CN115805020A - Method for rapidly preparing FAU type molecular sieve membrane by using nano molecular sieve seed crystal - Google Patents
Method for rapidly preparing FAU type molecular sieve membrane by using nano molecular sieve seed crystal Download PDFInfo
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- CN115805020A CN115805020A CN202211632375.0A CN202211632375A CN115805020A CN 115805020 A CN115805020 A CN 115805020A CN 202211632375 A CN202211632375 A CN 202211632375A CN 115805020 A CN115805020 A CN 115805020A
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Abstract
The invention discloses a method for rapidly preparing an FAU type molecular sieve membrane by using nano molecular sieve crystal seeds, which specifically comprises the following steps: step one, preparing reaction gel; step two, preparing nano FAU type molecular sieve seed crystals; step three, coating a support body seed crystal layer; step four, synthesizing an FAU type molecular sieve membrane; the invention relates to the technical field of inorganic film manufacturing. According to the method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve crystal seeds, the preparation of the nano crystal seeds with the size of 20-50nm is utilized, the hydrothermal synthesis time of the FAU type molecular sieve membrane can be obviously shortened, the characteristic of high stacking density of the crystal seed layers is utilized, the intercrystalline defects of the membrane layer are obviously reduced in the crystallization synthesis process, the separation selectivity of the membrane is improved, the production quality is improved, the process of removing the organic template agent by high-temperature calcination is not needed, the probability of forming the membrane layer defects due to the fact that the membrane layer and the support body are not matched in the thermal expansion process of the high-temperature calcination is avoided, and the preparation time of the FAU type molecular sieve membrane is shortened.
Description
Technical Field
The invention relates to the technical field of inorganic membrane manufacturing, in particular to a method for quickly preparing an FAU type molecular sieve membrane by using nano molecular sieve crystal seeds.
Background
The separation process is an important operation process in industrial production, and is widely applied to industries such as chemistry, medicine, food, environmental protection and the like, compared with the traditional separation technology, the membrane separation technology has excellent economic benefit, and it is estimated that compared with the traditional energy intensive technology (such as adsorption, absorption and rectification), the energy consumption cost of the membrane separation technology is reduced to 30% of the original cost, so that the development of the efficient membrane separation technology has very important significance, compared with an organic membrane, the zeolite molecular sieve membrane has excellent swelling resistance, high thermal stability and chemical stability, the common zeolite membrane separation pore size range is 0.38-0.74 nm, wherein the FAU type molecular sieve membrane has a larger pore size (0.74 nm), has larger permeation flux when separating a macromolecular mixture, has good hydrophilicity, and has better application prospects in the aspects of seawater desalination, organic solvent dehydration and the like.
The common method for preparing the FAU type molecular sieve membrane comprises an in-situ hydrothermal synthesis method and a secondary growth method, wherein the in-situ hydrothermal synthesis method is a method for directly growing zeolite crystals on the surface of a support to form a membrane, the method has strict requirements on the properties of the support, the synthesis time is usually long, and the growth of the membrane layer crystals is difficult to control and easy to form pinhole defects, for example, a method disclosed by Zhou et al (microporosined and mesoporous materials,2020, 292, 109713) adopts the in-situ synthesis method to prepare the FAU type molecular sieve membrane, the synthesis time is up to 24 hours at 75 ℃, the secondary growth is the most reported synthesis method, the secondary growth is realized by pre-coating the zeolite crystals on the support as seed crystals and then hydrothermally synthesizing the zeolite molecular sieve membrane, and the seed crystals on the surface of the support can effectively reduce the influence of the defects of the support on the membrane layer; the seed crystal can induce and accelerate the growth of crystal to significantly shorten the synthesis time of the membrane, however, the molecular sieve membrane prepared by the secondary growth method is significantly influenced by the size and shape of the seed crystal, at present, the size of the seed crystal used for preparing the molecular sieve membrane is usually from several hundred nanometers to several micrometers, the larger the size of the seed crystal, the lower the activity of the seed crystal, resulting in the longer the growth time of the membrane layer and the lower uniformity of the thickness of the membrane layer, in addition, the molecular sieve membrane prepared by the conventional secondary growth method still needs high-temperature calcination to remove the organic template agent, further reducing the production efficiency of the membrane preparation, and in addition, increasing the risk of the formation of membrane layer defects due to the thermal expansion of the membrane layer and the support body in the calcination process.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides a method for rapidly preparing an FAU type molecular sieve membrane by using nano molecular sieve crystal seeds, and solves the problems.
(II) technical scheme
In order to realize the purpose, the invention provides the following technical scheme: a method for rapidly preparing an FAU type molecular sieve membrane by using nano molecular sieve crystal seeds comprises the following steps:
step one, reaction gel preparation: adding an aluminum source, a mixed organic template and deionized water into a stirring tank according to a set molar ratio, uniformly mixing to prepare an aluminum source solution, adding a silicon source, an organic template and deionized water into the stirring tank according to the set molar ratio, uniformly mixing to prepare a silicon source solution, dropwise adding the aluminum source solution into the stirred silicon source solution, fully mixing to obtain a mixed solution, and continuously stirring and aging the mixed solution at room temperature for 24-72 hours to prepare a first reaction gel;
step two, preparing nano FAU type molecular sieve seed crystal: pouring the first reaction gel prepared in the first step into a reaction kettle, carrying out hydrothermal synthesis at 85-105 ℃ for 72-96h, and after the reaction is finished, carrying out centrifugal separation on a reaction product to obtain a nano FAU type molecular sieve seed crystal;
step three, coating a support seed crystal layer: adding the nano FAU type molecular sieve seed crystal prepared in the second step into deionized water to prepare a seed crystal solution with the concentration of 0.2-1wt%, and coating the seed crystal solution on a porous support body, wherein the coating mode comprises one of a wiping mode and a dip-coating mode of absorbent cotton soaked with the seed crystal solution, then placing the porous support body in an oven to dry so as to remove adsorbed moisture, and performing coating-drying cycle for 2-3 times to obtain the support body coated with the seed crystal layer;
step four, synthesizing an FAU type molecular sieve membrane: adding an aluminum source, an inorganic base, a silicon source and water into a stirring tank according to a set molar ratio, uniformly mixing, continuously stirring the solution at room temperature for 6-12h to prepare second reaction gel, putting the second reaction gel and the support body coated with the seed crystal layer prepared in the step three into a reaction kettle, performing hydrothermal synthesis at 70-95 ℃ for 1.5-4 h, quenching the reaction kettle after the reaction is finished, and cleaning and drying the membrane to obtain the FAU type molecular sieve membrane.
The invention is further configured to: the mol ratio of the aluminum source to the mixed organic template to the deionized water in the first step comprises: 1, (2-3.6) and (150-250), wherein the molar ratio of the silicon source, the organic template agent and the deionized water comprises: 1: (0.2-0.5): (9-16).
The invention is further configured to: the aluminum source in the first step and the fourth step is one of aluminum foil, aluminum hydroxide, aluminum isopropoxide, sodium aluminate and sodium metaaluminate, and the silicon source in the first step and the fourth step is one of sodium silicate, silica sol, white carbon black and ethyl orthosilicate.
The invention is further configured to: the mixed organic template agent in the first step is tetramethyl ammonium hydroxide in a molar ratio of: tetramethylammonium bromide =1.6, and the organic template in the first step is tetramethylammonium hydroxide, which is a mono-template.
The invention is further configured to: the average size of the nano FAU molecular sieve crystal seeds prepared in the second step is 20-50nm.
The invention is further configured to: the porous support body in the third step is made of one of silicon carbide, alumina and mullite materials, the making shapes include but are not limited to a sheet type, a disc type and a tube type, and the average pore diameter of the porous support body is 50-500nm.
The invention is further configured to: and the inorganic base in the fourth step is one of sodium hydroxide and potassium hydroxide.
The invention is further configured to: the thickness of the FAU type molecular sieve membrane prepared in the fourth step is 0.6-3.5 μm.
(III) advantageous effects
The invention provides a method for rapidly preparing an FAU type molecular sieve membrane by using nano molecular sieve crystal seeds. The method has the following beneficial effects:
(1) The invention has higher activity and kinetic growth speed by utilizing the preparation of the nano seed crystal with the size of 20-50nm, and can obviously shorten the hydrothermal synthesis time of the FAU type molecular sieve membrane.
(2) The invention makes use of the characteristic of high stacking density of the seed crystal layer formed by the nano-scale seed crystal, so that the interfacial defect of the FAU type molecular sieve membrane can be obviously reduced in the crystallization synthesis process, the separation selectivity of the membrane is improved, and the production quality is effectively improved.
(3) According to the invention, through the arrangement of the organic template agent, the process of removing the organic template agent through high-temperature calcination is not needed, the probability of forming the defect of the film layer due to the mismatching of the thermal expansion of the film layer and the support body in the high-temperature calcination process is avoided, the preparation time of the FAU type molecular sieve film is further shortened, the preparation process is simpler, the production cost is effectively reduced, and the method has the characteristic of easy popularization.
Drawings
FIG. 1 is an SEM image of FAU type molecular sieve seeds prepared in the first example of the present invention;
FIG. 2 is an XRD pattern of FAU type molecular sieve seed crystals prepared in example one of the present invention;
FIG. 3 is a surface SEM image of a FAU type molecular sieve membrane prepared according to a first embodiment of the present invention;
FIG. 4 is a SEM cross-section of a FAU type molecular sieve membrane prepared according to a first embodiment of the present invention;
FIG. 5 is an XRD pattern of an FAU type molecular sieve membrane prepared according to a first embodiment of the present invention;
FIG. 6 is a surface SEM image of an FAU type molecular sieve membrane prepared in comparative example I;
fig. 7 is a sectional SEM image of the FAU-type molecular sieve membrane prepared in comparative example one.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
Referring to fig. 1-7, the embodiment of the present invention provides the following technical solutions:
the first embodiment,
A method for rapidly preparing an FAU type molecular sieve membrane by using nano molecular sieve crystal seeds comprises the following steps:
step one, reaction gel preparation: aluminum isopropoxide, tetramethylammonium hydroxide (SDA), tetramethylammonium bromide (SDA) and deionized water are mixed according to the molar ratio: al (aluminum) 2 O 3 :SDA(1.6:1):H 2 Adding 200 into a stirring tank, uniformly mixing to prepare an aluminum source solution, and adding silica sol, tetramethylammonium hydroxide (SDA) and deionized water according to the molar ratio of: siO 2 2 :SDA:H 2 Adding O =1 2 O 3 :SiO 2 :SDA:H 2 O =1, 4.35, and aging the mixed solution at room temperature for 72 hours with continuous stirring to obtain a first reaction gel;
step two, preparing nano FAU type molecular sieve crystal seeds: pouring the first reaction gel prepared in the first step into a reaction kettle, performing hydrothermal synthesis at 100 ℃ for 96 hours, and after the reaction is finished, performing centrifugal separation on a reaction product to obtain nano FAU molecular sieve seed crystals;
step three, coating a support body seed crystal layer: adding the nano FAU type molecular sieve seed crystal prepared in the second step into a proper amount of deionized water to prepare a seed crystal solution with the concentration of 0.5wt%, dip-coating the porous support body in the seed crystal solution, then placing the porous support body in an oven for drying to remove adsorbed water, and performing dip-coating-drying circulation on the porous support body for 2 times to obtain the support body coated with the seed crystal layer;
step four, synthesizing an FAU type molecular sieve membrane: aluminum hydroxide, sodium silicate and water are mixed according to the molar ratio of Al 2 O 3 :Na 2 O:SiO 2 :H 2 Adding 5000 of an O =1.
In this example, the SEM result of the FAU type molecular sieve seed crystal is shown in fig. 1, and it can be seen that the average diameter of the prepared FAU type molecular sieve seed crystal is about 30nm;
the XRD result of the seed crystal is shown in fig. 2, and it can be known that the prepared FAU-type molecular sieve is a pure-phase FAU crystal;
the SEM characterization results are shown in figures 3 and 4, and it can be seen that the surface of the prepared film M1 is smooth, the smaller size of the crystal grains is about 0.2-0.5 μ M, the film layer is dense and the thickness is about 0.95 μ M;
the XRD spectrogram of the membrane is shown in figure 5, and the diffraction peak of the prepared FAU type molecular sieve membrane is consistent with the standard peak, which shows that the prepared membrane is a pure phase FAU type molecular sieve membrane;
the prepared membrane M1 performs pervaporation separation on 10wt% water/isopropanol mixed solution at 70 ℃, and the flux of the membrane is 2.5 kg/(M) 2 h) The separation factor was 850, indicating that the ultra-thin FAU membrane had excellent separation performance.
Example II,
Compared with the first embodiment, the difference is that:
in the fourth step, the FAU type molecular sieve membrane is hydrothermally synthesized for 4 hours in a reaction kettle at 85 ℃ to prepare the FAU type molecular sieve membrane M2.
In this example, the membrane prepared was a pure phase FAU type molecular sieve membrane;
the film layer is compact and has the thickness of about 2.6 mu m;
the prepared membrane M2 performs pervaporation separation on 10wt% water/isopropanol mixed solution at 70 ℃, and the flux of the membrane is 1.8 kg/(M) 2 h) The separation factor is 920, indicating that the ultra-thin FAU membrane has excellent separation performance.
Example III,
Compared with the first embodiment, the difference is that:
the molar composition of the aluminum source solution in the step one is Al 2 O 3 :SDA(1.6:1):H 2 O =1, 3.2 (tetramethylammonium hydroxide: tetramethylammonium bromide = 1.6) 2 :SDA:H 2 O =1, 0.4 2 O 3 :SiO 2 :SDA:H 2 O =1, 10.06, 306.55, to produce FAU-type molecular sieve membrane M3.
In this example, the average diameter of the prepared FAU type molecular sieve seed crystals was about 45nm;
the prepared membrane is a pure phase FAU type molecular sieve membrane, and the membrane layer is compact and has the thickness of about 1.5 mu m;
the prepared membrane M3 performs pervaporation separation on 10wt% water/isopropanol mixed solution at 70 ℃, and the flux of the membrane is 2.2 kg/(M) 2 h) The separation factor was 1020, indicating that the ultra-thin FAU membrane had excellent separation performance.
Comparative examples A,
Compared with example one, the difference is that the FAU type molecular sieve seed crystal in step two is the indiscriminate commercial FAU molecular sieve, the average size of the molecular sieve is about 1.2 μ M, and the FAU type molecular sieve membrane M4 is prepared.
In this comparative example, the average diameter of the FAU type molecular sieve seeds was about 1.2 μm;
the prepared membrane is a pure phase FAU type molecular sieve membrane, the SEM representation of the membrane is shown in attached figures 6 and 7, the surface of the membrane is rough, the larger size of crystal grains is 1.5-2 mu m, and the membrane has obvious crystal boundary;
the film layer is compact and has the thickness of about 11 mu m;
the membrane M4 thus prepared was tested for 10% by weight of water/iso-membrane at 70 ℃The propanol mixed solution is subjected to pervaporation separation, and the flux of the membrane is only 0.8 kg/(m) 2 h) The separation factor was 360, indicating that large seeds produced FAU membranes with thicker separation layers and relatively larger defects.
Claims (8)
1. A method for rapidly preparing FAU type molecular sieve membrane by nanometer molecular sieve crystal seeds is characterized by comprising the following steps: the method specifically comprises the following steps:
step one, reaction gel preparation: adding an aluminum source, a mixed organic template and deionized water into a stirring tank according to a set molar ratio, uniformly mixing to prepare an aluminum source solution, adding a silicon source, an organic template and deionized water into the stirring tank according to the set molar ratio, uniformly mixing to prepare a silicon source solution, dropwise adding the aluminum source solution into the stirred silicon source solution, fully mixing to obtain a mixed solution, and continuously stirring and aging the mixed solution at room temperature for 24-72 hours to prepare a first reaction gel;
step two, preparing nano FAU type molecular sieve seed crystal: pouring the first reaction gel prepared in the first step into a reaction kettle, carrying out hydrothermal synthesis at 85-105 ℃ for 72-96h, and after the reaction is finished, carrying out centrifugal separation on a reaction product to obtain nano FAU type molecular sieve seed crystals;
step three, coating a support seed crystal layer: adding the nano FAU type molecular sieve seed crystal prepared in the second step into deionized water to prepare a seed crystal solution with the concentration of 0.2-1wt%, coating the seed crystal solution on a porous support body, then placing the porous support body in an oven for drying to remove adsorbed moisture, and performing coating-drying circulation for 2-3 times to obtain the support body coated with the seed crystal layer;
step four, synthesizing an FAU type molecular sieve membrane: adding an aluminum source, an inorganic base, a silicon source and water into a stirring tank according to a set molar ratio, uniformly mixing, continuously stirring the solution at room temperature for 6-12h to prepare second reaction gel, putting the second reaction gel and the support body coated with the seed crystal layer prepared in the step three into a reaction kettle, performing hydrothermal synthesis at 70-95 ℃ for 1.5-4 h, quenching the reaction kettle after the reaction is finished, and cleaning and drying the membrane to obtain the FAU type molecular sieve membrane.
2. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: in the first step, the mol ratio of the aluminum source to the mixed organic template to the deionized water comprises: 1, (2-3.6) and (150-250), wherein the molar ratio of the silicon source, the organic template agent and the deionized water comprises: 1: (0.2-0.5): (9-16).
3. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: the aluminum source in the first step and the fourth step is one of aluminum foil, aluminum hydroxide, aluminum isopropoxide, sodium aluminate and sodium metaaluminate, and the silicon source in the first step and the fourth step is one of sodium silicate, silica sol, white carbon black and ethyl orthosilicate.
4. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: the mixed organic template agent in the first step is tetramethyl ammonium hydroxide in a molar ratio of: tetramethyl ammonium bromide =1.6, and the organic template in the first step is mono-template tetramethyl ammonium hydroxide.
5. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: the average size of the nano FAU molecular sieve crystal seeds prepared in the second step is 20-50nm.
6. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: and the porous support in the third step is made of one of silicon carbide, alumina and mullite materials, and the average pore diameter of the porous support is 50-500nm.
7. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: and the inorganic base in the fourth step is one of sodium hydroxide and potassium hydroxide.
8. The method for rapidly preparing the FAU type molecular sieve membrane by using the nano molecular sieve seed crystal according to claim 1, which is characterized in that: the thickness of the FAU type molecular sieve membrane prepared in the fourth step is 0.6-3.5 μm.
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