Application of enzyme treatment technology in bleaching process
Biological bleaching technology is a new kind of environmental protection bleaching technology, which can improve the bleachability of the pulp through the reaction of enzymes with chemical components in the pulp, and can also directly use enzymes to degrade lignin to improve the whiteness of pulp. The main enzymes used in biobleaching are hemicellulase and ligninase. Hemicellulase includes xylanase and mannase. Among them, xylanase is a series of enzyme complex that can degrade xylan into oligosaccharides and xylose monosaccharides. The lignin-carbohydrate complex (LCC) gradually disintegrates during the degradation of xylan, exposing more active structures. At the same time, the degradation of xylan will also make the structure of fiber cell wall become more loose, and more lignin is exposed, which improves the contact probability between bleaching additives and alkali and lignin, and then improves the bleachability of the pulp. Ligninase mainly includes laccase, lignin peroxidase, and manganese peroxidase. The biggest advantage of biological bleaching technology is that it reduces the use of chlorine-based bleaching aids, thereby reducing the formation of AOX and improving the performance of bleaching pulp.
AOX is a commonly used parameter to measure the pollution of the bleaching process. At present, ECF (Elemental Chlorine-Free Bleaching) has been popularized worldwide, and most of these ECF bleaching processes use chlorine dioxide as the main bleaching aid. AOX is a commonly used parameter to measure the pollution of the bleaching process. At present, ECF (Elemental Chlorine-Free Bleaching) has been popularized worldwide, and most of these ECF bleaching processes use chlorine dioxide as the main bleaching aid.
In the chlorine dioxide bleaching process, the main factors affecting the formation of AOX are the concentration and structure of lignin, the chlorine content of available chlorine, the reaction temperature, pH and the content of hexenuronic acid (Hex A). n the chlorine dioxide bleaching process, the main factors affecting the formation of AOX are the concentration and structure of lignin, the chlorine content of available chlorine, the reaction temperature, pH and the content of hexenuronic acid (Hex A). In order to reduce the formation of AOX, it is necessary to increase the rate of delignification and reduce the amount of bleaching aids, and enzyme-assisted bleaching can well meet these two conditions. Commonly used enzyme-assisted bleaching include xylanase bleaching, laccase bleaching, and compound enzyme synergistic bleaching.
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