(683d) Overcoming Propane Dehydrogenation Equilibrium Limitations Using a Catalyst/Membrane Hollow Fiber System

Propylene is one of the most diverse building blocks in the petrochemical industry. Propane dehydrogenation (PDH) is a promising technology for direct production of propylene and hydrogen. PDH is an endothermic reaction requiring elevated reaction temperatures. Unfortunately, under high temperature conditions, the rates of side reactions are increased, leading to lower selectivity, catalyst deactivation, and requiring costly catalyst regeneration.¹ The catalysts used commercially for this process include Pt nanoparticles, heavily promoted by Sn (Sn:Pt atomic ratio of ~5) and supported on Al₂O₃. The high concentration of Sn is required since the PtSn phase segregates and leads to the formation of a SnO₂ phase. For stable performance, these catalysts also require H₂ as a cofeed to mitigate carbon buildup. This reduces per-pass propylene conversion and lowers catalyst productivity. Herein, we report the design of a stable and selective catalyst for PDH operating at the thermodynamic limit without the addition of H₂ to the feed.² Furthermore, using reaction engineering, this superior catalyst performance is pushed beyond equilibrium limits, based on Le Châtelier’s principle.³ We couple our stable and selective Pt₁Sn₁/SiO₂ catalyst to a H₂-removing, Knudsen-driven SiO₂/Al₂O₃ hollow fiber membrane (where the catalyst is packed inside the membrane) to form a membrane/catalyst system that can overcome equilibrium limitations. Through removal of H₂ from the product stream, we obtain propylene yields beyond those at thermodynamic constraints. We explore different operating conditions guided by dimensionless numbers that govern these membrane/catalyst systems to obtain an overall improvement of ~10% above equilibrium limits at 580 °C, while maintaining a propylene selectivity of > 95% and good stability.

References

1. Chen, S. et al. Chemical Society Reviews. 2021, 50(5), 3315-3354.
2. Motagamwala, A. H.; Almallahi, R.; Wortman, J.; Igenegbai, V. O.; Linic, S. Science. 2021, 373(6551), 217-222.
3. Weyten, H. et al. Catalysis Today. 2000. 56(1-3), 3-11.