On the prevalence of side reactions during ionosolv pulping of Norway spruce with 1-butyl-3-methylimidazolium acesulfamate

Abstract

We report on the low efficiency of 1-butyl-3-methylimidazolium acesulfamate ([BMIM]Ace) at delignifying Norway spruce. A systematic kinetic and structural study of [BMIM]Ace pulping of spruce wood at 120 °C allowed shedding light on the structure of the reaction products and the nature of the reaction. In particular, wood residues and extracts were thoroughly characterized with a wide range of analytical techniques including 1H NMR, 13C NMR, 31P NMR, XRD, TGA, MS, FT-IR, conductivity, and elemental analysis. This extensive structural study evidenced prominent degradation of the acesulfamate anion into sulfate salts in lieu of the expected delignification. This unexpected behavior in view of previous reports of [BMIM]Ace pulping potency of wood is explained by extensive derivatization of minute lignin extracts with the sulfate salts, which can lead to an overestimation of delignification yields.