10-05: Clean fractionation of biomass into cellulose, hemicellulose sugars, and lignin

Organosolv pulping has been used to cleanly fractionate a variety of biomass feedstocks including undebarked hybrid poplar wood chips, sugarcane bagasse, rice hulls, and corn stover.  Solvent combinations were used that result in all polymeric components of the lignocellulose being obtained in high yield and good selectivity in three product streams.  The fractionation solvent consists of a mixture of alcohols and or ketones one of which is water immiscible and one is water miscible, with the balance being dilute aqueous acid.  A homogeneous solvent composition is selected for the initial treatment of the biomass at elevated temperature (140 – 160 ^oC).  After treatment the solvent composition is changed by addition of water or more of the water immiscible solvent to cause a phase separation that produces an aqueous phase containing the dissolved hemicellulosic sugars, an organic phase containing the dissolved lignin, and a residue of cellulosic fiber.  The solid fiber contains most (80-90%) of the cellulose in the biomass.  The fiber is extensively delignified (80-90% lignin removal) and has most (85-95%) of the hemicelluloses removed.  The cellulose fiber can be used for producing ethanol or could be upgraded to other higher value products.  Simultaneous saccharification and fermentation of the fiber from hybrid poplar gave ethanol yields as high as 98% in only two days.  The lignin stream is also very pure with <3% sugar contaminants.  A study of the effects of pulping severity on fractionation selectivity, on carbohydrate degradation, and on lignin molecular weight and functionality will be described.