411904 Producing Renewable Indoles By Thermo-Catalytic Conversion and Ammonization of Bio-Derived Furans over Zeolites and the Mechanism Study

Monday, November 9, 2015: 12:30 PM
355C (Salt Palace Convention Center)
Lujiang Xu, Ying Zhang and Qian Yao, Department of Chemistry, University of Science and Technology of China, Hefei, China

In this study we demonstrate that indoles can be directly produced by thermo-catalytic conversion of bio-derived furans with ammonia over zeolite catalysts. MCM-41, β-zeolite, ZSM-5 (Si/Al=50) and HZSM-5 catalysts with different Si/Al ratios (Si/Al=25, 50, 63, 80) were screened and HZSM-5 with Si/Al ratio as 25 showed best reactivity for indoles production due to the desired pore structure and acidity. Temperature displayed significant effect on the product distribution. The maximum yield of indoles was obtained at moderate temperatures around 500 °C. The weight hourly space velocity (WHSV) of furan to catalyst investigation indicated that a lower WHSV could cause the overreaction of furan over the catalyst to produce more aniline and pyridines, while a higher WHSV would cause the incomplete reaction of furan. Because ammonia served as both reactant and carrier gas, to supply sufficient reactant and keep desired reaction time, appropriate ammonia to furan molar ratio was important on furan conversion to indoles. Under the optimized conditions, the highest total carbon yield of indoles and their selectivity in the N-containing chemicals were 32% and 75%, respectively. 2-Methylfuran and the mixture of furan and 2-methylfuran were also studied, which demonstrated that more alkyl indoles could be selectively obtained via coupling reaction of different bio-derived furans. Based on the overall calculations and experiments, from furan to indole, ring-opening is the more favorable mechanism compared to the Diels-alder mechanism, and the pyrrole + furan pathway is more favorable compared to the pyrrole + pyrrole pathway. Furthermore, furfural was also used to produce indoles via thermo-catalytic conversion over zeolites. The maximal carbon yield of indoles (20.79%) was achieved by using HZSM-5 (Si/Al=25) catalyst at 650 °C with WHSV as 1.0 h-1 and NH3 to furfural molar ratio as 2. A possible reaction pathway from furfural to indoles was proposed based on the experimental and quantum calculation results, that is, furfural firstly reacted with ammonia to form furfural-imine, and then furfural-imine underwent a cracking reaction to form furan. Thereafter, furan was converted to pyrrole and finally to indoles.

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