A preparation method of high-silicon molecular sieve for adsorption and desorption of easily polymerized VOCs

Abstract

The present invention relates to the technical field of industrial flue gas purification, and in particular to a preparation method of a high-silicon molecular sieve for adsorption and desorption of easily polymerized VOCs, comprising: stirring tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide in a certain proportion for a period of time to prepare a clear solution, then transferring it into an autoclave for reaction for a period of time to obtain a FAU crystal nucleus solution; then mixing a certain proportion of silica sol, sodium aluminate, sodium hydroxide, an organic structure directing agent and deionized water into a gel, then adding the FAU crystal nucleus solution and stirring, loading it into an autoclave for crystallization, washing and drying the obtained solid, and finally calcining it in the air for a period of time to obtain a high-silicon molecular sieve. The present invention realizes the direct synthesis of high-silicon molecular sieves, solves the problem of pore blockage in traditional molecular sieves when adsorbing and desorbing easily self-polymerized VOCs, and has good application prospects and economic benefits in the field of industrial VOCs flue gas purification.

Description

Technical Field

[0001] The invention relates to the technical field of industrial flue gas purification, and in particular to a method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs. Background Art

[0002] In the past few decades, the emission of volatile organic compounds (VOCs) in industry and transportation has increased significantly, seriously endangering the entire ecosystem. The main source of VOCs emission in China is industrial sources (accounting for about 55.5% of all emission sources). VOCs industrial emissions mainly come from industries such as petrochemicals and coal chemicals, packaging and printing, and surface coating (furniture manufacturing, automobile manufacturing), with annual emissions exceeding 1 million tons. Adsorption is considered to be an effective method due to its high removal efficiency and low cost, and the VOCs recovered by desorption have commercial value. The key to the adsorption and concentration of low-concentration VOCs is the adsorption material. Zeolite materials with ordered microporous structures, large surface areas, and high thermal / hydrothermal stability have been proven to be innovative adsorbents for removing VOCs. Among them, the FAU family of molecular sieves has 3D 12-membered ring (MR) channels and spherical super cages (diameter ≈ 1.12nm). In order to reduce the acid sites of the molecular sieve and enhance the hydrophobicity of the FAU zeolite, repeated dealumination processes are used to obtain high-silicon counterparts. Moreover, these post-treatment procedures are complicated, time-consuming and labor-intensive, and cannot avoid the dealumination gradient, which is not as perfect as the directly synthesized zeolite structure.

[0003] At present, domestic molecular sieves cannot be thermally regenerated after adsorbing easily polymerized VOCs and have problems such as poor hydrophobicity, resulting in high VOCs treatment costs. Generally speaking, the regeneration of waste molecular sieves is completed by thermal methods. However, the difficulty lies in that after the molecular sieve adsorbs VOCs molecules with unsaturated bonds (such as styrene), under the catalytic action of the surface acidic sites, such VOCs will undergo a chain extension reaction and polymerize into high-boiling point macromolecular organic species. As the carbon chain continues to increase, its desorption temperature also increases. When the boiling point exceeds the maximum desorption temperature of the rotor (250°C), the high-boiling point polymers that have not been desorbed will clog the pores of the molecular sieve, reducing the service life of the rotor, thereby increasing the cost of VOCs waste gas treatment in the factory. In order to avoid the polymerization of styrene monomers through thermal treatment before the temperature of the waste molecular sieve rises to the point where styrene will be desorbed, it is best to directly synthesize high-silicon molecular sieves. Therefore, the present application uses a highly dispersed starting FAU crystal nucleus solution containing tetraethylammonium hydroxide (TEAOH) and a bulky organic structure directing agent (OSDA) in a low-alkalinity gel system to guide the crystal growth of a high-silicon FAU structure and synthesize a high-silicon molecular sieve in one step. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings existing in the prior art and propose a method for preparing a high-silicon molecular sieve for the adsorption and desorption of easily polymerized VOCs. The molecular sieve prepared thereby solves the industry problem of pore clogging when traditional molecular sieve materials adsorb and desorb easily polymerized VOCs, and has good application prospects and economic benefits in the field of industrial VOCs flue gas purification.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, the specific steps are as follows:

[0007] Step 1: Tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are stirred for a period of time in a certain proportion to prepare a mixed solution;

[0008] Step 2: The mixed solution in step 1 is transferred into an autoclave and reacted at a certain temperature for a period of time to obtain a FAU crystal nucleus solution;

[0009] Step 3: A certain proportion of silica sol, sodium aluminate, sodium hydroxide, an organic structure directing agent and deionized water are mixed to form an initial gel, and then the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel;

[0010] Step 4: The final gel in step 3 is placed in a high pressure reactor and crystallized at a certain temperature for several days to obtain a precipitate containing a high silicon molecular sieve;

[0011] Step 5: Wash the precipitate obtained in the reaction of step 4, dry and filter the obtained solid, and calcine it in a muffle furnace for a period of time to obtain a high-silicon molecular sieve.

[0012] Preferably, in step 1, the molar ratio of tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide is 1:0.2:0.02:1.2.

[0013] Preferably, in step 1, the stirring time of the mixed solution is 2 hours.

[0014] Preferably, in step 2, the reaction temperature of the autoclave is 50-100° C., and the reaction time is 12-48 hours.

[0015] Preferably, in step 3, the organic structure directing agent is any one or more of tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide and 15-crown ether-5.

[0016] Preferably, in step 3, the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, organic structure directing agent and deionized water is 1:(0.02-0.033):(0.08-0.12):(0.15-0.32):20.

[0017] Preferably, in step 3, the silicon dioxide in the FAU crystal nucleus solution accounts for 10% of the silicon dioxide in the initial gel.

[0018] Preferably, in step 4, the reaction temperature of the autoclave is 120° C., and the reaction time is 6.5 to 7 days.

[0019] Preferably, in step 5, the calcination heating rate of the muffle furnace is 1-10° C. / min, the constant temperature maintained during calcination is 500-600° C., and the calcination time is 5-6 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The high-silicon molecular sieve prepared by the present invention is used as an adsorbent, has a high specific surface area and pore volume, can effectively adsorb easily polymerized VOCs, and can be repeatedly desorbed and used.

[0022] 2. The preparation method of the present invention is easy to operate and can be used for large-scale industrial production.

[0023] 3. The present invention realizes the direct synthesis of high-silicon molecular sieves, solves the problem of pore blockage in traditional molecular sieves when adsorbing and desorbing self-polymerizing VOCs, and has good application prospects and economic benefits in the field of industrial VOCs flue gas purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD diagram of the high-silicon molecular sieve obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the advantages and features of the present invention, thereby making a clearer definition of the protection scope of the present invention. The embodiments described in the present invention are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0026] Embodiment 1:

[0027] A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, the specific steps are as follows:

[0028] Step 1, tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are mixed and stirred for 2 hours in a molar ratio of (1:0.2:0.02:1.2) to obtain a uniform mixed solution;

[0029] Step 2, transferring the mixed solution in step 1 into an autoclave, and reacting at 50-100° C. for 12-48 hours to obtain a FAU crystal nucleus solution;

[0030] Step 3, silica sol, sodium aluminate, sodium hydroxide, tetrabutylammonium hydroxide and deionized water are mixed in a molar ratio of (1:0.025:0.20:0.2:20) to form an initial gel, and then 10% of the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel;

[0031] Step 4, transferring the final gel in step 3 into an autoclave and reacting at 120° C. for 4.5 days to obtain a precipitate containing high-silicon molecular sieve;

[0032] Step 5: Wash the precipitate after the reaction in step 4, dry and filter the solid, heat it to 600°C at a heating rate of 2°C / min in a muffle furnace, and maintain this temperature for 6 hours. The obtained product is a high-silicon molecular sieve.

[0033] Figure 1 The XRD diagram of the prepared high-silicon molecular sieve is shown in Figure 2. Characterization shows that the prepared molecular sieve is a high-silicon molecular sieve.

[0034] The high-silicon molecular sieve prepared in Example 1 to solve the pore clogging problem during the desorption of easily polymerized VOCs was used for styrene adsorption, and a good adsorption effect was obtained. The experimental results show that: at room temperature, after this type of high-silicon molecular sieve adsorbs styrene to saturation, it can be desorbed quickly at 280°C, and no obvious carbon deposition is found. The adsorption efficiency can be maintained stable, showing an excellent desorption effect.

[0035] Embodiment 2:

[0036] A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, the specific steps are as follows:

[0037] Step 1, tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are mixed and stirred for 2 hours in a molar ratio of (1:0.2:0.02:1.2) to obtain a uniform mixed solution;

[0038] Step 2, transferring the mixed solution in step 1 into an autoclave, and reacting at 50-100° C. for 12-48 hours to obtain a FAU crystal nucleus solution;

[0039] Step 3, silica sol, sodium aluminate, sodium hydroxide, tetrabutylammonium hydroxide and deionized water are mixed in a molar ratio of (1:0.025:0.19:0.2:20) to form an initial gel, and then 10% of the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel;

[0040] Step 4, transferring the final gel in step 3 into an autoclave and reacting at 120° C. for 4.5 days to obtain a precipitate containing high-silicon molecular sieve;

[0041] Step 5: Wash the precipitate after the reaction in step 4, dry and filter the solid, heat it to 600°C at a heating rate of 2°C / min in a muffle furnace, and maintain this temperature for 6 hours. The obtained product is a high-silicon molecular sieve.

[0042] The high-silicon molecular sieve prepared in Example 2 to solve the clogging problem in the desorption process of self-polymerized VOCs was used for styrene adsorption, and a good adsorption effect was obtained. The experimental results showed that: at room temperature, after the high-silicon molecular sieve adsorbed styrene to saturation, it could be desorbed quickly at 280°C, and no obvious carbon deposition was found. The adsorption efficiency could be maintained stable, showing an excellent desorption effect.

[0043] Embodiment 3:

[0044] A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, the specific steps are as follows:

[0045] Step 1, tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are mixed and stirred for 2 hours in a molar ratio of (1:0.2:0.02:1.2) to obtain a uniform mixed solution;

[0046] Step 2, transferring the mixed solution in step 1 into an autoclave, and reacting at 50-100° C. for 12-48 hours to obtain a FAU crystal nucleus solution;

[0047] Step 3, silica sol, sodium aluminate, sodium hydroxide, tetrabutylammonium hydroxide and deionized water are mixed in a molar ratio of (1:0.025:0.18:0.2:20) to form an initial gel, and then 10% of the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel;

[0048] Step 4, transferring the final gel in step 3 into an autoclave and reacting at 120° C. for 4.5 days to obtain a precipitate containing high-silicon molecular sieve;

[0049] Step 5: Wash the precipitate after the reaction in step 4, dry and filter the solid, heat it to 600°C at a heating rate of 2°C / min in a muffle furnace, and maintain this temperature for 6 hours. The obtained product is a high-silicon molecular sieve.

[0050] The high-silicon molecular sieve prepared in Example 3 to solve the clogging problem in the desorption process of self-polymerized VOCs was used for styrene adsorption, and a good adsorption effect was obtained. The experimental results showed that: at room temperature, after the high-silicon molecular sieve adsorbed styrene to saturation, it could be desorbed quickly at 280°C, and no obvious carbon deposition was found. The adsorption efficiency could be maintained stable, showing an excellent desorption effect.

[0051] Embodiment 4:

[0052] A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, the specific steps are as follows:

[0053] Step 1, tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are mixed and stirred for 2 hours in a molar ratio of (1:0.2:0.02:1.2) to obtain a uniform mixed solution;

[0054] Step 2, transferring the mixed solution in step 1 into an autoclave, and reacting at 50-100° C. for 12-48 hours to obtain a FAU crystal nucleus solution;

[0055] Step 3, silica sol, sodium aluminate, sodium hydroxide, tetrabutylammonium hydroxide and deionized water are mixed in a molar ratio of (1:0.025:0.17:0.2:20) to form an initial gel, and then 10% of the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel;

[0056] Step 4, transferring the final gel in step 3 into an autoclave and reacting at 120° C. for 4.5 days to obtain a precipitate containing high-silicon molecular sieve;

[0057] Step 5: Wash the precipitate after the reaction in step 4, dry and filter the solid, heat it to 600°C at a heating rate of 2°C / min in a muffle furnace, and maintain this temperature for 6 hours. The obtained product is a high-silicon molecular sieve.

[0058] The high-silicon molecular sieve prepared in Example 4 to solve the clogging problem in the desorption process of self-polymerized VOCs was used for styrene adsorption, and a good adsorption effect was obtained. The experimental results showed that: at room temperature, after the high-silicon molecular sieve adsorbed styrene to saturation, it could be desorbed quickly at 280°C, and no obvious carbon deposition was found. The adsorption efficiency could be maintained stable, showing an excellent desorption effect.

[0059] Embodiment 5:

[0060] A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, the specific steps are as follows:

[0061] Step 1, tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are mixed and stirred for 2 hours in a molar ratio of (1:0.2:0.02:1.2) to obtain a uniform mixed solution;

[0062] Step 2, transferring the mixed solution in step 1 into an autoclave, and reacting at 50-100° C. for 12-48 hours to obtain a FAU crystal nucleus solution;

[0063] Step 3, silica sol, sodium aluminate, sodium hydroxide, tetrabutylammonium hydroxide and deionized water are mixed in a molar ratio of (1:0.025:0.16:0.2:20) to form an initial gel, and then 10% of the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel;

[0064] Step 4, transferring the final gel in step 3 into an autoclave and reacting at 120° C. for 4.5 days to obtain a precipitate containing high-silicon molecular sieve;

[0065] Step 5: Wash the precipitate after the reaction in step 4, dry and filter the solid, heat it to 600°C at a heating rate of 2°C / min in a muffle furnace, and maintain this temperature for 6 hours. The obtained product is a high-silicon molecular sieve.

[0066] The high-silicon molecular sieve prepared in Example 5 to solve the clogging problem in the desorption process of self-polymerized VOCs was used for styrene adsorption, and a good adsorption effect was obtained. The experimental results showed that: at room temperature, after the high-silicon molecular sieve adsorbed styrene to saturation, it could be desorbed quickly at 280°C, and no obvious carbon deposition was found. The adsorption efficiency could be maintained stable, showing an excellent desorption effect.

[0067] Comparative Example 1:

[0068] The activation method of commercial molecular sieves comprises the following steps:

[0069] Step 1, put 100 mg of commercial molecular sieve into a crucible and place it in a muffle furnace;

[0070] Step 2: Raise the temperature to 400°C at a rate of 2°C / min and maintain this temperature for 3 hours. After the reaction is completed, the product obtained is the activated molecular sieve.

[0071] The molecular sieve prepared in Control Example 1 was used for styrene adsorption. At room temperature, after the high-silicon molecular sieve was saturated with styrene, desorption was performed at 280°C. The color of the molecular sieve changed from white to yellow, indicating that styrene had undergone polymerization, and obvious carbon deposition appeared on the surface, indicating that its desorption effect was poor.

[0072] In summary, the present invention realizes the direct synthesis of high-silicon molecular sieves, solves the problem of pore blockage in traditional molecular sieves when adsorbing and desorbing self-polymerizing VOCs, and has good application prospects and economic benefits in the field of industrial VOCs flue gas purification.

[0073] The description and practice disclosed in the present invention are easy to think and understand for ordinary technicians in the technical field, and several improvements and modifications can be made without departing from the principles of the present invention. Therefore, modifications or improvements made without departing from the spirit of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs, characterized in that: The specific steps are as follows: Step 1: Tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide are stirred for a period of time in a certain proportion to prepare a mixed solution; Step 2: The mixed solution in step 1 is transferred into an autoclave and reacted at a certain temperature for a period of time to obtain a FAU crystal nucleus solution; Step 3: A certain proportion of silica sol, sodium aluminate, sodium hydroxide, an organic structure directing agent and deionized water are mixed to form an initial gel, and then the FAU crystal nucleus solution in step 2 is added and stirred for a period of time to form a final gel; Step 4: The final gel in step 3 is placed in a high pressure reactor and crystallized at a certain temperature for several days to obtain a precipitate containing a high silicon molecular sieve; Step 5: Wash the precipitate obtained in the reaction in step 4, dry and filter the obtained solid, and calcine it in a muffle furnace for a period of time to obtain a high-silicon molecular sieve; In step 1, the molar ratio of tetraethyl silicate, aluminum isopropoxide, sodium hydroxide and tetraethylammonium hydroxide is 1:0.2:0.02:1.2; In step 1, the stirring time of the mixed solution is 2 hours; In step 2, the reaction temperature of the autoclave is 50-100° C., and the reaction time is 12-48 hours; In step 3, the organic structure directing agent is tetrabutylammonium hydroxide; In step 3, the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, organic structure directing agent and deionized water is 1: (0.02-0.033): (0.08-0.12): (0.15-0.32): 20; In step 3, the silica in the FAU crystal nucleus solution accounts for 10% of the silica in the initial gel.

2. The method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs according to claim 1, characterized in that: In step 4, the reaction temperature of the high-pressure reactor is 120° C., and the reaction time is 6.5 to 7 days.

3. The method for preparing a high-silicon molecular sieve for adsorption and desorption of easily polymerizable VOCs according to claim 1, characterized in that: In step 5, the calcination heating rate of the muffle furnace is 1-10°C / min, the constant temperature maintained during calcination is 500-600°C, and the calcination time is 5-6h.

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