JP4366959B2 - Pretreatment method for wood chips for pulp - Google Patents

Description

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【図１】

【００２７】
【図２】

【００２８】
【発明の効果】
難蒸解性のユーカリ属(Eucalyptus)の単材チップまたは該ユーカリ属の材を含む混合材チップを、アルカリ性薬剤による蒸解に先立ち、熱水含浸工程とこれに続く保持工程とから成る熱水抽出工程で前処理することにより、後続の蒸解工程におけるアルカリ性薬剤の無駄な消費を抑え、蒸解性を低コストで改善することができる。また、活性アルカリ添加率を一定とした場合には、未晒パルプのカッパー価を低減でき、未晒パルプの白色度が向上するという効果がある。一方、従来の熱水抽出処理技術に比べ、本発明の熱水抽出処理は極めて短時間で良いため、該抽出処理に必要な熱エネルギーは少なく済み、熱水抽出処理設備の規模を小さくすることができるなどの優位な効果もある。[0001]
BACKGROUND OF THE INVENTION
A wood chip pretreatment method prior to cooking with an alkaline chemical solution, which is a digestibility when pulping a hard-to-cook Eucalyptus single material chip or a mixed material chip containing the Eucalyptus material with an alkaline chemical solution The present invention relates to a pretreatment method for wood chips that can be improved in a short time and at a low cost.
[0002]
[Prior art]
At present, most chemical pulp is produced by kraft cooking. Eucalyptus wood and southern wood have become 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.
[0003]
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.
[0004]
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, if the rate of addition of the alkaline chemical to the chip is constant, the eucalyptus wood that contains a large amount of the acidic extract component causes the problem of the high kappa value of unbleached pulp (in other words, the decrease in 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.
[0005]
Various problems of the above hard-to-cook materials are recognized for a long time, and countermeasures are being 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 the reaction is first performed with the remaining 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, extracting white eucalyptus with hot water for 4 to 24 hours improves the whiteness of kraft pulp and reduces the amount of active alkali added compared to the same kappa number In addition, it has been reported that there is no difference in pulp yield and chlorine consumption (see Non-Patent Document 2). In addition, it is clear that acidic extract components contained in eucalyptus wood can be easily lightened by oxidation with oxygen under alkaline conditions, and it is clear that black liquor combustion can be improved, so alkali oxidation pretreatment prior to kraft cooking Describes that the whiteness of the pulp can be improved (see Non-Patent Document 3). In addition, it 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 alkaline cooking liquor at 30 ° C. or more and below the elution temperature of alkali lignin, A pulp production method for cooking is shown (see Patent Document 1). Also, eucalyptus chips are used to rationally neutralize the acidity of a large amount of exudate that exudes from eucalyptus chips to reduce corrosion resistance to metals and to improve the digestibility of chips and to reduce cooking chemicals and bleaching chemicals. A method is described in which an alkali solution is sprayed on the substrate and the alkali is deposited so as to be 0.3 to 1.5% by weight with respect to the chip and then deposited for at least two weeks (see Patent Document 2). In addition, when cooking wood chips having a high amount of alkali-soluble extract components such as eucalyptus wood chips, the purpose of extracting the alkali-soluble extract components most effectively and advantageously is to remove the wood chips from 20 to the average thickness of the wood. A method is described in which alkali digestion is performed after passing between two metal rolls that have a 50% gap, face each other in opposite directions and rotate at a peripheral speed ratio of 1: 1.1 to 1.5 (Patent Document) 3).
[0006]
Examples of techniques for improving the concentration and flammability of black liquor after pulp digestion include 5 to 5% of dissolved substances in kraft pulp waste liquid of materials containing a large amount of polyphenols or tannins, such as southern materials such as eucalyptus. A technique is disclosed in which 35% is oxidatively decomposed with a required amount of pressurized air or the like to enable chemical recovery in the kraft method (see Patent Document 4). Also obtained by causticizing the green liquor or green liquor into the dilute waste liquid before concentration in the process of regenerating the liquor by causticizing the green liquor obtained by concentrating and burning the pulp cooking liquor mainly composed of eucalyptus wood After adding the white liquor to be mixed, air-oxidized, or after being air-oxidized or concentrated to some extent after air-oxidization, caustic soda is added to increase the pH of the waste liquid, and then it is concentrated to a predetermined concentration before burning. (See Patent Document 5).
[0007]
[Non-Patent Document 1]
Sloman, AR, Appita, 14 (2), 57 (1960)
[Non-Patent Document 2]
Nelson, PF, et al., Appita, 24 (2), 101 (1970)
[Non-Patent Document 3]
Hemingway, RWet al., Appita, 25 (6), 445 (1972)
[Patent Document 1]
Japanese Patent Publication No. 47-24162 [Patent Document 2]
Japanese Patent Laid-Open No. 53-134903 [Patent Document 3]
Patent No. 1506085 [Patent Document 4]
Japanese Patent Publication No. 48-42242 [Patent Document 5]
Patent No. 1021680 Specification [0008]
[Problems to be solved by the invention]
The problem to be solved by the present invention is that the digestibility during the pulping of a hard-to-digest Eucalyptus single material chip or a mixed material chip containing the Eucalyptus material with an alkaline chemical solution in a short time and The object is to provide a wood chip pretreatment method which can be improved at low cost.
[0009]
[Means for Solving the Problems]
Prior to the cooking step, a hard-to-digest eucalyptus genus chip or a mixed material chip containing the eucalyptus genus chip is impregnated with hot water using a decompression vessel or an impregnation apparatus and a holding vessel. By processing in the hot water extraction step comprising the holding step, the hot water soluble substance is efficiently extracted and removed from the chip, and the digestibility with the subsequent alkaline chemical solution is improved in a short time and at low cost.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The hardly digestible eucalyptus material to be treated according to the present invention is defined as 4% or more due to the difference of 72% sulfuric acid insoluble matter (Klarson lignin) before and after 1% alkali extraction. This eucalyptus material may be a single tree species, or a mixture of two or more tree species composed solely of the defined eucalyptus material. Moreover, it is a mixed product of the eucalyptus wood of the definition and other eucalyptus genus having a digestibility of normal level to easy level, or a hardwood material of another family / genus, but within the definition in the state of this mixed product. The hard-to-cook mixed material that enters can also be treated, and the mixed material may be the mixed material at the overseas chip loading stage, or the stage from the domestic pulp mill chip yard to the continuous digester The mixed material may be used.
[0011]
Although the amount of acidic extractables contained in refractory eucalyptus wood varies depending on the age of the tree, the place of production (in other words, the growth environment), etc., it is difficult to specify a specific tree species. As a tree species containing a lot of mushroom components, Eucalyptus (hereinafter abbreviated as E.) calophylla, E. citriodora, E. diversicolor, E. globulus, E. grandis, E. gummifera, E. marginata, E. nesophila, Old trees such as E.nitens, tree species rich in ellagitannic acid include E.amygdalina, E.camaldulensis, E.delegatensis, E.gigantea, E. muelleriana, E. obliqua, E.regnans, E. sieberiana, Old tree such as E. viminalis and tree species rich in leucoanthocyanidins include old tree such as E. camaldulensis and E. marginata.
[0012]
The hot water extraction step of the present invention comprises a hot water impregnation step and a subsequent holding step. In the step of impregnating the non-digestible wood chips with hot water, coarse chips and chip dust are removed, and the sized chips are processed. There are two types of impregnation methods: using a vacuum container and using an impregnation apparatus. As a result of this impregnation treatment allowing hot water to rapidly penetrate into the chip, the hot water extraction treatment can be completed in a short time. The hot water impregnation step can be installed at any location between the chip screening step and the cooking step, but in order to improve the hot water impregnation, the steaming vessel and the subsequent steps are desirable. This is because, by steaming, air in the chip is degassed so that hot water easily penetrates in the impregnation container, and the hot water softens the chip and the chip is easily compressed in the impregnation apparatus.
[0013]
In the impregnation method using a vacuum container, wood chips are put in an impregnation container, hot water at 50 to 95 ° C. is added, and the chips are impregnated with hot water. The hot water temperature is more preferably 50 to 80 ° C, further preferably 50 to 75 ° C. At this time, it is preferable to carry out under reduced pressure for the purpose of improving the impregnation. The liquid ratio (hot water volume / chip dry weight) is preferably 4.0 to 10.0 L / kg, and more preferably 4.0 to 6.0 L / kg. As long as the impregnation time under reduced pressure is 15 minutes, it is sufficient.
From the viewpoint of reducing the scale of the decompression vessel, it is preferably within 10 minutes, more preferably within 5 minutes. The impregnation is sufficient even in this short time.
[0014]
The impregnation method using an impregnation apparatus is a method of compressing wood chips and impregnating the hot water with the restoring force of the chips after being compressed or released. Any device can be used for the compression as long as it can sufficiently compress the wood chips. There is no particular limitation, and Andritz's Impresssfiner, Valmet's plex screw (Prex screw). Hot water may be mixed with the chip in advance and put into the impregnation apparatus, or hot water may be added to the chip within the impregnation apparatus. The chip compression ratio (volume before compression / volume after compression) in the impregnation apparatus is preferably 2: 1 to 16: 1, and more preferably 4: 1 to 16: 1. If the compression ratio is less than 2: 1, the hot water is not sufficiently impregnated, and no apparatus exceeds the compression ratio of 16: 1. The liquid ratio during impregnation is preferably 4.0 to 10.0 L / kg, more preferably 4.0 to 6.0 L / kg. The hot water temperature is preferably 50 to 95 ° C, more preferably 50 to 80 ° C, and still more preferably 50 to 75 ° C. The treatment time of the impregnation apparatus is as short as about 1 minute.
[0015]
The wood chip impregnated with hot water discharged from the impregnation container or impregnation apparatus is held at a predetermined concentration for a predetermined time under heating in the holding container. During this time, the acidic extraction component is sufficiently diffused into the hot water. The temperature in the holding container is preferably 50 to 95 ° C, more preferably 50 to 80 ° C, and still more preferably 50 to 75 ° C. The holding time including the time required for raising the temperature to a predetermined temperature depends on the temperature, and the shorter the time is, the higher the temperature is, but it may be a short time of 5 to 90 minutes, from the viewpoint of reducing the size of the holding container, 5 to 60 minutes is preferable, and 5 to 30 minutes is more preferable. Even in this short time, the acidic extractable material is sufficiently diffused. Next, the hot water after extraction is removed, and the chip is sufficiently washed with water. Insufficient cleaning increases the alkali consumption in the subsequent cooking process.
[0016]
Extraction and removal of organic acid substances such as polyphenols, ellagic acid and ellagitannic acid and low molecular weight carbohydrates at low cost by hot water extraction of refractory eucalyptus chips in subsequent cooking processes , Wasteful consumption of expensive alkaline chemicals can be suppressed.
[0017]
The chips after washing are sent to the cooking process and subjected to cooking with an alkaline agent under normal conditions (active alkali addition amount, sulfidity, liquid ratio, maximum temperature, holding time, H factor, etc.). Examples of this cooking include alkali cooking, kraft cooking, and modified kraft cooking such as MCC, EMCC, ITC, and Lo-solid. There are also no particular limitations on the cooking type such as 1 vessel liquid phase type, 1 vessel liquid phase / gas phase type, 2 vessel liquid phase / gas phase type, and 2 vessel liquid phase type. 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 14-22. 15-20 are more preferable.
[0018]
EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to these. In the following examples and comparative examples, the following chips were provided. The kraft cooking conditions and test methods are shown below.
1. Eucalyptus Chips Eucalyptus chips were collected from the chip yard of Nippon Paper Industries Co., Ltd. The eucalyptus chip is a mixed chip of several kinds of eucalyptus tree species, and is a chip in which refractory eucalyptus chips are mixed. The difference of 72% sulfuric acid insoluble before and after 1% alkali extraction is 4.5%, which is difficult to digest.
2. Adjustment of chip size The chips were sieved using a gyro shifter to remove coarse chips and chip dust, thereby obtaining chips of 9.5 to 25.4 mmφ. This chip was used in the following examples and comparative examples.
3. Kraft cooking methods and conditions
Kraft cooking was carried out using a 2.4L rotary autoclave.
(1) Active alkali addition rate: 13.5-16.0%
(2) Sulfide degree: 25%
(3) Liquid ratio: 2.5L / kg
(4) Maximum temperature: 160 ° C
(5) Retention time: 94 minutes (6) H factor: 830
4). TOC (Total Organic Carbon) measurement of the extract As a guideline for the amount of organic acidic substances and carbohydrates extracted in hot water, the total organic carbon content in the extract is calculated using the TOC-5000 total organic carbon meter (Shimadzu Corporation) ).
[0019]
[Example 1]
To a 2.4 L vacuum container, 300 g of eucalyptus chips and a hot water of 75 ° C. were added to obtain a liquid ratio of 5.0 L / kg. The pH of the water at this time (pH before extraction) was 7.8. Air in the container was sucked and the chip was impregnated with hot water for 10 minutes under vacuum. Next, the mixture of chips and hot water was immediately transferred to a 2.4 L rotary autoclave and heated to 75 ° C. over 10 minutes. The holding time at 75 ° C. was set to four levels of 10, 30, 50, and 70 minutes. After completion of the hot water extraction treatment, solid-liquid separation was performed to separate the extract into chips. The pH of the extract (pH after extraction) and the amount of TOC were measured. The separated chip was thoroughly washed. This chip was placed in a 2.4 L rotary autoclave and kraft-distilled with an active alkali addition rate of 14.0%. The unbleached pulp was measured for kappa number and hunter whiteness. The results are shown in Table 1, FIG. 1 and FIG.
[0020]
[Example 2]
Eucalyptus chips and 75 ° C hot water were added to give a liquid ratio of 5.0 L / kg. The pre-extraction pH was 7.8. This was processed at a compression ratio of 4: 1 using an impregnation apparatus plex screw (manufactured by Valmet), and the chips were impregnated with hot water. The passage time in the impregnation apparatus of the mixture of chips and hot water is within 1 minute. Next, the mixture of chips and hot water was immediately transferred to a 2.4 L rotary autoclave and heated to 75 ° C. over 10 minutes. The holding time at 75 ° C. was set to four levels of 20, 40, 60, and 80 minutes. After completion of the hot water extraction treatment, solid-liquid separation was performed to separate the extract into chips. The pH of the extract (pH after extraction) and the amount of TOC were measured. The separated chip was thoroughly washed. This chip was placed in a 2.4 L rotary autoclave and kraft-distilled with an active alkali addition rate of 14.0%. The unbleached pulp was measured for kappa number and hunter whiteness. The results are shown in Table 1, FIG. 1 and FIG.
[0021]
[Comparative Example 1]
Eucalyptus chips were kraft cooked as they were without hot water extraction. The active alkali addition rate was set at four levels of 13.5, 14.0, 15.0, and 16.0%. The unbleached pulp was measured for kappa number and hunter whiteness. The results are shown in Table 1 and FIG.
[0022]
[Comparative Example 2]
The extraction experiment which assumed the hot-water extraction process as described in the nonpatent literature 2 (Nelson, PF, et al., Appita, 24 (2), 101 (1970)) described in the prior art was conducted. Put a eucalyptus chip and water in a 2.4-liter rotary autoclave so that the liquid ratio is 5.0 L / kg, raise the temperature to 80 ° C. over 10 minutes, and maintain the holding time at 80 ° C. at 230, 470, 710, 950 1, 190, 1,430 minutes, and the total processing time of the total heating time and holding time was 4, 8, 12, 16, 20, 24 hours. After completion of the hot water extraction treatment, solid-liquid separation was performed to separate the extract into chips. The separated chip was thoroughly washed. This chip was placed in a 2.4 L rotary autoclave and kraft-distilled with an active alkali addition rate of 14.0%. The unbleached pulp was measured for kappa number and hunter whiteness. The results are shown in Table 1 and FIG.
[0023]
FIG. 1 compares Example 1, Example 2, and Comparative Example 1. FIG. 1-1 shows the relationship between the active alkali addition rate and the kappa number of unbleached pulp, and FIG. 1-2 shows the active alkali addition rate. Fig. 1-3 shows the relationship between the whiteness of the unbleached pulp, the relationship between the unbleached pulp kappa number and the total yield, and Fig. 1-4 shows the relationship between the kappa number of the unbleached pulp and the whiteness. From FIG. 1-1 and FIG. 1-2, compared with the same active alkali addition rate, Example 1 and Example 2 have a lower kappa number of unbleached pulp than Comparative Example 1, and whiteness of unbleached pulp. Can be seen to be higher. As a result of removing the acidic substance that wastes the alkaline chemical for cooking by the hot water extraction process of the present invention, the added alkaline chemical is mainly consumed for delignification of the chip, which is the original purpose of cooking. Conceivable. From FIG. 1-3 and FIG. 1-4, when comparing with the constant copper number of unbleached pulp, there is no big difference in the total yield and the whiteness.
[0024]
FIG. 2 compares Example 1, Example 2, and Comparative Example 2. FIG. 2-1 shows the relationship between the hot water extraction treatment time and the kappa number of unbleached pulp, and FIG. 2-2 shows the hot water extraction. The relationship between treatment time and whiteness of unbleached pulp was shown. In the hot water extraction process of Comparative Example 2, which is a conventional technique, a process time of about 4 hours is insufficient and about 10 hours are required for complete extraction of acidic substances. On the other hand, in Example 1 and Example 2 in which the penetration of hot water was promoted, it can be seen that sufficient extraction was performed even with a treatment time of about 30 minutes. This is also evident from the changes over time in the pH of the extract and the amount of TOC in Table 1. Therefore, it is clear that the hot water extraction process of the present invention is far superior to the conventional hot water extraction process technology.
[0025]
[Table 1]

[0026]
[Figure 1]

[0027]
[Figure 2]

[0028]
【The invention's effect】
A hot water extraction step comprising a hot water impregnation step followed by a holding step prior to cooking with an alkaline agent, a hard-to-digest Eucalyptus single material chip or a mixed material chip containing the Eucalyptus material By pre-treating, the wasteful consumption of the alkaline chemical in the subsequent cooking step can be suppressed, and the cooking property can be improved at a low cost. Moreover, when the active alkali addition rate is made constant, the kappa number of the unbleached pulp can be reduced, and the whiteness of the unbleached pulp is improved. On the other hand, compared with the conventional hot water extraction processing technology, the hot water extraction processing of the present invention can be performed in a very short time, so that the heat energy required for the extraction processing can be reduced and the scale of the hot water extraction processing equipment can be reduced. There is also an advantageous effect such as being able to.

Claims (1)

Prior to cooking with an alkaline chemical solution, hot-water impregnation is performed by impregnating a hard-to-cook Eucalyptus single material chip or a mixed material chip containing the Eucalyptus material with hot water using a decompression vessel or an impregnation apparatus. A wood chip pretreatment method comprising: a hot water extraction step comprising a step and a subsequent holding step of holding in a holding container .