Method and an apparatus for an enzymatic hydrolysis, a liquid fraction and a lignin fraction

A method for an enzymatic hydrolysis in which a plant based feed is fed to an enzymatic hydrolysis stage in which the plant based feed is hydrolysed by means of an enzyme to form a hydrolysed product, the method comprising:

• Treating a starting material by an acid hydrolysis and steam explosion and forming a plant based material, the plant based feed comprising the plant based material;
• Feeding an additive for preventing enzyme adsorption (i) to the enzymatic hydrolysis stage, (ii) to the plant based feed, which is fed to the enzymatic hydrolysis stage, (iii) to the plant based material, or (iv) to any combination thereof
• Adding the enzyme to the enzymatic hydrolysis stage after addition of the additive;
• Carrying out the enzymatic hydrolysis to generate the hydrolysed product;
• Supplying the hydrolysed product from the enzymatic hydrolysis stage to a first solid-liquid separation stage in which a lignin fraction comprising the additive and a liquid composition which comprises the enzyme are separated;
• Mixing the liquid composition with fresh plant based material in a mixing stage after the first solid-liquid separation stage to form a mixture;
• Feeding the additive to the fresh plant based material before the mixing stage or during the mixing stage;
• Separating a solid fraction which comprises the enzyme, and a liquid fraction from the mixture in a second solid-liquid separation stage after the mixing stage;
• and
• Feeding at least a part of the solid fraction which comprises the enzyme to the enzymatic hydrolysis stage.