Selective Production of Propylene from Methanol over Monolith-Supported Modified ZSM-5 Catalysts

The catalytic activity of ZSM-5 zeolites with a SiO ₂ /Al ₂ O ₃ molar ratio of 30, 50, 80, 280, and 410 was investigated in a fixed bed continuous flow reactor system and was found that the ZSM-5 zeolite with SiO ₂ /Al ₂ O ₃ molar ratio of 280 (HZ-280) exhibited best catalyst performance. The optimized reaction conditions achieved were 500 °C, 1 bar pressure, and weight hourly space velocity of 15 h ^-1 using methanol as feed. At optimum reaction conditions, HZ-280 exhibited propylene selectivity of 47.3% and propylene yield 17.4% with 100% methanol conversion. HZ-280 zeolite was modified with P, Ce, Fe, and La to select the best promoter to enhance propylene selectivity and yield. The best-modified catalyst obtained was HZ-280 with 0.1 wt % phosphorus loading, which further improved propylene selectivity by 14% and yield by 24.7%. Then, the monolith structured catalysts were prepared by single-layer (6.8%), double-layer (10.3%), and triple-layer (13.1%) coating of HZ-280 catalyst. HZ-280 single-layer-coated monolith-structured catalyst effectively increased propylene selectivity by 19.2% and yield by 34.5% with no liquid hydrocarbons in the product. HZ-280-coated monolith catalyst was regenerated and was reused for three cycles. Negligible activity loss was observed for methanol conversion and propylene selectivity. This reflects that the structured catalyst is viable and economical for commercial applications. Analytical techniques such as X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray, Brunauer-Emmett-Teller, and NH ₃ -temperature-programmed desorption were used for characterization of the catalysts.