Membrane materials for biogas purification and upgrading: Fundamentals, recent advances and challenges

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Biogas from the anaerobic digestion of organic waste stands as a renewable energy source with a large potential to reduce the global dependence on fossil fuels. Biogas applications as a vehicle fuel or natural gas substitute requires the separation of the main biogas components, namely methane and carbon dioxide. Such biogas separation is also necessary for valorizing carbon dioxide, which is a valuable molecule in food and beverage industries, chemical synthesis and greenhouses, among other industrial activities. While most biological technologies focused on biogas separation are still in the development phase, the use of membranes for this purpose has increased exponentially in the last decade due to its efficiency, compact design, economic feasibility, and easy scalability. This article provides a comprehensive overview of the current state of membrane technology, focusing on both fundamental principles and the latest advancements in membrane systems for biogas purification and upgrading. 6FDA-based polyimides and polymers of intrinsic microporosity offer promising prospects for advancing membrane technologies used in biogas upgrading. The incorporation of fillers, such as zeolites and metal-organic frameworks, into a polymer matrix to create mixed matrix membranes (MMMs) significantly enhances the overall performance (CO2 permeabilities up to 18,000 Barrer and CO2/CH4 selectivity values up to 85) and functionality of the membrane. However, the key challenges for MMMs remain in fabricating defect-free membranes with high CO2/CH4 selectivity and ensuring long-term stability over several months.