Green gasoline by catalytic fast pyrolysis of solid biomass derived compounds.

Owing to its low cost and large availability, lignocellulosic biomass is being studied worldwide as a feedstock for renewable liquid biofuels. Lignocellulosic biomass is not currently used as a liquid fuel because economical processes for its conversion have not yet been developed. Currently, there are several routes being studied to convert solid biomass into a liquid fuel which involve multiple steps thus greatly increasing the cost of biomass conversion. For example, ethanol production from lignocellulosic biomass involves multiple steps including pretreatment, enzymatic or acid hydrolysis, fermentation, and distillation. Dumesic and co-workers have demonstrated that diesel-range alkanes can be produced by aqueous-phase processing (APP) of aqueous carbohydrate solutions at low temperatures (100-300 8C). APP first requires that solid lignocellulosic biomass be converted into aqueous carbohydrates, which would require pretreatment and hydrolysis steps. At high temperatures (~800 8C), Dauenhauer et al. have shown that solid biomass can be reformed to produce synthesis gas through partial oxidation in an autothermal packed bed reactor over Rh catalysts. The ideal process for solid biomass conversion involves the production of liquid fuels from solid biomass in a single step at short residence times. Herein, we report that gasoline-range aromatics can be produced from solid biomass feedstocks in a single reactor at short residence times (less than 2 min) and intermediate temperatures (400–600 8C) by a method we call catalytic fast pyrolysis. Fast pyrolysis involves rapidly heating biomass (500 8Cs ) to intermediate temperatures (400–600 8C) followed by rapid cooling (vapor residence times 1–2 s). Fast pyrolysis produces a thermally unstable liquid product called bio-oil, which is an acidic combustible liquid containing more than 300 compounds. Bio-oils are not compatible with existing liquid transportation fuels including gasoline and diesel. To use bio-oil as a conventional liquid transportation fuel, it must be catalytically upgraded. As we show here, introduction of zeolite catalysts into the pyrolysis process can convert oxygenated compounds generated by pyrolysis of the biomass into gasolinerange aromatics. Catalytic fast pyrolysis first involves pyrolysis of solid biomass (e.g. cellulose) into volatile organics, gases, and solid coke. The organics then enter the zeolite catalyst where they are converted into aromatics, carbon monoxide, carbon dioxide, water, and coke. Inside the zeolite catalyst, the biomassderived species undergo a series of dehydration, decarbonylation, decarboxylation, isomerization, oligomerization, and dehydrogenation reactions that lead to aromatics, CO, CO2, and water. The challenge with selectively producing aromatics is to minimize the undesired formation of coke, which can be from homogeneous gas-phase thermal decomposition reactions or from heterogeneous reactions on the catalyst. The overall stoichiometry for the conversion of xylitol and glucose into toluene, CO, and H2O is shown in Equation (1) (76 and 24% carbon yields) and Equation (2) (63 and 36% carbon yields), respectively. Oxygen must be removed from the biomass-derived species as a combination of CO (or CO2) and H2O when aromatics are produced. The maximum theoretical yield of toluene from xylitol and glucose is 76 and 63%, respectively, when CO and H2O are produced as by-products.