A method for synthesizing molecular sieves under near-neutral fluoride-free conditions

Abstract

The present application relates to molecular sieve synthesis technology, and aims to provide a method for synthesizing molecular sieve under near neutral fluoride-free conditions. The method comprises the following steps: mixing a silicon source, a heteroatom, a template agent, an alkali source and deionized water, stirring uniformly at room temperature, adding seeds and continuing to stir uniformly; then, the mixture is transferred into a reaction kettle to perform hydrothermal reaction, and after the reaction is completed, the product is cooled to room temperature, filtered, and dried to obtain the target molecular sieve; the alkali source used is urea or ammonia water. The alkalinity of the synthesis system after crystallization is only 7-8, which reduces the cost of neutralization treatment step of waste water treatment and reduces the discharge of waste water. At the same time, due to the reduction of corrosion of low alkalinity to the equipment, the service life of the equipment can be prolonged; the ion exchange process is avoided in the synthesis process, which can reduce the investment cost and energy loss; compared with the hydrothermal synthesis under strong alkaline conditions, the product has higher raw material utilization, thermal stability and hydrothermal stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of molecular sieve synthesis method. Specifically relates to a method for synthesizing molecular sieves under near neutral fluoride-free conditions. BACKGROUND

[0002] Zeolites play an important role in the field of energy and environment due to their regular micropores, high specific surface area, excellent thermal and hydrothermal stability, and adjustable acid sites. The synthesis of molecular sieves is essentially the dissolution and polycondensation of silicon and aluminum sources, which is inseparable from the role of mineralizers. Generally, the crystallization of zeolites requires OH - or F - mineralizers to dissolve the silicon source, so zeolites are usually synthesized under alkaline conditions (pH > 10) or neutral conditions containing HF (pH = 6-8).

[0003] Commonly used alkaline mineralizers include alkali metal oxides or quaternary ammonium bases, such as Na2O, K2O, TPAOH, and TMAdaOH. With the discovery of highly reactive alkaline aluminosilicate precursors, OH - has been widely used as a mineralizer since 1967. US3308069 first disclosed that high-silicon Beta molecular sieves were synthesized when quaternary ammonium base TEAOH and alkali metal oxide Na2O were present simultaneously. In 1972, US3702886 disclosed the synthesis of ZSM-5 zeolite molecular sieves under strong alkaline conditions, opening up the large-scale industrial application of ZSM-5. However, the strong alkaline mother liquor can cause a large amount of silica to dissolve, resulting in low zeolite yield and reduced raw material utilization. Secondly, a large number of framework defects are easily formed under strong alkaline conditions, thereby reducing the thermal and hydrothermal stability of the zeolite.

[0004] In 1978, USP4073865 first disclosed a method for successfully synthesizing pure-silicon zeolite Silicalite-1 in a neutral system containing F - , reducing the pH value range of the molecular sieve synthesis mother liquor from alkaline to neutral. With the in-depth study of the mineralization of fluoride ions, it was found that fluoride ions can not only mineralize but also act as a structure-directing agent for tetrameric rings. Although F - as a mineralizer can synthesize perfect crystals with fewer framework defects and avoid complex ion exchange processes. However, F - has a strong corrosive effect on industrial equipment, and has not yet been implemented in industrial applications.

[0005] Since the existing strong alkaline mineralizers and fluoride ion mineralizers have their own shortcomings that cannot be ignored, it is particularly important to develop a more mild mineralizer. SUMMARY

[0006] The technical problem solved by the present application is to overcome the deficiencies in the prior art and provide a method for synthesizing molecular sieves under near-neutral fluoride-free conditions.

[0007] To solve the technical problem, the solution of the present application is:

[0008] The present application provides a method for synthesizing molecular sieves under near-neutral fluoride-free conditions, which is performed according to the following steps:

[0009] After the silicon source, heteroatom, template agent, alkali source and deionized water are mixed, they are first stirred uniformly at room temperature, then crystal seeds are added and continue to be stirred uniformly; then the mixture is transferred into a reaction kettle for hydrothermal reaction, after the reaction is completed, it is cooled to room temperature, and the product is filtered and dried to obtain the target molecular sieve;

[0010] The alkali source used is urea; the silicon source used is calculated as SiO2, the heteroatom is calculated as M2O3, and the alkali source is calculated as CO(NH2)2; the addition amount of each reaction raw material is controlled to make the molar ratio of SiO2, M2O3, template agent, CO(NH2)2, water and crystal seeds in the range of 1:0-0.017:0.1-0.3:0.03-0.1:13.3-30:0.05-0.1.

[0011] As a preferred scheme of the present application, urea is replaced by ammonia water as the alkali source, and the ammonia water used is calculated as (NH2) - , and its molar amount is twice that of urea; the water content in the ammonia water is also calculated as the amount of water, and deionized water is additionally added to meet the molar ratio requirement.

[0012] As a preferred scheme of the present application, the silicon source used is any one of fine silica gel, silica sol or white carbon black.

[0013] As a preferred scheme of the present application, the heteroatom used is any one of aluminum sulfate octadecahydrate, boehmite, boric acid or gallium nitrate, and the M2O3 refers to Al2O3, B2O3 or Ga2O3.

[0014] As a preferred scheme of the present application, the template agent used is any one of tetrapropylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium bromide or trimethyladamantylammonium bicarbonate.

[0015] As a preferred scheme of the present application, the mixed raw materials are stirred for 2h before the crystal seeds are added.

[0016] As a preferred scheme of the present application, the temperature of the hydrothermal reaction is controlled to be 160-180℃, and the reaction time is 3-7 days.

[0017] As a preferred scheme of the present application, the temperature of the drying is 80℃.

[0018] As a preferred scheme of the present application, the reaction kettle is a polytetrafluoroethylene stainless steel reaction kettle.

[0019] Invention principle description:

[0020] As early as the 1940s, R.M. Barrer began to study the hydrothermal synthesis of silica. His discovery that under relatively weak alkaline conditions, i.e. the pH of the synthesis system is 9-11, only adsorbents such as ANA and MOR can be obtained, and zeolites with higher commercial value cannot be obtained. When he increased the pressure and alkalinity of the system, he found that in the same hydrothermal system, the zeolite only needs a few hours to precipitate from the mother liquor. Since then, under the strong alkaline conditions provided by inorganic metal oxides, R.M. Milton and D.W. Breck have developed more than 20 kinds of low-silicon zeolites, and the zeolite has been greatly developed, and the strong alkaline synthesis condition is still used today.

[0021] It can be seen that alkalinity plays a very important role in the synthesis system of molecular sieve. The alkali source is usually considered as a mineralizer in subsequent research, and its most important function is to dissolve the silicon source. When strong alkali is added to the synthesis system, the silicon source is fully dissolved, the silicon supersaturation is increased, and the silicate monomers formed by the depolymerization of the silicon source further undergo polycondensation to form molecular sieves. Existing research generally believes that the synthesis of molecular sieves requires very high silicon supersaturation to complete the nucleation and subsequent growth of molecular sieves, so the use of strong alkali or strong acid has become a kind of inert thinking of molecular sieve synthesis technology. The current researchers generally use strong alkali or strong acid to realize the dissolution of the silicon source, and the pH of the molecular sieve synthesis system is greater than 10, or it is 6-8 under the condition of containing strong acid HF which can dissolve the silicon source. However, the use of strong alkali or strong acid brings great pressure to the requirements of wastewater discharge and equipment corrosion prevention, in addition, it also increases the production enterprise or research work cost and safety management requirements.

[0022] And the applicant's research team found through long-term experiments that when a weaker alkali source, urea, is used to dissolve the silicon source, the silicon source will also show a weak dissolution trend after long-time high-temperature treatment. The reason for the dissolution is that urea decomposes into NH3 and CO2 at high temperature, and the two substances dissolve in water to form a weak alkaline environment, and the silicon source is slowly dissolved by NH4OH in water. Therefore, according to the mineralization principle, it can be confirmed that urea can also play a certain mineralization role. When this mineralization is combined with different heteroatoms and templates for synthesis, a variety of molecular sieves with high commercial value can also be obtained by hydrothermal synthesis method.

[0023] In addition, similar to the mechanism of urea decomposition to produce alkaline NH4OH, weakly alkaline ammonia water can also play the same mineralization effect. However, since ammonia water does not have CO2 produced by urea decomposition to balance alkalinity, when ammonia water is used as an alkali source, the pH value range of the reaction system is slightly higher than that when urea is used as a mineralizer. When urea or ammonia water is used as an alkali source to participate in crystallization, the alkalinity of the hydrothermal synthesis system is close to neutral (pH value is only 7-8), thus greatly reducing the pressure of wastewater discharge and equipment corrosion.

[0024] Based on the above principle, the applicant proposes a weakly alkaline mineralizer which is more mild than the existing alkaline mineralizer and fluoride ion mineralizer, and can synthesize zeolite molecular sieves under near-neutral and fluoride-free conditions through hydrothermal synthesis. Compared with strong alkaline synthesis, the process has higher yield, is environmentally friendly, and has good thermal stability and hydrothermal stability.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] 1. In the application, urea or ammonia water is used as an alkali source, and the alkalinity of the synthesis system after crystallization is only 7-8, reducing the cost of neutralization treatment steps of wastewater treatment and reducing the discharge of wastewater. At the same time, due to the reduction of corrosion of low alkalinity to equipment, the service life of the equipment can be prolonged.

[0027] 2. In the application, no alkali metal ions are added in the molecular sieve synthesis process, and ammonium type molecular sieves can be directly obtained, avoiding the ion exchange process and reducing the investment cost and energy loss.

[0028] 3. In the application, due to the reduced solubility of silica in the weakly alkaline synthesis system, the prepared molecular sieves have higher yield than the molecular sieves hydrothermally synthesized under strong alkaline conditions, that is, the application has higher raw material utilization rate.

[0029] 4. The S-1 and ZSM-5 prepared in the application have higher thermal stability and hydrothermal stability than the molecular sieves hydrothermally synthesized under strong alkaline conditions.

[0030] 5. The application can synthesize various molecular sieves containing heteroatoms with high commercial value, and can be used in various industrial production processes. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 XRD spectrum of S-1 molecular sieves synthesized by the neutral system in the application;

[0032] Figure 2 Scanning electron microscope image of S-1 molecular sieves synthesized by the neutral system in the application;

[0033] Figure 3 XRD spectrum of silicon-aluminum ZSM-5 molecular sieves synthesized by the neutral system in the application;

[0034] Figure 4 Scanning electron micrograph of the silicon-aluminum ZSM-5 molecular sieve synthesized in the neutral system of the present application;

[0035] Figure 5 XRD spectrum of the silicon-boron ZSM-5 molecular sieve synthesized in the neutral system of the present application;

[0036] Figure 6 Scanning electron micrograph of the silicon-boron ZSM-5 molecular sieve synthesized in the neutral system of the present application.

[0037] Figure 7 XRD spectrum of the silicon-gallium ZSM-5 molecular sieve synthesized in the neutral system of the present application;

[0038] Figure 8 Scanning electron micrograph of the silicon-gallium ZSM-5 molecular sieve synthesized in the neutral system of the present application.

[0039] Figure 9 XRD spectrum of the silicon-aluminum ZSM-11 molecular sieve synthesized in the neutral system of the present application;

[0040] Figure 10 Scanning electron micrograph of the silicon-aluminum ZSM-11 molecular sieve synthesized in the neutral system of the present application.

[0041] Figure 11 XRD spectrum of the silicon-aluminum SSZ-13 molecular sieve synthesized in the neutral system of the present application;

[0042] Figure 12 Scanning electron micrograph of the silicon-aluminum SSZ-13 molecular sieve synthesized in the neutral system of the present application.

[0043] Figure 13 Product yield comparison chart of the examples and comparative examples of the present application.

[0044] Figure 14 Crystallinity comparison chart of the products of the examples and comparative examples of the present application before and after heat treatment at 1000°C for 30 hours, for evaluating heat stability.

[0045] Figure 15 Crystallinity comparison chart of the products of the examples and comparative examples of the present application before and after heat treatment at 1000°C for 30 hours, for evaluating heat stability. Figure 15 Crystallinity comparison chart of the products of the examples and comparative examples of the present application before and after heat treatment at 1000°C for 30 hours, for evaluating heat stability. DETAILED DESCRIPTION

[0046] The present application will be described in further detail below with reference to the accompanying drawings and specific embodiments:

[0047] Example 1: Synthesis of S-1 molecular sieve under the condition of urea / SiO2 (mole ratio, same below) = 0.03

[0048] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.03 g of urea were added, stirred until clear, and then 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave, and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing, and drying overnight at 80°C.

[0049] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0050] 1.0 Si02: 0.1 TPACl: 0.03 Urea: 13.3 H20: 0.05 seeds

[0051] The structure was analyzed by X-ray diffraction to be S-1 molecular sieve (attached Figure 1 , and it was seen from a scanning electron microscope photograph that the synthesized S-1 product had a uniform shape (attached Figure 2 ).

[0052] Example 2: Synthesis of S-1 molecular sieve under the condition of urea / Si02= 0.1

[0053] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.1 g of urea were added, stirred until clear, and then 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave, and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing, and drying overnight at 80°C.

[0054] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0055] 1.0 Si02: 0.1 TPACl: 0.1 Urea: 13.3 H20: 0.05 seeds

[0056] Example 3: Synthesis of S-1 molecular sieve under the condition of NH3-H20 / Si02= 0.06

[0057] To 3.949 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.068 g of ammonia water were added, stirred to clear, then 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, then 0.05 g of S-1 seed crystal was added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel reaction kettle, and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, after suction filtration, washing and drying at 80°C overnight, the final S-1 product was obtained.

[0058] The amount of each reaction material is converted to a molar ratio as follows:

[0059] 1.0 SiO2: 0.1 TPACl: 0.06 NH3·H2O: 13.3 H2O: 0.05 seed crystal

[0060] Example 4: Synthesis of S-1 molecular sieve under the condition of NH3·H2O / SiO2=0.2

[0061] To 3.949 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.068 g of ammonia water were added, stirred to clear, then 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, then 0.05 g of S-1 seed crystal was added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel reaction kettle, and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, after suction filtration, washing and drying at 80°C overnight, the final S-1 product was obtained.

[0062] The amount of each reaction material is converted to a molar ratio as follows:

[0063] 1.0 SiO2: 0.1 TPACl: 0.06 NH3·H2O: 13.3 H2O: 0.05 seed crystal

[0064] Example 5: Synthesis of S-1 molecular sieve under the condition of TPACl / SiO2=0.3

[0065] To 3.949 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.068 g of ammonia water were added, stirred to clear, then 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, then 0.05 g of S-1 seed crystal was added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel reaction kettle, and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, after suction filtration, washing and drying at 80°C overnight, the final S-1 product was obtained.

[0066] The amount of each reaction material is converted to a molar ratio as follows:

[0067] 1.0 SiO2: 0.3 TPACI: 0.03 Urea: 13.3 H2O: 0.05 Seed

[0068] Example 6: Synthesis of S-1 molecular sieve under the condition of TPABr / SiO2=0.1

[0069] 0.443 g of tetrapropylammonium bromide and 0.03 g of urea were added to 4 g of deionized water, stirred until clear, and then 1 g of fine silica gel was added to the above solution. After stirring at room temperature for 2 hours, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seed was added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel reaction kettle, and hydrothermal reaction was carried out in an oven at 180°C for 80 hours. After cooling to room temperature, after suction filtration, washing, and drying at 80°C overnight, the final S-1 product was obtained.

[0070] The amount of each reaction material was converted to a molar ratio as follows:

[0071] 1.0 SiO2: 0.3 TPACI: 0.03 Urea: 13.3 H2O: 0.05 Seed

[0072] Example 7: Synthesis of S-1 molecular sieve under the condition of H2O / SiO2=30

[0073] 0.443 g of tetrapropylammonium bromide and 0.03 g of urea were added to 4 g of deionized water, stirred until clear, and then 1 g of fine silica gel was added to the above solution. After stirring at room temperature for 2 hours, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seed was added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel reaction kettle, and hydrothermal reaction was carried out in an oven at 180°C for 80 hours. After cooling to room temperature, after suction filtration, washing, and drying at 80°C overnight, the final S-1 product was obtained.

[0074] The amount of each reaction material was converted to a molar ratio as follows:

[0075] 1.0 SiO2: 0.3 TPACI: 0.03 Urea: 13.3 H2O: 0.05 Seed

[0076] Example 8: Synthesis of S-1 molecular sieve under the condition of Seed / SiO2=0.08

[0077] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.03 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.08 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 180 °C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing, and drying overnight at 80 °C.

[0078] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0079] 1.0 Si02: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.08 Seed

[0080] Example 9: Synthesis of S-1 molecular sieve under the condition of Seed / Si02= 0.1

[0081] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.03 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.1 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 180 °C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing, and drying overnight at 80 °C.

[0082] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0083] 1.0 Si02: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.1 Seed

[0084] Example 10: Synthesis of S-1 molecular sieve under the condition of hydrothermal temperature 170 °C

[0085] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.03 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 170 °C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing, and drying overnight at 80 °C.

[0086] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0087] 1.0 SiO2: 0.1 TPACI: 0.03 Urea: 13.3 H2O: 0.05 Seed

[0088] Example 11: Synthesis of S-1 molecular sieve under hydrothermal reaction for 3 days

[0089] Example 11: Synthesis of S-1 molecular sieve under hydrothermal reaction for 3 days

[0090] The amount of each reactant is converted to molar ratio as follows:

[0091] 1.0 SiO2: 0.1 TPACI: 0.03 Urea: 13.3 H2O: 0.05 Seed

[0092] Example 11: Synthesis of S-1 molecular sieve under hydrothermal reaction for 3 days

[0093] Example 11: Synthesis of S-1 molecular sieve under hydrothermal reaction for 3 days

[0094] The amount of each reactant is converted to molar ratio as follows:

[0095] 1.0 SiO2: 0.1 TPACI: 0.03 Urea: 13.3 H2O: 0.05 Seed

[0096] Example 11: Synthesis of S-1 molecular sieve under hydrothermal reaction for 3 days

[0097] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride and 0.03 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous solution was formed, and then 0.05 g of S-1 seeds were added. After stirring for another 5 minutes, the final white mixture was transferred to a Teflon-lined stainless steel autoclave and hydrothermally treated at 180 °C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washed and dried at 80 °C overnight.

[0098] The amounts of the reaction materials were converted to molar ratios as follows:

[0099] 1.0 Si02: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.05 seeds

[0100] Example 14: Near-neutral synthesis of ZSM-5 molecular sieve with Si / Al = 100

[0101] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride, 0.056 g of aluminum sulfate octadecahydrate and 0.03 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous solution was formed, and then 0.05 g of S-1 seeds were added. After stirring for another 5 minutes, the final white mixture was transferred to a Teflon-lined stainless steel autoclave and hydrothermally treated at 180 °C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washed and dried at 80 °C overnight.

[0102] The amounts of the reaction materials were converted to molar ratios as follows:

[0103] 1.0 Si02: 0.005 Al203: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.05 seeds

[0104] The structure was analyzed by X-ray diffraction to be ZSM-5 molecular sieve (attached Figure 3 , and it could be seen from the scanning electron microscope photograph that the synthesized ZSM-5 product presented a uniform shape (attached Figure 4 ).

[0105] Example 15: Near-neutral synthesis of ZSM-5 molecular sieve with Si / Al = 30

[0106] Example 15: Near neutral synthesis of BS-1 molecular sieve with Si / B = 30

[0107] The amount of each reactant was converted to molar ratio as follows:

[0108] 1.0 Si02: 0.017 Al203: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.05 seeds

[0109] Example 16: Near neutral synthesis of BS-1 molecular sieve with Si / B = 30

[0110] Example 15: Near neutral synthesis of BS-1 molecular sieve with Si / B = 30

[0111] The amount of each reactant was converted to molar ratio as follows:

[0112] 1.0 Si02: 0.017 Al203: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.05 seeds

[0113] The structure of the product was analyzed by X-ray diffraction and was found to be BS-1 molecular sieve (Figure 1). Figure 5 The SEM picture of the product showed that the product was uniform in shape (Figure 2). Figure 6

[0114] Example 17: Near neutral synthesis of BS-1 molecular sieve with Si / B = 100

[0115] ​To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride, 0.01 g of boric acid and 0.03 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing and drying at 80°C overnight.

[0116] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0117] 1.0 Si02: 0.005 B203: 0.1 TPACI: 0.03 Urea: 13.3 H20: 0.05 seeds

[0118] Example 18: Near-neutral synthesis of GaS-1 molecular sieve with Si / Ga = 30

[0119] To 4 g of deionized water, 0.37 g of tetrapropylammonium chloride, 0.142 g of gallium nitrate and 0.06 g of urea were added and stirred until clear. To the above solution, 1 g of fine silica gel was added. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of S-1 seeds were added. After continuing to stir for 5 minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 180°C for 80 hours. After cooling to room temperature, the product was obtained by suction filtration, washing and drying at 80°C overnight.

[0120] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0121] 1.0 Si02: 0.017 Ga203: 0.1 TPACI: 0.06 Urea: 13.3 H20: 0.05 seeds

[0122] The structure was analyzed by X-ray diffraction to be GaS-1 molecular sieve (attached Figure 7 , and it was seen from a scanning electron microscope photograph that the synthesized GaS-1 product had a uniform shape (attached Figure 8 ).

[0123] Example 19: Near-neutral synthesis of GaS-1 molecular sieve with Si / Ga = 100

[0124] 0.37 g tetrapropylammonium chloride, 0.043 g gallium nitrate, and 0.06 g urea were added to 4 g deionized water and stirred until clear. Then, 1 g fine silica gel was added to the solution. After stirring at room temperature for 2 hours, a homogeneous aqueous solution was formed, and then 0.05 g S-1 seed crystals were added. After stirring for another 5 minutes, the resulting white mixture was transferred to a polytetrafluoroethylene stainless steel reactor and hydrothermally reacted in an oven at 180 °C for 80 hours. After cooling to room temperature, the mixture was filtered, washed, and dried overnight at 80 °C to obtain the final GaS-1 product.

[0125] The molar ratios of the reactants are calculated as follows:

[0126] 1.0 SiO2:0.005 Ga2O3:0.1 TPACl:0.06 Urea:13.3 H2O:0.05 Seed Crystal

[0127] Example 20: Near-neutral synthesis of ZSM-11 molecular sieve with Si / Al = 50

[0128] 0.537 g tetrabutylammonium bromide, 0.012 g boehmite, 0.196 g sodium chloride, and 0.03 g urea were added to 6 g deionized water and stirred until clear. Then, 1 g fine silica gel was added to the solution. After stirring at room temperature for 2 hours, a homogeneous aqueous solution was formed, and then 0.05 g ZSM-11 seed crystals were added. After stirring for another 5 minutes, the resulting white mixture was transferred to a polytetrafluoroethylene stainless steel reactor and hydrothermally reacted in an oven at 180 °C for 80 hours. After cooling to room temperature, the mixture was filtered, washed, and dried overnight at 80 °C to obtain the final ZSM-11 product.

[0129] The molar ratios of the reactants are calculated as follows:

[0130] 1.0 SiO2:0.01 Al2O3:0.2 NaCl:0.1 TBABr:0.03 Urea:20H2O:0.05 Seed Crystals

[0131] X-ray diffraction analysis revealed its structure to be ZSM-11 molecular sieve (see attached image). Figure 9 Furthermore, scanning electron microscope images show that the synthesized ZSM-11 product exhibits a uniform shape (see attached image). Figure 10 ).

[0132] Example 21: Near-neutral synthesis of ZSM-11 molecular sieve with Si / Al = 100

[0133] To 6 g of deionized water, 0.537 g of tetrabutylammonium bromide, 0.006 g of boehmite, 0.196 g of sodium chloride and 0.03 g of urea were added and stirred until clear. Then, 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of ZSM-11 seeds were added. After stirring for 5 more minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 180 °C for 80 hours. After cooling to room temperature, the final ZSM-11 product was obtained after suction filtration, washing and drying at 80 °C overnight.

[0134] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0135] 1.0 Si02: 0.005 Al203: 0.2 NaCl: 0.1 TBABr: 0.03 Urea: 20 H20: 0.05 seeds

[0136] Example 22: Near-neutral synthesis of SSZ-13 molecular sieve with Si / Al = 30

[0137] To 7.5 g of deionized water, 0.574 g of trimethyladamantylammonium chloride, 0.03 g of urea and 0.113 g of aluminum isopropoxide were added and stirred until clear. Then, 1 g of fine silica gel was added to the above solution. After stirring for 2 hours at room temperature, a homogeneous aqueous solution was formed, and then 0.05 g of SSZ-13 seeds were added. After stirring for 5 more minutes, the final white mixture was transferred to a polytetrafluoroethylene stainless steel autoclave and hydrothermally reacted in an oven at 160 °C for 7 days. After cooling to room temperature, the final SSZ-13 product was obtained after suction filtration, washing and drying at 80 °C overnight.

[0138] The amounts of the respective reaction materials were converted to molar ratios as follows:

[0139] 1.0 Si02: 0.017 Al203: 0.15 TMAdaCl: 0.03 Urea: 25 H20: 0.05 seeds

[0140] The structure was analyzed by X-ray diffraction to be SSZ-13 molecular sieve (see Figure 11 ), and it was observed from the scanning electron microscope photograph that the synthesized SSZ-13 product exhibited a uniform shape (see Figure 12 ).

[0141] Comparative experiment and result analysis

[0142] Comparative Example 1

[0143] Referring to Example 1, the template used is changed to strong base TPAOH, which also serves as the alkali source, so no additional alkali source is added. 1.353 g of tetrapropylammonium hydroxide is added to 2.985 g of deionized water, stirred to clarify, and then 1 g of fine silica gel is added to the above solution. After stirring for 2 hours at room temperature, a uniform aqueous solution is formed, and then 0.05 g of S-1 seed crystals are added. After continuing to stir for 5 minutes, the final white mixture is transferred to a polytetrafluoroethylene stainless steel autoclave, and hydrothermal reaction is carried out in an oven at 180°C for 80 hours. After cooling to room temperature, the S-1-TPAOH molecular sieve product is prepared after suction filtration, washing, and drying at 80°C overnight.

[0144] The amount of each reaction raw material is converted to a molar ratio as follows:

[0145] 1.0 SiO2: 0.1 TPAOH: 13.3 H2O: 0.05 seed crystal

[0146] Comparative Example 2

[0147] Referring to Example 1, the alkali source used is changed to strong base NaOH, NaOH / SiO2=0.225, and the other raw material proportions and reaction conditions remain unchanged, to prepare the S-1-NaOH molecular sieve product.

[0148] The amount of each reaction raw material is converted to a molar ratio as follows:

[0149] 1.0 SiO2: 0.1 TPAOH: 13.3 H2O: 0.05 seed crystal

[0150] Comparative Example 3

[0151] Referring to Comparative Example 1, an additional heteroatom Al2O3 is added, Al2O3 / SiO2=0.005, and the heteroatom is added in the form of aluminum sulfate octadecahydrate, and the other raw material proportions and reaction conditions remain unchanged, to prepare the Al-ZSM-5-TPAOH molecular sieve product.

[0152] The amount of each reaction raw material is converted to a molar ratio as follows:

[0153] 1.0 SiO2: 0.005 Al2O3: 0.1 TPAOH: 13.3 H2O: 0.05 seed crystal

[0154] Comparative Example 4

[0155] Referring to Comparative Example 2, an additional heteroatom Al2O3 is added, Al2O3 / SiO2=0.005, and the heteroatom is added in the form of aluminum sulfate octadecahydrate, and the other raw material proportions and reaction conditions remain unchanged, to prepare the Al-ZSM-5-NaOH molecular sieve product.

[0156] The amount of each reaction material is converted to molar ratio as follows:

[0157] 1.0 SiO2: 0.005 Al2O3: 0.1 TPACl: 0.225 NaOH: 13.3 H2O: 0.05 seed

[0158] Comparative Example 5

[0159] With reference to Comparative Example 1, heteroatom B2O3 was additionally added, B2O3 / SiO2= 0.017, the heteroatom was added in the form of boric acid, and the other raw material ratios and reaction conditions were unchanged, to prepare a B-ZSM-5-TPAOH molecular sieve product.

[0160] The amount of each reaction material is converted to molar ratio as follows:

[0161] 1.0 SiO2: 0.017 B2O3: 0.1 TPAOH: 13.3 H2O: 0.05 seed

[0162] Comparative Example 6

[0163] With reference to Comparative Example 2, heteroatom B2O3 was additionally added, B2O3 / SiO2= 0.017, the heteroatom was added in the form of boric acid, and the other raw material ratios and reaction conditions were unchanged, to prepare a B-ZSM-5-NaOH molecular sieve product.

[0164] The amount of each reaction material is converted to molar ratio as follows:

[0165] 1.0 SiO2: 0.017 B2O3: 0.1 TPACl: 0.225 NaOH: 13.3 H2O: 0.05 seed

[0166] Comparative Example 7

[0167] With reference to Comparative Example 1, heteroatom Ga2O3 was additionally added, Ga2O3 / SiO2= 0.017, the heteroatom was added in the form of gallium nitrate, and the other raw material ratios and reaction conditions were unchanged, to prepare a Ga-ZSM-5-TPAOH molecular sieve product.

[0168] The amount of each reaction material is converted to molar ratio as follows:

[0169] 1.0 SiO2: 0.017 Ga2O3: 0.1 TPAOH: 13.3 H2O: 0.05 seed

[0170] Comparative Example 8

[0171] With reference to Comparative Example 2, heteroatom Ga2O3 was additionally added, Ga2O3 / SiO2= 0.017, the heteroatom was added in the form of gallium nitrate, and the other raw material ratios and reaction conditions were unchanged, to prepare a Ga-ZSM-5-NaOH molecular sieve product.

[0172] The molar ratios of the reactants are calculated as follows:

[0173] 1.0SiO2:0.017Ga2O3:0.1TPACl:0.225NaOH:13.3H2O:0.05 Seed Crystals

[0174] The yield, thermal stability, and hydrothermal stability of the products in each embodiment and comparative example were measured, and the test results are as follows: Figures 13-15 .

[0175] according to Figure 13 Under near-neutral synthesis conditions, the yields of S-1 and various heteroatom-doped samples can reach 97%, with a maximum of 99.9%. However, under strongly alkaline conditions, regardless of whether NaOH or TPAOH is used as the alkali source, the yields are only around 83%–88%, with a maximum of only 88.3%, nearly 10% lower than the yields of samples synthesized under near-neutral conditions. This difference in yield under different synthesis conditions demonstrates that near-neutral synthesis has higher atom economy, with a much higher raw material utilization rate than traditional strongly alkaline synthesis, which is crucial for the industrial production of zeolites.

[0176] Figure 14 This is a comparison of the crystallinity of the samples before and after heat treatment at 1000℃ for 30 hours. Figure 15 This is a comparison of the crystallinity of the samples before and after hydrothermal treatment at 1000℃ in the presence of 100% H2O for 30 hours. Based on... Figure 14 Samples synthesized under near-neutral conditions showed 5%–8% higher thermal stability than those synthesized under strongly alkaline conditions. Figure 15 The samples synthesized under near-neutral conditions exhibit approximately 20% higher hydrothermal stability than S-1 and Al-ZSM-5 samples synthesized with NaOH as the alkali source, and 90% higher hydrothermal stability than S-1 samples synthesized with TPAOH as the alkali source. This high thermal and hydrothermal stability is crucial for the widespread industrial application of products synthesized under near-neutral conditions.

[0177] The above descriptions are merely several embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention. However, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for synthesizing molecular sieves under near neutral fluoride conditions, characterized in that, The method is performed according to the following steps: After the silicon source, the heteroatom, the template agent, the alkali source and the deionized water are mixed, the mixture is stirred uniformly at room temperature first, and then the crystal seed is added to continue stirring uniformly; then the mixture is transferred into a reaction kettle to perform hydrothermal reaction, and after the reaction is completed, the product is cooled to room temperature, and the target molecular sieve is obtained after filtration and drying, and the drying temperature is 80 DEG C; The alkali source used is urea; the silicon source used is calculated as SiO2, the heteroatom is calculated as M2O3, and the alkali source is calculated as CO(NH2)2, and the addition amount of each reaction raw material is controlled to make the molar ratio of SiO2, M2O3, template agent, CO(NH2)2, water and crystal seed in the range of 1:0~0.017:0.1~0.3:0.03~0.1:13.3~30:0.05~0.1; the pH value of the synthesis system after crystallization is 7~8.

2. The method of claim 1, wherein, Ammonia was used to replace urea as alkali source. The used ammonia was (NH2) - The molar amount of ammonia was twice that of urea. The water contained in ammonia was also calculated into the water amount, and deionized water was added to meet the molar ratio requirement.

3. The method according to claim 1 or 2, characterized in that, The silicon source used is any one of fine silica gel, silica sol or white carbon black.

4. The method according to claim 1 or 2, characterized in that, The heteroatom used is any one of aluminum sulfate octadecahydrate, boehmite, boric acid or gallium nitrate, and the M2O3 refers to Al2O3, B2O3 or Ga2O3.

5. The method according to claim 1 or 2, characterized in that, The template agent used is any one of tetrapropylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium bromide or trimethyladamantylammonium bicarbonate.

6. The method of claim 1 or 2, wherein, The mixed raw materials are stirred for 2h before the crystal seed is added.

7. The method of claim 1 or 2, wherein, The temperature of the hydrothermal reaction is controlled to be 160~180 DEG C, and the reaction time is 3~7 days.

8. The method of claim 1 or 2, wherein, The reaction kettle is a polytetrafluoroethylene stainless steel reaction kettle.

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