Unique structure of fibrous ZSM-5 catalyst expedited prolonged hydrogen atom restoration for selective production of propylene from methanol |
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Authors: | HU Hambali AA Jalil S Triwahyono SF Jamian NAA Fatah AA Abdulrasheed TJ Siang |
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Affiliation: | 1. School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia;2. Centre of Hydrogen Energy, Institute of Future Energy, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia;3. Faculty of Science, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia;4. Department of Chemical Engineering, University of Ilorin, PMB, 1515, Ilorin, Nigeria |
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Abstract: | A unique mesostructured fibrous silica@ZSM-5 (HSi@ZSM-5) catalyst was synthesized via microemulsion ZSM-5 zeolite seed assisted synthesis method and successfully applied in enhanced propylene formation in methanol to olefin (MTO) process. Characterization of the catalysts were carried out by FESEM, TEM, XRD, TGA, N2 adsorption-desorption, NH3 and KBr probed FTIR. Catalytic performance of as-synthesized catalyst was examined using a micro-pulse reactor and compared with the commercial HZSM-5. The reaction mechanism was elucidated by in-situ methanol FTIR spectroscopy. It was found that HSi@ZSM-5 produced higher propylene selectivity (56%) and was stable for long time on stream (80 h), nearly three-fold higher than that of commercial HZSM-5. In addition, HSi@ZSM-5 displayed higher rate of methanol dehydration, surface methoxy species generation and olefin methylation, indicating that alkene catalytic cycle is the dominant reaction mechanism. The higher selectivity towards propylene was correlated to the existence of moderate acidity which impeded the formation of paraffins and polymethylbenzene intermediates. These observations are further supported by KBr probed FTIR findings which revealed negligible paraffinic carbon species on HSi@ZSM-5. Thus, the unique fibrous silica@ZSM-5 retarded coke deposition due to suppression of undesired side reactions thereby signifying intensified propylene formation, which is highly desirable in commercial MTO processes. |
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Keywords: | Fibrous HSi@ZSM-5 Methanol dehydration Propylene Surface methoxy species |
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