High Brightness Pulps From Lignin Rich Waste Papers

Multi-stage process for bleaching of a recycle pulp containing at least about 50% Kraft fiber, comprising the steps of:

• a) contacting a cellulosic admixture of recycle containing fiber, said fiber containing at least about 50% Kraft fiber and no more than 20% mechanical pulp with a magnesium hydroxide generating species chosen from the group consisting of MgO and Mg(OH)2 in an amount of from 0.1 to 2.0 based on the OD weight of the pulp;
• b) contacting the admixture of pulp and Mg(OH)2 with H2O2 in an amount of from 0.1 to 5.0% based on the OD weight of the pulp and, optionally, oxygen under gauge pressure of at least 2 atm, while retaining a residual level of H2O2 in the admixture of at least about 0.1%;
• c) thereafter contacting the H2O2 containing mixture with a peroxide activating agent chosen from the group consisting of tetraacetylethylenediamine, and acetic anhydride, and thereby generating peracetic acid in situ;
• d) thereafter treating the brightened pulp with a reductive bleaching composition.

Multi-stage process for bleaching of a recycle pulp containing at least about 50% Kraft fiber, comprising the steps of:

• a) providing a fiberized admixture of recycle containing fiber, said fiber containing at least about 50% Kraft fiber and no more than 20% mechanical pulp, said pulp having an initial brightness of less than 65 as measured by ISO 2469/2470;
• b) contacting the fiber at low pressure and high consistency with:
• i. a magnesium hydroxide generating species chosen from the group consisting of MgO and Mg(OH)2 in an amount of from 0.1 to 2% based on the OD weight of the pulp;
• and
• ii. optionally, oxygen under gauge pressure of at least 2 atm;
• c) thereafter mixing and heating admixture of pulp and Mg(OH)2 by contacting it with steam;
• d) in the substantial absence of sodium containing bleaching chemicals, contacting the admixture of pulp and Mg(OH)2 with:
• i. H2O2 in an amount of from 0.1 to 5% based on the OD weight of the pulp and,
• ii. optionally, oxygen under gauge pressure of at least 2 atm;
• e) allowing the peroxide containing admixture to increase in brightness by at least about 5 points as measured by ISO 2469/2470;
• while retaining a residual level of H2O2 in the admixture of at least about 0.1%;
• f) contacting the H2O2 containing mixture with a peroxide activating agent chosen from the group consisting of tetraacetylethylenediamine, acetic anhydride and acetyl chloride and thereby generating peracetic acid in situ;
• g) thereafter treating the brightened pulp with a reductive bleaching composition chosen from the group consisting of sodium borohydride, sodium bisulfite, sodium hydrosulphite, SFS and FAS and recovering a pulp having a brightness of at least 75 as measured by ISO 2469/2470.

A method of bleaching recycled pulp comprising a combination of from 20 to 80% by weight of Kraft fiber and 80 to 20% by weight of lignin containing fiber, comprising the steps of:

• a) providing an admixture of from about 20 to about 80% by weight of Kraft fiber and from about 80 to about 20% by weight of lignin containing fiber;
• b) adding a magnesium hydroxide generating species to said admixture in an amount of from about 0.1 to about 2% by weight based on weight of Mg(OH)2 per weight of dry fiber,
• c) heating the admixture to a temperature of between about 50° C. and about 100° C.;
• d) adding hydrogen peroxide to said heated admixture in an amount of from about 0.1 to about 5% hydrogen peroxide based on the weight of 100% hydrogen peroxide per weight of dry fiber in said admixture, the mole ratio of hydrogen peroxide to magnesium hydroxide being from about 2 to 1 up to about 4 to 1;
• e) optionally, contacting said admixture of pulp, magnesium hydroxide generating species and hydrogen peroxide with oxygen under gauge pressure of at least 2 atm;
• f) retaining the admixture of pulp, hydrogen peroxide and magnesium hydroxide in a temperature range of from about 50° C. to about 100° C. until the residual level of unreacted hydrogen peroxide in the pulp is from about 0.1 to about 2% based on the dry weight of the fiber;
• g) adding an amount of a peroxide activating agent sufficient to convert the bulk of the residual hydrogen peroxide in the admixture in situ to peracetic acid;
• h) retaining the peracetic acid containing admixture at temperature of from at least about 50° C. to about 80° C. for period sufficient to react at least about 90% of said peracetic acid;
• i) thereafter washing and heating the pulp admixture;
• and
• j) subjecting the pulp admixture to a reductive bleaching process.

A method of bleaching recycled pulp comprising a combination of from 20 to 80% by weight of Kraft fiber and 80 to 20% by weight of lignin containing fiber, comprising the steps of:

• a) providing an admixture of from about 20 to about 80% by weight of Kraft fiber and from about 80 to about 20% by weight of lignin containing fiber;
• b) adding hydrogen peroxide to said admixture in an amount of from about 0.1 to about 5% by weight based on the weight of 100% hydrogen peroxide per weight of dry fiber;
• c) heating the admixture to a temperature of between about 50° C. and about 100° C.;
• d) adding a magnesium hydroxide generating species to said heated admixture in an amount of from about 0.1 to about 2% hydrogen peroxide based on weight of Mg(OH)2 per weight of dry fiber in said admixture, the mole ratio of hydrogen peroxide to magnesium hydroxide being from about 2 to 1 up to about 4 to 1;
• e) retaining the admixture of pulp, hydrogen peroxide and magnesium hydroxide in a temperature range of from about 50° C. to about 80° C. until the residual level of unreacted hydrogen peroxide in the pulp is from about 0.1 to about 2% based on the dry weight of the fiber;
• f) adding an amount of a peroxide activating agent sufficient to convert the bulk of the residual hydrogen peroxide in the admixture in situ to peracetic acid;
• g) retaining the peractic acid containing admixture at temperature of from at least about 40° C. to about 80° C. for period sufficient to react at least about 90% of said peracetic acid;
• h) thereafter washing and heating the pulp admixture;
• and
• i) subjecting the pulp admixture to a reductive bleaching process.

A method of bleaching recycled pulp comprising a combination of from 20 to 80% by weight of Kraft fiber and 80 to 20% by weight of lignin containing fiber, comprising the steps of:

• a) providing an admixture of from about 20 to about 80% by weight of Kraft fiber and from about 80 to about 20% by weight of lignin containing fiber;
• b) adding a peroxide activating agent;
• c) heating the admixture to a temperature of between about 40° C. and about 80° C.;
• d) adding hydrogen peroxide to said heated admixture;
• e) adding a magnesium hydroxide generating species to said admixture in an amount of from about 0.1 to about 2% by weight based on weight of Mg(OH)2 per weight of dry fiber, wherein the molar ratio of magnesium hydroxide to hydrogen peroxide is from about 2 to 1 up to about 4 to 1, and the amount of peroxide activating agent added is sufficient to convert from at least about 15 up to at least about 75 kg-moles (30 up to at least about 150 pound-moles) of hydrogen peroxide per ton of recycled fiber (dry basis) into peracetic acid;
• f) retaining the admixture of pulp, peroxide activating agent, hydrogen peroxide and magnesium hydroxide in a temperature range of from about 40° C. to about 80° C. until the residual level of unreacted hydrogen peroxide in the pulp is no more than about 0.5% based on the dry weight of the fiber;
• and the amount of residual peracetic acid in the pulp is no more than about 0.05% based on the dry weight of the fiber;
• g) adding an additional amount of hydrogen peroxide to the admixture, the amount being sufficient to generate at least about 5 pound-moles of peracetic acid in situ per ton of fiber;
• h) retaining the peracetic acid containing admixture at a temperature of from at least about 40° C. to about 80° C. for period sufficient to reduce the amount of peracetic acid present in the pulp admixture to from less than about 0.9 kg moles (2 pound moles) of peracetic acid per ton of fiber (dry basis) down to less than about 0.05 kg mole (0.1 pound mole);
• i) thereafter washing and heating the pulp admixture;
• and
• j) subjecting the pulp admixture to a reductive bleaching process.

A method of bleaching recycled pulp comprising a combination of from 20 to 80% by weight of Kraft fiber and 80 to 20% by weight of lignin containing fiber, comprising the steps of:

• a) providing an admixture of from about 20 to about 80% by weight of Kraft fiber and from about 80 to about 20% by weight of lignin containing fiber;
• b) adding a magnesium hydroxide generating species to said admixture in an amount of from about 0.1 to about 2% by weight based on weight of Mg(OH)2 per weight of dry fiber;
• c) heating the admixture to a temperature of between about 80 and about 100° C.;
• d) adding hydrogen peroxide to said heated admixture in an amount of from about 0.1 to about 5% hydrogen peroxide based on the weight of 100% hydrogen peroxide per weight of dry fiber in said admixture, the mole ratio of hydrogen peroxide to magnesium hydroxide being from about 2 to 1 up to about 4 to 1;
• e) retaining the admixture of pulp, hydrogen peroxide and magnesium hydroxide in a temperature range of from about 80° C. to about 100° C. until the residual level of unreacted hydrogen peroxide in the pulp is from about 0.1 to about 2 based on the dry weight of the fiber;
• f) adding an amount of a perhydroxyl generating agent sufficient to convert the bulk of the residual hydrogen peroxide in the admixture in situ to perhydroxyl ions;
• said perhydroxyl generating agent being chosen from the group consisting of sodium hydroxide, NA2CO3;
• and calcium hydroxide;
• g) retaining the admixture at temperature of from at least about 80° C. to about 100° C. for period sufficient to react at least about 90% of said peracetic acid;
• h) thereafter washing and heating the pulp admixture;
• and
• i) subjecting the pulp admixture to a reductive bleaching process.