| abstract |
The present invention provides a process for fractionating lignocellulosic biomass, comprising: contacting biomass with SO 2 , water, and optionally a first solvent, to produce intermediate solids; then contacting the intermediate solids with SO 2 , water, and a second solvent, to produce cellulose-rich solids and a liquid phase comprising hemicelluloses and lignin. The first concentration of SO 2 may be lower or higher than the second concentration of SO 2 . It is desirable to vary the SO 2 and solvent concentrations in different stages to optimize the removal of hemicellulose versus lignin. The resulting cellulose-rich material can contain very low hemicellulose, very low lignin, or both low hemicellulose and low lignin. High-purity cellulose is useful both for producing glucose as well as for cellulose products or derivatives. The hemicelluloses may be hydrolyzed to produce monomeric sugars, and the lignin may be recovered as a co-product. |