Bio-oil and biochar production from corn cobs and stover by fast pyrolysis

Authors: Mullen, Charles; Boateng, Akwasi; Goldberg, Neil; Lima, Isabel; Laird, David; Hicks, Kevin

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2009
Publication Date: 10/24/2009
Citation: Mullen, C.A., Boateng, A.A., Goldberg, N.M., Lima, I.M., Laird, D.A., Hicks, K.B. 2010. Bio-oil and biochar production from corn cobs and stover by fast pyrolysis. Biomass and Bioenergy. 34:67-74.

Interpretive Summary: The growing need for renewable energy requires conversion of cellulosic biomass (crop residues, energy crops) to complement the current corn to fuel ethanol industry. Corn stover is the largest source of crop biomass available in the United States and therefore is an important potential feedstock for producing these second generation biofuels. However, transportation of the large amount of corn stover that will be required for a second generation biofuels plant will be extremely expensive and difficult. Additionally, corn stover is not currently harvested because it is important that it is left on the field for soil quality purposes. Harvesting it can lead to ground and water pollution and decreased future crop yields. One type of biomass conversion, pyrolysis, involving heating the biomass to high temperatures, can help solve these problems because it produces dense liquids (bio-oil) that will be more cost effective to transport and solid biochar which can be applied to the soil to replace the harvested corn stover. Bio-oil can be further refined to transportation fuels at a central location. In this study, pyrolysis of two corn crop residues, corn cob and corn stover was performed and the products characterized. In both cases about 60% of the weight of the biomass was converted to bio-oil. Bio-oil had an energy content about half of what conventional diesel fuel has. About 20% of the biomass was converted to biochar for potential application to soil. This information will be important to those considering producing or refining bio-oil, those who advise corn growers and ultimately corn producers looking to add value to their crop residues.

Technical Abstract: Bio-oil and bio-char were produced from corn cobs and corn stover (stalks, leaves and husks) by fast pyrolysis using a pilot scale fluidized bed reactor. Yields of 60% (mass/mass) bio-oil (high heating values are ~20,000 kJ/kg, and densities > 1.0 g/mL) were realized from both corn cobs and from corn stover. The high energy density of bio-oil, ~20-32 times on a per unit volume basis over the raw corn residues, offers potentially significant savings in transportation costs particularly for a distributed “farm scale” biorefinery system. Bio-char yield was 18.9% and 17.0% (mass/mass) from corn cobs and corn stover, respectively. Deploying the bio-char coproduct, which contains most of the nutrient minerals from the corn residues, as well as a significant amount of carbon, to the land can enhance soil quality, sequester carbon, and alleviate environmental problems associated with removal of crop residues from fields.