CN108046407A - It is a kind of to use nano-CeO2/H2O2/O3The method of the acid used water difficult to degradate of system processing - Google Patents

Abstract

The invention discloses a method for treating acid waste water with heterogeneous catalysis of ozone and hydrogen peroxide. The catalyst was synthesized by pyrolysis nitrate method. The composition of the solid catalyst used in X-ray diffraction analysis (XRD) is ceria, and X-ray photoelectron spectroscopy (XPS) analysis proves that Ce ³⁺ and Ce ⁴⁺ exist simultaneously in the catalyst. Scanning electron microscope (SEM) observation of the catalyst morphology shows that the catalyst is a nanosphere aggregate. The catalyst synthesized by this method shows good activity for heterogeneously catalyzing the oxidation of refractory organic matter (such as: acetic acid) in acidic water by ozone hydrogen peroxide. Compared with the prior art, the solid catalyst prepared by the invention is simple to prepare, has low catalyst production cost, high catalytic activity and high application value.

Description

A method for treating acidic refractory wastewater using nano-CeO2/H2O2/O3 system

(1) Technical field

The invention relates to the field of wastewater treatment, in particular to a method for treating acidic refractory wastewater by adopting a nano-CeO ₂ /H ₂ O ₂ /O ₃ system.

The nano-CeO ₂ /H ₂ O ₂ /O ₃ system is used to efficiently treat refractory pollutants in acidic wastewater. Specifically, nano-cerium oxide is used as a catalyst to catalyze ozonation to treat refractory pollutants in acidic wastewater.

(2) Background technology

Since the 21st century, with the development of industrialization and urbanization, the situation of environmental pollution has become more and more serious. Problems such as industrial wastewater, urban domestic sewage, and river and lake pollution have had a great impact on national economic development, ecological environment, and human health. Most of these wastewaters contain biologically refractory pollutants such as polycyclic aromatic hydrocarbons, halogenated hydrocarbons, heterocyclic compounds, and organic pesticides, which are difficult to treat by traditional biochemical methods. Advanced oxidation process (AOPs) is one of the most promising methods for treating organic refractory wastewater. These include Fenton (H ₂ O ₂ /Fe ²⁺ ), Fenton-like, ozone-based advanced oxidation process (hereinafter referred to as AOP-O ₃ ), persulfate advanced oxidation technology, etc.

Ozone advanced oxidation technology has the advantages of green, high efficiency, and no secondary pollution, and has a good application prospect in sewage treatment. Most unsaturated and macromolecular aromatic organic compounds can directly react with ozone, but it is often accompanied by the generation of by-products such as a large number of small organic molecules, which are difficult to be directly oxidized by ozone. Selecting suitable catalysts such as transition metal oxides CuO, MnO ₂ , TiO ₂ , Fe ₂ O ₃ to catalyze ozone to generate more oxidative hydroxyl radicals (·OH) is the core content of the current research on advanced ozone oxidation. Ozone is more likely to generate hydroxyl radicals under alkaline conditions. However, due to the formation of organic acids, the solution tends to become acidic as the reaction progresses, making the degradation rate decrease or even stop. Ozone hydrogen peroxide coupling technology makes it possible to decompose ozone under acidic conditions to generate hydroxyl radicals. But the efficiency is still low.

In recent years, the heterogeneous catalytic H ₂ O ₂ /O ₃ system is one of the research hotspots. Titanium-Lewis acid, titanium-silicon molecular sieve (TS-1) and solid superacid (SZF) are several catalysts with higher efficiency that we have discovered in this year. No studies on cerium oxide in this area have been reported yet. In this work, nano-cerium oxide was prepared, and it was found that its catalytic H ₂ O ₂ /O ₃ system had a good removal effect on refractory small molecule acids under acidic conditions.

(3) Contents of the invention

The purpose of the present invention is to overcome the shortcomings of existing ozone-refractory acidic wastewater, and provide a wastewater treatment method that can efficiently catalyze ozone to generate hydroxyl radicals under acidic conditions (pH≤5), and degrade refractory organic small molecules acid. It is expected to solve the difficult problem of acid wastewater in the field of environmental water treatment.

A method for treating acidic refractory wastewater by using nano-CeO ₂ /H ₂ O ₂ /O ₃ system, comprising the following steps:

(1) Add nano-CeO ₂ solid catalyst and H ₂ O ₂ to acid wastewater containing organic pollutants and pH 1 to 5, and stir to obtain a mixed solution; the organic pollutants are monocyclic and polycyclic aromatic The mixture of one or more of family compounds, heterocyclic compounds, aliphatic hydrocarbons and derivatives thereof; the mass ratio of the organic pollutants, H ₂ O ₂ and nano-CeO ₂ solid catalyst is 1:0.5～4: 0.2～3;

(2) Passing ozone into the mixed liquid to carry out degradation reaction to obtain degraded waste water.

The degradation rate of organic pollutants in the H ₂ O ₂ /O ₃ system is very low under acidic conditions, and the addition of nano-CeO ₂ greatly improves the degradation rate of organic pollutants in the H ₂ O ₂ /O ₃ system under acidic conditions .

The nano-CeO ₂ /H ₂ O ₂ /O ₃ system of the present invention has higher degradation activity to acid refractory wastewater; the acid refractory wastewater contains organic pollutants that are difficult to treat by other advanced ozone oxidation techniques, preferably Small molecule organic acid wastewater in aliphatic hydrocarbon derivatives; the small molecule organic acid is preferably acetic acid.

In the embodiment of the present invention, the difficult-to-handle small molecule organic acid-acetic acid is used as the organic pollutant. When the above method is used to degrade acetic acid, the mechanism of action is that acetic acid usually occurs as a by-product in the degradation process of the above-mentioned macromolecular organic pollutant. Stable, under normal circumstances, only super oxidizing hydroxyl radicals can oxidize and decompose it. Generally, if acetic acid can be effectively degraded, it can be considered that other organic pollutants, such as aliphatic, aromatic and other macromolecular organic substances, can also be effectively and highly degraded.

When degrading wastewater with unknown concentrations of organic pollutants, it is necessary to measure the COD value of the wastewater first. According to the COD value of the wastewater, the quality of the organic wastewater contained in the wastewater can be estimated, so as to determine the H ₂ O ₂ and nano-CeO ₂ solids that need to be input Catalyst dosage.

Preferably, the nano-CeO ₂ solid catalyst is nano-cerium oxide synthesized by high-temperature thermal decomposition method using cerium nitrate hexahydrate as a precursor.

Further preferably, described nano- _CeO The preparation method of solid catalyst is:

(a) Weigh cerium nitrate hexahydrate and put it into a ceramic boat, put it into a muffle furnace, and heat it up to 550°C for 4 hours at a rate of 10°C min ^-1 in an air atmosphere to obtain a light yellow solid ;

(b) Thoroughly grinding the pale yellow solid in step (a) to obtain the nano-CeO ₂ solid catalyst.

Preferably, in the mixed liquid of step (1), the mass ratio of organic pollutants, H ₂ O ₂ and nano-CeO ₂ solid catalyst is 1:0.5～4:0.2～3; more preferably, organic pollutants, H The mass ratio of ₂ O ₂ and nano-CeO ₂ solid catalyst is 1:1～4:0.8～1.6; most preferably, the mass ratio of organic pollutants, H ₂ O ₂ and nano-CeO ₂ solid catalyst is 1:2 ~4:0.8.

Preferably, in step (2), the ozone is introduced in the form of O ₂ /O ₃ mixed gas, the flow rate of the mixed gas is 0.1-0.6 L·min ^-1 , and the ozone concentration is 1.4-39.2 mg·L ^{- 1} .

Compared with the prior art, the wastewater treatment method of the present invention has the following advantages:

(1) Under acidic conditions (pH ≤ 5), it can efficiently degrade acidic refractory wastewater, and the utilization rate of ozone can completely remove organic pollutants in acidic wastewater and avoid secondary pollution by by-products;

(2) The nano-CeO ₂ solid catalyst is easy to prepare, low in synthesis cost, high in catalytic efficiency, high in ozone utilization, and a good degradation effect can be achieved with a small amount of ozone dosage, and the catalytic application prospect is excellent.

(4) Description of drawings

Fig. 1 is the experimental setup diagram of acetic acid in catalytic ozone oxidation degradation water in the embodiment; Among the figure, 1-oxygen cylinder, 2-ozone generator, 3-flow meter, 4-ozone reactor, 5-circulating cooling water outlet, 6 - feed inlet, 7 - sampling port, 8 - circulating cooling water inlet, 71 - ozone absorbing device, 72 - ozone absorbing device, 8 - sampling port, 9 - material outlet, 10.1, 10.2 - ozone absorbing device.

Fig. 2 is nano-CeO ₂ The XRD characterization figure of solid catalyst;

Fig. 3 is nano- _CeO SEM characterization figure of solid catalyst;

Fig. 4 is nano-CeO _The XPS characterization figure of solid catalyst;

Figure 5 is a comparative effect diagram of different catalysts under the same conditions.

Fig. 6 is the effect diagram of CeO ₂ catalyzed degradation of acetic acid by different systems.

Figure 7 is a comparison chart of the amount of hydroxyl radicals produced in different systems.

(5) Specific implementation methods

The present invention will be further described below in conjunction with specific examples, but the protection scope of the present invention is not limited thereto.

The following examples all adopt the device shown in Fig. 1 to carry out wastewater treatment, which device comprises oxygen cylinder 1, ozone generator 2, flow meter 3, ozone reactor 4, ozone absorbing device 10.1, 10.2, ozone destroyer 11. The oxygen cylinder 1, the ozone generator 2, the flowmeter 3, the ozone reactor 4, the ozone absorbing device 10.2, and the ozone destroyer 11 are connected in series through pipelines in sequence, and the connection between the flowmeter 3 and the ozone reactor 4 The pipeline is provided with a two-way valve, and another passage of the two-way valve is connected to another ozone absorbing device 10.1. Described ozone reactor 4 is provided with circulating cooling water inlet 8 and cooling water outlet 5, is passed with circulating cooling water, and described ozone reactor 4 is also provided with feeding port 6 at its top, and is provided with sampling port 7 at the bottom , Outlet 9. The ozone absorbing devices 10.1, 10.2 adopt the most common form, two or more connected test tubes or other containers filled with 2% KI solution. The model of the ozone generator is CFS-1A, the model of the destroyer is ODF-003, the contact material is 316L stainless steel, the ozone reactor is ordinary glass, the inner diameter is 5cm, and the height is 75cm. The sand core at the bottom of the ozone reactor is a gas step device, and the connecting pipe All roads use silicone tubes.

Before the reaction, the ozone reactor was cleaned with secondary deionized water, and after pretreatment with ozone for 5 minutes, after emptying, the reactor was rinsed twice with secondary deionized water. The wastewater solution to be treated is configured with deionized water and placed in the ozone reactor 4, and an appropriate amount of catalyst is put into the ozone reactor 4. During the reaction, the oxygen flowing out of the oxygen cylinder 1 is used as the raw material gas, and the ozone is generated by the ozone generator to obtain the O ₂ /O ₃ mixed gas. The ozone concentration of the intake air is controlled by adjusting the discharge power and gas flow of the ozone generator, and the connection is opened. The two-way valve of the ozone reactor, the O ₂ /O ₃ mixed gas enters the reactor to react with the wastewater, degrades the wastewater, and the O ₂ /O ₃ mixed gas after passing through the ozone reactor leaves from the top of the reactor and passes through the ozone absorption device 10.2. After the ozone destroyer 11, it is discharged into the air. During the reaction period, samples were taken from the sampling port for analysis at regular intervals, and the water samples were bubbled with nitrogen for 3 minutes to terminate the oxidation reaction of ozone.

After the reaction, open the two-way valve connected to the ozone absorbing device 10.1, and absorb the ozone tail gas with 2% KI solution.

Preparation of nano- _CeO2 solid catalyst:

(1) take by weighing 5g cerous nitrate hexahydrate and put into ceramic boat;

(2) Put the sample weighed in step (1) into a muffle furnace, and raise the temperature to 550° C. for 4 h at a heating rate of 10° C.min ⁻¹ in an air atmosphere to obtain a light yellow solid;

(3) Transfer the light yellow solid in step (2) into an agate mortar and grind it thoroughly and store it to prepare a nano-CeO ₂ solid catalyst. Its XRD characterization diagram, SEM characterization diagram, and XPS characterization diagram are shown in Figure 2-4 shown. In the XRD diagram, the prepared catalyst component is CeO ₂ by comparing with the standard CeO ₂ card, and the SEM diagram shows that the catalyst is a 10-50nm nanosphere aggregate with a relatively high specific surface area. X-ray photoelectron spectroscopy (XPS) analysis shows that there are more Ce ³⁺ in the prepared CeO ₂ catalyst, which means that the catalyst has a lot of oxygen vacancies and has higher catalytic activity.

In the following examples, the detection method of acetic acid concentration: the pH value is measured with a pH precision acidity meter; the concentration of acetate ions in the solution is measured with a high performance liquid chromatography UltiMate 3000 (ThermoFisher Dionex Ultimate3000, USA), and the separation column model: C18 column ( 250×4.6mm, particle size 5mm), the eluent is a mixture of 0.0134mol phosphate buffer (pH=3) and methanol (950:50, V:V), the flow rate is 1.20mL·min ^-1 , UV The detection wavelength is 210nm.

Example 1

The finished catalyst prepared above was used for catalytic ozonation to degrade acetic acid wastewater (the concentration of acetic acid was 100 mg/L, the volume of the reaction solution was 250 ml, and the rest was water). The dosage of the catalyst is 0.08g/L, the dosage of hydrogen peroxide is 100mg/L, and then the pH value of the solution is adjusted to 3.0 with sulfuric acid. The experiment was carried out in a semi-batch mode under the condition that the flow rate of O ₂ /O ₃ mixture was 0.1L/min, and the ozone output was 9.9 mg/min. Samples were taken for testing after 30 minutes of reaction.

Comparative example 1-4

As a comparison, under the same experimental conditions, the following four sets of comparative experiments were done, namely H ₂ O ₂ /O ₃ , CeO ₂ /O ₃ , CeO ₂ /H ₂ O ₂ /O ₂ , and CeO ₂ /O ₂ systems Degrade the same concentration of acetic acid solution.

The concentration of acetic acid (initial concentration 100 mg/L) when the water sample was treated for 30 minutes is shown in Table 1.

Table 1

Embodiment 2-4

The finished catalyst prepared above is used to catalyze H ₂ O ₂ /O ₃ to degrade acetic acid wastewater (the concentration of acetic acid is 100 mg/L, the dosage of H ₂ O ₂ is 100 mg/L, the volume of reaction solution is 250 ml, and the rest is water) . The dosage of the catalyst is 0.08g/L, the experiment adopts the semi-batch method, the flow rate of the O ₂ /O ₃ mixture is 0.1L/min, and the ozone output is 9.9mg/min. .

Examples 2-4 use sulfuric acid to adjust the pH value of the solution to 1.0, 5.0, and 7.0 respectively, and other conditions are the same as in Example 1.

The concentration of acetic acid (initial concentration 100 mg/L) when the water sample was treated for 30 minutes is shown in Table 2.

Table 2

Example Example 2 Example 1 Example 3 Example 4 Acetic acid concentration (mg/L) 88.84 32.42 53.62 4.57

Embodiment 5-8

The finished catalyst prepared above was used to catalyze ozonation to degrade acetic acid wastewater (the concentration of acetic acid was 100 mg/L, the dosage of H ₂ O ₂ was 100 mg/L, the volume of reaction solution was 250 ml, and the rest was water). Then the pH was adjusted to 3.0 with sulfuric acid. The experiment adopts the semi-batch method,

The gas flow rate of O ₂ /O ₃ mixture is 0.1L/min, and the ozone output is 9.9mg/min. Samples are taken for testing after 30 minutes of the experimental reaction.

The dosages of the catalysts in Examples 5-8 were 0.02g/L, 0.04g/L, 0.16g/L, and 0.32g/L respectively, and other conditions were the same as in Example 1.

The concentration of acetic acid (initial concentration 100 mg/L) when the water sample was treated for 30 minutes is shown in Table 3.

table 3

Examples 9-12

The finished catalyst prepared above was used to catalyze ozonation to degrade acetic acid wastewater (the concentration of acetic acid was 100 mg/L, the dosage of H ₂ O ₂ was 100 mg/L, the volume of reaction solution was 250 ml, and the rest was water). The dosage of the catalyst is 0.08g/L, and the pH value is adjusted to 3.0 with sulfuric acid. The experiment was carried out in a semi-batch mode under the condition that the flow rate of O ₂ /O ₃ mixture was 0.1 L/min, and samples were taken for detection after 30 minutes of the experimental reaction.

The ozone yields of Examples 9-12 are 1.4mg/min, 4.5mg/min, 20.2mg/min, 39.2mg/min, and other conditions are the same as in Example 1.

The concentration of acetic acid (initial concentration 100 mg/L) when the water sample was treated for 30 minutes is shown in Table 4.

Table 4

Examples 13-15

The finished catalyst prepared above was used for catalytic ozonation to degrade acetic acid wastewater (the concentration of acetic acid was 100 mg/L, the volume of the reaction solution was 250 ml, and the rest was water). The dosage of the catalyst is 0.08g/L, and then the pH value is adjusted to 3.0 with sulfuric acid. The experiment was carried out in a semi-batch mode under the condition that the flow rate of O ₂ /O ₃ mixture was 0.1L/min, and the ozone output was 9.9 mg/min. Samples were taken for testing after 30 minutes of reaction.

The dosages of H ₂ O ₂ in Examples 13-15 were 50 mg/L, 200 mg/L, and 400 mg/L respectively, and other conditions were the same as in Example 1.

The concentration of acetic acid (initial concentration 100 mg/L) when the water sample was treated for 30 minutes is shown in Table 5.

table 5

Example 16

The finished catalyst prepared above was used for catalytic ozonation to degrade nitrobenzene wastewater (the concentration of nitrobenzene was 100 mg/L, the volume of the reaction solution was 500 ml, and the rest was water). The dosage of the catalyst is 0.08g/L, and then the pH value is adjusted to 3.0 with sulfuric acid. The experiment adopts the semi-batch method, under the condition that the flow rate of O ₂ /O ₃ mixture is 0.1L/min, and the ozone output is 9.9mg/min. The experimental reaction is 5min, 10min, 20min, 30min, 40min, and samples are taken to detect nitrobenzene Concentration, and measure COD.

Example 16 0min 5min 10min 20min 30min 40min Nitrobenzene concentration (mg/L) 100 50.92 25.25 0.4572 0 0 COD (mg/L) 190.1 151.6 84 54 48 32

Claims (8)

1. A method using nano-CeO ₂ /H ₂ O ₂ /O ₃ system to treat acidic refractory wastewater, characterized in that it comprises the following steps: (1) Add nano-CeO ₂ solid catalyst and H ₂ O ₂ to acidic wastewater containing organic pollutants and pH 1 to 5, and stir to obtain a mixed solution; the organic pollutants are monocyclic or polycyclic aromatic The mixture of one or more of family compounds, heterocyclic compounds, aliphatic hydrocarbons and derivatives thereof; the mass ratio of the organic pollutants, H ₂ O ₂ and nano-CeO ₂ solid catalyst is 1:0.5～4: 0.2～3; (2) Passing ozone into the mixed liquid to carry out degradation reaction to obtain degraded waste water. 2. The method for treating acidic refractory wastewater using nano-CeO ₂ /H ₂ O ₂ /O ₃ system according to claim 1, characterized in that: the nano-CeO ₂ solid catalyst is nitrite hexahydrate Cerium oxide is a precursor, nano cerium oxide synthesized by high temperature thermal decomposition method. 3. The method according to claim 2 adopting nano-CeO ₂ /H ₂ O ₂ /O ₃ system to treat acidic refractory wastewater, characterized in that, the preparation method of the nano-CeO ₂ solid catalyst is: ( a) Weigh cerium nitrate hexahydrate and put it into a ceramic boat, put it into a muffle furnace, and heat it up to 550° C. for 4 hours at a heating rate of 10° C.min ⁻¹ in an air atmosphere to obtain a light yellow solid; (b) Thoroughly grinding the pale yellow solid in step (a) to obtain the nano-CeO ₂ solid catalyst. 4. The method for treating acidic wastewater using nano-CeO ₂ /H ₂ O ₂ /O ₃ system according to claim 1, characterized in that, in the mixed solution of step (1), the organic pollutants, H ₂ The mass ratio of O ₂ to the nano-CeO ₂ solid catalyst is 1:1-4:0.8-1.6. 5. The method for treating acidic wastewater using nano-CeO ₂ /H ₂ O ₂ /O ₃ system according to claim 1, characterized in that, in step (2), the ozone is mixed with O ₂ /O ₃ The mixed gas flow rate is 0.1~0.6L·min ^-1 , and the ozone concentration is 1.4~39.2mg·L ^-1 . 6. The method for treating acidic refractory wastewater by using nano-CeO ₂ /H ₂ O ₂ /O ₃ system according to claim 1, characterized in that: the organic pollutants are aliphatic hydrocarbon derivatives. 7. The method for treating acidic refractory wastewater by adopting nano-CeO ₂ /H ₂ O ₂ /O ₃ system according to claim 6, characterized in that: the aliphatic hydrocarbon derivatives are small molecular organic acids. 8. The method for treating acidic refractory wastewater by adopting nano-CeO ₂ /H ₂ O ₂ /O ₃ system according to claim 7, characterized in that: the small molecular organic acid is acetic acid.