Ethanol is an attractive biomass-derived feedstock for the production of fuels and products since it is already produced at commercial scale from renewable biomass and waste sources. A flexible catalytic process was developed for the single-step conversion of ethanol to either n-butene-rich olefins or butadiene over Ag/ZrO2/SiO2 catalysts. N-Butene-rich olefins are valuable fuel precursors whereas butadiene is a highly desired conjugated diene used essentially in the production of tires. For this process, the operating conditions (ethanol + N2 vs. ethanol + H2) were found to dictate the product composition. When operating under an inert N2 atmosphere ethanol is converted to butadiene with a high yield of 70%. While operating under reducing H2 environment leads mainly to the formation of n-butene-rich olefins with yields reaching ~85%. DFT calculations have indicated that n-butene formation is energetically favored in the presence of H2. XPS measurements conducted under reaction conditions have indicated that the products composition depends of the oxidation state of Ag. Butadiene formation is favored in the presence of oxidized Ag2O whereas n-butene-rich olefins are produced with metallic Ag. Catalyst lifetime studies have also indicated a major effect of the environment (N2. vs H2) on the catalyst stability. Under inert environment, the catalyst deactivates due to coking and the conversion decreases from ~ 92% after 6 hours on stream to ~ 46% after 98 hours on stream. However, after oxidative treatment the activity is completely recovered. Under reducing environment the conversion is stable at ~80% for over 80 hours. However, changes in products selectivity and olefins/butadiene ratio occur with time on stream likely due to changes in the oxidation state of Ag with time. Overall, the Ag/ZrO2/SiO2 catalyst shows promise to be part of a marketable process for both butadiene and butenes-rich olefins production due to high selectivity to desired products, good stability in reducing environment, and relative low deactivation under inert atmosphere compared to the state-of-the-art, and catalyst regenerability.

Single step conversion of ethanol to butadiene and butenes over Ag/ZrO2/SiO2 catalysts

2019 Spring National Meeting

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