Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2009
Publication Date: 1/20/2010
Citation: Mullen, C.A., Boateng, A.A., Hicks, K.B., Goldberg, N.M., Moreau, R.A. 2010. Analysis and comparison of bio-oil produced by fast pyrolysis from three barley biomass/byproduct streams. Energy and Fuels. 24:699-706. Interpretive Summary: In order to meet the renewable fuels standards set by the US government, 21 billion gallons of advanced bio-fuels will need to be produced by 2022. Currently the largest source of renewable fuels is ethanol derived from the fermentation of corn grain. Corn ethanol, however, does not qualify as an “advanced bio-fuel,” and its production is greatly concentrated in Mid-Western United States. In order to develop bio-fuels industries for other areas of the United States, ARS has studied and developed the production of fuel ethanol from barley grain. In the Mid-Atlantic and Southeastern United States, barley can be grown in the winter, adding a fuel crop to a farmer’s rotation without interrupting the production of their traditional food crops. The production of winter barley grain and its fermentation to ethanol, produces co-products in the form of the unused parts of the plant, like straw and hulls as well as the unfermented part of the grain, know as Distillers Dried Grains (DDGS). These co-products of barley production are also potential feedstocks for the production of advanced bio-fuels. In this study we used a process called fast pyrolysis to convert these barley co-products into a dense liquid called bio-oil and analyzed its chemical and physical properties. Fast pyrolysis is done by rapidly heating the biomass in the absence of air and then quickly cooling the vapors. Bio-oil can be sent on to be upgraded into liquid transportation fuels or used as a starting material for synthetic chemicals. In each case, the production of bio-oil from the barley co-products was found to be feasible, with about 70% of the feedstock being converted to bio-oil. The bio-oils differed between feedstocks, with bio-oil from DDGS containing the most energy but also suffering from undesirable properties such as high viscosity and storage instability. Parallel studies in our laboratory are being done to understand and solve this instability problem. This information will be useful to those producing or considering producing ethanol from barley, and groups who advise farmers who may consider growing barley as an energy crop.
Technical Abstract: Fluidized bed fast pyrolysis was carried out on three different barley biomass coproduct streams, barley straw, barley hulls and DDGS from Saccharomyces cerevisiae fermentation of barley grain. Each of these are possible sources of feedstock for advanced bio-fuels production via fast pyrolysis as by-products of production of fuel ethanol from barley grain. Bio-oil yields from pyrolysis of each of these feedstocks were ~70%. Bio-char yields were 16-21% from the barley feedstocks. Bio-oil produced from straw and hulls had an energy content of 24-25 MJ/kg on a dry basis, while bio-oil produced from DDGS had a dry basis energy content >30 MJ/kg. The bio-oils were further characterized for composition and stability. None of the bio-oils was found to be stable as per ageing and stability tests measured by an increase in average molecular weight when stored under accelerated aging conditions, which is typical for biomass fast pyrolysis bio-oils. Instability was greatest for the bio-oil produced from the DDGS. Parallel studies in our laboratory are being done to understand and solve this instability problem. The results indicate that co-locating fast pyrolysis units in a barley ethanol plant will produce potentially usable and blendable liquid fuel from any of the barley processing value chain.