Investigation of lignin obtained by processing of Betula pendula with ionic liquids

Imidazolium-based ionic liquids bearing chloride, acetate, mesylate, and tosylate as anion were investigated for the treatment of birch (Betula pendula) bark to extract lignin. Although birch bark was previously extracted with methanol to remove low molecular weight organic compounds, various fatty acids and ferulic acid esters were analyzed in the lignin fraction using UPLC/ESI(â)-QTOFMS. GPC analysis shows differences in the molecular weight of the lignin samples obtained by treating bark with 1-butyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium tosylate. The use of 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium mesylate for the extraction of bark resulted in aromatic oligomers that are not fully soluble in the eluent used for GPC analysis. Therefore, the molecular weight as determined by GPC is only representative for the soluble part of these samples and not for the entire sample. Results obtained by investigation of the lignin samples extracted from bark using GPC and UPLC/ESI(â)-QTOFMS let us conclude that 1-butyl-3-methylimidazolium acetate is the most efficient ionic liquid among the solvents investigated for the extraction of lignin from bark. The high efficiency may be attributed to a high catalytic function of this ionic liquid in bound cleavage on the one hand and an active contribution of the acetate ion to trans-esterifications on the other hand.