JP2015030949A - Method of producing dissolving kraft pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique of producing high-quality dissolving kraft pulp efficiently.SOLUTION: A method of producing dissolving kraft pulp includes (a) a step of adding water to wood chips to hydrolyze hemicellulose contained in the wood chips, (b) a step of washing the wood chips after the hydrolysis to recover the wood chips, (c) a step of subjecting the recovered wood chips to craft digestion to produce pulp and (d) a step of subjecting the pulp after the craft digestion to an oxygen delignification treatment. In the step of the oxygen delignification treatment, a magnesium compound is added.

Description

  The present invention relates to a method for producing dissolved kraft pulp. In particular, according to the present invention, high-quality dissolved kraft pulp can be produced.

  Dissolved kraft pulp (DKP) is a dissolved pulp produced by a kraft cooking method (KP method). Dissolving pulp means a chemically purified pulp having high cellulose purity, and usually has an α-cellulose content of 90% or more. Dissolving pulp is widely used as a raw material for chemical fibers, cellophane, plastics, synthetic glues, and various other cellulose derivatives.

  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

  However, the structure of wood used as a raw material differs depending on the tree species, and even in the same tree species, there are differences in the apparent density and water permeability because of differences in growth conditions and collection sites.

  Therefore, when manufacturing a melt | dissolution kraft pulp by the prehydrolysis process, when carrying out the prehydrolysis of a wood chip, hydrolysis became non-uniform | heterogenous and there existed problems, such as a fall of the quality of the melt pulp obtained. In particular, coniferous trees are relatively difficult to digest and bleach, and there has been a demand for the development of a technique for efficiently producing high-quality dissolving pulp. Further, it is necessary to sufficiently reduce the kappa number in oxygen delignification, but there is also a problem that the pulp viscosity is greatly reduced.

  As a result of intensive studies on the above problems, when pre-hydrolyzed and kraft-cooked to produce dissolved pulp by subjecting the kraft-cooked pulp to oxygen delignification, magnesium oxide is added in the process of oxygen delignification. By adding, it discovered that the viscosity reduction of a pulp was suppressed and obtained a high quality melt | dissolution kraft pulp, and completed this invention.

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing a melt | dissolution kraft pulp by performing prehydrolysis, manufacture of the high quality melt | dissolution kraft pulp in which the fall of the viscosity was suppressed is made possible, fully reducing a copper number.

  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 Pinus genus, and Pseudotuga (hereinafter abbreviated as P.) menziesii (Dacrasfer) and P. japonica for Pinus radiata. 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.

Hydrothermal treatment step In the present invention, as a pretreatment before kraft cooking, hydrothermal treatment is performed on the chips 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.

  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 will be excessive and the α-cellulose content will be reduced, resulting in a decrease in pulp yield, and condensing of lignin will lead to deterioration in digestibility in the subsequent kraft cooking process. .

  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 of digestibility in the subsequent kraft cooking process. .

  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 tank (prehydrolysis tank) is preferably 1 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.

Chip Cleaning / Recovery Step Next, the pre-hydrolyzed wood chip is recovered by removing the pre-hydrolyzed solution and thoroughly washing the chip with water. 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 filter cloth is provided in a container used for prehydrolysis, and washing water is introduced from the lower part of the container and extracted from the screen for countercurrent washing.

The chips after washing the kraft cooking process are put together with the cooking liquor into the digester and used for kraft cooking. Moreover, you may use for cooking of correction craft 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. The kappa number of the unbleached pulp after washing is preferably 9-15, and may be 10-13.

  The kraft cooking step can be performed by putting the hydrothermally treated wood chips together with the kraft cooking liquid into 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. .

  The cooking solution preferably has an effective alkali addition rate of 16 to 22% by mass per weight of the dry wood chip. If the effective 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 degraded.

  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.

  Kraft cooking is preferably performed in a temperature range of 120 to 180 ° C, more preferably 140 to 160 ° 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. The cooking time in the present invention is the time from when the cooking temperature reaches the maximum temperature until the temperature starts to drop, and the cooking time is preferably 60 minutes to 600 minutes, preferably 120 minutes to 360 minutes. Further preferred. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 600 minutes, the pulp production efficiency deteriorates, which is not preferable.

  Moreover, the kraft cooking in this invention can set process temperature and process time by setting H factor (Hf) as a parameter | 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 viscosity of the dissolved kraft pulp obtained after kraft cooking (measured according to ISO5351) is 550 to 950 mL / g, and the viscosity of the dissolved kraft pulp after oxygen delignification (measured according to ISO5351) is 500 to 700 mL / g. It is preferable that By making the viscosity of dissolved kraft pulp obtained after kraft cooking and dissolved kraft pulp after oxygen delignification within these ranges, it is possible to suppress the pulp viscosity that occurs during the subsequent multi-stage bleaching treatment. it can. Pulp viscosity is an indicator of the degree of cellulose polymerization, but if the degree of cellulose polymerization is too low, the filterability of the viscose solution obtained from the dissolved pulp may be deteriorated. Moreover, it is thought that it is effective in the improvement of pulp quality by making the fall of the viscosity until oxygen delignification treatment mild.

  In the present invention, the unbleached pulp obtained after cooking is subjected to oxygen delignification treatment on the pulp obtained by kraft 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.

  In the present invention, an oxygen delignification treatment is performed in the presence of a magnesium compound in order to suppress a decrease in the viscosity of the pulp. The magnesium compound is preferably added in an amount of 0.01 to 0.1% by mass based on the pulp dry weight. When the added amount is less than 0.01% by mass, the reduction in the viscosity of the pulp is insufficient. If it exceeds 0.1% by mass, the effect of suppressing the viscosity will reach its peak, and the quality will decrease due to the increase in the amount of ash. Examples of the magnesium compound include magnesium oxide, magnesium hydroxide, magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium nitrate, magnesium lactate, and magnesium acetate, and magnesium oxide is preferable. The reason why low-water-soluble magnesium oxide is preferred is not clear, but it is preferentially adsorbed on the pulp fiber surface compared to highly water-soluble magnesium sulfate. It is believed that the pulp can be effectively protected from the reducing hydroxy radicals.

  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.

  In addition, you may add a magnesium compound in the alkali extraction stage which adds oxygen and / or hydrogen peroxide. Similar to the oxygen delignification treatment, the effect of suppressing the decrease in the viscosity of the pulp can be expected. The magnesium compound is preferably added in an amount of 0.01 to 0.1% by mass based on the pulp dry weight. When the added amount is less than 0.01% by mass, the reduction in the viscosity of the pulp is insufficient. If it exceeds 0.1% by mass, the effect of suppressing the viscosity will reach its peak, and the quality will decrease due to the increase in the amount of ash. Examples of the magnesium compound include magnesium oxide, magnesium hydroxide, magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium nitrate, magnesium lactate, and magnesium acetate, and magnesium oxide is preferable.

  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]
Radiata pine wood chips were sieved using a sieve (gyro shifter) to obtain wood chips of size 9.5 to 25.4 mm.

Using a rotary autoclave, water was added to this wood chip so as to have a liquid ratio of 3.2 (L / kg), and pre-hydrolysis was carried out at a pre-hydrolysis temperature of 170 ° C. for 30 minutes and P-factor = 550. .
After completion of the pre-hydrolysis, the chip and the pre-hydrolyzed solution were separated with a 300 mesh filter cloth, and hand-washed with 30 ° C. warm water at 60 ° C. for 15 seconds.
Subsequently, using a rotary autoclave again, the kraft cooking chemical solution was infiltrated at 150 ° C. for 85 minutes, and then cooked 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 conversion value) and a composition having a sulfidity of 28%, the liquid ratio of the wood chip to the cooking chemical was 3.2 (L / kg).
After digestion, the obtained unbleached pulp is subjected to oxygen delignification treatment, followed by chlorine dioxide treatment (D ₁ ) -alkali extraction / hydrogen peroxide treatment (Ep) -chlorine dioxide treatment (D ₂ ). Bleached dissolved kraft pulp was obtained. The treatment conditions are as follows, and the amount of chemical added is relative to the dry pulp weight.
・ Oxygen delignification treatment: Pulp concentration 10% by mass, oxygen addition amount 3.5% by mass, sodium hydroxide addition amount 3.0%, magnesium oxide addition amount 0.04%, temperature 98 ° C., 60 minutes (D ₁ ): Pulp concentration 10% by mass, chlorine dioxide addition amount 1.2% by mass, temperature 55 ° C., 60 minutes, alkali extraction / hydrogen peroxide treatment (Ep): pulp concentration 10% by mass, sodium hydroxide addition amount 0.93% by mass, hydrogen peroxide addition amount 1.03% by mass, temperature 70 ° C., 90 minutes, chlorine dioxide treatment (D ₂ ): pulp concentration 10% by mass, chlorine dioxide addition amount 0.66% by mass, temperature 75 ℃, 240 minutes

The viscosity of the dissolved kraft pulp after kraft cooking, the dissolved kraft pulp after oxygen delignification, and the bleached dissolved kraft pulp was measured by the following method, and the results are shown in Table 1. In addition, about the melt | dissolution kraft pulp after kraft cooking and the melt | dissolution kraft pulp after oxygen delignification, the whiteness was also measured about the melt | dissolution kraft pulp after oxygen delignification, and the white melt | dissolution kraft pulp.
-Copper number: measured according to JIS P 8221.
Viscosity: measured according to ISO5351
Whiteness: A handsheet was prepared according to JIS P 8209, and the ISO whiteness was measured according to JIS P 8148: 2001.

[Example 2]
Bleach-dissolved kraft pulp was produced in the same manner as in Example 1 except that the active alkali addition rate (AA) was 20% in kraft cooking. Table 1 shows the results of the kappa number, whiteness, and viscosity of the obtained dissolved kraft pulp after kraft cooking, the dissolved kraft pulp after oxygen delignification, and the bleached dissolved kraft pulp.

[Comparative Example 1]
A bleach-dissolved kraft pulp was produced in the same manner as in Example 1 except that magnesium oxide was not added in the oxygen delignification treatment. Table 1 shows the results of the kappa number, whiteness, and viscosity of the obtained dissolved kraft pulp after kraft cooking, the dissolved kraft pulp after oxygen delignification, and the bleached dissolved kraft pulp.

[Comparative Example 2]
A bleach-dissolved kraft pulp was produced in the same manner as in Example 2 except that magnesium oxide was not added in the oxygen delignification treatment. Table 1 shows the results of the kappa number, whiteness, and viscosity of the obtained dissolved kraft pulp after kraft cooking, the dissolved kraft pulp after oxygen delignification, and the bleached dissolved kraft pulp.

  As shown in Table 1, when oxygen delignification was bleached to an equivalent kappa number, the bleached dissolved kraft pulps of Comparative Examples 1 and 2 had a reduced viscosity compared to the bleached dissolved kraft pulps of Examples 1-2. Was big. Moreover, when it bleached completely to equivalent whiteness, the viscosity of the bleaching melt | dissolution kraft pulp of Examples 1-2 was higher than the comparative example.

Claims (3)

(A) hydrothermally treating wood chips to hydrolyze hemicellulose contained in the wood chips;
(B) a step of washing the treated wood chips and collecting the wood chips;
(C) a process of producing pulp by kraft cooking the recovered wood chips,
(D) a step of subjecting the kraft digested pulp to an oxygen delignification treatment,
A method for producing a dissolved kraft pulp, comprising adding a magnesium compound in the step of performing the oxygen delignification treatment.   The manufacturing method of the melt | dissolution kraft pulp of Claim 1 whose addition amount of a magnesium compound is 0.01-0.1 mass% with respect to pulp absolute dry weight.   The method for producing a dissolved kraft pulp according to claim 1 or 2, wherein the magnesium compound is magnesium oxide.