Preparation method of pulp

Abstract

The invention provides a preparation method of pulp, which comprises the following steps: acquiring wood chips as a cooking raw material, preparing cooking liquor, performing two-stage cooking to obtain crude pulp, performing alkali treatment on the crude pulp to obtain alkali treated pulp, sequentially performing chlorine dioxide primary bleaching D0, alkali extraction bleaching E1 and chlorine dioxide secondary bleaching D1 on the alkali-treated pulp to obtain bleached pulp, and performing acid treatment on the bleached pulp to obtain the pulp. According to the preparation method disclosed by the invention, a synergistic combination mode of staged cooking, alkali treatment and simplified bleaching is comprehensively adopted, so that the total yield of the pulp is increased by 1-10%, and the yield of the pulp is increased by 1-10%. The content of alpha-cellulose is greater than or equal to 98%, the intrinsic viscosity is greater than 500mL / g, the degree of polymerization is greater than 700, and the whiteness is greater than or equal to 90% ISO.

Description

Technical Field

[0001] This disclosure relates to the field of pulping technology, and more specifically, to a method for preparing pulp. Background Technology

[0002] As a high-purity cellulose carrier, dissolving pulp is typically prepared from lignocellulose biomass through chemical treatment processes such as cooking and bleaching. Cooking and bleaching are key steps in the pulping process: cooking involves treating plant fiber raw materials with chemical solutions under specific temperature and pressure conditions, causing lignin, hemicellulose, and non-cellulose components such as oils and resins to dissolve, thereby achieving the separation and dissociation of cellulose; bleaching further processes the pulp obtained from cooking to remove residual impurities and pigments, improving the purity and whiteness of the cellulose. These processes yield cellulose products suitable for specific industrial applications. However, existing cooking and bleaching technologies have the following problems:

[0003] First, the mainstream production methods for dissolving pulp using wood / non-wood fiber raw materials at present include the sulfite process and the pre-hydrolyzed sulfate process. Due to limitations in equipment and wastewater treatment, domestic dissolving pulp mainly uses the pre-hydrolyzed sulfate pulp method, which adds a pre-hydrolysis stage before the traditional sulfate pulping stage to achieve targeted removal of hemicellulose. However, the yield of the pulp produced is relatively low, generally only 30%-35% (relative to fiber raw materials), which is 12%-15% lower than that of ordinary pulp. Therefore, the raw material cost per ton of pulp is about 33% higher than that of ordinary pulp, which greatly reduces the profit margin of dissolving pulp.

[0004] Second, in existing technologies, cooking often uses a one-step high-temperature cooking method, which involves directly raising the temperature from 25°C to 170°C and holding it at 170°C for 1-3 hours. Although this can remove some hemicellulose, the high temperature inevitably leads to drastic degradation of cellulose, resulting in decreased viscosity, reduced yield, and high peak energy consumption.

[0005] Third, in existing technologies, conventional bleaching processes typically employ oxygen delignification combined with elemental chlorine-free bleaching (such as DED bleaching). However, the selective removal capacity of oxygen delignification is insufficient, easily leading to excessive degradation of cellulose and a decrease in pulp viscosity; while conventional DED bleaching has limited bleaching efficiency, making it difficult to increase whiteness to over 90% without damaging the fibers.

[0006] Fourth, those skilled in the art generally believe that extending the processing time or increasing the temperature is the only way to improve purity and whiteness, but this inevitably sacrifices the degree of fiber polymerization.

[0007] Therefore, there is an urgent need to provide a method for preparing pulp that can solve the first to fourth technical problems mentioned above. Summary of the Invention

[0008] In view of this, the present disclosure provides a method for preparing pulp to solve the first to fourth technical problems existing in the prior art.

[0009] The method for preparing pulp disclosed herein includes the following steps:

[0010] Wood chips are obtained as the cooking raw material, and the cooking raw material is screened and washed;

[0011] Prepare the cooking liquor using the sulfate process. Prepare a mixed solution of sodium hydroxide and sodium sulfide. The amount of alkali used (based on Na₂O) is 15%-25% of the oven-dry weight of the material; the degree of sulfidation (based on Na₂O) is 20%-40%.

[0012] A two-stage cooking process was used to obtain a crude pulp. In the first stage, the temperature was increased from 25℃ to 130℃-140℃ for 60-70 minutes, followed by a holding time of 30-90 minutes. In the second stage, the temperature was increased from 130℃-140℃ to 160℃-170℃ for 15-20 minutes, followed by a holding time of 30-90 minutes. The sum of the holding times for the first and second stages was 1-3 hours. The kappa value of the crude pulp was 15-20.

[0013] The coarse slurry is subjected to alkali treatment to obtain alkali-treated slurry. The alkali solution is at least one of sodium hydroxide and potassium hydroxide, the alkali solution concentration is 1%-10%, the temperature is 20℃-60℃, and the time is 30min-120min.

[0014] The alkali-treated slurry is subjected to sequential chlorine dioxide primary bleaching (D0), alkali extraction bleaching (E1), and chlorine dioxide secondary bleaching (D1) to obtain a bleached slurry; wherein,

[0015] The process conditions for one-time chlorine dioxide bleaching of D0 are as follows: pulp concentration of 10wt%-20wt%, time of 60min-120min, temperature of 70℃-95℃, chlorine dioxide dosage of 1.0%-2.5% relative to oven-dry pulp mass, and residual chlorine after bleaching of 0-0.1g / L.

[0016] The process conditions for alkaline extraction bleaching E1 are as follows: pulp concentration of 10wt%-20wt%, time of 60in-120min, temperature of 70℃-95℃, and sodium hydroxide dosage of 1.0%-2.0% relative to oven-dry pulp mass.

[0017] The process conditions for the secondary chlorine dioxide bleaching D1 are as follows: pulp concentration of 10wt%-20wt%, time of 60min-120min, temperature of 70℃-95℃, chlorine dioxide dosage of 0.5%-1.5% relative to oven-dry pulp mass, and residual chlorine after bleaching of 0-0.1g / L.

[0018] The bleached pulp is acid-treated to obtain pulp, with the amount of sulfuric acid being greater than 0 and less than or equal to 0.5% relative to the oven-dry pulp mass, and the amount of DTPA being 0.1%-2%.

[0019] Optionally, the liquid ratio in the cooking process is 1:3 to 1:6.

[0020] Optionally, the wood chips after screening have the following characteristics: length of 15mm-30mm, width not exceeding 20mm, and thickness of 3mm-5mm.

[0021] Optionally, the pulp has an α-cellulose content of ≥98%, an intrinsic viscosity of ≥500 mL / g, a degree of polymerization of ≥700, and a whiteness of ≥90% ISO.

[0022] Compared with the prior art, the pulp preparation method provided in this disclosure achieves at least the following beneficial effects:

[0023] First, the preparation method disclosed herein comprehensively employs a synergistic combination of segmented cooking, alkali treatment, and simplified bleaching. The cooking process utilizes segmented cooking, namely heating-holding-heating-holding, which gently reduces alkaline degradation of cellulose and avoids the cellulose dissolution loss caused by traditional high-temperature, long-term processing. This disclosure combines alkali treatment and simplified bleaching on the coarse pulp. After alkali treatment, the pulp is fluffy, with reduced content of residual hemicellulose and lignin, and the bleaching liquor penetrates evenly, reducing the need for repeated treatments due to discoloration or uneven bleaching. By integrating and optimizing the endpoints of the cooking and alkali treatment stages, the degree of cellulose degradation is controlled, ensuring that the cellulose retains sufficient strength while possessing high reactivity, thus enabling smooth subsequent bleaching. The pulp yield obtained by the preparation method disclosed herein is increased by 1%-10%, with an α-cellulose content greater than or equal to 98%, intrinsic viscosity greater than 500 mL / g, degree of polymerization greater than 700, and brightness greater than or equal to 90% ISO, achieving a balance between high yield and high quality.

[0024] Secondly, this disclosure also overcomes the technical bias in the field. Existing technologies often avoid excessive oxidation treatment before bleaching to prevent over-degradation of cellulose. However, this disclosure combines alkali treatment with simplified bleaching of the coarse pulp. By optimizing the endpoints of the cooking and alkali treatment stages, the degree of cellulose degradation is controlled, allowing the cellulose to retain sufficient strength while maintaining high reactivity, thus enabling subsequent bleaching to proceed smoothly. This combination of "cooking stage and alkali treatment endpoint control with simplified bleaching" is not technically illustrated in existing technologies.

[0025] Third, this disclosure breaks through the inverse relationship between purity and strength. In the prior art, the higher the purity (α-cellulose content), the lower the viscosity (degree of polymerization). The pulp obtained by the method of this disclosure achieves high purity (α-cellulose content greater than or equal to 98%) while maintaining a high viscosity (greater than 500 mL / g), which is unpredictable by those skilled in the art and yields unexpected technical results.

[0026] Fourth, the cumulative energy consumption effect of this disclosure is reduced. By adopting a combination of segmented heating and simplified bleaching, the overall processing technology is simplified, and steam and chemicals are reduced.

[0027] Of course, implementing any method of this disclosure does not necessarily require achieving all of the technical effects described above at the same time.

[0028] Other features and advantages of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0029] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.

[0030] Figure 1 This is a flowchart of the pulp preparation method provided in this disclosure. Detailed Implementation

[0031] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present disclosure.

[0032] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this disclosure or its application or use.

[0033] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0034] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0036] Combination Figure 1 This disclosure provides a method for preparing pulp, including the following steps:

[0037] S1, obtain wood chips as cooking raw material, and screen and wash the cooking raw material;

[0038] S2, for preparing the cooking liquor, uses the sulfate method for cooking, and prepares a mixed solution of sodium hydroxide and sodium sulfide. The amount of alkali used, calculated as Na2O, is 15%-25% of the dry weight of the material; the degree of sulfidation, calculated as Na2O, is 20%-40%.

[0039] S3 uses a two-stage cooking process to obtain coarse pulp. In the first stage, the temperature is raised from 25℃ to 130℃-140℃ for 60-70 minutes, followed by a holding time of 30-90 minutes. In the second stage, the temperature is raised from 130℃-140℃ to 160℃-170℃ for 15-20 minutes, followed by a holding time of 30-90 minutes. The sum of the holding times for the first and second stages is 1-3 hours. The kappa value of the coarse pulp is 15-20.

[0040] S4, the coarse pulp is subjected to alkali treatment to obtain alkali-treated pulp, the alkali solution is at least one of sodium hydroxide and potassium hydroxide, the alkali solution concentration is 1%-10%, the temperature is 20℃-60℃, and the time is 30min-120min;

[0041] S5, the alkali-treated slurry is subjected to sequential chlorine dioxide bleaching (D0), alkali extraction bleaching (E1), and chlorine dioxide bleaching (D1) to obtain a bleached slurry; wherein...

[0042] The process conditions for one-time bleaching of D0 with chlorine dioxide are as follows: pulp concentration of 10wt%-20wt%, time of 60min-120min, temperature of 70℃-95℃, chlorine dioxide dosage of 1.0%-2.5% relative to oven-dry pulp quality, and residual chlorine after bleaching of 0-0.1g / L.

[0043] The process conditions for alkaline extraction bleaching of E1 are as follows: pulp concentration of 10wt%-20wt%, time of 60in-120min, temperature of 70℃-95℃, and sodium hydroxide dosage of 1.0%-2.0% relative to oven-dry pulp mass.

[0044] The process conditions for secondary bleaching of D1 with chlorine dioxide are as follows: pulp concentration of 10wt%-20wt%, time of 60min-120min, temperature of 70℃-95℃, chlorine dioxide dosage of 0.5%-1.5% relative to oven-dry pulp quality, and residual chlorine after bleaching of 0-0.1g / L.

[0045] S6, acid treatment of bleached pulp to obtain pulp, with sulfuric acid dosage greater than 0 and less than or equal to 0.5% and DTPA dosage 0.1%-2% relative to oven-dry pulp quality.

[0046] Specifically, for S1, the appropriate wood species should be selected based on the purpose of cooking and the product requirements of the pulp, such as coniferous wood (pine, spruce, etc.) or broad-leaved wood (poplar, birch, eucalyptus, etc.).

[0047] The wood is then sliced ​​into chips using a chipper, and the chips are carefully screened and washed. Optionally, a vibrating screen or drum screen can be used to screen the wood chips. Chips with a length of 15mm-30mm, a width not exceeding 20mm, and a thickness of 3mm-5mm are selected. Of course, more uniform chip size improves the cooking effect, allowing chemicals to penetrate more evenly into each chip during cooking. Chips of similar size have similar specific surface areas and pore structures, resulting in a more consistent rate of chemical adsorption on the surface and diffusion into the interior. In sulfate cooking, chemicals such as sodium hydroxide and sodium sulfide can act on each chip simultaneously, allowing lignin, hemicellulose, and other components to degrade and dissolve synchronously, ensuring uniform delignification after cooking and providing stable raw materials for subsequent pulping. After screening, dust, sand, bark, and other impurities on the surface of the wood chips are washed away by stirring and soaking.

[0048] In step S2, the sulfate cooking process involves a cooking liquor composed of sodium hydroxide and sodium sulfide reacting chemically with lignin, hemicellulose, and other components in the wood chips under high temperature and pressure, causing them to dissolve and separate, thus obtaining relatively pure cellulose to provide raw materials for the subsequent pulping process. Optionally, for harder woods, a higher degree of sulfidation (e.g., 30%-40%) and a higher alkali content (e.g., 20%-25%) can be selected; while for easier-to-cook woods, a lower degree of sulfidation (e.g., 20%-30%) and a lower alkali content (e.g., 15%-20%) can be selected. No specific limitations are imposed here; the degree of sulfidation and the amount of alkali can be determined based on the type and quality of the raw materials and the cooking requirements.

[0049] It should be noted that there is no requirement for the order of S1 and S2; they can be performed simultaneously.

[0050] For step S3, which is the cooking process, a two-stage cooking method is adopted. In the first stage, the temperature is raised and then kept warm. In the second stage, the temperature is raised again and then kept warm again. Optionally, the cooking liquor ratio is 1:3-1:6, and preferably, the cooking liquor ratio is 1:4.

[0051] The first section is divided into heating and heat preservation, specifically...

[0052] Heating: Start the heating device to uniformly raise the temperature inside the cooking equipment from 25℃ to 130℃-140℃, and control the heating time to 60min-70min.

[0053] Insulation: Once the temperature reaches 130℃-140℃, maintain this temperature for 30-90 minutes. Optionally, the insulation time can be 60-90 minutes.

[0054] During the heat preservation stage, lignin begins to undergo preliminary degradation and dissolution reactions, and the chemicals fully contact and react with the components in the wood chips. Simultaneously, the first heat preservation is carried out at 130℃-140℃, which is a sensitive zone for hemicellulose degradation, allowing for more selective removal of hemicellulose compared to cellulose.

[0055] The second section is divided into heating and heat preservation, specifically...

[0056] Heating: Continue heating, rapidly increasing the temperature from 130℃-140℃ to 160℃-170℃ over a period of 15-20 minutes. Rapid heating accelerates the reaction rate and further promotes the removal of lignin.

[0057] Insulation: Insulate at 160℃-170℃ for 30-90 minutes. Optionally, the insulation time can be 60-90 minutes. This stage is the deep deligninization stage. By extending the insulation time, the kappa number in the pulp can be reduced to the target range of 15-20.

[0058] It should be noted that the sum of the heat preservation time of the first stage and the heat preservation time of the second stage should be 1-3 hours. Compared with the prior art of directly heating to 160℃-170℃ and holding for 1-3 hours, the total heat preservation time of this disclosure has not increased.

[0059] This disclosure employs a segmented heating alkali treatment during the cooking stage. The first holding temperature is 130℃-140℃, a sensitive range for hemicellulose degradation, allowing for more selective removal of hemicellulose compared to cellulose. The temperature is then raised to the target temperature of 160℃-170℃ for a second holding time of 30-90 minutes. The total holding time for both the first and second holding times remains 1-3 hours. Compared to existing technologies that directly heat to 160℃-170℃ and hold for 1-3 hours, this disclosure avoids prolonged exposure of cellulose at 160℃-170℃, achieving both energy saving and cellulose protection. Furthermore, this step provides a substrate with higher reactivity and fewer impurities for subsequent bleaching.

[0060] For step S4, the alkali treatment process, optionally, the alkali solution can be sodium hydroxide, potassium hydroxide, or a mixture of sodium hydroxide and potassium hydroxide. The alkali concentration can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or a range between any two values ​​from 1% to 10%, for example, 2% to 8%. Optionally, the temperature can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, or 60℃, or a range between any two values ​​from 25℃ to 60℃, for example, 30℃ to 50℃. Optionally, the time can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min, or a range between any two values ​​from 30 min to 120 min, for example, 60 min to 90 min.

[0061] After the alkali treatment in step S4, hemicellulose, degraded cellulose, and residual lignin in the pulp are physically dissolved, which reduces the difficulty of subsequent bleaching.

[0062] For step S5, which is the bleaching process, this disclosure adopts a simplified bleaching method, which does not use oxygen bleaching, but instead uses D0-E1-D1 bleaching.

[0063] For a single chlorine dioxide bleaching of D0 pulp, the pulp concentration is 10wt%-20wt%, the time is 60min-120min, the temperature is 70℃-95℃, the chlorine dioxide dosage is 1.0%-2.5% relative to the oven-dry pulp mass, and the residual chlorine after bleaching is 0-0.1g / L. Optionally, the pulp concentration can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%, or any range between 10% and 20%, such as 10%-15%. The time can be 60min, 70min, 80min, 90min, 100min, 110min, or 120min, or any range between 60min and 120min, such as 60min-90min. The temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, or 95℃, or a range between any two points between 70℃ and 95℃, such as 80℃-90℃. The chlorine dioxide dosage relative to the oven-dry pulp quality is 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, or 2.5%, or a range between any two points between 1.0% and 2.5%, such as 1.5%-2.0%.

[0064] For alkali extraction bleaching E1, the pulp concentration is 10wt%-20wt%, the time is 60min-120min, the temperature is 70℃-95℃, and the sodium hydroxide dosage is 1.0%-2.0% relative to the oven-dry pulp mass. Optionally, the pulp concentration can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%, or any range between 10% and 20%, for example, 10%-15%. The time can be 60min, 70min, 80min, 90min, 100min, 110min, or 120min, or any range between 60min and 120min, for example, 60min-90min. The temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, or 95℃, or a range between any two points between 70℃ and 95℃, such as 80℃-90℃. The sodium hydroxide dosage relative to the oven-dry pulp mass can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, or a range between any two points between 1.0% and 2.0%, such as 1.5%-2.0%.

[0065] For chlorine dioxide secondary bleaching D1, the pulp concentration is 10wt%-20wt%, the time is 60min-120min, the temperature is 70℃-95℃, the chlorine dioxide dosage is 0.5%-1.5% relative to the oven-dry pulp mass, and the residual chlorine after bleaching is 0-0.1g / L. Optionally, the pulp concentration can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%, or any range between 10% and 20%, for example, 10%-15%. The time can be 60min, 70min, 80min, 90min, 100min, 110min, or 120min, or any range between 60min and 120min, for example, 60min-90min. The temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, or 95℃, or a range between any two points between 70℃ and 95℃, such as 80℃-90℃. The chlorine dioxide dosage relative to the oven-dry pulp quality is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, or a range between any two points between 0.5% and 1.5%, such as 0.6%-1.0%.

[0066] This disclosure employs a combination of alkali treatment and bleaching for coarse pulp. After alkali treatment, hemicellulose, degraded cellulose, and residual lignin in the pulp are physically dissolved, reducing the difficulty of subsequent bleaching. At the same time, the pulp becomes more fluffy after alkali treatment, allowing the fibers to swell more fully in the bleaching solution, resulting in more uniform penetration of the bleaching solution and higher reaction efficiency.

[0067] The simplified bleaching process disclosed herein eliminates the oxygen bleaching process, thus avoiding cellulose damage caused by traditional processes that increase bleaching stages, temperatures, and chemical dosages in order to improve whiteness.

[0068] For step S6, which is an acid treatment process, the chelating agent DTPA is added. Optionally, the amount of sulfuric acid can be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any value between 0 and 0.5%, for example, the amount of sulfuric acid is 0.1%-0.4%. The amount of DTPA can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, or any value between 0.1% and 2%, for example, 0.3%-1%.

[0069] The acid treatment in this embodiment can accurately remove metal ions and residual bleaching agents introduced during the bleaching process, stabilize whiteness, and further improve purity.

[0070] The following are specific examples.

[0071] Example 1

[0072] This embodiment uses eucalyptus wood as the raw material.

[0073] a) Obtain eucalyptus wood chips as cooking raw material, and screen and wash them. The wood chips should be 15mm-30mm in length, no more than 20mm in width, and 3mm-5mm in thickness.

[0074] b) Cooking is carried out with a cooking liquor ratio of 1:4, a sulfidation degree of 30%, and an alkali amount of 18% of the dry weight of the material. The first stage of heat preservation is 140°C for 60 min, and the second stage of heat preservation is 160°C for 90 min. The resulting coarse pulp has a kappa value of 16.

[0075] c) Alkali treatment conditions for coarse pulp: alkali concentration (sodium hydroxide, potassium hydroxide, etc.) 7%, reaction at room temperature for 60 min to obtain alkali-treated pulp.

[0076] d) The alkali-treated slurry is bleached sequentially using D0E1D1 to obtain bleached slurry;

[0077] The process conditions for section D0 are: pulp concentration 10wt%, time 60min, temperature 80℃, and chlorine dioxide dosage 2.0% relative to oven-dry pulp mass.

[0078] The process conditions for section E1 are: pulp concentration 10wt%, time 60min, temperature 80℃, and sodium hydroxide dosage 2.0% relative to oven-dry pulp mass.

[0079] The process conditions for section D1 are: pulp concentration 10wt%, time 60min, temperature 80℃, and chlorine dioxide dosage 1.5% relative to oven-dry pulp quality.

[0080] e) Acid treatment of bleached pulp to obtain pulp, reaction time at room temperature for 60 min, addition of sulfuric acid of 0.5% (or adjustment of the system pH to 3.0 with sulfuric acid), and 1% DTPA (relative to oven-dry pulp).

[0081] Example 2

[0082] This embodiment uses poplar wood as the raw material.

[0083] a) Obtain poplar wood chips as cooking raw materials, and screen and wash them. The length of the wood chips is 15mm-30mm, the width is no more than 20mm, and the thickness is 3mm-5mm.

[0084] b) The pulp is cooked with a sulfurization of 28% and an alkali content of 17% of the dry weight of the material. The first stage of the cooking process is held at 135°C for 90 minutes. The second stage of the cooking process is held at 165°C for 90 minutes. The resulting pulp has a kappa value of 20.

[0085] c) Alkali treatment conditions for coarse pulp: alkali concentration (sodium hydroxide, potassium hydroxide, etc.) 8%, reaction at room temperature for 60 min to obtain alkali-treated pulp.

[0086] d) Bleaching the alkali-treated slurry with D0E1D1 to obtain bleached slurry.

[0087] The process conditions for section D0 are: pulp concentration 10wt%, time 60min, temperature 80℃, and chlorine dioxide dosage 2.0% relative to oven-dry pulp mass.

[0088] The process conditions for section E1 are: pulp concentration 10wt%, time 60min, temperature 80℃, and sodium hydroxide dosage 2.0% relative to oven-dry pulp mass; to obtain bleached pulp.

[0089] The process conditions for section D1 are: pulp concentration 10wt%, time 60min, temperature 80℃, and chlorine dioxide dosage 1.5% relative to oven-dry pulp quality.

[0090] e) Acid treatment of bleached pulp to obtain pulp, reaction time at room temperature for 60 min, addition of sulfuric acid of 0.5% (or adjustment of the system pH to 3.0 with sulfuric acid), and 1% DTPA (relative to oven-dry pulp).

[0091] Example 3

[0092] This embodiment uses birch wood as the raw material.

[0093] a) Obtain birch wood chips as cooking raw material, and screen and wash them. The length of the wood chips is 15mm-30mm, the width is no more than 20mm, and the thickness is 3mm-5mm.

[0094] b) Cook the material with a sulfurization of 30% and an alkali dosage of 17% of the dry weight of the material. The first stage of heat treatment is at 130°C for 90 minutes. The second stage of heat treatment is at 160°C for 60 minutes. The resulting coarse pulp has a kappa value of 18.

[0095] c) Alkali treatment conditions for coarse pulp: alkali concentration (sodium hydroxide, potassium hydroxide) 8%, reaction at room temperature for 60 min to obtain alkali-treated pulp;

[0096] d) The alkali-treated slurry is bleached sequentially using the D0-E1-D1 method to obtain the bleached slurry;

[0097] The process conditions for section D0 are: pulp concentration 10wt%, time 60min, temperature 80℃, and chlorine dioxide dosage 1.5% relative to oven-dry pulp quality.

[0098] The process conditions for section E1 are: pulp concentration 10wt%, time 60min, temperature 80℃, and sodium hydroxide dosage 2.0% relative to oven-dry pulp mass; to obtain bleached pulp.

[0099] The process conditions for section D1 are: pulp concentration 10wt%, time 60min, temperature 80℃, and chlorine dioxide dosage 1.0% relative to oven-dry pulp quality.

[0100] e) Acid treatment is performed on the bleached pulp to obtain pulp. The reaction time is 60 min at room temperature. The amount of sulfuric acid added is 0.5% (or the pH of the system is adjusted to 3.0 with sulfuric acid), and the amount of 1% DTPA is added (relative to oven-dry pulp).

[0101] Example 4

[0102] This embodiment uses euonymus as the raw material.

[0103] a) Obtain wood chips as cooking raw material, screen and wash them. The wood chips should be 15mm-30mm in length, no more than 20mm in width, and 3mm-5mm in thickness.

[0104] b) Cooking is carried out with a cooking liquor ratio of 1:3, a sulfidation degree of 20%, and an alkali amount of 15% of the dry weight of the material. The first stage of heat preservation is 130°C for 60 minutes; the second stage of heat preservation is 160°C for 30 minutes; a coarse pulp is obtained with a kappa value of 20.

[0105] c) Alkali treatment conditions for coarse pulp: alkali concentration (sodium hydroxide, potassium hydroxide, etc.) 6%, reaction at room temperature for 30 minutes to obtain alkali-treated pulp.

[0106] d) The alkali-treated slurry is bleached sequentially using D0E1D1 to obtain bleached slurry;

[0107] The process conditions for section D0 are: pulp concentration 10wt%, time 60min, temperature 70℃, and chlorine dioxide dosage 1.0% relative to oven-dry pulp mass.

[0108] The process conditions for section E1 are: pulp concentration 10wt%, time 60min, temperature 70℃, and sodium hydroxide dosage 1.0% relative to oven-dry pulp mass.

[0109] The process conditions for section D1 are: pulp concentration 10wt%, time 60min, temperature 70℃, and chlorine dioxide dosage 0.5% relative to oven-dry pulp quality.

[0110] e) Acid treatment of bleached pulp to obtain pulp, reaction time at room temperature for 60 min, addition of 0.1% sulfuric acid and 0.1% DTPA (relative to oven-dry pulp).

[0111] Example 5

[0112] This embodiment uses spruce as raw material.

[0113] a) Obtain spruce wood chips as cooking raw material, and screen and wash them. The wood chips should be 15mm-30mm in length, no more than 20mm in width, and 3mm-5mm in thickness.

[0114] b) Cooking is carried out with a cooking liquor ratio of 1:6, a sulfidation degree of 40%, and an alkali amount of 25% of the dry weight of the material. The first stage of heat preservation is 140°C for 90 min; the second stage of heat preservation is 170°C for 90 min; and a coarse pulp is obtained with a kappa value of 15.

[0115] c) Alkali treatment conditions for coarse pulp: alkali concentration (sodium hydroxide, potassium hydroxide, etc.) 10%, reaction at 60°C for 120 min to obtain alkali-treated pulp.

[0116] d) The alkali-treated slurry is bleached sequentially using D0E1D1 to obtain bleached slurry;

[0117] The process conditions for section D0 are: pulp concentration 20wt%, time 120min, temperature 95℃, and chlorine dioxide dosage 2.5% relative to oven-dry pulp mass.

[0118] The process conditions for section E1 are: pulp concentration 20wt%, time 120min, temperature 95℃, and sodium hydroxide dosage 2.0% relative to oven-dry pulp mass.

[0119] The process conditions for section D1 are: pulp concentration 20wt%, time 120min, temperature 95℃, and chlorine dioxide dosage 1.5% relative to oven-dry pulp quality.

[0120] e) Acid treatment of bleached pulp to obtain pulp, reaction time at room temperature for 60 min, addition of sulfuric acid at 0.5% and DTPA at 2% (relative to oven-dry pulp).

[0121] Example 6

[0122] This embodiment uses pine wood as the raw material.

[0123] a) Obtain pine wood chips as cooking raw material, and screen and wash them. The length of the wood chips is 15mm-30mm, the width is no more than 20mm, and the thickness is 3mm-5mm.

[0124] b) Cooking is carried out with a cooking liquor ratio of 1:5, a sulfidation degree of 30%, and an alkali amount of 20% of the dry weight of the material. The first stage of heat preservation is 135°C for 60 min; the second stage of heat preservation is 165°C for 60 min; a coarse pulp is obtained with a kappa number of 17.

[0125] c) Alkali treatment conditions for coarse pulp: alkali concentration (sodium hydroxide, potassium hydroxide, etc.) 8%, reaction at 40°C for 75 min to obtain alkali-treated pulp.

[0126] d) The alkali-treated slurry is bleached sequentially using D0E1D1 to obtain bleached slurry;

[0127] The process conditions for section D0 are: pulp concentration 15wt%, time 90min, temperature 80℃, and chlorine dioxide dosage 1.5% relative to oven-dry pulp quality.

[0128] The process conditions for section E1 are: pulp concentration 15wt%, time 90min, temperature 80℃, and sodium hydroxide dosage 1.5% relative to oven-dry pulp mass.

[0129] The process conditions for section D1 are: pulp concentration 15wt%, time 90min, temperature 80℃, and chlorine dioxide dosage 1.0% relative to oven-dry pulp quality.

[0130] e) Acid treatment of bleached pulp to obtain pulp, reaction time at room temperature for 60 min, addition of sulfuric acid at 0.3% and DTPA at 1% (relative to oven-dry pulp).

[0131] The slurry performance results after treatment by Examples 1, 2, 3, 4, 5, and 6 are shown in Table 1 below.

[0132] Table 1. Slurry performance results of Examples 1 to 6

[0133] Performance indicators Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Pulping yield / % 45.6% 46.3% 46.1% 48.7% 41.3% 45.8% <![CDATA[ Intrinsic viscosity / mL·g -1 > 511 550 594 589 507 541 Degree of aggregation 715 776 845 837 709 762 R10 / % 98.7 98.2 98.4 98.0 99.2 98.5 R18 / % 99.8 99.1 98.8 98.2 99.5 98.8 Whiteness / % 90.0 91.1 90.8 90.0 92.5 91.5 Ash content / % 0.15 0.08 0.06 0.21 0.02 0.07 Iron ions / ppm 17 15 18 25 11 20 Magnesium ions / ppm 62 45 30 70 29 51 Calcium ions / ppm 128 90 51 115 80 45 Copper ions / ppm ND ND ND ND ND ND

[0134] In Table 1, ND indicates that it was not detected.

[0135] While specific embodiments of this disclosure have been described in detail by way of example, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. A method for preparing pulp, characterized in that, Including the following steps: Wood chips are obtained as the cooking raw material, and the cooking raw material is screened and washed; Prepare the cooking liquor using the sulfate process. Prepare a mixed solution of sodium hydroxide and sodium sulfide. The amount of alkali used (based on Na₂O) is 15%-25% of the oven-dry weight of the material; the degree of sulfidation (based on Na₂O) is 20%-40%. A two-stage cooking process was used to obtain a crude pulp. In the first stage, the temperature was increased from 25℃ to 130℃-140℃ for 60-70 minutes, followed by a holding time of 30-90 minutes. In the second stage, the temperature was increased from 130℃-140℃ to 160℃-170℃ for 15-20 minutes, followed by a holding time of 30-90 minutes. The sum of the holding times for the first and second stages was 1-3 hours. The kappa value of the crude pulp was 15-20. The coarse slurry is subjected to alkali treatment to obtain alkali-treated slurry. The alkali solution is at least one of sodium hydroxide and potassium hydroxide, the alkali solution concentration is 1%-10%, the temperature is 20℃-60℃, and the time is 30min-120min. The alkali-treated slurry is subjected to sequential chlorine dioxide primary bleaching (D0), alkali extraction bleaching (E1), and chlorine dioxide secondary bleaching (D1) to obtain a bleached slurry; wherein, The process conditions for one-time chlorine dioxide bleaching of D0 are as follows: pulp concentration of 10wt%-20wt%, time of 60min-120min, temperature of 70℃-95℃, chlorine dioxide dosage of 1.0%-2.5% relative to oven-dry pulp mass, and residual chlorine after bleaching of 0-0.1g / L. The process conditions for alkaline extraction bleaching E1 are as follows: pulp concentration of 10wt%-20wt%, time of 60in-120min, temperature of 70℃-95℃, and sodium hydroxide dosage of 1.0%-2.0% relative to oven-dry pulp mass. The process conditions for the secondary chlorine dioxide bleaching D1 are as follows: pulp concentration of 10wt%-20wt%, time of 60min-120min, temperature of 70℃-95℃, chlorine dioxide dosage of 0.5%-1.5% relative to oven-dry pulp mass, and residual chlorine after bleaching of 0-0.1g / L. The bleached pulp is acid-treated to obtain pulp, with the amount of sulfuric acid being greater than 0 and less than or equal to 0.5% relative to the oven-dry pulp mass, and the amount of DTPA being 0.1%-2%.

2. The method for preparing pulp according to claim 1, characterized in that, The liquid-to-cook ratio is 1:3 to 1:

6.

3. The method for preparing pulp according to claim 1, characterized in that, The selected wood chips have a length of 15mm-30mm, a width of no more than 20mm, and a thickness of 3mm-5mm.

4. The method for preparing pulp according to claim 1, characterized in that, The pulp has an α-cellulose content of ≥98%, an intrinsic viscosity of ≥500 mL / g, a degree of polymerization of ≥700, and a whiteness of ≥90% ISO.

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