A facile approach to synthesize SSZ-13 membranes with ultrahigh N2 permeances for efficient N2/CH4 separations

A High-Performance N2-Selective MXene Membrane with Double Selectivity Mechanism for N2/CH4 Separation

Membrane-based separation process for unconventional natural gas purification (mainly N2/CH4 separation) has attracted more attention due to its considerable economic benefits. However, the majority of separation membranes at this stage, particularly N2-selective membranes, achieve the desired separation target by mainly relying on the diffusivity-selectivity mechanism. To overcome the limitation of a single mechanism, 2D lamellar MXene membranes with a double selectivity mechanism are prepared to enhance N2 permeance and N2/CH4 selectivity via introducing unsaturated metal sites into MXene, which can form specific interactions with N2 molecules and enhance N2 permeation. The resulting membranes exhibit an inspiring N2/CH4 separation performance with an N2 permeance of 344 GPU and N2/CH4 selectivity of 13.76. The collaboration of the double selectivity mechanism provides a new idea for the development of a novel N2-selective membrane for N2 removal and CH4 purification, which further broadens the application prospects of membrane separation technology in the field of unconventional natural gas purification.

Asymmetric pore windows in MOF membranes for natural gas valorization

To use natural gas as a feedstock alternative to coal and oil, its main constituent, methane, needs to be isolated with high purity¹. In particular, nitrogen dilutes the heating value of natural gas and is, therefore, of prime importance for removal². However, the inertness of nitrogen and its similarities to methane in terms of kinetic size, polarizability and boiling point pose particular challenges for the development of energy-efficient nitrogen-removing processes³. Here we report a mixed-linker metal-organic framework (MOF) membrane based on fumarate (fum) and mesaconate (mes) linkers, Zr-fum₆₇-mes₃₃-fcu-MOF, with a pore aperture shape specific for effective nitrogen removal from natural gas. The deliberate introduction of asymmetry in the parent trefoil-shaped pore aperture induces a shape irregularity, blocking the transport of tetrahedral methane while allowing linear nitrogen to permeate. Zr-fum₆₇-mes₃₃-fcu-MOF membranes exhibit record-high nitrogen/methane selectivity and nitrogen permeance under practical pressures up to 50 bar, removing both carbon dioxide and nitrogen from natural gas. Techno-economic analysis shows that our membranes offer the potential to reduce methane purification costs by about 66% for nitrogen rejection and about 73% for simultaneous removal of carbon dioxide and nitrogen, relative to cryogenic distillation and amine-based carbon dioxide capture.

Small-Pore Zeolite Membranes: A Review of Gas Separation Applications and Membrane Preparation

There have been significant advancements in small-pore zeolite membranes in recent years. With pore size closely related to many energy- or environment-related gas molecules, small-pore zeolite membranes have demonstrated great potential for the separation of some interested gas pairs, such as CO2/CH4, CO2/N2 and N2/CH4. Small-pore zeolite membranes share some characteristics but also have distinctive differences depending on their framework, structure and zeolite chemistry. Through this mini review, the separation performance of different types of zeolite membranes with respect to interested gas pairs will be compared. We aim to give readers an idea of membrane separation status. A few representative synthesis conditions are arbitrarily chosen and summarized, along with the corresponding separation performance. This review can be used as a quick reference with respect to the influence of synthesis conditions on membrane quality. At the end, some general findings and perspectives will be discussed.