(104a) Solar-Thermal Dehydrogenation of Propane to Propylene

This presentation describes an overview of a process concept for significantly reducing the carbon emissions from the conversion of propane to propylene by high temperature catalytic dehydrogenation. The carbon emissions of the existing process are due to the highly endothermic reaction, resulting in reactor temperatures of 600 ºC or higher, which is typically accomplished by combustion of refinery gas. We propose a method of providing all thermal energy for the process by solar heat. Pellets of a supported PtSn catalyst are heated by concentrated sunlight to temperatures between 600 and 900 ºC. The catalyst pellets are then transferred to a moving-bed, counter-flow reactor where feed pre-heating and the dehydrogenation reaction are driven by heat stored in the pellets. Cool pellets are then recycled to the solar concentrator to be reheated by solar energy.

Key challenges for this decarbonized process include (1) ensuring that catalyst design is suitable for selectivity and low coke formation across a wide range of elevated temperatures to reduce reactor stages, (2) achieving high solar absorptance and stability of catalyst pellets under rapid solar heating, and (3) optimizing throughput in the reactor for effective thermodynamic balance, heat transfer, and reaction time.

Work to-date to address these key challenges has included simulation, synthesis, characterization, and reaction kinetics measurements for a range of silica-supported PtSn catalysts. Data on solar absorption has also been collected for a variety of catalyst formulations and compared with candidate inert solar absorbing particles. A thermodynamics and kinetics analysis has been employed to investigate the proper operating conditions and mass flows for reactors at a variety of scales. Lessons learned to-date and a roadmap for development of this process concept will be presented.