Sustainable production of bioenergy and bio-char from the straw of high biomass soybean lines via fast pyrolysis

Authors: Boateng, Akwasi; Mullen, Charles; Goldberg, Neil; Hicks, Kevin; Devine, Thomas; Lima, Isabel; McMurtrey Iii, James

Submitted to: Journal of Environmental Progress and Sustainable Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2010
Publication Date: 4/30/2011
Citation: Boateng, A.A., Mullen, C.A., Goldberg, N.M., Hicks, K.B., Devine, T.E., Lima, I.M., Mcmurtrey Iii, J.E. 2010. Sustainable production of bioenergy and bio-char from the straw of high biomass soybean lines via fast pyrolysis. Journal of Environmental Progress and Sustainable Energy. 29(2):175-183.

Interpretive Summary: The US renewable fuel standards require production of 21 billion gallons of advanced bio-fuels from non-food biomass by year 2022. This biomass must come from non-food biomass including forest residues and agricultural residues. The problem with the latter is that if these residues are removed from the ground it may cause soil erosion. A previous study carried out to access the availability of biomass to support bio-energy production in the US found that if high-biomass soybeans could be grown in a no-till farming system in rotation with corn then as much as one ton of biomass could be removed for bio-energy production without depleting the soil. ARS set out to develop two high-biomass soybean lines which have the potential to produce grains and straw for bio-energy production. In this study we evaluated the production of bio-energy from the straw of these two soybean lines via the thermal conversion technology called pyrolysis. This is heating the straw in the absence of air to yield a liquid fuel called bio-oil that can be used for heating or upgraded to gasoline-type fuel. A sold co-product, bio-char, containing carbon and ash and some permanent gases is also produced during pyrolysis. The results indicate that these products can be produced in sufficient quantities that a sustainable farm system could be enhanced by the synergy between production of extra biomass in soybean cultivation, bio-fuel production, production and use of bio-char that can sequester carbon and amend the soil in addition to nitrogen fixation enabled by soil bacteria. This information will be useful to soybean growers and farmers who are looking for sustainable methods of agriculture and US bio-energy policy makers.

Technical Abstract: The straws of two high-biomass soybean lines developed at ARS for bioenergy were subjected to thermochemical conversion by fast pyrolysis. The objective was to evaluate the potential use of the straw for the production of liquid fuel intermediates that can be burned “as is” and/or potentially upgraded to transportation grade fuel and at the same time produce biochar as a coproduct that can be deployed as a soil amendment so food and bioenergy can be sustainably produced in a soybean farm system. The study shows that high yields of pyrolysis liquids (bio-oil) can be efficiently produced from the soybean straws using the fluidized-bed fast pyrolysis technology. Free flowing bio-oil in yields of the 70 wt% range was produced with heating values in excess of 20 MJ/kg. Accompanying this was 22 wt% mineral-rich bio-char that can be returned to the soil and up to 10 wt% combustible gases with the potential to partially power the pyrolysis system. A sustainable farm system may be enhanced by the synergy between production of extra biomass in soybean cultivation, lignocellulosic biofuel production, production and use of bio-char to sequester carbon and amend the soil in addition to nitrogen fixation by rhizobial bacteria. Actual data over several years will be necessary to fully evaluate a potential soybean farm biorefinery system by comprehensive life-cycle analysis.