Part III: The Price of Biofuels

While chemical engineers, microbiologists, agronomists, and others struggle to find ways of making cellulosic ethanol commercially competitive, a few synthetic biologists and metabolic engineers are focusing on an entirely different strategy. More than fifteen hundred miles away from the Midwest’s corn belt, several California-based, venture-backed startups founded by pioneers in the fledging field of synthetic biology are creating new microorganisms designed to make biofuels other than ethanol.
Ethanol, after all, is hardly an ideal fuel. A two-carbon molecule, it has only two-thirds the energy content of gasoline, which is a mix of long-chain hydrocarbons. Put another way, it would take about a gallon and a half of ethanol to yield the same mileage as a gallon of gasoline. And because ethanol mixes with water, a costly distillation step is required at the end of the fermentation process. What’s more, because ethanol is more easily contaminated with water than hydrocarbons are, it can’t be shipped in the petroleum pipelines used to cheaply distribute gasoline throughout the United States. Ethanol must be shipped in specialized rail cars (trucks, with their relatively small payloads, are usually far too expensive), adding to the cost of the fuel.

So instead of ethanol, the California startups are planning to produce novel hydrocarbons. Like ethanol, the new compounds are fermented from sugars, but they are designed to more closely resemble gasoline, diesel, and even jet fuel. “We took a look at ethanol,” says Neil Renninger, senior vice president of development and cofounder of Amyris Biotechnologies in Emeryville, CA, “and realized the limitations and the desire to make something that looked more like conventional fuels. Essentially, we wanted to make hydrocarbons. Hydrocarbons are what are currently in fuels, and hydrocarbons make the best fuels because we have designed our engines to work with them.” If the researchers can genetically engineer microbes that produce such compounds, it will completely change the economics of biofuels.

Technology Review