Bleaching recycled pulp with a reductive-oxidative sequence
AssigneeSociete Anonyme pour l'Etude et l'Exploitation l'Air Liquide, des Procedes Georges Claude
InventorsJack Kogan, Michel Muguet
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Abstract
The invention relates to a method of bleaching waste paper pulp. The pulp is first treated to a reductive chemical followed by acidification and washing or dewatering. The pulp is then subjected to ozone and then to hydrogen peroxide. The reductive chemical used is either formamidine sulphinic acid or sodium hydrosulfite.
Claims15
A method of bleaching waste paper pulp consisting of a first step of treating said pulp with a reductive chemical selected from the group consisting of formamidine sulphinic acid and sodium hydrosulfite followed by a second step consisting of an oxidative treatment wherein said oxidative treatment exposes said pulp to ozone and hydrogen peroxide and wherein the pH of the pulp is adjusted in between said first and second steps.
A method of bleaching waste paper pulp consisting of a first step of treating said pulp with a reductive chemical selected from the group consisting of formamidine sulphinic acid and sodium hydrosulfite followed by a second step consisting of an oxidative treatment wherein said oxidative treatment exposes said pulp to ozone and hydrogen peroxide and wherein a pH test is conducted on samples of the pulp prior to said first step, said pH test consisting of the steps of making several pulp samples, adjusting the pH of different samples to different values, contacting said samples with ozone under the same conditions and then measuring the brightness of each sample in order to determine the most appropriate pH for the pulp at least during the exposure to ozone in said second step whereby said pulp is treated to ozone in said second step at said most appropriate pH.
A method of bleaching waste paper pulp consisting of a first step of treating said pulp with a reductive chemical selected from the group consisting of formamidine sulphinic acid and sodium hydrosulfite followed by a second step consisting of an oxidative treatment wherein said oxide five treatment exposes said pulp to ozone and hydrogen peroxide and wherein said pH of the pulp is adjusted in between said first and second steps to between about 2 and 3 by treating said pulp with an acid between said first and second steps wherein said pulp is washed after said acid treatment and prior to subjecting the pulp to ozone.
Dependencies are inferred from the claim text.