Process for ozone bleaching of oxygen delignified pulp while conveying the pulp through a reaction zone
First Claim
1. A process for the manufacture of a bleached pulp having a certain GE brightness and a certain strength as indicated by a certain viscosity which comprises:
- chemically digesting a lignocelluloeic material to initially form a pulp;
oxygen delignifying the pulp to remove a substantial portion of the lignin therefrom, with the combination of the digesting and oxygen delignifying steps being conducted to form an intermediate pulp. having a specified amount of lignin and a specified viscosity; and
ozone delignifying the intermediate pulp with a gaseous mixture that contains ozone by adjusting the consistency of the pulp to a high consistency of above about 20%, adjusting the pH of the pulp to below about 4, and treating the pulp with an amount of the ozone containing gaseous mixture sufficient to remove a substantial portion, but not all, of the remaining lignin by intimately contacting and turbulently mixing the pulp particles with the gaseous mixture in a dynamic reaction zone by introducing the high consistency pulp into the reaction zone to fill the zone to at least about 10% by volume, dispersing the pulp substantially completely throughout the reaction zone while simultaneously conveying the pulp through the reaction zone in a plug flow-like manner at a dispersion index of about 7 or less thus exposing substantially all of the pulp to the ozone for reaction therewith for a sufficient time and at a temperature sufficient to allow access of the ozone to substantially all of the pulp for reaction therewith while the pulp advances through substantially all of the reaction zone, thus obtaining substantially uniform delignification of a significant portion of the pulp and forming a delignified pulp having a reduced amount of lignin and the certain strength, viscosity and GE brightness;
wherein the specified amount of lignin of the intermediate pulp is such that, after ozone delignification, the delignified pulp attains the certain GE brightness, and wherein the specified viscosity of the intermediate pulp is sufficiently high to permit the delignified pulp, after ozone delignification, to attain the certain strength as evidenced by the certain viscosity.
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Accused Products
Abstract
A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine or chlorine-containing compounds by oxygen delignifying the pulp to a K No. of about 14 or less and a viscosity of greater than about 10 cps and thereafter further delignifying the partially delignified pulp by lifting, displacing and tossing the pulp in a radial direction while advancing it in an axial direction in a plug flow-like manner with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 6 or less, a viscosity of at least about 7 cps and a GE brightness of at least about 35. The substantially delignified pulp may then be brightened to a final product having a GE brightness of at least about 75, or alternately up to about 83 or more by contacting the ozonated pulp with chlorine dioxide or a peroxide compound. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.
86 Citations
22 Claims
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1. A process for the manufacture of a bleached pulp having a certain GE brightness and a certain strength as indicated by a certain viscosity which comprises:
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chemically digesting a lignocelluloeic material to initially form a pulp; oxygen delignifying the pulp to remove a substantial portion of the lignin therefrom, with the combination of the digesting and oxygen delignifying steps being conducted to form an intermediate pulp. having a specified amount of lignin and a specified viscosity; and ozone delignifying the intermediate pulp with a gaseous mixture that contains ozone by adjusting the consistency of the pulp to a high consistency of above about 20%, adjusting the pH of the pulp to below about 4, and treating the pulp with an amount of the ozone containing gaseous mixture sufficient to remove a substantial portion, but not all, of the remaining lignin by intimately contacting and turbulently mixing the pulp particles with the gaseous mixture in a dynamic reaction zone by introducing the high consistency pulp into the reaction zone to fill the zone to at least about 10% by volume, dispersing the pulp substantially completely throughout the reaction zone while simultaneously conveying the pulp through the reaction zone in a plug flow-like manner at a dispersion index of about 7 or less thus exposing substantially all of the pulp to the ozone for reaction therewith for a sufficient time and at a temperature sufficient to allow access of the ozone to substantially all of the pulp for reaction therewith while the pulp advances through substantially all of the reaction zone, thus obtaining substantially uniform delignification of a significant portion of the pulp and forming a delignified pulp having a reduced amount of lignin and the certain strength, viscosity and GE brightness; wherein the specified amount of lignin of the intermediate pulp is such that, after ozone delignification, the delignified pulp attains the certain GE brightness, and wherein the specified viscosity of the intermediate pulp is sufficiently high to permit the delignified pulp, after ozone delignification, to attain the certain strength as evidenced by the certain viscosity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 16, 17, 18, 19, 20, 21, 22)
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8. The process which further comprises:
oxygen delignifying the pulp by; applying a first amount of alkaline material to brownstock pulp having a low consistency of less than about 5% by weight by combining the low consistency pulp with a sufficient quantity of alkaline material with uninterrupted mixing in a manner to ensure that all pulp fibers are exposed to the alkaline material to obtain a substantially uniform distribution of alkaline material throughout the pulp and then increasing the consistency of the alkaline material containing pulp to at least about 18% by weight to obtain high consistency pulp and to remove liquid while retaining the first amount of alkaline material substantially uniformly distributed throughout the high consistency pulp, said pulp fibers containing the alkaline material being directly passed from the combining step to the consistency increasing step; applying a second amount of alkaline material onto the high consistency pulp to obtain a total amount of alkaline material on the pulp of at least about 0.8 to 7 percent by weight based on the oven dry weight of the pulp, wherein at least about 55% of the total amount of alkaline material is applied to the pulp during the alkaline material combining step; and subjecting the increased consistency alkaline material containing pulp to high consistency oxygen delignification to obtain enhanced delignification of the pulp without a corresponding decrease in pulp viscosity compared to pulp which is not combined with alkaline material at low consistencies and form an intermediate pulp having a specified amount of lignin and having a specified viscosity. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
Specification