Plasma activation synthesis method and application of nanoscale BEA type molecular sieve

Abstract

The invention discloses a plasma activation synthesis method and application of a nanoscale BEA type molecular sieve in the technical field of molecular sieve synthesis, in raw materials used in the method, a silicon source is calculated by SiO2, an aluminum source is calculated by Al2O3, and the molar ratio of effective components of the raw materials is SiO2: Al2O3: template agent: pure water = (15-50): 1: (3.7-4.2): (60-80); the method comprises the following steps: carrying out plasma pretreatment on raw materials in an ion reactor, transferring the pretreated raw materials into a homogeneous reactor, carrying out a constant-temperature crystallization reaction, and adding strong acid into crystallized slurry as a flocculating agent for flocculation; and filtering, washing, drying, roasting and crushing the flocculate to obtain the nano-scale BEA type molecular sieve. The method is low in synthesis cost, the process is simple and easy to operate, the reaction is efficient and controllable, and the synthesized nano-scale BEA molecular sieve can be applied to adsorption separation of organic benzene substances in air and has the characteristics of high selectivity and high adsorption capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve material synthesis, and particularly relates to a method and use for synthesizing nanoscale BEA zeolite by plasma activation. Background Art

[0002] Benzene series in the air refer to a class of organic compounds that exist in the air and have adverse effects on human health, including benzene, toluene, o-xylene, m-xylene, p-xylene, etc. Common sources of benzene series pollution in daily life include factory emissions, vehicle exhaust, adhesives, paints, and wood-based panel furniture. As a first-class carcinogen, benzene can cause many chronic diseases after long-term exposure. Long-term inhalation of relatively high concentrations of toxic and harmful benzene series gases can cause headaches, dizziness, insomnia, and memory decline, and is prone to lead to blood system diseases.

[0003] Therefore, the treatment of benzene series-containing waste gas has attracted more and more attention and has become one of the key points in the treatment of air pollutants. According to different process flows and emission methods of benzene series-containing waste gas, there are different treatment technologies. Currently, more studied ones include adsorption method, absorption method, thermal destruction method, membrane separation method, biological method, photocatalysis method, and plasma method, etc. Among them, the most widely used is the adsorption method.

[0004] Zeolite molecular sieve is an inorganic crystal material, which is widely used in the fields of catalysis, adsorption, and ion exchange due to its regular pore structure, strong acidity, and high hydrothermal stability, and plays an irreplaceable role. It has been widely used in the petrochemical industry, detergent industry, fine chemical industry, etc. In the research of zeolite molecular sieves, the research on preparing molecular sieves and their functions from cheap natural minerals as raw materials is one of the most valuable researches in this field. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a plasma activation synthesis method for nanoscale BEA zeolite. The obtained zeolite has high selectivity and high adsorption capacity in the adsorption and separation of organic benzene.

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted: A plasma activation synthesis method for nanoscale BEA zeolite, comprising the following steps:

[0007] S1. Mix the raw material silicon source, aluminum source, template agent and pure water, and stir at room temperature to obtain a clear solution; the silicon source is one of silica sol, silicon powder, solid silica gel, fumed silica, water glass and tetraethyl orthosilicate; the aluminum source is one of alumina, aluminum hydroxide and sodium aluminate; the template agent is tetraethylammonium hydroxide; wherein, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the molar ratio of the effective components of each raw material is SiO2:Al2O3:template agent:pure water = (15 - 50):1:(3.7 - 4.2):(60 - 80);

[0008] S2. Transfer the clear solution in step S1 to a plasma reactor for plasma pretreatment; use direct current arc discharge to generate high-temperature plasma, and the high-energy plasma beam excites the active factors in the raw materials to undergo energy collision, and quickly form molecular sieve crystal nuclei after exchanging energy;

[0009] S3. Transfer the pretreatment liquid in step S2 to a homogeneous reactor for isothermal crystallization reaction;

[0010] S4. After the isothermal reaction in step S3 ends, add a strong acid as a flocculant to the crystallization slurry for flocculation;

[0011] S5. The flocculated flocs are filtered, washed, dried, calcined and pulverized to obtain nano-scale BEA type molecular sieve.

[0012] Furthermore, the silicon source is silicon powder and the aluminum source is alumina. Its cost is low, and it can effectively reduce the influence of heteroatoms in the silicon source and aluminum source on the crystallization product.

[0013] Furthermore, the particle size range of the silicon powder is 50 - 150 microns; the particle size range of the alumina is 60 - 90 microns; the template agent is diluted into a 25% mass fraction aqueous solution of tetraethylammonium hydroxide before use.

[0014] During plasma pretreatment, the vacuum degree is 100 - 150 Pa; the discharge power is 150 - 250 W; nitrogen is used as the protective carrier gas, and the carrier gas flow rate is 30 - 80 ml / min; the treatment time is 5 - 10 min.

[0015] Furthermore, in step S3, it is set to rise to 160 °C at a heating rate of 20 °C / h for isothermal crystallization reaction for 12 h; after the reaction ends, it is cooled to room temperature at a cooling rate of 30 °C / h to obtain a crystallization slurry.

[0016] Furthermore, the flocculant is solid oxalic acid; the addition amount is 0.5% of the total mass fraction of the slurry; the flocculation time is 2 - 4 h.

[0017] Further, in step S5, after washing, it is dried at 120-130°C for 20-25 h to volatilize moisture at a low temperature; then it is calcined at 500-560°C for 8-10 h to remove the flocculant and template agent at a high temperature, forming an open porous structure to ensure smooth pore channels and improve the adsorption capacity; then it is mechanically pulverized and pneumatically pulverized to obtain nano-sized BEA zeolite molecular sieve.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Generally, when preparing zeolite molecular sieve, it is necessary to add a certain proportion of high-crystallinity pure-phase seeds. The present invention uses a DC arc discharge to generate high-temperature plasma, and precisely controls important parameters such as the vacuum degree, discharge power, carrier gas flow rate, and treatment time of the plasma pretreatment. The high-energy plasma beam excites the active factors in the raw materials to undergo energy collision, and a large number of highly active free radical nano-sized crystal nuclei are rapidly formed after exchanging energy. It is transferred to a homogeneous reactor, and gradient temperature program control is carried out to avoid temperature fluctuations during the crystallization reaction, and regular crystals are rapidly formed in all directions. The whole process is simple and easy to operate, and the reaction is highly efficient and controllable.

[0020] 2. The preparation method of the present invention does not require specific silicon sources and aluminum sources, and silicon powder and alumina, which are low-cost and easily available, can be selected. The template agent is tetraethylammonium hydroxide, which is a key factor in the synthesis of BEA zeolite molecular sieve, can guide the formation of the unique crystal structure of the zeolite molecular sieve, and has a certain structure-directing effect. In addition, a strong alkaline system is beneficial to the crystal growth and crystallization of BEA zeolite molecular sieve, and tetraethylammonium hydroxide belongs to organic quaternary ammonium base, and its alkalinity is stronger than that of sodium hydroxide and potassium hydroxide.

[0021] 3. The prepared nano-sized BEA zeolite molecular sieve can be applied to the adsorption and separation of organic benzene substances in the air, and has the characteristics of high selectivity and high adsorption capacity for the pollution of organic benzene substances such as toluene, ethylbenzene, and xylene. It can control the pollution of organic benzene substances in the air. Specific embodiments

[0022] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0023] Example 1

[0024] This example provides a method and use for synthesizing nano-sized BEA zeolite molecular sieve by plasma activation, and the method includes the following steps:

[0025] S1. Mix the raw material silicon source, aluminum source, template agent and pure water. The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the molar ratio of the effective components of each raw material is SiO2:Al2O3:template agent:pure water = 30:1:3.9:70. Stir at room temperature to obtain a clear solution;

[0026] Among them, silicon powder is selected as the silicon source, with a particle size range of 50 - 150 microns and an effective SiO₂ content of 98% - 99.5%; alumina is selected as the aluminum source, with a particle size range of 60 - 90 microns and an effective Al₂O₃ content of 96% - 99%; a 25% aqueous solution of tetraethylammonium hydroxide by mass is selected as the template agent.

[0027] S2. Transfer the clarified solution from step S1 to a plasma reactor for plasma pretreatment. The vacuum degree of the plasma pretreatment is 130 Pa; the discharge power is 200 W; the carrier gas flow rate is 50 ml / min; the treatment time is 8 min; among them, high-purity nitrogen is used as the protective carrier gas, and the nitrogen purity is not less than 99.999%. It uses direct current arc discharge to generate high-temperature plasma, and the high-energy plasma beam excites the active factors in the raw materials to have energy collisions. After exchanging energy, molecular sieve crystal nuclei are quickly formed.

[0028] S3. Transfer the pretreatment solution from step S2 to a homogeneous reactor for isothermal crystallization reaction. It is heated to 155 - 160 °C at a heating rate of 35 °C / h and undergoes isothermal crystallization reaction for 70 - 75 h; after the reaction ends, it is cooled to room temperature at a cooling rate of 30 °C / h to obtain a crystallized slurry.

[0029] S4. After the isothermal reaction in step S3 ends, add solid oxalic acid as a flocculant to the crystallized slurry for 3 h; among them, the addition amount of solid oxalic acid is 0.5% of the mass fraction of the total slurry.

[0030] After flocculation, the material is filtered, washed, dried, calcined, and pulverized to obtain nano-scale BEA type molecular sieve. After washing, it is first dried at 120 °C for 24 h to volatilize water at low temperature; then it is calcined at 550 °C for 10 h to remove the flocculant and template agent at high temperature, and then mechanically pulverized and pneumatically pulverized to obtain nano-scale BEA type molecular sieve.

[0031] Example 2-a

[0032] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 150 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0033] Example 2-b

[0034] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 140 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0035] Example 2-c

[0036] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 120 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0037] Example 2-d

[0038] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 110 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0039] Example 2-e

[0040] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 100 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0041] Comparative Example 2-1

[0042] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 180 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0043] Comparative Example 2-2

[0044] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 160 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0045] Comparative Example 2-3

[0046] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 90 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0047] Comparative Example 2-4

[0048] Except that the vacuum degree of the plasma pretreatment in step S2 is changed to 80 Pa, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0049] Table 1 Comparison table of the influence of different vacuum degrees on the crystallinity of molecular sieve

[0050] Serial number Vacuum degree (Pa) Topological structure Relative crystallinity % (peak height method ≥ 120%) Example 1 130 BEA 130.48 Comparative example 2-1 180 BEA 110.39 Comparative example 2-2 160 BEA 117.42 Example 2-a 150 BEA 121.54 Example 2-b 140 BEA 128.46 Example 2-c 120 BEA 129.05 Example 2-d 110 BEA 125.93 Example 2-e 100 BEA 123.44 Comparative example 2-3 90 BEA 118.14 Comparative example 2-4 80 BEA 111.08

[0051] According to the comparison results in Table 1, as the vacuum degree of the plasma pretreatment continuously decreases, the crystallinity of the synthesized molecular sieve first increases and then decreases. Therefore, the vacuum degree of the plasma pretreatment is 100-150 Pa, preferably 130 Pa.

[0052] Example 3-a

[0053] Except that the discharge power of the plasma pretreatment in step S2 is changed to 150 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0054] Example 3-b

[0055] Except that the discharge power of the plasma pretreatment in step S2 is changed to 175 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0056] Example 3-c

[0057] Except that the discharge power of the plasma pretreatment in step S2 is changed to 225 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0058] Example 3-d

[0059] Except that the discharge power of the plasma pretreatment in step S2 is changed to 250 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0060] Comparative Example 3-1

[0061] Except that the discharge power of the plasma pretreatment in step S2 is changed to 100 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0062] Comparative Example 3-2

[0063] Except that the discharge power of the plasma pretreatment in step S2 is changed to 125 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0064] Comparative Example 3-3

[0065] Except that the discharge power of the plasma pretreatment in step S2 is changed to 275 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0066] Comparative Example 3-4

[0067] Except that the discharge power of the plasma pretreatment in step S2 is changed to 300 W, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0068] Table 2 Comparison table of the influence of different discharge powers on the crystallinity of molecular sieve

[0069] Serial number Discharge power (W) Topological structure Relative crystallinity % (peak height method ≥ 120%) Example 1 200 BEA 130.48 Comparative example 3-1 100 BEA 108.41 Comparative example 3-2 125 BEA 116.95 Example 3-a 150 BEA 123.30 Example 3-b 175 BEA 128.21 Example 3-c 225 BEA 130.16 Example 3-d 250 BEA 121.46 Comparative example 3-3 275 BEA 114.62 Comparative example 3-4 300 BEA 105.40

[0070] According to the comparison results in Table 2, as the discharge power of the plasma pretreatment increases, the crystallinity of the synthesized molecular sieve first increases and then decreases. Therefore, the discharge power of the plasma pretreatment is 150-250 W, preferably 200 W.

[0071] Example 4-a

[0072] Except that the carrier gas flow rate of the plasma pretreatment in step S2 is changed to 30 ml / min, the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0073] Example 4-b

[0074] Except that the carrier gas flow rate for the plasma pretreatment in step S2 was changed to 40 ml / min, the remaining steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0075] Example 4-c

[0076] Except that the carrier gas flow rate for the plasma pretreatment in step S2 was changed to 60 ml / min, the remaining steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0077] Example 4-d

[0078] Except that the carrier gas flow rate for the plasma pretreatment in step S2 was changed to 70 ml / min, the remaining steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0079] Example 4-e

[0080] Except that the carrier gas flow rate for the plasma pretreatment in step S2 was changed to 80 ml / min, the remaining steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0081] Comparative Example 4-1

[0082] Except that the carrier gas flow rate for the plasma pretreatment in step S2 was changed to 20 ml / min, the remaining steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0083] Comparative Example 4-2

[0084] Except that the carrier gas flow rate for the plasma pretreatment in step S2 was changed to 90 ml / min, the remaining steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0085] Table 3 Comparison Table of the Influence of Different Carrier Gas Flow Rates on the Crystallinity of Molecular Sieves

[0086]

[0087]

[0088] According to the comparison results in Table 3, as the carrier gas flow rate of the plasma pretreatment increases, the crystallinity of the synthesized molecular sieve first increases and then decreases. Therefore, the plasma pretreatment is carried out at 30 - 80 ml / min, preferably 50 ml / min.

[0089] Example 5-a

[0090] Except that the plasma pretreatment time in step S2 was changed to 5 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0091] Example 5-b

[0092] Except that the plasma pretreatment time in step S2 was changed to 6 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0093] Example 5-c

[0094] Except that the plasma pretreatment time in step S2 was changed to 7 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0095] Example 5-d

[0096] Except that the plasma pretreatment time in step S2 was changed to 9 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0097] Example 5-e

[0098] Except that the plasma pretreatment time in step S2 was changed to 10 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0099] Comparative Example 5-1

[0100] Except that the plasma pretreatment time in step S2 was changed to 4 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0101] Comparative Example 5-2

[0102] Except that the plasma pretreatment time in step S2 was changed to 11 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0103] Comparative Example 5-3

[0104] Except that the plasma pretreatment time in step S2 was changed to 13 min, the remaining steps and conditions were the same as those in Example 1, so they will not be described in detail here.

[0105] Table 4 Comparison table of the influence of different pretreatment times on the crystallinity of molecular sieves

[0106] Serial number Processing time (min) Topological structure Relative crystallinity % (peak height method ≥ 120%) Example 1 8 BEA 130.48 Comparative example 5-1 4 BEA 117.22 Example 5-a 5 BEA 124.55 Example 5-b 6 BEA 127.81 Example 5-c 7 BEA 129.19 Example 5-d 9 BEA 128.49 Example 5-e 10 BEA 126.40 Comparative example 5-2 11 BEA 114.15 Comparative example 5-3 13 BEA 110.97

[0107] According to the comparison results in Table 4, as the plasma pretreatment time prolongs, the crystallinity of the synthesized molecular sieve first increases and then decreases. Therefore, the plasma pretreatment time is 5-10 min, preferably 8 min.

[0108] Example 6-a

[0109] Except that the flocculation time in step S3 was changed to 2 h, the other steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0110] Example 6-b

[0111] Except that the flocculation time in step S3 was changed to 2.5 h, the other steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0112] Example 6-c

[0113] Except that the flocculation time in step S3 was changed to 3.5 h, the other steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0114] Example 6-d

[0115] Except that the flocculation time in step S3 was changed to 4 h, the other steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0116] Comparative Example 6-1

[0117] Except that the flocculation time in step S3 was changed to 1 h, the other steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0118] Comparative Example 6-2

[0119] Except that the flocculation time in step S3 was changed to 5 h, the other steps and conditions were the same as those in Example 1, so they will not be elaborated here.

[0120] Table 5 Comparison table of the influence of different flocculation times on the crystallinity of molecular sieves

[0121] Serial number Flocculation time (h) Topological structure Relative crystallinity % (peak height method ≥ 120%) Example 1 3 BEA 130.48 Comparative example 6-1 1 BEA 113.18 Example 6-a 2 BEA 123.83 Example 6-b 2.5 BEA 127.42 Example 6-c 3.5 BEA 129.05 Example 6-d 4 BEA 125.19 Comparative example 6-2 5 BEA 115.42

[0122] According to the comparison results in Table 5, as the flocculation time prolongs, the crystallinity of the synthesized molecular sieve first increases and then decreases. Therefore, the flocculation time is 2 - 4 h, preferably 3 h.

[0123] Example 7

[0124] This example provides a method and use for synthesizing nano-scale BEA type molecular sieve by plasma activation. The method includes the following steps:

[0125] S1. Mix the raw material silicon source, aluminum source, template agent and pure water. The silicon source is calculated as SiO2 and the aluminum source is calculated as Al2O3. The molar ratio of the effective components of each raw material is SiO2:Al2O3:template agent:pure water = 15:1:3.7:80. Stir at room temperature to obtain a clear solution;

[0126] Among them, silicon powder is selected as the silicon source, with a particle size range of 50 - 150 microns and an effective SiO₂ content of 98% - 99.5%; alumina is selected as the aluminum source, with a particle size range of 60 - 90 microns and an effective Al₂O₃ content of 96% - 99%; a 25% aqueous solution of tetraethylammonium hydroxide by mass is selected as the template agent.

[0127] S2. Transfer the clarified solution from step S1 to a plasma reactor for plasma pretreatment. The vacuum degree of the plasma pretreatment is 100 Pa; the discharge power is 250 W; the carrier gas flow rate is 30 ml / min; the treatment time is 10 min; among them, the high-purity nitrogen gas is used as the protective carrier gas, and the nitrogen purity is not less than 99.999%.

[0128] S3. Transfer the pretreatment solution from step S2 to a homogeneous reactor for isothermal crystallization reaction. Heat it to 155 - 160 °C at a heating rate of 35 °C / h and carry out isothermal crystallization reaction for 70 - 75 h; after the reaction ends, cool it to room temperature at a cooling rate of 30 °C / h to obtain a crystallization slurry.

[0129] S4. After the isothermal reaction in step S3 ends, add solid oxalic acid as a flocculant to the crystallization slurry, and the flocculation time is 2 h; among them, the addition amount of solid oxalic acid is 0.5% of the mass fraction of the total slurry.

[0130] S5. The flocculated material is filtered, washed, dried, calcined, and pulverized to obtain nano-scale BEA zeolite. First, dry it at 125 °C for 24 h to volatilize water at a low temperature; then calcine it at 550 °C for 9 h to remove the flocculant and template agent at a high temperature, and then carry out mechanical pulverization and pneumatic pulverization to obtain nano-scale BEA zeolite.

[0131] Example 8

[0132] This example provides a method and use for synthesizing nano-scale BEA zeolite by plasma activation. The method includes the following steps:

[0133] S1. Mix the raw material silicon source, aluminum source, template agent, and pure water. Among them, the silicon source is calculated as SiO₂, and the aluminum source is calculated as Al₂O₃. The molar ratio of the effective components of each raw material is SiO₂:Al₂O₃:template agent:pure water = 50:1:4.2:60, and stir at room temperature to obtain a clarified solution;

[0134] Among them, silicon powder is selected as the silicon source, with a particle size range of 50 - 150 microns and an effective SiO₂ content of 98% - 99.5%; alumina is selected as the aluminum source, with a particle size range of 60 - 90 microns and an effective Al₂O₃ content of 96% - 99%; a 25% aqueous solution of tetraethylammonium hydroxide by mass is selected as the template agent.

[0135] S2. Transfer the clarified solution from step S1 to a plasma reactor for plasma pretreatment. The vacuum degree of the plasma pretreatment is 150 Pa, the discharge power is 200 W, the carrier gas flow rate is 80 ml / min, and the treatment time is 5 min. Among them, the high-purity nitrogen gas is used as the protective carrier gas, and the nitrogen purity is not less than 99.999%.

[0136] S3. Transfer the pretreated solution from step S2 to a homogeneous reactor for isothermal crystallization reaction. Heat it up to 155 - 160 °C at a heating rate of 35 °C / h and carry out isothermal crystallization reaction for 70 - 75 h. After the reaction is completed, cool it to room temperature at a cooling rate of 30 °C / h to obtain a crystallized slurry.

[0137] S4. After the isothermal reaction in step S3 is completed, add solid oxalic acid as a flocculant to the crystallized slurry, and the flocculation time is 4 h. Among them, the addition amount of solid oxalic acid is 0.5% of the total mass fraction of the slurry.

[0138] S5. The flocculated material is filtered, washed, dried, calcined, and pulverized to obtain nano-scale BEA zeolite. First, dry it at 130 °C for 20 h to volatilize water at a low temperature. Then, calcine it at 560 °C for 10 h to remove the flocculant and template agent at a high temperature. After that, it is mechanically pulverized and pneumatically pulverized to obtain nano-scale BEA zeolite.

[0139] Example 9

[0140] This example provides a method and use for synthesizing nano-scale BEA zeolite by plasma activation. The method includes the following steps:

[0141] S1. Mix the raw material silicon source, aluminum source, template agent, and pure water. The silicon source is calculated as SiO2, and the aluminum source is calculated as Al2O3. The molar ratio of the active components of each raw material is SiO2:Al2O3:template agent:pure water = 45:1:3.8:65. Stir at room temperature to obtain a clarified solution.

[0142] Among them, the silicon source is silicon powder with a particle size range of 50 - 150 microns and an effective SiO2 content of 98% - 99.5%. The aluminum source is alumina with a particle size range of 60 - 90 microns and an effective Al2O3 content of 96% - 99%. The template agent is an aqueous solution of tetraethylammonium hydroxide with a mass content of 25%.

[0143] S2. Transfer the clarified solution from step S1 to a plasma reactor for plasma pretreatment. The vacuum degree of the plasma pretreatment is 120 Pa, the discharge power is 225 W, the carrier gas flow rate is 60 ml / min, and the treatment time is 7 min. Among them, the high-purity nitrogen gas is used as the protective carrier gas, and the nitrogen purity is not less than 99.999%.

[0144] S3. Transfer the pre-treatment liquid from step S2 to a homogeneous reactor, and carry out a constant-temperature crystallization reaction. Heat it to 155 - 160 °C at a heating rate of 35 °C / h, and carry out a constant-temperature crystallization reaction for 70 - 75 h. After the reaction is completed, cool it to room temperature at a cooling rate of 30 °C / h to obtain a crystallized slurry.

[0145] S4. After the constant-temperature reaction in step S3 is completed, add solid oxalic acid, a flocculant, to the crystallized slurry, and carry out a flocculation for 2.5 h. Among them, the addition amount of solid oxalic acid is 0.5% of the total mass fraction of the slurry.

[0146] S5. The flocculated material is filtered, washed, dried, calcined, and pulverized to obtain nano-scale BEA zeolite molecular sieve. First, dry it at 120 °C for 25 h to volatilize water at low temperature. Then, calcine it at 500 °C for 8 h to remove the flocculant and template agent at high temperature. After that, carry out mechanical pulverization and air-flow pulverization to obtain nano-scale BEA zeolite molecular sieve.

[0147] Comparative Example A

[0148] Except that step S1 is changed to "add crystal seeds to the raw materials to synthesize BEA zeolite molecular sieve, and the addition ratio of crystal seeds accounts for 0.3% of the total mass of the reaction raw materials", the other steps and conditions are the same as those in Comparative Example 1, so they will not be elaborated here.

[0149] Comparative Example B

[0150] Except that step S2 is changed to "do not use plasma pretreatment", the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0151] Comparative Example C

[0152] Except that step S1 is changed to "add crystal seeds to the raw materials to synthesize BEA zeolite molecular sieve, and the addition ratio of crystal seeds accounts for 0.3% of the total mass of the reaction raw materials", and step S2 is changed to "do not use plasma pretreatment", the other steps and conditions are the same as those in Example 1, so they will not be elaborated here.

[0153] Table 6 Comparison table of the influence of the crystallinity of the zeolite molecular sieve synthesized by different examples and comparative examples

[0154] Serial number Topological structure Relative crystallinity % (peak height method ≥ 120%) Example 1 BEA 130.48 Example 7 BEA 128.15 Example 8 BEA 122.70 Example 9 BEA 125.89 Comparative example A BEA 107.42 Comparative example B BEA 93.25 Comparative example C BEA 115.16

[0155] According to the comparison results in Table 6, when using plasma pretreatment, a high-energy plasma beam is generated to excite the active factors in the mixture to have an energy collision. After exchanging energy, a zeolite crystal nucleus is quickly formed, and the relative crystallinity of the synthesized nano-scale BEA zeolite molecular sieve is greater than 120%. When crystal seeds are added alone to the raw materials, during the energy collision process, the crystal seed structure is damaged, the induction effect is reduced, and the crystallinity is not good enough.

[0156] After roasting according to the above examples, the adsorption performance was simulated in the laboratory: the static saturated adsorption capacities of toluene, ethylbenzene and xylene; the dynamic saturated adsorption times of toluene and xylene. The relevant evaluation data are as follows:

[0157] Table 7 Comparison table of static saturated adsorption capacities of water, toluene and xylene

[0158]

[0159]

[0160] Table 8 Comparison table of dynamic saturated adsorption breakthrough times of toluene and xylene

[0161] Serial number Toluene ≥ 60000 s Ethylbenzene ≥ 60000 s Xylene ≥ 60000 s Example 1 68146 66140 66140 Example 7 66485 64962 64969 Example 8 65861 63094 63093 Example 9 66283 63225 63225 Comparative example A 45380 43296 43042 Comparative example B 36211 35843 33947 Comparative example C 57592 55705 55186

[0162] It can be obtained from Table 7 and Table 8 that: the static saturated adsorption capacities of toluene, ethylbenzene and xylene all meet the standards and are better than those of the comparative examples. Further, the dynamic saturated adsorption breakthrough time is higher than 60000 s, indicating that it has the advantages of high selectivity and high adsorption capacity for benzene adsorption.

[0163] In practical applications, the organic benzene substances in the air mainly include: benzene, toluene, xylene and other benzene substances. However, various influencing factors, such as temperature, humidity, air volume, concentration, etc., are crucial for studying the adsorption performance and stability of the molecular sieve adsorbent.

[0164] Table 9 Comparison table of actual application adsorption rates and cycle regeneration rates of each example

[0165]

[0166]

[0167] It can be obtained from Table 9 that: by simply changing the temperature or pressure for desorption to activate the molecular sieve, there are still relatively high adsorption rates and cycle regeneration rates, indicating that the plasma activation treatment has a significant impact on the technical effects of the present invention.

[0168] Example 10

[0169] On the basis of Example 1, the silicon source or aluminum source was changed singly. The silicon source was respectively one of liquid silica sol, solid silica gel, white carbon black, water glass and tetraethyl orthosilicate; the aluminum source could be one of aluminum hydroxide and sodium metaaluminate. The technical effects are shown in Table 10 below:

[0170] Table 10 Comparison table of the effects of silicon source and aluminum source on the crystallinity of molecular sieve

[0171]

[0172]

[0173] The above table shows that the silicon source can be one of liquid silica sol, solid silica gel, fumed silica, water glass and tetraethyl orthosilicate; the aluminum source can be one of aluminum hydroxide and sodium metaaluminate, and BEA zeolite with relatively high relative crystallinity can be obtained. However, using silicon powder as the silicon source and alumina as the aluminum source is the best solution, not only because of its low price, but also because it can reduce the influence of heteroatoms in the silicon source and aluminum source on the crystallization product.

[0174] Example 11

[0175] On the basis of Example 1, sodium hydroxide, potassium hydroxide, ammonia water and tetraethylammonium bromide aqueous solution with the same mass concentration are used as the template agent to replace tetraethylammonium hydroxide. The technical effects are shown in Table 11 below:

[0176] Table 11 Comparison table of the influence of silicon source and aluminum source on the crystallinity of zeolite

[0177]

[0178] The above table shows that a strongly alkaline system is beneficial to the crystal growth and crystallization of BEA zeolite. Among them, tetraethylammonium hydroxide belongs to an organic quaternary ammonium base and has the best technical effect. Therefore, tetraethylammonium hydroxide is selected as the template agent.

[0179] The present invention is not limited to the above embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations to some technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A plasma activation synthesis method for nano-scale BEA zeolite, characterized in that, It includes the following steps: S1. Mix the raw material silicon source, aluminum source, template agent and pure water, and stir at room temperature to obtain a clear solution; the silicon source is one of silica sol, silicon powder, solid silica gel, fumed silica, water glass and tetraethyl orthosilicate; the aluminum source is one of alumina, aluminum hydroxide and sodium aluminate; the template agent is tetraethylammonium hydroxide; wherein, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the molar ratio of the effective components of each raw material is SiO2:Al2O3:template agent:pure water = (15 - 50):1:(3.7 - 4.2):(60 - 80); S2. Transfer the clear solution obtained in step S1 to a plasma reactor for plasma pretreatment; use direct current arc discharge to generate high-temperature plasma, and the high-energy plasma beam excites the active factors in the raw materials to undergo energy collision, and quickly forms molecular sieve crystal nuclei after exchanging energy; S3. Transfer the pretreatment solution obtained in step S2 to a homogeneous reactor for isothermal crystallization reaction; S4. After the isothermal reaction in step S3 ends, add a strong acid as a flocculant to the crystallization slurry for flocculation; S5. The flocculated flocculant is filtered, washed, dried, calcined and pulverized to obtain nano-scale BEA type molecular sieve.

2. The plasma activation synthesis method of a nano-scale BEA type molecular sieve according to claim 1, characterized in that: The silicon source is silicon powder and the aluminum source is alumina.

3. The plasma activation synthesis method of a nano-scale BEA type molecular sieve according to claim 2, characterized in that: The particle size range of the silicon powder is 50 - 150 microns; the particle size range of the alumina is 60 - 90 microns; the template agent is diluted into a 25% mass fraction aqueous solution of tetraethylammonium hydroxide before use.

4. A plasma activation synthesis method of a nanoscale BEA type molecular sieve according to claims 1-3, characterized in that: The vacuum degree of the plasma pretreatment described in step S2 is 100 - 150 Pa; the discharge power is 150 - 250 W; nitrogen is used as the protective carrier gas, and the carrier gas flow rate is 30 - 80 ml / min; the treatment time is 5 - 10 min.

5. The plasma activation synthesis method of a nanoscale BEA type molecular sieve according to claims 1-3, characterized in that: In step S3, it is set to rise to 160 °C at a heating rate of 20 °C / h for isothermal crystallization reaction for 12 h; after the reaction ends, it is cooled to room temperature at a cooling rate of 30 °C / h to obtain a crystallization slurry.

6. The plasma-activated synthesis method of a nano-scale BEA type molecular sieve according to claims 1-3, characterized in that: The flocculant is solid oxalic acid; the addition amount is 0.5% of the mass fraction of the total slurry; the flocculation time is 2 - 4 h.

7. A method for synthesizing a plasma-activated nano-sized BEA zeolite according to claims 1-3, characterized in that, In step S5, after washing, it is dried at 120 - 130 °C for 20 - 25 h to volatilize water at low temperature; then it is calcined at 500 - 560 °C for 8 - 10 h to remove the flocculant and template agent at high temperature; and then it is mechanically pulverized and pneumatically pulverized to obtain nano-scale BEA type molecular sieve. Use of the nanoscale BEA zeolite obtained by the method according to claim 1, characterized in that: It is applied to the adsorption and separation of organic benzene substances in the air.

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