4.3e Organic Solvation Processes
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 OS pretreatment, the main mechanism involves the dissolution of lignin by organic solvent and then re-precipitation 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 water concentration. The effect is to: separate lignin from lignocellulosic biomass; solubilize hemicellulose; and increase pore size and surface area in the cell wall. Below is a schematic of a process diagram for OS pretreatment.
Schematic of Organosolv (OS) process. Biomass, water, 60% ethanol, and 1.25% H2SO4 undergo Organosolv pretreatment at 180 C for 60 minutes. After pretreatment, it goes to filtration, and the solids go to washing with water/ethanol to remove the pulp (cellulose). The liquids head to lignin precipitation which separates the lignin and the water soluble sugars. Any remaining ethanol is recycled.
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. Below is a schematic of COSLIF processing.
Schematic of Cellulose-solvent and organic-solvent lignocellulose fractionation (COSLIF). The raw material enters the digester with H3PO4 at 50 C. It then goes to the precipitation tank where it is treated with acetone. The material then enters washer 1 where it is treated with acetone where the black liquor is removed and goes to the distiller. The remaining material enters washer 2 where it is treated with water and the light liquor is removed and goes to the flash tank. All remaining material goes to the hydrolysis tank (50 C) and glucose is removed.
Black liquor: In the distiller acetone, acetic acid, and H3PO4 are removed and low MW lignin is extracted.
Light Liquor: In the flash tank, CaCO3 is added and acetone and H3PO4 are removed. Hemicellulose is extracted.
