(630c) Synergistic Optimal Synthesis of Sustainable Methanol Production through Integrated Renewable Energy Storage and Carbon Utilization

The compelling need for sustainable energy systems to combat the climate crisis has driven global focus on innovative approaches that optimize available resource utilization with minimized environmental harm. This shift hinges on aggressive integration of renewable energy resources (RES) into the fossil dominant global energy landscape. However, due to the intermittent nature of RES, they are faced with reliability challenges, necessitating efficient storage solutions for energy security. Furthermore, the imperative reduction of carbon emissions drives the exploration of carbon capture and sustainable utilization towards carbon-neutrality.

One promising route that facilitates renewable energy storage and carbon mitigation is the methanol production through carbon dioxide (CO₂) hydrogenation. As a versatile bulk chemical, methanol shows great potential as a clean energy carrier and carbon neutral fuel when produced with CO₂ free hydrogen (H₂). While this process offers a carbon neutral alternative, the high cost of producing green hydrogen from water electrolysis (the most mature renewable hydrogen source) due to high energy consumption have limited its competitiveness with conventional methanol. On the other hand, methane pyrolysis (MP) which decomposes methane into its constituent element of hydrogen (turquoise hydrogen) and solid carbon (C) offers a suitable CO₂-free hydrogen alternative when RES is used. Therefore, the synergistic integration of clean energy processes from available fossil and renewable resources becomes essential to address emissions sustainably.

This study proposes the synthesis of a novel optimal synergistic process design of methanol production through CO₂ hydrogenation with CO₂-free hydrogen from methane pyrolysis and water electrolysis. The process modeling and simulation of methane pyrolysis using the regenerative heat exchanger reactor (RHER), alkaline water electrolysis (AEL), CO₂ capture (renewable source and fossil source were tested), methanol synthesis and separation are carried out in Aspen Plus. The RHER is a counter current flow heat integrated moving bed reactor that uses electricity as energy source through ohmic heating patented by [1] and as presented by [2,3], the inherent heat exchange in the RHER reduces the energy consumption and other material cost that comes the high temperature methane pyrolysis process products. A detailed comparative techno-economic, energy and environmental analysis of the proposed process, turquoise and green methanol is performed. Sensitivity analysis is also performed to show parameters that influence process cost and it shows that MP is most sensitive to natural gas feed cost, and electrolysis to renewable electricity cost. The sale of carbon and oxygen byproduct was set to zero for base case, but also varied for sensitivity analysis. Considering the sensitivity analysis result, there is a need to find the optimal ratio for the synergy between MP and AEL for maximum plant profit. Thus, an optimization is performed to find the optimal ratio of MP to AEL H₂ required for maximum plant profit for the desired quantity of methanol, subject to process operating conditions, resource availability and environmental constraints.

The simulation results showed that the clean methanol plant electricity consumption was significantly reduced using MP hydrogen compared to AEL hydrogen for 50ktonnes/year methanol production, and for the synergic process the electricity consumed was also significantly for a 75/25 percent ratio of H₂ from MP and AEL respectively. The results of this study thus proffer a sustainable approach that tackles RES variability, minimize energy consumption while mitigating carbon emission. It also shows economic viability and potential competitiveness of low-carbon methanol. Furthermore, this study demonstrates that in the energy transition paradigm, natural gas could play an important role supporting RES, without necessarily emitting CO₂ to the atmosphere. This study is required for an optimally integrated process synthesis and design framework for approaches that improve the efficiency of available resource utilization with minimized environmental impact.

References

1. Jahnig CE, Silveston PL, Tyson CW. Hydrocarbon conversion process (U.S. Patent 2982622, May 1961).
2. Keipi T, Hankalin V, Nummelin J, Raiko R. Techno-economic analysis of four concepts for thermal decomposition of methane: Reduction of co2 emissions in natural gas combustion. Energy Convers Manage 2016;110:1–12.
3. Marquardt, A. Bode, S. Kabelac, Hydrogen production by methane decomposition: Analysis of thermodynamic carbon properties and process evaluation, Energy Conversion and Management, 2020; 221. https://doi.org/10.1016/j.enconman.2020.113125.