Torren R. Carlson

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.

Production of green aromatics and olefins by catalytic fast pyrolysis of wood sawdust

Catalytic fast pyrolysis of pine wood sawdust and furan (a model biomass compound) with ZSM-5 based catalysts was studied with three different reactors: a bench scale bubbling fluidized bed reactor, a fixed bed reactor and a semi-batch pyroprobe reactor. The highest aromatic yield from sawdust of 14% carbon in the fluidized bed reactor was obtained at low biomass weight hourly space velocities (less than 0.5 h−1) and high temperature (600 °C). Olefins (primarily ethylene and propylene) were also produced with a carbon yield of 5.4% carbon. The biomass weight hourly space velocity and the reactor temperature can be used to control both aromatic yield and selectivity. At low biomass WHSV the more valuable monocyclic aromatics are produced and the formation of less valuable polycyclic aromatics is inhibited. Lowering the reaction temperature also results in more valuable monocyclic aromatics. The olefins produced during the reaction can be recycled to the reactor to produce additional aromatics. Propylene is more reactive than ethylene. Co-feeding propylene to the reactor results in a higher aromatic yield in both continuous reactors and higher conversion of the intermediate furan in the fixed bed reactor. When olefins are recycled aromatic yields from wood of 20% carbon can be obtained. After ten reaction–regeneration cycles there were metal impurities deposited on the catalyst, however, the acid sites on the zeolite are not affected. Of the three reactors tested the batch pyroprobe reactor yielded the most aromatics, however, the aromatic product is largely naphthalene. The continuous reactors produce less naphthalene and the sum of aromatics plus olefin products is higher than the pyroprobe reactor.

Catalytic fast pyrolysis of wood and alcohol mixtures in a fluidized bed reactor

Catalytic fast pyrolysis (CFP) of pine wood, alcohols (methanol, 1-propanol, 1-butanol and 2-butanol) and their mixtures with ZSM-5 catalyst were conducted in a bubbling fluidized bed reactor. The effects of temperature and weight hourly space velocity (WHSV) on the product carbon yields and selectivities of CFP of pure pine wood and methanol were investigated. A maximum carbon yield of petrochemicals (aromatics + C2–C4olefins + C5 compounds) from pine wood of 23.7% was obtained at a temperature of 600 °C and WHSV of 0.35 h−1. A maximum petrochemical yield from methanol of 80.7% was obtained at a temperature of 400 °C and WHSV of 0.35 h−1. Thus, the optimal conditions for conversion of pine wood and methanol are different. The CFP of pine wood and methanol mixtures was conducted at 450 °C and 500 °C. The hydrogen to carbon effective (H/Ceff) ratio of the feed was adjusted by changing the relative amount of methanol and wood. The petrochemical yield was a function of the H/Ceff ratio and more petrochemicals are produced from biomass when methanol is added to the CFP process. Co-feeding of 12C pine wood and 13C methanol was carried out at 450 °C. The isotopic study showed that all the hydrocarbon products contained mixtures of 12C and 13C, indicating that the carbon is mixed within the zeolite. However, the distribution of carbon was skewed depending on the product. The toluene, xylene, propylene and butenes contained more 13C. The naphthalene and ethylene contain more 12C. Wood was also co-processed with 1-propanol, 1-butanol, and 2-butanol, which showed a similar effect as methanol with an increasing petrochemical yield with an increasing H/Ceff ratio of the feed. This paper demonstrates that CFP can selectively produce a mixture of compounds where the overall yield is a function of the H/Ceff ratio of the feed.

Depolymerization of lignocellulosic biomass to fuel precursors: maximizing carbon efficiency by combining hydrolysis with pyrolysis

In this paper we study the carbon efficiency of combining hydrolysis and pyrolysis processes using maple wood as a feedstock. A two-step hydrolysis of maple wood in batch reactors, that consisted of a thermochemical pretreatment in water followed by enzymatic hydrolysis, achieved an 88.7 wt% yield of glucose and an 85 wt% yield of xylose as liquid streams. The residue obtained was 80 wt% lignin. A combination of TGA and pyroprobe studies was used for the pyrolysis of pure maple wood, hemicellulose-extracted maple wood, and the lignin residue from the hydrolysis of maple wood. Pyrolysis of raw maple wood produced 67 wt% of condensable liquid products (or bio-oils) that were a mixture of compounds including sugars, water, phenolics, aldehydes, and acids. Pyrolysis of hemicellulose-extracted maple wood (the solid product after pretreatment of maple wood) showed similar bio-oil yields and compositions to raw maple wood while pyrolysis of the lignin residue (the final solid product of enzymatic hydrolysis) produced only 44.8 wt% of bio-oil. The bio-oil from the lignin residue is mostly composed of phenolics such as guaiacol and syringol compounds. Catalytic fast pyrolysis (CFP) of maple wood, hemicellulose-extracted maple wood, and lignin residue produced 18.8, 16.6 and 10.1 wt% aromatic products, respectively. Three possible options for the integration of hydrolysis with pyrolysis processes were evaluated based on their material and carbon balances: Option 1 was the pyrolysis/CFP of raw maple wood, option 2 combined hemicellulose extraction by hydrolysis with pyrolysis/CFP of hemicellulose-extracted maple wood, and option 3 combined the two-step hydrolysis of hemicellulose and cellulose sugar extraction with pyrolysis/CFP of the lignin residue. It was found that options 1, 2, and 3 all have similar overall carbon yields for sugars and bio-oils of between 66 and 67%.

Mechanistic Insights from Isotopic Studies of Glucose Conversion to Aromatics Over ZSM‐5

Due to its low cost and large availability, lignocellulosic biomass is being studied worldwide as a feedstock for renewable liquid biofuels. There are currently several routes being studied to convert solid biomass to a liquid fuel, which involve multiple steps, thus greatly increasing the cost of biomass conversion. We have recently shown that aromatics can be directly produced from solid biomass in a single step by catalytic fast pyrolysis (CFP) with ZSM-5 catalysts. The advantages of this approach are that aromatics can be directly produced from biomass in a single low-cost step with inexpensive zeolite-based catalysts. The desired reactions all occur inside the zeolite catalyst. Other researchers have used zeolite catalysts for conversion of biomass-derived feedstocks into aromatics, including the early work in the 1980 s by Chen et al. and Dao et al. on the conversion of aqueous sugar solutions and more recently pyrolysis oils and lignocellulosic feedstocks. The main challenge when using zeolite catalysts is controlling the complicated chemistry that occurs inside the catalyst pores. The objective of this study is to elucidate the reaction mechanism for conversion of biomass-derived oxygenates inside zeolite catalysts by performing isotopic studies. These findings give us insight into how we might control zeolite chemistry for the conversion of biomass into aromatics. Glucose is used as a model compound for cellulosic biomass in this study. We have previously shown that both glucose and cellulose yield similar product distributions when pyrolized in the presence of ZSM-5 catalyst. These previous findings suggest that both cellulose and glucose decompose to common intermediates. Therefore the mechanistic conclusions from this paper can be extended to more complicated cellulosic-type feedstocks. Catalytic pyrolysis of C and C glucose in the presence of ZSM-5 catalyst was conducted using a pyroprobe model 2000 analytical pyrolyzer. Products from the pyroprobe were sent directly to a GC/MS system via a helium carrier gas stream. In the first set of experiments, a 1:1 w/w mixture of pure C and C glucose was pyrolyzed at two different catalyst/feed ratios (2.3:1 and 19:1). In a second set of experiments a 1:1 w/w mixture of C benzene and C glucose was pyrolyzed to determine the role of single-ring aromatics in the formation of polycyclic aromatics. In the last set of experiments, a 1:1 w/w mixture of C naphthalene and C glucose was pyrolyzed to determine whether naphthalene is susceptible to alkylation reactions. Our experimental results indicate that three main reaction pathways dominate the formation of aromatics during the catalytic pyrolysis of glucose. The first step in catalytic pyrolysis is the homogenous thermal decomposition of glucose into volatile compounds like anhydrosugars (Scheme 1 a). These anhydrosugars then undergo dehydration, bond cleavage, and rear-