Corn stover pretreatment with Na2CO3 solution from absorption of recovered CO2

Authors: Garcia-Negron, Valerie; Toht, Matthew

Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2022
Publication Date: 11/3/2022
Citation: Garcia-Negron, V., Toht, M.J. 2022. Corn stover pretreatment with Na2CO3 solution from absorption of recovered CO2. Fermentation. https://doi.org/10.3390/fermentation8110600.
DOI: https://doi.org/10.3390/fermentation8110600

Interpretive Summary: Lignocellulosic biomass (e.g. grasses, woods, crop residues) suitable for fuel ethanol production via fermentation serves as an alternative renewable resource to corn or sugar to reduce dependance on fossil fuels. Pretreatment methods are used to improve cellulose digestibility during enzymatic hydrolysis, a vital step before fermentation to ethanol. In addition to ethanol fermentation it also produces carbon dioxide (CO2). Although renewably sourced, capture and utilization of this CO2 would increase the sustainability of fuel ethanol production. This work evaluated the feasibility of trapping the generated CO2 via formation of sodium carbonate and using that sodium carbonate as a reagent for biomass pretreatment. Here corn stover biomass was treated with sodium carbonate produced from carbon dioxide captured via absorption with a sodium hydroxide solution. Composition analysis of the pretreated biomass exhibited higher cellulose content (40.96%) and less lignin (16.50%) than the untreated biomass, indicating the pretreatment produced the desired effect. For the next step enzymatic hydrolysis, different durations and two enzyme ratios were compared. Glucose, the main direct precursor to ethanol was produced in higher yield for the pretreated biomass and cellulase-rich enzyme ratio where it surpassed 90% after 24 hours of hydrolysis. Consequently, sugar concentrations were relatively high in glucose, intermediate in xylose, and very low in arabinose. These results demonstrate the viability of capturing carbon dioxide and converting it into an efficient and economical sodium carbonate pretreatment for corn stover biomass.

Technical Abstract: Renewable resources such as lignocellulosic biomass are effective at producing fermentable sugars during enzymatic hydrolysis when pretreated. Optimizing pretreatment methods for delignification while maintaining sustainability and low processing costs requires innovative strategies such as reusing greenhouse gas emissions for materials processing. Corn stover, an agricultural waste residue, was pretreated with 2.2 M sodium carbonate produced from carbon dioxide captured via absorption in a 5 M sodium hydroxide solution. Composition analysis of the pretreated corn stover exhibited higher cellulose content (40.96%) and less lignin (16.50%) than the untreated biomass. Changes in the chemical structures are visible in the FTIR-ATR spectra, particularly in the cellulose and lignin-related absorption bands. The sugar released from hydrolysis was evaluated at different time intervals and by varying two enzyme ratios of CTec2-to-HTec2 (2:1 and 3:1). Enzymatic hydrolysis produced higher and more stable glucose yields for the pretreated biomass, surpassing 90% after 24 hours using the 3:1 enzyme ratio. Sugar concentrations notably increased after pretreatment and even more when using the cellulase-rich enzyme solution. The maximum glucose, xylose, and arabinose recovered were 44, 19, and 2.3 g/L. These results demonstrate the viability of capturing carbon dioxide and converting it into an efficient sodium carbonate pretreatment for corn stover biomass. Additional processing optimizations depend on the combination of physicochemical parameters selected.