If you ever buy retail biodiesel for your diesel vehicle, it turns out you might not be getting exactly what you paid for—or you may be getting quite a bit more.
In a new study, researchers from Woods Hole Oceanographic Institution used highly accurate radiocarbon testing on samples from 20 different biodiesel blenders to determine the biodiesel content of their fuel (so-called “splash blenders” mix pure biodiesel and diesel together before selling it at the pump).
The study found that blends sold as B20 biodiesel (20% biodiesel, 80% diesel) varied from 10% to 74% in actual biodiesel content.
“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.
Not only that, but high blends of biodiesel can freeze up in cold weather, making them a potential liability for some users. Questionable content is not a good thing for the biodiesel industry, but (we hope) it isn’t as endemic as the study suggests.
“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 is the first time such an accurate testing method has been used to measure biodiesel content. Radiocarbon dating is used to date fossils, and is an effective method here because biodiesel newly derived from plant material has a different carbon signature than ancient petroleum-diesel.
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Source: ES&T (Feb. 27, 08): Biodiesel: What’s in your tank?