NOVELTY - Fractionation of sugarcane bagasse biomass, comprises: (a) subjecting the biomass to auto-hydrolysis treatment without the addition of acid to obtain a pre-hydrolyzed bagasse biomass; (b) selectively extracting at the selected reaction pressure from the pre-hydrolyzed bagasse biomass a second liquid stream containing hemicellulose hydrolysis; (c) rapidly releasing the pre-selected reaction pressure for explosive decompression of the pre-hydrolyzed bagasse into pretreated fibrous solids, vapor and condensate; and (d) collecting the vapor and condensate from the explosive decompression.    USE - The continuous process is useful for fractionation of sugarcane bagasse biomass (claimed).    ADVANTAGE - The process efficiently recovers a hemicellulose concentrate that can be converted to value added products including ethanol.    DETAILED DESCRIPTION - A continuous process for fractionation of sugarcane bagasse biomass, comprises: (a) subjecting the biomass to auto-hydrolysis treatment without the addition of acid to obtain a pre-hydrolyzed bagasse biomass exposing the biomass to steam in a reaction vessel at a pre-selected temperature of 170 and 220 degrees C and a pre-selected reaction pressure of between 100 and 322 psig, for a pre-selected exposure time of between 5 to 90 minutes, to remove a desired amount of a hemicellulose fraction from the bagasse biomass and activate a cellulose fraction of the bagasse biomass; and subjecting the biomass to auto-hydrolysis treatment without the addition of acid to obtain a pre-hydrolyzed bagasse biomass during the exposing step at the pre-selected temperature and reaction pressure continually purging liquid condensate and vapor formed during the exposure step to remove and collect a first liquid stream containing water soluble compounds and a first vapor stream containing volatile chemicals; (b) selectively extracting at the selected reaction pressure from the pre-hydrolyzed bagasse biomass a second liquid stream containing hemicellulose hydrolysis and degradation components as a hemicellulose degradation stream; (c) rapidly releasing the pre-selected reaction pressure after the extracting step for explosive decompression of the pre-hydrolyzed bagasse into pretreated fibrous solids, vapor and condensate; and (d) collecting the vapor and condensate from the explosive decompression for separation and recovery of byproducts.    DESCRIPTION OF DRAWING(S) - The drawing shows a process diagram of a continuous pretreatment unit.    Moisture bagasse fibers (10)    Steam (20, 60, 61)    Preheating and conditioning (30)    Air vent (35, 50)    Modular screw device (40)    Inhibitory extracts (55)    Up flow tube (70)    Pretreatment reactor (80)    Water (90)    Hemicellulose (95, 110)    Counter current washer (100)    Cyclone (120)    Flash vapor (130)    Pure cellulose (140)