(228e) A System-Level Decision-Making Analysis of Liquid Organic Hydrogen Carrier (LOHC) Processes: A Case Study of Korea-Australia

The transition from a fossil fuel-based economy to a hydrogen economy is imperative, primarily due to the sustainability of hydrogen. Hydrogen only produces water after its utilization with greater gravimetric energy density compared to conventional fossil fuels. Especially, hydrogen can be utilized as an energy carrier of intermittent renewable energy. hydrogen produced using electricity generated from renewable energy sources can reduce the reliance on fossil fuels without CO₂ emission during its production, thereby contributing to achieving carbon neutrality. However, the transition to a hydrogen economy is challenged by its low volumetric energy density, which leads to an increase in transportation costs under ambient conditions, necessitating the appropriate hydrogen transportation method for long-distance.

Hydrogen storage may be majorly classified into two main categories: physical and chemical storage. Physical storage, such as high-pressure tanks and liquefaction, presents a lower complexity in processes and a higher technology readiness level (TRL), making it a more immediately viable option. However, the requirement for extreme conditions, such as cryogenic temperatures or high pressures, leads to continuous energy expenditure and hydrogen loss during transportation, posing a significant risk. On the other hand, chemical storage methods, which involve the hydrogenation of compounds such as liquid organic hydrogen carriers (LOHCs) or ammonia, offer a promising alternative. Although these methods currently exhibit a relatively lower TRL and require additional separation processes during dehydrogenation, their ability to transport hydrogen in a liquid state at ambient conditions with lower energy consumption makes them particularly suitable for long-distance transportation. Especially, LOHC is particularly advantageous due to its compatibility with established transportation systems for petroleum and chemical products, as well as its recyclable characteristics.

However, the vast array of LOHCs available complicates the selection of an optimal LOHC, as comparing all types is constrained by practical limitations. Therefore, in this study, we conducted decision-making of the process that uses the following LOHC systems: toluene/methylcyclohexane, dibenzyltoluene/perhydro-dibenzyltoluene, N-ethylcarbazole/perhydro-N-ethylcarbazole, and CO₂/methanol, which are named strategy 1 through 4. As decision-making criteria, the exergy efficiency, profitability, and global warming potential of the process are considered. To investigate those factors, a comprehensive analysis including exergy and techno-economic analyses, and life-cycle assessment is conducted based on a scenario transporting hydrogen from Australia to Korea as a representative.

Strategy 1 exhibits the least exergy efficacy (74.0%) because of its substantial energy consumption. However, despite employing a sophisticated separation process due to the volatile nature of TOL, the lowest minimum selling price of hydrogen (MHSP; $5.9/kg) was achieved. Conversely, strategy 2 exhibits the highest exergy efficiency and second lowest in terms of the MHSP, even with the most substantial global warming potential (GWP) primarily attributable to the substantial influence of dibenzyltoluene. In comparison to strategy 2, strategy 3 exhibits the most favorable exergy efficiency (77.4%) due to its minimal H₂ loss and reduced energy consumption. However, despite the effective hydrogen transportation capability of N-ethylcarbazole, strategy 3 incurred the highest MHSP ($9.6/kg) due to its high cost of N-ethylcarbazole. Lastly, since strategy 4 utilizes CO₂ captured from flue gas as LOHC, Strategy 4 was determined to be the most environmentally favorable alternative.

Based on the results obtained from the analyses, decision-making was conducted. Strategy 1 was found to be overwhelmingly beneficial, particularly when profitability takes precedence, while strategies 2 and 4 were selected at the vertices of exergy efficiency and GWP, respectively. In summary, this research provides valuable insights for policy-making by explicating the intricate dynamics of critical factors that are essential for devising successful strategies to transport hydrogen and achieve global carbon neutrality.