Liquid organic hydrogen carriers: Process design and economic analysis for manufacturing N-ethylcarbazole

This paper revisits the economics of manufacturing N-ethylcarbazole (NEC), a strong candidate for large-scale liquid organic hydrogen carrier (LOHC) supply chains, because of its high H₂ storage capacity (6 wt%), selective hydrogenation and dehydrogenation reactions, and favorable reaction enthalpy and reaction temperatures compared to other LOHC systems. Two different process routes for producing NEC from industrial chemicals are selected out of 10 possible options: one using aniline and the other using cyclohexanone and nitrobenzene as feedstock. The required capital and operational costs are estimated to determine a NEC break-even cost for a capacity of 225 ktpa. NEC break-even costs of $3.0 and $2.6 per kg LOHC are found for the routes. This is significantly less than the $40/kg cost that has generally been reported in literature for NEC, thus improving the economic viability of using NEC as LOHC. The total fixed capital costs are estimated to be $200 MM and $250 MM. Furthermore, the prices of the feedstock show the largest influence (76% and 72%) on the final NEC break-even costs. The overall LOHC price contribution to the levelized H₂ cost is estimated to be $0.77–$0.90 per kg H₂ for a 60-day roundtrip and $0.09–$0.10 per kg H₂ for a 7-day roundtrip. It is important to note that both routes rely heavily on laboratory scale data and the corresponding assumptions that stem from this limitation. Therefore, this research can serve as a guide to future experimental studies into validating the key assumptions made for this analysis.