Patent ID: 8758557

Claim:
A process for producing fibrous material from lignocellulosic raw material, comprising: preparing a solution of chemicals comprising sulphite (calculated as Na 2 SO 3 ), wherein the sulphite is present in the solution of chemicals an amount that is less than 25% of sulphite, based on the oven-dry amount of the lignocellulosic raw material; mixing the solution of chemicals with wood in a specified liquor ratio; heating the solution of chemicals and the wood to a temperature above room temperature; and then either of the following: removing a free-flowing solution of the chemicals and digesting the wood in a vapor phase; digesting the wood in a liquid phase and separating a free-flowing solution of the chemicals and the wood, wherein: the wood is softwood and the process produces a fibrous material comprising at least 15% of lignin, based on oven-dry fibrous material for softwood and a breaking length of between 8 km and 11 km, at a freeness of up to 15° SR; or the wood is hardwood and the process produces a fibrous material comprising at least 14% of lignin, based on oven-dry fibrous material for hardwood and a breaking length of between 5 km and 9.9 km, at a freeness of up to 20° SR, and wherein the digesting the wood is carried out at temperatures between 150° C. and 180° C., and wherein the fibrous material produced by the process has a yield of between 70% and about 85%; and the process further comprising beating the produced fibrous material to a maximum of 15° SR for softwood and to a maximum of 20° SR for hardwood.