HEMICELLULASES IN PULP BLEACHING PDF

Arasar The pH has a marked influence on the rate of enzymatic reactions. To avoid these problems, the liquor was squeezed out of a sample of the pulp and the pH of this bkeaching measured. The method of claim 5 wherein the enzyme preparation has a low cellulase content such that not more than about 2, FPU are added per ton of pulp. Role Of Biotechnology In Pulp And Paper Industry Open Access Journals The process comprises contacting the pulp with a lignin releasing effective amount of an enzyme system comprising lignin releasing enzymes, preferably endo-xylanase, which are contained in the supernatant of a T.

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Search Menu Abstract The utilization of hemicellulases in bleaching of kraft sulphate pulp is considered as one of the most important new large-scale industrial applications of enzymes. This is partly due to the great potential of an environmentally safe method. This method has in a short period also proven to be economically realistic. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres.

Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable. The hydrolysis of xylan or mannan in the inner fibre layers may also enhance the bleachability. In practical process conditions, properties of the enzymes such as substrate specificity and the pH and temperature optima are of utmost importance.

The benefits obtained by enzymes are dependent on the chemical bleaching sequence used as well as on the residual lignin content of pulp. The main goals in the enzyme-aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process and consequently lowering the AOX of the effluents.

In the production of TCF totally chlorine-free pulps, enzymes have also been successfully used for increasing the brightness of pulp.

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Hydrogen peroxide bleaching

Daishicage This is applied before carrying out the normal mechanical or chemical pulping. Mannanase Activity The same procedure as that for endo-xylanase was used except that galactomannan Sigma No. The filtrate was discarded and the pulp cake was resuspended in 10 L of water and filtered a total of four times. Analysis of the culture supernatant by SDS polyacrylamide gel electrophoresis reveals a set of at least 6 isoenzymes with xylanase activity. Use of enzymes can modify the fiber material. The extracted pulp is then washed with water to remove residual caustic. The influence of pH on enzymatic reactions may involve several different types of effects.

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Bleaching of wood pulp

The pulp would have been exposed to chlorine, extracted washed with a sodium hydroxide solution to remove lignin fragmented by the chlorination, treated with sodium hypochlorite, washed with sodium hydroxide again and given a final treatment with hypochlorite. An example of a modern totally chlorine-free TCF sequence is OZEPY where the pulp would be treated with oxygen, then ozone, washed with sodium hydroxide then treated in sequence with alkaline peroxide and sodium dithionite. Chlorine and hypochlorite[ edit ] Chlorine replaces hydrogen on the aromatic rings of lignin via aromatic substitution , oxidizes pendant groups to carboxylic acids and adds across carbon carbon double bonds in the lignin sidechains. Chlorine also attacks cellulose , but this reaction occurs predominantly at pH 7, where un-ionized hypochlorous acid , HClO, is the main chlorine species in solution.

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