Exxon: Tapping Algae and Plant Waste to Fuel a Sustainable Energy Future

McNeely is helping the company create the next generation of biofuels: energy sources that are sustainable and environmentally friendly. It’s a major challenge. There’s plenty of energy to be extracted from plant sources, she says, but today’s methods can be complicated and inefficient.

Right now one of the main renewable biofuels — known as “biodiesel,” which can be made from a wide variety of vegetable and waste oils — is often derived from oil-rich crops such as soybeans and palm fruit. The catch? Most of the plants used to make biodiesel are grown on land that could instead be used to produce crops for food and animal feed. Those acres are competing for freshwater and farmland, vital resources needed to feed an expanding global population.

To grow fuel in a wide range of environments that won’t compete with food production, scientists are exploring the huge potential of single-cell organisms such as algae and bacteria. Saltwater algae, for instance, can produce oil directly. And bacteria have the potential to unlock energy bound up in plant waste — so its growth isn’t competing with food — such as cornhusks or even sawdust.

These approaches may sound familiar. In the 2000s, alternative fuel sources like these seemed poised to enter the market. Although some fuels could be used directly in existing cars, the technology needed to make them truly sustainable and economical was still in development.

Today, those winds are shifting. Over the past decade, scientific and technical advances have allowed researchers to turbocharge ideas that previously took years to develop. And the stakes are huge. If this second generation of biofuel research is successful, it could provide cleaner, large-scale alternatives to diesel fuels for global transportation.

Farming algae on a large scale isn’t easy. Those contained ponds in Calipatria can each grow billions upon billions of algae cells, but maximizing production takes a bit of a green thumb — albeit a wet one. Every cell in the pond — not just those at the surface — needs equal amounts of sunlight, nutrients and carbon dioxide.

Brown and his team, in collaboration with ExxonMobil engineers, are currently fine-tuning their farming methods using natural species of algae, but in the near future, they hope to test lab-enhanced strains in the field, as well. SGI is working with appropriate regulatory authorities to establish proper protocols for this program.

If it works, they’ll be on their way to solving a tangle of thorny challenges: how to create raw materials for advanced biofuel on a massive scale, and how to do so using lands that wouldn’t otherwise support food crops, while relying primarily on saltwater instead of valuable fresh water.

The process promises to leave rich land open for food production and use carbon dioxide from the atmosphere as its carbon source to feed the algae. It’s a beguiling proposition.

“With ExxonMobil, we’re aiming to have the technical ability to produce 10,000 barrels of algae-based biofuel a day by 2025,” Brown says. “Eventually, we want to power something the size of UPS or FedEx’s global fleet with renewable diesel. That would be pretty aspirational. It’d be a real ‘We did it’ moment.”

The 10,000 barrels per day goal is just a start, McNeely says. If ExxonMobil and its partners can reach that milestone, the technology would allow them to scale up, potentially creating algae farms across the globe.

Building on processes that unlock the sugars embedded in the tough plant material, del Cardayre and his team have developed bacteria to transform those sugars into fuel. With techniques similar to those used on algae, REG has produced strains of harmless E. coli  that eat the sugars released from cellulose and spit out engine-ready biodiesel. They work like microscopic refineries.

“This E. coli  has the ability to quickly and selectively take in any fermentable sugar,” del Cardayre says, “and convert it into long, carbon-rich chains called fatty acid methyl esters — essentially a biodiesel molecule. Importantly, it doesn’t hold onto its fat the way most organisms do. That’s an advantage. Our E. coli  secretes the biodiesel, which makes the process very efficient.”

That efficiency is key to the future success of cellulosic biodiesel. With enough scale, and at the right price, it could someday play an important role in our overall transportation fuel mix, estimates McNeely. And the diversity of potential sources of raw materials is a big help: “The aim is not to have it come from just one source, like agricultural waste or wood pulp. The process needs to be flexible, so we can use whatever source is available.”

Producing diesel fuel from plant waste in this way would be a great benefit for society, McNeely says. It could transform plant waste into a revenue-earning resource for farmers, foresters and others. And it could cut greenhouse gas emissions from the vehicles that use it — trucks, trains, boats, cars and even planes — by more than 50 percent.

By researching existing life forms like algae and bacteria, ExxonMobil hopes one day to realize new sources for cleaner fuels at scale and, in the process, to make the future of energy literally green.