Process for biomass treatment

Process for the treatment of lignocellulosic biomasses with a process solvent selected from a eutectic solvent consisting of a hydrogen bond acceptor and of a hydrogen bond donor, an ionic liquid and a mixture of said eutectic solvent and said ionic liquid, said process comprising the following steps: A. mixing of the biomass with the process solvent and possibly separation of insoluble cellulose residues and/or inorganic material; B. treatment of the process solvent solution with water and lignin separation; C. separation of the hemicellulose from the mixture of process solvent and possibly water, the step C of hemicellulose separation is carried out by adding an organic solvent soluble in the solvent and in water, thus allowing the precipitation of the hemicellulose and its subsequent separation with conventional techniques from the liquid phase comprising process solvent, organic solvent and possibly water.