Dynamics of dibenzyl toluene hydrogenation and dehydrogenation reactors: design and simulation

Long-distance transport and long-term storage of H2 can be realized with Liquid Organic Hydrogen Carriers (LOHC) based on a two-step cycle: (1) hydrogenation of the LOHC molecule (i.e., H2 is covalently bound to the LOHC) and (2) dehydrogenation after transport and/or storage. Since the (optimal) LOHC is liquid at ambient conditions and shows similar properties to crude oil-based liquids (e.g. diesel and gasoline), its handling and storage is realized by well-known processes; thus, a stepwise adaptation of the existing crude oil-based infrastructure is technically possible. LOHC show economic advantages compared to compressed H2 and liquid H2 for long-term storage/long distance transport applications. The energetic efficiency of the systems depends on the dehydrogenation step. In this paper we will consider the details of thermodynamic and kinetic fundamentals of hydrogenation and dehydrogenation of a typical LOHC, namely Perhydro-Dibenzyl-Toluene. The fundamental chemical equilibrium expressions as a function of temperature and the catalytic kinetic expression for the reaction speed at different conditions are evaluated for the design of a dehydrogenation Continuous Stirred Tank Reactor. A process simulator (Aspen Plus v. 14.1™) is used to simulate the reactor at different operating conditions, focusing on the dynamic response of the reactor to any change in temperature, pressure, and inlet flow rate. The results obtained from the steady state simulation show a good agreement with experimental literature data. The results from dynamic simulation show that the time response of the reactor is compatible with the H2 production variations needed by fuel cells used for transportation.