Adsorptive catalyst and method for producing the same

Abstract

The present application relates to the VOCs waste gas treatment technical field, specifically relates to a kind of adsorption catalyst and its preparation method.The preparation method includes acidification sepiolite preparation adsorption carrier;The adsorption carrier, bromobenzene and bismuth nitrate are mixed uniformly according to mass ratio 1:(6-14):(0.1-0.5), then sealed, and heat stirring treatment is carried out under ultraviolet light environment, to obtain pre-catalyst;The pre-catalyst is suction filtered, and after second drying treatment, adsorption catalyst is obtained.The adsorption catalyst is prepared by the preparation method.The adsorption catalyst prepared in the present application is adsorbed and degraded, first by sepiolite adsorption carrier adsorbed low concentration VOCs, in the desorption process, visible light is used to irradiate adsorption catalyst at room temperature, and low concentration VOCs can be degraded.

Description

Technical Field

[0001] This invention relates to the field of VOCs waste gas treatment technology, specifically to an adsorption catalyst and its preparation method. Background Technology

[0002] Volatile organic compounds (VOCs) are among the major air pollutants, harming human health and hindering sustainable economic development. Therefore, efficient and stable VOCs treatment is essential. Common methods for treating low-concentration VOCs include adsorption, catalytic oxidation, and photocatalysis. However, these methods often suffer from the following problems: 1) Traditional adsorption media have short adsorption saturation periods and poor resistance to load shocks; 2) Catalytic oxidation requires additional heating to increase the catalytic temperature and has high operating costs; 3) Photocatalysis mostly relies on ultraviolet light and suffers from low catalytic efficiency.

[0003] In summary, there is a need to provide an adsorption catalyst and its preparation method to solve the problems existing in adsorption, catalytic oxidation and photocatalysis in the prior art. Summary of the Invention

[0004] The purpose of this invention is to provide an adsorption catalyst and its preparation method, the specific technical solution of which is as follows:

[0005] In a first aspect, the present invention provides a method for preparing an adsorption catalyst, comprising:

[0006] Step S1: Preparation of adsorbent support by acidifying sepiolite

[0007] First, the raw sepiolite powder is mixed with inorganic acid at a mass ratio of 1:5 and stirred at 110-130℃ for 4-8 hours to obtain acidified sepiolite. Second, the acidified sepiolite is taken out, filtered, and washed until the wash water is neutral. Finally, the acidified sepiolite is subjected to a first drying treatment and calcination treatment to obtain an adsorbent carrier.

[0008] Step S2: Preparation of adsorption catalyst

[0009] First, the adsorbent carrier, bromobenzene and bismuth nitrate are mixed at a mass ratio of 1:(6-14):(0.1-0.5), sealed, and subjected to thermal stirring under ultraviolet light to obtain a pre-prepared catalyst. Second, the pre-prepared catalyst is filtered and then dried a second time to obtain the adsorption catalyst.

[0010] Optionally, in step S1, the inorganic acid includes dilute nitric acid; the pH of the dilute nitric acid is 1-3.

[0011] Optionally, in step S1, the first drying process uses a drying temperature of 110-130℃ and a drying time of 4-8h.

[0012] Optionally, in step S1, the calcination process uses a calcination temperature of 350-450℃ and a calcination time of 2-4 hours.

[0013] Optionally, in step S1, the sepiolite powder is sepiolite powder with a particle size D90 < 20 μm.

[0014] Optionally, in step S2, the heating temperature used in the thermal stirring treatment is 50-60℃, the stirring time is 16-32h, and the stirring rate is 160-240rpm.

[0015] Optionally, in step S2, the second drying process uses a drying temperature of 110-130℃ and a drying time of 10-14h.

[0016] Optionally, in step S2, the wavelength of the ultraviolet light is 254 nm.

[0017] Optionally, in step S2, the bismuth nitrate salt includes bismuth nitrate pentahydrate.

[0018] In a second aspect, the present invention provides an adsorption catalyst prepared by the aforementioned method for preparing an adsorption catalyst.

[0019] The application of the technical solution of the present invention has at least the following beneficial effects:

[0020] (1) This invention provides a method for preparing an adsorption catalyst for low-concentration VOCs. During adsorption degradation, low-concentration VOCs are first adsorbed onto a sepiolite adsorption support. During desorption, the adsorption catalyst is irradiated with visible light at room temperature to complete the degradation of the low-concentration VOCs. Specifically:

[0021] In step S1 of this invention, acidifying sepiolite has the following effects: First, acid treatment can remove impurities such as Fe and Na oxides and carbonates from sepiolite, and also remove impurities within the sepiolite pores, increasing pore volume; Second, hydrogen ions in the inorganic acid replace calcium, magnesium, potassium, and sodium ions in the sepiolite interlayer, giving it active hydrogen atoms, generating new surfaces and improving its surface properties, modifying its pore size and structure, increasing microporosity, and enhancing its adsorption capacity. After the acidified sepiolite undergoes a first drying and calcination treatment, an acid-treated sepiolite adsorption carrier with good adsorption capacity is obtained; In step S2, bromobenzene plays two roles in the preparation of the adsorption catalyst: first, as a solvent, and second, as a bromine source; under high-frequency ultraviolet light irradiation, bromobenzene generates bromine free radicals, which immediately react with bismuth nitrate to generate bismuth oxybromo. Since bromine radicals are generated in situ via bromobenzene, the concentration of bromine radicals in the entire system remains low, resulting in small and uniform bismuth oxybromine particles that can be uniformly loaded onto the sepiolite adsorbent support. If hydrogen bromide or bromide salts are used to replace bromobenzene, the bromide ion concentration becomes very high upon addition, causing the bismuth oxybromine to grow rapidly, resulting in larger and less uniform particle sizes. Even with the dropwise addition of hydrogen bromide or bromide salts, fluctuations in bromide ion concentration always occur, leading to instability in the bismuth oxybromine formation process. Therefore, this invention uses bromobenzene to provide the bromine source.

[0022] From a catalytic mechanism perspective: low-concentration VOCs molecules are initially adsorbed by the sepiolite adsorbent support. Without BiOBr loading, when adsorption-desorption reaches equilibrium, apparent adsorption saturation occurs. At this point, the sepiolite adsorbent support without BiOBr loading can no longer be used to treat low-concentration VOCs. However, because the sepiolite adsorbent support is loaded with BiOBr, during the adsorption-desorption process, the desorbed low-concentration VOCs are degraded by the BiOBr loaded on the surface of the sepiolite pores under visible light at room temperature, turning into carbon dioxide and water. Thus, an apparent continuous adsorption effect can be achieved. In other words, the adsorption catalyst can complete the entire process of adsorption-desorption-BiOBr photocatalytic degradation of low-concentration VOCs on the sepiolite adsorbent support.

[0023] Analysis of the visible-light photocatalytic mechanism of BiOBr reveals that its valence band is composed of the np (n=2, 3, and 4) layers of Br and the 2p layer of O, while its conduction band is composed of the 6p layer of Bi. It possesses a unique layered structure consisting of alternating Br double layers and [BiO2] layers. During visible-light photocatalytic reactions, BiOBr generates sufficient photoelectrons and photoholes under visible light irradiation. Its unique layered structure provides ample reaction sites, allowing the atoms involved in the chemical reaction to be rapidly polarized, thus completing the catalytic reaction. Furthermore, as an indirect bandgap semiconductor, electrons generated by BiOBr must cross the K layer before reaching the semiconductor valence band. This solves the problem of rapid electron-hole recombination, thereby enhancing the photocatalytic activity.

[0024] (2) The adsorption catalyst prepared by the present invention according to the determined steps and process conditions can complete the degradation of low concentration VOCs and has strong practicality.

[0025] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0026] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the static experimental apparatus used in this invention;

[0028] Figure 2 The adsorption and degradation performance of the adsorption catalysts prepared in Examples 1-5 and Comparative Examples 1-7 of this invention on acetone gas under conditions without visible light is shown.

[0029] Figure 3 The adsorption and degradation performance of the adsorption catalysts prepared in Examples 1-5 of this invention on acetone gas under visible light conditions;

[0030] Figure 4 This describes the adsorption and degradation performance of the adsorption catalysts prepared in Comparative Examples 1-7 of this invention on acetone gas under visible light conditions.

[0031] Among them, 1. air inlet pipe, 2. air outlet pipe, 3. rubber stopper, 4. glass gas collecting bottle, 5. lamp tube, 6. optical dark box. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0033] Example 1:

[0034] A method for preparing an adsorption catalyst, comprising:

[0035] Step S1: Preparation of adsorbent support by acidifying sepiolite

[0036] First, sepiolite powder and dilute nitric acid were added to a hydrothermal reactor at a mass ratio of 1:5 and mixed. The mixture was stirred at 120°C for 6 hours to obtain acidified sepiolite. Second, the acidified sepiolite was removed, filtered, and washed until the wash water was neutral. Finally, the acidified sepiolite was subjected to a first drying treatment and a calcination treatment to obtain an adsorbent carrier.

[0037] Step S2: Preparation of adsorption catalyst

[0038] First, the adsorbent carrier, bromobenzene and bismuth nitrate are mixed at a mass ratio of 1:10:0.25, sealed, and subjected to thermal stirring under ultraviolet light to obtain a pre-prepared catalyst. Second, the pre-prepared catalyst is filtered and then dried a second time to obtain the adsorption catalyst.

[0039] In step S1, the pH of the dilute nitric acid is 2.

[0040] In step S1, the first drying process uses a drying temperature of 120°C and a drying time of 6 hours.

[0041] In step S1, the roasting process is carried out at a roasting temperature of 400°C for 3 hours.

[0042] In step S1, the sepiolite powder is sepiolite powder with a particle size D90 < 20 μm.

[0043] In step S2, the heating temperature for the thermal stirring treatment is 50°C, the stirring time is 24 hours, and the stirring rate is 200 rpm.

[0044] In step S2, the second drying process uses a drying temperature of 120°C and a drying time of 12 hours.

[0045] In step S2, the wavelength of the ultraviolet light is 254 nm.

[0046] In step S2, the bismuth nitrate salt is bismuth nitrate pentahydrate.

[0047] Example 2:

[0048] Unlike Example 1, the amount of bismuth nitrate is reduced in step S2. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are in a mass ratio of 1:10:0.1.

[0049] Example 3:

[0050] Unlike Example 1, the amount of bismuth nitrate is increased in step S2. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are in a mass ratio of 1:10:0.5.

[0051] Example 4:

[0052] Unlike Example 1, the amount of bromobenzene used in step S2 is reduced. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are used in a mass ratio of 1:6:0.25.

[0053] Example 5:

[0054] Unlike Example 1, the amount of bromobenzene is increased in step S2. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are in a mass ratio of 1:14:0.25.

[0055] Comparative Example 1:

[0056] Unlike Example 1, the amount of bismuth nitrate used in step S2 is zero.

[0057] Comparative Example 2:

[0058] Unlike Example 1, the amount of bismuth nitrate used in step S2 is too high. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are used in a mass ratio of 1:10:0.6.

[0059] Comparative Example 3:

[0060] Unlike Example 1, the amount of bromobenzene used in step S2 is too low. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are used in a mass ratio of 1:5:0.25.

[0061] Comparative Example 4:

[0062] Unlike Example 1, the amount of bromobenzene used in step S2 is too high. Specifically, the adsorbent carrier, bromobenzene and bismuth nitrate are used in a mass ratio of 1:15:0.25.

[0063] Comparative Example 5:

[0064] Unlike Example 1, in step S2, the ultraviolet light with a wavelength of 254 nm is replaced with ultraviolet light with a wavelength of 365 nm.

[0065] Comparative Example 6:

[0066] Unlike Example 1, the first drying and roasting processes are omitted in step S1.

[0067] Comparative Example 7:

[0068] Unlike Example 1, step S1 is omitted, and sepiolite powder is directly added to step S2 for use.

[0069] Ten g of each of the adsorption catalysts prepared in Examples 1-5 and Comparative Examples 1-7 were used to test their adsorption catalytic performance. The specific test methods are as follows:

[0070] (1) See Figure 1 A static experimental setup is constructed. Specifically, the static experimental setup includes an inlet pipe 1, an outlet pipe 2, a rubber stopper 3, a glass gas collecting bottle 4, a lamp tube 5, and an optical dark box 6. The glass gas collecting bottle 4 and the lamp tube 5 are both placed inside the optical dark box 6. The lamp tube 5 emits visible light when powered on. The rubber stopper 3 is installed at the gas collecting port of the glass gas collecting bottle 4. A first mounting hole and a second mounting hole are provided on the rubber stopper 3. The inlet pipe 1 passes through the first mounting hole and communicates with the glass gas collecting bottle 4. The outlet pipe 2 passes through the second mounting hole and communicates with the glass gas collecting bottle 4.

[0071] (2) A static experiment was conducted using a static experimental setup. Specifically, firstly, acetone solution was injected into a 3L glass gas collecting bottle 4 using a syringe through the inlet tube 1. Secondly, the opening of the inlet tube 1 was sealed with adhesive tape, and the glass gas collecting bottle 4 was left to stand for 10 hours until the concentration of acetone gas in the bottle was balanced. Then, a 1mL syringe was used to take samples through the outlet tube 2 every 10 minutes for half an hour, with a total of three samples taken each time. The concentration of the extracted acetone gas was detected by a gas chromatograph. If the concentration of acetone gas measured in the three samples was close to the same concentration value (i.e., the initial concentration of acetone gas was 300mg / m³), the static experiment was considered successful. 3 Once the acetone gas concentration in glass gas collecting bottle 4 reaches equilibrium, 10g of adsorption catalyst is added through the inlet of inlet tube 1. Then, using a 1mL syringe, the acetone gas concentration is sampled every 10 minutes for a total of six samplings. The acetone gas concentration is detected using a gas chromatograph, and a line graph of the catalytic efficiency of the adsorption catalyst is plotted. After each experiment, all components of the static experimental apparatus need to be cleaned and dried for later use.

[0072] Test conditions: Lamp 5 has a power of 9W and emits visible light; initial acetone gas concentration is 300mg / m³. 3 Temperature 25℃, normal pressure.

[0073] See Figure 2Under the condition of lamp 5 being powered off, i.e., without a light source, the adsorption performance of each adsorption catalyst for acetone gas was investigated. The results showed that, except for Comparative Examples 2 and 7, the adsorption effects of Examples 1-5 and Comparative Examples 1 and 3-6 on acetone gas were basically the same. Among them, the adsorption effect of Comparative Example 2 was poor, possibly because there was too much bismuth nitrate pentahydrate, which blocked the pores of the sepiolite, thus reducing the capacity of the sepiolite to adsorb acetone gas. Comparative Example 7 was poor because the sepiolite was not acidified (acidification has two functions: first, acid treatment can remove impurities such as Fe and Na oxides and carbonates from the sepiolite, and can also remove impurities in the sepiolite pores, increasing the pore volume; second, hydrogen ions in dilute nitric acid replace calcium, magnesium, potassium, and sodium ions in the sepiolite interlayer, giving it active hydrogen atoms, generating new surfaces and improving its surface properties, modifying its pore size and structure, increasing microporosity, and improving its adsorption capacity), thus resulting in poor adsorption capacity and the worst adsorption effect on acetone gas.

[0074] See Figure 3-4 Under the condition of lamp 5 being powered on, i.e., under visible light irradiation, the adsorption and degradation performance of each adsorption catalyst for acetone gas was investigated. The results showed that, under visible light conditions, the adsorption and degradation efficiency of acetone gas in Examples 1-5 was significantly higher than that under no light source conditions, indicating that the adsorption catalysts prepared in Examples 1-5 catalyzed the degradation of acetone gas under visible light. In Comparative Examples 1-7, Comparative Examples 2-4 and 6 also showed stronger adsorption and degradation effects on acetone gas than under no light source conditions, but not as good as Examples 1-5. In Comparative Example 2, excessive bismuth nitrate pentahydrate may have clogged the pores of the sepiolite, thus reducing its adsorption capacity for acetone gas and resulting in poor adsorption and degradation. In Comparative Example 3, insufficient bromobenzene production led to a lower number of bromine free radicals and consequently, less BiOBr synthesis, resulting in poor degradation. In Comparative Example 4, excessive bromobenzene, as a solvent, diluted the concentration of bismuth nitrate in the system, lowering the BiOBr synthesis rate and thus reducing the amount of BiOBr, leading to poor degradation. In Comparative Example 7, the sepiolite was not acidified, which enhances its adsorption capacity. As mentioned earlier, untreated sepiolite has poor adsorption capacity, resulting in poor adsorption and degradation of acetone gas. Comparative Example 5 showed adsorption and degradation effects under visible light irradiation that were essentially the same as those without light source. This is because the ultraviolet light with a wavelength of 365 nm was used in the BiOBr preparation process. Longer wavelengths result in lower energy, preventing bromobenzene from generating bromine free radicals and thus hindering BiOBr formation. Consequently, it had no degradation effect on acetone gas, resulting in a situation consistent with the absence of light source. Comparative Example 1, lacking bismuth nitrate pentahydrate, exhibited no catalytic degradation effect, so the presence or absence of visible light had little impact on it.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an adsorption catalyst, characterized in that, include: Step S1: Preparation of adsorbent support by acidifying sepiolite First, the raw sepiolite powder and inorganic acid are mixed at a mass ratio of 1:5 and stirred at 110-130℃ for 4-8 hours to obtain acidified sepiolite. Secondly, the acidified sepiolite is removed, filtered, and washed until the wash water is neutral; finally, the acidified sepiolite is dried and calcined to obtain the adsorption carrier. Step S2: Preparation of adsorption catalyst First, the adsorbent carrier, bromobenzene and bismuth nitrate are mixed at a mass ratio of 1:(6-14):(0.1-0.5), sealed, and subjected to thermal stirring under ultraviolet light to obtain a pre-prepared catalyst; second, the pre-prepared catalyst is filtered and then dried a second time to obtain the adsorbent catalyst; the wavelength of the ultraviolet light is 254nm.

2. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S1, the inorganic acid includes dilute nitric acid; the pH of the dilute nitric acid is 1-3.

3. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S1, the first drying process uses a drying temperature of 110-130℃ and a drying time of 4-8 hours.

4. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S1, the roasting process is carried out at a roasting temperature of 350-450℃ and a roasting time of 2-4h.

5. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S1, the sepiolite powder is sepiolite powder with a particle size D90 < 20 μm.

6. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S2, the heating temperature for the thermal stirring treatment is 50-60℃, the stirring time is 16-32h, and the stirring rate is 160-240rpm.

7. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S2, the second drying process uses a drying temperature of 110-130℃ and a drying time of 10-14h.

8. The method for preparing the adsorption catalyst according to claim 1, characterized in that, In step S2, the bismuth nitrate salt includes bismuth nitrate pentahydrate.

9. An adsorption catalyst, characterized in that, It is prepared by the method for preparing the adsorption catalyst as described in any one of claims 1-8.

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