The Peracetic Acid Bleaching Of Kraft Wheat Straw

With the increase of the environment conception, the bleaching process is gradually turning to the ECF (elemental chlorine-free) and TCF (total chlorine-free) bleaching sequence in the pulping industry. Peracetic acid is an excellent non-chlorine bleaching agents, it is also a strong oxidizing agent, not only as a delignification agent also as a bleaching agents and an activator, which means they can quite easily be introduced in existing ECF or TCF bleaching processes without large capital investment. The peracetic acid in wheat straw bleaching was investigated. The results indicated that the peracetic acid is a very effective non-chlorine bleaching agent.Firstly, the stabilization of the peracetic acid solution was researched. The temperature of the bleaching solution has a negative effect on the decomposition. Decomposition rate will be accelerated, while temperature was raised. Transition metal ions have the catalyze effect on the decomposition. When Fe³⁺, Fe²⁺, Cu²⁺and Mn²⁺ were added into the bleaching solution, the rate of decomposition will increase. Some of the stabilizing agents can inhibit the decomposition, such as potassium dihydrogen phosphate, ureophil, sodium hexametahposphate, sodium pyrophosphate, sodium silicate. The potassium dihydrogen phosphate and sodium silicate are more effective to Mn²⁺, and so are ureophil to Cu²⁺ and the sodium pyrophosphate to Fe²⁺.The stabilizing agents can keep the bleaching pH in an optimum range. When dosage of the stabilizing agents is 0.1%, the suitable pH range can be obtained. The brightness of the pulp was increased and Kappa number was decreased, at the same time, the viscosity of the pulp had no significant decrease. The neutral pH (7.0) was suitable for the peracetic acid bleaching.The experiment results indicated that the effect of bleaching temperature and pH on the brightness and viscosity of the pulp were significant, the effect of the dosage of the peracetic acid was not obvious. It's benefit to improve the brightness and viscosity when pH was increased. The viscosity of the pulp was decreased and the brightness of pulp was increased significantly when the temperature was raised.