Biorefining the future: modern biorefineries refined and redefined.

The last five years have seen a virtual explosion in worldwide interest in the production of fuels and chemicals from renewable materials. These renewables include agricultural residues such as corn stover and bagasse, wood and forestry residuals from lumber mills and woodland clearing, and soon, deliberately grown agricultural crops. This interest is being driven by the convergence of numerous public and governmental concerns and forces that include:

* the problem of climate change associated with greenhouse gas emissions from fossil carbon sources;

* sharply rising crude oil prices and the anticipated permanent increases in oil demand from rapidly developing nations such as China and India coupled with shrinking supply--the so-called "peak oil" scenario;

* energy security; and

* the economic impacts of higher oil prices on the economies of oil-importing countries such as the U.S., Australia, China, and Europe.

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Coupled with these concerns are anticipated advantages of the use of renewable materials that include higher incomes for domestic agriculture, reductions in trade imbalances, as well as a reduction in the need for agricultural subsidies from central governments for land set aside programs and crop surpluses.

As a result of these drivers, governments around the world are now providing huge budgets to stimulate research, technology development, and the commercial introduction of bio-based fuels, chemicals, and materials. Additionally, in the last three to five years, this area has attracted massive investments from well-recognized venture capitalists, major corporations like DuPont, Rohm and Haas, and Cargill, (1) and oil companies such as Petro-Canada, Shell, BP, and Chevron.

Such investments have been primarily targeted at start-up technology companies, but large in-house research and development programs are also now being funded by major corporations. These events are clearly laying the ground work for a new industry producing transportation fuels, chemicals, and materials from renewable resources, which conceivably could become as significant as today's oil industry.

Current status of renewable fuels and chemicals

The production of transportation fuels from renewable materials is not an entirely novel phenomenon. Brazil has a 30-year history of producing large quantities of transportation fuels (ethanol) from sugar cane juice and molasses. This program is stimulated by that country's very limited domestic supply of crude oil. The U.S. is now fully embarked on major federal and state government-endorsed programs to produce ethanol, presently from corn, but later from lignocellulosic biomass. With more than 100 ethanol plants having been constructed within the past five years, the U.S. now has the motor fuel ethanol capacity of well over five billion U.S. gallons per year.

Ethanol is not the only transportation fuel now being produced in bulk from renewable materials. Bio-diesel production utilizing palm oil, soybean oil, and various other plant lipids is now a significant commercial activity in several countries--especially in Europe where there is a greater proportion of diesel engine automobiles than in North America. Production of liquid transportation fuels from renewable materials is not the only area gathering strong commercial and investment interest. The high cost of crude oil is now making it possible for chemicals derived from renewable sources to compete with traditional petrochemicals and materials. Several recent major investments are leading the way. Cargill-owned NatureWorks is now producing a new polymer, polylactic acid (PLA), for use in fibres, fabrics, and films, from cornstarch in Nebraska (see ACCN, January 2004). (2) Chemical giant DuPont is producing another new polymer, Sorona, from 1,3 propanediol made by the fermentation of cornstarch-derived sugar. (3)

There has always been a specialty chemicals industry based on the recovery of valuable chemicals from plants, such as flavours, fragrances, pharmaceutical intermediates, and dietary components. With the new era of high oil prices many companies are now searching for renewable sources of commodity chemicals, chemical intermediates, polymers, adhesives, and coatings, as well as performance additives in plastics, lubricants, and resins. There is now broad acceptance of the fact that foods and feeds, such as sugar, corn, and cereal grains, cannot support an industry of the size contemplated. The only renewable material capable of supplying chemicals and fuels in the quantities required by modern society is lignocellulosic biomass. The question then arises as to the types of technologies required to produce the necessary fuels and chemicals.

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Technologies for bio-based chemicals production

One approach to the production of useful chemicals and materials from plant biomass is that of thermo-chemical conversion of the entire biomass into highly degraded organic compounds by pyrolysis, or into synthesis gas by gasification. These types of processes destroy most of the fine chemical structures present in biomass and yield gaseous or liquid mixtures that must be further processed to create the desired chemical products.

Another approach is the extraction, purification, and possible further chemical modification of biomass components for use directly in commerce. Examples include carrageenan from kelp, biodiesel from vegetable oils, and resin acids from the "extractives" of trees. In these processes, much of the original chemical structure and value of the biomass is retained in the final product.

A third approach is the treatment of plant materials to produce sugars from plant polysaccharides for use in microbial fermentations from which the products of fermentation are recovered. Examples of these are motor fuel ethanol from corn by yeast fermentation, PLA from Lactobacillus fermentations, and 1,3 propanediol from the DuPont engineered microorganism. This approach requires that the various polysaccharide components of the plant material be exposed to facilitate either acid-catalyzed or enzyme-catalyzed hydrolysis.

The biorefinery

All three of these general but disparate processes are now being described as biorefining, with the term "biorefinery" being used broadly to describe a facility that employs any of the various biorefining processes to convert plant materials into useful materials. In an attempt to clarify this term, the National Renewable Energy Laboratory (NREL) in Golden, CO, proposed two definitions. (4) "A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass. The biorefinery concept is analogous to today's petroleum refineries, which produce multiple fuels and products from petroleum. Industrial biorefineries have been identified as the most promising route to the creation of a new domestic biobased industry."

It is significant that the NREL definition of a biorefinery makes a comparison to the modern oil refinery. Modern oil refineries, faced with strong economic pressures from competitors in the same industry, process crude oil to create as many products as possible from the feedstock and eliminate as much waste as possible. Modern oil refineries attempt to preserve value by retaining the chemical properties of the components of the crude oil rather than reducing it to its lowest common chemical denominator (such as synthesis gas) from which more complex chemicals are reconstructed. Furthermore, today's oil refineries have developed their economics around flexible processes that allow them to modify their product output to take maximum advantage of the vagaries in market demand and in product prices. The oil refining industry recognizes that multiple products create an economic advantage compared with single product operations. The latter are totally dependent on a potentially variable, single-product price for their economic survival. It is clear that with such a strong example from the old oil industry that the new biorefining industry would do well to follow the same operational principles.

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The Lignol biorefinery process