Process for high consistency oxygen delignification followed by ozone relignification
First Claim
1. A process for delignifying and bleaching a lignocellulosic material which comprises:
- forming a brownstock pulp having a K No. of from about 10-24 by Kraft pulping, Kraft-AQ pulping or extended delignification of a lignocellulosic material;
decreasing the consistency of said pulp to about 1 to 4.5% by weight;
treating the decreased consistency pulp with a quantity of alkaline material in an aqueous alkaline solution having a concentration of alkaline material of between about 20 and 120 g/l by uninterrupted mixing for a time of between about 1 and 15 minutes such that the concentration of alkaline material in the decreased consistency pulp during this treating step ranges from about 6.5 to 13 g/l, so as to complete a substantially uniform distribution of the alkaline material throughout the pulp;
increasing the consistency of the alkaline treated pulp to between about 20 to 35% by weight to generate pressate while retaining at least about 1.4% by weight based on oven dry pulp of alkaline material on the increased consistency pulp, said pulp fibers containing the alkaline material being directly passed from the combining step to the consistency increasing step;
recycling a substantial portion of the pressate to the pulp treating step; and
subjecting the increased consistency 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 treated with alkaline material at low consistencies;
directing the partially delignified pulp to ozone delignification without any intervening delignification or bleaching steps;
further delignifying said oxygen delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a second K No. of about 5 or less, a second viscosity of greater than about 10 cps and a GE brightness of at least about 50% prior to any additional bleaching steps;
combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp;
extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp; and
bleaching the substantially lignin-free pulp to raise the GE brightness thereof to at least about 70%.
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Accused Products
Abstract
A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. 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.
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Citations
25 Claims
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1. A process for delignifying and bleaching a lignocellulosic material which comprises:
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forming a brownstock pulp having a K No. of from about 10-24 by Kraft pulping, Kraft-AQ pulping or extended delignification of a lignocellulosic material; decreasing the consistency of said pulp to about 1 to 4.5% by weight; treating the decreased consistency pulp with a quantity of alkaline material in an aqueous alkaline solution having a concentration of alkaline material of between about 20 and 120 g/l by uninterrupted mixing for a time of between about 1 and 15 minutes such that the concentration of alkaline material in the decreased consistency pulp during this treating step ranges from about 6.5 to 13 g/l, so as to complete a substantially uniform distribution of the alkaline material throughout the pulp; increasing the consistency of the alkaline treated pulp to between about 20 to 35% by weight to generate pressate while retaining at least about 1.4% by weight based on oven dry pulp of alkaline material on the increased consistency pulp, said pulp fibers containing the alkaline material being directly passed from the combining step to the consistency increasing step; recycling a substantial portion of the pressate to the pulp treating step; and subjecting the increased consistency 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 treated with alkaline material at low consistencies; directing the partially delignified pulp to ozone delignification without any intervening delignification or bleaching steps; further delignifying said oxygen delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a second K No. of about 5 or less, a second viscosity of greater than about 10 cps and a GE brightness of at least about 50% prior to any additional bleaching steps; combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp; extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp; and bleaching the substantially lignin-free pulp to raise the GE brightness thereof to at least about 70%. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A process for delignifying and bleaching lignocellulosic material which comprises:
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forming an unbleached brownstock pulp having a K No. of from about 10-24 by Kraft pulping, Kraft-AQ pulping or extended delignification of a lignocellulosic material; decreasing the consistency of said pulp to about 1 to 4.5% by weight; uniformly mixing the decreased consistency pulp with a quantity of alkaline material in an aqueous alkaline solution having a concentration of alkaline material of between about 20 and 120 g/l without interruption for a time of between about 1 and 15 minutes such that the concentration of alkaline material in the decreased consistency pulp during this mixing step ranges from about 6.5 to 13 g/l, so as to complete a substantially uniform distribution of the alkaline material throughout the pulp; increasing the consistency of the alkaline treated pulp after completion of the mixing step to between about 20 to 35% by weight by removing liquid to form high consistency brownstock while retaining at least about 1.4 percent by weight based on oven dry pulp of alkaline material on the increased consistency pulp, said pulp fibers containing the alkaline material being directly passed from the low consistency pulp mixing step to the consistency increasing step; recycling substantially all of the liquid removed from the pulp in the consistency increasing step to the low consistency pulp mixing step; subjecting the increased consistency 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 treated with alkaline material at low consistencies, to form a partially delignified pulp having a first K No. of about 10 or less and a first viscosity of greater than about 13 cps; directing the partially delignified pulp to ozone delignification without any intervening delignification or bleaching steps; further delignifying said oxygen delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a second K No. of about 5 or less, a second viscosity of greater than about 10 cps and a GE brightness of at least about 50% prior to any additional bleaching steps; combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp; extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp; and bleaching the substantially lignin-free pulp to raise the GE brightness thereof to at least about 70%. - View Dependent Claims (24, 25)
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Specification