Fractionation by Sequential Antisolvent Precipitation of Grass, Softwood, and Hardwood Lignins Isolated Using Low-Cost Ionic Liquids and Water

Abstract

In this study, fractionation by sequential anti-solvent precipitation was applied to ionoSolv lignins for the first time. Pretreatment with the aqueous low-cost protic ionic liquid N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4], 80 wt% in water) was applied to Miscanthus (herbaceous), willow (hardwood) and pine (softwood) to extract lignin. Then, lignin was sequentially precipitated by addition of water as anti-solvent. Fractionation appeared to be controlled by molecular weight of lignin polymers. Fractions isolated with minimal water volumes were shown to have high molecular weight, polydispersity, thermal stability and Tg (178 °C). Later precipitates were more monodisperse, had high phenolic and total hydroxyl content, lower thermal stability and Tg (136 °C). Addition of 1 g of water per g of dry IL was able to precipitate up to 90 wt% of lignin. Fractional precipitation represents a novel lignin isolation technique that can be performed as part of the lignin recovery procedure enabling a hig...