METHOD FOR PREPARING ZEOLITE CHA MEMBRANE

Abstract

In a method for preparing a zeolite CHA membrane, a gel conversion method is adopted to assist crystallization, seed solutions with different concentrations and sizes are successively coated on the surface of a porous support to obtain a seed layer, a synthetic gel is coated on the seed layer to obtain a gel layer, and then the porous support is subjected to a membrane crystallization reaction to obtain a zeolite CHA membrane. The method skips the conventional stage of converting the heterogeneous zeolite into the zeolite CHA seed, and directly takes a heterogeneous zeolite with the same secondary structural unit as that of zeolite CHA as a seed to directly prepare a zeolite CHA membrane on a support.

Claims

1. A method for preparing a zeolite CHA membrane, comprising the following steps: step (1), coating a seed layer: heterogeneous zeolite seeds are dispersed in deionized water to obtain heterogeneous zeolite seed solutions; a porous support is preheated at 70-200° C. for 2-5 hours, and then the heterogeneous zeolite seed solutions with two sizes or the same size are successively coated on the surface of the porous support and cured at 70-175° C. for 1-10 hours to obtain a uniform, dense and flawless heteroseed layer; the heterogeneous zeolite seeds are zeolite T, Y or SOD; step (2), preparing a synthetic gel: the synthetic gel is mainly composed of a silicon source, an aluminum source, a fluorine salt and an alkaline solution; the silicon source is silica sol; the aluminum source is sodium metaaluminate; the fluorine salt is a mixture of sodium fluoride and potassium fluoride, and the molar ratio of sodium fluoride to potassium fluoride is 1:1-5:1; the alkaline solution is a mixture of sodium hydroxide and potassium hydroxide; a stable SiO.sub.2-Na.sub.2O-K.sub.2O-Al.sub.2O.sub.3-MF(NaF+KF)-H.sub.2O synthetic gel system is formed by adding the aluminum source, the fluorine salt and the silicon source into the alkaline solution, stirring and aging; in the synthetic gel, the molar ratios of the components are as follows: SiO.sub.2/Al.sub.2O.sub.3=5-30; H.sub.2O/SiO.sub.2=26-70; (Na.sub.2O+K.sub.2O)/SiO.sub.2=0.24-2.6; Na/K=0.6-10; MF/SiO.sub.2=0-0.2; conditions for preparing the synthetic gel are as follows: stirring and aging at 20-40° C. for 12-48 hours; step (3), coating a gel layer: the synthetic gel obtained in step (2) is used as a coating solution and uniformly coated on the surface of the porous support after the seed layer is coated in step (1); step (4), forming a membrane by crystallization: the porous support coated with the synthetic gel is loaded into an auotoclave to crystallize and obtain a zeolite CHA membrane; the crystallization temperature is 100-180° C., and the crystallization time is 2-24 hours.

2. The method for preparing a zeolite CHA membrane according to claim 1, wherein in the step (1), when heteroseeds with different sizes are coated, a heteroseed with a large size is a large heteroseed, a heteroseed with a small size is a small heteroseed; in a large heterogeneous zeolite seed solution, the mass fraction of a large heterogeneous zeolite seed is 1%-3%, and the particle size of heterogeneous zeolite crystal is 0.6-3 μm; in a small heterogeneous zeolite seed solution, the mass fraction of a small heterogeneous zeolite seed is 0.2%-1%, and the particle size of heterogeneous zeolite crystal is 0.05-0.8 μm; when heteroseeds with the same size are coated, coating is repeated for 1-3 times.

3. The method for preparing a zeolite CHA membrane according to claim 1, wherein in the step (1), the method for obtaining the seed layer from the heterogeneous zeolite seed solutions on the surface of the porous support is an dip-coating method, a hot dip-coating method, a secondary temperature changing hot dip-coating method, a vacuum coating method, a spraying method, a wiping method or a spin coating method.

4. The method for preparing a zeolite CHA membrane according to claim 1, wherein in the step (3), the method for coating the gel layer is an dip-coating method, a hot dip-coating method, a vacuum method, a spraying method, a wiping method or a spin coating method.

5. The method for preparing a zeolite CHA membrane according to claim 3, wherein in the step (3), the method for coating the gel layer is an dip-coating method, a hot dip-coating method, a vacuum method, a spraying method, a wiping method or a spin coating method.

6. The method for preparing a zeolite CHA membrane according to claim 1, wherein the porous support is a tubular, flat-plate, hollow-fiber or multi-pore support; the material of the porous support is alumina, zirconia, mullite, stainless steel or metal mesh; and the pore size of the porous support is 0.02-40 μm.

7. The method for preparing a zeolite CHA membrane according to claim 3, wherein the porous support is a tubular, flat-plate, hollow-fiber or multi-pore support; the material of the porous support is alumina, zirconia, mullite, stainless steel or metal mesh; and the pore size of the porous support is 0.02-40 μm.

8. The method for preparing a zeolite CHA membrane according to claim 4, wherein the porous support is a tubular, flat-plate, hollow-fiber or multi-pore support; the material of the porous support is alumina, zirconia, mullite, stainless steel or metal mesh; and the pore size of the porous support is 0.02-40 μm.

Description

DESCRIPTION OF DRAWINGS

[0028] FIG. 1 is a scanning electron microscope (SEM) image of a surface of a zeolite CHA membrane synthesized in embodiment 1;

[0029] FIG. 2 is a scanning electron microscope (SEM) image of a cross section of a zeolite CHA membrane synthesized in embodiment 1;

[0030] FIG. 3 is an X-ray diffraction (XRD) pattern of a zeolite CHA membrane synthesized in embodiment 1;

[0031] FIG. 4 is an X-ray diffraction (XRD) pattern of a zeolite CHA membrane synthesized in embodiment 2; and

[0032] FIG. 5 is an X-ray diffraction (XRD) pattern of a zeolite CHA membrane synthesized in embodiment 3.

DETAILED DESCRIPTION

[0033] Specific embodiments of the present invention are further described below in combination with the drawings and the technical solution.

Embodiment 1

[0034] (1) α-Al.sub.2O.sub.3 support tube preprocessing: the support tube has an outer diameter of 12 mm, an inner diameter of 8 mm, an average pore size of 1-3 and a porosity of about 30%-40%; the outer surface of the support tube is sanded once with 800 mesh and 1500 mesh sandpaper; deionized water is used to remove residual sand particles on the support tube by ultrasonic oscillation, and this process is repeated for several times until the water used to wash the support tube is no longer turbid; then acid and alkali are successively used to remove the residue in the pores of the support by ultrasonic oscillation, and the support tube is washed with deionized water until neutral; finally, the support tube is placed in an oven to be dried and then placed in a muffle furnace to be calcined at 550° C. for 6 hours, and both ends of the support tube are sealed for use;

[0035] (2) The support tube obtained in step (1) is preheated at 120° C. for 5 hours, and then rapidly immersed in a zeolite T large seed (3 μm) suspension with a mass concentration of 1 wt. %; the support tube is dried overnight at room temperature, and cured at 120° C. for 1 hour to obtain a seed layer loaded support A.sub.1;

[0036] (3) Seeds on the surface of the support are wiped off with absorbent cotton; the seed layer loaded support A.sub.1 is preheated at 70° C. for 5 hours, and then immersed in a zeolite T small seed (0.8 μm) suspension with a mass concentration of 0.2 wt.%; the support is dried overnight, and cured at 120° C. for 5 hours to obtain a seed layer loaded support A.sub.2;

[0037] (4) A fluorine-free synthetic gel is prepared with a molar ratio of 0.75SiO.sub.2:0.05Al.sub.2O.sub.3:0.26Na.sub.2O:0.09K.sub.2O:25H.sub.2O, stirred and aged at room temperature for 12 hours;

[0038] (5) The seed layer loaded support A2 is immersed in the synthetic gel for about 20 seconds, loaded into a stainless steel crystallization kettle with a teflon liner and placed in a 180° C. oven for crystallization for 2 hours;

[0039] (6) The synthesized zeolite CHA membrane is washed to neutral with deionized water and dried in a 50° C. oven.

[0040] It can be seen from FIGS. 1-3 that the zeolite membrane obtained in the embodiment is a zeolite T & CHA membrane, which is suitable for ethanol dehydration. According to a pervaporation test of the zeolite T & CHA membrane prepared in embodiment 1, when the temperature is 75° C., the flux of 90 wt. % ethanol/water is 3.35 kg.Math.m.sup.−2.Math.h.sup.−1, and the separation factor is >10000.

Embodiment 2

[0041] (1) α-Al.sub.2O.sub.3 support tube preprocessing: the support tube has an outer diameter of 12 mm, an inner diameter of 8 mm, an average pore size of 1-3 μm, and a porosity of about 30%-40%; the outer surface of the support tube is sanded once with 800 mesh and 1500 mesh sandpaper; deionized water is used to remove residual sand particles on the support tube by ultrasonic oscillation, and this process is repeated for several times until the water used to wash the support tube is no longer turbid; then acid and alkali are successively used to remove the residue in the pores of the support by ultrasonic oscillation, and the support tube is washed with deionized water until neutral; finally, the support tube is placed in an oven to be dried and then placed in a muffle furnace to be calcined at 550° C. for 6 hours, and both ends of the support tube are sealed for use;

[0042] (2) The support tube obtained in step (1) is preheated at 175° C. for 3 hours, and then rapidly immersed in a zeolite T seed (0.8 μm) suspension with a mass concentration of 1 wt.%; the support tube is dried overnight at room temperature, and cured at 175° C. for 3 hours to obtain a seed layer loaded support B.sub.1;

[0043] (3) Seeds on the surface of the support are wiped off with absorbent cotton; the seed layer loaded support B.sub.1 is preheated at 175° C. for 3 hours, and then immersed in a zeolite T seed (0.8 μm) suspension with a mass concentration of 1 wt. % again; the support is dried overnight, and cured at 175° C. for 3 hours to obtain a seed layer loaded support B.sub.2;

[0044] (4) A synthetic gel is prepared with a molar ratio of 0.5SiO.sub.2:0.05Al.sub.2O.sub.3:0.42Na.sub.2O:0.2K.sub.2O:0.08MF(5NaF:1KF):25H.sub.2O, stirred and aged at room temperature for 24 hours;

[0045] (5) The seed layer loaded support B2 is immersed in the synthetic gel for about 30 seconds, loaded into a stainless steel crystallization kettle with a teflon liner and placed in a 150° C. oven for crystallization for 4 hours;

[0046] (6) The synthesized zeolite CHA membrane is washed to neutral with deionized water and dried in a 50° C. oven.

[0047] It can be seen from FIG. 4 that the zeolite membrane obtained in the embodiment is a zeolite CHA membrane, which is suitable for ethanol dehydration. According to a pervaporation test of the zeolite CHA membrane prepared in embodiment 2, when the temperature is 75° C., the flux of 90 wt. % ethanol/water is 4.68 kg.Math.m.sup.−2.Math.h.sup.−1, and the separation factor is >10000.

Embodiment 3

[0048] (1) α-Al.sub.2O.sub.3 support tube preprocessing: the support tube has an outer diameter of 12 mm, an inner diameter of 8 mm, an average pore size of 1-3 μm, and a porosity of about 30%-40%; the outer surface of the support tube is sanded once with 800 mesh and 1500 mesh sandpaper; deionized water is used to remove residual sand particles on the support tube by ultrasonic oscillation, and this process is repeated for several times until the water used to wash the support tube is no longer turbid; then acid and alkali are successively used to remove the residue in the pores of the support by ultrasonic oscillation, and the support tube is washed with deionized water until neutral; finally, the support tube is placed in an oven to be dried and then placed in a muffle furnace to be calcined at 550° C. for 6 hours, and both ends of the support tube are sealed for use;

[0049] (2) The support tube obtained in step (1) is preheated at 200° C. for 2 hours, and then rapidly immersed in a zeolite T large seed (0.6 μm) suspension with a mass concentration of 3 wt. %; the support tube is dried overnight at room temperature, and cured at 70° C. for 2 hours to obtain a seed layer loaded support C.sub.1;

[0050] (3) Seeds on the surface of the support are wiped off with absorbent cotton; the seed layer loaded support C.sub.1 is preheated at 100° C. for 2 hours, and then immersed in a zeolite T small seed (0.05 μm) suspension with a mass concentration of 1 wt. %; the support is dried overnight, and cured at 70° C. for 10 hours to obtain a seed layer loaded support C.sub.2;

[0051] (4) A synthetic gel is prepared with a molar ratio of 0.5SiO.sub.2:0.05Al.sub.2O.sub.3:0.26Na.sub.2O:0.09K.sub.2O:0.1MF(1NaF:1KF):35H.sub.2O, stirred and aged at room temperature for 48 hours;

[0052] (5) The seed layer loaded support C.sub.2 is immersed in the synthetic gel for about 60 seconds, loaded into a stainless steel crystallization kettle with a teflon liner and placed in a 100° C. oven for crystallization for 24 hours;

[0053] (6) The synthesized zeolite CHA membrane is washed to neutral with deionized water and dried in a 50° C. oven.

[0054] It can be seen from FIG. 5 that the zeolite membrane obtained in the embodiment is a zeolite CHA membrane, which is suitable for ethanol dehydration. According to a pervaporation test of the zeolite CHA membrane prepared in embodiment 3, when the temperature is 75° C., the flux of 90 wt. % ethanol/water is 4.12 kg.Math.m.sup.−2.Math.h.sup.−1, and the separation factor is 7703.