Catalytic Conversion of Biomass-Derived Ethanol to Liquid Hydrocarbon Blendstock: Effect of Light Gas Recirculation

We describe a light gas recirculation (LGR) method to increase the liquid hydrocarbon yield with a reduced aromatic content from catalytic conversion of ethanol to hydrocarbons. The previous liquid hydrocarbon yield is ∼40% from one-pass ethanol conversion over the V-ZSM-5 catalyst at 350°C and atmospheric pressure, where the remaining ∼60% yield is light gas hydrocarbons. In comparison, the liquid hydrocarbon yield increases to 80% when a simulated light gas hydrocarbon stream is co-fed at a rate of 0.053 mol g^-1 h^-1 with ethanol as a result of the conversion of most of the light olefins. The LGR also significantly improves the quality of the liquid hydrocarbon blendstock by reducing the aromatic content and overall benzene concentration. For 0.027 mol g^-1 h^-1 light gas mixture co-feeding, the average aromatic content in liquid hydrocarbons is 51.5% compared to 62.5% aromatic content in the ethanol only experiment. The average benzene concentration decreases from 3.75 to 1.5%, which is highly desirable because the United States Environmental Protection Agency (U.S. EPA) limits the benzene concentration in gasoline to 0.62%. As a result of a low benzene concentration, the blend wall for ethanol-derived liquid hydrocarbons changes from ∼18 to 43%. The remaining light paraffins and olefins can be further converted to valuable benzene, toluene, and xylenes (BTX) products (94% BTX in the liquid) over Ga-ZSM-5 at 500°C. Thus, the LGR is an effective approach to convert ethanol to liquid hydrocarbons with a higher liquid yield and low aromatic content, especially a low benzene concentration, which could be blended with gasoline in a much higher ratio than ethanol or ethanol-derived hydrocarbon blendstock.