Environmental and political problems created by our dependence on fossil fuels combined with diminishing petroleum resources are forcing society to search for renewable sources of energy. Plant biomass is the only current sustainable source of organic carbon, and biofuels, fuels derived from plant biomass, are the only renewable source of liquid fuels. Currently solid lignocellulosic biomass resources are significantly cheaper than petroleum (at $15 per barrel of oil energy equivalent) and abundant (have the energy content of 60 % of our domestic crude oil consumption). While biofuels have a tremendous potential to alleviate problems caused by fossil fuels, the major impediment to utilization of our lignocellulosic biomass resources is the lack of economical processes for conversion of biomass resources into fuels. The goal of the Huber research group is to develop the clean technology that will allow us to economically use our biomass and other sustainable resources for the production of cheap renewable gasoline, diesel fuel, jet fuel, and chemicals.
Whereas the petroleum industry has made continuous progress over the last 100 years by studying and improving petroleum chemistry, biorefining is only in its infancy. Biomass-feedstocks are significantly different than petroleum feedstocks because of their high oxygen content leading to low thermal stability and a high degree of functionality. The major scientific challenge is how to efficiently and selectively remove oxygen from biomass-derived molecules and to functionalize this feedstock into the targeted molecules that are compatible with petroleum based liquid fuels. Heterogeneous catalysis and chemical engineering hold the key that will allow the efficient conversion of biomass-derived molecules to fuels. Understanding and controlling this chemistry allows the efficient utilization of our vast domestic biomass-resources.
The Huber research group is developing new generations of catalysts, reactors, spectroscopic and imagining tools, and computational models that are essential for understanding and controlling the chemical transformation of biomass-derived oxygenates to fuels. The main research thrusts are the development of economical processes for the production of renewable gasoline, diesel fuel, jet fuel and petrochemicals. In this respect, we are developing clean catalytic technologies for the production of the full spectrum of products that are currently derived from petroleum-derived feedstocks, from renewable lignocellulosic biomass feedstocks. A number of these technologies are moving rapidly towards commercialization. Catalytic technologies developed by Professor Huber have been licensed by several companies that are focused on producing biofuels. George Huber is one of the most highly cited young scholars in the chemical sciences. In 2010 his research articles were cited 875 times according to Web of Science. One of his review papers  has received 470 citations and has been called the "bible of biofuels".
The Huber research group uses a wide range of chemical engineering tools to understand and optimize biomass conversion to fuels and chemicals, including: heterogeneous catalysis, kinetic modeling, reaction engineering, spectroscopy, analytical chemistry, nanotechnology, catalyst synthesis, conceptual process design, modeling of transport phenomena, and theoretical chemistry. These tools have been combined to develop a number of catalytic technologies for the production of clean fuels and chemicals that are discussed below in more detail.
1. Huber, G. W.; Iborra, S.; and Corma, A.; Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering, Chemical Reviews 106, 4044-4098 (2006).
Examples of Clean Catalytic Technologies being developed in the Huber Research Group
Catalytic Fast Pyrolysis
Catalytic fast pyrolysis (CFP™) is a technology for the direct conversion of solid biomass to gasoline-range aromatics and olefins that is being developed in the Huber research group [2-8]. CFP can produce aromatics and olefins from solid biomass including: wood, corn stover, bagasse, and energy crops. The aromatics can be used directly as petrochemicals or blended into gasoline as high octane components. Aromatics can be blended up to 25 wt% into gasoline. The olefins can be sold as petrochemicals. The annual global market for aromatics and olefins is $400 billion. Catalytic fast pyrolysis begins with pyrolysis of the solid biomass into anhydrosugars followed by dehydration to form furanic compounds as shown in Figure 1. These oxygenated species then enter the zeolite pores, undergoing a series of dehydration, decarbonylation and oligomerization reactions to form aromatics, olefins, CO, CO2 and water. Coke is formed from several routes including homogeneous decomposition reactions of the oxygenates and catalytic reactions inside the zeolite. Production of the desired aromatics is achieved by: (1) proper catalyst selection, (2) high heating rates to avoid unwanted thermal decomposition reactions, and (3) working at high catalyst to feed ratios.
Biofuels produced by pyrolysis technologies have been shown to have one-half to one-third the capital cost compared with biofuels produced from gasification or fermentation technologies. As the Huber research group has shown, addition of a catalyst into the pyrolysis reactor can be used to control the chemistry of the reactions that occur in pyrolysis process [2-8].
Some of the advantages of CFP compared to other technology include:
· Products with greater energy density (BTX ~ 1.5x ethanol)
· Products with higher market value (2009 BTX price ~ 1.5x ethanol)
· Products that have established markets and distribution infrastructure
· An efficient fluidized-bed reactor/regenerator system similar to a refinery cracker
· No process water consumption
· No process hydrogen requirement
· Low pressure operation with inexpensive catalysts
· All process heat requirements supplied from input biomass
· Well-established, easily scaled unit operations
· Short reactor residence times (4 s vapor residence time)
Figure 1 Proposed Reaction Scheme for Catalytic Fast Pyrolysis.
Key Publications from Huber Research Group on CFP:
2. Jungho Jae, Geoffrey A. Tompsett, Andrew J. Foster, Karl D. Hammond , Scott M. Auerbach, W. Curtis Conner, Raul F. Lobo, and George W. Huber, The Shape Selectivity of Zeolite Catalysts for Biomass Conversion, Journal of Catalysis (under review).
3. Jae, J.; Tompsett, G.A.; Lin, Y.C.; Carlson, T.R.; Shen, J.; Zhang, T.; Yang, B.; Taiying Wyman, C. E.; Conner, W. C.; and Huber, G.W.; Depolymerization of Lignocellulosic Biomass into Fuel Precursors: Maximizing Carbon Efficiency by Combining Hydrolysis with Pyrolysis; Energy and Environmental Science, (2010), 3, 358-365.
4. Torren R. Carlson, Yu-Ting Cheng, Jungho Jae and George W. Huber, Production of Green Aromatics and Olefins by Catalytic Fast Pyrolysis of Wood Sawdust, Energy and Environmental Science (in press) DOI: 10.1039/C0EE00341G.
5. Carlson, T. R.; Jae, J.; Lin, Y.C.; Tompsett, G. A. and Huber, G. W.; Catalytic Fast Pyrolysis of Glucose over ZSM-5, Journal of Catalysis (2010), 270(1), 110-124.
6. Carlson, T. R.; Jae, J.; and Huber, G. W.; Mechanistic Insights from Isotopic Studies of Glucose Conversion to Aromatics Over ZSM-5, ChemCatChem, 1, 107-110 (2009).
7. Carlson, T. R.; Tompsett, G. A.; Conner, W. C.; and Huber, G. W.; Aromatic Production from Catalytic Fast Pyrolysis of Biomass-derived Feedstocks, Topics in Catalysis 52, 241-252 (2009).
8. Carlson, T.R.; Vispute, T.P.; and Huber, G.W.; Green Gasoline by Catalytic Fast Pyrolysis of Solid Biomass-derived Compounds, ChemSusChem, 1, 397-400 (2008).
Pyrolysis-oil or bio-oil is the cheapest liquid fuel that can be made from lignocellulosic biomass. Several companies have demonstrated that bio-oils can economically be produced from wood on a commercial scale at costs less than $1.00 per gallon of gasoline energy equilvalent. However, the bio-oil is a very poor quality fuel that cannot be used in gasoline and diesel fuel engines for several reasons. Bio-oils have half the energy density compared to petroleum derived fuels due to their large oxygen content. Bio-oil is nearly insoluble with petroleum fuels. Bio-oils are acidic having a pH of around 2.5. Bio-oils also degrade with time. Bio-oils are a complex mixture of more than 300 different compounds. The Huber research group has demonstrated how the bio-oils can be used as a feedstock to make: petrochemicals , hydrogen  and alkanes . These papers have helped outline the key catalytic chemistry for bio-oil conversion and demonstrated that bio-oils are very valuable feedstocks to make liquid fuels.
The Huber group, in collaboration with Renewable Oil International, has helped design and operate a pilot plant reactor to make bio-oils as shown in Figure 2. We have developed analytical techniques to characterize the bio-oils and are in the process of developing reactor models for fast pyrolysis of bio-oils. These models will be used to scale up the existing reactors and help design improved pyrolysis reactors. They are based on the fundamental reactions that occur during the pyrolysis of solid biomass. We have recently identified the major reaction pathways cellulose pyrolysis and developed a simple intrinsic kinetic model for cellulose pyrolysis [11-12]. The speciation and kinetic data were in agreement with the literature, while the quantification of carbon-containing products was greatly improved. These studies provide an improved kinetic model of cellulose pyrolysis [11-12]. We are continuing to develop improved models for biomass pyrolysis as well as technology to upgrade the bio-oils into fuels and chemicals that can fit seamlessly into the existing infrastructure.
Figure 2 Pyrolysis oils and UMass pilot plant for production of pyrolysis oils.
Key papers published from Huber research group on bio-oil production and conversion:
9. Tushar P. Vispute, Huiyan Zhang, Aimaro Sanna, Rui Xiao, George W. Huber, Renewable Chemical Commodity Feedstocks from Integrated Catalytic Processing of Pyrolysis Oils, Science (2010) 330 1222-1227.
10. Vispute, T. P., Huber, G. W.; Production of hydrogen, alkanes and polyols by aqueous phase processing of wood-derived pyrolysis oils. Green Chemistry (2009), 11(9), 1433-1445.
11. Joungmo Cho, Jeffrey M. Davis, and George W. Huber; The Intrinsic Kinetics and Heats of Reactions for Cellulose Pyrolysis and Char Formation, ChemSusChem (2010) 3 1162-1165.
12. Lin, Y.C.; Cho, J.; Westmoreland, P.R.; and Huber, G.W.; Kinetics and Mechanism of Cellulose Pyrolysis, Journal of Physical Chemistry C (2009), 113(46), 20097-20107.
Gasoline Production by Aqueous Phase Hydrodeoxygenation
Biomass can be decomposed into aqueous carbohydrate solutions. A number of biomass species produce high levels of aqueous carbohydrates that are then fermented into ethanol. There are a number of challenge with fermentation of sugars included the high energy cost of distilling ethanol from water, they require sterile conditions, ethanol can only be blended with gasoline, and these processes have long residence times. Professor Huber has developed strategies for conversion of aqueous carbohydrate solutions by aqueous phase hydrodeoxygenation (APHDO) [13-17]. APHDO involves using solid heterogeneous catalysts to convert the aqueous carbohydrate solution into targeted gasoline range products or chemicals. APP can also be used to make hydrogen by Aqueous Phase Reforming (APR) [18-21]. We worked to develop the catalytic chemistry involved in hydrodeoxygenation of aqueous carbohydrate solutions. This reaction pathway involves three fundamental reactions :
(1) C-O bond cleavage by dehydration
(2) C-C bond cleavage by decarbonylation and retro-aldol condensation
We have been able to design improved catalysts that can produce gasoline in high yields (80 carbon %) from aqueous carbohdyrates by aqueous phase hydrodeoxygenation . We have also shown how this technology can be used to convert aqueous carbohydrate streams from maple wood .
Papers on Aqueous phase processing from Huber research group:
13. Ning Li, Geoffrey A. Tompsett, Taiyan Zhang, Jian Shi, Charlie E. Wyman, and George W. Huber; Green gasoline from aqueous phase hydrodeoxygenation of aqueous sugar solutions prepared by hydrolysis of maple wood, Green Chemistry (in press).
14. Ning Li; Geoffrey A. Tompsett; and George W. Huber; Renewable High Octane Gasoline by Aqueous Phase Hydrodeoxygenation of C5 and C6 Carbohydrates over Pt/Zirconium Phosphate Catalysts, ChemSusChem (2010) 3 1154-1157.
15. Hakan Olcay, Lijun Xu, Ye Xu, George W. Huber; Aqueous-phase hydrogenation of acetic acid over transition metal catalysts (cover story), ChemCatChem (2010) 2 1420-1424.
16. Lin, N.; and Huber, G. W.; Aqueous-phase hydrodeoxygenation of sorbitol: Identification of the reaction pathway, Journal of Catalysis (2010), 270(1), 48-59.
17. Huber, G.W.; Cortright, R.D.; and Dumesic, J.A.; Renewable Alkanes by Aqueous-Phase Reforming of Biomass Derived Oxygenates, Angewandte Chemie International Edition, 43, 1549-1551 (2004).
18. Davda, R. R.; Shabaker, J. W.; Huber, G. W.; and Dumesic, J. A.; A Review of Catalytic Issues and Process Conditions for Renewable Hydrogen and Alkanes by Aqueous-Phase Reforming of Oxygenated Hydrocarbons over Supported Metal Catalysts, Applied Catalysis B: Environmental (special issue on H2 Production), Applied Catalysis B: Environmental, 56, 171-186 (2005)
19. Huber, G. W.; Shabaker, J.W..; Evans, S.T.; and Dumesic, J. A.; Aqueous-phase reforming of ethylene glycol over supported Pt and Pd bimetallic catalysts, Applied Catalysis B: Environmental, 62, 226-235 (2006).
20. Shabaker, J. W.; Huber, G. W.; and Dumesic, J.A.; Aqueous-Phase Reforming of Oxygenated Hydrocarbons Over Sn-Modified Raney Ni Catalysts, Journal of Catalysis, 222, 180-191 (2004).
21. Huber, G. W.; Shabaker, J. W.; and Dumesic. J.A.; Raney Ni-Sn Catalyst for H2 from Biomass-Derived Hydrocarbons, Science, 300, 2075-2078 (2003).
Diesel and Jet Fuel Production by Aqueous Phase Processing
Professor Huber has also developed technologies to make diesel and jet fuel from aqueous carbohydrate solutions by APP [22-25]. Jet and Diesel fuel production involves an integrated four step approach. This approach has been used to convert waste hemicellulose streams derived from a paper mill into jet fuel . This approach requires the use of four different types of catalysts including: acid catalysts, base catalyst, metal catalyst and bifunctional metal/acid catalysts.
Key papers published from Huber research group on diesel and jet fuel production:
22. Rong Xing, Ayyagari.V. Subrahmanyam, Hakan Olcay, Wei Qi, G. Peter van Walsum, Hemant Pendse, and George W. Huber, Production of Diesel and Jet Fuel Range Alkanes from Waste Hemicellulose derived Solutions (cover story), Green Chemistry (2010) 12, 1933-1946.
23. R. Weingarten; J. Cho; Wm. Curtis Conner, Jr. and G. W. Huber; Kinetics of Furfural Production by Dehydration of Xylose in a Biphasic Reactor with Microwave Heating; Green Chemistry (2010) 12, 1423-1429.
24. Ayyagari V. Subrahmanyam; S. Thayumanavan; and George W. Huber; C-C Bond Formation Reactions for Biomass Derived molecules, ChemSusChem (2010) 3 1158-1161.
25. Huber, G. W.; Chheda, J.; Barrett, C. B.; and Dumesic, J. A.; Production of Liquid Alkanes by Aqueous-Phase Processing of Biomass-Derived Carbohydrates, Science, 308, 1446-2079 (2005)