Optimization of pretreatment condition for ethanol production from oxalic acid pretreated biomass by response surface methodology

• The xylan degradation was directly proportional to the degradation rate.
• The highest ethanol yield was obtained as 95.21% (34.54 g/L) from pretreated biomass.
• The ethanol yield is expected based on the proposed model.
• The optimal pretreatment condition was 82 mM of oxalic acid, 160 °C and 58 min.

The optimal pretreatment condition for ethanol production from yellow poplar by simultaneous saccharification and fermentation (SSF) was investigated using response surface methodology. The degradation rate of yellow poplar was gradually increased by increasing the pretreatment severity. The amount of xylan degradation was directly proportional to the degradation rate. The structural change in the pretreated biomass brought about oxalic acid pretreatment was studied by XRD, BET, and solid state CP/MAS 13C NMR. The results suggested that hemicelluloses and amorphous cellulose were hydrolyzed by oxalic acid pretreatment. The crystallinity value of the pretreated biomass increased until the combined severity factor (CSF) became 1.52, while it decreased when the CSF became 1.92 due to degradation of some of the crystalline cellulose under severe pretreatment conditions. The surface area of the pretreated biomass increased slightly from 0.49 to 1.01 m2/g due to the removal of hemicellulose during oxalic acid pretreatment. The highest ethanol yield obtained 95.21% when the pretreated biomass was used for SSF. Using response surface methodology, it was found that the optimal oxalic acid pretreatment condition: oxalic acid, 82 mM; temperature, 160 °C; and time, 58 min. This condition agreed well with that obtained by the model prediction.