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.