INTEGRATING A STATISTICAL APPROACH TO OPTIMIZE THE PRETREATMENT CONDITIONS FOR THE DECONSTRUCTION OF COTTON STALKS WITH A PROTIC IONIC LIQUID
Pages: 609-621 Published: 23 Nov 2017
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Abstract: Protic ionic liquid, triethylammonium hydrogen sulfate (TEAHSO4) was investigated in terms of its effects on the deconstruction of cotton stalks. Lignin was removed from the structure and obtained as an insoluble residue, precipitate. The biomass fraction with enriched cellulose content was subjected to enzymatic hydrolysis. The changes in the biomass digestibility with respect to the pretreatment conditions (biomass loading and pretreatment time) were analyzed via response surface optimization using the statistical software, JMP®. The enzymatic hydrolysis was monitored for 24 hours. The optimized conditions for biomass loading and pretreatment time were found as 16.2% and 24 h, respectively for the samples withdrawn at the 6th hour of the enzymatic reaction. On the other hand, optimized conditions were 20% and 24 h for the samples withdrawn at the 24th hour of the hydrolysis and the corresponding biomass digestibility was 47% according to the quadratic formula predicted by the statistical tool. The changes in the percentage yield of the precipitates, which were obtained following the water addition to the pulp free ionic liquid solution, were evaluated statistically as well. The optimum pretreatment condition that gave the maximum precipitate yield was found as 10% of biomass loading and 12.2 h of pretreatment time. Apparently, pretreatment at biomass loadings higher than 10% hindered the effective interaction of biomass and the ionic liquid and thus, decreased the removal of lignin from the biomass. However, utilization of biomass loading as high as 20% was favorable for the biomass digestibility. Precipitates were characterized via ATR-FTIR and investigated in terms of the chemical structure of lignin. Prolonged pretreatment periods demonstrated a destructive effect on the typical aromatic structure of lignin.