CN107096380B - Method and device for treating formaldehyde in air by catalytic oxidation - Google Patents

Abstract

The invention discloses a catalystA method and a device for treating formaldehyde in air by chemical oxidation. The method uses the integral carbon material as a carrier of the formaldehyde oxidation catalyst, and uses the excellent Joule thermal property, mechanical property and electrothermal conversion efficiency of the catalyst, and uses the catalyst as a pure resistance heating element to directly heat the catalyst in an electrothermal mode, so that unnecessary energy consumption is not caused by using other heating elements in the reactor. The method combines Ag/Co ₃ O ₄ The catalyst is loaded on an integral porous carbon material, then the integral carbon-based catalyst is placed in a reactor, and both ends of the catalyst are connected with metal electrodes and applied with voltage, so that the temperature of the catalyst is raised to 20-300 ℃; when the air containing 10-500ppm formaldehyde is used in 15000-90000ml h ^‑1 g ^‑1 The conversion rate of formaldehyde can reach more than 95% when the space velocity of the catalyst flows through the reactor. The method has the advantages of good formaldehyde catalytic oxidation effect, high energy utilization efficiency, small pressure drop of the reactor and simple and convenient operation.

Description

Method and device for catalytic oxidation treatment of formaldehyde in air

technical field

The invention belongs to the field of environmental protection and energy saving, and in particular relates to a method and a device for catalytic oxidation treatment of formaldehyde in air.

Background technique

Indoor harmful volatile organic compounds (Volatile Organic Compounds, VOC) refer to volatile hydrocarbons and their derivatives. Formaldehyde is the most representative pollutant in VOC. The main source is various glues and various adhesives brought by the chemical industry. Living in an environment containing formaldehyde for a long time is harmful to human eyes, cardiovascular and cerebrovascular, Very harmful to the respiratory system and nervous system. Formaldehyde has become one of the ubiquitous and serious indoor pollutants in my country due to its wide sources, great harm and long duration, and it is imminent to control formaldehyde. At present, the commonly used formaldehyde treatment methods mainly include adsorption method, biological method, catalytic oxidation method, thermal oxidation method, plasma method and so on. For VOCs that do not need to be recovered, such as formaldehyde, thermal oxidation and catalytic oxidation are more thorough treatment methods. Among them, the catalytic oxidation of formaldehyde is the method with the lowest cost and the easiest way to be widely used, and has a good application prospect in industrial formaldehyde treatment.

China stipulates that the maximum allowable concentration of formaldehyde in indoor air is 0.08mg/m ³ . In order to ensure a high conversion rate even in a low-concentration formaldehyde environment, higher requirements are placed on the activity of the catalyst. Catalysts for treating formaldehyde can be roughly divided into two categories: one is noble metal catalysts, such as Pt, Au, Pd, Rh, etc.; the other is transition metal oxides, such as MnO ₂ , CeO ₂ , Co ₃ O ₄ , etc. According to recent literature reports, catalysts with complex active components—such as the combination of noble metals and transition metal oxides, the combination of multiple transition metals, etc., can improve catalytic activity. The studies of Wu Jiang (Environ.Sci.Technol.2016, 50, 5370-5378) et al. and Tan Hongyi (Environ.Sci.Technol.2015, 49, 8675-8682) et al. have confirmed this point of view. Patent CN104353465 proposes a catalyst with a core-shell structure of Co ₃ O ₄ /CeO ₂ , which has good catalytic oxidation activity for formaldehyde at room temperature. Patent CN105013491 reports a NiCo ₂ O ₄ nanosheet catalyst prepared from nickel salt, cobalt salt, and surfactant, which has the advantages of high efficiency and low cost. Patent CN104722299 uses CeO ₂ nano cubes as the carrier, loaded with nano metal Pd particles as the active component, which can convert most or all formaldehyde into carbon dioxide and water at room temperature, without formic acid, carbon monoxide and other by-products.

In practical applications, most gas-solid phase reaction devices require the introduction of heating elements to heat the reaction system to reach the required temperature for the reaction. The invention uses electric energy as the energy input mode, and utilizes the Joule heat property of the monolithic carbon material to heat the catalyst. In the reaction device system, the monolithic catalyst loaded with active components acts as a pure resistance heating element, which efficiently converts the electric energy input by the DC stabilized power supply through both ends into heat energy, so that the monolithic catalyst itself can achieve partial reaction. desired temperature. While achieving efficient energy utilization, unnecessary energy consumption caused by introducing additional heating elements into the system is avoided.

Contents of the invention

In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method and device for catalytic oxidation treatment of formaldehyde in the air, which can be used to remove formaldehyde in indoor air or factory exhaust with high efficiency and low energy consumption.

The present invention adopts the following technical solutions.

A method for catalytic oxidation treatment of formaldehyde in air, comprising the following steps:

The monolithic carbon-based catalyst loaded with active components is placed in the reactor, the two ends of the monolithic carbon-based catalyst are clamped by metal electrodes, and the positive and negative electrodes of the power supply are connected with wires, and then the monolithic carbon-based catalyst is The catalyst inputs electric energy, using the Joule heat property of the monolithic carbon-based catalyst to make the monolithic carbon-based catalyst reach the required reaction temperature; A catalytic oxidation reaction takes place.

Preferably, the carrier of the monolithic carbon-based catalyst (ie monolithic carbon material) is monolithic mesoporous carbon material, monolithic three-dimensional graphene, monolithic carbon-based foam material and other monolithic carbon materials.

Further preferably, the preparation method of the monolithic mesoporous carbon material is: mix 3.0g resorcinol and 1.25g F127, add 9ml water and 11.4ml absolute ethanol, stir and dissolve, add 0.078g 1,6-hexanedi Amine, continue to stir for 30 minutes, add 4.45g formaldehyde solution (37%) until the solution is milky white, pour it into a mold and put it in a 90°C oven to cure for 4h, take it out and dry it, and heat it up to 800°C at a rate of 5°C/min under Ar atmosphere ℃ for 2h to prepare monolithic mesoporous carbon materials.

Further preferably, the preparation method of monolithic three-dimensional graphene is: the 10mg/ml graphene oxide solution that Hummers method is made is mixed with the polyvinyl alcohol of 5wt%, sucrose ultrasonically to obtain uniform suspension, then with toluene 1: 1 Mix to form a stable emulsion. Pour the emulsion into a mold, freeze it at -70°C and dry it with a lyophilizer, then keep it at 900°C for 2 hours under the atmosphere of 95% Ar/5% H ₂ for thermal reduction to obtain monolithic three-dimensional graphene.

Further preferably, the preparation method of the integral carbon-based foam material is as follows: the melamine foam material cut into a regular shape is directly carbonized at 800° C. for 2 hours under an Ar atmosphere to obtain the integral carbon-based foam material.

Preferably, the active component is one or both of Ag and Co.

Preferably, the preparation of the monolithic carbon-based catalyst comprises the following steps: placing the carrier of the monolithic carbon-based catalyst in an impregnating solution containing Ag ⁺ and Co ²⁺ for 1-20 h, taking it out and drying it in vacuum, Keeping at 300-800° C. for 1-8 hours in an inert atmosphere to obtain a monolithic carbon-based catalyst.

Further preferably, the impregnation solution is an aqueous solution of silver salt and cobalt salt, and the cobalt salt is at least one of cobalt nitrate, cobalt chloride and cobalt sulfate; the silver salt is silver nitrate.

Further preferably, the concentration of Ag ⁺ in the impregnating solution is 0-10wt%, and the concentration of Co2 ⁺ is 0-10wt%; the mass ratio of the carrier of the monolithic carbon-based catalyst to the impregnating solution is 1:(10 ~200).

Preferably, the metal electrode is a metal sheet electrode such as copper foam, nickel foam, or copper sheet.

Preferably, when the electric energy is input, the input voltage is 0-10V, and the core temperature of the monolithic carbon-based catalyst is 20-300°C.

Preferably, the formaldehyde content in the air is 10-500ppm, the gas flow rate is 50-300Ncm ³ /min, and the space velocity is 15000-90000ml h ^-1 g ^-1 .

A device for realizing the method for catalytic oxidation treatment of formaldehyde in air as described above, the device includes an integral carbon-based catalyst, a metal electrode, a reaction tube, a power supply, a temperature display, a thermocouple, a wire, an air inlet pipe, an air outlet pipe and a sealing ferrule; the integral carbon-based catalyst is placed in the reaction tube, the metal electrode is clamped at both ends of the integral carbon-based catalyst, and the two ends of the metal electrode are connected to the positive and negative electrodes of the power supply through wires; the thermocouple measurement end is inserted into the integral carbon-based catalyst At the center position, the other end of the thermocouple is connected to the temperature display; one end of the reaction tube is connected to the inlet tube, and the other end is connected to the outlet tube; the reaction tube, the inlet tube and the outlet tube are fixed by a sealed ferrule.

Preferably, the reactor is a cylindrical glass reaction tube.

Compared with the prior art, the present invention has the following advantages:

(1) As the carrier of the catalyst, the monolithic carbon material of the present invention can not only regulate the size of the monolithic catalyst through the size of the mold, but also the prepared catalyst has good mechanical strength, high specific surface area, and good gas permeability. The bed pressure is reduced, which is beneficial to the loading of the active components and the contact between the active components and the reactants.

(2) The present invention adopts an energy input method based on the Joule heat property of the monolithic carbon material, which is different from the way in which the traditional fixed bed reactor heats the entire reactor to make the catalyst reach the preset reaction temperature. The Joule heat property of the material, as a pure resistance heating element, converts the input electric energy into heat energy efficiently, so that the catalyst itself is heated to the temperature required for the reaction without heating other parts of the reactor that do not participate in the reaction, realizing Efficient use of energy.

Description of drawings

FIG. 1 is an SEM image of the monolithic mesoporous carbon catalyst in Example 12.

FIG. 2 is a TEM image of the monolithic mesoporous carbon catalyst in Example 12.

3 is an X-ray diffraction pattern of the monolithic mesoporous carbon catalyst in Example 12.

Fig. 4a is a graph showing the relationship between formaldehyde conversion and core temperature of monolithic mesoporous carbon catalysts with different loads in Examples 9-14.

Fig. 4b is a graph showing the relationship between formaldehyde conversion and input power density of monolithic mesoporous carbon catalysts with different loads in Examples 9-14.

Fig. 5 is a schematic diagram of a device for catalytic oxidation treatment of formaldehyde in air according to the present invention.

FIG. 6 is a physical diagram of the monolithic mesoporous carbon catalyst in Example 12.

Detailed ways

The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings and examples, but the present invention is not limited to the following examples.

The formaldehyde conversion rate in the following examples is measured by phenol reagent spectrophotometry (National Standard No. GB/T18204.2-2014).

The preparation method of monolithic mesoporous carbon material: mix 3.0g resorcinol and 1.25g F127 (poloxamer), add 9ml deionized water and 11.4ml absolute ethanol, stir to dissolve and add 0.078g 1,6 - Hexamethylenediamine, after continuing to stir for 30min, add 4.45g formaldehyde solution (concentration is 37wt%) until the solution is milky white, pour it into a mold and put it in a 90°C oven to solidify for 4h, then take it out and dry it. The temperature was raised to 800°C for 2 hours to obtain monolithic mesoporous carbon materials.

The preparation method of monolithic three-dimensional graphene: 5ml of 10mg/ml graphene oxide solution prepared by Hummers method is mixed with 2.5mg polyvinyl alcohol and 2.5mg sucrose ultrasonically to obtain a uniform suspension, and then with toluene in a volume ratio of 1: 1 Mix to form a stable emulsion. Pour the emulsion into a mold, freeze it at -70°C and dry it with a lyophilizer, then keep it at 900°C for 2 hours under an atmosphere of 95vol%Ar/5vol% _H2 for thermal reduction to obtain monolithic three-dimensional graphene.

The preparation method of the integral carbon-based foam material: the melamine foam material cut into a regular shape is directly carbonized at 800° C. for 2 hours under an Ar atmosphere to obtain the integral carbon-based foam material.

The reaction device in the following examples uses the device for catalytic oxidation treatment of formaldehyde in air according to the present invention, and the schematic diagram is shown in FIG. 5 . The device includes an integral carbon-based catalyst 1, a metal electrode 2, a reaction tube 3, a power supply 4, a temperature display 5, a thermocouple 6, a wire 7, an air inlet pipe 8, an air outlet pipe 9 and a sealing ferrule 10; The base catalyst is placed in the reaction tube, and the metal electrodes are sandwiched between the two ends of the integral carbon-based catalyst. The two ends of the metal electrode are connected to the positive and negative electrodes of the power supply through wires; It is connected with the temperature display; one end of the reaction tube is connected with the inlet tube, and the other end is connected with the outlet tube; the reaction tube, the inlet tube and the outlet tube are fixed by a sealed ferrule.

The working process of the device is as follows: the integral carbon-based catalyst is placed in the reaction tube, the two ends of the integral carbon-based catalyst are clamped by metal electrodes, and the two ends of the metal electrodes are connected to the positive and negative electrodes of the power supply with wires, and the sealed ferrule Fix the reaction tube, inlet pipe, and outlet pipe, then turn on the power, input electric energy to the monolithic carbon-based catalyst, use the Joule heat property of the monolithic carbon-based catalyst to make the monolithic carbon-based catalyst reach the required reaction temperature, when the device After reaching a constant temperature and steady state, the catalytic oxidation reaction can be maintained at a specific temperature without adjusting the power supply voltage; the temperature of the monolithic carbon-based catalyst is measured by a thermocouple inserted into the center of the monolithic carbon-based catalyst, and displayed on the temperature On the display, adjusting the voltage of the power supply can adjust the temperature of the carbon-based catalyst; the air containing formaldehyde is introduced into the intake pipe, and the formaldehyde undergoes a catalytic oxidation reaction in the process of passing through the heated integral carbon-based catalyst, and the reacted gas passes through The outlet pipe is discharged.

Examples 1-8

A monolithic mesoporous carbon material with a diameter of 15 mm and a thickness of 10 mm was placed in a beaker containing 30 ml of AgNO ₃ solution, and then vacuum treatment was performed to discharge the gas in the channel. The mass ratio of the monolithic mesoporous carbon material to the impregnating solution is 1:150, the solvent is deionized water, the Ag ⁺ content in the solution is shown in Table 1, and then placed in a shaker at a speed of 200rpm for 10 hours, and the vacuum After drying, the temperature was raised to 450°C at a rate of 5°C/min and kept for 5h under an Ar atmosphere to prepare a monolithic mesoporous carbon catalyst. The obtained monolithic mesoporous carbon catalyst was put into a cylindrical glass reaction tube with a diameter of 15 mm, and the two ends were pressed tightly with foam copper disc electrodes, and connected to the positive and negative electrodes of a DC stabilized voltage power supply. The core position temperature of the monolithic mesoporous carbon catalyst is 90°C, the reaction gas is a mixed gas containing 100ppm formaldehyde in air, the gas flow rate is 100Ncm ³ /min, and the space velocity is 30000ml h ^-1 g ^-1 , the conversion rate of formaldehyde is shown in the table 1.

Table 1

It can be seen from Table 1 that the formaldehyde conversion first increases with the increase of Ag ⁺ ion concentration and Ag loading, and then tends to be stable without significant change. When the concentration of Ag ⁺ ions was 2.5wt%, the conversion of formaldehyde was the highest.

Examples 9-16

Place the monolithic mesoporous carbon material in a beaker filled with 30ml AgNO ₃ /Co(NO ₃ ) ₂ impregnating solution, the solvent is deionized water, the concentration of Ag ⁺ and Co ²⁺ in the solution is the same as the obtained monolithic mesoporous carbon The conversion rate of formaldehyde of the catalyst at 90° C. is shown in Table 2, and the other conditions are consistent with those in Examples 1-8.

Table 2

It can be seen from Table 2 that the introduction of Co ²⁺ in the impregnation solution changed the prepared catalyst from a single Ag active component to an Ag/Co ₃ O ₄ two-component catalyst, which greatly improved the catalytic oxidation activity of formaldehyde. The sample in Example 12 showed the best activity, and its further characterization is shown in Figures 1-3. From the SEM image of the monolithic mesoporous carbon catalyst in Figure 1, it can be seen that it has a macroporous fluffy structure, and from the TEM image in Figure 2, the uniform distribution of mesoporous and catalyst particles can be observed. The XRD images of Fig. 3 further illustrate the presence of active components Ag _{and Co3O4} . Fig. 6 is a physical picture of the monolithic catalyst, and it can be observed that it has a regular macroscopic geometric structure and a pore structure visible to the naked eye on the surface. The regular macroscopic geometric structure provides it with good mechanical properties, and the hierarchical pore structure composed of macroscopic channels, macropores and mesopores provides the monolithic catalyst with a large specific surface area (565m ² /g), relatively Good gas permeability and low bed pressure drop. Figure 4a and Figure 4b show the corresponding relation curves of formaldehyde conversion rate, core temperature and input power density of monolithic mesoporous carbon catalysts with different loads in Examples 9-14.

Examples 17,18

The monolithic mesoporous carbon materials with three different carbon supports listed in Table 3 were placed in a beaker filled with 30ml AgNO ₃ /Co(NO ₃ ) ₂ impregnation solution, and then vacuum treatment was performed to discharge the gas in the channels. The monolithic carbon material is cylindrical, with a diameter of 15 mm and a thickness of 10 mm. The mass ratio of the impregnated solution to the impregnated solution is 1:150. The Ag ⁺ concentration in the impregnated solution is 1wt%, and the Co2 ⁺ concentration is 1wt%. The bed was impregnated at a speed of 200 rpm for 10 h, taken out for vacuum drying, and then heated to 450 °C at a rate of 5 °C/min for 5 h under an Ar atmosphere to prepare a monolithic carbon-based catalyst. The obtained three monolithic carbon-based catalysts were put into cylindrical glass reaction tubes with an inner diameter of 15 mm, and the two ends were pressed tightly with foam copper disc electrodes, and connected to the positive and negative electrodes of a DC stabilized voltage power supply. Adjust the input electric power so that the core temperature of the integral catalyst is 90°C, the reaction gas is a mixed gas containing 100ppm formaldehyde in air, the gas flow rate is 100 sccm, and the space velocity is 30000ml h ^-1 g ^-1 . The monolithic carbon materials and corresponding formaldehyde conversion rates of different carbon supports are shown in Table 3.

table 3

Examples 19-28

The monolithic mesoporous carbon material was placed in a beaker filled with AgNO ₃ /Co(NO ₃ ) ₂ impregnation solution, and then vacuum treatment was performed to discharge the gas in the pores. The mass ratio of the monolithic mesoporous carbon material to the impregnating liquid is 1:10-200. The concentration of Ag ⁺ in the impregnation solution is 1wt%, and the concentration of Co ²⁺ is 1wt%. The bed rotation speed and the formaldehyde conversion rate corresponding to the prepared catalyst are shown in Table 4, and the rest of the conditions are consistent with Example 1.

Table 4

Examples 29-33

The monolithic mesoporous carbon material was impregnated, taken out and vacuum-dried, then heated to 300-800°C at a rate of 5°C/min under Ar atmosphere and kept for 1-8 hours to prepare the monolithic mesoporous carbon-based catalyst. The different annealing temperatures and times of the catalyst and the corresponding formaldehyde conversion are shown in Table 5, and other conditions are consistent with Example 1.

table 5

Examples 34-40

Put the monolithic carbon-based catalyst prepared in Example 11 into a cylindrical glass reaction tube with a diameter of 15 mm, press the two ends with metal disc electrodes, and connect them to the positive and negative poles of the power supply. The input voltage is 0-10V, the core position temperature of the integral catalyst is 20-300°C, the reaction gas is a mixed gas containing 100ppm formaldehyde in the air, the gas flow rate is 100Ncm ³ /min, and the space velocity is 30000Ncm ³ h ^-1 g ^-1 . Table 6 shows the corresponding formaldehyde conversion rates for different metal electrodes, input voltages, and catalyst core temperatures.

Table 6

Examples 41-47

Put the monolithic carbon-based catalyst prepared in Example 12 into a cylindrical glass reaction tube with a diameter of 15 mm, press the two ends tightly with a foam copper disk electrode, and connect with the positive and negative poles of the power supply, and the input voltage 2.81V, the core temperature of the integral catalyst is 90°C, the reaction gas is a mixed gas containing 10-500ppm formaldehyde in the air, the gas flow rate is 50-300Ncm ³ /min, and the space velocity is 15-90L h ^-1 g ^-1 . The different formaldehyde concentrations, gas flow rates and space velocities in the mixed gas and the corresponding formaldehyde conversion rates are shown in Table 7.

Table 7

Example 48

A comparative experiment between the device of the present invention for catalytic oxidation treatment of formaldehyde in air and the traditional heating reaction device. The comparative experimental procedure using the traditional heating mode is similar to that of Example 12, the difference is that instead of inputting energy through a DC stabilized power supply, the reaction device is heated by an electric heating belt wound on the outer wall of the reaction tube, so that the catalyst bed The center of the layer reaches 90°C. Other conditions are consistent with Example 12.

Table 8

It can be seen from Table 8 that the conversion rate of formaldehyde in the reaction device of the present invention is slightly higher than that of the traditional heating method at the same reaction temperature, but the energy consumption of the present invention is greatly lower than that of the traditional heating reaction device.

The above-mentioned embodiments are only examples for clearly illustrating the present invention, rather than fully limiting the implementation. Those of ordinary skill in the art can also make other changes in different forms on the basis of the above description. It is impossible and unnecessary to give examples for all implementation modes here, but the obvious changes derived from this are still within the scope of the present invention. within the scope of protection.

Claims (8)

1. A method for treating formaldehyde in air by catalytic oxidation, which is characterized by comprising the following steps:

placing an integral carbon-based catalyst (1) loaded with an active component in a reaction tube (3), clamping two ends of the integral carbon-based catalyst by using metal electrodes (2), connecting the two ends of the integral carbon-based catalyst with the positive electrode and the negative electrode of a power supply (4) by using a lead (7), inputting electric energy into the integral carbon-based catalyst, and enabling the integral carbon-based catalyst to reach a required reaction temperature by utilizing the Joule heat property of the integral carbon-based catalyst; introducing air containing formaldehyde into the reactor, carrying out catalytic oxidation reaction on the formaldehyde in the process of passing through the heated integral carbon-based catalyst, wherein the core temperature of the integral carbon-based catalyst is 90-300 ℃, the carrier of the integral carbon-based catalyst is an integral mesoporous carbon material,

the preparation method of the integral mesoporous carbon material comprises the following steps:

mixing resorcinol, polypropylene glycol and addition polymer of ethylene oxide, adding water and ethanol, stirring for dissolving, adding 1, 6-hexamethylenediamine, continuously stirring, adding formaldehyde solution until the solution is milky white, solidifying, taking out for drying, and heating to obtain the integral mesoporous carbon material.

2. The method for treating formaldehyde in air by catalytic oxidation according to claim 1, wherein the active component is one or both of Ag and Co.

3. The method for catalytic oxidation treatment of formaldehyde in air according to claim 1, characterized in that the preparation of the monolithic carbon-based catalyst comprises the following steps: placing a carrier of an integrated carbon-based catalyst in a catalyst containing Ag ⁺ And Co ²⁺ Soaking in the soaking solution for 1-20h, taking out, vacuum drying, and maintaining at 300-800 ℃ for 1-8h in inert atmosphere to obtain the monolithic carbon-based catalyst.

4. The method for treating formaldehyde in air by catalytic oxidation according to claim 3, wherein the impregnating solution is an aqueous solution of silver salt and cobalt salt, and the cobalt salt is one or more of cobalt nitrate, cobalt chloride and cobalt sulfate; the silver salt is silver nitrate.

5. A method for treating formaldehyde in air by catalytic oxidation according to claim 3, characterized in that Ag in the impregnation liquid ⁺ The concentration of (C) is 0-10wt%, co ²⁺ The concentration of (2) is 0-10wt%; the mass ratio of the carrier of the integral carbon-based catalyst to the impregnating solution is 1 (10-200).

6. The method for treating formaldehyde in air by catalytic oxidation according to claim 1, wherein the metal electrode is copper foam, nickel foam or copper sheet.

7. The method for catalytic oxidation treatment of formaldehyde in air according to claim 1, wherein the input voltage is 0-10V when the electric energy is input.

8. The method for catalytic oxidation treatment of formaldehyde in air according to any one of claims 1 to 7, characterized in that the formaldehyde content in the air is 10 to 500ppm and the gas flow rate is 50 to 300Ncm ³ Per minute, space velocity of 15000-90000ml h ^-1 g ^-1 。

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