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By Robert Rapier on Oct 3, 2008 with no responses

Biodiesel, Green Diesel, and Jet Fuel

It is annoying to me that the definition of cellulosic ethanol has now been officially coopted in last year’s energy bill to include gasification processes. To me, that’s like redefining the definition of ‘birds’ to include ‘bats.’ This is all about marketing the ‘new’ cellulosic brand. But cellulosic ethanol has a 40-year history, and is distinct from biomass gasification (as I explained here).

Lately I have seen the definition green diesel made from hydrocracking processes creeping into the definition of biodiesel. While green diesel is a ‘bio’-diesel, it isn’t biodiesel. I have explained the differences here. But I just saw the distinction blurred again today in a story:

Using Plants Instead of Petroleum to Make Jet Fuel

Chemical engineers in North Dakota have successfully turned oil from plants—canola (rapeseed), coconuts and soybeans—into jet fuel indistinguishable from the conventional kind, according to U.S. government tests. Working with the U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA), scientists at the Energy & Environmental Research Center (EERC) at the University of North Dakota turned these plant oils into fuel that had a similar density, energy content and even freezing point.

“It’s got a freeze point of –47 degrees Celsius (–52.6 degrees Fahrenheit). Anyone familiar with biodiesel can tell you that’s no small feat,” says chemical engineer Chad Wocken, EERC environmental technologies research manager. “It’s processed so that it contains only the same hydrocarbon molecules present in petroleum fuel.”

Although he declined to explain the exact details of the process, Wocken says it is thermocatalytic—in other words, the engineers heat the plant oils in the presence of an undisclosed catalyst to create a slew of petroleum products. In fact, the process is not unlike conventional oil refining in that it produces everything from the kerosene used as aviation fuel to regular gasoline.

It’s no small feat primarily because it isn’t biodiesel. Don’t count on getting a tax credit for it, though. Congress in their infinite wisdom decided to continue giving conventional biodiesel priority over hydrocracked green diesel. But don’t get me started.

While I don’t want to downplay what these guys have done, there is a history here. Neste, Petrobras, and ConocoPhillips have been producing green diesel via hydrocracking vegetable oils or animal fats. Green diesel has also been produced via biomass gasification/Fischer-Tropsch by Choren. Further, Neste is already producing the fuel commercially, and is in the process of expanding production.

The novelty of what is being reported upon in the story seems to be the jet fuel aspect. The freeze point of conventional biodiesel is quite high, which makes it unsuitable for use as jet fuel. Green diesel has a much lower freeze point, and while I am not sure if Neste or Petrobras have produced jet fuel (which needs an even lower freeze point than diesel) with their hydrocracking process, they certainly could do so.