Lactic Acid-Proline Solvent Pretreatment of CS: Effects of Process Variables on Glucan, Xylan, and Lignin Composition

The aim of this study is to investigate the effect of temperature, duration, and water dilution on the composition of glucan, xylan, and lignin in cowpea shells (CS) pretreated with a neat and diluted Lactic acid-proline solvent. The composition of glucan, xylan, and lignin was analyzed using the NREL method. The highest xylan removal (12%) was achieved after a 6-hour pretreatment at 150°C, while 11.35% lignin removal was observed after 5 hours at the same temperature. The most significant increase in glucan content, reaching 78.3 %, was observed after 4 hours at 150°C using a 2.5% (w/w) water-diluted solvent. Comparing the effect of the neat solvents and diluted solvents it can be concluded that while the neat solvent promoted the dissolution of xylan and lignin, the addition of water preserved glucan from the harshness of the pretreatment. Therefore, the decision to dilute a natural deep eutectic solvent before its application in biomass pretreatment depends on the desired product from biomass fractionation (lignin or a carbohydrate-rich material) and pretreatment temperature. These findings provide a foundation for further investigations into optimizing the entire process.