Physical and chemical characteristics of pretreated pine sawdust and its enzymatic hydrolysis

J. KRUYENISKI; P. FERREIRA; M.G.V.S. CARVALHO; F.E. FELISSIA; MARÍA CRISTINA AREA

Congreso; IX Iberoamerican Conference on Pulp and Paper Research, CIADICYP; 2016

Pine sawdust, the most abundant and underutilized forest-industrial waste, can be used as rawmaterial in a biorefinery. The process for obtaining ethanol from cellulose in lignocellulosic wasteconsists of pretreatment, hydrolysis and fermentation. The chemical composition of the substrate andits accessibility (both related to pretreatment) are the most significant factors on enzymatic hydrolysis(EH). The aim of this work was to evaluate the effect of the physical and chemical characteristics ofa mixture of Pinus elliottii and Pinus taeda sawdust (forest-industrial residue) subjected to differentpretreatments, on its enzymatic digestibility. Eight pretreated materials of various chemicalcompositions were selected to evaluate crystallinity and porosity. The analyzed samples included thefollowing treatments: (1) initial sawdust (without pretreatment), (2) alkaline desresination followed bysteam explosion (SE), (3) SE and subsequent alkaline washing, (4) soda - anthraquinone (AQ)-oxygen treatment, (5) kraft- AQ, (6) soda ?AQ delignification, and (7, 8) soda ? ethanol (two samples).NREL (National Renewable Energy Laboratory) standards were used for the characterization of thefibrous material and as guide to evaluate enzymatic activity and hydrolysis. Crystallinity of the originaland treated residual solids was determined by X-ray diffraction. Distribution of pore volume in thestudied materials was evaluated by thermoporosimetry. The enzymatic hydrolysis was performed at2% consistency, pH 4.8 and 50ºC, with an enzymatic charge of 20 FPU/ g glucan and 40 IU/ g glucan.The reaction was monitored at 24, 48 and 72 h.Lignin content varied between 3.8 to 42.5% od depending on the pretreatment objective. Hydrolysisyield could be improved from 5.4% (exp. 1) to 96-100% (treatments 6 and 5 respectively). Correlationbetween EH yield and lignin content depends on the process objective (delignification orhemicelluloses extraction).Crystallinity index (CrI, calculated based on Segal equation) rises from 56.4% (without pretreatment)to a maximum of ̴76.0% in materials with low lignin content (< 7% od). CrI increases linearly from47% to 70% glucan (CrI 56.4% to 76%) and it stabilizes at its maximal value from there to 80% glucan.The evaluation of ΔPore volume/ΔDiameter against ΔDiameter shows a clearly defined modedistribution in the range 0.66 to 1.32nm, demonstrating that the applied treatments made increasethe number of pores but not the diameter of pore. The height of the peak increased in the followingorder of treatments: 1 < 6< 2-3 < 5