COMPARING LIQUID FUELS

The numbers behind ethanol, cellulosic ethanol, and biodiesel in the U.S.
Maywa Montenegro, December 4, 2006 (Grist)

- America devours oil like no other country…140 billion gallons of gasoline and 40 billion gallons of diesel…But rising prices, climate change, and seemingly endless crises in the Middle East have sparked a reckoning…
- [T]hree fuels have emerged to lead the U.S. biofuels pack…corn ethanol, cellulosic ethanol, and biodiesel…
Corn ethanol
- [A]mong environmentalists, however, the growing consensus is that corn-based ethanol is more fool's gold than eco-treasure…
- Conventional agriculture relies on fertilizer and pesticides derived from fossil fuels. Diesel powers the tractors and other machinery that plow, plant, and spray crops, as well as the vehicles that haul away the final product (due to ethanol's tendency to absorb water, it must be transported in special containers on trucks or trains instead of in the cheaper pipeline system used for oil and gasoline). Figure in the fuel -- mainly coal and natural gas -- burned in the distillation process, and experts reckon each gallon of ethanol takes the energetic equivalent of roughly three-quarters of a gallon of ethanol to produce…
- After accounting for the coal and natural gas burned to process it, the nitrous oxide -- a greenhouse gas hundreds of times more potent than CO2 -- generated from fertilizer production, and other factors, a recent study in Science found that ethanol use reduces greenhouse-gas emissions by just 13 percent compared to gasoline use…

- [D]omestic ethanol draws plenty of help from Washington… Since 1978, the fuel has qualified its producers for a [51 cents/gallon] federal tax credit…Ethanol producers also benefit from a 54 cent-per-gallon tariff on sugarcane ethanol imported from Brazil…

- U.S. automakers, also with a boost from Washington, are jumping on the ethanol bandwagon…the federal government's "dual-fuel loophole" provides automakers a 1.5 mile-per-gallon credit toward meeting fuel-economy standards -- without requiring that flex-fuel vehicles actually run on alternative fuel…flex-fuel vehicles run on ethanol blends less than 1 percent of the time…
Cellulosic ethanol
- Cellulosic ethanol, a fuel chemically identical to the conventional kind but instead derived from "biomass," a term encompassing everything from waste materials like corn stover and paper pulp to fast-growing plants like switchgrass, willow, and poplar. Roughly two-thirds of this cellulosic matter is complex carbohydrate, which can be broken down into fermentable sugars, and from there, into ethanol. Lignin makes up the remaining dry weight and carries an energy content similar to that of coal. Most models of cellulosic ethanol production, in fact, use lignin combustion to power the process, thereby closing the energy loop…

- [C]orn-based ethanol provides 26 percent more energy than is required for its production, while cellulosic provides 80 percent more energy. And while conventional ethanol reduces greenhouse-gas emissions 10 to 20 percent below gasoline levels, the reductions with cellulosic range from 80 percent below gasoline to completely CO2 neutral…
- A perennial prairie grass native to North America, switchgrass requires little water or fertilizer to grow and thrives in places unsuitable for most crops, ranging from the Gulf of Mexico to Canada and from the Atlantic to the Pacific. Some five to nine feet tall, this gangly weed also yields twice as much ethanol per acre as does corn…as many as 100 million acres of cropland and pasture will need to be devoted to switchgrass to produce enough ethanol to offset 25 percent of petroleum use. Currently, U.S. farmers have about 80 million acres in corn…
- [T]he U.S. is on track to consume 290 billion gallons of gasoline for transportation in 2050. By boosting fuel efficiencies and reigning in urban sprawl…we could feasibly cut this figure down to 108 billion gallons…the number of gallons of ethanol produced per ton of dry switchgrass could jump from 50 gallons to 117 gallons by 2050…current averages of five dry tons of grass per acre could easily double under a standard breeding program…switchgrass could be grown on a reasonable chunk of land to produce 165 billion gallons of ethanol by 2050. And because one gallon of ethanol contains 66 percent of the energy content of gasoline, 165 billion gallons of ethanol equates to -- you guessed it -- 108 billion gallons of gasoline…

- [I]t demands radical cuts in fuel usage…an infrastructure of pipelines and pumps specially designed to transport the hygroscopic fluid…an acidic or enzymatic digestion that splits it into simple sugars…In short, the shining promise of cellulosic is still just that…
Biodiesel
- [S]ome very American icons, ranging from Willie Nelson and Neil Young to Julia Roberts and Morgan Freeman, are hoping to lessen the impacts of our four-wheel love affair by championing biodiesel -- a fuel usually derived from soybean, palm, or oil-seed plants like canola and mustard, but also acquirable from waste animal and vegetable fats, and even, surprisingly, algae…Nationwide consumption of biodiesel tripled from 25 million gallons in 2004 to 75 million in 2005, and was expected to quadruple from that in 2006, reaching 300 million gallons…50 new larger-scale plants are under construction…
- [N]early 90 percent of all global biodiesel is produced and consumed [in Europe]…
- Over its lifetime, pure biodiesel emits about 78 percent less CO2 than conventional diesel. Burning biodiesel also reduces emissions of smog-forming hydrocarbons and particulate matter by about 50 percent, and emissions of sulfur oxides and sulfates by 100 percent…
- On the downside, all diesel engines -- whether fueled by conventional diesel or biodiesel -- still spew more toxic soot and smog-forming pollutants than gasoline engines, and this will likely remain true until cleaner "Tier 2" diesel emission standards go into full effect in 2009. So making the switch to biodiesel makes great environmental sense for the current fleet of diesel cars, buses, trucks, and heavy-duty equipment. But for individuals deciding on their next car purchase, a gasoline-powered hybrid (one that will soon be able to utilize cellulosic ethanol) remains the better choice…
- biodiesel production is highly efficient, generating 93 percent more energy than is required to make it…biodiesel reduces greenhouse-gas emissions by 41 percent compared with fossil fuels. When Tier 2 emissions standards bring biodiesel up to par with gasoline and ethanol for air pollutants, biodiesel seems like it should be a no-brainer for green energy.
And the Winner Is ...
- It is tempting, almost instinctive, to jump toward the most visible and abundant source for that energy -- in this case, corn…

- When it comes to biodiesel, limitations on the scale of production may be the greatest weakness…Ramping up worldwide cultivation of biodiesel crops is a possibility, but that will mean deforestation and the concomitant loss of biodiversity…
- Experts say that cellulosic ethanol stands a real chance to displace significant amounts of oil. But they also say this won't happen without great financial support from both the public and private sectors. It won't happen unless our political leadership implements greater efficiency standards and other incentives for companies to "go green." It won't happen unless we as individuals are willing to cut back on how much energy we consume, bottom line. And most important, it won't happen unless we call for a change…