Abstract
Adsorbable organic halogen (AOX) is generally formed by the reaction of residual lignin in pulps with chlorine dioxide during bleaching. Lignin has a complex structure. Different functional groups and bonds are present in lignin structures. Phenolic hydroxyl is one of the important functional groups in lignin, and it significantly influences the chemical properties and reactivity. To study the effect of phenolic hydroxyl on AOX formation, vanillyl alcohol (VA) was selected as the phenolic lignin model compound, and veratryl alcohol (VE) was selected as the non-phenolic lignin model compound in this study. The kinetics of AOX formation by the reaction of VA or VE with chlorine dioxide was studied. The effects of pH, chlorine dioxide, lignin model compound concentration and reaction temperature on AOX formation are discussed. The activation energies of the reaction of VA and VE with chlorine dioxide are 16 242.47 J mol−1 and 281.34 J mol−1, respectively. Thus, we found that the non-phenolic lignin can react with chlorine dioxide to form AOX more easily than phenolic lignin.
Highlights
During the process of pulp bleaching, the side reactions of HClO and Cl2 in chlorine dioxide solution with residual lignin are royalsocietypublishing.org/journal/rsos R
Scholars have used lignin model compounds to study degradation pathways and reaction mechanisms of different lignin structures [11,12,13], including the ways in which benzene rings and bonds break during reactions [14,15,16,17,18]
vanillyl alcohol (VA) was selected as the phenolic lignin model compound, and veratryl alcohol (VE) was selected as the non-phenolic lignin model compound
Summary
During the process of pulp bleaching, the side reactions of HClO and Cl2 in chlorine dioxide solution with residual lignin are royalsocietypublishing.org/journal/rsos R. AOX cannot be degraded; it can remain in 2 the environment for a long time. The structure of residual lignin in unbleached pulp is complex [2]. There are some different extraction processes, such as mechanical, physical, chemical and enzymatic treatments [3,4], to isolate lignin. Lignin model compounds can be used as a simplified way to study the change in specific lignin structures in related reactions [7]. Scholars have used lignin model compounds to study degradation pathways and reaction mechanisms of different lignin structures [11,12,13], including the ways in which benzene rings and bonds break during reactions [14,15,16,17,18]
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