Preparation method of pulp and its integrated equipment of cooking, bleaching and washing

Abstract

This invention discloses a method for preparing pulp and an integrated cooking, bleaching, and washing device. Deep purification is achieved through high-temperature, high-pressure cooking. Before bleaching, a magnesium sulfate solution is introduced to replace the waste liquid and form a protective layer. Mild bleaching is then performed under controlled conditions, followed by dehydration and drying for final shaping. The magnesium ions in the magnesium sulfate effectively inhibit the oxidative degradation of cellulose molecular chains by hydrogen peroxide in the alkaline bleaching environment, synergistically ensuring the high purity, high whiteness, high degree of polymerization, and excellent reactivity of the pulp product. After cooking, the magnesium sulfate solution is used for replacement and concentration control to remove impurities while inhibiting localized over-oxidation that may be exacerbated by uneven mixing. The device employs a multi-stage filtration structure, achieving step-by-step filtration by adjusting the filter pore size. Thus, efficient cooking, rapid washing, and mild, uniform bleaching are synergistically achieved within a single device.

Description

Technical Field

[0001] This invention relates to the field of pulp preparation technology, and more particularly to a method for preparing pulp and an integrated cooking, bleaching and washing device thereof. Background Technology

[0002] In existing technologies, conventional methods for preparing pulp typically involve using cotton linters or refined cotton, bamboo chips, or wood chips as raw materials. The pulp is then subjected to high-temperature, high-pressure alkaline or alkaline-oxygen cooking to remove most of the hemicellulose, waxes, and pigments. This is followed by a multi-stage bleaching process to further improve whiteness and purity. Finally, the pulp undergoes acid treatment, washing, dehydration, and drying to produce the finished product. This method emphasizes the purification of cellulose through multi-step chemical processing.

[0003] The main drawbacks of existing technologies are: complex process flow, cumbersome procedures, requiring multiple equipment and multiple procedures to be completed sequentially. Traditional multi-stage bleaching processes are complex, have long production cycles, and high energy consumption. They may also use chlorine-containing bleaching agents, which can easily generate environmentally unfriendly byproducts such as adsorbable organic halides. Furthermore, improper process control can easily lead to excessive or uneven degradation of cellulose molecular chains, affecting the degree of polymerization and the uniformity of pulp distribution, thereby ultimately restricting the performance and quality stability of fiber products.

[0004] Therefore, existing technologies need to be improved to solve the above problems. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art by providing a method for preparing pulp and an integrated cooking, bleaching and washing equipment thereof, aiming to solve the defects of the prior art, such as complex process flow, long production cycle, high energy consumption, and excessive degradation of cellulose and insufficient whiteness during pulp preparation.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing pulp, comprising the following steps:

[0007] S1: After mixing the fiber raw material with the liquid, place it in the reaction zone of the integrated cooking, bleaching and washing equipment for cooking; the cooking temperature is 155-165 ℃, and the cooking pressure is 0.6-0.7 MPa; the cooking volume ratio is the ratio of the volume of the liquid mixture to the volume of the reaction zone of the integrated cooking, bleaching and washing equipment, and the volume ratio is 1:2.5-3.5.

[0008] S2: Inject magnesium sulfate solution to replace the cooking waste liquid;

[0009] S3: Add bleaching agent, adjust the pH value to 10-11 at 70-80℃, and continue bleaching for 60-90 minutes.

[0010] S4: Drain the bleaching agent from the system, wash with water to remove residual liquid and impurities, and then dehydrate and dry to obtain the pulp.

[0011] In a preferred embodiment of the present invention, in step S1, the fiber raw material is one of cotton fiber, bamboo fiber, wood fiber, grass fiber and reed fiber, the length of the fiber raw material is 1-15 mm, the moisture content of the fiber raw material is 10-20%, the liquid is a 16-18 wt% sodium hydroxide aqueous solution, and the mass-volume ratio of the fiber raw material to the liquid is 1:6-8 (g / mL).

[0012] In a preferred embodiment of the present invention, in step S1, the cooking process specifically involves: placing the fiber raw material and the drug solution mixture in the reaction zone, sealing it, and heating it at a rate of 1-1.5°C / min until it reaches a temperature of 155-165°C, and then holding it at that temperature for 120-140 minutes.

[0013] In a preferred embodiment of the present invention, the concentration of the magnesium sulfate solution in step S2 is 3.0-4.0% by mass, the injection amount is 30-40% of the volume of the reaction zone, the temperature of the magnesium sulfate solution is 70-80°C, and the magnesium sulfate solution also contains disodium ethylenediaminetetraacetate at a mass concentration of 0.1-0.5%.

[0014] In a preferred embodiment of the present invention, after the magnesium sulfate solution in step S2 is injected to replace the cooking waste liquid, water is used for a second replacement, and the concentration of the magnesium sulfate solution after the second replacement is 0.2-0.3% by mass.

[0015] In a preferred embodiment of the present invention, the magnesium sulfate solution in step S2 is depressurized before injection, and the depressurization rate is 0.10-0.15 MPa / min until it is reduced to atmospheric pressure.

[0016] In a preferred embodiment of the present invention, the bleaching agent in step S3 is hydrogen peroxide, and the mass concentration of hydrogen peroxide in the hydrogen peroxide is 30-35%.

[0017] In a preferred embodiment of the present invention, the mass of the bleaching agent in step S3 is 4.0–4.6% of the mass of the fiber raw material.

[0018] In a preferred embodiment of the present invention, the wet pulp with a dryness of 35%-45% is obtained after dehydration in step S4, and the drying process is to dry at a temperature of 104-106°C for 120-180 minutes.

[0019] To achieve the above objectives, the second technical solution adopted by the present invention is: an integrated cooking, bleaching, and washing device for pulp, based on a pulp preparation method according to any one of claims 1-9, comprising:

[0020] The reaction zone, which is used to hold the fiber raw materials and sequentially carry out cooking, displacement washing and bleaching reactions, is made of 316L stainless steel.

[0021] A thermal control unit, connected to the reaction zone, is used to control the reaction temperature within the reaction zone, so that the temperature fluctuation range is controlled within ±5℃.

[0022] A pressure control unit, connected to the reaction zone, is used to monitor and control the pressure within the reaction zone;

[0023] The material conveying unit is connected to the reaction zone via pipelines and is used to convey various medicinal solutions and washing water into the reaction zone;

[0024] The stirring reaction unit is integrated into the inner cavity of the reaction zone to achieve efficient mixing and full reaction of the reactants; a primary filtration device is provided on the side wall of the reaction zone, which has a double-layer porous structure for pre-filtration of large particulate impurities in the materials; the bottom of the integrated cooking, bleaching and washing equipment is provided with an impurity discharge port to achieve directional discharge of impurities;

[0025] The solid-liquid separation unit is arranged around the reaction zone and adopts a gradient filtration structure. The gradient filtration structure includes a secondary filtration device and a tertiary filtration device arranged in sequence. The secondary filtration device and the tertiary filtration device are respectively provided with a double-layer porous structure. The secondary filtration device is used to remove small particulate impurities, and the tertiary filtration device is used to filter out reaction waste liquid.

[0026] The vacuum unit is located at the bottom of the integrated cooking, bleaching and washing equipment and is connected to the solid-liquid separation unit to provide vacuum power for the solid-liquid separation process.

[0027] The high-pressure gas conveying unit is located at the top of the integrated cooking, bleaching and washing equipment and is connected to the solid-liquid separation area and the reaction zone. It is used to push the filtered pulp back to the reaction zone.

[0028] A water circulation system, located between the material conveying unit and the solid-liquid separation unit, is used to collect reusable process water generated during the washing process, filter the reusable process water, and, when the treated water quality meets preset reuse requirements, convey it to the material conveying unit for recycling; and

[0029] The central control unit is connected to and controls the thermal control unit, pressure regulation unit, material conveying unit, stirring reaction unit, solid-liquid separation unit and water circulation system respectively, for executing the preset process program.

[0030] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0031] (1) This invention provides a method for preparing pulp, which achieves deep purification through high temperature and high pressure cooking, introduces magnesium sulfate solution to replace waste liquid and form a protective layer before bleaching, performs mild bleaching under controlled conditions, and finally sets the pulp by dehydration and drying. The magnesium ions in magnesium sulfate can effectively inhibit the oxidative degradation of cellulose molecular chains by hydrogen peroxide in the alkaline bleaching environment. Compared with the pulp preparation method in the prior art, this method simplifies the process while synergistically ensuring the high purity, high whiteness, high degree of polymerization and excellent reactivity of the pulp product.

[0032] (2) In this invention, the retention of an appropriate amount of magnesium ions in the system after replacement with magnesium sulfate solution helps to improve the stability of the subsequent alkaline hydrogen peroxide bleaching system and reduce the risk of excessive oxidative degradation of cellulose during the bleaching process. While achieving the replacement of residual waste liquid and dissolved impurities, the presence of an appropriate amount of magnesium ions is beneficial to maintaining the stability of the cellulose molecular chain, thereby taking into account the whiteness, purity and degree of polymerization of the pulp.

[0033] (3) In this invention, the volume ratio of the cooking process is controlled to be 1:2.5-3.5. When the volume ratio is too high, the space for stirring and mixing is insufficient, the contact and circulation between the liquid and the fiber is not sufficient, and the impurities are difficult to dissolve effectively, resulting in low α-cellulose content and whiteness. When the volume ratio is appropriate and the material ratio is reduced, the flow space between the liquid and the fiber increases, the material circulation is improved, the fiber and the cooking liquid are in more uniform contact, the impurity dissolution efficiency is improved, and the α-cellulose content and whiteness are increased accordingly. However, when the volume ratio is too small, the material ratio is too low, the liquid level is very low, the stirring cannot generate effective turbulence, the system is not mixed evenly, and the removal efficiency of impurities such as hemicellulose decreases, the residual impurities increase, and the α-cellulose content and whiteness both decrease.

[0034] (4) In this invention, magnesium sulfate solution is used for displacement and concentration control after cooking. Through the displacement effect of magnesium sulfate solution, impurities generated by small-volume cooking are reduced, and their interference with bleaching is solved. By precisely controlling the concentration of residual magnesium ions, a protective mechanism for cellulose is formed in the bleaching stage, which inhibits local over-oxidation that may be aggravated by uneven mixing. Compared with the prior art, the waste liquid is effectively separated and protective ions are introduced, which coordinates the contradiction between the low volume ratio required for cooking and the good reaction environment required for bleaching. Thus, efficient cooking and mild and uniform bleaching are achieved in a single device with a high filling rate, and the high purity and high whiteness of the product are ensured simultaneously.

[0035] (5) In this invention, the process is designed with 316L stainless steel steaming, bleaching and washing in one closed system, which reduces the introduction of impurities and energy loss in the intermediate links. It also achieves the goal of high fiber content, high whiteness and concentrated degree of polymerization through precise temperature, pH and time control, thereby improving the quality of the fiber.

[0036] (6) In this invention, each stage of the solid-liquid separation unit adopts a double-layer porous structure, which can precisely adjust the opening and closing state and effective pore size according to process requirements. The pores are closed during the cooking stage to ensure the airtightness of the equipment; the pores are opened and matched with the corresponding pore size during the filtration stage to achieve gradient filtration. The filter surfaces of the primary and secondary filtration devices are arranged around the lower part of the cavity. The filtered impurities settle to the bottom under the action of gravity, which can effectively avoid filter pore blockage and improve the filtration rate and filtration effect. The filter surface of the tertiary filtration device is arranged at the bottom of the cavity, which is conducive to the discharge of waste liquid. The gradient pore size design can realize the graded interception of impurities and the efficient discharge of reaction waste liquid. The filtration accuracy is controllable and stable.

[0037] (7) In this invention, the reaction zone can be adapted to different conditions of cooking, bleaching and washing processes. Each level of filtration device is independently controlled. The filtration parameters can be adjusted according to the characteristics of pulp and process requirements, adapting to the production needs of different types of pulp, and has a wide range of applications. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart illustrating the method steps of a preferred embodiment of the present invention;

[0040] Figure 2This is a structural diagram of a preferred embodiment of the present invention;

[0041] In the attached diagram: 100, reaction zone; 200, primary filtration device; 300, secondary filtration device; 400, tertiary filtration device. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0044] Application Overview:

[0045] In existing technologies, pulp preparation typically faces a key challenge: the multi-stage chemical treatments undertaken to achieve high whiteness, particularly the use of chlorine-containing bleaching agents or vigorous oxidative bleaching in strongly alkaline environments, can easily lead to excessive oxidative degradation of cellulose molecular chains. This results in reduced polymerization and uneven distribution in the final product, affecting its mechanical strength and the uniformity of subsequent reactions. Furthermore, the insufficient control over the bleaching process in traditional techniques makes it difficult to guarantee the stability of pulp whiteness, posing a risk of yellowing.

[0046] An unexpected discovery was made that first replacing the cooked pulp with a high-concentration, warm magnesium sulfate solution not only effectively removed residual degradation impurities but also preloaded the fibers with sufficient magnesium ions. Subsequently, a second water replacement was used to control the concentration of magnesium sulfate in the system at a low maintenance level. In the subsequent hydrogen peroxide alkaline bleaching environment, these uniformly distributed magnesium ions could preferentially adsorb around the active sites of the cellulose molecular chains, forming a protective layer. This effectively inhibited the indiscriminate attack of oxidants such as hydrogen peroxide on the hydroxyl groups on the glucose rings of cellulose, thus mechanistically preventing the breakage of the molecular chains.

[0047] Based on the above principles, this solution achieves significant technical results. It fundamentally alleviates the oxidative degradation of cellulose during the bleaching process, resulting in a higher degree of polymerization and more concentrated distribution in the final pulp, thus ensuring the product's reactivity and mechanical properties. Under the protection of magnesium ions, the bleaching effect of hydrogen peroxide is more selective, acting more efficiently on pigment molecules, thereby achieving superior and more stable whiteness within a shorter process. This method simplifies the traditional multi-stage bleaching process, improves production efficiency, and simultaneously optimizes product purity and quality.

[0048] like Figure 1 As shown, a method for preparing pulp includes the following steps:

[0049] S1: After mixing the fiber raw material with the chemical solution, it is cooked in an integrated cooking, bleaching, and washing equipment at 155-165℃ and 0.6-0.7MPa, specifically in reaction zone 100. By utilizing the intense chemical action of the strong alkaline solution at a high temperature of 155-165℃ and a pressure of 0.6-0.7MPa, the aim is to efficiently and rapidly hydrolyze and dissolve most non-cellulose impurities in the fiber raw material, including hemicellulose, lignin, pectin, and waxes, thereby significantly improving the purity of α-cellulose in the raw material. Reaction zone 100 is specifically the reaction area between the fiber raw material and the chemical solution. The integrated cooking, bleaching, and washing equipment is a single unit that simultaneously possesses cooking, bleaching, and washing functions.

[0050] S2: Inject magnesium sulfate solution to replace the cooking waste liquor. Before injection, a water washing process can be added or not, depending on the actual process requirements. If a water washing process is added, the cooked pulp is first washed to remove some of the cooking waste liquor adhering to the surface of the pulp before injecting the magnesium sulfate solution. If a water washing process is not added, the magnesium sulfate solution is directly injected into the cooked pulp. By injecting the magnesium sulfate solution, the high-concentration waste liquor after cooking is discharged using the principle of fluid displacement, achieving preliminary washing of the material. It also allows the fibers to be preloaded with sufficient magnesium ions. The introduced magnesium ions can act as a cellulose protectant in the subsequent alkaline bleaching process, effectively inhibiting the excessive oxidative degradation of cellulose molecular chains by the bleaching agent, thereby protecting the degree of polymerization and strength of the pulp.

[0051] S3: Add bleaching agent, bleach at 70-80℃, adjust pH to 10-11, and continue bleaching for 60-90 minutes; by moderately heating at 70-80℃ and precisely controlling the pH to a weakly alkaline environment of 10-11, the bleaching agent reaches its optimal activity state, thereby efficiently destroying and removing residual trace pigments and impurities in the fiber, minimizing damage to cellulose while ensuring reaction efficiency, and ultimately enabling the pulp to achieve the required high whiteness and chemical purity.

[0052] S4: The bleaching agent in the system is drained, and the pulp is washed with water to remove residual chemicals and impurities. It is then subjected to dehydration and drying processes to obtain the pulp. Dehydration removes most of the moisture to reduce subsequent energy consumption, while drying uses heat to further reduce the moisture content below safe levels. This not only prevents product spoilage but also fixes the physical structure of the pulp, giving it suitable porosity and reactivity, facilitating storage and transportation, and meeting the process requirements of subsequent fiber production.

[0053] The following will explain each step in detail:

[0054] In step S1,

[0055] The fiber raw material is one of cotton fiber, bamboo fiber, wood fiber, grass fiber, and reed fiber, with a fiber length of 1-15 mm and a moisture content of 10-20%. The chemical solution is a 16-18 wt% sodium hydroxide aqueous solution, and the mass-to-volume ratio of fiber raw material to chemical solution is 1:6-8 (g / mL). Bamboo and wood fibers can be replaced with bamboo chips and wood chips respectively during the cooking process. The dimensions of the bamboo and wood chips are: length 15-25 mm, width 10-20 mm, and thickness 3-5 mm.

[0056] As an example of technical effects and benefits, the cooking process is as follows: The fiber raw material and the chemical solution mixture are placed in reaction zone 100, sealed, and heated at a rate of 1-1.5℃ / min until reaching 155-165℃. This temperature is then maintained for 120-140 minutes. The volume ratio of the cooking process is 1:2.5-3.5. The volume ratio is the ratio of the volume of the liquid mixture loaded into the reaction zone to the total volume of the cooker.

[0057] Select short fibers of 1-15mm and control the moisture content to 10-20%. Use a high-concentration sodium hydroxide solution of 16-18wt% and mix at a liquid ratio of 1:6-8. This method facilitates the rapid and uniform penetration of the solution, ensuring that there is sufficient and effective chemical reagent in full contact with the fiber to efficiently hydrolyze hemicellulose and saponify oils and waxes.

[0058] A slow heating rate of 1-1.5℃ / min is crucial, allowing the chemical solution to fully penetrate the fiber before the reaction becomes violent, thus avoiding localized degradation of cellulose due to excessive temperature differences or uneven reactions, and ensuring the uniformity of the degree of polymerization in the final product. A final temperature of 155-165℃ and a sufficient holding time of 120-140min provide the necessary energy and time for the complete decomposition and dissolution of impurities, while a volume ratio of 1:3 maximizes equipment utilization and thermal efficiency while ensuring sufficient space for material tumbling.

[0059] As mentioned above, these parameters work synergistically to efficiently obtain a high-purity, highly reactive cellulose matrix with minimal damage to the molecular chains during the cooking process, laying a solid foundation for subsequent bleaching and ultimately becoming a high-quality fiber raw material.

[0060] In step S2,

[0061] The magnesium sulfate solution has a concentration of 3.0-4.0% by mass, and the injection volume is 30-40% of the 100-volume volume of the reaction zone. The temperature of the magnesium sulfate solution is 70-80℃. The magnesium sulfate solution also contains disodium ethylenediaminetetraacetate with a mass concentration of 0.1-0.5%.

[0062] After the magnesium sulfate solution is injected to replace the cooking waste liquid, water is used for a second replacement. After the second replacement, the concentration of the magnesium sulfate solution is 0.2-0.3% by mass.

[0063] Before injecting the magnesium sulfate solution, the pressure is reduced at a rate of 0.10-0.15 MPa / min until it reaches atmospheric pressure.

[0064] A magnesium sulfate concentration of 3.0-4.0% ensures a sufficient concentration of magnesium ions to form an effective protective layer during subsequent bleaching; an injection volume of 30-40% is to ensure complete displacement and dilution of the high-concentration alkaline waste liquid, creating a clean initial environment for bleaching; preheating the solution to 70-80℃ is to avoid a sudden drop in material temperature caused by cold liquid injection, thereby maintaining the heat required for subsequent bleaching reactions and improving energy efficiency.

[0065] The addition of 0.1-0.5% disodium ethylenediaminetetraacetate (EDTA) is a metal ion chelating agent that preferentially complexes transition metal ions such as iron and copper that may be present in the solution. These metal ions catalyze the decomposition of bleaching agents, generating free radicals that drastically degrade cellulose. The addition of disodium EDTA fundamentally eliminates this side reaction risk.

[0066] Controlling the pressure reduction rate at 0.10-0.15 MPa / min is a crucial safety and quality measure. Slow pressure reduction can prevent the slurry in the pot from flashing and boiling due to a sudden drop in pressure, thereby avoiding severe impact damage to the fiber structure and ensuring stable and safe production.

[0067] A second water replacement is performed until the magnesium sulfate concentration drops to 0.2-0.3%. This process not only washes away most of the residual waste liquid dissolved impurities, but also intentionally retains a trace but sufficient concentration of magnesium ions in the system, which can continue to play a protective role throughout the subsequent bleaching process, thus achieving a balance between replacing the waste liquid and protecting the cellulose.

[0068] As an example of the technical effects and benefits, using a higher concentration solution for initial displacement ensures that sufficient magnesium ions are rapidly adsorbed onto the cellulose while displacing the viscous waste liquid, establishing a preliminary protective layer for subsequent bleaching. If a high concentration is maintained throughout the process, precipitates such as magnesium hydroxide are easily generated during the high-temperature, strongly alkaline cooking process. These precipitates will coat the fibers, hindering the effective removal of impurities by the chemical solution. Simultaneously, a large amount of magnesium ions will be locked within the system along with impurities in the cooking waste liquid, unable to be discharged through displacement, resulting in residual impurities contaminating the product and affecting the reaction uniformity and whiteness during the bleaching stage.

[0069] By precisely diluting its concentration to the low level required to maintain its activity through secondary water replacement, impurities are washed away while sufficient magnesium ions are retained to continue their effectiveness in the bleaching environment. This timing is chosen because the cellulose surface is clean and highly active immediately after cooking, which is most conducive to magnesium ion adsorption. If added before or during cooking, magnesium ions will be largely lost or rendered ineffective during the high-temperature, strong-alkali cooking process, and cannot be retained for the bleaching stage where their protective function is most needed.

[0070] As an example of the technical effects and benefits, the high filling ratio of 1:2.5-3.5 creates a high-concentration cooking environment, which effectively removes impurities but also results in high viscosity and a large amount of residual impurities in the waste liquid. At this point, injecting a sufficient amount of magnesium sulfate solution for displacement efficiently removes this high-concentration waste liquid from the system and establishes a clean reaction environment for subsequent bleaching. Simultaneously, magnesium ions effectively neutralize the risk of excessive oxidation that may be caused by high-concentration cooking. This ensures both the intensity and efficiency of the initial cooking reaction and lays the foundation for subsequent gentle and precise bleaching, jointly guaranteeing the high purity and excellent molecular weight of the final product.

[0071] In step S3,

[0072] The bleaching agent is hydrogen peroxide, with a hydrogen peroxide concentration of 30-35% by mass. The bleaching agent accounts for 4.0-4.6% of the fiber raw material mass.

[0073] Using hydrogen peroxide with a mass concentration of 30-35% is a common industrial choice that balances stability, activity, and transportation costs. This concentration provides sufficient oxidation potential to strictly control the amount of bleach relative to the fiber within a low range of 4.0%-4.6%.

[0074] This carefully calculated low dosage is sufficient to safely and gently destroy the chromophores in the clean, protected, slightly alkaline environment created in the previous steps, completing the final whitening and purification. Too high a dosage is not only wasteful but will also break down the protective system, leading to a decrease in the degree of cellulose polymerization; while too low a dosage will fail to achieve the desired bleaching effect.

[0075] In step S4,

[0076] After dehydration, wet pulp with a dryness of 35%-45% is obtained. The drying process is carried out at a temperature of 104-106℃ for 120-180 minutes.

[0077] Controlling the dryness after dehydration to 35%-45% is an optimized intermediate state: if the wet pulp cake is too dry, the fibers will stick together tightly, increasing the energy consumption of subsequent crushing and drying, and easily forming hard lumps; if it is too wet, it means that the dehydration is insufficient, which will greatly increase the heat load and time cost of the drying process.

[0078] Choosing a temperature of 104-106℃ is crucial, as this temperature is much higher than the boiling point of water, effectively evaporating moisture while remaining significantly lower than the rapid decomposition temperature of cellulose. This avoids the risk of thermal degradation of cellulose molecules due to high temperatures and protects the degree of polymerization.

[0079] The longer drying time of 120-180 minutes ensures that heat and moisture migration can proceed gently and evenly, avoiding surface crusting and hardening due to excessively rapid drying. The final product is high-quality pulp with uniform moisture content, fluffy texture, and large specific surface area.

[0080] An integrated cooking and bleaching equipment for pulp includes:

[0081] Reaction zone 100 is used to contain fiber raw materials and sequentially carry out cooking, displacement washing and bleaching reactions. It is made of 316L stainless steel.

[0082] A thermal control unit is connected to the reaction zone 100 and is used to control the reaction temperature in the reaction zone 100 so that the temperature fluctuation range is controlled within ±5℃.

[0083] The pressure control unit is connected to the reaction zone 100 and is used to monitor and control the pressure within the reaction zone 100.

[0084] The material conveying unit is connected to the reaction zone 100 via pipelines and is used to convey various medicinal solutions and washing water into the reaction zone 100.

[0085] The stirring reaction unit is integrated into the inner cavity of the reaction zone to achieve efficient mixing and full reaction of the reactants. A primary filtration device 200 with a double-layered porous structure is installed on the side wall of the reaction zone for pre-filtration of large particulate impurities in the materials. The filtered impurities settle and collect at the bottom of the unit under gravity, and a dedicated impurity discharge port is provided at the bottom of the reaction zone for directional discharge of impurities.

[0086] The solid-liquid separation unit is arranged around the periphery of the reaction zone and employs a gradient filtration structure. This structure includes a secondary filtration device 300 and a tertiary filtration device 400 arranged sequentially. Both the secondary and tertiary filtration devices 300 have double-layered porous structures. The secondary filtration device 300 removes small particulate impurities, while the tertiary filtration device 400 filters out reaction waste liquid. The gradient filtration structure utilizes a relatively movable double-layered porous structure, allowing for precise adjustment of the pore opening and closing and pore size by controlling the displacement, adapting to the requirements of different process stages.

[0087] The vacuum unit is located at the bottom of the integrated cooking, bleaching and washing equipment and is connected to the solid-liquid separation unit to provide vacuum power for the solid-liquid separation process.

[0088] The high-pressure gas conveying unit is located at the top of the integrated cooking, bleaching and washing equipment and is connected to the solid-liquid separation area and the reaction zone. It is used to push the filtered pulp back to the reaction zone.

[0089] A water circulation system, located between the material conveying unit and the solid-liquid separation unit, collects reusable process water generated during the washing process, filters the reusable process water, and, when the treated water quality meets preset reuse requirements, conveys it to the material conveying unit for recycling; and

[0090] The central control unit is connected to and controls the thermal control unit, pressure regulation unit, material conveying unit, stirring and reaction unit, solid-liquid separation unit, vacuum unit, high-pressure gas conveying unit and water circulation system to execute the preset process program.

[0091] like Figure 2 As shown, the collaborative workflow of the preparation method and equipment is as follows: first, cooking is carried out, and after cooking, the pulp is filtered step by step. The filtered pulp is returned to the reaction zone for bleaching. After bleaching, it is filtered step by step again. The filtered pulp is returned to the reaction zone for water washing. After water washing, the finished pulp is discharged after multi-stage filtration.

[0092] The specific operating procedure is as follows: During the cooking reaction stage, the double-layer porous structure of each solid-liquid separation unit remains completely closed to ensure the airtightness of the preparation area and guarantee the stable progress of the cooking reaction. After the cooking reaction is completed, the solid-liquid separation process begins: First, the primary filter device 200 around the reaction zone is opened for pre-filtration to trap large particulate impurities; the filter surface is arranged on the lower side of the cavity, and the filtration power can be enhanced by pressurization or vacuuming. The filtered impurities settle to the bottom of the reaction cavity under gravity. After pre-filtration, a small amount of cleaning solution is immediately injected to rinse the pre-filter surface and the cavity. The rinsing solution carries the residual impurities and is discharged from the outlet at the bottom of the reaction cavity.

[0093] After entering the secondary filtration unit 300, the mixture is filtered by adjusting the pore size to intercept small particulate impurities. The filter surface is also arranged around the lower side of the cavity. The filtration effect can be enhanced by pressurization or vacuuming, and impurities settle to the bottom. After the secondary filtration is completed, a small amount of cleaning solution is injected to rinse the secondary filter surface and the cavity. The rinsing solution carries away residual impurities through the outlet at the bottom.

[0094] The pulp then enters a three-stage filtration unit 400. After passing through the three-stage filtration, the reaction waste liquid is discharged, while the clean pulp is temporarily stored in the three-stage filtration chamber. Through suction, the clean pulp is returned to the reaction zone for the next bleaching process.

[0095] Start the bleaching process. After bleaching is completed, repeat the above multi-stage filtration and online rinsing process. After the bleaching and filtration process is completed, send the clean pulp back to the reaction area for the next water washing process.

[0096] Finally, the washing process is started, and the washed pulp is discharged from the outlet after multi-stage filtration.

[0097] This system integrates cooking, filtration, bleaching, and washing into one unit. Compared with traditional decentralized equipment, it can significantly reduce the number of equipment, shorten the process flow, and reduce the floor space. At the same time, it avoids the transfer of materials between different containers, reduces material loss and process fluctuations, and improves production continuity and stability.

[0098] In the prior art, under the condition that the liquid-solid ratio remains unchanged, in order to improve the utilization rate of equipment and the thermal efficiency of cooking, a high-filling-rate cooking method is usually adopted, so that the liquid mixture occupies most of the effective volume of the cooker, thereby reducing the ineffective space inside the equipment, reducing the heating requirement of the cavity medium, and improving the thermal energy utilization rate and the unit equipment processing capacity.

[0099] However, if bleaching continues in the same equipment after cooking, the bleaching process requires not only uniform contact between the bleaching agent and the pulp, but also the flow of the replacement liquid to ensure timely removal of cooking waste and dissolved impurities. Due to the limited free space inside the equipment at high loading rates, the pulp agitation space and replacement liquid circulation space are restricted, hindering waste liquid replacement, impurity removal, and uniform diffusion of the bleaching agent. This easily leads to residual cooking waste and impurities remaining in the system, consuming the effective components of the bleaching agent, interfering with the bleaching reaction, and increasing the risk of localized over-oxidation of cellulose. Therefore, how to maintain the advantages of high loading rate cooking while creating a favorable reaction environment for subsequent bleaching has become a pressing technical problem that needs to be solved by existing technologies.

[0100] This invention involves injecting a magnesium sulfate solution after cooking to replace the cooking waste liquor. Combined with a secondary replacement to regulate the magnesium sulfate concentration in the system, this process removes residual cooking waste liquor and impurities, providing a clean and uniform reaction environment for bleaching. Simultaneously, it retains an appropriate amount of magnesium ions, which protect the cellulose during subsequent alkaline bleaching. This balances the high equipment utilization required for high-fill-rate cooking with the bleaching process's requirements for uniform mixing, replacement, and a mild reaction environment, achieving effective coordination between the cooking and bleaching processes.

[0101] After boiling, a sufficient amount of warm magnesium sulfate solution is injected to displace and remove the high-concentration waste liquid; then, through a second water displacement, the magnesium sulfate concentration in the system is precisely controlled at a low level of 0.2-0.3%. This achieves effective washing of residual impurities, creates a clean and uniform reaction environment for bleaching, and retains sufficient magnesium ions to play a protective role in subsequent alkaline bleaching, thus compensating for the inherent defects of small-volume containers in mixing and separation.

[0102] After cooking, magnesium sulfate solution is used for displacement and concentration control. Through the displacement effect of magnesium sulfate solution, impurities generated by small-volume cooking are reduced, and their interference with bleaching is resolved. By precisely controlling the concentration of residual magnesium ions, a protective mechanism for cellulose is formed during the bleaching stage, inhibiting local over-oxidation that may be aggravated by uneven mixing. Effective separation of waste liquid is achieved and protective ions are introduced, reconciling the contradiction between the low volume ratio required for cooking and the good reaction environment required for bleaching. Thus, efficient cooking and gentle, uniform bleaching are synergistically achieved in a single device with a high filling rate, ultimately ensuring the high purity and high whiteness of the product.

[0103] Example 1:

[0104] This embodiment provides a method for preparing cotton pulp, including the following steps:

[0105] S1: After mixing the fiber raw material with the chemical solution, the mixture is cooked in an integrated cooking, bleaching, and washing equipment at 160℃ and 0.65MPa. The fiber raw material is cotton fiber with a length of 6mm and a moisture content of 10%. The chemical solution is a 16wt% sodium hydroxide aqueous solution, and the mass-to-volume ratio of the fiber raw material to the chemical solution is 1:7 (g / mL). The cooking process is as follows: after placing the mixture of fiber raw material and chemical solution in the reaction zone, it is sealed and heated at a rate of 1.5℃ / min until it reaches 160℃. The temperature is then maintained for 140min, and the volume ratio of the cooking process is 1:2.5.

[0106] S2: Inject magnesium sulfate solution to replace the cooking waste liquid; the concentration of magnesium sulfate solution is 2.5% by mass, the injection amount is 40% of the reaction zone volume, the temperature of magnesium sulfate solution is 75℃, and the magnesium sulfate solution also contains 0.3% by mass disodium ethylenediaminetetraacetate.

[0107] After the magnesium sulfate solution is injected to replace the cooking waste liquid, water is used for a second replacement. After the second replacement, the concentration of the magnesium sulfate solution is 0.2% by mass.

[0108] Before the magnesium sulfate solution is injected, the pressure is reduced at a rate of 0.10 MPa / min until it reaches atmospheric pressure.

[0109] S3: Add bleaching agent, adjust pH to 10 at 75℃, and continue bleaching for 75 minutes; the bleaching agent is hydrogen peroxide, the mass concentration of hydrogen peroxide in the hydrogen peroxide is 35%, and the amount of hydrogen peroxide used is 4.5% of the mass of the fiber raw material.

[0110] S4: After bleaching, drain the bleaching reaction liquid from the system and inject water into the integrated cooking, bleaching and washing equipment to wash the pulp to remove residual bleaching agent, chemical solution and dissolved impurities; after washing, perform solid-liquid separation and dewatering to obtain wet pulp with a dryness of 40%, and then dry it at 105℃ for 160 minutes to obtain pulp.

[0111] Example 2:

[0112] The difference between this embodiment and Embodiment 1 is that the volume ratio of the cooking process is 1:3.0, while the rest are the same.

[0113] Example 3:

[0114] The difference between this embodiment and Embodiment 1 is that the volume ratio of the cooking process is 1:3.5, while the rest are the same.

[0115] Example 4:

[0116] The difference between this embodiment and Embodiment 3 is that the concentration of the magnesium sulfate solution after the second displacement is 0.25% by mass, while the rest are the same.

[0117] Example 5:

[0118] The difference between this embodiment and Embodiment 3 is that the concentration of the magnesium sulfate solution after the second displacement is 0.30% by mass, while the rest are the same.

[0119] Comparative Example 1:

[0120] The difference between this comparative example and Example 1 is that the volume ratio of the cooking process is 1:2.0, while the rest are the same.

[0121] Comparative Example 2:

[0122] The difference between this comparative example and Example 1 is that the volume ratio of the cooking process is 1:4.0, while the rest are the same.

[0123] Comparative Example 3:

[0124] The difference between this comparative example and Example 2 is that the concentration of the magnesium sulfate solution after the second displacement is 0.15% by mass, while the rest are the same.

[0125] Comparative Example 4:

[0126] The difference between this comparative example and Example 2 is that the concentration of the magnesium sulfate solution after the second displacement is 0.35% by mass, while the rest are the same.

[0127] Comparative Example 5:

[0128] This comparative example provides a method for preparing cotton pulp, including the following steps:

[0129] S1: After mixing the fiber raw material with the chemical solution, the mixture is cooked in an integrated cooking, bleaching, and washing equipment at 160℃ and 0.65MPa. The fiber raw material is cotton fiber with a length of 6mm and a moisture content of 10%. The chemical solution is a 16wt% sodium hydroxide aqueous solution, and the mass-to-volume ratio of the fiber raw material to the chemical solution is 1:7 (g / mL). The cooking process is as follows: after placing the mixture of fiber raw material and chemical solution in the reaction zone, it is sealed and heated at a rate of 1.5℃ / min until it reaches 160℃. The temperature is then maintained for 140min, and the volume ratio of the cooking process is 1:5.

[0130] S2: Inject magnesium sulfate solution to replace the cooking waste liquid; the concentration of magnesium sulfate solution is 2.5% by mass, the injection amount is 40% of the reaction zone volume, the temperature of magnesium sulfate solution is 75℃, and the magnesium sulfate solution also contains 0.3% by mass disodium ethylenediaminetetraacetate.

[0131] After the magnesium sulfate solution is injected to replace the cooking waste liquid, water is used for a second replacement. After the second replacement, the concentration of the magnesium sulfate solution is 0.2% by mass.

[0132] Before the magnesium sulfate solution is injected, the pressure is reduced at a rate of 0.10 MPa / min until it reaches atmospheric pressure.

[0133] S3: Add bleaching agent, adjust pH to 10 at 75℃, and continue bleaching for 75 minutes; the bleaching agent is hydrogen peroxide, the mass concentration of hydrogen peroxide in hydrogen peroxide is 35%, and the mass ratio of hydrogen peroxide to fiber raw material is 4.5%.

[0134] S4: After bleaching, drain the bleaching reaction liquid from the system and inject water into the integrated cooking, bleaching and washing equipment to wash the pulp to remove residual bleaching agent, chemical solution and dissolved impurities; after washing, perform solid-liquid separation and dewatering to obtain wet pulp with a dryness of 40%, and then dry it at 105℃ for 160 minutes to obtain pulp.

[0135] Comparative Example 6:

[0136] This comparative example provides a method for preparing cotton pulp, including the following steps:

[0137] S1: After mixing the fiber raw material with the chemical solution, the mixture is cooked in an integrated cooking, bleaching, and washing equipment at 160℃ and 0.65MPa. The fiber raw material is cotton fiber with a length of 6mm and a moisture content of 10%. The chemical solution is a 16wt% sodium hydroxide aqueous solution, and the mass-to-volume ratio of the fiber raw material to the chemical solution is 1:7 (g / mL). The cooking process is as follows: after placing the mixture of fiber raw material and chemical solution in the reaction zone, it is sealed and heated at a rate of 1.5℃ / min until it reaches 160℃. The temperature is then maintained for 140min, and the volume ratio of the cooking process is 1:3.0.

[0138] S2: Inject magnesium sulfate solution to replace the cooking waste liquid; the concentration of magnesium sulfate solution is 2.5% by mass, the injection amount is 40% of the reaction zone volume, the temperature of magnesium sulfate solution is 75℃, and the magnesium sulfate solution also contains 0.3% by mass disodium ethylenediaminetetraacetate.

[0139] Before the magnesium sulfate solution is injected, the pressure is reduced at a rate of 0.10 MPa / min until it reaches atmospheric pressure.

[0140] S3: Add bleaching agent, adjust pH to 10 at 75℃, and continue bleaching for 75 minutes; the bleaching agent is hydrogen peroxide, the mass concentration of hydrogen peroxide in hydrogen peroxide is 35%, and the mass ratio of hydrogen peroxide to fiber raw material is 4.5%.

[0141] S4: After bleaching, drain the bleaching reaction liquid from the system and inject water into the integrated cooking, bleaching and washing equipment to wash the pulp to remove residual bleaching agent, chemical solution and dissolved impurities; after washing, perform solid-liquid separation and dewatering to obtain wet pulp with a dryness of 40%, and then dry it at 105℃ for 160 minutes to obtain pulp.

[0142] Examples 1-5 and Comparative Examples 1-6 were tested for α-cellulose content and whiteness. The α-cellulose content was determined according to FZ / T50010.4-2011 "Determination of Type A Cellulose Content in Pulp for Viscose Fiber". The whiteness was determined according to GB / T 7974-2013 "Determination of Blue Light Diffuse Reflectance Factor D65 Brightness of Paper, Paperboard and Pulp (Diffuse / Vertical Method, Outdoor Daylight Conditions)". The data are shown in Table 1.

[0143] Table 1. α-cellulose content and whiteness test data for Examples 1-5 and Comparative Examples 1-6

[0144] Data source α-cellulose content (%) Brightness (whiteness) (%) Example 1 98.8 86 Example 2 99.2 88 Example 3 99.0 87 Example 4 99.4 90 Example 5 99.1 85 Comparative Example 1 98.3 83 Comparative Example 2 98.7 85 Comparative Example 3 98.6 85 Comparative Example 4 98.6 83 Comparative Example 5 97.8 81 Comparative Example 6 98.0 78

[0145] As shown in Table 1, the α-cellulose content and whiteness of Examples 1-5 are greater than those of Comparative Examples 1-6, indicating that this application has superiority.

[0146] In Examples 1-3 and Comparative Examples 1-2, as the volume ratio during the cooking process decreased from 1:2 to 1:4, the α-cellulose content and whiteness both showed a trend of first increasing and then decreasing. When the volume ratio was 1:2, the material proportion was too high, the space for stirring and mixing was insufficient, the contact and circulation between the liquid and the fiber was poor, and impurities were difficult to dissolve effectively, resulting in low α-cellulose content and whiteness. As the volume ratio gradually decreased and the material proportion decreased, the flow space between the liquid and the fiber increased, the material circulation improved, the contact between the fiber and the cooking liquid was more uniform, the efficiency of impurity dissolution increased, and the α-cellulose content and whiteness increased accordingly. However, when the volume ratio continued to decrease to 1:4, the material proportion was too low, the liquid level was very low, the stirring could not generate effective turbulence, the system was not mixed evenly, and the removal efficiency of impurities such as hemicellulose decreased, the residual impurities increased, resulting in a decrease in both α-cellulose content and whiteness.

[0147] In Examples 2, 4-5, and Comparative Examples 3-4, as the concentration of magnesium sulfate solution increased after the second replacement, the α-cellulose content and whiteness first increased and then decreased. This is because when the concentration is too low, magnesium ions are insufficient to effectively inhibit the oxidative degradation of cellulose chains by hydrogen peroxide in subsequent bleaching, leading to a decrease in polymerization degree and purity. Furthermore, the bleaching process may be too vigorous, damaging the fibers and affecting whiteness. When the concentration reaches the optimal range, the protective effect of magnesium ions reaches its peak, ensuring bleaching efficiency while inhibiting cellulose degradation, resulting in optimal purity and whiteness. However, when the concentration is too high, excessive magnesium salt deposition hinders the effective contact between the bleaching agent and residual pigments within the fiber, thus reducing the bleaching effect. Incomplete washing of impurities also slightly affects purity, causing both indicators to decline. Example 4 is the preferred embodiment.

[0148] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the claims.

Claims

1. A method for preparing pulp, characterized in that, Includes the following steps: S1: After mixing the fiber raw material with the pharmaceutical solution, it is placed in an integrated cooking, bleaching and washing equipment for cooking; the cooking temperature is 155-165 ℃, the cooking pressure is 0.6-0.7 MPa, and the cooking volume ratio is 1:2.5-3.

5. The volume ratio is the ratio of the volume of the liquid mixture to the volume of the reaction zone of the integrated equipment. The reaction zone is the reaction area between the fiber raw material and the pharmaceutical solution. S2: Inject magnesium sulfate solution to replace the cooking waste liquid; S3: Add bleaching agent, adjust the pH to 10-11 at 70-80℃, and continue bleaching for 60-90 minutes. S4: Drain the bleaching agent from the system, wash with water to remove residual liquid and impurities, and then dehydrate and dry to obtain the pulp.

2. The method for preparing pulp according to claim 1, characterized in that: In step S1, the fiber raw material is one of cotton fiber, bamboo fiber, wood fiber, grass fiber, and reed fiber, the fiber raw material length is 1-15mm, the fiber raw material moisture content is 10-20%, the medicinal solution is a 16-18wt% sodium hydroxide aqueous solution, and the mass-volume ratio of the fiber raw material to the medicinal solution is 1:6-8 (g / mL).

3. The method for preparing pulp according to claim 1, characterized in that: In S1, the cooking process specifically involves placing the fiber raw material and the drug solution mixture in the reaction zone, sealing it, and heating it at a rate of 1-1.5℃ / min until it reaches a temperature of 155-165℃. The temperature is then maintained for 120-140 minutes.

4. The method for preparing pulp according to claim 1, characterized in that: The magnesium sulfate solution in step S2 has a concentration of 3.0-4.0% by mass, and the injection volume is 30-40% of the volume of the reaction zone. The temperature of the magnesium sulfate solution is 70-80°C, and the magnesium sulfate solution also contains disodium ethylenediaminetetraacetate at a mass concentration of 0.1-0.5%.

5. The method for preparing pulp according to claim 4, characterized in that: In step S2, after the magnesium sulfate solution is injected to replace the cooking waste liquid, water is used for a second replacement. After the second replacement, the concentration of the magnesium sulfate solution is 0.2-0.3% by mass.

6. The method for preparing pulp according to claim 1, characterized in that: Before the magnesium sulfate solution is injected in step S2, the pressure is reduced at a rate of 0.10-0.15 MPa / min until it reaches atmospheric pressure.

7. The method for preparing pulp according to claim 1, characterized in that: The bleaching agent in S3 is hydrogen peroxide, and the mass concentration of hydrogen peroxide in the hydrogen peroxide is 30-35%.

8. The method for preparing pulp according to claim 7, characterized in that: The bleaching agent in S3 is 4.0–4.6% of the mass of the fiber raw material.

9. The method for preparing pulp according to claim 1, characterized in that: The dehydration process in S4 yields a wet pulp with a dryness of 35%-45%, and the drying process is carried out at a temperature of 104-106℃ for 120-180 minutes.

10. An integrated cooking, bleaching, and washing device for pulp, based on the pulp preparation method according to any one of claims 1-9, characterized in that, include: The reaction zone, which is used to hold the fiber raw materials and sequentially carry out cooking, displacement washing and bleaching reactions, is made of 316L stainless steel. A thermal control unit, connected to the reaction zone, is used to control the reaction temperature within the reaction zone, so that the temperature fluctuation range is controlled within ±5℃. A pressure control unit, connected to the reaction zone, is used to monitor and control the pressure in the reaction zone; The material conveying unit is connected to the reaction zone via pipelines and is used to convey various medicinal solutions and washing water into the reaction zone; The stirring reaction unit is integrated into the inner cavity of the reaction zone to achieve efficient mixing and full reaction of the reactants; a primary filtration device is provided on the side wall of the reaction zone, which has a double-layer porous structure for pre-filtration of large particulate impurities in the materials; the bottom of the integrated cooking, bleaching and washing equipment is provided with an impurity discharge port to achieve directional discharge of impurities; The solid-liquid separation unit is arranged around the reaction zone and adopts a gradient filtration structure. The gradient filtration structure includes a secondary filtration device and a tertiary filtration device arranged in sequence. The secondary filtration device and the tertiary filtration device are respectively provided with a double-layer porous structure. The secondary filtration device is used to remove small particulate impurities, and the tertiary filtration device is used to filter out reaction waste liquid. The vacuum unit is located at the bottom of the integrated cooking, bleaching and washing equipment and is connected to the solid-liquid separation unit to provide vacuum power for the solid-liquid separation process. The high-pressure gas conveying unit is located at the top of the integrated cooking, bleaching and washing equipment and is connected to the solid-liquid separation area and the reaction zone. It is used to push the filtered pulp back to the reaction zone. A water circulation system is installed between the material conveying unit and the solid-liquid separation unit to collect reusable process water generated during the washing process, filter the reusable process water, and transport it to the material conveying unit for recycling when the water quality meets the preset reuse requirements. as well as The central control unit is connected to and controls the thermal control unit, pressure regulation unit, material conveying unit, stirring reaction unit, solid-liquid separation unit and water circulation system respectively, for executing the preset process program.

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