A Multi-Prong Approach to Carbon Neutrality

By Stephen Paley | June 02, 2008
Several charges have recently been leveled at the biofuels industry. Misinformed critics have cited indirect land use issues, the food-versus-fuel debate, and the destruction of the Amazon rainforest as reasons to halt or eliminate the production of fuel ethanol. It's become clear the issues aren't going away anytime soon.

However, the industry is heading in a direction that will likely leave the accusations even more baseless. This article depicts an avenue of growth that greatly increases industry profit while eliminating negative connotations permanently.

Many promised future technologies may not materialize, or else may cause unexpected harm. Plug-in hybrids would save a large amount of crude oil but only by dramatically increasing the use of coal to make electricity. Any oil saved in one country is likely to be used elsewhere, so the world would end up burning the same amount of oil and a huge additional amount of coal—a scenario for catastrophic climate change. Although solar cells will have important local application, electricity generated for the nation by solar cell arrays in the desert Southwest is unlikely. Most of the energy is lost when transforming low-voltage direct current put out by solar cells to high-voltage alternating current for long distance transmission.

If done properly, ethanol can pick up much of the slack in a way that's sustainable, largely through a better match between suitable local biomass and a specific type of cellulosic ethanol production.

Cellulosic Ethanol, Limited Agricultural Acreage
The United States needs a cellulosic production process that uses little energy per unit of ethanol produced (i.e., high energy gain). Many companies are developing such a process. Infinite Renewable Energy has developed a microorganism-based, low-temperature, low-pressure process with an energy gain of 11:1 that generates almost no pollution per unit of ethanol produced. The cost of producing ethanol using this process is 70 cents per gallon. Such processes tend to be low cost and require low energy inputs, but they must also have a short cycle time to be commercialized, which takes some doing.

Several cellulosic processes can use mixtures of all types of biomass or cellulose including old newspapers and the organic portion of garbage, which is the third-largest source of the greenhouse gas methane in the atmosphere.

Using forage sorghum, which grows across much of the nation, less than 10 percent of U.S. farm acreage would produce enough biomass to replace all U.S. imported oil with cellulosic ethanol.

Other high-yielding ethanol crops that can be grown in the southern United States include sugarcane and a less water-intensive miscanthus/sugarcane hybrid developed at Texas A&M that yields 10,000 gallons of cellulosic ethanol per acre annually.

Cellulosic ethanol requires processing of so much biomass per unit of ethanol that it should be grown and transported no further than 20 miles from the distillery, or else transportation (and energy) costs become excessive. This, in turn, dictates a distillery size between 20 MMgy and 50 MMgy. This economic formula encourages local production by smaller distilleries and localized consumption of ethanol.

Achieving Carbon Neutrality
Ethanol can be produced in a carbon negative manner ("Coupling Carbon Sequestration with Novel Cellulosic Ethanol Technology," December 2006 EPM), but even without that ethanol made by a low energy process with suitable biomass grown within 20 miles of the distillery will be almost carbon neutral. The only reason ethanol is not carbon neutral is the fuel and energy-intensive materials used to cultivate and harvest biomass, and the energy used to transport the biomass and convert it into ethanol. Biofuel crops requiring little cultivation, which also reduce production costs, are thus desired. Weeds grow without any cultivation and some are prime candidates for cellulosic ethanol.

The cellulosic process can be made even closer to carbon neutral. Lignin, another easily separated component of biomass, if burned as fuel to power the ethanol-making process, introduces no fossil fuel carbon to increase the carbon positive nature of ethanol production, according to Argonne National Laboratories' "Well-to-Wheel Energy Use and Greenhouse Gas Emission of Advanced Fuel/Vehicle Systems" report released in June 2001. The microorganism-based process needs so little energy that it can be powered by the
lignin in the biomass.

The minerals left over after making ethanol can be returned to the local fields from which they came. A crop rotation cycle of food crop, biomass and fallow would enable sustainable production of both biomass and food provided climate change does not become pronounced. The result of the described cost and energy optimizations would produce ethanol that is almost carbon neutral.

Expanding Feedstock Sources
Maralfalfa, a crop requiring little or no cultivation and used as a cattle feed in Colombia, can produce sufficient biomass to produce 10,000 gallons of cellulosic ethanol per acre per year. One must be careful, however, deploying a process for cellulosic ethanol in South America that can use mixtures of all kinds of biomass. It could provide another reason for clearing rainforests since the cleared vegetation itself could be used to make ethanol. Colombia can become the Saudi Arabia of cellulosic ethanol production, but must prevent unregulated expansion of maralfalfa at the expense of grasslands and rainforest.

Another place to greatly expand production of low-cost ethanol without expanding biofuel crop acreage is Brazil, which uses 3 percent of its acreage to grow sugarcane for ethanol production. If Brazil switched to a cellulosic process it would increase its ethanol production by 30 percent and reduce its cost to about 54 cents per gallon.

One can grow many times the biomass per acre per unit of time by growing microalgae instead of rooted, land-based plants. Microalgae also require considerably fewer resources and much less energy to grow and harvest. We propose to grow and harvest microalgae in shallow desert freshwater pools. Using desert or arid, sparsely vegetated grassland for this purpose would not put net greenhouse gases into the atmosphere.

The microalgae would need to have high cellulose content (approximately 40 percent), be hardy enough to withstand extremes of daytime to nighttime temperatures, and outgrow stray, undesired stains that enter the pool. Many candidates of microalgae have these properties that can be adapted to local conditions.

Water for this process could be provided by a low-cost, low-energy process of large-scale desalination.

There may be merit to growing microalgae (phytoplankton) on the surface of the ocean for use as biomass. Stimulated growth of ocean algae has been demonstrated and could be carried out over a large (but—by choice—not continuous) area of ocean using a "fertilizing agent" in concentrations of parts per billion sprayed onto the ocean from an aircraft.

Enough microalgae could be grown in this manner to supply sufficient biomass for the entire world to abandon most energy applications of oil.

If phytoplankton is grown at sea for biomass, it would make sense to manufacture carbon-negative ethanol aboard large ships. The energy needed to power the process might be provided by easily separated lignin-like compounds in microalgae. Thus, fuel might not have to be brought to the ship to manufacture ethanol. Similarly, freshwater for ethanol manufacturing could be obtained from the ocean by reverse osmosis desalination.

Finally, another kind of microalgae could be used in a "bubbler" device to capture the carbon dioxide released during the biofuel-making process, rendering the ethanol carbon negative. These algae are to be disposed of in the deep ocean to sequester the carbon they capture. Since the ship is already at sea, disposal is simple. When its tanks are full the ship can come close to shore and offload its ethanol through buoy-supported lines.

The Need for Innovation
Many forms of cellulosic ethanol technology exist and there are various ways to implement them. Not all are equivalent. The motivation to follow a different path--to replace oil with a sustainable carbon-neutral process of fuel production and use--is evident as greenhouse gases in the atmosphere continue to rise and crude oil prices continue to soar. Change is made attractive, or at least palatable, by the large profit increase for growers and producers that the new path enables.

Two-thirds of all pioneering inventions during the first 70 years of the 20th century came from individuals and small companies, according to Thomas W. Harvey in "Technical Ventures—Catalysts for Economic Growth." Today such companies have difficulty gaining credibility and their innovations often go unrecognized. It is risky for small companies to apply for a patent that threatens a multinational company because changes in patent law enable the innovation to be stolen. Without patents, publishing in peer-reviewed journals—another source of credibility—is denied. Consequently, innovations needed for industry development may go unrecognized if they come from small companies. This daunting obstacle must be overcome to achieve sustainable, carbon-neutral fuel production.

Stephen Paley is the principal scientist at Agricultural Management Systems. Reach him at spaley1ams@aol.com or (405) 721-0064. The late George K. Oister contributed invaluable discussions and insights to this article.