Composite metal catalyst and application thereof in biological combined light treatment paper pulp bleaching

Abstract

The invention provides a composite metal catalyst and application thereof in biological combined light treatment paper pulp bleaching. The method comprises the following steps: dividing and brooming cooked paper pulp fibers by adopting biological pretreatment, and then carrying out illumination bleaching under simulated sunlight irradiation by adopting a metal photocatalyst (ZnO, ZFO, ZAO, ZMO and the like). According to the mild treatment method, the whiteness of the paper pulp is improved, and meanwhile it is guaranteed that fibers are not damaged. Compared with traditional chemical bleaching, biological combined light treatment bleaching has the advantages that the content of pollutants in wastewater is greatly reduced, meanwhile, reacted metal oxides can be recycled, and the combined treatment method can be used as a novel paper pulp fiber bleaching mode.

Description

Technical Field

[0001] This invention relates to the field of papermaking, and in particular to a composite metal catalyst and its application in bio- and photo-treated pulp bleaching. Background Technology

[0002] Pulp bleaching is a crucial step in obtaining high-brightness pulp in the pulp and paper industry. Existing industrial processes mostly employ elemental chlorine-free (ECF) sequences centered on chlorine dioxide, or completely chlorine-free (TCF) sequences primarily using hydrogen peroxide, ozone, and peracetic acid, often combined with steps such as oxygen delignification, chelation (Q), and alkali extraction (E). Although these chemical bleaching technologies are widely used, problems remain, including high chemical dependence, significant energy and water consumption, pressure to control effluent color and organic halogen (AOX) emissions, and a decrease in fiber viscosity and strength when achieving high brightness. For chemical pulps (such as sulfate and sulfite processes) requiring high brightness, how to reduce chemical usage while maintaining strength remains a key industry focus. For chemimechanical pulps (such as CMP and CTMP) with high lignin content, abundant residual chromophores and a pronounced tendency to yellow, the potential for reducing chemical consumption in traditional chemical sequences is limited. To reduce chemical consumption and improve selectivity, bio-enzyme pretreatment technology is gaining attention. Xylanase can selectively degrade hemicellulose and reduce hexaenoic acid (HexA)-related precursors, improving bleaching properties; laccase (with a mediator if necessary) can mildly modify the aromatic structure of lignin, reducing the subsequent chemical oxidation load. Existing research shows that enzymatic methods have the potential to reduce chemical consumption and improve strength retention under mild conditions, but their effectiveness is greatly affected by pulp type, metal ions, surfactant compatibility, and process window, and efficient adaptation to highly ligninized mechanical pulps remains a challenge.

[0003] On the other hand, photochemical / photocatalytic bleaching utilizes light to excite catalysts (such as TiO2, ZnO, g-C3N4, and their doped or composite systems) to generate reactive oxygen species in the aqueous phase for selective degradation of chromophores. It offers advantages such as mild conditions and the ability to be coupled with high-efficiency light sources like LEDs, and has been extensively reported in water treatment and organic pollutant degradation. However, when the photocatalytic process is directly applied to pulp systems, several challenges arise: insufficient effective photon flux due to light scattering / absorption by the pulp; low catalyst-fiber contact and retention efficiency; difficulty in catalyst dispersion and recovery; and process stability issues arising from differences in surface chemistry among different pulp types. Particularly for chemimechanical pulps with high lignin content, the absorption of light by chromophores and the free radical quenching effect are more pronounced, making it difficult to achieve industrially acceptable whiteness under mild conditions. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a composite metal catalyst.

[0005] Application of the above-mentioned composite metal catalyst in bio-photochemical combined treatment of pulp bleaching.

[0006] The objective of this invention is achieved through the following technical solution: A method for preparing a composite metal catalyst includes the following steps: Metal salt A and metal salt B were mixed and dissolved in water, NaOH was added, the mixture was heated and stirred to react, filtered, washed, dried, calcined, and cooled to obtain the composite metal catalyst.

[0007] The metal salt A is zinc chloride.

[0008] The metal salt B includes at least one of ferric chloride, aluminum chloride, and magnesium chloride.

[0009] The molar ratio of the metal elements in metal salt A and metal salt B is 1:2.

[0010] Both metal salt A and metal salt B are hydrates.

[0011] The amount of NaOH added is such that the pH is increased to 10.

[0012] The heating and stirring reaction conditions are as follows: reaction at 80°C for 1 to 2 hours.

[0013] The calcination conditions are calcination at 450℃ for 2 hours.

[0014] A composite metal catalyst was prepared by the above-described preparation method.

[0015] The application of the composite metal catalyst in photocatalytic bleaching of pulp.

[0016] A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: (1) Add enzymes and penetrants to the pulp, mix well, react, and filter; (2) Add catalyst to the pulp after treatment in step (1), mix well, bleach under light conditions, and filter after treatment; (3) The pulp obtained in step (2) is washed, the filtrate after washing is dried and the catalyst is recovered. The pulp is then processed into paper using a papermaking machine.

[0017] The pulp mentioned in step (1) includes at least one of the following: biological bast pulp, poplar chemical pulp, eucalyptus chemical pulp, paulownia chemical pulp, acacia chemical pulp, sulfate softwood pulp, sulfate hardwood pulp, sulfate bamboo pulp, sulfate wheat straw pulp, sulfate reed pulp, sulfite reed pulp, sulfate bagasse pulp, chemothermal refined softwood pulp, chemothermal refined hardwood pulp, and chemothermal refined bamboo pulp.

[0018] The pulp concentration in step (1) is 5-15 wt%; preferably 10 wt%.

[0019] The enzymes described in step (1) include xylanase and laccase; preferably, they include xylanase at a final concentration of 100 U / mL and laccase at a final concentration of 50 U / mL.

[0020] The penetrant mentioned in step (1) is PEG-400; preferably, it is PEG-400 with a final concentration of 0.05wt%.

[0021] The reaction conditions described in step (1) are 50-70°C and pH=6.5-7.5; preferably 60°C and pH=7.

[0022] The reaction time described in step (1) is 7 to 9 hours.

[0023] The catalyst mentioned in step (2) is a composite metal catalyst.

[0024] The amount of catalyst added in step (2) is 0.1 to 1% of the weight of the oven-dry pulp; preferably 0.2%.

[0025] The illumination in step (2) is simulated fluorescent lamp illumination; preferably, it is simulated fluorescent lamp illumination with a wavelength of 0-1000nm.

[0026] The illumination time mentioned in step (2) is 10 to 14 hours.

[0027] The light intensity mentioned in step (2) is 1–1000 mW / cm². 2 .

[0028] The present invention has the following advantages over the prior art: The bleaching method for low-concentration pulp of the present invention has the advantages of simple operation, simple equipment, low wastewater pollution, and little impact on pulp viscosity. It is suitable for bleaching pulp formed from wood and grass raw materials, as well as chemithermomechanical pulp or bio-pulp, and is suitable for large-scale industrial application.

[0029] The present invention has the following advantages over the prior art: (1) This invention develops a novel pulp bleaching technology that uses sunlight as the driving force for pulp bleaching, thereby reducing energy consumption during the bleaching process.

[0030] (2) The present invention uses a metal catalyst to replace the chemical consumption in traditional bleaching, completely eliminating the generation and emission of AOX from the source, and realizing green bleaching technology for pulp.

[0031] (3) The bio-photonic combined treatment used in this invention has a bleaching effect on pulp of different types and sources, which highlights the universality of the technology.

[0032] (4) The metal catalyst used in this invention can be recycled and reused after the reaction is completed, highlighting the sustainability of this bleaching technology. Attached Figure Description

[0033] Figure 1 This is a comparison of pulp before and after bleaching in Example 1; the left image shows the pulp before bleaching, and the right image shows the pulp after bleaching.

[0034] Figure 2 The images show a comparison of different types of pulp after bleaching in Example 9; the upper image shows the pulp before bleaching, and the lower image shows the pulp after bleaching.

[0035] Figure 3 The results are from the catalyst reuse performance verification experiment in Example 9. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0037] Unless otherwise specified in the following implementation plan, the test conditions are generally as per standard test conditions or the test conditions recommended by the reagent company. Unless otherwise specified, all materials and reagents used are commercially available.

[0038] The chemical and chemimechanical pulp used in this invention comes from Shandong Sun Paper Co., Ltd., and the bio-bast pulp used comes from South China University of Technology and is prepared according to the method described in the paper "One-step customized enzyme treatment catalyzes fiber dissociation and application based on structure of Wikstroemia bark".

[0039] The laccase and peroxidase were purchased from Zhejiang Tianhe Food Co., Ltd., and the xylanase was purchased from Guangdong Yiduoli Biotechnology Co., Ltd., with a xylanase activity of 30,000 U / mL. Titanium dioxide and zinc oxide were purchased from Maclean's Reagent Co., Ltd., and zinc chloride, ferric chloride, and polyethylene glycol were also purchased from Maclean's Reagent Co., Ltd. The neutral deionized water mentioned was prepared in-house by the laboratory of South China University of Technology.

[0040] Example 1 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: (1) Mix ZnCl2·nH2O and FeCl3·nH2O in a molar ratio of 1:2 and add them to water to prepare a mixed metal salt solution (room temperature, 600-800 rpm). Then add NaOH solution dropwise until pH=10, and stir for 1-2 h at 80 ℃. After the reaction is complete, the solid powder formed in the solution is separated by filtration using a G2 sintered glass funnel and washed repeatedly with hot water (at least 5 times). Finally, the water is replaced once with ethanol. The obtained powder is dried at 105 ℃, and the dried particles are ground and calcined in a muffle furnace. The temperature is increased to 450 ℃ at a rate of 2 ℃ / min and held for 2 h. After cooling, the metal catalysts ZnCl2-FeCl3 (ZFO-1) are obtained.

[0041] (2) Add a compound enzyme and a penetrant to 10 wt% pulp (biological bast pulp). The compound enzyme includes xylanase with a final concentration of 100 U / mL and laccase with a final concentration of 50 U / mL. The penetrant is PEG-400, and the addition amount is 0.05 wt% (based on oven-dry pulp). After mixing, react at 60℃ and pH=7 for 8 h. During the reaction, aeration is carried out every 30 min for 5 min using an aeration device. After the reaction is completed, the pulp is filtered and washed using a pulp bag.

[0042] (3) The washed pulp was mixed with catalyst ZFO-1, wherein the amount of ZFO-1 added was 0.2 wt% of the oven-dry pulp weight, and the moisture content of the pulp in the system was then controlled to be 80 wt%. (4) The pulp prepared above was irradiated with simulated fluorescent lamps (0-1000 nm) for 12 hours. During the irradiation process, water was continuously added to ensure that the moisture content was maintained at 80 wt%. The pulp was turned over every 4 hours to ensure that both sides were irradiated.

[0043] (5) After the reaction is complete, the pulp is filtered using a pulp bag and washed several times with a small amount of clean water until the filtrate is clear. The filtrate is collected and heated to dry in order to recover the ZFO-1 catalyst. The pulp is then used to make paper using a Kaiser process paper machine and the whiteness is measured.

[0044] Example 2 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method in Example 1, except that FeCl3 in step (1) was replaced with AlCl3·6H2O to prepare catalyst ZAO, and the subsequent treatment steps were the same.

[0045] Example 3 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method in Example 1, except that FeCl3 in step (1) was replaced with MgCl3·6H2O to prepare catalyst ZMO, and the subsequent treatment steps were the same.

[0046] Example 4 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method of Example 1, except that the catalyst added in step (3) was replaced with commercial photocatalyst ZnO.

[0047] Example 5 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method of Example 1, except that in step (4), the light source was a simulated fluorescent lamp and an ultraviolet filter (400-1000 nm).

[0048] Example 6 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method of Example 1, except that the light source in step (4) was replaced with a 0-400nm ultraviolet light source.

[0049] Example 7 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method of Example 1, except that the laccase in step (2) was replaced with peroxidase, and the final concentration was 50 U / mL.

[0050] Example 8 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method of Example 1, except that the molar ratio of ZnCl2 to FeCl3 in step (1) was adjusted to 1:4 to prepare catalyst ZFO-2, and the subsequent treatment steps were the same.

[0051] Comparative Example 1 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method in Example 1, except that no compound enzyme was added in step (2), while the other steps were the same.

[0052] Comparative Example 2 A method for bleaching pulp using a combination of biological and photochemical treatments includes the following steps: The pulp was bleached according to the method in Example 1, except that the fluorescent lamp irradiation treatment in step (4) was omitted, while the other steps were the same.

[0053] Example 9 9.1 Test of pulp whiteness after papermaking Take 1 g of pulp (octane-dry) and form it into sheets using the rapid Kayser papermaking method and determine its whiteness. For specific methods, please refer to GB / T7974-2013 "Determination of brightness (whiteness) of paper, paperboard and pulp - Diffuse / Vertical method".

[0054] Table 1. Changes in the whiteness of bio-plasma Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 Initial whiteness 40.42 40.42 40.42 40.42 40.42 40.42 40.42 40.42 40.42 40.42 Whiteness after bleaching 63.13 61.32 60.78 58.24 55.34 51.28 59.46 59.42 53.89 50.37 Experimental results are as follows Figures 1-2 As shown in Table 1, the results indicate that after pretreatment with laccase and xylanase, the whiteness of the pulp using ZFO as a photocatalyst was significantly improved to 63.13 at wavelengths of 0-1000 nm. Furthermore, the bleaching ability was best when the molar ratio of Zn to Fe was 1:2. In contrast, the effect of using different ratios of Zn with other elements was reduced. While the pulp obtained using commercial catalysts showed improved whiteness, the efficiency remained low. In addition, enzyme pretreatment plays an important role in the bleaching process. Compared with Comparative Example 1, enzyme pretreatment increased the degree of fiber fibrillation, thereby exposing more photocatalytic sites and improving the degradation of lignin, indirectly increasing the whiteness of the paper.

[0055] 9.2 Verification of Bleaching Effects of Different Pulps To verify the versatility of Example 1, different types of pulp were bleached using the method of Example 1 to verify its bleaching effect.

[0056] Experimental results are as follows Figure 2 As shown, it can be seen that even after replacing the pulp with poplar chemical pulp, eucalyptus chemical pulp, paulownia chemical pulp, and acacia chemical pulp, a good bleaching effect can still be achieved, proving that this method can handle different raw materials and achieve the same bleaching effect.

[0057] 9.3 Performance Verification of Catalyst Reuse To verify the performance changes of the catalyst after repeated use, the recovered ZFO-1 catalyst was bleached using the same method as in Example 1 to verify its effect, and the process was repeated 5 times.

[0058] Experimental results are as follows Figure 3 As shown, the catalyst still exhibits excellent bleaching ability after five cycles, demonstrating the significant advantages of ZFO-1 in terms of sustainability.

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite metal catalyst, characterized by The method comprises the following steps: The metal salt A and the metal salt B are mixed and dissolved in water, NaOH is added, and the reaction is stirred and heated, filtered, washed, dried, calcined, and cooled to obtain the composite metal catalyst.

2. The method for preparing the composite metal catalyst according to claim 1, wherein: The metal salt A is zinc chloride; The metal salt B comprises at least one of iron chloride, aluminum chloride, and magnesium chloride; The molar ratio of the metal elements in the metal salt A and the metal salt B is 1:

2.

3. The method for preparing the composite metal catalyst according to claim 1, wherein: The amount of NaOH added is added to pH = 10; The heating and stirring reaction is carried out at 80°C for 1-2h; The calcination is carried out at 450°C for 2h.

4. A composite metal catalyst prepared by any one of the methods for preparing the composite metal catalyst according to claims 1-3.

5. The composite metal catalyst according to claim 4 is used for photocatalytic bleaching of paper pulp.

6. A method for the biological combined photo-treatment of pulp bleaching, characterized in that The method comprises the following steps: (1) adding enzymes and penetrants to the paper pulp, mixing and reacting, and filtering; (2) adding the catalyst to the paper pulp treated in step (1), mixing, and bleaching under light conditions, filtering after the treatment is completed; (3) washing the paper pulp treated in step (2), drying the filtrate after washing to recover the catalyst, and processing the obtained paper pulp into paper by a sheet former.

7. The method for biologically combined photo-treatment of paper pulp bleaching according to claim 6, wherein: The paper pulp in step (1) comprises at least one of biological bast pulp, poplar chemical pulp, eucalyptus chemical pulp, camphor wood chemical pulp, acacia chemical pulp, kraft softwood pulp, kraft hardwood pulp, kraft bamboo pulp, kraft straw pulp, kraft reed pulp, sulfite reed pulp, kraft cane pulp, chemical hot-mechanical softwood pulp, chemical hot-mechanical hardwood pulp, and chemical hot-mechanical bamboo pulp; The concentration of the paper pulp in step (1) is 5-15wt%.

8. The method for biologically combined photo-treatment of paper pulp bleaching according to claim 6, wherein: The enzymes in step (1) comprise xylanase and laccase; The penetrant in step (1) is PEG-400; The reaction conditions in step (1) are 50-70°C and pH = 6.5-7.5; The reaction time in step (1) is 7-9h.

9. The method for biologically combined photo-treatment of paper pulp bleaching according to claim 6, wherein: The catalyst in step (2) is the composite metal catalyst according to claim 4; The amount of the catalyst added in step (2) is 0.1-1% of the weight of the absolutely dry paper pulp.

10. The method for biologically combined photo-treatment of paper pulp bleaching according to claim 6, wherein: The light in step (2) is simulated daylight lamp irradiation; The light time in step (2) is 10-14h. The light irradiation in step (2) has an intensity of 1 to 1000 mW / cm 2 .

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