Cooking method

A cooking method comprising:

• a) providing wood based cellulosic raw material comprising chips, pin chips, shavings, saw dust, or a combination thereof;
• b) pre-treating the wood based cellulosic raw material by steaming to provide pre-treated material;
• c) pre-hydrolyzing the pre-treated material with steam or water to provide pre-hydrolyzed material;
• d) grinding and compressing the pre-hydrolyzed material to release the HMW xylan from the pre-hydrolyzed material into a hydrolysate, and recovering the hydrolysate with the HMW xylan;
• e) neutralizing with sodium hydroxide with sulphur or with sodium hydroxide, or displacing with an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid;
• f) cooking in a cooking liquor comprising sodium hydroxide with sulphur or sodium hydroxide, or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid, to provide cooked cellulosic material in a spent liquor;
• g) grinding and compressing the cooked cellulosic material to release HMW lignin from the cooked material into the spent liquor, thereby providing a HMW lignin fraction in black liquor and a compressed cellulose fraction;
• h) displacing the black liquor with a displacing liquor containing 1-40% effective alkali as NaOH or acidic sulfite cooking liquor, or displacing with an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid;
• i) recovering the HMW lignin from the HMW lignin fraction in black liquor and from the displacing liquor;
• and
• j) recovering dissolving pulp from the compressed cellulose fraction;
• and wherein the grinding and compressing in step d) is carried out at the pre-hydrolyzing temperature used in step c), and to a consistency of at least 10% by weight.