Conversion Of Bio-ethanol To Propylene Catalyzed By Modified Nanoscale HZSM-5 Zeolites

In this paper, the catalytic performances of the nanoscale HZSM-5 zeolite modified by NaOH treatment, alkaline-phosphorous combined modification for the conversion of bio-ethanol to propylene were investigated. All catalysts were characterized by XRD, SEM, NMR, ICP-OES, N2 adsorption/desorption, NH3-TPD, Py-IR, and TG techniques to inwestigate the influence of physico-chemical properties of the nanoscale HZSM-5 catalysts on the performance for the conversion of bio-ethanol to propylene.The effect of alkali treatment conditions (NaOH concentration, treatment temperature and time) on pore structure, acidity and catalytic performance of nanoscale HZSM-5 zeolites for selective dehydration of bio-ethanol to propylene had been studied. The results showed that the newly developed mesopores enlarged on HZSM-5 zeolite by increasing the NaOH concentration, treatment temperature and time, among which the NaOH concentration was the most effective variable. By treating nanoscale HZSM-5 zeolite with appropriate concentrations of NaOH solution, the acid sites, pore volume and pore diameter increased, which resulted in higher propylene selectivity and better stability. However, excessive high NaOH concentration and high temperature treatment led to serious desilication, which would increase the amount of strong acid sites, resulting in a remarkable decrease both in propylene selectivity and catalyst stability.The alkaline-phosphorous co-modified nanoscale HZSM-5 zeolite showed better catalytic performance than the parent and single-modified samples. The results showed that the highest selectivity of propylene and the stability of the catalyst reached 25% and 110 h, respectively on the NaOH-H3PO4 co-modified HZSM-5 zeolite. And the highest selectivity of propylene and the stability of the catalyst reached 27% and 110 h, respectively on the Na2CO3-H3PO4 composite modified HZSM-5 zeolite. The enhanced catalytic performance can be attributed to the harmonious acid sites and the mesoporous structure by the modification with alkaline and phosphorous.