Sulfuric acid hydrolysis of isolated xylan: A statistical optimization approach

Sulfuric acid hydrolysis conditions for carbohydrates often represent a compromise resulting in suboptimal outcomes. Therefore, the sulfuric acid hydrolysis of xylan isolated from wheat straw hemicellulose was systematically investigated and optimized. The wheat straw xylan was obtained via saturated steam autohydrolysis followed by ethanol precipitation. This xylan was compared with standards derived from beech wood and corn cobs. A statistical experimental design was employed to elucidate the relationships between input (reaction temperature, reaction time and sulfuric acid weight fraction) and output parameters (xylose and furfural yields). Generally, reaction temperatures below 110 °C are preferred for hydrolysis of isolated xylan. For high xylose yields, a sulfuric acid weight fraction of 6 wt% is effective. A multi-objective optimization can be applied to simultaneously minimize furfural formation. Precipitated xylans require more severe hydrolysis conditions compared to the hydrolysates prior to precipitation due to lacking of biomass matrix including organic acids. With a simple hemicellulose-first process, wheat straw xylan of relatively high purity and without analytical matrix effects can be obtained. Within the investigation scope, the regression models provide a robust basis for optimizing acid hydrolysis parameters and highlight their critical role in carbohydrate analysis. Future work should investigate the transferability of the methodology.