CN108786490B - Mordenite membrane and preparation method thereof - Google Patents

Abstract

The invention discloses a mordenite membrane and a preparation method thereof, wherein a carrier of the mordenite membrane is alumina with uniformly distributed macropores and three-dimensionally communicated macropores, the pore diameter of the macropores of the alumina is 100-1000nm, and the porosity is 60-90%. The mordenite membrane is composed of mordenite with a two-dimensional sheet shape, the dimension of the mordenite in the long dimension direction is 20-700nm, the dimension of the mordenite in the short dimension direction is 10-60nm, and the mordenite vertically grows on the inner surface of the alumina macropore in the long dimension direction; the thickness of the mordenite membrane is 20-1000nm, preferably 20-700 nm. The mordenite membrane of the present invention can be used in H₂、N₂、O₂And the separation and purification fields of gas separation, alcohol water and dehydration of low-carbon hydrocarbons, and the like.

Description

Mordenite membrane and preparation method thereof

Technical Field

The invention belongs to the technical field of chemical catalytic materials, and relates to a mordenite membrane with a through structure and a preparation method thereof.

Background

The molecular sieve membrane has excellent thermal stability, chemical stability and mechanical strength, and the separation performance is greatly superior to that of an organic membrane, so that the molecular sieve membrane is widely applied to the separation field. The mordenite membrane belongs to one of inorganic membranes, and is provided with 0.67nm by 0.70 nm large pore channels and 0.26 nm by 0.56 nm small pore channels in the directions parallel to a c axis and an a axis respectively.

The catalytic science, 2002, 23(2), 145-149 synthesizes a mordenite membrane on an alumina carrier by a hydrothermal synthesis method, the aperture of an alpha-alumina macroporous ceramic tube is 1 mu m, the pipeline of the ceramic tube has a one-dimensional structure and does not have three-dimensional connectivity, the particle size of the mordenite in the obtained zeolite membrane is larger and reaches 4-5 mu m, and the shape of the mordenite is a long block.

CN 201110077262.4 provides a method for preparing mordenite membrane, which comprises using mordenite as seed crystal, directly introducing ultra-thin uniform seed crystal layer on the surface of porous carrier tube, and hydrothermally crystallizing under fluoride ion condition to obtain mordenite membrane. The porous carrier tube is made of alpha-alumina tube, mullite tube or stainless steel tube, the average pore diameter of the tube is 1-5 μm, and the carrier tube is of one-dimensional structure and has no three-dimensional connectivity. The mordenite adopts seed crystals with two sizes, and the particle size of the mordenite is still larger than 1 μm in the finally formed film, and the mordenite is in a long block shape.

CN01132198.9 adopts ceramic, glass and stainless steel as carriers to prepare the mordenite membrane, the thickness of the obtained zeolite membrane is 30-40 μm, the grain size of the mordenite is 20-30 μm, and the zeolite is in a long block shape.

In the above several methods for preparing mordenite membranes, there are problems that the pore diameter of the carrier is too large, the macropores do not have three-dimensional connectivity, and the crystal grain shape of mordenite is long block, the crystal grain is too large or the membrane layer is thick, which is not favorable for the performance of the mordenite membrane in some fields.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a mordenite membrane and a preparation method thereof. The mordenite membrane has a three-dimensional macroporous through structure, the membrane layer is continuous, the thickness of the membrane layer is not more than 1 mu m, and the zeolite forming the membrane layer is small-grain two-dimensional sheet mordenite, so that the mass transfer of materials is facilitated. The mordenite membrane of the present invention can be used in H₂、N₂、O₂And the separation and purification fields of gas separation, alcohol water and dehydration of low-carbon hydrocarbons, and the like.

The mordenite membrane of the invention has the carrier of alumina, the alumina macropores are uniformly distributed and are three-dimensionally communicated, the aperture of the macropores of the alumina is 100-1000nm, and the porosity is 60-90%; the mordenite membrane is composed of mordenite with a two-dimensional sheet shape, the dimension of the mordenite in the long dimension direction is 20-700nm, preferably 100-500 nm, the dimension of the mordenite in the short dimension direction is 10-60nm, and the mordenite vertically grows on the inner surface of the alumina macropore in the long dimension direction; the thickness of the mordenite membrane is 20-1000nm, preferably 20-700nm, and more preferably 100-500 nm.

The preparation method of the mordenite membrane comprises the following steps:

preparation of three-dimensional through macroporous alumina

(1) Uniformly mixing an inorganic aluminum source, polyethylene glycol, low carbon alcohol and/or water, and then adding pyridine for uniform mixing to form gel; wherein the viscosity-average molecular weight of the polyethylene glycol is 2000-;

(2) slowly pressurizing the gel product obtained in the step (1) to 2-15MPa, aging for 1-72 hours at the temperature of 10-80 ℃, preferably slowly pressurizing to 2-8MPa, aging at the temperature of 25-60 ℃, and aging for 5-24 hours;

(3) after aging in the step (2), slowly releasing pressure to normal pressure, and then soaking the aged mixture for a certain time by using low carbon alcohol or a mixed solution of the low carbon alcohol and water;

(4) and (4) removing the liquid phase from the mixture obtained in the step (3), and drying and roasting to obtain the macroporous alumina precursor.

Wherein, based on the total weight of the materials added in the step (1), the adding amount of water and/or low carbon alcohol is 10-60%, the adding amount of aluminum source is 15-45%, preferably 20-40%, and the adding amount of polyethylene glycol is 1-15%, preferably 3-7%.

In the above preparation steps, the pyridine and Al are³⁺Is 3.0 to 9.0, preferably 3.5 to 7.0.

The inorganic aluminum source is a water-soluble inorganic aluminum salt, can be one or more of aluminum chloride, aluminum nitrate and aluminum sulfate, and is more preferably aluminum chloride.

The lower alcohol is C5 or less alcohol, preferably one or more of methanol, ethanol, n-propanol and isopropanol, and more preferably ethanol and/or propanol.

The water and/or the lower alcohol may be mixed in any proportion.

The step (2) of pressurizing is to place the gel obtained in the step (1) in a closed pressure-resistant container, and then slowly introduce gas which does not physically or chemically react with the materials into the container, wherein the gas includes but is not limited to: one or more of air, inert gas, carbon dioxide, oxygen, and the like. Air is preferred for cost and safety reasons. During the pressing, the pressing rates were: not more than 0.5MPa/min, preferably 0.01-0.05 MPa/min. The pressure relief process in the step (4) should also be slow, and the pressure relief rate is not more than 1.0MPa/min, preferably not more than 0.5 MPa/min.

The lower alcohol in the step (3) is C5 or less, preferably one or more of methanol, ethanol, n-propanol and isopropanol, and preferably ethanol and/or propanol. When the mixed solution of the lower alcohol and the water is adopted in the step (3), the weight concentration of the lower alcohol is more than 60%. The lower alcohol used in the step (1) and the step (3) can be the same or different. The soaking time in the step (3) is 1 to 72 hours, preferably 24 to 48 hours.

The drying temperature in the step (4) is room temperature to 150 ℃, preferably 30 to 60 ℃, and the drying is carried out until no obvious liquid substance exists. The roasting conditions are as follows: 400-1200 ℃ for 1-24 hours, preferably 650-950 ℃ for 5-10 hours.

The macroporous alumina prepared by the method has the advantages that the diameter of macropores is 30-600nm, the macropores are uniformly distributed and are three-dimensionally communicated, and the porosity is 60% -90%.

Preparation of mordenite precursor liquid

Uniformly mixing a silicon source, an alkali source, N-methylpiperidine and water, carrying out closed hydrothermal treatment, cooling the material to room temperature, then adding an aluminum source into the material after the hydrothermal treatment, uniformly mixing, and aging to obtain the molecular sieve mother liquor.

The alkali source is alkali metal hydroxide, preferably sodium hydroxide; the silicon source is one or a composition of silica sol, silica gel, white carbon black, water glass, ethyl silicate-28, ethyl silicate-32 or ethyl silicate-40, diatomite and silicon alkoxide, and preferably one or more of silica sol, white carbon black, ethyl silicate-28, ethyl silicate-32 or ethyl silicate-40; the aluminum source is selected from one or a combination of sodium metaaluminate, aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum oxide, aluminum hydroxide and organic aluminum alkoxide, and preferably one or more of sodium metaaluminate, aluminum isopropoxide and aluminum sec-butoxide; the mixing mode is any one of mechanical stirring, magnetic stirring or oscillation.

The alkali source, the aluminum source, the water, the silicon source and the N-methylpiperidine are calculated by the following substances, and the proportional relationship is satisfied: SiO 2₂/Al₂O₃The mol ratio of N-methylpiperidine to SiO is 20-80₂Molar ratio of 0.05-0.25, H₂O/SiO₂The molar ratio is 20-100, OH^-/SiO₂The molar ratio is 0.7-1.0.

The closed hydrothermal treatment conditions are as follows: sealing and hydrothermally treating at 90-120 deg.C for 1-24 hr. The aging conditions are as follows: aging at 30-80 deg.C for 0.5-10 hr, preferably 1-6 hr, more preferably 2-5 hr under stirring, more preferably ultrasonic dispersing and stirring; wherein the ultrasonic conditions are: the energy density of ultrasonic dispersion is 0.2-4kW/L, and the time of ultrasonic and stirring action is 2-5 hours; the stirring mode comprises mechanical stirring and/or magnetic stirring.

Preparation of mordenite membrane

Soaking the three-dimensional through macroporous alumina in a silane coupling agent solution for wetting, taking out and drying, placing in a mordenite precursor solution for sealing, heating for crystallization, carrying out solid-liquid separation after crystallization reaction is finished, and roasting the obtained solid phase to obtain the mordenite membrane taking the three-dimensional through macroporous alumina as a carrier.

The silane coupling agent is at least one of KH550, KH560, KH570, KH580, KH602, KH792 and KH 902. The drying temperature is 40-180 ℃, and the drying time is 1-12 hours. The crystallization conditions are as follows: the crystallization temperature is 140-. The roasting conditions are as follows: roasting at 500-600 ℃ for 2-10 hours.

In the process of preparing the alumina, the adopted low molecular weight polyethylene glycol can be stably dispersed in the alumina gel under a normal pressure system, the solid-liquid separation of the gel cannot be induced, and only a small amount of macropores can be generated by the decomposition of the polyethylene glycol through high-temperature roasting. According to the invention, the gel system is placed under a high-pressure condition, so that the original metastable state gel is subjected to degeneration under high pressure, the polyethylene glycol is changed into a precipitate phase from being stably dispersed in the gel, the whole system is triggered to carry out solid-liquid separation, and finally macropores are generated in the material. Because the dispersibility of the low molecular weight polyethylene glycol is far higher than that of the high molecular weight polyethylene glycol, the low molecular weight polyethylene glycol used in the invention can reach higher dispersibility in gel before high-pressure induction of solid-liquid separation, more polyethylene glycol small aggregates are generated, and the large number of small aggregates can finally generate more three-dimensionally communicated macroporous pore passages.

In the preparation of the mordenite precursor solution, the mordenite precursor solution is fully converted into the soluble ionic high-activity silicate by moderate silicon source hydrothermal treatment under higher alkalinity. Meanwhile, when the silicon source is hydrothermally treated, the aluminum source is isolated at a milder temperature, so that the crystallization of the silicon source can be avoided. Then in a hydrothermal synthesis mordenite system, N-methylpiperidine modulates the growth mode of a zeolite precursor, and stirring and ultrasonic dispersion are jointly used, so that the generation of small-grain flaky mordenite is caused. The N-methylpiperidine used in the invention has less dosage, belongs to a large amount of organic intermediates, can use industrial products and has lower cost.

The method comprises the steps of firstly obtaining three-dimensional through macroporous alumina by a phase separation technical means, then preparing a mordenite precursor by a special template agent and a preparation measure, and then carrying out surface modification on the three-dimensional through macroporous alumina to ensure that a mordenite precursor liquid can be uniformly attached to the inner surface of a large pore of alumina to grow in a hydrothermal crystallization stage, and controlling the shape, the size and the thickness of a mordenite crystal by adjusting reaction conditions, thereby obtaining the mordenite membrane which takes the three-dimensional through macroporous alumina as a carrier and has a flaky small crystal grain shape and a membrane layer thickness of not more than 1 mu m.

The mordenite membrane can be used in the purification fields of gas phase separation, organic phase and water phase separation and the like, such as alcohol-water separation, acetic acid dehydration, low-carbon hydrocarbon dehydration separation and the like.

Drawings

FIG. 1 is a scanning electron microscope image of a mordenite membrane having a through macroporous structure of example 1 of the present invention.

Detailed Description

The process of the present invention is illustrated in detail by the following examples. The crystal form of the mordenite is characterized by adopting X-ray diffraction, and the silicon-aluminum ratio is detected by adopting an SEM-EDS method. The pore volume and the specific surface are tested by adopting a low-temperature nitrogen adsorption method, and the appearance and the size are observed and measured by adopting a scanning electron microscope.

Example 1

Preparing macroporous alumina: water, absolute ethyl alcohol, aluminum chloride and polyethylene glycol are uniformly mixed, pyridine is added, and the content of each component of the mixture is, by weight, 30% of water, 30% of ethanol, 25% of aluminum chloride, 3.0% of polyethylene glycol (viscosity average molecular weight 6000) and 20% of pyridine. After mixing uniformly, the obtained gel is placed in a closed container, compressed air is slowly introduced until the balance of 3MPa is reached, aging is carried out for 24 hours at 40 ℃, and the pressure is relieved to the normal pressure. And soaking the aged mixture in ethanol for 48 hours, removing the liquid phase after soaking, and drying at 40 ℃ until the product is not obviously reduced. Then roasting for 5 hours at 750 ℃, and then cooling to room temperature to obtain the macroporous alumina, wherein the average diameter of macropores of the macroporous alumina is 500nm, the macropores are uniformly distributed, and the macropores have three-dimensional connectivity and the porosity is 75% as observed by a scanning electron microscope.

Preparation of molecular sieve precursor liquid: at room temperature, silica sol, sodium hydroxide, water and N-methylpiperidine are stirred under magnetic forceMixing according to a certain proportion, then carrying out sealed hydrothermal treatment at 100 ℃ for 24 hours, cooling to room temperature, and then adding the metaaluminic acid into the solution and stirring uniformly. The final material proportion meets the following requirements: al (Al)₂O₃/SiO₂=20, N-methylpiperidine/SiO₂=0.25，OH^-/SiO₂=0.70，H₂O/SiO₂= 65. The mixture was then subjected to a combination of sonication (0.5 KW/L) and magnetic stirring at 40 ℃ for 2 hours.

Preparation of mordenite membrane: 10g of macroporous alumina is immersed in 100ml of 5% KH560 solution, taken out after wetting, and dried for 3 hours at 170 ℃. Then mixing the macroporous alumina and the mordenite precursor mother liquor according to the volume ratio of 1: 5. The crystallization temperature is 170 ℃, and the crystallization reaction is carried out for 12 hours. After the reaction, the product was washed and then calcined at 550 ℃ for 5 hours. The final composite is proved to contain mordenite by XRD detection, and mordenite Al is detected by SEM-EDS₂O₃/SiO₂18 (excluding aluminum in alumina), and the mordenite is in a flake form and grows in a long dimension direction perpendicular to the inner surface of alumina macropore, the long dimension size of zeolite crystal grains is about 100-400nm, the thickness is about 20-40nm, and the zeolite crystal grains belong to a small crystal grain range. The thickness of the zeolite membrane is about 100-400nm of the long dimension of the mordenite.

Example 2

Preparing macroporous alumina: the same as in example 1.

Preparation of molecular sieve precursor liquid: mixing silica sol, sodium hydroxide, water and N-methylpiperidine according to a certain proportion at room temperature under magnetic stirring, then sealing and carrying out hydrothermal treatment at 120 ℃ for 12 hours, cooling to room temperature, adding the standby sodium metaaluminate powder into the pretreated silicon source solution, and uniformly stirring. The final material proportion meets the following requirements: al (Al)₂O₃/SiO₂=60, N-methylpiperidine/SiO₂=0.25，OH^-/SiO₂=0.72，H₂O/SiO₂= 80. The mixture was then sonicated (1.0 KW/L) and stirred at 50 ℃ for 2 hours.

Preparation of mordenite membrane: the procedure is as in example 1, except that the crystallization conditions are: crystal at 185 deg.CTake 10 hours. The final composite is proved to contain mordenite by XRD detection, and mordenite Al is detected by SEM-EDS₂O₃/SiO₂46 (excluding aluminum in alumina), and the mordenite is in a plate shape and grows vertically to the inner surface of alumina macropore in a long dimension direction through observation of a scanning electron microscope, wherein the long dimension of zeolite crystal grains is about 300-400nm, and the thickness is about 40-60nm, which belongs to a small crystal grain range. The thickness of the zeolite membrane is about 300-400nm of the long dimension of the mordenite.

Example 3

Preparing macroporous alumina: uniformly mixing water, absolute ethyl alcohol, aluminum chloride and polyethylene glycol, and adding pyridine to form gel, wherein the mixture comprises the following components in parts by weight: 30% of water, 40% of ethanol, 20% of aluminum chloride, 4.5% of polyethylene glycol (molecular weight 8000) and 17% of pyridine. After mixing evenly, the obtained gel is placed in a closed container, compressed air is slowly introduced at the speed of 0.02 MPa/min until the balance of 6MPa is reached, the aging is carried out for 10 hours at the temperature of 40 ℃, and then the pressure is slowly released to the normal pressure at the speed of 0.3 MPa/min. And soaking the aged mixture in ethanol for 48 hours, removing the liquid phase after soaking, and drying at 40 ℃ until the product is not obviously reduced. Then roasting for 3 hours at 850 ℃, and then cooling to room temperature to obtain the macroporous alumina, wherein the average macropore diameter of the macroporous alumina is 800nm, the macropore distribution is uniform, and the macropores have three-dimensional connectivity and the porosity is 67% as can be observed from the shape of the macropores in the figure.

Preparation of molecular sieve precursor: the same as in example 2.

Preparing a mordenite and macroporous alumina composite: the same as in example 2. The final composite is proved to contain mordenite by XRD detection, and mordenite Al is detected by SEM-EDS₂O₃/SiO₂46 (not containing aluminum in alumina), and the mordenite is in a flake form and grows in a long dimension direction perpendicular to the inner surface of the alumina macropore by observation of a scanning electron microscope, wherein the long dimension of zeolite grains is about 500-700nm, and the thickness is about 50-60nm, which belongs to the small grain range. The thickness of the zeolite membrane is about 500-700nm of the long dimension of the mordenite.

Claims (9)

1. A mordenite membrane characterised in that: the carrier of the mordenite membrane is alumina, the macropores of the alumina are uniformly distributed and are communicated in a three-dimensional way, the aperture of the macropores of the alumina is 100-1000nm, and the porosity is 60-90%; the mordenite membrane is composed of mordenite with a two-dimensional sheet shape, the dimension of the mordenite in the long dimension direction is 20-700nm, the dimension of the mordenite in the short dimension direction is 10-60nm, and the mordenite grows in the long dimension direction vertical to the inner surface of the alumina macropore; the thickness of the mordenite membrane is 20-1000 nm.

2. A process for the preparation of a mordenite membrane as claimed in claim 1, which comprises:

preparation of macroporous alumina:

(1) uniformly mixing an inorganic aluminum source, polyethylene glycol, low carbon alcohol and/or water, and then adding pyridine for uniform mixing to form gel; wherein the viscosity-average molecular weight of the polyethylene glycol is 2000-; (2) slowly pressurizing the gel product obtained in the step (1) to 2-15MPa, and aging for 1-72 hours at the temperature of 10-80 ℃;

(3) after aging in the step (2), slowly releasing pressure to normal pressure, and then soaking the aged mixture for a certain time by using low carbon alcohol or a mixed solution of the low carbon alcohol and water; (4) removing a liquid phase from the mixture obtained in the step (3), and drying and roasting to obtain macroporous alumina;

(II) preparation of mordenite precursor liquid:

uniformly mixing a silicon source, an alkali source, N-methylpiperidine and water, carrying out closed hydrothermal treatment, cooling the material to room temperature, adding an aluminum source into the material after the hydrothermal treatment, uniformly mixing, and aging to obtain a mordenite precursor liquid; the closed hydrothermal treatment conditions are as follows: carrying out closed hydrothermal treatment at 90-120 ℃ for 1-24 hours; the aging conditions are as follows: the aging temperature is 30-80 ℃, and the aging time is 0.5-10 hours;

(III) preparing a mordenite membrane:

soaking the three-dimensional through macroporous alumina in a silane coupling agent solution for wetting, taking out and drying, placing in a mordenite precursor solution for closed temperature rise crystallization, after the crystallization reaction is finished, carrying out solid-liquid separation, and roasting the obtained solid phase to obtain the mordenite membrane taking the three-dimensional through macroporous alumina as a carrier.

3. The method of claim 2, wherein: in the preparation of the macroporous alumina, the total weight of the materials added in the step (1) is taken as a reference, the adding amount of water and/or low-carbon alcohol is 10-60%, the adding amount of an inorganic aluminum source is 15-45%, and the adding amount of polyethylene glycol is 1-15%; the molar ratio of the pyridine to the inorganic aluminum source is 3.0-9.0, wherein the inorganic aluminum source is Al³⁺And (6) counting.

4. The method of claim 2, wherein: in the preparation of the macroporous alumina, the inorganic aluminum source is water-soluble inorganic aluminum salt; the lower alcohol is C5 or less.

5. The method of claim 2, wherein: in the preparation of the macroporous alumina, the step (2) of pressurizing is to place the gel obtained in the step (1) in a closed pressure-resistant container, and then slowly introduce gas which does not generate physical or chemical reaction with materials into the container; during the pressing, the pressing rates were: not more than 0.5 MPa/min; the pressure relief rate of the pressure relief process in the step (3) is not more than 1.0 MPa/min.

6. The method of claim 2, wherein: in the preparation of the macroporous alumina, the lower alcohol in the step (3) is C5 or less; the soaking time in the step (3) is 1-72 hours.

7. The method of claim 2, wherein: in the preparation of the macroporous alumina, the diameter of macropores of the macroporous alumina is 30-600nm, the macropores are uniformly distributed and are three-dimensionally communicated, and the porosity is 60-90%.

8. The method of claim 2, wherein: in the preparation of the mordenite precursor liquid, the alkali source is alkali metal hydroxide; the silicon source is one or a composition of silica sol, silica gel, white carbon black, water glass, ethyl silicate-28, ethyl silicate-32, ethyl silicate-40, diatomite or silicon alkoxide; the aluminum source is selected from one or a combination of sodium metaaluminate, aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum oxide, aluminum hydroxide or organic aluminum alkoxide; the mixing mode is any one of mechanical stirring, magnetic stirring or oscillation.

9. The method of claim 2, wherein: in the preparation of the mordenite precursor liquid, the alkali source, the aluminum source, the water, the silicon source and the N-methylpiperidine are calculated by the following substances in proportion: SiO 2₂/Al₂O₃The mol ratio of N-methylpiperidine to SiO is 20-80₂Molar ratio of 0.05-0.25, H₂O/SiO₂The molar ratio is 20-100, OH^-/SiO₂The molar ratio is 0.7-1.0.

Images