Isolation of lignins from hardwood and softwood biomass samples, containing 26.1% and 28.1% lignin, respectively, has been performed with the use of alkaline and organosolv pretreatment methods. The effect of catalyst loading, ethanol content, particle size, and pretreatment time on the yields and properties of the isolated lignins were investigated. Alkaline lignins had higher carbohydrate contentup to 30% and exhibited higher molecular weights in the range of 3000 Da, with a maximum phenolic hydroxyl content of 1 mmol g −1 for birch and 2 mmol g −1 for spruce. Organosolv lignins, on the other hand, showed high purity93% or higherdespite the more extensive biomass dissolution into the pretreatment medium; they also exhibited a lower range of molecular weights between 600 and 1600 Da depending on the source and pretreatment conditions. Due to the lower molecular weight, phenolic hydroxyl content was also increased, reaching as high as 4 mmol g −1 with a simultaneous decrease in aliphatic hydroxyl content as low as 0.6 mmol g −1 . Efficient lignin dissolution of 62% for spruce and 69% for birch, achieved at optimal pretreatment conditions, was combined with extensive hemicellulose removal.

Abstract:The negative impact of fossil fuels and the increased demand for renewable energy sources has led to the use of novel raw material sources. Lignocellulosic biomass could serve as a possible raw material for anaerobic digestion and production of biogas. This work is aimed at using forest biomass, both softwood (spruce) and hardwood (birch), as a raw material for anaerobic digestion. We examined the effect of different operational conditions for the organosolv pretreatment (ethanol content, duration of treatment, and addition of acid catalyst) on the methane yield. In addition, we investigated the effect of addition of cellulolytic enzymes during the digestion. We found that inclusion of an acid catalyst during organosolv pretreatment improved the yields from spruce, but it did not affect the yields from birch. Shorter duration of treatment was advantageous with both materials. Methane yields from spruce were higher with lower ethanol content whereas higher ethanol content was more beneficial for birch. The highest yields obtained were 185 mL CH 4 /g VS from spruce and 259.9 mL CH 4 /g VS from birch. Addition of cellulolytic enzymes improved these yields to 266.6 mL CH 4 /g VS and 284.2 mL CH 4 /g VS, respectively.

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