2024 AIChE Annual Meeting

(204a) Fractionation Mechanism and Valorization Technology of Sugarcane Bagasse in Homogeneous System

Authors

Tan, X., Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences
Zhuang, X., Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences
Breaking the recalcitrance of sugarcane bagasse (SCB) through pretreatment steps is the basis for realizing the whole valorization of SCB. Different homogeneous pretreatment systems were constructed to investigate its depolymerization and enzymatic performance on SCB. In the study of fractionation of sugarcane bagasse by acetone /phenoxyethanol /water (APW) system, the optimum pretreatment conditions obtained by Box-Behnken design (BBD) were as follows: liquid-solid ratio of 15:1, 125 °C, 120 min, 0.17 M H2SO4, which could realize 98.12% deligninfication rate and 6 times higher cellulose enzymatic hydrolysis rate. Severity factor (CSF) was introduced to assess the correlation between pretreatment severity and delignification, and found that the lignin removal rate could reach 90% when CSF equals1.86. Using CSF is simpler and easier than that of BBD experimental design. Further correlation analysis to understand the properties of substrates that affect enzymatic hydrolysis was conducted, and found that fermentable sugar yields are affected by the surface area of cellulose, lateral order index, CrI, and specific surface area when the lignin content in the pretreated biomass is low.

Owing to the anticorrosion performance of the phenoxyethanol, the residue of the solvent may affect the fermentation efficiency of the residue. It was found that triethylene glycol (TEG) has the potential to be used as a pretreatment solvent owing to its biocompatibility, high boiling, low relative energy difference (RED) value (0.878) and miscible with water. The reaction conditions of alkaline TEG\H2O system were optimized by CSF and uniform design experimental methods. Most lignin could be removed while most carbohydrates were retained when CSF equals 8.5. Under the optimum conditions of 90 ℃, 180 min, 1% (w/v) NaOH and 40% (v/v) TEG/H2O, the delignification rate was over 80%, and the retention of carbohydrates and the enzymatic hydrolysis rate of residue were about 90%, respectively. In addition, the residue obtained by pretreatment can be directly hydrolyzed without washing, thus avoiding the generation of wastewater. Characterization of the recovered lignin revealed that TEGL had no condensed structure and that the β-O-4 bonds were well-preserved. The alkaline lignin-first strategy was proposed: under alkaline conditions, TEG can etherify with α position of β-O-4 bond to protect lignin structure.

A fermentation process without detoxification was developed based on alkaline TEG\H2O pretreatment, and wastewater generation was avoided. Firstly, it is found that alkaline TEG/H2O pretreatment is feasible on a large scale through scale-up experiments. Secondly, the process parameters of non-detoxified sugarcane bagasse (NDSCB) in ethanol production, methane production and alcohol-alkane co-production were detected. Both methane production and ethanol-methane co-production processes rebuild bacteria and methanogens, realize the degradation of TEG, and increase the methane production. Pretreatment residue and waste liquid can be directly converted into ethanol and methane fuel by microorganisms. Therefore, alkaline TEG/H2O system is suitable for developing green biorefinery process.

In summary, two kinds of homogeneous organic solvent pretreatment systems：acetone /phenoxyethanol /water (APW) system and alkaline TEG/H2O system was constructed to realize the high-value utilization of sugarcane bagasse in whole components. Based on alkaline TEG\H2O pretreatment, carbohydrates can be converted into ethanol liquid fuel and methane gas fuel by fermentation without detoxification, and the process completely avoids the generation of wastewater. At the same time, lignin with high pyrolysis activity or lignin nanoparticles can be obtained. In addition, the mechanism of component separation was explored and the alkaline lignin-first was proposed. This study has theoretical and practical reference value for building a bio-refining process which is technically economical and feasible.