CN114669201A - Preparation method of composite SSZ-13/MFI molecular sieve membrane - Google Patents
Preparation method of composite SSZ-13/MFI molecular sieve membrane Download PDFInfo
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Abstract
The invention discloses a preparation method of a composite SSZ-13/MFI molecular sieve membrane, which comprises the following steps: (1) preparing SSZ-13 and MFI molecular sieve seed crystals; (2) coating an SSZ-13 seed crystal layer on the surface of the porous carrier by a vacuum suction method; (3) preparing a layer of compact SSZ-13 molecular sieve membrane on the surface of the porous carrier by a secondary growth method; (4) introducing an MFI seed crystal layer on the surface of the SSZ-13 molecular sieve membrane by a dip-coating method; (5) and preparing a continuous MFI molecular sieve membrane layer on the SSZ-13 molecular sieve membrane by a secondary growth method to obtain the SSZ-13/MFI composite molecular sieve membrane. The MFI layer has stronger hydrophobic property and can improve SSZ-13 low temperature moisture resistance of the molecular sieve membrane. The composite SSZ-13/MFI molecular sieve membrane is used for separating wet CO2/CH4The mixed gas system has more excellent separation performance.
Description
Technical Field
The invention relates to a preparation method of an SSZ-13/MFI composite molecular sieve membrane, belonging to the field of preparation and application of molecular sieve membrane materials.
Background
In the purification of natural gas and biomass gas and the collection process of petroleum associated gas, CO 2Is of vital importance, in particular, is CO2/CH4And (4) separating a mixed gas system. CO 22As a main impurity component, the calorific value of the above gas is reduced, and in a humid environment, CO2The acid is easy to corrode the conveying pipeline, equipment and other facilities, and the service life of the pipeline equipment is influenced. So CO2The technology is one of the key research directions in the industry today. The membrane separation technology is a novel separation technology, has the advantages of high separation efficiency, low energy consumption, small occupied area, easy integration and the like, and can effectively reduce the separation energy consumption and cost in the energy gas separation. The molecular sieve membrane has regular molecular size pore channels, can realize the sieving separation of molecular sizes, shows potential application prospects in the field of gas separation, and attracts people's extensive attention. FAU, MFI, DDR and some CHA-type molecular sieve membranes for CO2/CH4The separation of the mixed system has been widely reported, in the separation test research of laboratory scale, the parameters of permeation rate, selectivity and the like shown by several types of molecular sieve membranes are close to or meet the industrial requirement of the energy gas separation, and the industrial application in a short period of time is expected to be realized. However, for practical separation applications, the stability of the membrane, including the resistance to impurity components, especially H in low temperature environments 2The tolerance of O is a key factor affecting the separation performance of the membrane.
The hydrophilic and hydrophobic properties of the molecular sieve are related to the silicon-aluminum ratio of the framework of the molecular sieve, and the higher the crystalline silicon-aluminum ratio of the surface of the molecular sieve membrane is, the stronger the hydrophobicity of the membrane is, and the better the tolerance of the membrane to water vapor in gas separation is. Mei et al [ Journal of Membrane Science 565 (2018) 358-]SAPO-34 molecular sieve membranes with low silicon content are reported for use with H2/CH4The system is separated, and the water vapor are separated at 0.675 vol% and 50%oC under, film ofH2Permeation rate ratio 25oC decreased by 60% in the dried system. The SSZ-13 molecular sieve membrane has higher silicon-aluminum ratio and certain hydrophobic property, and can be used for highly-corrected separation of natural gas and biomass gas. Patent CN104289115B discloses a method for preparing a high-silicon CHA type SSZ-13 molecular sieve membrane, and the author adopts a multi-template agent combination to prepare a high-performance SSZ-13 molecular sieve membrane on a porous ceramic support, and the membrane shows better chemical stability and certain characteristic of water vapor resistance. Lee et al [ ACS Appl. mater. Interfaces 2019, 11, 3946-]The CHA molecular sieve membranes with different silicon-aluminum ratios are prepared by using the synthetic sols with different silicon-aluminum ratios, and the CHA membranes are found to contain CO in water vapor along with the increase of the silicon-aluminum ratio of the membrane layer2/N2The system shows high selectivity, and the membrane with higher silicon-aluminum ratio shows better water vapor tolerance. Kosinov et al [ J. mater. chem. A, 2014,2, 13083- ]Synthesis of high silicon SSZ-13 molecular sieve membrane is reported and found 20oC, introducing water vapor of 2.2 kPa to the membrane to obtain CO of the membrane2The permeation rate is reduced by 80 percent, and the testing temperature is increased to 100oAnd after C, the influence of water vapor on the permeation rate of the membrane is weakened. Kida et al Separation and Purification Technology 197 (2018) 116-]The synthesis of all-silicon CHA molecular sieve membranes (Si/Al ratio ∞) was reported and the membranes were tested in detail for dry and humid CO2/CH4Separation performance in the system, at 25oC, introducing water vapor to make CO2The permeation rate is reduced by 50 percent, and CO is reduced2/CH4The selectivity decreases by as much as 85%, indicating that the low temperature moisture resistance of the all-silicon CHA film is still not ideal. However, Kida et al reported that water vapor is responsible for the CO of the membrane at high pressure2/CH4The selectivity had little effect. The above studies indicate that high silicon or even full silicon in the membrane layer plays a decisive role in the water vapor tolerance of the molecular sieve membrane. However, the preparation of the all-silicon CHA molecular sieve membrane is extremely difficult, both the CHA seed crystal and the membrane need to be realized under the condition that hydrofluoric acid HF is used as a mineralizer, the sol is pasty or powdery, the preparation steps are complex, the synthesis time of the membrane is long, and the repeatability is poor.
Compared with the all-silicon CHA type molecular sieve membrane, the synthesis of the all-silicon MFI type molecular sieve membrane is simpler, and the reaction condition is warmer And (d). And the all-silicon MFI type molecular sieve membrane has high hydrophobic property. The invention synthesizes an SSZ-13/MFI composite molecular sieve membrane material, and synthesizes an all-silicon MFI molecular sieve membrane layer on the surface of an SSZ-13 molecular sieve membrane. The MFI molecular sieve membrane layer of all silicon can effectively prevent water molecules from entering the SSZ-13 molecular sieve membrane pore canal, improve the low-temperature water vapor tolerance of the membrane material, and has little influence on the gas separation performance of the SSZ-13 molecular sieve membrane. The membrane material can be used for removing CO from natural gas, biomass gas and other systems under humid conditions2。
Disclosure of Invention
The invention aims to provide a preparation method of a composite SSZ-13/MFI molecular sieve membrane material. The composite molecular sieve membrane material has higher water vapor tolerance, solves the problem of water vapor tolerance of the conventional SSZ-13 molecular sieve membrane at low temperature, and can be used for removing CO from natural gas, biomass gas and other systems under humid conditions2. The SSZ-13/MFI composite molecular sieve membrane material consists of two continuous molecular sieve crystal layers: 1. SSZ-13 molecular sieve membrane substrate (separation layer) and 2. dense all-silicon MFI molecular sieve membrane layer (hydrophobic layer) on this substrate. Wherein, the size of the pore canal of the SSZ-13 molecular sieve membrane layer is 0.38 nm, and the molecular sieve membrane layer can be used for CO2/CH4Separating the system to obtain a separating layer; the MFI molecular sieve membrane layer of the all-silicon has high hydrophobicity, is a protective layer, can effectively prevent water molecules from entering the SSZ-13 molecular sieve membrane pore canal, and improves the water vapor tolerance of the membrane material. And the sizes of the pore passages of the MFI structure are far larger than that of the CO 2And CH4Molecule [ 2 ]aSinusoidal channels (0.51 nm. times.0.55 nm) andbaxial straight channels (0.53 nm x 0.56 nm)]At normal temperature, both gas molecules can permeate rapidly, and CO thereof2The permeation rate was comparable to a conventional SSZ-13 molecular sieve membrane without MFI layer.
In order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows:
a preparation method of a composite SSZ-13/MFI molecular sieve membrane comprises the following steps:
(1) preparation of SSZ-13 molecular sieve crystal: the method comprises the following steps of mixing raw materials of an aluminum source, a silicon source, a structure directing agent SDA, an alkali source and deionized water according to the molar ratio of the components: na (Na)2O/SiO2=0.05-0.2，SiO2/Al2O3=20-200，SDA/SiO2=0.05-0.5，H2O/SiO2Mixing the materials at a ratio of 25-50 =20-60, stirring vigorously to form a uniform soloAging for 6-48 h under C; the aged sol is put into a reaction kettle at 100-200- oCHydrothermal synthesis is carried out for 24-120 h, and after centrifugation, cleaning, drying and calcining, SSZ-13 molecular sieve crystals are obtained;
(2) SSZ-13 seed layer preparation: taking the SSZ-13 molecular sieve crystals synthesized in the step (1) as membrane synthesis seed crystals, grinding and dispersing, weighing a proper amount of crystals, adding the crystals into ethanol, and performing ultrasonic dispersion to form a uniform SSZ-13 seed crystal/ethanol suspension with the mass fraction of 0.02-2 wt%; coating SSZ-13 seed crystal on the surface of a porous carrier in a vacuum pumping coating mode, wherein the vacuum degree is 0.01-0.1 MPa, the pumping coating time is 5-60 s, and after drying treatment, forming a uniform and compact SSZ-13 molecular sieve seed crystal layer on the surface of the carrier;
(3) Synthesis of SSZ-13 molecular sieve membrane: the method comprises the following steps of mixing raw materials of an aluminum source, a silicon source, a structure directing agent SDA, an alkali source and deionized water according to the molar ratio of the components: the molar ratio of each component is as follows: na (Na)2O/SiO2=0.05-0.2，SiO2/Al2O3= 20-200，SDA/SiO2= 0.05-0.5，H2O/SiO2Mixing the materials at a ratio of 25-50 = 20-60oAging for 24-120 h under C, putting the seeded porous carrier in the step (2) into a stainless steel reaction kettle, pouring sol solution, and then adding 100 hoC-200 oCPerforming hydrothermal crystallization for 24-120 h to form an SSZ-13 molecular sieve membrane layer on the porous carrier. Cleaning and drying the obtained SSZ-13 molecular sieve membrane, and calcining the obtained SSZ-13 molecular sieve membrane in an ozone atmosphere to obtain the SSZ-13 molecular sieve membrane;
(4) preparing MFI molecular sieve crystals: the raw material silicon source, the structure directing agent SDA and the deionized water are mixed according to the molar ratio of the components: SDA/SiO2=0.05-0.5，H2O/SiO2Mixing the materials according to the ratio of =50-120, and aging the formed sol for 4-24 h at normal temperature; pouring the sol into a reaction kettle at the temperature of 120-oC, performing hydrothermal synthesis for 12-24 h, and centrifuging, cleaning, drying and calcining to obtain an MFI molecular sieve crystal;
(5) loading MFI crystal seeds on the SSZ-13 molecular sieve membrane: grinding the MFI molecular sieve crystal obtained in the step (4), weighing a proper amount of the MFI molecular sieve crystal, adding the MFI molecular sieve crystal into ethanol, dispersing the mixture through ultrasonic oscillation to obtain a suspension of the MFI molecular sieve, and adding cationic polymer polydienyl dialkyl ammonium salt with the total mass of 0.1-1% of the suspension into the suspension; vertically immersing the SSZ-13 molecular sieve membrane obtained in the step (3) in an MFI molecular sieve seed crystal suspension for 10-60 s, then extracting at a constant speed of 0.5-5 cm/min, and drying to form an MFI type molecular sieve crystal layer on the surface of the SSZ-13 molecular sieve membrane;
(6) Preparation of SSZ-13/MFI composite molecular sieve membrane: the silicon source, the structure directing agent SDA and the deionization are mixed according to the molar ratio of the components: SDA/SiO2=0.05-0.5，H2O/SiO2Mixing the materials according to the ratio of =50-120, and aging the formed clear sol for 4-24 h at normal temperature; and (3) placing the SSZ-13 molecular sieve membrane loaded with the MFI seed crystal obtained in the step (5) into a reaction kettle, pouring the sol, crystallizing at the temperature of 100-160 ℃ for 4-12 h, taking out the membrane tube, cleaning, drying, and calcining in an ozone atmosphere to obtain the SSZ-13/MFI composite molecular sieve membrane.
Preferably:
in the steps (1) and (3), the structure-directing agent SDA is adopted asN,N,N-trimethyladamantyl ammonium hydroxide,N,N, N-trimethyladamantyl ammonium bromide,N,N,N-trimethyladamantyl ammonium iodide,N,N,N-trimethylbenzylammonium hydroxide,N, N,N-trimethylbenzylammonium bromide,N,N,N-one or more combinations of trimethylbenzylammonium iodide or tetraethylammonium hydroxide.
In the step (1), the size of the prepared SSZ-13 molecular sieve seed crystal is 200-600 nm.
In the step (2), the porous carrier is a tubular or hollow fibrous carrier, and the material is alumina, mullite, cordierite, zirconia or silica.
In the steps (1), (3), (4) and (6), the silicon source is silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder.
The removal of the structure-directing agent SDA of the molecular sieve membrane synthesized in the steps (3) and (6) is carried out in an ozone atmosphere, the concentration range of the ozone is 10-150 mg/L, and the temperature is 150 ℃ and 250 ℃; the calcination time is 24-96 h; the heating rate is 0.2-10 ℃ per min.
And (3) preparing the SSZ-13/MFI composite molecular sieve membrane in the step (6) by using one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium iodide or tetraethylammonium bromide as a structure directing agent.
In the step (4), the prepared MFI type molecular sieve seed crystal is a uniform short columnar crystal with the diameter range of 50-1000 nm.
The cationic polymer polydienyl dialkyl ammonium salt in the step (5) is selected from polydiallyl dimethyl ammonium bromide, polydiallyl butyl dimethyl ammonium bromide, polydiallyl diethyl ammonium chloride or polydiallyl dimethyl ammonium chloride.
The invention has the beneficial effects that:
the SSZ-13/MFI composite molecular sieve membrane material consists of two continuous molecular sieve crystal layers: an SSZ-13 molecular sieve membrane substrate (separation layer) and a dense all-silicon MFI molecular sieve membrane layer (hydrophobic layer) on the substrate. Wherein, the SSZ-13 molecular sieve membrane layer has a pore channel size of 0.38 nm, is used as a separation layer, has gas separation effect, and can be used for CO 2/CH4Separating the system to obtain a separating layer; the MFI molecular sieve membrane layer of the all-silicon is high in hydrophobicity and is a protective layer, so that water molecules can be effectively prevented from entering an SSZ-13 molecular sieve membrane pore channel, the water vapor tolerance of the membrane material is improved, and the surface strength of the membrane material is improved. And the sizes of the pore passages of the MFI structure are far larger than that of the CO2And CH4Molecule [ 2 ]aSinusoidal channels (0.51 nm. times.0.55 nm) andbaxial straight channel (0.53 nm x 0.56 nm)]At normal temperature, both gas molecules can permeate rapidly, and CO thereof2The permeation rate was comparable to that of a conventional SSZ-13 molecular sieve membrane without an MFI layer.
The SSZ-13/MFI composite molecular sieve membrane material obviously improves the hydrophobic property of the membrane surface and the water vapor tolerance of the membrane material, solves the problem that the gas separation performance of the conventional SSZ-13 molecular sieve membrane is greatly reduced under the low-temperature and humid condition, can be used for separating natural gas, biomass gas and other systems under the humid condition, and has the permeation rate and the selectivity which are far higher than those of the conventional SSZ-13 molecular sieve membrane under the low-temperature condition.
The preparation method disclosed by the invention is simple in steps and high in repeatability, and has an industrial development prospect.
Drawings
FIG. 1X-ray diffraction (XRD) pattern of crystals of SSZ-13 molecular sieve prepared in example 1.
FIG. 2X-ray diffraction (XRD) pattern of all-silicon MFI-type molecular sieve crystals (Silicalite-1) prepared in example 1.
FIG. 3 is a Scanning Electron Microscope (SEM) picture of SSZ-13 molecular sieve crystals prepared in example 1.
FIG. 4 Scanning Electron Microscope (SEM) picture of all-silicon MFI molecular sieve crystals prepared in example 1 (Silicalite-1).
FIG. 5 is a Scanning Electron Microscope (SEM) picture of an SSZ-13 type molecular sieve membrane prepared in example 1.
FIG. 6 Scanning Electron Microscope (SEM) picture of composite SSZ-13 molecular sieve membrane prepared in example 1.
Figure 7X-ray diffraction (XRD) pattern of composite SSZ-13 molecular sieve membrane prepared in example 1.
Detailed Description
The technical solutions of the present invention are further described in detail by the following specific examples, but it should be noted that the following examples are only used for describing the content of the present invention and should not be construed as limiting the scope of the present invention.
Example 1
A preparation method of a composite SSZ-13/MFI molecular sieve membrane comprises the following steps:
(1) preparation of SSZ-13 molecular sieve seed: raw materials of aluminum source, silicon source (silica sol TM-40) and structure directing agent (N, N,N-trimethyladamantyl ammonium hydroxide TMAdaOH), sodium hydroxide and deionized water according to the molar ratio of the components: 10 Na 2O: 0.5 Al2O3: 100 SiO2: 4400 H2Mixing O20 TMADAOH, stirring the sol at room temperature for aging for 6 h, placing the aged sol in a reaction kettle, and allowing the sol to react at 180 deg.CThermally synthesizing for 120 h, centrifugally cleaning for many times, drying, and calcining for 48 h at 470 ℃ to obtain SSZ-13 molecular sieve crystals;
(2) SSZ-13 seed layer preparation: grinding the SSZ-13 molecular sieve crystal synthesized in the step (1), adding the grinded crystal into ethanol, and performing ultrasonic dispersion to form an SSZ-13 seed crystal/ethanol suspension with the mass fraction of 0.2 wt%. Coating SSZ-13 seed crystal on the surface of a porous alumina carrier in a vacuum pumping coating mode, wherein the vacuum degree is 0.02 MPa, the pumping coating time is 40 s, and after drying treatment, forming a uniform and compact SSZ-13 molecular sieve seed crystal layer on the surface of the carrier;
(3) synthesis of SSZ-13 molecular sieve membrane: raw materials of aluminum source, silicon source (silica sol TM-40) and structure directing agent (N,N, N-trimethyladamantyl ammonium hydroxide TMAdaOH), sodium hydroxide and deionized water according to the molar ratio of the components: 10 Na2O: 0.5 Al2O3: 100 SiO2: 4400 H2And (3) mixing 20 TMADAOH, aging the formed sol for 8 h at room temperature, putting the seeded porous carrier in the step (2) into a reaction kettle, pouring the sol solution, performing hydrothermal crystallization for 96 h at 160 ℃, and forming a layer of SSZ-13 molecular sieve membrane on the carrier. After the SSZ-13 molecular sieve membrane is washed for 1 hour and dried, the SSZ-13 molecular sieve membrane is calcined for 48 hours at 200 ℃ in an ozone/oxygen atmosphere of 80 mg/L (the heating rate and the cooling rate are both 0.5 ℃/min), and the SSZ-13 molecular sieve membrane is prepared;
(4) Preparing MFI molecular sieve seed crystal: tetraethyl orthosilicate, a structure directing agent TPAOH and deionized water according to the molar ratio of each component: SiO 22: TPAOH: H2O = 1: 0.12: 60, and the formed sol is aged for 12 h at normal temperature; hydrothermal synthesis of the sol at 150 ℃ for 12 h, centrifugal cleaning and drying, and then obtaining the sol at 470 oCCalcining to obtain MFI molecular sieve crystal;
(5) preparing an MFI seed crystal layer on the surface of the SSZ-13 molecular sieve membrane: grinding the MFI molecular sieve crystals synthesized in the step (4), dispersing the MFI molecular sieve crystals in absolute ethyl alcohol to form a suspension with the mass fraction of 0.2 wt%, and adding a cationic polymer which is polydiallyl dimethyl ammonium bromide and accounts for 0.2% of the total mass of the suspension; vertically immersing the SSZ-13 molecular sieve membrane in the suspension of the MFI type molecular sieve for 10-60 s, then uniformly extracting and drying at a speed of 0.5-5 cm/min, and forming an MFI type molecular sieve seed crystal layer on the surface of the SSZ-13 molecular sieve membrane;
(6) preparing an MFI type molecular sieve membrane: the silicon source tetraethyl orthosilicate structure directing agent TPAOH and water are prepared according to the molar ratio of the components: SiO 22: TPAOH: H2O = 1: 0.12: 60, stirring and aging the formed sol for 24 h at normal temperature to obtain stable clear sol; and (3) putting the seeded porous carrier obtained in the step (5) into the sol, performing hydrothermal crystallization for 12 hours at the temperature of 120 ℃, and forming a layer of MFI type molecular sieve membrane on the surface of the SSZ-13 molecular sieve membrane. After the composite SSZ-13 molecular sieve membrane is washed for 1 hour and dried, the composite SSZ-13 molecular sieve membrane is calcined for 48 hours at 200 ℃ in an ozone atmosphere of 80 mg/L (the heating rate and the cooling rate are both 0.5 ℃/min), and the composite SSZ-13 molecular sieve membrane is prepared;
The film (M1) prepared was used at 50 ℃ in equimolar CO at dry and relative humidity of 100%2/CH4The mixed system of (1) was subjected to a gas separation performance test, and the test results are shown in table 1.
Example 2
The procedure was as in example 1 except that the SSZ-13 molecular sieve membrane of step (3) was synthesized using the following components in the following molar ratios: 20 Na2O: 1 Al2O3: 100 SiO2: 6000 H2O is 10 TMAdaOH. 50 in steps (1) and (3)oAging at 200 deg.C for 48 h, and hydrothermal synthesizing at 200 deg.C for 72 h. The mass fraction of the SSZ-13 seed/ethanol suspension in the step (2) was 0.02 wt%.
The film (M2) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system of (1) was subjected to a gas separation performance test, and the test results are shown in table 1.
Example 3
The procedure used is as in example 1, except that the SSZ-13 molecular sieve membrane of step (3) has the following components in molar ratio: 5 Na2O: 5 Al2O3: 100 SiO2: 2000 H2O10 TMADAOH. In the step (2), the mass fraction of the SSZ-13 seed crystal/ethanol suspension is 2 wt%.
The film (M3) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system of (1) was subjected to a gas separation performance test, and the test results are shown in table 1.
Example 4
The procedure was as in example 1, except that the SSZ-13 molecular sieve membrane of step (3) was synthesized under conditions of 200 oC, reacting for 24 hours under the condition of C, wherein the structure directing agent in the steps (1) and (3) isN,N,N-trimethylbenzylammonium bromide. The structure directing agent in the step (6) is tetrapropylammonium bromide with the molecular weight of 100oHydrothermal crystallization is carried out for 12 hours under the condition of C.
The film (M4) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 1.
Example 5
The procedure used is as in example 1, except that 0.1% by weight of the cationic polymer added to the suspension in step (5) is polydiallyldiethylammonium chloride. The mol ratio of the synthetic sol of the MFI molecular sieve seed crystal in the step (4) is as follows: SiO 22: TPAOH: H2O = 1: 0.5: 200。
The film (M5) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 1.
Example 6
The procedure was as in example 1, except that 1% by mass of the cationic polymer polydiallyldimethylammonium bromide, based on the total mass of the suspension, was added in step (5). The mol ratio of the synthetic sol of the MFI molecular sieve membrane in the step (6) is as follows: SiO 22: TPAOH: H2O = 1: 0.05: 50。
The film (M6) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 1.
Example 7
The procedure was as in example 1, except that in step (6), the silicon source used to prepare the MFI molecular sieve membrane was water glass. And (6) carrying out hydrothermal crystallization for 4 hours at the temperature of 160 ℃. The calcination in the steps (3) and (6) is carried out for 96 h at 200 ℃ in an ozone atmosphere of 10 mg/L (the temperature rise and the temperature reduction rates are both 0.2 ℃/min).
The film (M7) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 1.
Example 8
The procedure was as in example 1, except that the conditions for synthesizing the MFI molecular sieve membrane in the step (6) were 160 ℃ for 4 hours. The calcination in the steps (3) and (6) is carried out for 72 h at 150 ℃ in 150 mg/L ozone atmosphere (the temperature rising and reducing rates are both 10 ℃/min).
The film (M8) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 1.
Comparative example 1
The procedure used was as in example 1, except that the synthesized SSZ-13 zeolite membrane was not treated with a secondary growth MFI zeolite membrane.
The film (M9) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 2.
Comparative example 2
The operation steps are as in example 1, except that the conditions for synthesizing the MFI molecular sieve membrane in the step (6) are that the reaction temperature is 120 ℃, the synthesis time is 2 hours, and the growth compactness of the MFI membrane layer is poor.
The film (M10) prepared was used for equimolar CO, dried at 50 ℃ and having a relative humidity of 100%2/CH4The mixed system was subjected to gas separation performance test, and the test results are shown in table 2.
TABLE 10.2 MPa for equimolar CO of SSZ-13/MFI composite molecular sieve membranes2/CH4Separation performance of mixed gas, test temperatureIs 50oC
TABLE 20.2 MPa, equimolar CO for SSZ-13/MFI composite molecular sieve membranes2/CH4Separation performance of mixed gas, test temperature is 50 DEGoC
Claims (9)
1. A preparation method of a composite SSZ-13/MFI molecular sieve membrane is characterized in that a prepared composite membrane material consists of two molecular sieve crystal layers with different structures, namely SSZ-13 and MFI, and the method comprises the following steps:
(1) preparation of SSZ-13 molecular sieve crystal: the method comprises the following steps of mixing raw materials of an aluminum source, a silicon source, a structure directing agent SDA, an alkali source and deionized water according to the molar ratio of the components: na (Na) 2O/SiO2=0.05-0.2，SiO2/Al2O3=20-200，SDA/SiO2=0.05-0.5，H2O/SiO2Mixing the materials, stirring the mixture vigorously to form a uniform sol, and stirring the sol at 25-50 DEG CoC, aging for 6-48 h; the aged sol is put into a reaction kettle at 100-200-oC, performing hydrothermal synthesis for 24-120 h, and centrifuging, cleaning, drying and calcining to obtain SSZ-13 molecular sieve crystals;
(2) SSZ-13 seed layer preparation: taking the SSZ-13 molecular sieve crystals synthesized in the step (1) as membrane synthesis seed crystals, grinding and dispersing, weighing a proper amount of crystals, adding the crystals into ethanol, and performing ultrasonic dispersion to form a uniform SSZ-13 seed crystal/ethanol suspension with the mass fraction of 0.02-2 wt%; coating SSZ-13 seed crystal on the surface of a porous carrier in a vacuum pumping coating mode, wherein the vacuum degree is 0.01-0.1 MPa, the pumping coating time is 5-60 s, and after drying treatment, forming a uniform and compact SSZ-13 molecular sieve seed crystal layer on the surface of the carrier;
(3) synthesis of SSZ-13 molecular sieve membrane: raw materials of aluminum source, silicon source and structure directing agentSDA, an alkali source and deionized water according to the molar ratio of the components: the molar ratio of each component is as follows: na (Na)2O/SiO2=0.05-0.2，SiO2/Al2O3=20-200，SDA/SiO2=0.05-0.5，H2O/SiO2Mixing the materials at a ratio of 25-50 =20-60oAging for 24-120 h under C, putting the seeded porous carrier in the step (2) into a stainless steel reaction kettle, and pouring sol solution into the reaction kettle at 100- oCPerforming hydrothermal crystallization for 24-120 h to form an SSZ-13 molecular sieve membrane layer on the porous carrier, and cleaning, drying and calcining the obtained SSZ-13 molecular sieve membrane at high temperature to remove the structure directing agent to obtain the SSZ-13 molecular sieve membrane;
(4) preparing MFI molecular sieve crystals: the raw material silicon source, the structure directing agent SDA and the deionized water are mixed according to the molar ratio of the components: SDA/SiO2=0.05-0.5，H2O/SiO2Mixing the materials according to the ratio of =50-200, and aging the formed sol for 4-24 h at normal temperature; pouring the sol into a reaction kettle at the temperature of 120-oC, performing hydrothermal synthesis for 12-24 h, and centrifuging, cleaning, drying and calcining to obtain an MFI molecular sieve crystal;
(5) loading MFI crystal seeds on the SSZ-13 molecular sieve membrane: grinding the MFI molecular sieve crystal obtained in the step (4), weighing a proper amount of the MFI molecular sieve crystal, adding the MFI molecular sieve crystal into ethanol, dispersing the mixture through ultrasonic oscillation to obtain a suspension of the MFI molecular sieve, and adding cationic polymer polydienyl dialkyl ammonium salt with the total mass of 0.1-1% of the suspension into the suspension; vertically immersing the SSZ-13 molecular sieve membrane obtained in the step (3) in an MFI molecular sieve seed crystal suspension for 10-60 s, then extracting at a constant speed of 0.5-5 cm/min, and drying to form an MFI type molecular sieve crystal layer on the surface of the SSZ-13 molecular sieve membrane;
(6) preparation of SSZ-13/MFI composite molecular sieve membrane: the silicon source, the structure directing agent SDA and the deionized water are mixed according to the molar ratio of the components: SDA/SiO 2=0.05-0.5，H2O/SiO2Mixing the materials according to the ratio of =50-120, and aging the formed clear sol for 4-24 h at normal temperature; putting the SSZ-13 molecular sieve membrane loaded with the MFI seed crystal obtained in the step (5) into a reaction kettle, pouring the sol, crystallizing at the temperature of 100-160 ℃ for 4-12 h, taking out a membrane tube, cleaning, drying, and calcining in an ozone atmosphereAnd (4) sintering to obtain the SSZ-13/MFI composite molecular sieve membrane.
2. The method for preparing a composite SSZ-13/MFI molecular sieve membrane according to claim 1, wherein in steps (1) and (3), the structure directing agent SDA is adoptedN,N,N-trimethyladamantyl ammonium hydroxide,N,N,N-trimethyladamantyl ammonium bromide,N,N,N-trimethyladamantyl ammonium iodide,N,N,N-trimethylbenzylammonium hydroxide,N,N,N-trimethylbenzylammonium bromide,N,N,N-one or more combinations of trimethylbenzylammonium iodide or tetraethylammonium hydroxide.
3. The method as claimed in claim 1, wherein the size of the SSZ-13/MFI molecular sieve seed crystals prepared in step (1) is 200-600 nm.
4. The method of claim 1, wherein in step (2), the porous carrier is tubular or hollow fibrous, and the material is alumina, mullite, cordierite, zirconia or silica.
5. The method for preparing the composite SSZ-13/MFI molecular sieve membrane according to claim 1, wherein in steps (1), (3), (4) and (6), the silicon source used is silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder.
6. The method as claimed in claim 1, wherein the removal of the structure directing agent SDA of the molecular sieve membrane synthesized in steps (3) and (6) is performed in an ozone atmosphere, the concentration of ozone is 10-150 mg/L, and the temperature is 150 ℃ and 250 ℃; the calcination time is 24-96 h; the heating rate is 0.2-10 ℃ per minute.
7. The method for preparing a composite SSZ-13/MFI molecular sieve membrane according to claim 1, wherein the structure-directing agent for preparing the SSZ-13/MFI composite molecular sieve membrane in step (6) is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium iodide or tetraethylammonium bromide.
8. The method for preparing the composite SSZ-13/MFI molecular sieve membrane according to claim 1, wherein in the step (4), the prepared MFI type molecular sieve seed crystals are uniform short columnar crystals with a diameter range of 50-1000 nm.
9. The method of claim 1, wherein the cationic polymer polydienyl dialkyl ammonium salt in step (5) is selected from polydiallyl dimethyl ammonium bromide, polydiallyl butyl dimethyl ammonium bromide, polydiallyl diethyl ammonium chloride, or polydiallyl dimethyl ammonium chloride.
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