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"Drop-In" Biofuels Solve Integration Issues?

NREL Fuels Performance Group Manager Matthew Thornton blends fuel additives at NREL's ReFUEL Lab.
Photo by Dennis Schroeder, NREL

"Drop-In" Biofuels Solve Integration Issues?

Lab works to create biofuels indistinguishable from conventional petroleum-based fuels.

Ever since its inception 36 years ago, the National Renewable Energy Laboratory (NREL) has been working to develop biofuels that can displace petroleum-based fuels and lessen our nation's oil dependence. That's a difficult challenge because, ideally, a new fuel would need to be compatible with the pipelines, blending stations, and fuel pumps that form the U.S. fuel infrastructure, which required a massive capital investment and many years to develop.

Of course, the fuel would also need to work well with vehicles, burning cleanly and providing the needed performance without causing damage. Failing to address these critical "integration issues" can make a fuel more difficult to distribute and use, potentially raising the fuel's cost and limiting its market.

The trick to avoiding such issues is to create new biofuels that, for all practical purposes, are indistinguishable from conventional petroleum-based fuels. To do so, biomass must be converted to hydrocarbon fuels, which consist of long chains of carbon atoms with many hydrogen atoms bound to that chain. Gasoline, for instance, is comprised mainly of hydrocarbons with seven to eleven carbon atoms in a chain, or C7 through C11 for short. Kerosene and jet fuel are primarily C12 to C15, while diesel fuel contains longer-chained hydrocarbons.

Such "drop-in" biofuels could literally be added into the existing fuel infrastructure without any changes. While motorists would not notice a difference in their fuel, a growing percentage of that fuel would come from natural, renewable resources such as grasses and trees rather than petroleum.

"Leveraging the existing oil refining infrastructure, the pipelines, refineries, storage systems, distribution, and dispensing systems, is a great advantage for drop-in biofuels," said Rich Bolin a manager for partnership development at NREL. "Oil refineries are incredibly capital-intensive; nobody has built a major, world-scale oil refinery in the United States since 1977, and the reason for that is that they're just too expensive to build. By being able to produce a fuel intermediate or a finished fuel, by biological or thermochemical means, and feed it into a refinery at various points lowers the production costs for those drop-in biofuels. Working with oil refineries will speed up the commercialization of drop-in biofuels and extend our crude oil resources."

The question is where, exactly, to drop in those biofuels? Some of the processes used to develop biofuels produce a heavy oil that theoretically could be processed into fuel in an existing refinery, while other processes result in products similar to the fuels that we're more accustomed to: gasoline, diesel fuel, and jet fuel. These three petroleum fuels are often considered the trinity of major transportation fuels that keep this country, and the world, on the move.

We also need to figure out what to make the biofuels from and how best to produce the drop-in biofuels.

A Consortium to the Rescue

A photo of the inside of a large, two-story research facility. A group of people in green hardhats can be seen looking down at a testing area as they stand by the red railing of the upper level (25781)

NREL's Integrated Biorefinery Research Facility has a 27,000-ft2, high-bay biochemical conversion pilot plant that can accommodate bench-to-pilot-scale processes for converting cellulosic biomass into a variety of fuels and chemicals—processes that can go through up to one ton of dry biomass per day.
Photo by Dennis Schroeder, NREL

The National Advanced Biofuels Consortium (NABC), which NREL and Pacific Northwest National Laboratory (PNNL) have co-led on behalf of the U.S. Department of Energy since early 2010, has been tasked with solving some of the challenges surrounding drop-in biofuel technology. The NABC has a three-year charter to winnow down the list of possible biomass conversion technologies, and to prepare one or two processes for scale-up to the pilot scale—a critical step for commercializing the process.

While NREL and PNNL are leading the effort, the consortium also includes three other national laboratories, four universities, and corporate partners that range from small start-up technology companies to major oil refiners including Tesoro and BP North America.

"The NABC is a two-stage effort," said Tom Foust, director of the NABC. "Stage one was to evaluate the landscape of promising hydrocarbon fuel production technologies from biomass and down-select to the ones that looked the most promising. Stage two is an ongoing two-year effort to develop those promising technologies to a pilot-ready state."

In its first year, the NABC investigated six process options for creating drop-in biofuels, narrowing the list to two main processes. The first involves fermenting biomass sugars, in a process similar to making beer, which is also the way that fuel ethanol is produced today. Fermentation uses yeast or some other microorganism to convert the sugars, and although it usually produces ethanol, the NABC is investigating fermentation processes that can generate diesel fuel.

Amyris, an integrated renewable fuels company, is leading this investigation, which uses a bioengineered yeast to produce farnesene. This 15-carbon molecule is one that can be converted into diesel fuel.

A close-up photo of a man's gloved hand as he fills a small test tube with yellow liquid from a faucet (20217)

Researcher Bob Lyons draws fermentation samples from a 9,000-liter fermentation vessel at NREL's Integrated Biorefinery Research Facility.
Photo by Dennis Schroeder, NREL

The second process the NABC is investigating is the catalytic conversion of sugars to fuels. Because this process relies on a chemical conversion, it completely avoids the use of microorganism. With the help of catalysts, a company called Virent Energy Systems has been able to produce the full trinity of major transportation fuels.

By the fall of 2013, the NABC will finish preparing these technologies for pilot scale, including conducting detailed engineering studies and environmental impact analyses.

Substitutes for Crude Oil

The NABC is also working to address the main technical challenges faced by two additional processes that produce crude oil substitutes: hydrothermal liquefaction and hydropyrolysis.

Hydropyrolysis is a version of pyrolysis, where heating biomass in the absence of oxygen yields an oily liquid. Hydropyrolysis adds pressurized hydrogen and specially tailored catalysts to the reactor, causing reactions that yield more of the "light" (small-chained) hydrocarbons that are found in gasoline and jet fuel.

Hydrothermal liquefaction, on the other hand, involves immersing the biomass at high temperature in water in the presence of catalysts or reactants to speed the reaction and control the final product. The reaction vessel is held at high pressure to keep the water from boiling.

Both hydrothermal liquefaction and hydropyrolysis show promise, but they aren't quite to the point where they could be scaled up to the pilot level. Rather than give up on the technologies, however, the NABC is trying to address the main technical challenges that are holding them back. The consortium aims to solve these challenges by the time its charter ends in late 2013.

NREL and the NABC

The NABC is obviously conducting important research in drop-in biofuels, and NREL is the lead organization for the NABC. But what, specifically, does NREL contribute? That question has several answers.

NREL's main hardware contribution is the use of its new pilot-scale biofuels facility, the Integrated Biorefinery Research Facility, where the biomass is treated and prepared for conversion into fuels. NREL's decades of experience in pretreatment technologies for converting biomass to ethanol is also relevant for drop-in biofuels.

However, NREL's most significant contribution to the NABC may be its ability to perform rigorous technical and economic analyses of the various chemical pathways and technologies that are under examination.

A photo of a man in front of a back-lit projections screen talking to a group of adults in a dark room (22394)

Congressional staff learn about biofuel research technology during a recent tour of NREL's lab facilities.
Photo by Dennis Schroeder, NREL

"NREL acted as a gatekeeper for the technologies," Foust explained. "It's very difficult to do that in a research environment because you have to define criteria, you have to have rigorous standards, you have to have complete transparency, you have to be unbiased, you have to have rigor in your economic analysis, and you have to have consistency. NREL did an exceptional job."

Looking Ahead: NREL to Ramp Up its Drop-In Biofuels Research

The NABC's work will be done by early in 2014, but its impact on NREL will be long lasting. For many years NREL has been a leading research organization in the conversion of biomass to ethanol, but as that technology matures, the lab is setting its sights on new goals. Most of the future emphasis will be on drop-in biofuels, which means that in a sense, the NABC came along at a perfect time for NREL.

"Starting in 2013, we're shifting the focus from cellulosic ethanol to drop-in biofuels," Foust said. "The NABC did a really nice job of setting the stage, giving us the research and the partnerships that we need to transition the whole program as seamlessly as we can."

Sustainable Transportation

Fall 2013 / Issue 5

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