Towards Carbon-Neutral Hydrogen: Integrating Methane Pyrolysis with Geothermal Energy

Methane pyrolysis produces hydrogen (H₂) with a solid carbon co-product, eliminating process CO₂ formation and enabling low-carbon supply when paired with renewable or low-carbon heat. This work develops and evaluates a hybrid geothermal–pyrolysis configuration in which an enhanced geothermal system (EGS) provides baseload preheat and isothermal hold, while electrical or solar-thermal top-up delivers the final approach to the catalytic setpoint. We (i) integrate field-scale geothermal operating envelopes to anchor heat-integration targets and duty splits; (ii) expand scalability considerations to include high-pressure reactor design, thermal management, and carbon separation/handling strategies that preserve co-product value; (iii) provide a techno-economic analysis (TEA) template that itemizes CAPEX/OPEX, incorporates carbon pricing/credits, and explicitly treats dual-product economics (H₂ plus carbon black); and (iv) reorganize the state-of-the-art chronologically, linking molten-media demonstrations, catalyst advances, and recent integration studies to deployment readiness. Process synthesis shows that allocating geothermal heat to the largest heat-capacity streams (feed, recycle, and melt/salt hold) reduces electric top-up demand and stabilizes reactor temperature, mitigating coking/sintering and narrowing carbon particle size distributions upstream of cyclones and polishing filters. High-pressure operation improves hydrogen partial pressure and equipment compactness but demands corrosion-resistant materials and careful thermal-stress management. The TEA framework—built from recent methane-pyrolysis studies and standard process-economics practice—highlights that levelized cost of hydrogen is co-dominated by (a) the specific electric duty and grid/onsite power carbon intensity and (b) the realizable price and specification of the carbon co-product; sensitivities to methane price, geothermal capacity factor, and conversion/selectivity are secondary but material. Overall, geothermal-assisted methane pyrolysis offers a practical path to turquoise hydrogen with a defensible value stack when carbon quality is preserved and heat integration is optimized. We conclude with design rules and reporting guidelines to accelerate site-specific FEED and near-term pilot deployment.