Process for peroxide bleaching of mechanical pulp using sodium carbonate and non-silicate chelating agents
First Claim
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1. A process for brightening mechanical and high yield hardwood pulp substantially free of silicate and caustic soda to produce a brightened pulp of brightness substantially equivalent to that obtained using the equivalent amount of peroxide in a silicate and caustic soda bleaching liquor comprising:
- (a) incorporating hardwood pulp into a silicate-free bleach solution to provide a consistency of about 5% to 45%, the bleach solution consisting essentially of about 2% to about 6% by weight sodium carbonate on an oven dry basis of pulp, about 0.2% to about 0.6% by weight silicate substitute selected from the group consisting of organic chelating agents, polyhydroxy compounds, and oligomers and polymers of hydroxy and carboxy compounds and mixtures thereof, and about 2% to about 7% by weight hydrogen peroxide on the oven dry basis of the pulp,(b) maintaining the bleach solution at a temperature of about 35°
C. to about 70°
C. for about 2 to about 6 hours, and(c) separating the pulp from at least part of the bleach solution thereby providing a bleached pulp and a residual solution.
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Abstract
A process is provided for peroxygen bleaching of high yield pulp in which sodium carbonate replaces sodium hydroxide and sodium silicate. The process employs a chelating agent as a substitute for the silicate normally required so that the process can operate as a closed cycle system.
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Citations
10 Claims
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1. A process for brightening mechanical and high yield hardwood pulp substantially free of silicate and caustic soda to produce a brightened pulp of brightness substantially equivalent to that obtained using the equivalent amount of peroxide in a silicate and caustic soda bleaching liquor comprising:
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(a) incorporating hardwood pulp into a silicate-free bleach solution to provide a consistency of about 5% to 45%, the bleach solution consisting essentially of about 2% to about 6% by weight sodium carbonate on an oven dry basis of pulp, about 0.2% to about 0.6% by weight silicate substitute selected from the group consisting of organic chelating agents, polyhydroxy compounds, and oligomers and polymers of hydroxy and carboxy compounds and mixtures thereof, and about 2% to about 7% by weight hydrogen peroxide on the oven dry basis of the pulp, (b) maintaining the bleach solution at a temperature of about 35°
C. to about 70°
C. for about 2 to about 6 hours, and(c) separating the pulp from at least part of the bleach solution thereby providing a bleached pulp and a residual solution. - View Dependent Claims (2, 3, 4)
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5. A process for brightening mechanical and high yield hardwood pulp substantially free of silicate and caustic soda to produce a brightened pulp of brightness substantially equivalent to that obtained using the equivalent amount of peroxide in a silicate and caustic soda bleaching liquor comprising:
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(a) incorporating hardwood pulp into a silicate-free, first stage bleach solution to provide a consistency of about 5% to 14%, the first stage bleach solution comprising about 2% to about 6% by weight sodium carbonate, about 0.2% to about 0.6% by weight silicate substitute selected from the group consisting or organic chelating agents, polyhydroxy compounds, and oligomers and polymers of hydroxy and carboxy compounds and mixtures thereof, and about 2% to about 7% by weight hydrogen peroxide on an oven dry basis of the pulp, (b) maintaining the first stage bleach solution at a temperature of about 35°
C. to about 70°
C. for about 2 to about 6 hours,(c) separating the pulp from at least part of the first stage bleach solution thereby providing a bleached pulp and a first stage residual solution, (d) incorporating the bleached pulp into a second stage bleach solution at a consistency of about 25% to about 45%, the second stage bleach solution comprising about 3% to about 4% sodium carbonate, about 0.3% to about 0.6% silicate substitute, and about 4% to about 6% hydrogen peroxide, (e) maintaining the second stage bleach solution at a temperature of about 35°
C. to about 70°
C. for about 2 to about 6 hours,(f) separating the pulp from at least part of the second stage bleach solution thereby providing a second stage bleached pulp and a second stage residual solution. - View Dependent Claims (6, 7, 8, 9, 10)
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Specification