A method for purifying softwood pulp and the purified softwood pulp and its use

Abstract

The application discloses a purification method of coniferous wood pulp, and purified coniferous wood pulp and application thereof, and belongs to the technical field of papermaking. The purification method of the coniferous wood pulp comprises the following steps: obtaining screened coniferous wood pulp by screening raw coniferous wood pulp; removing iron ions in the coniferous wood pulp by chelating the screened coniferous wood pulp and a chelating agent at 50 DEG C to 70 DEG C to obtain chelated coniferous wood pulp; obtaining alkali-treated coniferous wood pulp by alkali treatment of the chelated coniferous wood pulp; and removing resin components in the coniferous wood pulp by enzyme treatment of the alkali-treated coniferous wood pulp dispersed in water at 60 DEG C to 65 DEG C and pH of 6 to 9 to obtain insulating coniferous wood pulp. After the purification method is used, the metal ion content and dichloromethane extract of the coniferous wood pulp are significantly reduced, the ash content is effectively reduced, and the comprehensive performance meets the requirements of high-voltage electrical insulating pulp.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, specifically relating to a method for purifying softwood pulp, the purified softwood pulp, and its applications. Background Technology

[0002] High-end electrical paper requires pulp with high chemical purity and low metal ion content. However, due to systemic differences in tree species and purification processes, the manufacture of insulating wood pulp for high-end electrical paper still has shortcomings. Leading international suppliers such as Weidmann (Switzerland) and Munksjo (USA) have achieved synergistic optimization of fiber strength and electrochemical purity by leveraging high-quality coniferous species from their own exclusive forests and combining them with refined purification processes. Currently available domestically produced commercial wood pulp is mostly derived from mixed tree species, resulting in shortcomings such as shorter fibers, poor uniformity, and high impurity content.

[0003] The existing pulp purification processes and treatment methods in the industry mostly focus on removing metal ion impurities such as iron, calcium, and sodium from pulp. They have not yet formed an integrated purification system that coordinates the control of multiple impurities and multiple indicators. They cannot simultaneously take into account key indicators such as pulp ash content and dichloromethane extract, which often leads to incomplete pulp purification and fails to achieve synergistic improvement of pulp performance indicators. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for purifying softwood pulp, as well as the purified softwood pulp and its applications. After treatment using the purification method of this invention, the iron ion content and dichloromethane extract of the softwood pulp are significantly reduced, the ash content is effectively reduced, and the overall performance meets the requirements of high-voltage electrical insulation pulp, achieving a synergistic improvement in pulp performance indicators.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A method for purifying softwood pulp includes the following steps: The raw softwood pulp is screened to obtain screened softwood pulp.

[0006] The sieved softwood pulp and chelating agent are chelated at 50℃~70℃ to remove iron ions from the softwood pulp, resulting in chelated softwood pulp.

[0007] Alkali treatment is applied to chelated softwood pulp to obtain alkali-treated softwood pulp. During the alkali treatment process, a small amount of residual metal ions may be removed due to the dissolution or conversion of residual acidic salts into soluble forms, the increase of zeta potential, and the displacement and decomposition of metal complexes.

[0008] Alkali-treated coniferous wood pulp is dispersed in water and then subjected to enzymatic treatment at 60°C and pH 6-9 to remove the resin components from the insulating pulp, yielding coniferous wood insulating pulp. The resin components mainly include fatty acids, triglycerides, and waxes, which are naturally produced during the growth of the wood raw material. The coniferous wood insulating pulp obtained by this invention is used as an insulating pulp.

[0009] In a preferred embodiment of the present invention, the pH of the chelation treatment is 5-6, and the time is 30-90 minutes.

[0010] In a preferred embodiment of the present invention, the amount of chelating agent added is 0.2% to 0.5% of the mass of the oven-dried softwood pulp after sieving.

[0011] In a preferred embodiment of the present invention, the enzyme treatment time is 60 min.

[0012] In a preferred embodiment of the present invention, the enzyme used is lipase, and the amount of enzyme added is 300g / t.

[0013] Processing according to the above parameter range can effectively improve the purification effect of softwood pulp.

[0014] In a preferred embodiment of the present invention, the original coniferous wood pulp is Masson pine pulp, Simao pine pulp, or larch pulp; the chelating agent is ethylenediaminetetraacetic acid (EDTA). When using a chelating agent, such as EDTA, the metal ions are directly removed by forming highly stable chelates with the metal ions through chelation.

[0015] When the original softwood pulp is Masson pine pulp, since the iron ion content of Masson pine pulp is 32.2 mg / kg, which is within the first-grade range (28~40 mg / kg), the iron ion removal process does not require very strong conditions in principle, and the requirements can be met by chelation treatment.

[0016] When the original softwood pulp is Simao pine pulp, the iron ion content of Simao pine pulp has reached the standard of superior grade, but the ash content (0.47%) is also higher than the standard value. At the same time, its degree of polymerization is significantly lower than the standard, and it cannot withstand strong post-processing conditions. Therefore, chelation treatment can be selected.

[0017] In a preferred embodiment of the present invention, the alkali treatment method is as follows: after the pulp obtained after chelation treatment is washed twice with water, it is then washed with an alkaline solution. After the alkaline washing is completed, it is washed again with water to obtain the alkali-treated lignocellulose insulating pulp.

[0018] In a preferred embodiment of the present invention, the alkaline solution is a NaOH solution with pH=9 and temperature of 60°C.

[0019] In this invention, during alkali treatment, the pH value of the chelated softwood pulp is first brought to the standard range of 6-9 by water washing. Then, to address the issue of excessively high dichloromethane extract content, an enzymatic treatment process is added in series. This invention uses lipase for treatment.

[0020] The present invention also provides coniferous wood insulating pulp obtained by the above purification method.

[0021] The present invention also provides the application of the above-mentioned coniferous wood insulating slurry in the preparation of electrical insulating materials.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention employs chelation, alkali treatment, and enzyme treatment to purify softwood pulp. Chelation effectively removes iron ions from the pulp, and alkali treatment removes residual metal ions. However, chelation can cause a reverse increase in dichloromethane extractable (DME) content. This invention supplements the process with enzyme treatment to further reduce DME content. Because this method offers advantages such as high purification efficiency, strong raw material adaptability, and the ability to achieve synergistic compliance with multiple indicators, it can purify even different softwood pulps, such as Masson pine and Simao pine pulp. After purification, the iron ion content and DME content are significantly reduced, and the ash content is effectively decreased, thus meeting the overall performance requirements for high-voltage electrical insulation pulp. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart of the purification method of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0026] It should be noted that the terms "first," "second," etc., used in this specification are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0027] In some types of softwood pulp, such as Masson pine pulp and Simao pine pulp, the iron ion content exceeds the standard, or even if the iron ion content is low, the total ash content is high. Therefore, it is necessary to use certain chelation treatments to control their iron ion or ash content.

[0028] Chelation treatment is one possible way to remove catalytic metal ions from insulating pulp. Traditional chelation treatment is generally performed before the bleaching stage to prevent metal ions from participating in the oxidation reaction or catalytic action during bleaching, such as catalyzing the decomposition of hydrogen peroxide leading to localized over-oxidation of the pulp. For insulating oil-cellulose application systems, it is also necessary to remove catalytic metal ions as much as possible, cutting off their catalytic pathways for cellulose oxidation and degradation, thereby slowing down the aging process of the insulating paper. Therefore, chelation treatment of lignocellulose insulating pulp can be considered. In this invention, ethylenediaminetetraacetic acid (EDTA) is mainly used as the chelating agent.

[0029] Chelation treatment can effectively reduce the iron ion content in softwood pulp, but this step leads to an increase in dichloromethane extract content. Increased dichloromethane extract content indicates higher impurity levels, which may result in decreased dielectric strength, increased dielectric loss, and increased susceptibility to partial discharge or breakdown in insulating materials. It may also affect the material's thermal stability and aging performance, posing serious safety hazards.

[0030] In the industry, dichloromethane extractables refer to the sum of all hydrophobic organic substances in pulp that can be extracted by dichloromethane. These mainly include natural wood resin components such as resin acids, fatty acids, triglycerides, waxes, and sterols. These components are secretions from wood growth and are released during pulp production (especially when using woods with high resin content, such as pine). However, these resin components are insoluble in water and disperse in the pulp suspension as small droplets. These resins are difficult to completely remove during processing, resulting in the presence of dichloromethane extractables in the finished pulp.

[0031] Although the chelation treatment of softwood pulp in this invention reduces the iron ion content, it leads to an increase in the dichloromethane extract content. The specific reasons are as follows: The main reason for chelation treatment is likely that some resin acids and fatty acids react with calcium ions (Ca) in the pulp. 2+ ), magnesium ions (Mg 2+ Alkaline earth metal ions, such as α-alkali earth metal ions and some transition metal ions, combine to form metal soaps (salts) that are insoluble in water and dichloromethane. After the addition of EDTA, it will undergo a complexation reaction with various metal ions in the pulp, competitively removing the metal ions bound to the resin acid, thus releasing the resin acid from its metal salt state and restoring it to its free acid form.

[0032] This invention first incorporates an alkaline treatment process in series during the washing process. The reason for using alkaline treatment is twofold: firstly, it reduces the metal ion content due to the dissolution or conversion of residual acidic salts into soluble forms, the increase in zeta potential, and the displacement and decomposition of metal complexes. Secondly, the alkaline washing process also reduces water-soluble chloride and ash content, resulting in less pulp impurities and superior performance.

[0033] To address the problem of excessively high dichloromethane extract content, this invention incorporates an enzyme treatment process after alkali treatment to solve the issue of increased dichloromethane extract content.

[0034] In this invention, the enzyme used for enzyme treatment is lipase.

[0035] Lipases specifically target triglycerides (one of the main components causing resin adhesion). They do not act on lignin or cellulose and do not affect the strength of pulp fibers. Utilizing their biocatalytic properties, they hydrolyze hydrophobic triglycerides in pulp that easily aggregate and deposit into smaller, more hydrophilic, and easily dispersed glycerol and fatty acids, fundamentally destroying their ability to form sticky deposits. The products can be flushed away with the white water system or easily removed in subsequent processes.

[0036] The lipase used in this invention was purchased from Guangdong Yuanfeng Biotechnology Co., Ltd., model ENZYME118.

[0037] Example 1 This embodiment provides a purification method for softwood pulp. The virgin Masson pine pulp used has an iron ion content of 32.20 mg / kg, a dichloromethane extract content of 0.28%, a water-soluble chloride content of 89.0 mg / kg, a degree of polymerization of 1570, and an ash content (900℃) of 0.79%. The specific purification method includes the following steps: (1) Screening: Take 10g of oven-dried Masson pine pulp, dilute it to 1000mL, and use a Paul sieve with a 50-mesh sieve to sieve the original Masson pine pulp to remove fine fiber components, thus obtaining the sieved Masson pine pulp.

[0038] (2) Chelation treatment: Weigh 5.0g of the oven-dried pine pulp obtained after sieving in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% to obtain the pulp.

[0039] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.5% (based on the mass of oven-dried pine pulp after sieving). The pH of the pulp was adjusted to 5.5, and chelation treatment was carried out at a temperature of 70°C for 60 minutes. After the chelation treatment, the chelated pulp was obtained.

[0040] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a cake density of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a cake density of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained.

[0041] (4) Enzyme treatment: The washed pulp filter cake obtained in step (3) was dispersed in deionized water. The mass concentration of the pulp was adjusted to 5% based on the mass of the oven-dry washed pulp filter cake. The pH of the system was adjusted to 7.5, and the temperature was set to 60℃. 300 g / t (based on the mass of the oven-dry washed pulp filter cake) of lipase was added. The mixture was then magnetically stirred and kept warm for 60 min in a clean beaker. After the reaction was completed, the pulp was washed once by vacuum filtration with 300 mL of deionized water at 60℃. The dryness of the filtered pulp was about 25%, yielding Masson pine insulating pulp.

[0042] The obtained pine insulating slurry, after testing, had the following characteristics: iron ion content 24.7 mg / kg, dichloromethane extract content 0.29%, water-soluble chloride 40 mg / kg, degree of polymerization 1490, and ash content (900℃) 0.38%. This pine insulating slurry meets the requirements for subsequent use.

[0043] Example 2 This embodiment provides a purification method for softwood pulp. The virgin Pinus kesaurus pulp used has an iron content of 16.80 mg / kg, a dichloromethane extract content of 0.49%, a water-soluble chloride content of 53.2 mg / kg, a degree of polymerization of 844, and an ash content (900℃) of 0.47%. The specific purification method includes the following steps: (1) Screening: Take 10g of oven-dried Simao pine pulp, dilute it to 1000mL, and use a 50-mesh sieve and a Paul sieve analyzer to sieve the original Simao pine pulp to remove fine fiber components and obtain sieved Simao pine pulp.

[0044] (2) Chelation treatment: Weigh 5.0g of the sieved Simao pine pulp obtained in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% according to the mass of the oven-dry Simao pine pulp after sieving, to obtain the pulp.

[0045] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.2% (based on the mass of oven-dried Simao pine pulp after sieving). The pH of the pulp was adjusted to 5.5, and chelation treatment was carried out at a temperature of 70°C for 30 minutes. After the chelation treatment, the chelated pulp was obtained.

[0046] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a cake density of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a cake density of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained.

[0047] (4) Enzyme treatment: The washed pulp filter cake obtained in step (3) was dispersed in deionized water. The mass concentration of the pulp was adjusted to 5% based on the mass of the oven-dry washed pulp filter cake. The pH of the system was adjusted to 7.5, and the temperature was set to 60℃. 300 g / t (based on the mass of the oven-dry washed pulp filter cake) of lipase was added. The mixture was then magnetically stirred and kept warm for 60 min in a clean beaker. After the reaction was completed, the pulp was washed once by vacuum filtration with 300 mL of deionized water at 60℃. The dryness of the filtered pulp filter cake was about 25%, yielding Simao pine insulating pulp.

[0048] The test results showed that the iron ion content of the pine insulating slurry obtained in this embodiment was 14.1 mg / kg, the dichloromethane extract content was 0.32%, the water-soluble chloride content was 23 mg / kg, the degree of polymerization was 815, and the ash content (900℃) was 0.24%.

[0049] Example 3 This embodiment provides a method for purifying softwood pulp, using virgin Pinus sylvestris pulp. The specific purification method includes the following steps: (1) Screening: Take 10g of oven-dried Simao pine pulp, dilute it to 1000mL, and use a 50-mesh sieve and a Paul sieve analyzer to sieve the original Simao pine pulp to remove fine fiber components and obtain sieved Simao pine pulp.

[0050] (2) Chelation treatment: Weigh 5.0g of the sieved Simao pine pulp obtained in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% according to the mass of the oven-dry Simao pine pulp after sieving, to obtain the pulp.

[0051] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.5% (based on the mass of oven-dried Simao pine pulp after sieving). The pH of the pulp was adjusted to 5, and chelation treatment was carried out at a temperature of 50°C for 60 minutes. After the chelation treatment, the chelated pulp was obtained.

[0052] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a cake density of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a cake density of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained.

[0053] (4) Enzyme treatment: The washed pulp filter cake obtained in step (3) was dispersed in deionized water. The mass concentration of the pulp was adjusted to 5% based on the mass of the oven-dried washed pulp filter cake. The pH of the system was adjusted to 9, and the temperature was set to 63℃. 300 g / t (based on the mass of the oven-dried washed pulp filter cake) of lipase was added, and the mixture was magnetically stirred and kept warm for 60 min in a clean beaker. After the reaction was completed, the pulp was washed once by vacuum filtration with 300 mL of deionized water at 60℃. The dryness of the filtered pulp filter cake was about 25%, yielding Simao pine insulating pulp.

[0054] Example 4 This embodiment provides a method for purifying coniferous pulp, using virgin Masson pine pulp. The specific purification method includes the following steps: (1) Screening: Take 10g of oven-dried Masson pine pulp, dilute it to 1000mL, and use a Paul sieve with a 50-mesh sieve to sieve the original Masson pine pulp to remove fine fiber components, thus obtaining the sieved Masson pine pulp.

[0055] (2) Chelation treatment: Weigh 5.0g of the obtained pine pulp after sieving in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% according to the mass of the sieved oven-dry pine pulp to obtain the pulp.

[0056] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.2% (based on the mass of oven-dried pine pulp after sieving). The pH of the pulp was adjusted to 6, and chelation treatment was carried out at a temperature of 60°C for 90 minutes. After the chelation was completed, chelated pulp was obtained.

[0057] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a cake density of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a cake density of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained.

[0058] (4) Enzyme treatment: The washed pulp filter cake obtained in step (3) was dispersed in deionized water. The mass concentration of the pulp was adjusted to 5% based on the mass of the oven-dried washed pulp filter cake. The pH of the system was adjusted to 6, and the temperature was set to 65℃. 300 g / t (based on the mass of the oven-dried washed pulp filter cake) of lipase was added, and the mixture was magnetically stirred and kept warm for 60 min in a clean beaker. After the reaction was completed, the pulp was washed once by vacuum filtration with 300 mL of deionized water at 60℃. The dryness of the filtered pulp filter cake was about 25%, yielding Masson pine insulating pulp.

[0059] Example 5 This embodiment provides a method for purifying softwood pulp, using raw Pinus sylvestris pulp. The specific purification method includes the following steps: (1) Screening: Take 10g of oven-dried Simao pine pulp, dilute it to 1000mL, and use a 50-mesh sieve and a Paul sieve analyzer to sieve the original Simao pine pulp to remove fine fiber components and obtain sieved Simao pine pulp.

[0060] (2) Chelation treatment: Weigh 5.0g of the sieved Simao pine pulp obtained in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% according to the mass of the oven-dry Simao pine pulp after sieving, to obtain the pulp.

[0061] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.35% (based on the mass of oven-dried Simao pine pulp after sieving). The pH of the pulp was adjusted to 6, and chelation treatment was carried out at a temperature of 60°C for 50 minutes. After the chelation treatment, the chelated pulp was obtained.

[0062] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a cake density of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a cake density of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained.

[0063] (4) Enzyme treatment: The washed pulp filter cake obtained in step (3) was dispersed in deionized water. The mass concentration of the pulp was adjusted to 5% based on the mass of the oven-dry washed pulp filter cake. The pH of the system was adjusted to 8, and the temperature was set to 63℃. 300 g / t (based on the mass of the oven-dry washed pulp filter cake) of lipase was added, and the mixture was magnetically stirred and kept warm for 60 min in a clean beaker. After the reaction was completed, the pulp was washed once by vacuum filtration with 300 mL of deionized water at 60℃. The dryness of the filtered pulp filter cake was about 25%, yielding Simao pine insulating pulp.

[0064] Comparative Example 1 This comparative example provides a purification method for softwood pulp. The original Masson pine pulp used has an iron ion content of 32.20 mg / kg, a dichloromethane extract content of 0.28%, a water-soluble chloride content of 89.0 mg / kg, a degree of polymerization of 1570, and an ash content (900℃) of 0.79%.

[0065] The specific purification method is basically the same as in Example 1, except that the enzyme treatment in step (4) is not performed. The specific steps are as follows: (1) Screening: Take 10g of oven-dried Masson pine pulp, dilute it to 1000mL, and use a Paul sieve with a 50-mesh sieve to sieve the original Masson pine pulp to remove fine fiber components, thus obtaining the sieved Masson pine pulp.

[0066] (2) Chelation treatment: Weigh 5.0g of the oven-dried pine pulp obtained after sieving in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% to obtain the pulp.

[0067] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.5% (based on the mass of oven-dried pine pulp after sieving). The pH of the pulp was adjusted to 5.5, and chelation treatment was carried out at a temperature of 70°C for 60 minutes. After the chelation treatment, the chelated pulp was obtained.

[0068] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a dryness of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a dryness of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained, which is the pine insulating pulp.

[0069] The obtained pine insulating slurry, after testing, had the following characteristics: iron ion content 24.7 mg / kg, dichloromethane extract content 0.38%, water-soluble chloride 40 mg / kg, degree of polymerization 1490, and ash content (900℃) 0.38%.

[0070] Comparative Example 2 This comparative example provides a purification method for softwood pulp. The original Pinus sylvestris pulp used has an iron ion content of 16.80 mg / kg, a dichloromethane extract content of 0.49%, a water-soluble chloride content of 53.2 mg / kg, a degree of polymerization of 844, and an ash content (900℃) of 0.47%.

[0071] The specific purification method is basically the same as in Example 2, except that the enzyme treatment in step (4) is not performed. The specific steps are as follows: (1) Screening: Take 10g of oven-dried Simao pine pulp, dilute it to 1000mL, and use a 50-mesh sieve and a Paul sieve analyzer to sieve the original Simao pine pulp to remove fine fiber components and obtain sieved Simao pine pulp.

[0072] (2) Chelation treatment: Weigh 5.0g of the sieved Simao pine pulp obtained in step (1), disperse it with deionized water, and adjust the mass concentration of the pulp to 4.0% based on the mass of the oven-dry Simao pine pulp after sieving, to obtain the pulp.

[0073] Ethylenediaminetetraacetic acid (EDTA) was added to the pulp at a concentration of 0.2% (based on the mass of oven-dried Simao pine pulp after sieving). The pH of the pulp was adjusted to 5.5, and chelation treatment was carried out at a temperature of 70°C for 30 minutes. After the chelation treatment, the chelated pulp was obtained.

[0074] (3) Water washing and alkaline washing: The chelated pulp obtained in step (2) was subjected to four vacuum filtration and washing processes. The first, second, and fourth washings were performed with 300 mL of deionized water at 60°C. After filtration, the pulp filter cake had a dryness of about 25%. The third washing was performed with 300 mL of NaOH solution at pH 9 and 60°C. After filtration, the pulp filter cake had a dryness of about 25%. After the four vacuum filtration and washing processes, the washed pulp filter cake was obtained, which is the Simao pine insulating pulp.

[0075] After testing, the obtained Simao pine insulating slurry contained 14.1 mg / kg of iron ions, 0.41% of dichloromethane extract, 23 mg / kg of water-soluble chloride, 815 degrees of polymerization, and 0.22% of ash (at 900℃).

[0076] Taking Examples 1 and 2 as examples, after the softwood pulp is purified according to the purification method of the present invention, the iron ion content, dichloromethane extract content and ash content are effectively reduced, and its comprehensive performance can meet the requirements of high voltage electrical insulation pulp.

[0077] The above-described embodiments are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A method for purifying softwood pulp, characterized in that, Includes the following steps: The raw softwood pulp is screened to obtain screened softwood pulp; The sieved softwood pulp and chelating agent are chelated at 50℃~70℃ to remove iron ions from the softwood pulp, resulting in chelated softwood pulp. Alkali treatment was performed on the chelated softwood pulp to obtain alkali-treated softwood pulp. Alkali-treated softwood pulp is dispersed in water and subjected to enzymatic treatment at 60℃~65℃ and pH 6~9 to remove resin components from the softwood pulp, thus obtaining softwood insulating pulp.

2. The method for purifying softwood pulp according to claim 2, characterized in that, The chelation treatment was performed at pH 5-6 for 30-90 minutes.

3. The method for purifying softwood pulp according to claim 1, characterized in that, The amount of chelating agent added is 0.2% to 0.5% of the mass of the oven-dried softwood pulp after sieving.

4. The method for purifying softwood pulp according to claim 1, characterized in that, The enzyme treatment time was 60 minutes.

5. The method for purifying softwood pulp according to claim 1, characterized in that, The amount of enzyme added is 300g / t based on the weight of oven-dried softwood pulp after alkali treatment. The enzyme used is lipase.

6. The method for purifying softwood pulp according to claim 1, characterized in that, The original coniferous wood pulp was made from Masson pine pulp and Simao pine pulp; the chelating agent was ethylenediaminetetraacetic acid.

7. The method for purifying softwood pulp according to claim 1, characterized in that, The alkali treatment method is as follows: after chelating the softwood pulp, it is washed twice with water, then washed with an alkaline solution. After the alkaline washing is completed, it is washed again with water to obtain the alkali-treated softwood pulp.

8. The method for purifying softwood pulp according to claim 9, characterized in that, The alkaline solution is a NaOH solution with pH=9 and a temperature of 60℃.

9. A coniferous wood insulating pulp obtained by the purification method according to any one of claims 1 to 8.

10. The use of the coniferous wood insulating slurry of claim 9 in the preparation of electrical insulating materials.

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