Solvent Recovery from Fibers in a Lignocellulose Biorefinery: An Experimental Feasibility Study

Abstract

In a lignocellulose biorefinery, the complex structure of lignocellulosic biomass has to be disrupted for full valorization. This fractionation into the main constituents (lignin, hemicelluloses, and cellulose) can be achieved with organic solvents like alcohols and acetone. Recovery of the solvent is one of the main challenges of this process. Especially when using the cellulose-rich fraction directly as fiber fraction, solvent remaining in this fraction has to be removed for environmental and safety reasons. Currently, the solvent removal is based on flash evaporation and washing, resulting in excessive amounts of washing liquor with low solvent concentration. This research investigated vacuum drying and steam stripping in a paddle mixer as alternative methods for recovering solvent from the fiber fraction. Vacuum drying could lower the acetone content of stone groundwood fibers from 1,450.6 g/kg dry matter to around 0.10 g/kg dry matter within 8 min; steam stripping decreased the acetone content from 1,118.8 g/kg dry matter to around 0.17 g/kg dry matter within 12 min. Furthermore, both the drying and stripping experiments showed higher energy efficiencies than the corresponding simulation cases of conventional solvent recovery (except the cooling efficiency for steam stripping), although the simulation cases were ideal cases with maximum washing and rectification efficiency.