Catalytic removal method of chlorinated volatile organic compounds

Abstract

The invention provides a catalytic removal method of chlorinated volatile organic compounds. The catalytic removal method comprises the following steps: carrying out catalytic removal on reaction gas by adopting a gas-solid phase electro-catalytic reaction; wherein the reaction gas comprises a chlorinated volatile organic compound, and a working electrode of the gas-solid phase electrocatalytic reaction comprises a Pd composite titanium dioxide electrode. According to the invention, the gas-solid phase electro-catalytic reaction is adopted for catalytic removal of chlorinated volatile organic compounds, so that gas pollutants can directly reach the surface of the electrode, thereby effectively bypassing the bottleneck of a gas-liquid mass transfer link, remarkably improving the mass transfer and treatment efficiency, and improving the catalytic effect.

Description

Technical Field

[0001] This invention belongs to the field of catalytic removal technology of volatile organic compounds, and relates to a catalytic removal method for chlorinated volatile organic compounds. Background Technology

[0002] Chlorinated volatile organic compounds (Cl-VOCs), a significant class of volatile organic compounds (VOCs), are widely present in industries such as chemical, pharmaceutical, and electronics, resulting in large emissions and extremely high toxicity. Cl-VOCs not only persist in the atmosphere and water bodies but also readily migrate and bioaccumulate, posing a serious threat to ecosystems and human health. For example, some Cl-VOCs are highly carcinogenic, mutagenic, and teratogenic, inducing various chronic diseases of the respiratory and nervous systems. They also participate in photochemical reactions, promoting ozone and smog formation, further exacerbating environmental pollution. Therefore, achieving efficient control of these gaseous pollutants is of significant environmental and public health importance. Currently, although some progress has been made in Cl-VOC removal through various methods such as adsorption, membrane separation, combustion, catalytic oxidation, and biological treatment, these technologies generally suffer from low treatment efficiency, demanding operating conditions, and high operating costs, necessitating the development of more efficient and cost-effective treatment processes.

[0003] The recalcitrant nature of chlorinated volatile organic compounds (VOCs) is a result of the combined effects of structural stability, low bioavailability, environmental persistence, high toxicity, and technological limitations. Therefore, the core of their remediation lies in efficient dechlorination—reducing toxicity and improving biodegradability by breaking C-Cl bonds. However, this requires overcoming key scientific challenges such as high reaction energy barriers and selective control. Currently, while electrocatalytic dechlorination technology can reduce Cl-VOCs to harmless chloride ions under an applied electric field, achieving effective purification, its application in Cl-VOC pollution control is still in its early stages. The main obstacle is the extremely low mass transfer efficiency of Cl-VOCs. An efficient mass transfer process is a prerequisite for the effective removal of Cl-VOCs. Typically, gaseous Cl-VOCs need to dissolve in solution before diffusing to the electrode surface. However, due to their generally strong hydrophobicity, the gas-liquid mass transfer process is limited and inefficient.

[0004] Therefore, how to achieve effective catalytic removal of chlorinated volatile organic compounds (Cl-VOCs) and improve catalytic efficiency is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a catalytic removal method for chlorinated volatile organic compounds. This invention employs a gas-solid phase electrocatalytic reaction for the catalytic removal of chlorinated volatile organic compounds, allowing gaseous pollutants to directly reach the electrode surface. This effectively bypasses the bottleneck of the gas-liquid mass transfer process, significantly improving mass transfer and processing efficiency, and enhancing the catalytic effect.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a catalytic removal method for chlorinated volatile organic compounds, the catalytic removal method comprising:

[0008] The reaction gases are removed by gas-solid phase electrocatalytic reaction;

[0009] The reaction gas includes chlorinated volatile organic compounds, and the working electrode of the gas-solid phase electrocatalytic reaction includes a Pd composite titanium dioxide electrode.

[0010] When conventional electrocatalytic removal of chlorinated volatile organic compounds (Cl-VOCs) is used, they need to be dissolved in the electrode solution first and then diffused into the electrode. This mass transfer process seriously affects the removal efficiency. Furthermore, because Cl-VOCs have high hydrophobicity and extremely poor solubility, the catalytic effect is greatly reduced, which seriously affects the catalytic removal effect.

[0011] To address this issue, this invention employs a gas-solid phase electrocatalytic method for the catalytic removal of Cl-VOCs. Cl-VOCs directly reach the surface of the Pd (palladium) composite titanium dioxide working electrode in gaseous form, bypassing the bottleneck of the gas-liquid mass transfer process and improving the mass transfer efficiency. Furthermore, the Pd catalyst exhibits excellent catalytic activity and can generate a strong reducing agent—moving from H+ at a positive potential... + Hydrogen electrochemically adsorbed in (or H2O) simultaneously activates the C-Cl bond of R-Cl through adsorption, and then undergoes hydrogenolysis through the reaction of adsorbed Cl-VOCs with Hads. Subsequently, the products are desorbed. By composited with a Pd catalyst on the surface of a titanium dioxide electrode, the two work synergistically. Pd has higher catalytic activity and a more significant catalytic effect on Cl-VOCs. Cl-VOCs are dechlorinated and catalytically removed under the action of the Pd composite titanium dioxide working electrode. The dechlorination effect is excellent, and the removed chlorine is easy to recover, forming an effective resource recovery and avoiding the diffusion of chlorine into the gas phase and the generation of by-products. Furthermore, the catalytic removal method provided by this invention has a simple operation process, can be directly connected to polluted gas for reaction, does not require liquid electrolyte, and has high safety and applicability.

[0012] In the working electrode of this invention, Pd and titanium dioxide must be present simultaneously and neither can be omitted. The absence of Pd will result in the complete loss of dechlorination activity. Changing the type of electrode to be loaded, such as a titanium electrode, will seriously affect the dechlorination effect of Pd, and dechlorination needs to be achieved by increasing the loading of Pd.

[0013] Preferably, the volume concentration of chlorinated volatile organic compounds in the reaction gas is 10 ppm to 5000 ppm, such as 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 100 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, or 5000 ppm.

[0014] The catalytic removal method provided by this invention can effectively remove low concentrations of Cl-VOCs, and still has excellent catalytic removal effect under low concentration conditions, especially volume concentrations of 10ppm to 5000ppm (ppm is one part per million).

[0015] Preferably, the reaction gas further includes oxygen and a balance gas, wherein the balance gas includes a protective gas.

[0016] It is understood that the present invention does not specifically limit the protective gas, but its role is as a carrier gas. Conventional gases that do not participate in the reaction and play a protective role are all applicable to the present invention; for example, the protective gas includes, but is not limited to, nitrogen and / or inert gases, and the inert gases include argon and / or helium, etc.

[0017] In addition, the introduction of oxygen into the reaction gas of this invention, in addition to Cl-VOCs and protective gases, can simulate the environment of actual industrial waste gas, better demonstrating the catalytic effect and conforming to the application scenarios of actual flue gas pipelines.

[0018] Preferably, the volume concentration of oxygen in the reaction gas is ≤4%, for example, 0%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8% or 4%, etc.

[0019] This invention introduces an appropriate volume concentration of oxygen into the reaction gas, especially controlling it to below 4%, to avoid excessive oxygen content consuming H species, excessively affecting catalytic activity, and reducing the dechlorination effect. Furthermore, a volume concentration of ≤4% is more in line with the actual application scenarios of flue gas pipelines.

[0020] Preferably, the flow rate of the reactant gas is 15 mL / min to 50 mL / min, for example, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min or 50 mL / min.

[0021] In the process of catalytic removal of Cl-VOCs, the present invention has excellent dechlorination effect under a certain flow rate. It is preferred to adjust the flow rate to 15 mL / min to 50 mL / min for even better catalytic dechlorination effect.

[0022] Preferably, in the Pd-composite titanium dioxide electrode, Pd is loaded in the titanium dioxide electrode, and the Pd loading is 0.1 mg / cm³. 2 ~2mg / cm 2 For example, 0.1 mg / cm 2 0.3 mg / cm 2 0.5 mg / cm 2 0.8 mg / cm 2 1mg / cm 2 1.3 mg / cm 2 1.5 mg / cm 2 1.8 mg / cm 2 or 2mg / cm 2 wait.

[0023] This invention achieves control over the density, size, and morphology of Pd by adjusting the loading amount of Pd in ​​a titanium dioxide electrode, reaching 0.1 mg / cm³. 2 ~2mg / cm 2 It has the capacity to handle loads while also balancing economy and activity.

[0024] Preferably, the method for preparing the Pd composite titanium dioxide electrode includes:

[0025] Pd salt was mixed with a titanium dioxide electrode in the liquid phase, deposited and loaded, and then annealed in a reducing atmosphere to obtain the Pd composite titanium dioxide electrode.

[0026] The Pd loading method provided by this invention results in a more uniform distribution of Pd, relatively lower processing costs, and higher catalytic activity.

[0027] Optionally, the palladium salt includes at least one of palladium nitrate, palladium chloride, sodium tetrachloropalladiumate, or tetraamminepalladium sulfate.

[0028] Optionally, the reducing atmosphere includes a reducing gas and a protective gas, wherein the reducing gas includes hydrogen; and the hydrogen and the protective gas are mixed in any volume percentage, which can be adapted and adjusted by those skilled in the art according to actual needs.

[0029] Preferably, the annealing temperature is 200℃~450℃, such as 200℃, 225℃, 250℃, 275℃, 300℃, 325℃, 350℃, 375℃, 400℃, 425℃ or 450℃.

[0030] Preferably, the preparation method of the titanium dioxide electrode includes a hydrothermal re-sintering method.

[0031] In this invention, a titanium dioxide electrode prepared by hydrothermal reaction and sintering is used for Pd loading, resulting in superior dechlorination activity.

[0032] It is understood that this invention does not specifically limit the details of the preparation process for preparing titanium dioxide electrodes by hydrothermal re-sintering. Under the premise of not violating the overall technical concept of this invention, conventional hydrothermal reaction re-sintering preparation methods are applicable to this invention.

[0033] Example, but not limitation, of the present invention provides a method for preparing titanium dioxide electrodes by hydrothermal re-sintering:

[0034] The elemental titanium source is cleaned, then subjected to a hydrothermal reaction in an alkaline solution, followed by immersion in an acidic solution and then sintering to obtain the titanium dioxide electrode.

[0035] Optionally, the alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution; the concentration of the alkaline solution is 0.5 mol / L to 3 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0036] Optionally, the temperature of the hydrothermal reaction is 150℃~220℃, such as 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃ or 220℃; the time of the hydrothermal reaction is 5h~24h, such as 5h, 8h, 10h, 12h, 15h, 18h, 20h or 24h.

[0037] Optionally, the acidic solution includes an acid solution, the acid including hydrochloric acid, and the concentration of the acid solution is 0.5 mol / L to 3 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L.

[0038] Optionally, the sintering temperature is 400℃~600℃, for example 400℃, 450℃, 500℃, 550℃ or 600℃.

[0039] Preferably, the gas-solid phase electrocatalytic reaction further includes a counter electrode and an intermediate conductive layer, wherein the intermediate conductive layer is located between the working electrode and the counter electrode.

[0040] It is understood that the intermediate conductive layer in this invention serves to transport the chloride ions removed by the catalytic removal of Cl-VOCs at the working electrode to the counter electrode for recovery.

[0041] Furthermore, this invention does not limit the specific types of materials used for the intermediate conductive layer and the counter electrode. Conventional intermediate conductive layer types that enable chloride ion transport, as well as counter electrode types that do not affect the actual catalytic removal reaction, are all applicable to this invention.

[0042] As an example, but not a limitation, the intermediate conductive layer includes an anion exchange membrane, such as a quaternized polysulfone anion exchange membrane or a polyepoxychlorohydrin (PECH) anion exchange membrane.

[0043] As an example, but not a limitation, the counter electrode includes a nickel foam counter electrode.

[0044] Preferably, the electrode is subjected to water circulation treatment to recover chloride ions after catalysis.

[0045] In this invention, water circulation treatment on the electrode side can effectively recover chloride ions generated after dechlorination and migrate them back into the solution, avoiding the generation of gaseous HCl and chlorine. Without water phase migration and recovery, chloride ions after dechlorination may accumulate on the catalyst surface, leading to catalyst poisoning and affecting its use.

[0046] The specific water circulation system uses water including ultrapure water.

[0047] Preferably, the current density of the gas-solid phase electrocatalytic reaction is 5 mA / cm². 2 ~30mA / cm 2 For example, 5mA / cm 2 10mA / cm 2 15mA / cm 2 20mA / cm 2 25mA / cm 2 Or 30mA / cm 2 wait.

[0048] Preferably, the voltage of the gas-solid phase electrocatalytic reaction is -2V to -5V, such as -2V, -2.5V, -3V, -3.5V, -4V, -4.5V or -5V.

[0049] In this invention, although the introduction of oxygen may lead to a certain decrease in catalytic activity, the effect of oxygen on catalytic activity can be neutralized and offset by adjusting the voltage in the gas-solid phase electrocatalytic reaction process within a relatively high voltage range, especially within the range of -3.5V to -5V, thus ensuring the effective performance of dechlorination. Under the conditions of an anaerobic reaction system, the effect of dechlorination is not significant within a certain voltage range, especially within the range of -2V to -5V, and good dechlorination effect is achieved in both cases.

[0050] Preferably, the reaction temperature of the gas-solid phase electrocatalytic reaction is 20℃~30℃, for example, 20℃, 25℃ or 30℃.

[0051] The gas-solid phase electrocatalytic reaction of the present invention can be realized at room temperature (20℃~30℃), without the need for excessive current density and excessive voltage, and is simple to operate and highly reproducible.

[0052] Preferably, the ambient humidity of the reaction environment in the gas-solid phase electrocatalytic reaction is 0%~80%, for example, 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc.

[0053] The catalytic removal process of this invention is carried out under certain ambient humidity, which helps to ensure the water content of the membrane. The water content is positively correlated with the ion conduction rate. Furthermore, it can be proven that the catalytic removal of this invention has low requirements for the catalytic environment and can be adapted to various application scenarios.

[0054] Preferably, the catalytic removal method includes:

[0055] The reaction gas containing chlorinated volatile organic compounds is passed into a Pd composite titanium dioxide electrode and electrocatalytically removed by gas-solid phase contact. The chloride ions obtained by catalytic removal enter the counter electrode through the intermediate conductive layer and are recovered by water circulation at the counter electrode.

[0056] It should also be noted that the Cl-VOCs in this invention include, but are not limited to, at least one of chlorinated alkanes, chlorinated alkenes, or chlorinated aromatic hydrocarbons; the chlorinated alkanes include dichloromethane, trichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, or 1,2-dichloropropane, etc.; the chlorinated alkenes include vinyl chloride, trichloroethylene, or tetrachloroethylene, etc.; the chlorinated aromatic hydrocarbons include chlorobenzene, dichlorobenzene (including ortho, meta, and para dichlorobenzene), or hexachlorobenzene, etc.

[0057] Furthermore, this invention does not specifically limit the size of the electrodes in the gas-solid phase electrocatalytic reaction process; the size can be adaptively selected and adjusted according to different application scenarios.

[0058] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] To address this issue, this invention employs a gas-solid phase electrocatalytic method for the catalytic removal of Cl-VOCs. Cl-VOCs directly reach the surface of the Pd (palladium) composite titanium dioxide working electrode in gaseous form, bypassing the bottleneck of the gas-liquid mass transfer process and improving the mass transfer efficiency. Furthermore, the Pd catalyst exhibits excellent catalytic activity and can generate a strong reducing agent—moving from H+ at a positive potential... + Hydrogen electrochemically adsorbed in (or H2O) simultaneously activates the C-Cl bond of RCl through adsorption, and then undergoes hydrogenolysis through the reaction of adsorbed Cl-VOCs with Hads. Subsequently, the products are desorbed. By composited with a Pd catalyst on the surface of a titanium dioxide electrode, the two work synergistically. Pd has higher catalytic activity and a more significant catalytic effect on Cl-VOCs. Cl-VOCs are dechlorinated and catalytically removed under the action of the Pd composite titanium dioxide working electrode. The dechlorination effect is excellent, and the removed chlorine is easy to recover, forming an effective resource recovery and avoiding the diffusion of chlorine into the gas phase and the generation of by-products. Furthermore, the catalytic removal method provided by this invention has a simple operation process, can be directly connected to polluted gas for reaction, does not require liquid electrolyte, and has high safety and applicability. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of the catalytic removal method for chlorinated volatile organic compounds provided in a specific embodiment of the present invention. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0064] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0065] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0066] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0067] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0068] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0069] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0070] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0071] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0072] In some specific embodiments, the present invention provides a catalytic removal method for chlorinated volatile organic compounds, such as... Figure 1 The following is stated:

[0073] The reaction gas containing chlorinated volatile organic compounds is passed into a Pd-composite titanium dioxide electrode. Figure 1 At the cathode, electrocatalytic removal is performed using a gas-solid phase contact method. The chloride ions obtained from the catalytic removal pass through an intermediate conductive layer ( Figure 1 The anion exchange membrane in the middle enters the counter electrode ( Figure 1 At the anode end, water circulation is used at the electrode. Figure 1 The water is recycled in a way that allows for water recycling.

[0074] Example 1

[0075] This embodiment provides a catalytic removal method for chlorinated volatile organic compounds. Based on the catalytic removal method provided in the above specific embodiments, the catalytic removal method includes:

[0076] (a) Provide reaction gases: chlorobenzene at a volume concentration of 2000 ppm, O2 at a volume concentration of 4%, nitrogen as the balance gas, and humidity of 0%.

[0077] (b) Pd-loaded titanium dioxide electrode (Pd / TiO2): Titanium fiber paper was sonicated in acetone, ethanol and deionized water for 15 minutes each to remove impurities. A circular Ti fiber paper with a diameter of 3 cm was placed vertically in a Teflon-lined stainless steel autoclave containing 5 mol / L NaOH solution. The autoclave was heated to 180°C and held for 8 hours. Then it was cooled to room temperature, rinsed with deionized water, and then soaked in 1 mol / L HCl solution for 1 hour. Finally, it was sintered in air at 400°C for 2 hours to obtain the TiO2 electrode.

[0078] 100 μL of a solution containing 50 mmol / L Pd(NO3)2 was dropped onto a TiO2 substrate, dried at room temperature, and the deposition was repeated until the Pd loading reached 2 mg / cm³. 2 The final electrode, denoted as Pd / TiO2, was obtained by annealing at 300°C for 4 hours in a tube furnace (carrier gas: volume percentage, 10% H2 and 90% N2).

[0079] (c) Gas-solid phase electrocatalytic device: Pd / TiO2 working electrode, intermediate anion exchange membrane and counter electrode foam nickel electrode separated by anion exchange membrane, with ultrapure water circulating on the counter electrode side.

[0080] At 25℃ and 0% humidity, the reaction gas was introduced into the working electrode side of the Pd / TiO2 at a flow rate of 20 mL / min, allowing direct gas-solid contact with the working electrode, and the current density was 15 mA / cm². 2The applied bias voltage is -4.5V to carry out a gas-solid phase electrocatalytic reaction. Then, the catalytic dechlorination is converted into chloride ions, which are transferred to the counter electrode side through an anion exchange membrane. The chloride ions are then recovered by ultrapure water and returned to the liquid phase system to form HCl for resource recovery.

[0081] Example 2

[0082] This embodiment provides a catalytic removal method for chlorinated volatile organic compounds. Based on the catalytic removal method provided in the above specific embodiments, the catalytic removal method includes:

[0083] (a) Provide reaction gases: chlorobenzene at a volume concentration of 100 ppm, O2 at a volume concentration of 2%, nitrogen as the balance gas, and humidity of 50%.

[0084] (b) Pd-loaded titanium dioxide electrode (Pd / TiO2): Titanium fiber paper was sonicated in acetone, ethanol and deionized water for 15 minutes each to remove impurities. A circular Ti fiber paper with a diameter of 3 cm was placed vertically in a Teflon-lined stainless steel autoclave containing 5 mol / L NaOH solution. The autoclave was heated to 180°C and held for 8 hours. Then it was cooled to room temperature, rinsed with deionized water, and then soaked in 1 mol / L HCl solution for 1 hour. Finally, it was annealed in air at 400°C for 2 hours to obtain the TiO2 electrode.

[0085] 100 μL of a solution containing 50 mmol / L Pd(NO3)2 was dropped onto a TiO2 substrate, dried at room temperature, and the deposition was repeated until the Pd loading reached 1 mg / cm³. 2 The final electrode, denoted as Pd / TiO2, was obtained by annealing at 450°C for 4 hours in a tube furnace (carrier gas: volume percentage, 10% H2 and 90% N2).

[0086] (c) Gas-solid phase electrocatalytic device: Pd / TiO2 working electrode, intermediate anion exchange membrane and counter electrode foam nickel electrode separated by anion exchange membrane, with ultrapure water circulating on the counter electrode side.

[0087] At 25℃ and 50% humidity, the reaction gas was introduced into the working electrode side of the Pd / TiO2 at a flow rate of 50 mL / min, allowing direct gas-solid contact with the working electrode, and the current density was 5 mA / cm². 2 The applied bias voltage is -4.5V to carry out a gas-solid phase electrocatalytic reaction. Then, the catalytic dechlorination is converted into chloride ions, which are transferred to the counter electrode side through an anion exchange membrane. The chloride ions are then recovered by ultrapure water and returned to the liquid phase system to form HCl for resource recovery.

[0088] Example 3

[0089] The difference between this embodiment and Embodiment 1 is that the bias voltage applied in this embodiment during the gas-solid phase electrocatalytic reaction is -3.5V.

[0090] All other conditions remain the same as in Example 1.

[0091] Example 4

[0092] The difference between this embodiment and Embodiment 1 is that the bias voltage applied in the gas-solid phase electrocatalytic reaction process of this embodiment is -2V.

[0093] All other conditions remain the same as in Example 1.

[0094] Example 5

[0095] The difference between this embodiment and Embodiment 1 is that, in the gas-solid phase electrocatalytic reaction process of this embodiment, the volume concentration of oxygen in the reaction gas is 10%.

[0096] All other conditions remain the same as in Example 1.

[0097] The conversion rate and dechlorination recovery rate of chlorobenzene in Examples 1-5 were tested, and the test results are shown in Table 1.

[0098] Table 1

[0099]

[0100] From Table 1, we can obtain:

[0101] The catalytic removal method for chlorinated volatile organic compounds provided by this invention, based on data analysis of Examples 1 and 3-5, shows that when the reaction gas contains oxygen, under a certain oxygen content (≤4%), a relatively high voltage is used in the gas-solid phase electrocatalytic reaction, especially in the range of -3.5V to -5V, where the influence of oxygen on catalytic activity is relatively smaller, reducing the quenching of active hydrogen by oxygen. However, data analysis of Examples 1 and 5 shows that when the oxygen concentration in the reaction gas is relatively higher, exceeding 4%, even a relatively high reaction voltage will affect the amount of active hydrogen to some extent, thus affecting catalytic activity and the chlorobenzene conversion effect.

[0102] Example 6

[0103] The difference between this embodiment and Embodiment 1 is that the reaction gas in this embodiment does not contain oxygen, that is, the oxygen volume concentration is 0%.

[0104] All other conditions remain the same as in Example 1.

[0105] Example 7

[0106] The difference between this embodiment and Embodiment 6 is that the bias voltage applied during the gas-solid phase electrocatalytic reaction in this embodiment is -3.5V.

[0107] All other conditions remain the same as in Example 6.

[0108] Example 8

[0109] The difference between this embodiment and Embodiment 6 is that in this embodiment, the applied bias voltage is -2V during the gas-solid phase electrocatalytic reaction.

[0110] All other conditions remain the same as in Example 6.

[0111] Example 9

[0112] The difference between this embodiment and Embodiment 6 is that the bias voltage applied during the gas-solid phase electrocatalytic reaction in this embodiment is -1V.

[0113] All other conditions remain the same as in Example 6.

[0114] Example 10

[0115] The difference between this embodiment and Embodiment 6 is that the bias voltage applied during the gas-solid phase electrocatalytic reaction in this embodiment is -6V.

[0116] All other conditions remain the same as in Example 6.

[0117] The conversion rate and dechlorination recovery rate of chlorobenzene in Examples 6-10 were obtained by testing, and the test results are shown in Table 2.

[0118] Table 2

[0119]

[0120] From Table 2, we can obtain:

[0121] The catalytic removal method for chlorinated volatile organic compounds provided by this invention, based on data analysis of Examples 1 and 7, shows that catalytic removal under anoxic conditions also exhibits excellent dechlorination effects. However, data analysis of Examples 1 and 6-10 shows that in anoxic conditions, within a certain voltage range, especially -2V to -5V, the catalytic activity does not decrease. Beyond this range, the yield and selectivity of active hydrogen are affected to some extent, thereby reducing the interaction between chlorinated free radicals and chlorinated VOCs.

[0122] Example 11

[0123] The difference between this embodiment and Embodiment 1 is that in this embodiment, the Pd loading is 3 mg / cm³. 2 .

[0124] All other conditions remain the same as in Example 1.

[0125] Example 12

[0126] The difference between this embodiment and Embodiment 1 is that the preparation method of the titanium dioxide electrode in this embodiment includes:

[0127] Titanium fiber paper was ultrasonically treated in acetone, ethanol, and deionized water for 15 minutes each to remove impurities, and then sintered directly in an air atmosphere in a muffle furnace at a sintering temperature of 500°C for 3 hours to obtain the titanium dioxide electrode.

[0128] All other conditions remain the same as in Example 1.

[0129] Comparative Example 1

[0130] The difference between this comparative example and Example 1 is that the working electrode in this comparative example is Pd / Ti, and in the preparation method, the cleaned titanium fiber paper is directly loaded with palladium nitrate.

[0131] All other conditions remain the same as in Example 1.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is that the working electrode of this comparative example is a platinum (Pt) supported titanium dioxide electrode (Pt / TiO2), and in the preparation method, palladium nitrate is replaced with platinum nitrate.

[0134] All other conditions remain the same as in Example 1.

[0135] Comparative Example 3

[0136] The difference between this comparative example and Example 6 is that the working electrode of this comparative example is Pd / Ti, and in the preparation method, the cleaned titanium fiber paper is directly loaded with palladium nitrate.

[0137] All other conditions remain the same as in Example 6.

[0138] Comparative Example 4

[0139] The difference between this comparative example and Example 6 is that the working electrode of this comparative example is a platinum (Pt) supported titanium dioxide electrode (Pt / TiO2), and in the preparation method, palladium nitrate is replaced with platinum nitrate.

[0140] All other conditions remain the same as in Example 6.

[0141] Comparative Example 5

[0142] This comparative example provides a catalytic removal method for chlorinated volatile organic compounds, wherein the catalytic removal method involves a solution electrocatalytic reaction:

[0143] The reaction apparatus consists of a Pd / TiO2 working electrode, a Pt counter electrode, and an electrolyte of Na2SO4 solution. Both the working electrode and the counter electrode are located in the solution.

[0144] Catalytic reaction: At 25℃, chlorobenzene was introduced into the solution via aeration at a flow rate of 50 mL / min to carry out the electrocatalytic reaction, with a current density of 5 mA / cm². 2 The applied bias voltage is -4.5V.

[0145] The conversion rate and dechlorination recovery rate of chlorobenzene in Examples 11-12 and Comparative Examples 1-5 were tested, and the test results are shown in Table 3.

[0146] Table 3

[0147]

[0148] From Table 3, we can obtain:

[0149] Data analysis of Examples 1 and 11 showed that the Pd (palladium) loading in the working electrode was 0.1 mg / cm³. 2 ~2mg / cm 2 This can prevent excessive aggregation of Pd, achieve low-coordination uniform loading, and avoid excessive loading affecting Pd aggregation and reducing the selectivity of active hydrogen.

[0150] Data analysis of Examples 1 and 12 shows that, in the working electrode of the present invention, the titanium dioxide electrode prepared by hydrothermal re-sintering method is more conducive to the dispersion of Pd and the formation of small Pd particles.

[0151] Analysis of the data from Example 1 and Comparative Examples 1-2, Example 6 and Comparative Examples 3-4, and Comparative Example 5 shows that in the catalytic removal method for chlorinated volatile organic compounds provided by the present invention, the gas-solid phase electrocatalysis method and the specific combination of working electrodes must work together to achieve the catalytic removal of chlorinated volatile organic compounds at room temperature and to achieve a high chlorine recovery rate.

[0152] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A catalytic removal method for chlorinated volatile organic compounds, characterized in that, The catalytic removal method includes: The reaction gases are removed by gas-solid phase electrocatalytic reaction; The reaction gas includes chlorinated volatile organic compounds, and the working electrode of the gas-solid phase electrocatalytic reaction includes a Pd composite titanium dioxide electrode.

2. The catalytic removal method according to claim 1, characterized in that, The volume concentration of chlorinated volatile organic compounds in the reaction gas is 10 ppm to 5000 ppm.

3. The catalytic removal method according to claim 1 or 2, characterized in that, The reaction gas also includes oxygen and a balance gas, the balance gas including a protective gas; Preferably, the volume concentration of oxygen in the reactant gas is ≤4%.

4. The catalytic removal method according to claim 1 or 2, characterized in that, The flow rate of the reaction gas is 15 mL / min to 50 mL / min.

5. The catalytic removal method according to claim 1, characterized in that, In the Pd-composite titanium dioxide electrode, Pd is loaded in the titanium dioxide electrode at a loading rate of 0.1 mg / cm³. 2 ~2mg / cm 2 .

6. The catalytic removal method according to claim 1 or 5, characterized in that, The preparation method of the Pd composite titanium dioxide electrode includes: Pd salt was mixed with titanium dioxide electrode in liquid phase, deposited and loaded, and then annealed in a reducing atmosphere to obtain the Pd composite titanium dioxide electrode. Preferably, the preparation method of the titanium dioxide electrode includes a hydrothermal re-sintering method; Preferably, the annealing temperature is 200℃~450℃.

7. The catalytic removal method according to claim 1, characterized in that, The gas-solid phase electrocatalytic reaction also includes a counter electrode and an intermediate conductive layer, wherein the intermediate conductive layer is located between the working electrode and the counter electrode.

8. The catalytic removal method according to claim 7, characterized in that, The electrode is subjected to water circulation treatment to recover chloride ions after catalysis.

9. The catalytic removal method according to claim 1, characterized in that, The current density of the gas-solid phase electrocatalytic reaction is 5 mA / cm². 2 ~30mA / cm 2 Voltage is -2V to -5V, temperature is 20℃ to 30℃; Preferably, the ambient humidity of the reaction environment in the gas-solid phase electrocatalytic reaction is 0%~80%.

10. The catalytic removal method for chlorinated volatile organic compounds according to claim 1, characterized in that, The catalytic removal method includes: The reaction gas containing chlorinated volatile organic compounds is passed into a Pd composite titanium dioxide electrode and electrocatalytically removed by gas-solid phase contact. The chloride ions obtained by catalytic removal enter the counter electrode through the intermediate conductive layer and are recovered by water circulation at the counter electrode.

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