Modified 5a molecular sieve, its preparation and application

Abstract

The application discloses modified 5A molecular sieves, a preparation method and application thereof. The preparation method of the modified 5A molecular sieves comprises the following steps: (1) placing 5A molecular sieves in an ammonia water solution to perform ultrasonic treatment, then washing, first drying, and first calcining to obtain H-5A type molecular sieves; (2) adding sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol and carbomer into a hydrochloric acid solution to stir, and obtaining a mixed solution; (3) adding the H-5A molecular sieves into the mixed solution obtained in the step (2) to perform modification treatment, second drying and second calcining, and obtaining modified H-5A molecular sieves; and (4) placing the modified H-5A molecular sieves in a lithium salt solution to perform impregnation treatment, then performing third drying and third calcining, and obtaining modified 5A molecular sieves. The modified 5A molecular sieves have high adsorption capacity for ethane and propane, especially high adsorption and removal rates for ethane in VOCs, and good operation conditions.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, and particularly to a modified 5A molecular sieve for adsorbing small molecule alkanes, its preparation method, and its application. Background Technology

[0002] Among the VOCs emitted by the chemical industry, hydrocarbon molecules, represented by ethane and propane, have small molecular dynamics diameters and weak polarity, making them often difficult to remove. Current research on ethane and propane removal focuses on porous materials such as activated carbon and activated carbon fibers. Their abundant oxygen-containing and nitrogen-containing groups readily chemically adsorb VOC molecules or form stable hydrogen bonds, offering a significant adsorption capacity. However, activated carbon poses certain safety risks during storage, and carbon-based materials are not heat-resistant, leading to regeneration difficulties. Some research also focuses on metal-organic frameworks (MOFs). MOFs are zeolite-like materials with supramolecular microporous networks, characterized by high porosity, adjustable pore size, large specific surface area, structural plasticity, and high thermal stability. However, their high cost makes industrial production difficult. Molecular sieves possess adjustable-size, highly ordered microporous channels, rich framework structures, and good thermal stability, making them easy to regenerate. Among various types of molecular sieves, the effective pore size of the 5A molecular sieve with an LTA structure is approximately 0.51 nm, the kinetic diameter of ethane is 0.4 nm, and the kinetic boundary diameter of propane is approximately 0.43 nm. The pore window size of this molecular sieve conforms to the kinetic sieving of ethane and propane molecules, enabling effective adsorption of ethane and propane molecules into the pore interior. Furthermore, 5A molecular sieves synthesized by conventional methods only possess a microporous channel structure. The slow molecular diffusion rate and long molecular diffusion path within the micropores result in low utilization of the activity within the molecular sieve crystal, significantly limiting the rate of adsorption / desorption processes and consequently limiting the adsorption capacity. For ethane and propane in small molecule alkane VOCs, due to their weak polarity, adsorption is largely limited to the effects of van der Waals forces, resulting in weak adsorption and poor adsorption performance. Summary of the Invention

[0003] To address the problem that traditional 5A molecular sieves have weak adsorption capacity for small molecule alkanes in VOCs, and cannot fully adsorb ethane and propane molecules, this invention provides a modified 5A molecular sieve, its preparation method, and its application. The modified 5A molecular sieve exhibits strong adsorption capacity for ethane and propane, especially high adsorption and removal rate of ethane from VOCs, and operates under favorable conditions.

[0004] The first aspect of this invention provides a method for preparing modified 5A molecular sieves, comprising:

[0005] (1) The 5A molecular sieve was subjected to ultrasonic treatment in an ammonia solution, followed by washing, first drying, and first calcination to obtain H-5A type molecular sieve;

[0006] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol and carbomer to the hydrochloric acid solution, stir, and obtain a mixed solution;

[0007] (3) Add the H-5A molecular sieve obtained in step (1) to the mixed solution obtained in step (2) for modification treatment, followed by a second drying and a second calcination to obtain the modified H-5A molecular sieve.

[0008] (4) The modified H-5A molecular sieve obtained in step (3) is placed in a lithium salt solution for impregnation treatment, and then subjected to a third drying and a third calcination to obtain the modified 5A molecular sieve.

[0009] Furthermore, in step (1), the 5A molecular sieve is a commercial product, and the 5A molecular sieve has the following properties: a specific surface area of ​​350 m². 2 / g~550m 2 / g, pore volume 0.2cm 3 / g~0.5cm 3 / g, with an average pore size of 1nm to 5nm and an average particle diameter of 1mm to 3mm.

[0010] Further, in step (1), the mass concentration of the ammonia solution is 10wt% to 25wt%.

[0011] Further, in step (1), the volume ratio of the 5A molecular sieve to the ammonia solution is 1:5 to 10.

[0012] Further, in step (1), the conditions for ultrasonic treatment are: ultrasonic frequency of 2KHz~4KHz, ultrasonic temperature of 50℃~70℃, and time of 5h~15h.

[0013] Further, in step (1), the washing can be performed using conventional methods in the art. For example, rinsing with distilled water until the pH reaches 7.3–8.5. The first drying conditions are: a drying temperature of 60°C–150°C, preferably 80°C–120°C, and a drying time of 12h–24h. The first calcination conditions are: a calcination temperature of 400°C–700°C, preferably 450°C–650°C, and a calcination time of 3h–6h, with calcination taking place in an air atmosphere.

[0014] Further, in step (2), the mass concentration of the hydrochloric acid solution is 3wt% to 5wt%, preferably 3.5% to 4.5%.

[0015] Further, in step (2), the lignin sulfonate is selected from one or more of sodium lignin sulfonate, amine lignin sulfonate, and calcium lignin sulfonate.

[0016] Furthermore, in step (2), the average relative molecular mass of the polyethylene glycol is 600 to 800.

[0017] Further, in step (2), the mass ratio of lignin sulfonate, hydroxyethyl cellulose, polyethylene glycol and carbomer to hydrochloric acid (HCl) is 1:13-18:0.1-0.5:2-3:0.3-0.5.

[0018] Furthermore, in step (3), the volume ratio of the H-5A molecular sieve obtained in step (1) to the mixed solution obtained in step (2) is 1:7 to 10.

[0019] Further, in step (3), the conditions for the modification treatment are as follows: the modification is carried out under ultrasound, the frequency of the ultrasound is 2KHz~4KHz, the time is 5~10h, and the temperature is 50℃~100℃, preferably 60℃~80℃.

[0020] Further, in step (3), the conditions for the second drying are: a temperature of 60℃~150℃, preferably 80℃~120℃; and a time of 12h~24h. The conditions for the second calcination are: a calcination temperature of 400℃~700℃, preferably 450℃~650℃; and a time of 4h~8h; and calcination is carried out in an air atmosphere.

[0021] Further, in step (4), the lithium salt solution is at least one of lithium nitrate solution, lithium chloride solution, and lithium oxalate solution. The molar concentration of the lithium salt solution is 0.05–1 mol / L, preferably 0.25–0.5 mol / L.

[0022] Further, in step (4), the volume ratio of the modified H-5A molecular sieve to the lithium salt solution is 1:3 to 10. The impregnation treatment time is 12 to 48 hours, and the impregnation treatment temperature is 25°C to 75°C, preferably 40°C to 60°C. The number of impregnation treatments is preferably 3 to 6 times.

[0023] Further, in step (4), the conditions for the third drying are: a drying temperature of 60℃~150℃, preferably 80℃~120℃, and a drying time of 12h~24h. The conditions for the third calcination are: a calcination temperature of 400℃~700℃, preferably 450℃~650℃, a calcination time of 3h~6h, and calcination in an air atmosphere. The number of impregnation treatments is preferably 3~6 times.

[0024] A second aspect of the present invention provides a modified 5A molecular sieve prepared by the above method.

[0025] A third aspect of the present invention provides a modified 5A molecular sieve for adsorbing and separating small molecule alkanes in VOCs.

[0026] The adsorption separation process is as follows: using ethane and propane gases comprising 100–500 ppm as raw materials, the bed temperature is 15–32°C, the bed pressure is 0.1–2.5 MPa, and the mass hourly space velocity is 100–400 h⁻¹. -1 Under these conditions, the raw material comes into contact with the modified 5A molecular sieve, thereby undergoing adsorption and separation.

[0027] The modified 5A molecular sieve has an average particle size of 2 mm to 3 mm.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] In the process of modifying 5A molecular sieves, the first step is to replace them with H-type 5A molecular sieves, mainly by replacing the Na+ ions with larger diameter Na+ ions. + The removal of lignin provides a more unobstructed pore environment for subsequent modification. Lignosulfonates, hydroxyethyl cellulose, and polyethylene glycol are all good surfactants, and all possess functional groups such as hydroxyl, phenolic hydroxyl, alcoholic hydroxyl, and carboxyl groups, which enhance their adsorption capacity for small molecule hydrocarbons. After replacement with lithium salt solution, the diameter of the compensating cation increases, the Henry's constant increases, and the Li-5A molecular sieve exhibits a greater affinity for adsorbing small molecule alkanes. More importantly, Li... + After the compensating cation occupies the metal sites of the 5A molecular sieve, it can attract surfactants such as lignin sulfonate, hydroxyethyl cellulose, and polyethylene glycol, making the binding between these surfactants and the 5A molecular sieve tighter. This results in a more ideal synergistic adsorption effect of the surfactant and the compensating cation on small molecule alkanes, further enhancing the adsorption capacity of the 5A molecular sieve for ethane and propane molecules. Through the above technical solution, the modified 5A molecular sieve adsorbent prepared by this invention has the advantages of large adsorption capacity and high separation efficiency, further improving the adsorption capacity for ethane and propane in small molecule VOCs. Attached Figure Description

[0030] Figure 1 The image shows the XRD pattern of the modified 5A molecular sieve obtained in Example 1. Detailed Implementation

[0031] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0032] The technical solution and technical effects of the method of the present invention will be further described below with reference to embodiments and comparative examples, but the following embodiments do not constitute a limitation on the method of the present invention.

[0033] In this invention, CuKα is used as the radiation source, and an X-ray diffractometer (X'PertPROMPD type, Panaco GmbH, Netherlands) is used to test and analyze the crystal structure of the catalyst in the range of 2θ = 5° to 70°.

[0034] Example 1

[0035] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 / g, average pore size: 2.12nm, average particle diameter: 2.0mm), placed in 100mL of 25wt% ammonia solution and sonicated for 6h (ultrasonic frequency: 2KHz, ultrasonic temperature: 60℃), rinsed with distilled water until pH 7.5, then dried in an oven at 100℃ for 12h and calcined at 550℃ for 4h to obtain H-5A type molecular sieve.

[0036] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:14.5:0.15:2:0.44.

[0037] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the preliminarily modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:8), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 60℃, time is 6h), wash and place in an oven at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0038] (4) The secondary modified H-5A molecular sieve obtained in step (3) was placed in 100 mL of 0.25 mol / L lithium nitrate solution and impregnated at 45 °C for 24 h. After uniform mixing, it was dried at 100 °C for 12 h and calcined at 550 °C for 4 h. The above steps were repeated 3 times to obtain dried lithium-containing 5A molecular sieve. The XRD pattern is shown in [reference needed]. Figure 1 .

[0039] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0040] Example 2

[0041] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 / g, average pore size: 2.12nm, average particle diameter: 2.0mm), placed in 100mL of 20wt% ammonia solution and sonicated for 8h (ultrasonic frequency: 2KHz, ultrasonic temperature: 65℃), rinsed with distilled water until pH 8.0, dried in an oven at 100℃ for 12h, and calcined at 550℃ for 4h to obtain H-5A type molecular sieve.

[0042] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:16:0.15:2.5:0.4.

[0043] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the preliminarily modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:10), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 65℃, time is 6h), wash and place in an oven at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0044] (4) The secondary modified H-5A molecular sieve obtained in step (3) is placed in 100 mL of 0.5 mol / L lithium nitrate solution and immersed at 45 °C for 24 h. After uniform mixing, it is dried at 100 °C for 12 h and calcined at 550 °C for 4 h. The above steps are repeated 6 times to obtain dried lithium-containing 5A molecular sieve.

[0045] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0046] Example 3

[0047] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 / g, average pore size: 2.12nm, average particle diameter: 2.0mm), was placed in 100mL of 15wt% ammonia solution and sonicated for 8h (ultrasonic frequency: 4KHz, ultrasonic temperature: 70℃), rinsed with distilled water, washed until pH 8.5, dried in an oven at 80℃ for 24h, and calcined at 650℃ for 6h to obtain H-5A type molecular sieve.

[0048] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol and carbomer to a 5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600) and carbomer to HCl is 1:18:0.5:2:0.5.

[0049] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the pre-modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:10), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 70℃, time is 5h), wash and place in an oven at 80℃ for 24h, and calcine at 650℃ for 6h to obtain the secondary modified H-5A molecular sieve.

[0050] (4) The secondary modified H-5A molecular sieve obtained in step (3) is placed in 100 mL of 0.25 mol / L lithium nitrate solution, immersed at 60 °C for 24 h, mixed evenly, dried at 100 °C for 12 h, and calcined at 550 °C for 4 h. The above steps are repeated 5 times to obtain dried lithium-containing 5A molecular sieve.

[0051] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0052] Example 4

[0053] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 The sample (g, average pore size: 2.12 nm, average particle diameter: 2.0 mm) was placed in 100 mL of 25 wt% ammonia solution and sonicated for 6 h (ultrasonic frequency: 2 kHz, ultrasonic temperature: 50 °C). It was then rinsed with distilled water until the pH reached 7.5. After washing, it was dried in an oven at 100 °C for 12 h and calcined at 550 °C for 4 h to obtain H-5A type molecular sieve.

[0054] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:14.5:0.15:2:0.44.

[0055] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the preliminarily modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:8), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 50℃, time is 8h), wash and place in an oven at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0056] (4) The secondary modified H-5A molecular sieve obtained in step (3) is placed in 100 mL of 0.05 mol / L lithium nitrate solution, immersed at 25 °C for 24 h, mixed evenly, dried at 100 °C for 12 h, and calcined at 550 °C for 4 h. The above steps are repeated 3 times to obtain dried lithium-containing 5A molecular sieve.

[0057] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0058] Comparative Example 1

[0059] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 The sample (g, average pore size: 2.12 nm, average particle diameter: 2.0 mm) was placed in 100 mL of 25 wt% ammonia solution and sonicated for 6 h (ultrasonic frequency: 2 kHz, ultrasonic temperature: 50 °C). It was then rinsed with distilled water until the pH reached 7.5. After washing, it was dried in an oven at 100 °C for 12 h and calcined at 550 °C for 4 h to obtain H-5A type molecular sieve.

[0060] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:14.5:0.15:2:0.44.

[0061] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the preliminarily modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:8), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 60℃, time is 6h), wash and place in an oven at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0062] (4) The secondary modified H-5A molecular sieve obtained in step (3) is placed in 100 mL of 1.5 mol / L lithium nitrate solution and immersed at 25 °C for 24 h. After being mixed evenly, it is dried at 100 °C for 12 h and calcined at 550 °C for 4 h. The above steps are repeated 3 times to obtain dried lithium-containing 5A molecular sieve.

[0063] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0064] Comparative Example 2

[0065] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 / g, average pore size: 2.12nm, average particle diameter: 2.0mm), was placed in 100mL of 25wt% ammonia solution and sonicated for 6h (ultrasonic frequency: 2KHz, ultrasonic temperature: 60℃), rinsed with distilled water, washed until pH 7.5, dried in an oven at 100℃ for 12h, and calcined at 550℃ for 4h to obtain H-5A type molecular sieve.

[0066] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:14.5:0.15:2:0.44.

[0067] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the preliminarily modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:8), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 60℃, time is 6h), wash and place in an oven at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0068] (4) The secondary modified H-5A molecular sieve obtained in step (3) is placed in 100 mL of 0.04 mol / L lithium nitrate solution and immersed at 45 °C for 24 h. After uniform mixing, it is dried at 100 °C for 12 h and calcined at 550 °C for 4 h. The above steps are repeated 3 times to obtain dried lithium-containing 5A molecular sieve.

[0069] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0070] Comparative Example 3

[0071] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 / g, average pore size: 2.12nm, average particle diameter: 2.0mm), was placed in 100mL of 25wt% ammonia solution and sonicated for 6h (ultrasonic frequency: 2KHz, ultrasonic temperature: 50℃), rinsed with distilled water, washed until pH 7.5, dried in an oven at 100℃ for 12h, and calcined at 700℃ for 4h to obtain H-5A type molecular sieve.

[0072] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:14.5:0.15:2:0.44.

[0073] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the preliminarily modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:8), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 60℃, time is 6h), wash and place in an oven at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0074] (4) Dynamic evaluation of the adsorbent in the fixed-bed adsorption device: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23℃, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0075] Comparative Example 4

[0076] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 / g, average pore size: 2.12nm, average particle diameter: 2.0mm), was placed in 100mL of 25% ammonia solution and sonicated for 6h (ultrasonic frequency: 2KHz, ultrasonic temperature: 50℃), rinsed with distilled water, washed until pH 7.5, dried in an oven at 100℃ for 12h, and calcined at 700℃ for 4h to obtain H-5A type molecular sieve.

[0077] (2) The modified H-5A molecular sieve obtained in step (1) was placed in 100 mL of 0.25 mol / L lithium nitrate solution and immersed at 45 °C for 24 h. After being mixed evenly, it was dried at 100 °C for 12 h and calcined at 550 °C for 4 h. The above steps were repeated 3 times to obtain dried lithium-containing 5A molecular sieve.

[0078] (3) Dynamic evaluation of the adsorbent in the fixed-bed adsorption device: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23℃, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0079] Comparative Example 5

[0080] (1) Measure 20 mL of spherical 5A molecular sieve (commercial product, main properties are as follows: specific surface area: 550 cm²). 2 / g, pore volume: 0.35cm 3 The sample (g, average pore size: 2.12 nm, average particle diameter: 2.0 mm) was placed in 100 mL of 25% ammonia solution and sonicated for 6 h (ultrasonic frequency: 2 kHz, ultrasonic temperature: 60 °C). It was then rinsed with distilled water until the pH reached 7.5. After washing, it was dried in an oven at 100 °C for 12 h and calcined at 550 °C for 4 h to obtain H-5A type molecular sieve.

[0081] (2) Add sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol, and carbomer to a 3.5 wt% hydrochloric acid solution and stir until homogeneous to form a mixed solution. The mass ratio of sodium lignosulfonate, hydroxyethyl cellulose, polyethylene glycol (average relative molecular mass of 600), and carbomer to HCl is 1:19:0.05:4.5:0.65.

[0082] (3) Add the 5A molecular sieve from step (1) to the solution from step (2) (the volume ratio of the pre-modified 5A molecular sieve to the mixed solution obtained in step (2) is 1:8), mix evenly by ultrasonic oscillation (ultrasonic frequency is 2KHz, ultrasonic temperature is 60℃), wash and place in an oven to dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain the secondary modified H-5A molecular sieve.

[0083] (4) The secondary modified H-5A molecular sieve obtained in step (3) is placed in 100 mL of 0.25 mol / L lithium nitrate solution and immersed at 45 °C for 24 h. After being mixed evenly, it is dried at 100 °C for 12 h and calcined at 550 °C for 4 h. The above steps are repeated 3 times to obtain dried lithium-containing 5A molecular sieve.

[0084] (5) Dynamic evaluation of the adsorbent in the fixed-bed adsorption unit: The reaction gas was 200 ppm ethane gas and 200 ppm propane gas (balance gas: air), the modified 5A molecular sieve was packed to a height of 10 cm, the adsorbent bed temperature was 23 °C, the bed pressure was 0.2 MPa, and the space velocity was 400 h⁻¹. -1 The experimental results are shown in Table 1 below.

[0085] Table 1

[0086]

[0087] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing modified 5A molecular sieve, characterized in that, include: (1) The 5A molecular sieve was subjected to ultrasonic treatment in an ammonia solution, followed by washing, first drying, and first calcination to obtain H-5A type molecular sieve; (2) Add lignin sulfonate, hydroxyethyl cellulose, polyethylene glycol and carbomer to hydrochloric acid solution, stir to obtain a mixed solution; (3) Add the H-5A molecular sieve obtained in step (1) to the mixed solution obtained in step (2) for modification treatment, followed by a second drying and a second calcination to obtain the modified H-5A molecular sieve; (4) The modified H-5A molecular sieve obtained in step (3) is placed in a lithium salt solution for impregnation treatment, and then subjected to a third drying and a third calcination to obtain the modified 5A molecular sieve. In step (2), the mass ratio of lignin sulfonate, hydroxyethyl cellulose, polyethylene glycol and carbomer to hydrochloric acid is 1:13~18:0.1~0.5:2~3:0.3~0.5; The molar concentration of the lithium salt solution is 0.05~1 mol / L; The modified 5A molecular sieve is used to adsorb and separate small molecule alkanes from VOCs.

2. The preparation method according to claim 1, characterized in that, The volume ratio of the 5A molecular sieve to the ammonia solution is 1:5~10.

3. The preparation method according to claim 1, characterized in that, In step (1), the conditions for ultrasonic treatment are: ultrasonic frequency of 2KHz~4KHz, ultrasonic temperature of 50℃~70℃, and time of 5h~15h.

4. The preparation method according to claim 1, characterized in that, The first drying conditions are: a drying temperature of 60℃~150℃ and a drying time of 12h~24h; the first calcination conditions are: a calcination temperature of 400℃~700℃ and a calcination time of 3h~6h.

5. The preparation method according to claim 4, characterized in that, The first drying conditions are: a drying temperature of 80℃~120℃; the first calcination conditions are: a calcination temperature of 450℃~650℃.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass concentration of the hydrochloric acid solution is 3wt%~5wt%.

7. The preparation method according to claim 6, characterized in that, In step (2), the mass concentration of the hydrochloric acid solution is 3.5wt%~4.5wt%.

8. The preparation method according to claim 1, characterized in that, In step (2), the lignin sulfonate is selected from one or more of sodium lignin sulfonate, amine lignin sulfonate, and calcium lignin sulfonate.

9. The preparation method according to claim 1, characterized in that, In step (3), the conditions for the modification treatment are: the modification is carried out under ultrasound, the frequency of the ultrasound is 2KHz~4KHz, the time is 5~10h, and the temperature is 50℃~100℃.

10. The preparation method according to claim 1, characterized in that, In step (3), the conditions for the modification treatment are: temperature of 60℃~80℃.

11. The preparation method according to claim 1, characterized in that, In step (3), the conditions for the second drying are: temperature of 60℃~150℃ and time of 12h~24h; the conditions for the second calcination are: calcination temperature of 400℃~700℃ and time of 4h~8h.

12. The preparation method according to claim 11, characterized in that, In step (3), the conditions for the second drying are: a temperature of 80℃~120℃, and the conditions for the second roasting are: a roasting temperature of 450℃~650℃.

13. The preparation method according to claim 1, characterized in that, In step (4), the lithium salt solution is at least one of lithium nitrate solution, lithium chloride solution and lithium oxalate solution; the molar concentration of the lithium salt solution is 0.25~0.5 mol / L.

14. The preparation method according to claim 1, characterized in that, In step (4), the conditions for the third drying are: drying temperature of 60℃~150℃ and drying time of 12h~24h; the conditions for the third roasting are: roasting temperature of 400℃~700℃.

15. The preparation method according to claim 14, characterized in that, In step (4), the conditions for the third drying are: the drying temperature is 80℃~120℃, and the conditions for the third roasting are: the roasting temperature is 450℃~650℃.

16. A modified 5A molecular sieve prepared by the method according to any one of claims 1-15.

17. The application of the modified 5A molecular sieve according to claim 16 in the adsorption and separation of small molecule alkanes in VOCs.

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