JP2014001470A - Manufacturing method for dissolving kraft pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for manufacturing dissolving pulp having high quality by a kraft pulping method using conifer materials as raw materials.SOLUTION: There is provided a method for manufacturing dissolving pulp from conifer materials including the steps of: adding water to wood chips including conifer chips, processing the wood chips at a temperature ranging from 150 to 180°C for 30 to 400 minutes and performing decomposition or elution of hemi-cellulose components contained in the wood chips, (a); cleaning the wood chips after processing and collecting the wood chips, (b); and causing the wood chips collected to be subjected to a kraft pulping process and manufacturing pulp, (c).

Description

TECHNICAL FIELD OF THE INVENTION

  The present invention relates to a method for producing dissolving pulp from conifers. In particular, the present invention relates to a method for producing a high-quality dissolved kraft pulp from a material of the genus Larch that is hardly digestible and difficult to bleach.

Conventional technology

  Softwood is one of the main raw materials for dissolving kraft pulp. There are many types of conifers, and their digestibility and bleaching properties vary depending on the species, age, and location of production. It is well known that softwood contains a large amount of resin, which affects the digestibility and bleaching properties. Further, as substances other than lignin and resin that affect the digestibility and bleachability of pulp, there are a wide variety of low-molecular phenols that are plant pigments and precursors. These plant pigments are roughly classified into flavonoids, xanthones, and quinones. Proanthocyanidin-like substances and low-molecular-weight phenols belonging to the flavonoid pigments and polyphenols are known to be abundant in heartwood, especially in the coniferous trees of Larch, Togasawara, and Sugi. Yes. Especially in old-aged trees, the content increases. Therefore, in order to effectively utilize these hardly digestible and hardly bleachable materials as pulp materials, measures for reducing the influence of resins, proanthocyanidins and the like are necessary.

  Resins in coniferous wood are mainly composed of resins, oils and fats in a narrow sense. The composition of this narrowly defined resin is a resin acid (such as abietic acid and pimaric acid), a resin alcohol, and a resin, and the resin acid is the main component. Oils and fats are those in which glycerin and fatty acids are combined, and as fatty acids, palmitic acid, stearic acid, oleic acid, linolenic acid and the like are known.

  In the kraft cooking method, the resin contained in conifers consumes alkaline cooking liquor due to neutralization and saponification reaction with alkaline cooking liquor, so that the dissolution reaction of lignin, the original purpose of cooking, is hindered. The As a result, the kappa number of the pulp after cooking increases, and it becomes necessary to add a large amount of bleaching chemicals in the subsequent bleaching process, and the whiteness of the pulp after bleaching is reduced.

  Proanthocyanidins are condensed tannins existing in trees, that is, compounds obtained by condensing or polymerizing flavan-3-ols or flavan-3,4-diols as units, and these are treated by acid treatment with dianiline, delphinidin, and verargonidin. This name is given because it produces anthocyanidins. Accordingly, proanthocyanidins are dimer, trimer, tetramer, and even 30-mer macromolecular procyanidins, prodelphinidins, propelargonidines and the like and their stereoisomers. Is a generic term that includes In one embodiment, the proanthocyanidins are 2-30 mers having flavan-3-ol or flavan-3,4-ol represented by the following formula as a structural unit (wherein R1 is hydrogen, galloyl group) Or a glycopyranosyl group, R2 represents hydrogen or a hydroxyl group, and R3 and R4 represent hydrogen, a hydroxyl group, or a methoxy group).

  There are many phenolic hydroxyl groups in the molecular structure of proanthocyanidins. As can be seen from this, proanthocyanidins are acidic substances. Therefore, when kraft cooking of coniferous trees rich in proanthocyanidin-like substances and low molecular weight phenols such as Larch, Togasawara, Sugi, etc., phenolic substances such as proanthocyanidins are an alkaline cooking solution. And the dissolution reaction of lignin, which is the original purpose of cooking, is inhibited. In addition, proanthocyanidins react with lignin during cooking to produce colored materials that are highly difficult to bleach. As a result, the kappa number of the pulp after cooking increases, and it becomes necessary to add a large amount of bleaching chemicals in the subsequent bleaching process, and the whiteness of the pulp after bleaching is reduced. Proanthocyanidins are acid-decomposed in the bleaching stage where the reaction proceeds in the acidic region to produce anthocyanidins that are colored substances. Anthocyanidins develop color whether acidic or alkaline, and exhibit red in the acidic region and blue in the alkaline region. Therefore, if proanthocyanidins are not sufficiently removed by the end of cooking and a large amount of proanthocyanidins is brought into the bleaching process, bleached pulp is colored, causing a problem that the hue changes or whiteness decreases.

  The problem of coniferous resin has long been recognized and its countermeasures have been studied. However, in the case of the Kraft cooking method (KP method) in which an alkaline cooking solution is added, the resin is saponified and dispersed, so there are fewer resin obstacles compared to the sulfite cooking method (SP method). The main purpose was to reduce the amount of resin remaining in the bleached pulp. For example, Patent Document 1 discloses that a pulp suspension obtained by treating a lignocellulosic material is first adjusted in concentration, and then oxidized bleach containing a specific concentration of alkali (peroxide bleach, hypochlorite). A technique is described in which the pulp content is improved by reducing the resin content by applying a mechanical treatment in the presence of. Further, Patent Document 2 incorporates a hydrogen peroxide bleaching stage into a bleached kraft pulp (BKP) bleaching sequence, and a specific acid treatment is provided at the first stage to perform hydrogen peroxide bleaching before the bleaching without using a stabilizer. , A technique for obtaining high-quality pulp in terms of viscosity, whiteness, PC value, de-resin, and the like is disclosed.

  Although there is no mention of coniferous resins and proanthocyanidins, Patent Document 3 proposes a technique for producing bleached pulp with high whiteness from a hard-to-digest material of conifers. Specifically, an alkali solution of hydrogen peroxide added with an anthraquinone stabilizer and a chelating agent as auxiliary agents is used as a cooking chemical solution, and a hard-to-cook material of conifers is treated at 175 to 200 ° C., and a kappa number of 40 or less. Untreated bleached pulp, treated in two steps with an alkaline solution of hydrogen peroxide, and with a kappa number of 15 or less and a hunter whiteness of 60% or more until further whitening with a chlorine bleach The processing technique is shown. In Patent Document 4, lignocellulosic material is prehydrolyzed and subsequently subjected to alkali neutralization at 140 to 160 ° C., and the neutralized prehydrolyzed lignocellulose material is kraft-dissolved and dissolved. A method for producing pulp in a batch mode is disclosed.

Japanese Patent No. 1540750 JP-A-61-83389 Japanese Examined Patent Publication No. 63-35758 Japanese Patent No. 2984798

  As described above, phenolic substances such as proanthocyanidins contained in wood are considered to be one of the causative substances of difficult to digest and difficult to bleach. The presence of such a phenolic substance causes a colored substance to be produced in kraft cooking using an alkaline cooking liquid, and also causes a colored substance to be produced in bleaching after cooking. The present inventors investigated prior art that improved the digestibility and bleachability by actively removing phenolic compounds when producing pulp from larch, Togasawara, and Sugi. However, no such technology was found. In particular, larch and the like among conifers contain a large amount of arabinogalactan, so that the cooking efficiency tends to decrease and a technology for producing high-quality dissolving pulp is required.

  On the other hand, although not in the field of paper pulp, techniques for extracting proanthocyanidins have been reported in the fields of food and cosmetics. Proanthocyanidins are known to be useful as production raw materials for food and cosmetic antioxidants, deodorants, pharmaceuticals, and the like. For example, JP 2000-229834 A has proanthocyanidins as a main component. Regarding cosmetics containing pine resin-derived components, it is described that proanthocyanidins are extracted from pine bark such as French coastal pine, and examples of extraction solvents include water, ethanol, aqueous ethanol, benzene, and acetone. .

  The problem to be solved by the present invention is to provide a technique for producing high-quality dissolving pulp by a kraft cooking method using softwood as a raw material.

Although not limited to this, this invention includes the following invention.
(1) (a) A step of adding water to a wood chip containing a coniferous chip and treating it at a temperature of 150 to 180 ° C. for 30 to 400 minutes to decompose or elute hemicellulose contained in the wood chip, (b) A method for producing dissolved pulp from coniferous wood, comprising: washing wood chips after treatment and collecting the wood chips; and (c) kraft cooking the collected wood chips to produce pulp.
(2) In the step a, the following formula:
P factor = ∫exp (40.48-15106 / T) dt
[In the formula, T is an absolute temperature, and is integrated over time from the time when water is added to the wood chip until the end of cooking]
The method according to (1), wherein the treatment is performed so that the P factor represented by the formula is 350 to 800.
(3) The method according to (1) or (2), wherein the wood chip comprises a Larix wood chip.
(4) The method according to (1) or (2), wherein the wood chip comprises a Pinus wood chip.
(5) The method according to any one of (1) to (4), further comprising a step of bleaching the kraft digested pulp.

  ADVANTAGE OF THE INVENTION According to this invention, a melted pulp can be efficiently manufactured by the kraft cooking method using coniferous wood as a raw material.

BEST MODE FOR CARRYING OUT THE INVENTION

  The present invention relates to a method for producing dissolving pulp by kraft cooking. 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 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 including softwood chips. If the wood chip of this invention contains the chip | tip of coniferous wood, the size and tree species will not be restrict | limited in particular, The chip | tip of a single kind of wood or the mixture of 2 or more types of wood may be sufficient. In the present invention, a high-quality dissolving pulp can be efficiently produced even for tree species that are relatively difficult to digest and bleach, such as conifers. In the present invention, for example, a larch genus or a pine genus wood chip can be preferably used as the softwood chip. As for the genus Larix, for example, Larix (hereinafter abbreviated as L.) leptolepis (Larix), L. laricina (Tamarack), L. occidentalis (Larix larch), L. decidua (European larch), L. gmeliniii (Guimatsu) and the like. Examples of conifers other than the genus Larix include Pinus radiata (Pinus radiata) for Pinus genus and Pseudotsuga (hereinafter abbreviated as P.) menziesii (Dacrasfer), P. Regarding Cryptomeria japonica, such as japonica (Togasawara).

Pre-hydrolysis step In the present invention, as a pre-treatment prior to kraft cooking, the chip is hydrolyzed to decompose and remove the hemicellulose content in the wood chips into water-soluble sugars. The hydrolysis treatment (prehydrolysis) as a pretreatment is carried out 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 prehydrolysis 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 30 to 400 minutes, more preferably 35 to 250 minutes, and further preferably 40 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. .

  Moreover, the prehydrolysis process in this invention can set process temperature and process time by making P-factor (PF) into a parameter | index. The P-factor is a standard that represents 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 the time integration from the time when the chip 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 prehydrolysis treatment in the present invention is preferably performed in a range where the P factor (Pf) is 350 to 800. If it is less than Pf350, the removal of hemicellulose will become inadequate, and the delignification improvement effect by removing hemicellulose will also decrease. On the other hand, if it exceeds Pf800, hydrolysis becomes excessive and the α-cellulose content is reduced, resulting in a decrease in pulp yield, and condensing of lignin leads to deterioration in digestibility in the subsequent kraft cooking process.

  The prehydrolysis step can be performed by putting wood chips and water in a pressure-resistant container, but the shape and size of the container are not particularly limited. The liquid ratio of wood chips to water 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. . 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, an extraction screen can be provided in a container used for prehydrolysis, and washing water can be introduced from the bottom of the container and extracted from the screen for countercurrent cleaning.

The chips after washing the kraft cooking process are put into the digester together with the cooking liquor and subjected to kraft cooking under the general conditions (active alkali addition amount, sulfidity, liquid ratio, maximum temperature, holding time, H factor, etc.). 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. That is, the step of impregnating and holding the alkaline aqueous solution of the present application may be installed separately from the conventional apparatus or part for the permeation treatment of the cooking liquid. 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 10-22, and may be 12-20.

  The kraft cooking process can be performed by putting the pre-hydrolyzed wood chips together with the kraft cooking liquid in a pressure resistant container, but the shape and size of the container are not particularly limited. The liquid ratio of wood chips to water 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. .

  Kraft 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. 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 to 10 hours, preferably 60 minutes to 240 minutes. preferable. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 240 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 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 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 to 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) manufactured by the present invention has hemicellulose and various phenols removed, a high-quality dissolved kraft pulp can be easily manufactured by ordinary oxygen delignification treatment or bleaching treatment. Compared with the case where hardwood is used as a raw material, a high-quality dissolving pulp having a low hemicellulose content can be obtained.

  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
Wood chips made from larch were sieved using a sieving machine (gyro shifter) to obtain wood chips having a size of 9.5 to 25.4 mm.

  Using a rotary autoclave, water is added to this wood chip so that the liquid ratio becomes 3.2 (L / kg), and pre-hydrolysis is performed at a pre-hydrolysis temperature of 170 ° C. for about 50 minutes (P factor: about 500). It was.

After completion of the pre-hydrolysis, the chip and the pre-hydrolyzed liquid were separated with a 300 mesh filter cloth, and hand-washed with 30 ° C. warm water at 60 ° C. for 15 seconds.
Subsequently, the kraft cooking chemical solution was permeated again using a rotary autoclave at 150 ° C. for 85 minutes, and then cooking was performed at a cooking temperature of 158 ° C. for 230 minutes and H-factor (HF) = 1300. The chemical solution is changed at an active alkali addition rate (AA) of 18 to 24%, and the active alkali is 105 g / L (Na ₂ O conversion value), NaOH 75.6 g / L (Na ₂ O conversion value), Na ₂ S 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).

After the completion of cooking, the kappa number (KN), the total yield, and the amount of hemicellulose of the obtained unbleached pulp were measured by the following methods. The results are shown in Table 1.
-Copper value of unbleached pulp: Measured according to JIS P 8221.
Total yield: calculated from the absolute dry weight of wood chips before cooking and the absolute dry weight of unbleached pulp obtained after cooking.
-Amount of hemicellulose (amount of hemicell): Measured according to NREL / TP510-42618.

Example 2
Digestion was carried out in the same manner as in Example 1 except that the raw material was radiatapine, and the kappa number, total yield, and amount of hemicellulose of the obtained unbleached pulp were measured by the following methods. The results are shown in Table 1. .

Comparative Example 1
Kraft cooking was carried out in the same manner as in Example 1 except that pre-hydrolysis was performed for about 30 minutes (Pf: about 300) to obtain dissolved pulp. The unbleached pulp obtained was measured for kappa number, total yield, and hemicellulose content, and the results are shown in Table 1.

Comparative Example 2
Kraft cooking was performed in the same manner as in Example 1 except that prehydrolysis was performed for about 90 minutes (Pf: about 900) to obtain dissolved pulp. The unbleached pulp obtained was measured for kappa number, total yield, and hemicellulose content, and the results are shown in Table 1.

Comparative Example 3
Kraft cooking was carried out in the same manner as in Example 2 except that pre-hydrolysis was performed for about 30 minutes (Pf: about 300) to obtain dissolved pulp. The unbleached pulp obtained was measured for kappa number, total yield, and hemicellulose content, and the results are shown in Table 1.

Comparative Example 4
Kraft cooking was performed in the same manner as in Example 2 except that pre-hydrolysis was performed for about 90 minutes (Pf: about 900) to obtain dissolved pulp. The unbleached pulp obtained was measured for kappa number, total yield, and hemicellulose content, and the results are shown in Table 1.

Claims (5)

(A) adding water to wood chips containing softwood chips, treating the wood chips at a temperature of 150 to 180 ° C. for 30 to 400 minutes, and decomposing or eluting 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,
A method for producing dissolving pulp from coniferous wood. In the step a, the following formula:
P factor = ∫exp (40.48-15106 / T) dt
[In the formula, T is an absolute temperature, and is integrated over time from the time when water is added to the wood chip until the end of cooking]
The method according to claim 1, wherein the treatment is performed so that the P-factor represented by the formula is 350 to 800.   The method of claim 1 or 2, wherein the wood chips comprise Larix wood chips.   3. A method according to claim 1 or 2, wherein the wood chips comprise Pinus wood chips.   The method in any one of Claims 1-4 further including the process of bleaching the pulp which carried out the kraft cooking.