Deinking and bleaching treatment process for recycled waste paper

Abstract

The invention belongs to the technical field of recycled waste paper processing, and particularly relates to a deinking and bleaching treatment process for recycled waste paper. The deinking and bleaching treatment process for the recycled waste paper comprises the following steps: S1, cleaning, removing impurities, soaking and pulping; s2, performing steam explosion; s3, performing enzymolysis treatment; and S4, bleaching, washing and pulping. According to the deinking and bleaching treatment process for the recycled waste paper, the chemical, physical and biological combined deinking technology is integrated, the quality and efficiency of recycled paper production are comprehensively optimized, ink particles attached to the waste paper can be more effectively removed, the whiteness of the recycled paper is remarkably improved, the integrity of fibers is protected, fiber breakage and damage are reduced, and the service life of the recycled paper is prolonged. Therefore, the physical properties of the recycled paper, such as burst index, tensile index and tear index, are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of recycled waste paper processing, and in particular relates to a deinking and bleaching process for recycled waste paper. Background Art

[0002] In recent years, the global pulp and paper industry has encountered multiple challenges, with the core issues focusing on the fragility of the raw material supply chain and the growing pressure of environmental regulations. With the decline of global forest coverage and the strengthening of ecological conservation policies, exploring environmentally friendly raw material alternatives has become a key issue for the sustainable development of the paper industry. In this context, as an important part of the circular economy, the status and value of waste paper fiber recycling have become increasingly prominent. The recycling of waste paper fiber can not only effectively reduce the paper industry's dependence on virgin forest fiber, but also significantly reduce the exploitation of forest resources, thereby alleviating damage to the natural environment, which is in line with the global green, low-carbon and sustainable development vision. Through efficient recycling and reuse of waste paper, the paper industry can significantly reduce the negative impact on the environment while maintaining production, and promote the industry to transform towards a more environmentally friendly and resource-saving direction. The recycling and reuse of waste paper fiber can not only effectively alleviate the paper industry's dependence on virgin fiber, but also significantly reduce deforestation and reduce pressure on the environment, which is in line with the general trend of green, low-carbon and circular development.

[0003] However, waste paper reveals some inherent defects in the process of recycling, which restrict its wide application in the production of high-quality products: 1. Decreased swelling ability: During the recycling process, the fiber structure of waste paper fibers is damaged, resulting in a weakening of its ability to absorb water and swell. The decline in swelling ability directly affects the dispersion and bonding of fibers in pulp, and thus affects the uniformity and smoothness of paper. 2. Decreased paper strength: With the increase in the number of recycling times, the length and strength of waste paper fibers are gradually lost, resulting in a decrease in the mechanical strength of the produced paper (such as tensile strength and tear strength), which is difficult to meet certain high-demand application scenarios, such as high-end packaging materials, special paper products, etc. 3. Poor water filtration performance: The decline in the water filtration performance of waste paper fibers means that in the papermaking process, the filtration speed of the fiber suspension slows down, increasing energy consumption and extending the production cycle. It may also affect the drying efficiency and final flatness of the paper. In addition, in the existing deinking process, especially in the mechanical de-inking and washing stages, the fibers may be damaged and shortened. This leads to a decrease in the fiber length and strength of the recycled pulp, which in turn affects the quality and physical properties of the recycled paper.

[0004] Therefore, it is necessary to provide a deinking and bleaching treatment for recycled waste paper, which can improve the water filterability and bleaching performance of waste paper pulp and improve the deinking effect of waste paper, minimize fiber damage, and thus enhance the recycling of waste paper fibers. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a deinking and bleaching process for recycling waste paper. The deinking and bleaching process for recycling waste paper provided by the present invention integrates chemical, physical and biological deinking technologies, comprehensively optimizes the quality and efficiency of recycled paper production, can more effectively remove ink particles attached to waste paper, significantly improve the whiteness of recycled paper, and protect the integrity of fibers, reduce fiber breakage and damage, thereby improving the physical properties of recycled paper, such as bursting index, tensile index and tear index.

[0006] The technical solution of the present invention is:

[0007] A deinking and bleaching process for recycling waste paper comprises the following steps:

[0008] S1. Cleaning, impurity removal, soaking, and pulping: the recycled waste paper is cleaned and impurity removed, then soaked in a sodium hydroxide solution, and then a deinking agent is added to pulp to obtain a pretreated pulp;

[0009] S2, steam explosion: steam explosion treatment is performed on the pretreated pulp obtained in step S1;

[0010] S3, enzymatic hydrolysis: adjusting the pH of the pulp after steam explosion in step S2 to 7, and then performing a primary enzymatic hydrolysis; then adjusting the pH of the system to 4.5-5.5, then adding composite additives and laccase and α-amylase and stirring evenly, adjusting the system temperature to 5-15°C and standing for a period of time before performing a secondary enzymatic hydrolysis;

[0011] S4, bleaching, washing, pulping: adding bleaching agent to the pulp after enzymatic hydrolysis in step S3 for bleaching treatment, and then filtering and washing to obtain deinked pulp.

[0012] Furthermore, the amount of the deinking agent added in step S1 is 0.9-1.5wt% of the weight of the pulp soaked in the sodium hydroxide solution, and the deinking agent in step S1 is composed of isooctyl polyoxyethylene ether phosphate, sodium metasilicate and lauryl hydroxysulfobetaine in a weight ratio of (1-3:2-5:1), preferably (2:3:1).

[0013] Furthermore, the isooctyl alcohol polyoxyethylene ether phosphate is isooctyl alcohol polyoxyethylene ether phosphate OEP-98, purchased from Jinan Baoliyuan Chemical Co., Ltd.; the CAS number of the sodium metasilicate is 6834-92-0; and the CAS number of the lauryl hydroxysulfobetaine is 13197-76-7.

[0014] Furthermore, in step S1, the amount of sodium hydroxide solution used is 5 to 7 times the dry weight of the waste paper, the concentration of the sodium hydroxide solution is 0.3 to 0.5%, the soaking temperature is 50 to 60° C., and the soaking time is 20 to 30 minutes.

[0015] Furthermore, the pulping process in step S1 is carried out in a hydraulic pulper, the rotation speed of the pulping process is 600-800 r / min, and the processing time is 20-30 min.

[0016] Furthermore, the pressure during the steam explosion in step S2 is 1.3-1.5 MPa, preferably 1.4 MPa, the temperature is 130-150° C., and the processing time is 5-10 min.

[0017] The deinking and bleaching process for recycling waste paper provided by the present invention first removes dust, sand and other impurities on the surface of the waste paper by cleaning and impurity removal, thereby providing a clean substrate for subsequent chemical treatment, and then soaks the waste paper in an alkaline environment to fully swell it, and then adds a deinking agent to carry out pulping treatment, and the pretreated pulp after pulping is subjected to steam explosion treatment. Steam explosion is a physical treatment method, which acts on waste paper pulp through high-temperature and high-pressure steam to cause the fibers to expand rapidly and release pressure instantly, resulting in strong vibration and rapid expansion of the fibers. The present invention creatively adds a deinking agent composed of isooctyl alcohol polyoxyethylene ether phosphate, sodium metasilicate and lauryl hydroxysulfonyl betaine in a specific proportion during the treatment process using the steam explosion method, which can better destroy the close bonding between fibers and promote the separation of fibers, while accelerating the penetration of the deinking agent, so that the bonding force between the fibers and ink and other impurities is weakened, which helps to loosen and remove ink and other non-fiber impurities, and improve the deinking effect. In the above steps, the deinking agent and steam explosion are used, and the reaction conditions in the steps are controlled to comprehensively treat the pulp, which can effectively dissolve and separate the ink and adhesives without excessively damaging the fibers and destroying the integrity of the fibers, thereby effectively improving the physical properties of the recycled paper products, such as tensile strength, bursting index, tear index, etc.

[0018] Furthermore, the amount of cellulase added in the primary enzymatic hydrolysis of step S3 is 10-15 U / g, preferably 12 U / g, based on the dry weight of the waste paper in step S1; the temperature during the primary enzymatic hydrolysis is 50-55° C., and the enzymatic hydrolysis time is 12-18 h.

[0019] Furthermore, in the step S3, the amount of laccase added during the secondary enzymatic hydrolysis is 6 to 10 U / g, preferably 8 U / g, and the amount of α-amylase added is 5 to 8 U / g, preferably 6 U / g, based on the dry weight of the waste paper in step S1; the temperature during the secondary enzymatic hydrolysis is 35 to 45°C, and the enzymatic hydrolysis time is 12 to 24 hours.

[0020] Furthermore, the cellulase, laccase and α-amylase used in the present invention are all commonly used biological enzyme preparations in the prior art. The CAS number of the cellulase is 9012-54-8, the CAS number of the laccase is 80498-15-3, and the CAS number of the α-amylase is 9000-90-2.

[0021] Furthermore, after the enzymatic hydrolysis in step S3, the pH of the system is adjusted to 4.5-5.5, and then the composite auxiliary agent, laccase and α-amylase are added and stirred evenly, and then the temperature of the system is adjusted to 5-15° C. and allowed to stand for 3-5 hours.

[0022] Furthermore, the amount of the composite auxiliary agent added in step S3 is 1.2-2.0wt% of the weight of the pulp after one enzymatic hydrolysis, preferably 1.8wt%, and the composite auxiliary agent is composed of polyethylene glycol monooleate and tyrosine in a weight ratio of (3-6:2), preferably (5:2).

[0023] Furthermore, the CAS number of the polyethylene glycol monooleate is 9004-96-0.

[0024] In the present invention, the pulp after steam explosion treatment is first enzymolyzed with cellulase, and then a composite auxiliary agent composed of polyethylene glycol monooleate and tyrosine, laccase and alpha-amylase are added, and then a secondary enzymolysis is performed after standing at low temperature for a period of time. In the above steps, different types of enzymes are selected to perform two enzymolysis under a specific environment, and before the secondary enzymolysis, a composite auxiliary agent composed of polyethylene glycol monooleate and tyrosine, laccase and alpha-amylase are first added, and then standing at low temperature for a period of time, which can promote the stabilization of the enzymolysis product and the further separation of the ink particles, on the one hand, can improve the deinking efficiency and pulp whiteness, on the other hand, can reduce fiber damage, maintain the length and flexibility of the fiber, promote the cross-linking between pulp fibers, and further improve the fluidity of the pulp and the physical properties of the paper.

[0025] Furthermore, the bleaching agent in step S4 is composed of sodium salt of ethylenediaminetetraacetic acid and hydrogen peroxide, the amount of sodium salt of ethylenediaminetetraacetic acid added is 0.08-0.12wt% of the weight of the pulp after enzymatic hydrolysis in step S3, and the amount of hydrogen peroxide added in step S4 is 2.5-3.0wt% of the weight of the pulp after enzymatic hydrolysis in step S3.

[0026] Furthermore, the sodium salt of ethylenediaminetetraacetic acid is disodium ethylenediaminetetraacetate (disodium EDTA).

[0027] Furthermore, the bleaching treatment in step S4 is performed at a temperature of 60 to 80° C. and for a time of 30 to 60 minutes.

[0028] Furthermore, the filtering process in step S4 is to sequentially pass the bleached pulp through a coarse screen with a pore size of 1 to 3 mm and a fine screen with a pore size of 0.2 to 0.4 mm, and then adjust the pulp concentration of the deinked pulp to 4 to 6%.

[0029] Compared with the prior art, the deinking and bleaching process for recycled waste paper provided by the present invention has the following advantages:

[0030] (1) The deinking and bleaching process for recycled waste paper provided by the present invention integrates chemical, physical and biological deinking technologies, comprehensively optimizes the quality and efficiency of recycled paper production, can more effectively remove ink particles attached to waste paper, and significantly improve the whiteness of recycled paper.

[0031] (2) The deinking and bleaching process for recycled waste paper provided by the present invention also protects the integrity of the fibers and reduces fiber breakage and damage by precisely controlling the raw materials, reagents and process parameters of each step, thereby improving the physical properties of the recycled paper, such as the bursting index, tensile index and tear index.

[0032] (3) The deinking and bleaching process for recycled waste paper provided by the present invention improves the fiber recovery rate, which not only saves natural resources, but also improves production efficiency and economic benefits, and reduces the amount of harmful chemical reagents used in traditional deinking processes, and also reduces the emission of harmful chemicals, which is in line with the trend of green manufacturing. DETAILED DESCRIPTION

[0033] The present invention is further illustrated below through the description of specific implementation methods, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not deviate from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0034] In the following examples and comparative examples, reagents not otherwise specified are conventional reagents and can be purchased from conventional reagent production and sales companies. The methods used are all prior art unless otherwise specified.

[0035] Example 1

[0036] A deinking and bleaching process for recycling waste paper comprises the following steps:

[0037] S1. Cleaning, impurity removal, soaking and pulping: cut the recycled office waste paper into 3 cm pieces, rinse with running water to remove impurities on the surface, then add it into a sodium hydroxide solution with a concentration of 0.3% which is 5 times the dry weight of the waste paper and soak it for 20 minutes at a soaking temperature of 50°C to make the waste paper fully swell, then add a sodium oxide solution to soak a deinking agent with a concentration of 0.9wt% of the weight of the pulp, stir evenly and then carry out pulping treatment in a hydraulic crusher for 20 minutes at a speed of 800r / min to obtain pretreated pulp; the deinking agent is composed of isooctyl alcohol polyoxyethylene ether phosphate OEP-98, sodium metasilicate and lauryl hydroxysulfonobetaine in a weight ratio of (1:5:1);

[0038] S2, steam explosion: placing the pretreated pulp obtained in step S1 in a steam explosion device, and carrying out the process at a pressure of 1.3 MPa and a temperature of 130° C. for 10 min, followed by rapid decompression to release the material;

[0039] S3, enzymatic hydrolysis: the temperature of the pulp after steam explosion in step S2 is lowered to room temperature, the pH is adjusted to 7, and then cellulase is added, the amount of the cellulase added is 10U / g, based on the dry weight of the waste paper in step S1, and the enzymatic hydrolysis is carried out at a temperature of 50°C for 18 hours, and then the pH of the system is adjusted to 4.5, and then the composite auxiliary agent, laccase, and α-amylase are added and stirred evenly, and the temperature of the system is adjusted to 5°C and allowed to stand for 3 hours, the amount of the laccase added is 6U / g, and the amount of the α-amylase added is 5U / g, based on the dry weight of the waste paper in step S1, and then the enzymatic hydrolysis is carried out at a temperature of 50°C for 12 hours; the amount of the composite auxiliary agent added is 1.2wt% of the weight of the pulp after one enzymatic hydrolysis, and the composite auxiliary agent is composed of polyethylene glycol monooleate and tyrosine in a weight ratio of (3:2);

[0040] S4, bleaching, washing, and pulping: add 0.08 wt% of disodium ethylenediaminetetraacetate and 2.5 wt% of hydrogen peroxide to the pulp after enzymatic hydrolysis in step S3, and bleach it at 60°C for 60 minutes, and then pass it through a coarse sieve with a pore size of 1 to 3 mm and a fine sieve with a pore size of 0.2 to 0.4 mm in sequence; then wash the pulp with clean water until the pH value of the pulp is neutral, and then adjust the pulp concentration to 4% to obtain deinked pulp.

[0041] Example 2

[0042] A deinking and bleaching process for recycling waste paper comprises the following steps:

[0043] S1. Cleaning, impurity removal, soaking and pulping: Cut the recycled office waste paper into 3 cm pieces, rinse with running water to remove impurities on the surface, then add it into a sodium hydroxide solution with a concentration of 0.4% which is 6 times the dry weight of the waste paper and soak it for 25 minutes at a soaking temperature of 55°C to make the waste paper fully swell, then add a sodium oxide solution to soak a deinking agent which is 1.2wt% of the weight of the pulp, stir evenly and then carry out pulping treatment in a hydraulic crusher for 25 minutes at a speed of 700r / min to obtain pretreated pulp; the deinking agent is composed of isooctyl alcohol polyoxyethylene ether phosphate OEP-98, sodium metasilicate and lauryl hydroxysulfonobetaine in a weight ratio of (2:3:1);

[0044] S2, steam explosion: the pretreated pulp obtained in step S1 is placed in a steam explosion device, and is subjected to a steam explosion at a pressure of 1.4 MPa and a temperature of 145° C. for 8 minutes, followed by rapid decompression to release the material;

[0045] S3, enzymatic hydrolysis: the temperature of the pulp after steam explosion in step S2 is lowered to room temperature, the pH is adjusted to 7, and then cellulase is added, the amount of the cellulase added is 12U / g, based on the dry weight of the waste paper in step S1, the enzymatic hydrolysis is carried out at a temperature of 52°C for 16 hours, and then the pH of the system is adjusted to 5, and then the composite auxiliary agent, laccase, and α-amylase are added and stirred evenly, and the temperature of the system is adjusted to 10°C and allowed to stand for 4 hours, the amount of the laccase added is 8U / g, and the amount of the α-amylase added is 6U / g, based on the dry weight of the waste paper in step S1, and then the enzymatic hydrolysis is carried out at a temperature of 40°C for 18 hours; the amount of the composite auxiliary agent added is 1.8wt% of the weight of the pulp after one enzymatic hydrolysis, and the composite auxiliary agent is composed of polyethylene glycol monooleate and tyrosine in a weight ratio of (5:2);

[0046] S4, bleaching, washing, and pulping: add 0.1 wt% of disodium ethylenediaminetetraacetate and 2.7 wt% of hydrogen peroxide to the pulp after enzymatic hydrolysis in step S3, and bleach it at 70°C for 50 minutes, and then pass it through a coarse sieve with a pore size of 1 to 3 mm and a fine sieve with a pore size of 0.2 to 0.4 mm in sequence; then wash the pulp with clean water until the pH value of the pulp is neutral, and then adjust the pulp concentration to 5% to obtain deinked pulp.

[0047] Example 3

[0048] A deinking and bleaching process for recycling waste paper comprises the following steps:

[0049] S1. Cleaning, impurity removal, soaking and pulping: Cut the recycled office waste paper into 3 cm pieces, rinse with running water to remove impurities on the surface, then add it into a sodium hydroxide solution with a concentration of 0.5% which is 7 times the dry weight of the waste paper and soak it for 30 minutes at a soaking temperature of 60°C to make the waste paper fully swell, then add a sodium oxide solution to soak a deinking agent with a weight of 1.5 wt% of the pulp, stir evenly and then carry out pulping treatment in a hydraulic crusher for 30 minutes at a speed of 800 r / min to obtain pretreated pulp; the deinking agent is composed of isooctyl alcohol polyoxyethylene ether phosphate OEP-98, sodium metasilicate and lauryl hydroxysulfonobetaine in a weight ratio of (3:2:1);

[0050] S2, steam explosion: placing the pretreated pulp obtained in step S1 in a steam explosion device, and carrying out the process for 5 minutes at a pressure of 1.5 MPa and a temperature of 150° C., followed by rapid decompression to release the material;

[0051] S3, enzymatic hydrolysis: the temperature of the pulp after steam explosion in step S2 is lowered to room temperature, the pH is adjusted to 7, and then cellulase is added, the amount of the cellulase added is 15U / g, based on the dry weight of the waste paper in step S1, enzymatic hydrolysis is carried out at a temperature of 55°C for 12 hours, and then the pH of the system is adjusted to 5.5, and then a composite auxiliary agent, laccase, and α-amylase are added and stirred evenly, and the temperature of the system is adjusted to 15°C and allowed to stand for 5 hours, the amount of the laccase added is 10U / g, and the amount of the α-amylase added is 8U / g, based on the dry weight of the waste paper in step S1, and then enzymatic hydrolysis is carried out at a temperature of 35°C for 24 hours; the amount of the composite auxiliary agent added is 2.0wt% of the weight of the pulp after one enzymatic hydrolysis, and the composite auxiliary agent is composed of polyethylene glycol monooleate and tyrosine in a weight ratio of (6:2);

[0052] S4, bleaching, washing, and pulping: add 0.12 wt% of disodium ethylenediaminetetraacetate and 3.0 wt% of hydrogen peroxide to the pulp after enzymatic hydrolysis in step S3, and bleach it at 80°C for 30 minutes, and then pass it through a coarse sieve with a pore size of 1 to 3 mm and a fine sieve with a pore size of 0.2 to 0.4 mm in sequence; then wash the pulp with clean water until the pH value of the pulp is neutral, and then adjust the pulp concentration to 6% to obtain deinked pulp.

[0053] Comparative Example 1

[0054] Compared with Example 2, the difference is that the isooctyl alcohol polyoxyethylene ether phosphate OEP-98 in the deinking agent of step S1 is replaced by fatty alcohol polyoxyethylene ether AEO-9 (CAS No. 68213-23-0), and the other raw material components and preparation method are the same as those in Example 2.

[0055] Comparative Example 2

[0056] Compared with Example 2, the difference is that sodium metasilicate is not added to the deinking agent in step S1, and the amount of octanol polyoxyethylene ether phosphate OEP-98 is increased accordingly, that is, the deinking agent is composed of isooctyl alcohol polyoxyethylene ether phosphate OEP-98 and lauryl hydroxysulfonyl betaine in a weight ratio of (5:1). Other raw material components and preparation methods are the same as those in Example 2.

[0057] Comparative Example 3

[0058] Compared with Example 2, the difference is that the pressure during the steam explosion treatment in step S2 is 1.8 MPa and the temperature is 160° C., and the other raw material components and preparation method are the same as those in Example 2.

[0059] Comparative Example 4

[0060] Compared with Example 2, the difference is that after adding the composite auxiliary agent, laccase and α-amylase in step S3 and stirring evenly, the system temperature is not adjusted to 10°C and left to stand for 4 hours, but enzymolysis is directly carried out at a temperature of 40°C for 18 hours (secondary enzymolysis), and the other raw material components and preparation method are the same as those in Example 2.

[0061] Comparative Example 5

[0062] Compared with Example 2, the difference is that in step S3, no tyrosine is added to the composite auxiliary agent, only polyethylene glycol monooleate is added, that is, the addition amount of polyethylene glycol monooleate is 1.8wt% of the weight of the pulp after one enzymatic hydrolysis, and the other raw material components and preparation method are the same as those in Example 2.

[0063] Test Example 1: Performance test of paper products made from deinked pulp prepared by the present invention

[0064] Test method:

[0065] (1) The deinked pulps prepared in Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention were diluted to a pulp concentration of 1.2%, and then sheeted into a paper having a basis weight of 60 g / m2 by a rapid Kaiser forming method. 2 of paper.

[0066] (2) The test standards and test data are shown in Tables 1 and 2.

[0067] Table 1

[0068] Group Testing national standards Example 1 Example 2 Example 3 Residual ink amount (ppm) GB / T 20216-2016 219.6 204.9 213.1 Whiteness(%ISO) GB / T 7974-2013 86.3 88.6 87.6 Transverse folding endurance (times) GB / T 457-2008 39 43 41 <![CDATA[Bulk thickness (cm 3 ·g -1 )]]> GB / T 451.3-2002 2.1 2.2 2.1 Tensile index (N·m / g) GB / T 453-2002 55.6 59.6 56.4 <![CDATA[Burst index (KPa·m 2 ·g -1 )]]> GB / T 454--2002 3.71 3.85 3.74 <![CDATA[Tear index (mN·m 2 ·g -1 )]]> GB / T 455-2002 5.13 5.26 4.96

[0069] Table 2

[0070]

[0071] As shown in Table 1, the whiteness of the recycled paper prepared in Examples 1 to 3 of the present invention can reach 88.6% ISO, the residual ink content is low, and the paper has excellent physical properties. Compared with the embodiments of the present invention, the quality of the recycled paper prepared in Comparative Examples 1 to 5 is much lower than that in Examples 1 to 3 of the present invention. It can be seen that the preparation process provided by the present invention can effectively remove the ink particles attached to the waste paper, significantly improve the whiteness of the recycled paper, and protect the integrity of the fiber, reduce fiber breakage and damage, thereby improving the physical properties of the recycled paper, such as the bursting index, tensile index and tear index.

[0072] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A deinking and bleaching process for recycling waste paper, characterized in that: The steps include: S1. Cleaning, impurity removal, soaking, and pulping: the recycled waste paper is cleaned and impurity removed, then soaked in a sodium hydroxide solution, and then a deinking agent is added to pulp to obtain a pretreated pulp; S2, steam explosion: steam explosion treatment is performed on the pretreated pulp obtained in step S1; S3, enzymatic hydrolysis: the pH of the pulp after steam explosion in step S2 is adjusted to 7, and then cellulase is added to perform primary enzymatic hydrolysis; then the pH of the system is adjusted to 4.5-5.5, and then the composite auxiliary agent, laccase, and α-amylase are added and stirred evenly, and the temperature of the system is adjusted to 5-15°C and allowed to stand for a period of time before secondary enzymatic hydrolysis; S4, bleaching, washing, pulping: adding bleaching agent to the pulp after enzymatic hydrolysis in step S3 for bleaching treatment, and then filtering and washing to obtain deinked pulp.

2. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The amount of the deinking agent added in step S1 is 0.9-1.5wt% of the weight of the pulp soaked in the sodium hydroxide solution. The deinking agent in step S1 is composed of isooctyl polyoxyethylene ether phosphate, sodium metasilicate and lauryl hydroxysulfobetaine in a weight ratio of (1-3:2-5:1).

3. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The amount of sodium hydroxide solution used in step S1 is 5 to 7 times the dry weight of the waste paper, and the concentration of the sodium hydroxide solution is 0.3 to 0.5%; the soaking temperature is 50 to 60° C., and the soaking time is 20 to 30 minutes.

4. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The pulping process in step S1 is carried out in a hydraulic pulper, the rotation speed of the pulping process is 600-800 r / min, and the processing time is 20-30 min.

5. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The pressure during the steam explosion in step S2 is 1.3-1.5 MPa, the temperature is 130-150° C., and the processing time is 5-10 min.

6. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The amount of cellulase added in the primary enzymatic hydrolysis of step S3 is 10-15 U / g, based on the dry weight of the waste paper in step S1; the temperature in the primary enzymatic hydrolysis is 50-55° C., and the enzymatic hydrolysis time is 12-18 hours; In the secondary enzymatic hydrolysis process in step S3, the addition amount of laccase is 6-10U / g, and the addition amount of α-amylase is 5-8U / g, based on the dry weight of the waste paper in step S1; the temperature during the secondary enzymatic hydrolysis process is 35-45°C, and the enzymatic hydrolysis time is 12-24h.

7. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: After the enzymatic hydrolysis in step S3, the pH of the system is adjusted to 4.5-5.5, and then the composite auxiliary agent, laccase and α-amylase are added and stirred evenly, and then the temperature of the system is adjusted to 5-15° C. and allowed to stand for 3-5 hours.

8. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The amount of the composite auxiliary agent added in step S3 is 1.2-2.0 wt% of the weight of the pulp after one enzymatic hydrolysis, and the composite auxiliary agent is composed of polyethylene glycol monooleate and tyrosine in a weight ratio of (3-6:2).

9. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The bleaching agent in step S4 is composed of sodium salt of ethylenediaminetetraacetic acid and hydrogen peroxide. The amount of sodium salt of ethylenediaminetetraacetic acid added is 0.08-0.12wt% of the weight of the pulp after enzymatic hydrolysis in step S3. The amount of hydrogen peroxide added in step S4 is 2.5-3.0wt% of the weight of the pulp after enzymatic hydrolysis in step S3.

10. The deinking and bleaching process for recycled waste paper according to claim 1, characterized in that: The filtering process in step S4 is to sequentially pass the bleached pulp through a coarse screen with a pore size of 1 to 3 mm and a fine screen with a pore size of 0.2 to 0.4 mm, and then adjust the concentration of the deinked pulp to 4 to 6%.

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