Flat coffin-shaped silicalite-1 seed and zeolite membrane

Abstract

A kind of flat coffin type silicalite-1 seed and its zeolite membrane, the seed is prepared according to the proportion of TEOS:TPAOH:H2O:C2H5OH molar ratio is 1:0.15~0.25:50~200:1~4, hydrothermal reaction is carried out at 130~160 ℃ under autogenous pressure for 4~8 h.The zeolite membrane is obtained by coating the above-mentioned seed on the carrier, hydrothermal synthesis and then calcining in a programmed temperature rising and falling mode.The seed morphology is uniform, and the surface of the prepared silicalite-1 zeolite membrane is more continuous and dense by using matching carrier and programmed calcining process, and it shows good ethanol / water separation performance.

Description

TECHNICAL FIELD

[0001] The present application relates to silicalite-1 crystal seed and zeolite membrane thereof, in particular to a kind of concentrated low concentration ethanol / water pervaporation membrane, belong to membrane separation field. BACKGROUND

[0002] The selective purification of low concentration ethanol on the permeation side of the membrane using pervaporation membrane technology can effectively reduce the cost. Developing a high-performance alcohol-permeable membrane is the core of pervaporation ethanol purification. Silicalite-1 membrane has high thermal stability and uniform microporous structure, and its crystal structure does not contain Al, which has strong hydrophobicity, making it have great advantages in the separation of low concentration organic aqueous solution. Currently, most silicalite-1 molecular sieve membranes are synthesized by secondary growth method, i.e., first pre-coating seed on the carrier, and then growing continuous zeolite membrane by seed-induced nucleation. However, the morphology of the seed will affect the properties of the carrier, thereby affecting the formation of dense membrane. Moreover, most silicalite-1 molecular sieve membranes add a template during the synthesis process, and the template needs to be removed by calcination before application. The thermal removal of organic template in molecular sieve is a complex process, and factors such as pore size, template molecule shape, size, and molecular sieve bulk properties will affect the removal mode of the template. If the calcination method is not appropriate, cracks and other defects may occur on the surface of the membrane, resulting in reduced separation performance.

[0003] In addition, the morphology control of the crystal is greatly affected by the reaction conditions, and slight changes in operation may cause great changes in the morphology of the seed. Therefore, the morphology of the seed, the carrier and the membrane formation conditions may directly affect the performance of the membrane. SUMMARY

[0004] To solve the above technical problems, the present application provides a flat coffin-shaped silicalite-1 crystal seed and a zeolite membrane prepared therefrom, which has good performance in pervaporation separation of ethanol / water solution.

[0005] To achieve the above technical purpose, the first aspect of the present application provides a preparation method of flat coffin-shaped silicalite-1 crystal seed, comprising the following steps: mixing TEOS, TPAOH, H2O and C2H5OH in a molar ratio of 1:0.15-0.25:50-200:1-4, and then hydrothermally reacting at 130-160℃ under autogenous pressure for 4-8h to obtain a white solid, and calcining to obtain flat coffin-shaped silicalite-1 crystal seed.

[0006] Further, the molar ratio of TEOS:TPAOH:H2O:C2H5OH is 1:0.15-0.25:100-150:3-4.

[0007] Further, the temperature of the hydrothermal reaction is 130-150℃, and the time is 6-8h.

[0008] Further, the mixing of TEOS, TPAOH, H2O and C2H5OH is carried out by dissolving tetrapropylammonium hydroxide and ethanol in water, and then adding tetraethyl orthosilicate dropwise, and stirring for 24h or more.

[0009] Further, the calcination temperature is 500-600℃.

[0010] Further, the product after the hydrothermal reaction is subjected to a post-treatment process of washing, centrifugation and drying, and then calcination.

[0011] The technical purpose of the second aspect of the present application is to provide a flat coffin-shaped silicalite-1 seed crystal prepared by the above method. The flat coffin-shaped silicalite-1 seed crystal prepared by the present application has a thickness of 0.2-1.5μm, preferably 0.3-1μm; the cross section presents a set of axially symmetric hexagons with elongated opposite sides, the remaining four sides are equal in length, and the ratio of the long side to the short side is a, 1.2≤a≤2.5, preferably 1.5≤a≤2. The particle size in the cross section direction is 0.8-3.5μm, preferably 1-3μm.

[0012] The technical purpose of the third aspect of the present application is to provide a preparation method of a silicalite-1 zeolite membrane, comprising the following steps:

[0013] The seed crystal prepared by the above method is added to ethanol to form a seed crystal liquid, and the preheated carrier is immersed in the seed crystal liquid for coating. The carrier coated with the seed crystal is placed in a reaction kettle with a synthesis mother liquor formed by mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and water, and a silicalite-1 zeolite membrane is synthesized. After drying, the temperature rising rate is controlled at 5-0.5℃ / min, preferably 2-0.5℃ / min, and the temperature is raised to 500-600℃ and maintained for 6-12h. Then the temperature lowering rate is controlled at 5-0.5℃ / min, preferably 2-0.5℃ / min, and the temperature is lowered to room temperature to obtain a silicalite-1 zeolite membrane.

[0014] Further, the concentration of the seed crystal in the seed crystal liquid is 1-3wt%.

[0015] Further, the carrier is an α-Al2O3 ceramic tube, the pore size is 0.8-3.5μm, preferably 1-3μm, and the preheating temperature of the carrier is 80-120℃.

[0016] Further, the carrier is vertically immersed and taken out of the seed crystal liquid during seed crystal coating, and the coating is repeated 1-3 times, preferably 1-2 times. The residence time of the carrier in the seed crystal liquid during each coating is 10-60s. After each coating, the next coating is carried out after waiting for solidification.

[0017] Further, the mole ratio of tetraethyl orthosilicate, tetrapropyl ammonium hydroxide and water in the synthesis mother liquor is 1:0.15-0.25:50-200; and the mixture is stirred for 24 hours or more after mixing.

[0018] Further, the reaction temperature for synthesizing the zeolite membrane in the reaction kettle is 150-180 DEG C, and the reaction time is 12-36 hours.

[0019] The technical purpose of the fourth aspect of the present application is to provide the silicalite-1 zeolite membrane prepared by the above method.

[0020] The technical purpose of the fifth aspect of the present application is to provide a method for separating ethanol / water solution by pervaporation, which uses the above silicalite-1 zeolite membrane as the separation membrane.

[0021] In the above method, the separation temperature is 20-80 DEG C, preferably 20-70 DEG C. The concentration of alcohol in the ethanol / water solution to be separated is 1-30 wt%, preferably 5-15 wt%.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The present application adopts TEOS, TPAOH, H2O and C2H5OH as four raw materials to obtain flat coffin-shaped silicalite-1 crystal seeds under specific reaction control conditions, the morphology of which is uniform, and the silicalite-1 zeolite membrane prepared by using the matched carrier and the programmed calcination process has a more continuous and dense surface, and exhibits good ethanol / water separation performance.

[0024] Other features and advantages of the present application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM images of the flat coffin-shaped silicalite-1 crystal seeds (a) and the silicalite-1 zeolite membrane (b) prepared in Example 1;

[0026] Figure 2 SEM images of the round pie-shaped silicalite-1 crystal seeds (a) and the silicalite-1 membrane (b) prepared in Comparative Example 1;

[0027] Figure 3 SEM images of the long-c-axis coffin-shaped silicalite-1 crystal seeds (a) and the silicalite-1 membrane (b) prepared in Comparative Example 2;

[0028] Figure 4 SEM image of the silicalite-1 zeolite membrane prepared in Comparative Example 3;

[0029] Figure 5 Weight loss graph of the crystalline calcined template of Example 1, Comparative Example 1, Comparative Example 2 for thermogravimetric test;

[0030] Figure 6 Rate of weight loss graph of the crystalline calcined template of Example 1, Comparative Example 1, Comparative Example 2 for thermogravimetric test. DETAILED DESCRIPTION

[0031] The following non-limiting examples can provide a more complete understanding of the application to those of ordinary skill in the art, but are not intended to limit the application in any way.

[0032] Example 1

[0033] (1) Preparation of flat coffin-shaped silicalite-1 seeds: TEOS, TPAOH, H2O and C2H5OH were weighed according to the molar ratio of 1:0.2:150:4, tetrapropylammonium hydroxide (TPAOH) and ethanol (C2H5OH) were dissolved in deionized water, then tetraethyl orthosilicate (TEOS) was slowly added to the above solution under stirring, and the mixture was stirred at room temperature for 24 h, then transferred into a stainless steel reactor, and hydrothermally synthesized at 130°C for 8 h. After the reaction, a white precipitate was obtained, which was washed, centrifuged and dried, and then calcined at 550°C for 6 h to obtain flat coffin-shaped silicalite-1 seeds. The SEM image thereof is shown in FIG. 1(a), which has a thickness of 0.3-0.8 μm, and the cross section presents a group of axisymmetric hexagons with elongated opposite sides, and the remaining four sides are equal in length. The ratio of long side to short side is a, and 1.5≤a≤2. The particle size in the cross-sectional direction is 1-2.5 μm in size. Figure 1 (2) Silicalite-1 seed coating: the seeds were mixed with ethanol to form a 1 wt% seed suspension, the ceramic tube was sealed at both ends, preheated at 100°C for 1 h, quickly immersed vertically into the seed suspension, taken out after 60 s, dried in an oven at 60°C, and then the ceramic tube was preheated at 100°C again, quickly immersed vertically into the seed suspension, taken out after 60 s to ensure that the surface was covered with seeds, and finally calcined in a muffle furnace at 550°C for 6 h.

[0034] (2) Silicalite-1 seed coating: the seeds were mixed with ethanol to form a 1 wt% seed suspension, the ceramic tube was sealed at both ends, preheated at 100°C for 1 h, quickly immersed vertically into the seed suspension, taken out after 60 s, dried in an oven at 60°C, and then the ceramic tube was preheated at 100°C again, quickly immersed vertically into the seed suspension, taken out after 60 s to ensure that the surface was covered with seeds, and finally calcined in a muffle furnace at 550°C for 6 h.

[0035] (3) Preparation of silicalite-1 membrane: tetraethyl orthosilicate, tetrapropylammonium hydroxide and deionized water were mixed to form a synthesis solution in a molar ratio of 1:0.2:100, the ceramic tube coated with seeds was vertically placed in the synthesis solution in a stainless steel reactor, and hydrothermal synthesis was carried out at 160°C for 24h, then the silicalite-1 membrane tube was taken out, washed and dried, and finally the silicalite-1 zeolite membrane was calcined by a programmed temperature rising and falling method, the temperature rising rate was controlled at 0.5°C / min, the temperature was raised to 550°C and kept for 12h, then the temperature falling rate was controlled at 0.5°C / min until room temperature was reached. The SEM image of the obtained silicalite-1 zeolite membrane is as follows Figure 1 (b) The membrane is relatively flat and smooth without obvious cracks.

[0036] The silicalite-1 zeolite membrane was used for pervaporation separation of 5wt% ethanol / water solution, and the flux of the membrane was 2.47kg·m -2 ·h -1 at 30°C, and the ethanol on the permeation side was concentrated to 35.7wt% at one time.

[0037] Example 2

[0038] Except that the molar ratio of TEOS, TPAOH, H2O and C2H5OH in the preparation process of the flat coffin-shaped silicalite-1 seed in (1) was 1:0.2:100:4, the other reaction conditions were the same as those in Example 1. The synthesized seed silicalite-1 seed had a similar morphology to that of Example 1, the particle size in the cross-sectional direction was 1-1.5μm, and the silicalite-1 zeolite membrane obtained by using the seed had a relatively flat and smooth surface without obvious cracks.

[0039] The silicalite-1 zeolite membrane was used for pervaporation separation of 5wt% ethanol / water solution, and the flux of the membrane was 2.67kg·m -2 ·h -1 at 30°C, and the ethanol on the permeation side was concentrated to 33.2wt% at one time.

[0040] Example 3

[0041] Except that the hydrothermal reaction temperature in (1) was 150°C, the other reaction conditions were the same as those in Example 1. The synthesized seed silicalite-1 seed had a similar morphology to that of Example 1, the particle size in the cross-sectional direction was 1-3μm, and the silicalite-1 zeolite membrane obtained by using the seed had a relatively flat and smooth surface without obvious cracks.

[0042] The silicalite-1 zeolite membrane was used for pervaporation separation of 5wt% ethanol / water solution, and the flux of the membrane was 2.86kg·m-2 ·h -1 , the ethanol on the permeation side was concentrated to 30.1wt%.

[0043] Comparative Example 1

[0044] Except that no ethanol was added in (1), other reaction conditions were the same as those in Example 1. The average particle size of the round cake-shaped seeds was 500 nm, as shown in (a), and the prepared silicalite-1 zeolite membrane was as shown in (b). The surface of the zeolite membrane had more protrusions than the zeolite membrane of Example 1. Figure 2 Figure 2

[0045] The zeolite membrane was used for pervaporation separation of a 5wt% ethanol / water solution, and the flux of the membrane at 30℃ was 2.03kg·m -2 ·h -1 , and the ethanol on the permeation side was only concentrated to 15.7wt%.

[0046] Comparative Example 2

[0047] Except that the hydrothermal reaction temperature in (1) was 170℃, other reaction conditions were the same as those in Example 1. The morphology of the synthesized seeds was long c-axis coffin-shaped, and the SEM image thereof was as shown in (a). The seed morphology had a certain similarity to that of Example 1, but there were more seeds with a>2.5, which affected the uniformity of the seeds as a whole. The prepared seed silicalite-1 zeolite membrane was as shown in (b). Figure 3 Figure 3

[0048] The zeolite membrane was used for pervaporation separation of a 5wt% ethanol / water solution, and the flux of the membrane at 30℃ was 3.09kg·m -2 ·h -1 , and the ethanol on the permeation side was concentrated to 25.8wt%.

[0049] Comparative Example 3

[0050] Except that the silicalite-1 zeolite membrane was not subjected to the programmed temperature rising and falling method in (3), the rapid temperature rising was directly to 550℃, and the membrane was taken out after being calcined for 12h, the SEM of the silicalite-1 zeolite membrane after calcination was as shown in (a). It can be seen that the surface of the membrane had obvious crack defects. Figure 4

[0051] The zeolite membrane was used for pervaporation separation of a 5wt% ethanol / water solution, and the flux of the membrane at 30℃ was 3.44kg·m -2 ·h -1 , and the ethanol on the permeation side was only concentrated to 11.2wt%, which was obviously lower than that of the membrane prepared by the slow temperature rising method adopted in the present application. ​​​​​

[0052] In addition, the thermal gravimetric changes of the silicalite-1 zeolite membranes of step (3) of Example 1, Comparative Example 1 and Comparative Example 2 were measured, Figure 5 The weight loss graph of the calcined template of the crystals of Example 1, Comparative Example 1 and Comparative Example 2 tested by the thermal gravimetric instrument; Figure 6 The weight loss rate change graph of the calcined template of the crystals of Example 1, Comparative Example 1 and Comparative Example 2 tested by the thermal gravimetric instrument, Figure 5 and Figure 6 It is seen that the calcination temperature of the round disk crystals of Comparative Example 1 is lower than that of the coffin-shaped crystals of Example 1 and Comparative Example 2, i.e. the defect caused by the calcination stress is small, but the round disk crystals do not match the carrier, so the pervaporation performance is not high, which shows that the crystal type plays an important role in the membrane growth; in the weight loss rate change, the weight loss rate of the long c-axis coffin-shaped crystals of Comparative Example 2 is much greater than that of the flat coffin-shaped crystals, which shows that even if the program is low-speed calcination, the stress change caused thereby is greater than that of the flat coffin-shaped crystals, and defects are more likely to be caused. It can be seen that even if the membranes prepared by the same calcination method are different, the performance of pervaporation is still different, the matching of the crystals and the carrier and the membranes with low weight loss rate have higher performance.

Claims

1. A method for the pervaporative separation of an ethanol / water solution, characterized in that, The silicalite-1 zeolite membrane is used as a separation membrane, and the silicalite-1 zeolite membrane is prepared by the following steps: The white solid is obtained by mixing TEOS, TPAOH, H2O and C2H5OH in a molar ratio of 1:0.15-0.25:50-200:1-4, hydrothermal reaction at 130-160 ℃ under autogenous pressure for 4-8 h, and calcination at 500-600 ℃ to obtain flat coffin-shaped silicalite-1 seeds; The prepared flat coffin-shaped silicalite-1 seeds are suspended in ethanol to form a seed liquid, and the preheated carrier, which is an α-Al2O3 ceramic tube with a pore size of 0.8-3.5 μm, is immersed in the seed liquid for coating; the carrier coated with seeds is placed in a reaction kettle with a synthesis mother liquor formed by mixing tetraethyl orthosilicate, tetrapropylammonium hydroxide and water; the silicalite-1 zeolite membrane is synthesized, dried, and then heated at a rate of 5-0.5 ℃ / min to 500-600 ℃ and kept for 6-12 h, and then cooled at a rate of 5-0.5 ℃ / min to room temperature to obtain the silicalite-1 zeolite membrane.

2. The method of claim 1, wherein, In the preparation of the flat coffin-shaped silicalite-1 seeds, the molar ratio of TEOS:TPAOH:H2O:C2H5OH is 1:0.15-0.25:100-150:3-4.

3. The method of claim 1, wherein, In the preparation of the flat coffin-shaped silicalite-1 seeds, the hydrothermal reaction is carried out at a temperature of 130-150 ℃ for 6-8 h.

4. The method of claim 1, wherein, In the preparation of the flat coffin-shaped silicalite-1 seeds, the TEOS, TPAOH, H2O and C2H5OH are mixed by first dissolving the tetrapropylammonium hydroxide and ethanol in water, and then adding the tetraethyl orthosilicate dropwise, and stirring for more than 24 h.

5. The method of claim 1, wherein, In the preparation of the flat coffin-shaped silicalite-1 seeds, the product after the hydrothermal reaction is subjected to a post-treatment process of washing, centrifugation and drying, and then calcination.

6. The method of claim 1, wherein, The prepared flat coffin-shaped silicalite-1 seeds have a thickness of 0.2-1.5 μm, and the cross section presents a group of axially symmetric hexagons with elongated opposite sides, the remaining four sides being equal in length, and the ratio of the long side to the short side being a, 1.2≤a≤2.

5.

7. The method of claim 6, wherein, The prepared flat coffin-shaped silicalite-1 seeds have a thickness of 0.3-1 μm, and 1.5≤a≤2.

8. The method of claim 6, wherein, The prepared flat coffin-shaped silicalite-1 seeds have a particle size of 0.8-3.5 μm in the cross section direction.

9. The method of claim 8, wherein, The prepared flat coffin-shaped silicalite-1 seeds have a particle size of 1-3 μm in the cross section direction.

10. The method of claim 1, wherein, The heating rate is 2-0.5 ℃ / min, and the cooling rate is 2-0.5 ℃ / min.

11. The method of claim 1, wherein, The concentration of the seeds in the seed liquid is 1-3 wt%.

12. The method of claim 1, wherein, The pore size of the carrier is 1-3 μm, and the preheating temperature of the carrier is 80-120 ℃.

13. The method of claim 1, wherein, The carrier is vertically immersed in and taken out of the seed liquid during seed coating, and the coating is repeated 1-3 times, and the residence time of the carrier in the seed liquid during each coating is 10-60 s.

14. The method of claim 1, wherein, The molar ratio of tetraethyl orthosilicate, tetrapropyl ammonium hydroxide and water in the synthesis mother liquor is 1:0.15-0.25:50-200.

15. The method of claim 1, wherein, The reaction temperature for synthesizing the zeolite membrane in the reaction kettle is 150-180 DEG C, and the reaction time is 12-36h.

16. The method of claim 1, wherein, The separation temperature for separating ethanol / water solution by pervaporation is 20-80 DEG C.

17. The method of claim 1, wherein, The concentration of alcohol in the ethanol / water solution to be separated is 1-30wt%.

18. The method of claim 17, wherein, The concentration of alcohol in the ethanol / water solution to be separated is 5-15wt%.

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