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Work Proceeds on ASTM Biodiesel Specifications
In addition, other issues that do not apply for petroleum have been examined, and the team has had to come up with new testing methods. “Oxidation stability was a big one,” states Westbrook. “Here we borrowed from what was going on in Europe with a test method, and we voted to include that method in our specification. We’re not using the same specification limit, but we were able to borrow from work that was done over there and not have to repeat everything that we might normally have to do.” Another issue is of concern with biodiesel is low-temperature operability. Numerous groups are considering this problem, and Westbrook believes that the ASTM task force will soon bring out a new test method that will address it. “There’s a precipitate that comes out above the cloud point of the fuel,” says Westbrook. “The materials don’t show up in petroleum. It hasn’t been completely established what they are, but it’s been shown that, in many cases, they’re compounds that are unique to these biological raw materials.” Westbrook projects that D6751 will continue to evolve in the years ahead. “It’s an ongoing thing,” he says. “At some point perhaps we’ll get to the point where the spec will have very little change to it for three or four years in a row, but right now it’s still an ongoing effort to make sure that it’s the best specification that it can be.” Unlike some documents that, when published, are “set in stone almost,” the work on 6751won’t stop. “That’s one of the things that has been a hallmark of the B100 spec all along. The whole group has made a commitment that we will do the best we can to get the best test methods and the best specification limits into the specification, but as soon as there is new information or new data that says we should have done it this way or we should have set the limit here, we bring that out and vote to change it. The team learns all the time, says Westbrook. “And that’s been really good. As the chairman, I would say it’s been refreshing to see that everyone’s so willing to work and be flexible.” Along with the work on B100, the committee is working on a change to D975, Standard Specification for Diesel Fuel Oils, to allow up to 5% biodiesel in petroleum fuel. D975 is the specification most frequently used in commercial diesel fuel production sales and by the greatest number of regulators. Work is also underway on a specification for 6% to 20% biofuel blends, but it will be a completely new, standalone document. According to Westbrook, “It was done that way because there’s a lot of reference to biodiesel in petroleum throughout the country. Because it’s seen as an environmentally friendly thing to do, there are states and municipalities that are mandating these biodiesel blends. We decided that, because so many of them refer to 975, it would be best to use 975 wherever we could.” The group will keep the B6-to-B20 specification separate for two reasons. First, the properties are somewhat different, and second, the group felt that, because there is less controversy around B5 (engine manufacturers have agreed is that there is relatively little impact to the properties of the fuel if you add up to 5% biodiesel), they would be able to accomplish the task sooner. “If we were to try to write D975 to allow up to 20%, it would have taken a long, long time,” explains Westbrook. “And we’re trying to get things out as quickly as we can.” Steve Westbrook is a staff scientist at Southwest Research Institute in San Antonio, Texas.
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As biodiesel continues to penetrate the market, work is ongoing to refine existing standards as well as to develop new ones. Though ASTM D6751-07b, Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels, has already been published, the ASTM Committee on Biodiesel Fuel, under the leadership of chair Steve Westbrook, continually works to revise it. The Biodiesel Task Force performs most of the biodiesel work, and its chair is Steve Howell. “When we started with B100, none of the test methods that had to be used to specify B100 had ever really been tried with it,” says Westbrook. He and his colleagues started a process of interlaboratory study to evaluate testing methods that had long been in place for petroleum fuel to find out if they were valid for biodiesel. “In some cases,” he continues, “we’ve found that the methods just don’t work correctly at all with biodiesel as they’re currently written, and we’ve had to rewrite methods and go through a full interlaboratory study to get precision for those. So we’re working on several of the test methods that are already in 6751 to make sure they get that full approval to use with B100.”