Worldwide energy consumption has never been higher than it is today, due to society's way of living and an increasing human population (United Nations Department of Economic and Social Affairs, 2010, http://www.un.org/esa/population/) and (U.S. Energy Information Administration Independent Statistics and Analysis, 2010, http://www.eia.doe.gov/). The transportation sector accounts for about one fifth of the total energy consumption (B. van Ruijven et al., Energy Policy, 37: 4797 4808 (2009)). Thus, as the world's population grows and means of transportation become more readily available, it is unavoidable that the need for fuels will only increase in the future (M. Balat, Energy Conyers. Manage., 52: 858-875 (2011)). This increasing fuel need constitutes one of the major challenges of the near future, as present fuels are primarily produced from crude oil and these reserves are depleting (S. Sorrell, et al., Energ. Policy, 38: 5290-5295 (2010)).
Substantial research within the energy field is being performed in order to find alternative fuels to replace gasoline and diesel. The optimal solution would be an alternative fuel that is equivalent to the conventional fuels, i.e. compatible with the infrastructure, but also a fuel that is sustainable and will decrease CO2 emissions, thereby decreasing man's environmental footprint (R. Pachauri, A. Reisinger (Eds.), Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Technical Report. IPCC (2007)).
Biomass derived fuels could be the prospective fuel of tomorrow as they can be produced within a relatively short cycle and are considered benign for the environment (M. Balat, Energy Conyers. Manage., 52: 858-875 (2011); A. Roedl, Int. J. Life Cycle Assess., 15: 567-578 (2010)).
Bio-oil, in particular, is increasingly being recognized as an important feedstock (Lappas et al., “Production of Biofuels via Co-processing in Conventional Refining Processes,” Catalysis Today, 145:55-62 (2009); Bridgwater, “Review of Fast Pyrolysis of Biomass and Product Upgrading,” Biomass and Bioenergy, 38:68-94 (2012)) for thermochemical-based biorefinery applications for transportation fuels, energy and chemicals (Vitasari et al., “Water Extraction of Pyrolysis Oil: The First Step for the Recovery of Renewable Chemicals,” Biores. Technol. 102(14):7204-7210 (2011)) even though bio-oil exhibits negative characteristics.
Bio-oil contains 42-48 wt % oxygen (Oasmaa et al., “Fast Pyrolysis Bio-Oils from Wood and Agricultural Residues,” Energy & Fuels 24:1380-1388 (2009); Mohan et al., “Pyrolysis of Wood/Biomass for Bio-Oil: A Critical Review,” Energy & Fuels, 20:848-889 (2006)), which must be reduced by catalytic upgrading before co-feeding in a refinery unit to produce transportation fuels (Lappas et al., “Production of Biofuels via Co-processing in Conventional Refining Processes,” Catalysis Today, 145:55-62 (2009)). Several other problems to direct upgrading of bio-oil includes high water content (15-30%), limited stability, and high acidity (Lappas et al., “Production of Biofuels via Co-processing in Conventional Refining Processes,” Catalysis Today, 145:55-62 (2009); Oasmaa et al., “Fuel Oil Quality of Biomass Pyrolysis Oils—State of the Art for the End User,” Energy & Fuels, 13:914-921 (1999); Chiaramonti et al., “Power Generation using Fast Pyrolysis Liquids from Biomass,” Renew. Sust. Energy Rev. 11:1056-1086 (2007)).
Bio-oil, the liquid product of fast pyrolysis (i.e., thermal deconstruction) of biomass, superficially resembles petroleum. Both are dark, viscous liquids consisting of hundreds of organic compounds. The superficial similarities between petroleum and bio-oil have encouraged efforts to employ petroleum hydroprocessing in the upgrading of bio-oil, which has had limited success.
Bio-oil is an emulsion of predominantly lignin-derived phenolic oligomers in an aqueous phase containing primarily carbohydrate-derived compounds (D. Mohan, et al., Energy & Fuels, 20: 848-889 (2006)). Bio-oil has several characteristics that make it undesirable as fuel3, 4 such as poor storage stability (A. V. Bridgwater, Biomass and Bioenergy, 38: 68-94 (2012); L. Busetto, et al., Fuel, 90: 1197-1207 (2011); high acidity and corrosivity (L. Busetto, et al., Fuel, 90: 1197-1207 (2011); T. N. Pham, et al., Applied Catalysis B: Environmental, 145: 10-23 (2014); P. M. Mortensen, et al., Applied Catalysis A: General, 407: 1-19 (2011); F. d. M. Mercader, et al., Fuel, 89: 2829-2837 (2010)); low heating value, high viscosity, incomplete volatility (L. Busetto, et al., Fuel, 90: 1197-1207 (2011); S. Czernik and A. V. Bridgwater, Energy & Fuels, 18: 590-598 2004)); and immiscibility with petroleum fuels (D. Mohan, et al., Energy & Fuels, 20: 848-889 (2006); F. d. M. Mercader, et al, Fuel, 89: 2829-2837 (2010)).
For bio-oil to be upgraded into transportation fuels, both deoxygenation and saturation of bio-oil is required. However, attempts to use hydroprocessing at the severe conditions typical in petroleum refining leads to coke formation and poor yields of organic liquids. Petroleum consists of non-polar hydrocarbons that are relatively stable, requiring elevated temperatures and pressures (400-800° C. and 68-138 bar) (OSHA, ed. U. S. D. o. Labor, Washington, D.C., 2013) to encourage chemical transformations, whereas bio-oil consists of oxygenated organic compounds whose high degree of functionality makes them chemically reactive even at low temperatures and pressures. Attempts to catalytically upgrade bio-oil have been hampered by its poor thermal stability at elevated temperatures, leading to coke formation and rapid catalyst deactivation (15. J. Wildschut, et al., Applied Catalysis B: Environmental, 99: 298-306 (2010); X. Xu, et al., Chemosphere, 93: 652-660 (2013); X. Li, et al., Fuel, 116: 642-649 (2014); A. Ardiyanti, Ph.D., University of Groningen (2013); J. Wildschut, Ph.D., University of Groningen (2009)). Bio-oil is thermally unstable as a result of the high chemical reactivity of the various functional groups it contains, particularly carbonyl and vinyl groups.
A major problem with upgrading bio-oil is its poor thermal stability at elevated temperatures, leading to heavy tar and coke formation, which rapidly deactivates upgrading catalysts.11-17 (G. W. Huber, et al., Chemical Reviews, 106: 4044-4098 (2006); F. Huang, et al., Chemical Engineering & Technology, 33: 2082-2088 (2010); F. H. Mahfud, et al., Journal of Molecular Catalysis A: Chemical, 264: 227-236 (2007); J. Wildschut, et al., Industrial & Engineering Chemistry Research, 48: 10324-10334 (2009); J. Wildschut, et al., Applied Catalysis B: Environmental, 99: 298-306 (2010); X. Xu, et al., Chemosphere, 93: 652-660 (2013); X. Li, et al., Fuel, 116: 642-649 (2014)).
Studies have specifically implicated polymerization of phenolic compounds in bio-oil to form “asphalt-like” materials that dehydrate to coke and ultimately cause deactivation of the hydroprocessing catalyst (J. Wildschut, et al., Applied Catalysis B: Environmental, 99: 298-306 (2010); A. Ardiyanti, Ph.D., University of Groningen (2013)). Even when stored for long periods or heated in the absence of catalysts, bio-oil tends to polymerize (A. Ardiyanti, Ph.D., University of Groningen (2013)).
It is thought that the most important precursors to coke formation are the lignin-derived phenolic compounds (X. Li, et al., Fuel, 116: 642-649 (2014), which polymerize to heavy phenolic oligomers that dehydrate to coke18 and cause rapid catalyst deactivation (J. Wildschut, et al., Applied Catalysis B: Environmental, 99: 298-306 (2010); J. Wildschut, PhD, University of Groningen, (2009)). Unfortunately, these polymerization/condensation reactions are accelerated by the elevated temperatures typically employed in hydroprocessing (F. Huang, et al., Chemical Engineering & Technology, 33: 2082-2088 (2010) making conventional hydroprocessing of raw bio-oil counterproductive to achieving high carbon yields of fuel-range molecules.
Researchers have attempted to stabilize bio-oil at “milder” hydroprocessing conditions. For example, Baker and Elliott (E. G. Baker and D. C. Elliott, in Pyrolysis Oils from Biomass. Producing, Analyzing, and Upgrading, ed. A. C. Society, American Chemical Society, Washington D.C., 376: 228-240 (1988)) reduced hydroprocessing temperature and pressure to around 274° C. and 140 bar in the presence of cobalt and molybdenum (CoMo) catalyst. Although hydrogenation occurred with a conversion of 69 vol %, the loss of water and the saturation of carbon bonds increased the viscosity of the bio-oil (as measured at 60° C.) from 10 cP to 14,200 cP. Similarly, experiments with two-stage hydroprocessing in the temperature range of 150-450° C. and 207 bar using sulfided nickel molybdenum (NiMo) and CoMo catalysts also dramatically increased the viscosity of the bio-oil, yielding a “tar-like” product (E. G. Baker and D. C. Elliott, in Pyrolysis Oils from Biomass. Producing, Analyzing, and Upgrading, ed. A. C. Society, American Chemical Society, Washington D.C., 376: 228-240 (1988); L. Conti, et al., in Bio-Oil Production and Utilization, ed. A. V. B. a. E. N. Hogan, CPL Press, Newbury, UK, 198-205 (1996)). Likewise, although bio-oil stability improved after “mild” hydrotreating at 275° C. and 152 bar using a sulfided NiMo catalyst as measured by accelerated aging, but the viscosity of the upgraded bio-oil increased one thousand fold (L. Conti, et al., in Bio-Oil Production and Utilization, ed. A. V. B. a. E. N. Hogan, CPL Press, Newbury, UK, pp. 198-205 (1996); L. Conti, et al., in Developments in Thermal Biomass Conversion, eds. B. A. V. and D. G. B. Boocock, Blackie Academic and Professional, London, pp. 622-632 (1997); J. P. Diebold, ed. N. R. E. L. (NREL), Thermalchemie, Inc., Lakewood, pp. 1-38 (2000)).
More recently, Chaiwat et al. (W. Chaiwat, et al., Fuel, 112: 302-310 (2013)) performed a series of “mild hydroprocessing” studies on bio-oil (i.e., 250° C. and 56-62 bar pressure for 3.0 hours produced 7.8 wt % oil phase, 44.7 wt % water phase, and 20.2 wt % heavy compounds; 200° C. and 57-64 bar pressure for 3 hours produced 21.2 wt % oil phase, 43.3 wt % water phase, and 16.6 wt % heavy compounds). It was not clear whether the heavy compounds were suitable for hydrocracking to fuel range molecules. However, even if the heavy compounds were suitable, the yield of potentially upgradable compounds was clearly unacceptably low for commercial applications.
Additionally, a three-stage process for hydrotreating bio-oil was developed (S. B. Jones, et al., Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, Hydrotreating and Hydrocracking: A Design Case, Pacific Northwest National Laboratory, Richland (2009)). The first two stages, characterized as hydrotreating at 240° C., 170 bar and 370° C., 137 bar, respectively, were intended to partially deoxygenate and stabilize the bio-oil followed by more severe hydrocracking/hydrodeoxygenation at 425° C., 87 bar to produce fuel-range hydrocarbon molecules (S. B. Jones, et al., Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, Hydrotreating and Hydrocracking: A Design Case, Pacific Northwest National Laboratory, Richland (2009)). However, carbon yields under these conditions remained modest and rapid coking of catalysts remained a problem.
The present invention is directed to overcoming these and other deficiencies in the art.