Ayumi HACHISU1, Kazuaki NINOMIYA1, Kenji TAKAHASHI1, Kosuke KURODA1
1Kanazawa University, Kanazawa, Japan
Bioethanol from plant biomass is a promising alternative to fossil fuels. However, conversion to bioethanol involves high energy costs. To solve this problem, one-pot ethanol production (successive biomass pretreatment, enzymatic hydrolysis, and fermentation in a single vessel) is necessary, because multi-pot processes require high energy input. In addition, the one-pot process have to be based on a solvent with low?toxicity and under mild conditions. Ionic liquids can pretreat biomass under mild conditions [1], but the high toxicity of the ionic liquid prevents its use in the one-pot process. On the other hand, OE2imC3C, a liquid zwitterion with low toxicity, was used in the cellulose dissolution pretreatment [2], which makes it one of the most suitable solvents for the one-pot process. However, this one-pot process with OE2imC3C takes place at high temperatures (e.g. 120 °C) and need to dilute of pretreatment solvent before hydrolysis (e.g. eight times) [2], and further reduction of energy cost for pretreatment is required.
In this work, the minimum temperature and concentration conditions for pretreatment of plant biomass with OE2imC3C was investigated. The ionic liquid, [Emim]OAc, which is commonly used in the literature for cellulose pretreatment, was also evaluated for comparison. The pretreatment ability of OE2imC3C was lower than [Emim]OAc. On the other hand, the Kamlet-Taft β value of OE2imC3C, which indicates hydrogen bond acceptability, was 1.12, which is corresponding to that of [Emim]OAc [2]. We then sought the critical factors of the low pretreatment ability. The low xylan solubility [3] or high viscosity are hypothesized to be the critical factors. The effect of xylan solubility on pretreatment ability was investigated through the hydrolysis efficiency of hemicellulose in the pretreated biomass. The results indicated that xylan solubility did not significantly affect pretreatment ability. The effect of viscosity was examined by changing the pretreatment time to ignore viscosity, and viscosity significantly affected the pretreatment ability. Development of new liquid zwitterions with lower viscosity contributes to one-pot bioethanol production.
References
[1] Y. Fukaya et al., Green Chem., 10, 44-46 (2008)
[2] K. Kuroda et al., J. Am. Chem. Soc., 139, 16052-16055 (2017)
[3] R. Kadokawa, K. Kuroda et al., ACS Sustain. Chem. Eng., 9, 8686-8691 (2021)