The separation of methane and nitrogen in natural gas processing: A review

The efficient purification of natural gas, especially from unconventional sources such as shale, tight, and coal seam gas, is crucial for advancing the transition to a low-carbon economy. A key challenge in this process is the selective removal of nitrogen (N2), which shares similar physical and chemical properties with methane (CH4), complicating its separation and making it difficult to achieve the required purity levels for compression, transportation, and utilization. This review critically assesses the current state of CH4/N2 separation technologies and compares their performances numerically, including cryogenic distillation, absorption, adsorption, membrane separation, and hydrate-based processes. Each technology is evaluated based on its methane recovery efficiency, nitrogen removal performance, as well as the material, energy, and environmental impacts associated with its use. Despite notable advancements in these methods, challenges related to energy consumption, scalability, and cost-effectiveness persist, limiting their widespread industrial adoption. Future developments are suggested to focus on improving the efficiency and scalability of these processes. Cryogenic distillation will benefit from advancements in process optimization, including real-time monitoring and integration with renewable energy sources to reduce its energy demands. Membrane separation technologies are evolving towards the development of highly selective, molecularly engineered membranes that can improve separation efficiency. Adsorption processes are increasingly incorporating high-capacity materials such as porous carbon, zeolites and metal organic frameworks (MOFs) to enhance performance, while hydrate-based methods are advancing through the use of green accelerators and milder operating conditions. Collectively, these innovations aim to improve both the economic and environmental sustainability of natural gas purification, ultimately enabling more efficient, cost-effective, and eco-friendly utilization of natural gas resources in the future.