Photocatalytic oxidation combined treatment process and device for nitrochlorobenzene wastewater

Abstract

The invention discloses a photocatalytic oxidation combined treatment process and device for nitrochlorobenzene wastewater, and the process comprises the following steps: continuously feeding nitrochlorobenzene wastewater into a first-stage synergistic catalysis system, introducing ozone and hydrogen peroxide, and carrying out a synergistic oxidation reaction to obtain first-stage oxidized effluent; and continuously adding primary oxidation effluent into a secondary photocatalytic oxidation system, adding hydrogen peroxide, and carrying out an oxidation reaction under co-catalysis of ultraviolet light and a photocatalyst. The chromaticity of the wastewater is reduced to 500-1000 times by adopting ozone / hydrogen peroxide concerted catalysis, then the wastewater is connected with a subsequent improved secondary photocatalytic oxidation system for photocatalytic oxidation, and meanwhile, a thin wire is wound on an ultraviolet lamp sleeve with relatively high light intensity, so that turbulent flow near the sleeve can be enhanced, and more wastewater enters a strong ultraviolet light area; the photocatalyst is arranged on the reactor wall with relatively weak light intensity, so that the oxidation capacity of a weak ultraviolet region can be enhanced, the treatment capacity of the tubular reactor is improved, the treatment time is shortened, and the treatment cost is saved.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment technology, specifically relating to a photocatalytic oxidation combined treatment process and device for nitrochlorobenzene wastewater. Background Technology

[0002] Nitrochlorobenzene is an intermediate in many fine chemical products such as pharmaceuticals, pesticides, and dyes. Nitrochlorobenzene wastewater is brownish-red in appearance, with a pH > 12 and a COD of approximately 1500 mg / L. The main characteristic organic pollutants are nitrochlorobenzene and sodium nitrophenolate, with a salt content of approximately 2-4%, primarily composed of sodium nitrate, sodium sulfate, and sodium chloride. Currently, the main process flow for nitrochlorobenzene wastewater treatment involves ozone / hydrogen peroxide co-oxidation, ultrafiltration, nanofiltration, denitrification, and biological treatment to achieve discharge standards, as shown in the process flow of CN113087296B. Figure 1 As shown.

[0003] While the ozone / hydrogen peroxide synergistic oxidation unit can reduce COD from 1500 mg / L to around 130 mg / L, it does not completely remove large molecules such as nitrochlorobenzene and sodium nitrophenolate (5-10 ppm), leading to easy clogging and frequent replacement of the subsequent nanofiltration membrane. The COD degradation process is easier in the early stages and more difficult in the later stages. Due to the low concentration of ·OH produced, the existing ozone / hydrogen peroxide synergistic catalytic process is less efficient in the later stages of the reaction. Therefore, when using a single synergistic catalytic process, the cost of treating 1 ton of water to reduce COD to 130 mg / L is as high as over 100 yuan.

[0004] Photocatalysis can generate a large amount of ·OH, but it requires high wastewater color. Therefore, it can be used as a follow-up process to ozone / hydrogen peroxide synergistic catalysis. Existing photocatalytic tubular devices still require relatively long residence times for the removal of trace pollutants due to uneven flow and light field distribution. Since ultraviolet light attenuates continuously in water, the light field near the reactor wall is generally weak. Furthermore, due to friction, the water flow near the UV lamp wall and reactor wall is slow. The slower water flow near the UV lamp wall absorbs more UV light, while the water flow near the reactor wall receives less. This unevenness in the light and flow fields results in inefficient utilization of the reactor's internal space and UV light. Therefore, following ozone / hydrogen peroxide synergistic catalysis with photocatalysis, and improving existing photocatalytic tubular reactors, is expected to achieve efficient removal of characteristic pollutants at a lower treatment cost. Summary of the Invention

[0005] The present invention aims to optimize the oxidation treatment process and apparatus for nitrochlorobenzene, so as to solve the problems of incomplete removal of nitrochlorobenzene and sodium nitrophenolate and high treatment costs.

[0006] In a first aspect, the present invention provides a combined photocatalytic oxidation treatment device for nitrochlorobenzene wastewater, comprising a primary synergistic catalytic system and a secondary photocatalytic oxidation system;

[0007] The primary synergistic catalytic system comprises a circulating storage tank, an ozone generator, and a hydrogen peroxide storage tank connected to an ozone / hydrogen peroxide synergistic catalytic tower. The bottom of the circulating storage tank is connected to the bottom of the ozone / hydrogen peroxide synergistic catalytic tower via a circulating pump. The top of the ozone / hydrogen peroxide synergistic catalytic tower and the top of the circulating storage tank are connected via a pipeline. Wastewater enters from the inlet at the bottom of the circulating storage tank and exits from the outlet at the top of the circulating storage tank.

[0008] The secondary photocatalytic oxidation system is an ultraviolet / hydrogen peroxide catalytic system. The system is a tubular reactor with multiple ultraviolet lamps arranged side by side and a photocatalyst on the inner wall. Fine threads are wound around the outside of the ultraviolet lamps from the first end to the second end along the tube wall.

[0009] Furthermore, a thin thread with a diameter of 2-5 mm is wound around the outside of the UV lamp tube from the first end to the second end along the tube wall, with 5-10 turns. The winding of the thin thread can increase the local turbulence on the surface of the UV lamp tube, disturb the slower water flow near the UV lamp tube, and enhance the balanced absorption of UV light by the wastewater. Too many turns will block the UV light, and too few turns will reduce the turbulence effect near the lamp tube and affect the oxidation reaction effect. The preferred material for the thin thread is polytetrafluoroethylene.

[0010] Furthermore, a photocatalyst is placed on the inner wall of the tubular reactor, preferably a TiO2-based or carbon-based high-efficiency catalyst.

[0011] Furthermore, a photocatalyst is provided on the inner wall of the tubular reactor, and the photocatalyst is provided on the inner wall of the tubular reactor in the form of a coating.

[0012] Secondly, this invention provides a photocatalytic oxidation combined treatment process for nitrochlorobenzene wastewater, comprising the following steps:

[0013] S1: Nitrochlorobenzene wastewater is continuously fed into the primary co-catalytic system. At the same time, ozone and hydrogen peroxide are introduced into the system to carry out the ozone / hydrogen peroxide co-oxidation reaction. When the wastewater reaches a certain residence time in the primary co-catalytic system or the wastewater reaches a certain color, the primary oxidation effluent is obtained.

[0014] S2: The effluent from the primary oxidation process is continuously fed into the secondary photocatalytic oxidation system, while hydrogen peroxide is added to the system. Under the combined catalysis of ultraviolet light and photocatalyst, the oxidation reaction takes place to obtain the secondary oxidation effluent.

[0015] Furthermore, the primary synergistic catalytic system is a circulating system of ozone / hydrogen peroxide synergistic oxidation, which is a continuous inflow and outflow system. Wastewater entering the circulating storage tank is pumped into the ozone / hydrogen peroxide synergistic catalytic tower. The ozone generator and the hydrogen peroxide storage tank respectively supply ozone and hydrogen peroxide to the ozone / hydrogen peroxide synergistic catalytic tower. The wastewater is oxidized by the ozone / hydrogen peroxide synergistic catalytic tower. The primary oxidation effluent after oxidation treatment meets a certain color requirement and is discharged from the outlet at the top of the circulating storage tank.

[0016] Furthermore, in S1, when the residence time of wastewater in the primary co-catalytic system is 30-50 min, primary oxidation effluent is obtained.

[0017] Furthermore, in S1, the amount of ozone used per ton of wastewater is 1-3 kg, and the amount of hydrogen peroxide with a concentration of 30 wt% is 3-5 kg.

[0018] Furthermore, when the wastewater color is 500-1000 times, primary oxidation effluent is obtained.

[0019] Furthermore, in S2, the residence time of the primary oxidation effluent in the secondary photocatalytic oxidation system is 10-30 min.

[0020] Furthermore, in S2, the dosage of hydrogen peroxide corresponding to 30% per ton of wastewater is 8-15 kg.

[0021] Compared with the prior art, the advantages of this application are as follows:

[0022] (1) Due to the low concentration of ·OH generated, the existing ozone / hydrogen peroxide synergistic catalytic process has low efficiency in the later stage of the reaction and is more suitable as a pretreatment process for decolorization, bond breaking, etc. The present invention uses ozone / hydrogen peroxide synergistic catalysis to reduce the color of wastewater to 500-1000 times and then connects it to the improved secondary photocatalytic oxidation system for photocatalytic oxidation. Compared with using ozone / hydrogen peroxide synergistic catalysis throughout the process, it can significantly shorten the treatment time and save treatment costs.

[0023] (2) The secondary photocatalytic oxidation system can generate a higher concentration of ·OH, which has a higher oxidation capacity than ozone / hydrogen peroxide synergistic catalytic oxidation. It can efficiently remove large molecular organic substances such as nitrochlorobenzene and sodium nitrophenolate while reducing COD.

[0024] (3) The ozone and hydrogen peroxide remaining from the primary oxidation reaction can be further consumed in the secondary reaction, eliminating the need for an ozone tail gas destruction device, which is both safe and economical.

[0025] (4) Wrapping a thin thread around the sleeve of a high-intensity ultraviolet lamp can enhance turbulence near the sleeve, allowing more wastewater to enter the high-intensity ultraviolet light region; placing a photocatalyst on the reactor wall where the light intensity is weak can enhance the oxidation capacity in the weak ultraviolet light region, improve the treatment capacity of the tubular reactor, reduce treatment time, and save treatment costs. This scheme has a beneficial effect in the photocatalytic treatment of different wastewaters and is universally applicable. Attached Figure Description

[0026] Figure 1 It is a process flow diagram in the existing technology;

[0027] Figure 2 This is a process flow diagram of the present invention;

[0028] Figure 3 This is a schematic diagram of the first-stage synergistic catalytic system of the present invention;

[0029] Figure 4 This is a structural diagram of the two-stage photocatalytic reactor of the present invention;

[0030] Figure 5 This is a schematic diagram of the flow field on the surface of the ultraviolet lamp sleeve of the secondary photocatalytic reactor of the present invention;

[0031] Table 1 compares the operating parameters of the process of this invention with those of existing technologies for treating nitrochlorobenzene wastewater.

[0032] Figure 4 In the middle, 1-water inlet, 2-UV lamp tube, 3-fine wire, 4-photocatalyst, 5-sealing component, 6-UV lamp wiring terminal, 7-water outlet. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments.

[0034] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0036] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0037] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0038] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0039] Combination Figure 3 This invention provides a schematic diagram of a primary synergistic catalytic system. This system features continuous inflow and outflow and includes a circulating tank connected to an ozone / hydrogen peroxide synergistic catalytic tower, an ozone generator, and a hydrogen peroxide storage tank. The circulating tank is a container designed to increase residence time and turbulence. The bottom of the circulating tank is connected to the bottom of the ozone / hydrogen peroxide synergistic catalytic tower via a circulating pump. The top of the ozone / hydrogen peroxide synergistic catalytic tower and the top of the circulating tank are connected by a pipeline. Wastewater enters from the inlet at the bottom of the circulating tank and exits from the outlet at the top. Each inlet and outlet has a pump with a consistent flow rate. The wastewater entering the circulating tank is pumped into the ozone / hydrogen peroxide synergistic catalytic tower via the circulating pump, with a flow rate of 40 m³ / h. 3 / h, inflow and outflow rate 2 m³ 3 / h, the ozone generator and hydrogen peroxide storage tank respectively supply ozone and hydrogen peroxide to the ozone / hydrogen peroxide co-catalytic tower, and the primary oxidation effluent after oxidation treatment is discharged through the outlet at the top of the circulating storage tank.

[0040] Combination Figure 4 The present invention provides a schematic diagram of a two-stage photocatalytic reactor. The reactor is a tubular reactor with multiple ultraviolet lamps 2 arranged side by side and a photocatalyst 4 on the inner wall. The ultraviolet lamps 2 are wrapped with a thin wire 3 with a diameter of 2 mm and 5 turns. The connection between the ultraviolet lamps 2 and the ultraviolet lamp wiring 6 is sealed with a sealing element 5 to prevent leakage. The tubular reactor has an inlet 1 at one bottom end and an outlet 7 at the other top end.

[0041] The flow field on the surface of the UV lamp sleeve in the secondary photocatalytic reactor is as follows: Figure 5 As shown, the winding of the thin thread 3 can increase the local turbulence on the surface of the ultraviolet lamp tube 2, disturb the slower water flow near the ultraviolet lamp tube 2 (the thin thread blocks the water flow on the tube wall, causing the water near the tube wall to flow outward, and after passing through the thin thread, a stream of water will return, thus achieving the purpose of disturbance), and enhance the balanced absorption of ultraviolet light by the wastewater.

[0042] Example 1

[0043] Combination Figure 2 This embodiment provides a treatment process for nitrochlorobenzene wastewater, including the following steps:

[0044] S1: Nitrochlorobenzene wastewater is continuously fed into the primary co-catalytic system. At the same time, 2 kg / ton of ozone and 3 kg / ton of hydrogen peroxide are introduced into the system to carry out the ozone / hydrogen peroxide co-oxidation reaction. The residence time of the primary co-catalytic system is set to 30 min to obtain primary oxidation effluent.

[0045] S2: The effluent from the primary oxidation process is continuously fed into the secondary photocatalytic oxidation system. The apparatus used is a tubular reactor, with polytetrafluoroethylene (PTFE) wire wrapped around the UV lamp sleeve and a TiO2-based photocatalyst coating applied to the inner wall of the reactor. Simultaneously, hydrogen peroxide at a concentration of 10 kg / ton of water is added to the tubular reactor. Under the combined catalysis of UV light and the catalyst, an oxidation reaction is carried out for 20 minutes to obtain the secondary oxidation effluent.

[0046] The relevant data on wastewater treatment are shown in Table 1.

[0047] Comparative Example 1

[0048] This comparative example provides a treatment process for nitrochlorobenzene wastewater, comprising the following steps:

[0049] Nitrochlorobenzene wastewater was continuously fed into an ozone / hydrogen peroxide synergistic catalytic system. At the same time, 6.67 kg / ton of ozone and 10 kg / ton of hydrogen peroxide were introduced into the system to carry out the ozone / hydrogen peroxide synergistic oxidation reaction. The residence time of the circulation system was set to 70 min to obtain primary oxidation effluent.

[0050] The relevant data on wastewater treatment are shown in Table 1.

[0051] Comparative Example 2

[0052] This comparative example provides a treatment process for nitrochlorobenzene wastewater.

[0053] The difference between this comparative example and Example 1 is that one-quarter of the tubular reactor of the S2 photocatalytic oxidation system was transferred into the S1 co-catalytic system. A circulation system was formed between the S2 system and the S1 circulation tank via a circulation pump, resulting in a UV / ozone / hydrogen peroxide co-catalytic reaction. In this case, the residence time of the S2 photocatalytic oxidation system became 15 minutes.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that in S2, the purple outer sleeve was not wrapped with polytetrafluoroethylene thread.

[0056] The relevant data on wastewater treatment are shown in Table 1.

[0057] Comparative Example 4

[0058] The difference between this comparative example and Example 1 is that in S2, the purple outer tube was not wrapped with polytetrafluoroethylene thread, and the inner wall of the reactor was not coated with a TiO2-based photocatalyst.

[0059] The relevant data on wastewater treatment are shown in Table 1.

[0060] Table 1. Data on wastewater treatment and operating costs of different processes.

[0061]

[0062] In summary, the photocatalytic oxidation combined treatment process and apparatus for nitrochlorobenzene wastewater of this invention first uses an ozone / hydrogen peroxide synergistic catalytic process to reduce the color by 500-1000 times, and then connects to the improved photocatalytic oxidation process. This can achieve an effluent COD of less than 130 mg / L while reducing the concentrations of nitrochlorobenzene and sodium nitrophenolate to around 0.1 mg / L, which can greatly reduce the risk of subsequent processes. Compared with the existing ozone / hydrogen peroxide synergistic catalysis, the combined process and apparatus of this invention can also reduce the operating cost from 112.5 yuan / ton of water to 59.5 yuan / ton of water, which has a significant cost advantage. In addition, the effluent index of the first-stage synergistic catalytic process of Comparative Example 2 is slightly lower than that of the process of this invention, indicating that the treatment effect of UV / ozone / hydrogen peroxide synergy is better than that of ozone / hydrogen peroxide synergy. However, under the same treatment cost, the final effluent index of Comparative Example 2 is slightly worse than that of the process of this invention, indicating that reducing the color of the first-stage effluent to a low level before connecting to the second-stage photocatalytic process is the optimal process.

[0063] The above embodiments are merely preferred embodiments of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, or combinations made without departing from the spirit and principle of the present invention, such as various combinations of solutions in the embodiments, should be considered equivalent replacements and are all within the protection scope of the present invention.

Claims

1. A photocatalytic oxidation combined treatment device for nitrochlorobenzene wastewater, characterized in that, It includes a primary synergistic catalytic system and a secondary photocatalytic oxidation system; The primary synergistic catalytic system is a circulating system for ozone / hydrogen peroxide synergistic oxidation, comprising a circulating storage tank, an ozone generator, and a hydrogen peroxide storage tank connected to the ozone / hydrogen peroxide synergistic catalytic tower. The bottom of the circulating storage tank is connected to the bottom of the ozone / hydrogen peroxide synergistic catalytic tower via a circulating pump, and the top of the ozone / hydrogen peroxide synergistic catalytic tower and the top of the circulating storage tank are connected via a pipeline. Wastewater enters from the inlet at the bottom of the circulating storage tank and exits from the outlet at the top of the circulating storage tank. The secondary photocatalytic oxidation system is an ultraviolet / hydrogen peroxide catalytic system. The system is a tubular reactor with multiple ultraviolet lamps arranged side by side and a photocatalyst on the inner wall. Fine threads are wound around the outside of the ultraviolet lamps from the first end to the second end along the tube wall.

2. The apparatus as claimed in claim 1, characterized in that, A thin thread with a diameter of 2-5mm is wrapped around the outside of the ultraviolet lamp tube from the first end to the second end along the tube wall, with 5-10 turns.

3. The apparatus as described in claim 1, characterized in that, The thin thread is made of polytetrafluoroethylene.

4. The apparatus as claimed in claim 1, characterized in that, Photocatalysts are placed on the inner wall of the tubular reactor, preferably TiO2-based or carbon-based catalysts.

5. The apparatus as claimed in claim 1, characterized in that, A photocatalyst is provided on the inner wall of the tubular reactor, and the photocatalyst is applied to the inner wall of the tubular reactor in the form of a coating.

6. A photocatalytic oxidation combined treatment process for nitrochlorobenzene wastewater based on the apparatus described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Nitrochlorobenzene wastewater is continuously fed into the primary co-catalytic system. At the same time, ozone and hydrogen peroxide are introduced into the system to carry out the ozone / hydrogen peroxide co-oxidation reaction. When the wastewater reaches a certain residence time in the primary co-catalytic system or the wastewater reaches a certain color, the primary oxidation effluent is obtained. S2: The effluent from the primary oxidation process is continuously fed into the secondary photocatalytic oxidation system, while hydrogen peroxide is added to the system. The oxidation reaction takes place under the combined catalysis of ultraviolet light and photocatalyst.

7. The process as described in claim 6, characterized in that, In S1, when the wastewater stays in the primary synergistic catalytic system for 30-50 minutes, primary oxidation effluent is obtained.

8. The process as described in claim 6, characterized in that, When the color of the wastewater is 500-1000 times, primary oxidation effluent is obtained.

9. The process as described in claim 6, characterized in that, In S1, the amount of ozone used per ton of wastewater is 1-3 kg, and the amount of hydrogen peroxide with a concentration of 30 wt% is 3-5 kg.

10. The process as described in claim 6, characterized in that, In S2, the residence time of the primary oxidation effluent in the secondary photocatalytic oxidation system is 10-30 minutes; the dosage of 30% hydrogen peroxide per ton of wastewater is 8-15 kg.

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