A method for bleaching pulp based on coupling of oxygen nuclei with electric field gradients

Abstract

The application discloses a pulp bleaching method based on electric field gradient coupling oxygen nucleus. The method comprises the following steps: adding pulp into a reaction kettle, adding alkali and a protective agent, stirring and mixing, and heating; when the temperature is heated to 90-100 DEG C, the temperature is kept, a direct current electric field is applied to the reaction kettle and oxygen is introduced under high-speed stirring, and reaction is carried out for 3-5 min; reaction is carried out for 30-120 min under low-speed stirring. The method solves the problems of low reaction efficiency and low oxygen utilization rate in the existing oxygen delignification process. By applying a direct current electric field to the outer wall of the reaction kettle, the oxygen molecules are separated by the electric field force, and the combination ability with the surface of the pulp fiber is improved. The method significantly improves the removal efficiency of lignin, and significantly improves the pulp brightness and Kappa number. The application is suitable for the field of pulping and papermaking, and has important significance for the bleaching process with high environmental protection requirements.

Description

Technical Field

[0001] This invention relates to the field of pulp and paper making technology, and in particular to a pulp bleaching method based on electric field gradient coupling of oxygen nuclei. Background Technology

[0002] In the pulp and paper industry, oxygen delignification is a key process that aims to remove lignin from pulp using oxygen, thereby improving pulp quality. However, this process faces many challenges in practical applications. Pulp fibers typically carry a negative charge on their surface, a characteristic that significantly hinders oxygen from combining with them. At a microscopic level, the repulsive force between the charges weakens effective contact, making it difficult for oxygen to fully penetrate the fiber interior and drastically reducing mass transfer efficiency. Taking traditional processes as an example, under specific reaction conditions, due to poor mass transfer, only partial lignin removal can be achieved, leaving a large amount of lignin residue that severely impacts the subsequent properties of the pulp. In existing oxygen delignification processes, oxygen utilization is generally low. On the one hand, uneven oxygen distribution within the reaction system leads to waste in areas where oxygen concentration is too high to fully participate in the reaction, while in other areas, insufficient oxygen hinders complete reaction. On the other hand, unreasonable equipment structure and process parameters further exacerbate this problem. For example, the design of the reaction vessel fails to adequately consider the mixing effect between the gas and pulp, limiting their contact time and area, resulting in resource waste and increased production costs. Current oxygen delignification processes have limited bleaching effectiveness. Insufficient lignin removal prevents the effective removal of residual chromophores in the pulp, hindering efforts to improve pulp brightness. Even increasing oxygen dosage or extending reaction time cannot overcome this bottleneck and may even lead to excessive fiber degradation, impairing pulp strength and other physical properties. Furthermore, existing processes have stringent reaction conditions, resulting in poor production stability and hindering efficient and stable industrial-scale production.

[0003] Therefore, there is an urgent need to obtain a pulp bleaching method that can enhance the efficiency of oxygen delignification. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a pulp bleaching method based on electric field gradient coupling of oxygen nuclei. The objective of this invention is achieved through the following technical solution: A pulp bleaching method based on electric field gradient coupled oxygen nuclei includes the following steps: (1) Add pulp, alkali and protective agent to the reaction vessel, stir and mix well, and heat; (2) When heated to 90-100℃, maintain the temperature, apply a DC electric field to the reactor and introduce oxygen while stirring at high speed, and react for 3-5 minutes; (3) React at low speed for 30-120 min.

[0005] Further, the pulp mentioned in step (1) is obtained by cooking the pulping raw materials using the sulfate process; further still, the pulping raw materials include at least one of hardwood pulp, softwood pulp and bamboo pulp; and even further, the pulping raw materials include bamboo pulp.

[0006] Furthermore, the alkali mentioned in step (1) includes NaOH.

[0007] Further, the mass of the alkali mentioned in step (1) is 1.8 to 4% of the oven-dry pulp mass; even further, the mass of the alkali mentioned in step (1) is 2% of the oven-dry pulp mass.

[0008] Furthermore, the protective agent described in step (1) includes magnesium salts, and even more specifically MgSO4.

[0009] Further, the mass of the protective agent mentioned in step (1) is 0.4% to 0.7% of the oven-dry pulp mass; even further, the mass of the protective agent mentioned in step (1) is 0.5% of the oven-dry pulp mass.

[0010] Furthermore, the alkali and protective agent described in step (1) are added in the form of a solution.

[0011] Further, the heating rate in step (1) is 4 to 6 °C / min; even further, the heating rate in step (1) is 5 °C / min.

[0012] Furthermore, the heating described in step (2) is heating to 90°C.

[0013] Furthermore, the high-speed stirring mentioned in step (2) is stirring at a speed of 200 to 400 r / min; even further, it is stirring at a speed of 300 r / min.

[0014] Further, the electric field strength of the DC electric field applied in step (2) is 200 to 1800 V / m; even further, the voltage between the electrodes in step (2) is 1000 to 1800 V / m; and even further, the voltage between the electrodes in step (2) is 1000 V / m.

[0015] Furthermore, the electric field device used to apply the DC electric field in step (2) includes a power supply and electrodes; Furthermore, the power supply has an adjustable output voltage of 0-600V, providing a voltage of 40-360V to the electrodes, which are graphite electrodes. Furthermore, the length of the graphite electrode is 50% to 90% of the axial length of the reactor, and the width is 20% to 50% of the circumference of the bottom surface; even further, the length of the graphite electrode is 70% of the axial length of the reactor, and the width is 25% of the circumference of the bottom surface.

[0016] Furthermore, in step (2), when oxygen is introduced, the oxygen pressure is controlled to be 0.4 to 0.8 MPa; even further, the oxygen pressure is controlled to be 0.5 MPa.

[0017] Furthermore, the reaction described in step (2) is carried out for 3 minutes.

[0018] Further, the low-speed stirring mentioned in step (3) is: stirring at a speed of 100 to 180 r / min; even further, stirring at a speed of 180 r / min.

[0019] Furthermore, the reaction described in step (3) is carried out for 60 min.

[0020] The present invention has the following advantages and effects compared with the prior art: This invention solves the problems of low reaction efficiency and low oxygen utilization in existing oxygen delignification processes, and provides an improved process based on electric field-enhanced oxygen delignification. By applying a DC electric field to the outer wall of the reactor, the electric field force causes the oxygen molecules to separate by charge, enhancing their binding ability with the pulp fiber surface. Under the action of the electric field force, the oxygen molecules react with the pulp fibers, thereby removing lignin and improving the pulp's brightness and kappa value. This process not only significantly improves the lignin removal efficiency but also has a significant effect on improving pulp brightness and kappa value. This invention is applicable to the pulp and paper industry, and is particularly significant for bleaching processes with high environmental protection requirements. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the electric field device used in the method of the present invention; the numbers in the diagram are as follows: 1. Reactor; 2. Insulating heating jacket; 3. Electrode; 4. Power supply; 5. Discharge pipe; 6. Stirrer; 7. Pulping raw material feed pipe; 8. Reagent feed pipe; 9. Gas outlet pipe; 10. Oxygen inlet pipe. Detailed Implementation

[0022] 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.

[0023] The pulp used in the following examples was obtained by cooking bamboo pulp using the sulfate process. The pulp had a brightness of 27.0% ISO, a viscosity of 1140 mL / g, and a kappa value of 25.7. The bamboo pulp was sourced from Sichuan Yongfeng Paper Mill.

[0024] The following is a schematic diagram of the electric field device used to apply the electric field in the embodiments. Figure 1 As shown, electric field devices are installed on both sides of the reactor. The power supply for the electric field devices is a Siemens 6EP1336-3BA10 DC power supply with an adjustable output voltage of 0-600V and an accuracy of ±1%. The electrodes of the electric field devices are graphite electrodes. In the following embodiment, the length of the graphite electrode is 70% of the axial length of the reactor, and the width is 25% of the circumference of the bottom surface. The electrodes are isolated from the reactor wall by insulating material to ensure that the electric field can be formed normally and act on the reaction area.

[0025] Example 1 A pulp bleaching method based on electric field gradient coupled oxygen nuclei includes the following steps: (1) Add pulp, NaOH solution and MgSO4 solution to the reactor, so that the mass of NaOH is 2% of the dry pulp mass and the mass of MgSO4 is 0.5% of the dry pulp mass. Stir and mix well, and heat at a heating rate of 5℃ / min. (2) When the temperature rises to 90℃, maintain the temperature, increase the stirring speed to 300 r / min, apply a DC electric field to the reactor (the voltage between the electrodes of the electric field is 40V, the distance between the electrodes is 20cm, and the electric field strength is 200V / m) and introduce oxygen (control the oxygen pressure to 0.5MPa), and react for 3 minutes; (3) Reduce the stirring speed to 180 r / min and react for 60 minutes.

[0026] After the reaction was completed, the pulp was washed with a fixed amount of water. After washing, the pulp whiteness was tested according to ISO 2470-1:2016 "Paper, paperboard and pulp - Measurement of blue diffuse reflectance - Part 1: Indoor daylight conditions (ISO whiteness)" and the kappa value of the pulp was tested according to GB / T 1546-2018 "Determination of kappa value of pulp".

[0027] Test results show that the pulp brightness is 42.6% ISO and the kappa value is 14.12.

[0028] Example 2 The only difference between this embodiment and embodiment 1 is that the voltage between the electrodes of the electric field in step (2) is 120V, and the electric field strength applied to the reactor is 600V / m.

[0029] Tested results show that the pulp brightness is 43.6% ISO and the kappa number is 13.76.

[0030] Example 3 The only difference between this embodiment and embodiment 1 is that the voltage between the electrodes of the electric field in step (2) is 200V, and the electric field strength of the electric field applied to the reactor is 1000V / m.

[0031] Tested results: pulp brightness 45.9% ISO, kappa number 13.22.

[0032] Example 4 The only difference between this embodiment and embodiment 1 is that the voltage between the electrodes of the electric field in step (2) is 280V, and the electric field strength of the electric field applied to the reactor is 1400V / m.

[0033] Tested results show that the pulp brightness is 44.7% ISO and the kappa number is 13.57.

[0034] Example 5 The only difference between this embodiment and embodiment 1 is that the voltage between the electrodes of the electric field in step (2) is 360V, and the electric field strength of the electric field applied to the reactor is 1800V / m.

[0035] Tested results: pulp brightness 45.1% ISO, kappa number 13.34.

[0036] Comparative Example The only difference between this comparative example and Example 1 is that no DC electric field is applied.

[0037] Tested results: pulp brightness 38.9% ISO, kappa number 14.81.

[0038] The results of the above tests on pulp brightness and kappa number are shown in Table 1. The experiment shows that under a 200V electric field, the pulp brightness increased to 45.9% ISO (compared to 38.9% ISO without an electric field), and the kappa number decreased to 13.22 (compared to 14.81 without an electric field), effectively improving the efficiency of oxygen delignification. This method breaks through the bottleneck of traditional processes, significantly improving bleaching efficiency with the same chemical consumption, and is widely applicable to hardwood pulp, bamboo pulp, and other pulps.

[0039] Table 1

[0040] 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 pulp bleaching method based on electric field gradient coupled oxygen nuclei, characterized in that, It includes the following steps: (1) Add pulp, alkali and protective agent to the reaction vessel, stir and mix well, and heat; (2) When heated to 90-100℃, maintain the temperature, apply a DC electric field to the reactor and introduce oxygen while stirring at high speed, and react for 3-5 minutes; (3) React at low speed for 30–120 min; The electric field strength of the DC electric field applied in step (2) is 200–1800 V / m; The high-speed stirring mentioned in step (2) refers to stirring at a speed of 200-400 r / min; The low-speed stirring mentioned in step (3) is: stirring at a speed of 100 to 180 r / min.

2. The method according to claim 1, characterized in that, The pulp mentioned in step (1) is obtained by cooking pulping raw materials using the sulfate process.

3. The method according to claim 1, characterized in that, The alkali mentioned in step (1) includes NaOH; The protective agent mentioned in step (1) includes magnesium salts.

4. The method according to claim 1, characterized in that, The mass of the alkali mentioned in step (1) is 1.8 to 4% of the oven-dry pulp mass; The mass of the protective agent mentioned in step (1) is 0.4% to 0.7% of the oven-dry pulp mass.

5. The method according to claim 1, characterized in that, The heating mentioned in step (2) is heating to 90°C.

6. The method according to claim 1, characterized in that, The electric field strength of the DC electric field applied in step (2) is 1000 to 1800 V / m.

7. The method according to claim 1, characterized in that, In step (2), when oxygen is introduced, the oxygen pressure is controlled to be 0.4 to 0.8 MPa.

8. The method according to claim 1, characterized in that, The reaction described in step (2) is carried out for 3 minutes.

9. The method according to claim 1, characterized in that, The reaction described in step (3) is carried out for 60 min.

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