Divergent Feedstocks

One pine tree as good as another? Guess again
By Holly Jessen | November 15, 2011

In the process of researching various feedstocks for their startup company clients, Golden, Colo.-based Hazen Research Inc. noticed a trend. Feedstocks are not all created equal—even if that feedstock bears the same plant name.

In an independent study, Hazen discovered differences among lodgepole pine trees, says Brian Cooper, senior process engineer. Specifically, beetle-kill lodgepole pine trees respond differently to pretreatment and produce different products than healthy wood. “You could convert either one with relative ease with the known processes now,” he tells EPM. “It’s just that if you designed a process around one flavor of feedstock and then you switch to a different one, you could run into some pretty big problems.”

In a cost-benefit analysis, Hazen determined that for an integrated biorefinery producing ethanol and pyrolysis oil, revenues only varied by $13 depending on the output of the two products. Hazen calculated this based on a 2011 National Renewable Energy Laboratory model, which showed total revenues ranging from $269 to $256 based on $1.79 per gallon ethanol and $1.05 per gallon pyrolysis oil. Yield, however, varied widely, ranging from 783 pounds of ethanol and 382 pounds of pyrolysis oil compared to 1,759 pounds of pyrolysis oil and no ethanol.

The lesson is, pick your process based on your feedstock, Cooper says. Beetle-kill pine produces low-grade pyrolysis oil, so it would be better to maximize ethanol yield with that type of feedstock. With inefficient or non-existent hydrolysis of feedstock, however, pyrolysis is the better process. “The revenue differences are not that great, so you should consider both of those options,” he says.

What about the recent research from the University of Florida that will allow pine tree breeders to create a new pine variety in only six years, slashing the time element by more than half? Could this genetic technique revolutionize the bioenergy industry, because researchers can accurately predict traits for specific uses, such as ethanol or other biofuel production? Theoretically, yes, Cooper says. Especially if researchers could design a pine tree where the lignin component could be easily modified in the pretreatment or fermentation process. “That would be a watershed,” he says.

For now, however, revenues for producing ethanol out of softwood aren’t great enough to justify cultivating and harvesting a specific crop. Most economic models today are based on selective forest harvesting or waste wood—not cultivating new pine crops. “I would be afraid that your costs of that biomass would be so great that they would offset any yield improvements that you would get,” he says. 

—Holly Jessen