Peroxymonosulfuric Acid Treatment as an Alternative to Ozone for Totally Chlorine-free and Elementary Chlorine-free Bleaching of Hardwoods Prehydrolysis-kraft Pulp

Abstract

This study is focused on improving totally chlorine―free（TCF）and elementary chlorine―free（ECF）bleach- ing by using peroxymonosulfuric acid（Psa ）instead of ozone（Z）.Bleaching was conducted by a combination of oxygen（O）with Psa ,followed by alkali extraction with hydrogen peroxide（Ep ）and chlorine dioxide（D）stages in accordance with proposed sequences O―Psa ―Ep―Psa―Ep and O―Psa ―Ep―D. Increments in pulp consistency during the O stage and an addition of MgSO４ during the Ep stage were performed to improve pulp brightness and vis- cosity. The O―Psa―Ep―Psa―Ep sequence was compared with the O―Psa―Z―Ep sequence, and８７．３―８８．３％ ISO bright- ness was achieved by TCF bleaching corresponding to the O―Psa ―Ep―Psa―Ep sequence. However, the viscosity ob- tained after the final stage of the TCF bleaching was５．１―６．０cP, while the O―Psa ―Z―Ep sequence resulted in an ８３．１％ ISO brightness andviscosity of５．４cP. It was difficult to reach brightness above８８％ ISO with viscosities greater than６．２cP, which are the minimum standard levels for dissolving pulp, using the TCF bleaching se- quence. Further studies with better qualities of raw materials are required to investigate this possibility. Mean- while, brightness８８．１％ ISO and viscosity７．３cP were achieved by the ECF bleaching corresponding to the O― Psa ―Ep―Dsequence with only a０．５％ ClO２ dosage, which suggests a potential reduction in the usage of chlorine― containing chemicals during the ECF bleaching. Keywords：peroxymonosulfuric