Dr. David Tilman on Ethanol and Biodiesel (Proc. Nat. Acad. Sci.) & more

[jpak]

http://www.pnas.org/cgi/content/abstract/0604600103v1

Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels


Jason Hill, Erik Nelson , David Tilman, Stephen Polasky, and Douglas Tiffany

Contributed by David Tilman, June 2, 2006

abstract

Negative environmental consequences of fossil fuels and concerns about petroleum supplies have spurred the search for renewable transportation biofuels. To be a viable alternative, a biofuel should provide a net energy gain, have environmental benefits, be economically competitive, and be producible in large quantities without reducing food supplies. We use these criteria to evaluate, through life-cycle accounting, ethanol from corn grain and biodiesel from soybeans. Ethanol yields 25% more energy than the energy invested in its production, whereas biodiesel yields 93% more. Compared with ethanol, biodiesel releases just 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. Relative to the fossil fuels they displace, greenhouse gas emissions are reduced 12% by the production and combustion of ethanol and 41% by biodiesel. Biodiesel also releases less air pollutants per net energy gain than ethanol. These advantages of biodiesel over ethanol come from lower agricultural inputs and more efficient conversion of feedstocks to fuel. Neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all U.S. corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. Until recent increases in petroleum prices, high production costs made biofuels unprofitable without subsidies. Biodiesel provides sufficient environmental advantages to merit subsidy. Transportation biofuels such as synfuel hydrocarbons or cellulosic ethanol, if produced from low-input biomass grown on agriculturally marginal land or from waste biomass, could provide much greater supplies and environmental benefits than food-based biofuels.

<end abstract>

Corn grain EtOH has an EROEI of ~1.25 whereas soy biodiesel has an EROEI of 3.57...

http://bznotes.wordpress.com/2006/07/26/press-clippings-biodiesel-vs-ethanol/

Tilman on natural prairie ecosystems for biomass fuel...

http://www1.umn.edu/umnnews/Feature_Stories/Natural_prairie_holds_key_to_sustainable_fuels.html

Natural prairie holds key to sustainable fuels

As gas prices inch higher, the search is on for renewable, plant-based fuels that don't require fertilizer or pesticides, which both require energy to produce.

A solution may be at hand, from University ecologist David Tilman and two colleagues: Instead of growing a single fuel source crop, grow many species together because such plantations will yield more total vegetation--and do it more reliably--than any growing just one species.

The most cited ecologist in the world, Tilman has long been singing the praises of biodiversity, as the coexistence of many species is called.

In May, he and two colleagues (University forest resources professor Peter Reich and Johannes Knops of the University of Nebraska) published a paper in the journal Nature in which they sum up 12 years of experiments at the University's Cedar Creek Natural History Area. The longest-running experiment of its kind, it shows unequivocally that plots of land with numerous species produce much more "biomass" and suffer less from fluctuations in productivity than plots with only one or a few species. This makes diverse plantings the likeliest candidates to drive the "bio" revolution.

<more>

University of Minnesota Press Release...

http://www.ur.umn.edu/FMPro?-db=releases&-lay=web&-format=unsreleases/releasesdetail.html&ID=3017&-Find

Biodiversity key to sustainable biofuel according to U of M researcher’s findings

Contact: David Tilman, [phone]
Peggy Rinard, College of Biological Sciences, [phone]
Mark Cassutt, News Service, [phone]

MINNEAPOLIS / ST. PAUL (5/30/2006) -- Ecosystems containing many different plant species are not only more productive, they are also better able to withstand and recover from climate extremes, pests and disease over long periods of time.

These findings, published in the June 1 issue of Nature, are the culmination of 12 years of experiments conducted by David Tilman, Regents Professor of Ecology at the University of Minnesota, to explore the value of biodiversity. The research was carried out at Cedar Creek Natural History Area, near Cambridge, a field station operated by the university’s College of Biological Sciences.

“This is exciting because it shows that biodiversity can be used to produce a sustainable supply of biomass for biofuels,” Tilman says.

For more than 50 years, scientists have debated the hypothesis that biodiversity stabilizes ecosystems. The University of Minnesota study is the first to provide enough data -- gathered over a sufficient time period in an experiment that controlled biodiversity – to confirm the theory. The time period of the study allowed researchers to evaluate the average net effects of diversity on resistance to and recovery from drought, pests, disease and other disturbances. Tilman and his collaborators began the work in the early 1990s and began publishing a series of landmark papers in 1994.

Biodiversity of global ecosystems has decreased as global population has increased because diverse ecosystems such as forests and prairies have been cleared to make way for agricultural fields planted with monocultures, buildings and roads.

Tilman’s research has shown that ecosystems containing many different plant species are more productive than those containing only one of those species. A return to biodiversity may prove to be the key to meeting energy needs for the growing number of people on the planet and for restoring global ecosystems.

“Diverse prairie grasslands are 240 percent more productive than grasslands with a single prairie species,” Tilman says. “That’s a huge advantage. Biomass from diverse prairies can be used to make biofuels without the need for annual tilling, fertilizers and pesticides, which require energy and pollute the environment. High diversity allows us to produce biofuels with low inputs, and this means that we can get more energy from an acre of land, year after year, with high certainty. Because they are perennials, you can plant prairie grass once and mow it for biomass every fall essentially forever.”

The research was carried out in 168 plots, each of which was randomly planted with 1-16 perennial grasses and other prairie plants. Over 12 years, rainfall during the growing season varied more than twofold and average daily high temperatures ranged from 21.5 C to 24.4 C. Stability was dependent on diversity and root mass. Roots store nutrients and buffer against climate variations. Prairie plants, which are perennials, have far more root mass than crops such as corn, which must be replanted annually.

<end press release>

So there...

:P

[hunter]

1. Ouch. Biodiesel blows corn ethanol out of the water...

Not only that, it's soy biodiesel, not even canola, jatropha, or palm oil.

If it was me, the next numbers I'd be looking at would be a comparison of cellulosic ethanol and biomass derived synthetic fuels such as DME, methane, methanol, or gasoline.

My intuition is taking me down the path of air separation plants and synthesis:

O₂ + biomass --> CO + H₂ --> CH₃-O-CH₃ + electricity

Biomass in this case could be anything... Sewage sludge digestion products, forestry wastes, construction and demolition wastes, trash, perennial grass mowings, etc...

Currently DME is my favorite. It's a good household cooking fuel (it's a "bottled gas" liquid under pressure very much like propane) and burns relatively cleanly in diesel engines. In comparison methanol or ethanol are much more dangerous as household stove fuels (mostly because people tend to do dangerous things like carry them around in 2-liter soda bottles) and less efficient as motor fuels.