New insights in the fractionation of Pinus pinaster wood: sequential autohydrolysis, soda ethanol organosolv and acidic precipitation

Pinus pinaster wood (PPW) was fractionated by two different routes: (1) a two-steps system by soda ethanol organosolv (SEOS) followed by lignin precipitation (LP) and (2) a three-steps procedure encompassing autohydrolysis (AH) followed by SEOS and LP. In the two-steps route, the effect of ethanol mass fraction in the cooking liquor (15-55 wt.%) on pulps and lignins purities was studied. In the three-steps system, the effects of AH temperature (160-180 degrees C) and reaction time (30 and 60 min) on hemicelluloses removal were evaluated. Then the effects of AH temperature (175 and 180 degrees C) and ethanol concentration (15-35 wt.%) on SEOS derived pulps and lignins purities were considered. The SEOS reaction temperature (170 degrees C) and time (90 min) were kept constant in all SEOS experiments. In the case of the two-steps approach, pulps with lignin and hemicellulose contents as low as 6 and 15 wt.% (respectively), as well as precipitates having lignin contents up to 94 wt.% were obtained. Up to 81 wt.% of the cellulose and 66 wt.% of the lignin initially present in PPW were recovered in pulps and precipitates (respectively) by this fractionation pathway. When the three-steps fractionation was applied, up to 17 wt.% of the original biomass was recovered in AH liquors. Pulps having hemicellulose contents as low as 3 wt.% and lignin contents as low as 5 wt.% were produced by sequential AH and SEOS, while LP products presented lignin contents higher than 98 wt.%. The results show the potential of the three-steps fractionation towards a biorefinery-based bioeconomy.