Anthonares

Here at Anthonares.net I will be expanding my discussion of energy issues as they become politically and economically more prominent. This week’s Published Research Synopsis examines a review paper in the journal Science that lays out the path we will need to take to make biofuels and biomaterials competitive with petroleum-based products. The authors of this week’s paper look at each portion of the biomass product chain and discuss the engineering research (both chemical and genetic) that will enable the biomass revolution.

Producing products like plastic from biomass rather than petroleum will be an essential step in our global efforts to live sustainably. Petroleum and gas supplies are dwindling and finite (more on this in a later blog entry, I’ve gone too long without addressing this as a geoscientist), and our future settlements and civilizations in space will never have access to vast fossil fuel reserves. Additionally, improvements in biomaterials and biofuels processing can lead to total carbon neutrality; the carbon used to make fuel and plastics comes from plants and will eventually be recycled back into plants via the atmosphere.

Citation (online at CiteULike.org):
Ragauskas, A.J. and 13 others (2006). The Path Forward for Biofuels and Biomaterials. Science 311(5760), pp. 484-489.

Synopsis:
The authors discuss three major steps that will be necessary to ignite truly enable the biomass revolution; plants will need to be engineered, processing facilities will need to be improved, and technologies for converting plant wastes to fuels will need to be pioneered. When these three cornerstones are lain, the entire process of generating biofuels and biomaterials can be energy positive and carbon neutral.

Plants intended for human or animal consumption have been the focus of intense genetic engineering for thousands of years, but selective breeders have largely avoided long-life perennial plants like trees. Modern genetic engineers see a lot of room for improvement in terms of plant growth rates and resistance to stresses like pests or drought and hope to improve yields by a factor of two. Research is currently underway to improve the photosynthetic conversion of sunlight to plant energy, to increase nitrogen metabolism, to delay the onset of leaf senescence in the fall, to inhibit flowering and direct energy into biomass production, and to transfer genes into trees that would increase pest and drought resistance. The authors vision of a 21st century domesticated tree would bear as much resemblance to the wild type as does the a modern Hereford cattle to the wild Aurochs.

Biomaterials such as organic chemicals, fabrics, papers, fragrances, and pharmaceuticals are the most lucrative uses of many modern crops, and the domesticated trees and plants of the future will be no different. After harvest, these plants will be brought to processing facilities where they will undergo a series of solvent extraction steps. The authors discuss a variety of “green” solvent options including supercritical CO₂, near-critical water, and mixtures of gases such as CO₂ with methane or acetone. These so-called tunable solvents will be carefully tailored to extract first the commercially valuable molecules already in the plants including fragrances and pharmaceuticals. Next, the cellulose within the partially-digested plant will be processed into fabrics, plastics, and finally fuels.

Biofuels processing is an energy intensive process, and several studies have indicated that it is either energy neutral or slightly energy positive. One key area of research is how to economically break down cellulose. One idea is to introduce genes into plants that when expressed would produce cellulase that would break down the cellulose within the plants. This introduced gene would be given a chemical trigger that farmers would spray on the crops just before harvesting. Thus activated, the cellulase gene would cause the plant to literally digest itself. When the plants reach the factory, their already broken-down cellulose would be easily extracted and converted into ethanol and other biofuels. Current biofuel production is largely accomplished via bacterial fermentation, but those bacteria are incapable of converting certain sugars (such as pentoses and hexoses, or molecules built from 5 or 6 simple sugars) into ethanol. Genetic engineering may solve this problem by creating bacteria capable of this fermentation, thereby increasing the efficiency of biofuels manufacture even more. Wastes from this refining sequence will consist largely of the lignin in the plant cell walls that are currently burned to provide heat and energy for biofuels processing. But the lignin could still be processed further to produce additional biofuels and add further value to the processing stream.

Context:
In their review of current research and future efforts, the authors sell an enticing vision: we can wean ourselves off of petroleum use and still receive most of the benefits of its use. This research will be necessary even if we eventually switch to a hydrogen economy for two reasons: currently 5% of petroleum production goes to petrochemicals not fuel, and hydrogen is not a source of energy as would be biofuels. As long as we need plastics and the host of other petrochemicals harvested from oil, we will need biomass processing. Also, until we have the capability to generate enough energy to produce hydrogen for our vehicles, we will need a portable source of fuel. We are nowhere near that goal today, and expanding coal burning in order to generate enough hydrogen load the atmosphere with greenhouse gases nearly as quickly as burning petroleum derivatives. So, as both a transitional product and a long-term sustainable solution, we need to pursue the biofuels and biomaterials processing methods reviewed in this paper.

General Explanations:
Biofuels
Today’s biofuels come in two varieties: bioethanol and biodiesel. In the United States today, approximately 2% of our transportation fuel comes from bioethanol while about 0.01% is provided by biodiesel. This is primarily due to considerable acerage devoted to corn production from which bioethanol is derived, and the fact that waste products are used for bioethanol production whereas biodiesel is a primary product.

Bioethanol is an alcohol derived from bacterial fermentation of plants such as corn or cane sugar that have large quantities of solid wastes after harvesting. Most vehicles can burn pure ethanol with slight or no modifications. A common ethanol-based fuel is an 85/15 mixture of ethanol and gasoline called E85 that is often cheaper than gasoline at today’s prices. It burns more cleanly than gasoline in that it produces fewer smog-inducing nitrogen and sulfur oxides. Though today’s bioethanol is not entirely carbon-neutral, much of the carbon emitted through the tailpipe was part of a living plant no more than year earlier. Thus the net carbon emission is lower than traditional fuel. (image credit: Minnesota Public Radio)

Biodiesel is another biomass-derived fuel that can be burned in unmodified diesel engines. It burns more cleanly than traditional diesel fuel and is currently much closer to carbon neutrality than bioethanol. Biodiesel is produced using the oils in a variety of plants, such as the rapeseed. Unlike ethanol, biodiesel does not use the waste products from harvest, but further improvements could change this. Also, crops high in oils can be grown on land that is otherwise marginal for traditional farming. This increases effective arable land, and increases the economics of biodiesel production.