Researchers worldwide are trying to economically convert cellulosic biomass such as corn stover into "cellulosic ethanol." But Agricultural Research Service (ARS) scientists have found that it might be a cost-effective, energy-efficient and environmentally sustainable to use corn stover for generating an energy-rich oil called bio-oil and for making biochar to enrich soils and sequester carbon.
In the report, ARS specifically thanks the National Corn Growers Association for supporting this work and for the opportunity to present the preliminary results at the 2008 Corn Utilization and Technology Conference.
“NCGA consistently searches for innovative ways to increase profitability for corn farmers while advancing useful science,” said Jon Holzfaster, chair of the NCGA ethanol committee. “By using sustainable amounts of stover to produce energy, we can maximize the benefits of the crop while maintaining the delicate ecological balance farming requires.”
Stover is made up of the leaves, husks, cobs and stalks of the corn plant, and could provide an abundant source of feedstock for cellulosic ethanol production after the grain is harvested. By removing a sustainable portion stover from the field, researchers avoid possible pitfalls such as erosion, depletion of plant nutrients and acceleration of loss of soil organic matter.
Several ARS scientists collaborated with the NCGA to explore other options for using corn stover as biofuel feedstock. The researchers used fast pyrolysis, which is rapid heating in the absence of oxygen, to transform corn stover and cobs into bio-oil and biochar. They found that the bio-oil captured 70% of the total energy input, and the energy density of the bio-oil was five to 16 times the energy density of the feedstock.
This suggests it could be more cost-effective to produce bio-oil through a distributed network of small pyrolyzers and then transport the crude bio-oil to central refining plants to make "green gasoline," rather than transporting bulky stover to a large centralized cellulosic ethanol plant.
In addition, about 18% of the feedstock was converted into biochar, which contains most of the mineral nutrients in the corn residues. Using biochar as a soil amendment would return those nutrients to the soil, reduce leaching of other nutrients, help build soil organic matter and sequester carbon.
These findings were published online in the journal Biomass and Bioenergy.