A method for modifying a ts-1 molecular sieve

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a modification method of TS-1 molecular sieve. The application forms a temporary protective layer by pre-entering small molecule amine into part of the micropore channels of the TS-1 molecular sieve, and then uses in-situ etching of inorganic alkali to form mesopores in the un-protected channels. During the etching process, the channels into which the small molecule amine does not enter are pre-destroyed, and the small molecule amine protects the zeolite framework to a certain extent, slows down the breaking and removal of the skeleton bonds in the inorganic alkali etching process, exposes more internal active sites, and improves the catalytic performance of the cyclohexanone ammoximation reaction. The application does not need a template agent and secondary hydrothermal treatment, is low in cost and high in efficiency, and the obtained catalyst is high in activity in the cyclohexanone ammoximation and propylene epoxidation reactions.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and specifically to a method for modifying TS-1 molecular sieve. Background Technology

[0002] Cyclohexanone oxime is a key intermediate in the synthesis of caprolactam, which, as a monomer of nylon-6, has irreplaceable industrial value in fields such as synthetic fibers and engineering plastics. Traditional cyclohexanone oxime processes suffer from numerous byproducts, high corrosivity, and severe environmental pollution, failing to meet the demands of green chemical development. Currently, the cyclohexanone ammonoxime route, using titanium silicate molecular sieve (TS-1) as a catalyst and H2O2 as an oxidant, offers advantages such as mild reaction conditions, high selectivity, and environmental friendliness, and has become a focus of attention in both industry and academia. The isolated four-coordinate titanium active center in TS-1 can efficiently activate H2O2, promoting the formation of hydroxylamine intermediates, which then react with cyclohexanone to form oximes, achieving an atom-economical conversion.

[0003] However, in practical applications, the micropores (approximately 0.55 nm) of conventional TS-1 significantly restrict the mass transfer of larger molecules such as cyclohexanone (kinetic diameter approximately 0.6 nm), making it difficult for reactants to diffuse to active sites and limiting the reaction rate. High-boiling-point organic compounds generated by side reactions tend to accumulate in the micropores, causing blockage of active sites and rapid deactivation of the catalyst. Some titanium species exist in non-skeleton forms (such as TiO2), which not only lack catalytic activity but may also accelerate the ineffective decomposition of H2O2, reducing the utilization rate of the oxidant.

[0004] To address the aforementioned issues, modifying TS-1 to optimize its structure and surface properties has become a key strategy for improving its ammonium oxime performance. Currently, alkali treatment and hydrothermal post-treatment are two mainstream methods for TS-1 modification. Alkali treatment involves pretreating TS-1 with NaOH solution, which can desilicate and construct mesopores within the TS-1 molecular sieve, forming a microporous-mesoporous composite structure, significantly improving mass transfer efficiency and exposing more active sites. However, excessive desilication caused by alkali treatment can easily disrupt the integrity of the MFI framework of the TS-1 molecular sieve, leading to titanium loss or structural collapse, thus reducing the stability and activity of the molecular sieve. Furthermore, alkali treatment has poor selectivity for pores, failing to precisely protect specific microporous regions.

[0005] Compared to alkaline treatment, hydrothermal post-treatment of TS-1 can preserve the MFI framework structure of TS-1 molecular sieves while migrating non-framework titanium into the lattice through a self-healing mechanism, increasing the proportion of tetracoordinated titanium, and moderately expanding the pore size. However, the hydrothermal post-treatment method requires a secondary hydrothermal treatment using a template agent, which is cumbersome, costly, and has limited precision in pore control, failing to achieve selective protection of micropores and controllable construction of mesopores. Summary of the Invention

[0006] To address the technical challenges of existing TS-1 modification methods in simultaneously achieving selective protection of micropores and controllable construction of mesopores, as well as reducing the stability and activity of molecular sieves, this invention provides a modification method for TS-1 molecular sieves.

[0007] This invention utilizes the selective entry of small-molecule amines into some micropores of TS-1 molecular sieves to form a temporary protective layer. Then, an inorganic base is used to etch the remaining pores of the TS-1 molecular sieve in situ, constructing a mesoporous structure. During the etching process, pores where no small-molecule amines have entered are pre-disrupted, while the small-molecule amines interact with the TS-1 molecular sieve framework through hydrogen bonds and van der Waals forces, thus protecting the zeolite framework to a certain extent and slowing down the breaking and removal of silicon-oxygen-silicon and silicon-oxygen-titanium bonds during inorganic base etching, preventing excessive framework collapse. The method of this invention requires no template agent or secondary hydrothermal treatment, is simple to operate, and has low cost. It can effectively expose internal active sites while protecting the microporous structure, significantly improving the catalytic performance of the modified TS-1 molecular sieve in the cyclohexanone ammoxidation reaction.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows.

[0009] This invention provides a method for modifying TS-1 molecular sieve, comprising the following steps: TS-1 molecular sieve was impregnated and stirred with an amine reagent, and an inorganic alkaline solution was added for stirring and etching to obtain an etched sample. The etched sample was mixed with an ammonium solution for ion exchange, and after removing the solution, it was calcined to obtain a modified TS-1 molecular sieve. The amine reagent was at least one of diethylamine, triethylamine, ethanolamine, n-butylamine, hexamethylenetetramine solution, and ethylenediamine. The ratio of TS-1 molecular sieve to amine reagent was 1 g: 5 mL to 6 mL.

[0010] Preferably, the stirring etching is carried out at 40℃~80℃ for 0.2h~4h.

[0011] Preferably, the inorganic alkaline solution is at least one of sodium carbonate solution, potassium carbonate solution, sodium hydroxide solution, potassium hydroxide solution, and ammonia water.

[0012] Preferably, the concentration of the inorganic alkaline solution is 0.1 mol / L to 2 mol / L; the ratio of TS-1 molecular sieve to inorganic alkaline solution is 1 g: 10 mL to 100 mL.

[0013] Preferably, the concentration of the hexamethylenetetramine solution is 0.1 mol / L to 2 mol / L.

[0014] Preferably, the particle size of the TS-1 molecular sieve is 100nm to 400nm or 1μm to 2μm.

[0015] Preferably, the ammonium solution is an ammonium chloride solution; the concentration of the ammonium chloride solution is 0.1 mol / L to 2 mol / L; and the ratio of TS-1 molecular sieve to ammonium solution is 1 g: 50 mL to 200 mL.

[0016] Preferably, the roasting temperature is 500℃~600℃.

[0017] Preferably, the modification method of TS-1 molecular sieve includes the following steps: TS-1 molecular sieves were dehydrated and degassed under vacuum at 100℃~300℃ and cooled to room temperature to obtain pretreated TS-1 molecular sieves. The pretreated TS-1 molecular sieves were impregnated and stirred with an amine reagent to allow amine molecules to enter some of the micropores of the TS-1 molecular sieves. An inorganic alkaline solution was added and etched by stirring at 40℃~80℃ for 0.2h~4h to obtain an etched sample. The etched sample was mixed with an ammonium solution for ion exchange. After removing the solution, it was calcined at 500℃~600℃ to obtain modified TS-1 molecular sieves.

[0018] This invention involves pretreating TS-1 molecular sieves by vacuum dehydration and degassing, then adding a small-molecule amine reagent for impregnation and stirring. The small-molecule amine interacts with the molecular sieve framework through hydrogen bonds and van der Waals forces, selectively entering some micropores and forming a temporary protective layer. Subsequently, an inorganic alkaline solution is added for stirring and etching. The pores not occupied by the small-molecule amine are preferentially subjected to OH groups. - The silicon-oxygen-silicon and silicon-oxygen-titanium bonds are broken, dissolved, and removed during etching, forming a mesoporous structure. The protected microporous regions are preserved due to the steric hindrance and electronic effects of the small-molecule amine. After etching, ion exchange is performed to remove residual alkali metal ions, followed by calcination at 500℃–600℃ to completely decompose and release the small-molecule amine and ammonium ions within the pores, ultimately yielding a modified TS-1 molecular sieve with a microporous-mesoporous composite structure. In this process, the proportion of protected microporous regions in the TS-1 molecular sieve is controlled by adjusting the amount of small-molecule amine reagent, and the mesoporous scale is controlled by adjusting the concentration of the inorganic alkaline solution. These two factors synergistically achieve a balance between the microporous structure stability and mesoporous mass transfer efficiency of the TS-1 molecular sieve, fully exposing the internal titanium active centers and significantly improving the catalytic performance of the modified TS-1 molecular sieve in the cyclohexanone ammoxidation reaction.

[0019] The beneficial effects of this invention are: 1. This invention employs the synergistic effect of small molecule amines and inorganic bases to post-treat TS-1 molecular sieves. The small molecule amines pre-enter a portion of the micropores of the TS-1 molecular sieve, forming a temporary protective layer. Then, an inorganic base solution is added for selective etching. The small molecule amines that have entered the micropores protect these pores from etching by the inorganic base, while the pores that have not entered the small molecule amines are etched by the inorganic base to form mesopores. This improves the problem of excessive pore collapse during traditional alkali treatment, thereby enhancing the relative crystallinity and stability of the molecular sieve. The added small molecule amines and inorganic bases are inexpensive, require no template agents or secondary hydrothermal processes, and are suitable for industrial-scale mass production.

[0020] 2. This invention achieves spatial separation between the micropore protection region and the mesoporous etching region by selectively protecting the micropores of TS-1 molecular sieve with small molecule amines and directionally etching the unprotected pores with inorganic bases. This effectively controls the pore structure, exposing more internal active sites and providing a large number of active centers for the cyclohexanone ammonium oxime reaction. Compared with the untreated TS-1 molecular sieve powder, the post-treated TS-1 molecular sieve shows an increase in cyclohexanone conversion rate from 55.8% to 82.6%–88.6% and cyclohexanone oxime yield from 21.9% to 53.7%–75.8%, exhibiting excellent performance in the cyclohexanone ammonium oxime reaction. This can reduce actual industrial production costs and improve energy efficiency. Attached Figure Description

[0021] Figure 1 Scanning electron microscope (SEM) images of the modified TS-1 molecular sieves prepared in Examples 1 and 5, and control sample one of Comparative Example 1 and control sample two of Comparative Example 2. Specifically, (a) is an SEM image of control sample one of Comparative Example 1; (b) is an SEM image of the modified TS-1 molecular sieve of Example 1; (c) is an SEM image of control sample two of Comparative Example 2; and (d) is an SEM image of the modified TS-1 molecular sieve of Example 5.

[0022] Figure 2 The diagram shows the geometric structure of TS-1 molecular sieve-small molecule amine dimers constructed using the Gaussian 09 package. (a) represents TS-1 molecular sieve-ethylenediamine; (b) represents TS-1 molecular sieve-hexanediamine; (c) represents TS-1 molecular sieve-n-butylamine; (d) represents TS-1 molecular sieve-diethylamine; (e) represents TS-1 molecular sieve-triethylamine; (f) represents TS-1 molecular sieve-ethanolamine; (g) represents TS-1 molecular sieve-pyridine; (h) represents TS-1 molecular sieve-N,N-dimethylformamide; and (i) represents TS-1 molecular sieve-hexamethylenetetramine. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0024] This invention utilizes a small-molecule amine to pre-enter some micropores of a TS-1 molecular sieve to form a temporary protective layer, followed by in-situ etching of the unprotected pores with an inorganic base to create mesopores. During etching, pores without small-molecule amine entry are pre-damaged, while the small-molecule amine protects the zeolite framework to some extent, slowing down the breaking and removal of skeletal bonds during inorganic base etching, thus exposing more internal active sites and improving the catalytic performance of the cyclohexanone ammonium oxime reaction. This invention eliminates the need for template agents and secondary hydrothermal treatment, resulting in low cost, high efficiency, and a catalyst with high activity in the cyclohexanone ammonium oxime reaction and propylene epoxidation.

[0025] This invention provides a method for modifying TS-1 molecular sieve, comprising the following steps: TS-1 molecular sieves were dehydrated and degassed under vacuum at 100℃~300℃ and cooled to room temperature to obtain pretreated TS-1 molecular sieves. The pretreated TS-1 molecular sieves were impregnated and stirred with an amine reagent to allow amine molecules to enter some of the micropores of the TS-1 molecular sieves. An inorganic alkaline solution was added and etched by stirring at 40℃~80℃ for 0.2h~4h to obtain an etched sample. The etched sample was mixed with an ammonium solution for ion exchange. After removing the solution, it was calcined at 500℃~600℃ to obtain modified TS-1 molecular sieves.

[0026] This invention utilizes the Gaussian 09 package to construct the dimer geometry based on monomeric MEP analysis results. At the STO-3G theoretical level, with a default system temperature of 298K, the structure and frequency of dimers formed between TS-1 molecular sieve powder and small-molecule organic amines such as diethylamine and triethylamine are optimized. Based on this, the binding energy between dimer molecules is calculated, and the strength of weak intermolecular interactions is analyzed. This effectively screens small-molecule amines with strong interaction energy with TS-1 molecular sieve, providing effective protection for the inorganic alkali treatment process of TS-1 molecular sieve, avoiding blind experimental screening, and improving R&D efficiency.

[0027] The modified TS-1 molecular sieve of this invention has a BET specific surface area of ​​300 m². 2 / g~410m 2 / g, with a total pore volume of 0.38mL / g to 0.54mL / g and an average pore radius of 2.5nm to 2.8nm.

[0028] The modified TS-1 molecular sieve of the present invention can be used as a catalyst for the amination reaction of cyclohexanone.

[0029] The technical solution of the present invention will be further described below through specific embodiments. In the following embodiments, unless otherwise specified, the methods are conventional methods; the reagents and materials, unless otherwise specified, are commercially available. In the following embodiments, the preparation of TS-1 molecular sieve raw powder is based on existing technology, and the present invention does not limit the specific preparation method of TS-1 molecular sieve raw powder. The TS-1 molecular sieve is prepared from an inorganic silicon-organic titanium source, an organosilicon-organic titanium source, an inorganic silicon-inorganic titanium source, or an organosilicon-inorganic titanium source; the TS-1 molecular sieve is a nano-sized TS-1 molecular sieve or a micron-sized TS-1 molecular sieve; wherein the particle size of the nano-sized TS-1 molecular sieve is 100nm to 400nm, and the particle size of the micron-sized TS-1 molecular sieve is 1μm to 2μm.

[0030] Example 1 A method for modifying TS-1 molecular sieve includes the following steps: S1. Using silica sol as the silicon source and tetrabutyl titanate as the titanium source, TS-1 molecular sieve raw powder with a size of approximately 1 μm was prepared. The TS-1 molecular sieve raw powder was dehydrated and degassed under vacuum at 150°C for 2 h, and then cooled to room temperature to obtain pretreated TS-1 molecular sieve.

[0031] S2. Take 1g of pretreated TS-1 molecular sieve, add 5mL of n-butylamine, and impregnate and stir for 30min to allow the small molecule amine to enter part of the micropores of the TS-1 molecular sieve powder. Add 20mL of 0.35mol / L Na2CO3 solution, stir and etch the resulting suspension at 65°C for 30min, filter, wash, and dry for 10h to obtain the etched sample.

[0032] S3. Mix 50 mL of ammonium chloride solution with the dried etched sample, heat to 80 °C and stir for 2 h, then centrifuge to remove the solution; repeat the operation twice. After the last centrifugation, dry the sample and then calcine at 550 °C for 4 h to obtain the modified TS-1 molecular sieve.

[0033] Example 2 A method for modifying TS-1 molecular sieve differs from Example 1 in that: in step S2, a 0.5 mol / L Na2CO3 solution is used instead of the 0.35 mol / L Na2CO3 solution in Example 1, while the remaining steps are the same as in Example 1.

[0034] Example 3 A method for modifying TS-1 molecular sieve differs from Example 1 in that: in step S2, a 0.7 mol / L Na2CO3 solution is used instead of the 0.35 mol / L Na2CO3 solution in Example 1, while the remaining steps are the same as in Example 1.

[0035] Example 4 A method for modifying TS-1 molecular sieve differs from Example 1 in that: in step S2, a 0.2 mol / L NaOH solution is used instead of the 0.35 mol / L Na2CO3 solution in Example 1, while the remaining steps are the same as in Example 1.

[0036] Example 5 A method for modifying TS-1 molecular sieve differs from Example 1 in that: in step S1, tetraethyl orthosilicate is used as the silicon source and n-butyl titanate is used as the titanium source to prepare TS-1 molecular sieve raw powder with a size of approximately 200 nm. In step S2, diethylamine is used instead of n-butylamine in Example 1; a 0.05 mol / L KOH solution is used instead of the 0.35 mol / L Na₂CO₃ solution in Example 1; the remaining steps are the same as in Example 1.

[0037] Example 6 A method for modifying TS-1 molecular sieve differs from Example 1 in that: in step S1, tetraethyl orthosilicate is used as the silicon source and n-butyl titanate is used as the titanium source to prepare TS-1 molecular sieve raw powder with a size of approximately 200 nm. In step S2, 20 mL of 2 mol / L hexamethylenetetramine solution is used instead of n-butylamine in Example 1; and 0.1 mol / L NaOH solution is used instead of 0.35 mol / L Na2CO3 solution in Example 1. The remaining steps are the same as in Example 1.

[0038] Example 7 A method for modifying TS-1 molecular sieve differs from Example 1 in that: in step S1, tetraethyl orthosilicate is used as the silicon source and n-butyl titanate is used as the titanium source to prepare TS-1 molecular sieve raw powder with a size of approximately 200 nm. In step S2, 5 mL of triethylamine is used instead of n-butylamine in Example 1; a 0.2 mol / L NaOH solution is used instead of the 0.35 mol / L Na₂CO₃ solution in Example 1; the remaining steps are the same as in Example 1.

[0039] Comparative Example 1 Using silica sol as the silicon source and tetrabutyl titanate as the titanium source, TS-1 molecular sieve powder with a size of about 1 μm was prepared as control sample 1 and directly used in the cyclohexanone ammonium oxime reaction without performing the small molecule amine protection and inorganic base etching post-treatment in steps S2 and S3 of Example 1.

[0040] Comparative Example 2 In Example 5, TS-1 molecular sieve powder with a size of approximately 200 nm was prepared using tetraethyl orthosilicate as the silicon source and n-butyl titanate as the titanium source. This powder was used as control sample two and directly applied to the cyclohexanone ammonium oxime reaction without performing the small molecule amine protection and inorganic base etching post-treatment in steps S2 and S3 of Example 1.

[0041] Test 1: Microscopic morphology analysis.

[0042] Scanning electron microscopy (SEM) was performed on the modified TS-1 molecular sieves prepared in Examples 1 and 5, as well as control sample one of Comparative Example 1 and control sample two of Comparative Example 2. The results are as follows: Figure 1 As shown.

[0043] Scanning electron microscope image of control sample 1 in Comparative Example 1 is as follows: Figure 1 As shown in Figure (a), the scanning electron microscope image of the modified TS-1 molecular sieve of Example 1 is as follows. Figure 1 As shown in (b), the results show that, compared with control sample 1, the morphology and size of the modified TS-1 molecular sieve treated with small molecule amine reagent and inorganic base in Example 1 did not change significantly, and no obvious pores appeared on the surface.

[0044] The scanning electron microscope image of control sample 2 in Comparative Example 2 is as follows: Figure 1 As shown in (c), the scanning electron microscope image of the modified TS-1 molecular sieve of Example 5 is as follows. Figure 1 As shown in (d), the results show that, compared with control sample 2, the morphology and size of the modified TS-1 molecular sieve after treatment with small molecule amine reagent and inorganic base in Example 5 are basically unchanged. A small number of pores can be seen in the modified TS-1 molecular sieve of Example 5.

[0045] The scanning electron microscopy results above show that the modified TS-1 molecular sieve samples post-treated with small molecule amine reagents and inorganic bases in the embodiments of the present invention have a protective effect on the pore structure and Si-O-Ti in the samples. Specifically, the small molecule amines that enter the micropores protect these pores from etching by the inorganic bases, while the pores that do not enter the small molecule amines are etched by the inorganic bases to form mesopores. This improves the problem of excessive pore collapse during the traditional alkali treatment process and enhances the relative crystallinity and stability of the molecular sieve.

[0046] Test 3: Cyclohexanone oxime amination reaction.

[0047] The modified TS-1 molecular sieves prepared in Examples 1 to 7 and the TS-1 molecular sieves in Comparative Examples 1 and 2 were used as catalysts for the cyclohexanone ammoniation reaction, and the specific methods are as follows: A 100 mL three-necked round-bottom flask was used as the reactor, equipped with a reflux condenser and a magnetic stirring system. The modified TS-1 molecular sieves prepared in Examples 1-7 and the TS-1 molecular sieves in Comparative Examples 1-2 were used as catalysts, with a catalyst dosage of 0.25 g. An 8 wt% hydrogen peroxide aqueous solution was used as the oxidant, an 85 wt% tert-butanol solution was used as the reaction medium, and 25 wt% ammonia water was used as the ammonia source.

[0048] The specific operating steps are as follows: Add 3.8g of cyclohexanone, 11.2mL of tert-butanol solution and 0.25g of catalyst to a 100mL three-necked round-bottom flask, heat to 80℃, and add 17.2mL of hydrogen peroxide aqueous solution and 8.8mL of ammonia water in sequence at a uniform rate, controlling the addition time to be completed within 75min. Maintain the reaction temperature at 80℃ and continue stirring for 105min to stop the reaction and obtain cyclohexanone oxime.

[0049] The reaction products were analyzed by gas chromatography using the internal standard method to monitor the cyclohexanone conversion, cyclohexanone oxime yield, and selectivity during the reaction process. Quantitative detection was performed using an Agilent 7890B gas chromatograph with an HP-5 capillary column (30 m × 0.32 mm × 0.25 μm) and an FID detector. Chromatographic conditions were: initial temperature 60 °C held for 2 min, then increased to 250 °C at a rate of 10 °C / min. To ensure the accuracy of the analytical results, toluene was used as an internal standard, and the content of each component was quantitatively calculated using the internal standard method. The test results are shown in Table 1.

[0050] Table 1 Results of cyclohexanone oxime amination reaction for each catalyst Table 1 shows that the modified TS-1 molecular sieves prepared by etching with small molecule amines in Examples 1-7, as catalysts, exhibit significantly improved catalytic performance compared to the untreated TS-1 molecular sieve samples in Comparative Examples 1-2. Compared to Comparative Examples 1-2, the cyclohexanone conversion rate of the modified TS-1 molecular sieves in Examples 1-6 increased to 77.2%-88.6%, and the cyclohexanone oxime yield increased to 53.7%-75.8%, demonstrating that the post-treatment strategy of Examples 1-6 can effectively and selectively control the pore structure, constructing mesopores and exposing active sites while protecting the microporous framework. Moreover, the post-treatment effect of the nanoscale TS-1 molecular sieve in Example 5 is even better, with the cyclohexanone conversion rate of the modified TS-1 molecular sieve increasing to 88.6% and the cyclohexanone oxime yield increasing to 75.8%. In addition, the combination of weakly alkaline Na2CO3 solution and diethylamine is a better process parameter. Excessive alkali concentration or improper selection of amine type will lead to performance degradation, as seen in the modified TS-1 molecular sieves of Examples 6 and 7.

[0051] N2 adsorption-desorption tests were conducted on the modified TS-1 molecular sieves of Examples 1, 5, and 7, as well as the TS-1 molecular sieves of Comparative Examples 1 and 2. The results are shown in Table 2.

[0052] Table 2 Pore volume and specific surface area of ​​modified TS-1 molecular sieve and TS-1 molecular sieve Note: "-" indicates that there is no subsequent post-treatment process involving small molecule amines and alkaline solutions. S BET This represents the specific surface area of ​​BET. V total Indicates the total orifice volume.

[0053] Table 2 shows that the BET specific surface area and total pore volume of the unmodified micron-sized TS-1 molecular sieve sample (Comparative Example 1) are 340.6 m². 2 / g and 0.473mL / g, with an average pore radius of 2.78nm. In Examples 1 and 7, the modified TS-1 molecular sieves treated with triethylamine, n-butylamine (two small molecule amines), and inorganic base showed increased specific surface area and total pore volume.

[0054] The BET specific surface area and total pore volume of the unmodified nano-sized TS-1 molecular sieve sample (Comparative Example 2) were 454.6 m². 2 With concentrations of 0.359 mL / g and an average pore radius of 1.58 nm, the modified TS-1 molecular sieve treated with diethylamine and KOH solution in Example 5 showed increased specific surface area and total pore volume. This demonstrates that appropriate small-molecule amine reagents and alkali modification can effectively control the pore structure of micron- and nano-sized TS-1 molecular sieves, resulting in increased specific surface area and total pore volume.

[0055] Test 3: Interaction energy analysis.

[0056] This invention uses the Gaussian 09 package to form a stable dimer between small molecule amine reagents and TS-1. By calculating the binding energy between the small molecule amine reagents and TS-1 molecular fragments, the types of small molecule amine reagents with strong interactions with the microporous structure of TS-1 can be quickly screened. This provides an effective basis for selecting protective agents in the process of inorganic base treatment of TS-1, reduces experimental exploration, and improves research and development efficiency.

[0057] Specifically, this invention uses the Gaussian 09 package to perform theoretical calculations on the interaction between small molecule amine reagents and TS-1 molecular sieves. Based on the monomeric MEP analysis results, the geometric structures of the active center of TS-1 molecular sieve (Ti(OSi(OH)3)4) and small molecule amine reagents forming dimers, such as Ti(OSi-(OH)3)4…NH(CH2CH3)2, Ti(OSi-(OH)3)4…N(CH2CH3)3, and Ti(OSi-(OH)3)4…NH2(CH2CH2)NH2, were constructed and optimized. Optimization and frequency calculations were performed at the STO-3G level, and the most stable (lowest energy) geometric configuration was obtained, as shown in [the original text]. Figure 2 The main structural parameters are listed in Table 3.

[0058] Based on the obtained stable geometry of the dimer, the intermolecular binding energy is calculated, and the interaction energy is calculated according to the following formula: In the formula, Δ E di This represents the energy difference between the dimer and monomer molecules that may form. E AB E represents the total energy of the possible dimer AB that may form. A The energy of the monomer TS-1 molecular sieve; E B The energy is for the monomeric small molecule amine reagent.

[0059] Table 3. Interaction energies between various amine molecules and TS-1 molecular sieve to form dimers Table 3 shows that the interaction energies between n-butylamine, diethylamine, and ethanolamine molecules and TS-1 molecular sieve to form dimers are 1.359991 kJ / mol, 1.393941 kJ / mol, and 1.539865 kJ / mol, respectively. These interaction energies are moderate, indicating that the amine molecules provide good protection for the microporous structure of the TS-1 molecular sieve and improve its catalytic oxidation performance. The interaction energies between ethylenediamine and 1,6-hexanediamine molecules and TS-1 molecular sieve to form dimers are -0.135503 and -0.084423 kJ / mol, respectively, indicating a larger interaction and a poorer protection for the microporous structure of the amine molecules. The interactions between pyridine, N,N-dimethylformamide, triethylamine, and hexamethylenetetramine molecules and TS-1 molecular sieve to form dimers are slightly smaller, and the protection of the microporous structure of the amine molecules is not ideal.

[0060] In summary, by using the Gaussian 09 package to calculate the stable dimers formed by small molecule amines and TS-1 molecular sieves, as well as the binding energies between small molecule amines and TS-1 molecular fragments, protective agents with moderate binding energies can be quickly screened. This provides an effective basis for selecting protective agents in the process of inorganic alkali treatment of TS-1 molecular sieves, reduces experimental exploration, and improves research and development efficiency.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for modifying TS-1 molecular sieve, characterized in that, Includes the following steps: TS-1 molecular sieve was impregnated and stirred with amine reagent, and then an inorganic alkaline solution was added and stirred to etch the sample to obtain an etched sample. The etched sample was mixed with an ammonium solution for ion exchange, and after removing the solution, it was calcined to obtain a modified TS-1 molecular sieve. The amine reagent is at least one of diethylamine, triethylamine, ethanolamine, n-butylamine, hexamethylenetetramine solution, and ethylenediamine; the ratio of TS-1 molecular sieve to amine reagent is 1g: 5mL to 6mL; the concentration of inorganic alkali solution is 0.1mol / L to 2mol / L.

2. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The stirring etching process involves stirring at 40℃ to 80℃ for 0.2h to 4h.

3. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The inorganic alkaline solution is at least one of sodium carbonate solution, potassium carbonate solution, sodium hydroxide solution, potassium hydroxide solution, and ammonia water.

4. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The ratio of TS-1 molecular sieve to inorganic alkaline solution is 1g:10mL~100mL.

5. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The concentration of the hexamethylenetetramine solution is 0.1 mol / L to 2 mol / L.

6. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The particle size of the TS-1 molecular sieve is 100nm~400nm or 1μm~2μm.

7. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The ammonium solution is an ammonium chloride solution; the concentration of the ammonium chloride solution is 0.1 mol / L to 2 mol / L. The ratio of TS-1 molecular sieve to ammonium solution is 1g: 50mL to 200mL.

8. The modification method of TS-1 molecular sieve according to claim 1, characterized in that, The roasting temperature is 500℃~600℃.

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