THE TCF BLEACHING OF NS-AQ ASPEN HIGH YIELD CHEMICAL PULP

The paper is to study the TCF bleaching of high-yield chemical pulp of NS-AQ aspen (digester yield 63.7%, Kappa number 37.3, brightness 50.0%ISO,intrinsic viscosity 1,340ml/g ). Under the suitable conditions ( oxygen pressure 0.6MPa, 85℃, 80min.,NaOH 5%, MgSO4 0.3%, consistency 11% ), oxygen delignification, can increase the brightness of pulp to 64.9%ISO, substantially decrease Kappa number to 9,11. Before the oxygen delignification pretreating pulp by acidic chelant ( Qa ) under conditions of pH 3.0, 30min, 40℃, DTPA 0.25%, consistency 15%,and after the Qa strengthening oxygen delignification by H2O2 ( Op, H2O2 2% ) can increase the brightness of pulp to 77.1%ISO, decrease Kappa number and intrinsic viscosity to 6.36 and 984ml/g, respectively.After the Op, pretreat pulp by chelant once again ( pH 6.0, 60℃, consistency 12%, other as the Qa ),and following this pretreatment do bleach with 1% H2O2, namely using Qa-Op-Q-P bleaching sequence,resulting in the brightness 84.8%ISO, Kappa number 5.01, intrinsic viscosity 792ml/g, total bleaching loss 12.17% for bleached pulp.