(522a) 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 an alternative approach using solar thermal heating of a moving catalyst bed instead of the reactor feed as the source of heat for the reaction; catalysts are heated to high reaction temperatures 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: Pt₃Sn₁/SiO₂, Pt₁Sn₁/SiO₂, and Pt₁Sn₃/SiO₂ at 773K-973K for 10h time-on-stream. All catalysts showed high propylene selectivity at 773K-873K. However, Pt₃Sn₁/SiO₂ and Pt₁Sn₁/SiO₂ exhibited a decrease in activity over time-on-stream while the tin-rich catalyst (Pt₁Sn₃/SiO₂) maintained a stable activity. At 973K, thermal dehydrogenation tends to dominate over catalytic dehydrogenation reaction. However, Pt₁Sn₃/SiO₂ catalyst gave the highest selectivity and stability compared to other catalysts. We expand on prior literature in this space, focusing on tin-rich catalysts at 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 products but decreases the desorption energy for propylene. The FTIR spectroscopy of adsorbed CO and TEM analysis of the catalyst before and after reaction will also be determined.