POTASSIUM HYDROXIDE PRETREATMENT OF NAPIER GRASS: CONDITIONS FOR ENHANCED REDUCING SUGAR AND BIOETHANOL PRODUCTION

Abstract

The recalcitrance of lignocellulosic feedstock needs to be altered for to produce fuels and chemicals. Pretreatment is used to enhance the reactivity of cellulose and the digestibility of biomass, resulting in the effective generation of fermentable sugars. Potassium hydroxide (KOH) is particularly effective at selectively removing lignin from biomass without excessively degrading cellulose and hemicellulose. Moreover, KOH is generally less corrosive than sodium hydroxide (NaOH), leading to lower maintenance costs for pretreatment equipment. In present study, Napier grass was utilized as the substrate for reducing sugar production. Proximate analysis indicated that Napier grass contains approximately 28.50±0.12% hemicellulose, 34.15±0.08% cellulose and 26.41±0.04% lignin. With the use of the Box-Behnken Design (BBD) method, pretreatment conditions were improved. The ideal conditions for KOH pretreatment of Napier grass were determined to be 6% KOH, 180 °C temperature, and a pretreatment time of 120 min. Higher yields of reducing sugars (43.29 g/L) were achieved by this optimized condition. By analyzing the experimental data, ANOVA helps in developing a reliable model that predicts the ideal conditions for increasing reducing sugar yield. Desirability functional studies were employed in optimization to identify ideal conditions that satisfy multiple criteria simultaneously, and the design was validated by trial experiments to ensure accuracy. Desirability studies confirmed that the optimal yield of reducing sugars, approximately 43.72 g/L, was achieved with 6.79% KOH concentration, at a temperature of 178.4°C, and a pretreatment duration of 119.6 min. The results are closely resembles the experimental values predicted by the response surface model. Substrates pretreated with higher KOH concentrations yielded more ethanol (72 g/L) from Saccharomyces cerevisiae in SSF tests compared to those pretreated with lower KOH concentrations.