Enhanced mass transfer upon switchable ionic liquid mediated wood fractionation

“The fractionation of lignocellulosic biomass to its major components is the primary step towards the conversion of biomass-based biopolymers to commodity chemicals in the integrated biorefinery process. Wood chips encased in a SpinChem® device and attached to the stirrer of a batch autoclave were usedtogether with switchable ionic liquids (SILs) for the selective fractionation of hemicelluloses and lignin. Stirring of the wood chips in the SpinChem® device facilitated the diffusion of SIL into the chips through forced recirculation and at the same time avoiding mechanical fibrillation. The treatment of birch chips (Betula pendula) with SILs comprising 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), monoethanolamine (MEA) and CO2 at 120 °C in a SpinChem® device resulted in the fractionation of 82 wt.% hemicelluloses and 90 wt.% lignin, leaving the cellulose-rich non-dissolved material partially fibrillated and softened. The dissolved hemicelluloses and lignin were selectively precipitated using isopropanol and recovered from the spent SIL.”

Highlights:

• “The novel SpinChem® device has been shown as efficient for the enhancement of mass transfer involving solid–liquid systems applicable as a stirrer to establish forced fluid flow through wood chips. The concept provides a unique opportunity for biomass fractionation in stirred vessels in the absence of mechanical fibrillation and the ease of separation (washing). The SpinChem® device is also an important tool for screening of solids, such as heterogeneous catalysts and multiphase reaction”
• “Mechanical fibrillation, a key problem associated with stirring wood chips in a reactor, was avoided by using the SpinChem® device and SIL for the fractionation of birch chips. The turbulent flow of SIL through the rotating basket resulted in SIL transport into wood chips leading to enhanced fractionation of hemicellulose and lignin in the absence of mass and heat transfer limitations.”