Hydrogenation of liquid organic hydrogen carriers: Process scale-up, economic analysis and optimization

Hydrogen has been proposed as energy vector because it can be produced from renewable energy sources and its use produces no carbon dioxide. Moreover, many industrial processes (e.g., steel industry, ammonia, and fertilizer industry, etc.) are also adopting renewable-produced hydrogen as raw material, replacing traditional fossil sources. In this context, the storage and transportation of hydrogen using liquid organic hydrogen carriers (LOHC) is interesting to deal with the discontinuous production of renewable energies. The work addressed the study of the hydrogenation process for three compounds, 3,5-dibenzyl toluene, 2-methyl indole and N-ethylcarbazole, on Ni and Ru-based catalysts. The reactor consisted of a three-phase slurry stirred tank reactor, which has been scale-up together with the rest of the process equipment units using Aspen Hysys simulation software. The hydrogen storage cost has been determined applying an economic evaluation to the overall process. The most important costs of the process are the reactor cost and the cost of raw materials (the liquid organic hydrogen carrier). The main design variables, plant capacity, reactor temperature and pressure, were optimized to reduce the storage cost. The liquid organic hydrogen carrier with the minimum storage cost at the optimum operating conditions is 3,5-dibenzyl toluene with a reactor configuration of two parallel tanks.