Energy & Fuels 2006, 20, 1727-1737
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Biorefineries: Current Status, Challenges, and Future Direction Sandun Fernando,* Sushil Adhikari, Chauda Chandrapal, and Naveen Murali Department of Agricultural and Biological Engineering, Mississippi State UniVersity, Mississippi State, Mississippi 39762 ReceiVed March 2, 2006. ReVised Manuscript ReceiVed May 16, 2006
Conventional resources mainly fossil fuels are becoming limited because of the rapid increase in energy demand. This imbalance in energy demand and supply has placed immense pressure not only on consumer prices but also on the environment, prompting mankind to look for sustainable energy resources. Biomass is one such environmentally friendly renewable resource from which various useful chemicals and fuels can be produced. A system similar to a petroleum refinery is required to produce fuels and useful chemicals from biomass and is known as a biorefinery. Biorefineries have been categorized in three phases based on the flexibility of input, processing capabilities, and product generation. Phase I has less or no flexibility in any of the three aforementioned categories. Phase II, while having fixed input and processing capabilities, allows flexibility in product generation. Phase III allows flexibility in all the three processes and is based on the concept of high-value low-volume (HVLV) and low-value high-volume (LVHV) outputs. This paper reviews the concept of biorefinery, its types, future directions, and associated technical challenges. An approach of streamlining biorefineries with conventional refineries in producing conventional fuels is also presented. Furthermore, twelve platform chemicals that could be major outputs from an integrated biorefinery are also discussed.
1. Introduction Currently, the energy requirements of the world are largely met by fossil fuels. The limited deposits of these fossil fuels coupled with environmental problems, such as greenhouse gases, have prompted mankind to look for sustainable resources as alternatives to meet the increasing energy demand. Biomass is one of the few resources that has the potential to meet the challenges of sustainable and green energy systems. “Biomass is a plant matter of recent (nongeologic) origin or material derived there from and could be used to produce various useful chemicals and fuels”.1 A system similar to a petroleum refinery called a “biorefinery” has been proposed to produce useful chemicals and fuels from biomass. According to National Renewable Energy Laboratory (NREL), “a biorefinery is a facility that integrates conversion processes and equipments to produce fuels, power, and chemicals from biomass”.2 To achieve the goals of sustainable development, biorefineries have to play a dominant role in the coming millennia. An effort has been made in this paper to review the biorefinerys’ development to date and its future directions. 2. The Biorefinery Concept The concept of producing products from agricultural commodities (i.e., biomass) is not new. However, using biomass as an input to produce multiple products using complex processing methods, an approach similar to a petroleum refinery where * To whom correspondence should be addressed. Phone: +1 662 325 3282. Fax: +1 662 325 3853. E-mail:
[email protected]. (1) Lynd, L. R.; Jin, H.; Michels, J. G.; Wyman, C. E.; Dale, B. Bioenergy: background, potential, and policy. Available from http:// rmtools.org/ref/Lynd_et_al_2002.pdf (June 24, 2005). (2) National Renewable Energy Laboratory. Conceptual biorefinery. Available from http://www.nrel.gov/biomass/biorefinery.html (August 1, 2005).
Figure 1. Simple three-step biomass-process-products procedure.4
fossil fuels are used as input, is relatively new. Biomass consists of carbohydrates, lignin, proteins, fats, and to a lesser extent, various other chemicals, such as vitamins, dyes, and flavors.3 The goal of a biorefinery is to transform such plentiful biological materials into useful products using a combination of technologies and processes. Figure 1 describes the elements of a biorefinery in which biomass feedstocks are used to produce various useful products such as fuel, power, and chemicals using biological and chemical conversion processes. The main goal of a biorefinery is to produce high-value lowvolume (HVLV) and low-value high-volume (LVHV) products using a series of unit operations. The operations are designed to maximize the valued extractibles while minimizing the waste streams by converting LVHV intermediates into energy. The high-value products enhance the profitability, while the highvolume fuels help to meet the global energy demand. The power produced from a biorefinery also helps to reduce the overall (3) Askew, M. The biorefinery concept. Available from http://europa.eu.int/comm/research/energy/pdf/renews3.pdf (August 1, 2005).
10.1021/ef060097w CCC: $33.50 © 2006 American Chemical Society Published on Web 06/27/2006
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Figure 2. Dry mill ethanol process plant.8
Figure 3. Representation of whole-crop biorefinery process and products.6
cost.2 In contrast to a petroleum refinery, a biorefinery uses renewable resources and produces fuels and chemicals that contribute less to environmental pollution. Table 1 depicts the increase in biobased products sales worldwide from 1983 to 1994. This clearly shows there is a growing interest in biobased products. Similarly, Table 2 depicts the United States targets for biobased products in the selected years. 3. Types of Biorefineries Three types of biorefineries known as phase I, II, and III have been described by Kamm et al.6 and Van Dyne et al.7 A phase (4) Sokhansanj, S.; Cushman, J.; Wright, L. Collection and delivery of biomass for fuel and power production. Available from http://www.tennesseebiomass.com/storage.php (June 27, 2005).
I biorefinery plant has fixed processing capabilities and uses grain as a feedstock. A dry mill ethanol plant, illustrated in Figure 2, is an example of a phase I biorefinery which produces a fixed amount of ethanol, other feed products, and carbon dioxide and has almost no processing flexibility.6,7 A process involving current wet milling technology could be considered a phase II biorefinery which uses grain feedstock as input similar to dry milling. However, it has the capability (5) Biobased Industrial Products: Research and Commercialization Priorities; The National Academies Press: Washington, DC, 2000. (6) Kamm, B.; Kamm, M. Principles of biorefinery. Appl. Microbiol. Biotechnol. 2004, 64, 137-145. (7) Dyne, D. L. V.; Blase, M. G.; Clements, L. D. A strategy for returning agriculture and rural America to long-term full employment using biomass refineries. In PerspectiVes on New Crops and New Uses; Janick, J., Ed.; ASHS Press: Alexandria, VA, 1999.
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Figure 4. Representation of green biorefinery process and products.6 Table 1. Worldwide Sales of Biotechnology Products, 1983 and 1994a fuel and industrial ethanol high-fructose syrups citric acid monosodium glutamate lysine enzymes specialty chemicals total a
1983 ($ millions)
1994 ($ millions)
800 1600 500 600 200 400 1300 5400
1500 3100 900 800 700 1,000 3000 11 000
Table excludes pharmaceutical products.5 Table 2. United States Biobased Industry Targets5 biobased production levels
biobased product liquid fuelsa organic chemicalsb materialsc
current level
future target intermediate (2020)
future target ultimate (2090)
1-2% 10%
10% 25%
up to 50% >90%
90%
95%
99%
a
Large-scale production of biobased ethanol is a long-term possibility and the projection assumes advanced technologies are in place for processing lignocellulosic materials. b Include oxygenated chemicals such as butanol or butyl butyrate that can be processed into other intermediate and specialty chemicals traditionally dependent on fossil fuel feedstocks. c Include traditional forest products such as lumber, as well as novel biopolymers, such as bioplastics. Many new products in this market will be high-value materials that cannot be produced from petroleum feedstocks.
to produce various end products and far more processing flexibility6,7 depending upon a product demand, prices, and contract obligations. The typical products are starch, highfructose corn syrup, ethanol, and corn oil. A phase III, the most developed biorefinery, uses a mix of biomass feedstocks and
yields an array of products by employing combination of technologies.6 It allows a mix of agricultural feedstocks, has the ability to use various types of processing methods, and has the capability to produce a mix of higher-value chemicals while coproducing ethanol.9 It is based on both the HVLV and LVHV principles. The Phase III biorefineries, namely, whole-crop, green, and lignocellulose feedstock (LCF) biorefineries, are still in research and development.6 3.1. Whole-Crop Biorefinery. A whole-crop biorefinery processes and consumes the entire crop to obtain useful products. Raw materials such as wheat, rye, triticale, and maize can be used as input in the feedstock in the unit operations of a wholecrop biorefinery as depicted in Figure 3. The process of converting biomass into energy is initiated by mechanical separation of biomass into different components that are then treated separately. Biomass is the starting material for the production of syngas where syngas can be used as the basic material for the synthesis of fuels and methanol using the Fischer Tropsh process.6 Corn either can be used directly after grinding to meal or can be converted to starch. Further processing can be carried out as follows: (i) breaking up, (ii) plasticization, (iii) chemical modification, and (iv) biotechnological conversion via glucose. 3.2. Green Biorefinery. A green biorefinery is a multiproduct system which handles its refinery cuts, product, and fractions (8) Lasure, L. L.; Zhang M. Bioconversion and biorefineries of the future. Available from http://www.pnl.gov/biobased/docs/biorefineries.pdf (August 1, 2005). (9) Tyson, K. S.; Bozell, J.; Wallace, R.; Petersen, E.; Moens, L. Biomass oil analysis: research needs and recommendations. NREL Technical Report. Available from http://www.eere.energy.gov/biomass/pdfs/34796.pdf (August 1, 2005).
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Figure 5. Representation of LCF biorefinery process and products.6
Figure 6. Sugar-lignin platform biorefinery.12
in accordance with the physiology of the corresponding plant material as described by Kamm et al.6 and illustrated in Figure 4. A green biorefinery uses natural wet feedstocks derived from
untreated products, such as grass, green plants, or green crops as inputs, which are produced in large quantities in green plants. The first step of the refinery is to treat the green biomass
Biorefineries
Energy & Fuels, Vol. 20, No. 4, 2006 1731 Table 3. Composition of Bio-oil Compounds, Part I
type acids
esters
aromatics
compound
wt %
type
compound
formic (methanoic) acetic (ethanoic)
0.3-9.1 0.5-12 0.1-1.8 0.1-0.9
nitrogen compounds
ammonia methylamine pyridine methyl pyridine methanol ethanol 2-propene-1-ol isobutanol 3-methyl-1-butanol furan 2-methyl furan furfural 3-methyl-2(3h)furanone furfural alcohol furoic acid methyl furoate 5-methylfurfural 5-OH-methyl-2-furfural dimethyl furan 2-methoxy phenol 4-methyl guaiacol ethyl guaiacol eugenol isoeugenol 4-propylguaiacol acetoguiacone
hydroxyacetic 2-butenic (crotonic) butanoic pentanoic (valeric) 2-Me butenoic 4-oxypentanoic hexanoic (caproic) benzoic heptanoic methyl formate methyl acetate methyl propionate butyrolactone methyl crotonate methyl n-butyrate valerolactone angelicalactone methyl valerate benzene toluene xylenes naphthalene phenanthrene fluoranthene chrysene
alcohols 0.1-0.5 0.1-0.8 0.1-0.4 0.1-0.3 0.2-0.3 0.3 0.1-0.9
furans
0.1-0.9 0.2 0.1-1.2
substances in their natural form using wet-fractionation to produce a fiber-rich press cake and a nutrient-rich green juice. The press cake contains cellulose, starch, valuable dyes and pigments, crude drugs, and other organics, whereas the green juice includes proteins, free amino acids, organic acids, dyes, enzymes, hormones, other organic substances, and minerals. The pressed cake can be also used for the production of green feed pellets, as a raw material for the production of chemicals, such as levulinic acid, and for conversions to syngas and synthetic fuels.6 3.3. Lignocellulose Feedstock (LCF) Biorefinery. LCF consists of three basic chemical fractions: (i) hemicellulose, five carbon sugar polymers, (ii) cellulose, six carbon glucose polymers, and (iii) lignin, phenol polymers.9 A LCF biorefinery as depicted in Figure 5 uses hard fibrous plant materials generated by lumber or municipal wastes. Initially, plant material is cleaned and broken down into the three fractions (hemicellulose, cellulose, and lignin) via chemical digestion or enzymatic hydrolysis. Hemicellulose and cellulose can be produced by alkaline (caustic soda) and sulfite (acidic, bisulfite, alkaline, etc.). Lignin in plant materials is broken down with enzymes such as ligninases, lignin peroxidases, laccases, and xylanolytic enzymes. The sugar polymers (hemicellulose and cellulose) are converted to their component sugars (Figure 5) through hydrolysis. In the case of hemicellulose, it consists of short, highly branched chains of sugars. In contrast to cellulose, which is a
Figure 7. Conceptual map of SPB and syngas platform-based biorefinery.2
guaiacols
wt %
0.4-2.4 0.6-1.4
0.1-0.3 0.1-0.2 0.1-1.1 0.1 0.1-5.2 0.4 0.1-0.6 0.3-2.2 0.1-1.1 0.1-1.9 0.1-0.6 0.1-2.3 0.1-7.2 0.1-0.4 0.8
polymer of only glucose, a hemicellulose is a polymer of five different sugars. It contains five-carbon sugars (usually D-xylose and L-arabinose), six-carbon sugars (D-galactose, D-glucose, and D-mannose), and uronic acid. The hydrolysis process of hemicellulose results in aforementioned sugars. The following chemical reactions provide a general overview of the conversions that take place in a LCF biorefinery.
lignocellulose + H2O ) lignin + cellulose + hemicellulose hemicellulose + H2O ) xylose xylose (C5H10O5) + acid catalyst ) furfural (C5H4O2) + 3H2O cellulose (C6H10O6) + H2O ) glucose (C6H12O6) The xylose fraction from hemicellulose is important because it can be converted to furfural which is one of the starting materials for nylon 6.6 Furthermore, furfural has many uses: it can be used in the refining of motor oils, as a precursor of certain plastics, and as cleaning agents in liquid fuels. The hydrolysis of cellulose to glucose can be carried out either by enzymatic processing or chemical processing7 which produces useful products, such as ethanol, acetic acid, acetone, butanol, succinic acid, and other fermentation products. Although the hemicellulose and cellulose fractions have numerous uses, it is not yet the case for lignin. Currently, lignin has limited uses such as an adhesive or binder and as a fuel for direct combustion. However, the lignin scaffold has tremendous potential to produce various forms of monoaromatic hydrocarbons, which, if isolated in an economically efficient way, could add significant value to the primary LCF process. It should be noticed that there are no obvious, natural enzymes to split the naturally occurring lignin into its basic monomers as easily as is possible for naturally formed polymeric carbohydrates or proteins.6 The LCF plant in Missouri produces around 180 × 106 tons of ethanol and 323 × 103 tons of furfural annually from daily feedstock consumption of 4000 tons.7 If substantial
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Figure 8. Schematic of an integrated biorefinery.13 Table 4. Composition of Bio-oil Compounds, Part II type ketones
compound acetone 2-butenone 2-butanone (MEK) 2,3-butandione cyclopentanone 2-pentanone 3-pentanone 2-cyclopentenone 2,3-pentenedione
wt %
type
compound
2.8
wt %
type
aldehydes formaldehyde 0.1-3.3 sugars acetaldehyde 0.1-8.5 0.3-0.9 2-propenal (acrolein) 0.6-0.9 2-butenal trace 2-methyl-2-butenal 0.1-0.5 pentanal 0.5 phenols phenol 0.1-3.8 2-methyl phenol 0.1-0.6 0.2-0.4 3-methyl phenol 0.1-0.4 miscellaneous oxygenates 3-Me-2-cyclo-penten2ollone 0.1-0.6 4-methyl phenol 0.1-0.5 Me-cyclopentanone 2,3-dimethyl phenol 0.1-0.5 2-hexonone 2,4-dimethyl phenol 0.1-0.3 methylcyclohexanone 2,6-dimethyl phenol 0.1-0.4 2-Et-cyclopentanone 0.2-0.3 3,5-dimethyl phenol dimethlycyclopentenone 0.3 2-ethyl phenol 0.1-1.3 trimethylcyclopentenone 0.1-0.5 2,4,6-TriMe phenol 0.3 trimethylcyclopentenone 0.2-0.4 1,2-DiOH benzene 0.1-0.7 syringols 2,6-DiOMe phenol 0.7-4.8 1,3-DiOH benzene 0.1-0.3 methyl syringol 0.1-0.3 1,4-DiOH benzene 0.1-1.0 4-ethyl syringol 0.2 alkenes 2-methyl propene propyl syringol 0.1-1.5 dimethyl 0.7 cyclopentene syringal dehyde 0.1-1.5 R-pinene 4-propenyl syringol 0.1-0.3 dipentene
microbial conversion of glucose can be carried out, it can be used as an alternative route 6,10,11 for the petrochemically produced substances, such as hydrogen, methane, propanol, and acetone. In a more modern approach, the U.S. Department of Energy/ NREL have described conversion technologies for expanded biomass based on the “platforms” because the basic technology would generate base or platform chemicals from which industry could make a wide range of fuels, chemicals, materials, and (10) Zeikus, J. G.; Jain, M. K.; Elankovan, P. Biotechnology of succinic acid production and markets for derived industrial products. Appl. Microbiol. Biotechnol. 1999, 51, 545-552. (11) Willke, T.; Vorlop, K. D. Industrial bioconversion of renewable resources as an alternative to conventional chemistry. Appl. Microbiol. Biotechnol. 2004, 66, 131-142.
compound
wt %
levoglucosan glucose fructose D-xylose D-arainose cellobiosan 1,6-anhydroglucofuranose 4-methoxy catechol hydroxyacetaldehyde
0.4-1.4 0.4-1.3 0.7-2.9 0.1-1.4 0.1 0.6-3.2 3.1 0.6 0.9-13
acetol (hydroxyacetone) methylal dimethyl acetal acetyloxy-2-propanone 2-OH-3-Me-2-cyclopentene-1-one methyl cyclopentenolone 1-acetyloxy-2-propanone 2-methyl-3-hydroxy-2-pryrone 2-Methoxy-4-methylanisole 4-OH-3-methoxybenzaldehyde maltol
0.7-7.4
0.8 0.1-0.5 0.1-1.9 0.1 0.2-0.4 0.1-0.4 0.1-1.1
power. Five platforms have been suggested: sugar platform biorefineries (SPBs), thermochemical or syngas platform, biogas platform, carbon-rich chains platform, and plant products platform. The “sugar platform” focuses on the fermentation of sugars extracted from biomass feedstocks. The objective is to biologically process the sugars to produce fuel, such as ethanol, or other building block chemicals. SPBs are closely related to LCF biorefineries in the conventional nomenclature. The unit operation of a SPB is provided in Figure 6. The thermochemical or syngas platform focuses on the gasification of the biomass feedstocks. This approach converts the solid biomass into gaseous and liquid fuels by mixing it with limited oxygen prior to combustion. Various components produced through this process can be separated into fuels or
Biorefineries
valuable chemicals. NREL’s main focuses are on the SPB and “syngas” platforms. The concept of these two biorefinery platforms is described in Figure 7. The biogas platform is a widely used technology particularly in developing countries for producing cooking gas. This platform decomposes biomass with natural microorganisms in closed tanks known as anaerobic digesters. The process produces methane and carbon dioxide. The carbon-rich chains platform uses plant oils, such as soybean, corn, palm, and canola oils, which are presently used for food and chemical production. Transesterification of the vegetable oil or animal fat produces fatty acid methyl esters, commonly known as biodiesel. Biodiesel is already in use as an important commercial air-emission reducing additive or substitute for petroleum diesel. Selective breeding and genetic engineering can be used to develop plant strains that produce greater amounts of desirable feedstocks, chemicals, or even compounds that the plant does not naturally produce. The intention is to perform the biorefining in the biological plant itself rather than in an industrial plant. This approach is known as the plant products platform. 3.4. Integrated Biorefinery. The biorefinery types that we discussed previously are based on one conversion technology to produce various chemicals. A biorefinery is a capital-intensive project, and when it is based on just one conversion technology, as is the case for the previously described biorefineries, it increases the cost of outputs (or products) generated from such biorefineries. Hence, several conversion technologies (thermochemical, biochemical, etc.) are combined together to reduce the overall cost, as well as to have more flexibility in product generation and to provide its own power. Figure 8 provides a schematic of an integrated biorefinery. Three different platforms, namely: thermochemical, sugar, and nonplatform or existing technologies are integrated. An integrated biorefinery produces various products, which include electricity produced from thermochemical and bioproducts from the combination of sugar and other existing conversion technology platforms. An emerging concept in the biorefinery arena is conversion of bio-oil, the product from biomass pyrolysis, which could be routed via a conventional petrochemical refinery (Figure 8) to generate various chemicals. The advantage of this route is that all necessary infrastructures for the separation and purification of products generated are already in place. This concept makes perfect sense since most petroleum refineries are well equipped to handle variable feedstock with the assumption that no two batches of crude oil are the same. Tables 3 and 4 give the composition of bio-oil compounds. Bio-oil chemical properties vary with the feedstock but woody biomass typically produces a mixture of 30% water, 30% phenolics, 20% aldehydes and ketones, 15% alcohols, and 10% miscellaneous compounds.14 A process known as hydrodeoxygenation (HDO) could be applied to replacing oxygen by hydrogenation of the raw bio-oils. After several HDO treatment steps the bio-oil could be transformed into a liquid hydrocarbon with properties similar to those of petroleum crude oil.15 The deoxygenated bio-oils can potentially be refined in existing petroleum refineries, with only minor adjustments to the current (12) National Renewable Energy Laboratory. Available from http:// www.eere.energy.gov/biomass/pdfs/sugar_enzyme.pdf (August 1, 2005). (13) Energy Efficiency and Renewable Energy, Office of the Biomass Program. Multiyear Analysis Plan (FY04-FY08). (August 15, 2005). (14) Bridgewater, A.; Czernik, C.; Diebold, J.; Mekr, D.; Radlein, P. Fast Pyrolysis of Biomass: A Handbook; CPL Scientific Publishing Services, Ltd: Newbury, U.K., 1999; p 188.
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petroleum industry refinery infrastructure that is set up for hydrodesulfurization (HDS) process.16 HDO treatment of biooils with metallic catalysts, such as sulfated Co, Mo, W, or Ni, have been adopted from the petroleum industry.16-25 It has been shown that a two-stage process is required.17,26 The first stage applies a mild hydrogenation at relatively low temperatures below about 270 °C. Full HDO of bio-oils requires temperatures above 300 °C which results in polymerization of the highly oxygenated compounds in raw bio-oils.27 It is also important to standardize the quality requirements of biorefinery products at the onset of this technology to minimize variability. Such standardization will help focus future research to attain products with specific quality. As an example, it will be helpful for bio-oil researchers to know the minimum qualities to target if bio-oil is to be routed through a petroleum refinery. Identifying these minimum qualities is a challenge, especially, because of the multidisciplinary nature of the subject and should be done in close collaboration with petroleum engineers, bioenergy engineers, chemists, and biologists. As with petrochemical refineries, the main objective of the bio-oil-based biorefinery is to produce multiple products, including higher-value chemicals, as well as fuels and power. Hence, it is important to look at the value-added chemicals produced from the integrated biorefinery, which economically and technically support the production of fuel and power produced from these refineries. NREL and PNNL (Pacific Northwest National Laboratory) researchers carried out an exhaustive study to identify valuable sugar-derived chemicals and materials that could serve as an economic driver to the integrated biorefinery.28 Increased productivity, lower production cost, and efficiency could be achieved by employing operations (15) Scholze, B. Long-term stability, catalytic upgrading, and application of pyrolysis oilssimproving the properties of a potential substitute for fossil fuels. Dissertation, Department of Physical Chemistry, University of Hamburg, Hamburg, Germany, 2002. (16) Bridgewater, A. v.; Cottam, M. L. Opportunities for biomass pyrolysis liquids production and upgrading. Energy Fuels 1992, 6, 113120. (17) Baker, E. G.; Elliott, D. C. Catalytic hydrotreating of biomassderived oils. In Pyrolysis Oils from Biomass; Soltes, E. J., Milne., T. A., Eds.; American Chemical Society Symposium Series 376; American Chemical Society: Washington, DC, 1988; p 353. (18) Centeno, A.; David, O.; Vanbellinghen, C.; Maggi, R.; Delmon, B. Behaviour of catalysts supported on carbon in hydrodeoxygenation reactions. In DeVelopments in Thermochemical Biomass ConVersion; Bridgewater, A. V., Boocock, D. G. B., Eds.; Blackie Academic and Professional: London, 1997; Vol. 1, p 1648. (19) Conti, L.; Scano, G.; Boufala, J.; Mascia, S. Bio-crude oil hydrotreating in a continuous bench-scale plant. In DeVelopments in Thermochemical Biomass ConVersion; Bridgewater, A. V.; Boocock, D. G. B., Eds.; Blackie Academic and Professional: London, 1997; Vol. 1, p 1648. (20) Elliot, D. C.; Schiefelbein, G. F. Liquid hydrocarbon fuels from biomass. Am. Chem. Soc., DiV. Fuel Chem. 1989, 34 (4), 1160-1166. (21) Ferrari, M.; Delmon, B.; Grange, P. Influence of the impregnation order of molybdenum and cobalt in carbon supported catalysts for hydrodeoxygenation reactions. Carbon 2002, 40, 497-511. (22) Oasmaa, A.; Boocock, D. G. B. The catalytic hydrotreatment of peat pyrolysate oils. Can. J. Chem. Eng. 1992, 70, 294-300. (23) Puente, G.; Gil, A.; Pis, J. J.; Grange, P. Effects of support surface chemistry in hydrodeoxygenation reactions over CoMo/activated carbon sulfided catalysts. Langmuir 1999, 15, 5800-5806. (24) Zhang, S. P.; Yan, Y. J.; Ren, Z.; Li, T. Study of hydrodeoxygenation of bio-oil from the fast pyrolysis of biomass. Energy Sources 2003, 25, 57-65. (25) Czernik, S.; Maggi, R.; Peacoke, G. V. C. Review of methods for upgrading biomass-derived fast pyrolysis oils. In Fast Pryolysis of Biomass: A Handbook; Bridgewater, A. V., Ed.; CPL Press: Newbury, U.K., 2002; Vol. 2, p 425. (26) Gagnon, J.; Kaliaguine, S. Catalytic hydrotreatment of vacuum pyrolysis oils from wood. Ind. Eng. Chem. Res. 1988, 27 (10), 1783-1788. (27) Elliott, D. C.; Neuenschwander, G. G. Liquid fuels by low-severity hydrotreating of biocrude. DeV. Thermochem. Biomass ConVers. 1996, 1, 611-621.
1734 Energy & Fuels, Vol. 20, No. 4, 2006 Table 5. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Four Carbon 1,4-Diacids (succinic, furmaric, and malic acid)a
Fernando et al. Table 7. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of 3-Hydroxy Propionic Acid (3-HPA)a
a
Family 1, reductions; family 2, dehydrations.
Table 8. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Aspartic Acida
a Family 1, reduction; family 2, reductive aminations; family 3, direct polymerization.
Table 6. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of 2,5-Furan Dicarboxylic Acid (FDCA)a
a Family 1, selective reductions; family 2, dehydration to anhydrides; family 3, direct polymerizations.
a
Family 1, reduction; family 2, direct polymerization.
that lower the overall energy intensity of the biorefinery’s unit and drive down all production costs by maximizing the use of all feedstock components, byproducts and waste streams, (28) Aden, A.; Bozell, J.; Holladay, J.; White, J.; Manheim, A. Top Value Added Chemicals from Biomass; Pacific Northwest National Laboratory and National Renewable Energy Laboratory: Richland, WA, 2004; p 76.
economies of the scale, common processing operations, materials, and equipment. Details of some of the important valueadded chemicals have been reviewed in a paper published elsewhere.28 The NREL and PNNL study has reduced list of 300 initially selected candidates to 30 potential candidates through an iterative process based on the petrochemical model using building blocks, chemical data, known market data, properties, performance of the potential candidates, and the prior industry experiences of the PNNL and NREL team. The list of these 30 potential candidates was further reduced to 12 by evaluating the potential markets for the building blocks and their derivatives and the technical complexity of the synthesis pathway.
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Table 9. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Glucaric Acida
Table 11. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Itaconic Acida
a
Family 1, reduction; family 2, direct polymerization.
Table 12. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Levulinic Acida a
Family 1, dehydration; family 2, direct polymerizations.
Table 10. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Glutamic Acida
a
Family 1, hydrogenation/reduction.
4. Top 12 Building Blocks The following list includes top twelve building blocks identified by the NREL and PNNL study.28 • 1,4-succinic, -fumaric, and -malic acids • 2,5-furan dicarboxylic acid • 3-hydroxy propionic acid • aspartic acid • glucaric acid • glutamic acid • itaconic acid • levulinic acid • 3-hydroxybutyrolactone • glycerol
a
Family 1, reductions; family 2, oxidations; family 3, condensations.
• sorbitol • xylitol/arabinitol The NREL and PNNL study analyzed the synthesis for each of the top building blocks and their derivatives as a two-part pathway, where the first part is the transformation of the sugars into the building blocks and the second part is the conversion of the building blocks to secondary chemicals or families of derivatives. Biological transformations account for the majority of the routes from plant feedstocks to building blocks, but
1736 Energy & Fuels, Vol. 20, No. 4, 2006 Table 13. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of 3-Hydroxybutyrolactonea
a
Family 1, reduction; family 2, direct polymerization.
Table 14. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Glycerola
a Family 1, oxidation; family 2, bond breaking (hydrogenolysis); family 3, direct polymerization
chemical transformations predominate in the conversion of building blocks to molecular derivatives and intermediates. The challenges and complexity of these pathways, as briefly examined by the NREL and PNNL study to highlight R&D needs that could help improve the economics of producing these building blocks and derivatives, have been described here for each of the twelve building blocks (Tables 5-16). 5. Conclusion and Final Remarks The paper has discussed the concept of biorefineries, different types of biorefineries, future directions, and associated technical
Fernando et al. Table 15. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Sorbitola
a Family 1, dehydration; family 2, bond cleavage (hydrogenolysis); family 3, direct polymerization.
Table 16. Building Blocks, Pathways, Their Transformation to Derivatives, Technical Barriers, and Potential Uses of Xylitol/Arabinitola
a Family 1, oxidation; family 2, bond cleavage (hydrogenolysis); family 3, direct polymerization.
challenges. The biorefinery concept is still in its infancy. It is important to formulate standards for the products obtained from the biorefineries, if not available, starting from the onset of the technology so that the variability of the intermediate products is minimal to the streamline with existing technologies. One factor that needs critical thinking is whether modern biorefineries should be geared toward producing an entirely new line of chemicals/products, such as platform chemicals that are precursors to high value chemicals, or to produce raw material that
Biorefineries
could be starting feedstock for existing refineries or chemical plants. The answer to this paradigm will help in long-term sustainability of the integrated biorefineries and also help in continual use of the infrastructure network that is already in
Energy & Fuels, Vol. 20, No. 4, 2006 1737
place which took decades if not centuries to develop to where it is today. EF060097W
