Introduction
Forest biomass can be used to create a wide range of industrial and consumer “bioproducts,” including transportation and heating fuels, wood-based chemicals, product “fillers” and more. New uses for sustainably harvested wood have the potential to strengthen timber markets, stimulate forest management and the conservation of forests, revitalize rural communities, ease society’s reliance on non-renewable fossil fuels, and reduce greenhouse gas emissions. Depending on processing technologies and development strategy, an emerging bioproducts industry also has the potential to transform industrial facilities like pulp and paper mills into “biorefineries” able to manufacture a wide array of products at a single location.
Many chemicals were originally developed using raw materials such as natural plant oils and wood. For instance, two common industrial chemicals, acetic acid and methanol, were produced primarily from wood into the first part of the Twentieth Century (Kirkpatrick 1933). Additionally, the USDA Forest Service notes that a hardwood distillation industry once existed in the United States, numbering roughly 50 facilities in the mid-1930s (USDA 1956). However, chemical production migrated away from using agricultural products as raw materials to using oil, natural gas, and coal as a feedstock due to their lower cost in raw materials and processing. The financial economics of relying on oil and natural gas worked well for many years. However, this may be changing. Prices for oil and natural gas have been extremely volatile in recent years. Faced with rising prices and the knowledge that oil and natural gas resources are finite, the chemical industry has begun to seek new feedstocks, including forest biomass.
The forest-based bioproducts industry is in its infancy. This paper reviews the factors driving innovation within the sector, and then reviews the processes and products under development. We close by examining the range of issues likely to affect the emergence of a commercially-viable bioproducts sector. In our analysis, we define forest-based biofuels and bioproducts as “wood-derived processed fuels and chemicals, generated through conversion of the chemicals found in wood into other forms, and generally serving as replacements for petroleum-derived products currently in the marketplace” (Innovative Natural Resource Solutions 2006). We do not include solid wood fuels used for thermal energy in conventional combustion technologies (e.g., firewood and wood pellets), or the production of electricity from the burning of wood at biomass-fired power plants.
Drivers of Innovation
Growing Human Population, Climate Change, and Peak Oil
Rising energy costs, increasing human populations, and concerns over climate change and the use of fossil fuels are driving global efforts to transition toward a sustainable “green” bioeconomy (Kates et al. 2001). Since the mid-1800s, human population and technological development have largely relied upon ever-increasing use of fossil fuels. Beginning with coal and, more recently oil and natural gas, abundant and inexpensive fossil fuels provided the foundation for the industrial and agricultural revolutions of the 19th and 20th Centuries. Today, fossil fuels provide the vast amounts of energy needed to support the world’s 6.7 billion people and the increasingly integrated global economy.
Fossil fuels represent an extraordinarily dense form of energy. Indeed, after processing, a barrel of oil will yield roughly 42 gallons of gasoline with an embodied work equivalent of 25,000 man-hours, or 12.5 men working 2,000 hours over the course of a year. Even at crude oil’s peak price in May of 2008 at $147/barrel, this work-equivalent costs roughly $12/man-year. In the U.S., per capita consumption of roughly 60 barrels of oil per year converts to the work equivalent of 767 man-years per person.
Given the finite and non-renewable nature of fossil fuels, maintaining current levels of population and economic activity will be a challenge (Smil 2008). Already, a growing body of evidence demonstrates that individual oil fields, as well as regions, experience a roughly bell-shaped production curve where production increases over time, reaches a peak, and then begins to decline. First identified by geologist M. King Hubbert in 1956, peak oil production—referred to as Hubbert’s Peak—occurred in the United States in the early 1970s. Since then, oil production has peaked in all non-OPEC countries, including the former Soviet Union. At present, the Middle East—particularly Saudi Arabia—contains the world’s largest remaining reserves, and when these reserves peak, so too will global production. Many analysts believe that the global peak will occur within 10 to 20 years; others suggest that peak production has already occurred or is imminent (Simmons 2005).
Global population is projected to reach 9.2 billion by 2050 before stabilizing—a 37% increase from today (United Nations 2007). Providing even basic sustenance for an additional 2.5 billion people will be a challenge given that many terrestrial and aquatic ecosystems are already in decline due to human pressures (Foley et al. 2005, Worm et al. 2006). Compounding this is the arrival of peak oil, with rising oil extraction costs, falling production, and increased demands from a growing population.
Policy Response
Rising oil prices coupled with concerns over carbon emissions, climate change, and the geo-politics of oil-rich nations has lead to renewed efforts to foster alternative energy sources. Yet replacing fossil fuels will not be easy, and rather than thinking of an oil substitute, analysts envision a transition to a portfolio of alternative energy sources. These include nuclear power, as well as renewable or “clean” technologies like biomass, wind, hydro, and solar. Currently, renewable energy sources provide less than 9% of U.S. energy needs (U.S. Department of Energy 2008).
Some liquid biofuels are already being produced. Brazil has made substantial strides in fermenting sugars for ethanol, while the U.S. initially focused on starch hydrolysis and fermentation. Similar to the programs in Brazil, sugar-cane related production systems are being developed in Asia and the Pacific. Perhaps even more widespread than the sugar-cane related production has been the development and use of oilseed crops for biodiesel. Two common sources of biodiesel are rapeseed oil in Europe and palm oil in Malaysia and Indonesia. Research is being conducted on other oilseed plants, such as Jatropha spp., that may be useful in increasing biodiesel production without requiring high value agricultural or forest lands (FAO 2008).
Emerging policies at the state, regional, national and international level are spurring efforts to develop alternative energy. In the U.S., the Biomass R&D Technical Advisory Panel, established by Congress, set forth a vision of replacing 30% of current U.S. petroleum consumption with biofuels by 2030 (Perlack et al. 2005). Already, biomass has surpassed hydropower as the largest domestic source of renewable energy, and currently comprises 3% of total energy consumption in the U.S. Achieving the 30% benchmark would require roughly 1 billion tons of biomass/year—a level of production considered feasible based on a review of U.S. agricultural and forest lands (Perlack et al. 2005).
Already, renewable energy standards or portfolios enacted by various states have expanded markets for electricity generated from woody forest biomass. And the Energy Independence and Security Act (EISA) of 2007, signed into law in late 2007, includes a “renewable fuel standard” that will increase the use of renewable fuels by 500%. Under EISA, fuel producers are required to supply 36 billion gallons of ethanol by 2022, nearly 60% of which is to come from cellulosic (i.e., non-corn starch) sources like woody biomass, switchgrass, and agricultural wastes. In addition to these domestic efforts, policies beyond the Americas in Europe and elsewhere to transition from fossil fuels to renewable sources of energy and feedstocks will create new and expanding markets for new technologies, as well as markets for industrial and consumer feedstocks and products (European Union 2006).
Forest-based Bioproducts
Processing Technologies and Products
Wood is a complex biopolymer comprised of a chemically bound admixture of cellulose, hemicelluloses, lignin, and a variety of other extraneous components. The fundamental challenge in producing feedstocks for new materials is in selectively controlling the amount and degree of separation of the biopolymer components. The utilization of forest biomass in novel products requires an understanding of the component separation processes and their impact on the resulting material properties of the biopolymer components.
Biomass is broken down into its intermediate components via one of two processes. Biochemical conversion breaks biomass into sugars using either enzymatic or chemical processes. These sugars are then converted to ethanol and other compounds through fermentation. Thermochemical conversion uses heat to break biomass into its intermediates, and then upgrades these components into fuels and other bioproducts using heat, pressure, and chemical catalysts.
A wide range of products can potentially be derived from woody biomass. Indeed, just as oil broken-down into its basic carbon structures can yield an array of valuable products ranging from fuels to plastics and fertilizers, so too can the carbon and sugars in wood. Current forest-based bioproducts research focuses on the identification of technologies that can be used to create new products from wood. Many of these technologies are nearing commercial viability. A major thrust of bioproducts research is to provide pure feedstocks for subsequent processing into high-value chemicals or polymers. As of mid-2008, the U.S. had five operational cellulosic biofuel projects, with eight under construction, and another 34 in planning stages (EESI 2008).
Conversion Processes
Fermentation—Fermentation is an old and well-understood biological process in which enzymes break down simple sugars and convert these into alcohols, including fuel-grade ethanol. In the Americas, most ethanol fuel is produced from high sugar crops like corn in the U.S., and sugar cane in Brazil. Using food grains for energy, however, has generated global concerns over food availability and pressures to convert forests to cropland (Righelato and Spracklen 2007, United Nations 2007). Technologies to produce “second generation” biofuels like cellulosic ethanol from low-sugar feedstocks (e.g., woody biomass and agricultural wastes) are less mature and face obstacles in reaching commercial scale due to high concentrations of difficult to ferment 5-carbon sugars, as opposed to the 6-carbon sugars such as glucose found in grains. For fermentation-derived products, ethanol has received the most attention. Additional products include antibiotics, lysine, and monosodium glutamate, as well as gluconic, lactic, acetic and malic acids. Additional high-value chemicals can be derived from these foundational building blocks.
Gasification—Gasification converts biomass to syngas through rapid heating in a reduced-oxygen environment. Syngas is a mixture of hydrogen (H2) and carbon monoxide (CO). Because syngas is gaseous, it readily mixes with oxygen and thus results in a more efficient and cleaner fuel than the liquid- or solid-phase feedstocks from which it was created. A wide range of feedstocks can be used in gasification processes, including bark, wood chips, sawdust, agricultural residues, animal and papermill waste, coal, and even crude oil. Most gasification projects generate thermal heat or electricity. In addition, the hydrogen in syngas can be isolated and used to power fuel cells. Additional products include synthetic diesel fuel, acetic acid, dimethly ether (a propane substitute), methanol, ethanol, propanol, and butanol.
Pyrolysis—Pyrolysis is a thermal process where biomass is rapidly heated in an oxygen-free environment to a set temperature, then rapidly cooled to distill the volatile products created during the process. Pyrolysis oil, also referred to as bio-oil, is the primary product of pyrolysis. Bio-oil can be used as a fuel, or as a platform to develop other high-value chemicals. Other products include phenolic resin, fuel additives, and food flavorings.
Fractionation—Fractionation, the least developed conversion process, breaks wood into its constituent components of cellulose, hemicellulose, and lignin. Fractionation processes include steam explosion, dilute acid and hot water extractions, and aquous/solvent treatments. Potential products include a wide range of chemicals, including levulinic acid, xylitol, and alcohols—especially ethanol for transportation fuel. Levulinic acid is an important intermediate chemical for a host of other products, including diesel fuel additives, synthetic fibers, pharmaceuticals, pesticides, plastics and rubber.
The wood constituents created under fractionation offer a wide range of potential products. For example, additional research focuses on the utility of wood biopolymer components in the creation of composite materials and “smart devices,” with an emphasis on lignocellulose nanomaterial applications. Utilization of lignocellulose nanomaterials, whether in composites or devices, requires that their surfaces and interfaces be tailored to the specific material requirements of the application. For example, modification of the fiber/matrix interface in polymer-based composites governs the critical dimensions needed to accommodate shear forces for a given fiber diameter. Similarly, dispersion of nanofibers on a supporting surface or self-assembly of individual fibers in 3-dimensional nanostructures requires control of interactions between the materials themselves, and their environment.
The nanoscale architecture of lignocellulose materials can be quite complex, involving highly aligned crystalline regions, random molecular assemblies, and/or amorphous components. Indeed, it is this rich nanostructure that is responsible for the wide range of chemical, mechanical, electrical, and optical properties that may potentially be exploited in these materials. Materials characterization at all length scales—from molecular conformations and individual nanofibers, and microcomposites to macrocomposite structures—is extremely fundamental to the development and utilization of these materials in a variety of commercial applications.
Forest-based Biorefinery Development
A forest-based biorefinery would take woody biomass as a feedstock and using the processes described above, convert it to a range of valuable products just as a conventional oil refinery converts petroleum to various products. The biorefinery model seeks to develop an industry based on a sustainable, low-cost feedstock—the lower grade wood supply—that adds value by selling into a wide variety of small but higher-value markets. Like the oil refining sector, biorefineries are likely to be anchored with a relatively large volume commodity product, such as paper, which enables the economy of scale necessary to process large quantities of raw material. Where the biorefinery model differs from the existing pulp and paper industry is that instead of using the residual wood components as a boiler fuel, which is a low value use, they are used for higher-value products. This is accomplished through separating the wood components and then using each for their own highest-value use. Cellulose is structurally strong, and so finds high value use in paper and construction materials. Lignin is the highest energy-containing component in wood and thus represents the best component to burn in a boiler or to upgrade into higher-value fuels such as energy-dense liquid transportation fuels. Hemicellulose is a relatively poor fuel for combustion, but is valuable as a food source for organisms that produce higher-value chemical products such as organic acids and higher alcohols. As technology for deriving higher-value products from carbohydrate-rich resources improves, both the value of the products and the ability to make use of lower grade feedstock materials will improve.
Factors Affecting Development of the Industry
The transition to a global bioeconomy presents both challenges and opportunities for the world’s forests. Already, forests provide a wide range of goods and services, and play a critical role in sustaining rural economic development, including both the forest products and recreation sectors. Forests also provide a growing list of increasingly recognized and valued ecosystem services like carbon sequestration, wildlife habitat, and the maintenance of water quality and quantity.
The transition to a renewable resource based bioeconomy will place ever-greater demands on the world’s forests. It is likely that forests in developed countries will see perhaps the greatest changes. There, a century of increasing fossil fuel use has relieved demands on forests for energy and raw material needs, resulted in increased forest area and volumes. This trend—rising population and economic activity amidst a resurgent forested landscape—is an historic anomaly, and efforts to avoid past patterns of deforestation could emerge as a primary challenge for forest managers (Perlin 1991).
Forest Management
The emergence of a forest-based bioproducts industry could affect the management of forest resources in a number of ways. First, increased demands for biomass will likely place increased demands on forests to produce more volume. While this could result in unsustainable harvest levels, shorter rotations, or practices that degrade site quality over time, increased demands could also stimulate investment in stand productivity. In addition, these demands could spur new and improved markets for trees with limited merchantability due to species, size, and/or stem quality. As a bioproducts industry takes shape and processing technologies developed, preferences for different species as feedstocks will emerge, thereby affecting stand management and harvest practices (see below). Finally, pressures to remove more woody biomass during harvests will increase the competition for wood, including bark and foliage valued on-site for use as habitat or for its role in nutrient cycling, soil quality, aesthetics, and erosion control.
Forest Operations and Feedstock Delivery
The emergence of a bioproducts industry could affect current harvest and transport practices in a number of ways. For example, feedstock specifications with respect to species, bark content, foliage, and impurities will affect how harvests are conducted. Increased demands for chipped woody biomass could have significant impacts on the composition and hence capitalization requirements of the logging sector. For example, in comparison with traditional whole-tree or cut-to-length systems, the specialized equipment needed to profitably harvest small diameter stems is expensive, as are the chippers and vans used to process and transport chips. These cost considerations may present significant barriers to increasing wood supplies in many regions of the Americas.
Research on forest biomass harvesting is finding that significant economic hurdles exist in harvesting and transporting feedstocks to processing facilities (Benjamin et al. 2009a). These hurdles compound those already facing the existing industry, which include rising logging and energy costs, and increased global competition. Handling forest biomass presents the greatest challenge for forest operations because logging residue has a very low value and bulk density (Andersson et al. 2002). Specialized equipment is expensive to own and operate, and machine function must be carefully matched with harvest method. As a result, logging contractors are reluctant to invest in expensive equipment that can only perform limited functions (e.g., bundle logging residue), so integration with existing harvest systems is a critical factor in controlling machine utilization and operating costs (Eckardt 2007, Ryans 2008).
The bioproducts industry is also dependent upon the physical and human infrastructure needed to efficiently deliver these feedstocks to processing centers. In short, there must be sufficient capacity within the existing sector to supply forest biomass—otherwise the bioenergy and bioproducts industries will have to compete with traditional wood processing facilities for both raw material and contractor services.
A range of potential biomass harvest systems and stand treatments could to produce feedstocks from forests. As a result, an emerging bioproducts industry could create opportunities for silvicultural treatments in areas that would otherwise be uneconomical. This creates a need to assess the economic feasibility and ecological impact of new treatments that might result from increased processing of logging residues, harvest of previously unmerchantable material, and possibly shorter rotation ages.
Finally, current harvest guidelines are likely to be insufficient in addressing feedstock demands for the bioproducts industry. As a result, new guidelines will be needed to help contractors, landowners, and foresters make better field decisions regarding biomass harvest and retention levels. Ecological research will be needed to identify harvest methods that minimize site impacts while protecting long-term forest productivity.
Entering the Marketplace
The emergence of the bioproducts industry must by necessity take place within already-established forest products and energy sectors. Moreover, many bioproducts technologies are still in their early development stages, and must scale-up from bench-level research to pilot-scale and beyond before reaching commercial viability. Economic values dictate that cellulose should be used as wood fiber as much as possible before being subjected to chemical or enzymatic depolymerization. Hemicelluloses are low in heat-value and should be exploited as a new feedstock for chemicals and materials production, instead of simply being burnt.
Site selection is likely to be critical given the reliance on nearby feedstocks and opportunities for co-location with potential waste streams. Moreover, much needs to be learned about how to transform existing economic clusters like the forest products sector, into successful and competitive players in the emerging global bioeconomy (Benjamin et al. 2009b). To be successful, an emerging forest bioproducts industry requires realistic projections of future raw material availability, including the character, quantity, and location of wood supplies (Perlack et al. 2005). Comprehensive regional evaluations of future wood supplies must account for ongoing changes in the forestry sector, urbanization and changing land use, the production of feedstock substitutes like agricultural wastes, and the complex interactions that are certain to develop between the forest resource and an emerging forest bioproducts industry (Alig et al. 2004, Stein et al. 2005).
To be successful and expand beyond technical feasibility and resource availability, the forest bioproducts industry must be able to compete in a global market economy. Here, product life cycle analysis, industrial ecology with respect to process-location decisions, economies of scale, regional market interactions, and technological learning are critically important. Furthermore, the economic feasibility and global competitiveness of the forest products industry in a particular region can be strongly influenced by state and federal environmental policies – policies driven and sustained by societal preferences (see below). As a result, the success of a forest bioproducts industry will be strongly affected by a host of forest and environmental policy choices.
Life Cycle Sustainability Assessment for Bioproducts
Life cycle assessment (LCA) is increasingly being used to support decisions related to product and technology development, adoption of environmental technologies and policies, carbon foot-printing, eco-labeling and marketing, emission inventories, and even the development of sustainable supply chains. The scaling-up and commercialization of novel bench-scale forest-based biotechnologies requires the use of LCA to assess its environmental performance in comparison with traditional petroleum-based products. ISO 14040 guidelines and requirements state that environmental sustainability claims of products and technologies cannot be made without first comprehensively evaluating the environmental life cycle implications of a product system (ISO 2006a,b). Thus, it is critical that any new products and technologies that are developing in the emerging bio-economy be assessed holistically with regard to their life cycle environmental impacts.
To comprehensively ascertain the potential environmental consequences of any product system, it is advisable to perform life cycle impact assessment (LCIA) through characterization modeling which aims to understand and evaluate the magnitude and significance of the potential environmental impacts of a product system (ISO 2006a,b). By conducting LCIA and interpreting its results with critical review (i.e., completeness, consistency, and sensitivity checks), an environmental sustainability claim can be made to show whether lignocellulosic biomass-based products are really superior or equivalent to petroleum-based products—claims that are increasingly valued in the marketplace.
In addition to science-based LCA, any practitioner is faced with unavailability and uncertainty issues due to cumulative effects of defining functional units, model imprecision, input uncertainty, and data variability (ISO 2006a,b). Thus, performing uncertainty and sensitivity analyses are needed to show the robustness of LCA results. This is particularly challenging for emerging products and technologies that are in the early stages of development as in the bioproducts industry. Another interesting development in LCA methodology is the need to incorporate social and economic dimensions in product and technology developments.
Waste disposal and management due to production of bioproducts is another concern. The principles of industrial ecology—where the wastes of one product system could be a potential feedstock into another product system to produce value-added products—is applicable here and should eventually lead to the creation of industrial symbiotic clusters/networks. These and other challenging issues using LCA and the principles of industrial ecology and sustainability science in fostering the development of the bioeconomy and industrial symbiosis are at the forefront of technology research and development.
Social Acceptability
As the forest bioproducts industry develops, it must continually anticipate, assess and respond to how it is likely to be perceived by a variety of stakeholder groups. A growing consensus recognizes that while food-based bioproducts can help us effectively manage the increasing demand and global warming impacts of petroleum-based products, there are serious limitations in using corn, sugarcane, wheat and grain crops. Instead, non-food sources such as agricultural crop residues, switchgrass, wood wastes, industrial and municipal wastes, and dedicated energy crops will play an increasingly vital role in expanding bioproduct supply chains (Ahmed 2008).
Within the forest sector itself, primary stakeholders include forestland owners, loggers and truckers, and processors. Each of these groups may potentially hold different views and interests regarding the industry. For example, large industrial forestland owners are well acquainted with biomass operations, while small non-industrial owners are not. How these groups view industry-driven changes in harvest practices is uncertain, but initial research suggests that increased biomass removals from stands will raise concerns over long-term site productivity, water quality, and wildlife habitat (Benjamin et al. 2009b). For loggers and truckers, the industry’s need for new equipment like chippers and chip vans could be met with skepticism given recent price swings in the energy markets. Finally, existing wood processors are unlikely to welcome increased competition for wood supplies, although new enterprises that generate demand for wastes or increase competition for by-products like sawdust could be viewed favorably.
Secondary stakeholders include a host of other interests not directly tied to the growing, harvest, transport and processing of woody biomass. These range from local governments, civic organizations and the general public, to environmental NGOs and the non-forestry related business community. Here, views towards the emergence of a bioproducts industry are likely to span the gamut from enthusiastic support to caution or even outright opposition. Public officials and many business interests will likely endorse new jobs and opportunities to capture value-added production while reducing the currency outflows needed to purchase fossil fuels. For the environmental community, stakeholder perceptions are likely to be especially complex, with the benefits of bioproducts as a sustainable, carbon-neutral substitute for fossil fuels viewed as a tradeoff with concerns over the environmental impacts of increased extractive demands on forestlands (Righelato and Spracklen 2007).
It is likely that stakeholders will evaluate the impacts of an emerging forest bioindustry based on expected impacts on the forest resource, processing, and end use. These views will be dynamic and subject to wide uncertainties. They will also likely exhibit geographic variation, with rural resource-based residents and communities favoring forest sector growth, while more ecologically-conscious suburban and urban residents expressing concerns over environmental tradeoffs. As a result, efforts will be needed to
understand and anticipate stakeholder concerns as they emerge.
Addressing such public values will be an important precursor to the development and sustenance of policies designed to foster the emergence of a bioproducts industry. Policy options include the setting of low carbon fuel standards like those enacted under EISA, research collaboration, tax incentives, grants and loan guarantees, and public education and outreach (EESI 2008). Also important are efforts to ensure reliable feedstocks such as programs that promote sustainable forestry and agriculture, and interagency collaboration (EESI 2008).
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Bioproducts V3
Submitted for Posting 15 September 2010
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