Biomass has come center stage in the pursuit of reduced dependence on finite – not to mention geopolitically sensitive – quantities of fossil fuels such as petroleum, coal and natural gas. And while ethanol produced from corn is one promising path for biomass, it is by no means the only one. The number of known viable raw materials is vast, and the assortment of feasible downstream chemical building blocks and end products continues to diversify.
With such an array of routes for an industry still in its infancy comes an array of hurdles. And as with the maturation of fossil-fuel processing, many, if not all, of the challenges facing biomass today will be met as chemical engineering know-how keeps making headway.
While there are various methods for biomass conversion, the European Biomass Industry Association (EUBIA; Brussels, Belgium; www.eubia.org) groups them into four basic categories (Figure 1): direct combustion, thermochemical conversion processes (including pyrolysis and gasification), biochemical processes (including anaerobic digestion and fermentation) and physicochemical processing (the route to biodiesel). The technology of choice depends on the chemical makeup of the particular raw material and downstream product.
Growing options upstream
The catch-22 with processing biomass is that the same precursors that require the fewest and simplest processing steps, such as monomeric sugars and starches, are also important sources of food because, quite simply, they also break down easily in the human body. Take ethanol, for example, today’s most plentiful biofuel. According to the Worldwatch Institute (Washington, D.C., www.worldwatch.org), the raw material for over 40% of worldwide ethanol production is sugar cane, which owes its preeminence to Brazil, the current biofuel leader. Corn ranks in at a close second, given that it is the feed material for current commercial ethanol production in the U.S.
Therefore, due to the aspirations for large-scale biomass contribution in the long term, today’s midterm research efforts are refocusing on feedstocks that can meaningfully contribute to sustainable energy and chemistry without jeopardizing sustainability of the world’s food supply.
Another motivation to diversify feedstock options lies in the world’s enormous fuel and chemical demand. "Even if all of the corn and soy being grown in the U.S. right now were used to make biodiesel in its 100% vegetable oil form," says Geeta Agashe, director of the petroleum and energy practice for Kline & Co.’s (Little Falls, N.J.; www.klinegroup.com) research division, "it would only satisfy about 15% of the current demand for diesel fuel." Making the situation even grimmer, many other non-food products rely on corn or soy, for example, as a base component, she adds.
On the other hand, using feedstocks that would otherwise go to waste, biomass may indeed be able to lessen the demand for petroleum, says Jim Greenwood, president and CEO of the Biotechnology Industry Organization (BIO; Washington, D.C.; bio.org). "[The U.S.] could produce 25% of our transportation fuel need by 2015 if we dramatically ramp up biorefinery development," he says. Feedstocks for such complexes are to include agricultural, municipal, and forestry wastes as well as fast-growing, cellulose-rich energy crops such as switchgrass. The choice depends on what is readily available in a given location.
"In some parts of the world, there is only limited availability of land to produce food crops and therefore no surplus which can be used for energy crops," explains Phil New, senior vice president of BP’s (London; www.bp.com) fuels management group. BP has committed $9.4 million to a project by The Energy and Resources Institute (TERI; New Delhi, India, www.teri.res.in) in the Indian state of Andhra Pradesh to demonstrate feasibility of producing biodiesel from Jatropha Curcas, a inedible, oil-bearing crop. The project, expected to take 10 years, will cultivate around 8,000 hectares currently designated as wasteland with Jatropha and install the equipment needed – seed crushing, oil extraction and processing – to make 9 million L/yr of biodiesel.
On the cellulosic front, researchers at Purdue University (West Lafayette, Ind.; www.purdue.edu) are using genetic tools to design a hybrid poplar tree that readily and inexpensively could yield the substances needed to produce alternative fuels. The three-year, $1.4 million study by Purdue faculty members Clint Chapple, Richard Meilan and Michael Ladisch is funded by U.S. Department of Energy (Washington, D.C.; www1.eere.energy.gov/biomass/), which recently announced goals to replace 30% of the fossil fuel used annually in the U.S. for transportation by 2030. "We need a bioenergy crop that can grow many places year-round," Meilan says. "The genus Populus includes about 30 species that grow across a wide climatic range from the subtropics in Florida to sub-alpine areas in Alaska, northern Canada and Europe." (For more on poplar for biofuel production, see p. 16.)
The idea that local materials, such as palm oil in Hawaii, are most economical is the basis for Nolan Clark’s research at the Agricultural Research Service (ARS; Washington, D.C.; www.ars.usda.gov), Renewable Energy and Manure Management Research Unit in Bushland, Tex. Inspired by his work on biodiesel, one Arctic village uses fish-oil biodiesel to fuel generators that provide the town’s electricity. Clark and colleagues are also working on a manure-coal fuel to heat buildings and provide more affordable heat source for making ethanol.
Meanwhile, Degussa AG’s (Düsseldorf; www.degussa.com) Deputy Chairman of the Board of Management, Alfred Oberholz, visualizes the use of such bio-based raw materials as 3-hydroxy propionic acid and 3-hydroxy isobutyric acid as progenitors for high-volume aliphatic organics.
Cultivation downstream
In the long term, the biorefinery will hit its stride, producing a range of downstream chemicals, fuels and other products (CE, May 2006, pp. 27). Meanwhile, such downstream possibilities continue to emerge. According to The Catalysts Group Resources (CGR; Spring House, Pa.; www.catalystgrp.com), chemicals made from biomass currently make up about 5% of global chemical sales. This share is expected to increase to 10–20% by 2010. About 200 products are currently made by fermentation, of which the top four are ethanol, citric acid, gluconic acid, and lactic acid, CGR says. While the complete landscape is too vast and fast-growing to describe concisely, a number of downstream chemicals and building blocks that can be made from biomass are also listed in the box, p. 22.
The E.coli strain developed by Metabolic Explorer (Clermont-Ferrand, France; www.metabolic-explorer.com) promises a cost-competitive way to make propylene glycol from renewable resources, with acetone as a coproduct. The market for propylene glycol is around 1.5 million m.t./yr, for production of unsaturated polyesters, liquid laundry detergents, antifreeze and coolant, and other products.
Another key application for biomass is bioremediation. As part of National Pollution Prevention Week in St. Louis, Mo. last month, Solutia Inc. (St. Louis; www.solutia.com) was hailed by the U.S. EPA’s New Chemicals Pollution Prevention Program for Dequest PB, a biodegradable product used in water and process treatment. The
Dequest PB Series is made from chicory root, which is, itself, renewable.
Symbiotic advancement
While corn-derived ethanol and plant-oil derived biodiesel are just two slices of biomass’s much larger downstream pie, current viability to reduce greenhouse gases and petroleum-based fuels have put them in the spotlight for now. Ultimately, such attention will bode well for alternative downstream routes, too, DOE says, as many of the innovations have crossover potential.
For example, Purdue professor Li-fu Chen (photo) and research assistant Qin Xu have developed an environmentally friendly ethanol-to-corn method that is said to cost less than current methods. Using a machine designed to make plastics, the method grinds corn kernels and liquefies starch at high temperatures. The water input required in typical wet-milling is cut by 90%, Chen says. Wastewater output is cut by 95%, and electricity use is reduced by 47%. The method also produces corn oil, corn fiber, gluten and zein, protein that can be used in making biodegradable plastics.
And, while enzymatic extraction of cellulose from wood byproducts to produce the sugar glucose is being eyed for its potential to make ethanol, under different reaction conditions the fermentation of glucose instead produces glycerol, which was considered to be low in value until recently. Researchers from the U.S. and Brazil have developed a process that breaks down glycerol to hydrogen and carbon monoxide over a platinum catalyst under relatively mild conditions (225–300°C). According to J.A. Dumesic, one of the researchers from the University of Wisconsin (www.engr.wisc.edu), the process is attractive because glucose yields higher concentrations of glycerol than it does ethanol, 25% compared to 5%. In the ethanol option, that alcohol must then be removed by (energy-intensive) distillation, whereas the glycerol-containing solution can be used as is, either to produce methanol or to generate longer-chain alkanes by means of the Fischer-Tropsch process.
Alternatively, researchers at the Georgia Institute of Technology (Atlanta, Ga.; www.gatech.edu/) are looking at a way to offset the economic obstacles to the realization of cellulosic-ethanol biorefineries. Charles Eckert, a professor in the School of Chemical and Biomolecular Engineering, and his colleagues are exploring three environmentally friendly solvent and separation systems – gas-expanded liquids, supercritical fluids and near-critical water – to produce specialty chemicals, pharmaceutical precursors and flavorings from a small portion of the ethanol feedstock. These green processes could yield side-stream chemicals worth up to $25/lb, he says. Eckert and his colleagues have already demonstrated production of vanillin, syringol and syringaldehyde from a paper-mill black-liquor sidestream. They have also proposed a process to win levulinic acid, glucaric acid and other chemicals from the pre-pulping of wood chips.
Catalysts, enzymes pave the way
Enzymes as biological catalysts will continue to be vital in the refinement and improvement of natural raw materials as well as sustainable production processes. Currently, there is access to a limited amount of relevant biocatalysts, says the Biotechnology Research And Information Network AG (BRAIN; Zwingenberg, Germany; www.brain-biotech.de). Limitations are largely due to challenges in cultivating potentially interesting donor organisms such as bacteria, fungi, and algae. BRAIN will serve as the industrial partner in a newly formed research team comprising researchers in academia, to bring together synergistic approaches such as double emulsion technology, high-throughput enzyme-screening and metagenomics to facilitate discovery, production and application of technical enzymes.
Likewise, Mascoma Corp. (Cambridge, Ma.; www.mascoma.com), a company involved in converting cellulosic biomass to ethanol, is forging alliances with Dartmouth College (Hanover, NH; www.dartmouth.edu). An exclusive worldwide license agreement will allow Mascoma to research and produce ethanol from cellulosic biomass based on several patents from Dartmouth.
Also expanding their licensing agreement are Industrial Biotechnology Corp. (IBC; Sarasota, Fla.; www.industrialbiotechnology.com) and Isis Innovation Limited (www.isis-innovation.com), the technology transfer company of Oxford University (www.ox.ac.uk), both Oxford, U.K.. Isis will include IBC in the exclusive rights of the Cytochrome P-450 technology. The Cytochrome P-450 applies to the use of specific enzymes as biocatalysts to carry out the molecular transformation that enables relatively low-value substrates to be converted into high-value chemicals, often in a single step. Preliminary market analysis shows that this technology can biologically manufacture over 15,000 commercially available chemicals, says IBC. These include a variety of alcohols, aldehydes, ketones and carboxylic acids.
Given this development alone, truly, the horizons for biomass are broad.