Improving Hybrid Poplars as a Renewable Source of Ethanol Fuel
Source: DOE Success Story (
click here to go to the source)
Challenge
The National Biofuels Initiative aims to replace 30% of fossil fuel used for light duty vehicle
transportation in the United States by 2030. Cellulosic biomass—including wastes (agricultural,
forestry, municipal, industrial/food processing) and energy crops (fast-growing grasses and
trees)—is expected to be an important source for ethanol production. In addition, it can be burned
to produce steam and electricity.
Most ethanol from biomass now comes from starch-based biomass, such as corn, which easily
breaks down into sugars for fermentation. Starch-based ethanol production is a well-developed,
relatively mature technology, but lacks a low-cost, large-volume alternative to corn for feedstock.
Cellulose and hemicellulose make up the bulk of all trees, grasses, and other plant matter—a
supply large enough to compete with oil fields—and researchers are developing processes to
produce ethanol from those renewable resources.
Innovating Solutions
GreenWood Resources saw potential in growing poplar trees—remarkable for their sheer biomass
productivity—to make ethanol. GreenWood's objective was to develop fast-growing and disease-
resistant hybrid poplars that offer maximum levels of cellulose and/or hemicellulose, optimizing
the growing cycle and economics of farming poplars as an energy feedstock.
With DOE EERE SBIR Phase I funding, GreenWood was able to conduct a study that established
the feasibility of hybridizing poplar trees for biomass feedstock.
This study identified the primary traits needing improvement in order to make poplars a better fuel source for biochemical (fermentation) conversion to ethanol, including wood-specific gravity, lignin content, ratio of syringyl-to-guaicyl (S/G) lignin forms, and glucose and xylose content.
With a follow-on DOE SBIR Phase II award, GreenWood began a hybridization program with an inheritance study to examine how selective breeding can improve the biofuels properties of the world's most productive hybrid poplar pedigree:
Populus x generosa. GreenWood built on an existing relationship with Washington State University in conducting this program and in developing a rapid assessment technique for efficiently determining critical energy characteristics of trees in the field.
The DOE SBIR Phase II project also involved field trials of a range of elite hybrid varieties in
demonstration plots established at 12 locations throughout the western U.S. to test the range of
genetic adaptability. To explore the benefits possible through tree farm management, GreenWood
closely integrated their research and development efforts with their operational tree farms and
with local energy developers.
The inheritance study was the foundation for continuing work in selective breeding of poplars
for high energy value. The rapid assessment technique, which uses near-infrared spectroscopy
to characterize the calorific value, chemical composition, and specific gravity of a feedstock
tree, enables staff to determine the essential energy properties of trees during regular in-field
measurements, avoiding expensive and time-consuming lab tests.
Poplars have a wide range of uses beyond energy conversion, as well—including chips for
pulping and logs for veneers and sawn wood products. The demonstration plots showed the
economic feasibility of growing poplars solely for energy production and for a combination of
saw logs and residual ethanol feedstock. On one plot located near an ethanol production facility
in Boardman, Oregon, poplar is being grown as a dedicated energy crop to supply feedstock for
