Combined Electrolysis and Steam Methane Reforming for Optimized, Sustainable Methanol and Green Hydrogen Production
Authors: Hemauer Johanna , Bohn Jan-Peter , Rehfeldt Sebastian , Klein Harald 
Published: December 2024

The depletion of fossil raw materials and the environmental impact of their combustion is forcing the chemical industry to change. Increased social awareness and governmental regulations, supported by subsidies, accelerate this necessary change. In hard-to-abate sectors and chemical production processes where direct electrification is not applicable, green hydrogen is a key component for decarbonization. Green hydrogen, produced through water electrolysis powered by renewable energies, couples the power and chemical industries, realizing indirect electrification within the chemical industry.

Methanol is an important hydrogen derivate, serving as a base chemical, fuel or gasoline additive, alongside its potential role as a hydrogen carrier and CO2 sink. Following ammonia, methanol is the second largest hydrogen consumer in the chemical sector, with growing demand in the future due to its use, e.g., as a drop-in fuel in overseas transportation. Traditionally, methanol is produced from fossil feedstocks such as natural gas. In a steam methane reforming or autothermal reforming process, natural gas and steam are converted to synthesis gas. This synthesis gas contains hydrogen, carbon monoxide and CO2 and reacts to methanol in a subsequent process step.

Recent progress in catalyst development allows for economic methanol synthesis directly from green hydrogen and CO2, consequently replacing fossil feedstock with water, green electricity and CO2 from unavoidable or biological sources or captured from ambient air. The amount of green hydrogen produced by electrolysis to meet the overall demand for methanol requires a substantial scale-up of electrolysis technology and large amounts of green electricity, which is currently a long-term prospect. Therefore, transitional solutions with a reduced carbon footprint and, thus, a lower consumption of fossil raw materials are necessary to cover the demand for methanol in the short to medium term.

We present a transitional solution that combines a proton exchange membrane (PEM) electrolysis parallel to a steam methane reformer to produce conventional synthesis gas mixed with hydrogen and CO2 for downstream methanol synthesis. This combination aims to produce both, low-carbon methanol and green hydrogen. It serves as a bridging solution to meet the growing methanol demand with today's limited availability and volatility of renewable energy until a sufficient technical readiness level and scale-up of electrolysis technology is achieved and renewable energy becomes more abundant.

The combined process is investigated and optimized depending on its boundary conditions, such as power, natural gas or biogas availability, feedstock costs, direct and indirect CO2 emissions, product flexibility and intensive schemes. We will demonstrate the influence of these parameters on the overall process in order to determine whether a bivalent feed approach for sustainable methanol synthesis with a green hydrogen by-product is advantageous in certain scenarios.

Results are obtained from a detailed process simulation of the overall process chain. Therefore, a PEM electrolysis model is developed on a cell level, and a flexible electrolysis plant following a fluctuating power profile is considered in the overall optimization model. Furthermore, PEM electrolysis is being assessed for its compatibility and integration with traditional processes. This evaluation includes studying the impact of varying synthesis gas compositions on the methanol production process, as well as the overall feasibility of the process concept.