CN112813713B - Preparation method of special pulp for producing lyocell fibers from bamboo willows - Google Patents
Preparation method of special pulp for producing lyocell fibers from bamboo willows Download PDFInfo
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21B1/00—Fibrous raw materials or their mechanical treatment
- D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
- D21B1/06—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by dry methods
- D21B1/061—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by dry methods using cutting devices
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C1/00—Pretreatment of the finely-divided materials before digesting
- D21C1/02—Pretreatment of the finely-divided materials before digesting with water or steam
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C7/00—Digesters
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
- D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
- D21C9/144—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 and other bleaching agents in a multistage process
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
- D21D5/02—Straining or screening the pulp
Abstract
A preparation method of special pulp for producing lyocell fibers from bamboo willows belongs to the technical field of pulp pulping. Comprises the following steps: bamboo willow slice material preparation, neutral high-temperature prehydrolysis, alkaline high-temperature cooking, coarse pulp washing and screening, oxygen delignification, multi-section bleaching, multi-section washing, acidification and chelation treatment, low-concentration sand removal and screening and pulp making of finished products. The invention has the technical effects and advantages that: the metal ions have great influence on the production of the lyocell fibers, and the removal rate of the metal ions in the fibers is higher after acidification in the production process; the bamboo willow pulp special for the lyocell fibers produced by the invention has the following quality indexes: polymerization degree: 450-650, alpha cellulose is more than or equal to 91%, R10 is more than or equal to 91%, R18 is more than or equal to 93%, ash content is less than or equal to 0.1%, fe is less than or equal to 2.0ppm, ca is less than or equal to 50ppm, mg is less than or equal to 50ppm, and whiteness is more than or equal to 92%.
Description
Technical Field
The invention belongs to the technical field of pulp pulping, and relates to a preparation method of special pulp for producing lyocell fibers by bamboo willow.
Background
Lyocell fiber (Lyocell) is commonly called as "velveteen", is made from natural plant fiber as a raw material, is known in the middle of the 90 s of the 20 th century, and is known as the most valuable product in artificial fiber history in the last half century. The Lyocell fiber has various excellent performances of natural fiber and synthetic fiber, lyocell is green fiber, raw materials of Lyocell are inexhaustible cellulose in nature, a production process has no chemical reaction, a used solvent is non-toxic, the recovery rate of the solvent can reach more than 99%, and the production process is green and environment-friendly, so the Lyocell fiber is called as '21 st century green fiber'.
The lyocell fiber industry has a monopoly status, foreign countries begin to basically monopolize the austria lanjing company, the productivity is small, in recent years, along with further digestion and absorption of the lyocell fiber production technology by domestic enterprises, the lyocell fiber production technology slowly becomes a relatively mature solvent method regenerated cellulose fiber industrial production technology, the single-line production capacity of new projects in China is further improved, the lyocell industry in China is steadily developed, and the capacity of 100 million tons of productivity is expected to be achieved in the coming years.
The raw material for producing the special pulp for the lyocell fibers is wood (broadleaf wood or needle-leaved wood), and because the market demand is small, the production factory is mainly in the countries such as the United states, south Africa and the like at present, the productivity is small, and the total yield is low; no manufacturers for producing the pulp special for the lyocell fiber exist in China. The domestic wood pulp is mainly dissolving pulp for making paper pulp and common viscose fiber.
The bamboo willow is a new hybrid variety of willow and bamboo, is a new willow plant of Salix genus of Salicaceae family introduced from the United states in recent years, has plant points between willow and bamboo, has wide adaptability in the national range, and has wide range of cultivation areas. The bamboo willows are divided into different strains according to different adaptive areas and characteristics, and only a plurality of strains of non-blue bamboo willows, bamboo willow No. 5 and bamboo willow No. 3 are stored at present. The bamboo willow has great growth potential and high growth speed, and the height of the bamboo willow can reach more than 20 meters. The research on the characteristics of the bamboo willow, the fiber quality and the pulping performance by a domestic research institution shows that the wood density of the bamboo willow is 0.384-0.443 g/cm 3 A range; the ash content, the cold and hot water extract and the 1 percent NaOH extract of the bamboo willow are higher than that of fast-growing poplar but lower than that of hybrid tree, the content of lignin and pentosan is equivalent to that of the fast-growing poplar, but the content of cellulose is lower than that of the fast-growing poplar by 3 percent, the average fiber length of the bamboo willow is 0.84mm, the fiber cell wall is thin, the wall cavity ratio is small, the bamboo willow is suitable for producing paper pulp, the bamboo willow is an excellent raw material for papermaking, the introduction and planting time is not long, the application of the bamboo willow in the papermaking industry at present is still limited in a laboratory stage, and the application of the bamboo willow in the production of lyocell fibers is blank.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a preparation method of special pulp for producing lyocell fibers by using bamboo willows.
A preparation method of special pulp for producing lyocell fibers by bamboo willow comprises the following steps: bamboo willow slices preparation, neutral high-temperature prehydrolysis, alkaline high-temperature cooking, coarse pulp washing and screening, oxygen delignification, multi-section bleaching, multi-section washing, acidification and chelation treatment, low-concentration sand removal and screening and pulp making of finished products.
The invention has the technical effects and advantages that: the metal ions have great influence on the production of the lyocell fibers, and the removal rate of the metal ions in the fibers is higher after acidification in the production process; the quality indexes of the bamboo willow pulp special for the lyocell fiber produced by the invention are as follows: polymerization degree: 450-650, alpha cellulose is more than or equal to 91%, R10 is more than or equal to 91%, R18 is more than or equal to 93%, ash content is less than or equal to 0.1%, fe is less than or equal to 2.0ppm, ca is less than or equal to 50ppm, mg is less than or equal to 50ppm, and whiteness is more than or equal to 92%.
Detailed Description
It will be apparent that those skilled in the art can make many modifications and variations based on the spirit of the present invention.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element, component or section is referred to as being "connected" to another element, component or section, it can be directly connected to the other element or section or intervening elements or sections may also be present. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art.
The following examples are further illustrative in order to facilitate the understanding of the embodiments, and the present invention is not limited to the examples.
Example 1:
a method for preparing special pulp for producing lyocell fibers by using bamboo willows, which widens the production method and the raw material source of the special pulp for the lyocell fibers.
The method comprises the following process steps: bamboo willow slices preparation, neutral high-temperature prehydrolysis, alkaline high-temperature cooking, coarse pulp washing and screening, oxygen delignification, multi-section bleaching, multi-section washing, acidification and chelation treatment, low-concentration sand removal and screening and pulp making of finished products.
The method comprises the following specific steps:
step 1), bamboo willow slicing and material preparation: the raw wood bamboo willow is cut into wood chips, the length of the wood chips is 15-25 mm, the thickness of the wood chips is 3-5 mm, and the width of the wood chips is about 20mm.
Step 2), neutral high-temperature prehydrolysis: the reaction tower is a vertical stainless steel tower, the upper part is fed in and the lower part is discharged out, the batch production is carried out, and the hydrolysate can be circulated strongly; during hydrolysis, the temperature is 150-175 ℃, and the time is 30-180 min;
step 3), the alkaline high-temperature cooking process comprises the following steps: in the initial stage of cooking, firstly, the hot cooking liquor is filled into a pot, so that the temperature in the pot is higher, the alkali consumption (caustic soda) of the cooking liquor is 12-28%, the degree of vulcanization is 10-40%, the liquor ratio is 1: 2-5, then the cooking liquor is directly heated and cooked, the steam is heated to the maximum temperature of 155-170 ℃, and the heat preservation time is 40-80 min. And pumping and placing the pot after the cooking is finished.
Step 4), coarse pulp washing and screening: the coarse pulp from the cooking process is first screened in a combined screening and removing section, the fine pulp is washed in a double-roller pulp washer to extract black liquor, and the washed pulp enters an oxygen delignification system. The washing can be carried out by multi-section washing equipment, strong dehydration and replacement are combined, the extraction rate is high, and the washing factor is high; unbleached pulp is primarily washed to remove solids dissolved in the pulp during cooking and to prepare the pulp for the subsequent oxygen delignification stage.
Step 5), oxygen delignification procedure: the method comprises the steps of adopting a two-stage oxygen delignification process, directly dropping 10% pulp into a vertical pipe in front of a medium consistency pulp pump, simultaneously adding low-pressure steam and NaOH solution into the vertical pipe, then pumping the pulp into a medium consistency mixer by using a medium consistency pump, adding oxygen and medium-pressure steam into the mixer, fully mixing the pulp with the steam and the oxygen, then feeding the mixed pulp into a rising tower from the bottom of a first-stage oxygen delignification reaction tower for oxygen delignification reaction, discharging the pulp subjected to oxygen delignification into the vertical pipe in front of the medium consistency pulp pump in a second-stage oxygen delignification reaction tower through a discharger on the top of the tower, and discharging the pulp subjected to secondary oxygen delignification reaction into a pulp storage tower. The pulp after oxygen removal is washed by multi-stage washing equipment and then enters a bleaching process. Alkali amount for oxygen removal step: 2% -4%, the first-stage oxygen consumption: 3-4%, the first-stage oxygen desorption residence time is 30-60 min, the temperature is 80-90 ℃, and the second-stage oxygen dosage is as follows: 1-2%, retention time 60min, temperature 70-90 deg.C. PH is more than or equal to 11 at the end of oxygen desorption
Step 6), multi-stage bleaching process: the bleaching adopts three-stage bleaching process, which comprises a primary chlorine dioxide bleaching process, an oxygen enhanced alkali extraction process and a secondary chlorine dioxide bleaching process; the specific operation steps are as follows:
step a, a primary chlorine dioxide bleaching process: sending the unbleached pulp subjected to oxygen delignification to a chlorine dioxide mixer by using a medium-concentration pump, then sending the chlorine dioxide mixer into a bleaching tower, enabling the pulp to perform upflow reaction in the tower, then discharging the pulp into a medium-concentration pump through a top pulp scraper device, sending the pulp into a pulp washer for washing, and sending the washed pulp into the medium-concentration pump. The concentration of the slurry in the process is about 10 percent, and the dosage of chlorine dioxide added into the mixer is 1 to 1.5 percent; the pulp of the bleaching tower stays for 120-180 min at the temperature of 70-90 ℃;
step b, oxygen enhanced alkali extraction: adding NaOH solution into a vertical pipe of a medium concentration pump, adding alkali to adjust the pH value to 10-12, then sending the slurry into an upflow reaction tower, adding oxygen, hydrogen peroxide and steam before the slurry enters the reaction tower, and mixing by using a mixer. The pulp from the reaction tower enters a pulp washer through a medium-concentration pump for washing again. The dosage of oxygen is 0.5 to 1 percent, and the dosage of hydrogen peroxide is 1 to 1.5 percent; the pulp of the bleaching tower stays for 30-60 min at the temperature of 70-90 ℃;
step c, secondary chlorine dioxide bleaching process: the washed pulp is pumped into a mixer by a medium-concentration pump to be added with ClO 2 And mixing the solutions, sending the mixed pulp to a bleaching tower again, adding steam before the pulp enters a reaction tower, enabling the pulp to perform upflow reaction in the tower, then discharging the pulp into a medium-concentration pump through a top pulp scraper device, and sending the pulp to a pulp washer for washing again. Adding sodium thiosulfate into the washed slurry to remove residual chlorine. The using amount of the chlorine dioxide is 0.5 to 1 percent; the pulp of the bleaching tower stays for 60-120 min at the temperature of 70-80 ℃;
step 7), acidification and chelation treatment process: the washed slurry enters an acidification tower (tank) for acidification, inorganic acid sulfuric acid or hydrochloric acid and steam are added before entering the tower, and a chelating agent auxiliary agent is added after acidification. At the time of acidification, the slurry concentration is 5%, PH: 1-2, the temperature is 30-50 ℃, the time is 30-60min, and the EDTA dosage is 0.1 percent. The acidified pulp is sent to a pulp washer for washing again.
Step 8), a low-concentration desanding screening step and a pulp manufacturing step, wherein the pulp is washed by multiple sections again, subjected to low-concentration desanding screening, and screened by a selection system combining three sections of fine screens and two sections of low-concentration desanding, wherein the pulp concentration is 1%, and the pulp is manufactured and cut by a long-mesh multi-cylinder paper machine or a mesh air cushion pulp machine. The finished pulp is 800x600 specification or roll pulp.
Example 2:
a method for preparing pulp special for producing Lyocell fiber by using bamboo willow uses bamboo willow as a raw material and comprises the following process steps: bamboo willow slices are prepared, neutral high-temperature prehydrolysis, alkaline high-temperature cooking, coarse pulp washing and screening, oxygen delignification, multi-section bleaching, multi-section washing, acidification and chelation treatment, low-concentration sand removal and screening, and finished pulp is manufactured by paper making. Wherein:
step 1, bamboo willow slicing and material preparation: peeling raw wood bamboo willow, cutting into wood chips, and screening qualified wood chips by a wood chip screen, wherein the wood chips have the specification of 15-25 mm in length, 3-5 mm in thickness and about 20mm in width.
Step 2, prehydrolysis: feeding the qualified wood chips into the top of a hydrolysis tower by a feeding screw, loading the mixed steam into the tower, introducing steam into the tower, heating to 160 ℃, and keeping the temperature for 50min; and after the hydrolysis is finished, extracting hydrolysate.
Step 3, alkaline high-temperature cooking: the alkali consumption of the cooking liquor is 22%, the vulcanization degree is 30%, the liquor ratio is 1: 4.5, cooking is carried out according to the cooking program, steam heating is carried out until the maximum temperature is 165 ℃, and the heat preservation time is 60min. And pumping the spraying pot after the cooking is finished.
And 4, washing and screening coarse pulp: firstly, screening by a combined screening and removing section, washing good pulp by a two-channel double-roller pulp washer, and performing oxygen delignification on the washed pulp;
step 5, oxygen delignification procedure: the method comprises the steps of adopting a two-stage oxygen delignification process, directly dropping 10% slurry into a vertical pipe in front of a medium consistency slurry pump, simultaneously adding low-pressure steam and NaOH solution into the vertical pipe, then pumping the mixture into a medium consistency mixer by using a medium consistency pump, adding oxygen and medium-pressure steam into the mixer, fully mixing the slurry with the steam and the oxygen, then entering a rising tower from the bottom of a first-stage oxygen delignification reaction tower for oxygen delignification reaction, discharging the slurry after the oxygen delignification reaction into the vertical pipe in front of the medium consistency slurry pump in a second-stage oxygen delignification reaction tower through a discharger at the top of the tower, and discharging the slurry after a secondary oxygen delignification reaction into a slurry storage tower. The pulp after oxygen removal is washed by multi-stage washing equipment and then enters a bleaching process. Alkali amount for oxygen removal step: 3%, first-stage oxygen dosage: 4%, first-stage oxygen removal retention time of 40min, temperature of 80 ℃, second-stage oxygen consumption: 2%, retention time 60min, temperature 80 ℃. PH is more than or equal to 11.5 at the end of oxygen desorption
Step 6, a multi-stage bleaching process:
(1) Once ClO 2 A bleaching process: the pulp with the concentration of 10 percent after oxygen delignification is pumped into a chlorine dioxide mixer by a medium-concentration pump and then enters an up-flow bleaching tower, and ClO is added into the mixer 2 The using amount is 1.5 percent; introducing steam, and staying the slurry for 90min at 80 ℃; then the medium-concentration pump is sent to a double-roller washer for washing.
(2) The oxygen-enhanced alkali extraction process: the washed slurry with the concentration of 10 percent is sent into an upflow reaction tower by a medium consistency pump; adding NaOH solution into a vertical pipe of a medium concentration pump, adjusting the pH value to 12, adding oxygen, hydrogen peroxide and steam, and mixing by using a mixer. The oxygen consumption is 1%, and the hydrogen peroxide consumption is 1%; standing bleaching tower slurry at 80 deg.C for 60min; the pulp from the reaction tower enters a double-roller pulp washer through a medium-concentration pump for washing again.
(3) Secondary ClO 2 Bleaching process: sending the washed pulp to the mixer again through a medium-concentration pump to be added with ClO 2 Mixing the solution, adding steam, and feeding the mixed slurry into an upflow bleaching tower again, wherein the use amount of chlorine dioxide is 1%; the pulp of the bleaching tower stays for 60min at the temperature of 80 ℃; then discharged into a medium consistency pump through a top pulp scraper device and sent to a double-roller pulp washer for washing again. Adding sodium thiosulfate into the washed slurry to remove residual chlorine. And removing residual chlorine.
Step 7, acidification and chelation treatment: and (3) delivering the washed slurry with the concentration of 5% of a low-concentration slurry pump into an acidification tower for acidification, and adding a mixer or a hydrochloric acid, steam and Ethylene Diamine Tetraacetic Acid (EDTA) agent before the slurry enters the tower. (ethylenediaminetetraacetic acid, EDTA for short, is an auxiliary agent) PH: at 40 deg.c and temperature not higher than 2 deg.c, EDTA in 0.1 wt% for 60min. The acidified pulp is sent to a double-roller pulp washer for washing again.
Step 8, a papermaking process: the pulp is screened by low-concentration desanding, a selection system combining three sections of fine screens and two sections of low-concentration desanding is adopted, the pulp concentration is 1% during screening, and the pulp is manufactured and rolled by a mesh air cushion pulp machine.
The quality indexes of the produced bamboo willow pulp special for the lyocell fiber are as follows:
polymerization degree: 483, alpha-cellulose 91.6%, R10:91.8%, R18:92%, ash content: 0.09%, fe:2.0ppm, whiteness: 92 percent.
Example 3:
a method for preparing pulp special for producing Lyocell fiber by using bamboo willow uses bamboo willow as a raw material and comprises the following process steps: preparing bamboo willow materials, performing neutral high-temperature prehydrolysis, performing alkaline high-temperature cooking, washing and screening coarse pulp, performing oxygen delignification, bleaching in multiple sections, washing in multiple sections, performing acidification and chelation treatment, performing low-concentration sand removal screening, and making finished pulp by using paper. Wherein:
step 1, bamboo willow material preparation: the bamboo willow chips are purchased outside, the water content of the wood chips is 42 percent, the qualified rate of the wood chips is more than 99 percent, the qualified wood chips are 15-25 mm long, 3-5 mm thick and 20mm wide.
Step 2, a prehydrolysis process: feeding wood chips into the top of a hydrolysis tower by a feeding screw, loading the mixed steam into the tower, introducing steam into the tower, heating to 165 ℃ for 60min; and after the hydrolysis is finished, extracting the hydrolysate.
And 3, alkaline high-temperature cooking: the alkali consumption of the cooking liquor is 25%, the vulcanization degree is 35%, the liquor ratio is 1: 4.5, cooking is carried out according to the cooking program, steam is heated to the highest temperature of about 165 ℃, and the heat preservation time is 60min. And pumping the spraying pot after the cooking is finished.
And 4, washing and screening coarse pulp: firstly, screening by a combined screening and removing section, washing good pulp by a two-roller pulp washer, and enabling the washed pulp to enter an oxygen delignification process;
step 5, oxygen delignification procedure: the method comprises the steps of adopting a two-stage oxygen delignification process, directly dropping 10% pulp into a vertical pipe in front of a medium consistency pulp pump, simultaneously adding low-pressure steam and NaOH solution into the vertical pipe, then pumping the pulp into a medium consistency mixer by using a medium consistency pump, adding oxygen and medium-pressure steam into the mixer, fully mixing the pulp with the steam and the oxygen, then feeding the mixed pulp into a rising tower from the bottom of a first-stage oxygen delignification reaction tower for oxygen delignification reaction, discharging the pulp subjected to oxygen delignification into the vertical pipe in front of the medium consistency pulp pump in a second-stage oxygen delignification reaction tower through a discharger on the top of the tower, and discharging the pulp subjected to secondary oxygen delignification reaction into a pulp storage tower. The pulp after oxygen removal is washed by multi-stage washing equipment and then enters a bleaching process. Alkali amount for oxygen removal step: 4%, first-stage oxygen dosage: 4%, first-stage oxygen removal retention time of 40min, temperature of 80 ℃, second-stage oxygen consumption: 2%, retention time 60min, temperature 80 ℃. PH is more than or equal to 11.5 at the end of oxygen desorption
Step 6, a multi-stage bleaching process:
(1) Primary ClO 2 A bleaching process: the pulp with the concentration of 10 percent after oxygen delignification is pumped into a chlorine dioxide mixer by a medium-concentration pump and then enters an up-flow bleaching tower, and ClO is added into the mixer 2 The using amount is 1.5 percent; introducing steam, and staying the slurry for 90min at 80 ℃; the medium consistency pump is then sent to a two-roll washer for washing.
(2) And an oxygen enhanced alkali extraction process: the washed slurry with the concentration of 10 percent is pumped into an upflow reaction tower by a medium-consistency slurry pump; adding NaOH solution into a vertical pipe of a medium concentration pump, adjusting the pH value to 12, adding oxygen, hydrogen peroxide and steam, and mixing by using a mixer. The oxygen consumption is 1%, and the hydrogen peroxide consumption is 1.5%; standing bleaching tower slurry at 80 deg.C for 60min; the pulp from the reaction tower enters a double-roller pulp washer through a medium-consistency pump for washing again.
(3) Secondary ClO 2 Bleaching process: sending the washed pulp to the mixer again through a medium-concentration pump to be added with ClO 2 Mixing the solutions, adding steam, and feeding the mixed pulp into an upflow bleaching tower again, wherein the using amount of chlorine dioxide is 1%; standing bleaching tower slurry at 80 deg.C for 60min; then discharged into a medium consistency pump through a top pulp scraper device and sent to a double-roller pulp washer for washing again. Adding sodium thiosulfate into the washed slurry to remove residual chlorine.And (4) removing residual chlorine completely.
And 7, acidification and chelation treatment process: the slurry after washing, the concentration of the low thick slurry pump is 5 percent is sent into an acidification tower for acidification, and is added with a mixer or hydrochloric acid, steam and EDTA agent before entering the tower. pH during acidification: at 40 deg.c and temperature not higher than 2 deg.c, EDTA in 0.1 wt% for 60min. The acidified pulp is sent to a double-roller pulp washer for washing again.
Step 8, a papermaking process: the pulp is screened by low-concentration desanding, a selection system combining three sections of fine screens and two sections of low-concentration desanding is adopted, the pulp concentration is 1 percent during screening, and the finished pulp is manufactured and coiled by a mesh air cushion pulp machine.
The quality indexes of the produced bamboo willow pulp special for the lyocell fiber are as follows:
polymerization degree: 467, alpha cellulose 91.2%, R10:91.3%, R18:92.6%, ash: 0.09%, fe:2.0ppm, whiteness: 92 percent of
As described above, although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that many modifications are possible without substantially departing from the spirit and scope of the present invention. Therefore, such modifications are also all included in the scope of protection of the present invention.
Claims (1)
1. A preparation method of special pulp for producing lyocell fibers by bamboo willow is characterized by comprising the following steps: bamboo willow slices preparation, neutral high-temperature prehydrolysis, alkaline high-temperature cooking, coarse pulp washing and screening, oxygen delignification, multi-section bleaching, multi-section washing, acidification and chelation treatment, low-concentration sand removal and screening and pulp making of finished products;
the method comprises the following specific steps:
step 1), bamboo willow slicing and material preparation: cutting the raw bamboo willow into wood chips, wherein the wood chips are 15-25 mm long, 3-5 mm thick and 20mm wide;
step 2), neutral high-temperature prehydrolysis: the reaction tower is a vertical stainless steel tower, the upper part is fed in and the lower part is discharged out, the batch production is carried out, and the hydrolysate is circulated strongly; during hydrolysis, the temperature is 150-175 ℃, and the time is 30-180 min;
step 3), the alkaline high-temperature cooking process comprises the following steps: at the initial stage of cooking, firstly, putting the hot cooking liquid into a pot to enable the temperature in the pot to reach higher temperature; the alkali consumption of the cooking liquor is 12-28%, the degree of vulcanization is 10-40%, the liquor ratio is 1: 2-5, then directly heating and cooking, heating the steam to the maximum temperature of 155-170 ℃, keeping the temperature for 40-80 min, and pumping and placing the pot after the cooking is finished;
step 4), coarse pulp washing and screening: the coarse pulp from the cooking process is firstly screened by a combined screening section, the fine pulp is sent to a double-roller pulp washer to be washed and black liquor is extracted, and the washed pulp enters an oxygen delignification system; washing is carried out by using multi-section washing equipment, and strong dehydration and replacement are combined with each other; the unbleached pulp is mainly washed to remove solid matters dissolved in the pulp in the cooking process and prepare for the subsequent oxygen delignification stage of the pulp;
step 5), oxygen delignification process: adopting a two-stage oxygen delignification process, directly dropping 10 percent pulp into a vertical pipe in front of a medium consistency pulp pump, simultaneously adding low-pressure steam and NaOH solution into the vertical pipe, then pumping the pulp into a medium consistency mixer by using a medium consistency pump, adding oxygen and medium-pressure steam into the mixer, fully mixing the pulp with the steam and the oxygen, then entering a rising tower from the bottom of a first-stage oxygen delignification reaction tower for oxygen delignification reaction, discharging the pulp subjected to oxygen delignification to the vertical pipe in front of the medium consistency pump of a second-stage oxygen delignification reaction tower through a discharger on the top of the tower, and discharging the pulp subjected to secondary oxygen delignification reaction to a pulp storage tower; the pulp after oxygen removal is washed by multi-section washing equipment and then enters a bleaching process; alkali amount for oxygen removal step: 2% -4%, first-stage oxygen consumption: 3% -4%, the first-stage oxygen desorption residence time is 30-60 min, the temperature is 80-90 ℃, and the second-stage oxygen consumption: 1 to 2 percent, the retention time is 60min, and the temperature is 70 to 90 ℃; the PH value is more than or equal to 11 when the oxygen desorption is finished;
step 6), a multi-stage bleaching process: the bleaching adopts three-stage bleaching process, which comprises a primary chlorine dioxide bleaching process, an oxygen enhanced alkali extraction process and a secondary chlorine dioxide bleaching process;
the specific operation steps are as follows:
step a, a primary chlorine dioxide bleaching process: sending unbleached pulp subjected to oxygen delignification to a chlorine dioxide mixer by using a medium-concentration pump, then sending the pulp into a bleaching tower, enabling the pulp to perform upflow reaction in the tower, then discharging the pulp into the medium-concentration pump through a top pulp scraper device, sending the pulp into a pulp washer for washing, sending the washed pulp into the medium-concentration pump, wherein the pulp concentration in the process is 10%, and the using amount of chlorine dioxide added into the mixer is 1% -1.5%; the pulp of the bleaching tower stays for 120-180 min at the temperature of 70-90 ℃;
step b, oxygen enhanced alkali extraction: adding NaOH solution into a vertical pipe of a medium concentration pump, adding alkali to adjust the pH value to 10-12, then sending the slurry into an upflow reaction tower, adding oxygen, hydrogen peroxide and steam before the slurry enters the reaction tower, and mixing by using a mixer; the pulp from the reaction tower enters a pulp washer through a medium-concentration pump for washing again; the dosage of the oxygen is 0.5 to 1 percent, and the dosage of the hydrogen peroxide is 1 to 1.5 percent; the pulp of the bleaching tower stays for 30-60 min at the temperature of 70-90 ℃;
step c, secondary chlorine dioxide bleaching process: the washed slurry is pumped into a mixer by a medium-concentration pump to be added with ClO 2 Mixing the solutions, sending the mixed pulp to a bleaching tower again, adding steam before the pulp enters a reaction tower, enabling the pulp to perform upflow reaction in the tower, then discharging the pulp into a medium-concentration pump through a top pulp scraper device, and sending the pulp to a pulp washer for washing again; adding sodium thiosulfate into the washed pulp to remove residual chlorine; the using amount of the chlorine dioxide is 0.5 to 1 percent; the pulp of the bleaching tower is kept for 60 to 120min at the temperature of between 70 and 80 ℃,
step 7), acidification and chelation treatment process: acidifying the washed slurry in an acidification tower, adding inorganic acid sulfuric acid or hydrochloric acid and steam before the slurry enters the tower, and adding a chelating agent auxiliary agent after the slurry is acidified; at the time of acidification, the slurry concentration is 5%, PH: 1-2, the temperature is 30-50 ℃, the time is 30-60min, and the EDTA dosage is 0.1 percent; washing the acidified pulp again by a pulp washer;
step 8), a low-concentration desanding screening step and a pulp manufacturing step, wherein the pulp is washed in multiple sections again, subjected to low-concentration desanding screening, and screened by adopting a selection system combining three sections of fine screens and two sections of low-concentration desanding, wherein the pulp concentration is 1%, and a long-mesh multi-cylinder paper machine or a mesh-sandwiched air cushion pulp machine is used for manufacturing and cutting and forming; the finished pulp is 800x600 specification or roll pulp;
the special pulp for producing the lyocell fibers by the produced bamboo willow has the following quality indexes:
polymerization degree: 483, alpha-cellulose 91.6%, R10:91.8%, R18:92%, ash content: 0.09%, fe:2.0ppm, whiteness: 92 percent.
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