JP2015200056A - Method of producing dissolved craft pulp continuously - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing dissolved craft pulp continuously and efficiently and thereby producing saccharides and furfural from the hydrolysis liquid in high concentrations.SOLUTION: A method of producing dissolved craft pulp continuously includes (a) a step of adding warm water to wood chips, (b) a step of treating the wood chips hydrothermally in a hydrolysis oven to hydrolyze hemicellulose contained in the wood chips, (c) a step of separating wood chips after the hydrothermal treatment from hydrolysis liquid and (d) a step of craft-digesting the separated wood chips to obtain dissolved craft pulp. In the step (c), a part of the hydrolysis liquid is drawn from a strainer of the hydrolysis oven and, together with warm water in the step (a), added to the wood chips.

Description

  The present invention relates to a method for continuously producing dissolved kraft pulp, in a step of hydrolyzing wood chips to hydrolyze hemicellulose contained in the wood chips in a prehydrolysis kettle having at least one strainer. It is related with the method of continuously manufacturing a melt | dissolution kraft pulp characterized by extracting a part of and adding a part of hydrolysis liquid to the hot water added to a wood chip in the front process.

  Dissolving pulp used for rayon production or the like generally has a high α-cellulose content of 88 to 98%. α-cellulose is a portion that does not dissolve when pulp is treated with 17.5% sodium hydroxide, and cellulose is the main component (TAPPI standard T203om-83). In order to produce dissolving pulp, it is necessary to increase the content of α-cellulose, and for this purpose, a considerable amount of hemicellulose contained in the raw material wood must be removed, thereby producing a considerable amount of production. There will be a cost. Known techniques for removing hemicellulose include, for example, a prehydrolysis process (prehydrolysis process) before kraft cooking and a cold caustic extraction process in a bleaching process. In addition, if hemicellulose such as pentosan remains in the dissolved pulp, filtration and spinning in the production of rayon and the like may become difficult, and problems may occur in fiber characteristics such as rayon.

  In Patent Document 1, lignocellulose material is prehydrolyzed, followed by alkali neutralization at 140 to 160 ° C., and the neutralized prehydrolyzed lignocellulosic material is kraft-cooked to dissolve kraft. A method for producing pulp in a batch mode is disclosed.

Japanese Patent No. 2984798

  In the prehydrolysis treatment before kraft cooking, sugars and furfurals are generated in the prehydrolyzed solution. Therefore, these useful substances can be produced simultaneously with the production of dissolving pulp.

  An object of the present invention is to provide a method for efficiently continuously producing dissolved kraft pulp and producing saccharides and furfurals at a high concentration from a hydrolyzate.

As a result of intensive studies on the above problems, the present inventors provide a method for efficiently and continuously producing dissolved kraft pulp and producing saccharides and furfurals in a hydrolyzed solution at a high concentration by the following method. Found that it would be possible.
(A) adding warm water to the wood chips,
(B) a step of hydrolyzing wood chips to hydrolyze hemicellulose contained in the wood chips in a prehydrolysis tank having at least one strainer;
(C) a step of separating the wood chips and hydrolyzed liquid after hydrothermal treatment;
(D) a step of kraft cooking the separated wood chips to obtain a dissolved kraft pulp;
In a method for continuously producing dissolved kraft pulp,
In the step (c), a part of the hydrolyzed liquid is extracted from the strainer of the pre-hydrolysis kettle and added together with the hot water added to the wood chips in the step (a). how to.

  According to the present invention, dissolved kraft pulp can be efficiently and continuously produced, and saccharides and furfurals can be produced at a high concentration from the hydrolyzate.

  The present invention relates to a technique for producing dissolved kraft pulp. In the present invention, the dissolved kraft pulp (DKP) is a dissolved pulp produced by a kraft cooking method (KP method). The dissolving pulp means a chemically purified pulp having high cellulose purity, and in a preferred embodiment, the α-cellulose content is 90% or more. Generally, wood contains three major components of cellulose, lignin, and hemicellulose, and a small amount of resin and ash, but dissolved pulp has high cellulose purity, chemical fiber, cellophane, plastic, synthetic glue, and various other celluloses. Widely used as a raw material for derivatives.

The raw material of the present invention is wood chips. In the present invention, it is preferable to include wood chips made of softwood, and the size and tree species are not particularly limited, and may be a single kind of wood chip or a chip in which two or more kinds of wood are mixed. In the present invention, a high-quality dissolving pulp can be efficiently produced even if it is a softwood species that is relatively difficult to digest or bleach. As a softwood chip used in the present invention, for example, a larch genus or a pine genus wood chip can be suitably used. For example, Larix (
L.) Leptolepis (larch), L. laricina (Tamarac), L. occidentalis (Larix larch), L. decidua (European larch), L. gmelinii (Guimatsu)
Etc. Examples of conifers other than the genus Larix include Pinus radiata for the genus Pinus, Pseudotuga (hereinafter abbreviated as P.) menziesii (Dacrasfer), P. japonica, For example, Cryptomeria japonica can be mentioned for the genus Sugi.

  In the present invention, hardwood wood chips can be used as a raw material. As a hardwood wood chip, for example, a Eucalyptus wood chip can be suitably used. For the Eucalyptus genus, Eucalyptus (hereinafter abbreviated as E.) calophylla, E. citriodora, E .; diversiccolor, E.I. globulus, E.I. grandis, E .; gummifera, E .; marginata, E.M. nesophila, E.I. nitens, E.I. amygdalina, E .; camaldulensis, E .; delegenasis, E.I. gigantea, E .; muelleriana, E.M. obliqua, E .; regnans, E .; Sieberiana, E.I. viminalis, E .; camaldulensis, E .; marginata and the like.

Process of adding warm water Wood chips are added with warm water before the hydrothermal treatment process. Hot water is added between the tip bottle and the prehydrolysis kettle, for example, with a tip meter screw or tip tube.

Prehydrolysis process (hydrothermal treatment process)
In the present invention, as a pretreatment before cooking, the wood chips are hydrothermally treated to decompose and remove the hemicellulose content in the wood chips into water-soluble sugars. Hydrothermal treatment (prehydrolysis) as pretreatment is performed by treating wood chips with high-temperature water. The water to be added may be hot water or steam. Since an organic acid or the like is generated by the progress of hydrolysis, the pH of the treatment liquid is generally 2 to 5.

  Hydrothermal treatment is performed in a prehydrolysis kettle having at least one strainer. The pre-hydrolysis tank removes the hemicellulose content by continuously hydrolyzing the wood chips while moving in the pre-hydrolysis tank while maintaining the pressure and heating conditions of the wood chips supplied from the top supply port. . Wood chips and hydrolyzate from which hemicellulose has been removed are discharged from the bottom of the prehydrolysis tank and supplied to the kraft digester. Moreover, a hydrolyzate can be taken out from the strainer provided in the prehydrolysis kettle.

  In the step of adding warm water to the wood chips, a part or all of the extracted hydrolyzate is added together with warm water. It is preferable to add the hydrolyzate so as to be 20 to 80%, more preferably 40 to 80%, based on the total amount of hot water added to the wood chips. When the added amount of the hydrolyzed liquid is less than 20%, the increase in the concentration of saccharides and furfurals in the obtained hydrolyzed liquid is small. When the added amount of the hydrolyzed liquid exceeds 80%, the concentration of saccharides and furfurals in the hydrolyzed liquid is high, but the yield decreases because the amount of hydrolyzed liquid decreases.

  The hydrothermal treatment is preferably performed in a temperature range of 150 to 180 ° C. If temperature is less than 150 degreeC, removal of hemicellulose will become inadequate, and when it exceeds 180 degreeC, hydrolysis will become excess and alpha-cellulose content will also fall. The treatment time is not particularly limited, but is preferably 15 to 400 minutes, more preferably 20 to 250 minutes, and even more preferably 25 to 150 minutes. When the treatment time is too short, the removal of hemicellulose becomes insufficient, and the delignification improving effect due to the removal of hemicellulose is also reduced. On the other hand, if the treatment time is too long, hydrolysis becomes excessive and the α-cellulose content is reduced, resulting in a decrease in pulp yield, and condensing of lignin causes deterioration in digestibility in the subsequent cooking step.

  In the hydrothermal treatment in the present invention, the treatment temperature and treatment time can be set using the P factor (Pf) as an index. The P-factor is a standard indicating the total amount of heat given to the reaction system in the prehydrolysis treatment, and is expressed by the following formula in the present invention, and time integration is performed from the time when chips and water are mixed until the end of cooking. To calculate.

Pf = ∫ln ⁻¹ (40.48-15106 / T) dt
[Wherein T represents an absolute temperature at a certain point]
The hydrothermal treatment in the present invention is preferably performed in a range where the P factor (Pf) is 350 to 900, more preferably 500 to 800. If Pf is less than 350, the removal of hemicellulose is insufficient, and the effect of improving delignification due to the removal of hemicellulose is also reduced. On the other hand, when Pf exceeds 900, hydrolysis becomes excessive and the α-cellulose content is reduced, leading to a decrease in pulp yield, and condensing of lignin leads to deterioration in digestibility in the subsequent digestion step.

  The hydrothermal treatment step can be performed by putting wood chips and water in a pressure resistant container (prehydrolysis kettle), but the shape and size of the container are not particularly limited.

  The ratio when supplying wood chips and water to the hydrothermal treatment kettle (prehydrolysis kettle) is preferably 1.0 to 2.3 L / kg. The ratio of wood chips to water supplied to the prehydrolysis kettle is also called the dynamic liquid ratio and is shown as the amount of water per kg of wood chips. If the dynamic liquid ratio is less than 1.0 L / kg, the amount of water is too small relative to the wood chips, resulting in insufficient hydrolysis. If the liquid ratio exceeds 2.3 L / kg, the top of the prehydrolysis tank In this case, it is not preferable because the gas phase portion cannot be sufficiently secured. The water includes not only water supplied with the wood chip but also water contained in the wood chip, drain water, and the like.

  Moreover, the ratio of the wood chip and water in the prehydrolysis kettle can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and 2.0 to 4.0 L / kg is more preferable. If the liquid ratio is less than 1.0 L / kg, hydrolysis is insufficient because the amount of water is too small relative to the wood chips, and if the liquid ratio exceeds 5.0 L / kg, the size of the container becomes excessive. Therefore, it is not preferable. Moreover, you may add a small amount of mineral acid as needed.

  The prehydrolyzed liquid generated by hydrothermal treatment contains saccharides generated by hydrolysis of hemicellulose and organic substances mainly composed of furfurals. That is, in the present invention, in addition to the dissolved kraft pulp, it is possible to simultaneously produce sugars and furfurals. Examples of the furfurals to be produced include furfural and 5-hydroxymethylfurfural. In addition, saccharides to be produced are oligosaccharides, monosaccharides, etc., and oligosaccharides include xylooligosaccharides, cellooligosaccharides, galactooligosaccharides, etc., and monosaccharides to be produced include xylose, arabinose, glucose, galactose, mannose, etc. Is mentioned.

Chip Recovery Step Next, in the present invention, the hydrolyzed wood chip and the hydrolysis waste liquid are separated, and the hydrolysis waste liquid and the wood chip are recovered. In a preferred embodiment, the wood chips after the prehydrolysis treatment are separated from the prehydrolysis waste liquid, and then the chips are sufficiently washed with water and collected. Insufficient cleaning can cause adverse effects in subsequent cooking steps.

  Washing and removal of the hydrolyzed liquid can be performed by using a general solid-liquid separator. For example, a solid-liquid separation device such as an extraction screen or a filter cloth can be provided in the prehydrolysis kettle, and washing water can be introduced from the bottom of the container and extracted from the screen for countercurrent washing.

The chips after the cooking process are washed together with the cooking liquor and put into a cooking kettle and used for cooking under general conditions. Moreover, you may use for cooking of correction methods, such as MCC, EMCC, ITC, and Lo-solid. Also, there are no particular limitations on cooking types such as 1 vessel liquid phase type, 1 vessel gas phase / liquid phase type, 2 vessel liquid phase / gas phase type, and 2 vessel liquid phase type. Preferably, the unbleached pulp that has been cooked is washed with a washing device such as a diffusion washer after extracting the cooking liquor. In the case of softwood, the kappa number of unbleached pulp after washing is preferably 10-22, and may be 12-20. In the case of hardwood, it is preferably 5-20, and may be 6-16.

  The cooking process can be performed by putting the hydrothermally treated wood chips together with the cooking liquid in a pressure resistant container, but the shape and size of the container are not particularly limited. The liquid ratio between the wood chip and the chemical solution can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and more preferably 2.0 to 4.0 L / kg. .

When the wood chip is a conifer, the cooking solution preferably has an active alkali addition rate (AA) per weight of the dry wood chip of 16 to 22% by mass. If the active alkali addition rate is less than 16% by mass, the removal of lignin and hemilulose becomes insufficient, and if it exceeds 22% by mass, the yield and quality are reduced. Here, the active alkali addition rate is obtained by converting the total addition rate of NaOH and Na ₂ S as the addition rate of Na ₂ O, and multiplying NaOH by 0.775 and Na ₂ S by 0.795. Therefore, it can be converted into the addition rate of Na ₂ O.

  Moreover, in this invention, you may add the alkaline cooking liquid containing 0.01-1.5 mass% quinone compound per absolutely dry chip | tip to a digester. If the addition amount of the quinone compound is less than 0.01% by mass, the addition amount is too small to reduce the kappa number of the pulp after cooking, and the relationship between the kappa number and the pulp yield is not improved. Furthermore, the reduction of wrinkles and the suppression of the decrease in viscosity are insufficient. Moreover, even if the addition amount of a quinone compound exceeds 1.5 mass%, the further reduction of the kappa number of the pulp after cooking and the improvement of the relationship between a kappa number and a pulp yield are not recognized.

  The quinone compound used is a quinone compound, hydroquinone compound or precursor thereof as a so-called known cooking aid, and at least one compound selected from these can be used. Examples of these compounds include anthraquinone, dihydroanthraquinone (for example, 1,4-dihydroanthraquinone), tetrahydroanthraquinone (for example, 1,4,4a, 9a-tetrahydroanthraquinone, 1,2,3,4-tetrahydroanthraquinone). Methyl anthraquinone (eg 1-methyl anthraquinone, 2-methyl anthraquinone), methyl dihydroanthraquinone (eg 2-methyl-1,4-dihydroanthraquinone), methyl tetrahydroanthraquinone (eg 1-methyl-1,4,4a) , 9a-tetrahydroanthraquinone, 2-methyl-1,4,4a, 9a-tetrahydroanthraquinone) and the like, anthrahydroquinone (generally 9,10-dihydroxyanthracene), Tyranthrahydroquinone (for example, 2-methylanthrahydroquinone), dihydroanthrahydroanthraquinone (for example, 1,4-dihydro-9,10-dihydroxyanthracene) or an alkali metal salt thereof (for example, disodium salt of anthrahydroquinone, 1 , 4-dihydro-9,10-dihydroxyanthracene disodium salt), and precursors such as anthrone, anthranol, methylanthrone, and methylanthranol. These precursors have the potential to convert to quinone compounds or hydroquinone compounds under cooking conditions.

  The cooking is preferably performed in a temperature range of 120 to 220 ° C, more preferably 150 to 180 ° C. If the temperature is too low, delignification (decrease in the kappa number) is insufficient, while if the temperature is too high, the degree of polymerization (viscosity) of cellulose decreases. In addition, the cooking time in the present invention is the time from when the cooking temperature reaches the maximum temperature until the temperature starts to decrease, but the cooking time is preferably 120 minutes or more and 10 hours, preferably 60 minutes or more and 240 minutes or less. preferable. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 10 hours, the pulp production efficiency deteriorates, which is not preferable.

  In the cooking in the present invention, the processing temperature and the processing time can be set using the H factor (Hf) as an index. The H factor is a standard representing the total amount of heat given to the reaction system during the cooking process, and is represented by the following equation. The H factor is calculated by time integration from the time when chips and water are mixed until the end of cooking.

Hf = ∫exp (43.20-16113 / T) dt
[Wherein T represents an absolute temperature at a certain point]
In the present invention, the unbleached pulp obtained after cooking can be subjected to various treatments as necessary.

  In one embodiment, oxygen delignification treatment can be performed on pulp obtained by cooking. As the oxygen delignification used in the present invention, a known medium concentration method or high concentration method can be applied as it is. In the case of the medium concentration method, the pulp concentration is preferably 8 to 15% by mass, and in the case of the high concentration method, it is preferably performed at 20 to 35% by mass. Sodium hydroxide and potassium hydroxide can be used as the alkali in oxygen delignification, and oxygen gas includes oxygen from a cryogenic separation method, oxygen from PSA (Pressure Swing Adsorption), VSA (Vacuum Swing Adsorption). Oxygen etc. from) can be used.

The reaction conditions for the oxygen delignification treatment are not particularly limited, but the oxygen pressure is 3 to 9 kg / cm ² , more preferably 4 to 7 kg / cm ² , the alkali addition rate is 0.5 to 4% by mass, and the temperature is 80%. ~ 140 ° C, treatment time is 20 to 180 minutes, and other conditions can be applied. In the present invention, the oxygen delignification treatment may be performed a plurality of times.

  The pulp that has been subjected to the oxygen delignification treatment is then sent to a washing step, and after washing, it is sent to a multistage bleaching step to perform a multistage bleaching treatment. The multi-stage bleaching treatment of the present invention is not particularly limited, but acid (A), chlorine dioxide (D), alkali (E), oxygen (O), hydrogen peroxide (P), ozone (Z), It is preferable to combine a known bleaching agent such as peracid and a bleaching aid. For example, the first stage of the multistage bleaching process uses a chlorine dioxide bleaching stage (D) or an ozone bleaching stage (Z), the second stage is an alkali extraction stage (E), the hydrogen peroxide stage (P), the third stage or later. A bleaching sequence using chlorine dioxide or hydrogen peroxide is preferably used. The number of stages after the third stage is not particularly limited, but considering energy efficiency, productivity, etc., it is preferable to finish in three or four stages in total. Further, a chelating agent treatment stage with ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) or the like may be inserted during the multistage bleaching treatment.

  Since the dissolved kraft pulp (DKP) produced by the present invention is free of hemicellulose and various phenols, high-quality dissolved kraft pulp can be easily produced by ordinary oxygen delignification treatment or bleaching treatment. .

  EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example. Unless otherwise specified, in the present invention,% and the like are based on weight, and the numerical range includes the end points.

[Example 1]
Dissolved kraft pulp was continuously produced by an apparatus equipped with a prehydrolysis kettle and a kraft digester as shown in FIG.
Add warm water to the wood chip of Radiata pine with a chip meter screw so that the liquid ratio is 3.2 (L / kg), continuously put it into the prehydrolysis kettle 4, and at a prehydrolysis temperature of 170 ° C., Hydrolysis was performed while changing the P factor. The pH of the treatment solution after the hydrolysis treatment was 3.3. At this time, the hydrolyzed solution was extracted from the strainer 5, and a part of the extracted hydrolyzed solution was added so as to be 20% with respect to the total amount of hot water added to the wood chips. This hydrolyzed solution was measured for furfural concentrations and Brix values according to the following analysis method. The Brix value is also called sugar content and is a measurement value measured with a Brix meter (sugar meter), which is a measure of the amount of sugar in the solution. 1 Brix is a sucrose concentration of 1% by mass. Equivalent to.
Subsequently, the wood chips were put into the kraft digester 6 and subjected to kraft cooking at a cooking temperature of 158 ° C. for 210 minutes and H factor (Hf) = 1500. The chemical solution had an active alkali addition rate (AA) of 16.5%, an active alkali of 105 g / L (Na ₂ O conversion value), NaOH of 75.6 g / L (Na ₂ O conversion value), Na ₂ S of 29.4 g / L ( Na ₂ O equivalent value) and a composition having a sulfidity of 28%, and the liquid ratio between the wood chip and the cooking chemical was 3.2 (L / kg).
Measurement of concentration of furfurals in the hydrolyzate: An HPLC system (manufactured by Shimadzu) equipped with an RI detector (RID-10A) was used. An ion exchange column (Aminex-HPX-87P, 300 × 7.8 mm) was used as the column, and an eluent of 5 mM sulfuric acid was measured at a flow rate of 1.0 ml / min.
-Measurement of Brix value in hydrolyzed solution: The hydrolyzed solution was filtered through a filter having a pore size of 0.45 µm, and the Brix value of this filtrate was measured with a Brix meter (PAL-1, manufactured by Atago Co., Ltd.).

[Example 2]
Dissolved kraft pulp was continuously produced in the same manner as in Example 1 except that a part of the extracted hydrolyzate was added to 80% of the total amount of hot water added to the wood chips.

  FIG. 2 shows the relationship between the concentration of furfurals in the hydrolyzed solutions of Examples 1 and 2 and the P-factor. From FIG. 2, when the hydrolysis liquid added to the wood chip is increased from 20% (Example 1) to 80% (Example 2) with respect to the total amount of hot water, the concentration of furfurals in the hydrolysis liquid increases. It is obvious.

  FIG. 3 shows the relationship between the Brix value and the P-factor in the hydrolyzed solutions of Examples 1 and 2. From FIG. 2, when the hydrolysis solution added to the wood chips is increased from 20% (Example 1) to 80% (Example 2) with respect to the total amount of warm water, the Brix value in the hydrolysis solution, that is, the concentration of sugars. It is clear that increases.

It is a figure which shows the apparatus for implementing the method of manufacturing continuously the dissolving pulp which is one embodiment of this invention. It is a graph which shows the relationship between the density | concentration of the furfurals in the hydrolysis liquid of Example 1, 2 and P-factor. It is a graph which shows the relationship between the Brix value in the hydrolysis liquid of Examples 1 and 2, and P-factor.

DESCRIPTION OF SYMBOLS 1 Tip bottle 2 Tip meter screw 3 Tip tube 4 Prehydrolysis kettle 5 Strainer 6 Kraft cooking kettle 7 Hot water 8 Hydrolysis liquid

Claims (4)

(A) adding warm water to the wood chips,
(B) a step of hydrolyzing wood chips to hydrolyze hemicellulose contained in the wood chips in a prehydrolysis tank having at least one strainer;
(C) a step of separating the wood chips and hydrolyzed liquid after hydrothermal treatment;
(D) a step of kraft cooking the separated wood chips to obtain a dissolved kraft pulp;
In a method for continuously producing dissolved kraft pulp,
In the step (c), a part of the hydrolyzed liquid is extracted from the strainer of the prehydrolysis kettle and added together with the hot water added to the wood chips in the step (a) to continuously produce a dissolved kraft pulp. Method.   The method for continuously producing a dissolved kraft pulp according to claim 1, wherein the hydrolysis liquid is added so as to be 20 to 80% of the total amount of warm water added to the wood chips.   3. The melting craft according to claim 1, wherein the strainer of the prehydrolysis tank is installed between a supply port for supplying wood chips and a discharge port for discharging hydrolyzed wood chips. A method for continuously producing pulp.   A method for continuously producing a dissolved kraft pulp according to any one of claims 1 to 3, wherein a saccharide and / or furfural is obtained from the hydrolyzate.

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