(530d) Liquid Phase Propylene Epoxidation with Nb-Based Mesoporous Silicates

Current commercial routes to propylene oxide (PO) production are mainly the chlorohydrin process, different hydroperoxide based processes and hydrogen peroxide-based propylene oxide (HPPO) process. While the chlorohydrin process suffers from high environmental impact due to much waste generation, the hydroperoxide processes depend on stable by-product value for economic sustainability. Among these processes, the HPPO process is the most eco-friendly¹ as it produces only H₂O as by-product, uses mild operating conditions and provides PO selectivity of 95%. There continues to be interest in alternative PO processes using inexpensive and robust catalysts that maximize PO selectivity and H₂O₂ utilization. Following our recent work on Nb-based heterogeneous catalytic system for ethylene epoxidation², we investigated such catalysts for propylene epoxidation under similar operating liquid-phase conditions as those for the HPPO process. Our results reveal that Nb-EISA catalyst prepared using Evaporation Induced Self Assembly (EISA), shows exceptional overall performance with nearly total PO selectivity (>99%) and H₂O₂ utilization (>99%) with high productivity (3200 mg/h/g) with mild Nb leaching (1 %). The superior performance of Nb-EISA catalysts is attributed to the predominantly Lewis acidic nature of the Nb-EISA catalysts with relatively low Brønsted acidity compared to mesoporous silicates prepared by other techniques. The ability to easily create propylene-expanded liquids phases by pressure-tuning plays a significant role in enhancing the PO yield. Detailed parametric studies (T, P, catalyst loading, Nb content etc.) will be presented along with catalyst characterization results.

References:

1. Lee, H. J.; Shi, T. P.; Busch, D. H.; Subramaniam, B. Chem. Eng. Sci. 62 (2007), 7282-7289.

2. Yan, W.; Ramanathan, A.; Patel, P. D.; Maiti, S. K.; Laird, B. B.; Thampson, W. H.; Subramaniam, B. J. Catal. 336 (2016), 75-84.