Method for producing ethanol using cellulosic biomass as raw material

A method for producing ethanol using cellulosic biomass as a raw material, comprising:

• a first hydrolytic saccharification step of adding a volatile organic acid to a slurry of cellulosic biomass and hydrothermally treating the slurry in a supercritical or subcritical state to saccharify/decompose hemicellulose contained in the cellulosic biomass into C5 sugars;
• a first solid-liquid separation step of subjecting the slurry after the first hydrolytic saccharification step to solid-liquid separation;
• a recovery step of adding sulfuric acid to a C5 saccharified solution obtained in the first solid-liquid separation step, and then subjecting the C5 saccharified solution to air stripping treatment or distillation treatment to recover the volatile organic acid contained in the C5 saccharified solution;
• a second hydrolytic saccharification step of slurrying a dewatered cake obtained in the first solid-liquid separation step by adding water and hydrothermally treating the slurry in a supercritical or subcritical state to saccharify/decompose cellulose contained in the cellulosic biomass into C6 sugars;
• a second solid-liquid separation step of subjecting the slurry after the second hydrolytic saccharification step to solid-liquid separation;
• a fermentation step of subjecting the C5 saccharified solution after the recovery step and a C6 saccharified solution obtained in the second solid-liquid separation step to alcoholic fermentation;
• and
• a distillation step of distilling a fermented liquid obtained in the fermentation step to concentrate ethanol,
• wherein the volatile organic acid recovered in the recovery step is reused as all or part of the volatile organic acid to be added to the slurry in the first hydrolytic saccharification step.