Biodiesel: What's in your tank?
A new study finds that not all biodiesel blends contain what they advertise.
Some biodiesel blends for sale in the U.S. do not contain the amount of biodiesel advertised, according to new research published in ES&T (DOI: 10.1021/es071814j). Chemist Christopher Reddy of Woods Hole Oceanographic Institution and colleagues analyzed both pure biodiesel and blends from more than 20 distributors and small U.S. retailers. They found that blends sold as 20% biodiesel contained as little as 10% or as much as 74% biodiesel.
"It's a huge problem for the industry," says Teresa Alleman of the National Renewable Energy Laboratory, who recently completed a study showing that biodiesel manufacturers have improved the overall quality of pure biodiesel over the past year. If consumers pay a premium for biodiesel that they aren't getting, she says, public confidence could be shaken. Also, blenders receive a tax credit based on the amount of biodiesel used, which could mean some sellers have received larger credits than they merit.
Biodiesel is sold today mainly as a blend with petroleum diesel, because blends containing less than 20% biodiesel (termed B20) can be used in most diesel engines. Blends containing more than 20% biodiesel can damage hoses and gaskets in cars manufactured before 1993 and also can freeze in cold temperatures. "This could cause fuel filter plugging, or in the worst case, the fuel solidifies in the tank," says Gerhard Knothe, a biofuel researcher at the U.S. Department of Agriculture. Concerned consumers can ask retailers how they are blending fuel and whether they participate in the voluntary BQ-9000 biodiesel certification program, Knothe says.
The federal Renewable Fuels Standard and tax incentives are helping the biodiesel industry grow at a breakneck pace. "There's been a bit of dot-com mentality, with a lot of people getting into the business," Knothe says. The industry has been left scrambling to set standards and ensure reliability. Many states adopt and enforce fuel standards set by ASTM International for chemical and physical properties; these currently are designed for pure biodiesel.
"It's mostly the smaller mom-and-pop retailers that are mixing it themselves" that have problems, Reddy says. These operations often use a simple method called splash blending, in which biodiesel is poured into regular diesel in a tank or truck. Improper measurement or mixing during splash blending can lead to incorrect blends. In areas where the biodiesel industry is more developed, such as Minnesota where law requires all diesel sold to contain 2% biodiesel, more sophisticated mixing equipment heads off problems. For example, tanker trucks in some places can drive up to a "rack" with computer-controlled blending done to order.
"This wasn't a Morley Safer type of project [where I was] looking for blends to be off," Reddy says, referring to the 60 Minutes investigative journalist. Reddy is a marine chemist who studies oil spills, and he stumbled across the inaccurate blends during the course of work on the environmental effects of biodiesel spills. Some of the retail samples he obtained were "all over the place" in biodiesel content, he says, and he decided to investigate further.
The research is the first to apply highly precise radiocarbon measurements to biodiesel mixtures. Radiocarbon is also used to determine the ages of fossils, because this form of carbon decays predictably over time. In this case, the team measured the radiocarbon content of retail mixes and calculated biodiesel content by using the fact that petroleum diesel, as an ancient fossil fuel, no longer contains any radiocarbon. Biodiesel, derived from plants grown recently, does contain radiocarbon.
Radiocarbon testing is more expensive than other methods for testing biodiesel blends, such as infrared spectroscopy. However, radiocarbon is more accurate across all of the plant sources of biodiesel, Reddy says, and is the only method that directly measures the content of renewable carbon in a fuel mixture. That measure could be used to certify fuel in states that require a given percentage of fuel to be made from renewable resources.
The biodiesel industry is trying to rein in the problem, says Amber Pearson, a spokesperson for the National Biodiesel Board, by working with ASTM on standards that will include biodiesel blends. States will then have to adjust their own regulations to include blend verification.
