Use of New Enzymatic Delignification and Bleaching Concepts for the Treatment of High Kappa Pulps and for “Cold Cooking”, 2003 Fall Technical Conference

It can be demonstrated that recently-published enzymatic procedures favored for the delignification/bleaching of low kappa pulps (e.g. after O2-delignification and/ or D-stages) can also be useful for the cooking pretreatment of sawdust, “wood peeling chips” and (in a limited manner) wood chips when carried out under certain circumstances and in an optimized manner. These procedures include:

• the hydrolase mediated oxidation system (HOS),
• other dioxirane-producing and peroxynitrous acid-generating systems,
• new laccase-based oxidation procedures with special activating compounds like oxocarbons, special keto-hydrazides,
• oxidoreductase/lipase-based procedures for the generation of fatty hydroxamic acids as oxidoreductase activators,
• combinations thereof and
• peroxide-activating systems with ferrocene-related compounds.

During a treatment (4 hours retention time, at pH 4-6, at 50- 60o C and ca. 10% consistency) of high kappa pulps, i.e. pulps such as sulfate and sulfite pulps directly after cooking, delignification rates of up to 45% and more can be obtained while the strength properties are maintained. Treatments of e.g. sawdust and “wood peeling chips” before cooking with significantly reduced chemical charges or reduced cooking time also become feasible using higher enzyme and chemical concentrations. Delignification rates of up to 50% can be obtained for e.g. hardwood (beech) or softwood (spruce) under similar conditions to the above-mentioned treatments. Besides these new applications of the above-mentioned enzymatic delignification approaches, some results dealing with the possibility of performing multistage bleaching with different enzymatic oxidizing systems based on different mechanisms of lignin attack will be summarized.