Advances in membrane technology for nitrogen-methane separation with focus on design performance and future trends

Abstract

The energy-intensive nature of nitrogen/methane (N₂/CH₄) separation in natural gas upgrading presents a persistent industrial challenge due to the close physicochemical properties of the two gases. This review systematically evaluates recent frontier advancements in polymeric, inorganic and mixed matrix membranes (MMMs) with emerging nanostructured membrane architectures for efficient N₂/CH₄ separation. Emphasis is placed on the design of membrane materials with metal-organic frameworks (MOFs), hydrogen-bonded organic frameworks (HOFs), carbonized MOF derivatives, and 2D MXene nanosheets, which allow the selective control of molecular sieving, sorption selectivity, and transport pathways. The high-performance MMMs, including HOF-21/6FDA-DAM, Ni-MOF-74/SBS, and ACU/PVA, have shown great advancements in permeability-selectivity trade-offs with improved filler-polymer compatibility, pore engineering, and design of functional sites. Notably, recent studies on the use of Cr-activated MXene membranes demonstrate outstanding N2 permeance (381 GPU) and selectivity (13.76), revealing the potential of lamellar structures with unsaturated metal sites in N2-philic separations. Critical comparative analysis reveals convergences in metal site coordination, filler dispersion strategies, and divergences in membrane architecture and gas affinity orientation (CH4-philic vs. N2-philic). Although the performance at laboratory scale is promising, there remain critical issues in the control of agglomeration, long-term stability, and scalability to realistic feed conditions. Future directions are proposed to address these limitations through hybrid membrane configurations, process integration, and rational material–structure–performance correlations. This review provides a comprehensive platform for the rational design of next-generation membranes, advancing the feasibility of energy-efficient N₂/CH₄ separation.