CN116712993A

CN116712993A - Mn-Ce catalyst for catalyzing and burning VOC waste gas

Info

Publication number: CN116712993A
Application number: CN202310157637.0A
Authority: CN
Inventors: 王祖文; 郭娜; 王骏星
Original assignee: Wuhan Zhangsheng Technology Co ltd
Current assignee: Wuhan Zhangsheng Technology Co ltd
Priority date: 2023-02-23
Filing date: 2023-02-23
Publication date: 2023-09-08

Abstract

The application discloses a Mn-Ce catalyst for catalyzing and burning VOC waste gas. The catalyst is prepared by taking metal salt as a precursor through roasting, and the preparation method is that manganese-based metal salt is taken as a precursor, other metal salts are taken as a modifier, citric acid is taken as a complex, and the catalyst is prepared through roasting by a metal salt pyrolysis method. In particular according to a Mn, ce molar ratio of 4: the catalyst prepared by 1 has the conversion rate of toluene up to 90% at about 200 ℃, the conversion rate of ethyl acetate up to 90% at about 180 ℃ and the conversion rate of chlorobenzene up to 90% at 350 ℃. The precursor for preparing the catalyst has the advantages of less material consumption, simple preparation method, short time consumption, high-efficiency and stable catalytic activity on VOC waste gas, and industrial production prospect.

Description

Mn-Ce catalyst for catalyzing and burning VOC waste gas

Technical Field

The application relates to the technical field of waste treatment, in particular to a Mn-Ce catalyst for catalyzing and burning VOC waste gas.

Background

With the rapid development of national economy, ecological and social problems caused by organic waste gas of VOCs discharged by industry are increasingly serious. VOCs are the formation of particulate matter (PM 2.5) and ozone (O) ₃ ) Is of importance beforeThe mutual coupling between VOCs and other atmospheric pollutants causes regional environmental quality deterioration and frequent occurrence of atmospheric pollutants such as dust haze, photochemical smog and the like. And VOCs have the characteristics of irritation, high toxicity, durability, photochemical reactivity and the like, and have serious influence on human beings and natural environments.

The VOCs treatment technology adopted at home and abroad at present comprises the following steps: adsorption/absorption methods, membrane separation techniques, condensation methods, plasma techniques, photocatalytic techniques, direct combustion methods, catalytic combustion methods, and the like. The catalytic combustion method has the advantages of low ignition temperature, no secondary pollution, high removal efficiency and the like, and is widely concerned. The core of catalytic combustion technology is the catalyst, and generally common catalyst systems include noble and non-noble metal catalysts. Noble metal catalysts, although having high activity, are expensive and easy to sinter at high temperatures; the non-noble metal catalyst has the advantages of cheap and easily available raw materials, polyvalent state, high electron transfer rate, good thermal stability and the like of transition metal, but has lower activity than noble metal. Manganese is commonly present in nature in the form of a manganese oxide mineral, and due to the availability and low cost of materials, the manganese element has multiple valence states (Mn ²⁺ 、Mn ³⁺ 、Mn ⁴⁺ ) And variable structures (delta-, alpha-, gamma-, R-, and beta-MnO ₂ ) Resulting in excellent redox properties, mnO _x Heterogeneous catalysts have received considerable attention as catalytic oxidation reactions. The thermal stability of the composite manganese oxide is improved compared with that of single manganese oxide, the doping of metals such as Ce, co, cu, fe and the like can form solid solution to increase lattice defects, and in addition, the strong interaction of the composite manganese oxide and manganese enhances the oxygen activating capacity and promotes the oxidation-reduction process of a manganese system, so that the activity of the catalyst is improved.

In the related art, the preparation method of the manganese-based catalyst mainly comprises a sol-gel method, a coprecipitation method, a template method, a glycine combustion method and the like, however, the preparation methods are either complex in operation or relatively time-consuming, and the content of the prepared catalyst finished product is low. Therefore, the manganese-based catalyst prepared by the method has high low-temperature activity, low cost and simple preparation process, and is a problem to be solved in the current catalytic combustion of VOCs.

Disclosure of Invention

In view of the above, the present application provides a Mn-Ce catalyst for catalytic combustion of VOC exhaust gas, which can improve catalytic activity.

In the related art, the preparation method of the manganese-based catalyst mainly comprises a sol-gel method, a coprecipitation method, a template method, a glycine combustion method and the like. In which a more common sol-gel method is typically represented. The sol-gel process for preparing a manganese-based catalyst has been disclosed by CN21153125352a, and the general preparation process is: A. preparing a manganese oxide precursor, namely dispersing water-soluble manganese salt such as manganese nitrate in water, adding citric acid for complexing, dispersing in water, adding alkali such as ammonia water for gel reaction, and obtaining the manganese oxide precursor. B. The manganese oxide precursor is separated from the aqueous phase and calcined at a temperature of about 622 ℃.

It is common in the industry that the catalytic activity of a catalyst is closely related to the preparation method in addition to the elemental composition, and the preparation method and synthesis conditions determine the crystal phase, structure, morphology, specific surface area, active species distribution, and the like of the catalyst, so that the catalyst is a critical factor affecting the activity of the catalyst.

The present inventors have found from previous studies of sol-gel methods that, although the preparation process conditions are easy to operate and the process is simple, the method is very limited in catalytic activity. The key procedures for restricting the catalytic activity in the implementation process of the sol-gel method are mainly shown in the following steps of system experimental demonstration: first, particle size stability of the sol formed from water-soluble manganese ions colloidal particle size, dispersion stability are easily affected by external factors such as acid-base environment, material molar ratio and temperature. Second, during firing, there is often a concomitant escape of solvent molecules, which can easily impact the solid phase microstructure, causing disorder or uncontrollable solid phase crystal forms.

Based on the inventive findings, the present inventors have proposed a metal salt pyrolysis method, i.e., solid-phase dispersing a manganese salt and a doped metal salt, followed by calcination to thermally decompose. Solid phase dispersion is a process that allows these raw materials to undergo molecular level infiltration, and the calcination process carried out thereafter is essentially a process that can remove volatile impurities in the catalyst, and solid phase reaction occurs on the surface to obtain a certain pore structure and specific surface area, forming an active phase that is advantageous for the catalytic activity of the catalyst, so that the calcination process is actually an activation process in the process of preparing the catalyst. Through the two processes of one-step implementation, the crystal form and the form of the prepared product are controllable, so that the catalytic activity is improved.

Thus, the present application has been created.

The application provides a Mn-Ce catalyst for catalyzing and burning VOC waste gas, which is obtained by carrying out solid-phase dispersion on manganese salt, metal salt and citric acid and then roasting.

It should be understood that as an exemplary implementation of the solid phase dispersion, it may be dry milling, i.e. milling citric acid, manganese salt, metal salt, respectively, to a powder state in an agate mortar.

Suitably, but not limited to, the manganese salt is at least one of manganese acetate, manganese oxalate, manganese carbonate.

Suitably, but not limited to, the metal salt is at least one of cerium nitrate, cobalt nitrate, lanthanum nitrate, samarium nitrate, copper nitrate, tin nitrate.

Suitably, but not by way of limitation, the molar ratio of the sum of the manganese salt and the metal salt to citric acid is 1 (2.5-2).

Suitably, but not by way of limitation, the molar ratio of the sum of the manganese salt and the metal salt to citric acid is 1:1.5.

suitably, but not by way of limitation, the manganese salt and metal salt molar ratio is 1: (2.25-4).

Suitably, but not by way of limitation, the manganese salt and metal salt molar ratio is 1:2.25.

Suitably, but not by way of limitation, the firing temperature is 422 to 522 ℃. In another embodiment of the application, the calcination temperature conditions during catalyst preparation were varied, with calcination temperatures of 422 ℃, 4522 ℃ and 5222 ℃, respectively. Although the catalytic activity of the catalyst can be improved by increasing the calcination temperature to increase the surface acid sites. However, related researches show that the catalytic activity of the catalyst cannot be increased continuously along with the increase of the roasting temperature, and even the catalytic activity of the catalyst tends to be greatly reduced. Preferably, the catalyst has the best catalytic effect under the condition that the roasting temperature of the catalyst is 4222 ℃.

Suitable, but not limiting, heating conditions for the firing process are: the temperature rising rate is 2.52 ℃/min, the temperature rises to 422-522 ℃, and the roasting is continued for 2-4 hours after the target temperature is reached.

<VOCs>

VOCs referred to herein include, but are not limited to, one or more of alkanes, alkenes, aromatics, halogenated hydrocarbons, aldehydes, esters.

The concentration of the VOC gas is from 522 to 32222ppm by reference.

The reaction space velocity of the VOC catalytic combustion is 62222-962222 ml.g ^-1 ·h ^-1 。

The application has the following beneficial effects:

1. the Mn-Ce catalyst realizes complete catalytic combustion of VOC at higher airspeed, higher concentration and lower temperature.

2. The preparation method has the characteristics of low cost, simple process steps and the like, and has the prospect of large-scale industrialized application.

Drawings

The technical solution and other advantageous effects of the present application will be made apparent by the following detailed description of the specific embodiments of the present application with reference to the accompanying drawings.

FIG. 1 is a schematic view of a catalytic combustion device for VOCs.

Fig. 2 shows a graph of VOC conversion as a function of temperature according to example 1 of the present application.

Fig. 3 shows a graph of VOC conversion as a function of temperature according to example 2 of the present application.

Fig. 4 shows a graph of VOC conversion as a function of temperature according to example 3 of the present application.

Fig. 5 shows a graph of VOC conversion as a function of temperature according to example 4 of the present application.

Fig. 6 shows a graph of VOC conversion over time according to example 4 of the present application.

Fig. 7 shows a graph of VOC conversion over time based on a feed formulation according to comparative example 1 (sol gel process), example 4 (pyrolysis process).

Fig. 8 shows a graph of VOC conversion over time based on a further feed formulation according to comparative example 1 (sol gel process), example 4 (pyrolysis process).

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below in connection with the embodiments of the present application. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to fall within the scope of the application.

In the description of the present application, it should be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically connected, electrically connected or can be communicated with each other; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

The following disclosure provides many different embodiments, or examples, for implementing different features of the application. In order to simplify the present disclosure, components and arrangements of specific examples are described below. They are, of course, merely examples and are not intended to limit the application. Furthermore, the present application may repeat reference numerals and/or letters in the various examples, which are for the purpose of brevity and clarity, and which do not themselves indicate the relationship between the various embodiments and/or arrangements discussed. In addition, the present application provides examples of various specific processes and materials, but one of ordinary skill in the art will recognize the application of other processes and/or the use of other materials.

Catalytic combustion of Mn-based catalysts

Grinding citric acid, manganese salt and metal salt with certain mass respectively in an agate mortar to powder state, uniformly mixing according to different molar ratios, spreading in a dry cupel, putting in a muffle furnace to carry out thermal decomposition at different temperatures, heating at a rate of 2.5 ℃/min, preserving heat for 32h after reaching a target temperature, taking out a sample when the temperature is reduced to room temperature, grinding and screening the sample into particles with a size of 42-62 meshes for later use, and obtaining the Mn-based catalyst.

Putting a certain amount of the catalyst into a quartz reaction tube, and introducing a certain amount of VOCs gas and N ₂ And O ₂ . At a constant flow rate (VOCs, N ₂ 、O ₂ Total flow 1222 mL/min), the conversion of the reactants and the CO at the corresponding temperatures were detected by programmed temperature adjustment ₂ Optionally, the VOCs catalytic combustion device is shown in FIG. 1.

The following specific examples were carried out in accordance with the methods of catalytic combustion of Mn-based catalysts, which embody only some of the key specific process parameters.

Example 1

The introduced VOC is 12222ppm toluene, the reaction space velocity is 622222ml g-1 h-1, the catalyst precursor is manganese acetate tetrahydrate and cerium nitrate, and the mole ratio of Mn to Ce is 1: (2,2.25,1,4) the catalyst calcination temperature was 4222 ℃.

Example 2

The VOC is 1222ppm of ethyl acetate, the reaction space velocity is 622222ml g-1 h-1, the catalyst precursor is manganese acetate tetrahydrate and cerium nitrate, and the mole ratio of Mn to Ce is 1:2.25, the calcination temperature of the catalyst was 422 ℃.

Example 3

The introduced VOC is 1222ppm of toluene, the reaction space velocity is 622222ml g-1 h-1, the catalyst precursor is manganese acetate tetrahydrate and cerium nitrate, and the mole ratio of Mn to Ce is 1:2.25, the calcination temperature of the catalyst was 422℃at 452℃and 522 ℃.

Example 4

The VOC is 1222ppm of chlorobenzene, the reaction space velocity is 622222ml g-1 h-1, the catalyst precursor is manganese acetate tetrahydrate and cerium nitrate, and the mole ratio of Mn to Ce is 1: (2,2.25,1,4) the calcination temperature of the catalyst was 422 ℃.

Comparative example 1

The VOC introduced was 1222ppm of chlorobenzene and the reaction space velocity was 622222ml g-1 h-1.

The preparation method adopts a sol-gel method to obtain the gel, and specifically comprises the following steps: manganese acetate tetrahydrate, cerium nitrate and citric acid are added into a proper amount of water, and the mole ratio of Mn to Ce is 1: (2,2.25) and performing ultrasonic dispersion for 32min to obtain a dispersion liquid A. Transferring the dispersion liquid A into a beaker, dispersing at high speed by adopting a shearing machine, and adding ammonia water to adjust the pH of the system to 9 to obtain a liquid separating liquid B. Filter residue was filtered off from dispersion B with suction. The filter residue is put into a muffle furnace and baked at 422 ℃. The temperature rising mode of the roasting is to raise the temperature at the speed of 2.5 ℃/min, keep the temperature for 32 hours after reaching the target temperature, take out the sample when the temperature is reduced to the room temperature, grind and screen the sample into particles with the size of 42-62 meshes for standby, and obtain the Mn-based catalyst.

Evaluation

A. Catalytic Activity test

The reactant VOCs (liquid phase, toluene, chlorobenzene, ethyl acetate) were injected by microinjection pump and then reacted with N ₂ 、O ₂ Mixing in a gas mixing tank, entering a fixed bed reactor for catalytic combustion, wherein the total gas volume is 1222mL/min, O ₂ The amount of catalyst was 122mL/min, and the 2-catalyst charge was 1222mg. The gas before and after the catalytic reaction enters a gas chromatograph for continuous on-line monitoring. The catalyst reactivity was reacted at a temperature at which the VOC conversion was 92%.

B. Catalytic stability test

The catalyst was a 22h catalytic reaction carried out continuously at a temperature of 352 ℃.

C. Test results

The results of the catalytic activity test of the catalyst obtained in example 1 on VOCs are shown in FIG. 2. As can be seen from FIG. 2, the activity (222 ℃) of the catalyst with Mn to Ce molar ratio of 4:1 is significantly higher than that of MnO without other doping _x 、CeO _x Catalyst and other molar ratios of Mn-Ce catalyst. The modification of Ce increases the active oxygen mobility of the catalyst, mn ⁴⁺ The interaction of Mn with Ce increases the catalytic activity of the catalyst.

The results of the catalytic activity test of the catalyst of example 2 on VOCs are shown in FIG. 3. As can be seen from FIG. 3, the catalyst catalytic activity increases with increasing temperature, ethyl acetate conversion at 165℃reaches 92%, and CO at 192 ℃ ₂ The conversion rate reaches 92%, which shows that the ethyl acetate can be deeply oxidized under the action of the catalyst without other byproducts.

Example 3 catalyst vs. VOCs catalytic activity test results are shown in fig. 4. When the roasting temperature is increased from 422 ℃ to 522 ℃, the activity of the catalyst on VOCs is reduced, and the catalytic activities of the catalyst on toluene at 222 ℃ at 422 ℃, 452 ℃ and 522 ℃ are 92%, 55% and 62% respectively. Therefore, considering the cost problem under the condition of ensuring higher activity, it is considered that the calcination temperature is most suitable to be 422℃when preparing the catalyst.

Example 4 the results of the catalyst activity test and stability test on VOC are shown in fig. 5 and 6. As can be seen from FIG. 5, the activity (352 ℃) of the catalyst with Mn to Ce molar ratio of 4:1 is significantly higher than that of MnO without other doping _x 、CeO _x Catalyst and other molar ratios of Mn-Ce catalyst. In addition, as can be seen from fig. 5, the catalyst prepared by the pyrolysis method can completely catalyze and oxidize VOC at 222 ℃ under the condition of roasting at 422 ℃, and shows good low-temperature catalytic performance.

As can be seen in FIG. 6, the catalyst was stable for long term operation at 3522℃and CO ₂ The conversion rate is 72-12%, which shows that the catalyst has high conversion rate of toluene and good effect on halogenated hydrocarbon treatment.

Comparative example 1 the results of the catalyst activity test and stability test on VOC are shown in fig. 7 and 1, wherein fig. 7 and 1 represent example 4 by pyrolysis and comparative example 1 by sol-gel method. As can be seen from fig. 7 and fig. 1, the catalyst prepared by the preparation method has a significantly lower catalytic effect on chlorobenzene than the catalyst of example 4.

The present application is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present application are intended to be included in the scope of the present application.

Claims

1. The Mn-Ce catalyst for catalyzing and burning VOC waste gas is characterized in that the Mn-Ce catalyst is obtained by solid-phase dispersing manganese salt, metal salt and citric acid and then roasting.

2. The Mn-Ce catalyst of claim 1, wherein the calcination temperature is 422 to 522 ℃.

3. The Mn-Ce catalyst of claim 1, wherein the manganese salt is at least one of manganese acetate, manganese oxalate, manganese carbonate.

4. The Mn-Ce catalyst of claim 1, wherein the metal salt is at least one of cerium nitrate, cobalt nitrate, lanthanum nitrate, samarium nitrate, copper nitrate, tin nitrate.

5. The Mn-Ce catalyst of claim 1, wherein the molar ratio of the sum of manganese salt and metal salt to citric acid is 1 (2.5-2).

6. The Mn-Ce catalyst of claim 1, wherein the molar ratio of the sum of manganese salt and metal salt to citric acid is 1:1.5.

7. the Mn-Ce catalyst of claim 1, wherein the molar ratio of manganese salt to metal salt is 1: (2.25-4).

8. The Mn-Ce catalyst of claim 1, wherein the molar ratio of manganese salt to metal salt is 1:2.25.

9. the Mn-Ce catalyst of claim 1, wherein the firing treatment is performed under heating conditions of: the temperature rising rate is 2.52 ℃/min, the temperature rises to 422-522 ℃, and the roasting is continued for 2-4 hours after the target temperature is reached.