The present invention relates to a process forthe bleaching of kraft pulps with non-chlorinechemicals, employing a sequential reaction of oxidativeenzymes and hydrogen peroxide. The kraft pulp can befrom conventional or extended pulping, or from an oxygendelignification step. The enzyme reaction is monitoredby methanol release which results from thedemethylation of lignin. The process of the presentinvention essentially comprises three steps. The firststep is the oxidation of kraft pulp either with manganeseperoxidase enzyme in the presence of Mn(II) salts,hydrogen peroxide and chelator, or with laccase enzymepreferably in the presence of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), or acombination of both enzymes in a crude mixture astypically produced by certain fungi. The Mn(II) salts andchelator may already be present in sufficient amount inthe pulp. This first step is performed at an acidicpH, and moderate temperatures for a period of timebetween 30 and 240 minutes. The two subsequent stepsare the removal of metals from the pulp and thealkaline hydrogen peroxide treatment. These steps areperformed under standard conditions as known by thoseskilled in the art. The resulting pulp is surprisinglybrighter and of lower lignin content than would beobtained without the enzyme treatment.
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