A method for degrading vocs by advanced oxidation coupled with wet scrubbing process

Abstract

The application discloses a method for degrading VOCs by using a high-level oxidation coupling wet washing process. x The strong active species such as sulfate radicals and hydroxyl radicals generated by activating the PMS solution by the catalyst are degraded into small molecules, even carbon dioxide and water. In the application, the oxidant is added into the reactor body drop by drop by using a peristaltic pump, so that the removal rate of VOCs and the stability of the mineralization rate are effectively improved, the utilization rate of the oxidant is improved, and the process is low in energy consumption, simple in operation and difficult to cause secondary air pollution.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of volatile organic compound treatment, and relates to a method for degrading VOCs by using advanced oxidation coupled with a wet scrubbing process. BACKGROUND

[0002] In recent years, the mainstream remediation technology for volatile / semi-volatile organic contaminated sites is in-situ thermal desorption technology. The technology is to input heat energy to migrate the pollutants to the gas phase, and then treat the tail gas to achieve the remediation purpose. The tail gas discharged by the technology is complex in composition and contains difficult-to-degrade pollutants such as benzene series, halogenated hydrocarbons and esters. In addition, VOCs have the characteristics of structural stability, high hydrophobicity and strong persistence, and need strong oxidizing technology and high gas-liquid mass transfer efficiency to achieve deep degradation.

[0003] The bubble reactor is a reactor in which gas is bubbled from the bottom of the reactor through the liquid layer, the reactants in the gas phase are dissolved into the liquid phase and react, and the stirring action of the bubbles can fully mix the gas-liquid two phases, so that the mass transfer and heat transfer efficiency is high. At the same time, the bubble reactor has the advantages of simple structure, stable operation, low investment and maintenance cost. However, in practical application, when it comes to strongly hydrophobic and difficult-to-degrade pollutants, the low gas-liquid mass transfer efficiency will greatly affect the removal effect of the pollutants, thereby limiting the application.

[0004] The advanced oxidation process based on persulfate (SR-AOPs) refers to the generation of strong oxidizing active species such as sulfate radicals, hydroxyl radicals and superoxide radicals by some physical activation methods, so as to react violently with organic pollutants, and then completely mineralize them into carbon dioxide, water and small molecules. Compared with other free radicals, sulfate radicals have higher oxidation-reduction potential, longer half-life, wider pH tolerance range and higher selectivity. The activation methods of persulfate mainly include heat treatment, ultraviolet light, ultraviolet light and metal ions. Patent CN109675435A discloses a system for degrading organic waste gas by vacuum ultraviolet combined with persulfate. The system uses UV lamp to activate persulfate, needs input of external energy, has high economic cost, and is intermittent operation. SUMMARY

[0005] The purpose of the present application is to provide a method for degrading VOCs by using advanced oxidation coupled with a wet scrubbing process, which has low energy consumption, simple operation and high environmental benefits.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A method for degrading VOCs by using advanced oxidation coupled with a wet scrubbing process, comprising the following steps:

[0008] (1) At room temperature, cobalt nitrate hexahydrate and manganese acetate tetrahydrate are added to ultrapure water, stirred until completely dissolved, to prepare solution A; Kaolin or Al2O3 is added to solution A, and stirred to allow ion exchange between Kaolin or Al2O3 and metal ions to prepare solution B; solution B is continuously stirred at 80℃ until it is evaporated to dryness, and dried for 12 h to obtain a catalyst precursor; the catalyst precursor is calcined to obtain MnCoO x catalyst;

[0009] (2) A certain amount of MnCoO x catalyst / suspension medium is arranged inside the reactor body, and the reactor body is aerated from the bottom gas distributor; a PMS (potassium hydrogen persulfate) solution is pumped into the reactor body by a peristaltic pump; VOCs waste gas is upwardly introduced into the MnCoO x catalyst / suspension medium in the reactor body, and under the action of the catalyst, the VOCs waste gas is degraded by active substances generated by the PMS solution, and the tail gas is discharged through the gas outlet; the liquid level in the reactor body is controlled during the entire reaction process.

[0010] Preferably, in step (1), the molar ratio of cobalt nitrate hexahydrate, manganese acetate tetrahydrate, Kaolin or Al2O3 is 0.5:0.5:1; the ion exchange is allowed to occur for 8-12 h; the calcination is performed in a tube furnace, the calcination protection is nitrogen, the calcination temperature is 500-600℃, the calcination time is 1-2 h, and the temperature rising rate is 3-5℃ / min.

[0011] Preferably, in step (2), the ratio of MnCoO x catalyst to suspension medium is 0.5 ~ 10g / L.

[0012] Preferably, in step (2), the PMS solution is pumped into the reactor body by a peristaltic pump, the PMS solution pump-in rate is counted per minute, 20 ~ 100g PMS is consumed to degrade 1mg VOCs, and the concentration of the PMS solution is 25 ~ 250g / L.

[0013] Preferably, in step (2), the liquid level in the reactor body is controlled to be 50~70% of the height of the reactor body during the entire reaction process.

[0014] Preferably, in step (2), the concentration of the VOCs waste gas is 100-1000 ppm.

[0015] Preferably, in step (2), the VOCs are benzene series or chlorobenzene.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) The activation mode of the oxidant is selected to utilize transition metals for activation, effectively saving energy, and the MnCoO x The catalyst preparation method is simple, the catalyst cost is low, and mass production is suitable.

[0018] (2) Compared with other existing wet processes, the bubble reactor has small floor area, simple equipment, easy operation, convenient maintenance, low operation cost, and good impact load resistance.

[0019] (3) Compared with intermittent operation, continuous operation can simultaneously realize steady improvement of removal rate and mineralization rate, effectively reduce the risk of secondary air pollution, and improve the utilization rate of oxidant. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The process flow chart of the method for degrading VOCs by the advanced oxidation coupling wet washing process.

[0021] Figure 2 The catalytic degradation effect comparison chart of benzene under different dosages of MnCoO x / Kaolin catalyst.

[0022] Figure 3 The catalytic degradation effect comparison chart of chlorobenzene under different dosages of oxidant.

[0023] Figure 4 The catalytic degradation effect chart of benzene with different concentrations.

[0024] Figure 5 The catalytic degradation effect chart of benzene using MnCoO x / Al2O3 catalyst.

[0025] Figure 6 The catalytic degradation effect comparison chart of benzene under different running modes.

[0026] Figure 7 The carbon dioxide generation comparison chart of benzene under different running modes.

[0027] The drawing mark: 1-PMS solution storage device, 2-gas distributor, 3-catalyst / suspension medium, 4-solid-liquid separator. DETAILED DESCRIPTION

[0028] The application will be further described in detail below in combination with examples and drawings.

[0029] As Figure 1As shown, the advanced oxidation coupling wet washing device provided by the application comprises a reactor body, a PMS solution supply device and a liquid level control device, the reactor body is used for degrading VOCs waste gas, the PMS solution supply device is used for providing PMS solution for the reactor body, and the liquid level control device is used for controlling the liquid level of the dispersion medium in the reactor body. The reactor body comprises a gas distributor 2 and a catalyst / suspension medium 3 inside, the PMS solution supply device comprises a first peristaltic pump and a PMS solution storage device 1, the liquid level control device comprises a solid-liquid separator 4, a second peristaltic pump and a recovery tank, the VOCs waste gas is upwardly raised in the form of bubbles through the gas distributor 2 at the bottom of the reactor body and enters the catalyst / suspension medium 3 inside the reactor body, the oxidant (PMS solution) provided by the PMS solution supply device enters the catalyst / suspension medium 3, and under the action of the catalyst, the VOCs waste gas is degraded into small molecules, even carbon dioxide and water by strong active species such as sulfate radicals and hydroxyl radicals generated by the catalyst-activated PMS solution, tail gas is discharged through a gas outlet, the second peristaltic pump of the liquid level control device continuously extracts the solution in the reactor body to control the liquid level to be constant, and the solid in the solution is intercepted by the solid-liquid separator 4.

[0030] Example 1

[0031] 0.3 g, 0.2 g and 0.1 g of MnCoO x / Kaolin catalysts were respectively weighed and dispersed in a reactor containing 100 ml of ultrapure water, and ultrasonic waves were used to uniformly disperse the catalysts. 300 ppm of benzene was introduced into the reactor from the bottom. Before the reaction, 0.6 g of PMS was dissolved in 12 ml of ultrapure water and uniformly dispersed. When the reaction started, the first peristaltic pump of the PMS solution supply device and the second peristaltic pump of the liquid level control device were simultaneously opened. The pump-in speed of the first peristaltic pump was 50 g of PMS consumed per minute for degrading 1 mg of VOCs. Finally, the tail gas was monitored.

[0032] Figure 2 In the MnCoO x / Kaolin catalyst and suspension medium ratio of 3.0 g / L, 2.0 g / L and 1.0 g / L, the removal rates of benzene were 96.9%, 97.8% and 93.6%, respectively.

[0033] Example 2

[0034] 0.2 g of MnCoO x / Kaolin catalyst was dispersed in a reactor containing 100 ml of ultrapure water, and ultrasonic was used to make it uniform. 300 ppm of chlorobenzene was introduced from the bottom of the reactor. 1.2 g, 0.6 g, and 0.3 g of PMS were respectively dissolved in 12 ml of ultrapure water, and were uniformly dispersed. When the reaction started, the first peristaltic pump of the PMS solution supply device and the second peristaltic pump of the liquid level control device were simultaneously opened. The pump-in speed of the first peristaltic pump was 100 g PMS, 50 g PMS, and 25 g PMS per minute for degrading 1 mg of VOCs, respectively. Finally, the tail gas was monitored.

[0035] Figure 3 In the embodiment, when the pump-in speed of the first peristaltic pump was 100 g PMS, 50 g PMS, and 25 g PMS per minute for degrading 1 mg of VOCs, respectively, the removal rates of chlorobenzene were 97.8%, 97.7%, and 95.5%, respectively.

[0036] Example 3:

[0037] 0.14 g of MnCoO x / Kaolin catalyst was dispersed in a reactor containing 100 ml of ultrapure water, and ultrasonic was used to make it uniform. 300 ppm and 700 ppm of benzene were respectively introduced from the bottom of the reactor. 0.42 g of PMS was dissolved in 12 ml of ultrapure water before the reaction, and was uniformly dispersed. When the reaction started, the first peristaltic pump of the PMS solution supply device and the second peristaltic pump of the liquid level control device were simultaneously opened. The pump-in speed of the first peristaltic pump was 35 g PMS per minute for degrading 1 mg of VOCs. Finally, the tail gas was monitored.

[0038] Figure 4 In the embodiment, when 300 ppm and 700 ppm of benzene were introduced, the removal rates of benzene were 98.6% and 93.1%, respectively.

[0039] Example 4:

[0040] 0.4 g of MnCoO x / Al2O3 catalyst was dispersed in a reactor containing 100 ml of ultrapure water, and ultrasonic was used to make it uniform. 300 ppm of benzene was introduced from the bottom of the reactor. 0.42 g of PMS was dissolved in 12 ml of ultrapure water before the reaction, and was uniformly dispersed. When the reaction started, the first peristaltic pump of the PMS solution supply device and the second peristaltic pump of the liquid level control device were simultaneously opened. The pump-in speed of the first peristaltic pump was 35 g PMS per minute for degrading 1 mg of VOCs. Finally, the tail gas was monitored.

[0041] Figure 5 In the embodiment, when MnCoOx The removal rate of benzene was 98.7% when the benzene was catalytically degraded by / Al2O3 catalyst.

[0042] Example 5:

[0043] Accurately weigh 0.14 g of MnCoO x The / Kaolin catalyst was dispersed in a reactor containing 100 ml of ultrapure water and ultrasonically homogenized, and 300 ppm of benzene was introduced into the reactor from the bottom. Before the reaction, 0.42 g of PMS was dissolved in 12 ml of ultrapure water and uniformly dispersed, and at the start of the reaction, the first peristaltic pump of the PMS solution supply device and the second peristaltic pump of the liquid level control device were simultaneously opened, the pump-in speed of the first peristaltic pump was counted in minutes, 35 g of PMS was consumed to degrade 1 mg of VOCs, and finally, the tail gas was monitored.

[0044] Comparative Example 1

[0045] This comparative example is basically the same as Example 4, the only difference being that the PMS solution is added to the reactor at one time.

[0046] Figure 6 And Figure 7 In the above, the removal rate and mineralization of benzene are better in continuous operation than in intermittent operation.

Claims

1. A method for degrading VOCs using an advanced oxidation-coupled wet scrubbing process, characterized in that, Includes the following steps: (1) At room temperature, cobalt nitrate hexahydrate and manganese acetate tetrahydrate were added to ultrapure water and stirred until completely dissolved to obtain solution A; Kaolin or Al2O3 was added to solution A and stirred to allow Kaolin or Al2O3 to fully exchange ions with metal ions to obtain solution B; solution B was stirred continuously at 80°C until it was evaporated to dryness, and dried for 12 h to obtain the catalyst precursor; The catalyst precursor was calcined to obtain MnCoO x catalyst; (2) A certain amount of MnCoO is placed inside the reactor body. x The catalyst suspension medium is aerated from the gas distributor at the bottom of the reactor body. Potassium persulfate solution enters the reactor body via a peristaltic pump. VOCs exhaust gas rises upwards through the gas distributor at the bottom of the reactor body and enters the MnCoO2 within the reactor body. x The catalyst is a suspension medium. Under the action of the catalyst, the VOCs waste gas is degraded by the active substances produced by the potassium persulfate solution, and the tail gas is discharged through the outlet. The liquid level in the reactor body is controlled throughout the reaction process.

2. The method as described in claim 1, characterized in that, In step (1), the molar ratio of cobalt nitrate hexahydrate, manganese acetate tetrahydrate, Kaolin, or Al2O3 is 0.5:0.5:1; the time for sufficient ion exchange is 8-12 h; calcination is carried out in a tube furnace, with nitrogen as the calcination protection, a calcination temperature of 500-600℃, a calcination time of 1-2 h, and a heating rate of 3-5℃ / min.

3. The method as described in claim 1, characterized in that, In step (2), MnCoO x The ratio of catalyst to suspension medium is 0.5 ~ 10 g / L.

4. The method as described in claim 1, characterized in that, In step (2), potassium persulfate solution is introduced into the reactor body through a peristaltic pump. The pumping rate of potassium persulfate solution is measured in minutes. It takes 20 to 100 g of potassium persulfate to degrade 1 mg of VOCs. The concentration of potassium persulfate solution is 25 to 250 g / L.

5. The method as described in claim 1, characterized in that, In step (2), the liquid level inside the reactor body is controlled to be 50-70% of the reactor body height throughout the entire reaction process.

6. The method as described in claim 1, characterized in that, In step (2), the concentration of VOCs in the exhaust gas is 100-1000 ppm.

7. The method as described in claim 1, characterized in that, In step (2), VOCs are benzene compounds or chlorobenzene.

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