Comparative assessment of hydrogen pathways in a biogas–LNG–assisted methanation and power system: 4E analysis and multi-objective optimization

• Novel system uses LNG cooling, CO₂ capture, and waste heat recovery. • Compared PEME, Alkaline, and Vanadium Chloride methane production methods. • Vanadium Chloride method shows highest exergy efficiency and lowest cost. • Methane and hydrogen yields are highest in Vanadium Chloride configuration. • Multi-criteria analyses and Grey Wolf optimization are performed. This work proposes and evaluates a novel integrated energy system for renewable methane synthesis, offering a comparative analysis of three hydrogen production routes: alkaline electrolysis, proton exchange membrane electrolysis, and the vanadium chloride thermochemical cycle. The study’s core focus lies in seeking the best method for hydrogen and subsequently methane production while incorporating LNG as the exclusive cooling and CO₂ capture medium to mitigate water-based thermal pollution to enhance process integration. Through a detailed techno-economic and multi-objective optimization via the Gray Wolf Optimizer, the system’s performance was assessed in terms of exergy efficiency, methane production rate, output power, levelized cost of products, and environmental impact. The findings reveal that while all configurations achieve high integration efficiency, the vanadium chloride-based system significantly outperforms the electrolysis alternatives, achieving superior exergy efficiency, lower product cost, and markedly higher methane yields. The integrated comparative framework and novel system configuration presented here offer valuable insights for future deployment of multi-product renewable energy systems. Under optimal conditions, the proton exchange membrane electrolysis system achieves an exergy efficiency of 31.65 %, a levelized cost of 0.131 $/kWh, and an emission index of 0.533 kg/kWh. The alkaline system shows similar performance, with an exergy efficiency of 31.84 %, a levelized cost of 0.130 $/kWh, and an emission index of 0.531 kg/kWh. Among the three systems, the vanadium chloride system demonstrates the best performance, achieving an exergy efficiency of 38.82 %, the lowest levelized cost of 0.106 $/kWh, and an emission index of 0.474 kg/kWh. Moreover, the vanadium chloride system achieves the shortest payback period at 5.96 years. This work highlights the strategic potential of renewable methane as a long-term, storable, and grid-compatible energy carrier, supporting the transition to decarbonized energy systems.