A method for fractionating fibrous
biomass comprising
cellulose,
hemicellulose and
lignin components to separate said
lignin,
cellulose and
hemicellulose from one another comprises: (a) shredding said fibrous
biomass; (b) concurrently with or subsequent to said shredding, contacting said
biomass with an
aqueous solution of a
nitrate ion source at a concentration of about 0.1-0.3% at a temperature in the range of about 60° to about 80° C. to initiate
nitration of the
lignin component of said biomass; (c) submerging said partially nitrated biomass in an
aqueous solution of a
nitrate ion source in the presence of an aluminum compound at a temperature within the range of about 75-100° C. for a time sufficient to complete the
nitration of said lignin component; (d) contacting the nitrated biomass produced in step (c) with an alkaline extraction liquor comprising NH4OH at an initial concentration sufficient to solubilize said nitrated lignin component and said
hemicellulose component from said
cellulose component of said biomass; e) recovering said cellulose from said extraction liquor containing said solubilized nitrated lignin and hemicellulose components, wherein said cellulose comprises at least about 88%
alpha cellulose; (f) treating said extraction liquor with an acid to precipitate lignin contained therein, and (g) separating said lignin from soluble hemicellulose in said extraction liquor. The recovered cellulose component comprises at least 88%
alpha cellulose and is useful as a starting material for the production of
ethanol.