Patent ID: 6325892
Filing Date: 2001-12-04
Classification: D21C

Abstract:
A method for the oxygen delignification of sulphite chemical pulp, comprising the steps of:treating a sulphite chemical pulp slurry in a reactor under oxygen overpressure at a pH of from substantially 8 to substantially 13 with an effective amount of an alkali source over a period of time sufficient to complete delignification of the sulphite chemical pulp wherein the alkali source is selected from the group consisting of MgO, Mg(OH).sub.2, NaOH, and mixtures thereof; andadding an effective amount of borohydride compound reducing agent which is substantially non-reactive with the oxygen to provide a sulphite chemical pulp with enhanced strength properties and increased viscosity, with the proviso that borohydride compound addition is carried out simultaneously with the oxygen delignification in the reactor, the borohydride compound reducing agent being added in situ during an oxygen stage.