A recent article, "The Path Forward for Biofuels and Biomaterials"¹ in the prestigious journal Science outlines how advances in genetics, biotechnology, process chemistry and engineering are leading to a new manufacturing concept for converting renewable biomass to transportation fuels and other useful products. In the article researchers at Georgia Tech, Oak Ridge National Laboratory and Imperial College, London outline how the integration of agroenergy crops and new biorefinery technologies will converge in new manufacturing units called biorefineries.

The recent renewal of interest in biofuels reflects the U.S. Department of Energy's goal of replacing 30% of the U.S liquid petroleum transportation fuel consumption with biofuels. The timely publication in Science on January 27, 2006 came just in advance of the President's State of the Union Address where he declared "America is addicted to oil," and announced his desire to break this addiction by funding new technologies. The President's 2007 budget request calls for an increase from $91 to $150 million in funding for the biofuels initiative.² The Administration's interest in biofuels comes at a time when there are serious questions about the world's supply of recoverable oil. The importance of energy diversity is once again at the forefront of the public debate.

In the Science article Arthur Ragauskas of Georgia Tech and the article's coauthors argue that the transition from an economy based on fossil fuel derived from petroleum to an economy based on renewable biomass needs to be accelerated. The engines for this change are biorefineries, which work like modern oil refineries to produce multiple fuels and chemicals from biomass feedstocks. "The Path Forward for Biofuels and Biomaterials" focuses on how the important changes will come from total integration of new plant resources, synthesis of biomaterials and the generation of biofuels and biopower.

Plant Resources
A recent DOE/USDA study determined that the U.S. has the potential to supply the estimated 1 billion tons of feedstocks needed annually to achieve the DOE goal of replacing 30% of current U.S. petroleum transportation fuel consumption with renewable biomass.³ Converting this potential to reality requires improvements in recovery, yields, and land management strategies. Ragauskas and his coauthors consider the main challenge for biomass production to be the development of feedstocks that can double biomass yields per acre. They show how recent advances in plant genetics are providing researchers the tools to reach that goal. Improved mechanisms for the capture of sunlight by photosynthesis using genetic modifications have already been demonstrated in both plants and photosynthetic bacteria. Manipulations of the genes that control a plant's nitrogen metabolism have also been shown to increase biomass yields. For example, trials of transgenic poplars show increases in growing height of 40%.

Another path toward improving the productiveness of biomass is to increase the cellulose content of the plant, while reducing the content of less useful lignins. These genetic changes can also alter lignin structure so that more sugars are released during digestion. The article also points to other potential roles of genetic engineering in improving biomass production via improving resistance to disease and environmental stress, the delay or prevention of plant reproduction, and the delay or shortening of winter dormancy periods.

The President's new Biofuels Initiative calls for resources intended to enable ethanol produced from sources other than corn starch to become cost competitive by 2012. This will require lowering the cost of feedstocks, as well as driving advances in conversion technologies.

Synthesis of Biomaterials
Just as modern petroleum refineries produce byproduct chemicals, so will biorefineries produce byproduct biomaterials. The diversification from petroleum to biomass provides the chemical industry with the opportunity to use chemical feedstocks that eliminate or reduce the need for some expensive oxidation processes, and reduce dependence on catalysts and complex synthesis processes. Bio-derived plastics, such as polyactic acid, which are currently in large-scale production for food packaging and in the apparel industry, are good examples of the applications of alternative feedstocks.

A barrier to a greater use of biomass is the lack of developed efficient methods for separation, refining and conversion into chemicals and fuels. Separation is the dominant energy use in current chemical processing.⁴ While distillation is the most important unit operation of separation in petroleum refineries, biorefineries will depend more on solvent-based extraction methods.

The authors envision biorefineries operating in a two-step process. In the first step operations will extract the high-value chemicals already present in biomass such as fragrances, flavoring agents, food products and high-value nutraceuticals. The second and the main stage of processing plant polysaccharides and lignins will require the development of innovative separation and depolymerization process chemistries. The authors mention the use of supercritical CO₂, near critical water and gas-expanded liquids as potential solvents that could overcome these challenges.

However, since only around 5% of the crude oil processed by a conventional refinery results in chemical products, biomaterials offer minimal opportunities for reducing petroleum consumption. According to one of the paper's co-authors, Jonathan Mielenz of the Oak Ridge National Laboratory, "While chemical co-products are important to support the biorefinery, the real goal is displacement of petroleum with a liquid transportation fuel such as ethanol."⁵

The Generation of Biofuels and Biopower
The main stage of biorefining will be the production of biofuels. Current U.S. bioethanol plants use fermentation of starch from corn. In Brazil, bioethanol made from sugarcane accounts for 20% of the country's transportation fuel, and is cheaper than gasoline per mile driven.⁶ However, the full potential of biofuels lies not in the use of grains or other food products, but in the use of lower cost corn stover, straws, and forest product residues. The processing of these high cellulose and hemicellulose materials is the key challenge for the development of efficient biorefineries.

The authors outline several pathways toward cost-effective depolymerization of lignocellulosics, including pretreatment, combining cellulase/hemicellulase treatments with other process steps, or developing plants that can synthesize the enzymes needed. Another promising field of research is developing organisms that can convert all the sugars in particular plants to ethanol. Other workers are investigating nonbiological processes including the removal of oxygen from carbohydrates to produce oxygenated hydrocarbons.

A second hurdle for biorefineries is finding uses for the lignin component of lignocellulosics. Lignin residues from paper pulping are currently burned for heat and power, but lignin thermal cracking offers the potential to generate feedstocks that can be upgraded to potential liquid biofuels.

As with any industrial process, biorefineries will generate waste streams that will be difficult to convert to useful materials. Biomass residues have the potential to be converted to syngas by thermochemical conversion only if feeds can be kept clean of the components that could poison the noble metal catalysts involved in downstream refining processes. Tar and chlorides are the primary products that would require treatment.

Conclusion
A recent DOE solicitation will co-fund development of new biorefineries. A $160 million solicitation will fund up to three biorefinery projects (60/40 industry/government cost share) that will use non-food-based biomass. The goal of the awarded projects will be to show that once constructed, commercial biorefineries making cellulosic ethanol can be operated profitably.⁷

The authors of the Science article have shown that biorefineries are necessary for serving our transportation fuel needs, will be environmentally sustainable and are technically feasible. The next step is to take biorefineries into the mainstream.

¹Ragauskas, A.J. et al., 2006, The Path Forward for Biofuels and Biomaterials, Science v 311 p. 484-489.
²President Bush Proposes Energy Initiative to Reduce Oil Imports. February 1, 2006, EERE press release
³R. D. Perlack et al., Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply (U.S.Department of Energy and U.S. Department of Agriculture, April 2005; available at http://feedstockreview.ornl.gov/pdf/ billion_ton_vision.pdf)
⁴Materials for Separation Technologies: Energy and Emission Reduction Opportunities, Oak Ridge National Laboratory and BCS, Incorporated, available at http://www.eere.energy.gov/industry/imf/pdfs/separationsreport.pdf
⁵Jonathan Mielenz, personal communication 3-17-06
⁶As Brazil Fills Up on Ethanol, It Weans Off Energy Exports, Wall Street Journal, 1-9-06>
⁷DOE Announces $160 Million for Biorefinery Construction and Highlights New Agricultural Program to Promote Biofuels, DOE Press Release, 2-22-06