Enzymatic hydrolysis of pine pretreated with ethanol and sodium hydroxide

JULIA KRUYENISKI ; FERNANDO E. FELISSIA; CAMILA M. IMLAUER; MARÍA C. AREA

Congreso; 3er Congreso Iberoamericano sobre Biorrefinerías; 2015

Pine sawdust, the most abundant and underutilizedforest-industrial waste, can be used as raw materialin a biorefinery. A possible product is bioethanol,obtained from cellulose present in this waste.The process involves three stages: pretreatment,enzymatic hydrolysis and fermentation. One ofthe most influencing factor in the hydrolysis is thechemical composition of the substrate, which isdirectly linked with the kind and conditions of thepretreatment to which the material was subjected.The aim of this work was to study the enzymaticdigestibility of pine sawdust submitted to alkaline- ethanol pretreatments. The experiments wereconducted under two alkaline charges (15 and 25%of sodium hydroxide on dried wood), two differenttimes (60 and 90 minutes), liquor/wood ratio of 5/1,maximum temperature of 170ºC, and an alcohol/waterratio of 35/65. As reference, and to analyze synergiceffects, the material was also treated separately witheach reactive (soda and ethanol). The pretreatedmaterials presented different chemical compositions,e.g., lignin contents varied from 3 to 22% on driedwood. NREL (National Renewable Energy Laboratory)standards were used for the characterization of thefibrous material. NREL standards were used alsoas guide to make the enzymatic activity and thehydrolysis. The enzymatic hydrolysis was performedat 2% consistency, pH 4.8 and 50ºC, with an enzymaticcharge of 20 FPU/ g glucans and 40 IU/ g glucans.The reaction was monitored every 24 hours until 72hours. DNS methodology was used to measure thepercentage of reducing sugars after the enzymatichydrolysis. The effect of alkaline charge on yieldsof reducing sugars was significant (p-value< 0.05),whereas the time did not show any effect. Ethanol andsoda exhibited a positive synergy effect on the yield ofreducing sugars. Results also suggest the existenceof a negative correlation between the yield of reducingsugars and lignin content of the pretreated material.Highest yield from the enzymatic hydrolysis wasobtained with alkali-ethanol pretreatment using a highcharge of soda, this material have a content of ligninlower than 7%.