The feasibility of using renewable natural gas (RNG), or biomethane, as a feedstock for steam methane reforming (SMR) presents a promising pathway to reduce the carbon intensity of hydrogen production. SMR is the dominant method for hydrogen production, accounting for nearly all commercially produced hydrogen today. However, conventional SMR relies on fossil-based natural gas, resulting in significant CO2 emissions. Substituting fossil natural gas with RNG offers a way to decarbonize this process while leveraging existing SMR infrastructure. This analysis examines the emissions profiles, purification requirements, supply chain challenges, and real-world applications of RNG-based SMR.

RNG is derived from organic waste sources such as landfills, wastewater treatment plants, and agricultural waste through anaerobic digestion or thermal gasification followed by upgrading to pipeline-quality gas. When used in SMR, RNG can significantly lower the carbon footprint of hydrogen production. The emissions profile of RNG-based SMR depends on the source of the biogas and the upgrading process. On a lifecycle basis, RNG sourced from landfill gas can reduce greenhouse gas emissions by over 70% compared to fossil natural gas. Agricultural waste-derived RNG can achieve even higher reductions, provided methane leakage during feedstock collection and processing is minimized. The CO2 produced during SMR is biogenic, meaning it originates from recently fixed carbon rather than fossil sources, which can be considered carbon-neutral if managed properly.

Purification is a critical step in preparing RNG for SMR. Raw biogas typically contains 50-70% methane, with the remainder consisting of CO2, trace contaminants such as hydrogen sulfide, siloxanes, and moisture. Upgrading to biomethane involves removing these impurities to meet pipeline standards, usually requiring a methane content of at least 90%. Technologies such as pressure swing adsorption, amine scrubbing, and membrane separation are commonly employed. For SMR applications, additional purification may be necessary to prevent catalyst poisoning. Sulfur compounds, in particular, must be reduced to sub-ppm levels to avoid deactivating the nickel-based catalysts used in SMR. This adds complexity and cost compared to fossil natural gas, which is already pipeline-ready.

The supply chain for RNG presents several challenges. Feedstock availability is geographically dispersed, often located far from existing SMR facilities. This necessitates investments in collection, processing, and transportation infrastructure. Unlike fossil natural gas, which benefits from an extensive and centralized pipeline network, RNG supply chains are fragmented. Seasonal variability in feedstock availability, such as agricultural waste, further complicates consistent supply. Additionally, competition for RNG from other applications, including direct use in heating and transportation, can limit its availability for hydrogen production.

Despite these challenges, several pilot projects have demonstrated the viability of RNG-based SMR. In California, the H2Renewables project integrates landfill-derived RNG into an SMR plant to produce low-carbon hydrogen for fuel cell vehicles. The project highlights the importance of co-locating RNG production with hydrogen facilities to minimize transportation costs. In Europe, the HySTRA initiative explores the use of RNG in large-scale SMR with carbon capture and storage (CCS) to achieve negative emissions. These projects underscore the potential of RNG to decarbonize hydrogen production while providing lessons on optimizing feedstock logistics and purification processes.

A comparison of emissions between fossil-based and RNG-based SMR reveals clear advantages for the latter. Fossil SMR emits approximately 9-10 kg of CO2 per kg of hydrogen produced. In contrast, RNG-based SMR can reduce emissions to 3-4 kg CO2 per kg of hydrogen, with further reductions possible when combined with CCS. The table below summarizes key differences:

Emissions Profile Fossil SMR RNG-Based SMR
CO2 Emissions (kg/kg H2) 9-10 3-4
Methane Leakage Risk Moderate High (feedstock-dependent)
Carbon Intensity High Low to Neutral

The higher methane leakage risk associated with RNG is a concern, as methane is a potent greenhouse gas. Mitigation strategies include improved feedstock handling and leak detection systems during biogas upgrading and distribution.

From a regulatory perspective, incentives such as renewable hydrogen credits and low-carbon fuel standards can improve the economic viability of RNG-based SMR. Policies that support RNG feedstock development, such as subsidies for anaerobic digesters, can also enhance supply chain resilience. However, the scalability of RNG for hydrogen production is limited by feedstock availability. Even with maximal RNG deployment, it is unlikely to fully replace fossil natural gas in SMR without significant advancements in waste-to-energy technologies.

In conclusion, RNG offers a feasible and lower-carbon alternative to fossil natural gas in SMR, with demonstrated success in pilot projects. Key challenges include purification requirements, supply chain logistics, and competition for feedstock. While not a complete solution, RNG-based SMR can play a transitional role in decarbonizing hydrogen production, particularly in regions with abundant organic waste resources. Future efforts should focus on optimizing RNG supply chains, reducing purification costs, and integrating CCS to maximize emissions reductions.