Surface modification method of ZSM-5 molecular sieve porous material
The H-ZSM-5 molecular sieve is treated by ion exchange of macromolecular organic salt solution, and the problems of cumbersome operation and channel blockage in the prior art are solved, and the ZSM-5 molecular sieve with high activity, high selectivity and stability are achieved, which is suitable for 2 Selective adsorption and catalytic reaction of toluene.
Patent Information
- Application Number
- CN202411399023.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-09
- Publication Date
- 2025-01-10
AI Technical Summary
The existing ZSM-5 molecular sieve surface modification method is cumbersome and consumes energy. It is easy to cause pore blockage and acidic center damage, reducing the activity and stability of the catalyst, especially in the selective adsorption of xylene. .
The H-ZSM-5 molecular sieve was ion exchanged by macromolecular organic salt solution. Through the oil bath stirring and calcining steps, the H+ ion exchange between the cation and the surface layer of the molecular sieve was controlled, the acidic sites on the surface were eliminated and the orifice size was reduced, and the high activity was formed. , Highly selective and high stability ZSM-5 molecular sieve.
It achieves the improvement of xylene selectivity while maintaining high activity and stability, and is suitable for gas adsorption and catalytic reactions, significantly improving the selectivity of paraxylene and toluene conversion, avoiding the problems of pore blockage and acidic center damage.
Smart Images
Figure CN119281372A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a surface modification method of a ZSM-5 molecular sieve porous material, and belongs to the preparation field of molecular sieve porous materials. Background Art
[0002] ZSM-5 molecular sieve is a porous material that is used in the fields of adsorption treatment of industrial waste gas, acid catalytic reaction, etc., such as: adsorption of volatile organic compounds (VOCs), selective adsorption and separation of small molecule gases, industrial catalytic reaction of aromatic compounds, etc.
[0003] The main components of VOCs are hydrocarbons, benzene series, amines, alcohols, ethers, esters, etc. They have a wide range of sources and may further react in the air to produce photochemical smog, which can seriously damage human health. Molecular sieves have great advantages in VOCs adsorbents due to their non-flammability, adsorption stability and low cost. Molecular sieve particles have a uniform pore structure, which is conducive to the absorption of molecules smaller than the diameter of the molecular sieve cavity, and the intercrystalline pores formed between the particles also have the function of preferentially adsorbing molecules of different polarities and unsaturated molecules. Therefore, molecular sieves can screen VOCs molecules of different polarities, different saturations, different molecular sizes and different boiling points. Therefore, ZSM-5 can generally be modified to increase its adsorption or screening performance. For example, the molecular sieve can be treated with acid or alkali (such as NaOH, HNO3) solution to increase the mesopore volume of the molecular sieve to increase its adsorption performance; it can be customized to selectively adsorb aromatic VOCs compounds by methods such as loading oxides to reduce the pore size and hydrothermal treatment to reduce the surface acidity. After the ZSM-5 is modified by reducing the pore size, it can also be used in the process of selectively absorbing N2 and CO2 doped in natural gas or separating CH4 and CO2 in biogas and landfill gas to achieve better results.
[0004] Para-xylene (PX) is an important organic chemical raw material. ZSM-5 molecular sieve is a commonly used molecular sieve catalyst for toluene alkylation to produce PX because it has a unique ten-membered ring channel with a kinetic diameter comparable to that of benzene, toluene and para-xylene. Although ZSM-5 molecular sieve has excellent activity and stability, the acid sites on the outer surface of ZSM-5 molecular sieve will cause the generated PX to undergo isomerization reaction during the alkylation process, thereby reducing the para-selectivity of the catalyst. In order to improve the selectivity of PX, the acid sites on the outer surface can be appropriately modified and the opening size of the pores can be appropriately adjusted to give it better shape selectivity. Commonly used ZSM-5 molecular sieve modification methods include multi-step impregnation method, silanization method, hydrothermal treatment method, acid-base treatment method, etc. Such modification methods often have problems such as cumbersome operation, high energy consumption, channel blockage, and destruction of the acidic center inside the channel, which reduces the activity and stability of the catalyst.
[0005] Therefore, it is necessary to develop a relatively simple surface modification method for ZSM-5 molecular sieves, which can improve the PX selectivity while maintaining the high activity and high stability of the porous material; at the same time, the modified ZSM-5 molecular sieve can also be applied to the field of gas adsorption. Summary of the invention
[0006] In view of the problems of cumbersome operation, high energy consumption, pore blockage, and destruction of acidic centers inside the pores in existing modification technologies, a relatively simple surface modification method of ZSM-5 molecular sieve is provided, which can improve the selectivity of para-xylene while maintaining high activity and high stability. The modified ZSM-5 molecular sieve can also be used in the field of gas adsorption.
[0007] In order to solve the above technical problems, the surface modification method of the ZSM-5 molecular sieve porous material of the present invention is carried out according to the following steps:
[0008] (1) placing the H-ZSM-5 molecular sieve in a macromolecular organic salt solution;
[0009] (2) stirring the solution obtained in step (1) in an oil bath at 40 to 80° C. for 3 to 12 hours, then cooling, filtering and washing with water until neutral;
[0010] (3) The material after cooling, filtering and washing in step (2) is dried at 100° C., placed in a muffle furnace, heated to 500° C., and calcined for 3 h to obtain the ZSM-5 molecular sieve porous material after ion exchange.
[0011] As a limitation of the present invention, the H-ZSM-5 molecular sieve described in the above step (1) of the present invention is a homemade molecular sieve, which is specifically prepared according to the following steps:
[0012] (1) Dissolve 1.11-10.11 g of NaOH in deionized water, slowly add tetrapropylammonium hydroxide (TPAOH) and stir until a clear and transparent solution is obtained;
[0013] (2) Add 1.14-10.43 g NaAlO2 to the solution obtained in the above step (1), continue stirring, and slowly add silica sol using a peristaltic pump. After the addition is completed, continue stirring for 12 hours to obtain a mixed solution with a ratio of each material of: n(SiO2):n(Al2O3):n(NaOH):n(TPAOH):n(H2O)=1:0.08-0.011:0.15-0.35:0.35:50. Continue stirring to obtain a clear and transparent precursor solution;
[0014] (3) transferring the precursor solution obtained in step (2) to a crystallization reactor lined with polytetrafluoroethylene, placing it in an oven at 150-200° C. for crystallization for 3 days, filtering, washing, and drying to obtain a white powder without template removal;
[0015] (4) placing the white powder obtained in step (3) in a muffle furnace, heating to 550° C., and calcining for 8 h to obtain a NaZSM-5 molecular sieve;
[0016] (5) The NaZSM-5 molecular sieve obtained in step (4) was quenched by 1 mol·L -1 The NH4Cl solution was ion exchanged three times, dried, placed in a muffle furnace, heated to 550°C, and calcined for 4 hours to finally obtain the H-ZSM-5 molecular sieve.
[0017] As a limitation of the present invention, the macromolecular organic salt solution in step (1) of the present invention is one of sodium oxalate, sodium citrate, potassium oxalate or potassium citrate; the mass ratio of the H-ZSM-5 molecular sieve to the macromolecular organic salt solution is 10 to 100.
[0018] The surface-modified ZSM-5 molecular sieve porous material of the present invention can be used for the alkylation of toluene and dimethyl carbonate to synthesize p-xylene. The specific application method is as follows: 1.0 g of surface-modified ZSM-5 molecular sieve porous material with a particle size of 20 to 30 mesh is placed in a fixed bed reactor, the temperature of the vaporization chamber is raised to 150°C, the temperature of the reactor is raised to 300 to 420°C, and under the protection of inert gas Ar and N2, after the temperature reaches the set value, the raw materials toluene and dimethyl carbonate are pumped into the reactor at a molar ratio of 2 to 4:1 through a micro-constant flow pump, and the mass space velocity is 5h -1 , flow through the bed to react, and obtain the reaction liquid after condensation. The toluene conversion rate and para-xylene selectivity are quantitatively analyzed by gas chromatography.
[0019] After adopting the above technical solution, the present invention has achieved the following beneficial effects compared with other methods:
[0020] The present invention selects anion sodium salt or potassium salt whose volume is larger than the pore size of the molecular sieve, and utilizes the electrostatic attraction of anion to cation to control the cation M + (Na + , K + ) only with H on the surface of ZSM-5 molecular sieve + Ion exchange occurs, replacing the H + This method is simple and easy to use, and can eliminate the surface acidity of the molecular sieve while retaining the internal activity of the molecular sieve and reducing the pore size, thereby obtaining a highly active, highly selective, and highly stable ZSM-5 molecular sieve porous material. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1This is a SEM image of the ZSM-5 molecular sieve porous material prepared in Example 8. It can be seen from the image that the porous material is composed of grains of about 300 nm and has a cuboid-like morphology.
[0022] Figure 2 The toluene conversion rate and PX selectivity obtained in the toluene alkylation reaction of Example 8 are shown in the figure. It can be seen from the figure that the ZSM-5 molecular sieve treated with ion exchange of sodium oxalate solution remains stable after 20 hours of reaction and does not show deactivation. DETAILED DESCRIPTION
[0023] The present invention will be further described with reference to the following examples, but it should be understood that these examples are only for illustration and should not be construed as limitations of the present invention.
[0024] Example 1
[0025] Homemade H-ZSM-5 molecular sieve with SiO2 / Al2O3 of 25 was prepared according to the following molar ratio: n(SiO2):n(Al2O3):n(NaOH):n(TPAOH):n(H2O)=1:0.08:0.15:0.24:50. First, 2.4g of NaOH was dissolved in deionized water, and tetrapropylammonium hydroxide (TPAOH) was slowly added, and the solution was stirred until it was clear and transparent. Then 1.64g of NaAlO2 was added and continued to stir, and then silica sol was slowly added using a peristaltic pump to obtain a clear and transparent precursor. The precursor was transferred to a crystallization kettle with a polytetrafluoroethylene liner, and then placed in an oven at 170°C for crystallization for 3 days. After filtration, washing and drying, a white powder without template removal was obtained, which was placed in a muffle furnace, heated to 550°C, and calcined for 8h to obtain NaZSM-5 molecular sieve. After 1mol·L -1 The NH4Cl solution was ion exchanged three times, dried, placed in a muffle furnace, heated to 550°C, and calcined for 4 hours to obtain H-ZSM-5 molecular sieve.
[0026] Embodiments 2 to 9
[0027] The H-ZSM-5 molecular sieve prepared in Example 1 was placed in a 0.005-0.1 mol·L -1 In the sodium oxalate solution, the mass ratio of H-ZSM-5 molecular sieve to sodium oxalate solution is 1:100, and ion exchange is carried out in an oil bath at 40-80°C for 6 hours, and then cooled, filtered and washed with water, dried in an oven at 100°C, and finally placed in a muffle furnace, heated to 500°C, and calcined for 3 hours to obtain the xNa(y)-ZSM-5 molecular sieve after ion exchange, where x represents the sodium oxalate concentration and y represents the oil bath temperature.
[0028] Example 10
[0029] The H-ZSM-5 molecular sieve prepared in Example 1 was placed in a 0.0133 mol·L -1 In the sodium citrate solution, the mass ratio of H-ZSM-5 molecular sieve to sodium citrate solution is 1:100, ion exchange is carried out in an oil bath at 80°C for 6 hours, and then cooled, filtered and washed with water, dried in an oven at 100°C, and finally placed in a muffle furnace, heated to 500°C, and calcined for 3 hours to obtain 0.0133Na(80)-ZSM-5 molecular sieve.
[0030] Embodiment 11
[0031] The H-ZSM-5 molecular sieve prepared in Example 1 was placed in a 0.02 mol·L -1 In a potassium oxalate solution, in which the mass ratio of H-ZSM-5 molecular sieve to potassium oxalate solution is 1:100, ion exchange is carried out in an oil bath at 80°C for 6 hours, and then cooled, filtered and washed with water, dried in an oven at 100°C, and finally placed in a muffle furnace, heated to 500°C, and calcined for 3 hours to obtain 0.02K(80)-ZSM-5 molecular sieve.
[0032] Example 12
[0033] The H-ZSM-5 molecular sieve prepared in Example 1 was placed in a 0.0133 mol·L -1 In a potassium citrate solution, the mass ratio of H-ZSM-5 molecular sieve to potassium oxalate solution is 1:100, ion exchange is carried out in an oil bath at 80°C for 6 hours, and then cooled, filtered and washed with water, dried in an oven at 100°C, and finally placed in a muffle furnace, heated to 500°C, and calcined for 3 hours to obtain 0.0133K(80)-ZSM-5 molecular sieve.
[0034] The above embodiment is applied to the reaction of alkylation of toluene and dimethyl carbonate to synthesize p-xylene, and the specific steps are as follows: 1.0 g of surface-modified ZSM-5 molecular sieve with a particle size of 20 to 30 mesh is placed in a fixed bed reactor, the temperature of the vaporization chamber is raised to 150° C., the temperature of the reactor is raised to 400° C., and under the protection of inert gases Ar and N2, after the temperature reaches the set value, the raw materials toluene and dimethyl carbonate are pumped into the reactor in a molar ratio of 4:1 through a micro-constant flow pump, and the mass space velocity is 5h -1 , flow through the bed layer for reaction, and obtain the reaction liquid after condensation. The toluene conversion rate and the selectivity of p-xylene are quantitatively analyzed by gas chromatography. The molecular sieve preparation conditions, toluene conversion rate and PX selectivity are shown in Table 1.
[0035] Table 1 Comparison of the activity of ZSM-5 molecular sieves obtained by different preparation methods
[0036]
[0037]
[0038] Comparative Example 1
[0039] A 10% SiO2-loaded ZSM-5 molecular sieve was prepared by an impregnation method. A certain amount of the ZSM-5 molecular sieve prepared in Example 1 was placed in a tetraethyl orthosilicate solution. After the mixture was evenly mixed, a cyclohexane solution with a mass ratio of 10 times that of the molecular sieve was added. The mixed solution was stirred for 20 minutes, then evaporated in an oil bath at 70°C, and finally dried in an oven at 120°C overnight to obtain a 10% SiO2 / ZSM-5 molecular sieve.
[0040] Comparative Example 2
[0041] The 10% MgO-loaded ZSM-5 molecular sieve was prepared by an equal volume impregnation method. A certain concentration of magnesium nitrate solution was prepared. A certain amount of the ZSM-5 molecular sieve prepared in Example 1 was placed in a beaker. The magnesium nitrate solution was evenly added dropwise to the beaker containing the ZSM-5 molecular sieve using a pipette. After it was completely absorbed, it was allowed to stand for 2 hours, dried in an oven at 80°C overnight, and finally placed in a muffle furnace, heated to 550°C, and calcined for 5 hours to obtain a 10% MgO / ZSM-5 molecular sieve.
[0042] Comparative Example 3
[0043] The 15% MgO-loaded ZSM-5 molecular sieve was prepared by an equal volume impregnation method. A certain concentration of magnesium nitrate solution was prepared. A certain amount of the ZSM-5 molecular sieve prepared in Example 1 was placed in a beaker. The magnesium nitrate solution was evenly added dropwise to the beaker containing the ZSM-5 molecular sieve using a pipette. After it was completely absorbed, it was allowed to stand for 2 hours, dried in an oven at 80°C overnight, and finally placed in a muffle furnace, heated to 550°C, and calcined for 5 hours to obtain a 15% MgO / ZSM-5 molecular sieve.
[0044] Comparative Example 4
[0045] The H-ZSM-5 molecular sieve prepared in Example 1 was placed in a 0.04 mol·L -1 In a sodium nitrate solution, the mass ratio of H-ZSM-5 molecular sieve to sodium nitrate solution is 1:100, ion exchange is carried out in an oil bath at 80°C for 6 hours, and then cooled, filtered and washed with water, dried in an oven at 100°C, and finally placed in a muffle furnace, heated to 500°C, and calcined for 3 hours to obtain 0.04Na(80)-ZSM-5 molecular sieve.
[0046] The above comparative example is applied to the reaction of alkylation of toluene and dimethyl carbonate to synthesize p-xylene. The specific steps are as follows: 1.0 g of surface-modified ZSM-5 molecular sieve with a particle size of 20 to 30 mesh is placed in a fixed bed reactor, the temperature of the vaporization chamber is raised to 150°C, the temperature of the reactor is raised to 400°C, and under the protection of inert gases Ar and N2, after the temperature reaches the set value, the raw materials toluene and dimethyl carbonate are pumped into the reactor in a molar ratio of 4:1 through a micro-constant flow pump, and the mass space velocity is 5h -1 , flow through the bed layer for reaction, and obtain the reaction liquid after condensation. The toluene conversion rate and the selectivity of p-xylene are quantitatively analyzed by gas chromatography. The toluene conversion rate and the PX selectivity are shown in Table 2.
[0047] Table 2 Comparison of the activity of ZSM-5 molecular sieves obtained in the examples and comparative examples
[0048] Molecular sieve source Molecular sieve name Toluene conversion rate (%) PX selectivity (%) Example 8 0.02Na(80)-ZSM-5 40 87 Comparative Example 1 <![CDATA[10%SiO2 / ZSM-5]]> 20 40 Comparative Example 2 10%MgO / ZSM-5 25 59 Comparative Example 3 15%MgO / ZSM-5 14 65 Comparative Example 4 0.04Na(80)-ZSM-5 47 55
[0049] It can be seen that the ZSM-5 molecular sieve porous material treated by ion exchange in the present invention has a significantly improved PX selectivity in the toluene alkylation reaction compared with the unmodified material, and the molecular sieve porous material obtained by the present invention has a higher toluene conversion rate and stability compared with other modification methods. This modification method eliminates the surface acidity of the molecular sieve and reduces the pore size, and the obtained molecular sieve will be widely used in the fields of catalysis and adsorption.
[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A surface modification method for a ZSM-5 molecular sieve porous material, characterized in that The method is carried out according to the following steps: (1) placing the H-ZSM-5 molecular sieve in a macromolecular organic salt solution of a certain concentration; (2) stirring the solution obtained in step (1) in an oil bath at 40 to 80° C. for 3 to 12 hours, then cooling, filtering and washing with water until neutral; (3) The material obtained in step (2) after cooling, filtering and washing with water is dried at 100° C., placed in a muffle furnace, heated to 500° C., and calcined for 3 h to obtain the ZSM-5 molecular sieve porous material after ion exchange.
2. The surface modification method of a ZSM-5 molecular sieve porous material according to claim 1, characterized in that The H-ZSM-5 molecular sieve described in step (1) is a homemade molecular sieve, and the H-ZSM-5 molecular sieve is prepared according to the following steps: (1) Dissolve 1.11-10.11 g of NaOH in deionized water, slowly add tetrapropylammonium hydroxide (TPAOH) and stir until a clear and transparent solution is obtained; (2) Add 1.14-10.43 g NaAlO2 to the solution obtained in the above step (1), continue stirring, and slowly add silica sol using a peristaltic pump. After the addition is completed, continue stirring for 12 hours to obtain a mixed solution with a ratio of each material of: n(SiO2):n(Al2O3):n(NaOH):n(TPAOH):n(H2O)=1:0.08-0.011:0.15-0.35:0.35:
50. Continue stirring to obtain a clear and transparent precursor solution; (3) transferring the precursor solution obtained in step (2) to a crystallization reactor lined with polytetrafluoroethylene, placing it in an oven at 150-200° C. for crystallization for 3 days, filtering, washing, and drying to obtain a white powder without template removal; (4) placing the white powder obtained in step (3) in a muffle furnace, heating to 550° C., and calcining for 8 h to obtain a Na-ZSM-5 molecular sieve; (5) The Na-ZSM-5 molecular sieve obtained in step (4) was quenched by 1 mol·L -1 The NH4Cl solution was ion exchanged three times, dried, placed in a muffle furnace, heated to 550°C, and calcined for 4 hours to obtain the H-ZSM-5 molecular sieve.
3. The surface modification method of a ZSM-5 molecular sieve porous material according to claim 1, characterized in that The macromolecular organic salt solution in step (1) is one of sodium oxalate, sodium citrate, potassium oxalate or potassium citrate.
4. The surface modification method of a ZSM-5 molecular sieve porous material according to claim 1, characterized in that The mass ratio of the H-ZSM-5 molecular sieve to the macromolecular organic salt solution in step (1) is 10 to 100.