Pretreatment of Sweet Sorghum Bagasse for Ethanol Production Using Na₂CO₃ Obtained by NaOH Absorption of CO₂ Generated in Sweet Sorghum Juice Ethanol Fermentation

(1) Background: Commercial production of fuel ethanol currently uses sugarcane and corn as feedstocks. Attempts to develop other renewable feedstocks that are more abundant have led to lignocellulosic biomass, which requires pretreatment prior to enzymatic hydrolysis to generate fermentable sugars. One of the largest cost components of pretreatment is chemical cost. Ethanol fermentation also produces large quantities of CO₂ as a co-product contributing to global warming. (2) Methods: Sweet sorghum has emerged as a potential new feedstock for ethanol production. In the present study, the CO₂ produced in sweet sorghum juice (SSJ) fermentation was captured by absorption in 5 M NaOH. The resultant Na₂CO₃ solution was used for pretreatment of sweet sorghum bagasse (SSB), which is the solid residue in SSJ extraction. The pretreated SSB was fermented in SSJ to produce additional ethanol. (3) Results: CO₂ absorption efficiency of 92.0% was observed. Pretreatment of SSB by the obtained Na₂CO₃ solution resulted in no loss of glucan and only 8.1 wt% loss of xylan. Ethanol yield from glucan in the pretreated SSB was 81.7% theoretical. (4) Conclusions: CO₂ from SSJ fermentation captured as Na₂CO₃ could be used for efficient SSB pretreatment. Further study focusing on pretreatment process optimization is needed.