Efficacy of alkaline peroxide pretreatment on Eucalyptus grandis as effective lignin removal strategy for production of ethanol using enzymatic hydrolysis

The dried bark of Eucalyptus grandis (EG) was treated in alkaline (NaOH) and alkaline peroxide (NaOH along with H₂O₂) solution at 60 °C (AHP-60), 80 °C (AHP-80) and in an autoclave at 121 °C and a pressure of 15 lb/ \({{\text{in}}}^{2}\) ${\text{in}}^2$ (AAHP). The structural and chemical changes during pretreatment with alkaline and alkaline peroxide were observed through FTIR, XRD analysis and DNS assay. The effects of NaOH and H₂O₂ concentration and temperature on lignin removal efficiency and production of reducing sugar were studied. Kinetic parameters of enzymatic hydrolysis and fermentation were evaluated. The results indicated the removal of lignin and easy accessibility of cellulose as the crystallinity of the pretreated Eucalyptus grandis increased. The lignin removal was highest (73.20%) for AAHP. A maximum reducing sugar yield of 215.5 mg/g was also obtained from the same pretreatment conditions confirming the recalcitrance nature of lignin is the key inhibitory factor for the production of reducing sugars. During enzymatic hydrolysis, glucose concentration is observed to be increased over time with the increase in substrate concentration for a particular enzyme loading. EG in AAHP upon enzymatic hydrolysis generates the highest amount of reducing sugar and yields better ethanol conversion (9.941 g/g). The kinetic parameters from hydrolysis and fermentation indicate no inhibition of enzymes by substrate and product.