Waste paper recycling method and application thereof

Abstract

The invention relates to a waste paper recycling method and application thereof, and belongs to the technical field of waste paper recycling. The invention provides a waste paper recycling method which comprises the following steps: S1, adding a compound enzyme into a reaction kettle, heating to 40-50 DEG C, adding waste paper, pulping, performing ultrasonic treatment, performing enzymolysis, and filtering to obtain pretreated fiber pulp; s2, transferring the pretreated fiber pulp into a photocatalytic reaction tank for reaction; s3, spraying a nano material to form a Zeta potential gradient, transferring into an electromagnetic field treatment device, carrying out directional arrangement, dehydrating, and drying to obtain paper; wherein the compound enzyme is prepared from cellulase, xylanase, laccase and pullulanase. According to the method, key indexes such as deinking efficiency, fiber protection, bleaching performance and mechanical strength are remarkably improved, the technical bottleneck in recycling of the oil-containing waste packing paper is successfully solved, and a breakthrough scheme is provided for production of high-added-value regenerated paper pulp.

Description

Technical Field

[0001] The present invention relates to the technical field of waste paper recycling, and in particular to a waste paper recycling method and application thereof. Background Art

[0002] In the papermaking industry, recycling waste paper is crucial for conserving resources, reducing costs, and minimizing environmental pollution. This is particularly true in the area of ​​process paper, where cold-rolled stainless steel mills produce a significant amount of oily waste paper. This oily waste paper is recycled from cold-rolled stainless steel mills and, during use in the rolling process, absorbs residual rolling oil from the stainless steel sheet surface, resulting in an oil content of 10-15%. Furthermore, since the paper used in the rolling process is often recycled and rewound from flattening and rewinding lines, there are typically 3-7 joints per 10,000 meters within the roll, and these joints are typically bonded using conventional double-sided tape, making recycling more challenging.

[0003] At present, there are many problems with traditional waste paper treatment processes: First, there is a prominent contradiction between low deinking efficiency and fiber damage. Existing waste paper deinking processes mostly use strong alkali / surfactant treatment, which will lead to excessive fiber degradation, with a damage rate of more than 15% and a deinking rate of less than 80%, making it difficult to effectively retain the fibers while cleaning the paper; second, the bleaching process faces the dual bottlenecks of pollution and energy consumption. Traditional chlorine-based bleaching agents will produce adsorbable organic halides (AOX), which pollute the environment, and single hydrogen peroxide bleaching needs to be carried out at high temperatures of 70-90°C, which not only has high energy consumption and can only achieve a whiteness of 75% ISO, but also reduces the fiber crystallinity, resulting in strength degradation; third, the performance degradation of regenerated fibers is irreversible. After recycling, the fibers are severely keratinized and the tensile strength decreases by 30%-40%, which cannot meet the mechanical performance requirements of process padding paper, limiting its application in high-value-added process padding paper.

[0004] Therefore, there is an urgent need to develop a method for recycling waste paper that solves the above problems through multi-dimensional optimization to meet the application in process padding. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present application provides a method for recycling waste paper and its application. The method of the present application significantly improves key indicators such as deinking efficiency, fiber protection, bleaching performance, and mechanical strength, successfully solving the technical bottleneck in the recycling of oil-containing waste padding paper and providing a breakthrough solution for the production of high-value-added recycled pulp.

[0006] In a first aspect, the present application provides a method for recycling waste paper, comprising the following steps: S1: Add complex enzyme into the reactor, raise the temperature to 40-50°C, add waste paper pulp, perform ultrasonication and enzymatic hydrolysis, and then filter to obtain pretreated fiber pulp; S2: transferring the pretreated fiber pulp into a photocatalytic reaction tank for reaction; S3: Spraying nanomaterials to form a Zeta potential gradient, transferring them to an electromagnetic field treatment device for directional arrangement, dehydration, and drying to form paper; Wherein, the complex enzyme comprises cellulase, xylanase, laccase and pullulanase.

[0007] Optionally, the complex enzyme further comprises manganese peroxidase.

[0008] Optionally, the photocatalyst in the photocatalytic reaction tank is a TiO2 / MOFs heterojunction.

[0009] Optionally, the photocatalyst in the photocatalytic reaction tank is a TiO2 / ZIF-8 heterojunction.

[0010] Optionally, the S2 is divided into three stages: Stage 1: Add 1.0-3.0% H2O2, disperse evenly, then introduce CO2 supercritical fluid and react under strong ultraviolet light for 30-60 minutes; The second stage: drain the residual liquid, add 3.0-5.0% H2O2, increase the UV intensity and react for 20-40 minutes; The third stage: drain the residual liquid, add 0.5-1.5% H2O2, reduce the ultraviolet light intensity and react for 10-30 minutes, filter, and wash the fiber with warm water until neutral.

[0011] Optionally, the nanomaterial is a nanocellulose suspension.

[0012] Optionally, the nanomaterial is pH-responsive nanocellulose-chitosan composite microspheres.

[0013] In a second aspect, the present application provides an application of the method according to the first aspect in process padding paper.

[0014] In summary, this application includes at least one of the following beneficial technical effects: 1. This application achieves efficient deinking at 40℃-50℃ by optimizing the composition of the complex enzyme and establishing an enzyme-ultrasound synergistic system, with a deinking rate of over 90%. At the same time, the fiber integrity is effectively preserved during the directional degradation of lignin and stickies, breaking through the contradiction between deinking efficiency and fiber damage in traditional chemical treatment.

[0015] 2. This application achieves high whiteness (above 85% ISO) through heterojunction photocatalyst optimization, supercritical CO2 mass transfer enhancement and gradient reaction design.

[0016] 3. After the nanocellulose / chitosan composite layer is oriented by the electromagnetic field, the tensile strength and folding resistance of the regenerated fiber are significantly improved, making its performance surpass that of the original fiber and meeting the strict requirements of the process pad paper on mechanical properties. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below with reference to the examples. Unless otherwise specified, the raw materials are all commercially available and the process parameters can be adjusted according to actual production.

[0018] Raw materials: oily waste paper (oil content 12%, joint density 5 / 10,000 meters), cellulase (enzyme activity 10,000 U / g), xylanase (enzyme activity 8,000 U / g), laccase (enzyme activity 5,000 U / g), pullulanase (enzyme activity 10,000 U / g), manganese peroxidase (CAS: 114995-15-2), 30% hydrogen peroxide solution, nanocellulose suspension (particle size 80 nm, solid content 2%), nanocellulose-chitosan composite microspheres (particle size 50 nm, shell containing carboxymethyl groups).

[0019] Example 1 A method for recycling waste paper, comprising the following steps: S1 enzyme pretreatment: In a 50 L reactor, 30 L of deionized water was added, the pH was adjusted to 5.2 (citric acid-sodium citrate buffer), 2.0% complex enzymes (cellulase (55%), xylanase (25%), laccase (10%), pullulanase (10%)) were added, and the temperature was raised to 48°C; 10 kg of waste paper pulp (3% concentration) was added, and 40 kHz ultrasonic waves (200 W power) were simultaneously turned on. After enzymatic hydrolysis for 30 minutes, the fibers were filtered and washed twice with 30°C warm water to obtain pretreated fiber pulp. S2 gradient photocatalysis: The first stage: the pretreated fiber pulp was transferred into a photocatalytic reaction tank containing a TiO2 / MOFs heterojunction photocatalyst (TiO2 to MOFs mass ratio of 1:0.5), 1.5% H2O2 (based on pulp weight) was added, and after uniform dispersion, CO2 supercritical fluid (pressure 9 MPa) was introduced, and the ultraviolet light intensity was 50 mW / cm 2 The reaction was continued for 40 min; Stage 2: Drain the residual liquid, add 2.0% H2O2, and increase the UV intensity to 80mW / cm 2 , the pressure was maintained at 9 MPa and the reaction was continued for 30 min; The third stage: drain the residual liquid, add 1.0% H2O2, and reduce the UV intensity to 30mW / cm 2 , after reacting for 20 min, filter and wash the fiber with 40°C warm water until neutral; S3 fiber function enhancement: The bleached fiber pulp concentration was adjusted to 2%, and the nanocellulose suspension was evenly sprayed through a microfluidic nozzle (spraying amount 50g / m 2 ), adjust the pH of the system to 6.5 (adjusted with acetic acid), form a Zeta potential gradient (+20mV to -10mV), transfer to an electromagnetic field treatment device (magnetic field intensity 0.5T, electric field intensity 10kV / m), align for 15 minutes, dehydrate and then dry into paper.

[0020] Example 2 The complex enzyme in S1 is adjusted to: Cellulase (50%), xylanase (25%), laccase (10%), pullulanase (10%), manganese peroxidase (5%), the total addition amount is 2.0%.

[0021] The rest is consistent with Example 1.

[0022] Example 3 Photocatalyst optimization in S2: TiO2 / ZIF-8 heterojunction (mass ratio 1:4) was used.

[0023] The rest is consistent with Example 1.

[0024] Example 4 The complex enzyme in S1 is adjusted to: Cellulase (50%), xylanase (25%), laccase (10%), pullulanase (10%), manganese peroxidase (5%), the total addition amount is 2.0%.

[0025] Photocatalyst optimization in S2: TiO2 / ZIF-8 heterojunction (mass ratio 1:4) was used.

[0026] The rest is consistent with Example 1.

[0027] Example 5 pH-responsive nanocellulose-chitosan composite microspheres were used to replace the nanocellulose suspension, and the rest were the same as in Example 1.

[0028] Comparative Example 1 The complex enzyme in S1 was adjusted to cellulase (65%), xylanase (25%), and lipase (10%), with a total addition amount of 2.0%. The rest was consistent with Example 1.

[0029] Comparative Example 2 S2 was bleached with hydrogen peroxide alone: ​​60° C. for 40 min; and 3% H 2 O 2 bleached (80° C. for 2 h). Other treatments were the same as in Example 1.

[0030] Comparative Example 3 S3 was not sprayed with the nanocellulose suspension, and the rest was the same as in Example 1.

[0031] Performance testing The same batch of oily waste padding paper (oil content 10%-15%, joint density 3-7 / 10,000 meters) was treated according to the method of the present invention (Examples 1-5) and the control method (Comparative Examples 1-3), and the recovered pulp and papermaking properties were tested.

[0032] The deinking rate is based on the comparison of the ink residue (ERIC value) before and after treatment, and the effective residual ink concentration is determined according to GB / T24320-2021.

[0033] The fiber damage rate was calculated by fiber length distribution and tensile strength loss rate, and the fiber morphology was observed under a microscope and the mechanical properties were tested.

[0034] Stickies removal rate: Measure the average stickies area S1 per unit mass of waste paper before treatment, and then measure the average stickies area S2 per unit mass of waste paper after filtration and drying; Stickies removal rate (%) = S2 / S1*100%.

[0035] Whiteness is measured according to ISO 2470 (D65 light source).

[0036] The tensile strength is measured according to ISO 1924-2 (unit: N·m / g).

[0037] The folding endurance is determined according to ISO 5626 (number of double folds).

[0038] Table 1 Table 2 Test items Example 1 Example 5 Comparative Example 3 Tensile strength (N·m / g) 36.2 43.5 21.5 Folding endurance (times) 125 139 90 The test results are shown in Table 1-Table 2: As shown in Table 1, Examples 1-2 utilize a more diverse array of enzymes compared to Comparative Example 1. Different enzymes are specifically assigned to degrade multiple components in inks and adhesives, enabling precise pollutant degradation and avoiding excessive fiber treatment. Furthermore, the enzymes in Examples 1-2 further synergize with the reaction conditions (pH and ultrasound), improving overall efficiency. Comparative Example 1, however, suffers from a single enzyme type and insufficient targeting, resulting in incomplete deinking and increased fiber damage, further demonstrating the necessity of collaborative enzyme design.

[0039] As shown in Table 1, compared to Comparative Example 2, Examples 1-4 achieve targeted and efficient utilization of active oxygen through heterojunction photocatalyst optimization, enhanced supercritical CO₂ mass transfer, and gradient reaction design, fundamentally resolving the conflict between bleaching depth and fiber protection. Comparative Example 2, on the other hand, relies on traditional high-temperature chemical bleaching, resulting in inefficient active oxygen generation and fiber damage.

[0040] As shown in Table 2, compared to Comparative Example 3, Examples 5 and 1 utilize nanofibers to fill pores, forming a "fiber-nanofiber" composite structure. The nanofibers act as "bridges" connecting adjacent fibers, distributing stress through hydrogen bonding and mechanical interlocking, achieving breakthroughs in both tensile strength and folding resistance. Comparative Example 3, on the other hand, relies solely on hydrogen bonding within native fibers, resulting in significant pores between fibers. Furthermore, stress concentrates at weak points during folding or stretching, leading to rapid fracture.

[0041] Those skilled in the art will further appreciate that the present invention may be implemented in other specific forms without departing from its spirit or central features. Since the foregoing description of the present disclosure discloses only exemplary embodiments thereof, it should be understood that other variations are considered to be within the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments described in detail herein.

Claims

1. A method for recycling waste paper, characterized in that: The following steps are involved: S1: Add complex enzyme into the reactor, raise the temperature to 40-50°C, add waste paper pulp, perform ultrasonication and enzymatic hydrolysis, and then filter to obtain pretreated fiber pulp; S2: transferring the pretreated fiber pulp into a photocatalytic reaction tank for reaction; S3: Spraying nanomaterials to form a zeta potential gradient, transferring to an electromagnetic field treatment device for directional arrangement, dehydration, and drying into paper; Wherein, the complex enzyme comprises cellulase, xylanase, laccase and pullulanase.

2. The method for recycling waste paper according to claim 1, characterized in that: The complex enzyme also includes manganese peroxidase.

3. The method for recycling waste paper according to claim 1, characterized in that: The photocatalyst in the photocatalytic reaction tank is a TiO2 / MOFs heterojunction.

4. The method for recycling waste paper according to claim 1, characterized in that: The photocatalyst in the photocatalytic reaction tank is a TiO2 / ZIF-8 heterojunction.

5. The method for recycling waste paper according to claim 1, characterized in that: The S2 is divided into three stages: Stage 1: Add 1.0-3.0% H2O2, disperse evenly, then introduce CO2 supercritical fluid and react under strong ultraviolet light for 30-60 minutes; The second stage: drain the residual liquid, add 3.0-5.0% H2O2, increase the UV intensity and react for 20-40 minutes; The third stage: drain the residual liquid, add 0.5-1.5% H2O2, reduce the UV intensity and react for 10-30 minutes, filter, and wash the fiber with warm water until neutral.

6. The method for recycling waste paper according to claim 1, characterized in that: The nano material is a nano cellulose suspension.

7. The method for recycling waste paper according to claim 1, characterized in that: The nano material is pH-responsive nano cellulose-chitosan composite microspheres.

8. Use of the method according to any one of claims 1 to 7 in craft padding.

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