JPH06501290A - Pulp alkali addition method for high consistency oxygen delignification - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Pulp alkali addition method for high consistency oxygen delignification Field of invention The present invention provides a method for treating wood valves, and more particularly, a method for treating wood valves that is highly deriged without adversely affecting strength. This invention relates to a process for oxygen delignification of brown raw materials for the production of colored bulbs.

Background of the invention Wood contains mostly cellulose and hemicellulose fibers and amorphous non-fibrous lignin ( This helps to hold the fiber parts together). hemicellulose and cellulose cellulose is sometimes collectively referred to as holocellulose. Wood processing for manufacturing valves During processing, the wood becomes a fibrous material by removing a significant portion of the lignin from the wood. is converted to Thus, paper and paper product manufacturing methods generally use wood chips, usually in the form of wood chips. includes a bulbing stage where the wood is converted into a fibrous material. Several different valving methods is known in the industry. They are generally mechanically pulped, chemically pulped or separated. Classified as chemical valving.

There are various chemical valving methods such as sulfite method, bisulfite method, soda method and Kraft method. including methods of Kraft process is the main form of chemical pulping.

Chemical pulping operations typically process wood chips in a cooking vessel, where they are steamed in a chemical solution. (understood). In the Kraft method, the cooking liquor is sodium hydroxide. and sodium sulfide. After the required cooking period, it is softened and dephosphorized. The grated wood chips are separated from the cooking liquor to produce the fibrous material of the bulb.

Bulbs manufactured by chemical pulping are “brownstock” It is called.

Brown stock is typically washed to remove cooking liquor and then made from unbleached grade paper. processed for the production of paper products or bleached for the production of high brightness paper products .

Lignin chromophore is the main cause of bulb coloration, so most of the bleaching of brown raw materials The method requires further delignification of the brown feedstock. For example, brown raw materials are reacted with elemental chlorine in an alkaline solution or with hypochlorite in an alkaline solution. This further delignification can be carried out using These steps are typically followed by a second step. A reaction with chlorine oxide is carried out to produce a fully bleached product. oxygen delignification is a method that has been increasingly used in recent years for bleaching bulbs.

After all, it uses cheap bleach chemicals and can be incinerated in a recovery boiler. This is because it can reduce environmental pollutants by producing by-products. oxygen delignification followed by chlorine or chlorine dioxide, which requires fewer bleaching chemicals and And because the bleaching takes place in the oxygen stage, the bleaching step, which produces few environmental pollutants, is frequent. It is often done.

In some bleaching methods, the valves have low to moderate levels of valve consistency. It is bleached while being maintained. Valve consistency is the solid fibrous material in the valve. This is a guideline for the ratio (%) of Bals having a consistency of less than about 10% by weight Valve consistency is said to be in the low to medium range. low con Methods requiring bleaching at cystic to intermediate consistency are listed below. described in the license and publications. U.S. Patent No. issued to Kirk et al. 4, 198.266, U.S. Patent Policy issued to Markham et al. No. 4,431,480, U.S. Patent No. 4.2 issued to Prough. 20.498, and “Low-consistency OxygenDel ignification in a Pipeline Reactor - Kiek et al.'s document entitled "A Pilot 5 study" TAPP 1. 1978 May. Each of the above is a valve with a range of low to medium consistency. describes an oxygen delignification process operating on

U.S. Patent No. 4.806.203 issued to Elton Periodic removal of potash is essential to prevent redeposition of dissolved lignin to the valve. alkaline extraction (preferably performed against a chlorinated valve). Ru. If too short or too long a period of time elapses at this stage, the method Shows little benefit.

Oxygen delignification of wood pulp is carried out in a pressurized reactor by producing a fluffed high-copper material. This can be done for cystic valves. Valve consistency is typically is maintained at about 20% to 30% by weight during the oxygen delignification process. Approximately 5.6 to approx. Oxygen gas at a pressure of 7.0 kg/Cm” gauge pressure (80 to 10,100 psi is introduced) and reacted with high consistency pulp. G, smog (Smoo) k), Handbook for Pu1p and Paper Tech See n-ologists, Chapter 11.4 (1982). Conventional deoxygenation In lignin operations, post-cooking valves are cleaned and dehydrated to produce high-consistency coal. Produces matte. The valve mat is then sprayed with alkaline liquid onto the surface of the mat. Sometimes covered with a thin film or layer of the liquid. Al sprayed onto the mat The amount of potash is about 0.8-7% by weight of the bone-dry bulb.

The previously used high consistency oxygen delignification methods have several drawbacks.

Patented, spraying lye onto high-consistency pulp mats is Despite the generally porous nature of such mats, even distribution of solutions into the fibrous material It is currently known that it does not give a distribution. As a result of this uneven distribution, high cost The area of the cystic mat, usually the exterior, has been exposed to excessive amounts of lye. It will be done. This overexposure results in non-selective degradation of the holocellulose material, resulting in at least It is also thought that localized relatively weak valves may occur. On the other hand, high consistency dye Other parts of the kit, typically its interior, are not sufficiently exposed to the lye. In some cases, the desired degree of delignification may not be achieved. In this way, the total The quality of the image will deteriorate.

Summary of the invention The present invention provides enhanced delignification of valves in high consistency oxygen delignification processes. It provides a novel method for obtaining nitrogen selectivity, in this case oxygen dephosphorization. Gunin valves provide greater strength and lower rigs than could be achieved by prior art methods. It has a nin content.

According to the invention, the brown stock valve is cleaned to initial consistency. bar This initial consistency of the powder is then reduced to less than about 10% by weight, preferably 5% by weight. % to produce a low consistency valve. alkaline substances , in such a way as to obtain a substantially uniform distribution of the desired amount of alkaline material in the bulb. Combining low-consistency sea pulp with a predetermined amount of alkaline material in an alkaline aqueous solution applied to low consistency pulps. This uniformity of alkaline substances distribution, whether alkaline substances apply only to high-consistency pulp or compared to methods that are only applied to low consistency pulps in very small quantities. to help increase delignification selectivity during high-consistency oxygen delignification. is sufficient.

To complete the application of alkaline material to the valve, the consistency of the valve is , and then increased to at least about 18% to produce a high consistency pulp. Ru. The process of increasing pulp consistency involves adding a desired amount of alkaline material to the bulk. pressate containing alkaline substances while being distributed and retained throughout the chamber. The low-consistency pulp is pressed or otherwise treated in such a way as to remove Including managing.

A predetermined amount of this squeeze fluid may be held in a holding tank (so that the squeeze fluid is Despite the intermittent or discontinuous operation of the cystinity increase process, alkaline The mixture may be continuously returned directly to the mixing process or recycled directly. All of this squeezed liquid part or at least a significant part (i.e. greater than 50%, preferably about 75%) ~95%) is recycled directly to the low consistency mixing step. Remaining squeezed liquid part The water is sent to the brown material valve washer or plant recovery system to remove water from the water balance in the mixing chamber. can maintain the same status.

The amount of alkaline substances retained in high consistency pulp is ry “OD”) at least about 0.8 to 7% by weight based on the valve, especially About 1.5-4% by weight for southern conifers and about 1-3.8% by weight for hardwoods. It is. The valve then undergoes oxygen delignification, thereby increasing the delignification. is achieved.

The present invention also provides high consistency oxygen delignification for alkaline substance treatment valves. Facilitate the bulb bleaching method followed by. These methods use fewer bleaching chemicals and are Compared to conventional high-consistency valve oxygen delignification paper products, to produce bleached paper products with superior strength. Also, the method is with higher strength (i.e., higher viscosity) after oxygen delignification compared to as evidenced by similar lignin content (i.e., K No., or kappa number). This makes it possible to obtain good delignification selectivity. Moreover, the method of the present invention compared to normally treated bulbs when exposed to the same amount of bleach chemicals. This makes it possible to obtain a bulb exhibiting high whiteness.

Brief description of the drawing FIG. 1 is a schematic diagram of the invention, and Figure 2 shows that the treatment with alkaline substances according to the present invention is compared with that typical of the prior art. Bulb viscosity and K No. for softwood bulbs delignified with oxygen .

It is a graph showing the relationship between.

Description of preferred embodiments The present invention applies to bulk pulp produced by kraft pulping or other chemical pulping methods. provides high-quality, high-strength delignified wood pulp from The preferred raw material is wood chips or other fibrous material, as by the raft or kraft AQ method; This is an unbleached brown raw material pulp obtained by cooking pulp in a cooking liquor.

With reference to Figure 1, wood chips l and white containing sodium hydroxide and sodium sulfide Liquid 2 is introduced into digester 3. Enough white liquor is introduced into the digester. should cover most of the wood chips. The contents of the digester are then white liquor or Cook at a temperature and time sufficient to substantially impregnate the wood chips and complete the cooking reaction. It gets heated.

This wood chip cooking process is commonly known as Kraft cooking or the Kraft method. The valves produced by this method are made from kraft pulp or kraft brown raw material. known as. Depending on the lignocellulosic raw material, it can be obtained by conventional kraft methods. Delignification results obtained by using the extended delignification technique or the Kraft AQ method can be increased. Furthermore, these techniques improve the strength and viscosity of the bulb during the cooking stage. preferred for obtaining the maximum degree of reduction in the K No. of the valve without adversely affecting the temperature characteristics. Yes.

When using the Kraft AQ method, the amount of anthraquinone in the cooking liquor is The amount should be at least about 0.01% by weight based on the OD type weight of the wood being used. 0.02% to about 0.1% is generally preferred. A during kraft pulping process Incorporation of intraquinone can be used without adversely affecting the desired strength properties of the residual cellulose. It contributes considerably to the removal of nin. Additionally, the additional cost associated with anthraquinones is Due to cost savings in chemicals used in the bleaching process following the oxygen delignification of the valve. Partially offset.

Instead of or in addition to Kraft AQ, Kamya MCC method, Beloit RDH and the Sunds 5upper Batch method. There is also the use of extended delignification techniques. In addition, these methods can reduce residual cellulose The ability to remove even more of the lignin during cooking without adversely affecting the desired strength properties of give.

Digester 3 is a black liquor containing reaction products of lignin solubilization together with brown raw material 4. Manufacture. The cooking process is typically followed by cleaning for recycling and recovery. In addition to removing most of the dissolved organic matter and cooking chemicals, the screening step ( (not shown) and is passed through a valve or screening device at this stage. The fiber bundles that were not separated by pulping are removed. Next, brown raw material 4 is blown Sent to tank 5.

The brown material 6 leaving the blow tank 5 is sent to a washer 7 which connects the valve to the first controller. Wash to consistency. The washed pulp 8 is then introduced into the mixing chamber 9 where it is over a period of time sufficient to distribute the desired amount of alkaline material into the pulp. substantially uniformly with sufficient fresh alkaline material 10 and circulating alkaline material 14A. be combined. During this treatment, the consistency of the brown raw pulp is reduced and approximately It is kept below 10% by weight, preferably below about 5% by weight. valve consistency The sea is generally greater than about 0.5%. Consistin is smaller than that. This is because it is not economical to treat in this way. Most preferred condition The range is 0.5-4.5%.

Those skilled in the art will be able to determine the appropriate amount of lye (i.e. concentration and flow rate) and pulp processing at this step. The treatment time can be selected to obtain the desired amount of alkaline material distribution in the valve. . In particular, the sodium hydroxide aqueous solution is applied to bone dry pulp after the consistency increasing process. At least about 0.8% to about 7% by weight of sodium hydroxide based on the valve. Combined with low consistency pulp in an amount sufficient to provide thorium. especially A useful source of sodium hydroxide is oxidized white liquor.

Those skilled in the art will recognize the additives used in or combined with low consistency pulp. The difference between the “amount” of the ludic substance and the “amount” applied to or retained in the valve. clearly acknowledge and understand. After the consistency increase step, the valve is loaded with the desired amount. In order to retain the alkaline material, a fairly large amount of alkaline material is placed in the mixing chamber 9 at a low concentration. Needs to be combined with cystin sea pulp. Thus, used in the mixing chamber The amount of alkaline material (i.e. present) increases the consistency of the valve. actually applied to the valve (i.e. retained within or on the pulp). ) is always greater than the quantity. Also, all alkaline substances are added to the valve in the mixing chamber 9. was used to obtain a uniform distribution of alkaline substances in the low-consistency valve, which is amount applied to the valve after the consistency increase step (this is due to the high consistency of the valve) (desired for Chinshi oxygen delignification). For high consistency sea pulp The preferred amount of alkaline material actually retained is generally about 1 for southern conifers. ．． 5 to 4%, and in the case of hardwoods, about 1 to 3.8%.

The low consistency mixing step is performed by keeping the brown stock valve on for at least 1 minute, preferably homogeneously mixing with the aqueous alkaline solution for about 15 minutes or less. alkali Mixing when the aqueous solution is substantially uniformly distributed throughout the low-consistency valve The process is completed. Processing times of less than about 1 minute generally yield a substantially uniform distribution. do not give enough time to This is typically achieved after about 10-15 minutes of mixing. be done. Continuing to mix for longer periods does not adversely affect the method, but , further benefits regarding the distribution of alkaline substances in the bulb are not obtained with longer mixing times. Moreover, it is necessary to increase the equipment capacity and provide a long residence time. Such a big equipment capacity increases the investment cost for the equipment of the method.

The mixing process of the present invention can be carried out over a wide range of temperature conditions. From room temperature to about 66℃Cl5 Temperature ranges from about 32°C (90°F) to about 66°C (1 Temperatures in the range of 50° F.) are preferred. Normal pressure or elevated pressure can be used.

The amount of alkaline aqueous solution present in the mixing process of the present invention is determined by the specific process of the delignification reaction. can vary significantly depending on process parameters. This amount of aqueous alkaline material Such variations are within the scope of this invention. As recognized by those skilled in the art, the scope of the invention The amount of lye that is effective for It depends on the degree of lignin and the concentration of the particular solution used. Alkali of the present invention The aqueous solution may include a sodium hydroxide solution having a concentration of about 20 to about 120 g/l. is preferable. This solution is mixed with low consistency sea pulp, resulting in total The mixture contains between 6.5 and 13.5 g/I of alkaline material, preferably approximately 9 g/I. It has concentration. Thus, at these concentrations of alkaline substances, temperatures of 49-66 °C (120 5-15% of 3-5% consistency sea pulp at a temperature of ~150'F) For a minute treatment, such a uniform distribution of alkaline substances is obtained in the valve. Ru. According to a preferred embodiment of the present invention, the aqueous sodium hydroxide solution sufficient to provide from about 15 to about 30% by weight of sodium hydroxide. Added to low consistency pulp in amounts.

The bulb 11 treated with alkaline material is passed to the thickening unit 12 where the bulb is lube consistency, e.g. at least about 18% by weight, preferably about 2% by weight. It is increased by squeezing from 1% to 35% by weight. Preferred implementation of the above For embodiments, consistency is increased by up to 29% and high consistency Sea pulp 17 is sent to oxygen delignification reactor 20.

In addition, the pulp consistency increasing step is carried out by using residual liquid or pressing liquid 13 (this is an alkali (including substances). This squeezed liquor is circulated to preserve the medicine.

The consistency of valve 8 entering mixing chamber 9 is high consistency leaving thickener 12 Consistency similar to that of Chinshi Pulp 17 (approximately or slightly ), the amount of alkaline material used in the mixing process is minimized. . After all, all the squeezed liquid is returned to the mixing chamber 9 as shown at 14A in FIG. directly circulated and retained within the low consistency pulp alkaline processing stage. This is because it is advantageous to be able to Required to replace the amount applied to the valve Additional alkaline material 10 is added to the mixing chamber 9.

If desired, a holding tank 16 may be included to contain the squeeze fluid 13. child The holding tank 16 is used for intermittent or discontinuous generation of compressed material 3 from the thickener 12. Although it is raw, it provides a constant flow of pressed liquid containing alkaline substances to the mixing chamber 9. Smooth continuous operation of the method is achieved by being able to accumulate an amount of the squeezed liquid 13 such that help.

Thus, the holding tank 16 is used in the low consistency sea pulp alkaline treatment process. It provides a reservoir of alkaline material that can be continuously delivered to the mixing chamber 9 for use. for example, This tank is installed for plants with a capacity of 1000 dry tons per year (AI) Has sufficient volume to handle the squeezed liquor generated by the Lucari treatment process It should be sized approximately 6000 cubic feet.

As mentioned above, the brown raw material 6 is washed in the washing machine 7. A suitable source of plant water Although the conventional washing machine used can be used to wash the brown material 6, the method It is advantageous to use a source of wash water that is recycled from other processes in the process. thus, Washer 7 includes a split shower to accommodate wash water from another downstream source. It is explained as something that

A first portion 27 of the filtrate 26 of the oxygen stage washer 23 is circulated to the washer 7 and its It can be used advantageously by reducing the amount of water used by the process. This filtrate Preferably, the portion 27 passes through a first shower in the washer 7. The second shower A portion 14B of the squeezed fluid 14 is sent to the valve. These parts 14B and 27 are valves 6 and also circulate the alkaline material to the valve (as it is cleaned). used for. Most of the alkaline substances in the squeezed liquid portion 14B are mixed with the valve. and enters the mixing chamber 9. The washer effluent 15 is discharged to the plant recovery system. Maintain water balance in the mixing chamber.

Rather than circulating the squeeze fluid to the second shower of the washer 7, a low consistency shear Preferably, it is circulated to the mixing chamber 9 for use in the alkali treatment step.

This is due to the possible loss of alkaline material to the recovery system (that is, to the washer effluent). 2. Avoid "leakage" (which would occur if the squeeze fluid 14 was introduced into the washer 7 due to a "leakage").

The consistency of the brown material 6 entering the washer 7 is the consistency of the brown material 6 leaving the thickener 12. If the consistency is similar to that of the material, drain the squeezed liquid from the thickener 12. It is possible to operate the method shown in fig. A closed system is obtained, which All the squeezed liquid is circulated directly to the mixing chamber 9. increased consistency The amount of alkaline material “loss” due to valve retention is determined by the amount of alkaline material “loss” in the mixing chamber 9 or holding tank 1. easily replaced by additional alkaline material 10 added to 6. In this arrangement , the amount of alkaline material used in the method is minimized. After all, Arca Is recycled material lost through planned or unplanned discharges into the plant recovery system? It is et al.

The consistency of the brown raw material 6 entering the washer 7 exits the thickener 12 through a valve. If the consistency is lower than 17, the liquid accumulation is due to the circulation of the squeezed liquid 14A. occurs gradually in the mixing chamber 9. In order to eliminate this situation, the squeezed liquid portion 14C is It is necessary to maintain the water balance in the mixing chamber 9 by discharging it into the plant recovery system. one Generally, a significant amount of the squeeze liquor 14A is greater than 5Q%, preferably about 75-95%. A portion is circulated directly to the mixing chamber 9, and the remaining squeezed liquid portion is sent to the plant recovery system at 14C. be discharged. In addition, the remaining squeezed liquid portion passes through 14B to the splitter of the washer 7. You may be sent to the shower.

The flow of squeeze fluid 14 is such that portion 14A is continuously sent to mixing chamber 9, while portion 14 B is divided so that it is continuously sent to the washing machine 7 via a split shower. I can do it. In this arrangement, the squeeze fluid portion 14A provides at least 50% of the total squeeze fluid flow 14. 0%, preferably about 75-95%, with the squeezed liquid portion 14B making up the remainder. . The wash filtrate 15 from the washer 7 is then discharged into the plant recovery system and into the mixing chamber 9. to maintain water balance. Also, a second portion 28 of the filtrate 26 of the oxygen stage washer 23 is discharged to the plant recovery system.

The valve 17 containing the alkaline material is then advanced to the oxygen delignification reactor 20; There it is brought into contact with oxygen gas 21 by any known method. Main departure Suitable conditions for oxygen delignification include keeping the bulb temperature at approximately 90-130°C. approximately 5.6 to approximately 7.0 kg of oxygen at 10 n” gauge pressure (80 to I00 psig) Including introducing gas into a high consistency valve. High consistency sheba The average contact time between the lube and oxygen gas ranges from about 15 minutes to about 60 minutes.

After oxygen delignification in reactor 20, delignification valve 22 connects cleaning unit 23 to The valve is then flushed with 24 ml of water to remove dissolved organics and A high quality, low coloring bulb 25 is manufactured. From here, valve 25 is used for subsequent bleaching steps. can be sent to produce fully bleached products.

An additional advantage of the present invention is obtained during subsequent bleaching of the oxygen delignification valve 25. I can do it. Such bleaching uses ozone, peroxide, chlorine, chlorine dioxide, and hypochlorite. This can be done with any of a wide variety of bleaching agents, including acid salts and the like. Ordinary chlorine/dioxide salt A bare bleach method is used to increase the whiteness of bulbs treated with the above alkaline substances. compared to bleaching bulbs that are oxygen delignified by conventional techniques. A reduced amount of total active chlorine is used. Chlorine-containing drugs used according to the invention The total amount of products is based on the same raw material with low valve consistency and not treated with alkaline substances. This is reduced by about 15-35% by weight compared to the amount required for the valve. Similarly, chlorine /If the valve is treated with chlorine dioxide and subsequently subjected to an alkaline extraction step, Bulb bleaching method with low consistency and not uniformly mixed with alkaline substances and A considerably reduced amount of alkaline material is required at this stage. Extraction process The amount of alkaline material used in the low consistency reduced by about 25-40% by weight with respect to valves treated with alkaline substances in the sea. .

provide cost advantages in terms of reduced amounts of chemicals required for processing such as In addition, the method of the present invention also reduces the amount of environmental pollutants produced by the use of chlorine. Do a little. This is because a reduced amount of chlorine is used. Furthermore, that Due to the low usage of chemicals in this part of the system, The amount of pollutants in wastewater is reduced accordingly, reducing wastewater treatment equipment and associated costs. with similar savings.

Example In order to illustrate the advantages and superior performance of the method of the invention, the processing operations shown in FIG. Several tests were conducted using the .

For the terminology used here, delignification selectivity refers to the ligation remaining in the valve. A measure of cellulose decomposition relative to the degree of lignin, strong It is an indicator of the ability of the method to produce valves. Regarding oxygen delignification of special valves Differences in delignification selectivity can be determined, for example, by valve viscosity versus K This can be shown by comparing the ratio of -values. Regarding the present invention, the lignin content of the valve is The amount can be measured either by K No. or Kappa number. Those skilled in the art can It is possible to recognize differences in the values of , and to convert one number into another if desired Ru. Unless otherwise specified, 40m1K No. will be reported.

The viscosity of the bleach bulb represents the degree of polymerization of cellulose in the bleach bulb, such as represents the valve as . On the other hand, K No. represents the amount of lignin remaining in the bulb. vinegar.

Therefore, oxygen delignification reactions with high selectivity have high strength (i.e. high viscosity) and Resulting in a bleached bulb with low lignin content (i.e. tK No.).

Example 1 (Prior art high consistency valve alkali treatment) K No. of about 24 , (Kappa number of 30.9) Southern pine kraft brown raw material with alkaline solution The brown raw material is compressed to a consistency of about 30-36% by weight without treatment. A consistency matte was produced. Brown material matte based on bulb dry weight 10% hydroxide in an amount sufficient to yield about 2.5% by weight of sodium hydroxide as sprayed with sodium chloride solution. Dilute the brown raw material matte with diluted water to approximately 27% consistency. It was added in an amount sufficient to control the consistency. Then high consistency brown raw material The mat was subjected to oxygen delignification using the following conditions. II (1℃, 30 minutes 5.6 kg/am' gauge pressure (80 psig) of oxygen. manufactured according to this procedure. The manufactured oxygen delignification valve was tested and showed a KNo of 3 and a kappa number of 15,2. ) and a CE[l viscosity of approximately 14.8 cps. This oxygen removal The gunin valve was further bleached by known techniques. Oxygen delignification valve and complete The strength and physical properties of the bleach bulbs are shown in Tables 1 and 2, respectively.

Table 1 Comparative Example 1 of the results of oxygen stage delignification of valves produced according to Examples 1 and 2 Example 2 K No, 13 9 Viscosity (cps) 14.8 14.0 Ratio of viscosity/K No. 1.14 1.55 Table 2 Comparative example 1 and example 2 of complete bleaching strength properties of bulbs manufactured according to example 1 and example 2 Final 'G, E.

Whiteness, % 8383 C, S, freeness tearing length, - specific tearing strength, DI11! tearing length, b ratio tearing Strength, DIn! 65g 6.42 55.7? , 00 55.5516 8. 25 73.6 8.35 67.4337 g, 80 74.1 9.07 71.8 Three steps of oxygen delignified pulp bleaching: chlorine, alkaline extraction and dioxide I did it with chlorine. Bleaching conditions and extraction conditions in Table 3 and chemical preparations listed in Table 4 (% based on OD bulb) for final bleaching bath of 83G, E, brightness. Got the rub. The bulbs were also thoroughly cleaned between bleaching steps.

Table 3 Bleaching conditions of the chlorine stage, extraction stage and chlorine dioxide stage for Examples 1 and 2 Chlorine stage floor hours, minutes 15 Temperature, ℃50 Consistency, %3 extraction stage hours, minutes 60 Temperature, ℃70 Consistency, %12 chlorine dioxide stage hours, minutes 120 Temperature, ℃60 Consistency, %12 Table 4 Amount of bleaching chemicals used in the chlorine stage, extraction stage and chlorine dioxide stage % 3.6 2.4 Chlorine dioxide, % 0.6 0.4 extraction stage Sodium hydroxide, % 1.5 1.5 Examples 2-5 (low consistency valve Examples 2 to 5 are treated with alkaline substances only at low consistency The degree of delignification obtained during high consistency oxygen delignification for valves The benefits in terms of efficiency and delignification selectivity are explained.

Example 2 The same Matsukraft brown raw material used in Example 1 is introduced into the mixing chamber as shown at 9 in Figure 1. did. A brown stock consistency of approximately 3% by weight is prepared in the mixing chamber by adding sufficient dilution water. - obtained. Add sufficient volume of 10% NaOH solution to reference the OD valve. Then 30% NaOH was added. Brown raw material and sodium hydroxide aqueous solution at room temperature The alkaline material was mixed with the brown raw material by uniform mixing for about 15 minutes. Then get The brown raw material containing alkaline substances is pressed to a consistency of approximately 27% by weight. Ta. After squeezing, the sodium hydroxide content of the fibers was equal to about 2.5%, as in Example 1.

The alkali-treated brown stock was then subjected to the oxygen delignification operation described in Example 1. So I bleached it.

The oxygen delignification valve was then washed to remove organic matter. The resulting oxygen stage Lube has a K No of 9, (kappa number of 10,8) and a CHD viscosity of 14.0. had. The oxygen bleached bulb was further bleached by known techniques under the conditions given in Example 1. Ta. The properties of the oxygen delignification valve and full bleaching valve of this example are also shown in Table 1, respectively. and shown in Table 2.

As can be seen from the comparison of Examples 1 and 2, the operation of Example 2 is similar to the prior art method of Example 1 (this (applying all alkaline substances to a high consistency valve) Manufacture an oxygen delignification valve that has lignin ((fX No.) at approximately the same viscosity. Built.

Additionally, using a low-consistency sea-alkali treatment of the valve according to Example 2 , provides increased delignification without significant changes in strength properties. thus , increased delignification selectivity is obtained.

41B No. of the valve manufactured according to Example 2, as a result of the subsequent bleaching step can be adjusted to accommodate highly delignified valves. In this way, this The bleaching stage of the bulb is not treated with alkaline substances with low consistency Bulbs require less bleach (as shown in Table 4) or shorter bleaching times .

Sea urchin produced normally (i.e. without using a low consistency sea alkali treatment step) Compare with the same valve. High consistency for subsequent oxygen delignification of the valve The average sodium hydroxide dose applied to Chinshi valve only is 4 per air-dry ton. It was found to be 5 pounds (Ib/l) or 2.3%. At that level, oxygen The average decrease in K No. per membrane lignin reactor was IO units. high con Applied only to low consistency valves before cystic acid oxygen delignification At the same level of sodium hydroxide, the average K No during delignification decreased by 13 It turned out to be a unit. This was a 30% increase compared to the prior art.

Average K No. and viscosity for conventional valves are 12.1 and 14.4 cp respectively It was s.

Regarding the low consistency alkaline material processing method, the viscosity is approximately the same (14,0 cps ), the average K No. was 8.3 as shown in Table 5. This is about 4 This corresponds to an increase in delignification selectivity of 1 bulb (1.69 vs. 1.19).

Faults associated with valves prepared according to the low-consistency sea-alkali treatment method described above. The white plant response is compared to the bleach plant response for a normally prepared valve; It is shown in Table 5 below.

Comparison of valve properties and bleaching chemicals K No, 21.9 20.5 Viscosity (cps) 21.5 20.5 Ratio of viscosity/K No. 0.98 1. 00, delignification stage KNo. 12.1 8.3 Viscosity (cps) 14.4 14. .

Ratio of viscosity/K No. 1.19 1.69 Alkali, lb/l 39.4 4 6.0 Delignification (%) 44.7 59.5Ch, lt+/l 51.2 34.4 C1og, lb/l 7.0, 4.6 Total activity CLlb/l 69. 4 46.4 Extraction stage NaDH, Ib/l,, 35.2'23.8CIOs, lb/l 10. 6 9.0 Viscosity (cps) 12.6 1.1.9 Contaminants 2.5 5.6 Table 5 shows that the total active chlorine usage in the next step of bleaching was reduced by about 1/3 (immediately 69.4 bonds/ton vs. 46.4 pounds/ton). In addition, the extraction stage The sodium hydroxide requirement of 5 lb/l). Chlorine dioxide in the final bleaching step was reduced by about 1/6 (9 l b/ vs. 10.6 lb/l).

Example 4 A comparative test similar to Example 3 was conducted on hardwoods. Again, compared to normal processing, the Oxygen is removed using a treatment method that applies only to valves with low potash consistency. It was found that a considerably large reduction in K No during the delignification reaction was obtained. Wide The sodium hydroxide dose for oxygen delignification of leaf trees is 27 lb/l, i.e. 1.4 %. A reduction of about 5 units of K during the delignification process is obtained by conventional methods. Ta. The same level of sodium hydroxide used by the low consistency method above. An average K No. reduction of approximately 763 units was obtained. This is almost 50% corresponds to an increase.

The average K No. and viscosity of hardwood were found to be 7.6 and 16 cps, respectively. It was. Regarding the above low consistency treatment, K No. of 6 and 17.7 The viscosity was obtained.

In addition, K at the same viscosity (16 cps) as the conventional alkaline substance treatment valve. No. was found to be 5.8. As shown in Table 6, about 40% An increase in lignin selectivity (2.95 vs. 2.10) is obtained.

Additionally, the delignification selectivity is determined by the change in viscosity vs. K between the brown feed and the delignification valve. It can be expressed in terms of the change in No. Alkaline only at low consistency When valves treated with the material are compared to valves of the prior art, there is an increase in delignification. There is a large increase in delignification selectivity with respect to the degree of delignification. 4 units of K No. Regarding changes, the average change in viscosity is It was 4 cps. In contrast, produced by low consistency valve processing For the same valve, the change in K No. for the same change in viscosity was 7 units.

Expressed in terms of selectivity ratio, the selectivity of the low consistency treated valve is 1.75 The selectivity of the conventional method was 1 (cps/K No.). this corresponds to an increase of approximately 75%.

For bleaching chemical applications, using the low-consistency sea-alkaline treatment described above A comparison of the bleach plant response of the prepared oxygen delignification valves is shown in Table 6. Compare with manufactured oxygen delignification valve.

Table 6 K No, 12J 13.0 Viscosity (cps) 21.6 23.4 Ratio of viscosity/K No. 1.75 1.800, delignification stage KNo. 7.6 6.0 Viscosity (cps) 16.0 17.7 Ratio of viscosity/K No. 2.10 2.95 Alkali, lb/l 27.6 2 6.4 Delignification (%) 3g, 0 54. OCb, lb/l 27.0 2 2.7CIOr, lb/l 5.6 4.7 Total active CLlb/l 41.6 34.9 NaOH, lb/l 18.9 13 ．． 3 chlorine dioxide bleaching stages Cl0f, Ib/l 5.5 4.7 Viscosity (cps) 14.6 14.9 Dirt 32.0 34.0 Table 6 shows the total active chlorine used in the chlorine stage. The volume is reduced by about 1/6 (i.e. 34.9 l compared to 41.6 + b/l) b/l), while the alkali requirement in the extraction stage is 2 compared to the conventional valve. was reduced by more than 9% (i.e. 13.3 lb/l vs. 1.8.9 lb/l ).

Chlorine dioxide in the final bleaching step was reduced by 14% (i.e., 4.7 lb / vs. 5.51 b/l). The properties of the final valve with respect to viscosity and contaminant values are approximately It was almost the same.

Example 5 Effect of low consistency alkaline material treatment on valves before oxygen delignification In order to explain its contribution to the overall effectiveness of fruit and kappa number reduction and total yield. In order to improve the kappa number and yield of ordinary brown raw material and low kappa number Kura 7l-/A Measurements were made for both Q brown raw materials. The results are shown in Table 7.

Time Initial Final Yield Yield Final viscosity Brown raw material (min) Kappa number Kappa – value (%) Kappa value (%) (CPS) Conventional’ 5 28.1 26.5 99.5 12.0 95.2 14.7 Conventional” 1,5 28.1. 27 ．． 5 98.7 13.4 96.3 15. IK/AQ" 5 21.6 2 0.3 10Q, 0 8.9 96.7 15.2/AQ' 5 21. ．． 6 -8.1 97.2 13.9' 2.49A NaOH ! 2゜1% NaOH 32.1% NaOH 42.6% NaOH Sodium hydroxide for 5 minutes at a consistency of 3% (2 for the valve after squeezing) ．． 4%) to a regular kraft brown stock with a kappa number of 28.1. Regarding, the initial kappa number decreased by 1.6 units to the post-treatment kappa number of 26.5. . This is due to the total kappa number reduction (12 , a kappa number of 0). low consistency sea alkaline The yield of the processing step was 99.5%. Almost half of the 0.5% loss in yield is due to the rig. due to loss of nin and the rest due to loss of carbohydrates. Total yield after oxygen delignification was 95.2%.

The same brown raw material was extracted with sodium hydroxide for 15 minutes at a consistency of 3%. 2.1%). The initial kappa number is 27.5. It decreased by 0.6 units. This is a low-consistency sea-alkali treatment and oxygen delignification process. contributed 4.2% to the total kappa number decrease experienced after the conversion (kappa number of 13.4). It was equivalent. The yield of the alkali treatment step was 98.7%.

2. To the valve after sodium hydroxide straining for 5 minutes at 3% consistency. For low kappa number Kraft/AQ brown stock treated with copper The value decreased by 1.3 units to 20.3. This decrease in kappa number occurs after oxygen delignification. This represented a 10% contribution to the total kappa number reduction experienced (kappa number of 8,9).

Virtually no yield loss was detected during the alkaline treatment step. After oxygen delignification The total yield loss was 96.7%. The second oxygen of the same Kraft/AQ brown raw material Delignification produced a similar kappa number of 8.1 and a yield of 97.2%.

This example 5 shows that a significant amount of delignification was caused by the low consistency sea-alkali treatment of the valve. Indicates that this will not occur during processing. This example also shows low consistency up to about 15 minutes. This shows that there is no significant difference in the time of treatment with alkaline substances in the sea. but However, as further illustrated by Examples 2-5, low consistency sea alkali treatment subsequent high consistency cyacid compared to normally treated valves Significantly increases the relative amount of delignification obtained during the sub-delignification process. Also, this An example of this is that the method allows valves to reach very low kappa numbers without significantly reducing viscosity. This shows that brown raw materials with low kappa numbers are effective in this process.

The uniform distribution of alkaline substances in the valve during the low-consistency mixing process fibers can be mixed with alkaline substances even more optimally than is possible with the prior art. and ensure that. This means that delignified brown raw materials are generally obtained by conventional techniques. The subsequent deoxygenation in terms of strength and degree of delignification is superior to that of Provides increased delignification selectivity in lignin. In addition, oxygen delignification reaction The delignification selectivity of the reaction is unexpectedly improved.

If alkaline substances are applied only to high consistency pulp as in the prior art, In this case, up to 50% delignification (i.e., reduction in K No. can be achieved with little damage to the part (and thus little loss of strength) . In the present invention, oxygen delignification can be carried out with little damage to the cellulosic portion of the valve. (K No. of the acquisition valve, generally at least about 60%) It is possible to obtain a drop. If desired, reductions of 70% or more can be obtained. Ru.

For example, when entering the oxygen delignification stage, the special valve valve K No. Approximately 10 to 26 depending on the type of wood and the type of pulping performed on the particular wood. range. After delignification, K No. is reduced to about 5-IO. to coniferous trees Regarding that, K No.

is generally in the range of 20-24 (target 21) before delignification and after delignification. In addition, KNo ranges from 8 to 1O. For hardwoods, before delignification 10~ 14 (K No. of target 12.5> and K No. of 5 to 7 after delignification are Generally obtained by nature.

For either type of valve, the viscosity before delignification is generally 19 or higher. , higher than about 13 after delignification (generally 14 or higher for softwoods, and higher than about 14 for hardwoods) 15 or more). Typically, this change in viscosity before and after delignification is approximately 6 cps or less. Furthermore, the change in viscosity per change in K No. is approximately 17 units. It was found that the decrease in K No. up to

Thus, delignification selectivity increases compared to prior art delignification methods. a low consistency alkaline material mixing step with at least a 20% increase in Enhanced by Avoiding deterioration of the cellulose component of the valve is achieved by oxygen delignification. This is evident by the minimal change in viscosity between the front and rear valves.

Example 6 The data presented in Examples 2-5, along with a number of other predicted and observed values, are shown in Figure 2. Conifers were summarized in a graph diagram. Also, Figure 2 shows the results from the actual test. generated from the combined data, as well as numerous other estimates and observations. The curve includes a viscosity vs. softwood curve from the prior art pulp processing method of Example 1. This shows the relationship between K No.

As shown in FIG. 2, the prior art method of Example 1 is based on the curve labeled prior art. Typical valve properties are obtained after oxygen delignification as specified by K No, low At high viscosity levels, while obtaining effective delignification as measured by It is desirable to maintain the specified pulp strength. Figure 2 shows increased delignification (low K No.) compared to the low delignification and viscosity values according to the prior art curves. In comparison, the curve representing the present invention for low consistency sea pulp alkaline material treatment can be achieved with a given viscosity value according to .

Example 7 The following laboratory tests were carried out to determine the uniform content of alkaline substances in pulp according to the method of the invention. Included to further explain how to obtain the fabric.

Unbleached brown raw material Matsubaru with K No. of 19.54 and viscosity of 24.9 prepared. One sample each of two samples of this valve with a consistency of 7.7% and 3% NaOH at a temperature of 60° C. for 15 minutes. Then the bar The consistency of the bulb is increased to 27%, and the NaOH content of the bulb is approximately 0.67. It was found that %. This valve was added for 5 minutes without further addition of alkaline substances. -6 kg 10 n' (80 psi) pressure, 110°C temperature for 30 minutes It was sent to an oxygen delignification reactor.

Two additional samples of unbleached pulp of 3% each were then added to the Treated by application of approximately 35% Na0)1 at a temperature of 60°C for 1 and 15 min. did. The consistency of the bulb was then adjusted to maintain a 3% NaOH content in the bulb. However, the valve increases to 27% and without adding further alkaline substances. at a pressure of 5.6 kg/am” (80 psi) and a temperature of 110°C for 30 minutes. and sent to an oxygen delignification reactor. The results are shown in Table 8 below.

oxygen delignification later nature Mixing time K No., Viscosity sample valve (minutes) (25 ml) (cps) A 7.7 1 1? , 37 23.2B 7.7 1 1 ? ,43　22.6C7,71517,7724,3 D 7.7 15 17.34 22.0E 3.0 1 8.74 14.8 F 3.0 + 8.34 14.8 G 3.0 15 8.24 15.3H3,0158,7314,3 The treated pulp of Samples E-H had a higher amount (i.e. 3%) of hydroxyl acid than the bulbs of Samples A-D. retains sodium. First, a large amount of sodium hydroxide mixed with the valve. This is because they are combined. Samples E-H had at least about 55.3% of the valves' K No. , and on the other hand, the decrease in K No. of samples A-D was very small, at most It is about 11.3%. Thus, samples (E-H) treated by the method of the present invention increases delignification by about 49.6% over the comparative sample.

For the same unbleached brown stock bulb in this example, the previous test was repeated with the following changes: repeated.

change change 1st stage: NaOH, %324 consistency on valve, %3. 53 Temperature, ℃48 48 Oxygen stage: NaOH, % on bulb 0.44 3 consistency, % 2020 Na0)1 treatment times for each modification were both 2 and 15 minutes. attention As shown, the consistency of unbleached bulbs was almost the same (3.5% vs. 3%).

The results are shown in Table 9.

Table 9 oxygen delignification later nature Consistency Mixing time K No. Viscosity GE valve (minutes) Kakiri Awa) Bao Shi and Kogyo! 1 3.5 2 15.75 23.4 24.8J 3.5 2 +5.34 22.4 25.2K 3.5 15 14.78 22.6 25.9L 3.5 15 15.00 22.7 25.5M 3 ．． 0 2 8.59 13.3 36.6N 3.0 2 8.29 14.2 35.30 3.0 15 8.14 13.1 36.3P 3.0 15 8.44 13.8 36.5 NaO mixed with low consistency pulp Due to the increased amount of H, a large amount of NaOH is retained in high consistency pulp . Because of this increased amount of NaOH, samples M to P had a low (both approximately 56% K No. , while sample 1-L only obtains a decrease of about 24.4% at most. . Again, the sample prepared according to nature (M-P) was smaller than the comparison sample (both 4 A 1.9% increased delignification is obtained. As noted earlier, this For uniform mixing and distribution of the appropriate amount of sodium hydroxide in the pulp Due to the increased amount of sodium hydroxide retained in high consistency sea pulp It is.

The invention disclosed herein is well calculated to meet the above objectives. Although it is clear that many modifications and embodiments can be devised by those skilled in the art, it is understood that be understood. The following claims cover all such modifications and improvements as come within the true spirit and scope of the invention. and embodiments.

international search report 691215 old K No, (40ml)

Claims (25)

[Claims] 1. Low consistency is achieved by reducing the consistency of the brown raw material pulp to less than about 10% by weight. Produces high consistency pulp, low consistency pulp, and pulps with alkaline materials. mixed with a predetermined amount of alkaline material with substantially uniform distribution throughout the mixture, and increasing the consistency of the pulp containing the lactic material to at least about 18% by weight; By applying alkaline substances to brown raw material pulp, high consistency pulp can be obtained. and in an amount of at least about 0.8 to 7% by weight based on the bone dry weight of the pulp. The press liquid is removed while applying alkaline substances to the high consistency pulp (as described above). of the alkaline material is substantially uniformly distributed throughout the high consistency pulp. ), A significant portion of the squeezed liquor is directly circulated to the alkaline material mixing process, and the alkali material Brown raw material pulp is produced by oxygen delignification of high consistency pulp containing High consistency characterized by obtaining increased delignification selectivity of A method for obtaining increased delignification selectivity of brown stock pulp during oxygen delignification. 2. The consistency of the brown raw material pulp is higher than that of the high consistency pulp. consistency, and virtually all of the squeezed liquid is added to the alkaline mixing process. 2. A method according to claim 1, which involves direct circulation. 3. Applying the squeeze fluid in case of intermittent or discontinuous operation of the consistency increasing process Accumulate a predetermined amount of squeeze fluid for continuous circulation directly to the lukewarm material mixing process. 2. The method of claim 1, further comprising: 4. The oxygenated delignified pulp is washed, thus producing a wash water effluent and the alkaline Wash some of the water effluent to wash the brown raw pulp before applying the potash material. 2. The method of claim 1, further comprising cycling. 5. A portion of the pressing liquor to wash the brown raw pulp before applying the alkaline substance 5. The method of claim 4, further comprising cycling. 6. When the pulp is mixed with a predetermined amount of alkaline material, it contains less than about 5% by weight. A method according to claim 1 having a consistency. 7. Before oxygen delignification, the pulp consistency is approximately 25-35% by weight. A method according to appended claim 1. 8. K of high consistency pulp with little damage to the cellulose content of the pulp. No. Claims to obtain increased delignification selectivity by reducing the The method described in item 1 of the scope. 9. High consistency pulp from about 10 to 26% before delignification to after delignification Claims for obtaining increased delignification selectivity by reducing the The method described in paragraph 8. 10. The brown raw material pulp is unbleached softwood pulp, and The method according to claim 1, wherein the amount of alkaline material contained is about 1.5 to 4% by weight. Law. 11. The brown raw material pulp is unbleached hardwood pulp, and The method according to claim 1, wherein the amount of alkaline material contained is about 1 to 3.8% by weight. Law. 12. The brown raw material pulp is washed to the initial consistency and the initial coating of the washed pulp is Reduce consistency to less than about 10% by weight to produce low consistency pulp low-consistency pulp with substantially uniform distribution of alkaline substances throughout the pulp. Mix it with a predetermined amount of alkaline material while making it into a pulp, and the consistency of pulp Alkaline substances are added to the brown raw material pulp by increasing the content to at least about 2% by weight. application to obtain high consistency pulp and a low Alkaline material in an amount of at least about 0.8 to 7% by weight to high consistency pulp. Remove the squeezing liquid while feeding (the above amount of alkaline material is (substantially uniformly distributed throughout the press), a significant portion of the squeezed liquor is mixed with alkaline substances. The high consistency pulp that is circulated throughout the process and contains alkaline substances is deoxygenated. Obtaining increased delignification selectivity of brown raw material pulp by The brown raw material pulp is increased during the high consistency oxygen delignification characterized by How to obtain delignification selectivity. 13. The consistency of brown raw material pulp is higher than that of high consistency pulp. Wash to some initial consistency so that virtually all of the squeezed fluid is alkalized. 13. The method according to claim 12, wherein the potash material is recycled to the mixing step. 14. The consistency of the brown stock pulp is lower than that of the high consistency pulp. washing to a good initial consistency, resulting in at least about 75% of the squeezed liquid being 13. The method according to claim 12, wherein the alkaline material is recycled to the alkaline substance mixing step. 15. The remainder of the squeezed liquid is sent to the brown raw material washing process to wash the brown raw material pulp. 15. The method of claim 14, further comprising: 16. The oxygenated delignified pulp is washed, thus producing a wash water effluent and the washing Claims further comprising recycling a portion of the purified water effluent to the brownstock pulp washing process. The method according to paragraph 15. 17. In case of intermittent or discontinuous operation of consistency increasing process further comprising accumulating a predetermined amount of squeeze fluid for continuous circulation; K No. 1 of high consistency pulp with almost no damage to the cellulose component of the pulp. of 50% or more, and from about 10-26 before delignification to about 5-26 after delignification Claim 12 Obtaining increased delignification selectivity by reducing the The method described in section. 18. An unbleached brown raw material pulp having a consistency of less than about 10% by weight is applied. in an alkaline aqueous solution for a given time and a given temperature related to the amount of the alkaline substance. All the pulp fibers are exposed to the alkaline solution by uniformly mixing with the amount of alkaline material. substantially complete a substantially uniform distribution of alkaline material in the pulp. Tie, After the completion of the mixing process, the dry weight of the pulp is calculated for subsequent oxygen delignification. The composition is enriched with at least about 0.8 to 7% by weight of an alkaline substance as a pulp by removing liquid from the pulp while retaining it in the pulp consistency to at least about 18% by weight (in this case, the aqueous alkaline The pulp fibers containing liquid are passed directly from the mixing step to the consistency increasing step). , Aluminum a significant portion of the liquid removed from the pulp during the consistency increasing process. Circulate directly to the potash material mixing process and increase the consistency of the alkali Substantially delignify pulp containing substances during oxygen delignification High consistency of unbleached pulp during oxygen delignification characterized by How to obtain refined delignification. 19. the unbleached pulp has a consistency of about 0.5 to 4.5% by weight, and Increase the consistency of the pulp by at least about 25 times during the consistency increase step. 19. The method of claim 18, further comprising increasing the amount by %. 20. At least about the amount of liquid removed from the pulp during the consistency increasing process According to claim 18, 75 to 95% is directly recycled to the alkaline substance mixing step. the method of. 21. High consistency pulp KNo. from about 10 to 26 before delignification. of the pulp during oxygen delignification by decreasing to about 5-10 after delignification. Increased delignification of at least about 50% with little damage to the cellulosic components 20. The method of claim 19, further comprising obtaining ion selectivity. 22. increased delignification selectivity of at least about 60% and Gunin pulp is treated with conventional pulp that is not homogeneously mixed with alkaline substances before delignification. A subsequent bleaching process using a substantially reduced amount of bleaching chemicals compared to further comprising subjecting the pulp to whiteness substantially equivalent to that of conventional pulp. A method according to claim 21. 23. If the bleach is chlorine or chlorine dioxide and the chlorine-containing chemicals used 23. The method of claim 22, wherein the total amount is reduced by about 15-35% by weight. 24. Bleached pulp is subjected to alkaline extraction process and regular pulp is subjected to alkaline extraction process. said alkaline material in a substantially reduced amount compared to the amount required to 23. The method of claim 22, further comprising use in an extraction step. 25. The amount of alkaline material used in the extraction process is reduced by about 25-40% by weight A method according to claim 24.