Paper pulp bleaching method based on electric field gradient coupling oxygen nucleus

Abstract

The invention discloses a paper pulp bleaching method based on electric field gradient coupling oxygen nucleus. The method comprises the following steps: adding paper pulp into a reaction kettle, adding alkali and a protective agent, uniformly stirring and mixing, and heating; when heating to 90-100 DEG C, keeping the temperature, stirring at a high speed, applying a direct-current electric field into the reaction kettle, introducing oxygen, and reacting for 3-5 minutes; and reacting for 30-120 minutes under low-speed stirring. The method solves the problems of low reaction efficiency and low oxygen utilization rate in the existing oxygen delignification process. A direct-current electric field is applied to the outer wall of the reaction kettle, oxygen molecule charges are separated by means of electric field force, and the combining capacity with the paper pulp fiber surface is improved. According to the method, the removal efficiency of lignin is remarkably improved, and the whiteness and kappa number of the paper pulp are remarkably improved. The method is suitable for the field of pulping and papermaking, and particularly has important significance on a bleaching process with relatively high environmental protection requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of pulp and paper making processes, and particularly to a pulp bleaching method based on the coupling of an electric field gradient and oxygen nuclei. Background Art

[0002] In the field of pulp and paper making, oxygen delignification is a key process aimed at removing lignin from pulp using oxygen to improve pulp quality. However, this process faces many challenges in practical applications. The surface of pulp fibers usually carries negative charges, which significantly hinders the combination of oxygen with them. At the microscopic level, the repulsive force between charges weakens their effective contact, making it difficult for oxygen to fully penetrate into the fiber interior, greatly reducing the mass transfer efficiency. Taking traditional processes as an example, under specific reaction conditions, due to poor mass transfer effects, only partial lignin can be removed, and a large amount of lignin remains, seriously affecting the subsequent properties of the pulp. In existing oxygen delignification processes, the oxygen utilization rate is generally low. On the one hand, due to the uneven distribution of oxygen in the reaction system, the oxygen concentration is too high in some areas but cannot fully participate in the reaction, resulting in waste; while in some areas, the reaction cannot proceed thoroughly due to insufficient oxygen. On the other hand, the unreasonable setting of equipment structure and process parameters further exacerbates this problem. For example, the design of the reaction vessel fails to fully consider the mixing effect of gas and pulp, limiting the contact time and contact area between the two, causing resource waste and increasing production costs at the same time. The bleaching effect of the current oxygen delignification process is limited. Due to the insufficient removal of lignin, the chromophores remaining in the pulp cannot be effectively removed, making it difficult to improve the whiteness of the pulp. Even if the oxygen dosage is increased or the reaction time is extended, it is difficult to break through the bottleneck of the bleaching effect, and it may also cause negative problems such as excessive fiber degradation, damaging the physical properties such as the strength of the pulp. In addition, the existing process has relatively strict requirements for reaction conditions, resulting in poor stability of the production process and making it difficult to achieve efficient and stable industrial 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 the present invention is to overcome the shortcomings and deficiencies of the prior art and provide a pulp bleaching method based on the coupling of an electric field gradient and oxygen nuclei. The purpose of the present invention is achieved by the following technical solutions: A pulp bleaching method based on the coupling of an electric field gradient and oxygen nuclei, which includes the following steps: (1) Add pulp, alkali, and a protective agent to a reaction kettle, stir and mix evenly, and heat. (2) When heated to 90 - 100 °C, maintain the temperature, and while stirring at high speed, apply a DC electric field into the reaction kettle and introduce oxygen, and react for 3 - 5 min; (3) React for 30 - 120 min while stirring at low speed.

[0005] Further, the pulp described in step (1) is obtained by kraft pulping of pulping raw materials; furthermore, the pulping raw materials include at least one of hardwood pulp, softwood pulp, and bamboo pulp; still further, the pulping raw materials include bamboo pulp.

[0006] Further, the alkali described in step (1) includes NaOH.

[0007] Further, the mass of the alkali described in step (1) is 1.8 - 4% of the dry pulp mass of the pulp; furthermore, the mass of the alkali described in step (1) is 2% of the dry pulp mass of the pulp.

[0008] Further, the protective agent described in step (1) includes magnesium salt, and further includes MgSO 4 .

[0009] Further, the mass of the protective agent described in step (1) is 0.4% - 0.7% of the dry pulp mass of the pulp; furthermore, the mass of the protective agent described in step (1) is 0.5% of the dry pulp mass of the pulp.

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

[0011] Further, the heating rate of the heating described in step (1) is 4 - 6 °C / min; furthermore, the heating rate of the heating described in step (1) is 5 °C / min.

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

[0013] Further, the high-speed stirring described in step (2) is stirring at a rotation speed of 200 - 400 r / min; more specifically, it is stirring at a rotation speed of 300 r / min.

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

[0015] Further, the electric field device for applying the DC electric field described in step (2) includes a power supply and electrodes; Further, the output voltage of the power supply is adjustable from 0 to 600 V, providing a voltage of 40 to 360 V to the electrode, and the electrode is a graphite electrode; Further, 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 circle; 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 circle.

[0016] Further, when introducing oxygen in step (2), 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] Further, the reaction in step (2) is a reaction for 3 minutes.

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

[0019] Further, the reaction in step (3) is a reaction for 60 minutes.

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

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

[0022] The following further describes the present invention in detail in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0023] The pulp used in the following examples was obtained by kraft cooking of bamboo pulp. The whiteness of the pulp was 27.0% ISO, the viscosity was 1140 mL / g, and the kappa number was 25.7. The bamboo pulp was sourced from Sichuan Yongfeng Paper Mill.

[0024] The schematic diagram of the electric field device used to apply the electric field in the following examples is as Figure 1 shown. The electric field device was placed on both sides of the reaction kettle. The power supply of the electric field device was a Siemens 6EP1336-3BA10 DC power supply. The output voltage of the power supply was adjustable from 0 to 600 V with an accuracy of ±1%. The electrodes of the electric field device were graphite electrodes. In the following examples, the length of the graphite electrode was 70% of the axial length of the reaction kettle, and the width was 25% of the circumference of the bottom circle. The electrodes were isolated from the reaction kettle wall by insulating materials to ensure that the electric field could be formed normally and act on the reaction area.

[0025] Example 1 A pulp bleaching method based on the coupling of oxygen nuclei by electric field gradient, which comprises the following steps: (1) Add pulp into the reaction kettle, add NaOH solution and MgSO 4 solution, such that the mass of NaOH is 2% of the dry pulp mass of the pulp, and the mass of MgSO 4 is 0.5% of the dry pulp mass of the pulp. Stir and mix evenly, and heat at a heating rate of 5 °C / min. (2) When the temperature rises to 90 °C, keep the temperature, increase the stirring speed to 300 r / min, apply a DC electric field to the reaction kettle (the voltage between the electrodes of the electric field is 40 V, the distance between the electrodes is 20 cm, and the electric field strength is 200 V / m), and introduce oxygen (control the oxygen pressure to be 0.5 MPa), and react for 3 minutes. (3) Reduce the stirring rate to 180 r / min and react for 60 minutes.

[0026] After the reaction is completed, wash the pulp with a quantitative amount of water. After washing, detect the whiteness of the pulp according to the standard of ISO 2470 - 1:2016 "Paper, board and pulp - Measurement of diffuse blue reflectance factor - Part 1: Indoor daylight conditions (ISO whiteness)", and detect the kappa number of the pulp according to GB / T 1546-2018 "Determination of kappa number of pulp".

[0027] After testing: the whiteness of the pulp was 42.6% ISO, and the kappa number was 14.12.

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

[0029] Test results: pulp brightness is 43.6% ISO, and Kappa number is 13.76.

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

[0031] Test results: pulp brightness is 45.9% ISO, and Kappa number is 13.22.

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

[0033] Test results: pulp brightness is 44.7% ISO, and Kappa number is 13.57.

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

[0035] Test results: pulp brightness is 45.1% ISO, and Kappa number is 13.34.

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

[0037] Test results: pulp brightness is 38.9% ISO, and Kappa number is 14.81.

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

[0039] Table 1

[0040] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A pulp bleaching method based on electric field gradient coupling oxygen nuclei, characterized in that: It includes the following steps: (1) Add pulp, alkali and protective agent into the reactor, stir and mix, and heat; (2) When heated to 90-100°C, maintain the temperature, apply a DC electric field to the reactor and introduce oxygen under high-speed stirring, and react for 3-5 minutes; (3) React for 30 to 120 min under low-speed stirring.

2. The method according to claim 1, characterized in that: The pulp described in step (1) is obtained by boiling pulping raw materials by the kraft process.

3. The method according to claim 1, characterized in that The base described in step (1) includes NaOH; The protective agent in step (1) includes a magnesium salt.

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

5. The method according to claim 1, characterized in that The heating in step (2) is heating to 90° C. The high-speed stirring in step (2) is stirring at a rotation speed of 200 to 400 r / min.

6. The method according to claim 1, characterized in that The electric field strength of the DC electric field applied in step (2) is 200 to 1800 V / m.

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

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

9. The method according to claim 1, characterized in that: The reaction in step (2) was carried out for 3 min.

10. The method according to claim 1, characterized in that The low-speed stirring in step (3) is: stirring at a speed of 100 to 180 r / min; The reaction in step (3) was carried out for 60 min.

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