JP2825346B2 - Environmentally improved bleaching method for lignocellulosic materials - Google Patents

Abstract

(i) Wood chips are chemically digested to provide lignocellulosic pulp followed by e.g. washing and screening (ii) pulp is then O2 delignified and (iii) comminuted and O3 treated for further delignification and bleaching. Pulp prod. obtd. in (iii) can be further brightened by addn. of CO2 or a peroxide. Typically at end of step (ii) pulps have a K number of 10 or less and viscosity above 13cps.. Corresp. values at completion of (iii) are 5 or less and above 10cps.. Digestion in (i) is e.g. by Kraft pulping. Pulp pH in (iii) is pref. 1-4 and temp. is ambient.

Description

Description: FIELD OF THE INVENTION The present invention is a novel environment for delignify and bleach lignocellulosic pulp that does not require the use of elemental chlorine and produces pulp of acceptable strength. On the methods allowed above. Also, the use of this method reduces the amount of environmental pollutants.

BACKGROUND OF THE INVENTION Wood contains two main components, fibrous carbohydrates, for example, a cellulose fraction and non-fibrous components. The polymer chains that form the fibrous cellulosic portion of wood are aligned with each other and form strong associative bonds with adjacent chains. The non-fibrous portion of wood is known as lignin. Includes three-dimensional polymeric materials formed primarily from phenylpropane units. While some of the lignin is between the cellulosic fibers and binds them to solid materials, a significant portion of the lignin is also distributed within the fibers themselves.

Wood must first be converted to pulp for use in papermaking. Pulp can be defined as wood fibers that can be slurried or suspended and then deposited on a screen to form a sheet (eg, a sheet of paper). The methods used to carry out the pulping process usually involve physical or chemical treatment of the wood, or a combination of these two treatments, which change the chemical form of the wood and reduce the resulting product. Give desired properties. Thus, there are two main types of pulping techniques, mechanical pulping and chemical pulping. In mechanical pulping, wood is physically separated into individual fibers. In chemical pulping, wood chips are digested with a chemical solution to solubilize some of the lignin, thus allowing its removal. Commonly used chemical pulping methods are broadly classified as (1) the soda method, (2) the sulfite method, and (3) the kraft method, with the last method being the most commonly used and the following various known methods: Can be improved.

The soda method is known in the art. It uses sodium hydroxide (NaOH) as an active reagent to break down lignin and aid in its removal. Also, the sulfite method is known in the art (eg, Handbook for Pulp & Pap
er Technologists-Chapter 6; Sulfite Pulping (TAPPI, US
See A)).

The kraft process, along with many of its variations, is the basic chemical process used to make paper. Handbook for P
ulp & Paper Technologists-Chapter 7; Kraft Pulping (TA
PPI, basic Kraft process, as described in USA) involves digesting wood chips in an aqueous solution of sodium hydroxide (NaOH) and sodium sulfide (Na ₂ S).
This method is very effective for pulping other more easily pulped species of wood, such as northern hardwoods and softwoods, as well as more difficult-to-treat wood such as southern softwoods. Similarly, the kraft process generally produces relatively high strength pulp. Since its use results in reduced erosion on the cellulose component of the wood.

The improved kraft technique may result in less degradation of the polymer structure of the cellulosic fibers during pulping, and thus the loss of strength of the resulting paper product is reduced as compared to paper products produced by conventional kraft processes. One improved kraft pulping process is "extended delignification"
This is known in the art as a specific order, or at different locations in the digester apparatus, or at different times, or while reducing the severity of chemical erosion of the pulping liquor on the cellulose fibers, while increasing the amount of lignin. A broad term used in the art to include various improved crafting techniques, such as removing and re-injecting coolant in a defined order to add pulping chemicals to more effectively remove It is. Other improvements to the craft method are craft-
This is an AQ method in which a small amount of anthraquinone is added to the kraft pulping liquor to promote delignification and limit erosion of the cellulose fibers that make up the wood.

A variety of alternative extended delignification techniques are known in the art and are described in TAPPI, 68 (11), 70 (1985) by VAKor.
Kamyr modified continuous steaming (MCC) as described by telainen and EA Backlund; Beloit rapid displacement heating as reported by RSGrant in TAPPI, 66 (3), 120 (1983). RDH); and B. Petter in Pulp and Paper, 59 (11), 90 (1985)
Includes Sunds Cold Blow steaming as reported by sson and B. Ernerfeldt.

Cooking of wood by the kraft or modified kraft process results in the formation of a dark slurry of cellulose fibers known as "brownstock". The dark color of brown stock is due to the fact that not all of the lignin is removed during the digestion and is chemically modified during pulping to form chromophore groups. Thus,
In order to lighten the color of the brownstock pulp, that is, to make it suitable for use in printing paper and writing and other white paper applications, by the addition of delignifying substances and also by "bleaching" Alternatively, it is necessary to continue the removal of residual lignin by chemically converting the residual lignin into a colorless compound by a method known as "brightening".

However, prior to bleaching the pulp, after the chemical treatment involved in the pulping process has been completed, the cooking material is usually transferred to a separate blow tank. In the blow tank,
The pressure generated during the initial chemical treatment of the lignocellulosic material is released and the pulp material is separated into fibrous material.
The resulting fiber material is then subjected to a series of washing steps to remove a combination of residual chemicals and soluble materials (eg, lignin) separated from the fiber material during the pulping process. Often, the pulp is also not unraveled for special treatment (re-steaming, mechanical grinding, etc.) (undefi
bered) is subjected to one or more screening steps designed to separate a majority of the wood.

The residue from the washing process (commonly referred to as black liquor) is collected, concentrated, and then incinerated in an environmentally safe manner in a collection boiler. Techniques for black liquor recovery, concentration and combustion are conventional and known in the art.

The delignification process and the bleaching process are performed on the washed fiber material in a series of steps using a selected combination of chemical reactants. The prior art has suggested various combinations of chemical treatments. Moreover, the individual processing steps have been rearranged in an almost infinite number of combinations and permutations. Therefore, to simplify the description of the various bleaching processes and bleaching systems, the use of character codes
It is commonly used in combination to describe the particular chemical reactants used and the sequence of process steps.

Below, the character codes used in the appropriate places are as follows:

C = chlorination-reaction with elemental chlorine in acidic medium.

E = alkali extraction-dissolution of the reaction product with NaOH.

E ₀ = solubility of the reaction product by oxidizing an alkaline extraction -NaOH and oxygen.

D = chlorine dioxide - reaction with ClO ₂ in acidic medium.

P = peroxide-reaction with peroxide in alkaline medium.

O = reaction with elemental oxygen in oxygen-alkali medium.

O _m = improved oxygen-homogeneous alkali treatment of low consistency to medium consistency pulp, followed by reaction of high consistency pulp with oxygen.

Z = ozone-reaction with ozone.

Homogeneous reaction with ozone - Z _m = improved ozone.

C / D-a mixture of chlorine and chlorine dioxide.

H = hypochlorite-reaction with hypochlorite in alkaline solution.

O _m and Z _m are improvement processes of the present invention and are described in more detail in the detailed description of the invention.

Delignification and bleaching of wood pulp by using elemental chlorine has been common for many years. Illustrative examples of bleaching lignocellulose pulp include, for example,
Campbell et al., U.S. Pat.No. 1,957,937, Cranford
U.S. Pat.No. 2,975,169 and Kindron et al. U.S. Pat.No. 3,462,344, and Handbook for Pulp
& Paper Technologists-Chapter 11; Bleaching (§11.3)
(TAPPI, USA).

However, while elemental chlorine has been found to be an effective bleach, it is cumbersome and potentially dangerous for both factory individuals and equipment. For example, the effluent from chlorine bleaching processes contains a large amount of chloride produced as a by-product of these processes. These chlorides readily corrode the processing equipment and thus require the use of expensive materials in the construction of such factories. Furthermore,
Chloride accumulation in the plant eliminates recirculation of the washer filtrate after the chlorination step in closed system operation, without the use of recovery systems that require extensive and therefore expensive improvements. . In addition, concerns about the potential environmental effects of chlorinated organics in effluents (the U.S. Environmental Protection Agency considers them toxic to humans and animals) are of considerable concern to government demands. Permit bleach factories that produce changes and include standards that cannot be met with conventional bleaching or pollution control techniques.

To avoid these drawbacks, the paper industry has attempted to reduce or eliminate the use of elemental chlorine and chlorine-containing compounds from multi-stage bleaching processes on lignocellulosic pulp. The requirement that high levels of pulp brightness be required for many applications seeking to use such pulp complicates these efforts.

In this regard, efforts have been made to develop bleaching processes in which chlorine-containing agents are replaced for example by oxygen for the purpose of bleaching pulp. The use of oxygen allows the circulation of the effluent from this stage for recovery, but also allows a considerable reduction in the use of elemental chlorine. Some methods of bleaching pulp with oxygen and delignifying, for example, Richer U.S. Pat.Nos. 1,860,432, Grangaard et al. U.S. Pat.Nos. 2,926,114 and 3,024,158, Gaschke
U.S. Pat.No. 3,274,049 to Meylan et al. U.S. Pat.
No. 84,533; Watanabe U.S. Pat.No. 3,251,730; Rerolle
U.S. Pat.No. 3,423,282 to Farley, U.S. Pat.
No. 1,699; Kooi U.S. Pat.No. 4,619,733 and P. Christen
Sen, “Bleaching of Sulphate Pulps with Hydrogen P
eroxide ", Norsk Skogindustri, 268-271 (1973). Alkali pretreatment of pulp prior to oxygen delignification is suggested by Elton U.S. Patent No. 4,806,203.

However, the use of oxygen is not a completely satisfactory solution to the problems found with elemental chlorine. Oxygen is not as selective a delignifying agent as elemental chlorine, but the KNo. Of pulp using conventional oxygen delignification methods. Can be reduced by a limited amount until there is uneven erosion on the cellulosic fibers, ie unacceptable erosion. Also, after oxygen delignification, residual lignin has conventionally been removed, typically by chlorine bleaching, to obtain fully bleached pulp, but with a much reduced amount of chlorine. Was. However, even at such reduced chlorine concentrations,
Corrosive chlorides eventually reach unacceptable levels of concentration during closed cycle operation.

In order to avoid the use of chlorine bleach, attempts have been made to remove such residual lignin by using ozone during the bleaching of chemical pulp. Although ozone appears initially to be an ideal material for bleaching lignocellulosic materials, the extraordinary oxidizing properties of ozone and its relatively high cost have traditionally been satisfactory for lignocellulosic materials, especially for southern softwoods. It limited the development of ozone bleaching methods. Ozone easily reacts with lignin and KNo. But effectively attack carbohydrates (which make up the cellulose fibers) under most conditions and significantly reduce the strength of the resulting pulp. Similarly, ozone is very sensitive to process conditions such as pH with respect to its oxidative and chemical stability, and such changes can significantly alter the reactivity of ozone to lignocellulosic materials.

Since the turn of the century, when the ability to delignify ozone was first recognized, a great deal of constant research has been conducted by many skilled persons to develop commercially viable methods of using ozone to bleach lignocellulosic materials. Was done. In addition, numerous publications and patents have been issued in this field, and there have been reports of attempts to perform ozone bleaching on a non-commercial, medium-scale basis. For example, U.S. Pat. No. 2,466,633 to Brabender et al. Discloses that ozone is adjusted to a moisture content of 25-55% (adjusted to oven drying consistency) and a range of 4-7.
It describes a bleaching process that is passed through pulp having a pH.

Other non-chlorine bleaching sequences are described by S. Rothenberg, D. Robinso
n and Jojnsonbaugh, “Bleaching of Oxygen Pulps wit
h Ozone ", Tappi, 182-185 (1975) -Z, ZEZ, ZP and ZP
_a (P _a -peroxyacetic acid); and N. Soteland, “Ble
aching of Chmical Pulps With Oxygen and Ozone ", Pul
p and Paper Magazine of Canada; T153-58 (1974) -O
It is described in ZEP, OP and ZP.

Singh, U.S. Pat. No. 4,196,043, also discloses a multi-stage bleaching process, which also attempts to eliminate the use of chlorine compounds, including examples involving hardwoods. It is known to those skilled in the art that hardwoods are more likely to bleach than most conifers. This method is characterized by one to three bleaching stages and a final treatment with alkaline hydrogen peroxide, each stage being separated by alkali extraction.
One such sequence is a common shorthand command in the paper industry.
It can be described as ZEZEP. According to this method, the effluent from each processing stage is recovered, preferably earlier than the stage from which it was obtained, for use in a bleaching operation,
Can circulate. This patent also provides a so-called countercurrent effluent stream.

Despite all the work done in this field, no commercially viable method for the production of ozone-bleached lignocellulosic pulp, especially southern softwood pulp, has not been disclosed before and many failures have been made. Had been reported.

The present invention solves the problems found in the prior art as described herein, and in a commercially viable manner with substantially no chlorinated organic emissions, minimal coloration and BOD emissions. A novel combination of pulping and bleaching steps to produce high grade bleached pulp is provided.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to delignify and bleach lignocellulosic pulp without the use of elemental chlorine bleaches to substantially reduce or eliminate environmental pollution and to be energy efficient, It is to provide a multi-step method to optimize the physical properties of pulp in a cost effective way. The present invention is applicable to virtually all wood species, including hard-to-bleach conifers in the southern United States.

Thus, using the methods described herein, a partially delignified pulp having a certain viscosity and lignin content is produced, and the viscosity and lignin content of the partially delignified pulp are increased. It may be of sufficient viscosity and lignin to allow it to be further delignified with ozone while maintaining the viscosity at a level such that the cellulose component is not significantly chemically degraded. .

The method of the present invention includes three or more steps with some possible variations within and between steps. These steps can be described as follows.

The first step is delignification of wood chips to lignocellulosic pulp using any one of several chemical pulping processes, followed by washing and removal of most of the dissolved organic matter and cooking chemicals for circulation and recovery Accompanied by Screening of the pulp to remove bundles of fibers not separated by pulping is usually involved. This delignification process can be performed on softwoods in the southern United States, for example, with K Nos. In the range of about 20-24 (target 21). The pulp typically has a capriethylenediamine ("CED") viscosity in the range of about 21-28, and a GE whiteness in the range of about 15-25 (also referred to below as GEB). Done in For hardwoods in the southern United States, KNos in the range of about 10-14 (target 12.5).
And pulp having a CED viscosity of about 21-28 is typically obtained.

Among the useful embodiments of this first step are: a. Kraft pulping using a continuous or batch cooking stage; b. Extended delignification using staged alkali addition and countercurrent final cooking Continuous digestion kraft pulping with c. Batch digestion kraft pulping with extended delignification using high speed liquid displacement and low temperature blowing techniques; d. Continuous or batchwise digestion stage Kraft-AQ pulping with extended delignification using, but not limited to.

The extended delignification techniques described in (b) and (c) above include, for example, the Kamyl MCC technique, Beloit RDH technique and Sands Cold Blow Steaming technique described in the background section of this specification. May be included. Depending on the type of lignocellulosic material used, the above-mentioned soda and sulfite methods can be used.

The second step of the method involves an oxygen delignification treatment to further remove lignin without significant loss of strength of the cellulosic fibers. This includes washing and removal of dissolved organics and alkalis for circulation and recovery. Also, pulp screening is sometimes performed after oxygen delignification.

During the oxygen delignification step, the KNo. Of the pulp of increased consistency is increased. At least about 45% not let little damage cellulose component of the pulp (with respect to O) ~ least about 60% (with respect to O _m) is reduced. In addition, KNo. The ratio of viscosity to viscosity is typically reduced by at least 25%. With respect to the above softwood pulp using O _m, about 7
10 KNo. And viscosities of about 13 or more are easily obtained. For hardwood pulp, a KNo. And a viscosity of about 13 or more is obtained after the oxygen delignification step.

Among the possible embodiments for this step are: a. Conventional oxygen delignification (O), including alkaline oxygenation of the pulp at low pulp consistency, intermediate pulp consistency, or high pulp consistency; or b. Alkaline treatment at low pulp consistency to intermediate pulp consistency (ie, less than about 10% by weight);
This is followed by a high pulp consistency oxygen treatment (ie, about 20
% By weight) (O _m ), but is not limited thereto.

For end uses of pulp that do not require whiteness greater than about 35% GEB (often referred to as semi-bleached pulp)
It is possible to use pulp that has been directly treated in step 2 only in the papermaking process.

Third step of the present method involves gaseous ozone bleaching treatment in acidic particular process parameters to obtain highly selective removal and bleaching of lignin with minimal degradation of cellulose (Z or Z _m) . Among these process parameters are chelating agents for metal ion regulation, pH
Control, pulp particle size control, pulp consistency, ozone concentration and gas / pulp contact control. Prior to treatment with ozone, a chelating agent, such as oxalic acid, diethylenetriaminepentaacetic acid ("DTPA") or ethylenediaminetetraacetic acid ("EDTA"), may be added to the pulp, substantially reducing the metal ions contained therein. Can be combined. Further, the pH of the pulp is preferably adjusted to a range of about 1-4 before the third step. This can be done by adding a sufficient amount of acidic material to the pulp. Advantageously, the consistency of the pulp is increased to about 35-45% by weight and the particle size of the fiber flocs is milled to a size of about 5 mm or less prior to the ozone delignification step. A washing step of the dissolved organics for circulation and recovery is included.

During the ozone step, the pulp is preferably fiberized at ambient temperature or at a pulp temperature of at least less than about 120 ° F. Ozone may be provided, for example, by an ozone-containing gas, which may include oxygen or air. If an ozone / oxygen mixture is used, the ozone concentration should be about 1-8.
%, While for ozone / air mixtures an ozone concentration of about 1-4% by volume is allowed.
In the ozone reactor, the substantially delignified pulp is advanced in a manner that exposes substantially all of the pulp particles to ozone in a uniform manner.

Treating pulp with ozone at high consistency without particular attention to pulverization of the pulp fibers or proper contact between the individual fibers and the reactant gas stream always results in uneven ozone bleaching of the fibers. The present application designates such non-uniform ozonation with the letter "Z". The use of the improved ozone technology of the present invention, where the fibers are milled to a size of about 5 mm or less, and yet properly and closely contacted with the ozone gas stream to provide uniform delignification,
It referred to herein as "Z _m".

After the second step, the KNo. Pulp with significant amounts of ozone has a KNo. (Which typically results in pulp properties being poor and detrimentally affected by excessive ozonolysis of the pulp cellulose fibers). It was found that this was not suitable for the third step. KNo. Of less than 10 If the pulp having the following is ozonated, a lower concentration of ozone is used and only a minimal amount of cellulolysis occurs. The Z process or product from the Z _m steps relating to the southern United States of softwood or hardwood described above raw materials, about 5
KNo., Generally in the range of about 3 to 4 (target 3.5). , About 1
A GE of 0 or greater and at least 50% (typically about 54% or greater for softwood and 63% or more for hardwood)
It is a pulp having whiteness.

Among the embodiments useful in this process are: a. Treatment of acidified pulp by countercurrent contact of ozone in oxygen or air carrier gas; or b. By co-current contact of ozone in oxygen or air carrier gas Processing of acidified pulp includes, but is not limited to.

An additional bleaching step is then performed to reduce the pulp to the desired fully bleached state, i.e., about 70, using several possible and well-recognized bleaching and extraction processes.
It may be used to have a GE whiteness level of ~ 95%. Among the useful embodiments are: a. A normal extraction step with washing, followed by a peroxide step with washing; (ie, EP); b. A normal alkali extraction and washing step, followed by washing A normal chlorine dioxide step (ie, ED); c. A normal alkali extraction step and a washing step, followed by a normal chlorine dioxide step with washing, followed by a repetition of the extraction and chlorine dioxide steps (ie, EDED); or d. an extraction step with increased oxygen or oxygen and peroxide, followed by a normal chlorine dioxide step: ie (E _o ) D or (E
_op ) D, but is not limited to these.

In another embodiment, the extraction step comprises subjecting the substantially delignified pulp to a predetermined time correlated to the amount of alkaline material that solubilizes a significant portion of the lignin remaining in the pulp. And combining with an effective amount of an alkaline substance in an aqueous alkaline solution at a predetermined temperature. Thereafter, a portion of the aqueous alkaline solution can be extracted to remove substantially all the solubilized lignin therefrom.

Subsequent to the extraction step, the substantially delignified pulp is treated in an additional bleaching step, resulting in a GE of the resulting pulp.
Brightness can be increased to at least about 70%. Preferred brighteners include chlorine dioxide or peroxide.

The (E _o ) D embodiment, the (E _op ) D embodiment or the EDED embodiment obtains the highest whiteness level. For the ED embodiment, the filtrate of the chlorine dioxide stage cannot be recycled to chemical recovery due to the presence of inorganic chlorides unless treated. However, since this is the only required sewage filtrate from the process, a significant reduction in effluent volume, color, COD, BOD, and chlorinated organics is obtained. Less than 2 pounds per ton of colorant, less than 2 pounds per ton of BOD ₅ and less than 2 pounds (about 0.91 kg), preferably less than 0.8 pounds (about 0.36 kg) of total organic chloride (TOCl ) Can be obtained. Also, the filtrate of the chlorine dioxide stage can be processed in a membrane filtration process that allows for substantially complete circulation. In the EP embodiment, the chlorinated material is not formed in the bleaching process, resulting in a process in which virtually all of the liquid filtrate can be recycled and recovered, with little effluent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the preferred method of the present invention, wherein solid lines represent pulp flow and dashed lines represent effluent flow.

 FIG. 2 is a schematic diagram of a preferred method of the present invention.

FIG. 3 is a cross-sectional view of a portion of the ozonizer shown in FIG. 2 taken along line 3-3.

FIG. 3A is a cross-sectional view of a portion of the preferred ozonizer shown in FIG. 2 taken along line 3-3.

FIG. 4 is a comparison of recycle and waste streams for various pulping processes.

DETAILED DESCRIPTION OF THE INVENTION The present invention delignifies and bleaches pulp while minimizing the extent of erosion on the cellulose portion of wood, thus producing a product having acceptable strength for the production of paper and various paper products. For a new method for.
For convenience in understanding the improvements over the prior art provided by the use of the presently disclosed delignification and bleaching processes, definitions of some parameters involved in the various stages of the delignification / bleaching process are provided below. .

A. General Definitions The following definitions are used herein.

"Consistency" is defined as the amount of pulp fiber in the slurry, expressed as a percentage of the total weight of oven dried fiber and water. It is also sometimes referred to as pulp consistency. The consistency of the pulp depends on the operation and type of dewatering equipment used. The following definition is Ry
dholm, Pulping Processes, Interscience Publishers, 19
65, 862-863 and TAPPI Monograph No. 27, The Bleachi
ng of Pulp, edited by Rapson, The Technical Association o
f Based on definitions found in Pulp and Paper Industry, 1963, pp. 186-187.

"Low consistency" is in the range of 6%, usually 3 to
Includes 5% range. It is a suspension which can be pumped by a conventional centrifugal pump and which can be obtained using a decker and a filter without using press rolls.

"Intermediate consistency" is about 6-20%. 15%
Is a demarcation point within the intermediate consistency (dividing p
oint). Below 15%, that consistency can be obtained with a filter. This is the consistency of the pulp mat exiting the vacuum drum filter in brown stock washing and bleaching systems. The consistency of the slurry from the washer, i.e., a brownstock washer or a bleach stage washer, is 9-15%.
Above about 15%, press rolls are required for dewatering.
Rydholm states that the usual range of intermediate consistency is 10-18%, while Rapson states that it is 9-15%. The slurry can be pumped by special machinery even though it is still a coherent liquid phase at elevated temperatures and under some compression.

"High consistency" is about 20% to about 50%. Lidholm states that its normal range is 25-35%, and Rapson states that its range is 20-35%. These consistency can be obtained only by using a press. The liquid phase is completely absorbed by the fibers and the pulp can be pumped over very short distances.

Further, as used herein, "pulp" is used in its ordinary sense and refers to the cooking of lignocellulosic material to form brown stock. Pulping includes, for example, kraft, kraft-QA and extended delignification forms.

The term "modified kraft process" is used herein to include extended delignification and all other modified kraft processes other than the Kraft-AQ process. This is because this method has gained special status and approval in the art and is otherwise known by its name. Also, the oxygen delignification step after completion of pulping is not considered an extended delignification. Rather, we chose to call it the first step in a delignification process for bleaching or whitening pulp.

There are two main types of measurements to determine the completeness of the pulping or bleaching process, ie, the “degree of delignification” and the “whiteness” of the pulp. The degree of delignification is usually used for the pulping process and the initial bleaching stage. It tends to be less accurate when only a small amount of lignin is present in the pulp, ie at a later bleaching stage. Brightness factors are commonly used for bleaching processes. This is because the pulp is slightly colored and tends to be more accurate when its reflectivity is high.

There are many ways to measure the extent of delignification,
Most are variants of the permanganate test. A typical permanganate test is the permanganate value or "KNo." (This is the number of cubic centimeters of 1/10 normal potassium permanganate solution consumed by 1 g of oven dried pulp under specified conditions) Is given). It is measured by TAPPI Standard Test T-214.

There are several methods for measuring the whiteness of pulp. This parameter is usually a measure of reflectivity, and its value is expressed as a percentage of a scale. A common method is GE whiteness, which is expressed as a percentage of the maximum GE whiteness measured by TAPPI standard method TPD-103.

Further, where appropriate, the character codes set forth in the background section are used to represent the various stages of pulping in the detailed description of the invention.

B. Process Steps of the Invention As shown below, the values obtained by using the pulping, delignification and bleaching processes of the present invention (ie,
KNo. , Viscosity and GE whiteness) demonstrate the ability of this process to increase the degree of lignin removal from the pulp and minimize the resulting degradation of cellulose. After the oxygen delignification step and prior to whitening, the pulp has a KNo. Of about 5-10, preferably about 7-10, for US softwood. And is partially delignified to about 5-7 for hardwoods in the United States. This partially delignified pulp is approximately
It has a viscosity of at least 10, generally at least 13, preferably at least 14 (for softwood pulp) or at least 15 (for hardwood). This partially delignified material thus has good strength and suitable viscosity, so that it can withstand the action of ozone. The partially delignified pulp is exposed to ozone to further delignify the pulp, and thus the KNo. Of the pulp for both softwood and hardwood. And the pulp GE brightness increases by at least about 50-70%. For softwoods, GE whiteness of about 54% or more is typically obtained, while for hardwood pulp, about 63%
The above values are obtained. Thereafter, the brightness of the pulp is further increased by alkaline extraction and an additional bleaching step using chlorine dioxide or peroxide.

Thus, for convenience in understanding the present invention, FIG. 1 graphically illustrates the various steps used to pulp, delignify and whiten pulp in accordance with the present invention. As shown in FIG. 1, the present invention comprises: (a) a step of pulping a lignocellulosic material, whereby the pulping chemical is recovered by methods known in the art,
(B) washing the pulp to remove chemical residues from the pulping liquor together with residual lignin (usually the pulp for removing bundles of fibers not separated during pulping); (C) screening of the pulp with an alkaline oxygen delignification step (ie O or O _m ); (d) washing the partially delignified pulp obtained in step (c) above. To remove dissolved organics from the oxygenation (if necessary, screening may be performed at this time, while at least a portion of the effluent from this step may be recycled to the previous step) (E) chelating and acidifying the pulp to bind the metal ions and adjust the pH to the desired level; (f) contacting the pulp with ozone to further delignify and partially bleach the material. You Step (ie, Z or
Z _m); (g) with washing the ozonated pulp, at least a portion recycled to the previous step to step of the effluent from this step; step of removing (h) caustic extraction to residual lignin (I) washing the extracted pulp and circulating at least part of the effluent to the previous step; (j) adding a second bleach (ie whitening and bleaching the pulp) (K) washing the bleached pulp to obtain a bleached product having a GE brightness of about 70-90%; and (l) at least one of the effluents from the P bleaching stage. Recirculating the effluent from the D-bleach stage to the sewage or, after appropriate treatment, circulating the effluent to the previous stage.

1. Pulping The first step of the process of the present invention (improving the amount of lignin removed from the lignocellulosic material and minimizing the amount of cellulose degradation can be used) involves a pulping process. is there. The particular pulping process used in the process of the present invention depends largely on the type of lignocellulosic material, and more particularly on the type of wood used as starting material. Further, as shown in FIG. 1, the pulping liquor used in chemical pulping technology can be recovered and reused by methods known in the art. Typically, this step is followed by a screening step, as well as a wash to remove most of the dissolved organics and cooking chemicals for circulation and recovery, where the pulp is passed to a screening device. To remove bundles of fibers that were not separated by pulping.

The craft method is generally allowed to be used on all woods compared to other noted methods. Because the final pulp obtained from the kraft process has acceptable physical properties, brown stock pulp is also dark in color.

Depending on the lignocellulose starting material, the results obtained with the conventional kraft process can be enhanced by the use of extended delignification techniques or the Kraft-AQ process. In addition, these techniques do not adversely affect the strength and viscosity properties of the pulp, and do not affect the KNo. It is preferred to obtain the maximum viscosity of the decrease.

When using the Kraft-AQ method, the amount of anthraquinone in the cooking liquor should be at least about 0.01% by weight, based on the oven dry weight of the wood to be pulped, from about 0.02 to about 0.1%. The amounts are generally preferred. Incorporation of anthraquinone in the kraft pulping process contributes significantly to lignin removal without adversely affecting the desired strength properties of the residual cellulose. Further, additional costs of anthraquinone, subsequent Z _m step, is partially offset by the cost savings of chemicals E step and step D or P steps.

Craft-AQ separate or possibly Craft-AQ
In addition, extended delignification techniques such as the Kamil MCC method, the Beloit RDH method and the Sands Cold Blow method for batch digesters are used. These techniques also provide the ability to remove more lignin during pulping without adversely affecting the desired strength properties of the residual cellulose.

2. Oxygen delignification The next step in the process of the invention relates primarily to the part of the bleaching process that involves the removal of residual lignin from the treated brownstock pulp. In the method of the present invention,
This step involves an oxygen delignification step. The solid materials removed at this stage are oxygenated materials, which, like the black liquor, can be recovered, concentrated and then incinerated in a conventional recovery boiler in an environmentally safe manner. At least a portion of the liquid phase is circulated as shown in FIG.

It has been found that the oxygen delignification step allows removal of an increased percentage of lignin remaining in the brownstock pulp and can be performed in a manner that does not result in a corresponding unacceptable reduction in pulp viscosity. In general, the identified process is the following low consistency ~
The brown stock pulp from the pulping process at an intermediate consistency is treated with the required amount of alkali required for the oxygen delignification step to ensure uniform application of the alkali, and then the consistency is increased to increase the consistency. It is carried out by delignification at consistency. High consistency delignification is preferred,
Low or medium consistency oxygen delignification techniques may be used instead of high consistency delignification.

Preferably, the high consistency oxygen delignification step is performed in the presence of an aqueous alkaline solution at a pulp consistency of about 25% to about 35%, more preferably at about 27%. This improved process (O _m ) reduces residual lignin from brownstock pulp as compared to 45-50% that can be removed in a conventional oxygen delignification step without the previously expected undesirable reduction in relative viscosity. At least 60%
Enables removal. Because of the unique process capabilities of this improved process, it clearly constitutes a preferred oxygen process for use in the method of the present invention.

The processing steps of the improved oxygen process (O _m ) are wood pulp,
Preferably, the kraft brown stock pulp is substantially homogeneously combined with the aqueous alkaline solution while reducing the consistency of the pulp to less than about 10%, preferably about 5% by weight.
Including maintaining less than. The aqueous alkaline solution may comprise from about 0.5% to about 4% active alkali after thickening based on the oven-dried weight of the brownstock pulp, more preferably about 2.5% active alkali after thickening based on the oven-dried weight of the brownstock pulp. Is preferably present in an amount sufficient to provide

This step distributes the aqueous alkaline solution evenly into the low consistency brown stock, yet ensures that substantially all of the brown stock fibers are exposed to a uniform application of the alkaline solution. Surprisingly, the brownstock pulp treated in this way is not substantially delignified in the treatment process, but it also has a higher consistency than the brownstock treated with alkali solutions at high consistency by the commonly used methods. In the subsequent high-consistency oxygen delignification step, delignification is more effectively performed. Local inhomogeneities in the distribution of alkali in normal high consistency pulp are avoided, thus eliminating the associated inhomogeneous oxygen delignification.

Thus, this uniform distribution step preferably involves combining the pulp with the aqueous alkaline solution for at least about 1 minute, preferably up to about 15 minutes. Processing times of less than about 1 minute are generally not considered to provide sufficient time to obtain a substantially uniform distribution, while processing times of greater than about 15 minutes are not expected to produce further substantial benefits. You.

Further, the preferred alkali treatment of the pulp according to the present invention may be performed at a wide range of temperature conditions. According to a preferred implementation, the processing steps are performed at a temperature from about room temperature to about 66 ° C (150 ° F), with temperatures in the range of about 32 ° C (90 ° F to about 66 ° C (150 ° F) being more preferred. Atmospheric pressure or high pressure may be used.
The process is completed when the aqueous alkaline solution is substantially uniformly distributed in the low consistency pulp. The amount of aqueous alkaline solution present during the treatment step can vary greatly according to the particular process parameters of the delignification reaction. The amount of the alkaline solution effective for the purpose of the present invention is
It mainly depends on the degree of delignification desired in the oxygen bleaching step and the strength of the particular solution used. The aqueous alkaline solution used preferably comprises a sodium hydroxide solution having a concentration of about 20 to about 120 g / l. This solution is mixed with the low consistency pulp, so that
The whole mixture has a concentration of alkaline substance of about 6.5-13.5 g / l, preferably of about 9 g / l. Thus, for 5-15 minutes treatment of 3-5% consistency pulp at a temperature of 49 ° C. (120 ° F.) to about 66 ° C. (150 ° F.) at these concentrations of alkaline material. A uniform distribution of the alkaline material is obtained in the pulp.

According to a preferred embodiment of the present invention, the aqueous sodium hydroxide solution comprises from about 15% by weight, based on dry pulp weight,
It is added to the low consistency pulp in an amount sufficient to provide about 30% by weight of sodium hydroxide. Other sources of alkali having an equivalent sodium hydroxide content, such as oxygenated white liquor from conventional kraft recovery and regeneration cycles, may also be used.

Following the low consistency caustic treatment described above, the consistency of the treated pulp is increased to a value greater than about 20%, preferably from about 25% to about 35%. Several methods for increasing the consistency of pulp, such as pressing wood pulp and removing liquid therefrom, are effective and known in the art.

Thereafter, oxygen delignification is performed with high consistency. Methods for dissolving gaseous oxygen in the liquid phase of high consistency pulp to effect delignification thereof are effective and known in the art. Any of these known methods are believed to be suitable for use in the present invention. However, the oxygen delignification of the present invention requires about 5.6 kg / cm ² (8
Gaseous oxygen 0 psig) ~ about 7.0kg / cm ² (100psig) is introduced into the liquid phase of high consistency pulp, it preferably includes keeping the temperature of the pulp to about 90 ° C. ~ about 130 ° C. therebetween. Preferably, the average contact time between the high consistency pulp and the gaseous oxygen is from about 20 minutes to about 60 minutes.

By following the preferred process of the present invention, the KNo. Of the pulp after the oxygen delignification step of at least about 60% without substantially damaging the cellulose portion of the pulp.
Can be obtained. By comparison, normal oxygen delignification requires about a year before cellulose degradation occurs.
50% KNo. Can only be obtained. Thus, the preferred process of the present invention is at least 20 times less delignified than prior art delignification processes.
%, I.e., 50% to at least about 60% KNo. Give a drop. A reduction of 70% or more can be further obtained with minimal cellulolysis. The avoidance of decomposition of the cellulose component of the pulp is evident by a minimal change in the viscosity of the pulp treated according to the invention.

After entering the oxygen delignification step, the pulp KNo. Is about 10-26 depending on the type of wood
(E.g., for kraft pulping, about 10-14, target 12.5 for hardwood, about 20-24, target 21 for softwood), while after oxygen delignification, KNo. Generally ranges from about 5 to 10.

A processing mechanism for performing the method of the present invention is shown graphically in FIG. The steps set forth therein represent a preferred mode of operation that tends to maximize certain advantages of the present invention. Wood chips 2 are introduced into digester 4, where they are cooked in a liquid, for example a liquid of sodium hydroxide and sodium sulfide. The steaming apparatus 4 comprises a kraft brown stock 8 and a black liquor 6 containing a reaction product of solubilizing lignin.
Is generated. The brown stock is preferably processed in a washing device that includes a blow tank 10 and a washer 21 where residual liquid contained in the pulp is removed. Many methods for cleaning brown stock, for example, diffusion cleaning,
Rotating pressure washing, horizontal belt filtration, and dilution / extraction are effective and are known in the art. All of these methods are within the scope of the present invention. Also, the screening of brown stock has not been unraveled due to special treatment (unde
Often done before or after the washing step to remove most of the fibered) wood.

The washed brown stock is introduced into processing equipment 14, where it is treated with an alkaline solution and maintained at a consistency of less than about 10%, preferably less than about 5%. The process of the present invention preferably includes means for introducing make-up caustic 16 into the treatment stage to maintain the desired caustic application rate. Processed pulp18
Is passed to a thickener 20 where the consistency of the pulp is increased, for example, by pressing to at least about 20% by weight, preferably from about 25% to about 35%.
The removed liquid 22 from the thickening device 20 is preferably returned to the cleaning device 12 for further use. Thickening device 20
High consistency "pressed" produced in
Brown stock 24 is advanced to an oxygen delignification reactor 26 where it is contacted with gaseous oxygen 28.
Delignified Brownstock 30 is blow tank
Preferably, the pulp is passed through 32 and then to a second washer 34, where the pulp is washed with water to remove dissolved organics, resulting in a high quality, low color pulp 36. Preferably, at least a portion of the effluent 38 from this cleaning step is returned to the cleaning apparatus 12 for use.
The effluent 13 from the washing device 12 can be circulated to the blow tank 10 or finally to the black liquor line 6 alone or, if necessary, together with all or part of the effluent 38. Also, partially delignified pulp obtained after oxygen delignification may be screened to remove unseparated fiber bundles from the pulp for further processing, such as mechanical grinding. Good. From here, pulp
36 may be sent to a subsequent bleaching stage to produce a fully bleached product.

In a particularly preferred method of the present invention as shown in FIG. 2, kraft pulping of wood may be performed to take advantage of ozone bleaching, followed by the improved low consistency of the above. Alkaline treatment / high consistency oxygen delignification operation (O _m ) may be performed.
For conifers, as described above, this combination has a KNo. Of about 8-10, preferably 9, And a pulp having a viscosity greater than about 13-14. Also craft wood AQ
Pulping followed by a conventional oxygen delignification step (ie, O, high consistency alkali treatment, followed by high consistency oxygen delignification)
It is possible to obtain pulp with similar properties. Also, instead of kraft AQ pulping, an extended delignification process, followed by a conventional oxygen delignification step, can be used to obtain pulp with the desired properties. Also, a combination of kraft pulping and an extended delignification process technology, such as a Kamil MCC process, a Beloit RDH process or a Sands Cold Blow Steaming process as described in the Background section of this specification, Subsequent conventional oxygen delignification is effective but less preferred due to increased cost or process steps.

All of the various pulping and oxygen delignification steps are carried out before the ozone with the above KNo. And the viscosity value can be used in combination.

Conventional kraft pulping followed by conventional oxygen delignification is generally acceptable to the present invention, except for certain hardwoods such as aspen, which are relatively easy to delignify and bleach. Not done. For a given wood species, the combination of these usual techniques
Usually, a large amount of ozone is used during the ozonation process, accompanied by a great deal of cellulose degradation.

Through the use of the present invention, ozone consumption can be extended by several alternative routes, such as conventional kraft cooking, as described above, followed by an improved oxygen delignification step (O _m ), or Kraft pulping with modified delignification (eg, Kamil MCC, Beloit RDH or Sands Cold Blow), followed by a conventional oxygen delignification step (O), or Kraft AQ cooking followed by a conventional It can be reduced by using an oxygen delignification step (O). Further reductions in ozone consumption include improved kraft pulping with prolonged delignification (Kamil MCC, Beloit RDH or Sands Gold Blow),
Then use a modified oxygen delignification step (O _m ) or a Kraft AQ cooking process with extended delignification (Kamyl MCC, Beloit RDH or Sands Gold Blow) followed by normal oxygen It is obtained both when a delignification step (O) is performed. Use of all of these techniques in one process, i.e. an improved craft with prolonged delignification (Kamyl MCC, Beloit RDH or Sands Gold Blow)
AQ cooking followed by an improved oxygen delignification process (O _m )
The use of further reduces ozone consumption. The reduction in ozone consumption generally allows the viscosity of the pulp to be maintained at an acceptable level.

The advantages of using the high consistency oxygen delignification bleaching process (O _m ) described above can be attributed to the KNo. And the viscosity is clearly shown by comparing the relevant process under otherwise substantially the same process conditions. Using conventional kraft pulping operations and conventional high consistency oxygen delignification bleaching, the resulting pulp typically has a KNo.
And a viscosity of about 15. This KNo. Is too large to allow for subsequent delignification using the ozone step of the present invention. However, the use of conventional kraft pulping with improved high consistency oxygen bleaching, surprisingly, has a KNo. Pulp having a viscosity of greater than about 12-14. This preferred pulp KNo. Enables the use of the ozone delignification bleaching stage of the present invention.

3. Ozone Step The next step in the method of the present invention is the ozone delignification and bleaching of the oxygen delignified brownstock pulp. This ozonation is carried out in an ozone reactor, which is described in more detail below and comprises FIGS.
Shown in 3A. Prior to treatment of the pulp with ozone, the pulp is conditioned to ensure the most effective selective delignification of the pulp and to minimize the chemical attack of ozone on cellulose. Charged pulp 36 is sent to a mixing chamber 40, where it is diluted to a low consistency. Acids 42, for example, sulfuric acid, formic acid, acetic acid, etc. are added to the low consistency pulp and the pH of the pulp in the mixing chamber 40
In the range of about 1-4, preferably 2-3. The pH is adjusted as described above. This is because the relative effectiveness of ozone bleaching of pulp is known to depend on the pH of the pulp mixture. It is clear that low pH has no beneficial effect on the subsequent treatment of the pulp, while
Increasing the pH above about 4-5 results in reduced viscosity and increased ozone consumption.

The acidified pulp is treated with a chelating agent 44 to complex any metals or metal salts that may be present in the pulp. This chelation step is used to render such metals non-reactive or harmless in the ozone reactor, so that
They do not decompose ozone and thus reduce the efficiency of lignin removal and do not reduce the viscosity of cellulose.

Chelating agents are known per se and include, for example, polycarboxylates and polycarboxylate derivatives, such as di-, tri-, and tetra-carboxylates, amides, and the like. For reasons of cost and effectiveness, preferred chelators for this ozonation include DTPA, EDTA and oxalic acid. Amounts of these chelating agents ranging from about 0.1% to about 0.2% by weight of the oven-dried pulp are generally effective, but additional amounts may be required if high metal ion concentrations are present .

The effectiveness of the ozone bleaching process is controlled by several interrelated process parameters, including pH levels and the amount of metal salts in the pulp as described above. Another very important parameter is the consistency of the pulp during the ozone bleaching stage. The pulp to be bleached must contain sufficient water so that the water is present as a continuous phase in the individual fibers, ie the fibers should be fully saturated with water. The water in the fibers allows the transfer of ozone from the gaseous ozone atmosphere to treat the outer surface of the fibers, and perhaps more importantly, to allow the ozone to reach the individual fibers via the aqueous phase. Allows it to be moved into difficult interiors, thereby providing more complete removal of lignin from the fibers. On the other hand, the consistency should not be so low that the ozone is diluted and tends to chemically degrade the pulp rather than bleach it.

The preferred range of consistency (especially for softwoods in the southern United States) has been found to be about 28% to about 50%, with best results being obtained at about 38% to about 45%. Within the above ranges, favorable results are obtained as indicated by the relative amount of delignification, the relatively low amount of cellulose degradation, and the significant increase in brightness of the treated pulp.

The reaction temperature at which ozone bleaching occurs is likewise an important regulator of the process of the present invention. The ozone step can be effectively carried out at a temperature up to a critical temperature, at which point the reaction starts and causes excessive decomposition of the cellulose. This critical temperature will vary considerably depending on the particular type of wood used to produce the pulp and the history of prior treatment of the pulp. The maximum temperature of the pulp fibers at which the reaction is to take place should not exceed the temperature at which excessive decomposition of the cellulose occurs, which can be up to about 49 ° C to 66 ° C (120 ° F to 150 ° F) for softwoods in the southern United States It is.

The ozone gas used in the bleaching process may be used as a mixture of ozone and oxygen and / or an inert gas, or may be used as a mixture of ozone and air.
The amount of ozone that can be successfully incorporated into the process gas is limited by the stability of the ozone in the gas mixture. Typically, an ozone gas mixture comprising about 1-18% by weight of ozone in an ozone / oxygen mixture, or about 1 to 1% in an ozone / air mixture.
An ozone gas mixture containing 4% ozone is suitable for use in the present invention. The high concentration of ozone in the ozone gas mixture allows for the use of relatively small reactors and short reaction times for processing equal volumes of pulp, thereby reducing the capital expenditure required for the equipment. However, ozone gas mixtures containing small amounts of ozone tend to be less expensive to produce and can reduce operating costs.

Yet another regulator is the relative weight of ozone used to bleach a given amount of pulp. This amount is determined, at least in part, by the amount of lignin (the amount removed during the ozone bleaching process) that is balanced against the relative amount of cellulose degradation that is acceptable during ozone bleaching.
According to a preferred embodiment of the present invention, an amount of ozone that reacts with about 50% to about 70% of the lignin present in the pulp is used. The total amount of lignin in the pulp is about 3-4 KNo. Obtained after this step. Are not removed during the ozone bleaching process, as demonstrated by This is because the absence of all ozone in the reaction zone causes the ozone to react excessively with the cellulose, considerably reducing the degree of polymerization of the cellulose. In a preferred method of the invention, the amount of ozone added, based on the oven dry weight of the pulp, is between 3 and 4 KNo. Typically about 0.2% to reach
~ 1%. Larger amounts may be required if significant amounts of dissolved solids are present in the system.

The reaction time used in the ozone bleaching step is determined by the desired rate of completion of the ozone bleaching reaction as indicated by complete or substantially complete consumption of the ozone used. This time varies depending on the concentration of ozone in the ozone gas mixture (the relatively more enriched ozone mixture reacts more quickly) and the relative amount of lignin that it is desired to remove. Preferably, the time required is less than 2 minutes, but the operation can take considerably longer depending on other reaction parameters.

An important feature of the present invention is that the pulp is bleached uniformly. This feature allows the pulp to be broken into discrete floc particles of sufficiently small diameter and sufficiently low bulk density that the ozone gas mixture completely penetrates most of the fiber flocs (eg, including fiber agglomeration). Partially obtained by milling. It is not feasible to completely separate the pulp fibers into distinct fibers during milling. Generally, the floc particles obtained from the milling have a relatively compressed central core surrounded by a plurality of outwardly extending fibers. For the purposes of the present invention, floc particle size is determined by measuring what is determined to be the smallest diameter of this relatively unfluffed central core.

Bleaching uniformity also depends heavily on certain other process parameters, but floc particle sizes up to 5 m
When limited to m, preferably less than 3 mm, substantially most uniform treatment of these particles is demonstrated by observation of a small number of dark, poorly bleached floc cores. As can be seen, it can be easily obtained. When the floc particle size was greater than about 5 mm, the bleaching was uneven, as evidenced by the majority of dark, poorly bleached floc cores. It is therefore important to obtain sufficient pulverization so that most flocs have an average size of less than about 5 mm for their uniform ozonation.

Yet another important process parameter is that during the ozone bleaching process, the particles to be bleached are mixed so as to allow access of the ozone gas mixture to all surfaces of the floc and uniform access of the ozone gas mixture to all flocs. That is, it should be exposed to the ozone bleaching mixture. The mixing of the pulp in the ozone gas mixture is comparable to the result obtained with a stationary bed of flocs, where some of the flocs are separated from the ozone gas relative to the other flocs and thereby less bleached than the other flocs. Yields excellent results with regard to uniformity.

Moving the flocs to expose the flocs to the ozone gas mixture results in uniform treatment of the flocs with each other. This treatment results in the desired amount of lignin being uniformly removed from the pulp without excessive degradation of the cellulose in the fibers containing the flocs. Adjustment of the ozonation of the present invention by the use of adjusted particle size and by turbulence during ozonation typically results in GE whiteness, KN
o. And a final pulp having a change in viscosity of less than about 5%. By comparison, if the treatment is heterogeneous (this is typically the case with a static bed reactor (ie,
(Such as in a reactor where the particles are not agitated during the ozonation), some portions of the bed are substantially excessively bleached, while others remain relatively unreacted. This is because the flow of the ozone gas mixture in the stationary bed reactor is not uniform.

Treating pulp with ozone at high consistency without particular attention to pulverization of the pulp fibers or proper contact between the individual fibers and the reactant gas stream always results in uneven ozone bleaching of the fibers. The present application designates such non-uniform ozonation with the letter "Z". Use of the above-described improved ozone technology of the present invention, where the fibers are milled to a size of about 5 mm or less, yet in proper and close contact with the ozone gas stream to provide uniform delignification. It is herein was designated "Z _m".

Pulp exiting the ozone reactor has a GE whiteness of at least about 50%, typically about 50-70%, and conifers typically have about 55%
That is all. Pulp (for hardwood or softwood) also has a KNo. Of about 3-4 (goal 3.5). Which has the value
At this stage of the process, you are quite satisfied with the pulp.

An apparatus particularly suitable for ozone bleaching according to the invention is shown in FIGS.
And in FIG. 3A. As described above, the washed pulp 36 is sent to a mixing chamber 40, where it is treated with an acid 42 and a chelating agent 44. The acidified, chelated, low consistency pulp 46 is introduced into a thickening device 48, such as a twin roll press, for removing excess liquid 50 from the pulp, where the consistency of the pulp is at a desired level. To be increased. At least a part of this excess liquid 50 may be circulated to the mixing chamber 40, and the remaining part is sent to the blow tank 32. The resulting high consistency pulp 52 is then passed through a screw feeder 54, which acts as a gas seal for ozone gas, and then through a pulverizer 56, such as a fluffer, where the pulp is pre-treated. It is comminuted into pulp fiber flocks 60 of a determined size (which should be no more than about 5 mm, as described above). The finely divided particles are then introduced into a dynamic ozone reaction chamber 58, which is a conveyor 62 driven by a motor 64 as shown. Conveyor 62 is used to remove the pulp particles so that the entire surface of the particles can become exposed to the ozone gas mixture 66 during pulp transfer.
Specially designed for mixing and transporting 60. FIG.
As further shown in FIG.
Is placed in a dilution tank 68.

FIG. 3 shows an ozone reactor showing the arrangement of pulp particles 60 as they are conveyed into the reactor by conveyor 62.
FIG. 58 is a cross-sectional view of FIG. Figure 3A shows the finely pulverized particles in the reaction chamber.
FIG. 7 is a cross-sectional view of a preferred conveyor utilizing a paddle-like arrangement for moving into 58.

The process of FIG. 2 shows that the pulp is treated with ozone simultaneously with the ozone gas mixture. However, also part of the pulp which has been bleached to the greatest extent, the ozone-containing gas is passed in a counter-current direction to the flow of pulp 60, so that the newly introduced ozone mixture containing the greatest amount of ozone May be contacted first. The pulp entering the reactor has the highest lignin content and first comes into contact with the ozone mixture which comes out and exits nearby, thereby giving the optimal opportunity to actually consume all the ozone.
This is an effective method for stripping ozone from ozone / oxygen or ozone / air mixtures.

If the ozone 66 is contacted with the pulp in a co-current manner, as shown in FIG. 2, the remaining spent ozone gas 70 can be recovered from the dilution tank 68. In tank 68,
Dilution water 72 (which can also be used as an ozone gas seal) is added to reduce the consistency of the pulp to a low level, and the bleached pulp during subsequent processing steps
Facilitates 74 moves.

The spent ozone gas 70 from the dilution tank 68 is sent to a carrier gas pretreatment stage 76, where an oxygen or air carrier gas 78 is added. This mixture 80 is sent to an ozone generator 82, where an appropriate amount of ozone is generated to obtain the desired concentration. The appropriate ozone / air mixture 66 is then sent to an ozone reactor 58 for delignification and bleaching of the pulp.

After completion of the ozone bleaching step, the substantially delignified pulp 74 is again thoroughly washed in a washer 84 as shown in FIG. 2 and at least a portion of the recovered water 86 is removed from the process. Significant environmental benefits result from the elimination of liquid that is circulated to the washer 34, thereby draining into the sewer.

Bleached low consistency pulp after ozonation
74 has a reduced amount of lignin and therefore has a lower K
No. And has an acceptable viscosity. The resulting KNo. The exact value of the viscosity and the viscosity will depend on the particular treatment the pulp has undergone. For example, pulped in a conventional kraft process, first delignified by improved high consistency oxygen delignification (O _m ), followed by ozone, preferably an improved homogeneous ozonation (Z _m The softwood pulp in the southern United States, which is further delignified by), typically has a KNo. Of about 3-4. And a viscosity of about 10. Craft AQ
Conifers in the southern United States that are pulped and then subjected to improved high consistency oxygen bleaching (O _m ) and improved uniform ozonation (Z _m ) typically have a KNo. And having a viscosity greater than about 12.

The resulting pulp 74 has significantly higher whiteness than the starting pulp. For example, southern conifers have a GE whiteness of about 15% to 25% after the pulping process and about 25% after oxygen bleaching.
It has a GE brightness of ~ 45% and, after the ozone bleaching process, a GE brightness of about 50% to 70%.

4. Alkaline extraction The washed pulp 88 from the ozone stage is then subjected to a sufficient amount of alkaline material in an extraction vessel 92 for performing the extraction.
Combined with 90. Thus, the pulp 88 is exposed to an aqueous alkaline solution at a predetermined temperature for a predetermined period of time in a vessel 92 that correlates to the amount of alkaline substance that solubilizes a significant portion of the lignin remaining in the pulp. Is done. The extraction process also increases the brightness of the pulp by a GE brightness of typically about 2 points. Thereafter, the alkali-treated pulp 94 is sent to a washing device 96, in which the aqueous solution of alical is washed from the pulp to remove substantially all of the solubilized lignin from the pulp, and thus is substantially free of lignin. Produce pulp. This step is well known to those skilled in the art and need not be further annotated here. The examples illustrate preferred extraction parameters for this step in the process. At least a part of the recovered alkaline solution 98 is circulated to the cleaning device 84. Once again, an important environmental advantage
This solution results from the elimination of sewage drainage.

In some cases, particularly where a high final brightness is targeted, the extraction step may be enhanced by incorporating oxygen treatment into the caustic extraction step (E ₀ ). This alternative is also known to those skilled in the art and does not require further annotation here.

5. Additional bleaching stages For most papermaking purposes, final brightness in the range of 50-65 is insufficient. Thus, to further increase the GE whiteness to a more desirable range of about 70-95%, the pulp is subjected to whitening bleaching, which mainly converts the lignin chromophore groups remaining in the pulp to a colorless state. The purpose is to:

After extracting the pulp and washing again, it is ozone bleached,
Whitening and bleaching of the extracted pulp can be performed using various materials. As shown in FIG. 2, the washed pulp 10
0 is combined with the selected bleach 102 in the bleach container 104. Preferred bleaches are chlorine dioxide or peroxide. After bleaching, the pulp 106 is washed with water 114 in a washer 108 and the effluent is circulated 110 or sewage treated 1
12. When circulated, at least a portion of the wash water stream 110 is sent to the washing device 96. The resulting bleached pulp can then be recovered and used for various applications.

One of the major substances used conventionally and generally highly effective is chlorine dioxide (D) (see FIG. 1). According to the invention, a suitable amount of chlorine dioxide is about 80%
It enables high strength pulp with higher GE whiteness to be obtained. Because the pulp entering the chlorine dioxide stage is relatively low in lignin, chlorine dioxide whitening bleaching may be performed in the presence of only about 0.25% to about 1% chlorine dioxide, based on the oven dry weight of the pulp.

The chlorine dioxide used in the whitening process is preferably prepared by a process that does not contain elemental chlorine.
However, and also less favorably, chlorine dioxide with a minimal amount of elemental chlorine almost increases the relative amount of undesirable pollutants due to the relatively small amount of lignin present in ozone bleached pulp. Can be used without. When chlorine dioxide is used, the effluent from the final bleaching step of the present invention is exceptionally low and can be safely discharged as shown in FIG.

However, if the effluent from the final chlorine dioxide bleaching step is not allowed to drain, the stream can be further purified by being treated in a membrane filtration process such as reverse osmosis. This technique gives a clean filtrate that can be recycled back to the previous bleaching stage for further use. This has the advantage of reducing the use of fresh water. Furthermore, the concentrated chloride stream obtained from membrane filtration is relatively small in volume.

Very high pulp brightness, eg, 92-95% GEB, may be desired, in which case an additional bleaching step may be required. Additional extraction and chlorine dioxide treatment are common choices, resulting in an O _m Z _m EDED bleaching sequence.

Instead of using chlorine dioxide for final whitening, whitening bleaching may also be performed with hydrogen peroxide, as shown in FIG. This technique bleaching cycle (e.g., O _m Z _m EP sequence) that does not contain a complete chlorine giving, in this case, chlorinated materials are not produced in the bleaching process, the extraction liquid product is cumbersome filtration Can be cycled easily without the need for skill. However, when peroxides are used as bleaching agents, pulp from softwood or hardwood has a KNo. Is the final product after the peroxide bleaching stage,
It should be reduced to a level of about 6 before the ozonation step in order to obtain a pulp of acceptable brightness, ie a GE brightness of more than about 80%. This is because peroxide is not as effective in bleaching as chlorine dioxide. However, peroxides give acceptable results if a completely chlorine / chlorine free process is desired.

Typical peroxide brighteners and their use in this process are conventional, and those skilled in the art are aware of suitable concentrations, types and uses of such peroxides. Hydrogen peroxide is preferred.

The washed and whitened pulp has a GE brightness of about 70-95%, preferably about 80-95%. Also, the physical properties of this pulp are determined by the usual CEDED process or OC / DE
Equivalent to the physical properties obtained with pulp produced by the D process.

6. Circulation of the wash effluent In any pulp process, the treatment of the filtrate is a significant factor in the overall economics or cost of operation of the process, and the water used in the process must be supplied to a suitable source. Requires both approach and treatment of effluent before discharge.

In an effort to reduce the water demands of the process, it is desirable to circulate as much effluent as possible. This practice cannot be used in processes that use chlorine or multi-stage chlorine dioxide. This is because the effluent produced by these processes contains a large amount of chloride produced by the by-products of such chemicals. Thus, the circulation of these effluents results in chloride accumulation, which in turn results in corrosion of the processing equipment or use of expensive components. In addition, such circulating effluents
Before these effluents can be discharged from the factory, they require significant treatment, and thus expense equipment and processing chemicals.

As shown in FIG. 4, a normal CEDED process or O
The use of C / DED technology creates significant disposal problems with the effluent resulting from the cleaning process due to the large amount of chlorine-containing compounds found therein. As noted above, these streams cannot be circulated and are preferably processed before discharge to the environment. Effluent circulation may be used to reduce water usage, but thereafter the treatment equipment may experience increased corrosion rates due to the increased amount of chloride in the circulated effluent .

However, in contrast, the use of the O _m Z _m ED process of the present invention results in the production of a slightly minimal amount of chlorinated material in the wash water, which can be safely drained, i.e. Can be discharged to sewage within protection standards. This effluent can also be treated by reverse osmosis to obtain a cleaner filtrate, which can be recycled to the previous bleaching stage as indicated for subsequent use without accumulating chloride. Is also good. If a D bleaching stage is desired, a process may be employed to reduce the demand for chlorine dioxide. The E ₀ process allows the pulp to achieve a high level of whiteness, but requires additional expense due to the use of sodium hydroxide and oxygen in this process. Also, industrial procedures for preparing chlorine dioxide are known, whereby the amount of residual chlorine is minimized (eg, R8 process versus R3 process). These chlorine-reduced chemicals are preferably used in stage D to reduce the amount of chloride in the wash water effluent.

Instead of O _m Z _m ED, the O _m Z _m EP process of the present invention can be used to obtain significant additional advantages over the prior art in that no chlorinated compounds are formed. This allows all effluent to be circulated without creating chloride accumulation problems in the process wash water stream.

Therefore, the process of the present invention is based on effluent volume, coloration,
Significant advantages arise with respect to the reduction of COD, BOD and chlorinated organics. In addition, the vents of the cleaning equipment require treatment prior to discharge since the effluent used for the cleaning step contains a significantly reduced amount of chloride compared to prior art processes using chlorine. Do not carry chlorinated organic compounds or gases.

Examples The scope of the present invention is further described with reference to the following examples. These examples are given for illustrative purposes only and should not be considered as limiting the scope of the invention in any way. % Of all chemicals unless otherwise stated
Is calculated based on the weight of the oven dried (OD) fiber. Also, those skilled in the art understand that the target whiteness value need not be accurately obtained. What happens
This is because a GEB value of ± 2% from the target is acceptable. Example 11
In all the examples having a D stage, except for R, R is known to contain a 6: 1 ratio of chlorine dioxide to elemental chlorine.
A type-3 chlorine dioxide solution was used.

Example 1 (Comparative Example) Normal kraft pulp was produced by steaming data pine chips in an experimental batch manner according to the conditions in Table 1. The resulting pulp has a KNo. And a viscosity of 27.1 cps. The kraft pulp is then subjected to a conventional oxygen treatment (Tables 2 and 5) followed by a conventional OC / DED sequence (Table 3).
And OZ _m ED bleaching order (Tables 4 and 5)
Bleached to final target brightness of 3GEB. The ozone bleaching step was performed at a 35% consistency with a 0.61% ozone application.

As shown in Tables 6 and 7 below, OZ _m ED bleaching under these conditions resulted in pulp with acceptable strength properties compared to the OC / DED reference pulp with a target 83% GE brightness. . Under these conditions, the OZ _m ED pulp had a limiting viscosity of 9.7 cps. Strength properties are 2.5 D
% OZ _m ED pulp. The target brightness was achieved only with an excess of chlorine dioxide charge. OZ _m E pulp corresponding to chlorine dioxide treatment shows that high whiteness can be obtained only by significantly increasing ozone application, which results in a considerable loss of pulp viscosity and strength.

Example 2 Kraft / AQ brown stock was prepared from loblolly pine chips in a laboratory batch digester as described in Table 8. Brown stock K obtained
No. Was 18.3 and the viscosity was 20.6 cps. Craft /
The AQ pulping conditions did not result in unacceptable degradation of the pulp strength as evidenced by viscosity, KNo. Resulted in a pulp having a much lower lignin content than in Example 1.

The Kraft / AQ brown stock was then further bleached to a target brightness of 83% GEB using the normal OC / DED and OZ _m ED sequences as shown in Tables 2, 3, 4 and 5. . The use of Kraft AQ pulping technology is a low KNo. With acceptable viscosity properties due to the ozone bleaching sequence. Has achieved its goal of producing starting pulp. Ozone bleaching stage,
Carried out at 35% consistency with 0.35% of the ozone application, it has reached the whiteness of the target by using 1.6% ClO ₂ in the final D stage.

As shown in Tables 9 and 10 below, the optical properties as measured by the whiteness response in the final chlorine dioxide stage were improved and the strength properties were acceptable compared to the OC / DED criteria.

Example 3 (Comparative Example) KNo. The pine craft brownstock having the following properties was pressed to a consistency of about 30-36% by weight to produce a high consistency mat. Brown stock mat, about 2.5% based on dry weight of pulp
10% of the amount sufficient to yield wt% sodium hydroxide
With sodium hydroxide solution. A sufficient amount of dilution water was added to adjust the brownstock mat to a consistency of about 27%. The high consistency brownstock mat was then subjected to oxygen delignification using the following conditions. 110 ° C, 30 minutes, 5.6kg / cm ² (80ps
ig) O ₂ .

Example 4 The pine kraft brownstock of Example 3 was introduced into a treatment vessel along with a sufficient volume of a 10% NaOH solution to make an addition of 30% NaOH based on oven dried pulp. Sufficient dilution water was added to obtain a brown stock consistency of about 3% by weight in the processing vessel. The brown stock and the aqueous sodium hydroxide solution were uniformly mixed at room temperature with a ribbon mixer for about 15 minutes. The treated brownstock was then pressed to a consistency of about 27% by weight. After pressing, the sodium hydroxide of the fibers was equal to about 2.5% as in Example 3. The treated brownstock was then delignified according to the oxygen delignification procedure described in Example 3. Table comparison
See Figure 11.

As can be seen from a comparison of Examples 3 and 4, the preferred method of the present invention using low consistency alkali addition followed by high consistency oxygenation (O _m ) with little change in strength properties A bleached brownstock with greater delignification (low consistency) than the process of the art was produced.

The low KNo. As a result of the pulp, the subsequent bleaching step may be adjusted to prepare a pulp containing high brightness, low lignin. Thus, the bleaching stage of such pulp requires less bleach or shorter bleaching time than pulp not treated according to the present invention.

The O _m pulp made from pine by the process of Example 4 Example 5 present invention, the normal (0) (i.e., without using the alkaline treatment step of the low consistency) comparing the produced pulp. The average caustic dosage for high consistency oxygen delignification of brownstock pulp was found to be 45 pounds per ton oven dried or 2.3%. In that amount, the average KNo. Per oxygen delignification reactor is The drop was 10 units. For the same amount of caustic applied to the pulp by the preferred processing step, the average KNo. During delignification. The reduction was found to be 13 units, a 30% improvement over the normal process.

This advantage in delignification selectivity can also be demonstrated by comparison of pulp viscosity. Average KNo. For ordinary pulp. And viscosity are 12.1 and 14.4 cp, respectively.
s. Regarding the preferred treatment process of the present invention,
Average KNo. At substantially the same viscosity (14.0 cps) Is
It was 8.3.

Also, the selectivity of delignification is determined by the change in viscosity between brown stock pulp and the corresponding treated pulp versus KNo.
Can be expressed as a change. The selectivity of oxygen delignification is described in KNo. Changes of 10KNo. Declines fairly quickly when starting to exceed units. The decrease in selectivity is caused by a predetermined KNo. It is observed as a rapid increase in the change in viscosity relative to the change in viscosity. For example, a KNo. For a change in, a corresponding change in viscosity is expected to be 12-13 cps. In contrast, the KNo. Same change of (12 units)
In contrast, the change in viscosity was found to be about 6 cps.
KNo. The change in viscosity per change in pulp is between 16 and 17 for pulp obtained using the preferred treatment process of the present invention.
Unit KNo. It is clear that the change is constant until the change. Table 12 shows the results.

Example 6 Southern pine pulp was combined with the uniform alkaline treatment described in Examples 4 and 5 to provide an improved oxygen delignification process (O _m ) having the conditions of Table 2 and the following table
Manufactured on a running 600TDD fine paper process using the conditions indicated in 13. The O-stage pulp produced by this novel process had the properties required to successfully complete a bleaching process using ozone as described in embodiments of the present invention. Oxygen stage pulp has a KNo. Of 7.9. (Compare about 12 typical normal O-stage KNos.). The viscosity of the delignified pulp was 15 cps and was hardly reduced by the high degree of delignification obtained by using the improved oxygen process. This pulp could then be further bleached using any of the many process embodiments described herein to produce pulp having acceptable final strength and optical properties.

C / DED bleaching of this pulp was completed in the laboratory as described in Table 14 to provide a basis for comparison of properties.

The ozone bleaching step was performed in a pilot plant reactor as shown in FIG. Table 15 shows the operating conditions of the pilot plant reactor.

The ozone bleached pulp produced in the pilot plant reactor is then treated in the laboratory with an extraction stage and a chlorine dioxide stage as described in Table 5 above to obtain the final bleached pulp at the target brightness. Manufactured. Only 1.0
% Of the charge in the final D stage of ClO ₂ was used for the fiber.

The strength and optical properties of the ozone bleached pulp were acceptable as compared to normal OC / DED standards and the results of the comparison are shown in Tables 16 and 17 below.

EXAMPLE 7 To further illustrate the utility and range of applicability of the method of the present invention, southern hardwood fibers from a mixed hardwood containing primarily rubber and oak were bleached with ozone in the pilot plant described in Example 6 above. did. Conventional oxygen stage pulp produced at a 600 TPD mill was treated with ozone in a pilot plant reactor. Oxygen stage pulp has a KNo. Of 5.7. And 1
Had a viscosity of 4.1.

A portion of the O-stage pulp was final bleached in the laboratory according to the usual C / DED sequence to provide a reference for comparison. Table 18 shows the C / DED conditions.

Table 19 shows the processing conditions of the ozone reactor. Then final bleached pilot plant Z _m stage pulp to target brightness of the normal E stage, and D stage as shown in Table 20. A D-stage ClO ₂ charge of only 0.35% was used for the OD pulp. Table 21 and Table 21
Acceptable compared to criteria as shown in 22.

Example 8 A comparative test similar to Example 5 was performed on kraft hardwood pulp produced in the laboratory from a mixed hardwood containing primarily rubber and oak. Again, a significantly larger KNo. For oxygen delignification reactors using an improved oxygen process (O _m ). It has been found that a decrease in the water content can be obtained as compared with the ordinary oxygen treatment (O). The average caustic dose for hardwood was 27 pounds / ton, or 1.4%. This means that about 5 units of KNo. Decreased. For the same amount of caustic used by the improved oxygen process of the present invention, an average KN of about 7.3 units
o. , A nearly 50% increase.

This advantage of delignification selectivity can also be shown by comparing pulp viscosities. Average hardwood KNo. And the viscosities were found to be 7.6 and 16 cps, respectively. In connection with the present invention, a KNo. And a viscosity of 17.7. The same viscosity as untreated pulp (16 cps)
KNo. Was found to be 5.8.

Also, the selectivity of delignification is determined by the change in viscosity between brown stock pulp and the corresponding improved oxygenated pulp versus KNo. Can be expressed in terms of changes in When comparing conventional oxygenated pulp with the pulp of the present invention, there is a significant decrease in delignification selectivity with respect to the increased degree of delignification. 4 units of KNo. The average change in viscosity was 4 cps for the pulp produced by the normal process. In contrast, the KNo. For the same change in viscosity for pulp made by the modified oxygen method. Was 7 units. Expressed in terms of the ratio of selectivities of delignification, the selectivity for the improved method was 1.8 KNo./cps and for the normal process was 1 KNo./cps, an increase of 80%. The results are shown in Table 23.

Example 9 A series of experiments was performed with the usual oxygen delignification step (O).
Performed in a pilot plant using pulp from a 600 TPD paper mill. These experiments were performed to show the effect of pH on the ozone bleaching process using southern hardwoods. The reactor operating conditions were kept constant at the conditions shown in Table 24, with the pH of the ozone stage being the only variable.

As can be seen from Table 25 below, the effect of pH on the ozone bleaching process is significant at low pH and beneficially improves the selectivity of the bleaching process.

Example 10 Several comparative properties are important to show the beneficial effects of making a fully bleached pulp using the OZ _m ED process. Typical operating data and effluent measurements were collected from an operating plant using the CEDED and OC / DED bleaching sequences for southern pine. These properties were compared to those of the effluent produced by the OZ _m ED sequence using the OZ _m ED pulp and effluent prepared in Example 1. See Table 26 for normal CEDED order. See Tables 2 and 3 above for normal OC / DED order. Also, regarding the OZ _m ED order, Tables 4 and 5 above
checking ... Effluent CEDED sequence, combined C, and it is E _1, D _1, effluent E ₂ and D ₂ It should be noted. The OC / DED effluent is a combined effluent of C / D, E and D, and the OZ _m ED effluent is a stage D effluent, each exhibiting some effluent properties. The table below
As shown at 27, the ozone bleaching sequence substantially reduces the environmental impact of the effluent from the bleaching process. EPA method 110.2 was used to measure coloration. From this data, it can be seen that the present invention provides a colorant of less than about 2 pounds / ton, a BOD ₅ value of less than about 2 pounds / ton, and a value of less than about 2, preferably about 0.2.
It can be seen that it gives an effluent with an amount of less than 8 total organic chlorides.

Example 11 Southern pine kraft pulp was bleached using three modifications of the basic OZED sequence. In the first sequence (OZ _m ED), pulp, normal oxygen, improved ozone, the ratio 6 caustic extract and ClO ₂ / Cl _2: prepared in 1 R-3 sequence dioxide Bleaching was performed as shown in Tables 4 and 5 using chlorine. In a second sequence, a modified oxygen process ( _Om ) was used, and again, the final stage used R-3 type chlorine dioxide. In a third sequence, the modified oxygen process (O _m ) was used once again, and the final stage used an R-8 chlorine dioxide solution in a 95: 1 ratio. Table 28 shows the significant environmental impacts provided by using the improved oxygen process ( _Om ). Further, the R-8 bleaching solution had a remarkable effect.

Example 12 Southern loblolly pine pulp was prepared by the Kraft process and Kraft / AQ pulping process described in Tables 1 and 8 above. Furthermore, the pulp is subjected to the usual oxygen delignification and the improved oxygen delignification described in Examples 4 and 5, the effect of combining these processes on the ozone bleaching sequence (minimum in terms of pulp strength). Effect on prolonging delignification). As can be readily seen from Table 29, these processes have a cumulative effect. Extremely low O _m Z _m E KNo. Can be reached. Conversely, a target O _m Z _m E KNo. Of about 3.5 for the previously described ozone bleaching process. Can significantly reduce the amount of ozone required to reach. In addition, the cumulative effect is very low O _m Z _m E KNo. There when required for functional peroxide stage, resulting in Matsuparupu southern capable sufficiently bleached by O _m Z _m EP process.

Example 13 Southern conifers, i.e., data pine, were prepared using the normal CEDED order shown in Table 26, using the normal OC / DED order shown in Tables 2 and 3 above, and 4 and bleached to the target 83 GEB brightness using the OZ _m ED sequence shown in Table 5. The wood-based dirt is purified and added to the OZ _m ED starting brown stock in an amount of 0.75% by weight to obtain CED
The ability of this sequence to remove dirt compared to ED and OC / DED bleaching was examined. Effective Black Are
a), the soil properties of these sequences measured as bark and tying fiber were comparable.

Example 14 This example illustrates the range of applicability of the ozone bleaching process of the present invention. Bleached pulp can be produced over a wide range of product brightnesses using a suitable combination of ozone and chlorine dioxide charges, minimizing environmental impact and operating costs. As shown in Table 30 below,
Products with whiteness of 65% GEB or higher can be produced with various combinations of ozone and chlorine dioxide while retaining significant strength properties.

While it is clear that the invention disclosed herein is well adapted to meet the above objectives, it will be understood that many modifications and embodiments will occur to those skilled in the art,
It is intended that the appended claims cover all such modifications and embodiments that fall within the true spirit and scope of the invention.

Continued on the front page (72) Inventor Gandeck Thomas P. United States of America New Jersey 08618 Trenton Pershing Avenue 11 (72) Inventor Piclin Michael A. United States of America New Jersey 08805 Brand Brook Windsor Street 559 (72) Inventor Rosen Allen, United States of New Jersey 08648 Lawrenceville Pinnell Drive 3 (56) References JP-A-53-90402 (JP, A) JP-A-56-79797 (JP, A) JP-A-52-148204 (JP, A) 501383 (JP, A)

Claims (18)

(57) [Claims] 1. A method for delignifying and bleaching a lignocellulosic material, said method comprising pulping the lignocellulosic material to produce pulp and then delignifying the pulp with oxygen. Partially delignifying to form a partially delignified pulp, adjusting the pH of the partially delignified pulp to 4 or less by adding an acidic substance, and increasing the consistency of the pulp to 20-50% Milling the pulp to produce discontinuous particles of the increased consistency pulp having a diameter and density small enough such that most of the resulting pulp particles are completely infiltrated by the ozone gas; Bringing said discontinuous particles in intimate contact with a gas mixture comprising ozone in a dynamic reaction zone and wherein said particles are in a reaction zone. Mixing, so that the ozone reaches all surfaces of most of the pulp particles for reaction with the ozone, leaving most, but not all, of the lignin remaining in the pulp. Treating the pulp particles with a gas mixture comprising ozone to remove pulp, further delignifying the particles of the pulp having increased consistency to obtain a highly and uniformly delignified pulp. Method. 2. The partially delignified pulp has a viscosity of 13 cp.
s, the amount of lignin is indicated by a K No. of 10 or less,
The method of claim 1, wherein the highly uniformly delignified pulp has a viscosity of 10 cps or more, a K No. of 5 or less, and a GE brightness of at least 50%. 3. The method of claim 1 or 2, wherein the ozone delignification step comprises adding a chelating agent to the pulp to render the metal ions in the pulp non-reactive with ozone. 4. An oxygen delignification step comprising: (1) treating pulp with an aqueous solution of an alkaline substance to distribute the alkaline substance throughout the pulp; and (2) reducing the consistency of the pulp after the alkaline treatment.
3. The method of claim 1, wherein the pulp containing the alkaline substance of increased consistency is subjected to high consistency oxygen delignification to obtain a partially delignified pulp. 3. The method according to 3. 5. The method of claim 4 wherein the step of treating the aqueous alkaline solution further comprises adjusting the consistency of the pulp to a low to intermediate consistency before treating the pulp with an aqueous solution of an alkaline substance. 6. The method of claim 5, wherein the pulp is brown stock pulp and at least a substantial portion of the liquid obtained from the alkaline solution during the process of increasing the consistency of the pulp is recycled to the alkaline treatment step. 7. An oxygen delignification step wherein the consistency of the pulp is reduced to a low consistency of 5% or less, and the low consistency pulp is exposed to and mixed with an aqueous solution of an alkaline substance. The pulp is treated with an alkaline substance in an aqueous alkaline solution to complete a highly uniform distribution of the alkaline substance throughout the pulp, and the consistency of the alkaline treated pulp is reduced by removing liquid from the pulp by 20-35. Weight percent, and upon completion of the treatment, causes the pulp of the increased consistency to retain at least 1.4% by weight of the alkaline material, based on the oven dried pulp, wherein the alkaline material-containing pulp is combined with the alkaline material and the pulp. Was moved directly from the combining process to the consistency increasing process. Recycling the liquid removed from the pulp in the consistency increasing step to the low consistency pulp treatment step and subjecting the increased consistency alkaline material-containing pulp to high consistency oxygen delignification. Achieves enhanced delignification of the pulp without a corresponding decrease in pulp viscosity as compared to pulp not treated with alkali substances at low consistency, and the combination of the above steps and this oxygen delignification step provides The following KN
4. The method of claim 1, 2 or 3 comprising providing a partially delignified pulp having a viscosity of greater than or equal to 13 and 13 cps. 8. The partially delignified pulp is directed to an ozone delignification step without any intervening delignification or bleaching steps, wherein the ozone delignification step comprises the consistency of the partially delignified pulp. The 28-42
%, And milling the pulp of increased consistency into discrete particles having a size of 5 mm or less. 9. The method of claim 1, further comprising extracting the delignified pulp, the extracting step comprising: (1) mixing the highly and uniformly delignified pulp with an alkaline substance in an aqueous alkaline solution; Solubilizing and dissolving any lignin remaining in the delignified pulp; and (2) then removing the alkaline aqueous solution to remove the dissolved lignin from the pulp to produce a lignin-free pulp. The method according to any one of claims 1 to 8, comprising: 10. The method of claim 9, further comprising bleaching the lignin-free pulp with a bleaching agent to increase the GE whiteness of the lignin-free pulp to produce a bleached pulp.
The described method. 11. The method of claim 10, wherein said bleach is chlorine dioxide.
The described method. 12. The method according to claim 10, wherein said bleach is a peroxide. 13. The process according to claim 10, 11 or 12, wherein the GE brightness of the bleached pulp is increased to 70-90%. 14. A method for delignifying and bleaching a lignocellulosic material, comprising: pulping the lignocellulosic material to produce a pulp; washing the pulp; oxygen delignifying the pulp to a K of 10 or less. No. and 13c
producing a partially delignified pulp having a viscosity greater than or equal to ps; washing the partially delignified pulp; pH of the partially delignified pulp by adding an acidic substance to the partially delignified pulp The consistency of the pulp is increased to about 20-50%; the pulp is crushed to a diameter small enough that most of the resulting pulp particles are completely infiltrated by ozone gas. Producing discrete particles of said pulp having increased consistency and density; bringing said discrete particles into intimate contact with a gas mixture comprising ozone in a dynamic reaction zone and moving said particles through the reaction zone Mixing ensures that the ozone reaches the entire surface of most of the pulp particles due to the reaction with ozone, but not all that remains in the pulp. Treats the pulp particles with a gas mixture containing ozone to remove most of the lignin to ozone delignify the partially delignified pulp to a K No. of 5 or less, a viscosity of 10 cps or more, and a viscosity of at least 50 cps. % To obtain a highly and uniformly delignified pulp having a GE brightness of 1%; washing the delignified pulp; (1) mixing the delignified pulp with an alkaline substance in an aqueous alkaline solution; Solubilizing and dissolving any lignin remaining in the delignified pulp; and (2) subsequently collecting the alkaline aqueous solution to remove the dissolved lignin from the pulp to produce a lignin-free pulp. The lignin-free pulp is washed; the lignin-free pulp is bleached with a bleaching agent to reduce GE whiteness. Which method comprises washing the and bleaching pulp; by pressure to produce a bleached pulp. 15. The method according to claim 14, wherein the bleaching agent is a peroxide and at least a portion of the bleached pulp washing water waste is recycled to at least one preceding washing step. . 16. The bleaching agent is chlorine dioxide and the waste water of the bleached pulp is treated to remove chlorides to produce a treated filtrate, and at least a portion of the treated filtrate is then ligninized. 15. The process according to claim 14, wherein the process is directed to a pulp-free washing step. 17. The pulp washing step obtained from one or more steps includes: (1) washing the pulp with washing water recycled from the next step; and (2) separating the pulp from the washing water waste liquid from which the pulp is obtained. do it,
And (3) directing at least a portion of the wastewater to the pulp washing step immediately before.
The method described in the section. 18. The lignin-free pulp is washed by recycling at least a portion of the bleached pulp wash water or the treated filtrate, and then highly and uniformly dispersing at least a portion of the lignin-free pulp wash water. Washing the delignified pulp together with the delignified pulp, and then combining at least a portion of the wash water of the delignified pulp with the partially delignified pulp to form the partially delignified pulp And then washing the pulp by combining at least a portion of the wash water of the partially delignified pulp with the pulp, thereafter separating the pulp from the pulp wash water and subsequently collecting and recovering the wash water Concentrated before incineration in a boiler, characterized in that the bleached pulp wash water waste or treated filtrate has a total amount of organic chloride of 0.91 kg / ton or less. The method according to any one of claims 14 to 16, wherein