Comparison of Acidic, Alkaline, and Sequential Deep Eutectic Solvent Pretreatment Methods for Crescentia cujete Linn. Fruit Rind Katrina J. Adajar (1,a*), Lemmuel L. Tayo (2,b)
1School of Graduate Studies, Mapua University, Intramuros, Manila, 1002, Metro Manila, Philippines
2School of Health Sciences, Mapua University, Makati City, 1205, Metro Manila, Philippines
a*kjadajar[at]mymail.mapua.edu.ph, bLLtayo[at]mapua.edu.ph,
Abstract
The application of choline chloride-based deep eutectic solvents for efficient lignocellulosic biomass fractionation were studied using different pH range and sequential treatment. Acidic choline chloride and lactic acid, alkaline choline chloride and monoethanolamine, and sequential DES systems with varying molar ratios of 2:1, 1:1, and 1:2 were evaluated for the pretreatment of Crescentia cujete Linn. fruit rind under 1 to 2 h thermal conditions. The effects of key physicochemical properties, particularly pH and viscosity, on delignification and cellulose enrichment were investigated, while FTIR and SEM analyses were employed to examine structural changes in the treated biomass. Results showed that pH and viscosity exert only limited influence on biomass fractionation. A moderate positive correlation between pH and lignin removal with r value equal to 0.38 suggesting that more basic conditions may enhance delignification, whereas viscosity exhibited a comparable negative correlation, indicating improved mass transfer in lower-viscosity systems. However, the model demonstrated low explanatory power with R^2 equal to 0.283 and was not statistically significant, indicating that these factors alone do not strongly govern lignin removal. Similarly, cellulose enrichment showed negligible dependence on pH and viscosity, with very low model fit. Among the treatments, the acidic ChCl and La/1:1 system at 2 h achieved the most balanced performance, yielding 46.23 percent cellulose enrichment and 27.9 percent lignin removal. Although sequential treatments resulted in slightly higher cellulose content of 47.08 percent, they caused substantial hemicellulose degradation, indicating excessive fractionation severity. These findings highlight that solvent composition and treatment conditions play a more critical role than physicochemical properties alone in governing biomass fractionation.
Keywords: deep eutectic solvents (DES), sequential pretreatment, lignocellulosic biomass, delignification
