Modeling and optimal design for biobutanol production from mixed sugars (glucose and xylose) by a continuous fermentation process with ex situ butanol recovery (ESBR)

Abstract

Recently, research for the production of biofuel using $2^{nd}$ generation biomass, non-edible biomass, instead of $1^{st}$ generation biomass, edible biomass, is going on. The biosugar is originated in lignocellulosic biomass has hexose and pentose (e.g., xylose) which is hardly uptake by microbes besides of 1st generation biomass contains glucose mainly. Even though biobutanol has better fuel properties than bioethanol, it is very hard to achieve economics by using traditional batch fermentation due to low productivity of biobutanol from inhibition and toxicity of butanol in the fermenter. Research of genetic engineered microbe and continuous fermentation systems to be maintained proper butanol concentration in a fermenter for alleviating the inhibitory effect on cell growth and production due to butanol toxicity is carried on.

In this research, a mathematical model for the continuous fermentation process with ex-situ butanol recovery (ESBR) for biobutanol production using glucose and xylose is developed. This study proposes a concentration-dependent weighting factor to describe simultaneous utilization of glucose and xylose and develops a dynamic model with the integration of the kinetic models of fermentation and adsorption. The model parameters are estimated from experimental data of batch and fed-batch fermentation with in-situ butanol recovery (ISBR) in a lab and updated and validated with experimental data of fed-batch fermentation with ex-situ butanol recovery (ESBR) for the reliability of the model. Based on the unconstructed model, multi-objective optimization and sensitivity analysis are performed to improve the butanol productivity and to reduce the sugar loss, and single-objective optimization is conducted to maximize the profit of butanol production at cyclic steady state (CSS) condition. Optimal operating conditions are suggested in cases of different sugar ratio in feed, butanol threshold in a fermenter, and inclusion of a harvest tank. Through the systematic approach, the design of the harvest tank for commercial scale is proposed to achieve better economic feasibility.