George W. Huber

Renewable Chemical Commodity Feedstocks from Integrated Catalytic Processing of Pyrolysis Oils

A Little Help from Hydrogen Biomass may one day displace petroleum as the chemical industrys primary feedstock. Currently, though, the primary hurdle for incorporating plant-derived material into existing process feeds is the high proportion of oxygen in its molecular frameworks. Rapid heating of the biomass followed by high-temperature treatment with zeolite catalysts can yield tractable quantities of useful commodity compounds such as ethylene and benzene, but much of the carbon is wasted in the process—diverted either toward gaseous CO and CO2, or solid coke. Vispute et al. (p. 1222) show that an intermediate step, in which hydrogen is catalytically incorporated into the heated material prior to zeolite treatment, can substantially raise the yield of useful products by reducing susceptibility to coking. The addition of hydrogen helps boost the yield of useful commodity compounds from pyrolized biomass. Fast pyrolysis of lignocellulosic biomass produces a renewable liquid fuel called pyrolysis oil that is the cheapest liquid fuel produced from biomass today. Here we show that pyrolysis oils can be converted into industrial commodity chemical feedstocks using an integrated catalytic approach that combines hydroprocessing with zeolite catalysis. The hydroprocessing increases the intrinsic hydrogen content of the pyrolysis oil, producing polyols and alcohols. The zeolite catalyst then converts these hydrogenated products into light olefins and aromatic hydrocarbons in a yield as much as three times higher than that produced with the pure pyrolysis oil. The yield of aromatic hydrocarbons and light olefins from the biomass conversion over zeolite is proportional to the intrinsic amount of hydrogen added to the biomass feedstock during hydroprocessing. The total product yield can be adjusted depending on market values of the chemical feedstocks and the relative prices of the hydrogen and biomass.

Catalytic Transformation of Lignin for the Production of Chemicals and Fuels.

and Fuels Changzhi Li,† Xiaochen Zhao,† Aiqin Wang,† George W. Huber,†,‡ and Tao Zhang*,† †State Key Laborotary of Catalysis, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ‡Department of Chemical and Biological Engineering, University of WisconsinMadison, Madison, Wisconsin 53706, United States

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.

The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

Lignocellulosic biofuels have a tremendous potential to reduce problems caused by our dependence on fossil fuels. The current roadblock with biofuels is the lack of economical conversion technologies. Heterogeneous catalysis offers immense potential in helping to make lignocellulosic biofuels a commercial reality. In this article we discuss the central role of heterogeneous catalysis in biomass conversion. We review the science of catalysis and the different routes to make biofuels. During the last several decades multiple new spectroscopic, theoretical, and synthesis tools are available that allow us to study catalysis at a molecular level. These new tools will allow us to rapidly develop new catalytic processes for the production of cost-efficient lignocellulosic biofuels.

Aqueous-phase reforming of methanol and ethylene glycol over alumina-supported platinum catalysts

The rates of aqueous-phase reforming of methanol and ethylene glycol to form H2 and CO2 were measured under kinetically controlled reaction conditions at temperatures of 483 and 498 K over alumina-supported platinum catalysts. Results show that the rates of formation of H2 from aqueous solutions of methanol (from 1 to 10 wt%) are similar to the rates of conversion of ethylene glycol, suggesting that CC bond cleavage is not rate limiting for ethylene glycol reforming. Aqueous-phase reforming of both oxygenated hydrocarbons over Pt/Al2O3 leads to nearly 100% selectivity for the formation of H2 (compared to the formation of alkanes), suggesting that methanation or Fischer–Tropsch reactions involving CO/CO2 and H2 do not appear to be important over platinum-based catalysts under the conditions of the present study. The rate of production of hydrogen is higher order in methanol (0.8) compared to ethylene glycol (0.3–0.5), and the reaction is weakly inhibited by hydrogen (−0.5 order) for both feedstocks. The rates of aqueous-phase reforming of methanol and ethylene glycol show apparent activation barriers of 140 and 100 kJ/mol, respectively, from 483 K and 22.4 bar total pressure to 498 K and 29.3 bar total pressure. Low levels of CO (<300 ppm) are detected in the gaseous effluents from aqueous-phase reforming of methanol and ethylene glycol over alumina-supported Pt catalysts, suggesting that water–gas shift processes are operative under the aqueous-phase reforming conditions of this study. The observed reaction kinetics for ethylene glycol of this study can be explained by a reaction scheme involving quasi-equilibrated adsorption of ethylene glycol, water, H2, and CO2, combined with irreversible steps involving dehydrogenation of adsorbed ethylene glycol to form adsorbed C2O2 species, cleavage of the CC bond to form adsorbed CO species, further dehydrogenation leading to adsorbed CO∗, and removal of adsorbed CO∗ by water-gas shift. Aqueous-phase reforming of methanol may take place by a similar reaction scheme, without the step involving cleavage of the CC bond. The nearly first-order reaction kinetics with respect to methanol can be explained by weaker adsorption of methanol compared to molecular adsorption of ethylene glycol.

Aqueous-Phase Reforming of Ethylene Glycol Over Supported Platinum Catalysts

Aqueous-phase reforming of 10 wt% ethylene glycol solutions was studied at temperatures of 483 and 498 K over Pt-black and Pt supported on TiO2, Al2O3, carbon, SiO2, SiO2-Al2O3, ZrO2, CeO2, and ZnO. High activity for the production of H2 by aqueous-phase reforming was observed over Pt-black and over Pt supported on TiO2, carbon, and Al2O3 (i.e., turnover frequencies near 8-15 min-1 at 498 K); moderate catalytic activity for the production of hydrogen is demonstrated by Pt supported on SiO2-Al2O3 and ZrO2 (turnover frequencies near 5 min-1); and lower catalytic activity is exhibited by Pt supported on CeO2, ZnO, and SiO2 (H2 turnover frequencies lower than about 2 min-1). Pt supported on Al2O3, and to a lesser extent ZrO2, exhibits high selectivity for production of H2 and CO2 from aqueous-phase reforming of ethylene glycol. In contrast, Pt supported on carbon, TiO2, SiO2-Al2O3 and Pt-black produce measurable amounts of gaseous alkanes and liquid-phase compounds that would lead to alkanes at higher conversions (e.g., ethanol, acetic acid, acetaldehyde). The total rate of formation of these byproducts is about 1-3 min-1 at 498 K. An important bifunctional route for the formation of liquid-phase alkane-precursor compounds over less selective catalysts involves dehydration reactions on the catalyst support (or in the aqueous reforming solution) followed by hydrogenation reactions on Pt.

Catalytic conversion of biomass-derived feedstocks into olefins and aromatics with ZSM-5: the hydrogen to carbon effective ratio

Catalytic conversion of ten biomass-derived feedstocks, i.e.glucose, sorbitol, glycerol, tetrahydrofuran, methanol and different hydrogenated bio-oil fractions, with different hydrogen to carbon effective (H/Ceff) ratios was conducted in a gas-phase flow fixed-bed reactor with a ZSM-5 catalyst. The aromatic + olefin yield increases and the coke yield decreases with increasing H/Ceff ratio of the feed. There is an inflection point at a H/Ceff ratio = 1.2, where the aromatic + olefin yield does not increase as rapidly as it does prior to this point. The ratio of olefins to aromatics also increases with increasing H/Ceff ratio. CO and CO2 yields go through a maximum with increasing H/Ceff ratio. The deactivation rate of the catalyst decreases significantly with increasing H/Ceff ratio. Coke was formed from both homogeneous and heterogeneous reactions. Thermogravimetric analysis (TGA) for the ten feedstocks showed that the formation of coke from homogeneous reactions decreases with increasing H/Ceff ratio. Feedstocks with a H/Ceff ratio less than 0.15 produce large amounts of undesired coke (more than 12 wt%) from homogeneous decomposition reactions. This paper shows that the conversion of biomass-derived feedstocks into aromatics and olefins using zeolite catalysts can be explained by the H/Ceff ratio of the feed.

Kinetics of furfural production by dehydration of xylose in a biphasic reactor with microwave heating

In this paper we report a kinetic model for the dehydration of xylose to furfural in a biphasic batch reactor with microwave heating. There are four key steps in our kinetic model: (1) xylose dehydration to form furfural; (2) furfural reaction to form degradation products; (3) furfural reaction with xylose to form degradation products, and (4) mass transfer of furfural from the aqueous phase into the organic phase (methyl isobutyl ketone - MIBK). This kinetic model was used to fit experimental data collected in this study. The apparent activation energy for xylose dehydration is higher than the apparent activation energy for the degradation reactions. The biphasic system does not alter the fundamental kinetics in the aqueous phase. The organic layer, which serves as “storage” for the extracted furfural, is crucial to maximize product yield. Microwave heating does not change the kinetics compared to heating by conventional means. We use our model to describe the optimal reaction conditions for furfural production. These conditions occur in a biphasic regime at higher temperatures (i.e. 170 °C) and short reaction times. We estimate that at these conditions furfural yields in a biphasic system can reach 85%. At these same conditions in a monophase system furfural yields are only 30%.

Production of jet and diesel fuel range alkanes from waste hemicellulose-derived aqueous solutions

In this paper we report a novel four-step process for the production of jet and diesel fuel range alkanes from hemicellulose extracts derived from northeastern hardwood trees. The extract is representative of a byproduct that could be produced by wood-processing industries such as biomass boilers or pulp mills in the northeastern U.S. The hemicellulose extract tested in this study contained mainly xylose oligomers (21.2 g/l xylose after the acid hydrolysis) as well as 0.31 g/l glucose, 0.91 g/l arabinose, 0.2 g/l lactic acid, 2.39 g/l acetic acid, 0.31 g/l formic acid, and other minor products. The first step in this process is an acid-catalyzed biphasic dehydration to produce furfural in yields up to 87%. The furfural is extracted from the aqueous solution into a tetrahydrofuran (THF) phase which is then fed into an aldol condensation step. The furfural-acetone-furfural (F-Ac-F) dimer is produced in this step by reaction of furfural with acetone in yields up to 96% for the F-Ac-F dimer. The F-Ac-F dimer is then subject to a low-temperature hydrogenation to form the hydrogenated dimer (H-FAF) at 110–130 °C and 800 psig with a 5 wt% Ru/C catalyst. Finally the H-FAF undergoes hydrodeoxygenation to make jet and diesel fuel range alkanes, primarily C13 and C12, in yields up to 91%. The theoretical yield for this process is 0.61 kg of alkane per kg of dry xylose derived from the hemicellulose extract. Experimentally we were able to obtain 76% of the theoretical yield for the overall process. We estimate that jet and diesel fuel range alkanes can be produced from between