NOVELTY - Processing (m1) a lignocellulosic biomass including cellulose, hemicellulose and lignin fractions, involves applying concentrated organic acid vapors containing at least 50 wt.% of organic acids to the biomass to at least partly depolymerize the hemicellulosic and lignin materials in the biomass; drying the weak-acid treated biomass to provide high solids content material as to be pelletized; and pelletizing the material from the drying step.    USE - For processing lignocellulosic biomass, particularly fractionating the biomass including cellulose, hemicellulose and lignin fractions, which are used in a ruminant feed, in the synthesis of ethanol, lysine, threonine, lactic, gluconic or other organic acids, and for preparing fuel additive product for transportation fuels (claimed), and also in the preparation of biobased fuels.    ADVANTAGE - By accomplishing the solubilization of hemicelluloses and lignin into readily extractible fractions through the use of hot organic acid vapors permeating through the biomass, in contrast, there is no need with the present method to process the same large quantities of formic acid and water as used in the prior pulping processes. Also the lesser concentrations of formic acid are used as compared to the conventional, liquid-based formic acid fractionation methods, further reducing the formic acid recovery requirements of the fractionation. The formic acid that is used is recovered by azeotropic distillation as contemplated in a pulping type application. Because of the smaller amounts of water and acid involved, the formic acid that is recovered for recycle is recovered simply and without need for breaking the water-formic acid azeotrope, through the use of organic co-solvents and through simple distillation. Because of the comparatively much smaller amounts of organic acid used in the present method to accomplish the fractionation for further processing of a lignocellulosic biomass as compared to the previously-known pulping processed, the organic acid that remains after the fractionation also simply neutralized in whole or in part.