A high-silica FAU zeolite with a high proportion of exposed acidic sites, its preparation method and application

Abstract

The present invention relates to a high-silica FAU molecular sieve with a high proportion of exposed acid sites, a method for preparing the same by microstructure assembly, and an application thereof. The molecular sieve adsorbent has a FAU molecular sieve configuration, and its chemical composition molar ratio is Al2O3: mSiO2: nM2O. The elemental composition contains a relatively large amount of tetravalent element Si and a relatively small amount of trivalent element Al, and the molar ratio of oxides (m = SiO2 / Al2O3) is in the range of 5-20. This kind of molecular sieve is synthesized by using an initial gel prepared from crown ether, alkali, water, a silicon source and an aluminum source, adjusting the charge density of the double template agent, and assembling different cage structures of the FAU molecular sieve, while realizing the regulation of the proportion of exposed acid sites. Compared with commercial molecular sieves such as Beta and NaY, the high-silica FAU molecular sieve with a high proportion of exposed acid sites in the present invention can be applied to the adsorption and separation of phenolic substances in the liquid phase system, especially preferentially adsorbing a large amount of phenol in the phenol isooctane solution and preferentially adsorbing 2,5-dimethylphenol in the 2,5-dimethylphenol aqueous solution.

Description

Technical Field

[0001] The present invention relates to a high-silica FAU zeolite adsorbent with a high proportion of exposed acidic sites and a preparation method thereof, which can efficiently adsorb phenol in a phenol isooctane solution and 2,5-dimethylphenol in a 2,5-dimethylphenol aqueous solution, and belongs to the field of liquid-phase adsorption separation. Background Art

[0002] With the shortage of fossil fuels and the increasing carbon emission problem, biomass oil, as a clean alternative energy, has entered various energy-intensive industries. Biomass is mainly composed of low-price grass plants such as forestry wood, agricultural straw, and reeds, and its sources are relatively extensive and convenient to obtain. Among them, the main chemical components in biomass include cellulose, hemicellulose, and lignin. Compared with cellulose with glucose as the basic unit and hemicellulose with pyranose sugars as the basic unit, lignin forms an aromatic polymer through phenylpropane as the structural unit, and the structural units are connected by ether bonds and carbon-carbon bonds. Based on the basic units and composition methods of the three, the carbon-hydrogen-oxygen ratio of cellulose is 1:1.7:0.8, the carbon-hydrogen-oxygen ratio of lignin is 1:1.3:0.3, and due to the complexity of its composition units, lignin does not have a relatively unified molar coefficient ratio, but the carbon-oxygen ratio (~0.8) is significantly higher than that of lignin and is relatively close to the carbon-hydrogen-oxygen ratio of natural petroleum (1:1.6:0.05). However, considering the still high oxygen content in lignin, it needs to be reduced by high-temperature hydrocracking and other methods to finally obtain primary bio-oil raw materials mainly composed of phenols and long-chain alkanes. Since phenolic substances will produce toxic waste gases during combustion and harm human health, they must be removed before use. Although traditional pyrolysis can remove the phenolic substances inside, this method requires a large amount of energy consumption and high cost, which limits the development of the process. In contrast, the adsorption method has a quite broad application prospect due to its low cost, mild reaction conditions, environmental friendliness and other advantages.

[0003] Among the adsorption separation methods of phenolic substances, the currently widely used adsorption materials include activated carbon, resin, molecular sieve, etc. Activated carbon has high adsorption efficiency and a large surface area. However, the regeneration method using hot steam can cause polymerization reactions of phenolic materials on the surface of activated carbon, greatly reducing the sustainability of material utilization. Resin has a macroporous structure, can accommodate phenolic substances with a relatively large molecular dynamic diameter, and has good reversibility and regenerability, making it an ideal adsorbent. However, its selectivity for adsorbing different phenolic substances is relatively low; in high-concentration phenolic solutions, due to the swelling phenomenon, it cannot exhibit the excellent performance shown at low concentrations, so its actual application scenarios are limited. In contrast, molecular sieves, which can be effectively applied to small-scale separation occasions, have the characteristics of high adsorption capacity, high selectivity, high regenerability, and anti-toxicity, and are thus gradually being used for the separation of phenol in bio-oil.

[0004] As an adsorbent with a long history and excellent performance, molecular sieves are widely used in the industrial field. In the adsorption of phenols, molecular sieves have a relatively large pore volume and pore diameter and a relatively regular pore structure, showing good adsorption capacity. Ibrahim Khalil et al. carried out in-situ dehydration activation treatment on commercially available FAU-type molecular sieves and found that compared with common adsorbents such as ZSM-5, MCM-41, silica gel, alumina, and activated carbon, FAU has a relatively high phenol adsorption capacity in the phenol-isooctane system. At the same time, among FAU molecular sieves, the phenol adsorption capacity of high-silica FAU molecular sieves has been significantly improved (Journal of Hazardous Materials 2020, 384, 121397). However, the currently common high-silica FAU molecular sieves mainly use molecular sieve precursors with a relatively low silicon-aluminum ratio and increase the silicon-aluminum ratio value through multiple acid treatment processes to remove aluminum. Although this method improves the silicon-aluminum ratio to a certain extent, the specific surface area and strength will decrease significantly; at the same time, the defect sites generated during the dealumination process will make it difficult for the adsorbed phenol molecules to desorb, and side reactions such as coking and carbon deposition will occur during the thermal desorption process. In contrast, the one-step synthesis method avoids the acid treatment process and can effectively avoid the problems of decreased specific surface area, strength, and defect sites. Therefore, there is an urgent need to develop a new one-step synthesis method for high-silica FAU molecular sieves.

[0005] At present, the one-step synthesis of high-silica FAU zeolite is mainly achieved by using different organic structure-directing agents for synthesis. Patent CN 109502604 B reported that choline, which is relatively inexpensive and green, was used as the organic structure-directing agent to prepare FAU zeolite with a silica-alumina ratio of 6.3. Patent CN 105439168 A further used tetraethylammonium hydroxide and tetrabutylammonium hydroxide with a smaller charge density for regulation, and increased the silica-alumina ratio to 6.6 and 6.8. In addition, Patent CN 111825104 A also selected N,N-dimethyl-3,5-dimethylpiperidinium hydroxide with a larger molecular weight and a higher degree of charge dispersion to provide a directing effect, and the silica-alumina ratio was also increased to a relatively high level. However, the methods reported in the above patents all rely on reducing the charge density of the organic structure-directing agent to increase the silica-alumina ratio, which will reduce the number of balanced aluminum sites in the supercage, resulting in a decrease in the number of acidic sites in the supercage. Ibrahim Khalil et al. proved that the adsorption of phenol by FAU zeolite requires the hydroxyl groups (acidic sites) in the supercage of the zeolite to act and selectively separate (Chemical Engineering Journal 2020, 402, 126264). Therefore, the method of reducing the charge density will also lead to a decrease in the number of acidic sites in the supercage of FAU zeolite, resulting in a decrease in the adsorption activity and selectivity of phenol. Therefore, it has become an urgent task to develop a one-step synthesis method for high-silica FAU zeolite with a high proportion of exposed acidic sites.

[0006] In view of the fact that there is no reported synthesis method for directionally regulating the proportion of acidic sites in the supercage of high-silica FAU zeolite at present, the present invention adjusts the dual organic structure-directing agents with different charge densities, directionally assembles different cage structures of FAU zeolite, and synthesizes high-silica FAU zeolite with a high proportion of exposed acidic sites in one step. Finally, it is applied to the adsorption and separation of phenolic substances in the liquid phase system, which can preferentially adsorb a large amount of phenol in the phenol-isooctane solution and preferentially adsorb a large amount of 2,5-dimethylphenol in the 2,5-dimethylphenol aqueous solution. Summary of the Invention

[0007] The invention purpose, implementation key points, synthesis process and specific implementation manner of the present invention will be elaborated in detail below:

[0008] The purpose of the present invention is to provide a high-silica FAU zeolite adsorbent with a high proportion of exposed acidic sites. By adjusting the dual organic structure-directing agents with different charge densities, different cage structures of FAU zeolite are directionally assembled, and high-silica FAU zeolite with a high proportion of exposed acidic sites is synthesized in one step. It can preferentially adsorb a large amount of phenol in the separation of phenol and isooctane, and preferentially adsorb a large amount of 2,5-dimethylphenol in the separation of 2,5-dimethylphenol aqueous solution.

[0009] To achieve the above object, the present invention uses silicon-containing oxide and aluminum-containing oxide as the initial gel, and by adjusting the composition of templating agents with different charge densities and selecting appropriate synthesis conditions, a high-silica FAU zeolite with a high proportion of exposed acid sites is successfully synthesized, obtaining a zeolite with a high acid site to aluminum site ratio and a large adsorption capacity for phenols, which is very suitable as an adsorbent for liquid separation, especially as an adsorbent for phenol in the separation of phenol and isooctane, and 2,5-dimethylphenol in the separation of 2,5-dimethylphenol and water.

[0010] 1. The technical solution of the present invention is a high-silica FAU zeolite with a high proportion of exposed acid sites, and its chemical composition molar ratio is aYO2:bX2O3:cM2O, where M is a monovalent element or a monovalent cation. When performing X-ray diffraction measurement, characteristic peaks are present at least at the following 4 crystal plane spacings d: the first crystal plane spacing d = 14.2 ± 0.2, the second crystal plane spacing d = 8.7 ± 0.2, the third crystal plane spacing d = 7.4 ± 0.2, and the fourth crystal plane spacing d = 5.6 ± 0.2.

[0011] 2. The zeolite of the present invention has the FAU zeolite configuration recognized by the International Zeolite Association (IZA). Its characteristics are confirmed by X-ray diffraction measurement. However, in the actual measurement process, due to differences in the measurement environment, crystal growth direction, elemental composition within the crystal, adsorbed substances, and crystal defect conditions, there are certain differences between the positions of each peak and the peak intensities of each peak actually measured and the positions and peak intensities of each peak specified by IZA.

[0012] 3. The X-ray diffraction measurement light source is not limited to Cu Kα, and Co Kα, Mo Kα, and Ag Kα can also be used as the light source for phase analysis. The morphological form of the test raw material can be powder, emulsion, or solid particles.

[0013] 4. The zeolite of the present invention is synthesized using macromolecular organic templating agents with different charge densities. Therefore, after the hydrothermal reaction is completed, the synthesized zeolite precursor needs to be heated and calcined to remove the macromolecular templating agent.

[0014] 5. In the chemical composition of the above FAU zeolite adsorbent, the ratio of the oxide of the tetravalent element Y to the oxide of the trivalent element X is m, and 5 ≤ m ≤ 20. Among them, 10 ≤ a ≤ 20, 0.05 ≤ b ≤ 0.4, and 0 < c ≤ 2.5.

[0015] 6. The above FAU zeolite adsorbent is measured by pyridine infrared adsorption spectroscopy. The acid amount is 650 - 950 μmol·g -1 , preferably 750 - 950 μmol·g -1 , more preferably 800 - 950 μmol·g -1The Lewis acid amount is 90 - 220 μmol·g -1 , preferably 130 - 190 μmol·g -1 , more preferably 150 - 170 μmol·g -1 . The ratio of the molar amount of acid sites to the total molar amount of X sites is 0.1 - 0.4, preferably 0.15 - 0.4, more preferably 0.2 - 0.4 (representing exposed acidic sites).

[0016]

Synthesis method of molecular sieve

[0017] The present invention provides a high - silica FAU molecular sieve adsorbent with a high proportion of exposed acidic sites. By adjusting the double organic template agents with different charge densities, the different cage structures of FAU molecular sieve are directionally assembled, and a high - silica FAU molecular sieve with a high proportion of exposed acidic sites is synthesized at one time. It can be effectively applied to the adsorption and separation of liquids, especially the adsorption and separation of phenol - isooctane and the separation of 2,5 - dimethylphenol in water. The synthesis method is hydrothermal method. In the chemical composition of the molecular sieve, Y is Si element and X is Al element. The specific preparation steps are as follows:

[0018] (a) Add the Al source, deionized water, Si source, inorganic structure - directing agent, and FAU seed crystals into the reaction kettle in sequence, then add the double organic template agents with different charge densities, stir evenly to obtain the initial gel, transfer it to the reaction kettle, and obtain the precursor of the molecular sieve described in claim 1 after hydrothermal synthesis reaction;

[0019] (b) Filter, wash, and dry the molecular sieve precursor after the reaction in step (a), and then heat and activate to remove the organic matter in the molecular sieve precursor to obtain the calcined matrix;

[0020] (c) Mix the calcined matrix obtained in step (b) with the solution containing M compound, and perform ion exchange several times at a certain temperature, and the ion exchange time for each time is several hours; the salt solution of monovalent element contains one or more ions of monovalent elements.

[0021] (d) Calcine the molecular sieve ion - exchanged with metal element ions obtained in step (c) in the air, cool it after calcination is completed, take it out and store it in a drying dish.

[0022] (e) According to needs, steps (c) and (d) can be repeated several times to achieve the optimal loading amount of M oxide.

[0023] <Molecular sieve synthesis raw materials>

[0024] The Al source described in step (a) includes, but is not limited to, one or more of alkoxyaluminum, aluminum salts, activated alumina, pseudoboehmite, or pseudo-boehmite, preferably alkoxyaluminum, aluminum salts, activated alumina, or pseudoboehmite, more preferably alkoxyaluminum or aluminum salts. Its mass concentration in the initial gel is 3-10%, preferably 4-7%.

[0025] The Si source described in step (a) includes, but is not limited to, one or more of silica sol, silica gel, activated silica, or orthosilicate, preferably silica sol, silica gel, or activated silica, more preferably silica sol and silica gel. Its mass concentration in the initial gel is 5-25%, preferably 10-25%.

[0026] The inorganic structure-directing agent described in step (a) includes, but is not limited to, one or more of sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium chloride, potassium chloride, cesium chloride, preferably sodium hydroxide, potassium hydroxide, sodium chloride, or potassium chloride, more preferably sodium hydroxide or sodium chloride. Its mass concentration in the initial gel is 0.2-0.8%, preferably 0.3-0.7%.

[0027] The SAR value of the FAU seed crystals described in step (a) is 50-70, preferably 60. Its mass concentration in the initial gel is 0.6-1.8%. SAR is the molar ratio of SiO2 to Al2O3.

[0028] The template agent in the chemical composition of the FAU molecular sieve adsorbent described in step (a) is a certain macromolecular compound, and its composition includes, but is not limited to, electron-donating elements such as O, C, N, etc., preferably C, N, more preferably N. The macromolecular template agent includes one or a mixture of several of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, choline, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. Its mass concentration in the initial gel is 14-28%, preferably 17-21%.

[0029] In step (c), the M compound includes oxides, inorganic salts, organic salts of one or more of the elements H, Li, Na, K, Cs, Ag, or NH4 + ions, or a mixture of any several of them; the solid-liquid ratio of the calcined matrix to the solution containing the M compound in step (c) is 1 g: 4-6 mL, and the molar concentration of the solution containing the M compound is 2-8 mol / L. The number of ion exchange times is selected from 1-10 times, preferably 4-6 times, and the ion exchange time for each time is 1 h. During the repeated implementation of step (c), the types of monovalent elements can be different.

[0030] <Preparation of the initial gel>

[0031] In step (a) of the present invention, the formulation process of the initial gel is affected by the dissolution sequence and dissolution conditions. Generally, raw materials containing aluminum oxide, raw materials containing silicon oxide, inorganic salts, and seeds are added, stirred and aged, then the template agent is dissolved in water, and then the initial gel is obtained. The aging time is selected to be 12 - 36 h, preferably 20 - 28 h.

[0032] <Hydrothermal synthesis>

[0033] In the hydrothermal synthesis process of step (a), the above-mentioned initial gel together with the reaction kettle is transferred into a pressure-resistant container, tightened and heated in a rotary reaction furnace with hot air for reaction, or left to react in an oven at a certain temperature. The reaction temperature of the hydrothermal synthesis is usually controlled above 100 °C, preferably above 120 °C, more preferably above 130 °C; the upper limit temperature of the reaction is controlled below 200 °C, preferably below 180 °C, more preferably below 150 °C. The reaction time is usually controlled above 3 d, preferably above 4 d, more preferably above 5 d; the upper limit of the reaction time is usually controlled below 25 d, preferably below 20 d, more preferably below 15 d.

[0034] <Post-treatment after hydrothermal synthesis>

[0035] In the processes of filtration, washing, and drying in step (b), the drying process temperature is selected to be 60 - 200 °C, preferably 80 - 100 °C. The drying time is selected to be 12 - 36 h, preferably 12 - 24 h. The molecular sieve after drying needs to be heated and calcined to remove the template agent inside the molecular sieve to have adsorption and catalytic properties. The calcination temperature is selected to be 400 - 800 °C, preferably 500 - 600 °C. The calcination time is selected to be 0.5 - 24 h, preferably 1 - 24 h, more preferably 3 - 10 h.

[0036] In step (c), the solid-liquid ratio of the calcined matrix to the solution containing compound M is 1 g : 4 - 6 mL, and the molar concentration of the solution containing compound M is 2 - 8 mol / L. The number of ion exchange times is selected to be 1 - 10 times, preferably 4 - 6 times, and the ion exchange time for each time is 1 h.

[0037] The calcination temperature of the ion-exchanged molecular sieve obtained in step (d) is selected to be 400 - 800 °C, preferably 450 - 600 °C. The calcination time is selected to be 3 - 12 h, preferably 5 - 9 h. The FAU molecular sieve adsorbent in actual use is in the form of raw powder or formed state after granulation.

[0038]

Use of the present invention

[0039] The FAU molecular sieve described in the present invention can be applied to the adsorption separation of phenol isooctane solution and the adsorption separation of 2,5-dimethylphenol aqueous solution. Compared with the traditional FAU molecular sieve, it can preferentially adsorb a large amount of phenol and 2,5-dimethylphenol.

[0040] The FAU zeolite adsorption separation liquid described above can be operated at 283 - 313 K, preferably 293 - 303 K.

[0041] The FAU zeolite adsorption separation liquid described above can be operated at a mass fraction of 0.1 - 1.5 w.t.%.

[0042]

Advantages of the present invention

[0043] (1) In the present invention, the synthesis of high-silica-alumina FAU zeolite uses dual templates with different charge densities. The prepared product has a high proportion of exposed acidic sites, which can avoid the problem of low proportion of effective active sites in the traditional one-step synthesis of high-silica Y zeolite and improve the adsorption efficiency of the zeolite. At the same time, compared with commercial Y zeolite, it effectively avoids the decrease in specific surface area, strength and defects caused by acid treatment, so as to avoid the decrease in adsorption activity and regeneration performance, as well as problems such as coking and carbon deposition during the activation treatment process.

[0044] (2) The FAU zeolite in the present invention has a high silica-alumina ratio, and the amounts of H and Na ions used to balance the framework charge are small. At present, the costs of Li and Ag used for ion exchange are both high and the amounts used are large. Therefore, using the H-FAU and Na-FAU zeolites with the best performance in the present invention is beneficial to reducing the manufacturing cost of the zeolite.

[0045] (3) The high-silica-alumina FAU zeolite in the present invention has low polarity and strong hydrophobicity, which can avoid high powder loss rate during the manufacture of the adsorbent.

[0046] (4) The templates for preparing FAU zeolite in the present invention are easy to obtain and inexpensive, which can effectively reduce the manufacturing cost in industrial production. Description of the drawings

[0047] Table 1 is the characteristic crystal plane spacing of Na-FAU-1 in Example 1;

[0048] Table 2 is the characteristic crystal plane spacing of Na-FAU-2 in Example 2;

[0049] Table 3 is the characteristic crystal plane spacing of Na-FAU-3 in Example 3;

[0050] Table 4 is the characteristic crystal plane spacing of Na-FAU-4 in Example 4;

[0051] Table 5 is the amounts of B acid, L acid and total acid of different zeolites in Comparative Example 1;

[0052] Table 6 is the adsorption capacity of different zeolites for phenol in phenol isooctane in Comparative Example 1;

[0053] Table 7 is the adsorption capacity of different zeolites for 2,5-dimethylphenol in 2,5-dimethylphenol water in Comparative Example 2;

[0054] Figure 1 It is a schematic diagram of the XRD test results of Na-FAU-1 in Example 1;

[0055] Figure 2 It is a schematic diagram of the XRD test results of Na-FAU-2 in Example 2;

[0056] Figure 3 It is a schematic diagram of the XRD test results of Na-FAU-3 in Example 1;

[0057] Figure 4 It is a schematic diagram of the XRD test results of Na-FAU-4 in Example 1. Detailed implementation manners

[0058] The present invention will be described in detail below through examples, but the present invention is not limited to these examples.

[0059]

Instrument characterization

[0060] <X-ray diffraction determination>

[0061] The X-ray diffraction determination instrument is Panalytical X’Pert PRO, the detection light source is CuKα, the tube voltage is 40 kV, the tube current is 40 mA, the detection angle range is 5-50°, and the detection time is 10 min. The present invention determines the phase structure of the synthesized molecular sieve by X-ray diffraction. The ground sample powder is added into the square hole on the glass plate, and then the glass plate is inserted into the axis position of the goniometer. Under the irradiation of the Cu Kα light source, the probe rotates at a speed of 2θ / min. In addition, the light source is not limited to CuKα, and Co Kα, Mo Kα, and Ag Kα can also be used as the light source for phase analysis. The raw material form for testing can be powder, emulsion or solid particles.

[0062] <Inductively coupled plasma spectroscopy determination>

[0063] The inductively coupled plasma spectroscopy (ICP) determination is carried out using PerkinElmer Optima8x00. The present invention determines the contents of the tetravalent element Si, the trivalent element Al, and the monovalent element or monovalent cation M in the synthesized molecular sieve by inductively coupled plasma spectroscopy. The standard sample is diluted to make a concentration gradient absorption curve. The sample is dissolved with hydrofluoric acid and then diluted with water, and then the concentration of each element in the sample is determined by measuring the absorption peak intensity.

[0064] <Determination of the acid amount of molecular sieve>

[0065] The acidic active sites of the molecular sieve were analyzed using pyridine adsorption and FT-IR spectroscopy (Nicolet 6700 spectrometer equipped with a DTGS detector). The sample was pressed into a self-supporting wafer and degassed under vacuum at 400 °C for 1 h before adsorption measurements. After cooling to 50 °C, 25 mbar of gaseous pyridine was introduced into the sample cell until saturation. Thermal desorption was carried out at 150 °C to remove weakly adsorbed pyridine species. The amounts of Lewis acid and -1 Brønsted acid sites were quantified by integrating the areas of the absorption bands at 1455 and 1554 cm respectively. Absorption extinction coefficients: ε(B) = 1.67 cm·μmol -1 and ε(L) = 2.22 cm·μmol -1 .

[0066] <Liquid Adsorption Measurement>

[0067] Liquid volumetric adsorption measurement was carried out using an Agilent Q2000 gas chromatograph. The liquid adsorption capacity of the present invention was tested by liquid adsorption measurement. Phenol / isooctane was measured at 298 K. Approximately 200 mg of the sample was placed in a beaker and then placed in a constant temperature water bath at 25 °C and stirred for 2 h. The adsorbed solution was allowed to settle, and the supernatant was taken and injected into the gas chromatograph for measurement. All samples were calcined at 400 - 600 °C for more than 6 h before adsorption.

[0068]

Example

[0069] The FAU seeds in the examples of the present invention were purchased from Tianjin Nanhua Catalyst Co., Ltd., model NKF-3.

[0070] <Example 1>

[0071] 2.6 g of NaAlO2 (mass percentage of NaAlO2 > 98%) was added to 20 g of water and dissolved, and then 2 g of a 20 w.t.% NaOH aqueous solution (mass percentage of NaOH > 96%), 14 g of choline hydroxide (45% aqueous), and 6 g of an aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (35% aqueous) were added in sequence and stirred evenly. After the solution became clear, 15 g of Ludox AS-40 (40% aqueous silicon solution) was added dropwise, and stirring was continued until the solution was fully mixed; 1 g of FAU seeds (SAR = 60) was added and aged for 48 h to obtain an initial gel. The gel mixture was transferred to a pressure-resistant container and sealed, and dynamically crystallized at a reaction temperature of 130 °C and autogenous pressure for 5 d. After the hydrothermal reaction was completed, the reaction solution was cooled, filtered, and washed to obtain a crystalline product. The obtained crystals were dried at 100 °C for 12 h to obtain a powdery product.

[0072] The obtained powdery product was calcined in a muffle furnace at 550 °C for 6 h to obtain the powdery product Na-FAU-1. The obtained product was subjected to phase analysis by XRD. The crystal plane spacings at the positions of the characteristic peaks in Na-FAU-1 are shown in Table 1. The schematic diagram of the XRD test results is shown in Figure 1 , indicating that the synthesized molecular sieve has the FAU molecular sieve configuration recognized by IZA. The elemental composition of the above sample was analyzed by ICP, and the analysis results showed that the SAR value of Na-FAU-1 was 12.0.

[0073] 5 g of the obtained Na-FAU-1 was contacted with 25 mL of 6 mol / L ammonium chloride solution at 80 °C for 4 times, 1 h each time. Between each contact, filtration and drying were carried out to obtain NH4-FAU-1. The obtained molecular sieve powder was calcined in air: heated to 450 °C at a rate of 1 °C / min, maintained at 450 °C for 10 min, then continued to be heated to 500 °C at a rate of 1 °C / min, then maintained at 500 °C for 5 h, and then cooled to 100 °C to obtain H-FAU-1 (chemical composition: Al2O3: 12SiO2: H2O). The dried sample was taken out and stored in a desiccator.

[0074] The above Na-FAU-1 and H-FAU-1 were used for the adsorption separation of phenol and isooctane. The adsorption capacity of the samples was measured on an Agilent Q2000. The adsorbed liquids were phenol (99%) and isooctane (99%). The prepared Na-FAU-1 or H-FAU-1 was put into a 1 w.t.% phenol isooctane solution according to a solid-liquid ratio of 20 g / L, and stirred at a speed of 500 r / min. The adsorption process lasted for 2 h in total. To avoid the influence of tiny molecular sieve particles on the adsorption results, the reaction liquid was allowed to stand for 2 h, and the supernatant was taken. It was successively extracted with 45-μm and 22-μm filter tips, and the obtained solution was put into a gas chromatograph for determination. Determination parameters: injection port 300 °C, oven 90 °C, column temperature was raised from 90 to 190 °C at a heating rate of 40 °C / min and lasted for 2 min, and the detector was a hydrogen flame detector with a temperature of 300 °C. The adsorption capacities of Na-FAU-1 and H-FAU-1 for phenol were 21 mg / g and 213 mg / g, respectively.

[0075] Table 1 Characteristic crystal plane spacings of Na-FAU-1

[0076] Interplanar spacing (d) 1 14.206 2 8.702 3 7.421 4 5.632 5 4.873 6 4.6713 7 4.334 8 4.137

[0077] <Example 2>

[0078] 70 g of TEAOH (35% aqueous), 5 g of aluminum sec-butoxide (mass fraction of aluminum sec-butoxide > 98%) were added to 40 g of water and dissolved. Then, 34 g of tetraethyl orthosilicate (mass percentage content calculated as SiO2 > 28%) was added successively, and the mixture was stirred evenly. After the solution became clear, 5 g of choline chloride (mass fraction of choline chloride > 98%), 0.5 g of NaCl (mass fraction of NaCl > 99.5%) and 1 g of FAU seed crystal (SAR = 60) were gradually added, and aging was carried out for 24 h to obtain an initial gel. The gel mixture was transferred into a pressure-resistant container and sealed, and dynamically crystallized at a reaction temperature of 100 °C and autogenous pressure for 22 d. After the hydrothermal reaction was completed, the reaction solution was cooled, filtered and washed to obtain a crystalline product. The obtained crystals were dried at 100 °C for 12 h to obtain a powdery product.

[0079] The obtained powdery product was calcined in a muffle furnace at 550 °C for 6 h to obtain a powdery product Na-FAU-2. The obtained product was subjected to phase analysis by XRD. The crystal plane spacing at the characteristic peak in Na-FAU-2 is shown in Table 2. The schematic diagram of the XRD test results is shown in Figure 2 , indicating that the synthesized molecular sieve has the FAU molecular sieve configuration recognized by IZA. The elemental composition of the above sample was analyzed by ICP. The analysis results show that the SAR value of Na-FAU-2 is 6.8.

[0080] 5 g of the obtained Na-FAU-2 was contacted with 25 mL of 6 mol / L ammonium chloride solution at 80 °C for 4 times, 1 h each time. Between each contact, filtration and drying were carried out to obtain NH4-FAU-2. The obtained molecular sieve powder was calcined in air: heated to 450 °C at a rate of 1 °C / min, maintained at 450 °C for 10 min, then continued to be heated to 500 °C at a rate of 1 °C / min, then maintained at 500 °C for 5 h, and then cooled to 100 °C to obtain H-FAU-2 (chemical composition: Al2O3: 6.8SiO2: H2O). The dried sample was taken out and stored in a drying dish.

[0081] The above Na-FAU-2 and H-FAU-2 were used for the adsorption separation of phenol and isooctane. The adsorption capacity of the samples was measured on the Q2000 of Agilent. The adsorbed liquids were phenol (99%) and isooctane (99%). The prepared Na-FAU-2 or H-FAU-2 was added into a 1 w.t.% phenol-isooctane solution at a solid-liquid ratio of 20 g / L, and stirred at a speed of 500 r / min. The adsorption process lasted for 2 h in total. To avoid the influence of tiny molecular sieve particles on the adsorption results, the reaction liquid was allowed to stand for 2 h, and the supernatant was taken and extracted successively with 45-μm and 22-μm filter tips. The obtained solution was put into a gas chromatograph for determination. The determination parameters were as follows: the injection port was 300 °C, the oven was 90 °C, the column temperature was raised from 90 °C to 190 °C at a heating rate of 40 °C / min and held for 2 min, and the detector was a flame ionization detector with a temperature of 300 °C. The adsorption capacities of Na-FAU-2 and H-FAU-2 for phenol were 9 mg / g and 160 mg / g respectively.

[0082] Table 2 Characteristic crystal plane spacings of Na-FAU-2

[0083]

[0084]

[0085] <Example 3>

[0086] 50 g of TPAOH (40% aqueous), 2 g of aluminum sec-butoxide (mass fraction of aluminum sec-butoxide > 98%) were added to 40 g of water and dissolved, and then 34 g of tetraethyl orthosilicate (mass percentage content calculated as SiO2 > 28%) was added successively and stirred evenly. After the solution became clear, 5 g of choline chloride (mass fraction of choline chloride > 98%), 0.5 g of NaCl (mass fraction of NaCl > 99.5%) and 1 g of FAU seed crystal (SAR = 60) were gradually added, and aged for 24 h to obtain an initial gel. The gel mixture was transferred into a pressure-resistant container and sealed, and crystallized dynamically at a reaction temperature of 120 °C and autogenous pressure for 14 d. After the hydrothermal reaction was completed, the reaction solution was cooled, filtered and washed to obtain a crystalline product. The obtained crystals were dried at 100 °C for 12 h to obtain a powdery product.

[0087] The obtained powdery product was calcined in a muffle furnace at 550 °C for 6 h to obtain a powdery product Na-FAU-3. The obtained product was analyzed by XRD for its phase. The crystal plane spacings at the characteristic peaks in Na-FAU-3 are shown in Table 3, and the schematic diagram of the XRD test results is shown in Figure 3 , indicating that the synthesized molecular sieve has the FAU molecular sieve configuration recognized by IZA. The elemental composition of the above samples was analyzed by ICP, and the analysis results showed that the SAR value of Na-FAU-3 was 11.2.

[0088] The obtained 5 g of Na-FAU-3 was contacted with 25 mL of 6 mol / L ammonium chloride solution at 80 °C for 4 times, each time for 1 h. Between each contact, filtration and drying were carried out to obtain NH4-FAU-3. The obtained molecular sieve powder was calcined in air: heated to 450 °C at a rate of 1 °C / min, maintained at 450 °C for 10 min, then continued to be heated to 500 °C at a rate of 1 °C / min, then maintained at 500 °C for 5 h, and then cooled to 100 °C to obtain H-FAU-3 (chemical composition: Al2O3: 11.2SiO2: H2O). After taking out the dried sample, it was placed in a drying dish for storage.

[0089] The above-mentioned Na-FAU-3 and H-FAU-3 were used for the adsorption separation of phenol and isooctane. The adsorption capacity of the samples was measured on the Q2000 of Agilent. The adsorbed liquids were phenol (99%) and isooctane (99%). The prepared Na-FAU-3 or H-FAU-3 was put into a 1 w.t.% phenol-isooctane solution according to the solid-liquid ratio of 20 g / L, and stirred at a rotation speed of 500 r / min. The adsorption process lasted for 2 h in total. In order to avoid the influence of tiny molecular sieve particles on the adsorption results, the reaction liquid was allowed to stand for 2 h, and the supernatant was taken. It was successively extracted with 45-micron and 22-micron filter tips, and the obtained solution was put into a gas chromatograph for determination. The determination parameters were as follows: injection port 300 °C, oven 90 °C, column temperature was raised from 90 to 190 °C at a heating rate of 40 °C / min and lasted for 2 min, and the detector was a hydrogen flame detector with a temperature of 300 °C. The adsorption capacities of Na-FAU-3 and H-FAU-3 for phenol were 35 mg / g and 260 mg / g respectively.

[0090] Table 3 Characteristic crystal plane spacings of Na-FAU-3

[0091] Interplanar spacing (d) 1 14.179 2 8.665 3 7.343 4 5.648 5 4.723 6 4.127 7 3.870 8 3.740

[0092] <Example 4>

[0093] Dissolve 50 g of TBAOH (40% aqueous), 2 g of aluminum sec-butoxide (mass fraction of aluminum sec-butoxide > 98%) in 40 g of water, and then successively add 34 g of tetraethyl orthosilicate (mass percentage content calculated as SiO2 > 28%), and stir evenly. After the solution becomes clear, gradually add 5 g of choline chloride (mass fraction of choline chloride > 98%), 0.5 g of NaCl (mass fraction of NaCl > 99.5%), and 1 g of FAU seed crystal (SAR = 60), and age for 24 h to obtain the initial gel. Transfer the gel mixture into a pressure-resistant container and seal it, and carry out dynamic crystallization at a reaction temperature of 130 °C and autogenous pressure for 6 d. After the hydrothermal reaction is completed, cool the reaction solution, filter, and wash to obtain the crystalline product. Dry the obtained crystals at 100 °C for 12 h to obtain a powdery product.

[0094] The obtained powdery product was calcined in a muffle furnace at 550 °C for 6 h to obtain the powdery product Na-FAU-4. The obtained product was subjected to phase analysis by XRD. The interplanar spacings of the characteristic peaks in Na-FAU-8 are shown in Table 4. The schematic diagram of the XRD test results is shown in Figure 4 , indicating that the synthesized molecular sieve has the FAU molecular sieve configuration recognized by IZA. The elemental composition of the above sample was analyzed by ICP, and the analysis results showed that the SAR value of Na-FAU-4 was 18.2.

[0095] Contact 5 g of the obtained Na-FAU-4 with 25 mL of 6 mol / L ammonium chloride solution at 80 °C for 4 times, each time for 1 h, and filter and dry between each contact to obtain NH4-FAU-4. The obtained molecular sieve powder was calcined in air: heated at a rate of 1 °C / min to 450 °C, maintained at 450 °C for 10 min, then continued to be heated at a rate of 1 °C / min to 500 °C, then maintained at 500 °C for 5 h, and then cooled to 100 °C to obtain H-FAU-4 (chemical composition: Al2O3: 18.2SiO2: H2O). The dried sample was taken out and stored in a drying dish.

[0096] The above-mentioned Na-FAU-4 and H-FAU-4 were used for the adsorption separation of phenol and isooctane. The adsorption capacity of the samples was measured on an Agilent Q2000. The adsorbed liquids were phenol (99%) and isooctane (99%). The prepared Na-FAU-4 or H-FAU-4 was added to a 1 w.t.% phenol-isooctane solution at a solid-liquid ratio of 20 g / L and stirred at a speed of 500 r / min. The adsorption process lasted for 2 h in total. To avoid the influence of tiny molecular sieve particles on the adsorption results, the reaction liquid was allowed to stand for 2 h, and the supernatant was taken and filtered successively with 45-μm and 22-μm filter tips. The obtained solution was put into a gas chromatograph for determination. The determination parameters were as follows: the injection port was at 300 °C, the oven was at 90 °C, the column temperature was raised from 90 °C to 190 °C at a heating rate of 40 °C / min and held for 2 min, and the detector was a flame ionization detector at 300 °C. The adsorption capacities of Na-FAU-4 and H-FAU-4 for phenol were 42 mg / g and 303 mg / g, respectively.

[0097] Table 4 Characteristic crystal plane spacings of Na-FAU-4

[0098] Interplanar spacing (d) 1 14.175 2 8.712 3 7.440 4 5.648 5 4.729 6 4.350 7 3.888 8 3.748

[0099] <Comparative Example 1>

[0100] A certain amount of commercial molecular sieves were taken, namely NKF-1 from Nankai (named H-FAU-5 with a silica-alumina ratio of 11), NKF-2 (named H-FAU-6 with a silica-alumina ratio of 22), NKF-3 (named H-FAU-8 with a silica-alumina ratio of 33), NKF-4 (named H-FAU-9 with a silica-alumina ratio of 40), and TOSOH-1 from TOSOH (named H-FAU-7 with a silica-alumina ratio of 30). They were calcined in air to ensure the removal of impurities: heated to 580 °C at a rate of 5 °C / min, maintained at 580 °C for 6 h, and then cooled to 100 °C. The dried samples were taken out and stored in a desiccator.

[0101] The acid amounts of the above-prepared hydrogen-type molecular sieves and commercial molecular sieves were measured. The samples were pressed into self-supporting wafers and degassed under vacuum at 400 °C for 1 h before adsorption measurement. After cooling to 50 °C, 25 mbar of gaseous pyridine was introduced into the sample cell until saturation. Thermal desorption was carried out at 150 °C to remove weakly adsorbed pyridine species. The amounts of Lewis acid and -1 acid sites were quantified by integrating the areas of the absorption bands at 1455 and 1554 cm

[0102] The adsorption capacities of the molecular sieves prepared above and commercial molecular sieves for phenol adsorption samples were measured on an Agilent Q2000. The adsorbed liquids were phenol (99%) and isooctane (99%). The prepared molecular sieves were added to a 1 w.t.% phenol isooctane solution at a solid-liquid ratio of 20 g / L and stirred at a speed of 500 r / min. The adsorption process lasted for 2 h. To avoid the influence of tiny molecular sieve particles on the adsorption results, the reaction liquid was allowed to stand for 2 h, and the supernatant was taken. It was successively extracted using 45-μm and 22-μm filter tips, and the obtained solution was put into a gas chromatograph for determination. The measurement parameters were as follows: injection port temperature 300 °C, oven temperature 90 °C, column temperature was increased from 90 °C to 190 °C at a heating rate of 40 °C / min and held for 2 min, and the detector was a flame ionization detector with a temperature of 300 °C. The phenol adsorption amounts of different commercial molecular sieves under normal pressure are shown in Table 6.

[0103] <Comparative Example 2>

[0104] The adsorption capacities of the molecular sieves prepared above and commercial molecular sieves for 2,5-dimethylphenol adsorption samples were measured on a SHIMADZU UV-2600. The adsorbed liquids were 2,5-dimethylphenol (99%) and deionized water. The prepared molecular sieves were added to a 2,5-dimethylphenol aqueous solution with a mass fraction of 0.2 g / L at a solid-liquid ratio of 20 g / L and stirred at a speed of 700 r / min. The adsorption process lasted for 24 h. To avoid the influence of tiny molecular sieve particles on the adsorption results, the reaction liquid was allowed to stand for 2 h, and the supernatant was taken. It was successively extracted using 45-μm and 22-μm filter tips, and the obtained solution was put into an ultraviolet spectrophotometer for determination. The measurement parameter was a wavelength of 260 nm. Samples were taken 3 times and the average value was taken. The 2,5-dimethylphenol adsorption amounts of commercial molecular sieves under normal pressure are shown in Table 7.

[0105] Table 5 The amounts of Brønsted acid, Lewis acid and total acid of different molecular sieves

[0106]

[0107]

[0108] Table 6 The phenol adsorption capacities of different molecular sieves for phenol isooctane solution

[0109] Molecular sieve name Adsorption capacity (mg / g) Na-FAU-1 21 Na-FAU-2 9 Na-FAU-3 35 Na-FAU-4 42 H-FAU-1 213 H-FAU-2 160 H-FAU-3 260 H-FAU-4 303 H-FAU-5 44 H-FAU-6 96 H-FAU-7 112 H-FAU-8 137 H-FAU-9 141

[0110] Table 7 The 2,5-dimethylphenol adsorption capacities of different molecular sieves

[0111]

[0112]

[0113] The content described in this specification is only an enumeration of the implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as limited to the specific forms stated in the embodiments.

Claims

1. A high-silica FAU zeolite with a high proportion of exposed acidic sites, having a chemical composition molar ratio of aYO2:bX2O3:cM2O, where M is a monovalent element or a monovalent cation; when performing X-ray diffraction measurement, it has characteristic peaks at least at the following 4 crystal plane spacings d: the first crystal plane spacing d = 14.2 ± 0.2, the second crystal plane spacing d = 8.7 ± 0.2, the third crystal plane spacing d = 7.4 ± 0.2, and the fourth crystal plane spacing d = 5.6 ± 0.2; It has the FAU zeolite configuration recognized by the International Zeolite Association (IZA); the elemental composition contains more tetravalent element Y and less trivalent element X. As determined by nuclear magnetic resonance spectroscopy and inductively coupled plasma spectroscopy, the molar ratio of oxides m = YO2 / X2O3, and 5 ≤ m ≤ 20; where 10 ≤ a ≤ 20, 0.05 ≤ b ≤ 0.4, and 0 < c ≤ 2.5; Quantitatively determined by pyridine infrared adsorption spectroscopy, the amount of Brönsted acid is 650 - 950 μmol·g -1 ; the amount of Lewis acid is 90 - 220 μmol·g -1 ; the ratio of the molar amount of Brönsted acid sites to the total molar amount of X sites is 0.1 - 0.4; In the chemical composition of the molecular sieve, Y is Si element and X is Al element, and the preparation method It includes the following processes: (a) Sequentially add an Al source, deionized water, a Si source, an inorganic structure-directing agent, and FAU seeds into a reaction kettle, then add a double organic template agent with different charge densities, stir evenly, carry out aging to obtain an initial gel, transfer it into a pressure-resistant container and seal it. Assemble different cage structures of FAU zeolite through organic template agents with different charge densities, and after hydrothermal synthesis reaction, obtain a zeolite precursor with different proportions of exposed acidic sites; (b) Filter, wash, and dry the zeolite precursor after the reaction in step (a), and then heat and activate to remove the organic matter in the zeolite precursor to obtain a calcined matrix; (c) Mix the calcined matrix obtained in step (b) with a solution containing a compound of monovalent element M, carry out ion exchange several times at a certain temperature, and the ion exchange time for each time is several hours; control the number of ion exchange times in step (c) to make the final oxide M2O reach the required loading amount; (d) Calcine the zeolite ion-exchanged with metal element ions obtained in step (c) in air, cool it after calcination is completed, take it out and store it; The Al source described in step (a) includes one or more of alkoxyaluminum, aluminum salts, activated alumina, pseudoboehmite, or pseudo-boehmite, and its mass concentration in the initial gel is 3 - 10%; The Si source described in step (a) includes one or more of silica sol, silica gel, activated silica, or orthosilicate ester, and its mass concentration in the initial gel is 5 - 25%; The organic template agent described in step (a) includes two components. The first component is choline, and the second component is N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide, and its mass concentration in the initial gel is 14 - 28%; The inorganic structure-directing agent described in step (a) includes one or more of sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium chloride, potassium chloride, or cesium chloride, and its mass concentration in the initial gel is 0.2 - 0.8%; The SAR value of the FAU seed described in step (a) is 50 - 70, and its mass concentration in the initial gel is 0.6 - 1.8%; SAR is the molar ratio of SiO2 to Al2O3; The aging time in step (a) is selected to be 12 - 36 h, the temperature of the hydrothermal synthesis reaction is 100 - 130 °C, and the reaction time is 3 - 24 d; In step (c), the M compound includes H element or an oxide, inorganic salt, or organic salt of NH 4+ ion, or a mixture of any one or several of them. In step (c), the solid-liquid ratio of the calcined matrix to the solution containing the M compound is 1 g: 4 - 6 mL, the molar concentration of the solution containing the M compound is 2 - 8 mol / L, the number of ion exchange times is selected as 1 - 10 times, and the ion exchange time for each time is 0.5 - 2 h.

2. The high-silica FAU zeolite with a high proportion of exposed acidic sites according to claim 1, wherein: Quantitatively determined by pyridine infrared adsorption spectroscopy, the amount of Brönsted acid is 750 - 950 μmol·g -1 ; the amount of Lewis acid is 130 - 190 μmol·g -1 ; the ratio of the molar amount of Brönsted acid sites to the total molar amount of X sites is 0.15 - 0.

4.

3. The high-silica FAU zeolite with a high proportion of exposed acid sites according to claim 2, characterized in that: Quantitatively determined by pyridine infrared adsorption spectroscopy, the amount of Brönsted acid is 800 - 950 μmol·g -1 ; the amount of Lewis acid is 150 - 170 μmol·g -1 ; the ratio of the molar amount of Brönsted acid sites to the total molar amount of X sites is 0.2 - 0.

4.

4. The high-silica FAU zeolite with a high proportion of exposed acid sites according to claim 1, characterized in that The Al source described in step (a) is alkoxyaluminum, aluminum salt, activated alumina or pseudoboehmite, and its mass concentration in the initial gel is 4 - 7%; The Si source described in step (a) is silica sol, silica gel or activated silica, and its mass concentration in the initial gel is 10 - 25%; The organic template agent described in step (a) has a mass concentration of 14 - 20% in the initial gel; The inorganic structure - directing agent described in step (a) is sodium hydroxide, potassium hydroxide, sodium chloride or potassium chloride, and its mass concentration in the initial gel is 0.3 - 0.7%; The SAR value of the FAU seed described in step (a) is 60; The aging time in step (a) is selected to be 20 - 28 h, and the reaction time of the hydrothermal synthesis reaction is 5 - 15 d.

5. A high-silica FAU zeolite with a high proportion of exposed acid sites according to claim 4, characterized in that The Al source described in step (a) is alkoxyaluminum or aluminum salt; The Si source described in step (a) includes silica sol or silica gel; The inorganic structure - directing agent described in step (a) includes sodium hydroxide or sodium chloride.

6. The high-silica FAU zeolite with a high proportion of exposed acid sites according to claim 1, characterized in that The temperature for heat activation in step (b) is 500 - 600 °C, and the heat activation time is 2 - 8 h.

7. The high-silica FAU zeolite with a high proportion of exposed acidic sites according to claim 1, characterized in that In step (c), the number of ion - exchange times is selected to be 4 - 6 times.

8. The high-silica FAU molecular sieve with a high proportion of exposed acidic sites according to claim 1, characterized in that In step (d), the calcination temperature is 400 - 800 °C, and the calcination time is selected to be 3 - 12 h.

9. The high-silica FAU zeolite with a high proportion of exposed acid sites according to claim 8, characterized in that In step (d), the calcination temperature is 450 - 600 °C, and the calcination time is selected to be 5 - 9 h.

10. The application of the high - silica FAU molecular sieve with a high proportion of exposed acidic sites as described in claim 1 in the adsorption and separation of phenolic substances in a liquid - phase system, which preferentially adsorbs a large amount of phenol in a phenol - isooctane solution, or preferentially adsorbs 2,5 - dimethylphenol in a 2,5 - dimethylphenol aqueous solution.

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