(511e) Solar-Thermal Dehydrogenation of Propane to Propylene

Propane dehydrogenation (PDH) is an energy-intensive process that depends on the combustion of natural gas as a means of heating the reactor feed streams. We propose solar thermal heating of the moving catalyst bed instead of the reactor feed as the source of heat for the reaction. Catalysts are heated to high reaction temperature between by exposing it to solar radiation. The hot catalyst is then transferred to a moving-bed, counter-current reactor where both feed preheating and dehydrogenation are driven by the heat stored in the catalyst pellets. Cool pellets are recycled back to the solar concentrator to be reheated by solar energy. Key considerations include designing a thermally stable catalyst with high propylene selectivity and minimal side reactions. To date, simulation, characterization, and reaction kinetics measurement have been performed using silica supported PtSn catalysts: Pt₃Sn/SiO₂, PtSn/SiO₂, and PtSn₃/SiO₂. The platinum-rich catalyst (i.e., Pt₃Sn/SiO₂) showed a continuous decrease in activity over the span of 10 h of time-on-stream while the activity of the tin-rich catalyst was stable with a selectivity of 99% over the span of 10 h of time-on-stream. We expand on the prior literature in this space, focusing on tin-rich catalysts and high temperatures, and we interpret rates and reaction orders in the context of DFT calculations which shows that at higher reaction temperature, the presence of excess tin increases the activation barrier for deep dehydrogenation of propylene and for the formation of other side reaction product but decreases the desorption energy for propylene. The FTIR spectroscopy of adsorbed CO will also be determined.