8-36: Increase in enzyme accessibility by oxygen delignification and mechanical refining for green liquor pretreated biomass

Enzymatic hydrolysis still remains an expensive process and thus, the amount of enzyme dosage must be reduced to make the overall process more financially attractive.  Oxygen delignification and mechanical refining were performed as post-treatments on alkaline green-liquor (sodium carbonate and sodium sulfide) pretreated biomass to reduce enzyme dosage.  Enzyme reduction of 50% (from 10 FPU/g to 5 FPU/g) was achieved when post-treatments was applied for pretreated woody biomass at the same level of enzymatic conversion.  The improvement was found more effective on non-woody biomass.  The post-treatments increased the enzymatic conversion from 51% to 79% for non-woody biomass at the low alkaline charge and enzyme dosage.  Total carbohydrate of 73% was recovered from raw materials considering the yield of pre- and post-treatments.  To investigate enzyme accessibility, which might be responsible for the increase in carbohydrate conversion, samples were evaluated in a wet state using two independent analyses; Simons’ staining and DSC thermoporometry methods.  A strong correlation was found between carbohydrate conversion and measured properties.  Especially, the increase by refining was higher compared to that by oxygen delignification, which suggests that fibrillation by the shearing force of a refiner could open up the biomass cell wall structure.  Images from FE-SEM also confirmed highly fibrillated surface when biomass was mechanically refined.  According to the results in this study, carbohydrate conversion was improved by oxygen delignification and mechanical refining through the increase in enzyme accessibility measured by Simons’ staining and DSC thermoporometry methods.