JP5242834B1 - Kraft cooking method and pulp yield improver - Google Patents

Abstract

The present invention provides a kraft cooking method capable of remarkably improving a pulp yield without requiring a large-scale equipment change and a pulp yield improver used therefor.
In a kraft cooking method in which pulp raw material is cooked in black liquor containing sodium hydroxide and sodium sulfide, a cationic polymer compound is added to the black liquor. The cationic polymer compound preferably contains at least one of a crosslinked cationic polymer, a linear cationic polymer, and a cationized starch.
[Selection figure] None

Description

The present invention relates to a kraft cooking method capable of remarkably improving a pulp yield and an additive used therefor in a step of cooking a pulp raw material in black liquor. By implementing the present invention, the yield of pulp raw materials in the pulp manufacturing industry can be greatly improved, which can greatly contribute to resource saving of forest resources and CO ₂ reduction.

Pulp uses forest resources as its raw material, and how to obtain pulp with high yield from pulp raw materials such as wood chips is an extremely important technology for saving forest resources, saving energy, and reducing CO ₂ .

  Conventional papermaking methods using lignocellulosic materials such as wood chips as pulp raw materials include 1) a chemical pulp method in which chemical defibration is performed, and 2) a mechanical pulp method in which defibration is performed by mechanical processing such as a refiner. . Among these, the chemical pulp method has an advantage that it is easy to adjust the whiteness and physical properties of the pulp. Among the chemical pulp manufacturing methods, the kraft cooking method, in which cooking is performed with sodium hydroxide and sodium sulfide, has excellent pulp strength, there are few restrictions on the wood species used, and cooking chemical recovery technology has been established. For this reason, it has become the mainstream manufacturing method. In the kraft cooking method, cellulose fibers (generally called pulp) and cooking waste liquid (generally called black liquor) containing most of lignin, which is an organic substance that binds the fibers to each other, are obtained.

Examples of the method for improving the yield of pulp include a method for preventing dissolution of cellulose and hemicellulose constituting the pulp by adding a pulp yield improver. For example, 1) A method in which a quinone compound is added in the cooking step, promotes delignification, oxidizes and stabilizes the terminal group of cellulose, thereby preventing cellulose elution (Patent Documents 1 and 2), 2) Oxidizing the cooking chemical to convert sodium sulfide to polysulfide sulfur or adding sulfur directly to the cooking chemical prevents oxidation of hemicellulose into the highly alkaline cooking chemical by protecting the end groups of hemicellulose by oxidation. Further, there are a method for improving the pulp yield (Non-Patent Document 1), a method in which the above 1) and 2) are combined (Patent Document 3), and the like.
However, the cost of adding chemicals is large compared to the effect of improving the pulp yield, and the current situation is that they are not so popular.

  As a method for improving the yield of pulp, it has also been proposed to improve the cooking process itself (Non-Patent Documents 2 and 3). However, since this involves a major equipment change, enormous capital investment costs are required.

Japanese Patent Laid-Open No. 52-37803 JP-A-53-45404 JP 2002-115190 A

Akira Yamaguchi “Polysulfide cooking of factory chips”, Kyokupa Gikyo Magazine Vol.33, 491-499 (1979) Parsad, Brijender; et al. "Mill closure with high-kappa pulping and extended oxygen delignification" Tappi. Journal, Vol. 79, No. 9 144-152 (1996) Gunobu, “Yield Evaluation Method for Cooked Pulp Using COMPACT COOKING TM Method and KOBUDOMARI Method”, Proceedings of Annual Conference of Paper Association of Paper Technology, 2003, 49-59 (2003)

  The present invention has been made in view of the above-described conventional situation, and does not require major equipment change, and a kraft cooking method capable of remarkably improving pulp yield and a pulp yield improver used therefor. Providing is a problem to be solved.

  The present inventor does not prevent the dissolution of hemicellulose itself in the black liquor in the cooking process like the conventional pulp yield improver described above, but adsorbs hemicellulose which is easy to dissolve to the pulp to thereby obtain a pulp yield. As a result of diligent research, the present invention has been completed.

  That is, the kraft cooking method of the present invention is characterized in that a cationic polymer compound is added to the black liquor in the kraft cooking method in which pulp raw material is cooked in black liquor containing sodium hydroxide and sodium sulfide. To do.

In the cooking process, most of the lignin and hemicellulose contained in the wood chips, which are pulp raw materials, are eluted in the black liquor. While lignin ionized and dissolved in black liquor is positively charged, hemicellulose is negatively charged, and cellulose, which is the main component of pulp, is slightly negatively charged. Here, when a cationic polymer compound is added to the black liquor, the cationic polymer compound is adsorbed to hemicellulose and cellulose by Coulomb force. Then, the hemicellulose and the cationic polymer compound adsorbed on the cellulose are entangled and aggregated. As a result, hemicellulose is integrated with cellulose, and the yield of pulp mainly composed of cellulose or hemicellulose is improved.
That is, the present invention does not suppress the elution of hemicellulose or cellulose into the cooking chemical solution as in the conventional pulp yield improver, but the adsorbed hemicellulose once adsorbed to the cellulose and recovered. It is based on a completely different technical idea from technology.
Therefore, according to the kraft cooking method of the present invention, a large equipment change is not required, and the pulp yield can be remarkably improved.

According to the test results of the inventors, the pulp yield can be reliably increased by using at least one of a crosslinked cationic polymer, a linear cationic polymer and a cationized starch as the cationic polymer compound. .
The crosslinked cationic polymer preferably contains dimethylamine, ammonia, and epichlorohydrin as polymer constituent units, and polyethyleneimine is also preferred.
The linear cationic polymer preferably contains acryloyloxyethyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride and acrylamide as polymer constituent units.
Further, the cationized starch preferably contains a tertiary amino group and / or a quaternary ammonium group.

  According to the kraft cooking method of the present invention, the pulp yield can be significantly improved by adding a specific cationic polymer compound to the black liquor without making a major facility improvement. As a result, the manufacturing cost can be reduced, the energy intensity can be improved by improving the energy intensity, and further, it can contribute to the saving of forest resources.

It is a schematic diagram of the general continuous cooking apparatus used for a kraft cooking method.

<Raw materials>
In the kraft cooking method of the present invention, lignocellulosic biomass is used as a raw material. Specifically, woods such as hardwoods and conifers, and non-woods such as kenaf, bagasse and bamboo are mentioned. The effect of the present invention is recognized when any of these raw materials is used, but the effect of the present invention is great particularly when hardwood is used as the raw material.

<Pulp yield improver>
Such raw materials are treated with black liquor. The pulp yield improver of the present invention is added to this black liquor, but there are no particular restrictions on the place of addition and the properties of the black liquor, and it can be applied to black liquors such as cooking and washing steps. Among them, the cooking process composed of a digester, its associated equipment, and a blow tank is effective because the concentration of hemicellulose dissolved in the black liquor is high.

  In the pulp yield improver of the present invention, a cationic polymer compound can be used as its active ingredient. The cationic polymer compound refers to a polymer having a cationic functional group such as an amino group, and examples thereof include a crosslinked cationic polymer, a linear cationic polymer, and a cationized starch.

Here, the crosslinked cationic polymer is a polymer compound having a cationic functional group in the molecule, obtained by polymerization of one or more kinds of monomers,
A polymer obtained by linking polymer compounds with a cross-linking agent to make it larger, or a monomer itself acting as a cross-linking agent to form a polymer compound having a network structure. Specifically, for example, a polymer containing dimethylamine or diethylamine, which is known as an additive for inkjet recording paper, ammonia, and epichlorohydrin as monomer units (see JP-A-10-147057), polyethyleneimine, modified polyethylene Imine and the like. The modified polyethyleneimine refers to one obtained by reacting a part or all of primary or secondary amino groups in polyethyleneimine with another compound, or reacting ethyleneimine with another polymer. Here, the other compound capable of reacting with part or all of the primary or secondary amino group in the polyethyleneimine is not particularly limited, and examples thereof include aldehyde compounds, ketone compounds, alkyl halide compounds, isocyanates. Examples thereof include compounds, thioisocyanate compounds, active olefin compounds, epoxy compounds, cyanamide compounds, guanidine compounds, urea, thiourea, carboxy compounds, acid anhydrides or acyl halide compounds. In addition, other polymers that can react with ethyleneimine are not particularly limited, and examples thereof include carboxy-containing acrylic resins and polyalkylene glycols.

  The linear cationic polymer refers to a polymer compound having a cationic functional group in the molecule, obtained by reaction of one or more types of monomers, and having a structure spreading in a chain. Specifically, for example, acryloyloxyethyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, which is used as a sludge dehydrating agent, a polymer containing acrylamide as a monomer unit, and the like can be cited (Japanese Patent Laid-Open No. 62). -2622799).

  The cationized starch refers to starch having a cationic functional group obtained by reacting starch with a cationizing agent. Specifically, for example, a tertiary amino group obtained by cationizing raw starch such as corn starch, tapioca starch, potato starch with diethylaminoethyl chloride hydrochloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride, or 4 Examples thereof include cationized starch containing a quaternary ammonium group. For example, Neotac # 30T (trade name) manufactured by Nippon Shokuhin Kako Co., Ltd. can be used.

  The pulp yield improver of the present invention can be made into a stock solution in which a cationic polymer compound is dissolved in water or black liquor collected from a process in consideration of handleability. Furthermore, an antifoaming agent etc. can also be mix | blended in the range which does not reduce the effect of this invention.

  When a crosslinked cationic polymer or a linear cationic polymer is used as a pulp yield improver, the preparation method is not particularly limited, and a liquid polymer may be added to the black liquor as it is, or a solvent such as water. It may be added to the black liquor after being dissolved in. There is no restriction | limiting in particular in the compounding ratio of this polymer and solvents, such as water, What is necessary is just to select suitably in consideration of a handleability and addition amount. Moreover, there is no restriction | limiting in particular also about those mixing order, You may add this polymer to solvents, such as water, and vice versa.

  The preparation method when using cationized starch as a pulp yield improver is to cationize by dispersing about several percent of cationized starch in water at room temperature and then heating to about 80 ° C. It is preferable to dissolve starch into starch.

<Craft cooking>
Next, the kraft cooking method using the pulp yield improver of the present invention will be described.
FIG. 1 shows a continuous cooking apparatus 1 used for the kraft cooking method. This apparatus comprises a vertically long digester 2 and a raw material supply device 3 for sending a mixture of pulp raw material and white liquor from the top of the digester 2. The digester 2 is divided into an infiltration zone I, an upper digestion zone C1, a lower digestion zone C2, and a washing zone W in order from the top of the tower. And between the upper cooking zone C1 and the lower cooking zone C2, the cooking screen 5 is provided so that the flow path of a pulp raw material and black liquor may be surrounded. Similarly, an extraction screen 6 is provided between the lower cooking zone C2 and the cleaning zone W. Further, a cleaning screen 7 is similarly provided at the lowermost end of the cleaning zone W.
The black liquor filtered by the cooking screen 5 is supplied to the lower part of the upper cooking zone C 1 by the upper cooking circulation line 8. The black liquor filtered by the extraction screen 6 is supplied to the lower part of the lower cooking zone C2 by the lower cooking circulation line 9. Further, the cleaning black liquor filtered by the cleaning screen 7 is supplied to the bottom of the digester 2 through the cleaning circulation line 10.

  In the continuous cooking apparatus 1 configured as described above, a mixture of pulp raw material and white liquor is supplied to the top of the digester 2 by the raw material supply apparatus 3. And a vapor | steam is supplied to a tower top part from the vapor | steam supply apparatus which is not shown in figure, and it heats up to predetermined temperature. Further, in the infiltration zone I, the white liquor penetrates into the pulp raw material, and the cooking reaction is started. In the upper cooking zone C1 and the lower cooking zone C2, lignin and hemicellulose are eluted from the pulp raw material by the cooking reaction, and the white liquor becomes a black liquor in which lignin, hemicellulose and the like are dissolved. At this time, the black liquor filtered by the cooking screen 5 provided at the lower end of the cooking zone C1 is supplied to the lower part of the upper cooking zone C1 by the upper circulation line 8. Further, the black liquor filtered by the extraction screen 6 provided at the lower end of the cooking zone C2 is also supplied to the lower part of the lower cooking zone C2 by the lower cooking circulation line 9. The pulp that remains without dissolving in the black liquor is mainly composed of cellulose. The pulp thus obtained is washed countercurrently with the washing black liquor in the washing zone W, then blown and sent to a blow tank (not shown). The washing black liquor filtered by the washing screen 7 is supplied to the bottom of the digester 2 through the washing circulation line 10.

  The pulp yield improver of the present invention increases the pulp yield by adding it to the black liquor. If added to the black liquor, there are no particular restrictions on the location of addition. For example, it is preferable to add to the circulation line (top circulation line 4, upper digestion circulation line 8, lower digestion circulation line 9) of the digester 2 where good stirring can be expected. Thereby, hemicellulose eluted in the black liquor can be adsorbed to the pulp efficiently.

  The pulp yield improver of the present invention is generally added to the black liquor continuously or intermittently using a chemical injection pump. Moreover, you may dilute and add with solvents, such as water, with the addition amount and the capability of a chemical injection pump.

  Since the amount of the pulp yield improver added to the black liquor varies depending on the properties of the black liquor, it is desirable to carry out a selection test in advance. In the case of a crosslinked cationic polymer, the dry weight is 5 to 300 mg / kg, preferably 7 to 200 mg / kg, more preferably 10 to 150 mg / kg, and in the case of a linear cationic polymer, 50 to 1000 mg / kg, preferably 100 to 700 mg / kg, more preferably 150 to 500 mg / kg, in the case of cationized starch, 10 to 700 mg / kg, preferably 50 to 500 mg / kg, more preferably 90 to 350 mg / kg. The pulp yield improves as the amount of the pulp yield improver increases. However, in the high addition range, the yield cannot be improved enough to meet the increase in the amount added. It is preferable to add within the range.

  According to the pulp production method of the present invention, by adding the pulp yield improver of the present invention to the black liquor, the hemicellulose in the black liquor is efficiently recovered and adsorbed on the cellulose in the pulp. A high-yield pulp can be produced.

Hereinafter, embodiments embodying the present invention will be described in detail.
<Pulp yield improver>
As pulp yield improvers, the following crosslinked cationic polymers (Examples 1 to 3), linear cationic polymers (Example 4) and cationized starch (Example 5) were prepared. Details are shown below.

[Crosslinked cationic polymer]
Example 1
A 1 L three-necked flask was charged with 178.5 g (1.98 mol) of a 50% aqueous dimethylamine (DMA) solution and 1.4 g (0.02 mol) of a 25% aqueous ammonia (NH3) solution, and 93.1 g of ions were added thereto. Exchange water was added and mixed to make uniform. Subsequently, 185 g (2.0 mol) of epichlorohydrin (ECH) was added while keeping the reaction solution at 50 ° C. or lower. After the addition of ECH, the mixture was aged at 60 ° C. for 4 hours. Then, the reaction was stopped by adjusting to pH 4.2 with sulfuric acid, and the pulp yield improver of Example 1 was obtained. This pulp yield improver was composed of a crosslinked cationic polymer, and the weight average molecular weight determined by liquid chromatography was 35,000.

(Example 2)
A 1 L three-necked flask was charged with 178.5 g (1.98 mol) of a 50% aqueous dimethylamine (DMA) solution and 1.4 g (0.02 mol) of a 25% aqueous ammonia (NH3) solution, and 93.1 g of ions were added thereto. Exchange water was added and mixed to make uniform. Subsequently, 185 g (2.0 mol) of epichlorohydrin (ECH) was added while keeping the reaction solution at 50 ° C. or lower. After the addition of ECH, the mixture was aged at 60 ° C. for 12 hours. Subsequently, 1.9 g (0.02 mol) of ECH and 1.4 g (0.02 mol) of 25% NH 3 aqueous solution were added, and a crosslinking reaction was performed at 80 ° C. for 4 hours. Then, the reaction was stopped by adjusting to pH 4.2 with sulfuric acid, and the pulp yield improver of Example 2 was obtained. This pulp yield improver was composed of a crosslinked cationic polymer, and the weight average molecular weight determined by liquid chromatography was 160,000.

(Example 3)
A 1 L three-necked flask was charged with 178.5 g (1.98 mol) of a 50% aqueous dimethylamine (DMA) solution and 1.4 g (0.02 mol) of a 25% aqueous ammonia (NH3) solution, and 93.1 g of ions were added thereto. Exchange water was added and mixed to make uniform. Subsequently, 185 g (2.0 mol) of epichlorohydrin (ECH) was added while keeping the reaction solution at 50 ° C. or lower. After the addition of ECH, the mixture was aged at 60 ° C. for 12 hours. Subsequently, 1.9 g (0.02 mol) of ECH and 1.4 g (0.02 mol) of 25% NH 3 aqueous solution were added, and a crosslinking reaction was performed at 80 ° C. for 8 hours. Then, the reaction was stopped by adjusting to pH 4.2 with sulfuric acid, and the pulp yield improver of Example 3 was obtained. This pulp yield improver was composed of a crosslinked cationic polymer, and the weight average molecular weight determined by liquid chromatography was 360,000.

[Linear cationic polymer]
Example 4
In a 1 L beaker, 53.6 g (20 mol%) of an 80% aqueous solution of acryloyloxyethyltrimethylammonium chloride, 74.8 g (20 mol%) of an 80% aqueous solution of acryloyloxyethyldimethylbenzylammonium chloride, and 47.3 g of acrylamide ( 60 mol%) was added, and 360.1 g of ion-exchanged water was added thereto and mixed to be uniform. After heating to 40 ° C. and deoxygenation with nitrogen gas, 1.5 cc of 1% aqueous solution of ammonium persulfate and 1.5 cc of 1% aqueous solution of sodium hydrogen sulfite are added to initiate polymerization, and polymerization is performed for 16 hours. And the pulp yield improver of Example 4 was obtained. The pulp yield improver was composed of a linear cationic polymer, and the weight average molecular weight determined by liquid chromatography was 4.5 million.

[Cationized starch]
(Example 5)
The pulp yield improver of Example 5 is a cation-modified product (quaternary ammonium) of tapioca starch (trade name: Neotac # 30T, manufactured by Nippon Shokuhin Kako Co., Ltd.).

(Example 6)
In Example 6, polyethyleneimine was used as a pulp yield improver. Polyethylene P (trade name) manufactured by BASF (BSF) was used as the polyethyleneimine.

-Evaluation-
The pulp yield improvers of Examples 1 to 6 prepared as described above were subjected to the following two pulp yield tests.
(Pulp yield test 1)
The black liquor extracted from the continuous digester of the actual apparatus was filtered with a filter paper to remove the suspended matter. On the other hand, the unbleached pulp blown from the continuous digester of the same actual apparatus was thoroughly washed. 692 g of filtered black liquor and 23 g (absolutely dry weight) of washed unbleached pulp were placed in a 2 L stainless steel vat, and the temperature was controlled at 70 ° C. while stirring. The condition of the test temperature of 70 ° C. simulates the temperature environment in the cooking process from the blow line to the blow tank. 30 minutes after the unbleached pulp was charged, a predetermined amount of the pulp yield improver of Examples 1 to 6 was added, and after 60 minutes, the black liquor-pulp mixture was filtered with filter paper to separate the pulp and black liquor. . The obtained pulp was sufficiently washed with fresh water, and the yield improvement rate (%) of the pulp was calculated by the following formula.
X: Weight of completely dry pulp before test (g)
Y: Weight of completely dried pulp after test (g)
Pulp yield improvement rate (%) = (Y−X) / X × 100
In addition, the measurement of the absolute dry pulp weight was performed according to the measuring method of "mass of the absolute dry sample" described in JIS P8203.

As a result, as shown in Table 1, it was found that when the pulp yield improvers of Examples 1 to 6 were added, the pulp yield was significantly increased as compared with the case where no pulp was added. The condition of the test temperature of 70 ° C. in the pulp yield test 1 is a simulation of the temperature environment around the blow line to the blow tank in the cooking process. It was proved that the pulp yield can be increased by adding.
Moreover, in any pulp yield improver, it was found that the pulp yield increases when the amount added is increased. It was found that the addition amount of the crosslinked cationic polymers of Examples 1 to 3 and Example 6 was effective from 10 mg to 150 mg in dry weight with respect to 1 kg of black liquor. Moreover, it turned out that 150 mg to 500 mg is effective in the linear cationic polymer of Example 4. Moreover, 90 mg to 350 mg was found to be effective for the cationized starch of Example 5.

(Pulp yield test 2)
In the pulp yield test 2, the stainless steel bat used as a container in the pulp yield test 1 was replaced with an autoclave, and the reaction temperature was increased to 150 ° C. The condition of the test temperature of 150 ° C. imitates the temperature environment around the circulation line of the digester in the cooking process. About others, it is the same as that of the pulp yield improvement test method 1, and description is abbreviate | omitted. The test results are shown in Table 2.

  From Table 2, even in the condition of the test temperature of 150 ° C. in the pulp yield test 2, when the pulp yield improver of Examples 1 to 6 is added, the pulp yield is significantly improved as compared with the case where no pulp is added. I understood. The condition of the test temperature of 150 ° C. in the pulp yield test 2 imitates the temperature environment around the circulation line of the digester in the cooking process. Therefore, the pulp yield improver of the present invention is around the circulation line of the digester. It has been proved that the pulp yield can be increased even in the case of adding.

  The present invention is not limited to the description of the embodiments of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

DESCRIPTION OF SYMBOLS 1 ... Continuous cooking apparatus, 2 ... Digesting pot (I ... Osmosis zone, C1 ... Upper cooking zone, C2 ... Lower cooking zone, W ... Washing zone), 3 ... Raw material supply apparatus, 4 ... Top circulation line, 5 ... Cooking screen , 6 ... Extraction screen, 7 ... Cleaning screen, 8 ... Upper cooking circulation line, 9 ... Lower cooking circulation line, 10 ... Cleaning circulation line

Claims (12)

In the kraft cooking method in which pulp raw material is cooked in black liquor containing sodium hydroxide and sodium sulfide,
A kraft cooking method, wherein a cationic polymer compound (except for a cationic polymer compound forming a polyelectrolyte complex with an anionic polymer compound) is added to the black liquor.   The kraft cooking method according to claim 1, wherein the cationic polymer compound contains at least one of a crosslinked cationic polymer, a linear cationic polymer, and a cationized starch.   The kraft cooking method according to claim 2, wherein the crosslinked cationic polymer contains dimethylamine, ammonia, and epichlorohydrin as polymer constituent units.   The kraft cooking method according to claim 2, wherein the crosslinked cationic polymer is polyethyleneimine.   The craft according to any one of claims 2 to 4, wherein the linear cationic polymer contains acryloyloxyethyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride and acrylamide as polymer constituent units. Cooking method.   The kraft cooking method according to any one of claims 2 to 5, wherein the cationized starch contains a tertiary amino group and / or a quaternary ammonium group. A pulp yield improver for use in a kraft cooking method for cooking pulp raw material in black liquor containing sodium hydroxide and sodium sulfide,
A pulp yield improver comprising a cationic polymer compound (excluding a cationic polymer compound that forms a polyelectrolyte complex with an anionic polymer compound).   The pulp yield according to claim 7, wherein the cationic polymer compound includes one or more selected from the group of a crosslinked cationic polymer, a linear cationic polymer, and a cationized starch. Rate improver.   9. The pulp yield improver according to claim 8, wherein the crosslinked cationic polymer contains dimethylamine, ammonia, and epichlorohydrin as polymer constituent units.   9. The pulp yield improver according to claim 8, wherein the crosslinked cationic polymer is polyethyleneimine.   11. The linear cationic polymer contains acryloyloxyethyltrimethylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, and acrylamide as a polymer constituent unit, according to any one of claims 8 to 10. Pulp yield improver.   The pulp yield improver according to any one of claims 7 to 11, wherein the cationized starch contains a tertiary amino group and / or a quaternary ammonium group.

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