Catalyst for efficiently purifying refractory VOCs (Volatile Organic Compounds) as well as preparation method and application of catalyst

Abstract

The invention belongs to the technical field of waste gas treatment, and discloses a catalyst for efficiently purifying refractory VOCs (Volatile Organic Compounds) as well as a preparation method and application thereof. According to the catalyst, a stable spinel structure is constructed through a Cu-Mn double-metal synergistic effect, the T50 and T90 of the catalyst are 232 DEG C and 245 DEG C respectively under the conditions that the air speed of the catalyst is 60000 mL. G <-1 >. H <-1 > and 300 ppm m-xylene treatment is carried out, the T50 and T90 of the catalyst are lower than those of catalysts of the same type mentioned by published results at present, the conversion rate of 100% is kept at 250 DEG C for 48 hours, and the conversion rate of the catalyst is higher than that of the catalyst of the same type mentioned by the published results. Excellent low-temperature activity and long-term stability are shown. Compared with the prior art, the catalyst provided by the invention effectively solves the key problems of insufficient activity and poor stability of a pure Mn3O4 catalyst while maintaining the advantage of low cost. The preparation method is simple in process, low in cost and suitable for industrial production, and an effective solution is provided for treatment of degradation-resistant VOCs.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste gas treatment, and specifically relates to a catalyst for efficiently purifying difficult-to-treat VOCs, and a preparation method and application thereof. Background Art

[0002] With the development of industrialization, the emission of large amounts of volatile organic compounds (VOCs) has aroused widespread concern about environmental and health issues. Benzene series (represented by benzene, toluene, and xylene (BTX)) is an important class of anthropogenic volatile organic compounds (AVOCs). As an important industrial solvent, xylene is widely used in industrial solvents such as coatings, inks, and resins due to its excellent solubility. It is also a key synthetic raw material for the manufacture of medicines and pesticides and an important intermediate for high-value-added chemical products. However, as an organic substance, its volatile physical properties lead to significant emission risks throughout its life cycle from production, storage, and transportation to process operations and terminal use. This is especially true in the typical process links involving heating and open operations such as ink mixing and drying, paint spraying, and rubber vulcanization in the printing industry. Among the isomers of xylene, xylene has a high ozone generation potential (OFP) and secondary organic aerosol generation potential (SOAFP), which has a significant impact on regional PM. 2.5 The production of m-xylene significantly contributes to the generation of oxygen and oxygen, which will have a significant impact on regional air quality. Therefore, precise and efficient control of m-xylene is crucial for improving the regional environment and the quality of human life. The molecular structure of m-xylene presents a technical bottleneck for efficient and energy-efficient catalytic oxidation. The addition of methyl groups enhances conjugation with the benzene ring and produces significant steric hindrance. This requires a higher energy input for the catalytic oxidation of m-xylene to occur.

[0003] Catalytic oxidation is an excellent method to reduce energy input, but when faced with difficult-to-degrade VOCs, it is still necessary to increase the energy input. Therefore, the development of catalysts for difficult-to-degrade VOCs is of great significance for saving energy. Although the current precious metal catalysts have excellent activity, they are expensive and easily poisoned. Mn3O4 spinel catalyst is a typical transition metal oxide catalyst (CN118956444A), which has a variable Mn valence and oxygen utilization capacity. It is a potential catalyst in the catalytic oxidation process, but its performance in degrading xylene still has huge development potential, but in the actual treatment process, the catalytic ability still needs to be improved. Therefore, the development of a new Mn-based spinel catalyst with high catalytic activity, excellent stability and low cost is a key breakthrough point in solving the practical problems of difficult-to-degrade VOCs treatment. Summary of the Invention

[0004] In view of the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a highly efficient catalyst for purifying difficult-to-treat VOCs, as well as its preparation method and application. By constructing a Cu-Mn bimetallic synergistic system, a highly efficient catalyst with a spinel structure was successfully developed. While maintaining the low cost advantage, it effectively solves the key issue of insufficient activity of pure Mn3O4 catalysts, and the prepared catalyst has excellent stability. The preparation method of the present invention is simple, low-cost, suitable for industrial production, and provides an effective solution for the treatment of difficult-to-treat VOCs.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a highly efficient catalyst for purifying difficult-to-treat VOCs, as well as its preparation method and application. The catalyst is a bimetallic oxide with a spinel structure, wherein the bimetallic elements are copper and manganese. The prepared catalyst is designated CuMn2O4. The catalyst has a predominantly mesoporous structure and is a stacked nanoparticle structure.

[0007] The catalyst of the present invention is 60000mL·g -1· h -1 Under the treatment conditions of space velocity and concentration of 300ppm of meta-xylene, the temperatures at which the conversion rates reached 50% and 90% were 234°C and 246°C respectively, and the conversion rate was maintained at 100% at 250°C for 48 hours.

[0008] A method for preparing a catalyst for efficiently purifying difficult-to-treat VOCs comprises the following steps:

[0009] (1) Dissolve Cu(NO3)2·3H2O and Mn(NO3)2 in deionized water at a molar ratio of Cu:Mn=1:(1.8-2.2) to form a homogeneous solution;

[0010] (2) Under magnetic stirring, the homogeneous solution is slowly added dropwise to the alkaline solution and stirred for 3-4 hours to allow the metal salt to fully precipitate;

[0011] (3) The precipitate is repeatedly washed and centrifuged until it becomes neutral, dried, ground, and calcined to obtain a CuMn2O4 catalyst.

[0012] Furthermore, in step (1), the Mn(NO3)2 is an aqueous solution with a mass percentage concentration of 50%, and is dispersed in 30-40 mL of deionized water to form a homogeneous solution, and the Cu(NO3)2·3H2O is a 0.25-0.30 mol / L solution prepared by using high-grade pure Cu(NO3)2·3H2O.

[0013] Furthermore, in step (2), the alkaline solution is a NaOH solution, and its amount is as follows in molar ratio: n(OH - ):n(Cu 2+ +Mn 2+ )=(2.5-3.0):1 stoichiometric ratio.

[0014] Furthermore, in step (2), the dropwise addition is controlled to be dropwise addition so that the metal salt is fully precipitated;

[0015] Furthermore, in step (3), the drying condition is drying at 70-80°C for more than 12 hours;

[0016] Furthermore, in step (3), the calcination rate is 3-5°C / min, the temperature is raised to 450-460°C, and the calcination time is 3.0-3.5 hours.

[0017] In the present invention, the CuMn2O4 catalyst is used in the treatment of difficult-to-degrade VOCs. The catalyst is suitable for treating industrial organic waste gas containing meta-xylene, and is particularly suitable for the catalytic oxidation of waste gas from the printing, coating and rubber industries.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] 1. The CuMn2O4 spinel catalyst prepared by the present invention was subjected to the treatment conditions of simulated industrial waste gas (300ppm m-xylene, space velocity 60000mL·g -1 ·h -1 ) showed excellent catalytic performance: the conversion of meta-xylene remained 100% at 250 ° C and operated continuously for 48 hours, T 50 and T 90 As low as 234℃ and 246℃ respectively, the comprehensive performance is better than that of similar catalysts (collected published data of the same type of T 90 ).

[0020] 2. A Cu-Mn bimetallic combination was used to develop an efficient and stable spinel structure catalyst, which not only effectively solved the key problem of insufficient activity of traditional catalysts in VOCs purification, but also maintained the good stability of the catalyst, and has outstanding advantages in the field of difficult-to-degrade VOCs purification.

[0021] 3. The preparation method of the present invention uses inexpensive metal precursors and can obtain high-performance catalysts through a simple co-precipitation process. It has outstanding advantages such as simple process, low cost, and good repeatability, and has significant potential for industrial application.

[0022] 4. The key to sample preparation in this invention lies in the calcination temperature. Since the valence of Mn in the CuMn2O4 catalyst is an intermediate state (+3), calcining at too high a temperature may result in the formation of MnO2 (+4), while calcining at too low a temperature may result in the formation of MnO (+2), both of which prevent the formation of the CuMn2O4 spinel structure. Therefore, the calcination temperature must be strictly controlled during the preparation of the CuMn2O4 catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 X-ray diffraction (XRD) patterns of the catalysts prepared in Examples 1-4 of the present invention;

[0024] Figure 2 Raman spectra of the catalysts prepared in Examples 1-4 of the present invention;

[0025] Figure 3 Scanning electron microscope (SEM) images of the catalysts prepared in Examples 1-4 of the present invention; wherein, (a, b) Mn3O4; (c, d) CoMn2O4; (e, f) CuMn2O4; (g, h) ZnMn2O4

[0026] Figure 4 Nitrogen adsorption and desorption curves and pore size distribution diagrams of the catalysts prepared in Examples 1-4 of the present invention;

[0027] Figure 5 This is a test chart of the activity of the catalysts prepared in Examples 1-4 of the present invention.

[0028] Figure 6 This is a stability test chart of the catalyst prepared in Example 1 of the present invention.

[0029] Figure 7 This is a test chart of the water resistance of the catalysts prepared in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to specific embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0031] The active ingredients of the present invention include, but are not limited to, the elements described in the following examples, and the preparation methods described include, but are not limited to, the preparation methods described in the following examples. Any modification or equivalent substitution of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention shall be included in the scope of protection of the present invention.

[0032] Example 1

[0033] This application example provides a method for preparing a spinel phase catalyst CuMn2O4, and the specific steps are as follows:

[0034] (1) Weigh 8 mmol of Cu(NO3)2·3H2O and 16 mmol of Mn(NO3)2 (50 wt% aqueous solution) and dissolve them in 30 mL of deionized water to form a homogeneous solution;

[0035] (2) According to the molar ratio of n(OH - ):n(Cu 2+ +Mn 2+ )=3:1 to prepare 30mL NaOH solution; slowly add the homogeneous solution in (1) dropwise to 30mL NaOH solution under magnetic stirring to fully precipitate the metal salt. Stir the mixture for 3 hours;

[0036] (3) The precipitate was repeatedly washed with deionized water, centrifuged until neutral, and dried at 80°C for 12 h;

[0037] (4) The dried product in (3) was ground into powder, placed in a muffle furnace and heated to 450°C at 5°C / min, and calcined for 3.0 hours. The obtained catalyst was recorded as CuMn2O4.

[0038] Example 2

[0039] This application example provides a method for preparing a spinel phase catalyst Mn3O4, and the specific steps are as follows:

[0040] (1) 24 mmol of Mn(NO3)2 (50 wt% aqueous solution) was dissolved in 30 mL of deionized water to form a homogeneous solution;

[0041] (2) According to the molar ratio of n(OH - ):n(Mn 2+ )=3:1 to prepare 30mL NaOH solution; slowly add the homogeneous solution in (1) dropwise to 30mL NaOH solution under magnetic stirring to fully precipitate the metal salt. Stir the mixture for 3 hours;

[0042] (3) The precipitate was repeatedly washed with deionized water, centrifuged until neutral, and dried at 80°C for 12 h;

[0043] (4) The dried product in (3) was ground into powder, placed in a muffle furnace and heated to 450°C at a rate of 5°C / min, and calcined for 3.0 hours. The obtained catalyst was recorded as Mn3O4.

[0044] Example 3

[0045] This application example provides a method for preparing a spinel phase catalyst CoMn2O4, and the specific steps are roughly the same as those in Example 1. The difference from Example 1 is that in step (1), Cu(NO3)2·3H2O is replaced by an equimolar amount of Co(NO3)2·6H2O; in step (2), the molar ratio of n(OH - ):n(Co 2+ +Mn 2+ )=3:1 to prepare 30mL NaOH solution, and the obtained catalyst was recorded as CoMn2O4.

[0046] Example 4

[0047] This application example provides a method for preparing a spinel phase catalyst ZnMn2O4, and the specific steps are roughly the same as those in Example 1. The difference from Example 1 is that in step (1), Cu(NO3)2·3H2O is replaced by an equimolar amount of Zn(NO3)2·6H2O; in step (2), the molar ratio of n(OH - ):n(Zn 2+ +Mn 2+ )=3:1 to prepare 30mL NaOH solution, and the obtained catalyst was recorded as ZnMn2O4.

[0048] Example 5

[0049] The catalyst is a sample of the catalyst obtained in Example 1 after performance testing in a fixed bed reactor. The test conditions are: m-xylene 300ppm, reaction space velocity 60000mL·g -1 ·h -1 The catalyst dosage was 0.1 g. A temperature programming mode was used: first, equilibrate at 160°C for 90 minutes, followed by temperature intervals of 180°C, 200°C, 220°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, and 310°C. Each temperature step took 10 minutes to rise and was maintained for 50 minutes.

[0050] Example 6

[0051] The catalyst is a sample of the catalyst obtained in Example 2 after performance testing in a fixed bed reactor. The test conditions are: m-xylene 300ppm, reaction space velocity 60000mL·g -1 ·h -1 The catalyst dosage was 0.1 g. A temperature programming mode was used: first, equilibrate at 160°C for 90 minutes, followed by temperature intervals of 180°C, 200°C, 220°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, and 310°C. Each temperature step took 10 minutes to rise and was maintained for 50 minutes.

[0052] Example 7

[0053] The catalyst is a sample of the catalyst obtained in Example 3 after performance testing in a fixed bed reactor. The test conditions are: m-xylene 300ppm, reaction space velocity 60000mL·g -1 ·h -1 The catalyst dosage was 0.1 g. A temperature programming mode was used: first, equilibrate at 160°C for 90 minutes, followed by temperature intervals of 180°C, 200°C, 220°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, and 310°C. Each temperature step took 10 minutes to rise and was maintained for 50 minutes.

[0054] Example 8

[0055] The catalyst is a sample of the catalyst obtained in Example 4 after performance testing in a fixed bed reactor. The test conditions are: m-xylene 300ppm, reaction space velocity 60000mL·g -1 ·h -1 The catalyst dosage was 0.1 g. A temperature programming mode was used: first, equilibrate at 160°C for 90 minutes, followed by temperature intervals of 180°C, 200°C, 220°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, and 310°C. Each temperature step took 10 minutes to rise and was maintained for 50 minutes.

[0056] Sample analysis

[0057] 1. X-ray diffraction (XRD) characterization

[0058] Figure 1 The XRD patterns of the catalysts prepared in Examples 1-4 of the present invention are shown in FIG. Figure 1 The crystal structure information of the synthesized catalysts can be known: the diffraction peaks of the Mn3O4, CoMn2O4, CuMn2O4 and ZnMn2O4 catalysts all match their corresponding standard cards (PDF#24-0734, 18-0408, 74-2422, 77-0470), and no diffraction peaks of other phases were found, indicating that the specific spinel structure material has been successfully synthesized.

[0059] 2. Raman characterization

[0060] Figure 2 The Raman diagram of the catalyst prepared in Examples 1-4 of the present invention. Figure 2It can be seen that the synthesized catalysts all have a spinel configuration, and the vibration peaks belonging to the octahedral Mn-O metal bond and the metal-oxygen bond vibration peaks of the A-site element appear respectively. In addition, it is found that the vibration peak of the octahedral Mn-O metal bond of the CuMn2O4 catalyst shifts most significantly to low wavenumbers, which indicates that its Mn-O bond force constant is the lowest and oxygen atoms are more likely to migrate to the surface for reaction, which means that catalysis can occur faster in the catalytic reaction.

[0061] 3. Scanning electron microscopy (SEM) characterization

[0062] Figure 3 The SEM images of the catalysts prepared in Examples 1-4 of the present invention are shown in FIG. Figure 3 All catalysts exhibited a stacked nanoparticle structure. Due to differences in metal ion radius, the particle sizes of the different catalysts (Cu, Co, and Zn) varied somewhat. Comparison of characterization results (such as XRD) confirmed that all three catalysts were successfully synthesized, with structural characteristics varying depending on the metal type.

[0063] 4. Nitrogen adsorption-desorption isotherm and pore size distribution curve

[0064] Figure 4 Nitrogen adsorption-desorption isotherms and pore size distribution curves for the catalysts prepared in Examples 1-4 of the present invention. Analysis of the catalyst pore structure through nitrogen adsorption-desorption experiments revealed that all catalysts exhibited type IV adsorption isotherms and H3-type hysteresis loop characteristics. Pore size distribution results confirmed that the synthesized catalysts were primarily mesoporous, with CuMn2O4 exhibiting the largest pore volume, followed by CoMn2O4, ZnMn2O4, and Mn3O4.

[0065] 5. Activity test

[0066] Figure 5 The activity test diagram of the catalyst prepared in Examples 1-4 of the present invention for the catalytic oxidation of m-xylene is shown in the figure. As shown in the figure, the CuMn2O4 catalyst exhibits the best catalytic performance. 50 and T 90 They are 234°C and 246°C respectively, which are 10°C and 16°C lower than those of Mn3O4, which confirms that the Cu-Mn bimetallic synergistic effect significantly improves the low-temperature activity of the catalyst. In order to more comprehensively evaluate the technical advantages of the present invention, Table 1 (see at the end) collects the performance data comparison of various types of xylene oxidation catalysts reported in recent years. It can be found that the CuMn2O4 described in this patent has obvious performance advantages over the same type of manganese oxide catalyst or spinel catalyst, and Cu and Mn elements are common catalyst elements in industrial applications and are widely available. At the same time, the preparation method has mild preparation conditions and is easy to achieve scale-up production, which has practical production and application significance.

[0067] 6. Stability test

[0068] Figure 6 This is a stability diagram of the catalyst CuMn2O4 prepared in Example 1 of the present invention. In order to demonstrate the industrial application possibility of the catalyst, the temperature stability test at the maximum conversion rate was selected. It can be found that the CuMn2O4 catalyst is stable at 250°C (T 99 ) and 60000mL·g -1 ·h -1 The m-xylene conversion efficiency was maintained at 100% after continuous operation for 48 hours under the space velocity condition.

[0069] 7. Water resistance test

[0070] Figure 7 This is a water resistance test chart for the CuMn2O4 catalyst prepared in Example 1 of the present invention. In order to cope with the actual catalytic environment where water vapor exists, different water vapor contents were selected to conduct water resistance tests on the prepared CuMn2O4 catalyst. It can be found that the conversion rate of the CuMn2O4 catalyst decreased slightly when the water vapor volume fraction was 5%, but the overall conversion rate remained above 90%, and it recovered in time after the water vapor was turned off. When the water vapor volume fraction increased to 10%, the CuMn2O4 catalyst was impacted for a short time, but after continued operation, the meta-xylene conversion rate was able to recover to around 90%, indicating that it has adapted to the water vapor conditions. This shows that the CuMn2O4 catalyst has excellent water resistance.

[0071] Table 1 Performance data of various xylene catalysts

[0072]

[0073]

[0074] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A highly efficient catalyst for purifying difficult-to-treat VOCs, characterized in that: The catalyst is a bimetallic oxide with a spinel structure, wherein the bimetallic elements are copper and manganese respectively; and the specific bimetallic chemical formula of the catalyst is CuMn2O4; the catalyst is mainly a mesoporous structure, which is a nanoparticle stacking structure.

2. A highly efficient catalyst for purifying difficult-to-treat VOCs according to claim 1, characterized in that: The catalyst was 60000 mL·g -1· h -1 Under the treatment conditions of space velocity and concentration of 300 ppm of meta-xylene, the temperatures at which the conversion rates reached 50% and 90% were 234°C and 246°C, respectively, and the conversion rate was maintained at 100% at 250°C for continuous operation for 48 hours.

3. The method for preparing a catalyst for efficiently purifying difficult-to-treat VOCs according to claim 1 or 2, comprising the following steps: (1) Cu(NO3)2·3H2O and 50% Mn(NO3)2 solution were dissolved in deionized water at a molar ratio of Cu:Mn=1:(1.8-2.2) to form a homogeneous solution; (2) Add the homogeneous solution dropwise to the alkaline solution under stirring and continue stirring for 3-4 hours to allow the metal salt to fully precipitate; (3) The precipitate is repeatedly washed and centrifuged until it becomes neutral, dried, ground, and calcined to obtain a CuMn2O4 catalyst.

4. The preparation method according to claim 3, characterized in that In step (1), the Mn(NO3)2 is an aqueous solution with a mass percentage concentration of 50%, and is dispersed in 30-40 mL of deionized water to form a homogeneous solution, and the Cu(NO3)2·3H2O is a 0.25-0.30 mol / L solution of Cu(NO3)2·3H2O.

5. The preparation method according to claim 3, characterized in that: In step (2), the alkaline solution is NaOH solution, and its amount is based on n(OH - ):n(Cu 2+ +Mn 2+ )=(2.5-3.0):1 stoichiometric ratio.

6. The preparation method according to claim 3, characterized in that: In step (2), the dropping method is controlled to dropwise addition so that the metal salt is fully precipitated.

7. The preparation method according to claim 3, characterized in that: In step (3), the drying condition is drying at 70-80° C. for more than 12 hours.

8. The preparation method according to claim 3, characterized in that: In step (3), the calcination conditions are to increase the temperature to 450-460°C at a rate of 3-5°C / min, and the calcination time is 3.0-3.5 hours.

9. Use of the catalyst according to claim 1 or 2 in the treatment of difficult-to-degrade VOCs.

10. The application according to claim 9, characterized in that: The catalyst is used for catalytic oxidation of waste gas from the printing, coating and rubber industries; the waste gas contains meta-xylene.

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