JP6581137B2 - Method for producing dissolved kraft pulp - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

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

Conventional technology

  Hardwood is one of the main raw materials for dissolving kraft pulp. Eucalyptus wood and southern wood are becoming the main raw materials for hardwood kraft pulp. There are many types of eucalyptus wood, and their digestibility and bleaching properties differ depending on the species, age, and location of production.

Eucalyptus wood is broadly divided into ash type and blood wood type, and the ash type has a relatively small problem when used industrially as a pulp material because the amount of extracted components is small.
On the other hand, in the blood wood type, various problems due to the acidic extract components occur, and a mitigation measure is necessary.

  Eucalyptus wood contains polyphenols called quino and acidic extraction components such as ellagic acid. The kino component is a secretion of a tree mainly composed of condensed tannin, has a color tone from light yellow to deep red, and has different characteristics depending on the tree species. Ellagic acid is present in the wood in a free state, but is mainly present in the form of ellagitannic acid formed from gallic acid and ellagic acid. This ellagitannic acid is hydrolyzed during cooking to ellagic acid. Ellagic acid exhibits strong acidity and is easily oxidized under alkaline conditions, becomes a quinone type, strongly adsorbs to pulp cellulose, and adversely affects pulp whiteness. Furthermore, at high temperature and high pressure, it is easy to polymerize due to its phenolic property, and becomes a sticky substance.

The said acidic extraction component contained in a eucalyptus material will reduce a pulp yield, if there is much content. Also, alkaline chemicals such as alkaline cooking and kraft cooking are wasted. This consumption is faster than alkali consumption due to elution of lignin. For this reason, when the addition rate of the alkaline chemical to the chip is constant, the eucalyptus material containing a large amount of the acidic extract component causes a problem of high kappa value of unbleached pulp (in other words, decreased whiteness), This increases the load of the subsequent bleaching process, and causes problems such as increased use of bleaching chemicals or reduced whiteness of bleached pulp. Or when the kappa number of the pulp after cooking is made constant, the alkali addition rate with respect to a chip | tip must be raised, and the problem that the cost of pulping increases will be caused.
In addition, problems such as generation of scale derived from extracted components in washer, diffuser, etc., or the viscosity of concentrated black liquor significantly increases and the vacuum evaporation becomes poor, which deteriorates the flammability of black liquor in the recovery boiler. cause.

Countermeasures for various problems of the above-mentioned poorly digestible materials have been studied.
For example, in the case of alkaline cooking, lignin and carbohydrates consume alkali, but acidic extract components react with alkali more quickly than these. A two-stage cooking method has been devised in which a reaction is first performed with the residual alkali in the black liquor and then the white liquor is added for cooking (see Non-Patent Document 1).

  Also, in research using an experimental digester, the whiteness of kraft pulp can be improved and the amount of active alkali added can be reduced by extracting eucalyptus wood with hot water for 4 to 24 hours compared with the same kappa number. It is reported that there is no difference between the pulp yield and the chlorine consumption (see Non-Patent Document 2).

  Furthermore, it is clear from Non-Patent Document 3 that the acidic extraction component contained in the eucalyptus material can be easily lightened by oxidation with oxygen under alkaline conditions and can improve black liquor flammability. It is described that the whiteness of the pulp can be improved by alkali oxidation pretreatment prior to cooking.

  Patent Document 1 relates to a pulp production method by alkali cooking of wood containing quino substances, and in particular, wood chips containing quino substances are pretreated with an alkaline cooking liquid at 30 ° C. or higher and below the elution temperature of alkali lignin. Thus, a pulp manufacturing method is disclosed in which a quino material is leached and then cooked.

  Patent Document 2 aims to rationally neutralize the acidity of a large amount of exudate exuded from eucalyptus chips to reduce the corrosion resistance against metal and improve the digestibility of chips and reduce cooking chemicals and bleaching chemicals. As described above, a method of spraying an alkaline solution on eucalyptus chips and depositing the alkali so as to be 0.3 to 1.5% by weight with respect to the chips and then depositing for at least two weeks is shown.

  In Patent Document 3, for the purpose of extracting the alkali-soluble extract component most effectively and advantageously when cooking wood chips having a large amount of alkali-soluble extract components such as eucalyptus chips, the average thickness of the wood is described. Method of passing through two metal rolls having a gap of 20 to 50% and rotating in opposite directions and rotating at a circumferential speed ratio of 1: 1.1 to 1.5, followed by alkali digestion It is shown.

  Patent Document 4 discloses a technique for improving black liquor concentration and flammability after pulp cooking, for example, a kraft pulp waste liquid of a material containing a large amount of polyphenols or tannins, such as a southern material such as eucalyptus. A technique is disclosed in which 5-35% of dissolved substances are oxidatively decomposed with a required amount of pressurized air or the like to enable chemical recovery in the kraft method.

  In Patent Document 5, in a processing step of concentrating and burning the pulp liquor mainly composed of eucalyptus wood to causticize the green liquor and regenerating the cooked liquor, green liquor or green liquor is added to the dilute waste liquid before concentration. After adding causticized white liquor, mixing, air oxidizing, or concentrating to some extent after air oxidation, adding caustic soda to raise the pH of the waste liquid, then concentrating to a predetermined concentration and burning It is shown.

  In Patent Document 6, a lignocellulosic material is prehydrolyzed and subsequently subjected to alkali neutralization at 140 to 160 ° C., and the neutralized prehydrolyzed lignocellulosic material is kraft-cooked to dissolve pulp. Is disclosed in a batch fashion.

Japanese Examined Patent Publication No. 47-24162 JP-A-53-134903 Patent No. 1506085 Japanese Examined Patent Publication No. 48-42242 Patent No. 1021680 Japanese Patent No. 2984798

Sloman, A. R., Appita, 14 (2), 57 (1960) Nelson, P. F., et al., Appita, 24 (2), 101 (1970) Hemingway, R.W., et al., Appita, 25 (6), 445 (1972)

  As described above, the mushroom component and the like contained in wood are considered to be one of the causative substances of non-digestibility and non-bleachability. Such a kino component causes a colored substance to be produced in kraft cooking using an alkaline cooking solution, and also causes a colored substance to be produced in bleaching after cooking.

  In view of such a situation, the present inventors have examined a technique for improving digestibility and bleaching by actively removing mushroom components when producing pulp from Eucalyptus hardwood. 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 hardwood.

Although not limited to this, this invention includes the following invention.
(1) (a) A step of adding water to wood chips containing hardwood chips, treating the 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 method for producing dissolved pulp from hardwood material, comprising: washing wood chips after treatment and collecting the wood chips; and (c) producing pulp by kraft cooking of the collected wood chips.
(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 Eucalyptus wood chip.
(4) The method according to any one of (1) to (3), wherein the hardwood chips include blood wood type Eucalyptus broadleaf chips.
(5) The method according to any one of (1) to (4), further comprising a step of bleaching the kraft digested pulp.

  According to the present invention, dissolving pulp can be efficiently produced by kraft cooking using hardwood 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 other cellulosic materials. Widely used as a raw material for derivatives.

The raw material of the present invention is a wood chip including a hardwood chip. As long as the wood chip of the present invention includes a chip of hardwood, its 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, high-quality dissolving pulp can be efficiently produced even for hardwoods that are considered to be relatively difficult to digest and bleach. In the present invention, for example, Eucalyptus wood chips can be suitably used as the hardwood chips. Regarding the Eucalyptus genus, tree species rich in mushroom components include Eucalyptus (hereinafter abbreviated as E.) calophylla, E. citriodora, E. diversicolor, E. globulus, E. grandis, E. gummifera, E. marginata, E Aged trees such as nesophila and E. nitens, and tree species rich in ellagitannic acid include E. amygdalina, E. camaldulensis, E. delegatensis, E. gigantea, E. muelleriana, E. obliqua, E. regnans, E Aged trees such as sieberiana and E. viminalis and tree species rich in leucoanthocyanidins include old trees such as E. camaldulensis and E. marginata.

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 55.

  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, the hydrolysis becomes excessive and the α-cellulose content is reduced, leading to a decrease in pulp yield, and the degradation of the digestibility in the subsequent kraft cooking process is caused by the condensation of lignin.

  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. If necessary, a small amount of mineral acid may be added.

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. The unbleached pulp that has been cooked is washed with a device such as a diffusion washer after extracting the cooking liquor. The kappa number of unbleached pulp after washing is preferably 5-20, and may be 6-16.

  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 140 to 170 ° 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 a time from when the cooking temperature reaches the maximum temperature until the temperature starts to decrease, but the cooking time is preferably 60 minutes or more and 320 minutes or less, and preferably 60 minutes or more and 240 minutes or less. Is preferred. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 320 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.) 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) produced by the present invention is free of hemicellulose and quino components, high-quality dissolved kraft pulp can be easily produced by ordinary oxygen delignification treatment or bleaching treatment. Although hardwood contains a larger amount of hemicellulose than conifers, the present invention provides a high-quality dissolved pulp having a hemicellulose content equivalent to that of conifers.

  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 eucalyptus and globulas 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 was added to this wood chip so that the liquid ratio became 3.2 (L / kg), and prehydrolysis was performed at a prehydrolysis temperature of 170 ° C. for 50 minutes (P factor: about 500). .

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 160 ° C. for 60 minutes and H-factor (HF) = 600. The chemical solution was changed at an active alkali addition rate (AA) of 16 to 20%, and an active alkali of 105 g / L (Na ₂
O conversion value), NaOH 75.6 g / L (Na ₂ O conversion value), Na ₂ S 29.4 g / L (Na ₂ O conversion value), composition of 28% sulfidity, liquid ratio of wood chips and cooking chemicals 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 performed in the same manner as in Example 1 except that the raw material was domestic hardwood (domestic L wood mix chip), and the kappa number, total yield, and amount of hemicellulose of the resulting 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 carried out in the same manner as in Example 1 except that pre-hydrolysis was carried out 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: 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 (8)

(A) Water is added to wood chips containing hardwood chips, and the following formula:
P factor = ∫exp (40.48-15106 / T) dt
[Wherein, T is the absolute temperature from the time when water is added to the wood chip to the end of pre-hydrolysis]
Pre-hydrolysis for decomposing or elution of hemicellulose contained in wood chips using water at a temperature of 150-180 ° C. for 30-400 minutes so that the P-factor of pre-hydrolysis represented by Process,
(B) removing the pre-hydrolyzed solution , washing the treated wood chips with water, and collecting the wood chips;
(C) Kraft cooking of the collected wood chips in a pressure-resistant container at a temperature of 140 to 170 ° C. for 60 to 320 minutes and a liquid ratio of kraft cooking liquid per kg of wood chips of 1.0 to 5.0 L / kg Process,
A process for producing dissolved kraft pulp.   The method according to claim 1, wherein the kraft cooking is performed at 140 to 160 ° C.   The method according to claim 1 or 2, wherein kraft cooking is carried out in a pressure-resistant container at a liquid ratio of kraft cooking liquid per kg of wood chips of 1.0 to 4.5 L / kg.   The method in any one of Claims 1-3 whose cellulose content of melt | dissolution kraft pulp is 90% or more.   The method according to claim 1, wherein the hardwood chip is a Eucalyptus hardwood chip.   The method according to claim 1, wherein the hardwood chip comprises a blood wood type Eucalyptus broadleaf chip.   The method according to claim 1, wherein the hardwood chip comprises a Eucalyptus globulus chip.   The method according to any one of claims 1 to 7, further comprising a step of bleaching the kraft digested pulp.