A high-silica LTA molecular sieve for efficiently capturing low-concentration CO2 in a humid environment, its preparation method and application

Abstract

The present invention relates to a high-silica LTA molecular sieve for efficiently capturing low-concentration CO2 in a humid environment, its preparation method and application. The molecular sieve has an LTA molecular sieve configuration, and its chemical composition molar ratio is aAl2O3:bSiO2. The elemental composition contains more tetravalent element Si and less trivalent element Al, and the molar ratio (m = SiO2 / Al2O3) of the oxides is in the range of 2-10. This kind of molecular sieve is synthesized by using an inorganic structure-directing agent, water, a silicon source and an aluminum source to prepare an initial gel, adjusting the charge density of a double organic template agent, and assembling different cage structures of the LTA molecular sieve, so as to achieve a high silicon-aluminum ratio and high water resistance at the same time. Compared with commercial molecular sieves, the high-silica LTA molecular sieve in the present invention can preferentially adsorb a large amount of CO2 in a CO2 / N2 system with water vapor. When applied to a humid environment with 97% relative humidity, the molecular sieve of the present invention can maintain a CO2 adsorption capacity of about 90% or more and has good cyclic regeneration ability.

Description

Technical Field

[0001] The present invention relates to a high-silica LTA zeolite for efficiently capturing low-concentration CO2 in a humid environment, a preparation method and an application thereof. The high-silica LTA zeolite can preferentially adsorb a large amount of CO2 in a CO2 / N2 system in a humid environment and has good cyclic regeneration ability. Background Art

[0002] The increase in the concentration of carbon dioxide in the atmosphere has caused a series of problems. How to reduce the atmospheric CO2 concentration is of great significance. Carbon capture, utilization and storage (CCUS) is an effective method for dealing with CO2 emissions. Selectively separating CO2 from natural gas and capturing low-concentration CO2 from the atmosphere are of technical importance for improving gas purity and preventing corrosion of industrial facilities. Among the proposed technologies to address these challenges, adsorption-driven CO2 capture using various ordered nanoporous materials is considered an alternative to the current commercial process using aqueous amine solutions due to its low energy requirement for regeneration and non-corrosiveness (Chem. Soc. Rev., 2020, 49, 8584 - 8686). Compared with other solid adsorbents such as metal-organic frameworks, zeolites have advantages in terms of physicochemical stability and synthesis cost.

[0003] Zeolites are a representative type of adsorbent due to the characteristics of their porous structures. Zeolites are aluminosilicate solids formed as a three-dimensional framework mainly containing oxygen, silicon and aluminum, having a relatively large pore volume and pore diameter and a relatively regular pore structure, showing good adsorption ability. The kinetic diameter of CO2 and N2 have attracted extensive attention of small-pore zeolites because the effective size of their 8-membered rings (8MRs) can be adjusted to restrict the entry of larger N2 molecules while allowing smaller CO2 molecules to be adsorbed. Zeolite 13X has been found to be able to remove some carbon dioxide from flue gas at low temperatures and the surface can be controlled by post-modification of the zeolite such as ion exchange (Applied Energy, 2017, 191: 87 - 98).

[0004] The pore diameter of traditional zeolite A (framework type LTA, Si / Al = 1.0) can be adjusted by changing the type of balanced cations introduced into the framework so that its pore diameter is in the range of to , resulting in significant changes in CO2 adsorption capacity and selectivity. However, due to the low hydrothermal stability and low hydrophobicity of the classic LTA zeolite, the A-type molecular sieves currently on the market are mostly used as desiccants and water absorbents. Patent CN110467196A reports a method for preparing a type A molecular sieve without a template, which can be obtained by crystallizing at 40°C for 7 hours, and the synthesis method is simple and convenient; Patent CN110498423A reports a method for producing a type A molecular sieve using a gelling agent, which is crystallized at 70-100°C for 1-6 hours, and a nano-scale molecular sieve of 400-800nm is obtained after ultrasound, which is smaller than the 2μm A-type molecular sieve on the market; Patent CN107986296B reports a high silicon-aluminum ratio A-type molecular sieve with a silicon-aluminum ratio of 1.5-8. By adding seed crystals, the synthesis cycle can be shortened, the yield can be increased, and the use of organic templates can be reduced. It is mainly used in the field of SCR denitrification.

[0005] In order to prepare molecular sieves with high silicon-aluminum ratios, the charge density mismatch method of Moscoso et al. seems to work well for small pore zeolite synthesis (US6713041, 2004.), because LTA, ERI and UFI zeolites can be prepared in this way. Corma et al. proposed that they prepared the so-called ITQ-29 in a fluoride medium synthesis. Although mainly pointed to LTA in the form of germanosilicate and pure silicate, the authors also showed aluminosilicate LTA by using TMA to combine two identical large aromatic π-π stacking cations of the large supramolecular OSDA complex. This part self-assembles in solution and is incorporated into a large cage (Nature 2004, 431, 287-290.). Professor Suk Bong Hong found that adding 1,2-dimethyl-3-(4-methylbenzyl)imidazolium and tetramethylammonium to a silica-alumina solution and then adding hydrogen fluoride (HF) can show LTA zeolites with different Si / Al ratios of 8.3 (Acs Catalysis, 2016, 6 (4)). In addition, a Cu / LTA catalyst with a Si / Al ratio of 17 was synthesized using a similar organic structure-directing agent, which showed excellent high-temperature activity and heat resistance in the selective catalytic reduction of ammonia NH3-SCR (Applied Catalysis, B. Environmental, 2019, 243.). Niklas Hedin's team conducted K + Ion exchange to obtain NaK-ZK-4 molecular sieve (K +The ionic content is 26%). Under the atmosphere of 15% CO2 + 85% N2 and the test temperature and pressure of 273K and 101Kpa, an adsorption capacity of 3.4 mmol / g and a selectivity greater than 800 are obtained (Langmuir, 2014, 30(32).); Corma synthesized LTA zeolites with silica-alumina ratios of 1, 2, 3.5, and 5 respectively. The LTA zeolite with Si / Al = 5 achieved an adsorption capacity of 5.58 mmol / g under the gas conditions of CO2 / CH4 / He = 48:48:4 and the pressure and temperature of 500Kpa and 303K (Langmuir, 2010, 26(3): 1910-7). However, the currently existing LTA zeolite molecular sieves with high silica-alumina ratios cannot simultaneously improve the water resistance and adsorption performance. Therefore, it is necessary for us to obtain a higher proportion of exposed active sites by adjusting the formula. At the same time, in order to commercialize the catalyst, it is necessary to find a cheap organic directing agent and a more environmentally friendly and economical synthesis method.

[0006] The problem to be solved by the present invention is to provide a method for producing aluminosilicate zeolite with an LTA structure having a high silica-alumina ratio, and this method uses economical synthesis raw materials compared with existing products. In view of the fact that there is almost no report on the adsorption and capture of CO2 in a humid environment by high-silica LTA-type molecular sieves at present, the present invention synthesizes an LTA molecular sieve with a high silica-alumina ratio in one step by adjusting a double organic template agent with different charge densities to directionally assemble different cage structures of the LTA molecular sieve, and finally applies it to the adsorption and separation of low-concentration CO2 in a humid environment. The CO2 / N2 system preferentially adsorbs CO2 and has good cyclic regeneration performance. Summary of the Invention

[0007] Aiming at the above technical problems existing in the prior art, the purpose of the present invention is to provide a high-silica LTA molecular sieve for efficiently capturing low-concentration CO2 in a humid environment, its preparation method and application.

[0008] The present invention synthesizes an LTA molecular sieve with a high silica-alumina ratio in one step by adjusting a double organic template agent with different charge densities to directionally assemble different cage structures of the LTA molecular sieve, and finally applies it to the CO2 / N2 system in a humid environment, and preferentially adsorbs a large amount of CO2. When applied to a humid environment (RH = 97%), the molecular sieve of the present invention can maintain a CO2 adsorption capacity of about 90% or more and has good cyclic regeneration ability.

[0009] To achieve the above object, the present invention uses a silicon-containing compound and an aluminum-containing compound to prepare an initial gel. By adjusting the composition of templating agents with different charge densities and selecting appropriate synthesis conditions, an LTA molecular sieve with a high silicon-aluminum ratio is successfully synthesized, obtaining a molecular sieve with a high specific surface area and capable of adsorbing a large amount of CO2 in a humid environment. An adsorption test experiment for low-concentration carbon dioxide was also conducted.

[0010] 1. The technical solution of the present invention is a high-silica LTA molecular sieve for efficiently capturing low-concentration CO2 in a humid environment, with a chemical composition molar ratio of aAl2O3:bSiO2. The elemental composition contains more tetravalent element Si and less trivalent element Al, where 0.1 ≤ a ≤ 0.5, 1 ≤ b ≤ 5, and the molar ratio of the oxide SiO2 / Al2O3 is m, 2 ≤ m ≤ 10.

[0011] When performing X-ray diffraction measurement, it has characteristic peaks at least within the following 4 interplanar spacings d: the first interplanar spacing d = 12.09 ± 0.2, the second interplanar spacing d = 8.55 ± 0.2, the third interplanar spacing d = 6.98 ± 0.2, and the fourth interplanar spacing d = 6.04 ± 0.2.

[0012] 2. The molecular sieve described in the present invention has the LTA molecular sieve configuration recognized by the International Zeolite Association (IZA). Its characteristics are confirmed by X-ray diffraction measurement.

[0013] 3. The X-ray diffraction measurement 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 forms for testing can be powder, emulsion, or solid particles.

[0014] 4. The molecular sieve described in the present invention is synthesized using macromolecular organic templating agents with different charge densities. Therefore, after the hydrothermal reaction is completed, the synthesized molecular sieve precursor needs to be heated and calcined to remove the macromolecular templating agent.

[0015] 5. In the composition of the above LTA molecular sieve, the molar ratio m of the oxide = SiO2 / Al2O3 has a value of 5.4 - 8.6.

[0016]

Synthesis method of molecular sieve

[0017] The present invention provides a preparation method for a high-silica LTA molecular sieve for efficiently capturing low-concentration CO2 in a humid environment. By adjusting the dual organic templating agents with different charge densities, the different cage structures of the LTA molecular sieve are directionally assembled, and an LTA molecular sieve with a high silicon-aluminum ratio is synthesized at one time. The specific preparation steps are as follows:

[0018] (a) Add the Al source, deionized water, Si source, inorganic structure-directing agent, and LTA seeds into the reactor in sequence. Then add the dual organic templating agents with different charge densities, stir evenly, and age to obtain the initial gel. Transfer it to a polytetrafluoroethylene pressure-resistant container and seal it. Then transfer the polytetrafluoroethylene pressure-resistant container to an oven for hydrothermal synthesis. Assemble different cage structures of LTA zeolite through the organic templating agents with different charge densities to obtain the zeolite precursor.

[0019] (b) Filter, wash, and dry the zeolite precursor after the reaction in step (a) is completed. Then heat and activate it by calcining in air in a tubular furnace to remove the organic matter in the zeolite precursor. After calcination, cool it, take it out and store it, and the preparation is completed.

[0020] <Zeolite synthesis raw materials>

[0021] The Al source described in step (a) includes, but is not limited to, one or more of alkoxyaluminum, aluminum salts, activated alumina, pseudo-boehmite, or pseudo-boehmite, preferably alkoxyaluminum, aluminum salts, activated alumina, or pseudo-boehmite, more preferably alkoxyaluminum or aluminum salts.

[0022] 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 esters, preferably silica sol, silica gel, or activated silica, more preferably silica sol or silica gel.

[0023] The inorganic structure-directing agent described in step (a) includes 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.

[0024] The SAR value of the LTA seeds described in step (a) is 2-10, preferably the SAR value is 2.

[0025] The organic templating agent described in step (a) includes one or a mixture of several of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, choline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, or tetrabutylammonium hydroxide.

[0026] In the initial gel of step (a), the mass concentration of the Al source is 2-8%, preferably 2.5-5%; the mass concentration of the Si source is 5-30%, preferably 5-22%; the mass concentration of the dual organic templating agent is 10-19%, preferably 12-18%; the mass concentration of the inorganic structure-directing agent is 2-5%, preferably 3-4%; the mass concentration of the LTA seeds is 0.35-1%, preferably 0.39-0.7%.

[0027] <Preparation of the initial gel>

[0028] In the preparation process of the initial gel in step (a) of the present invention, it is affected by the dissolution order and dissolution conditions. Generally, an Al source, deionized water, an Si source, an inorganic structure-directing agent, and LTA seeds are added, and then the double organic template agent is dissolved in water to obtain the initial gel. The aging time is selected to be 12 - 60 h, preferably 40 - 48 h.

[0029] <Hydrothermal synthesis>

[0030] In the hydrothermal synthesis process of step (a), the above-mentioned initial gel together with the reaction kettle is transferred into a polytetrafluoroethylene pressure-resistant container, tightened, and then heated and reacted with hot air in a rotary reaction furnace, or left standing in an oven to react at a certain temperature. The reaction temperature of the hydrothermal synthesis is generally controlled above 100 °C, preferably above 120 °C; the upper limit temperature of the reaction is controlled below 180 °C, preferably below 150 °C, and more preferably below 130 °C. The reaction time is generally controlled above 3 d, preferably above 6 d; the upper limit of the reaction time is generally controlled below 20 d, preferably below 14 d.

[0031] <Post-treatment after hydrothermal synthesis>

[0032] In the processes of filtration, washing, and drying in step (b), the drying temperature is selected to be 60 - 200 °C, preferably 80 - 100 °C. The drying time is selected to be 12 - 36 h, preferably 12 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 - 12 h, preferably 2 - 8 h.

[0033]

Use of the present invention

[0034] The high-silica-alumina-ratio LTA molecular sieve described in the present invention can preferentially adsorb a large amount of CO2 in the CO2 / N2 system in a humid environment. When applied to a humid environment, the molecular sieve of the present invention can maintain a CO2 adsorption capacity of about 90% or more and has good cyclic regeneration ability.

[0035] The adsorption and separation of gases by the LTA molecular sieve described above can be operated at 273 - 353 K, preferably 293 - 323 K.

[0036] The adsorption and separation of gases by the LTA molecular sieve described above can be operated at a CO2 concentration below 10,000 ppm.

[0037]

Advantages of the present invention

[0038] (1) The proportion of exposed acidic sites of the high-silica-alumina-ratio LTA molecular sieve in the present invention is high, and a balance can be obtained between water resistance and adsorption performance, and the adsorption amount in the cyclic test is high.

[0039] (2) The synthesis method of the high silica-alumina ratio LTA molecular sieve in the present invention uses dual templates with different charge densities. Compared with commercial A-type molecular sieves, it has a higher specific surface area, still has a high adsorption capacity in a humid environment, and has good water resistance.

[0040] (3) The high silica-alumina ratio LTA molecular sieve in the present invention has low polarity and strong hydrophobicity, can still have a good adsorption effect in a humid environment, and is easy to recycle and regenerate.

[0041] (4) The organic templates for preparing the LTA molecular sieve in the present invention are easy to obtain and low in price, while the organic structure-directing agents for current high silica LTA molecular sieves are high in cost and toxic. This method can effectively reduce the manufacturing cost in industrial production. Description of the Drawings

[0042] Table 1 shows the characteristic crystal plane spacings of Na-LTA-1 in Example 1;

[0043] Table 2 shows the characteristic crystal plane spacings of Na-LTA-2 in Example 2;

[0044] Table 3 shows the characteristic crystal plane spacings of Na-LTA-3 in Example 3;

[0045] Table 4 shows the characteristic crystal plane spacings of Na-LTA-4 in Example 4;

[0046] Table 5 shows the adsorption capacities and reduction amplitudes of different molecular sieves for 10% CO2 in dry gas and wet gas (RH = 97%) environments at 313K in Examples 1-4 and Comparative Example 1;

[0047] Table 6 shows the adsorption cycle test results of different molecular sieves for low-concentration CO2 in Example 1 and Comparative Example 1; Table 7 shows the specific surface areas, micropore specific surfaces, total pore volumes, and micropore volumes of different molecular sieves in Examples 1-4 and Comparative Example 2;

[0048] Table 8 shows the amounts of Bronsted acid, Lewis acid, and total acid of different molecular sieves in Examples 1-4 and Comparative Example 2;

[0049] Figure 1 is a schematic diagram of the XRD test results of Na-LTA-1 in Example 1;

[0050] Figure 2 is a schematic diagram of the XRD test results of Na-LTA-2 in Example 2;

[0051] Figure 3 is a schematic diagram of the XRD test results of Na-LTA-3 in Example 3;

[0052] Figure 4 is a schematic diagram of the XRD test results of Na-LTA-4 in Example 4;

[0053] Figure 5 It is a schematic diagram of the adsorption cycle test results of Na-LTA-1 in Example 1. Detailed implementation manners

[0054] The present invention will be described in detail below through examples, but the present invention is not limited to these examples.

[0055]

Instrument characterization

[0056] <X-ray diffraction determination>

[0057] 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, 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.

[0058] <Inductively coupled plasma spectroscopy determination>

[0059] 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.

[0060] <Static adsorption test>

[0061] At a temperature of 77 K, the specific surface area of the material is measured using the size of nitrogen molecules. An automatic specific surface area and porosity analyzer (3-Flex) is used to obtain the adsorption / desorption curve and the pore size distribution curve. The specific surface area and pore volume of the material are calculated by Brunauer-Emmett-Teller (BET), T-Plot and Density functional theory (DFT) algorithms.

[0062] <Dynamic adsorption test>

[0063] Gas adsorption measurement was carried out using an Agilent 8860 gas chromatograph, with a TCD detector and a HayeSep Q chromatographic column for adsorption testing. The gas adsorption selectivity was tested by gas adsorption measurement in the present invention. The CO2 / N2 adsorption isotherm was measured at 288 - 313 K. Approximately 1000 mg of the sample was placed in a sample tube and then placed in a set constant temperature water bath. The cylinder gas was a standard gas configured with 10% CO2 and 90% N2, and the gas flow rate was 5 ml / min. All samples were activated at 350 °C for more than 6 h before the adsorption test.

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

[0065] The active acid 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 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 respectively. Absorption extinction coefficients: ε(B) = 1.67 cm·μmol -1 and ε(L) = 2.22 cm·μmol -1 .

[0066]

Example

[0067] The LTA seeds in the examples of the present invention were purchased from Tianjin Nanhua Catalyst Co., Ltd., model NKF-4A.

[0068] <Example 1>

[0069] 2.6 g of NaAlO2 (mass percentage of NaAlO2 > 98%) was added to 25 g of water and dissolved, and then 2.5 g of NaCl (mass percentage of sodium chloride > 99.5%), 30.5 g of tetraethylammonium hydroxide (35% aqueous), and 2.5 g of tetramethylammonium chloride (mass percentage of tetramethylammonium chloride > 99%) were added in sequence and stirred evenly. After the solution was clarified, 13 g of Ludox AS-40 (40% aqueous silicon solution) was added dropwise, and stirring was continued until the solution was fully mixed; 0.3 g of LTA seeds (SAR = 2) was added and aged for 48 h to obtain an initial gel. The gel mixture was transferred into a polytetrafluoroethylene pressure-resistant container and sealed, and dynamically crystallized at a reaction temperature of 130 °C and autogenous pressure for 6 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.

[0070] The obtained powdery product was calcined in a muffle furnace at 550 °C for 6 h to obtain the powdery product Na-LTA-1. The obtained product was subjected to phase analysis by XRD. The crystal plane spacings at the characteristic peaks in Na-LTA-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 LTA 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-LTA-1 is 6.6.

[0071] The above Na-LTA-1 was used for the low-concentration CO2 adsorption test experiment. The adsorption capacity of the sample was measured on an Agilent 8860 gas chromatograph. The detector was a TCD, and the chromatographic column used was a HayeSep Q column. Measurement parameters: inlet temperature 150 °C, column oven temperature 120 °C, detector temperature 250 °C, the column oven temperature was raised to 120 °C at a heating rate of 40 °C / min, and then held at 120 °C for 2 min. The gas flow rate of the mixed gas in the chromatographic operation was 5 ml / min.

[0072] The gas used for the adsorption test was a mixed gas composed of 10% CO2 and 90% N2 (when measuring wet gas, the mixed gas was bubbled through a water vapor bottle to simulate a wet gas environment with RH = 97%). Weigh 1 g of the prepared Na-LTA-1 and add it to a U-shaped tube. First, activate it at 350 °C for 6 h, and then place it in a 40 °C constant temperature water bath for the adsorption test experiment. The inlet flow rate of the mixed gas in the U-shaped tube during the test experiment was 5 ml / min. In order to avoid the influence of too fine particle size of the molecular sieve on the pressure drop, the prepared molecular sieve needs to be sieved through a 40-60 mesh sieve; in order to avoid the influence of dead volume in the pipeline, before the adsorption test, the empty U-shaped tube without the molecular sieve was subjected to an empty tube adsorption test as the dead volume of the instrument, and then the adsorption amount of the measured molecular sieve was subtracted by the dead volume for dead volume correction. The measured adsorption capacity of Na-LTA-1 for CO2 under wet gas was 2.87 mmol / g, and the adsorption capacity of CO2 under dry gas is shown in Table 5.

[0073] Table 1 Characteristic crystal plane spacings of Na-LTA-1

[0074] Interplanar spacing (d) 1 12.096 2 8.486 3 6.937 4 6.005 5 5.377 6 4.922 7 4.264 8 4.019

[0075] <Example 2>

[0076] Dissolve 3.55 g of aluminum sec-butoxide (mass percentage of aluminum sec-butoxide > 96%) in 25 g of water, then successively add 2.5 g of NaCl (mass percentage of sodium chloride > 99.5%), 27.4 g of tetraethylammonium hydroxide (25% aqueous), and 3 g of tetramethylammonium chloride (mass percentage of tetramethylammonium chloride > 99%), and stir evenly. After the solution becomes clear, slowly add dropwise 13 g of Ludox AS-40 (40% aqueous silicon solution), and continue stirring until the solution is fully mixed; add 0.5 g of LTA seed crystals (SAR = 2), and age for 48 h to obtain the initial gel. Transfer the gel mixture into a sealed polytetrafluoroethylene pressure-resistant container, 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.

[0077] After calcining the obtained powdery product in a muffle furnace at 550 °C for 6 h, a powdery product Na-LTA-2 is obtained. The obtained product is subjected to phase analysis by XRD. The interplanar spacings at the positions of the characteristic peaks in Na-LTA-2 are shown in Table 2, and the schematic diagram of the XRD test results is shown in Figure 2 , indicating that the synthesized molecular sieve has the LTA molecular sieve configuration recognized by IZA. The elemental composition of the above sample is analyzed by ICP, and the analysis results show that the SAR value of Na-LTA-2 is 5.8.

[0078] The above Na-LTA-2 is used for the low-concentration CO2 adsorption test experiment. The adsorption capacity of the sample is measured on an Agilent 8860 gas chromatograph. The detector is TCD, and the chromatographic column uses a HayeSep Q column. Measurement parameters: injection port 150 °C, column oven 120 °C, detector 250 °C, the column oven temperature is raised to 120 °C at a heating rate of 40 °C / min, and then held at 120 °C for 2 min. The gas flow rate of the mixed gas in the chromatographic operation is 5 ml / min.

[0079] The gas used in the adsorption test is a mixed gas composed of 10% CO2 and 90% N2 (when measuring moisture, the mixed gas is bubbled through a water vapor bottle to simulate a moisture environment with RH = 97%). Weigh 1 g of the prepared Na-LTA-2 and add it to a U-shaped tube. First, perform an activation treatment at 350 °C for 6 h, and then place it in a constant temperature water bath at 40 °C for the adsorption test experiment. During the test experiment, the inlet flow rate of the U-shaped tube is 5 ml / min of the mixed gas. To avoid the influence of too fine particle size of the molecular sieve on the pressure drop, the prepared molecular sieve needs to be sieved through a 40-60 mesh sieve; to avoid the influence of dead volume in the pipeline, before the adsorption test, the empty U-shaped tube without the loaded and unloaded molecular sieve is used for the empty tube adsorption test as the dead volume of the instrument, and then the dead volume correction is carried out by subtracting the dead volume from the measured adsorption capacity of the molecular sieve. The measured adsorption capacities of Na-LTA-2 for CO2 under moist gas are 2.74 mmol / g respectively, and the adsorption capacities of CO2 under dry gas are shown in Table 5.

[0080] Table 2 Characteristic crystal plane spacings of Na-LTA-2

[0081]

[0082]

[0083] <Example 3>

[0084] Dissolve 2.58 g of aluminum sec-butoxide (mass percentage of aluminum sec-butoxide > 96%) in 25 g of water, and then add 2 g of tetramethylammonium chloride (mass percentage of tetramethylammonium chloride > 99%) and 25 g of tetraethylammonium hydroxide (25% aqueous) and 2.5 g of NaCl (mass percentage of sodium chloride > 99.5%) in sequence. After the solution becomes clear, gradually add 16 g of tetraethyl orthosilicate (mass percentage calculated as SiO2 > 28%) and stir evenly. Add 0.5 g of LTA seed crystal (SAR = 2) and carry out aging for 48 h to obtain the initial gel. Transfer the gel mixture into a polytetrafluoroethylene 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, filter, and wash the reaction solution to obtain the crystalline product. Dry the obtained crystals at 100 °C for 12 h to obtain a powdery product.

[0085] After calcining the obtained powdery product in a muffle furnace at 550 °C for 6 h, a powdery product Na-LTA-3 is obtained. The obtained product is analyzed by XRD for its phase. The crystal plane spacings at the characteristic peaks in Na-LTA-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 LTA molecular sieve configuration recognized by IZA. Use ICP to analyze the element composition of the above sample, and the analysis results show that the SAR value of Na-LTA-3 is 5.6.

[0086] The above Na-LTA-3 was used for the low-concentration CO2 adsorption test experiment. The adsorption capacity of the sample was measured on an Agilent 8860 gas chromatograph, with a TCD detector and a HayeSep Q column. The measurement parameters were as follows: the injection port was at 150 °C, the column oven was at 120 °C, the detector was at 250 °C, the column oven temperature was raised to 120 °C at a heating rate of 40 °C / min and then held at 120 °C for 2 min, and the gas flow rate of the mixed gas during the chromatographic operation was 5 ml / min.

[0087] The gas used for the adsorption test was a mixed gas composed of 10% CO2 and 90% N2 (when measuring wet gas, the mixed gas was bubbled through a water vapor bottle to simulate a wet gas environment with RH = 97%). 1 g of the prepared Na-LTA-3 was weighed and added to a U-shaped tube. First, it was activated at 350 °C for 6 h, and then placed in a 40 °C constant temperature water bath for the adsorption test experiment. The inlet flow rate of the mixed gas in the U-shaped tube during the test experiment was 5 ml / min. To avoid the influence of too fine molecular sieve particle size on the pressure drop, the prepared molecular sieve was sieved through a 40-60 mesh sieve; to avoid the influence of dead volume in the pipeline, an empty U-shaped tube without the loaded and unloaded molecular sieve was used for the empty tube adsorption test as the dead volume of the instrument before the adsorption test, and then the dead volume correction was carried out by subtracting the dead volume from the measured adsorption amount of the molecular sieve. The measured adsorption capacity of Na-LTA-3 for CO2 under wet gas was 2.56 mmol / g, and the adsorption capacity of CO2 under dry gas is shown in Table 5.

[0088] Table 3 Characteristic crystal plane spacings of Na-LTA-3

[0089] Interplanar spacing (d) 1 12.102 2 8.513 3 6.895 4 6.015 5 5.406 6 4.899 7 4.251 8 4.082

[0090] <Example 4>

[0091] 2 g of aluminum hydroxide (mass percentage of aluminum hydroxide > 99%) was added to 20 g of water and dissolved, and then 29.1 g of tetramethylammonium hydroxide (40% aqueous), 2 g of tetramethylammonium chloride (mass percentage of tetramethylammonium chloride > 99%), and 2.5 g of NaCl (mass percentage of sodium chloride > 99.5%) were added in sequence. After the solution was clarified, 16 g of tetraethyl orthosilicate (mass percentage calculated as SiO2 > 28%) was gradually added and stirred evenly. 0.5 g of LTA seed crystals (SAR = 2) was added and aged for 48 h to obtain an initial gel. The gel mixture was transferred to a polytetrafluoroethylene pressure-resistant container and sealed, and dynamically crystallized at a reaction temperature of 130 °C and autogenous pressure for 6 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.

[0092] The obtained powdery product was calcined in a muffle furnace at 550 °C for 6 h to obtain the powdery product Na-LTA-4. The obtained product was subjected to phase analysis by XRD. The crystal plane spacing at the characteristic peaks in Na-LTA-4 is 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 LTA 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-LTA-4 is 5.4.

[0093] The above Na-LTA-4 was used for the low-concentration CO2 adsorption test experiment. The adsorption capacity of the sample was measured on an Agilent 8860 gas chromatograph. The detector was TCD, and the chromatographic column used was a HayeSep Q column. Determination parameters: inlet temperature 150 °C, column oven temperature 120 °C, detector temperature 250 °C, the column oven temperature was raised to 120 °C at a heating rate of 40 °C / min, and then held at 120 °C for 2 min. The gas flow rate of the mixed gas in the chromatographic operation was 5 ml / min.

[0094] The gas used for the adsorption test was a mixed gas composed of 10% CO2 and 90% N2 (when measuring wet gas, the mixed gas was bubbled through a water vapor bottle to simulate a wet gas environment with RH = 97%). 1 g of the prepared Na-LTA-4 was weighed and added to a U-shaped tube. First, it was activated at 350 °C for 6 h, and then placed in a 40 °C constant temperature water bath for the adsorption test experiment. The inlet flow rate of the mixed gas in the U-shaped tube during the test experiment was 5 ml / min. In order to avoid the influence of too fine molecular sieve particle size on the pressure drop, the prepared molecular sieve needs to be sieved through a 40-60 mesh sieve; in order to avoid the influence of dead volume in the pipeline, an empty U-shaped tube without loading and unloading molecular sieve was used for the empty tube adsorption test as the dead volume of the instrument before the adsorption test, and then the dead volume correction was carried out by subtracting the dead volume from the measured adsorption amount of the molecular sieve. The measured adsorption capacity of Na-LTA-4 for CO2 under wet gas was 2.30 mmol / g, and the adsorption capacity of CO2 under dry gas is shown in Table 5.

[0095] Table 4 Characteristic crystal plane spacing of Na-LTA-4

[0096]

[0097]

[0098] <Comparative Example 1>

[0099] A certain amount of three commercial molecular sieves, namely 4A molecular sieve (silica-alumina ratio of 1) from Nankai Chemical Reagent Factory, 4A molecular sieve (silica-alumina ratio of 1) from Zhuoran Environmental Protection Co., Ltd., and 4A molecular sieve (silica-alumina ratio of 1) from Shentan Environmental Protection Co., Ltd., and a high-silica LTA molecular sieve with a silica-alumina ratio of 5 prepared by referring to Croma literature (Langmuir, 2010, 26(3): 1910-7) were taken. The obtained molecular sieves were named Na-LTA-5, Na-LTA-6, Na-LTA-7, and Na-LTA-8 in sequence. After the dried samples were taken out, they were stored in a drying dish.

[0100] The above-mentioned Na-LTA-5, Na-LTA-6, Na-LTA-7, and Na-LTA-8 were used for low-concentration CO2 adsorption test experiments. The adsorption capacity of the samples was measured on an Agilent 8860 gas chromatograph. The detector was a TCD, and the chromatographic column used was a HayeSep Q column. Chromatographic determination parameters: injection port 150 °C, column oven 120 °C, detector 250 °C. The column oven temperature was raised to 120 °C at a heating rate of 40 °C / min, and then held at 120 °C for 2 min. The gas flow rate of the mixed gas in the chromatographic operation was 5 ml / min.

[0101] The gas used for the adsorption test was a mixed gas composed of 10% CO2 and 90% N2 (when measuring wet gas, the mixed gas was bubbled through a water vapor bottle to simulate a wet gas environment with RH = 97%). 1 g of the prepared Na-LTA-5, Na-LTA-6, Na-LTA-7, and Na-LTA-8 were respectively weighed and added to a U-shaped tube. First, they were activated at 350 °C for 6 h, and then placed in a water bath for adsorption test experiments. The inlet flow rate of the mixed gas in the U-shaped tube during the test experiment was 5 ml / min. In order to avoid the influence of too fine particle size of the molecular sieve on the pressure drop, the prepared molecular sieve needed to be sieved through a 40-60 mesh sieve; in order to avoid the influence of dead volume in the pipeline, an empty U-shaped tube without loading and taking out the molecular sieve was used for empty tube adsorption test as the dead volume of the instrument before the adsorption test, and then the dead volume correction was carried out by subtracting the dead volume from the measured adsorption amount of the molecular sieve. The adsorption amounts of various molecular sieves for 10% low-concentration CO2 in dry gas and wet gas environments (RH = 97%) at 40 °C are shown in Table 5.

[0102] Subsequently, adsorption cycle tests were carried out on Na-LTA-1, Na-LTA-5 and Na-LTA-8. The adsorption capacity of the samples was measured on an Agilent 8860 gas chromatograph, with a TCD detector and a HayeSep Q column. The gas used for the adsorption test was a mixture of 10% CO2 and 90% N2, and the mixture was bubbled through a water vapor bottle to simulate a humid environment with RH = 97%. Weighed 1 g of the prepared Na-LTA-1, Na-LTA-5 and Na-LTA-8 were added to a U-shaped tube respectively. First, they were activated at 350 °C for 6 h, and then placed in a 40 °C water bath for the adsorption test. The inlet flow rate of the U-shaped tube during the test was 5 ml / min of the mixture gas. To avoid the influence of too fine particle size of the molecular sieve on the pressure drop, the prepared molecular sieve was sieved through a 40-60 mesh sieve; to avoid the influence of dead volume in the pipeline, an empty U-shaped tube without the molecular sieve was used for the empty tube adsorption test as the dead volume of the instrument before the adsorption test, and then the dead volume was corrected by subtracting the dead volume from the measured adsorption amount of the molecular sieve. Chromatographic determination parameters: injection port 150 °C, column oven 120 °C, detector 250 °C, the column oven temperature was raised to 120 °C at a heating rate of 40 °C / min, and then held at 120 °C for 2 min. The gas flow rate of the mixture gas during the chromatographic operation was 5 ml / min. The desorption temperature was still 40 °C, and the gas flow rate was purged with nitrogen at 20 ml / min until the peak area of CO2 in the chromatogram decreased to almost 0. Then, the second 40 °C adsorption experiment was carried out. The parameters used in the second adsorption test were as above. Finally, the second desorption experiment and the third adsorption test... were repeated many times in turn to detect the adsorption cycle performance of the molecular sieve at 40 °C. The adsorption cycle performance of the molecular sieve is shown in Table 6 and Figure 5 。

[0103] <Comparative Example 2>

[0104] A certain amount of commercial molecular sieves of 4A type (silica-alumina ratio of 1) from Nankai Chemical Reagent Factory, 4A type (silica-alumina ratio of 1) from Zhuoran Environmental Protection Co., Ltd., and 4A type (silica-alumina ratio of 1) from Shentan Environmental Protection Co., Ltd., and a high-silica LTA molecular sieve with a silica-alumina ratio of 5 prepared according to the reference Croma literature (Langmuir, 2010, 26(3): 1910-7) were taken. The obtained molecular sieves were named Na-LTA-5, Na-LTA-6, Na-LTA-7 and Na-LTA-8 in turn. The dried samples were taken out and stored in a drying dish.

[0105] Weigh about 0.2 - 0.3 g of the sample and measure the specific surface area of the material at a temperature of 77 K using the size of nitrogen molecules. Use a fully automatic specific surface area and porosity analyzer (3-Flex) to obtain the adsorption or adsorption / desorption curve and the pore size distribution curve. Calculate the specific surface area and pore volume of the material through the Brunauer-Emmett-Teller (BET), T-Plot, and Density functional theory (DFT) algorithms. The specific surface area and pore volume of different molecular sieves are shown in Table 7.

[0106] Determine the acid amount of the molecular sieve prepared above and the commercial molecular sieve. Press the sample into a self-supporting wafer and degas it under vacuum at 400 °C for 1 hour before adsorption measurement. After cooling to 50 °C, introduce 25 mbar of gaseous pyridine into the sample cell until saturation. Conduct thermal desorption at 150 °C to remove weakly adsorbed pyridine species. Quantify the amounts of Lewis acid and -1 acid sites by integrating the areas of the absorption bands at 1455 and 1554 cm respectively. The acid amounts of different molecular sieves are shown in Table 8.

[0107] Table 5 Adsorption capacity and reduction amplitude of 10% CO2 for different molecular sieves in dry gas and wet gas (RH = 97%) environments at 313 K

[0108]

[0109] Table 6 Adsorption cycle test of different molecular sieves for low-concentration CO2 under wet gas (RH = 97%) conditions

[0110]

[0111] Table 7 Specific surface area, microporous specific surface area, total pore volume, and microporous volume of different molecular sieves

[0112] Molecular sieve name <![CDATA[S BET (m 2 g -1 )]]> <![CDATA[S mic (m 2 g -1 )]]> <![CDATA[V t (cm 3 g -1 )]]> <![CDATA[V mic (cm 3 g -1 )]]> Na-LTA-1 734 719 0.278443 0.278512 Na-LTA-2 721 705 0.269254 0.268452 Na-LTA-3 705 690 0.264542 0.262538 Na-LTA-4 698 687 0.260387 0.259873 Na-LTA-5 362 342 0.152325 0.132195 Na-LTA-6 380 361 0.160391 0.139236 Na-LTA-7 301 292 0.152423 0.131456 Na-LTA-8 725 692 0.254833 0.238000

[0113] Table 8 Amounts of Bronsted acid, Lewis acid, and total acid of different molecular sieves

[0114]

[0115] The content described in this specification is only a list 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. Application of a high-silica LTA molecular sieve in efficiently capturing low-concentration CO2 in a humid environment, characterized in that The high-silica LTA molecular sieve has the LTA molecular sieve configuration recognized by the International Zeolite Association (IZA). Its chemical composition molar ratio is aAl2O3: bSiO2, and the elemental composition contains more tetravalent element Si and less trivalent element Al, where 0.1 ≤ a ≤ 0.5, 1 ≤ b ≤ 5, and the molar ratio of oxide SiO2 / Al2O3 is m, m = 5.4 - 8.6; When performing X-ray diffraction measurement, it has characteristic peaks at least within the following 4 interplanar spacings d: the first interplanar spacing d = 12.09 ± 0.2, the second interplanar spacing d = 8.55 ± 0.2, the third interplanar spacing d = 6.98 ± 0.2, and the fourth interplanar spacing d = 6.04 ± 0.2; The preparation method of the high-silica LTA molecular sieve includes the following processes: (a) Sequentially add an Al source, deionized water, an Si source, an inorganic structure-directing agent, and LTA seeds into a reaction kettle. Add a double organic template agent with different charge densities, stir evenly, age to obtain an initial gel, transfer it into a polytetrafluoroethylene pressure-resistant container and seal it. Then transfer the polytetrafluoroethylene pressure-resistant container to an oven for hydrothermal synthesis. Assemble different cage structures of the LTA molecular sieve through the organic template agent with different charge densities to obtain a molecular sieve precursor; (b) Filter, wash, and dry the molecular sieve precursor after the reaction in step (a). Then heat and activate it by air calcination in a tube furnace to remove the organic matter in the molecular sieve precursor. After the calcination is completed, cool it, take it out and store it, and the preparation is completed; The double organic template agent in step (a) is a mixture of any two of N,N-dimethyl-3,5-dimethylpiperidine hydroxide, choline, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, or tetrabutylammonium hydroxide; The inorganic structure-directing agent in step (a) includes one or more of sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium chloride, potassium chloride, and cesium chloride.

2. The application according to claim 1, characterized in that The Al source in step (a) includes one or more of alkoxyaluminum, aluminum salts, activated alumina, pseudoboehmite, or pseudoboehmite. The Si source in step (a) includes one or more of silica sol, silica gel, activated silica, or tetraethyl orthosilicate. The SAR value of the LTA seeds in step (a) is 2 - 10; The aging time in step (a) is selected to be 12 - 60 h, and the temperature of the hydrothermal synthesis reaction is 100 - 130 °C, and the reaction time is 3 - 20 d.

3. The application according to claim 2, characterized in that The Al source in step (a) includes alkoxyaluminum, aluminum salts, activated alumina, or pseudoboehmite; The Si source in step (a) includes silica sol, silica gel, or activated silica; The inorganic structure-directing agent in step (a) includes sodium hydroxide, potassium hydroxide, sodium chloride, or potassium chloride; The SAR value of the LTA seeds in step (a) is 2; The aging time in step (a) is selected to be 40 - 48 h, and the temperature of the hydrothermal synthesis reaction is 100 - 130 °C, and the reaction time is 6 - 14 d.

4. The application according to claim 1, characterized in that In the initial gel of step (a), the mass concentration of the Al source is 2-8%; the mass concentration of the Si source is 5-30%; the mass concentration of the double organic template is 10-19%; the mass concentration of the inorganic structure-directing agent is 2-5%; the mass concentration of the LTA seed crystal is 0.35-1%.

5. The application according to claim 4, characterized in that In the initial gel of step (a), the mass concentration of the Al source is 2.5-5%; the mass concentration of the Si source is 5-22%; the mass concentration of the double organic template is 12-18%; the mass concentration of the inorganic structure-directing agent is 3-4%; the mass concentration of the LTA seed crystal is 0.39-0.7%.

6. The application according to claim 1, wherein In step (b), the temperature for calcination heating activation is 500-600 °C, and the heating activation time is 2-8 h.

7. The application according to claim 1, wherein The concentration of CO2 in the gas to be separated is lower than 10000 ppm.

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