A method for preparing a high-ammonia-uptake acidic zeolite molecular sieve

Abstract

The application relates to the field of molecular sieve technology, in particular to a preparation method of a high-ammonia-adsorbing acid zeolite molecular sieve, and specifically comprises the following steps: performing alkali fusion activation on fly ash to obtain a calcine; performing hot water leaching and dissolution on the calcine, pre-sedimenting aluminum, solid-liquid separation and purification and constant volume to obtain a sodium silicate solution and a sodium metaaluminate solution; performing precursor liquid preparation, hydrothermal crystallization, solid-liquid separation and washing on the basis of the sodium silicate solution and the sodium metaaluminate solution to obtain a P-type molecular sieve wet filter cake; performing ammonium exchange, ammonium removal calcination and step-by-step pore formation on the P-type molecular sieve wet filter cake to obtain a hydrogen type P-type molecular sieve dry powder; and performing atomization loading, drying and surface modification on the hydrogen type P-type molecular sieve dry powder to obtain an ammonia-adsorbing acid zeolite molecular sieve, so that the preparation of the high-ammonia-adsorbing acid zeolite molecular sieve is realized by using fly ash, and the comprehensive cost and ammonia-adsorbing effect are achieved.

Description

Technical Field

[0001] This application relates to the field of molecular sieve technology, and in particular to a method for preparing a highly amino acid-absorbing zeolite molecular sieve. Background Technology

[0002] Acidic zeolite molecular sieves can be used to modify and prepare superabsorbent polymers (SAPs), which can then be applied to products such as diapers to compensate for the insufficient ammonia adsorption capacity and weak deodorization ability of SAPs. Currently, acidic zeolite molecular sieves are mainly prepared by hydrothermal synthesis, involving steps such as gel preparation, crystallization, post-treatment to prepare the acidic form, and optimization for high ammonia adsorption. A general reference can be found in the preparation method of a highly dispersed zeolite molecular sieve, as described in announcement number CN103204515B.

[0003] In response to the trend of resource reuse, some synthetic routes use solid waste resources as inexpensive silicon and aluminum sources. For example, there is a method for preparing P-type molecular sieves using fly ash as raw material, which is disclosed in CN104291349B. After the fly ash is pretreated and activated, sodium silicate and sodium aluminate are prepared, and then the molecular sieve is synthesized.

[0004] However, the molecular sieves made from fly ash are mainly sodium-type, which tend to adsorb heavy metals and calcium and magnesium ions. They are not suitable for the manufacture of absorbent resins that require ammonia adsorption in urine, such as those used in hygiene products. There is currently a lack of a route to modify sodium-type molecular sieves into hydrogen-type molecular sieves that can have better ammonia adsorption effects. Summary of the Invention

[0005] In order to achieve excellent ammonia absorption performance while reducing raw material costs, this application provides a method for preparing a highly ammonia-absorbing zeolite molecular sieve.

[0006] The preparation method of a hyperabsorbent zeolite molecular sieve provided in this application adopts the following technical solution.

[0007] A method for preparing a highly amino acid-absorbing zeolite molecular sieve includes the following steps.

[0008] S1. Alkali fusion activation of fly ash to obtain calcined product;

[0009] S2. The calcined material is extracted with hot water, aluminum is pre-precipitated, solid-liquid separation is performed, and the purified and diluted to a final volume to obtain sodium silicate solution and sodium aluminate solution.

[0010] S3. Based on sodium silicate solution and sodium aluminate solution, the precursor solution is prepared, hydrothermal crystallization is carried out, solid-liquid separation and washing are performed to obtain P-type molecular sieve wet filter cake.

[0011] S4. The wet filter cake of P-type molecular sieve is subjected to ammonium exchange, deammonium calcination and stepwise pore formation to obtain hydrogen-type P-type molecular sieve dry powder.

[0012] S5. The hydrogen-type P-type molecular sieve dry powder is atomized, loaded, dried, and surface modified to obtain amino acid-absorbing zeolite molecular sieve.

[0013] By adopting the above technical solutions, ammonium exchange deammoniation and stepwise pore-forming processes, a P-type molecular sieve framework with weak acidity, high Brønsted acid sites, and hierarchical pores is directionally constructed to solve the problem of poor selectivity of existing strong basic molecular sieves in promoting urease ammonia production and ammonia absorption under high-salt urine. Combined with atomization functional loading and surface modification processes, multiple functions compatible with water-absorbing resins are simultaneously endowed to the molecular sieve.

[0014] Optionally, in the S4 process, the wet filter cake of P-type molecular sieve and ammonium chloride solution are first mixed and then separated and repeated several times to obtain ammonium-type P-type molecular sieve wet filter cake. Then, the wet filter cake of ammonia-type P-type molecular sieve is dried and calcined to remove ammonium ions to obtain hydrogen-type P-type molecular sieve. Then, the hydrogen-type P-type molecular sieve is dealuminized using organic acid and then guided to form pores.

[0015] By adopting the above technical solution, the multiple ammonium exchange process ensures the full exchange of sodium ions in the molecular sieve framework, avoiding residual sodium ions that could lead to excessive alkalinity in the product or deterioration of the water absorption performance of the water-absorbing resin.

[0016] First, deammonium calcination is performed to obtain hydrogen-form molecular sieves. Then, organic acid dealuminization and guided pore formation are carried out stepwise to achieve precise and controllable construction of acidic sites and hierarchical pore formation, avoiding the collapse of molecular sieve framework and crystal form destruction caused by simultaneous processing.

[0017] First, aluminum is removed to create fresh defect sites, and then pores are formed by guiding the process. Mesopores / macropores can be constructed at the defect sites in a directional manner. This ensures that the molecular sieve has a high density of ammonia-absorbing sites and forms hierarchical channels that are adapted to the rapid mass transfer of ammonia molecules. It takes into account both rapid ammonia capture and long-term ammonia locking performance, and solves the industry pain point of ammonia odor rebound during the wearing cycle of diapers.

[0018] Optionally, the organic acid comprises, by weight, 15-25 parts of citric acid monohydrate and 3-7 parts of L-lactic acid.

[0019] By adopting the above technical solution, a compound system is used with citric acid monohydrate as the main dealuminizing agent and L-lactic acid as the auxiliary dealuminizing agent. The strong acidity of citric acid can efficiently remove aluminum from the molecular sieve framework and construct a high-density strong B-acid ammonia adsorption site. The weak acidity of L-lactic acid can gently regulate the dealuminization rate and avoid the collapse of the molecular sieve framework and crystal destruction caused by local over-dealuminization.

[0020] Optionally, the dealumination temperature is 85°C and stirring is performed for 40 minutes, and PEG4000 is added to the guide hole.

[0021] By adopting the above technical solution, the dealumination parameters of 85℃ and 40min are precisely matched with the peak range of the dealumination rate of P-type molecular sieve, which can efficiently and gently remove aluminum from the main skeleton and form a sufficient number of fresh defect sites. This avoids both the insufficient acid sites caused by too short a dealumination time / too low temperature and the skeleton collapse caused by too long a dealumination time / too high temperature.

[0022] After dealumination, PEG4000 is added for guided pore formation, which can accurately capture fresh defect sites formed by dealumination and directionally construct 3-6nm mesopores and 10-20nm macropores. This forms a three-level hierarchical pore structure of micropore ammonia locking, mesopore mass transfer and macropore permeation. It not only retains the long-term locking ability of micropores for ammonium ions, but also greatly improves the mass transfer rate of free ammonia molecules, achieving the capture of more than 80% of free ammonia within 10 minutes, which is perfectly suited to the working conditions of rapid ammonia production after infant urination.

[0023] PEG4000 is a water-soluble polymer that can be completely removed by washing with water, leaving no residue and making it environmentally friendly.

[0024] Optionally, the ammonium exchange temperature is 60℃, the mixture is stirred at a constant temperature for 60 minutes, then allowed to stand for 30 minutes before centrifugation. The deammonium calcination is first dried at 120℃ for 6 hours, and then heated to 480℃ for 3 hours.

[0025] By adopting the above technical solution, the ammonium exchange parameter can ensure the full exchange of ammonium ions with sodium ions in the molecular sieve framework, avoiding the problem of excessive alkalinity of the product caused by residual sodium ions and the deterioration of water absorption and retention performance when blended with water-absorbing resin in the future.

[0026] In this deammonia removal process, drying first completely removes free water and capillary water from the molecular sieve pores, avoiding the collapse of the molecular sieve skeleton and pore blockage caused by rapid vaporization of moisture during calcination; constant temperature calcination at 480℃ completely removes ammonium ions and stably converts it into hydrogen-type molecular sieve, avoiding sintering of the molecular sieve skeleton and pore shrinkage caused by high-temperature calcination, and ensuring the integrity of the pore structure of the modified molecular sieve.

[0027] Optionally, in step S5, the hydrogen-type P-type molecular sieve dry powder is first preheated, and then the functional aqueous solution is atomized and sprayed into the preheated hydrogen-type P-type molecular sieve dry powder to perform dual-function loading of urease inhibition and skin soothing. Then, it is dried in situ by ventilation, and finally, it is grafted and modified with a silane coupling agent and dried.

[0028] By adopting the above technical solution, the molecular sieve dry powder is preheated first, which can ensure that the powder temperature is uniform, avoid local condensation and powder agglomeration after the functional aqueous solution is sprayed in, and ensure that the functional components are evenly dispersed.

[0029] By using atomized spraying for functional loading, urease inhibitors and skin-soothing ingredients can be uniformly penetrated into the molecular sieve hierarchical channels as micron-sized droplets, without the problems of surface aggregation or uneven loading, and at the same time, long-term sustained release of functional components can be achieved.

[0030] In-situ ventilation and drying can quickly remove moisture from the system and prevent functional components from precipitating out due to cooling or degrading at high temperatures;

[0031] Silane coupling agent grafting modification can introduce polymerizable carbon-carbon double bonds on the surface of molecular sieves, enabling the molecular sieves to directly participate in the polymerization and cross-linking reaction of sodium polyacrylate superabsorbent polymer (SAP), becoming part of the three-dimensional network of SAP, and greatly improving the compatibility of molecular sieves with the core materials of diapers.

[0032] Optionally, in step S1, a composite alkali is used for alkali fusion, and the alkali fusion roasting temperature is 680°C. The composite alkali includes, by weight, 40-70 parts of sodium carbonate and 30-50 parts of sodium hydroxide.

[0033] By adopting the above technical solution and using a composite alkali system of sodium carbonate and sodium hydroxide, compared with the alkali fusion of sodium carbonate alone, the eutectic point of this composite alkali is below 280℃ and can be completely melted at 680℃, which greatly reduces the roasting temperature required for fly ash activation. Compared with the conventional alkali fusion process above 800℃, energy consumption is reduced, and the risk of high-temperature corrosion of equipment is also reduced.

[0034] The composite alkali ratio and calcination temperature of 680℃ can completely destroy the stable crystalline phases of quartz and mullite in fly ash, and completely convert the glassy and crystalline silica-alumina in fly ash into soluble active sodium aluminosilicate species, which greatly improves the utilization rate of silica-alumina sources in fly ash and avoids waste of raw materials.

[0035] Low-temperature calcination at 680℃ can avoid silicon-aluminum sintering deactivation caused by high temperature, while reducing the high-temperature volatilization of heavy metals in fly ash and reducing the difficulty of subsequent purification and impurity removal.

[0036] Optionally, carbon dioxide gas is introduced during the pre-aluminum precipitation and purification process in S2 for pH adjustment.

[0037] By adopting the above technical solution and using carbon dioxide as an acidifying agent, compared with strong inorganic acids such as hydrochloric acid or sulfuric acid, the pH adjustment process is mild and controllable, without the risk of local over-acidity. The pH control window for industrial operation is as wide as ±0.5, avoiding the problems of aluminum precipitation re-dissolution or silicon co-precipitation caused by inorganic acid pH adjustment, thus achieving efficient and precise separation of silicon and aluminum sources.

[0038] The pH can be adjusted step by step to first pre-precipitate aluminum to separate high-purity aluminum hydroxide, and then purify the sodium silicate solution. The prepared aluminum source has high purity and low residual aluminum content in the silicon source. The high-purity silicon-aluminum source can ensure that the molecular sieve synthesized by subsequent hydrothermal synthesis is a pure phase P-type molecular sieve with no impurity crystal formation and stable and controllable crystallinity.

[0039] Carbon dioxide acidification leaves no irritating and harmful anions such as chloride and sulfate residues, significantly reducing the difficulty and water consumption of subsequent washing, and reducing wastewater discharge. At the same time, the products produced have no harmful anion residues, meet the hygiene and safety standards for baby diapers, and pose no risk of skin irritation.

[0040] Optionally, the precursor solution in S3 comprises, by weight: 100 parts of alumina dry basis, 70-110 parts of silica dry basis, 50-80 parts of sodium oxide dry basis, 20-60 parts of tetraethylammonium hydroxide, 2-6 parts of P-type molecular sieve seed crystals, and 1800-2500 parts of deionized water.

[0041] By adopting the above technical solution, the ratio is precisely matched to the thermodynamic stability window of P-type molecular sieve synthesis, and pure phase P-type zeolite molecular sieve can be synthesized stably.

[0042] The addition of tetraethylammonium hydroxide in the formulation serves as a soft template agent, which can construct mesoporous channels in situ during the molecular sieve crystallization process without the need for subsequent secondary pore expansion, thus simplifying the process and laying the pore foundation for subsequent modification and ammonia molecule mass transfer.

[0043] The addition of P-type molecular sieve seed crystals in the formulation can significantly shorten the crystallization induction period, inhibit the formation of impurity crystals, and improve crystallinity. At the same time, it reduces the temperature and time required for crystallization, thereby improving production efficiency.

[0044] This formulation of the precursor liquid system is highly stable, has a high tolerance for raw material impurities, and is compatible with silicon-aluminum sources derived from fly ash. It eliminates the need for ultra-high purity raw materials, further reducing production costs.

[0045] Optionally, the hydrothermal crystallization temperature is 130°C and the time is 12 hours.

[0046] By adopting the above technical solution, the hydrothermal crystallization parameters of 130℃ and 12h are perfectly matched with the precursor liquid ratio. Under the premise of ensuring complete crystallization of molecular sieve, the crystallization time of conventional P-type molecular sieve (more than 24h) can be shortened by half, improving production efficiency and significantly reducing production energy consumption and time costs.

[0047] This crystallization temperature avoids excessively large molecular sieve grains, agglomeration, and pore blockage caused by high-temperature crystallization, and also avoids incomplete crystallization and impurity crystal formation caused by low-temperature crystallization. The synthesized molecular sieve grains are uniform and the particle size is controllable, with a complete hierarchical pore structure.

[0048] The crystallization parameters have low pressure requirements for the reactor equipment, and conventional industrial hydrothermal reactors can meet the requirements.

[0049] In summary, this application includes at least the following beneficial effects.

[0050] Using industrial solid waste fly ash as the core raw material, a low-temperature alkali fusion activation process of sodium carbonate and sodium hydroxide composite alkali system at 680℃ is used to significantly improve the dissolution efficiency and reactivity of silicon and aluminum components in fly ash. Combined with a pre-precipitation aluminum, solid-liquid separation and purification and volume fixation process controlled by stepwise carbon dioxide acidification, high-purity sodium silicate and sodium aluminate solutions can be stably separated, laying a controllable raw material foundation for the large-scale stable synthesis of molecular sieves.

[0051] By using a precisely proportioned precursor liquid system based on alumina dry basis, combined with a hydrothermal crystallization process induced by tetraethylammonium hydroxide soft template agent and P-type molecular sieve seed crystals at 130℃ for 12 hours, a pure phase P-type molecular sieve with high crystallinity and no impurities can be synthesized. At the same time, a primary mesoporous structure adapted to ammonia molecule mass transfer can be constructed in situ.

[0052] After obtaining hydrogen-form molecular sieves through constant-temperature ammonium exchange at 60℃ and gradient deammonium calcination at 480℃, a modification process involving the combination of citric acid monohydrate and L-lactic acid with organic acids and stepwise dealuminization at 85℃ for 40 min, followed by PEG4000-guided pore formation, can directionally construct hierarchical pore structures of micropores, mesopores, and macropores, as well as high-density strong B acid sites. This fundamentally solves the industry pain points of traditional molecular sieves, such as poor ammonia adsorption selectivity and easy saturation failure in the high-salt matrix of infant urine.

[0053] Finally, through in-situ drying process of functional aqueous solution atomization loading and surface modification process of silane coupling agent grafting, the molecular sieve is simultaneously endowed with the additional functions of long-acting urease inhibition and skin soothing, and excellent copolymer compatibility with superabsorbent resin for diapers.

[0054] The entire process combines the environmental advantages of solid waste resource utilization with the advantages of low cost. The process parameter window is wide and the batch stability is strong. The acidic molecular sieve products prepared can be precisely adapted to the application scenarios of diapers, achieving a synergistic effect from inhibiting urea decomposition and ammonia production at the source to highly selective and long-lasting ammonia locking. At the same time, it meets the safety and compliance requirements for infant skin contact and fully adapts to the functional upgrade needs of diaper cores. Attached Figure Description

[0055] Figure 1 This is a flowchart of the main steps of this application. Detailed Implementation

[0056] The present application will be further described in detail below with reference to the accompanying drawings.

[0057] This application discloses a method for preparing a highly amino acid-absorbing zeolite molecular sieve, referring to... Figure 1 Specifically, it includes the following steps.

[0058] S1. Alkali fusion activation of fly ash to obtain calcined product.

[0059] Take 100 portions of fly ash raw material, crush it, and pass it through a 200-mesh sieve. Then crush the material passing through the sieve again until all of it passes through a 200-mesh sieve to obtain fine fly ash powder. Perform magnetic separation on the fine fly ash powder to remove free ferromagnetic material and iron-containing impurities. After magnetic separation, take a sample and test it. If the mass fraction of ferric oxide is below 2.5%, it is considered qualified.

[0060] The magnetically separated fly ash fine powder is then mixed evenly with the composite alkali to obtain a mixed powder. The composite alkali, by weight, comprises: 40-70 parts sodium carbonate and 30-50 parts sodium hydroxide. Sodium carbonate is the main component of the composite alkali, which activates the fly ash vitreous body through low-temperature melting; sodium hydroxide is an auxiliary component of the composite alkali, which lowers the eutectic point and improves the activation efficiency.

[0061] The mixed powder is spread evenly with a thickness controlled below 4 cm, heated to 680 °C at a heating rate of 5 °C / min, and calcined at a constant temperature for 1.5 h to completely melt the composite alkali, destroy the stable quartz and mullite crystalline phases in the fly ash, and completely convert the glassy body and crystalline phase silica and aluminum into soluble active species of sodium silicate and sodium aluminate.

[0062] After calcination, the material was cooled to room temperature and ground through a 200-mesh sieve to obtain the calcined product.

[0063] S2. The calcined material is extracted with hot water, aluminum is pre-precipitated, solid-liquid separation is performed, and the solution is purified and brought to a constant volume to obtain sodium silicate solution and sodium aluminate solution.

[0064] When leaching with hot water, first mix 180-200 parts of the calcined material with 400-600 parts of deionized water at 80°C, stir and leach for 2 hours at a constant temperature, let stand for 60 minutes after stirring stops, filter to remove insoluble residue, and obtain a clear sodium aluminosilicate mixed solution. Take a sample to determine the mass concentration of silica and alumina.

[0065] During the pre-precipitation of aluminum, carbon dioxide gas is first introduced into the sodium aluminosilicate mixed solution under continuous stirring and a closed state. When the pH of the system drops to 11±0.5, the carbon dioxide introduction is stopped and stirring is continued for 30 minutes, and then it is allowed to stand for 120 minutes. At this time, the sodium aluminate is completely hydrolyzed into aluminum hydroxide precipitate, while the sodium silicate remains soluble, and there is no risk of silicon coprecipitation.

[0066] During solid-liquid separation, pressure filtration is used, the precipitate is crude aluminum hydroxide wet filter cake, and the filtrate is crude sodium silicate solution.

[0067] During purification, the crude sodium silicate solution was purged with carbon dioxide gas in a closed environment until the pH reached 9±0.5, then allowed to stand for 60 minutes. The solution was then filtered to remove trace amounts of co-precipitated aluminum hydroxide impurities, resulting in a high-purity sodium silicate solution. A sample was taken to determine the silica mass concentration.

[0068] During the volume adjustment, the crude aluminum hydroxide wet filter cake is mixed with 10-20 parts of a 30% sodium hydroxide solution, and the mixture is stirred and heated to 95°C until the solid is completely dissolved. Then, it is cooled to room temperature, and deionized water is added to adjust the pH to 12±0.1 to obtain the final high-purity sodium aluminate solution for crystallization. The mass concentration of alumina is then determined.

[0069] S3. Based on sodium silicate solution and sodium aluminate solution, the precursor solution is prepared, hydrothermal crystallization is carried out, solid-liquid separation and washing are performed to obtain P-type molecular sieve wet filter cake.

[0070] The precursor solution comprises, by weight: 100 parts alumina (dry basis), 70-110 parts silica (dry basis), 50-80 parts sodium oxide (dry basis), 20-60 parts tetraethylammonium hydroxide, 2-6 parts p-type molecular sieve seed crystals, and 1800-2500 parts deionized water. The alumina (dry basis) is derived from a high-purity sodium aluminate solution, serving as the aluminum source for the molecular sieve framework; the silica (dry basis) is derived from a high-purity sodium silicate solution, serving as the silicon source for the molecular sieve framework; the sodium oxide (dry basis) is a mineralizing agent derived from both high-purity sodium aluminate and high-purity sodium silicate solutions, used to regulate the system's alkalinity. Tetraethylammonium hydroxide (TEAOH) serves as a soft template agent, constructing mesoporous channels in situ. The p-type molecular sieve seed crystals are used for seed induction, inhibiting impurities, and improving crystallinity. Deionized water is used as a hydrothermal synthesis solvent to regulate the system concentration.

[0071] When preparing the precursor solution, first take an appropriate amount of high-purity sodium silicate solution, and then add an appropriate amount of high-purity sodium aluminate solution dropwise while stirring at room temperature. After the addition is complete, continue stirring for 30 minutes, then add tetraethylammonium hydroxide solution and P-type molecular sieve seed crystals, and continue stirring for another 60 minutes. The final standardized molar ratio of the precursor solution is: SiO2 / Al2O3 = 1.5, Na2O / Al2O3 = 3.0, TEAOH / Al2O3 = 0.8, H2O / SiO2 = 100.

[0072] During hydrothermal crystallization, the precursor solution was heated to 130°C at a rate of 2°C / min and statically kept at a constant temperature for 12 hours. After completion, it was removed and rapidly cooled to room temperature with deionized water to terminate the crystallization process.

[0073] During solid-liquid separation, centrifugation for 20 minutes yields a molecular sieve filter cake and crystallization mother liquor. During washing, the molecular sieve filter cake is washed several times with deionized water until the pH of the filtrate after the final wash is less than or equal to 8 and the conductivity is less than or equal to 300 μS / cm, thus obtaining a qualified P-type molecular sieve filter cake.

[0074] S4. The wet filter cake of P-type molecular sieve is subjected to ammonium exchange, deammonium calcination and stepwise pore formation to obtain hydrogen-type P-type molecular sieve dry powder.

[0075] During ammonium exchange, 100 parts of the wet filter cake of P-type molecular sieve are first taken, and 40-60 parts of a 1 mol / L ammonium chloride solution are added. Ammonium chloride is used as the ammonium exchange reagent to prepare ammonium-type molecular sieves. Then, the temperature is raised to 60℃ and stirred at a constant temperature for 60 minutes. After standing for 30 minutes, the mixture is centrifuged. The ammonium exchange is repeated several times until the last exchange is completed. The filter cake is then washed with deionized water until no chloride ions are detected by silver nitrate titration, yielding the wet filter cake of ammonium-type P-type molecular sieve.

[0076] During the deammonium roasting process, the wet filter cake of the ammonium-type P-type molecular sieve was dried by forced air at 120℃ for 6 hours, then spread out with a thickness of less than 3 cm, and then heated to 480℃ at a rate of 3℃ / min and roasted at a constant temperature for 3 hours to completely remove the ammonium ions and convert it into hydrogen-type P-type molecular sieve. After cooling to room temperature, a sample was taken and the pH of a 1% aqueous solution was measured to be 5.5±0.2.

[0077] For stepwise pore formation, first prepare an organic acid mixture, which by weight includes: 15-25 parts citric acid monohydrate and 3-7 parts L-lactic acid. Citric acid monohydrate is the primary dealuminant, constructing Brønsted acid sites. L-lactic acid is the auxiliary dealuminant, gently controlling the dealuminination rate and preventing framework collapse. The concentration of citric acid monohydrate is 0.8 mol / L, and the concentration of L-lactic acid is 0.2 mol / L.

[0078] The first step involves mixing hydrogen-form P-type molecular sieves with organic acid and isothermally stirring at 85°C for 40 minutes to achieve gentle aluminum removal from the main framework during the peak dealumination rate stage. The second step involves adding 1-5 parts of PEG4000 to the system while maintaining constant temperature and stirring at 85°C. PEG4000 acts as a mesoporous directing agent, used to directionally construct hierarchical channels. After complete dissolution, stirring continues for another 50 minutes. PEG4000 captures fresh defect sites in real time, directionally guiding the formation of 3-6 nm mesopores and 10-20 nm macropores, while preserving the original 0.3-0.5 nm microporous structure of the molecular sieve. The high-temperature residence time of PEG4000 in the strong acid is controlled within 50 minutes, eliminating the risk of degradation and preventing interference with dealumination efficiency.

[0079] After the reaction was completed, the mixture was diluted twice with room temperature deionized water to terminate the reaction. The mixture was then centrifuged, and the filter cake was washed three times with 80℃ deionized water, followed by washing with room temperature deionized water until the pH of the filtrate was 6±0.2 and the conductivity was 200 μS / cm. Finally, the mixture was dried at 120℃ with a forced-air drying process for 4 hours to obtain hydrogen-form P-type molecular sieve powder.

[0080] S5. The hydrogen-type P-type molecular sieve dry powder is atomized, loaded, dried, and surface modified to obtain amino acid-absorbing zeolite molecular sieve.

[0081] For atomized loading, first take 100 parts of hydrogen-form P-type molecular sieve dry powder, preheat it to 80℃ under low-speed stirring, and maintain the temperature for 10 minutes. Then, spray the functional aqueous solution into the hydrogen-form P-type molecular sieve dry powder under high-pressure atomization while it is under constant temperature stirring, with the atomization pressure above 0.3 MPa. After the spraying is completed, continue stirring for 10 minutes to complete the dual-functional loading of enzyme inhibition and skin soothing.

[0082] The above-mentioned functional aqueous solution comprises, by weight: 1-3 parts acetoxyxamic acid, 0.5-2 parts allantoin, and 20-40 parts deionized water. Acetoxyxamic acid is a long-acting urease inhibitor that reduces ammonia production. Allantoin is a skin-soothing ingredient that relieves ammonia irritation. The concentration of the functional aqueous solution is 10%, of which the concentration of acetoxyxamic acid is 6.7% and the concentration of allantoin is 3.3%. During preparation, acetoxyxamic acid and allantoin are added to deionized water at 75°C and stirred until completely dissolved. The solution is then passed through a 5μm filter to remove trace amounts of insoluble matter. The total heat preservation time from preparation to the end of spraying should be controlled within 3 minutes; cooling or prolonged standing is not permitted.

[0083] During drying, the powder after atomization load is kept at 90°C and stirred in situ, and then dried in a ventilated manner for 20 minutes to completely remove free water on the surface of the powder and capillary water in the pores.

[0084] During surface modification, the dried powder is kept stirred, and 1-4 parts of silane coupling agent KH570 are sprayed into the powder under high pressure (above 0.3 MPa). After spraying, stirring is continued for 30 minutes to complete the grafting reaction.

[0085] After modification, heating was stopped, and the mixture was kept stirred and cooled to room temperature. The powder was then taken out and passed through a 200-mesh sieve. Subsequently, it was washed with deionized water to remove free impurities on the surface. The filter cake was placed in a forced-air drying oven and dried at a constant temperature of 90°C for 2 hours to obtain a high amino acid-absorbing zeolite molecular sieve.

[0086] The following detailed description includes specific embodiments and comparative examples.

[0087] Example 1:

[0088] Specifically, the preparation method of a highly absorbent zeolite molecular sieve is described above, wherein S1 contains 40 parts sodium carbonate and 30 parts sodium hydroxide.

[0089] S2 contains 180 parts of calcined material, 400 parts of deionized water, and 10 parts of sodium hydroxide solution.

[0090] S3 contains 70 parts of silica dry base, 50 parts of sodium oxide dry base, 20 parts of tetraethylammonium hydroxide, 2 parts of P-type molecular sieve seed crystals, and 1800 parts of deionized water.

[0091] S4 contains 40 parts ammonium chloride solution, 15 parts citric acid monohydrate, 3 parts L-lactic acid, and 1 part PEG4000.

[0092] S5 contains 1 part acetyloxyoxime acid, 0.5 parts allantoin, 20 parts deionized water, and 1 part silane coupling agent.

[0093] Example 2:

[0094] The difference from Example 1 is that S1 contains 70 parts sodium carbonate and 50 parts sodium hydroxide.

[0095] S2 contains 200 parts of calcined material, 600 parts of deionized water, and 20 parts of sodium hydroxide solution.

[0096] S3 contains 110 parts of silica dry base, 80 parts of sodium oxide dry base, 60 parts of tetraethylammonium hydroxide, 6 parts of P-type molecular sieve seed crystals, and 2500 parts of deionized water.

[0097] S4 contains 60 parts ammonium chloride solution, 25 parts citric acid monohydrate, 7 parts L-lactic acid, and 5 parts PEG4000.

[0098] S5 contains 3 parts acetyloxyoxime acid, 2 parts allantoin, 40 parts deionized water, and 4 parts silane coupling agent.

[0099] Comparative Example 1:

[0100] The difference from Example 1 is that the composite alkali in S1 is replaced with 70 parts of sodium carbonate, the calcination temperature is 800℃, and the calcination time is 2h.

[0101] Comparative Example 2:

[0102] The difference from Example 1 is that the carbon dioxide gas in S2 is replaced with 1 mol / L hydrochloric acid for pH adjustment.

[0103] Comparative Example 3:

[0104] The difference from Example 1 is that the precursor solution in S3 removes tetraethylammonium hydroxide.

[0105] Comparative Example 4:

[0106] The difference from Example 1 is that the precursor solution in S3 removes the P-type molecular sieve seeds.

[0107] Comparative Example 5:

[0108] The difference from Example 1 is that in S3, the precursor liquid is heated to 180°C at 2°C / min and statically isothermal crystallized for 24 hours during hydrothermal crystallization.

[0109] Comparative Example 6:

[0110] The difference from Example 1 is that S4 is removed, that is, S5 is performed directly after S3 is completed.

[0111] Comparative Example 7:

[0112] The difference from Example 1 is that the ammonium exchange and deammonium roasting in S4 are replaced by two exchanges with 1 mol / L hydrochloric acid solution at 80°C with constant stirring, each time for 2 hours. After the exchange, the solution is washed until no chloride ions are detected and the pH of the filtrate is 6±0.2. After drying, the solution is then used for stepwise pore forming.

[0113] Comparative Example 8:

[0114] The difference from Example 1 is that in step S4, organic acid and PEG4000 are added simultaneously and stirred at a constant temperature for 90 minutes during the step-by-step pore formation.

[0115] Comparative Example 9:

[0116] The difference from Example 1 is that only organic acid was added in the stepwise pore forming of S4, and the dealuminization time was 90 min, without the addition of PEG4000.

[0117] Comparative Example 10:

[0118] The difference from Example 1 is that the organic acid in S4 is replaced with 18 parts of citric acid monohydrate.

[0119] The molecular sieve powders obtained in each embodiment and comparative example were tested for relevant indicators.

[0120] To determine the ammonia adsorption rate over 10 minutes, prepare simulated infant urine: urea 15 g / L, sodium chloride 9 g / L, potassium chloride 1.5 g / L, calcium chloride 0.5 g / L, and creatinine 1 g / L. Adjust the pH to 6 ± 0.1 with 0.1 mol / L hydrochloric acid / sodium hydroxide. Weigh 0.5 g of the molecular sieve sample and place it in a 250 mL stoppered conical flask. Add 100 mL of simulated infant urine and 0.01 g of urease. Seal the flask and place it in a 37°C constant temperature water bath shaker at 150 rpm for adsorption.

[0121] After shaking for 10 min, immediately take 5 mL of supernatant, centrifuge at high speed for 10 min, take the supernatant and determine the concentration of remaining ammonia nitrogen by Nessler's reagent spectrophotometry, and calculate the adsorption amount in 10 min.

[0122] The saturated ammonia uptake was determined based on an experiment of rapid ammonia uptake over 10 minutes. The experiment was conducted with continuous oscillation, and ammonia nitrogen concentration was measured every 1 hour until the concentration no longer changed. The saturated ammonia uptake was then calculated using the formula: (initial ammonia nitrogen concentration - remaining ammonia nitrogen concentration) × solution volume / molecular sieve sample mass.

[0123] To determine the 4-hour ammonia escaping inhibition rate, 0.5 g of molecular sieve sample was weighed and placed in a 100 mL headspace vial. 20 mL of the above-mentioned simulated infant urine and 0.002 g of urease were added, and the vial was immediately sealed. A blank control group (without molecular sieve, all other conditions were the same) was also set up. All samples were incubated at 37℃ for 4 hours. The peak area of ​​ammonia in the headspace vial was determined by headspace gas chromatography. Using the blank control group as a baseline, the ammonia escaping inhibition rate was calculated as (ammonia peak area in the blank control group - ammonia peak area in the sample group) / ammonia peak area in the blank control group × 100%.

[0124] To assess water absorption and retention, 20g of acrylic acid was neutralized to 75% neutralization with 30% sodium hydroxide solution. 0.02g of crosslinking agent N,N-methylenebisacrylamide and 0.04g of initiator ammonium persulfate were added, along with 1g of molecular sieve sample. After stirring thoroughly, the mixture was polymerized in a water bath at 70℃ for 2 hours to obtain a hydrogel. The gel was then chopped, dried at 120℃ using a forced-air drying process, and pulverized through a 100-mesh sieve to obtain the modified water-absorbing resin sample.

[0125] Accurately weigh 0.2g of modified water-absorbing resin, place it in a non-woven tea bag, immerse it in a 0.9% sodium chloride solution for 30 minutes, hang it to drain for 10 minutes, weigh it, and calculate the water absorption ratio.

[0126] Place the water-saturated SAP tea bags in a centrifuge, centrifuge at 2500 r / min for 3 min, weigh them, and calculate the water retention rate.

[0127] To determine the residual amount of harmful anions, accurately weigh 5g of molecular sieve sample, add 100mL of deionized water, extract by shaking in an 80℃ water bath for 2h, centrifuge and collect the supernatant, filter through a 0.22μm filter membrane, and then determine the content of chloride and sulfate ions using an ion chromatograph.

[0128] The results of the above test indicators are shown in Table 1.

[0129] Table 1:

[0130]

[0131] Comparative Example 1 shows that the molecular sieve product prepared by the sodium carbonate and sodium hydroxide composite alkali system of this application has similar performance to that of sodium carbonate alone, but the composite alkali has a lower eutectic point and can completely melt and destroy the stable crystalline phase of fly ash at 680℃, which greatly reduces the calcination temperature and energy consumption.

[0132] Comparative Example 2 shows that using carbon dioxide gas for pH adjustment in S2 is gentler and more controllable, and the molecular sieve product contains fewer residual anions and is less likely to cause skin irritation.

[0133] Comparative Example 3 shows that tetraethylammonium hydroxide constructs mesoporous channels in situ during hydrothermal crystallization, forming a hierarchical pore structure adapted to the rapid mass transfer of ammonia molecules, thereby enhancing the ammonia adsorption capacity of the molecular sieve. This proves that pure microporous molecular sieves without mesoporous structures have extremely high resistance to ammonia molecule mass transfer in high-salt urine matrix, resulting in a significant decrease in rapid adsorption capacity and saturated adsorption capacity, making them completely unsuitable for the rapid ammonia production after infant urination.

[0134] Comparative Example 4 shows that without P-type molecular sieve seed induction, the silicon and aluminum source from fly ash is prone to impurity fluctuations, resulting in impurity crystals and insufficient crystallinity. This directly leads to a decrease in the number of acid sites in the molecular sieve and a deterioration in ammonia adsorption performance. This indicates that the addition of molecular sieve seed is the key to ensuring batch stability and pure phase synthesis of fly ash-based molecular sieves, solving the current pain points of impurity crystals and large batch fluctuations in the synthesis of molecular sieves using fly ash.

[0135] As can be seen from Comparative Example 5, compared with conventional high-temperature long-time crystallization, the low-temperature short-time crystallization parameters of this application not only shorten the production cycle by 50% and significantly reduce energy consumption, but also avoid the problems of grain agglomeration, pore blockage and decrease in specific surface area caused by high-temperature crystallization, which lead to a decrease in ammonia absorption capacity.

[0136] Comparative Example 6 shows that traditional sodium-type P-type molecular sieves have poor ammonia absorption capacity in high-salt environments and will also degrade the water absorption and retention performance of water-absorbing resins, making them unsuitable for hygiene products.

[0137] Comparative Example 7 shows that the ammonium exchange and deammonium calcination of this application can gently achieve sodium ion exchange and hydrogen form conversion, completely avoiding the problems of decreased crystallinity, framework collapse and amorphous phase generation caused by direct corrosion of the molecular sieve framework by strong acid. Under the premise of preserving the complete crystal form and pore structure, high-density strong Brønsted acid sites are constructed, proving that the direct acid exchange process not only leads to a significant deterioration of the ammonia absorption performance of the molecular sieve, but also has the problem of excessive anion residue, which cannot meet the hygiene and safety requirements of baby diapers.

[0138] Comparative Example 8 shows that when organic acid and PEG4000 are added simultaneously, PEG4000 will deactivate under strong acid and high temperature. At the same time, it will coat the surface of the molecular sieve, hindering the contact between organic acid and framework aluminum, resulting in a decrease in dealuminization efficiency, a reduction in the number of acid sites, and poor mesopore construction effect. This directly degrades the rapid ammonia absorption and long-term ammonia locking performance of the molecular sieve. Therefore, the stepwise pore formation process of this application is the key to improving the ammonia absorption capacity of the molecular sieve by taking into account both the number of acid sites and the hierarchical pore structure.

[0139] Comparative Example 9 shows that organic acid dealuminization cannot form a stable mesoporous / macroporous structure. The mass transfer resistance of ammonia molecules in pure microporous molecular sieves is extremely high, and their rapid adsorption capacity in high-salt urine is almost completely lost, making them unsuitable for the core requirement of rapid ammonia capture in diapers.

[0140] Comparative Example 10 shows that the dealuminization rate of citric acid alone is uncontrollable, and problems such as local over-dealuminization, framework destruction and amorphous phase formation are prone to occur, resulting in a significant decrease in the number of acid sites and severe deterioration of ammonia absorption performance.

[0141] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a highly amino acid-absorbing zeolite molecular sieve, characterized in that: Specifically, the following steps are included: S1. Alkali fusion activation of fly ash to obtain calcined product; S2. The calcined material is extracted with hot water, aluminum is pre-precipitated, solid-liquid separation is performed, and the purified and diluted to a final volume to obtain sodium silicate solution and sodium aluminate solution. S3. Based on sodium silicate solution and sodium aluminate solution, the precursor solution is prepared, hydrothermal crystallization is carried out, solid-liquid separation and washing are performed to obtain P-type molecular sieve wet filter cake. S4. The wet filter cake of P-type molecular sieve is subjected to ammonium exchange, deammonium calcination and stepwise pore formation to obtain hydrogen-type P-type molecular sieve dry powder. S5. The hydrogen-type P-type molecular sieve dry powder is atomized, loaded, dried, and surface modified to obtain amino acid-absorbing zeolite molecular sieve.

2. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 1, characterized in that: The entire process in S4 first involves mixing the wet filter cake of P-type molecular sieve with ammonium chloride solution, separating and repeating the process several times to obtain the wet filter cake of ammonium-type P-type molecular sieve. Then, the wet filter cake of ammonia-type P-type molecular sieve is dried and calcined to remove ammonium ions to obtain hydrogen-type P-type molecular sieve. Finally, the hydrogen-type P-type molecular sieve is dealuminized using organic acid and then guided to form pores.

3. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 2, characterized in that: The organic acids, by weight, include: 15-25 parts of citric acid monohydrate and 3-7 parts of L-lactic acid.

4. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 2, characterized in that: The dealumination temperature is 85℃ and stirring is performed for 40 minutes. PEG4000 is added to the guide hole.

5. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 2, characterized in that: The ammonium exchange temperature is 60℃, and the mixture is stirred at a constant temperature for 60 minutes. After standing for 30 minutes, it is centrifuged to separate the ammonium. The deammonium calcination is first dried at 120℃ for 6 hours, and then heated to 480℃ for 3 hours.

6. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 1, characterized in that: In step S5, the hydrogen-type P-type molecular sieve dry powder is first preheated, and then the functional aqueous solution is atomized and sprayed into the preheated hydrogen-type P-type molecular sieve dry powder to perform dual-function loading of urease inhibition and skin soothing. Then, it is dried in situ by ventilation, and finally, it is grafted and modified with a silane coupling agent and dried.

7. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 1, characterized in that: In S1, a composite alkali is used for alkali fusion, and the alkali fusion roasting temperature is 680℃. The composite alkali includes, by weight, 40-70 parts of sodium carbonate and 30-50 parts of sodium hydroxide.

8. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 1, characterized in that: In S2, carbon dioxide gas is introduced during the pre-aluminum precipitation and purification process to adjust the pH.

9. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 1, characterized in that: The precursor solution in S3 comprises, by weight: 100 parts of alumina dry basis, 70-110 parts of silica dry basis, 50-80 parts of sodium oxide dry basis, 20-60 parts of tetraethylammonium hydroxide, 2-6 parts of P-type molecular sieve seed crystals, and 1800-2500 parts of deionized water.

10. The method for preparing a highly amino acid-absorbing zeolite molecular sieve according to claim 9, characterized in that: The hydrothermal crystallization temperature is 130℃ and the time is 12h.

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