High-quality dissolving pulp and preparation method thereof

Abstract

The invention provides high-quality dissolving pulp and a preparation method thereof, and belongs to the technical field of dissolving pulp, the preparation method comprises the following steps: S1, loading wood flour into a spherical digester, adding a sodium hydroxide solution, controlling temperature and pressure, preserving heat and cooking to obtain coarse pulp; s2, deionized water is added into the crude pulp, the pH is adjusted, xylanase is added, then an activating auxiliary agent is added, activating treatment is conducted, pretreated pulp is obtained, and the activating auxiliary agent is a mixture of hydrosulfite and citric acid; s3, a chelating agent is added into the pretreated slurry, purified slurry is obtained, and the chelating agent is sodium tripolyphosphate cross-linked modified chitosan; and S4, carrying out bleaching treatment on the purified pulp by adopting chlorine dioxide, and obtaining the high-quality dissolving pulp after the bleaching is completed. According to the high-quality dissolving pulp prepared by the method, the alpha cellulose content can reach 94.2% or above, the iron content is 20 ppm or below, and the whiteness is 85% or above.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of dissolving pulp, and particularly relates to high-quality dissolving pulp and a preparation method thereof. BACKGROUND

[0002] Dissolving pulp, also known as special pulp and refined pulp, is mainly used for producing viscose fiber as a textile raw material, and is also used as a raw material for products such as glass paper, sterilization filter paper in the pharmaceutical industry, acetate fiber (cigarette filter), and nitrocellulose.

[0003] Dissolving pulp is usually made of wood plant fibers in nature through chemical processing. High-quality dissolving pulp can ensure the processing performance of fibers, so that the produced fibers have good uniformity and high spinnability. With the rise of green textiles, the market demand for high-quality dissolving pulp is increasing. The existing preparation methods have some problems that are difficult to overcome when producing high-quality dissolving pulp. For example, during the chemical treatment process, part of the plant fibers is easily damaged, resulting in a decrease in cellulose content. It is difficult to accurately control the reaction conditions in the process. The prepared dissolving pulp has certain limitations in increasing the content of methyl cellulose and reducing the content of iron. Although some methods can increase the content of methyl cellulose to a certain extent, they introduce more impurities, causing the content of iron to exceed the standard. Moreover, these processes are mostly high in energy consumption and complex in process, which not only increases the production cost, but also causes great pressure on the environment.

[0004] Therefore, it is of great significance to develop a new preparation method that can not only increase the content of methyl cellulose of dissolving pulp to a higher standard, but also effectively reduce the content of iron, and has the advantages of energy saving, environmental protection, and simple operation, to promote the development of the dissolving pulp technical field and meet the demand of the viscose fiber industry for high-quality raw materials. SUMMARY

[0005] To solve the problems in the background art, the present application provides a high-quality dissolving pulp and a preparation method thereof.

[0006] The technical scheme provided by the present application is as follows. A preparation method of high-quality dissolving pulp, comprising the following steps: S1. Wood chips are crushed and passed through a 20-60 mesh screen to obtain wood powder. The wood powder is loaded into a steaming ball, and a sodium hydroxide solution with a mass concentration of 6-10% is added, wherein the solid-liquid ratio is 1:30-40. The pressure is increased to 0.6-1.0 MPa, the temperature rising rate is controlled at 5-10℃ / min, and after the temperature is raised to 185-205℃, the reaction is maintained for 1.5-2.5h. The steam is released, the product after reaction is taken out, filtered, and the crude pulp is obtained; S2. The crude pulp is put into an activation tank, deionized water is added, the pH value is adjusted to 4-6, xylanase is added in an amount of 100-500 activity units per gram of crude pulp, an activation aid is added, activation treatment is carried out, after the activation is completed, heating to boiling is performed, the activation is terminated, and cooling is performed, to obtain pretreated pulp slurry, wherein the activation aid is a mixture of bisulfite and citric acid; S3. A chelating agent is added to the pretreated pulp slurry, adsorption treatment is performed for 0.5-1 h, to obtain purified pulp slurry, wherein the chelating agent is crosslinked modified chitosan sodium tripolyphosphate; S4. The purified pulp slurry is bleached with chlorine dioxide, the amount of chlorine dioxide used is 0.8-1.2%, the bleaching temperature is 70-80℃, the bleaching time is 0.5-1.5 h, and after the bleaching is completed, the high-quality dissolving pulp is obtained.

[0007] Preferably, the chelating agent in step S3 is prepared by the following steps: A1. Chitosan is dissolved in an acetic acid solution with a mass fraction of 1-3%, to obtain a chitosan acetic acid solution, the mass fraction of chitosan in the acetic acid solution is 0.3-0.5%, and stirring and dissolution are performed, to obtain the chitosan acetic acid solution; A2. Alpha amylase is added to the chitosan acetic acid solution, stirring is performed for 0.5-1 h, to obtain a mixed solution, sodium tripolyphosphate is added to the mixed solution under stirring, and stirring is continued for 20-40 min, to obtain a modified chitosan solution.

[0008] Preferably, the amount of chelating agent added in step S3 is 0.2-0.4% of the mass of the pretreated pulp slurry.

[0009] Preferably, the mass ratio of bisulfite to citric acid in the activation aid in step S2 is 20:0.8-1.2.

[0010] Preferably, the concentration of the activation aid in the pulp slurry in step S2 is 20-30 g / L, and the activation treatment time is 2-4 h.

[0011] Preferably, the amount of alpha amylase added in step A2 is 10-100 activity units / g of the chitosan acetic acid solution.

[0012] Preferably, the content of sodium tripolyphosphate in the mixed solution in step A2 is 1-2 g / L.

[0013] The application further provides a high-quality dissolving pulp, which is prepared by the preparation method described in the above technical solution.

[0014] The application has the following beneficial effects: 1. Xylanase as a hemicellulase can effectively dissolve impurities in the activated activator coarse pulp, and the bisulfite and citric acid in the activated activator can improve the activity of xylanase, significantly improve the dissolution efficiency, effectively reduce the content of early-stage impurities, and improve the content of alpha cellulose in the dissolved pulp.

[0015] 2. Chitosan as a chelate can form a coordination bond with iron ions in the solution through the amino nitrogen and hydroxyl oxygen on the molecular chain, thereby playing a major role in removing iron ions. Alpha amylase and sodium tripolyphosphate as auxiliary agents can be combined with chitosan in a physical crosslinking manner, which helps the adsorption of chitosan to iron ions and avoids the secondary deposition of iron ions, thereby effectively improving the removal rate of iron ions.

[0016] 3. The crosslinking modification treatment of the activated activator and chitosan can be used in combination to reduce the introduction and adhesion of impurities to the pulp, enhance the anti-pollution ability of the fibers, thereby reducing the content of late-stage impurities and further improving the content of alpha cellulose in the dissolved pulp. DETAILED DESCRIPTION

[0017] The present application will be further described in detail below in combination with examples.

[0018] The raw materials of the examples and comparative examples of the present application are all ordinary commercially available, except for special instructions.

[0019] Example 1 A high-quality dissolved pulp is prepared by the following steps: S1. Wood chips are crushed and passed through a 40-mesh screen to obtain wood powder, which is loaded into a digester. A sodium hydroxide solution with a mass concentration of 8% is added, and the solid-liquid ratio is 1:35. The pressure is increased to 0.8 MPa, and the heating rate is controlled at 8 ℃ / min. After heating to 195 ℃, the temperature is maintained for 2 h. The steam is released, and the product after reaction is removed, filtered, and a coarse pulp is obtained; S2. The coarse pulp is put into an activation tank, deionized water is added, and the pH value is adjusted to 5. Xylanase is added at an amount of 300 units of activity per gram of coarse pulp, and an activation aid is added. The concentration of the activation aid in the pulp solution is 25 g / L. The activation treatment is performed for 3 h. After the activation is completed, heating is performed to boiling, the activation is terminated, and the pretreated pulp solution is obtained. The activation aid is a mixture of sodium bisulfite and citric acid with a mass ratio of 20:1; S3. A chelating agent is added to the pretreated pulp solution at a mass fraction of 0.3% of the pretreated pulp solution, and adsorption treatment is performed for 0.5 h to obtain purified pulp; S4. The purified pulp is bleached with chlorine dioxide. The amount of chlorine dioxide used is 1.0%, the bleaching temperature is 75 ℃, and the bleaching time is 1 h. After bleaching is completed, the high-quality dissolved pulp is obtained.

[0020] The chelating agent in step S3 is prepared by the following steps: A1. Dissolve chitosan in an acetic acid solution with a mass fraction of 2% to obtain a chitosan acetic acid solution, the mass fraction of chitosan in the acetic acid solution being 0.4%, and stir to dissolve to obtain the chitosan acetic acid solution; A2. Add alpha amylase to the chitosan acetic acid solution, the amount of alpha amylase added to the chitosan acetic acid solution being 50 activity units / g, and stir for 0.5 h to obtain a mixture, and add sodium tripolyphosphate to the mixture while stirring, the content of sodium tripolyphosphate in the mixture being 1.5 g / L, and continue to stir for 30 min to obtain a modified chitosan solution.

[0021] In step S1, the wood chips are poplar wood from a wood processing plant in the southern region of Xinjiang, the length of the wood chips being 30-80 mm, and the width and thickness being 15-30 mm.

[0022] Example 2 A high-quality dissolving pulp is prepared by the following steps: S1. Crush the wood chips and pass them through a 20-mesh screen to obtain wood powder, and then load the wood powder into a digester, add a sodium hydroxide solution with a mass concentration of 6%, wherein the solid-liquid ratio is 1:30, increase the pressure to 0.6 MPa, control the temperature increase rate to be 5 ℃ / min, and heat to 185 ℃, and then maintain the temperature for 1.5 h, release the steam, cool, and then take out the product after reaction, filter, and obtain a crude pulp; S2. Add deionized water to the crude pulp in an activation tank, adjust the pH value to 4, add xylanase at an amount of 100 activity units per gram of crude pulp, and then add an activation aid, the concentration of the activation aid in the pulp being 20 g / L, and then perform activation treatment for 2 h, heat to boiling after the activation is completed, terminate the activation, and then cool to obtain a pretreated pulp, wherein the activation aid is a mixture of potassium bisulfite and citric acid with a mass ratio of 20:0.8; S3. Add a chelating agent to the pretreated pulp, the amount of the chelating agent being 0.2% of the mass of the pretreated pulp, and then perform adsorption treatment for 0.5 h to obtain purified pulp; S4. Perform bleaching treatment on the purified pulp using chlorine dioxide, the amount of chlorine dioxide being 0.8%, the bleaching temperature being 70 ℃, and the bleaching time being 0.5 h, and then obtain the high-quality dissolving pulp after the bleaching is completed.

[0023] The chelating agent in step S3 is prepared by the following steps: A1. Dissolve chitosan in an acetic acid solution with a mass fraction of 1% to obtain a chitosan acetic acid solution, the mass fraction of chitosan in the acetic acid solution being 0.3%, and stir to dissolve to obtain the chitosan acetic acid solution; A2. Add α-amylase to the chitosan acetate solution at a concentration of 10 activity units / g, stir for 1 hour to obtain a mixture, add sodium tripolyphosphate to the mixture while stirring at a concentration of 1g / L, and continue stirring for 20 minutes to obtain a modified chitosan solution.

[0024] In step S1, the wood chips are made from poplar wood from a timber processing plant in southern Xinjiang. The wood chips are 30-80mm long and 15-30mm wide and thick.

[0025] Example 3 A high-quality dissolving slurry is prepared by the following steps: S1. Crush the wood chips and pass them through a 60-mesh sieve to obtain wood powder. Put the wood powder into a steaming ball and add a 10% sodium hydroxide solution with a solid-liquid ratio of 1:40. Increase the pressure to 1.0 MPa and control the heating rate at 10℃ / min. After heating to 205℃, keep it at the temperature for 2.5 hours. Release the steam, cool, take out the product after the reaction, filter, and obtain a crude pulp. S2. Put the coarse pulp into the activation tank, add deionized water, adjust the pH to 6, add xylanase at a rate of 500 activity units per gram of coarse pulp, and then add activation aid at a concentration of 30 g / L in the pulp. Activate for 2 hours. After activation, heat to boiling, stop activation, cool, and obtain pretreated pulp. The activation aid is a mixture of sodium bisulfite and citric acid in a mass ratio of 20:1.2. S3. Add 0.4% (by mass) of chelating agent to the pretreated slurry and perform adsorption treatment for 1 hour to obtain purified slurry; S4. The purified slurry is bleached with chlorine dioxide at a dosage of 1.2%, a bleaching temperature of 80°C, and a bleaching time of 1.5 hours. After bleaching, the high-quality dissolving slurry is obtained.

[0026] The chelating agent in step S3 is prepared by the following steps: A1. Chitosan is dissolved in a 3% acetic acid solution to prepare a chitosan acetic acid solution. The mass fraction of chitosan in the acetic acid solution is 0.5%. The solution is stirred and dissolved to obtain a chitosan acetic acid solution. A2. Add α-amylase to chitosan acetate solution at a concentration of 100 activity units / g, stir for 0.5 h to obtain a mixture, add sodium tripolyphosphate to the mixture while stirring at a concentration of 2 g / L, and continue stirring for 40 min to obtain a modified chitosan solution.

[0027] In step S1, the wood chips are made from poplar wood from a timber processing plant in southern Xinjiang. The wood chips are 30-80mm long and 15-30mm wide and thick.

[0028] Example 4 A high-quality dissolving slurry is prepared by the following steps: S1. Crush the wood chips and pass them through a 20-mesh sieve to obtain wood powder. Put the wood powder into a steaming ball and add a 10% sodium hydroxide solution with a solid-liquid ratio of 1:30. Increase the pressure to 1.0 MPa and control the heating rate at 5℃ / min. After heating to 205℃, keep it at the temperature for 1.5 hours, release the steam, cool, take out the product after the reaction, filter, and obtain a crude pulp. S2. Put the coarse pulp into the activation tank, add deionized water, adjust the pH to 6, add xylanase at a rate of 100 activity units per gram of coarse pulp, and then add activation aid at a concentration of 30 g / L in the pulp. Activate for 4 hours. After activation, heat to boiling, stop activation, cool, and obtain pretreated pulp. The activation aid is a mixture of potassium bisulfite and citric acid in a mass ratio of 20:0.8. S3. Add 0.4% (by weight of the pretreated slurry) of chelating agent to the pretreated slurry and perform adsorption treatment for 0.5 hours to obtain purified slurry; S4. The purified slurry is bleached with chlorine dioxide at a dosage of 1.2%, a bleaching temperature of 70°C, and a bleaching time of 1.5 hours. After bleaching, the high-quality dissolving slurry is obtained.

[0029] The chelating agent in step S3 is prepared by the following steps: A1. Chitosan is dissolved in a 1% (w / w) acetic acid solution to prepare a chitosan acetic acid solution. The mass fraction of chitosan in the acetic acid solution is 0.5%. The solution is stirred and dissolved to obtain a chitosan acetic acid solution. A2. Add α-amylase to chitosan acetate solution at a concentration of 10 activity units / g, stir for 1 hour to obtain a mixture, add sodium tripolyphosphate to the mixture while stirring at a concentration of 1g / L, and continue stirring for 40 minutes to obtain a modified chitosan solution.

[0030] In step S1, the wood chips are made from poplar wood from a timber processing plant in southern Xinjiang. The wood chips are 30-80mm long and 15-30mm wide and thick.

[0031] Example 5 A high-quality dissolving slurry is prepared by the following steps: S1. Crush the wood chips and pass them through a 60-mesh sieve to obtain wood powder. Load the wood powder into a steaming ball and add a 6% sodium hydroxide solution with a solid-liquid ratio of 1:40. Increase the pressure to 0.6 MPa and control the heating rate at 10℃ / min. After heating to 185℃, keep the temperature and cook for 2.5 hours. Release the steam, cool, take out the reaction product, filter, and obtain a crude pulp. S2. Put the coarse pulp into the activation tank, add deionized water, adjust the pH to 4, add xylanase at a rate of 500 activity units per gram of coarse pulp, and then add activation aid at a concentration of 20 g / L in the pulp. Activate for 2 hours. After activation, heat to boiling, stop activation, cool, and obtain pretreated pulp. The activation aid is a mixture of sodium bisulfite and citric acid in a mass ratio of 20:1.2. S3. Add 0.2% (by mass) of chelating agent to the pretreated slurry and perform adsorption treatment for 1 hour to obtain purified slurry; S4. The purified slurry is bleached with chlorine dioxide at a dosage of 0.8%, a bleaching temperature of 80°C, and a bleaching time of 0.5 h. After bleaching, the high-quality dissolving slurry is obtained.

[0032] The chelating agent in step S3 is prepared by the following steps: A1. Chitosan is dissolved in a 3% acetic acid solution to prepare a chitosan acetic acid solution. The mass fraction of chitosan in the acetic acid solution is 0.3%. The solution is stirred and dissolved to obtain a chitosan acetic acid solution. A2. Add α-amylase to chitosan acetate solution at a concentration of 100 activity units / g, stir for 0.5 h to obtain a mixture, add sodium tripolyphosphate to the mixture while stirring at a concentration of 1 g / L, and continue stirring for 40 min to obtain a modified chitosan solution.

[0033] In step S1, the wood chips are made from poplar wood from a timber processing plant in southern Xinjiang. The wood chips are 30-80mm long and 15-30mm wide and thick.

[0034] Comparative Example 1 The only difference between this comparative example and Example 1 is that no activating agent was added in step S2, as detailed below: S2. Put the coarse pulp into the activation tank, add deionized water, adjust the pH to 5, add xylanase at a rate of 300 activity units per gram of coarse pulp, and activate for 3 hours. After activation, heat to boiling, stop activation, cool, and obtain pretreated pulp. Comparative Example 2 The only difference between this comparative example and Example 1 is that in step S3, the chitosan was not cross-linked in the preparation of the chelating agent; that is, α-amylase and sodium tripolyphosphate were not added. Specifically: The chelating agent in step S3 is prepared by the following steps: A1. Chitosan is dissolved in a 2% (w / w) acetic acid solution to prepare a chitosan acetic acid solution. The mass fraction of chitosan in the acetic acid solution is 0.4%. The solution is stirred and dissolved to obtain the chitosan acetic acid solution. A2. Stir the chitosan acetate solution for 1 hour to obtain a modified chitosan solution.

[0035] Comparative Example 3 The only difference between this comparative example and Example 1 is that no activating agent was added in step S2, and chitosan was not cross-linked modified in the preparation of the chelating agent in step S3.

[0036] Proof of effectiveness The performance of the dissolving slurries prepared in Examples 1-5 and Comparative Examples 1-3 was tested, and the specific results are shown in Table 1: Table 1

[0037] Results Analysis Analysis of Examples 1-5 and Comparative Examples 1-3, combined with the data in Table 1, shows that the preparation method provided in this application can effectively remove impurities, reduce iron content, and increase the methyl cellulose content of the dissolving pulp, ultimately obtaining a high-quality dissolving pulp. The high-quality dissolving pulp prepared by this invention has a methyl cellulose content of over 94.2%, an iron content of less than 20 ppm, and a whiteness of over 85%. Specific analysis is as follows: As can be seen from Comparative Example 1 and Example 1, the addition of bisulfite and citric acid in the activating agent can increase the alpha-cellulose content of the dissolving pulp. As can be seen from Comparative Example 2 and Example 1, the addition of α-amylase and sodium tripolyphosphate to cross-link the chitosan can improve the iron ion removal rate and effectively reduce the iron content. Comprehensive analysis of Comparative Examples 1-3 and Example 1 shows that the combined use of the activating agent and the cross-linking modification treatment of chitosan results in a significantly greater increase in the alpha-cellulose content than the sum of the increases when the activating agent and the cross-linking modification treatment of chitosan are used alone. This indicates that the combined use of the two can produce a synergistic effect, which can significantly increase the alpha-cellulose content of the dissolving pulp and ultimately obtain a high-quality dissolving pulp.

[0038] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0039] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a high-quality dissolving slurry, characterized in that, Includes the following steps: S1. Crush the wood chips and pass them through a 20-60 mesh sieve to obtain wood powder. Load the wood powder into a steaming ball and add a 6-10% sodium hydroxide solution with a solid-liquid ratio of 1:30-40. Increase the pressure to 0.6-1.0 MPa and control the heating rate at 5-10℃ / min. After heating to 185-205℃, keep the temperature and cook for 1.5-2.5 hours. Release the steam, cool, remove the reaction product, filter, and obtain a crude pulp. S2. Put the coarse pulp into the activation tank, add deionized water, adjust the pH to 4-6, add xylanase at a rate of 100-500 activity units per gram of coarse pulp, add activation aid, and carry out activation treatment. After activation, heat to boiling, stop activation, cool, and obtain pretreated pulp. The activation aid is a mixture of bisulfite and citric acid. S3. Add a chelating agent to the pretreated slurry and perform adsorption treatment for 0.5-1h to obtain purified slurry, wherein the chelating agent is sodium tripolyphosphate cross-linked modified chitosan. S4. Bleaching the purified slurry with chlorine dioxide at a concentration of 0.8-1.2%, at a bleaching temperature of 70-80℃, and for a bleaching time of 0.5-1.5h, yielding the high-quality dissolving slurry.

2. The preparation method according to claim 1, characterized in that, The chelating agent in step S3 is prepared by the following steps: A1. Dissolve chitosan in an acetic acid solution with a mass fraction of 1-3% to prepare a chitosan acetic acid solution. The mass fraction of chitosan in the acetic acid solution is 0.3-0.5%. Stir to dissolve and obtain the chitosan acetic acid solution. A2. Add α-amylase to the chitosan acetate solution and stir for 0.5-1 h to obtain a mixture. Add sodium tripolyphosphate to the mixture while stirring and continue stirring for 20-40 min to obtain a modified chitosan solution.

3. The preparation method according to claim 1, characterized in that, In step S3, the amount of chelating agent added is 0.2-0.4% of the mass of the pretreated slurry.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of bisulfite to citric acid in the activating agent is 20:0.8-1.

2.

5. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the activating agent in the slurry is 20-30 g / L, and the activation treatment time is 2-4 h.

6. The preparation method according to claim 2, characterized in that, In step A2, the amount of α-amylase added to the chitosan acetate solution is 10-100 activity units / g.

7. The preparation method according to claim 2, characterized in that, In step A2, the sodium tripolyphosphate content in the mixture is 1-2 g / L.

8. A high-quality dissolving slurry, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

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