Structural modification of pine and poplar wood by alkali pretreatment to improve ethanol production

The softwood pine and hardwood poplar were subjected to NaOH and Na2CO3 alkaline pretreatments for their conversion into ethanol. The resulting solids were characterized in detail for structural modifications. Both alkaline pretreatments enhanced ethanol yields, and the NaOH pretreatment at 93 °C resulted in the highest increase in ethanol yields of 297.5 and 249.5 % for pine and poplar woods, respectively, as compared to untreated woods. In all cases, the content of lignin and hemicellulose in pretreated solids was decreased by the pretreatments, while glucan contents, accessible surface area, and enzymatic hydrolysis yields were increased. New correlations between the accessible surface area, lignin removal, and the ethanol yields were obtained for both feedstocks, indicating that the accessibility of enzyme to the surface area is the most important factor affecting enzymatic hydrolysis. The results also showed that the solute exclusion technique is a simple approach that can be applied to predict ethanol yields from pine and poplar. Among the pretreatment conditions employed for soft- and hardwood, the NaOH pretreatment at 93 °C is the most efficacious. The glucose yields were 8.4 % and 13.1 % for untreated pine and poplar woods, respectively. However, pretreatment at 93 °C with NaOH increased the glucose yield to 46.5 % and 69.3 % for pine and poplar, respectively.