Process And Mechanism Of Eucalyptus Pulp Bleaching Catalysed By Cu²⁺/Co²⁺

In recent years, with the rapid development of national economy, the increasingly demand of some paper whiteness and the more stringent emission requirements of paper industry, it is the inevitable trend that clean production is carried out, chlorine-based agent is reduced, chlorine free agent is used for pollution-free bleaching in pulp industry. Therefore, many countries have researched totally chlorine free (TCF) bleaching. It is key to improve the efficiency of TCF bleaching.In order to develop new no-(little) pollution bleaching technology, in this experiment Cu2+/Co2+ was used as the catalyst in pretreatment raising TCF bleaching efficiency of eucalyptus (Leizhou NO.102) oxygen delignified kraft pulp. The bleaching process and interactions of lignin and catalyst were studied, the principle that catalytic pretreatment enhances the bleaching efficiency was provided.This paper used Cu2+/Co2+, persulfate, acetic acid and O2 as the catalytic pretreatment system and evaluated the catalytic performance which is based on the brightness, viscosity, physical strength and lignin degradation product. The reasonable catalytic conditions are as follows:(1) Cu2+0.01%, molar ratio of ammonium persulfate and Cu2+ 2:1, HAc 20%, atmospheric oxygen, pulp concentration 5%, temperature 70℃. (2) Co2+ 0.01%, molar ratio of ammonium persulfate and Co2+ 2:1, HAc 20%, atmospheric oxygen, pulp concentration 5%, temperature 70℃. (3) Cu2+/Co2+ 0.01%, molar ratio of ammonium persulfate and Cu2+/Co2+ 2:1, HAc20%, atmospheric oxygen, pulp concentration 5%, temperature 70℃,time 2h.The brightness and viscosity of eucalyptus oxygen delignified kraft pulp bleached by O-Cat-Ep-P are as follows:Cu2+ catalytic pretreatment,82.9%ISO,787 mL·g-1; Co2+ catalytic pretreatment,82.2%ISO,791mL·g-1; Cu2+/Co2+catalytic pretreatment,81.9%ISO, 762 mL·g-1. The catalytic pretreatments increased the brightness and viscosity of the resultant bleached pulp compared to the control.Structural changes and degradation products of residual lignin of eucalyptus oxygen delignified kraft pulp were analysed with FTIR, GPC,1H-NMR, elemental analysis, GC-MS during the Cu2+/Co2+ catalytic bleaching to explore the mechanism of lignin degradation.