Posted on Dec 01, 2010
The fuel ethanol industry in the United States continues to grow and will reach 10.5 billion gallons in 2009 (RFA, 2009a). Ethanol production still can not keep up with the increasing demand (RFA, 2009b). Congress mandates an increase in domestic renewable and alternative fuels production to 36 billion gallons per year by 2022 in the 2007 Energy Independence and Security Act, or EISA (Public Law 110-140). Biofuels usage will reach 20.5 billion gallons by 2015 and corn ethanol will be capped at around 15 billion gallons (CBO, 2009). Therefore, a big portion of that renewable biofuels must be produced from alternative feedstocks. Sweet sorghum with its prominent agricultural features such as low fertilizers and water requirements, shorter grow period, and high biomass yields (up to 20-30 dry tons/hectare) is a very promising energy crop (Geng et al., 1989; Rooney 2007). Furthermore, it is not a food crop and can grow on diverse marginal lands, so there will be no end-use and land-use conflict issues either. Approximately 40-45% of the sweet sorghum dry mass are fermentable sugars and starch (equivalent to corn yield of ~200 bu/acre). If all of them are converted to ethanol, potential ethanol yield could reach 600-650 gal/acre (comparing with 440-460 gal/acre of corn) (Wu et al., 2009). The greatest challenge for sweet sorghum as a feedstock for ethanol production is its short harvest period and the extreme instability of the juice. According to Report from International Conference on Sorghum for Biofuels (Houston, TX, 8/19-8/22, 2008), storage and transportation issues are more critical for sorghum than most other biomass feedstocks, especially for sweet sorghum due to its rapid change in sugar content or sugar degradation after harvest. Up to 50% of total fermentable sugars in sweet sorghum juices will be lost if stored at room temperature for a week (Wu et al., 2009). Similar ranges of losses have been reported for sugarcane industries (Solomon 2009). Cost effective processing approaches to significantly extent the storage stability of sweet sorghum juice will turn seasonal rush operation into a year-around production process, which will greatly benefit all sectors related with sweet sorghum ethanol production ranging from sweet sorghum growing farmers, feedstock logistic companies, and ethanol industry.
The long-term goal of this proposed research is to develop affordable processing techniques to extend the storage stability of sweet sorghum juice, so that sweet sorghum based ethanol facilities can be run year around rather than a seasonal operation. The short-term goal is to evaluate several approaches for their ability to extend the storage stability of sweet sorghum juice and establish a most cost effective process. The research will focus on 1) development of innovative devices to stabilize sweet sorghum juice; 2) characterizing the sweet sorghum juices after treated with different techniques; and 3) evaluating the storage stabilities and ethanol fermentation performance of the treated sweet sorghum juices.
The proposed research will deliver the state-of-the-art processing technology for stabilizing sweet sorghum juice. This would help sweet sorghum to play a bigger role in the fast growing bioethanol industry, to sustain the ethanol industry to realize the goal set by the 2007 EISA as well as to revive sweet sorghum related rural economy. The success of this project will generate informative data and knowledge for large-scale processing and storage of sweet sorghum juice for fuel ethanol production, extend the actual harvest period, and turn sweet sorghum ethanol plants from seasonal operation to year around production. Our proposed research addresses the Mission of USCP of “USCP commits to effectively investing checkoff dollars to increase producer profitability and enhance the sorghum industry” and this research addresses the technical area of “research the benefit and limiting issues for sugar conversion and storage in sweet sorghum” described in the RFP.