CN112209406A - Preparation method of CHA/AEI composite molecular sieve, composite molecular sieve and application thereof - Google Patents

Preparation method of CHA/AEI composite molecular sieve, composite molecular sieve and application thereof Download PDF

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CN112209406A
CN112209406A CN201910629824.8A CN201910629824A CN112209406A CN 112209406 A CN112209406 A CN 112209406A CN 201910629824 A CN201910629824 A CN 201910629824A CN 112209406 A CN112209406 A CN 112209406A
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molecular sieve
aei
cha
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丁佳佳
刘红星
钱坤
管洪波
张玉贤
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China Petroleum and Chemical Corp
Sinopec Shanghai Research Institute of Petrochemical Technology
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Abstract

The invention discloses a preparation method of a CHA/AEI composite molecular sieve. The method adopts at least two AEI structure molecular sieves with defects as seed crystals, and comprises the following steps: and adding the seed crystal into gel prepared from a silicon source, an aluminum source, a phosphorus source, a template agent and water, and then crystallizing under a hydrothermal condition to prepare the CHA/AEI composite molecular sieve. The invention also discloses a CHA/AEI composite molecular sieve prepared by the method, and the CHA/AEI composite molecular sieve is used as a catalyst in a process for preparing low-carbon olefin from an oxygen-containing compound, and shows excellent low-carbon olefin selectivity and longer catalyst service life.

Description

Preparation method of CHA/AEI composite molecular sieve, composite molecular sieve and application thereof
Technical Field
The invention relates to a CHA/AEI composite molecular sieve, a preparation method thereof and application thereof in a process for preparing low-carbon olefin from an oxygen-containing compound.
Background
In 1984, united states of america united carbides (UCC) invented a silicoaluminophosphate molecular sieve (SAPO molecular sieve for short) with a pore size of about 0.4 nm. The SAPO molecular sieve is prepared from AlO4、SiO4And PO4Crystal network structure composed of tetrahedrons, pore channels in the crystal being formed by Si4+Substituted P5+Or Al3+The resulting acidity can be either replaced with a metal to produce acidity. Wherein the crystal structure of the SAPO-34 molecular sieve is a CHA type structure, the basic composition structural units of the SAPO-34 molecular sieve are double six-membered rings and CHA cages, the crystal structure of the SAPO-18 molecular sieve is an AEI structure, and the microporous pore channel structure of the molecular sieve is similar to the CHA structure. Among SAPO series of molecular sieves, SAPO-34 molecular sieve is widely used in modern petroleum processing industry because of its good thermal and hydrothermal stability, moderate acidity, high specific surface area and highly ordered microporous channels. The most interesting is that the SAPO-34 molecular sieve is applied to methanol-to-olefin (MTO) reaction, the conversion rate of methanol can reach 100 percent, the selectivity of ethylene and propylene can exceed 75 percent, and C5 +The content of the components is small and almost no aromatic hydrocarbon is generated. The SAPO-18 molecular sieve has weaker surface acidity, and shows excellent catalytic performance and longer catalyst stability in the MTO process.
However, the conventional SAPO-18 molecular sieve and the SAPO-34 molecular sieve are both microporous molecular sieves, and the eutectic molecular sieve formed by the two is also a microporous molecular sieve. The relatively long and narrow channels of the microporous molecular sieve present serious shape-selective limitation, which on one hand hinders the contact of raw material molecules with active centers inside the channels, and on the other hand limits the diffusion and mass transfer of reactants, intermediate transition products and final products, and the channels are easily blocked due to carbon deposit, so that the catalyst is inactivated, and the exertion of the catalytic performance is limited. For example, CN101076401A discloses a silicoaluminophosphate molecular sieve comprising intergrowth of CHA and AEI structures.
In order to overcome the defects of a single microporous structure molecular sieve material, numerous researchers prepare a novel molecular sieve combining the advantages of various pore channels, namely, the hierarchical pore structure molecular sieve material has two pore channel systems of micropores and mesopores/macropores, so that the diffusion performance of the material can be greatly improved, the catalytic performance of the material is improved, and the material has good catalytic conversion performance in reactions involving macromolecules and reactions needing rapid diffusion.
Therefore, a preparation method is proposed, which comprises adding a mesoporous template into a gel system and then carrying out hydrothermal synthesis. Choi et al reported that AlPO with mesoporous structure is synthesized by one-step hydrothermal synthesis by using silanized long-chain alkyl quaternary ammonium salt as template agent4N-series molecular sieves (Choi M, Srivastava R, Ryoo R.chemical Communications, 2006; (42): 4380-4382.); subsequently, Danilina and chrysolel, etc. are hydrothermally synthesized into SAPO-5(Danilina N, Krumeich F, van Bokhovin J. journal of Catalysis,2010,272(1):37-43.) and SAPO-34 molecular sieve (Chenolol, Ronghui, Ding et al. advanced school chemistry, 2010; 31(9): 1693-); fan and the like can synthesize SAPO-11 molecular sieve with rich mesoporous structure under the conventional hydrothermal condition by adding long-chain organic phosphine as a mesoporous template (Fan Y, Xiao H, Shi G, et al. journal of Catalysis,2012,285(1): 251-259.); cui and others use polyethylene glycol (PEG) as a mesoporous template to synthesize SAPO-34 molecular sieve with a hierarchical pore structure under hydrothermal conditions, and the size of the mesopores can be changed by adjusting the amount of PEG (Cui Y, Zhang Q, He J, et al. Yang et al take silanized surfactant as mesoporous template agent to synthesize SAPO-34 with multi-level pore structure under the microwave-assisted condition, and the results show that the introduction of microwave can not only effectively shortenThe crystallization time (only 2 hours are needed to complete the crystallization process), and the synthesized product has higher specific surface area and mesoporous volume (Yang S, Kim J, Chae H, et al materials Research Bulletin, 2012; 47(11): 3888-3892.). Although the SAPO-34 molecular sieve with a hierarchical pore structure can be prepared by introducing the mesoporous template into a synthesis system of the molecular sieve in the synthesis process, the suitable template is expensive, and the process of removing the template is difficult to control.
In summary, although the preparation of the hierarchical pore materials is a hot spot of research by many researchers at present, the existing methods for preparing the hierarchical pore SAPO molecular sieves have the disadvantages of complicated operation process, high cost and the like, and the structures of the molecular sieves are damaged while the mesoporous template is removed. Therefore, the method has important practical significance in reducing the preparation cost, simplifying the operation procedure and developing a simple and efficient preparation route of the hierarchical pore SAPO molecular sieve.
Disclosure of Invention
The invention provides a preparation method and application of a CHA/AEI composite molecular sieve. The CHA/AEI composite molecular sieve prepared by the method is used as a catalyst in a process of preparing low-carbon olefin from an oxygen-containing compound, and shows excellent low-carbon olefin selectivity and longer service life of the catalyst.
In a first aspect, the present invention provides a method for preparing a CHA/AEI composite molecular sieve, wherein at least two AEI structural molecular sieves having defects are used as seed crystals, the method comprising: adding the seed crystal into gel prepared from a silicon source, an aluminum source, a phosphorus source, a template agent and water, and then crystallizing under a hydrothermal condition to prepare the CHA/AEI composite molecular sieve; the two AEI structure molecular sieves with defects are respectively a seed crystal I and a seed crystal II;
the seed crystal I and the seed crystal II contain micropores, macropores and mesopores, wherein the proportion of the specific surface area of the macropores and the mesopores in the total specific surface area of the seed crystal I to the total specific surface area is 5-9%, and the proportion of the pore volume of the macropores and the mesopores in the total pore volume is 10-14%; the specific surface area of the macropores and the mesopores accounts for 12-20% of the total specific surface area of the seed crystal II, and the pore volume of the macropores and the mesopores accounts for 16-35% of the total pore volume.
The mesoporous aperture of the seed crystal I is distributed in the range of 2-50 nanometers, and the macroporous aperture is distributed in the range of 50-300 nanometers; the mesoporous aperture of the seed crystal II is distributed in 2-50 nanometers, and the macroporous aperture is distributed in 500-1000 nanometers.
The mass ratio of the seed crystal I to the seed crystal II is (10-50): (50-90), preferably (20-40): (60-80).
The AEI structure molecular sieve with defects is obtained by a step of modifying the AEI structure molecular sieve through post-treatment, and defect crystals with different pore channel structures can be obtained by controlling the treatment conditions. The AEI structure molecular sieve is a microporous AEI structure molecular sieve, and can be prepared by a conventional method or obtained by commercial methods. The AEI structure molecular sieve can be a completely crystallized dry AEI structure molecular sieve containing a template agent, or an AEI structure molecular sieve obtained by roasting the molecular sieve at high temperature to remove the template agent.
The crystal seed I adopts an organic alkaline modifier to treat the modified AEI structure molecular sieve at 30-48 ℃ for 3-5 h, and the crystal seed II adopts an organic acidic modifier to treat the modified AEI structure molecular sieve at 70-100 ℃ for 5-10 h.
The organic alkaline modifier is tetraethyl ammonium hydroxide, and the organic acidic modifier is at least one of oxalic acid and citric acid. The concentration of the alkaline modifier is 0.005-0.05 mol/L, and the concentration of the acidic modifier is 0.1-0.5 mol/L.
The post-treatment modification comprises the step of contacting the completely crystallized AEI structure molecular sieve with an alkaline or acidic modifier. The mass ratio of the alkaline modifier to the AEI structure molecular sieve dry basis is (25-70): 1. the mass ratio of the acidic modifier to the AEI structure molecular sieve dry basis is (25-70): 1.
the aluminum source, the silicon source, the phosphorus source, the template agent and water (Al)2O3：SiO2：P2O5：R：H2O) in a molar ratio of 1: (0.05-2): (0.05-1.5): (1-10): (10-200), preferably 1: (0.1-1.5): (0.2-1.2): (2-8): (30-150); the total adding amount of the seed crystal I and the seed crystal II is 1.5% ~ up to20%, preferably 3% to 15% by mass. Wherein R is a template agent.
The aluminum source is at least one selected from aluminum isopropoxide, pseudo-boehmite or alumina, the silicon source is at least one selected from tetraethoxysilane, white carbon black or silica sol, the phosphorus source is at least one selected from phosphoric acid, phosphate and phosphorous acid, and the template agent is at least one selected from tetraethylammonium hydroxide, triethylamine, diethylamine or morpholine.
The conditions for crystallization under the hydrothermal condition are as follows: the temperature is 150-250 ℃, preferably 170-210 ℃, and the time is 3-50 hours, preferably 10-35 hours.
The method for preparing the CHA/AEI composite molecular sieve further comprises the steps of washing, drying and roasting the crystallized product. The washing, drying and roasting are conventional technical means in the field.
The invention provides a CHA/AEI composite molecular sieve prepared by the method, wherein the mass content of the AEI structure molecular sieve in the CHA/AEI composite molecular sieve is 2-13%.
In the CHA/AEI composite molecular sieve, Al2O3：P2O5：SiO2In a molar ratio of 1: (0.2-0.8): (0.1-0.6).
The CHA/AEI composite molecular sieve has X-ray diffraction peaks substantially as set forth in the following table.
Figure BDA0002128323340000041
Preferably, the CHA/AEI composite molecular sieve further comprises X-ray diffraction peaks in the X-ray diffraction pattern substantially as shown in the Table.
Figure BDA0002128323340000042
Figure BDA0002128323340000051
The CHA/AEI composite molecular sieve has a sponge structure and has micropores, mesopores and macropores.
In the CHA/AEI composite molecular sieve, the diameter of a micropore is not more than 1 nanometer, preferably 0.3-0.7 nanometer, and the diameter of a macropore is distributed in 50-1000 nanometers, preferably 80-500 nanometers; the diameter of the mesopores is distributed in the range of 8-40 nm, preferably 10-30 nm.
The pore volume contributed by the micropores is 0.10-0.40 cm3A/g, preferably 0.15 to 0.30 cm3Per gram; the pore volume contributed by the meso-macropore is 0.02-0.50 cm3Per gram, preferably 0.05 to 0.30 cm3Per gram.
The CHA/AEI composite molecular sieve is in a cubic crystal shape, and the crystal size is 0.1-5.0 microns.
The third aspect of the invention provides an application of the CHA/AEI composite molecular sieve in the reaction of preparing olefin from an oxygen-containing compound.
The oxygen-containing compound is selected from methanol, ethanol, n-propanol, isopropanol and C4-20At least one of alcohol, methyl ethyl ether, dimethyl ether, diethyl ether, diisopropyl ether, formaldehyde, dimethyl carbonate and dimethyl ketone, preferably methanol and/or dimethyl ether. The olefin comprises ethylene, propylene, or a combination thereof.
The CHA/AEI composite molecular sieve is adopted to react at the temperature of 200-700 ℃ and the weight hourly space velocity of 1-1000 hours in the olefin preparation reaction of oxygen-containing compounds-1The pressure is 0.5 kPa-5 MPa.
The method is based on defect site-oriented synthesis of the CHA/AEI composite molecular sieve in the defect crystal, and has the following advantages:
(1) the novel CHA/AEI composite molecular sieve is prepared by adopting the seed crystal I and the seed crystal II with different defects, and the operation process is simple and easy to implement;
(2) and the technology for preparing olefin from methanol is developed to the present, the yield of diene (ethylene and propylene) is generally 80-83%, and on the basis, if the yield is improved by 0.5 percent, the economic benefit is very considerable for a ten-thousand-ton device. The CHA/AEI composite molecular sieve prepared by the method is used as a catalyst active component in the process of preparing olefin from oxygen-containing compounds, shows good catalytic performance, can improve the yield of diene (ethylene + propylene) by more than 1 percent, can also obviously improve the reaction stability of the catalyst by more than 10 percent, and obtains better technical effect.
Drawings
Fig. 1 is an XRD spectrum and SEM photograph of the defect seed crystal I prepared [ example 2 ];
fig. 2 is an XRD spectrum and an SEM photograph of the composite molecular sieve prepared [ example 4 ];
fig. 3 is an XRD spectrum and an SEM photograph of the molecular sieve prepared [ comparative example 1 ];
fig. 4 is an XRD spectrum and an SEM photograph of the composite molecular sieve prepared [ comparative example 2 ].
Detailed Description
As one embodiment of the present invention, it should be noted that the scope of the present invention is not limited by these specific embodiments, but is defined by the claims.
In the present invention, the pore volume, also referred to as pore volume, means the volume of pores per unit mass of the molecular sieve.
In the present invention, in the XRD data of the molecular sieve, W, M, S, VS represents the diffraction peak intensity, W is weak, M is medium, S is strong, and VS is very strong. Generally, W is less than 20, M is 20-40, S is 40-70, and VS is greater than 70.
In the present invention, the molecular sieve (referred to as a single crystal) has a crystal morphology of a sponge structure, particularly a primary crystal morphology of a sponge structure, when observed with a Scanning Electron Microscope (SEM). Here, the crystal morphology refers to an external shape that a single molecular sieve crystal exhibits in an observation field of the scanning electron microscope. In addition, the term "native" refers to a structure that the molecular sieve objectively and directly assumes after production, and does not mean a structure that the molecular sieve assumes after production and after artificial treatment.
In the present invention, XRD data is measured by X-ray diffractometer model AXS D8Advance of Bruker GermanyObtaining the crystal structure and the calculation of relative crystallinity of the characterization molecular sieve; n is a radical of2The adsorption-desorption data are measured by an American Mack ASAP-2020 adsorption instrument and are used for measuring the specific surface area, the pore volume and the pore size distribution of the molecular sieve; mercury intrusion data and pore size distribution are measured by a Thermo full-automatic mercury intrusion instrument and are used for representing the macroporous pore size distribution of the molecular sieve; SEM pictures were obtained from a field emission scanning electron microscope, FEI Quanta200F, the netherlands, and used to characterize the morphology of the molecular sieves.
The technical solution of the present invention is further illustrated by the following specific examples.
[ example 1 ]
Preparing the AEI structure molecular sieve only containing micropores.
With silica sol (with SiO)230 wt% concentration), pseudoboehmite (calculated as Al)2O3The calculated concentration is 70wt percent) and the phosphoric acid (the concentration is 85wt percent) are respectively a silicon source, an aluminum source and a phosphorus source, N, N-diisopropylethylamine is taken as a template agent according to the SiO2：Al2O3：P2O5：C8H19N：H2O ═ 0.6: 1.0: 0.9: 1.6: 55, and crystallizing the mixture at 180 ℃ for 4 days. And after crystallization is finished, cooling, filtering and washing the crystallized product, and drying for 6 hours at 100 ℃ to obtain the conventional AEI structure molecular sieve only containing micropores, which is marked as A.
XRD characterization results show that the synthesized molecular sieve has characteristic diffraction peaks of the AEI structure molecular sieve, and the synthesized product is the pure AEI structure molecular sieve; SEM pictures show that the prepared AEI structure molecular sieve is a cubic crystal, and the surface of the crystal is smooth.
The micropore volume of A is 0.25cm3The pore diameter of the micropores is distributed in the range of 0.3 to 0.5 nm.
From the above characterization results, it can be confirmed that the conventional microporous AEI structure molecular sieve having high crystallinity is prepared.
[ example 2 ]
Preparing the AEI structure molecular sieve with crystal defects, namely the seed crystal I.
The starting material was taken from a conventional AEI structure molecular sieve a prepared as per [ example 1 ] containing only micropores.
10g of molecular sieve A is weighed and placed in 0.02 mol/L TEAOH solution, wherein the using amount of the TEAOH solution is 0.25L, and after stirring for 4 hours at 45 ℃, the product B is obtained after filtration, washing and drying. The XRD spectrum of B is shown in figure 1, and the molecular sieve has the characteristic diffraction peak of the molecular sieve with the AEI structure.
B, as shown in FIG. 1, the surface of the molecular sieve has obvious pore structure, and the molecular sieve crystal has a large number of defects
The aperture of the micropores of the B is distributed in the range of 0.3-0.5 nm, the aperture of the mesopores is distributed in the range of 10-35 nm, and the aperture of the macropores is distributed in the range of 50-250 nm.
The pore volume contributed by the micropores was 0.23cm3Per g, pore volume of 0.03cm contributed by macropores and mesopores3(ii) in terms of/g. Therefore, the proportion of the macropore and mesopore volume to the total pore volume is 12%.
The proportion of the specific surface area of macropores and mesopores in the total specific surface area is 8%.
Example 3 a molecular sieve with AEI structure having crystal defects, seed II, was prepared.
The starting material was taken from a conventional AEI structure molecular sieve a prepared as per [ example 1 ] containing only micropores.
Weighing 10g of molecular sieve A, placing the molecular sieve A in 0.2 mol/L citric acid solution, wherein the dosage of the citric acid solution is 0.4L, stirring the solution for 8 hours at 80 ℃, and filtering, washing and drying the solution to obtain a product C.
The XRD spectrum of C is similar to that of B, and the molecular sieve has the characteristic diffraction peak of AEI structure molecular sieve, but the intensity of the characteristic diffraction peak is weaker than that of B.
The SEM photograph of C is similar to that of B, the crystal of the molecular sieve has a remarkable pore structure, and the crystal of the molecular sieve has a large number of defects, namely C has more and larger pores and more remarkable defect sites compared with B.
The aperture of the micropores of the C is distributed in the range of 0.3-0.5 nm, the aperture of the mesopores is distributed in the range of 18-35 nm, and the aperture of the macropores is distributed in the range of 700-950 nm.
The pore volume contributed by the micropores is0.20cm3Per g, pore volume of 0.08cm contributed by macropores and mesopores3(ii) in terms of/g. Therefore, the proportion of the macropore and mesopore volume to the total pore volume is 29%.
The proportion of the specific surface area of macropores and mesopores in the total specific surface area is 18%.
[ example 4 ]
Preparing the CHA/AEI composite molecular sieve with the sponge structure morphology.
With silica sol (with SiO)230 wt% concentration), pseudoboehmite (calculated as Al)2O3The calculated concentration is 70wt percent) and the phosphoric acid (the concentration is 85wt percent) are respectively a silicon source, an aluminum source and a phosphorus source, and triethylamine NEt3And tetraethylammonium hydroxide TEAOH as a template agent according to SiO2：Al2O3：P2O5：NEt3：TEAOH：H2O1.0: 1.0: 0.6: 2.0: 1.0: 50, and finally adding the crystal seeds I and II prepared by the methods of [ example 2 ] and [ example 3 ], wherein the total addition amount of the products B and C is 8 percent of the solid content, wherein the mass ratio of the products B and C is 40: 60. after addition of the products B and C, the mixture was crystallized at 200 ℃ for 24 hours. And after crystallization is finished, cooling, filtering and washing the crystallized product, drying at 120 ℃ for 6 hours, and roasting at 550 ℃ for 5 hours to obtain the CHA/AEI composite molecular sieve, which is marked as D.
The XRD spectrum of D is shown in figure 2, and it can be seen from figure 2 that the synthesized molecular sieve has the characteristic diffraction peaks of the CHA/AEI molecular sieve, and the mass content of the AEI structure molecular sieve in the composite molecular sieve is 6% and the mass content of the CHA structure molecular sieve is 94% by using the XRD quantitative method.
D SEM photograph is shown in FIG. 2, the CHA/AEI composite molecular sieve has a cubic morphology, and a large number of pores are visible in the crystal.
D, the pore diameter of the micropores is distributed in the range of 0.3-0.5 nm, the pore diameter of the mesopores is distributed in the range of 10-25 nm, and the pore diameter of the macropores is distributed in the range of 200-450 nm; the pore volume contributed by the micropores was 0.22cm3(ii)/g, pore volume contributed by mesopores of 0.05cm3Per g, pore volume contributed by macropores of 0.11cm3/g。
According to XRD pattern, SEM photograph, N2The results of physical adsorption and mercury intrusion characterization are sufficient to prove that the prepared CHA/AEI composite molecular sieve with the multi-level pore structure and the spongy morphology.
[ example 5 ]
Preparation of CHA/AEI composite molecular sieve with sponge structure morphology
Similarly [ example 4 ], except that the seed crystal I and the seed crystal II are used to remove the template after calcination, the product is designated as E.
The XRD spectrum of E is similar to that of FIG. 2, and it can be known that the composite molecular sieve contains 5% by mass of molecular sieve with AEI structure and 95% by mass of molecular sieve with CHA structure by XRD quantification method.
E, SEM photograph is similar to that of figure 2, the molecular sieve has a cubic shape with a sponge structure, and a large number of coarse holes and medium holes can be seen in the crystal.
E, the pore diameter of the micropores is distributed in the range of 0.3-0.5 nm, the pore diameter of the mesopores is distributed in the range of 10-20 nm, and the pore diameter of the macropores is distributed in the range of 200-500 nm; the pore volume contributed by the micropores was 0.21cm3(ii)/g, pore volume contributed by mesopores of 0.08cm3Per g, pore volume contributed by macropores of 0.10cm3/g。
According to XRD pattern, SEM photograph, N2The results of physical adsorption and mercury-pressing characterization are enough to prove that the prepared hierarchical porous structure composite SAPO molecular sieve with the spongy morphology.
[ example 6 ]
Preparation of CHA/AEI composite molecular sieve with sponge structure morphology
The same [ example 5 ] except that the mass ratio of the added products B and C is 30: 70, the resulting product is designated F.
The XRD spectrum of F is similar to that of FIG. 2, and the mass content of the molecular sieve with AEI structure in the composite molecular sieve is 5% and the mass content of the molecular sieve with CHA structure in the composite molecular sieve is 95% by using an XRD quantitative method.
The SEM photograph of F is similar to that of FIG. 2, the molecular sieve has a cubic morphology with a sponge structure, and a large number of coarse holes and medium holes are visible in the crystal.
The aperture of the F micropore is distributed in 0.3-0.5 nanometer, and the aperture of the mesoporous is distributed in 10-15 nanometerThe pore diameter of the macropores is distributed in 100-400 nanometers; the pore volume contributed by the micropores was 0.20cm3(ii)/g, pore volume contributed by mesopores of 0.12cm3Per g, pore volume contributed by macropores of 0.05cm3/g。
According to XRD pattern, SEM photograph, N2The results of physical adsorption and mercury intrusion characterization are sufficient to prove that the prepared CHA/AEI composite molecular sieve with the multi-level pore structure and the spongy morphology.
[ example 7 ]
A CHA/AEI composite molecular sieve having a sponge structure morphology was prepared as in example 5, except that the total amount of the added products B and C was 13% of the solid content, and the resulting product was designated G.
The XRD spectrum of G is similar to that of FIG. 2, and the mass content of AEI molecular sieve and the mass content of CHA molecular sieve in the composite molecular sieve are respectively 10% and 90% by XRD quantification method.
The SEM photograph of G is similar to that of FIG. 2, the molecular sieve has a cubic morphology with a sponge structure, and a large number of coarse holes and medium holes are visible in the crystal.
G, the pore diameter of the micropores is distributed in the range of 0.3-0.5 nm, the pore diameter of the mesopores is distributed in the range of 20-40 nm, and the pore diameter of the macropores is distributed in the range of 300-500 nm; the pore volume contributed by the micropores was 0.19cm3(ii)/g, pore volume contributed by mesopores of 0.12cm3Per g, pore volume contributed by macropores of 0.11cm3/g。
According to XRD pattern, SEM photograph, N2The results of physical adsorption and mercury intrusion characterization are sufficient to prove that the prepared CHA/AEI composite molecular sieve with the multi-level pore structure and the spongy morphology.
Comparative example 1
As in example 5, except that no seed crystals were added during the synthesis, the resulting product was noted as H.
The XRD pattern of H is shown in FIG. 3, which shows that the synthesized molecular sieve has the characteristic diffraction peak of CHA molecular sieve.
The SEM photograph of H is shown in FIG. 3, and it can be seen that the crystals of the molecular sieve are cubic, the grain size is 3-5 μm, and the surface is smooth.
The aperture of the H micropores is distributed in 0.3-0.5 nanometer, and the pore volume contributed by the micropores is0.24cm3And/g, no obvious mesopore and macropore pore size distribution.
According to XRD spectrogram, SEM photograph and N2And the physical adsorption characterization result proves that the prepared molecular sieve is a cubic SAPO molecular sieve only containing micropores.
Comparative example 2
As in example 5 except that defect free AEI seeds prepared as in example 1 were added during the synthesis, the resulting product was designated I.
The XRD spectrum of I is shown in FIG. 4, and it can be seen from FIG. 4 that the synthesized molecular sieve has the characteristic diffraction peaks of CHA/AEI molecular sieve, and the mass content of AEI structure molecular sieve in the composite molecular sieve is 6% and the mass content of SAPO-34 molecular sieve is 94% by using XRD quantitative method.
The SEM photograph of I is shown in FIG. 4, and it can be seen that the crystal of the molecular sieve is cubic, the grain size is 0.3-1 μm, and the surface of the crystal of the molecular sieve is smooth.
The aperture of the micropores of I is distributed in 0.3-0.5 nanometer, and no meso/macroporous distribution exists. The pore volume contributed by the micropores was 0.24cm3/g。
According to XRD, SEM, N2The result of physical adsorption characterization is enough to prove that the prepared composite SAPO molecular sieve is cubic.
[ example 8 ]
The molecular sieves obtained in examples 4 to 7 and comparative examples 1 to 2 were tabletted to prepare catalysts for the reaction of producing olefins from methanol. A fixed bed catalytic reaction device is adopted, a reactor is a stainless steel tube, and the used process conditions are considered as follows: the loading of the catalyst is 2.0g, the reaction temperature is 460 ℃, and the weight space velocity is 3h-1The pressure was 0.1MPa, and the evaluation results are shown in Table 1. As can be seen from Table 1, when the composite molecular sieve of the invention is used in MTO reaction, diene yield can be obviously improved, and the catalyst has better stability.
TABLE 1
Figure BDA0002128323340000111
Note: in the present invention, the yield of each product is by volume.
[ example 9 ]
Tabletting the molecular sieve D obtained in example 4, crushing to 40-60 meshes, and evaluating the catalytic performance of MTO by using a fixed bed reactor, wherein the used process conditions are as follows: the loading of the catalyst was 0.3g, and the catalyst was activated by introducing nitrogen at 500 ℃ for 2.0 hours and then cooled to 400 ℃. The methanol is carried by nitrogen, the flow rate of the nitrogen is 15mL/min, and the weight space velocity of the methanol is 2.0h-1And analyzing the obtained product by gas chromatography, wherein the service life of the catalyst is 950min, and the yield of the diene is 89.2%.

Claims (13)

1. A method for preparing a CHA/AEI composite molecular sieve, wherein at least two molecular sieves with defective AEI structures are used as seed crystals, the method comprises the following steps: adding the seed crystal into gel prepared from a silicon source, an aluminum source, a phosphorus source, a template agent and water, and then crystallizing under a hydrothermal condition to prepare the CHA/AEI composite molecular sieve; the two AEI structure molecular sieves with defects are respectively a seed crystal I and a seed crystal II;
the seed crystal I and the seed crystal II contain micropores, macropores and mesopores; wherein, the proportion of the specific surface area of the macropores and the mesopores in the total specific surface area of the seed crystal I is 5-9%, and the proportion of the pore volume of the macropores and the mesopores in the total pore volume is 10-14%; the specific surface area of the macropores and the mesopores accounts for 12-20% of the total specific surface area of the seed crystal II, and the pore volume of the macropores and the mesopores accounts for 16-35% of the total pore volume.
2. The method of claim 1, wherein: the mesoporous aperture of the seed crystal I is distributed in the range of 2-50 nanometers, and the macroporous aperture is distributed in the range of 50-300 nanometers; the mesoporous aperture of the seed crystal II is distributed in 2-50 nanometers, and the macroporous aperture is distributed in 500-1000 nanometers.
3. The method of claim 1, wherein: the mass ratio of the seed crystal I to the seed crystal II is (10-50): (50-90), preferably (20-40): (60-80).
4. The production method according to claim 1 or 2, characterized in that: the crystal seed I adopts an organic alkaline modifier to treat the modified AEI structure molecular sieve at 30-48 ℃ for 3-5 h, and the crystal seed II adopts an organic acidic modifier to treat the modified AEI structure molecular sieve at 70-100 ℃ for 5-10 h.
5. The method of claim 4, wherein: the organic alkaline modifier is tetraethyl ammonium hydroxide, and the organic acidic modifier is at least one of oxalic acid and citric acid; the concentration of the alkaline modifier is 0.005-0.05 mol/L, and the concentration of the acidic modifier is 0.1-0.5 mol/L.
6. The production method according to claim 4 or 5, characterized in that: the mass ratio of the alkaline modifier to the AEI structure molecular sieve dry basis is (25-70): 1; the mass ratio of the acidic modifier to the AEI structure molecular sieve dry basis is (25-70): 1.
7. the method of claim 1, wherein: the aluminum source, the silicon source, the phosphorus source, the template agent and the water are Al2O3：SiO2：P2O5：R：H2The molar ratio of O is 1: (0.05-2): (0.05-1.5): (1-10): (10-200), preferably 1: (0.1-1.5): (0.2-1.2): (2-8): (30-150); the total adding amount of the seed crystal I and the seed crystal II is 1.5-20% of the solid content of the gel, preferably 3-15% by mass, wherein R is a template agent.
8. The method of claim 1, wherein: the aluminum source is at least one selected from aluminum isopropoxide, pseudo-boehmite or alumina, the silicon source is at least one selected from tetraethoxysilane, white carbon black or silica sol, the phosphorus source is at least one selected from phosphoric acid, phosphate and phosphorous acid, and the template agent is at least one selected from tetraethylammonium hydroxide, triethylamine, diethylamine or morpholine.
9. The method of claim 1, wherein: the conditions for crystallization under the hydrothermal condition are as follows: the temperature is 150-250 ℃, preferably 170-210 ℃, and the time is 3-50 hours, preferably 10-35 hours.
10. A CHA/AEI composite molecular sieve characterized by: the CHA/AEI composite molecular sieve is prepared by adopting the method of any one of claims 1 to 9, wherein the mass content of the AEI structure molecular sieve in the CHA/AEI composite molecular sieve is 2-13%.
11. The CHA/AEI composite molecular sieve of claim 10, wherein: the CHA/AEI composite molecular sieve has a sponge structure and has micropores, mesopores and macropores; the diameter of the micropores is not more than 1 nanometer, preferably 0.3-0.7 nanometer, and the diameter of the macropores is distributed in 50-1000 nanometers, preferably 80-500 nanometers; the diameter of the mesopores is distributed in 8-40 nanometers, preferably 10-30 nanometers;
the pore volume contributed by the micropores is 0.10-0.40 cm3A/g, preferably 0.15 to 0.30 cm3Per gram; the pore volume contributed by the mesopores and the macropores is 0.02-0.50 cm3Per gram, preferably 0.05 to 0.30 cm3Per gram.
12. The CHA/AEI composite molecular sieve of claim 10, wherein: the CHA/AEI composite molecular sieve is in a cubic crystal shape, and the crystal size is 0.1-5.0 microns.
13. The use of the CHA/AEI composite molecular sieve of any of claims 10 to 12 in an oxygenate to olefin reaction.
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CN114832853B (en) * 2022-04-29 2023-06-23 四川大学 Cu-based mixed crystal molecular sieve NH 3 SCR catalyst and method for producing same

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