Post treatments to enhance enzymatic hydrolysis yield of steam exploded pine sawdust

ACUÑA, A.A.; AREA M.C.; FELISSIA, F.E.; STOFFEL, R.B.; GASSA, L.M.

Espoo

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

Aalto University, VTT, Åbo Akademi University, RIADICYP, PROVALOR

Enzymatic hydrolysis (EH) yield of the lignocellulosic materials is mainly dependent on cellulose accessibility and lignin content. Steam explosion (SE) has been claimed as one of the most successful option for hemicelluloses extraction from wood and for enhancing cellulose susceptibility to enzymatic attack. A previous study has shown that despite the effectiveness achieved in the hemicelluloses extraction (90%) of slash pine sawdust by SE (200ºC, 3% on dry weight (od) of H2SO4 for 5 min) EH yield was not good (20.3% glucan, 20 FPU/g glucan at 72 h). One reason could be the high lignin content of the material after the SE process. In order to evaluate the effect of lignin on EH, the exploded material was subjected to different delignifying processes: soda/anthraquinone (soda/AQ), alkaline organosolv, alkaline hydrogen peroxide and alkaline oxygen. An H-Factor of 3850 with 28% od of NaOH was used in the soda/AQ process. The organosolv process was carried out with an ethanol/water solution (23/77) with 28% od of NaOH at 170ºC for 140 min. The peroxide stage was accomplished using 20% H2O2 at 100ºC for 2 h. The O2 treatment was carried out with an alkaline load of 15% od of NaOH, for 2 h at 100ºC, maintaining an O2 pressure of 6 Kg/cm2 into the reactor. The resulting material was washed with water after all pretreatments. Materials obtained from each stage were subjected to enzymatic hydrolysis according to the LAP NREL / TP-510-42629 standard with commercial enzymes from Sigma Aldrich (20 FPU/g glucan). The chemical composition of the pretreated materials was determined by liquid chromatography. The delignification yield was above 60% for the soda/AQ and the alkaline organosolv processes. Oxidative processes failed to achieve a significant degree of delignification. However, the maximum HE yield (36%) was reached after the oxygen stage. This improved performance may be due to lower adsorption of enzymes by lignin due to a decrease of free phenolic groups and lignin redistribution produced during this stage. Despite improvements achieved after the delignifying treatments, EH performance remained low. This could indicate that physicochemical changes are produced in pine sawdust during the SE (condensation of lignin, etc.) that hinder subsequent delignification and therefore are negative for the EH.