1a. Objectives (from AD-416):
Objective 1: Design, optimize, and implement LMAA (Low Moisture Anhydrous Ammonia) pretreatment, which lead to improved digestibility for subsequent bioconversion (ISU) Objective 2: Develop fermentation process for conversion of fermentable sugars (C5 and C6 obtained from pretreated corn stover) to butanol (ERRC) Objective 3: Design and fabricate in-field LMAA pretreatment reactor for continuous operation (ISU and ERRC) Objective 4: Characterize and evaluate the effects of the LMAA pretreatment on biomass quality during long period of storage. e.g., for retention of carbohydrate and inhibition of growth of fungi or other microorganisms (ISU)
1b. Approach (from AD-416):
Objective 1: Freshly harvested corn stover will be used, which will be directly contacted with anhydrous ammonia in a designed reactor under very low pressure, termed as ammoniation step. After the ammoniation step, biomass will be subjected to the second step of treatment, which is called pretreatment step. We will explore wide range of reaction conditions to find an optimal and suitable condition for in-field pretreatment system, i.e. different reaction temperatures (40-150°C) and reaction times (1-168 h). Pretreated biomass will be directly saccharified and fermented with no additional washing step. Objective 2: A two-stage fermentation process will be developed and optimized. In the first stage, the pretreated corn stover will be hydrolyzed with commercial enzymes (cellulases, xylanases) to generate a stream rich in glucose and xylose, which in turn will be fermented by Clostridium tyrobutyricum to produce butyric acid. A fed-batch process will be developed for maximizing the final butyric acid concentration. Both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) configurations will be considered. In the second stage, butyric acid will be converted to butanol by selected butanol-producing organisms such as Clostridium acetobutylicum and Clostridium beijerinckii. Immobilized-cell reactor will be used to increase cell density, which in turn will increase butanol productivity (g/l-h), and to restrict cell growth, which in turn will increase butanol yield (g/g sugar consumed). The gas produced during butanol fermentation, which is mostly CO2, will be generated at sufficient rates to fluidize the biocatalyst pellets, thus providing mixing in the reactor. The use of a two-stage process will allow each stage to be optimized separately. Objective 3: Our team has the required technical skills and hands-on experience for design and fabrication of continuous pretreatment reactor. The PI had worked at ERRC on ammoniation of corn kernel for improvement of fractionation in 2005-2006 and a team at ERRC had designed and built a pilot scale corn ammoniator. Our initial reactor design will be based on our previous model, but it will be significantly modified and redesigned for this project. Objective 4: Characterization of pretreated biomass will be carried out to evaluate the effects of the LMAA pretreatment on biomass quality during long periods of storage. Extensive chemical composition analyses will be conducted over the long term storage from 1 week to 10 months. Desirable outcome of this task will be higher carbohydrate retention with no significant degradaion of fermentable sugars and zero or low growth of fungi or other microorganisms.
3. Progress Report:
The pilot-scale ammoniator was reassembled and corn stover was obtained from Iowa State University. Plan was made to test the flow of corn stover through the ammoniator followed by pretreatment of corn stover in this reactor with anhydrous ammonia gas. Laboratory-scale anhydrous ammonia pretreatment equipment also was set up to test the pretreatment of corn stover using the low moisture anhydrous ammonia process at smaller scale.