Abstract: Final chlorine dioxide bleaching of lignocellulosic materials is most effective at a near-neutral pH but present industrial practice typically targets a final pH of between 3.5 and 4.0 because of the difficulty in achieving and maintaining near-neutral pH cost effectively. The in situ formation of bicarbonate before the addition of chlorine dioxide provides a way of maintaining the required near-neutral pH. Near-neutral final chlorine dioxide bleaching also produces a bleached pulp that is in a state that responds more effectively to fluorescent whitening or optical brightening agents.

Abstract: The present invention provides an improved process for chlorine dioxide bleaching of chemical pulps in an aqueous suspension, which uses magnesium hydroxide or magnesium oxide. The process involves the addition of magnesium hydroxide or magnesium oxide to the pulp, in addition to chlorine dioxide, maintaining the mixture at a pH between about 2.5 to 7.5 for about 1 or more hours, most suitably between about 1-4 hours. This process can be used in the D1 or D2 stage of a typical D0EopD1E2D2 bleaching sequence, as well as in the chlorine dioxide brightening stage of other three, four, five, and six-stage bleaching sequences of either the so-called ECF process, or those containing elemental chlorine (Cl2). The temperature is between about 40 to about 90° C., and the pulp consistency is between about 1 to about 16%.

Abstract: The present invention relates to a process for the control of pitch in an aqueous medium by adding surface-reacted natural calcium carbonate or an aqueous suspension comprising surface-reacted calcium carbonate and having a pH greater than 6.0 measured at 20° C., to the medium, wherein the surface-reacted calcium carbonate is a reaction product of natural calcium carbonate with carbon dioxide and one or more acids, the use of the surface-reacted natural calcium carbonate for pitch control, as well as to a combination of a surface-reacted natural calcium carbonate and talc for pitch control, and the resulting composites.

Abstract: Final chlorine dioxide bleaching of lignocellulosic materials is most effective at a near-neutral pH but present industrial practice typically targets a final pH of between 3.5 and 4.0 because of the difficulty in achieving and maintaining near-neutral pH cost effectively. The in situ formation of bicarbonate before the addition of chlorine dioxide provides a way of maintaining the required near-neutral pH. Near-neutral final chlorine dioxide bleaching also produces a bleached pulp that is in a state that responds more effectively to fluorescent whitening or optical brightening agents.

Abstract: The method is for bleaching cellulose pulp in a bleach line that has at least two bleaching steps. The filtrate distribution is led up through the bleaching line counter-currently to the flow of cellulose pulp established in the bleaching line. A single joint main conduit is used for the bleaching steps. Wash filtrates obtained from the wash steps, used after or before the bleaching step, are led in conduits to branch locations on the main conduit that are positioned downstream of the branch location for drawing off of wash and/or dilution liquor for the wash step in question. All branch points in the joint main conduit are in fluid communication with one another along the main conduit.

Abstract: This invention provides a process for treating chemical woodpulp, or chemical cellulose including cotton linter, including the step of applying an electron processing technology (EPT) step to chemical woodpulp, or chemical cellulose, as the case may be, on an in-line basis to provide control of pulp viscosity or degree of polymerization (DP). The invention also provides a method of process control in treating the aforementioned woodpulp or cellulose, including the step of using radiation dose-viscosity relationship curve for applying an EPT step on an in-line basis. The in-line EPT step may, in one form of the invention, replace and hence eliminate a chemical DP reduction step.

Abstract: The method is for bleaching cellulose pulp in a bleach line that has at least two bleaching steps. The filtrate distribution is led up through the bleaching line counter-currently to the flow of cellulose pulp established in the bleaching line. A single joint main conduit is used for the bleaching steps. Wash filtrates obtained from the wash steps, used after or before the bleaching step, are led in conduits to branch locations on the train conduit that are positioned downstream of the branch location for drawing off of wash and/or dilution liquor for the wash step in question. All branch points in the joint main conduit are in fluid communication with one another along the main conduit.

Abstract: Bleached, Kraft chemical pulp having increased hemicellulose content compared to conventional Kraft chemical pulps. In one embodiment, the pulp has a hemicellulose content greater than about 17 weight percent as measured by the 18% caustic solubility test. In another aspect, a method for making wood cellulose pulp having increased hemicellulose content compared to conventional Kraft chemical pulps. In the method, a lignocellulosic material is pulped in caustic sulfide to provide a first brownstock, which is treated with oxygen to provide a second brownstock, which is then bleached to provide the pulp product.

Abstract: Bleached, Kraft chemical pulp having increased hemicellulose content compared to conventional Kraft chemical pulps. In one embodiment, the pulp has a hemicellulose content greater than about 17 weight percent as measured by the 18% caustic solubility test. In another aspect, a method for making wood cellulose pulp having increased hemicellulose content compared to conventional Kraft chemical pulps. In the method, a lignocellulosic material is pulped in caustic sulfide to provide a first brownstock, which is treated with oxygen to provide a second brownstock, which is then bleached to provide the pulp product.

Abstract: The invention relates to a method of bleaching cellulose pulp in a bleach line having at least two bleaching steps D1, D2 of alkaline or acidic type, and a bleaching line for the method, in which the filtrate distribution is led up through the bleaching line in counter-current to the flow of cellulose pulp established in the bleaching line. Instead of a conventional filtrate distribution including filtrate tanks, a single joint main conduit 1 is used for the bleaching steps of the same type. Wash filtrate obtained from the wash steps of the same type used after or before the bleaching step, is led to a branch point A2, A4, A6 on the main conduit 1, that is positioned after the branch point for drawing off of wash and/or dilution liquor for the wash step in question A1, A3, A5, A7. All branch points in the joint main conduit are in open communication with each other in the main conduit, at least as seen in a direction from the last bleaching step.

Abstract: The present invention relates to a method for end-bleaching of pulp containing metal ions after a sequence comprising alkaline bleaching stages only and optionally treatment with complex forming agent, wherein the end-bleaching comprises two chlorine dioxide stages at a pulp concentration of 8-20% and pH 2.5-4.5 wherein the pulp after the first chlorine dioxide stage is washed and dewatered to a concentration of 12-50% for removal of the out-dissolved metal ions and that alkali thereupon is added to the pulp for fast alkali extraction and increase of pH to 8-14, whereupon the pulp is provided with acid and chlorine dioxide and introduced into the second chlorine dioxide stage.

Abstract: The present invention discloses methods of bleaching chemical pulp that combine xylanase enzymes with hydrogen peroxide, peracids, or a mixture. The method comprises the steps of carrying out a chemical pulping operation, optionally followed by delignifying the pulp with oxygen, then combining xylanase enzymes with hydrogen peroxide, peracids, or a mixture to bleach the pulp. The method allows the mill to use both xylanase and peracids in a single bleaching tower to decrease the usage of chlorine dioxide and other bleaching chemicals. The pulp bleaching method of the present invention may be performed in a pulp mill as part of a complex pulp bleaching process.

Abstract: The invention relates to methods for reducing the amount of halogenated organics produced during a halogen bleaching process for lignocellulosic pulp fibers. According to the disclosed invention, it has been discovered that the use of a chelating agent prior to a non-halogen containing bleaching stage of a pulp bleaching process is effective to increase the brightness of the resulting bleached pulp without the need to increase the amount of halogen compounds required to obtain the same pulp brightness and without adversely affecting the pulp viscosity and yield.

Abstract: An environmentally friendly (ECF), yet commercially viable, process produces fully bleached (typically having a brightness of over 89 or 90% ISO) cellulose pulp using a (ZEND) treatment. Typically pulp is produced in an essentially sulphur-free pulping process (such as an soda/AQ process), and is then treated by a D-EO-, D-EP-, or D-EOP-sequence before the (ZEND) treatment. Optional oxygen delignification may also be used, and subsequent elemental-chlorine-free bleaching sequences may also be employed, although normally not necessary since the pulp after the (ZEND) treatment has high brightness and good viscosity (e.g. over 21 cP).

Abstract: A process for the bleaching of lignin present in pulp fibers in an aqueous environment such as a pulp suspension. The invention also relates to a process for producing paper or board from pulp containing bleached lignin. According to the invention carbon dioxide is used for the bleaching of lignin.

Abstract: The use of low specific gravity wood from thinning operations, for example, will produce a lower brownstock viscosity for a given kappa number target. A differential of 200-cP falling ball pulp viscosity has been detected from Kraft cooks of low and high specific gravity wood. Using low specific gravity wood can reduce the bleach stage temperature and the chemical dose needed in the bleach plant to produce lyocell pulp specifications. Low specific gravity wood also increases the ability to reduce pulp viscosity to very low levels without increasing the copper number of the pulp or the concentration of carbonyl in the pulp above acceptable levels.

Abstract: A method of bleaching chemical pulp, comprising two bleaching stages (D0 and, respectively, D1) with chlorine dioxide as dominating bleaching chemical and at least one intermediate alkaline bleaching stage (E). The ingoing pulp is dewatered to a concentration of 25-40% before the first chlorine dioxide stage (D0) and to 10-40% after the second chlorine dioxide stage (D1). Filtrate from the dewatering after the second chlorine dioxide stage (D1) is re-cycled and utilized for controlling the pulp concentration to 8-15% of the dewatered pulp to the first chlorine dioxide stage (D0).

Abstract: The specification discloses an improved bleaching sequence which provides significant reduction in filtrate volumes and amounts of absorbable organic halide (AOX), color, and chemical oxygen demand (COD) in the effluent. These reductions are achieved without adversely affecting the brightness and viscosity properties of the bleached pulp and without a high capital cost and operating cost penalty or impact on existing mill processes. The bleaching sequence according to the invention for reducing filtrate volumes is an EOD1EOPD2 or EOPD1EOPD2 bleaching sequence wherein substantially all of the filtrates from the later bleaching stages are recycled to earlier bleaching stages and eventually treated in the initial EO or EOP stage prior to discharge from the plant.

Abstract: Provided is a process for bleaching pulp with ozone. The process involves preparing a slurry of cellulosic pulp having a consistency in fibers of from 1 up to 5 weight %. Such a low consistency slurry is then mixed with high partial pressure ozone under high shear conditions. The ozone is then maintained in contact with the cellulosic fibers to effect bleaching of the fibers. The present process offers the advantages of bleaching using a low consistency slurry, with the added advantages of employing ozone.

Abstract: In a method and apparatus for treating pulp, a peroxide treatment of chemical pulp, i.e., both sulphite pulp and kraft pulp, is used to quickly reduce the Kappa number of the pulp. The method involves treating a chemical pulp with at least hydrogen peroxide or its equivalent, the kappa number of which chemical pulp has been brought to a level below 20 by either at least cooking or cooking and delignifying. The pulp is treated in a fast alkaline or neutral peroxide stage (Pk) (e.g. a small reactor having a volume of, or proportional to, less than about 90 cubic meters for 1500 tons per day pulp treatment) to reduce the kappa number by 1-10 units, and preferably by 3-7 kappa units, in which treatment the reaction time is less than 10 minutes, and is preferably less than 5 minutes. The pulp is then transferred substantially without intermediate washing of any type to a bleaching tower, and then bleached further in an acidic bleaching step (e.g. a D or Z step) in the bleaching tower.

Abstract: Collection of a post-chlorination washer filtrate and recycle thereof to acidify a wood pulp stream entering the initial chlorine dioxide bleaching stage is provided in order to reduce the formation of barium scale.

Abstract: In the treatment of cellulose pulp in connection with bleaching, the pulp is first cooked and, if necessary, oxygen delignified in order to reduce the Kappa number below 24, preferably below 14, and after that the pulp is treated in an acid stage at a pH of 2-5 and at a temperature range of 75-130° C. in order to reduce the Kappa number by 2-9 units. To prevent essential weakening of the strength properties of the pulp in the acid stage treatment tower, the retention time, t min, is 30 to 300 minutes and the treatment temperature, T° C.

Abstract: A method for the manufacture of bleached cellulose pulp, in conjunction with which lignocellulose material is digested to form cellulose pulp by means of an alkaline digestion liquor, and the cellulose pulp in the form of a suspension is screened, if necessary, and subjected in series to at least oxygen gas delignification/bleaching (O), if required, chlorine dioxide bleaching (D) and bleaching with non chlorine-containing, oxidative bleaching agent (O, P, Z), with the various bleaching stages interspersed with washing and/or reconcentration of the cellulose pulp in at least one stage, characterized in that complexing agents are added to the cellulose pulp in conjunction with the chlorine dioxide bleaching. It is also important for the mol quotient of the cellulose pulp for magnesium/manganese, during bleaching with a non chlorine-containing, oxidative bleaching agent, to be maintained at or brought to a value exceeding 20, and preferably exceeding 40.

Abstract: A bleached pulp having a high brightness and a satisfactory pulp viscosity is produced from a lignocellulosic material with a high efficiency by subjecting an aqueous slurry of a pulp to a bleaching step including at least one stage in which the pulp is bleached with chlorine dioxide under a pressure of, for example, 0.0980 to 0.883 MPa (1.0 to 9.0 kg/cm2), created by a compressed gas, preferably at a pH of 2 to 5, at a temperature of 50 to 120° C. and in a pulp consistency of 5 to 40%.

Abstract: A method which enhances the effectiveness of chlorine dioxide bleaching of lignocellulosic materials. It is effected by adding to the chlorine dioxide bleaching stage an aldehyde compound at a concentration of from about 0.01% to about 20%, by weight of the oven-dried lignocellulosic material.

Abstract: This process involves feeding cellulose into an extruder with an acid solution. The extruder is comprised of a screw and a barrel. The screw is rotated so as to pressurize the cellulose, and the cellulose undergoes acid hydrolysis and forms microcrystalline cellulose. The invented process can be accomplished by using pure cellulose or a lignocellulosic material as the starting material. If a lignocellulosic material is used, then a basic solution is added to it and the lignocellulosic material is fed through an extruder so as to obtain a mixture comprising lignin, hemicellulose and cellulose. The lignin and hemicellulose are extracted and the remaining cellulose is processed, as discussed previously, to form microcrystalline cellulose.

Abstract: Methods of bleaching cellulose pulp using chlorine dioxide and ozone in one and the same single stage of a bleaching sequence having a plurality of stages are presented. In its broadest embodiment the method comprises controlling a ratio of chlorine dioxide to ozone within a single stage of a first bleaching sequence in a range effective to achieve strength characteristics of a final paper elaborated from the first bleaching sequence at least as great as strength characteristics when compared to a control bleaching sequence, the control bleaching sequence being the same in all respects as the first bleaching sequence except not employing ozone in a stage, and for essentially the same final brightness of pulp elaborated from the first and the control bleaching sequence. Cellulose pulps made using the methods of the invention are also described.

Abstract: A method for improving the preparation of chemical cellulosic wood pulp for use in papermaking, and specifically to enhancement of the quality of a kraft pulp which has been subjected to a chlorine dioxide/chlorine bleaching stage and thereafter subjected to ozonation prior to an extraction stage in the bleaching sequence. The improved pulp of the present invention exhibits reduced total organically bound chlorine residues in the wood pulp and adsorbed organic halides (AOX) in the effluent, and has good brightness and viscosity. The advantages of the present invention may be accomplished by means of a bleaching sequence that employs a minimum of stages, namely (D.fwdarw.C)ZED or D.sub.c ZED with attendant relatively lower capital investment than heretofore possible.

Abstract: A process for the delignification and bleaching of chemical pulp utilizes an acid treatment stage aimed at reducing the quantity of hexene uronic acids present in the pulp by at least 30%, and a pH adjustment stage of the pulp aimed at depositing or redepositing ions of alkaline-earth metals on the fibres of the pulp. The process further includes a washing stage of the pulp and a treatment stage of the pulp with an oxidizing agent. A chelating agent is added to the pulp before and/or during the acid treatment stage and/or before or during the pH adjustment stage or between the pH adjustment stage and washing stage.

Abstract: A process for peroxide bleaching of pulp using magnesium oxide as sole alkaline source wherein said pulp is bleached in the presence of hydrogen peroxide for a maximum period of 180 minutes and achievement of a maximum target ISO brightness of 65 in regard to freshly prepared pulp characterized in that said magnesium oxide is utilized as MgO particles having a particle size of 5-500 microns and a particle surface area (PSA) of between 20-60 m.sup.2 /g. By using such parameters, a peroxide bleaching process may be carried out most efficiently on a commercial scale.

Abstract: A process for bleaching chemical pulp for paper manufacturing comprising delignifying and bleaching chemical pulp which has been treated by cooking by simultaneous use of chlorine dioxide, a peroxide, and at least one reaction catalyst selected from the group consisting of oxoacids of elements of Groups IV, V and VI and salts of these acids. Formation of organic chlorine compounds as by-products is suppressed by decreasing the amount of chlorine dioxide used in the ECF bleaching process in the first stage, and thus environmental toxicity in the waste water discharged from the bleaching process is decreased. Chemical pulp having a high degree of brightness is economically produced because increase in the production capacity is not required at all or suppressed to the minimum, and the investment cost is reduced to the minimum when the bleaching with chlorine in the first stage is converted into the bleaching with chlorine dioxide which is an ECF bleaching process.

Abstract: A process for bleaching cellulosic pulp to a G.E. brightness of at least about 75 and a viscosity of at least about 14 wherein the effluent from the bleaching process is of reduced colored matter content and exhibits reduced COD. The process comprises DZD stages without interstage treatment of the pulp other than by an optional water wash.

Abstract: A process for bleaching wood pulp is provided comprising subjecting the wood pulp, after brown stock washing, to an oxygen delignification stage, a washing sequence, a first chlorine dioxide bleaching stage, an oxidative extraction stage, at least one final chlorine dioxide bleaching stage and then recycling the filtrate from the oxidative extraction stage countercurrently through the bleaching plant and brown stock washing. Additionally, and quite beneficially, the filtrate from the first chlorine dioxide bleaching stage is also recycled countercurrently through the brown stock washing thereby significantly reducing the environmental impact associated with the manufacture of bleach wood pulp.

Abstract: A post-digestion treatment method for cellulosic pulps which reduces the generation of dioxins and other chlorinated organics in the pulp, treatment effluent and/or the paper product produced from the pulp. In the treatment, the pulp, following digestion, is washed with a liquid that is essentially free of dioxins or dioxin precursors and simultaneously adjusted in consistency to at least a medium, and preferably a high consistency. Thereafter, the pulp is contacted with a chlorination agent selected from the group consisting of gaseous chlorine dioxide, gaseous chlorine, and gaseous chlorine dioxide which contains a minor amount of gaseous chlorine.

Abstract: A process for bleaching wood pulp is provided comprising subjecting the wood pulp, after brown stock washing, to an oxygen delignification stage, a washing sequence, a first chlorine dioxide bleaching stage, an oxidative extraction stage, optionally at least one final chlorine dioxide bleaching stage and then recycling the filtrate from the oxidative extraction stage counter-currently through the bleaching plant and brown stock washing. Additionally, and quite beneficially, the filtrate from the first chlorine dioxide bleaching stage is also recycled counter-currently through the brown stock washing thereby significantly reducing the environmental impact associated with the manufacture of bleach wood pulp.

Abstract: In the bleaching of kraft cellulosic pulps employing a stage in which the pulp is contacted simultaneously with gaseous chlorine and ozone, the improvement in which the pulp at a low to high consistency is initially chlorinated with hypochlorous acid and thereafter is contacted substantially simultaneously with gaseous chlorine and ozone. The pulp so processed exhibits enhanced brightness and good viscosity, and the process produces low quantities of environmentally undesirable chlorinated organics. The bleaching sequence of M(C+Z).sub.g ED is disclosed.

Abstract: An elementally chlorine-free method for the delignification and bleaching of pulp which involves the use of a neutral monoperoxysulfate bleaching step to delignify and thus brighten the pulp. The process achieves good selectivities above about 3 even at high delignification degrees of 60% or greater.

Abstract: The use of hot water extraction (pH 7-8, 165.degree. F.) in place of an alkaline extraction in pulp bleaching sequences between an ozone delignification stage alkaline wash and a brightening stage allows higher strength pulp to be achieved at essentially the same brightness levels using reduced overall amounts of bleaching chemicals. In addition, effluents from pulp washing stages following these treatments can be recycled without generating scale in process equipment because the solubility of salts that could form such scale is significantly greater in these effluents.

Abstract: A process for bleaching a chemical paper pulp, including, in the order recited, subjecting the chemical paper pulp to treatment with oxygen in a preliminary delignification stage which does not employ chlorine in an acidic medium or a combination of chlorine and chlorine dioxide in an acidic medium; subjecting the chemical paper pulp to treatment with peroxymonosulphuric acid in a peroxymonosulphuric acid stage carried out at a temperature ranging between 75.degree. and 100.degree. C. for a period ranging between 70 and 150 minutes and at a pulp consistency of ranging between 12 and 25% of dry matter; and subjecting the chemical paper pulp to treatment with alkaline hydrogen peroxide in an alkaline hydrogen peroxide stage.

Abstract: The present invention discloses a process for treating filter rods comprising cellulose acetate tow waste comprising the steps of:a. cutting said filter rods so that fiber of said cellulose acetate have a fiber length of less than about 4 inches; andb. treating said cut filter rods with an aqueous base until at least 5% of acetyl groups on said cellulose acetate has been hydrolyzed.Filter rods treated in this manner are suitable for use in various paper products. The process of the present invention may further include a step for repulping the cut filter rods to repulp any included plugwrap.Modified fiber comprising cellulose acetate wherein at least 5% of acetyl groups on said cellulose acetate have been hydrolyzed, said fiber having a length of less than about 4 inches, are also disclosed.Paper products comprising between about 5 and about 90% of the fiber of claim 21 and paper pulp are also disclosed.

Abstract: A process for bleaching wood pulp is provided comprising subjecting the wood pulp, after brown stock washing, to an oxygen delignification stage, a washing sequence, a first chlorine dioxide or ozone bleaching stage, an oxidative extraction stage, an ozone activation stage followed by a chlorine dioxide bleaching stage in the absence of an intermediate washing stage.

Abstract: A method of bleaching chemical pulp in a sequence comprising at least four bleaching steps with final bleaching in a first and a second chlorine dioxide step. Between the chlorine dioxide steps an alkaline extraction is carried out, and washing takes place between the first chlorine dioxide step and extraction. Immediately after said washing step, NaOH is charged in an amount of 4-10 kg/ton pulp. Thereafter an oxidizing agent is admixed in an amount of at maximum 2 kg/ton pulp. After 15-120 seconds an acid is added for terminating the oxidation treatment and for lowering the pH-value, but without effecting a complete neutralization of residual alkaline.

Abstract: A process for delignifying a lignocellulosic material comprising exposing the material to a mixture of peracid and ozone. Preferred peracids include Caro's acid and peracetic acid. Also disclosed is a kraft pulp delignification mixture comprising in combination: (a) water; (b) a kraft pulp at 1-40% consistency; (c) a peracid; and (d) from 0.1 to 5.0% ozone on pulp.

Abstract: In a multi-stage bleaching sequence for kraft pulps employing a chlorine-containing bleaching agent in the first and final stages thereof and an intermediate alkaline extraction stage, the improvement for enhancing the brightness of the pulp and reducing the quantity of dioxin or chlorinated organics comprising contacting the pulp, in a mixer, at an acidic pH and a temperature of below about 60.degree. C. with a mixture of ozone and oxygen at a pressure of between about 60 and 80 psig wherein the quantity of ozone introduced to the pulp is between about 0.2% and about 0.4%, based on pulp.

Abstract: A process for bleaching wood pulp is provided comprising subjecting the wood pulp, after brown stock washing, to an oxygen delignification stage, a washing sequence, a first chlorine dioxide bleaching stage, an oxidative extraction stage, at least one final chlorine dioxide bleaching stage and then recycling the filtrate from the oxidative extraction stage countercurrently through the bleaching plant and brown stock washing. Additionally, and quite beneficially, the filtrate from the first chlorine dioxide bleaching stage is also recycled countercurrently through the brown stock washing thereby significantly reducing the environmental impact associated with the manufacture of bleach wood pulp.

Abstract: A process for the chlorine-free bleaching of pulps in an aqueous suspension which comprises forming the suspension with a consistency of 3 to 20 mass percent; introducing into the suspension an ozone-containing gas having an ozone content of 20 to 300 g/m.sup.3 in an amount corresponding to at most 2 mass percent ozone calculated on dry pulp of the suspension during vigorous agitation of the suspension to form a reaction mixture; maintaining a pressure of the ozone-containing gas at a pressure of 1 to 15 bar during introduction into the suspension; and controlling reaction conditions during contact of the ozone-containing gas with the suspension to maintain a reaction temperature of 15.degree. to 80.degree. and a pH value of 1 to 8.

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.

Abstract: A high-efficiency wood pulp bleaching process to produce wood pulps with higher brightness at equal chlorine dioxide usage or of equal brightness at significantly reduced chlorine dioxide usage. The process comprises reacting the chlorine dioxide with wood pulp at a pH of about 5-10 for about 5-40 minutes and then acidifying the mixture to a pH of about 1.9-4.2. The mixture is then allowed to react for about 2 or more hours to complete the two-step high/low pH bleaching process.

Abstract: Secondary pulp is deinked and bleached by contacting the pulp simultaneously with oxygen, alkali, and a surfactant in a reaction zone followed by washing to recover a secondary fiber product. Simultaneous contacting with oxygen and surfactant yields higher pulp brightness than sequential contacting in oxygen bleaching and washing stages, and enhances bleachability in further bleaching stages.

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.