Preparation method of hydrophobic VOCs adsorbent NaY-MCM-41

Abstract

The present invention relates to a method for preparing a hydrophobic VOCs adsorbent NaY-MCM-41. The method is characterized in that NaY molecular sieve is prepared by crystallization reaction using attapulgite, a resource-rich and inexpensive silica-alumina source, and MCM-41 is further loaded on its surface to obtain the hydrophobic adsorbent NaY-MCM-41. The silica-alumina source used in the present invention is resource-rich, inexpensive, and environmentally friendly. The prepared adsorbent has excellent saturated adsorption capacity and good hydrophobicity, making it easy to produce and apply in industry.

Description

Technical Field

[0001] The present invention relates to a VOCs adsorbent, and in particular to a method for preparing a hydrophobic VOCs adsorbent. Background Art

[0002] Volatile organic compounds (VOCs) are atmospheric pollutants with a boiling point between 50°C and 260°C at room temperature and pressure. They are produced by everything from petrochemical production and fuel vehicle exhaust emissions to the use of construction materials and decorative coatings. The indiscriminate emission of VOCs can lead to photochemical smog, exacerbate haze pollution, and severely damage the natural ecological environment. Furthermore, long-term exposure to VOCs can affect human health, causing respiratory diseases and other problems. Therefore, the control of VOCs has become a major issue that urgently needs to be addressed in contemporary air pollution, and adopting appropriate methods to effectively control them is of great significance.

[0003] Adsorption technology is considered one of the most advantageous methods for treating VOCs, especially for low-concentration VOCs. The advantages of adsorption are simple equipment, safe operation, and high efficiency for treating VOCs with concentrations less than 1000 ppm.

[0004] NaY molecular sieve is made of AlO4 5- and SiO4 4- The tetrahedral structure is formed by cross-linking shared oxygen atoms and possesses advantages such as a stable inorganic chemical structure, a large specific surface area, good regeneration, and non-flammability. It has been widely used as an adsorbent. Molecular sieves are typically produced by crystallizing silicates and aluminates in a certain ratio. The main chemical components of attapulgite are SiO2 and Al2O3. Acid and alkali washing can destroy its crystal structure and release SiO2 and Al2O3. my country has abundant attapulgite mineral resources, and its price is one-quarter that of traditional industrial aluminosilicates. Synthesizing molecular sieves from attapulgite can effectively utilize mineral resources, reduce production costs, and minimize industrial pollution. However, VOCs waste gas associated with industrial production often contains water vapor. Water molecules interact with the aluminum in the molecular sieve framework, competing with the VOCs for adsorption, resulting in low gas removal efficiency and a sudden drop in adsorption capacity.

[0005] In a previous study, Lv et al. (Microporous and Mesoporous Materials 294(2020)109869) used NH4Cl to ion exchange NaY to produce NH4Y while washing away some non-framework aluminum. High-temperature hydrothermal dealumination was then used to produce the USY-650 adsorbent. At a relative humidity of 50%, its saturated adsorption capacity for toluene increased from 8 mg / g to 41 mg / g. Dealumination increased the Si / Al ratio of the molecular sieve, but also destroyed its pore structure.

[0006] Xu et al. (Separation and Purification Technology 329(2024)124914) combined high-temperature hydrothermal treatment with acid treatment to dealumination modification of NaY molecular sieve, effectively improving the hydrophobicity of the adsorbent, and the saturated adsorption capacity of toluene at relative humidity RH=50% increased from 29 mg / g to 121 mg / g. However, traditional acid dealumination and high-temperature hydrothermal dealumination methods cause irreversible damage to the structure of the material, resulting in a decrease in adsorption performance. They require precise control of acid strength, acid dosage, and treatment time, which makes implementation difficult. Summary of the Invention

[0007] The present invention aims to provide a method for preparing a hydrophobic VOC adsorbent using attapulgite as a raw material. To address the problem of acid dealumination and high-temperature hydrothermal dealumination hydrophobic modification damaging the original crystal structure of NaY, this patented method loads a pure silicon hydrophobic molecular sieve, MCM-41, onto NaY to form a multi-level porous hydrophobic material. This method offers a mild reaction, simple process, preserves the original microporous structure of NaY, and utilizes inexpensive raw materials, improving the molecular sieve's VOC adsorption performance under humid conditions.

[0008] The technical solution of the present invention is: a method for preparing a hydrophobic VOCs adsorbent NaY-MCM-41, the specific steps of which are as follows:

[0009] (1) adding attapulgite to an acid solution, acid-washing for a period of time, washing with deionized water until neutral, and drying to obtain pretreated attapulgite;

[0010] (2) mixing the pretreated attapulgite with a sodium hydroxide solution to form a slurry, transferring the slurry to a muffle furnace for calcination to obtain a solid, adding the solid to deionized water for ultrasonication, and centrifuging to obtain the supernatant as a silicon and aluminum source;

[0011] (3) adding silica sol to the silicon-aluminum source, stirring, and transferring to a hydrothermal reactor for crystallization; after the hydrothermal reaction is completed, filtering, washing, and drying the product to obtain NaY molecular sieve;

[0012] (4) Dissolve hexadecyltrimethylammonium bromide (CTAB) in deionized water, add silica sol and NaY prepared in step (3), add acid solution dropwise to adjust the pH, transfer to a hydrothermal reactor for crystallization, wash, dry, and calcine after the hydrothermal reaction to obtain NaY-MCM-41 molecular sieve adsorbent.

[0013] Preferably, the acid in step (1) is one of hydrochloric acid or nitric acid; the acid concentration is 1 to 3 mol / L; the pickling time is 1 to 6 hours; and the volume ratio of the mass of the attapulgite to the acid solution is 1:(30 to 50) g / mL.

[0014] Preferably, the concentration of the sodium hydroxide solution in step (2) is 0.5-2 mol / L; the volume ratio of the mass of attapulgite to the sodium hydroxide solution is 1:(1-2) g / mL.

[0015] Preferably, in step (2), the calcination temperature is 300-600° C., the calcination time is 3-6 hours, the ultrasonic time is 0.5-2 hours, the centrifugal speed is 1000-4000 rpm, and the centrifugal time is 1-4 hours.

[0016] Preferably, the mass ratio of the silicon-aluminum source to the silica sol in step (3) is (4-7):1; the mass fraction of SiO2 in the silica sol is 30%-60%.

[0017] Preferably, the stirring speed in step (3) is 300-500 rpm, the stirring time is 3-6 hours, the crystallization temperature is 90-160° C., and the crystallization time is 24-96 hours.

[0018] Preferably, the mass ratio of CTAB, deionized water, NaY and silica sol described in step (4) is 1: (10-20): (0.5-3): (3-8); the mass fraction of SiO2 in the silica sol is 30%-60%; the acid solution is one of sulfuric acid or hydrochloric acid, and the pH value is adjusted to 10-12.

[0019] Preferably, in step (4), the crystallization temperature is 100-120° C., and the crystallization time is 12-24 hours; the calcination temperature is 300-600° C., and the calcination time is 3-6 hours.

[0020] Beneficial effects:

[0021] (1) The present invention uses attapulgite as raw material to prepare the adsorbent, which has the advantages of abundant resources, low price, and green environmental protection.

[0022] (2) The adsorbent prepared by the present invention has a multi-level pore structure, excellent hydrophobicity and VOCs adsorption performance.

[0023] (3) The adsorbent prepared by the present invention has low cost and simple preparation method, which is conducive to industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Diagram of the fixed-bed adsorbent evaluation apparatus; 1. Toluene standard gas; 2. High-purity nitrogen; 3. Mass flowmeter; 4. Stop valve; 5. High and low-temperature constant-temperature water bath; 6. Ball valve; 7. Three-way ball valve; 8. Adsorption fixed bed; 9. Gas chromatograph. DETAILED DESCRIPTION

[0025] Example 1

[0026] (1) 100 g of attapulgite was mixed with 3000 mL of 2 mol / L hydrochloric acid, stirred continuously for 3 h, filtered and washed to neutrality, and dried to obtain the pretreated attapulgite.

[0027] (2) 10 g of pretreated attapulgite was mixed with 20 mL of 0.5 mol / L sodium hydroxide solution, stirred to form a slurry, and then transferred to a muffle furnace and calcined at 300°C for 6 hours to obtain a solid. 5 g of the solid was mixed with 30 mL of deionized water, sonicated for 2 hours, and centrifuged at 1000 rpm for 4 hours. The supernatant was used as the silica-alumina source.

[0028] (3) 5 g of silica sol (SiO2 60 wt%) was added dropwise to 20 g of silicon-aluminum source under vigorous stirring. The mixture was stirred at 500 rpm for 3 hours until uniformly mixed. The mixture was then transferred to a hydrothermal autoclave and crystallized at 90°C for 96 hours. The NaY molecular sieve was then filtered, washed, and dried.

[0029] (4) 1 g CTAB, 10 g deionized water, 0.5 g NaY, and 3 g silica sol (SiO2 60 wt%) were uniformly mixed, adjusted to pH = 10 with 1 mol / L dilute sulfuric acid, and then transferred to a hydrothermal kettle for crystallization at 120 °C for 12 h. After filtration, washing, and drying, the mixture was transferred to a muffle furnace at 300 °C and calcined for 6 h to obtain 0.5-NaY / MCM-41 adsorbent.

[0030] Example 2

[0031] (1) 100 g of attapulgite was mixed with 3000 mL of 1 mol / L nitric acid, stirred continuously for 4 hours, filtered and washed to neutrality, and dried to obtain the pretreated attapulgite.

[0032] (2) 10 g of pretreated attapulgite was mixed with 15 mL of 1 mol / L sodium hydroxide solution, stirred to form a slurry, and then transferred to a muffle furnace and calcined at 400°C for 5 hours to obtain a solid. 5 g of the solid was mixed with 30 mL of deionized water, sonicated for 1.5 hours, and centrifuged at 2000 rpm for 3 hours. The supernatant was used as the silica-alumina source.

[0033] (3) 5 g of silica sol (SiO2 40 wt%) was added dropwise to 25 g of silicon-aluminum source under vigorous stirring. The mixture was stirred at 500 rpm for 4 hours until uniformly mixed. The mixture was then transferred to a hydrothermal autoclave and crystallized at 100°C for 72 hours. The NaY molecular sieve was then filtered, washed, and dried.

[0034] (4) 1 g CTAB, 15 g deionized water, 1.0 g NaY, and 4 g silica sol (SiO2 60 wt%) were uniformly mixed, adjusted to pH 10 with 1 mol / L dilute sulfuric acid, and then transferred to a hydrothermal kettle for crystallization at 100 °C for 16 h. After filtration, washing, and drying, the mixture was transferred to a muffle furnace at 400 °C and calcined for 5 h to obtain 1.0-NaY / MCM-41 adsorbent.

[0035] Example 3

[0036] (1) 100 g of attapulgite was mixed with 4000 mL of 1 mol / L hydrochloric acid, stirred continuously for 6 hours, filtered and washed to neutrality, and dried to obtain the pretreated attapulgite.

[0037] (2) 10 g of pretreated attapulgite was mixed with 10 mL of 1.5 mol / L sodium hydroxide solution, stirred to form a slurry, and then transferred to a muffle furnace and calcined at 500°C for 4 hours to obtain a solid. 5 g of the solid was mixed with 30 mL of deionized water, sonicated for 1 hour, and centrifuged at 3000 rpm for 2 hours. The supernatant was used as the silica-alumina source.

[0038] (3) 5 g of silica sol (SiO2 30 wt%) was added dropwise to 30 g of silicon-aluminum source under vigorous stirring. The mixture was stirred at 400 rpm for 5 hours until uniformly mixed. The mixture was then transferred to a hydrothermal autoclave and crystallized at 120°C for 48 hours. The mixture was filtered, washed, and dried to obtain NaY molecular sieve.

[0039] (4) 1 g CTAB, 20 g deionized water, 1.5 g NaY, and 5 g silica sol (SiO2 40 wt%) were uniformly mixed, adjusted to pH 12 with 1 mol / L dilute sulfuric acid, and then transferred to a hydrothermal kettle for crystallization at 120 °C for 20 h. After filtration, washing, and drying, the mixture was transferred to a muffle furnace at 500 °C and calcined for 4 h to obtain 1.5-NaY / MCM-41 adsorbent.

[0040] Example 4

[0041] (1) 100 g of attapulgite was mixed with 5000 mL of 3 mol / L nitric acid, stirred continuously for 1 hour, filtered and washed to neutrality, and dried to obtain the pretreated attapulgite.

[0042] (2) 10 g of pretreated attapulgite was mixed with 10 mL of 2 mol / L sodium hydroxide solution, stirred to form a slurry, and then transferred to a muffle furnace and calcined at 600°C for 3 hours to obtain a solid. 5 g of the solid was mixed with 30 mL of deionized water, sonicated for 0.5 hours, and centrifuged at 4000 rpm for 1 hour. The supernatant was used as the silica-alumina source.

[0043] (3) 5 g of silica sol (SiO2 30 wt%) was added dropwise to 35 g of silicon-aluminum source under vigorous stirring. The mixture was stirred at 400 rpm for 6 hours until uniformly mixed. The mixture was then transferred to a hydrothermal autoclave and crystallized at 140°C for 24 hours. The NaY molecular sieve was then filtered, washed, and dried.

[0044] (4) 1 g CTAB, 20 g deionized water, 2.0 g NaY, and 6 g silica sol (SiO2 40 wt%) were uniformly mixed, adjusted to pH 12 with 1 mol / L dilute hydrochloric acid, and then transferred to a hydrothermal kettle for crystallization at 110 °C for 24 h. After filtration, washing, and drying, the mixture was transferred to a muffle furnace at 600 °C and calcined for 3 h to obtain 2.0-NaY / MCM-41 adsorbent.

[0045] Example 5

[0046] (1) 100 g of attapulgite was mixed with 5000 mL of 3 mol / L hydrochloric acid, stirred continuously for 1 hour, filtered and washed to neutrality, and dried to obtain the pretreated attapulgite.

[0047] (2) 20 g of pretreated attapulgite was mixed with 40 mL of 2 mol / L sodium hydroxide solution, stirred to form a slurry, and then transferred to a muffle furnace and calcined at 450°C for 5 hours to obtain a solid. 5 g of the solid was mixed with 30 mL of deionized water, sonicated for 1 hour, and then centrifuged at 2000 rpm for 3 hours. The supernatant was used as the silica-alumina source.

[0048] (3) 5 g of silica sol (SiO2 40 wt%) was added dropwise to 25 g of silicon-aluminum source under vigorous stirring. The mixture was stirred at 300 rpm for 4 hours until uniformly mixed. The mixture was then transferred to a hydrothermal autoclave and crystallized at 100°C for 72 hours. The NaY molecular sieve was then filtered, washed, and dried.

[0049] (4) 1 g CTAB, 20 g deionized water, 2.5 g NaY, and 7 g silica sol (SiO2 30 wt%) were uniformly mixed, adjusted to pH 10 with 1 mol / L dilute hydrochloric acid, and then transferred to a hydrothermal kettle for crystallization at 110 °C for 24 h. After filtration, washing, and drying, the mixture was transferred to a muffle furnace at 600 °C and calcined for 3 h to obtain 2.5-NaY / MCM-41 adsorbent.

[0050] Example 6

[0051] (1) 100 g of attapulgite was mixed with 4000 mL of 2 mol / L nitric acid, stirred continuously for 3 hours, filtered and washed to neutrality, and dried to obtain the pretreated attapulgite.

[0052] (2) 20 g of pretreated attapulgite was mixed with 30 mL of 1.5 mol / L sodium hydroxide solution, stirred to form a slurry, and then transferred to a muffle furnace and calcined at 550°C for 3 hours to obtain a solid. 5 g of the solid was mixed with 30 mL of deionized water, sonicated for 1.5 hours, and centrifuged at 3000 rpm for 2 hours. The supernatant was used as the silica-alumina source.

[0053] (3) 5 g of silica sol (SiO2 30 wt%) was added dropwise to 30 g of silicon-aluminum source under vigorous stirring. The mixture was stirred at 300 rpm for 5 hours until uniformly mixed. The mixture was then transferred to a hydrothermal autoclave and crystallized at 120°C for 48 hours. The NaY molecular sieve was then filtered, washed, and dried.

[0054] (4) 1 g CTAB, 20 g deionized water, 3.0 g NaY, and 8 g silica sol (SiO2 30 wt%) were uniformly mixed, adjusted to pH = 10 with 1 mol / L dilute hydrochloric acid, and then transferred to a hydrothermal kettle for crystallization at 120 °C for 24 h. After filtration, washing, and drying, the mixture was transferred to a muffle furnace at 550 °C and calcined for 3 h to obtain 3.0-NaY / MCM-41 adsorbent.

[0055] Comparative Example 1

[0056] The preparation method is the same as that of Example 1, except that the treatment of loading MCM-41 in step (4) is omitted.

[0057] Comparative Example 2

[0058] The preparation method is the same as that of Example 2, except that the treatment of loading MCM-41 in step (4) is omitted.

[0059] Comparative Example 3

[0060] The preparation method is the same as that of Example 3, except that the treatment of loading MCM-41 in step (4) is omitted.

[0061] Comparative Example 4

[0062] The preparation method is the same as that of Example 4, except that the treatment of loading MCM-41 in step (4) is omitted.

[0063] Comparative Example 5

[0064] The preparation method is the same as that of Example 5, except that the treatment of loading MCM-41 in step (4) is omitted.

[0065] Comparative Example 6

[0066] The preparation method is the same as that of Example 6, except that the treatment of loading MCM-41 in step (4) is omitted.

[0067] Use Figure 1The fixed-bed adsorption apparatus shown in the figure evaluates adsorbent performance. Toluene standard gas and high-purity nitrogen are mixed at a predetermined ratio through a mass flow meter to achieve the inlet concentration. After the inlet concentration stabilizes for ten minutes, a three-way ball valve is connected to the fixed bed to begin the experiment. When the outlet concentration equals the inlet concentration, the three-way ball valve is switched to bypass, halting the experiment. The relative humidity is controlled by opening and closing the shutoff valve on the high-purity nitrogen pipeline.

[0068] 0.1g of adsorbent was placed in a quartz tube, secured at both ends with glass wool. The inner diameter of the quartz tube was 9mm, the adsorbent particle size was between 20-40 mesh, and the adsorption temperature was controlled using a high-low temperature thermostat. The toluene concentration at the inlet of the device was 200ppm, the air velocity was 90,000mL / (g·h), and the adsorption temperature was 25°C. The toluene concentration at the outlet was measured using a gas chromatograph according to the formula:

[0069]

[0070] The saturated adsorption capacity was calculated.

[0071] Where: Q is the saturated adsorption capacity, mg / g; C0 is the initial concentration of toluene, mg / m 3 ; Ci is the outlet concentration at time i, mg / m 3 ;t s is the time required for adsorption to reach saturation, min; F is the air flow rate through the adsorption column, mL / min; w is the mass of the filled adsorbent, g.

[0072] The test results of the saturated adsorption performance of toluene by the adsorbents prepared at different relative humidity are shown in Table 1.

[0073] Table 1 Saturated adsorption capacity of toluene by adsorbents at different relative humidity

[0074]

[0075]

[0076] From the comparison of the two sets of data in Table 1, it can be seen that the saturated adsorption capacity of toluene by the adsorbent loaded with pure silicon molecular sieve MCM-41 is slightly improved under dry conditions (RH=0); while under humid conditions of RH=60%, its saturated adsorption capacity of toluene is significantly improved, among which the adsorption capacity of toluene by 2.5NaY / MCM-41 is as high as 137.8 mg / g, which is about 8.07 times higher than that of its corresponding control sample.

Claims

1. A method for preparing a hydrophobic VOCs adsorbent NaY-MCM-41, comprising the following steps: (1) adding attapulgite to an acid solution, acid-washing for a period of time, washing with deionized water until neutral, and drying to obtain pretreated attapulgite; (2) mixing the pretreated attapulgite with a sodium hydroxide solution to form a slurry, transferring the slurry to a muffle furnace for calcination to obtain a solid, adding the solid to deionized water for ultrasonication, and centrifuging to obtain the supernatant as a silicon and aluminum source; (3) adding silica sol to the silicon-aluminum source, stirring, and transferring to a hydrothermal reactor for crystallization; after the hydrothermal reaction is completed, filtering, washing, and drying the product to obtain NaY molecular sieve; (4) dissolving hexadecyltrimethylammonium bromide (CTAB) in deionized water, adding silica sol and the NaY molecular sieve prepared in step (3), dropping sulfuric acid solution or hydrochloric acid solution to adjust the pH to 10-12, transferring to a hydrothermal reactor for crystallization, washing, drying, and calcining after the hydrothermal reaction to obtain a NaY-MCM-41 molecular sieve adsorbent; wherein the mass ratio of CTAB, deionized water, NaY molecular sieve, and silica sol is 1:(10-20):(0.5-3):(3-8); and the mass fraction of SiO2 in the silica sol is 30%-60%.

2. The preparation method according to claim 1, characterized in that The acid described in step (1) is one of hydrochloric acid or nitric acid; the concentration of the acid is 1 to 3 mol / L; the pickling time is 1 to 6 hours; and the volume ratio of the mass of the attapulgite to the acid solution is 1:(30 to 50) g / mL.

3. The preparation method according to claim 1, characterized in that The concentration of the sodium hydroxide solution in step (2) is 0.5 to 2 mol / L; the volume ratio of the mass of attapulgite to the sodium hydroxide solution is 1: (1~2)g / mL.

4. The preparation method according to claim 1, characterized in that In step (2), the calcination temperature is 300-600° C., the calcination time is 3-6 hours, the ultrasonic time is 0.5-2 hours, the centrifugal speed is 1000-4000 rpm, and the centrifugal time is 1-4 hours.

5. The preparation method according to claim 1, characterized in that The mass ratio of the silicon-aluminum source to the silica sol described in step (3) is (4-7):1; the mass fraction of SiO2 in the silica sol is 30%-60%.

6. The preparation method according to claim 1, characterized in that The stirring speed in step (3) is 300-500 rpm, and the stirring time is 3 to 6 hours; the crystallization temperature is 90 to 160° C., and the crystallization time is 24 to 96 hours.

7. The preparation method according to claim 1, characterized in that In step (4), the crystallization temperature is 100-120° C., and the crystallization time is 12 to 24 hours; the roasting temperature is 300 to 600° C., and the roasting time is 3 to 6 hours.

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