Algae, Evolution, and the Future of Biofuels
FEBRUARY 13, 2013 by JACOB BORDEN
The fiscal cliff deal that greeted New Year's Day included language qualifying algal biofuels for the $1.01-per-gallon blending tax credit available already to cellulosic and advanced biofuels. Once again, rather than letting market-based evolution work out how to replace fossil fuels, the government has decided it can pick the winner.
This of course has reignited both sides of a long-running debate, either touting algae as fuel sources of the future, or dismissing them as so much "pond scum." I have made a career of biologically derived liquid transport fuels (LTFs) and would like to offer some clarifying information.
Algae are amazing creatures. They or something like them created the petroleum deposits on earth from which we derive our LTFs, working their magic over many millennia. The potential energy yield from an acre of land, if this process could be run at 100 percent efficiency, is truly impressive, so scientists have been tinkering with algae growth and genetics.
Here are the numbers: Of the sun's energy that makes it to earth, only about 17 percent reaches the surface, translating annually into 7,000 megajoules of light energy on a square meter of “standard” earth surface area. Only 53 percent of sunlight is photosynthetically active; about 70 percent of this actually makes contact and is absorbed by chlorophyll. Algae are able to convert 32 percent of chlorophyll-bound energy into fat. If everything worked perfectly, algae could produce approximately 15,000 to 20,000 gallons of liquid fuel per acre per year.
The science is well understood. In a nutshell, algae convert sunlight into molecules by reversing our digestive process. We eat sugars, extract energy, and expel "end-metabolites" of CO2 and water. Algae and other photosynthetic organisms take these metabolic dead ends and turn them back into the stuff of life: DNA, protein, and fat. They absorb sunlight with the enzyme chlorophyll, using the energy to bond CO2 with water, and store excess energy as fat. Some obese strains of algae generate 25 percent and sometimes even 50 percent of their body mass as fat.
It takes more processing to convert this fat into useful LTFs. Fat from algae can be extracted from the non-fat using methods similar to those for extracting soybean and canola oil—with a chemical solvent and/or with mechanical "breaking" of the cells. Both processes take a considerable amount of energy, but do produce a net output of fatty oils. Extracted oils can then be converted into the biological equivalent of diesel. Biodiesel, such as Willie Nelson's BioWille, is only the most prominent example. UOP and Neste Oil, among others, have competing technologies for converting oils into "green diesel," with a near-identical chemical fingerprint to diesel.
But here's where, as a biochemical engineer, I must recommend caution. There’s an industry adage that goes, “Once you solve the science, everything else is just engineering.” But that “just engineering” is another way of saying that it usually doesn't work perfectly. If you don't want just a teaspoonful but rather 60 billion gallons of bio-equivalent diesel, it's not as simple as building more and bigger test tubes. There are certain to be issues and limits associated with scaling up.
Take just one example: Two of the ingredients, CO2 and water, are simple to combine; they make soda water. But scaling that up to account for all of the CO2 produced by U.S. diesel combustion—more than 440 million metric tons annually—presents a host of problems. For one thing, actually converting that much CO2 to soda would fill Lake Tahoe. Then you have to source the CO2. The air contains plenty, but has to be concentrated to be of any practical use. Industrial and utility combustion off-gases are rich in CO2, but are also dirty and not necessarily located where the sun shines brightly enough. Then we have to bring the water, CO2, algae, and sunlight together in some processing machinery. Will we use open ponds or enclosed plastic or glass bioreactors? Open ponds raise environmental contamination issues. Enclosed reactors would require a lot of plastic and glass that reflect light. In all cases, pumping water and mixing CO2 are energy intensive.
And the Winner Is…
What's my point? That each scale-up issue and parasitic energy load reduces the actual gallons per acre per year to well below the number of theoretical gallons. So the land area equivalent needed to replace diesel with algae may be Connecticut, or it may be Alaska. Algae may not even work out as an engineering solution to LTF production. We simply don't know yet, and we won't until the market is allowed to allocate capital to the thousands of engineering R&D projects that need to be completed before a practical biofuels industry is in place.
ExxonMobil invested heavily in photosynthetic algae technology. You probably saw their commercials. Joule Unlimited, a biotech startup company, manipulates the genetics of blue-green algae (which is actually a photosynthetic bacterium) to directly produce diesel analogues that transfer across the cell membrane and alleviate the need for physical extraction. Dynamic Energy is a joint venture between Tyson Foods and Syntroleum for converting animal fats and inedible greases into green diesel. Chevron and an international lumber company, Weyerhaeuser, also have a joint venture between them, Catchlight Energy, with a "longer term focus on direct conversion of biomass to hydrocarbons." Royal Dutch Shell and BP Biofuels—the business unit of BP where I worked as principal engineer—have both invested in Brazilian sugar-cane ethanol. Both have also invested in biotech companies with cellulosic ethanol and advanced biofuel technologies. And I was part of a technology collaboration between BP and Royal DSM, looking into non-photosynthetic organisms as an alternative to algae-derived diesel.
Who's right? I don't know. What I do know is that no one in the government knows, either. I do know that biofuels are worth investigating as a potentially cost-effective means of producing a substantial supply of LTFs for the world. Mother Nature uses an evolutionary process that involves testing and rejecting millions of systems over billions of years before winners emerge. We don’t need that much time, but we do need the patience to let market-based economic evolution take place. Let's give the market-based evolutionary process an opportunity to work its wonders.