Separation and recovery of the constituents from lignocellulosic biomass by using ionic liquids and acetic acid as co-solvents for mild hydrolysis

Previously, ionic liquids were found to partially dissolve lignocellulosic biomass. Here, it is reported that the biomass itself does not dissolve directly, but that it is hydrolyzed first before the constituents (cellulose, hemicellulose and lignin) dissolve into the ionic liquid. By addition of an acidic catalyst, this hydrolysis step can take place at milder conditions. Acetic acid is chosen as a suitable acidic catalyst, because it is already present in lignocellulosic biomass in the form of acetyl groups on the hemicellulose. Here, it is shown that acetic acid also works as co-solvent, increasing the solubility of the constituents of lignocellulosic biomass in the ionic liquid. The milder conditions for hydrolysis result in a higher degree of utilization of the lignocellulosic biomass, whereby all constituents can be fully recovered and further processed and the ionic liquid can be reused.

Research highlights▶ Lignocellulosic biomass is firstly hydrolyzed before it can dissolve in an ionic liquid. ▶ Addition of an acidic catalyst enhances the rate of hydrolysis and subsequently the rate of biomass dissolution. ▶ Acetic acid is a suitable acidic catalyst that is present in lignocellulosic biomass. ▶ Acetic acid also works as co-solvent for the dissolution of lignocellulosic biomass in an ionic liquid. ▶ The hydrolysis of lignocellulosic biomass in an ionic liquid + acetic acid system takes lace at milder conditions with considerable less degradation.