(473c) An Integrated Fermentation Process with in-Situ Product Separation for High-Titer and High-Rate Butanol Production from Lignocellulosic Biomass Hydrolysate

In this study, we aimed to produce n-butanol, an industrial solvent and advanced biofuel, from agricultural residues in an integrated bioprocess using genome-engineered clostridia in a fibrous bed bioreactor (FBB) with continuous gas stripping for in-situ butanol recovery. Biofuel production has been limited by low product yield, productivity, and titer; whereas biorefinery using lignocellulosic feedstocks suffers from high capital and operating costs associated with pretreatments and cellulose hydrolysis, which also generate highly toxic inhibitors negatively affecting fermentation performance. We have engineered a clostridia strain as a superior cell factory that not only can produce n-butanol from both glucose and xylose simultaneously with high yield and productivity, but also has a high tolerance to butanol and hydrolysate inhibitors and can use biomass hydrolysates directly without detoxification. This novel cell factory is robust for butanol production but has not been used in industrial fermentation. Thus, butanol production from glucose, xylose, and acetate present in the corn stover hydrolysate by the engineered clostridia immobilized in the FBB was investigated first in sequential batch fermentations to evaluate the fermentation kinetics and long-term process performance (product titer, rate, and yield) and stability. In general, stable production of butanol at a high titer (>18 g/L), yield (>0.3 g/g), and productivity (>0.5 g/L/h) was obtained in more than 15 consecutive batches over a period of one month. Then, the fermentation was operated with in-situ gas stripping to continuously separate butanol from the fermentation broth and the gas-stripped butanol was collected via an in-line condenser, generating a high-concentration (>80% v/v) and high-purity (>95%) butanol suitable for direct biofuel application. The in-situ gas stripping not only facilitated the continuous separation and production of butanol for an extended period of time, but also increased the productivity due to reduced butanol toxicity to cells. Our techno-economic analysis (TEA) indicated that the integrated biobutanol fermentation process would be energy efficient and could substantially reduce the biobutanol cost to less than $2.5/gal, competitive for applications as industrial solvent and advanced biofuel. The integrated fermentation process with engineered clostridia is thus promising for industrial production of biobutanol, which can also reduce green house gas emissions by more than 50%.