阅读说明：本技术 一种多孔级lsx沸石分子筛无模板制备方法 (Template-free preparation method of porous LSX zeolite molecular sieve ) 是由 仝林昌 向梅 吴泽颖 邓瑶瑶 于 2021-08-24 设计创作，主要内容包括：本发明涉及一种多孔级LSX沸石分子筛无模板制备方法,包括如下步骤：碱性环境下,在含有钠源、铝源的水溶液中逐滴加入含有硅源的水溶液,搅拌均匀,加入晶种,继续搅拌,转移至烘箱先进行加热老化,然后升温进行水热反应,待反应完成后去除产物洗涤、烘干、煅烧后得到多孔级LSX沸石分子筛；钠源为氯化钠和氢氧化钠,所示铝源为铝酸钠,硅源为硅溶胶；投料量按照摩尔比为Na-(2)O:Al-(2)O-(3):SiO-(2):H-(2)O＝5.85:1:2.2:(90-110)。本发明无模板法制得的LSX沸石分子筛具有多级孔结构,结晶度高达97％、BET高达1000m～(2)/g以上。(The invention relates to a template-free preparation method of a porous LSX zeolite molecular sieve, which comprises the following steps: under an alkaline environment, dropwise adding an aqueous solution containing a silicon source into an aqueous solution containing a sodium source and an aluminum source, uniformly stirring, adding seed crystals, continuously stirring, transferring to an oven, heating for aging, heating for hydrothermal reaction, removing a product after the reaction is finished, washing, drying and calcining to obtain the porous LSX zeolite molecular sieve; the sodium source is sodium chloride and sodium hydroxide, the aluminum source is sodium aluminate, and the silicon source is silica sol; the feed amount is Na according to the molar ratio 2 O:Al 2 O 3 :SiO 2 :H 2 O ═ 5.85:1:2.2 (90-110). The LSX zeolite molecular sieve prepared by the template-free method has a multi-stage pore structure, the crystallinity is up to 97 percent, and the BET is up to 1000m 2 More than g.)

1. A template-free preparation method of a porous LSX zeolite molecular sieve is characterized by comprising the following steps:

under an alkaline environment, dropwise adding an aqueous solution containing a silicon source into an aqueous solution containing a sodium source and an aluminum source, uniformly stirring, adding seed crystals, continuously stirring, transferring to an oven, heating for aging, heating for hydrothermal reaction, removing a product after the reaction is finished, washing, drying and calcining to obtain the porous LSX zeolite molecular sieve;

the sodium source is sodium chloride and sodium hydroxide, the aluminum source is sodium aluminate, and the silicon source is silica sol;

with Na₂O represents the total amount of sodium contained in sodium aluminate, sodium hydroxide and sodium chloride, expressed as Al₂O₃Represents the amount of aluminum element in sodium aluminate in terms of SiO₂The amount of silicon element in the silica sol is shown, and the feeding amount is Na according to the molar ratio₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:(90-110)。

2. The template-free preparation method of the porous LSX zeolite molecular sieve of claim 1, wherein the seed crystal is LSX molecular sieve, and the amount of the seed crystal is 0.2% of the total mass of the sodium source, the aluminum source, the silicon source and the water.

3. The template-free preparation method of the porous LSX zeolite molecular sieve of claim 1, wherein the dosage is Na in molar ratio₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:100。

4. The template-free preparation method of the porous LSX zeolite molecular sieve of claim 3, wherein the aging temperature is normal temperature to 70 ℃ and the aging time is 1-24 h.

5. The template-free preparation method of the porous LSX zeolite molecular sieve of claim 4, wherein the aging temperature is 50-60 ℃ and the aging time is 3-4 h.

6. The template-free preparation method of the porous LSX zeolite molecular sieve of claim 5, wherein the aging temperature is 55 ℃ and the aging time is 3 h.

7. The template-free preparation method of the porous LSX zeolite molecular sieve as claimed in claim 3, wherein the temperature of the hydrothermal reaction is 100-110 ℃ and the time is 2-3 h.

8. The template-free preparation method of the porous LSX zeolite molecular sieve of claim 7, wherein the hydrothermal reaction is performed at 100 ℃ for 2 h.

Technical Field

The invention relates to the technical field of zeolite molecular sieve synthesis, in particular to a template-free preparation method of a porous LSX zeolite molecular sieve.

Background

Faujasite (FAU) can be divided into X-type zeolite molecular sieves and Y-type zeolite molecular sieves according to different silica-alumina ratios, wherein the X-type zeolite molecular sieves with the silica-alumina molar ratio of 1.0-1.1 are called LSX zeolite molecular sieves. The LSX zeolite molecular sieve is alkaline and has good adsorption and shape-selective catalytic performances, so that the LSX zeolite molecular sieve has wide attention in the fields of industrial catalysis, adsorption separation, ion exchange and the like. However, the currently reported LSX zeolite molecular sieves are all microporous structures, and the processing of compounds with larger molecular structures and compositions and more complex compounds is difficult, so that the LSX zeolite with a hierarchical pore structure needs to be prepared, but related research reports are rare.

Regarding the synthesis of the zeolite molecular sieve with the hierarchical pore structure, long-chain aminosilane is generally adopted as an organic template, but the template has complex synthetic process, high price and serious environmental pollution, so that the zeolite production cost is high, and the method also does not accord with the social trend of low-carbon sustainable development at present. Therefore, the invention tries to develop a method for synthesizing the hierarchical pore LSX zeolite molecular sieve without using an organic template, which not only reduces the synthesis cost, but also is safe and environment-friendly.

Disclosure of Invention

In order to solve the technical problems that the existing LSX zeolite molecular sieve has a microporous structure and does not have a multi-level pore structure and a template agent is adopted in the synthesis process, a more simple and convenient template-free preparation method of the porous LSX zeolite molecular sieve is provided. The invention directly synthesizes the high-crystallinity LSX zeolite molecular sieve with a hierarchical pore structure without using an organic template.

In order to achieve the above purpose, the invention is realized by the following technical means:

a template-free preparation method of a porous LSX zeolite molecular sieve comprises the following steps:

under an alkaline environment, dropwise adding an aqueous solution containing a silicon source into an aqueous solution containing a sodium source and an aluminum source, uniformly stirring, adding seed crystals, continuously stirring, transferring to an oven, heating for aging, heating for hydrothermal reaction, removing a product after the reaction is finished, washing, drying and calcining to obtain the porous LSX zeolite molecular sieve;

the sodium source is sodium chloride and sodium hydroxide, the aluminum source is sodium aluminate, and the silicon source is silica sol;

with Na₂O represents the total amount of sodium contained in sodium aluminate, sodium hydroxide and sodium chloride, expressed as Al₂O₃Represents the amount of aluminum element in sodium aluminate in terms of SiO₂To representThe amount of silicon element in the silica sol is Na according to the molar ratio₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:(90-110)。

Further, the seed crystal is a microporous LSX molecular sieve (microporous LSX molecular sieve with the pore diameter less than 2nm), and the dosage of the seed crystal is 0.2% of the total mass of the sodium source, the aluminum source, the silicon source and the water.

Preferably, the feeding amount is Na according to a molar ratio₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:100。

And further, the aging temperature is normal temperature-70 ℃ and the aging time is 1-24 h.

Preferably, the aging temperature is 50-60 ℃ and the aging time is 3-4 h.

More preferably, the temperature of the aging is 55 ℃ and the time is 3 h.

Furthermore, the temperature of the hydrothermal reaction is 100-110 ℃, and the time is 2-3 h.

Preferably, the temperature of the hydrothermal reaction is 100 ℃ and the time is 2 h.

The beneficial technical effects are as follows:

the invention uses silica sol as a silicon source, and adds a small amount of seed crystals to directly synthesize the hierarchical pore LSX zeolite molecular sieve by a hydrothermal method under the condition of not using an organic template agent, wherein micropores (the pore diameter is less than 2nm) and mesopores (the pore diameter is between 2 and 50 nm) exist in the LSX zeolite molecular sieve synthesized by the invention. Compared with the LSX zeolite molecular sieve synthesis method in the prior art, the synthesis process is simpler and more convenient, is easier to operate and realize, and is lower in synthesis cost and more environment-friendly. The LSX zeolite molecular sieve synthesized by the method has a multi-stage pore channel structure and high crystallinity which can reach more than 90 percent.

Drawings

Fig. 1 is an XRD chart of products of examples 1-6 with different water-aluminum ratios, wherein the a-curve is 120 for example 1, the b-curve is 110 for example 2, the c-curve is 105 for example 3, the d-curve is 100 for example 4, the e-curve is 95 for example 5, and the f-curve is 90 for example 6.

Fig. 2 is an XRD pattern of products of examples 4 and 7-11 with different molar ratios of sodium chloride and sodium hydroxide, wherein the a-curve is example 7NaCl: NaOH 10:0, the b-curve is example 8NaCl: NaOH 9:1, the c-curve is example 9NaCl: NaOH 8:2, the d-curve is example 4NaCl: NaOH 7:3, the e-curve is example 10NaCl: NaOH 6:4, and the f-curve is example 11NaCl: NaOH 5: 5.

FIG. 3 is an XRD pattern of the products obtained for different aging temperatures for examples 12-18, where the a-curve is the aging temperature of 40 ℃ for example 12, the b-curve is the aging temperature of 45 ℃ for example 13, the c-curve is the aging temperature of 50 ℃ for example 14, the d-curve is the aging temperature of 55 ℃ for example 15, the e-curve is the aging temperature of 60 ℃ for example 16, the f-curve is the aging temperature of 70 ℃ for example 17, and the g-curve is the aging temperature of 80 ℃ for example 18.

FIG. 4 is an XRD pattern of the products obtained in examples 15 and 19-21 with different aging times, wherein a is a curve of 1h aging time of example 19, b is a curve of 2h aging time of example 20, c is an aging time of 3h of example 15, and d is an aging time of 4h of example 21.

FIG. 5 is an XRD pattern of the products of comparative examples 1-3 and example 15 as shown in FIG. 5, wherein curve a is the product of the process of comparative example 1, curve b is the product of the process of comparative example 2, curve c is the product of the process of comparative example 3, and curve d is the product of the process of example 15.

FIG. 6 is a graph of the nitrogen adsorption profile of the hierarchical pore LSX zeolite molecular sieve of example 15.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention and the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless specifically stated otherwise, the numerical values set forth in these examples do not limit the scope of the invention. Techniques, methods known to those of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.

The experimental methods of the following examples, which are not specified under specific conditions, are generally determined according to national standards; if no corresponding national standard exists, the method is carried out according to the universal international standard or the standard requirement proposed by related enterprises. Unless otherwise indicated, all parts are parts by weight and all percentages are percentages by weight.

Example 1

Solution A2.5 g of NaAlO₂Dissolving to 25mLH₂O is in;

solution B5.7 ml of silica sol was dissolved to 8.2mLH₂O is in;

adding 6.051g of NaCl and 1.775g of NaOH into the solution A, stirring for 0.5h, slowly dropwise adding the solution B, stirring for 0.5h, adding 0.1g of seed crystal, stirring for 0.5h, and aging at normal temperature for 24 h; then the mixture is moved into a reaction kettle for sealing and reacts for 6.0h at the temperature of 90 ℃; and naturally cooling the reaction kettle to room temperature, carrying out vacuum filtration, washing for 2 times in 1000ml of deionized water until the pH value is neutral, and drying in an oven at 100 ℃ for 12 hours.

Molar ratio of materials in the system of the example Na₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:120。

Examples 2 to 6

Examples 2 to 6 were prepared in the same manner as in example 1 except that Na was used₂O:Al₂O₃:SiO₂:H₂The molar ratio of O is different.

Molar ratio of materials Na in example 2₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:110。

Molar ratio of materials Na in example 3₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:105。

Molar ratio of materials Na in example 4₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:100。

Molar ratio of materials Na in example 5₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:95。

Molar ratio of materials Na in example 6₂O:Al₂O₃:SiO₂:H₂O＝5.85:1:2.2:90。

Examples 7 to 11

The preparation methods of examples 7 to 11 were the same as in example 4, except that the amounts of NaCl and NaOH added to the solution A were different.

Example 8 to solution A, 8.64g NaCl, 0g NaOH were added.

Example 8 to solution A was added 7.78g NaCl, 0.59g NaOH.

Example 9 to solution A, 6.91g NaCl, 1.18g NaOH were added.

Example 10 to solution A was added 5.18g NaCl, 2.36g NaOH.

Example 11 to solution A was added 4.32g NaCl, 2.96g NaOH.

Examples 12 to 21

The preparation methods of examples 12 to 21 were the same as in example 4 except that the aging temperature and time were different.

In example 12, the aging was carried out at 40 ℃ for 3 hours.

In example 13, the aging was carried out at 45 ℃ for 3 hours.

In example 14, the aging was carried out at 50 ℃ for 3 hours.

In example 15, the aging was carried out at 55 ℃ for 3 hours.

In example 16, the aging was carried out at 60 ℃ for 3 hours.

In example 17, the aging was carried out at 70 ℃ for 3 hours.

In example 18, the aging was carried out at 80 ℃ for 3 hours.

In example 19, the aging was carried out at 55 ℃ for 1 hour.

In example 20, the temperature was 55 ℃ for 2 hours.

In example 21, the aging was carried out at 55 ℃ for 4 hours.

The experimental parameters of the above examples are shown in Table 1.

The above examples were subjected to crystallinity and specific surface area tests, and the results are shown in Table 1.

TABLE 1 Experimental parameters of the above examples

The crystallinity (%) of the product of the above example was measured and calculated using an X-ray diffractometer, and the crystallinity calculation formula, crystallinity ═ (diffraction peak intensity/total intensity) × 100%, data processing was performed using jade software. S_BETThe nitrogen adsorption was measured by a physical adsorption apparatus.

As can be seen from table 1, the LSX zeolite molecular sieve must be synthesized in an alkaline environment. The condition for obtaining LSX zeolite molecular sieve with high crystallinity (more than 80 percent) must be Na₂O:Al₂O₃:SiO₂:H₂The molar ratio of O is 5.85:1:2.2:100, wherein the molar ratio of NaCl to NaOH is 7:3, the LSX zeolite molecular sieve with the crystallinity of more than 80 percent can be obtained by aging at 50-60 ℃ for 3-4h and carrying out hydrothermal reaction at 100 ℃ for 2h, and the specific surface area of the LSX zeolite molecular sieve is more than 630m²/g。

And (4) characterizing the crystal form of the product by using an X-ray diffractometer for the product. The XRD patterns of the products of examples 1-6 with different water-to-aluminum ratios are shown in fig. 1, wherein the a-curve is 120 for example 1, the b-curve is 110 for example 2, the c-curve is 105 for example 3, the d-curve is 100 for example 4, the e-curve is 95 for example 5, and the f-curve is 90 for example 6. As can be seen from fig. 1, as the water-to-aluminum ratio decreased from 120 to 100, the LSX zeolite crystallinity increased, but as the water-to-aluminum ratio continued to decrease, the zeolite crystallinity decreased. This is because the chloride ions in sodium chloride have a certain structure-directing action, and the reduction of the water-aluminum ratio results in incomplete dissolution of sodium chloride, and the structure-directing action of the chloride ions is not exerted, resulting in a decrease in crystallinity. Therefore, the optimal water-aluminum ratio is selected to be 100.

XRD patterns of products of examples 4 and 7-11 with different molar ratios of NaCl and NaOH are shown in fig. 2, where the a-curve is for example 7NaCl: NaOH 10:0, the b-curve is for example 8NaCl: NaOH 9:1, the c-curve is for example 9NaCl: NaOH 8:2, the d-curve is for example 4NaCl: NaOH 7:3, the e-curve is for example 10NaCl: NaOH 6:4, and the f-curve is for example 11NaCl: NaOH 5: 5. As can be seen from fig. 2, the crystallinity of LSX zeolite increased with increasing sodium hydroxide content from 10:0 to 7: 3. However, the sodium hydroxide content increased from 6:4 to 5:5, and no LSX zeolite could be synthesized. This is because LSX zeolite has strict requirements on the pH of the synthesis system, and when it is too low, LSX zeolite cannot be formed, and when it is too high, SOD zeolite is formed. Therefore, the optimal molar ratio of sodium chloride to sodium hydroxide is selected to be 7: 3.

XRD patterns of the products obtained in examples 12-18 at different aging temperatures are shown in FIG. 3, wherein the a-curve is the aging temperature of 40 ℃ for example 12, the b-curve is the aging temperature of 45 ℃ for example 13, the c-curve is the aging temperature of 50 ℃ for example 14, the d-curve is the aging temperature of 55 ℃ for example 15, the e-curve is the aging temperature of 60 ℃ for example 16, the f-curve is the aging temperature of 70 ℃ for example 17, and the g-curve is the aging temperature of 80 ℃ for example 18. As can be seen from FIG. 3, the aging temperature below 50 ℃ or above 60 ℃ resulted in significant SOD zeolite impurity phases. This is because aging is the nucleation period of the zeolite, at which the nuclei of different zeolites compete with one another. The formation of the nuclei requires absorbed energy, overcoming the energy barrier. The aging temperature is too low, so that the nuclei do not absorb enough energy and the LSX zeolite cannot be formed. The aging temperature is too high, and the absorbed energy is too much to form SOD zeolite with a compact pore structure. The optimum ageing temperature was therefore chosen to be 55 ℃.

XRD patterns of products obtained in example 15 and examples 19-21 with different aging times are shown in FIG. 4, wherein a curve is 1h aging time of example 19, b curve is 2h aging time of example 20, c curve is 3h aging time of example 15, and d curve is 4h aging time of example 21. As can be seen from fig. 4, the crystallinity of the LSX zeolite increased significantly as the aging time increased from 1h to 3h, but too long aging time resulted in a decrease in the crystallinity of the LSX zeolite. This is because the system is in the induction period before 3h, and the X-type molecular sieve is in the nucleation stage, and the nucleation amount of the X-type molecular sieve is less. And the aging time is prolonged, so that more stable SOD zeolite is generated. Therefore, the optimal aging time was selected to be 3 hours.

Comparative example 1

10g of biosilica (refluxing in 1mol/L hydrochloric acid solution for 1 hour) was mixed into 82g of 14.5 wt% NaOH solution to prepare a sodium silicate solution. The solution is heated and stirred for 0.5h at 70 ℃, after the biological silica gel is almost dissolved, the solution is filtered, and the filtrate is placed in a beaker. In a first beaker, 2.5g of sodium aluminate are dissolved in 10.0ml of deionized water. In a second beaker, 4.26g NaOH and 2.84g KOH were dissolved in 18.8ml deionized water, the two beaker solutions were mixed and stirred for 0.5h, the prepared sodium silicate solution was added to the mixture, stirred for 0.5h again, aged for 3h at 70 ℃ and then put into a kettle to crystallize for 4h at 93 ℃. Molar ratio of materials in system Na₂O:K₂O:Al₂O₃:SiO₂:H₂O is 2.5:0.75:0.45:1.0: 55.45. The crystallinity of the microporous LSX zeolite prepared is shown in table 2. Comparative example 1 method provenance: the green synthesis for environmental treatment.

Comparative example 2:

dissolving 2.5g of sodium metaaluminate in 22.5ml of deionized water, adding 4.92 g of NaOH and 2.56g of KOH after complete dissolution, adding 5.0ml of water glass after complete dissolution, generating gel under the stirring condition, aging at 50 ℃ for 24h, putting into a kettle, crystallizing, and reacting at 100 ℃ for 4.0 h. Molar ratio of materials in system Na₂O:K₂O:Al₂O₃:SiO₂:H₂O is recorded as 6.00:1.5:1.0:2.0: 100. The crystallinity of the microporous LSX zeolite prepared is shown in table 2. Comparative example 2 method provenance: synthesis and physiochemical Properties of NaK, K, Na, and Li Forms of LSX Zeolite.

Comparative example 3:

2.5g of sodium metaaluminate are dissolved in 30.6ml of deionized water, and after complete dissolution, 1.50 g of NaOH is addedAdding 2.32g of KOH, adding 4.82ml of water glass after complete dissolution, generating gel under the stirring condition, aging for 24h, filling into a kettle, crystallizing, and reacting for 4.0h at 100 ℃. Molar ratio of materials in system Na₂O:K₂O:Al₂O₃:SiO₂:H₂O is recorded as 3.165:1.36:1.0:1.926: 128. Comparative example 3 method statement: synthesis and catalysis of co-crystallized zeolite composite of LSX/A feed Tontiisirin.

The crystallinity of the microporous LSX zeolites prepared in comparative examples 1-3 and example 15 above is shown in table 2.

TABLE 2 crystallinity and specific surface area for comparative examples 1-3, example 15

As shown in Table 2, the LSX zeolite molecular sieve prepared by the method of the invention has better specific surface area which reaches 1000m²More than g.

The XRD patterns of the products of comparative examples 1-3, example 15 are shown in fig. 5, where curve a is the product of the process of comparative example 1, curve b is the product of the process of comparative example 2, curve c is the product of the process of comparative example 3, and curve d is the product of the process of example 15. As can be seen from fig. 5, the LSX zeolite molecular sieves produced by each of the methods have a relatively high degree of crystallinity.

The BET adsorption curve of the product of example 15 of the invention is shown in FIG. 6, and it can be seen from FIG. 6 that the adsorption isotherm of LSX zeolite is type IV isotherm, and the desorption curve shows that the pore diameter of LSX zeolite is 14.2nm, thus proving that the LSX zeolite synthesized by the method of the invention is a hierarchical pore product.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.