Biorefineries are dedicated facilities that convert the sugars, oils and proteins derived from renewable biomass into biofuels, chemicals and materials such as plastics and polymers. The concept is modeled on the petroleum refinery, in which crude oil is converted into fuels and chemicals that provide multiple product and revenue streams. Just as a barrel of oil can be broken down into constituent parts that add up to more by volume and value than the original barrel, the objective of a biorefinery is to develop as many product and value streams as possible from biomass. This optimization and efficiency are essential for economic and environmental sustainability.
There are many existing biorefineries in the United States that process corn into sugars (such as high fructose corn syrup), oils, animal feeds and food ingredients (such as xanthan gum). More than 200 ethanol biorefineries have been built, primarily using the corn's starch for biofuel and the remaining protein and fat for animal feed and vegetable oils. Some of these first-generation biorefineries are looking to create product and value streams from the cellulosic bran in the kernel and the stover (leaves and stalks) of the corn plant for additional product and value streams.
There has been rapid growth in construction of corn ethanol biorefineries since 2005, when the Renewable Fuel Standard (RFS) was first enacted, due to the economic opportunity presented by high oil prices and the phase out of methyl tertiary butyl ether (MTBE) in gasoline [4
]. details this growth. The RFS was enacted in the United States in recognition of the national security implications of overreliance on foreign supplies of petroleum, the energy security implications of oil's price volatility, and the ongoing environmental costs of fossil fuel use. Corn ethanol biorefineries that coproduce animal feed (distillers grains, corn gluten meal and corn gluten feed) and corn oil have very simple economic models that displace some use of petroleum for fuel and feed. Much more sustainable models that fractionate the corn kernel for additional value streams are now being developed, and use of renewable energy sources for power and electricity generation are in development. Petroleum's price volatility affects the entire value chain for petroleum refineries, pushing industry to seek replacements for the “entire barrel of oil.”
Growth of corn ethanol refining, 2000–2011. Construction of new ethanol biorefineries and expansion of existing production capacity accelerated following the adoption of the nation's first RFS in 2005.
There are a growing number of demonstration and pilot-scale biorefineries across North America that plan to use locally produced biomass, including starches such as sorghum; cellulosic feedstocks such as grasses, woody biomass (fast-growing trees and shrubs or forestry residues); municipal solid waste; and algae. Cellulosic biomass is the most abundant source of carbon, and its ubiquity makes it potentially the lowest-cost source of renewable sugars for biorefineries. A great deal of industrial biotech research and development has focused on enzymatic conversion of cellulose to sugars and consolidated metabolic bioprocessing of cellulose to higher value molecules.
The challenge for any biorefinery is to establish a reliable supply chain for sufficient feedstock at a stable price. In the United States, there are well-established supply chains for pricing and delivery of corn. Collection, harvesting, storage and transport of other biomass feedstocks – including corn stover – are in development, but rely to a large degree on expectations that market demand among biorefineries will exist. Biotechnology is playing an important role in increasing productivity for many biomass feedstocks, utilizing the same tools that have enabled increased production of corn and soy, namely pesticide and herbicide resistance. Genetic engineering tools applied to commercial production of microbes are being applied to algae – including gene shuffling, gene transfer, and even synthetic biology – to increase the productivity of target strains.
Biorefineries are expected to follow common business imperatives of industrial ecology. To remain economically competitive, they must continually innovate, increase efficiency, and develop new product and value streams. Biorefineries must seek to maximize the use of biomass, recycle waste streams as input for new product streams, and utilize heat from primary processes as energy for secondary processes. Biotech routes to a wide array of chemical products are being developed for integration into biorefineries, allowing for diversification of product and value streams.