JP6305715B2 - Method for producing dissolving pulp - Google Patents

Description

  The present invention relates to a dissolving pulp manufacturing technique including a prehydrolysis step (hydrothermal treatment step). In particular, according to the present invention, in the production of dissolving pulp, the manufacturing process of dissolving pulp can be appropriately controlled by analyzing the Brix value of the prehydrolyzed effluent.

  The present invention also relates to a technique for estimating the P factor, which is an important factor in the prehydrolysis step, by analyzing the Brix value of the prehydrolyzed effluent and managing the quality of the dissolved pulp.

  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. Further, if hemicellulose such as pentosan remains in the dissolved pulp, filtration and spinning in the production of rayon 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.

JP-T 09-507697 (Patent No. 2984798)

  In the production of dissolving pulp (dissolving kraft pulp) by kraft cooking, a technique is known in which pre-hydrolysis treatment (hydrothermal treatment) is applied to wood chips before kraft cooking to remove hemicellulose and the like contained in the wood chips. Since prehydrolysis (hydrothermal treatment) affects kraft cooking, which is a subsequent process, it is important in the production of dissolved kraft pulp to appropriately manage and control the prehydrolysis.

  The processing temperature and processing time (residence time) are known as factors affecting the prehydrolysis step (hydrothermal treatment step), and the P factor (Pf) is used as an index representing the total amount of heat given to the reaction system. Are known.

  However, it is difficult to accurately measure the residence time in the hydrothermal treatment process in continuous operation, and therefore it may be difficult to calculate an accurate P factor in actual operation. In addition, since it is difficult to grasp the residence time, if the residence time cannot be appropriately adjusted, the quality of the resulting dissolved pulp will be deteriorated, resulting in a large loss in the production of the dissolved pulp.

  It is also possible to actually analyze the wood chip after the prehydrolysis treatment and determine the prehydrolysis effect by sugar analysis or the like. However, since analysis such as sugar analysis is complicated and time-consuming, it is difficult to perform sugar analysis in order to control the manufacturing process at the actual manufacturing site of dissolved kraft pulp.

  Thus, conventionally, there has been no method for simply evaluating the prehydrolysis state in a short time for the prehydrolysis treatment in the production of dissolved kraft pulp. In view of such a situation, an object of the present invention is to develop a technique for appropriately managing the prehydrolysis treatment in the production of dissolving pulp and appropriately controlling the manufacturing process of dissolving pulp.

  As a result of intensive studies on the above problems, the present inventors have found that the state of prehydrolysis can be appropriately grasped by the Brix value (Brix value) of the prehydrolysis drainage liquid, and have completed the present invention. That is, the present inventors have found that the Brix value of the prehydrolyzed effluent has a high correlation with the P factor of the prehydrolyzed treatment, and is also related to the kappa number and the amount of hemicellulose of the obtained pulp. And in manufacture of the dissolving pulp provided with a pre-hydrolysis process, it becomes possible to control the manufacturing process of a dissolving pulp simply and appropriately by using the Brix value of pre-hydrolysis drainage as a parameter | index.

Although not limited to this, this invention includes the following aspect.
(1) (a) a step of hydrothermally treating wood chips to hydrolyze hemicellulose contained in the wood chips, (b) a step of separating and recovering the wood chips after hydrolysis and the hydrolysis drainage, c) A method for producing dissolved pulp, comprising the step of measuring the Brix value of the recovered hydrolyzed effluent, and (d) digesting the recovered wood chips to obtain dissolved pulp.
(2) The method according to (1), wherein the recovered wood chips are kraft-digested to obtain dissolved kraft pulp.
(3) From the Brix value of the prehydrolyzed effluent, the following formula 1 in step (a):
Pf = ∫ln-1 (40.48-15106 / T) dt (Formula 1)
[Wherein T represents the absolute temperature of the prehydrolyzed solution]
The method according to (1) or (2), further comprising a step of estimating a P factor (Pf) represented by:
(4) The method according to any one of (1) to (3), further including a step of estimating the kappa number and / or hemicellulose content of the dissolving pulp obtained in the step (c) from the Brix value of the prehydrolyzed effluent. the method of.
(5) The method according to any one of (1) to (4), wherein the temperature and / or residence time of the prehydrolyzed liquid in step (a) is controlled using the Brix value of the prehydrolyzed liquid as an index.
(6) A pre-hydrolysis kettle for hydrothermally treating wood chips, and an absorbance measuring machine for measuring the Brix value of the pre-hydrolysis drainage discharged from the pre-hydrolysis kettle, Equipment for manufacturing.
(7) The apparatus according to (6), further comprising a digester for digesting the wood chips hydrothermally treated in the prehydrolysis tank.

  ADVANTAGE OF THE INVENTION According to this invention, in manufacture of melt | dissolution pulp provided with a prehydrolysis process, the manufacture process of melt | dissolution pulp can be easily and appropriately controlled by using the Brix value of prehydrolysis waste liquid as a parameter | index. In particular, according to the present invention, it is possible to estimate the P-factor of the prehydrolysis treatment (hydrothermal treatment), the characteristics of the obtained pulp, and the like in continuous operation and the like, so that it is possible to manage the manufacturing process of dissolved pulp online.

  The reason why the Brix value of the prehydrolysis drainage is an appropriate index for the prehydrolysis treatment is considered as follows. That is, the prehydrolysis drainage generated by hydrothermal treatment contains organic substances mainly composed of hemicellulose-derived saccharide eluted from the chip, and the amount of these organic substances and the Brix value are highly correlated. It is considered that the degree of the prehydrolysis treatment can be evaluated by the Brix value of the decomposition effluent.

FIG. 1 is a graph showing the relationship between the Brix value of prehydrolyzed effluent and the prehydrolyzed solid content (Experimental Example 1). FIG. 2 is a graph showing the relationship between the Brix value of the prehydrolysis drainage and the Pf value of the prehydrolysis treatment (Experimental Example 1). FIG. 3 is a graph showing the relationship between the Pf value of the prehydrolysis treatment and the hemicellulose content of the dissolved kraft pulp (Experimental Example 1). FIG. 4 is a graph showing the relationship between the Brix value of prehydrolyzed effluent and the hemicellulose content of dissolved kraft pulp (Experimental Example 1). FIG. 5 is a graph showing the relationship between the Pf value of the prehydrolysis treatment and the kappa number of the dissolved kraft pulp (Experimental Example 1). FIG. 6 is a graph showing the relationship between the Brix value of prehydrolyzed effluent and the kappa number of dissolved kraft pulp (Experimental Example 1). FIG. 7 is a graph showing the relationship between the Brix value of the prehydrolysis waste liquid and the Pf value of the prehydrolysis treatment (Experimental Example 2). FIG. 8 is a graph showing the relationship between the Brix value of prehydrolyzed effluent and the hemicellulose content of dissolved kraft pulp (Experimental Example 2). FIG. 9 is a graph showing the relationship between the Brix value of prehydrolyzed effluent and the kappa number of dissolved kraft pulp (Experimental Example 2).

  The present invention relates to a technology for producing dissolving pulp. The dissolving pulp means a chemically purified pulp having a high cellulose purity, and in a preferred embodiment, the α-cellulose content (content) is 90% or more, and a higher α-cellulose content can also be obtained ( For example, 93% or more, 96% or more, 98% or more). Here, the α-cellulose content of the pulp is a portion that does not dissolve when the pulp is treated with 17.5% sodium hydroxide. 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.

  In a preferred embodiment, the dissolving pulp of the present invention is a dissolving sulfite (sulfite) pulp and / or a dissolving kraft pulp, and the dissolving sulfite pulp (DSP) is a dissolving pulp produced by a sulfite method, a dissolving kraft pulp (DKP). ) Is a dissolving pulp produced by the kraft cooking method (KP method).

  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 (hereinafter abbreviated as 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.

Prehydrolysis process (hydrothermal treatment process)
In the present invention, as a pretreatment before cooking, the 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.

  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 an organic substance mainly composed of sugars generated by hydrolysis of hemicellulose. It was found that there is a correlation between the Brix value, which is an indicator of the amount of organic matter, and the P factor. The Brix value is also called sugar content, and is a measurement value measured with a Brix meter (sugar content meter), which is a measure of the amount of water-soluble organic substances or water-soluble inorganic substances such as sugars, organic acids, salts, etc. in the solution. 1 Brix corresponds to a sucrose concentration of 1% by mass. As demonstrated in the experimental examples described later, there is a correlation between the Brix value and the P factor, and the above-mentioned Brix value increases as the amount of organic substances eluted increases as the prehydrolysis progresses.

  As described above, in order to obtain a high-quality dissolving pulp, it is necessary to set the P-factor within an appropriate range. However, it is difficult to accurately measure the residence time of wood chips in continuous operation. The residence time may vary depending on the state. If the relationship between the P factor and the Brix value of the prehydrolyzed liquid is expressed in advance in a calibration curve or a mathematical formula, the P factor can be estimated from the Brix value of the prehydrolyzed liquid. More specifically, hydrothermal treatment is performed with different P factors by changing the temperature and residence time, the Brix value is measured for the prehydrolyzed liquid obtained at that time, and the relationship between the P factor and the Brix value is expressed by a calibration curve or a mathematical formula. Expressed in Furthermore, if the correlation with the quality (kappa number, hemicellulose content) of the pulp after cooking in the subsequent step is converted into data, it can be used as a measure of the pulp quality after cooking.

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 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 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.

In the present invention, the Brix value of the recovered hydrolyzed effluent is measured. The Brix value can be measured by measuring the refractive index with a Brix meter (sugar meter), and the Brix value of the prehydrolyzed effluent can be measured by a conventional method.

  In the production of dissolving pulp (DP), it is possible to determine whether hemicellulose and various phenols are properly removed by appropriately managing the P factor of the prehydrolysis treatment. High quality dissolving pulp can be easily produced by oxygen delignification treatment or bleaching treatment.

  As described above, the absorbance of the prehydrolyzed effluent at a wavelength of 260 to 300 nm has a high correlation with the P factor, so that it is not a P factor that is difficult to measure in actual operation. It is possible to estimate the degree of the decomposition treatment and the characteristics of the finally obtained dissolving pulp. Specifically, if the relationship between the Brix value of the prehydrolyzed effluent and the properties such as the kappa number and / or hemicellulose content of the resulting dissolved pulp is expressed in advance in a calibration curve or a mathematical formula, this correlation data Based on the absorbance described above, the quality of the resulting dissolved pulp can be estimated.

  In the present invention, the prehydrolysis step can be controlled using the Brix value of the prehydrolyzed liquid as an index. That is, by controlling the temperature and / or residence time of the prehydrolyzed liquid using the above-mentioned Brix value as an index, the entire system can be easily and appropriately controlled.

Dissolving pulp production apparatus From another viewpoint, the present invention can be understood as a dissolving pulp production apparatus. That is, the present invention is an apparatus for producing dissolving pulp, and measures the Brix value of a pre-hydrolysis tank for hydrothermally treating wood chips and a pre-hydrolysis waste liquid discharged from the pre-hydrolysis tank. A Brix measuring machine. In a further preferred embodiment, the apparatus of the present invention further comprises a digester for digesting wood chips hydrothermally treated in the prehydrolysis tank.

  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.

Experimental 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 equipped with a thermometer, water was added to 200 g of this wood chip absolutely dry so that the liquid ratio became 3.2 (L / kg), and the prehydrolysis treatment was carried out batchwise at a temperature of 168 to 170 ° C. went. The residence time in the prehydrolysis was changed in the range of 0.05 minutes (3 seconds) to 70 minutes, and the P factor was changed in the range of 150 to 950 (samples 2 to 8). In the table below, sample 1 is a sample obtained by kraft cooking without pre-hydrolysis treatment.

  After completion of the prehydrolysis, the chip and the prehydrolyzed liquid were separated with a 300 mesh filter cloth to obtain a prehydrolyzed chip and a prehydrolyzed effluent. The prehydrolyzed effluent was filtered through a filter having a pore size of 0.45 μm, and the Brix value of the filtrate was measured with a Brix meter (PAL-1, manufactured by Atago Co., Ltd.). The solid content concentration of the filtrate was also measured.

  Furthermore, the prehydrolyzed chip was hand-washed with 60 ° C. hot water, 15 times the amount of the chip, for 30 seconds.

Then, again using a rotary autoclave, infiltrate the kraft cooking chemical solution at 150 ° C. for 85 minutes, and then kraft cooking at a cooking temperature of 158 ° C. for 210 minutes and H factor (Hf) = 1500. Pulp was obtained. The kraft cooking chemical solution has an active alkali addition rate (AA) of 16.5%, an active alkali of 105 g / L (converted value of Na ₂ O), NaOH of 75.6 g / L (converted value of Na ₂ O), Na ₂ S of 29.4 g / The composition of L (Na ₂ O equivalent value) and sulfidity 28%, the liquid ratio of wood chips and cooking chemical liquid was 3.2 (L / kg).

About the unbleached kraft melt | dissolution pulp obtained by kraft cooking, the kappa number and hemicellulose content were measured in accordance with the following method.
-Copper number (KN): Measured according to JIS P 8221.
-Amount of hemicellulose: Measured according to NREL / TP510-42618.

FIG. 1 shows the relationship between the Brix value of the prehydrolyzed effluent and the solid content concentration. As is clear from FIG. 1, the Brix value of the prehydrolyzed effluent and the solid content concentration have a very high correlation (R ² = 0.9487), and the Brix value of the prehydrolyzed effluent is the primary concentration and the primary content. (Linear) relationship.

  FIG. 2 shows the relationship between the Brix value of the prehydrolyzed effluent and the P factor. As is clear from FIG. 2, the Brix value of the prehydrolyzed effluent and the P factor showed a correlation, and in particular, a high correlation was shown in the region where the P factor was 100 to 700 (Brix value was 2 to 6).

  FIG. 3 shows the relationship between the P factor and the hemicellulose content of the dissolved kraft pulp, and FIG. 4 shows the relationship between the Brix value of the prehydrolyzed effluent and the hemicellulose content of the dissolved kraft pulp. As shown in FIG. 3, the amount of hemicellulose in the dissolved kraft pulp decreases as the P factor of the prehydrolysis treatment increases, and the amount of hemicellulose in the dissolved kraft pulp decreases by increasing the degree of the prehydrolysis treatment. I understand. As is clear from FIG. 4, the hemicellulose content of the dissolved kraft pulp decreased as the Brix value of the prehydrolyzed effluent increased. From this result, it is understood that the quality of the dissolved kraft pulp (the amount of hemicellulose) can be predicted using the Brix value of the prehydrolyzed effluent, similarly to the P factor.

  Further, FIG. 5 shows the relationship between the P factor and the kappa number of the dissolved kraft pulp, and FIG. 6 shows the relationship between the Brix value of the prehydrolyzed effluent and the kappa number of the dissolved kraft pulp. As is clear from FIGS. 5 and 6, the relationship between the Brix value of the prehydrolysis waste liquid and the kappa number of the pulp was the same as the relationship between the P factor and the kappa number of the dissolved kraft pulp.

  Here, as can be seen from FIG. 5, when the P factor increases, the kappa number efficiently decreases to a certain region. This tendency is the same in the case of the Brix value of the prehydrolyzed effluent (FIG. 6). When the Brix value of the prehydrolyzed effluent is set to a specific range, the kappa number of the resulting dissolved kraft pulp is efficiently increased. Can be reduced.

  Therefore, in the past, the P-factor was used to predict and control the prehydrolysis treatment and the quality of the resulting dissolved kraft pulp, but the prehydrolysis treatment and the dissolved kraft were determined using the Brix value of the prehydrolysis wastewater. It was found that the pulp production process can be controlled.

Experimental example 2
The experiment was conducted in the same manner as in Experimental Example 1 except that the raw material wood chips were changed from Radiata Pine wood chips to larch wood chips.

  The results are shown in Table 2 and FIGS. As is clear from FIG. 7, it was shown that the Brix value of the prehydrolyzed effluent correlates with the P factor even when the wood chip as the raw material is changed.

  As in Experimental Example 1, it was shown that the Brix value of the prehydrolyzed effluent correlates with the kappa number of the dissolved kraft pulp and the amount of hemicellulose (FIGS. 8 and 9).

  Further, as in Experimental Example 1, it was found that there is an appropriate range for efficiently reducing the kappa number when the Brix value is used as an index.

Claims (7)

(A) a step of hydrolyzing wood chips in a pressure resistant container at 150 to 180 ° C. for 15 to 400 minutes to hydrolyze hemicellulose contained in the wood chips;
(B) a step of separating and recovering the wood chip after hydrolysis treatment and the hydrolysis drainage;
(C) measuring the Brix value of the recovered hydrolyzed effluent,
(D) cooking the recovered wood chips to obtain dissolved pulp;
A method for producing dissolving pulp.   The method according to claim 1, wherein the recovered wood chips are kraft-distilled to obtain dissolved kraft pulp. From the Brix value of the prehydrolyzed effluent, the following formula 1 in step (a):
Pf = ∫ln ⁻¹ (40.48-15106 / T) dt (Formula 1)
[Wherein T represents the absolute temperature of the prehydrolyzed solution]
The method according to claim 1, further comprising a step of estimating a P-factor (Pf) represented by: The method in any one of Claims 1-3 which further includes the process of estimating the kappa number and / or hemicellulose content of the dissolving pulp obtained at a process ( d ) from the Brix value of a prehydrolysis waste liquid.   The method according to any one of claims 1 to 4, wherein the temperature and / or residence time of the prehydrolyzed liquid in step (a) is controlled using the Brix value of the prehydrolyzed liquid as an index. A prehydrolysis kettle for hydrothermal treatment of wood chips at 150-180 ° C. for 15-400 minutes ;
An absorbance measuring machine for measuring the Brix value of the prehydrolyzed effluent discharged from the prehydrolyzing kettle;
An apparatus for producing dissolving pulp.   The apparatus according to claim 6, further comprising a digester for digesting the wood chips hydrothermally treated in the prehydrolysis tank.