Steam Methane Reforming (SMR) is the most widely used method for hydrogen production, accounting for approximately 95% of global hydrogen supply. While it is a mature and cost-effective technology, its environmental impact, particularly its carbon footprint, is a significant concern. The process involves reacting methane with steam under high temperatures to produce hydrogen and carbon monoxide, followed by a water-gas shift reaction to convert CO into additional hydrogen and CO₂. The result is a high yield of hydrogen but also substantial CO₂ emissions.

On average, conventional SMR emits between 8 to 12 kg of CO₂ per kg of hydrogen produced. This range depends on factors such as feedstock quality, process efficiency, and plant configuration. The majority of emissions originate from two sources: the combustion of natural gas to provide heat for the endothermic reforming reaction and the subsequent CO₂ released during the water-gas shift reaction. Without mitigation, these emissions contribute significantly to global greenhouse gas (GHG) accumulation.

The environmental impact of unabated SMR is substantial. Given that global hydrogen production exceeds 70 million tons annually, mostly from SMR, the associated CO₂ emissions reach hundreds of millions of tons each year. This makes hydrogen production a major industrial source of CO₂, comparable to emissions from entire countries. Methane leakage during natural gas extraction and transport further exacerbates the climate impact, as methane has a global warming potential 28-36 times higher than CO₂ over a 100-year period.

Carbon capture and storage (CCS) offers a pathway to reduce emissions from SMR. When applied, CCS can capture 85-95% of the CO₂ generated, lowering emissions to approximately 1-2 kg of CO₂ per kg of hydrogen. The captured CO₂ is then compressed, transported, and stored underground in geological formations such as depleted oil and gas fields or deep saline aquifers. This approach, known as blue hydrogen, bridges the gap between conventional SMR and fully decarbonized alternatives.

However, integrating CCS with SMR presents technical and economic challenges. One major issue is the energy penalty associated with capture processes. CO₂ separation typically requires additional energy, reducing overall plant efficiency by 10-20%. The most common capture method, amine scrubbing, demands significant heat for solvent regeneration, increasing fuel consumption. Advanced capture technologies, such as pressure-swing adsorption or membrane separation, may reduce energy penalties but are still under development for large-scale deployment.

Capture efficiency is another challenge. While high capture rates are achievable, residual emissions persist due to incomplete CO₂ separation and fugitive releases. Additionally, the purity of captured CO₂ affects storage feasibility. Impurities such as nitrogen or sulfur compounds can complicate transport and injection, requiring additional treatment steps.

Infrastructure for CO₂ transport and storage is another limiting factor. Effective CCS requires proximity to suitable geological storage sites, which are not universally available. Building pipelines for CO₂ transport is capital-intensive, and public acceptance of underground storage remains a hurdle in some regions. Regulatory frameworks for long-term liability and monitoring of stored CO₂ are still evolving, adding uncertainty to large-scale deployment.

Despite these challenges, several large-scale SMR-CCS projects have demonstrated feasibility. For example, the Quest project in Canada captures over 1 million tons of CO₂ annually from hydrogen production for oil refining. Similarly, the Hydrogen to Humber Saltend project in the UK aims to produce low-carbon hydrogen with CCS for industrial use. These initiatives highlight the potential of CCS to decarbonize existing hydrogen infrastructure while leveraging established SMR technology.

The cost of CCS-equipped SMR remains higher than conventional SMR due to capital and operational expenses for capture, compression, and storage. Current estimates suggest blue hydrogen costs between 1.5 to 2.5 times more than unabated SMR, depending on natural gas prices and CCS implementation costs. However, as carbon pricing mechanisms expand and CCS technology matures, the economic gap may narrow.

In summary, conventional SMR is a high-emission process that significantly contributes to global CO₂ levels. While CCS can drastically reduce these emissions, its integration introduces energy penalties, efficiency losses, and infrastructure demands. Addressing these challenges requires continued technological advancements, supportive policies, and investment in CO₂ transport and storage networks. Without CCS, SMR’s carbon footprint remains unsustainable in a decarbonizing energy landscape. However, with effective CCS deployment, SMR can play a transitional role in scaling low-carbon hydrogen production while cleaner alternatives develop.

The future of SMR hinges on balancing its immediate advantages—low cost and scalability—with the imperative to minimize emissions. As regulations tighten and carbon markets evolve, the adoption of CCS will determine whether SMR remains a viable pathway or gives way to greener alternatives. For now, blue hydrogen represents a critical step toward reducing the carbon intensity of hydrogen production without abandoning existing infrastructure.