organic frameworks, metal–organic frameworks, and graphene and its derivatives) also play a crucial role. It is likely that such a concept of membranes will be explored in the coming years. Therefore, the goal of this review study is to give the latest insights into the use of ultrathin selective barriers, highlighting and describing the primary membrane preparation protocols applied, such as atomic layer deposition, in situ crystal formation, interfacial polymerization, Langmuir–Blodgett technique, facile filtration process, and gutter layer formation, to mention just a few. For this, the most recent approaches are addressed, with particular emphasis on the most relevant results in separating gas molecules. A brief overview of the fundamentals for the application of the techniques is given. Finally, by reviewing the ongoing development works, the concluding remarks and future trends are also provided.
Highlights
Membrane gas separation has attracted the attention of chemical engineers for the selective separation of gases
This is due to the fact that they can be synthesized with a defect-free morphology, obtained by means of speci c procedures applied for their preparation, including atomic layer deposition (ALD), solvothermal crystallization, interfacial crystallization, electrophoretic deposition (ED), chemical vapor deposition (CVD), Langmuir–Blodgett (LB) deposition, facile ltration process, and gutter layer formation.[28,29]
Two nal remarks dealing with this technique are that: (i) ller nanoparticles can be incorporated during the interfacial polymerization (IP) process by maintaining the thickness of the membrane skin layer to an attractive value of ca. 100 nm and is able to be operated up to 250 C with H2/CO2 selectivity of 14.6 and a H2 permeance higher than 600 gas permeation unit (GPU); (ii) it can be applied to other polymer systems different from the typical polyamides used in the beginning of the development of the TFC membranes,[34] as recently demonstrated by Shan et al.[37] with the preparation of benzimidazole-linked polymer (BILPs) membranes with H2/CO2 selectivity up to 40, high pressure resistance, and long-term stability (800 h in the presence of moisture)
Summary
Review used as llers are contributing to the reduction in the drawbacks of polymer-based membranes, such as aging, plasticization phenomenon, and stability (e.g., physical, chemical, and thermal).[18,19,20,21] the unsuitable merging, including poor compatibility at the interface as well as membrane preparation protocol, make the ller–polymer membranes show speci c defects (see Fig. 1), e.g., new non-selective pathways for gas transport (case 3), which lead to an increase in the permeability but compromise on the selective properties.[22]. It is important to point out that industrialized state-of-theart technologies were used to fabricate reverse osmosis and nano ltration membranes since the end seventies[34] based on the interfacial polymerization (IP) of aromatic polyamides producing the so-called thin- lm composite membranes (i.e., TFC and TFN membranes when incorporating llers), which have endured two new evolutions They have been recently applied for gas separation with good performance in H2/CO2 separation with H2 permeance in the range of 330–350 GPU.[27,35] TFC membranes have controlling skin layers in the range of ca. By reviewing the ongoing development works, the concluding remarks and future perspectives are addressed
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