JP6518287B2 - Method of producing dissolved kraft pulp - Google Patents

Description

  The present invention relates to a method of making dissolved kraft pulp. In particular, the present invention relates to a method for producing a dissolved kraft pulp having a high α-cellulose content of 95% or more.

  The dissolving pulp used for the production of cellulose acetate generally has a high α-cellulose content of 92% or more. The α-cellulose is a portion which does not dissolve when the pulp is treated with 17.5% sodium hydroxide, and cellulose is the main component. To obtain this degree of alpha-cellulose content, significant amounts of hemicellulose must be removed, for example, by steam prehydrolysis prior to digestion of kraft pulp, or by alkaline extraction in the bleaching process, There is a considerable manufacturing cost. High contents of pentosan and other hemicelluloses are not preferred in order to achieve sufficient acetylation in the production of cellulose acetate.

  In U.S. Pat. No. 5,952,015, lignocellulosic material is prehydrolyzed, followed by alkali neutralization treatment at 140-160.degree. C., and the neutralized prehydrolyzed lignocellulosic material is kraft digested and dissolved kraft A process is disclosed for producing pulp in batch mode.

Japanese Patent Publication No. 9-507697

However, the method of Patent Document 1 can not sufficiently remove hemicellulose, and can not produce a dissolved kraft pulp suitable for cellulose acetate use.
An object of the present invention is to provide a technique for efficiently producing a dissolved kraft pulp having a high α-cellulose content, which is useful for cellulose acetate applications.

  As a result of earnestly examining the above problems, it is difficult to dissolve the dissolved pulp obtained by kraft digestion by performing prehydrolysis (prehydrolysis) at a relatively low temperature and high alkali concentration. We have found that hemicellulose can be removed efficiently and that a dissolved kraft pulp with a high α-cellulose content can be produced, thus completing the present invention.

Although not limited to this, the present invention includes the following aspects.
(1) Producing a dissolved kraft pulp comprising the steps of: kraft-digesting pre-hydrolyzed wood chips; subjecting the digested pulp to oxygen delignification; and subjecting the oxygen-delignified pulp to alkali purification The method as described above, wherein the pulp is treated in an alkali purification step with a sodium hydroxide concentration of 3 to 25% by mass, a temperature of 20 to 50 ° C., and a treatment time of 10 to 60 minutes.
(2) The method according to (1), wherein the α-cellulose content of the dissolved kraft pulp is 95% or more.
(3) The method according to (1) or (2), wherein the hemicellulose content of the dissolved kraft pulp is 2.5% or less.
(4) Dissolved kraft pulp manufactured by the method according to any one of (1) to (3). (5) A method for producing cellulose acetate, comprising producing dissolved kraft pulp by the method according to any one of (1) to (3), and producing cellulose acetate using the dissolved kraft pulp as a raw material.
(6) Cellulose acetate manufactured by the method as described in (5).

  According to the present invention, it is possible to efficiently produce a dissolved kraft pulp having a high α-cellulose content and a low hemicellulose content. The dissolved kraft pulp obtained according to the invention is suitable for applications where high alpha cellulose content is required, such as cellulose acetate applications.

  In the present invention, dissolved kraft pulp (DKP) is a dissolved pulp produced by kraft digestion (KP method). Dissolving pulp means a chemically refined pulp with high cellulose purity, and in a preferred embodiment, the α-cellulose content is 90% or more. In general, wood contains three major components of cellulose, lignin, hemicellulose, and a small amount of resin, ash, etc. However, dissolved pulp has high cellulose purity, chemical fiber, cellophane, plastic, synthetic paste, and various other cellulose-based materials It is widely used as a raw material of derivatives.

  The dissolved kraft pulp of the present invention is prepared by kraft digesting pre-hydrolyzed wood chips, subjecting the obtained unbleached kraft pulp to oxygen delignification and further treating it in at least one alkali purification step to dissolve kraft pulp Manufacture. In the alkali purification step, treatment is carried out with a sodium hydroxide concentration of 3 to 25% by mass, a temperature of 20 to 50 ° C., and a time of 10 minutes to 60 minutes.

  In the case of using kraft pulp dissolved in the present invention as a raw material of cellulose acetate, it is preferable that the α-cellulose content is 95% or more and the hemicellulose content is 2.5% or less. Since cellulose acetate is used as a raw material for an optical material of a liquid crystal display device, such as a hard coat film, an antireflective film, an antiglare film, etc., it is particularly required that the cellulose purity is high. Since the dissolved kraft pulp is digested under alkaline conditions, a hemicellulose component which is difficult to dissolve in alkali remains. In the present invention, hemicellulose can be efficiently removed from pulp by treating pulp under high alkali concentration and low temperature conditions, ie, sodium hydroxide concentration of 3 to 25 mass%, temperature of 20 to 50 ° C., and time of 10 minutes to 60 minutes. Could be removed.

  The raw material of the present invention is wood chips. The wood chip of the present invention is not particularly limited in its size or tree type as long as it contains either softwood or hardwood chips, and even if it is a single type of wood chip, it is a chip in which two or more kinds of wood are mixed. May be. In the present invention, high-quality dissolved pulp can be efficiently produced even for tree species that are considered relatively difficult to digest or bleach, such as softwood.

As chips of softwood used in the present invention, for example, larch and pine wood chips can be suitably used. With regard to Larch, for example, Larix (hereinafter abbreviated as L.) leptolepis (Larch), L. perfringens. laricina (Tamalac), L. occidentalis (Saibu Larch), L. L. decidua (European larch), L. gmelinii (Guimatsu) etc. are mentioned. Moreover, as conifers other than Larch, for example, Pinus radiata (P. radiata) such as Pinus radiata (P. radiata), Pseudotsuga (hereinafter abbreviated as P.) menziesii (D. ク ラ ス フ フ ァ ー ー), P. As for the cedar genus, such as japonica (Togasawara), Cryptomeria japonica etc. can be mentioned.

  In the present invention, for example, Eucalyptus wood chips can be suitably used as hardwood chips. As Eucalyptus species, Eucalyptus (hereinafter abbreviated as E.) calophylla, E. coli as a tree species containing a large amount of quino component. citriodora, E .. diversicolor, E. globulus, E.I. grandis, E.I. gummifera, E.I. marginata, E.I. nesophila, E.I. Examples of old trees such as Nitens and tree species containing a large amount of ellagtannic acid include E. coli. amygdalina, E .. camaldulensis, E. coli. delegatensis, E. gigantea, E.I. muelleriana, E.I. obliqua, E.I. regnans, E.I. sieberiana, E. Examples of old trees such as viminalis and tree species containing a large amount of leucoanthocyanidins include E. coli. camaldulensis, E. coli. An aged tree such as marginata can be mentioned.

Pre-hydrolysis Step In the present invention, as pretreatment before kraft digestion, the chips are subjected to a hydrolysis treatment to decompose hemicellulose components in wood chips into water-soluble sugars and remove them. Hydrolysis treatment (prehydrolysis) as pretreatment is carried out by treating wood chips with hot water. The water to be added may be hot water or steam. Since the progress of hydrolysis produces an organic acid and the like, the pH of the treatment solution is generally 2 to 5.

  The prehydrolysis treatment is preferably performed in a temperature range of 150 to 180 ° C. If the temperature is less than 150 ° C., hemicellulose removal is insufficient, and if it exceeds 180 ° C., the hydrolysis is excessive and the α-cellulose content also decreases. The treatment time is not particularly limited, but is preferably 30 to 400 minutes, more preferably 35 to 250 minutes, and still more preferably 40 to 150 minutes. If the treatment time is too short, removal of hemicellulose will be insufficient, and the effect of improving the delignification by removal of hemicellulose will also be reduced. On the other hand, if the treatment time is too long, the hydrolysis is excessive and the α-cellulose content is reduced to cause a decrease in pulp yield, and the lignin condensation causes deterioration in digestibility in the subsequent kraft digestion process. .

  Moreover, the prehydrolysis process in this invention can set process temperature and processing time by making a 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 represented by the following formula in the present invention, and the time integration from the time the chip and water are mixed to the completion of the digestion Calculated by doing.

PF = ∫ln ⁻¹ (40.48-15106 / T) dt
[Wherein, T represents the 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 Pf 350, removal of hemicellulose will be insufficient, and the improvement effect of delignification by removal of hemicellulose will also decrease. Moreover, when Pf 800 is exceeded, hydrolysis is excessive and the α-cellulose content is reduced to cause a decrease in pulp yield, and condensation of lignin causes deterioration in digestibility in the subsequent kraft digestion step.

Although a prehydrolysis process can be performed by putting a wood chip and water in a pressure resistant container (prehydrolysis pot), the shape or size of the container is not particularly limited.
It is preferable that the ratio at the time of supplying a wood chip and water to a prehydrolysis pot shall be 1-2.3 L / kg. The ratio of wood chips to water supplied to the prehydrolysis kettle is also called the dynamic liquor ratio and is expressed as the amount of water per kg of wood chips. If the dynamic liquid ratio is less than 1.0 L / kg, hydrolysis is insufficient because there is too little water relative to the wood chips, and the liquid ratio is 2.3 L / kg.
Is not preferable because a sufficient gas phase can not be secured at the top of the prehydrolysis pot. The water includes not only water supplied with the wood chips but also water contained in the wood chips, drain water and the like.

  In the prehydrolysis step, 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 2.0 to 4 0 L / kg is more preferred. If the liquid ratio is less than 1.0 L / kg, hydrolysis is insufficient because the amount of water in the wood chips is too small, and if the liquid ratio exceeds 5.0 L / kg, the size of the container becomes too large. Not so desirable. Also, if necessary, a small amount of mineral acid may be added.

  Next, the pre-hydrolyzed wood chips are recovered by removing the pre-hydrolysis solution and washing the chips thoroughly with water. Inadequate washing can have adverse effects in the subsequent digestion step.

  Washing and removal of the hydrolyzate can be performed by using a general solid-liquid separation device or the like. For example, an extraction screen may be provided in a container used for prehydrolysis, and washing water may be introduced from the lower portion of the container and extracted from the screen for countercurrent cleaning.

Kraft cooking process The chips after washing are put into a digester together with cooking liquor and subjected to kraft cooking under general conditions. Moreover, you may use for cooking of MCC, EMCC, ITC, modified kraft methods, such as Lo-solid. Further, the digestion type such as 1-vessel liquid phase type, 1-vessel vapor phase / liquid phase type, 2-vessel liquid phase / gas phase type, 2-vessel liquid phase type, etc. is not particularly limited. That is, the step of impregnating the alkaline aqueous solution of the present invention and holding the same may be installed separately from the device or part intended for the infiltration treatment of the conventional cooking liquid. Preferably, the unbleached pulp that has been digested is washed with a washing apparatus such as a diffusion washer after extracting cooking liquor. In the case of softwood, the kappa number of the unbleached pulp after washing is preferably 10-22, and may be 12-20. In the case of hardwoods, it is preferably 5 to 20, and may be 6 to 16.

  The kraft digestion step can be carried out by placing the prehydrolyzed wood chips together with the kraft digestion solution 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. .

  It is preferable to carry out the kraft cooking in a temperature range of 120 to 220 ° C., more preferably 150 to 180 ° C. When the temperature is too low, delignification (reduction of Kappa number) is insufficient, while when the temperature is too high, the degree of polymerization (viscosity) of cellulose is reduced. In addition, the cooking time in the present invention is the time from when the cooking temperature reaches the maximum temperature to when the temperature starts to decrease, but the cooking time is preferably 120 minutes to 10 hours, and 60 minutes to 240 minutes. preferable. If the digestion time is less than 60 minutes, pulping does not proceed, and if it exceeds 240 minutes, the pulp production efficiency is unfavorably deteriorated.

  Moreover, the kraft cooking in this invention can set processing temperature and processing time by making H-factor (HF) into a parameter | index. H-factor is a standard that represents the total amount of heat given to the reaction system during the digestion process, and is represented by the following equation. The H-factor is calculated by time integration from the time when the chips and water are mixed to the time when the digestion is completed.

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

Oxygen Delignification Step In the present invention, the pulp obtained by kraft cooking is subjected to an oxygen delignification treatment. As the oxygen delignification used in the present invention, known medium concentration method or high concentration method can be suitably applied. The medium concentration method is preferably performed at a pulp concentration of 8 to 15% by mass, and the high concentration method is performed at 20 to 35% by mass. Sodium hydroxide or potassium hydroxide can be used as the alkali in oxygen delignification, and oxygen gas from the cryogenic separation method, oxygen from PSA (Pressure Swing Adsorption), VSA (Vacuum Swing Adsorption) can be used as oxygen gas. 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 mass%, and the temperature is 80 The treatment time is 20 to 180 minutes, and other known conditions can be applied. In the present invention, the oxygen delignification treatment may be performed multiple times.

  In the present invention, lignin can be efficiently removed from pulp by subjecting the dissolving pulp obtained by kraft cooking to oxygen delignification treatment. In particular, oxygen delignification is environmentally preferable as compared to chlorination delignification, and is suitable for removing lignin.

Alkali Purification Step In the present invention, the oxygen delignified pulp is purified with alkali to remove the hemicellulose remaining in the pulp. As described above, since dissolved kraft pulp is digested under alkaline conditions, a hemicellulose component which is difficult to dissolve in alkali remains in the pulp. Therefore, in the present invention, the pulp is treated at a high alkali concentration and at a low temperature to remove hemicellulose contained in the pulp. Specifically, the alkali treatment is performed on the pulp at a sodium hydroxide concentration of 3 to 25% by mass, a temperature of 20 to 50 ° C., and a time of 10 minutes to 60 minutes.

  This alkali purification step can also be performed as part of a multistage bleaching step. In one aspect, the pulp subjected to the oxygen delignification process may be sent, for example, to a washing step, and after washing, may be sent to a multistage bleaching process to perform a multistage bleaching process. The multistage bleaching process 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 preferred to combine known bleaching agents such as peracids and bleaching aids. For example, the first stage of the multistage bleaching process uses chlorine dioxide bleaching stage (D) and ozone bleaching stage (Z), the second stage uses alkali extraction stage (E) and hydrogen peroxide stage (P), and the third and subsequent stages Preferably, a bleaching sequence using chlorine dioxide or hydrogen peroxide is used. The number of stages after the third stage is not particularly limited, but in consideration of energy efficiency, productivity, etc., it is preferable that the process ends in three or four stages in total. In addition, a chelating agent treatment stage with ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) or the like may be inserted during multistage bleaching.

  EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto. In the present invention,% and the like are by weight unless otherwise specified, and the numerical range includes the end point.

Example 1
Wood chips made of Eucalyptus globulus were sieved using a sieving machine (gyro shifter) to obtain wood chips of 9.5 to 25.4 mm in size.

  Using a rotary autoclave (volume: about 2.5 L), add water to this wood chip so that the liquid ratio is 3.2 L / kg, and pre-hydrate for about 50 minutes at 170 ° C (P factor: about 500) It was disassembled.

After completion of the prehydrolysis, the chip and the prehydrolyzate were separated using a 300 mesh filter cloth, and hand washing was carried out with 15 times the amount of chip with 60 ° C. warm water for 30 seconds.
Subsequently, the kraft digestion solution was infiltrated again at 150 ° C. for 85 minutes using a rotary autoclave, and then kraft digestion was performed at a digestion temperature of 160 ° C. for 60 minutes (H factor: about 600). Kraft cooking solution contains active alkali 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), degree of sulfurization 28% The liquid ratio between wood chips and cooking chemical was 3.2 L / kg.

After completion of the 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 ). A bleached dissolved kraft pulp was obtained. The treatment conditions are as follows, and the amount of chemical added is based on the weight of dry pulp.
-Oxygen delignification treatment: Pulp concentration 23% by mass, oxygen addition amount 2.9% by mass, sodium hydroxide addition amount 2.2%, temperature 98 ° C, 60 minutes-Chlorine dioxide treatment (D ₁ ): Pulp concentration 10% %, Chlorine dioxide addition amount 1.2 mass%, temperature 55 ° C., 60 minutes · alkaline extraction / hydrogen peroxide treatment (Ep): pulp concentration 10 mass%, sodium hydroxide addition amount 0.93 mass%, hydrogen peroxide Addition amount: 1.03 mass%, temperature: 70 ° C, 90 minutes, chlorine dioxide treatment (D ₂ ): pulp concentration: 10 mass%, chlorine dioxide addition amount: 0.33 mass%, temperature: 75 ° C, bleaching solution obtained for 240 minutes For kraft pulp, prepare a slurry so that the pulp concentration is 10% by mass, add 40% by mass (sodium hydroxide concentration 4% by mass) of sodium hydroxide to the weight of dry-dried pulp, temperature 3 ° C., was alkali refining processing time 30 min.

After thoroughly washing the obtained dissolved pulp with water, the hemicellulose content and α-cellulose content of the dissolved pulp were measured by the following methods.
Hemicellulose content: measured according to NREL / TP510-42618.
-Alpha-cellulose content: It measured according to TAPPI T203.

Example 2
Bleached and dissolved kraft pulp was prepared in the same manner as in Example 1 except that the amount of sodium hydroxide added was 80% by mass (sodium hydroxide concentration: 8% by mass) in alkali purification.

Example 3
Bleached and dissolved kraft pulp was prepared in the same manner as in Example 2 except that the temperature was 40 ° C. in alkali purification.

Example 4
Bleached and dissolved kraft pulp was prepared in the same manner as in Example 2 except that the temperature was 50 ° C. in alkali purification.

Comparative Example 1
Bleached and dissolved kraft pulp was prepared as described in Example 1 except that no alkaline purification was performed.

  Table 1 shows the results. As apparent from Table 1, the bleached and dissolved kraft pulps of Examples 1 to 4 have a hemicellulose content of less than 2.5% and an α-cellulose content of 95% or more, and are suitable as a raw material for cellulose acetate there were.

Claims (9)

Pre-hydrolyzing treatment, removing the pre-hydrolyzing solution and then washing the wood chips with water and recovering;
Kraft digesting the recovered wood chips;
Subjecting the digested pulp to oxygen delignification,
Alkaline purifying the oxygen delignified pulp for 10 to 60 minutes under conditions of sodium hydroxide concentration 3 to 25% by mass and 20 to 50 ° C .;
A process for producing dissolved kraft pulp for producing cellulose acetate , comprising
Pre-hydrolysis treatment is as follows:
P factor = ∫ exp (40.48-15106 / T) dt
[Wherein, T is the absolute temperature at a certain point in the prehydrolysis treatment]
Using water in the form of hot water at 150 to 180 ° C. for 40 to 150 minutes so that the P factor of prehydrolysis represented by is 350 to 800, the liquid ratio of water per 1 kg of wood chips is The above method, which is carried out in a pressure-resistant container at a pressure of 1.0 to 5.0 L / kg.   The method according to claim 1, wherein the prehydrolysis treatment is performed under the condition that the liquid ratio of water per kg of wood chips is 1.5 to 5.0 L / kg.   The method according to claim 1 or 2, wherein the prehydrolyzate is removed using a solid-liquid separator.   The method according to any one of claims 1 to 3, wherein the kraft cooking is carried out at 120 to 220 ° C for 60 to 240 minutes.   The method according to any one of claims 1 to 4, wherein the kraft digestion is carried out in a pressure-resistant vessel under the condition that the liquor ratio of kraft cooking liquor per 1 kg of wood chips is 1.0 to 5.0 L / kg.   The method according to any one of claims 1 to 5, wherein the oxygen delignification treatment is performed under conditions of an alkali addition rate of 0.5 to 4% by mass and 80 to 140 ° C. The method according to any one of claims 1 to 6 , wherein the α-cellulose content of the dissolved kraft pulp is 95% or more. The method according to any one of claims 1 to 7 , wherein the hemicellulose content of the dissolved kraft pulp is 2.5% or less. A method for producing cellulose acetate, comprising producing dissolved kraft pulp by the method according to any one of claims 1 to 8 and producing cellulose acetate using the dissolved kraft pulp as a raw material.