The next process type is using an organic solvent, such as the Organosolv (OS) process or the Cellulose solvent- and Organic Solvent-based LIgnocellulose Fractionation (COSLIF) process. For the OS pretreatment, the main mechanism involves the dissolution of lignin by organic solvent and then re-precipitated by adding an antisolvent, such as acidified water. This method was first introduced as a pulping method for papermaking. The organic solvents commonly used are acetone, ethanol, methanol, etc., in an aqueous solution of 20-60% water. Key parameters include temperature, residence time, chemical addition, and the water concentration. The effect is to: separate lignin from lignocellulosic biomass; solubilize hemicellulose; and increase pore size and surface area in the cell wall. Figure 5.24 shows a schematic of a process diagram for OS pretreatment.
Another organic solvent based process is cellulose-solvent and organic-solvent lignocellulose fractionation (COSLIF). For this process, an organic solvent is introduced to dissolve cellulose prior to Organosolv processing. Figure 5.25 shows a schematic of COSLIF processing.