Method for treating cellulosic material

The present invention provides a method comprising: (i) contacting a cellulose-comprising input material with an aqueous hydrolyzing solution comprising at least 35% wt. of at least one mineral acid to form a hydrolyzate comprising a mixture of water-soluble carbohydrates and optionally a solid fraction; (ii) contacting said hydrolyzate with an extractant comprising a first solvent S1, to form a first (preferably solid) residue (preferably comprising precipitated carbohydrates, e.g. mono-, di- and/or oligo-saccharides) and an acid-comprising extract; (iii) separating said acid-comprising extract from said first residue; (iv) modifying said acid-comprising extract to form a second (preferably liquid) residue (preferably comprising dissolved carbohydrates) and an acid-comprising modified extract; (v) fractionating said modified extract into an S1-enriched fraction and an acid-enriched fraction; (vi) reusing said SI-enriched fraction to form said extractant; and (vii) reusing said acid-enriched fraction to form said aqueous hydrolyzing solution; wherein (a) at least 10% wt. of the cellulose is hydrolyzed and said mixture of water-soluble carbohydrates comprises monosaccharides, disaccharides and/or oligosaccharides; (b) SI forms a single phase when mixed with an identical weight of 70% sulfuric acid aqueous solution at 25° C.; (c) S1 comprises at least 65% wt. of said extractant; and (d) said acid-comprising extract comprises at least 60% wt. of the acid and at least 5% wt. of the carbohydrates in said hydrolyzate.