Preparation method and application of cu-beta zeolite catalyst for preparing caprolactam from caprolactone

Abstract

The present application belongs to the field of catalytic technology of petroleum chemical industry, and relates to a preparation method and application of Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone. The main technical feature of the present application is that, using dealuminated Beta zeolite as a carrier, copper is loaded in the pores of the zeolite carrier by using an improved ammonia evaporation method. The core of the improved ammonia evaporation method is to immerse the zeolite carrier in a copper-ammonia complex solution with equal volume, so that the copper-ammonia complex mainly deposits copper hydroxide in the pores of the zeolite carrier during the ammonia evaporation process. After the copper hydroxide deposited in the pores of the zeolite carrier is calcined and reduced by hydrogen, high-dispersed nano and sub-nano copper particles can be directly formed at the hydroxyl hole lattice defect sites in the pores, and the latter obtains the anti-sintering ability through the close interaction with the hydroxyl hole. When the Cu-Beta zeolite catalyst prepared by the method of the present application is applied to the reaction of preparing caprolactam from caprolactone by gas-solid phase hydrogenation of ammonia, the activity and selectivity are high, and the stability is good.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical catalysis technology, and relates to a method for preparing and applying a Cu-Beta zeolite catalyst for the production of caprolactam from caprolactone. Background Technology

[0002] ε-Caprolactam (CPL) is a white, solid organic compound, the vast majority of which is used in the production of polycaprolactam chips, with a smaller portion used in the production of lysine and pharmaceutical intermediates. Among the downstream products of polycaprolactam chips, nylon-6 fibers and engineering plastics consume approximately 70% and 20%, respectively. The remaining polycaprolactam chips are processed into packaging films and food preservation films.

[0003] Nylon-6 was the world's first developed synthetic fiber product. The most outstanding advantage of nylon-6 fiber is its superior abrasion resistance compared to all other fibers. It is 10 times more abrasion-resistant than cotton and 20 times more abrasion-resistant than wool. Simultaneously, nylon-6 fiber is 1-2 times stronger than cotton, 4-5 times stronger than wool, and 3 times stronger than viscose fiber. Adding a small amount of polyamide fiber to blended fabrics can significantly improve their abrasion resistance, elastic recovery rate, and flexural strength. Furthermore, nylon-6 fiber also has good moisture absorption and dyeability. Nylon-6 fiber can be used as both civilian and industrial yarn. Civilian nylon yarn is used to make shirts, sweaters, pajamas, carpets, blankets, curtain cords, and bags, etc.; industrial yarn is used to make tents, car tires, drive belts, hoses, cables, fishing nets, ropes, and insulation materials, etc.

[0004] Currently, the benzene-based caprolactam production process has become the mainstream production process for caprolactam. This process mainly includes three basic steps: benzene to cyclohexanone, cyclohexanone to cyclohexanone oxime, and cyclohexanone oxime rearrangement to caprolactam.

[0005] The production of cyclohexanone from benzene is the first step in the benzene-based caprolactam process. Industrially, there are two main process routes: cyclohexane oxidation and cyclohexene hydration. Since 2017, cyclohexene hydration has surpassed cyclohexane oxidation to become the world's largest source of cyclohexanone.

[0006] The production of cyclohexane from cyclohexane mainly employs a liquid-phase oxidation method. This method uses benzene and hydrogen as starting materials. First, benzene is hydrogenated to obtain cyclohexane. Then, cyclohexane undergoes air oxidation and saponification to produce cyclohexanone and cyclohexanol. Finally, cyclohexanol is dehydrogenated to yield cyclohexanone. This method features mild process conditions, simple operation, and mature technology. Its main disadvantages are a low product yield (only 75%-80%), high raw material consumption, high energy consumption, numerous and difficult-to-separate byproducts, and environmental unfriendliness.

[0007] The cyclohexene hydration method is a cyclohexanone production technology developed by Asahi Kasei Corporation of Japan in the 1980s (Japanese Patent JP 60104031A, 1985), which can achieve a benzene utilization rate of 99.5%. The first step of this technology involves the selective hydrogenation of benzene to cyclohexene (approximately 80%) in the presence of a ruthenium-based catalyst, with cyclohexane as a byproduct. The second step involves separating the cyclohexene and hydrating it with water in the presence of a solid acid catalyst to produce cyclohexanol. The third step involves the dehydrogenation of cyclohexanol in the presence of a Cu-Si catalyst to produce cyclohexanone. Compared to the cyclohexane oxidation method, the cyclohexene hydration method for producing cyclohexanone has a simpler reaction process and avoids the problems of coking and the generation of waste alkali. However, this process has low production efficiency and high energy consumption.

[0008] The production of cyclohexanone oxime from cyclohexanone is the second and most crucial step in the benzene-based caprolactam process. Common production processes for this step include the hydroxylamine sulfate process (HSO), the hydroxylamine phosphate process (HPO), the nitric oxide reduction process (NO), and the ammonium oxime process (HAO).

[0009] The hydroxylamine sulfate process works as follows: First, NH3 is catalytically oxidized to a mixture of NO and NO2. This mixture is then absorbed by (NH4)2CO3 solution to obtain NH4NO2. Next, NH4NO2 is reduced with SO2 at low temperature to generate hydroxylamine disulfonate, which is then hydrolyzed to hydroxylamine sulfate. Second, cyclohexanone undergoes an oxime reaction with hydroxylamine sulfate to produce cyclohexanone oxime. This process requires the neutralization of free sulfuric acid with NH3, resulting in the formation of ammonium sulfate as a byproduct. The amount of ammonium sulfate byproduct is 2.5-2.7 tons of ammonium sulfate per ton of cyclohexanone oxime. The main disadvantages of this process are the large consumption of SO2 and the production of ammonium sulfate as a byproduct, which is detrimental to the production efficiency of caprolactam. Furthermore, the hydroxylamine sulfate process also suffers from a long production process, high energy consumption, and large emissions of waste. These disadvantages limit the development of the hydroxylamine sulfate process.

[0010] The hydroxylamine phosphate process was developed by Royal DSM (DSM) of the Netherlands. The first step involves the reduction of phosphoric acid and ammonium nitrate with hydrogen under Pd / C catalysis to prepare hydroxylamine phosphate salt. The second step involves reacting cyclohexanone with the hydroxylamine phosphate salt in a buffer solution of ammonium dihydrogen phosphate to generate cyclohexanone oxime. After separation of the cyclohexanone oxime, 60% nitric acid solution is added to replenish the consumed nitrate ions. The phosphoric acid and ammonium nitrate can be returned to the hydroxylamine synthesis process for reuse. The disadvantages of the hydroxylamine phosphate process are the requirement for a precious metal catalyst and the complexity of the process operation.

[0011] The nitric oxide reduction process was jointly developed by BASF (Germany), Inventa (Switzerland), and Zaklady Azotowe (Poland). The first step involves reacting ammonia and oxygen to generate nitric oxide, which is then hydrogenated in an aqueous sulfuric acid solution under a platinum catalyst to form hydroxylamine sulfate. The second step involves oximating the hydroxylamine sulfate with cyclohexanone to generate cyclohexanone oxime. This method is technically mature, consumes low amounts of ammonia and hydrogen, and does not produce ammonium sulfate as a byproduct in the formation of hydroxylamine. However, the use of oxygen and hydrogen in the process increases the risk of accidents. Furthermore, the platinum catalyst used in this process is susceptible to poisoning by arsenic, mercury, and aluminum ions present in the aqueous sulfuric acid solution.

[0012] The cyclohexanone ammoniation oxime process (HAO process) was proposed by Armor of United Chemical Company in 1980. Initially, this method used oxygen as the oxidant and amorphous silica as the catalyst to catalyze the reaction of cyclohexanone, oxygen, and ammonia at 467 K to prepare cyclohexanone oximes. This reaction method is applicable to other ketones. For example, acetone, 3-pentanone, 2-methylcyclohexanone, and acetophenone can all generate their corresponding oximes under certain conditions. This preparation method is simple and does not require the additional synthesis of hydroxylamine salts. However, the conversion rate of cyclohexanone is not ideal (54%) and the selectivity for cyclohexanone oximes is low (51%). In addition, the byproducts generated in the reaction remain on the catalyst, accelerating catalyst coking and deactivation.

[0013] In 1987, US Patent 4745221 first disclosed a new technical route for the liquid-phase ammonium oximeation of cyclohexanone catalyzed by TS-1, also known as the ammonium oximeation method. Specifically, this route uses tert-butanol and water as solvents to react cyclohexanone with ammonia and hydrogen peroxide under TS-1 catalysis to produce cyclohexanone oxime, achieving a high yield of over 99%. It also avoids the formation of low-value ammonium sulfate, making it environmentally friendly, and has already achieved large-scale industrial application. Compared with the hydroxylamine sulfate and hydroxylamine phosphate methods, the ammonium oximeation method has advantages such as low hydrogen consumption, short production process, simple control, low requirements for equipment and pipeline materials, and smaller investment and land area.

[0014] Those familiar with this field know that the ammonium oximation process has achieved significant success in industrial applications. However, this process still faces several challenges. For example, the recycling of large amounts of tert-butanol solvent increases separation costs; byproducts generated during the reaction deactivate the TS-1 catalyst; titanium-silicon molecular sieve catalysts are expensive, resulting in high amortized costs; the ammoniation of cyclohexanone to produce cyclohexanone oxime is a liquid-phase reaction, and the titanium-silicon molecular sieve catalyst is exposed to a strongly alkaline environment for extended periods, making it impossible to avoid the dissolution of the skeletal silicon on the catalyst. This not only leads to ineffective catalyst loss but also shortens the catalyst's lifespan, affecting the stable operation of the ammonium oximation reaction system; furthermore, liquid-solid phase reactions suffer from high mass transfer resistance, and the internal diffusion problem of the catalyst has a serious impact.

[0015] The Beckmann rearrangement of cyclohexanone oxime to caprolactam is the third and crucial step in the benzene-based caprolactam production process. Currently, approximately 90% of industrial caprolactam production processes require the Beckmann rearrangement. There are two process routes for caprolactam production via the Beckmann rearrangement: liquid-phase rearrangement and gas-phase rearrangement.

[0016] Liquid-phase Beckmann rearrangement is currently the most important process for caprolactam production. This process has a long history of industrialization and is relatively mature. Using fuming sulfuric acid as a catalyst, the liquid-phase Beckmann rearrangement offers mild reaction conditions, high selectivity, high caprolactam yield, and relatively stable product quality. However, the use of highly corrosive fuming sulfuric acid causes equipment corrosion, and each ton of caprolactam produces 1.5–1.8 tons of ammonium sulfate as a byproduct. Furthermore, the process consumes a large amount of liquid ammonia, and in addition to the problem of low-value ammonium sulfate byproducts, there are difficulties in handling the large amounts of neutralization heat, which to some extent affects the technical and economic viability of the process.

[0017] Compared with the liquid-phase Beckmann rearrangement process, the gas-phase Beckmann rearrangement is a more advanced process. Since the late 1980s, researchers have been working on using solid acid catalysts instead of fuming sulfuric acid for the Beckmann rearrangement of cyclohexanone oxime. The published literature AFINIDAD (Spain), 1981, 38(373):225-227 reported on the Beckmann rearrangement of cyclohexanone oxime on a series of AlPO4 / γ-Al2O3 catalysts. The results showed that the reaction activity increased with increasing catalyst acidity. However, the selectivity of the rearrangement reaction decreased, with the highest yield of the gas-phase Beckmann rearrangement of cyclohexanone oxime reaching 73.1%. The published literature Shokubai, 1989, 31(6):365-368 reported on the gas-phase Beckmann rearrangement of cyclohexanone oxime catalyzed by high-silica ZSM-5 molecular sieve in 1989. Currently, the high-silica ZSM-5 molecular sieve-catalyzed gas-phase Beckmann rearrangement has become a novel technology for caprolactam production. This gas-phase Beckmann rearrangement technology can complete the conversion of cyclohexanone oxime to caprolactam under the action of a solid acid catalyst. This process does not use fuming sulfuric acid, eliminating the need for sulfuric acid neutralization and thus avoiding the production of the byproduct ammonium sulfate. This significantly reduces the consumption of liquid ammonia during caprolactam production, avoiding problems such as equipment corrosion and environmental pollution, and has attracted widespread interest.

[0018] US Patent 4717769 (1987) discloses a method for the solid-phase rearrangement reaction of cyclohexanone oxime using a high silica-alumina oxide molar ratio (>500) MFI-type molecular sieve as a catalyst. The reaction is carried out at a weight hourly space velocity (WHSV) of 11.7 h⁻¹. -1 Under these conditions, the conversion rate of cyclohexanone oxime remained at 100% after 15.3 hours of reaction. However, the selectivity of caprolactam was very low (83.5%).

[0019] US Patent 6303099 (2000) discloses a method for the Beckmann rearrangement of cyclohexanone oxime using modified high-silica zeolite as a catalyst. Its key feature is that the modified catalyst is obtained by post-treatment of molecular sieve powder with a high molar ratio of silicon to aluminum oxide using a nitrogen-containing base. The reaction is carried out at a weight hourly space velocity (WHSV) of 8 h⁻¹. -1 Under the condition of reacting for 5.5 hours, the conversion rate of cyclohexanone oxime was 99.5%, and the selectivity of caprolactam was 96.2%.

[0020] Chinese patent CN1883803A (2005) also discloses a method for the Beckmann rearrangement reaction of cyclohexanone oxime using modified high-silica zeolite as a catalyst. Its technical feature is that the modified catalyst is obtained by post-treatment of pure silicon and high-silica alumina oxide molecular sieves with a molar ratio of hydrofluoric acid. The reaction is carried out at a reaction temperature of 370℃, atmospheric pressure, and a space velocity of 8 h⁻¹. -1 Under the condition of a carrier gas flow rate of 60 mL / min, after 20 hours of reaction, the feed conversion rate was 98.3% and the product selectivity was 98.5%. This essentially achieved the best possible reaction results.

[0021] In addition to patent literature, many journal articles also cover the gas-phase Beckmann rearrangement of cyclohexanone oxime to produce caprolactam.

[0022] For example:

[0023] The publicly available literature *Studies in Surface Science and Catalysis*, 1993, 78:615-622, reports the catalytic performance of AlPO4 and AlPO4 / TiO2 catalysts for the gas-phase Beckmann rearrangement of cyclohexanone oxime. The results show that the reaction activity increases with increasing catalyst acidity, but the selectivity for caprolactam decreases. Within the temperature range of 200–400 °C, both the activity and selectivity of the AlPO4 and AlPO4 / TiO2 catalysts increase with increasing temperature. Under the same reaction conditions, the AlPO4 / TiO2 catalyst exhibits superior activity and selectivity compared to the AlPO4 catalyst. Increasing the TiO2 content in the AlPO4 / TiO2 catalyst reduces the surface acidity, leading to decreased catalyst activity and increased selectivity.

[0024] The published literature *Applied Catalysis A: General*, 1999: 99-108, reports the catalytic performance of Al and B-modified β-zeolite catalysts for the gas-phase Beckmann rearrangement of cyclohexanone. The study found that, similar to [B]-ZSM-5, both [B]-β and [Al]-β zeolites exhibited significantly improved selectivity for caprolactam when the reaction temperature and pressure were decreased. However, at lower reaction temperatures and pressures, the catalyst deactivation rate accelerated. In contrast, the deactivation of [B]-β zeolite was more severe, approximately fifteen times that of [Al]-β zeolite. The study also revealed that the active center for the cyclohexanone oxime Beckmann rearrangement catalyzed by [Al]-β and [B]-β zeolites is the ortho-silanol group.

[0025] In 2003, Sumitomo Chemical Co., Ltd. of Japan pioneered the development and industrial application of gas-phase Beckmann rearrangement technology for cyclohexanone oxime. According to a report in the publicly available literature *Contemporary Petroleum & Petrochemical*, 2019, 27(04):32-36, Sumitomo Chemical's gas-phase rearrangement technology utilizes a fluidized bed reactor, with high-silica MFI molecular sieve as the catalyst, methanol as the solvent, and nitrogen as the carrier gas. The reaction is carried out at a temperature of 350-400℃ and a weight hourly space velocity of 8 h⁻¹. -1 Under these conditions, the conversion rate of cyclohexanone oxime can reach over 99%, and the selectivity of caprolactam can reach over 95%. The Research Institute of Petroleum Processing at Sinopec has also developed a similar gas-phase rearrangement technology, but using a radially moving bed reactor, achieving a cyclohexanone oxime conversion rate of over 99.9% and an average caprolactam selectivity of 96.5%. By the end of 2020, pilot-scale and intermediate-scale technical research had been completed.

[0026] The published literature *Applied Catalysis A: General*, 2005: 145-153 reports the catalytic performance of a series of composite metal oxide catalysts for the gas-phase Beckmann rearrangement of cyclohexanone oxime. The study found that the composite oxide TiO2-ZrO2 prepared by co-precipitation using ammonia as a co-precipitant, followed by the preparation of the B2O3 / TiO2-ZrO2 catalyst using an equal-volume impregnation method, achieved a 100% conversion and a selectivity of 97.4% for the Beckmann rearrangement reaction. These results are significantly superior to those of B2O3 / SiO2-Al2O3, B2O3 / SiO2-TiO2, B2O3 / SiO2-ZrO2, B2O3 / Al2O3-TiO2, and B2O3 / Al2O3-ZrO2 catalysts. Within the range of 500–700℃, increasing the calcination temperature is beneficial for the formation of moderately strong acid centers, thereby increasing the conversion rate and product selectivity of cyclohexanone oxime. However, when the calcination temperature exceeds this range, a large amount of B2O3 crystalline phase appears, which is detrimental to the catalytic activity and selectivity of B2O3 / TiO2-ZrO2. Studies have found that polar solvents facilitate the desorption of the reaction product caprolactam from the active centers, improving caprolactam selectivity and extending the catalyst's lifespan. Acetonitrile is the most polar and therefore the best solvent in the research solution. In the deactivation and regeneration studies of the B2O3 / TiO2-ZrO2 catalyst, it was found that the pore size distribution and structure of the deactivated catalyst remained unchanged, only the number of acid centers decreased. Surface carbonization is the main cause of catalyst deactivation. The deactivated catalyst can completely recover its activity after calcination at 600℃ for 8 hours.

[0027] The publicly available literature *Catalysis Communications*, 2005:53-56, reports the catalytic performance of different β-zeolite catalysts for the gas-phase Beckmann rearrangement of cyclohexanone oxime. These different β-zeolite catalysts include a boric acid-impregnated modified Hβ molecular sieve catalyst (B₂O₃ / Hβ), a series of Ti-Hβ molecular sieves synthesized by liquid-solid isomorphous substitution of Hβ molecular sieves with Ti(SO₄)₂ solution, and modified catalysts obtained by treating Hβ molecular sieves with ammonia. The results show that compared with the hydrothermally synthesized Hβ molecular sieve parent material, the BET surface area of ​​the Ti-Hβ molecular sieve and the ammonia-modified Hβ molecular sieve is larger. The BET surface area of ​​the B₂O₃ / Hβ catalyst modified with 9.09 wt% boron oxide is smaller. However, the total acidity and the amount of weak acids in the three modified catalysts are increased, especially the amount of weak Brønsted acids. In the Beckmann rearrangement reaction, the activity and selectivity of the above modified catalysts are increased, and the deactivation rate is reduced. Based on the above results, the authors hypothesize that in the gas-phase Beckmann rearrangement reaction, the weak Brønsted acidic site is the true catalytic active center.

[0028] The published paper *Catalysis Today*, 2012:289-299, reports a study on the synthesis of caprolactam under different conditions using niobium pentoxide (Nb₂O₅)-impregnated amorphous silica gel as a low-cost catalyst (Nb₂O₅ / SiO₂). The results show that, using Nb₂O₅ / SiO₂ as the catalyst, the conversion of cyclohexanone oxime is close to 100%, and the selectivity for caprolactam is as high as 98%.

[0029] Those familiar with the field know that the gas-phase Beckmann rearrangement reaction faces two major challenges in its technological development. Firstly, cyclohexanone oxime needs to participate in the reaction in the gas phase. However, cyclohexanone oxime itself has a relatively high boiling point (203°C at ambient pressure) and poor high-temperature thermal stability, undergoing condensation and deterioration at 160°C. Therefore, ensuring the vaporization of cyclohexanone oxime without deterioration is a challenging problem that must be addressed in the development of the gas-phase rearrangement process. Secondly, the catalyst is prone to deactivation in the gas-phase rearrangement reaction. To ensure the continuous and stable progress of the reaction, how to restore the catalyst activity online has also become a challenge that needs to be solved in the development of the gas-phase Beckmann rearrangement. These two issues remain obstacles to the large-scale industrialization of the cyclohexanone oxime gas-phase Beckmann rearrangement method.

[0030] Given the current technological status of existing benzene-based caprolactam production processes and the challenges in developing new processes, it is imperative to explore alternative approaches to obtain a new, highly efficient caprolactam preparation process that eliminates low-value byproducts (such as ammonium sulfate), avoids equipment corrosion and environmental pollution, achieves high atom utilization, and has low energy consumption (low carbon emissions).

[0031] A literature review revealed that as early as 1957, Shell first disclosed a method for producing caprolactam from caprolactone in US Patent US2817646. Specifically, this method uses a hydrogenation catalyst (such as neutral Raney nickel) at 175-200°C and 7-40 atm to prepare caprolactam from ammonia, hydrogen, and caprolactone. However, the main products of this reaction are actually various amides, such as polyamides, aminoamides, and hydroxyamides. The yield of caprolactam is only about 4%. Clearly, the poor selectivity of this method renders it impractical.

[0032] In 1961, Union Carbide Corporation (UCC) disclosed a method for preparing caprolactam in US Patent 3000879. The method involved heating a 25% aqueous solution of 6-hydroxyhexylamide to 300-475°C in a closed container, and preparing caprolactam via a non-catalytic reaction under high pressure (up to 15 MPa), achieving a 30% single-pass caprolactam yield. Undoubtedly, for a bulk chemical, achieving industrial-scale production using batch reactors under high temperature and pressure is unimaginable.

[0033] In the same year, Union Carbide disclosed another process for producing caprolactam from caprolactone in US Patent 3000800. Specifically, this process involves mixing caprolactone with an aqueous solution of ammonia or a primary amine under high pressure (P>22.1 MPa) and conditions above the critical temperature of ammonia and water (373℃<T>473℃) to produce caprolactam through a non-catalytic reaction. This method has been successfully industrialized, but the process can only be carried out under high temperature and pressure, resulting in enormous energy consumption. Moreover, the non-catalytic reaction under high temperature and pressure easily forms polymers, leading to a low actual yield of caprolactam, not exceeding 50%. This is likely the main reason why Union Carbide later shut down its caprolactone-based caprolactam production line. On the other hand, at that time, the caprolactone raw material came from the oxidation reaction of cyclohexanone and peracetic acid. Peracetic acid is a strong oxidizing agent and extremely unstable. Peracetic acid can explode when exposed to high heat, reducing agents, or in the presence of metal ions. In fact, peracetic acid concentrations greater than 45% are explosive, and it can even explode at -20℃. Therefore, the production process of caprolactone at that time was extremely dangerous. This may also be an important reason why Union Carbide later shut down its caprolactam production line starting from caprolactone.

[0034] In 1964, Teijin Corporation of Japan disclosed a catalytic method for preparing caprolactam from amide derivatives of caprolactone, 6-hydroxyhexanoamide, or 6-hydroxyhexanoic acid in US patents US3317516 and US3317517. Specifically, the catalytic method disclosed in the aforementioned patents involves heating caprolactone, 6-hydroxyhexanoamide, or 6-hydroxyhexanoic acid amide derivatives, along with ammonia water, to 200-400°C in a high-pressure reactor under the catalysis of a hydrogenation catalyst containing at least one or a combination of noble metals, cobalt, and nickel, to obtain caprolactam with less coloration. This method can be used under a hydrogen atmosphere. Clearly, the reaction conditions of this catalytic method are relatively mild. However, the single-pass yield of caprolactam obtained by this method is also low, with a maximum of only 45.1%, therefore, the method is not economically viable.

[0035] In 1965, Union Carbide disclosed a continuous two-stage process for producing caprolactam in US Patent 3320241. The technological background for this process was that it was already known that the non-catalytic reaction of caprolactone with ammonia under high temperature and pressure could produce caprolactam. However, the reaction under high temperature and pressure was unsuitable for industrial applications. First, due to reaction equilibrium limitations, the single-pass yield was relatively low. Second, the reaction process produced a large amount of irreversible byproducts. Because the yield of each step was very low, the reaction intermediates and unconverted caprolactone had to be recycled, which increased energy consumption and carbon emissions. Furthermore, the separation process was very complex due to the large amount of irreversible byproducts generated. All of these factors resulted in excessively high operating costs. Therefore, the new process proposed in this patent involved reacting a mixture of caprolactone, ammonia, and water at a relatively low temperature in the first-stage conversion, with the reaction time controlled to allow for a large-scale conversion of caprolactone into the reaction intermediates. Then, in the second-stage conversion, the products of the first-stage conversion reaction are converted under the high temperature (300-400℃) and ultra-high pressure (136-680 standard atmospheres) required for the formation of caprolactam. Downstream of the two-stage conversion reaction is the separation stage. The task of the separation stage is to separate caprolactam from the mixture containing caprolactone and reaction intermediates, and to recycle unreacted products and intermediates back to the first stage for further conversion. Because the intermediates can be converted throughout the entire two-stage process after returning to the first stage, the long reaction time is beneficial for maximizing the conversion to the target product, caprolactam. The caprolactam separated from the second-stage reaction mixture must undergo multiple purification steps to become pure. All residues generated during product purification can be recycled back to the first stage for further conversion, aiming to convert them into the target product as much as possible. This process can achieve a caprolactam yield of 90.2%. The process is complex, and the second step is still a high-pressure reaction, placing extremely high demands on production equipment and management, making industrialization difficult.

[0036] In 1966, Kanekabuchi Co., Ltd. of Japan disclosed a catalytic method for preparing caprolactam from caprolactone in the gas phase in British patent GB1109540. This method involves first vaporizing caprolactone and a certain amount of water, then mixing it with ammonia and hydrogen. The mixed gas is then subjected to a catalytic reaction at 120-350°C and atmospheric pressure using a copper chromite catalyst. This method can achieve a 100% conversion rate of caprolactone and a 97% selectivity for caprolactam. However, the resin generated by the polymerization side reaction deposits on the catalyst, leading to rapid catalyst deactivation, which is a major obstacle to the industrial application of this method. Furthermore, the copper chromite catalyst used in this method is toxic and generates a large amount of chromium-containing wastewater during the preparation process, which is detrimental to environmental protection.

[0037] In 1967, DuPont Canada disclosed a non-catalytic method for the production of caprolactam from caprolactone in Canadian patent CA770148. This method involves reacting caprolactone or polycaprolactone with ammonia in a stainless steel reactor at 305-365°C, with the reaction carried out at 18-45 MPa, achieving a single-pass yield of caprolactam of up to 85%. The method provided in this patent indicates that polycaprolactone is a byproduct that can be reversibly converted into the desired product.

[0038] In 1968, Stamicarbon of the Netherlands disclosed a non-catalytic process for producing caprolactam by reacting caprolactone with ammonia in an inert organic solvent in US Patent 3401161. The reaction is carried out at very high temperatures and pressures (T>330℃, 125 atm>P>90 atm), and the yield of caprolactam can reach up to 60%. Suitable organic solvents include pyridine, dibutyl ether, diacyl ether, dioxane, toluene, xylene, decahydronaphthalene, heptane, and octane.

[0039] In 1970, Union Carbide disclosed a non-catalytic method for the preparation of caprolactam from caprolactone under high temperature and pressure in US Patent 3,497,500. The method emphasized the importance of removing a portion of the carbon dioxide produced in the reaction system. Simply put, according to this patent, in the reaction of caprolactone to caprolactam under high temperature and pressure, the presence of excess carbon dioxide in the reaction system is detrimental to obtaining a satisfactory caprolactam yield.

[0040] In 1972, Kanekabuchi Corporation of Japan disclosed a method for preparing caprolactam using copper chromite as a catalyst in US Patent 3,652,549. The copper chromite catalyst was obtained by co-precipitation using copper nitrate and ammonium dichromate as raw materials and ammonia as a precipitant. The technical features of the catalyst preparation process include: after filtration, dehydration, low-temperature drying (75-80°C, 20h), and high-temperature decomposition of the precipitate generated by the co-precipitation reaction, it is further soaked in dilute acetic acid solution. The catalyst precursor after soaking is then filtered, washed with water, and dried (125°C, 12h) to become the catalyst. Before being used in a fixed-bed reactor, the catalyst needs to be tableted. Before the reaction, the catalyst also needs to be subjected to hydrogen reduction treatment at 200°C. The atomic ratio of chromium to copper in the copper chromite catalyst is 0.1-5, preferably 0.1-3. The catalyst may also contain a third metal component (Ba, Ca, Mg, Sr, Al, Ga, Ti, V, Mn, Fe, Co, Ni, Zn, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Pd, As, Bi, Sb). The atomic ratio of the third metal component to copper is 0.001-1, preferably 0.01-0.2. The raw material for preparing caprolactam conforms to the general formula X-(CH2)4-COY. Wherein, X = CHO, -CH(OR)(OR1), -COOH, -COONH4, -CONH2, or COR2; Y = OH, ONH4, NH2, or OR3. The reaction is carried out in a fixed-bed reactor in a gas-solid phase manner, with a reaction temperature range of 170-300℃ and a hydrogen partial pressure of 0.1-1.5 atm. The feed also includes ammonia and water vapor, with preferred dosage ranges (molar ratio to feed) of 2-50 and 10-100, respectively. When dimethyl adipate is used as the feed, the reaction results with a copper chromite catalyst containing a small amount of zinc are: feed conversion rate of 99% and caprolactam selectivity of 95%; the reaction results with a copper chromite catalyst containing a small amount of Mo are: feed conversion rate of 100% and caprolactam selectivity of 96%.

[0041] In 1975, Teijin Corporation of Japan disclosed a catalytic process for producing caprolactam from C1-C4 alkyl esters of caprolactone or 6-hydroxyhexanoic acid in US Patent 3888845. Specifically, the patent disclosed a process for producing caprolactam through a gas-solid phase catalytic reaction using C1-C4 alkyl esters of caprolactone or 6-hydroxyhexanoic acid, along with hydrogen and ammonia as raw materials. This process is characterized by low reaction temperature and pressure, high conversion rate of C1-C4 alkyl esters of caprolactone or 6-hydroxyhexanoic acid, and high selectivity for caprolactam. The solid catalyst used in this process consists of three parts: A, B, and C. A is an oxide support selected from titanium dioxide, alumina, silica, and a composite of alumina and silica; B is the main metal component of the catalyst—copper; and C is the trace metal component of the catalyst—selectively nickel or chromium. The catalyst can be prepared by deposition precipitation. The preferred support is anatase titanium dioxide. The weight ratio of copper to support is 0.5-200, preferably 5-100, and more preferably 10-70. The atomic ratio of Ni(Cr) to Cu is 0.001-1, preferably 0.005-0.25. The gas-solid phase catalytic reaction for producing caprolactam from C1-C4 alkyl esters of caprolactone or 6-hydroxyhexanoic acid can be carried out at 200-320°C and 0.01-2 atm, preferably at 220-310°C and 0.1-1.2 atm. The optional ranges for hydrogen and ammonia amounts are 5-70 (H2 / ester molar ratio) and 1-50 (NH3 / ester molar ratio), respectively, with preferred ranges of 10-50 (H2 / ester molar ratio) and 2-25 (NH3 / ester molar ratio), respectively. Furthermore, this process emphasizes the importance of the hydrogen to ammonia molar ratio and the addition of water to the reactor feed. In general, employing a suitable hydrogen to ammonia molar ratio is beneficial for improving reaction selectivity. Adding water to the reactor feed not only reduces side reactions and improves caprolactam selectivity but also slows down catalyst deactivation. The selectable range for the hydrogen to ammonia molar ratio is 0.2-30, with a preferred range of 0.5-15; the selectable range for the water / ester molar ratio is 0-50, with a preferred range of 5-30. Under optimal conditions, the conversion rate of caprolactone to caprolactam can reach up to 99%, and the selectivity of caprolactam can reach up to 90%. The problem is that catalyst deactivation due to carbon deposition is relatively rapid. However, this patent provides two catalyst regeneration methods. One method is redox treatment, and the other is steam treatment. The redox treatment is actually regeneration first using molecular oxygen carbonization, followed by hydrogen reduction of the catalyst. Molecular oxygen carbonization can be carried out in a temperature range of 100-800℃, preferably in a temperature range of 150-500℃. The charcoal burning time is 20 minutes to 20 hours; the hydrogen reduction after charcoal burning can be carried out in a temperature range of 170-350℃, preferably in a temperature range of 170-270℃.The steam treatment can be carried out at a temperature between 100-500°C, preferably between 200-400°C. The steam treatment time is 20 minutes to 20 hours. The steam treatment can also be carried out in the presence of hydrogen, and it is preferable to reduce the catalyst with hydrogen after the steam treatment. The hydrogen reduction can be carried out at a temperature range of 170-350°C, preferably between 170-270°C.

[0042] In 2012, German patent DE102012006946A1 disclosed a novel catalytic process for producing caprolactam from D-glucose via adipic acid and caprolactone. In the caprolactone-to-caprolactam reaction, this patent used a Cu-Mo-Ti catalyst, and the reactants, in addition to caprolactone, included ammonia and hydrogen. This method can achieve a caprolactam yield of 80%.

[0043] In 2018, Chinese patent CN108774172A disclosed a catalytic method for preparing caprolactam and N-substituted caprolactam using caprolactone and ammonia (amine) as raw materials. Its key technical feature is that the reactor is a fixed bed. The catalyst packed in the fixed bed reactor is particulate SO4 with a diameter of Φ = 4.0–6.0 mm. 2- / M X O Y Solid superacid. This patent emphasizes that the superacid catalyst used should always be under nitrogen protection. The reaction is carried out under atmospheric pressure and nitrogen protection. The selectable reaction temperature range is 180-320℃, with a preferred range of 220-280℃; the selectable molar ratio of caprolactone to ammonia (amine) is 1-1.5, with a preferred range of 1.1-1.3. The method also requires the use of a solvent. The solvent refers to water, benzene, toluene, xylene, and cyclohexane. The amount of solvent added is 1-2 times the total weight of caprolactone and ammonia (amine).

[0044] In addition to the patents mentioned above, several journal articles have also covered the research on the synthesis of caprolactam from caprolactone. For example:

[0045] In 1977, the journal *Journal of the Chemical Society of Japan*, 1977, (7), pp. 1013-1017, reported the catalytic effect of a Cu-TiO2 catalyst on the gas-phase ammonolysis of caprolactone to caprolactam. The ammonolysis reaction was carried out under normal pressure, and the products, in addition to caprolactam, included 6-hydroxyhexanonitrile, 6-hydroxyhexanoamide, adiponitrile, and polymers. The paper demonstrated through blank experiments that a simple solid acid catalyst led to the production of 6-hydroxyhexanonitrile, while a simple copper catalyst showed almost no catalytic activity for the conversion of caprolactone. The Cu-TiO2 catalyst required reduction with hydrogen before use, and the reaction required the presence of hydrogen during the reaction. The catalyst activity decreased rapidly over time, presumably due to the polymer coating on the catalyst surface.

[0046] In 2001, the Japanese publication Kobunshi Ronbunshu, 58(12), 679-684 (2001) reported a study on the non-catalytic preparation of caprolactam from caprolactone and ammonia in supercritical water (T>374℃, P>22.1MPa). This study proposed a reaction mechanism for the preparation of caprolactam from caprolactone, suggesting that 6-hydroxyhexanoamide is the intermediate. 6-hydroxyhexanoamide undergoes dehydration and ring closure to generate caprolactam. The study also investigated the effects of reaction temperature, water density, and ammonia concentration. The results showed that at 380℃ and 38MPa (where the water density is 0.5 g / cm³), the reaction proceeded smoothly. 3 The conversion rates of caprolactone and ammonia, as well as the yield of caprolactam, increased with increasing reaction time. The yield of caprolactam reached 79.2% after 60 minutes of reaction. However, the high temperature and high pressure conditions of supercritical water increase equipment costs and operational difficulty, and also increase safety risks.

[0047] In 2022, the published paper ChemSusChem, 2022, 15(16) reported a reaction process for preparing caprolactam from 6-hydroxyhexanoic acid by bio-enzyme catalysis, but its practical value is not great.

[0048] In summary, the preparation of caprolactam from caprolactone eliminates the cyclohexanone oxime Beckmann rearrangement step in the existing benzene-based caprolactam process and avoids the problems associated with the cyclohexanone ammoniation step, making it a promising new route for caprolactam production. However, the technology for preparing caprolactam from caprolactone has not received sufficient attention. Existing processes and catalysts for caprolactam preparation from caprolactone are mainly based on patents and papers published in the 1970s and earlier. Generally, the early proposed reaction processes can be divided into non-catalytic and catalytic methods. Non-catalytic methods require high-temperature and high-pressure reaction conditions. Due to thermodynamic limitations and the formation of byproducts, the caprolactam yield of non-catalytic methods is relatively low. In contrast, catalytic methods offer milder reaction conditions, are thermodynamically advantageous, help avoid side reactions, and reduce equipment investment, energy consumption, and production costs, thus benefiting industrial applications. However, catalytic methods require highly active, selective, and resilient catalysts, and existing catalysts do not meet the needs of industrial applications. Summary of the Invention

[0049] The purpose of this invention is to provide a method for preparing and applying a Cu-Beta zeolite catalyst for the gas-solid phase catalytic reaction of caprolactone to caprolactam via hydroamination.

[0050] Specifically, the Cu-Beta zeolite catalyst provided by this invention for the gas-solid phase catalytic reaction of caprolactone to caprolactam is a catalyst prepared by loading copper in the pores using a modified ammonia stripping method with dealuminated Beta zeolite as a support.

[0051] Research has revealed that, for the gas-solid phase catalytic reaction of caprolactone to caprolactam via hydroamination, supported copper-based catalysts show the greatest promise for industrial application in terms of catalytic activity and selectivity. However, from the perspective of catalyst stability, deactivation is the biggest challenge for its industrial application. The deactivation of copper-based catalysts in the gas-solid phase catalytic reaction of caprolactone to caprolactam via hydroamination is not solely due to coking. The sintering problem of highly dispersed copper particles is also a significant cause of catalyst deactivation. Those familiar with the field know that coking deactivation is a temporary deactivation of the catalyst, and its catalytic activity can generally be restored through various regeneration methods, thereby extending the catalyst's lifespan. In contrast, sintering deactivation is generally a permanent deactivation of the catalyst, having the greatest impact on its lifespan.

[0052] The main advantage of the Cu-Beta zeolite catalyst provided by this invention is that the copper particles therein acquire anti-sintering ability due to the hydroxyl groups of the zeolite support stabilizing them, allowing the copper-based catalyst to be used without the addition of anti-sintering aids such as chromium and nickel.

[0053] First, the main feature of the Cu-Beta zeolite catalyst provided by the present invention is that it uses dealuminated Beta zeolite as a support.

[0054] Catalysts for the catalytic synthesis of caprolactam from caprolactone, as described in existing patents and academic papers, are mainly unsupported bulk copper chromite catalysts and copper catalysts supported on amorphous single oxide supports (such as titanium dioxide, alumina, and silica) and binary composite oxide supports (such as silica and alumina) with the addition of a second metal component, nickel or chromium. Those skilled in the art know that unsupported copper chromite catalysts have a small specific surface area and few exposed metal active sites, resulting in high metal consumption and low catalytic efficiency. Supporting copper, copper-nickel, and copper-chromium on amorphous oxide supports (single oxide supports and binary composite oxide supports) can overcome the problems of unsupported catalysts; however, supported copper catalysts are prone to sintering and deactivation, posing a significant challenge for industrial applications. Adding chromium to supported copper catalysts to form a copper chromite phase can improve their resistance to sintering. However, chromium is a metal with limited use. Clinically, chromium and its compounds primarily harm the human skin, respiratory, and digestive systems; even low chromium concentrations can have strong toxic effects on the human body. Therefore, catalysts with added chromium encounter significant challenges in preparation, use, and the harmless disposal of spent catalysts. Adding nickel to supported copper catalysts can improve the anti-sintering properties of copper. However, our research results indicate that for the reaction from caprolactone to caprolactam, introducing a large amount of nickel into the supported copper catalyst significantly reduces the catalyst's ability to catalyze the gas-solid phase hydroammoniation of caprolactone to caprolactam. For example, under the same conditions, a copper-amorphous silica catalyst (10 wt.% Cu) prepared using fumed silica (chemical silica) as a support, when doped with a small amount of nickel (Ni:Cu = 0.3), showed a 15-20% decrease in its ability to catalyze the hydroammoniation of caprolactone to caprolactam. In the relevant patent (US3888845), although nickel is considered a preferred additive for supported copper catalysts, its addition is strictly limited to the Ni:Cu range of 0.001-1 (atomic ratio), preferably 0.005-0.25. Undoubtedly, the addition of a small amount of nickel can improve the anti-sintering ability of supported copper catalysts. However, the effect of a small amount of nickel alone is not enough to properly solve the problem of sintering deactivation of supported copper catalysts.

[0055] In fact, the problem of sintering deactivation of supported copper catalysts is a common problem. Copper-based catalysts have been widely used in alcohol dehydrogenation, carbonyl hydrogenation, ester hydrogenolysis, ammoniation, hydrocarbon hydrogenation, isomerization, and hydrogenolysis reactions of C-C bonds and C-Si bonds, etc., because of their low price and environmental friendliness. The main reason for the easy sintering and growth of highly dispersed copper particles is that copper metal has a large ionic radius, a low melting point (1083 °C), and low Tammann temperature and Hüttig temperature. Supported copper catalysts can sinter at a temperature of 170 °C. Someone summarized the thermal stability of common metal catalysts and gave the following order: Ag < Cu < Pd < Fe < Ni < Co < Pt < Rh < Ru < Ir < Os < Re. It can be seen from this that the thermal stability of copper is lower than that of most common metal catalysts.

[0056] The present invention prepares a supported copper catalyst with dealuminated Beta zeolite as the carrier, aiming to disperse and stabilize the supported copper particles by using a large number of hydroxyl nest lattice defect sites in the dealuminated Beta zeolite. A large number of hydroxyl nest lattice defect sites in the dealuminated Beta zeolite can be generated by removing framework aluminum from the Beta zeolite crystal by a conventional acid treatment method. When the Beta zeolite is subjected to acid dealumination treatment, for each removed framework aluminum, four Si-O-Al bonds ([Al-(OSi)4] - + 4H2O = [Al(OH)4] - + 4≡Si-OH, [Al(OH)4] - + 4H + = Al 3+ + 4H2O, and the total reaction equation is [Al-(OSi)4] - + 4H + = Al 3+ + 4≡Si-OH), generating a hydroxyl nest lattice defect site surrounded by four silanol groups (≡Si-OH).

[0057] The main idea of ​​this invention comes from the inventor's previous work. In his previous work, the inventor had conducted in-depth research on the physicochemical properties and catalytic functions of hydroxyl lattice defect sites in the MFI zeolite family (ZSM-5, B-ZSM-5, Silicalite-1(S-1) and TS-1). The following public documents record some representative research work: Silicalite-1zeolite acidification by zinc modification and its catalytic properties for isobutane conversion, RSC Advances, 2018, 33(8), p.18663-1867; Pt supported on Znmodified silicalite-1zeolite as a catalyst for n-hexane aromatization, JOURNAL OF ENERGY CHEMISTRY,2018,(36),p.96-103; Operando Dual Beam FTIR Study of Hydroxyl Groups and Zn Species over Defective HZSM-5Zeolite Supported ZincCatalysts,Catalysts,2019,1(9),p.100; Effect of Zeolitic Hydroxyl Nests on theAcidity and Propane Aromatization Performance of Zinc Nitrate Impregnation-Modified HZSM-5Zeolite, Industrial & Engineering Chemistry Research, 2020, 37(59), p.16146-16160. Liu Guodong. Study on surface acidity and catalytic performance of ZnO-modified nano-silicalite-1 zeolite [D]. Dalian University of Technology, 2020.; Lin Long. Characterization, modification and catalytic performance of defective ZSM-5 zeolite [D]. Dalian University of Technology, 2022.). In short, the above research results show that silanolites located in the zeolite hydroxyl lattice defect sites are more chemically active than isolated silanolites on the outer surface of zeolite crystals because they easily form hydrogen bonds.Furthermore, it is particularly worth mentioning that in their research on zinc nitrate impregnation of defective all-silica zeolite S-1 and defective ZSM-5 zeolite and the preparation of zinc oxide-modified catalysts, the inventors discovered an important phenomenon: zinc oxide preferentially resides at the hydroxyl-dwelling lattice defect sites of the zeolite. Moreover, the zinc oxide residing at these zeolite hydroxyl-dwelling lattice defect sites are all highly dispersed sub-nanometer zinc oxide species. These research experiences provided important scientific guidance for this invention.

[0058] However, this invention does not use defective MFI zeolites (e.g., defective all-silica zeolite S-1 and deboronized B-ZSM-5 zeolite) as the support for preparing the copper-supported catalyst. Instead, it selects dealulated Beta zeolite as the support for preparing the copper-supported catalyst. This is not because the hydroxyl-dwelling lattice defect sites in defective MFI molecular sieves (e.g., defective all-silica zeolite S-1 and deboronized B-ZSM-5 zeolite) cannot disperse and stabilize copper particles, nor is it because the copper-supported catalyst prepared using defective MFI molecular sieves (e.g., defective all-silica zeolite S-1 and deboronized B-ZSM-5 zeolite) is ineffective for catalyzing the gas-solid phase reaction from caprolactone to caprolactam. Rather, it is because the cylindrical channels of MFI family zeolites are ten-membered rings. When the loading of metallic copper is slightly large, the effective size of the channels will be significantly reduced, which is not conducive to the diffusion of the reactant caprolactone (seven-membered ring) within the pores, nor is it conducive to the formation and diffusion of caprolactam products, which are also seven-membered rings. Therefore, it is not conducive to the preparation of catalysts with high activity, high selectivity and strong resistance to deactivation.

[0059] Those familiar with this field know that Beta zeolite, as a crystalline porous catalytic material, shares similar advantages with MFI zeolite, such as: (1) Both are high-silica zeolites, thus exhibiting high thermal and hydrothermal stability, good regeneration performance, and allowing for repeated regeneration and reuse after catalyst fabrication; (2) Both possess cylindrical channels and a three-dimensional intersecting pore system, providing networked channels for molecular diffusion, resulting in good pore diffusion and strong anti-clogging ability, which is beneficial for maintaining long-term activity stability of the catalyst during continuous reaction. In addition, Beta zeolite has unique features compared to MFI zeolite. On the one hand, the three-dimensional cylindrical channels of Beta zeolite are all macropores with twelve-membered rings. In the three-dimensional channel system of Beta zeolite, there is a set of Z-shaped curved channels parallel to the

[001] direction with an elliptical cross-section and a diameter of 0.56 nm × 0.65 nm; there are also two sets of straight channels parallel to the

[100] and

[010] directions respectively, with elliptical cross-sections and a diameter of 0.66 nm × 0.77 nm. In contrast, the three-dimensional cylindrical channels of MFI zeolite are all central holes of ten-membered rings. In the channel system of MFI zeolite, there is a set of straight channels parallel to the (100) crystal plane with an approximately circular cross-section (channel size 0.53 nm × 0.56 nm) and two sets of Z-shaped curved channels parallel to the (010) crystal plane with opposite directions and elliptical cross-sections (channel size 0.51 nm × 0.55 nm). It is conceivable that the relatively loose macroporous structure of Beta zeolite is not only more suitable for the intrapore diffusion of the reactant caprolactone (a seven-membered ring), but also for the formation and intrapore diffusion of caprolactam, which is also a seven-membered ring product. Therefore, it is more conducive to the preparation of catalysts with high activity, high selectivity, and strong resistance to deactivation. In fact, Beta zeolite is the only zeolite molecular sieve among industrially produced zeolite catalytic materials that simultaneously possesses the advantages of a high silica-alumina oxide molar ratio, a three-dimensional cross-channel system, and all channels being twelve-membered ring macropores.

[0060] On the other hand, the framework aluminum of Beta zeolite can be easily and completely removed by acid treatment, resulting in a high density of hydroxyl pit defects on the crystal framework. This characteristic is rare in industrially produced zeolite catalysts and is unmatched by MFI zeolite. During acid dealumination of Beta zeolite, removing one piece of framework aluminum requires acid dissociation of four Si-O-Al bonds ([Al-(OSi)4)). - +4H₂O=[Al(OH)₄] - +4≡Si-OH, [Al(OH)4] - +4H + =Al 3+ +4H₂O, the overall reaction equation is [Al⁻(OSi)₄]⁻ - +4H + =Al 3++4≡Si-OH) generates a hydroxyl-dwelling lattice defect site surrounded by four silanol groups (≡Si-OH). In MFI zeolites, the hydroxyl-dwelling lattice defect sites in the defective all-silica zeolite S-1 are randomly formed during the hydrothermal synthesis of S-1 zeolite in alkaline media, and their number and distribution are poorly controllable. Although the framework aluminum content of ZSM-5 zeolite has a wide adjustable range, its lower limit of the silicon-aluminum molar ratio (Si / Al) can reach about 10, and its upper limit can reach all-silica zeolite, i.e., Silicalite-1 (S-1). However, it is difficult to completely remove the framework aluminum of ZSM-5 zeolite. Therefore, in the research on the preparation of titanium-atom hybridized ZSM-5 zeolite using post-synthesis methods, the general practice is to first synthesize boron-containing ZSM-5 zeolite (B-ZSM-5), and then remove boron from B-ZSM-5 zeolite to obtain a ZSM-5 zeolite support with a high density of hydroxyl-dwelling defect sites on the framework.

[0061] In summary, this invention does not use MFI zeolites with hydroxyl-containing lattice defect sites (e.g., defective all-silica zeolite S-1 and deboronized B-ZSM-5 zeolite) as the support for preparing the copper catalyst. Instead, it selects Beta zeolite with hydroxyl-containing lattice defect sites as the support for preparing the copper catalyst. The main reason is that, for the purposes of this invention, Beta zeolite possesses unparalleled material advantages, combining a high silica-alumina oxide molar ratio framework, a three-dimensional twelve-membered ring cross-channel system, and easy complete removal of framework aluminum. Furthermore, Beta zeolite was one of the earliest catalytic materials to be industrially synthesized; it can be obtained in large quantities commercially or easily prepared in-house using a hydrothermal synthesis method.

[0062] Secondly, the Cu-Beta zeolite catalyst preparation method provided by this invention is characterized by the use of a modified ammonia stripping method to load copper onto a dealuminated Beta zeolite support. The core of this modified ammonia stripping method for loading copper involves impregnating the zeolite support with an equal volume of copper-ammonia complex solution. During this process, the capillary aggregation of the zeolite support draws most of the complex solution into the pores, allowing the copper hydroxide generated during ammonia stripping to be directly deposited within the pores of the Beta zeolite. Therefore, in subsequent drying, calcination, and hydrogen reduction processes, copper hydroxide can first be converted into copper oxide within the zeolite pores, and then further converted into sub-nanometer and nanoparticles of metallic copper. These sub-nanometer and nanoparticles of metallic copper can be directly captured by the hydroxyl-containing lattice defect sites primarily located in the zeolite pores during their formation, thus being promptly dispersed and stabilized.

[0063] Those familiar with this field know that the ammonia stripping method is one of the most commonly used methods for preparing copper-based catalysts. Ube Industries Ltd. (US4 440 873 (1984), EP0 064 241B1 (1985)) of Japan first proposed using the ammonia stripping method to prepare Cu / SiO2 catalysts for the solid-phase hydrogenation of dimethyl oxalate to ethylene glycol and glycolates. The earliest proposed ammonia stripping method is as follows: First, prepare a copper-ammonia complex solution. Dissolve a soluble copper-containing compound in water to obtain an aqueous solution containing copper ions. Then, add an appropriate amount of concentrated ammonia to the aqueous solution containing copper ions to make the pH value greater than 10, for example, to reach a pH value of 10-12. This yields a deep blue transparent solution containing the copper-ammonia complex. Second, use silica sol as a precursor for the SiO2 support and mix it with the copper-ammonia complex. That is, add the silica sol to the deep blue transparent solution containing the copper-ammonia complex and stir thoroughly to ensure uniform mixing. The mixing process can be carried out under atmospheric and pressurized conditions, from room temperature to 150°C; the third step is ammonia stripping. This involves stripping the mixture containing the copper-ammonia complex to obtain a solid catalyst precursor. Ammonia stripping can be carried out under pressurized and depressurized conditions, with a preferred temperature range of 60-90°C; the fourth step is the pretreatment of the solid catalyst precursor. This step refers to the pretreatment of the solid catalyst precursor before hydrogen reduction, including drying and washing. Pre-calcination is also an option. The temperature range for pre-calcination is 400-800°C, preferably 500-750°C; the fifth step is hydrogen reduction. The pretreated solid catalyst precursor is subjected to hydrogen reduction. The hydrogen reduction time is 1-15 hours, and the reduction temperature range is 150-500°C, preferably 200-400°C.

[0064] US Patent 4,440,873 provides examples of soluble copper-containing compounds that can be used to prepare copper-ammonia complex solutions, including copper nitrate, copper sulfate, copper oxalate, copper chloride, and copper acetate, with copper nitrate being the preferred option. Example 1 describes the preparation of a Cu / SiO2 catalyst by ammonia stripping as follows: (1) 19.0 g of copper nitrate (Cu(NO3)2·3H2O) is dissolved in 200 ml of water to obtain an aqueous solution containing copper ions. Then, 60 ml of concentrated ammonia solution is added to the solution, and the pH is adjusted to 11-12 to obtain a deep blue solution containing copper-ammonia complex; (2) 66.6 g of silica sol (30 wt.% SiO2) is added to the copper-ammonia complex solution and stirred at room temperature for several hours; (3) The reaction mixture from step (2) is subjected to ammonia stripping treatment by heating. Ammonia stripping continues until most of the water is evaporated, yielding a solid product; (4) The solid product is dried at 120°C for 12 hours. The dried material was thoroughly washed with water and then dried again. The drying conditions were 140℃×14h; (5) The dried material was subjected to hydrogen reduction treatment. The reduction conditions were 350℃×2-3h. The prepared Cu / SiO2 catalyst contained approximately 20wt.% copper.

[0065] In summary, the earliest proposed process for preparing Cu / SiO2 catalysts using the ammonia stripping method has the following characteristics: Firstly, the amorphous silica support is not pre-fabricated but generated in situ during the ammonia stripping process using silica sol as a precursor. Specifically, during ammonia stripping, the silica sol is converted into silica gel. Simultaneously, the copper-ammonia complex loses ammonia to form copper hydroxide precipitate, which is deposited on the silica gel surface. This process is dynamic. That is, the silica gel particles continuously grow after formation, while the copper hydroxide precipitate is also continuously formed. As the silica gel particles grow, the copper hydroxide precipitate is deposited and reacted on its surface, resulting in a layered loading state of silica gel and copper hydroxide. Later, researchers in this field pointed out (J. Catal. 257 (2008) 172–180) that this ammonia stripping method is essentially a homogeneous deposition-precipitation method, and the prepared Cu / SiO2 catalyst is a layered copper silicate. Secondly, a diluted copper-ammonia complex solution was prepared and used. The volume of this copper-ammonia complex solution is significantly excessive relative to the liquid holding capacity (pore volume) of the final silica gel. The aqueous solvent needs to be removed through post-treatment processes such as filtration or evaporation. The loading and dispersion mechanism of copper on the silica support is deposition and precipitation; that is, as the silica gel particles grow, copper hydroxide precipitates and reacts on their surface, achieving a uniform loading state through layer-by-layer mixing of silica gel and copper hydroxide. It is conceivable that if the silica support were not generated during ammonia stripping but prefabricated, using this diluted and excessively large (the solution volume is significantly excessive relative to the total pore volume of the silica support) copper-ammonia complex solution for ammonia stripping would inevitably lead to a large amount of copper hydroxide being deposited on the outer surface of the support particles, resulting in an uneven loading of copper—less copper inside the pores and more copper outside the pores.

[0066] Some scholars have prepared copper-based catalysts supported on amorphous oxide supports using the earliest proposed ammonia stripping method for the gas-solid phase hydrogenation of dimethyl oxalate to ethylene glycol. For example, related research has been reported in published literature J. Catal. 257 (2008) 172–180 and Appl. Catal. A: Gen. 458 (2013) 82–89, involving amorphous oxide supports of silica and binary composites of silica and titanium dioxide. When silica was used as the support, silica sol (Ludox AS-40) was used as a precursor. When the binary composite of silica and titanium dioxide was used as the support, silica sol (JN30, Qingdao Haiyang Chem. Co., Ltd.) and titanium dioxide sol were used as precursors. After ammonia stripping (when the slurry pH dropped to 6-7), the amorphous oxide-supported copper hydroxide solid product was obtained by filtration.

[0067] Some researchers have improved upon the previously proposed ammonia stripping method when preparing Cu / SiO2 catalysts for the gas-solid phase hydrogenation reaction of dimethyl oxalate. Specifically, in the published papers J. Am. Chem. Soc. 2012, 134, 13922-13925 and J. Catal. 297 (2013) 142–150, researchers reported the ammonia evaporation hydrothermal (AEH) method. This method essentially involves transferring the ammonia stripping product (a slurry containing copper hydroxide / silica gel precipitate, pH = 6-7) from the traditional ammonia stripping method (the earliest proposed method) to a high-pressure synthesis reactor and hydrothermally treating it at 190–210 °C for 12 h. The solid product is then subjected to conventional filtration, washing, drying, calcination, and hydrogen reduction treatment. In other words, this method does not improve the ammonia stripping method itself, but rather adds a hydrothermal post-treatment step to the ammonia stripping product before the conventional post-treatment. It is important to emphasize that the procedures before hydrothermal post-treatment in the ammonia stripping hydrothermal method are no different from those in the traditional ammonia stripping method. The silica support is generated in situ using silica sol as a precursor. The diluted and excess aqueous solvent of the copper-ammonia complex solution is removed by filtration. In the published literature J.Phys.Chem.C 2015, 119, 13758-13766, researchers added urea as a precipitation aid when preparing the copper-ammonia complex solution. Other procedures are identical to those in the traditional ammonia stripping method. The silica support was generated in situ using silica sol (Ludox AS-40, 40wt.% SiO2) as a precursor. The diluted and excess copper ammonia complex solution was removed by filtration. In the published literature Natural Gas Chemical Industry (C1 Chemistry and Chemical Engineering), 2013, 38(3):43-47, Natural Gas Chemical Industry (C1 Chemistry and Chemical Engineering), 2014, 39(5):31-34, and Journal of Shenyang University of Chemical Technology, 2016, 30(3):212-216, the researchers used pre-made JN-25 type alkaline silica gel (original particle size 10nm, Qingdao Ocean Chemical Co., Ltd.) as the support for the Cu / SiO2 catalyst prepared by the ammonia stripping method. In order to achieve a uniform deposition effect, a certain amount of silica sol was also added as a precursor for in situ generation of silica gel support. To overcome the problem of reduced silica sol usage when using pre-prepared JN-25 alkaline silica gel as a support for Cu / SiO2 catalysts, researchers also tried adding hexadecyltrimethylammonium bromide (CTAB) surfactant to the prepared copper ammonia complex aqueous solution to disperse the silica sol and generate mesopores in the in-situ generated silica gel.Other procedures are identical to the traditional ammonia stripping method. In the published literature RSC Adv., 2015, 5, 29040–29047 and Applied Catalysis A: General 509 (2016) 66–74, researchers used pre-prepared titanium dioxide (P25, Degussa Co., Ltd.) as the support for their Cu / TiO2 catalyst prepared by the ammonia stripping method, and other procedures were identical to the traditional ammonia stripping method. It should be noted that the P25 type TiO2 support is a low specific surface area support with underdeveloped capillaries. Therefore, the prepared Cu / TiO2 catalyst does not have a uniform deposition effect. That is, the supported copper hydroxide is mainly present on the outer surface of the titanium dioxide support. X-ray diffraction analysis of the calcined sample showed obvious CuO phase diffraction characteristic peaks at 2θ = 35.5°, 38.7°, and 48.7°, indicating poor dispersion of its hydrogen reduction product—metallic copper.

[0068] Furthermore, it is worth mentioning that in the published literature Applied Catalysis A, General 539 (2017) 59–69, researchers used pre-fabricated ordered mesoporous silica (OMS) as the support for their Cu / OMS catalyst prepared by ammonia stripping. To reduce the destructive effect of the alkalinity of the copper-ammonia complex solution on the ordered mesopores of the pre-fabricated silica support, the researchers also appropriately reduced the ammonia concentration in the prepared copper-ammonia complex solution (which they considered an improvement to the ammonia stripping method). Apart from these two points, the improved ammonia stripping method described in this study is no different from the traditional method. After ammonia stripping (when the slurry pH drops to 6-7), the diluted and excess aqueous solvent of the copper-ammonia complex solution is finally removed by filtration, thus obtaining a solid product loaded with copper hydroxide. The results show that after loading copper onto the pre-prepared silica support using the ammonia stripping method, the ordered mesoporous structure of the support was largely destroyed, and a large amount of layered copper silicate was present in the catalyst. This indicates that the pre-prepared silica support was largely dissolved into silica sol during contact with the copper-ammonia complex solution, and the silica sol produced a uniform deposition and precipitation effect with copper hydroxide during the ammonia stripping process. In the published literature Journal of Catalysis 280 (2011) 77–88, researchers also used pre-prepared mesoporous silica (HMS) as the support for their Cu / HMS catalyst prepared by the ammonia stripping method. In addition, the researchers added a water-soluble nickel salt (nickel nitrate) to the prepared copper-ammonia complex aqueous solution, so that the prepared copper-based catalyst contained metallic nickel (CuxNi / HMS). The ammonia stripping method used in this study is identical to the traditional ammonia stripping method, except for the use of a pre-prepared mesoporous silica support and the addition of a water-soluble nickel salt (nickel nitrate) to the prepared copper-ammonia complex aqueous solution, which introduces nickel as a catalyst. The ammonia stripping operation is carried out at 90°C. After stripping (when the slurry pH drops to 7-8), the diluted and excess aqueous solvent of the copper-ammonia complex solution is removed by filtration, yielding a solid product loaded with copper hydroxide and nickel hydroxide. Similarly, in this study, the ordered mesoporous structure of the HMS silica was largely destroyed after loading copper and nickel using the ammonia stripping method (the specific surface area decreased by more than 50%). Furthermore, XRD characterization results showed that the prepared supported catalyst sample exhibited characteristic diffraction peaks of the metal oxide phase before hydrogen reduction (calcined at 450°C for 4 h) and characteristic diffraction peaks of the metallic phase after hydrogen reduction, indicating that the copper and nickel were unevenly loaded and poorly dispersed on the HMS support.

[0069] According to the literature review, apart from a recent published paper in Science (Science10.1126 / science.adj1962(2023).) reporting the preparation of a supported copper catalyst on a dealaluminized Beta zeolite support using the ammonia stripping method for the solid-phase hydrogenation reaction of dimethyl oxalate, no other research on the preparation of supported metal catalysts on zeolite supports using the ammonia stripping method has been found domestically or internationally to date. It should be noted that the recent research published in Science used the traditional ammonia stripping method to prepare a supported copper catalyst on a dealaluminized Beta zeolite support. The specific procedure is as follows: First, 0.23 g of Cu(NO3)2·3H2O was dissolved in 100 ml of ammonia solution (containing 0.75 g of NH3·H2O) and stirred at room temperature for 10 min to prepare a copper-ammonia complex aqueous solution; second, 1.94 g of dealaluminized Beta zeolite support (Beta-deAl) was added to the copper-ammonia complex solution, and ammonia stripping was performed under vigorous stirring. The ammonia stripping temperature was 80℃, and the stripping time was 6 hours. In the third step, after ammonia stripping, the diluted and excess aqueous solvent of the copper-ammonia complex solution was removed by filtration. In the fourth step, the obtained solid product was dried overnight at 100℃ and calcined at 400℃ for 3 hours to obtain the catalyst. In the fifth step, to catalyze the hydrogenation reaction of dimethyl oxalate using this catalyst, it was reduced with hydrogen at 400℃ for 3 hours. It is evident that in this study, except for the catalyst support being a pre-prepared dealullated Beta zeolite (obtained by acid dealullating a Si / Al = 13 Al-Beta zeolite parent material with 13 MH NO3 solution at 80℃ for 12 hours), the other procedures were identical to the traditional ammonia stripping method. In the prepared copper-ammonia complex solution, the copper ion concentration was very low (only about 9.5 mmol / L); when preparing the catalyst using the ammonia stripping method, the initial liquid-to-solid ratio was as high as about 51.5 (ml / g), meaning the volume of the copper-ammonia complex solution was significantly excess over the zeolite support. The results showed that although the prepared copper catalyst Cu / Beta-deAl supported on dealubilized Beta zeolite had a very low copper content (approximately 3 wt.% Cu), its specific surface area loss was as high as 15% (due to the excessive dissolution and desilication of the dealubilized Beta zeolite caused by the excess copper ammonia complex solution (NH3 / Cu molar ratio 22.5), which destroyed the framework structure). Furthermore, its XRD pattern still showed obvious characteristic diffraction peaks of metallic copper (2θ = 43.3°). Transmission electron microscopy revealed that the copper in the fresh catalyst was mainly supported on the outer surface of the dealubilized Beta zeolite, with a relatively large particle size (due to the excessive deposition of copper hydroxide outside the zeolite channels during ammonia stripping caused by the use of diluted and excess copper ammonia complex solution). It required redispersibility via a reverse Ostwald ripening process after methanol vapor post-treatment to transfer the copper into the zeolite channels.This study fully demonstrates that when preparing molecular sieve-supported copper catalysts using dealubilized Beta zeolite as a support via copper ammonia complex, the traditional ammonia stripping method reported in the literature for silica supports cannot be used. Otherwise, the following problems will occur: (1) Excess copper ammonia complex solution will deposit a large amount of copper outside the zeolite channels during the ammonia stripping process; (2) Dealubilized Beta zeolite will undergo a desilication reaction in excess copper ammonia complex solution (pH = 10-12) (ammonia stripping temperature 80℃), which will damage the crystal structure.

[0070] Therefore, this invention proposes an improved ammonia stripping method, different from known practices, to meet the need for loading metallic copper within the pores of zeolite supports, especially easily desiliconized high-silica zeolite supports such as dealuminolite (Beta zeolite).

[0071] Furthermore, a key feature of this invention is that the provided Cu-Beta zeolite catalyst is intended for the production of caprolactam from caprolactone under gas-solid phase reaction conditions. To date, neither published patents nor other literature has addressed this application of Cu-Beta zeolite catalysts. This reaction system is unique. This is primarily because the reaction for the production of caprolactam from caprolactone under gas-solid phase reaction conditions involves the simultaneous use of water vapor, hydrogen, and ammonia. This is a demanding application scenario for copper-based catalysts.

[0072] As mentioned earlier, the catalytic methods for producing caprolactam from caprolactone described in existing patents and academic papers mainly use two types of catalysts: one is an unsupported bulk copper chromite catalyst, and the other is a copper catalyst supported on a single oxide support (such as titanium dioxide, alumina, or silica) or a binary composite oxide support (such as silica and alumina) with the addition of a second metal component, nickel or chromium. In the supported copper catalyst (with the addition of a second metal component, nickel or chromium), both the single oxide and the binary composite oxide used as the support are amorphous.

[0073] The gas-solid phase reaction state is a suitable pathway for the hydroamination of caprolactone to caprolactam via catalysis. As mentioned earlier, the catalytic methods for preparing caprolactam from caprolactone disclosed by Kanekabuchi Co., Ltd. (BOSEKI KABUSHIKI KAISHA) in British Patent GB1109540 (1966) and US Patent 3652549 (1972), as well as by Teijin Co., Ltd. in US Patent US3888845 (1975), all employ a gas-solid phase reaction state.

[0074] As is well known, gas-solid phase reaction is a common form of heterogeneous catalysis, specifically referring to the catalytic reaction in which reactants in gaseous form contact with a solid catalyst. In the field of heterogeneous catalysis, gas-solid phase reaction is sometimes simply referred to as gas phase reaction. Gas-solid phase reaction is a reaction form with mild reaction conditions, high mass and heat transfer efficiency, and very simple operation. For gas-solid phase reaction, the process of reactants being converted into products on the catalyst consists of seven elementary steps: (1) external diffusion of reactants. In this step, reactants pass through the adsorption film on the surface of the solid catalyst and come into contact with the outer surface of the catalyst; (2) internal diffusion of reactants. In this step, reactants diffuse into the pores on the surface of the solid catalyst to approach the catalytic active center within the pores; (3) chemical adsorption of reactants on the catalytic active center. In this step, reactant molecules are activated and become activated molecules; (4) surface reaction. In this step, reactants are converted into adsorbed product forms on the active center of the catalyst; (5) product desorption. In this step, the adsorbed product is removed from the catalytic active center; (6) internal diffusion of products. This step is the process by which product molecules move from the pores to the outer surface of the catalyst after leaving the catalytic active center; (7) External diffusion of the product. In this step, product molecules leave the pores on the outer surface of the solid catalyst, pass through the adsorption film on the surface of the solid catalyst, detach from the solid catalyst particles, and become reaction products.

[0075] The Cu-Beta catalyst provided by this invention is suitable for the gas-solid phase hydroamination catalytic reaction conditions for the production of caprolactam from caprolactone, as described in existing related patents and academic papers. As mentioned earlier, in 1966, Kanekabuchi Co., Ltd. of Japan first disclosed a gas-solid phase catalytic method for preparing caprolactam in British Patent GB1109540. Specifically, caprolactone and a certain amount of water were first vaporized, then mixed with ammonia and hydrogen. The mixed gas underwent a catalytic reaction at 120-350°C and atmospheric pressure using a copper chromite catalyst. In 1972, Kanekabuchi Co., Ltd. of Japan again disclosed a method for preparing caprolactam in US Patent 3652549, which was also a gas-solid phase catalytic method. Specifically, this method used a fixed-bed reactor, with a reaction temperature range of 170-300°C and a hydrogen partial pressure of 0.1-1.5 atm. The feed also includes ammonia and water vapor, with preferred dosage ranges (molar ratios to feedstock) of 2-50 and 10-100, respectively. In 1975, Teijin Corporation of Japan disclosed a method for preparing caprolactam in US Patent 3888845, which is also a gas-solid phase catalytic method. Specifically, the gas-solid phase catalytic reaction can be carried out at 200-320°C and 0.01-2 atm, preferably at 220-310°C and 0.1-1.2 atm. The selectable dosage ranges for hydrogen and ammonia are 5-70 (H2 / ester molar ratio) and 1-50 (NH3 / ester molar ratio), respectively, with preferred ranges of 10-50 (H2 / ester molar ratio) and 2-25 (NH3 / ester molar ratio), respectively. Furthermore, this process emphasizes the importance of the hydrogen to ammonia molar ratio and the addition of water to the reactor feed. In general, using a suitable hydrogen to ammonia molar ratio is beneficial for improving the selectivity of the reaction. Adding water to the reactor feed can not only reduce side reactions and improve caprolactam selectivity, but also slow down the deactivation rate of the catalyst. The selectable range for the hydrogen to ammonia molar ratio is 0.2-30, with a preferred range of 0.5-15; the selectable range for the water / ester molar ratio is 0-50, with a preferred range of 5-30.

[0076] In summary, based on existing patents and academic papers, the gas-solid phase hydroamination catalytic reaction for the production of caprolactam from caprolactone requires water, ammonia, and hydrogen as feedstock in addition to caprolactone. The molecular formula of the caprolactone feedstock (C6H2O) is... 10 O2) and the molecular formula of caprolactam product (C6H) 11(NO) It is not difficult to see that ammonia and hydrogen are also reaction raw materials, and water vaporization into water vapor is a diluent gas. The selectable range of reaction temperature is 120-350℃, the selectable range of reaction pressure is 0.01-2 atm, and the selectable ranges of the molar ratios of ammonia-ester, hydrogen-ester, and water-ester are 1-50, 5-70, and 0-100, respectively; the preferred range of reaction temperature is 220-300℃, the preferred range of reaction pressure is 0.1-1.2 atm, and the preferred ranges of the molar ratios of ammonia-ester, hydrogen-ester, and water-ester are 2-25, 10-50, and 5-30, respectively. To facilitate a better understanding of the implementation effects of the present invention by those skilled in the art, the catalytic performance of the provided Cu-Beta zeolite catalyst in the gas-solid phase hydroamination reaction of caprolactone to caprolactam is evaluated in this invention, and the reaction conditions used are within the above ranges.

[0077] The technical solution of this invention:

[0078] A method for preparing a Cu-Beta zeolite catalyst for the synthesis of caprolactam from caprolactone, comprising the following steps:

[0079] The first step is to prepare a dealuminated Beta zeolite support.

[0080] Engineers skilled in the art can, according to the requirements of this invention, combine their own work experience with conventional acid dealumination methods in relevant literature, to obtain a dealuminated Beta zeolite support from a Beta zeolite parent material. The requirements of this invention are as follows:

[0081] (1) Select Beta zeolite parent material

[0082] The aforementioned Beta zeolite matrix refers to silica-alumina Beta zeolite. This invention does not limit the grain size of the Beta zeolite matrix, nor does it limit the production process of the Beta zeolite matrix. However, to facilitate the implementation of this invention, the following limitations are imposed on the Beta zeolite matrix: 1) The Beta zeolite matrix is ​​free of impurities; 2) The Beta zeolite matrix exhibits good crystallinity; 3) The molar ratio of silica-alumina oxides (SiO2 to Al2O3) in the Beta zeolite matrix is ​​suitable.

[0083] The presence of impurities in the Beta zeolite matrix can be confirmed by X-ray polycrystalline powder diffraction (XRD). Those skilled in the art know that the molar ratio of silicon to aluminum oxide (SiO2 to Al2O3) in Beta zeolite produced by hydrothermal synthesis is typically between 10 and 200 (US3 308 069 (1967)). Beta zeolite products with lower SiO2 to Al2O3 molar ratios generally may contain mordenite (MOR) impurities, while Beta zeolite with higher SiO2 to Al2O3 molar ratios generally may contain ZSM-5 zeolite impurities. By sampling and performing XRD analysis on the Beta zeolite matrix, and comparing the XRD patterns of the samples with standard diffraction cards for Beta zeolite, MOR zeolite, and ZSM-5 zeolite, it can be determined whether the sample's XRD pattern contains characteristic peaks of MOR zeolite and ZSM-5 zeolite impurities, thus determining whether the Beta zeolite matrix is ​​a pure Beta zeolite phase.

[0084] Theoretically, the crystallinity of the Beta zeolite matrix can also be analyzed using XRD, with the relative crystallinity index used as a measure. However, the XRD relative crystallinity index requires comparing the sum of the intensities of the medium-intensity characteristic diffraction peaks (2θ = 7.6-8°) and the highest-intensity characteristic diffraction peaks (2θ = 22-23°) of the Beta zeolite matrix with the sum of the intensities of the corresponding diffraction peaks of a reference sample (standard Beta zeolite with 100% crystallinity). Furthermore, there is no universally defined reference sample. Additionally, the intensities of the medium-intensity and highest-intensity characteristic diffraction peaks (2θ = 7.6-8° and 2θ = 22-23°) of Beta zeolite are significantly affected by post-processing conditions such as calcination. Therefore, using the XRD relative crystallinity index to determine the crystallinity of the purchased or synthesized Beta zeolite matrix has poor universality. Therefore, this invention recommends using the specific surface area index of the Beta zeolite matrix to measure whether the crystallinity of the purchased or synthesized Beta zeolite matrix meets the requirements. Based on our statistical results of the literature reports on the specific surface area of ​​Beta zeolite, the BET specific surface area of ​​well-crystallized Beta zeolite produced by hydrothermal synthesis is generally not less than 450 m². 2 / g. Engineers skilled in the art can use conventional nitrogen physical adsorption methods to first measure the nitrogen adsorption isotherm data of the Beta zeolite matrix, and then calculate its BET specific surface area value according to the BET model. In summary, this invention requires that the BET specific surface area value of the Beta zeolite matrix used be ≥450m². 2 / g indicates that its crystallization is good.

[0085] The molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) is a key indicator of the Beta zeolite matrix. This is because, on the one hand, the lower the molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) in the Beta zeolite matrix, i.e., the higher the skeletal aluminum content, the more hydroxyl lattice defect sites can be used to disperse and stabilize nano- and sub-nano-sized copper particles in the dealuminated Beta zeolite support. On the other hand, pure-phase Beta zeolite with a very low molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) is difficult to synthesize using hydrothermal methods. Moreover, after the Beta zeolite matrix with a very low molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) is converted into a dealuminated Beta zeolite support by acid dealumination, the skeletal thermal stability is poor, which leads to a loss of crystallinity during the subsequent calcination process for preparing Cu-Beta zeolite catalysts, resulting in deteriorated catalyst performance. Therefore, the suitable range for the molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) in the Beta zeolite matrix required by this invention is between 10 and 200, preferably between 20 and 100, and more preferably between 25 and 60. The analysis of the molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) in the Beta zeolite matrix can be performed using conventional chemical analysis methods (tipping), or using X-ray fluorescence spectrometry (XRF) or inductively coupled plasma atomic emission spectrometry (ICP). This invention recommends using the simple and rapid XRF method.

[0086] The Beta zeolite matrix conforming to the requirements of this invention can be obtained commercially or synthesized in-house. Engineers skilled in the art can also synthesize the Beta zeolite matrix conforming to the requirements of this invention based on their own experience and other literature reports.If synthesizing the Beta zeolite matrix yourself, the following methods reported in patents and publications are available: US3308 069 (1967), EP187 522A2 (1986), US4 847 055 (1989), CN1 086 792A (application date 1993.9.20), CN1 108 213A (application date 1994.3.11), CN1 108 214A (application date 1994.3.11), CN1154 341A (application date 1996.1.11), CN1 154 242A (application date 1996.1.9), CN1 154 342A (application date 1996.1.11), CN1 268 545A (application date 1999.3.30), CN1 133 497C (application date 1999.3.30), CN1108 275C (application date 1999.9.10), CN1 100 004C (application date 2000.5.19), CN1 335 258A (application date 2001.2.28), CN1 116 227C (application date 2001.3.12), CN101 205 072B (application date 2006.12.18), Chem. Comm., 1996, 625; J. Mater. Chem., 1998, 8(9), 2137-2145; Microporous and Mesoporous Materials 21(1998) 305-313; Applied Catalysis A-GENERAL,166(1998),97–103;Microporous and Mesoporous Materials 48(2001)23-29;Microporous and Mesoporous Materials 56(2002)1–10.;Journal of Molecular Catalysis A:Chemical252(2006)76–84;Microporous and Mesoporous Materials 94(2006)1–8; J.Mater.Sci.41(2006)1861-1864; Cryst.Res.Technol.44,No.4,379-385(2009)DOI10.1002 / crat.200800474; Microporous and Mesoporous Materials 143(2011)97-103;RSC Adv. 2019, 9, 3653-3660.

[0087] (2) Preparation of dealuminized Beta zeolite carrier

[0088] As mentioned earlier, conventional acid dealumination methods can be used to prepare dealusion-coated Beta zeolite supports based on a Beta zeolite matrix. This invention requires the dealusion-coated Beta zeolite support to have the highest possible molar ratio of silicon to aluminum oxides (SiO2 to Al2O3), meaning that as much skeletal aluminum as possible should be removed from the Beta zeolite matrix. A suitable range for the molar ratio of silicon to aluminum oxides (SiO2 to Al2O3) of the dealusion-coated Beta zeolite support meeting the requirements of this invention is ≥700, preferably ≥800, and more preferably ≥900. Because the dealusion-coated Beta zeolite has a high molar ratio of silicon to aluminum oxides (SiO2 to Al2O3) and a low aluminum content, accurate determination of this ratio requires inductively coupled plasma atomic emission spectrometry (ICP) or atomic absorption spectrometry (AA). This invention recommends using ICP.

[0089] When performing acid dealumination on the Beta zeolite matrix, efforts should be made to remove all skeletal aluminum. Excessive skeletal aluminum residue on the dealuminated Beta zeolite support is detrimental because the strong acidity of the skeletal aluminum accelerates coking and deactivation of the Cu-Beta zeolite catalyst and reduces the catalyst's selectivity for the caprolactam main product.

[0090] Although the skeletal aluminum of Beta zeolite is easy to remove, and dealuminate Beta zeolite carriers that meet the requirements of this invention can be prepared based on the Beta zeolite matrix using high-temperature steam dealumination, dealumination with complexing agents such as EDTA, dealumination with organic acid solutions, dealumination with inorganic acid (concentrated hydrochloric acid, concentrated nitric acid) solutions, or any combination of the above methods, considering the production cost, process complexity, and difficulty in treating the waste liquid generated during dealumination, this invention recommends using concentrated nitric acid aqueous solution dealumination to prepare dealuminate Beta zeolite carriers that meet the requirements of this invention.

[0091] Engineers skilled in the art can, based on their experience or by referring to the specific practices disclosed in the following documents, perform acid dealumination treatment on the Beta zeolite matrix with concentrated nitric acid aqueous solution to prepare a dealuded Beta zeolite support that meets the requirements of this invention: Chemical Communications, 1998, 1: 87-88; Micropor. Mesopor. Mater., 1999, 31: 163-173; Micropor. Mesopor. Mater., 2001, 49: 103–109; Micropor. Mesopor. Mater., 2008, 110: 480–487; Micropor. Mesopor. Mater., 2012, 163: 122-130; ACS Catalysis, 2014, 4(8): 2801-2810.

[0092] When preparing dealugenized Beta zeolite carriers by acid dealumination of Beta zeolite matrix using concentrated nitric acid aqueous solution, the concentration of the nitric acid aqueous solution, the ratio of acid to zeolite (liquid-solid ratio), and the temperature and time of acid treatment are all important factors affecting the degree of acid dealumination of the Beta zeolite matrix. Ultimately, the influence of these factors on the dealumination of the Beta zeolite matrix is ​​reflected in the residual aluminum content of the dealugenized Beta zeolite carrier. However, if a dealugenized Beta zeolite carrier with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3) that meets the requirements cannot be obtained after one dealumination, it is entirely possible to achieve the desired silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) through secondary or even multiple dealuminations. This invention recommends using 13M concentrated nitric acid as the dealugenizing acid solution, with an acid volume of 20:1 (ml / g). Under these conditions, the dealumination reaction is carried out at 95℃ for 20 hours. After the dealumination reaction, the solid product is first recovered through solid-liquid separation, then washed with water until the pH value is neutral, and then dried at 80-200℃ for 3-24 hours, followed by calcination at 500℃-600℃ for 3-8 hours to obtain dealuminized Beta zeolite. After dealumination, the Beta zeolite matrix generates a large number of hydroxyl lattice defect sites, which increases its water absorption and moisture absorption capacity. Therefore, it should be sealed and stored for later use.

[0093] The second step involves loading copper into the pores of a dealuminolite Beta zeolite support using a modified ammonia stripping method to prepare a Cu-Beta zeolite catalyst.

[0094] As mentioned above, the core of the improved ammonia stripping method of this invention is to impregnate a dealuminated Beta zeolite support with an equal volume of copper-ammonia complex solution. During this process, the capillary action of the zeolite channels draws most of the complex solution into the channels, achieving the deposition of copper hydroxide and loaded metallic copper within the channels. The specific steps are as follows:

[0095] (1) Preparation of dilute ammonia water base solution and saturated copper ammonia complex solution: Prepare a dilute ammonia water base solution with pH value of 11-12 by diluting 4.4g of industrial ammonia water (containing 25-28wt.% NH3) to 100ml of deionized water, and seal and store for later use; then prepare ... store for later use; and then prepare a dilute ammonia water base solution with pH value of 11- 2+ A copper-ammonia complex was synthesized by reacting copper nitrate trihydrate (Cu(NO3)2·3H2O) as a soluble copper compound with industrial ammonia water in a molar ratio of 1:4 to ammonia molecules. Finally, the copper-ammonia complex was dissolved in a dilute ammonia solution at room temperature to prepare a saturated solution, which was then sealed and stored for later use. The concentration of copper-ammonia complex ions in the saturated solution was approximately 0.4 mol / L (0.4 M), and the solution was deep blue and clear.

[0096] It should be noted that although US Patent 4,440,873 (1984) has described soluble copper-containing compounds that can be used to prepare copper ammonia complex solutions, including copper nitrate, copper sulfate, copper oxalate, copper chloride, and copper acetate, considering that sulfate and chloride ions will increase the burden of subsequent water washing, and that oxalate and acetate ions have corrosive problems, this invention recommends the use of copper nitrate (Cu(NO3)2·3H2O).

[0097] (2) Impounding the zeolite support with an equal volume of copper-ammonia complex solution: First, determine the saturated water absorption rate of the zeolite support, and calculate the amount of copper-ammonia complex solution needed for equal volume impregnation. Then, calculate the required concentration of the copper-ammonia complex solution according to the copper loading of the Cu-beta zeolite catalyst to be prepared. When the calculated concentration is equal to 0.4 M, directly impregnate the zeolite support with the saturated copper-ammonia complex solution in equal volume; when the calculated concentration is lower than 0.4 M, appropriately dilute the saturated copper-ammonia complex solution with a dilute ammonia base solution before impregnating the zeolite support in equal volume; when the calculated concentration is higher than 0.4 M, recalculate the concentration of the copper-ammonia complex solution for each equal volume impregnation by performing multiple equal volume impregnations, and prepare the required concentration of the copper-ammonia complex solution using a dilute ammonia base solution and the saturated copper-ammonia complex solution for each equal volume impregnation. After each impregnation, the dealuminized Beta zeolite support must be subjected to ammonia stripping treatment.

[0098] The equal-volume impregnation is carried out at room temperature in a closed container. During this process, the zeolite support draws the copper-ammonia complex solution into the zeolite channels through capillary coagulation, thereby allowing the copper-ammonia complex ions to contact and interact with the hydroxyl lattice defect sites in the channels. The suitable range for the equal-volume impregnation time is 0.5-24 h, the preferred range is 1-12 h, and the more preferred range is 2-6 h.

[0099] (3) Ammonia stripping: The ammonia stripping process can be carried out under normal pressure or reduced pressure. The suitable range for ammonia stripping temperature and time is 50-100℃ and 0.5-48h, the preferred range is 60-90℃ and 1-24h, and the even more preferred range is 65-85℃ and 3-12h. During the ammonia stripping process, the copper-ammonia complex decomposes to generate ammonia gas and copper hydroxide. The former is absorbed by water, and the latter is deposited in the zeolite channels and hydroxyl lattice defect sites.

[0100] (4) Dehydration and drying treatment after ammonia stripping: The suitable range of drying temperature and time is 100-200℃ and 0.5-48h, respectively; the preferred range of drying temperature and time is 110-170℃ and 1-24h, respectively; and the more preferred range of drying temperature and time is 120-150℃ and 3-12h, respectively.

[0101] (5) Calcination treatment after ammonia stripping: This step is used to convert the copper hydroxide precipitate deposited in the zeolite channels and hydroxyl lattice defect sites into nano and sub-nanometer copper oxide particles, thereby obtaining the catalyst precursor. Calcination is carried out in an air atmosphere, with suitable calcination temperature and time ranges of 350-650℃ and 0.5-24h, preferred calcination temperature and time ranges of 400-600℃ and 1-12h, and more preferred calcination temperature and time ranges of 450-550℃ and 2-6h.

[0102] (6) Hydrogen reduction treatment of catalyst precursor: The finished Cu-Beta zeolite catalyst was obtained. The suitable ranges for reduction temperature, time, and hydrogen flow rate (expressed as hydrogen volume hourly space velocity, defined as the volume of hydrogen passing through a unit volume of catalyst per unit time, in ideal gas terms) were 280-600℃, 0.5-20h, and 1-2000h, respectively. -1 The preferred ranges are 300-550℃, 1-15h, and 10-1500h, respectively. -1 More preferably, the ranges are 350-500℃, 2-8h, and 20-1000h, respectively. -1 .

[0103] The Cu-Beta zeolite catalyst obtained by the above preparation method is used to catalyze the gas-solid phase hydroammoniation of caprolactone to caprolactam.

[0104] As mentioned above, a key feature of this invention is that the provided Cu-Beta zeolite catalyst is used for catalyzing the gas-solid phase hydroammoniation reaction of caprolactone to produce caprolactam.

[0105] However, this invention does not limit the specific method for the gas-solid phase hydroamination of caprolactone to produce caprolactam. Engineers skilled in the art can refer to the methods disclosed in relevant patents and other literature to carry out the gas-solid phase hydroamination of caprolactone. Based on relevant patents and other literature, this invention summarizes the following suitable reaction conditions for the gas-solid phase hydroamination of caprolactone for reference: the suitable reaction temperature range is 120-350℃, the suitable reaction pressure range is 0.01-2 atm, and the suitable feed space velocity (WHSV) of caprolactone is 0.1-5 h⁻¹. -1 The suitable ranges for the molar ratios of amine-ester, hydrogen-ester, and water-ester are 1-50, 5-70, and 0-100, respectively; the preferred range for the reaction temperature is 220-300℃; the preferred range for the reaction pressure is 0.1-1.2 atm; and the preferred range for the feed space velocity (WHSV) of caprolactone is 0.2-2 h⁻¹. -1 The preferred ranges for the molar ratios of amine-ester, hydrogen-ester, and water-ester are 2-25, 10-50, and 5-30, respectively.

[0106] To facilitate the explanation of the catalyst and its preparation method of this invention and to avoid unnecessary complexity, a typical procedure for the gas-solid phase hydroamination of caprolactone to produce caprolactam on a Cu-Beta zeolite catalyst is described below, using a small-scale fixed-bed reactor in the laboratory as an example: The small-scale fixed-bed reactor adopts a top-feed, bottom-discharge operation mode, with the Cu-Beta zeolite catalyst loaded in the isothermal zone of the reactor. The upper and lower spaces of the catalyst bed are filled with inert ceramic balls. The upper section of the reactor, containing the ceramic balls, serves as the vaporization and preheating zone for the raw materials. For convenience, caprolactone, water, and ammonia can be mixed and fed using a micro-metering pump, while the hydrogen feed is controlled by a mass flow meter. The reaction is carried out under fixed conditions: reaction temperature 280℃, reaction pressure 1 atm, and caprolactone feed space velocity (WHSV) 0.6 h⁻¹. -1 The molar ratios of amine-ester, hydrogen-ester, and water-ester are 6, 50, and 30, respectively.

[0107] The beneficial effects of this invention are:

[0108] First, this invention uses an improved ammonia stripping method to prepare a Cu-Beta zeolite catalyst on a dealuaged Beta zeolite support. This allows the copper-ammonia complex to primarily deposit copper hydroxide within the zeolite channels during the ammonia stripping process. The copper hydroxide deposited in the zeolite channels, after calcination and hydrogen reduction, directly forms highly dispersed nano- and sub-nano-sized copper particles at the hydroxyl-dwelling lattice defect sites within the channels. These highly dispersed nano- and sub-nano-sized copper particles interact closely with the hydroxyl-dwelling lattice defect sites and are stabilized by the active silanol groups within the hydroxyl-dwellings. This allows for use under harsh conditions involving water vapor, hydrogen, and ammonia without the need for anti-sintering agents such as chromium or nickel. Second, the core of the improved ammonia stripping method used in this invention is the impregnation of the dealuaged Beta zeolite support with an equal volume of copper-ammonia complex solution. Because the amount of copper-ammonia complex solution used is small, it helps to suppress the silica-dissolving effect of the alkaline solution (pH = 10-12) on the destroying of the dealubilized Beta zeolite framework. This facilitates the dispersion and stabilization of highly dispersed nano and sub-nano copper particles by the hydroxyl groups of the dealubilized Beta zeolite, which is beneficial for preparing highly active, selective, and stable Cu-Beta zeolite catalysts. Furthermore, this invention utilizes Cu-Beta zeolite catalysts for the gas-solid phase hydroammoniation of caprolactone, which will significantly reduce the industrialization difficulty of the technology route for producing caprolactam from caprolactone. Attached Figure Description

[0109] Figure 1 The images show the XRD patterns of the dealuminated Beta zeolite support (Beta24c) generated after acid dealuminating of the Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 24, and the XRD patterns of the Cu-Beta zeolite catalyst (Cu3-Beta24c-1) with a copper content of 3 wt.% prepared by the modified ammonia stripping method using Beta24c as the support.

[0110] Figure 2 The images show the hydroxyl region infrared spectrum of the dealuminated Beta zeolite support (Beta24c) generated after acid dealuminating of the Beta zeolite parent material with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 24, and the hydroxyl region infrared spectrum of the Cu-Beta zeolite catalyst (Cu3-Beta24c-1) with a copper content of 3 wt.% prepared by the modified ammonia stripping method using Beta24c as the support.

[0111] Figure 3 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the Cu3-Beta24c-1 catalyst.

[0112] Figure 4This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of a Cu3-Beta24c-1 catalyst sample calcined at high temperature (550℃×3h).

[0113] Figure 5 The images show the XRD patterns of the dealuminated Beta zeolite support (Beta24c) generated after acid dealuminating of the Beta zeolite parent material with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 24, and the XRD patterns of the Cu-Beta zeolite catalyst (Cu3-Beta24c-CE1) with a copper content of 3 wt.% prepared by the conventional ammonia stripping method using Beta24c as the support. Detailed Implementation

[0114] The effectiveness of this invention can be evaluated by characterizing the physicochemical properties of the prepared Cu-Beta zeolite catalyst and by testing its catalytic performance in the gas-solid phase hydroammoniation of caprolactone to caprolactam.

[0115] In characterizing the physicochemical properties of Cu-Beta zeolite catalysts, the focus can be on characterizing the crystal structure damage, the occupancy of hydroxyl groups, the high dispersion of the supported metallic copper, and the resistance of copper particles to sintering.

[0116] The damage to the Beta zeolite crystal structure can be characterized using X-ray polycrystalline powder diffraction (XRD). If ammonia stripping leads to significant damage to the Beta zeolite crystal structure, the intensity of the characteristic diffraction peak at 2θ = 22-23° in the catalyst's XRD pattern will be significantly reduced. Using a dealuminated Beta zeolite support as a reference, the degree of relative crystallinity reduction in the zeolite support within the Cu-Beta zeolite catalyst can also be estimated.

[0117] The occupancy of hydroxyl sites in Cu-Beta zeolite catalysts can be qualitatively determined by obtaining the hydroxyl vibration infrared spectrum of the catalyst using Fourier transform infrared spectroscopy (FT-IR) and comparing it with the hydroxyl vibration infrared spectrum of the dealuminolite Beta zeolite support. The more nano- and sub-nanometer copper particles located in the hydroxyl sites, the stronger the characteristic infrared band of the hydroxyl sites in the catalyst (located in the 3300-3600 cm⁻¹) will be. -1 The stronger the broadened absorption band between the two, the weaker the absorption band will be, and vice versa.

[0118] Furthermore, the high dispersion of supported metallic copper in the Cu-Beta zeolite catalyst can be observed using transmission electron microscopy (TEM); the anti-sintering properties of the copper particles can be determined by combining calcination treatment with TEM observation. The catalytic activity (caprolactam yield) of the catalyst in the gas-solid phase hydroammoniation of caprolactone to caprolactam can also be assessed by observing the decline in its catalytic activity (caprolactam yield).

[0119] The catalytic performance of Cu-Beta zeolite catalyst in the gas-solid phase hydroammoniation of caprolactone to caprolactam can be evaluated using a small-scale fixed-bed laboratory reactor. The operating methods and reaction conditions are as described previously. The composition of the reaction products was analyzed by gas chromatography (GC) using an FID detector and an OV-1701 column. The conversion of caprolactone and the selectivity of caprolactam were calculated using the internal standard method (1,4-dioxane as the internal standard). The product of the caprolactone conversion and the caprolactam selectivity was used as the yield data for caprolactam and served as the evaluation index for catalyst activity.

[0120] The present invention will be further illustrated by the following embodiments, but the present invention is not limited to these embodiments.

[0121] Example 1: This example illustrates how, according to the present invention, a Cu-Beta zeolite catalyst is prepared by loading copper into the pores of dealubilized Beta zeolite using a modified ammonia stripping method. This method better preserves the crystal structure of the dealubilized Beta zeolite support and allows the loaded metallic copper to primarily exist as highly dispersed nano- and sub-nano-sized copper particles located at hydroxyl-containing lattice defect sites within the zeolite pores. These particles are then stabilized by the active silanol groups within the hydroxyl-containing lattice sites, improving the resistance to sintering. The prepared Cu-Beta zeolite catalyst is suitable as a catalyst for the gas-solid phase hydroammoniation of caprolactone to caprolactam.

[0122] First, a Cu-Beta zeolite catalyst was prepared according to the embodiment provided in this invention:

[0123] The first step is to prepare a dealuminated Beta zeolite support.

[0124] (1) Following the hydrothermal crystallization method provided in US Patent 3,308,069 (1967), a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 25 was synthesized as a raw material for preparing a dealuminized Beta zeolite support. After conventional filtration, washing, drying (110°C, 12 h), and calcination to remove the template agent (540°C, 6 h), the synthesized Beta zeolite matrix was observed by TEM to have a grain size of less than 100 nm, classifying it as nano-Beta zeolite. XRD analysis revealed no impurities. Calculations based on its nitrogen physical adsorption data showed a BET specific surface area of ​​approximately 550 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was approximately 24, as determined by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix.

[0125] (2) The Beta zeolite matrix was treated with concentrated nitric acid to prepare a dealuminized Beta zeolite carrier.

[0126] First, a concentrated nitric acid solution with a molar concentration of 13M was prepared. Then, 20g of the dried and calcined Beta zeolite precursor, prepared as described above, was added to a three-necked flask containing 400ml of 13M concentrated nitric acid solution under stirring, at a liquid-to-solid ratio of 20:1 (ml / g). The dealuminization process was carried out at 95°C for 20 hours. During the dealuminization reaction, the three-necked flask was kept under reflux. After the dealuminization reaction was completed, the solution was cooled to room temperature and filtered to recover the solid product. Then, it was washed with water, dried (overnight at 110°C), and calcined (550°C, 3 hours) to obtain a dealuminized Beta zeolite support (designated Beta24c, where the lowercase "c" indicates the hydroxyl groups generated in the Beta zeolite during dealuminization). The molar ratio of silicon and aluminum oxides (SiO2 to Al2O3) of the dealuminized Beta zeolite support was determined to be 980 by ICP. This is suitable as a support for the catalyst of this invention. Store in a sealed container for later use, avoiding moisture absorption.

[0127] The second step involves loading copper into the pores of dealubilized Beta zeolite using a modified ammonia stripping method to prepare a Cu-Beta zeolite catalyst.

[0128] (1) Prepare a dilute ammonia base solution and synthesize a copper-ammonia complex using copper nitrate trihydrate (Cu(NO3)2·3H2O). Then, prepare a saturated solution of the copper-ammonia complex at room temperature. The pH of the dilute ammonia base solution is 11-12, and it is prepared by adding 4.4g of industrial ammonia (containing 25-28wt.% NH3) to 100ml of deionized water. The copper-ammonia complex is obtained by reacting Cu(NO3)2·3H2O with industrial ammonia at a molar ratio of copper ions to ammonia molecules of 1:4. The saturated solution of the copper-ammonia complex is obtained by dissolving the copper-ammonia complex in the dilute ammonia base solution, which contains approximately 0.4M of the copper-ammonia complex.

[0129] (2) A Cu-Beta zeolite catalyst with a copper loading of 3 wt.% was prepared by impregnating the zeolite support with an equal volume of copper ammonia complex solution. First, 5 g of calcined and sealed dealugenized Beta zeolite support (Beta24c) was taken and titrated with deionized water until all samples were uniformly wetted but no free liquid water appeared. A total of 6 ml of deionized water was consumed, and the water absorption rate of the dealugenized Beta zeolite support (Beta24c) was calculated to be 1.2 ml / g. Based on a 10 g support feed amount, a total of 12 ml of copper ammonia complex solution was required. The concentration of the copper ammonia complex solution required based on a copper loading of 3 wt.% was approximately 0.39 M. That is, the calculated concentration of the required copper ammonia complex solution was very close to the concentration of the saturated copper ammonia complex solution. Therefore, 10 g of dealugenized Beta zeolite support (Beta24c) was directly impregnated with an equal volume of 12 ml of saturated copper ammonia complex solution. The impregnation was carried out at room temperature for 4 h.

[0130] (3) The impregnated material of equal volume was subjected to ammonia stripping treatment under normal pressure. The ammonia stripping temperature was 80℃ and the ammonia stripping time was 10h. During this process, due to capillary coagulation, the copper-ammonia complex that entered the zeolite channels gradually deposited in the zeolite channels in the form of copper hydroxide after losing ammonia gas.

[0131] (4) The material after ammonia stripping is dehydrated and dried. Drying temperature: 110℃; drying time: 12 hours.

[0132] (5) The dried material is roasted. The roasting temperature is 500℃ and the roasting time is 3h. After roasting, the copper hydroxide deposited in the zeolite channels is converted into nano and sub-nano copper oxide particles, thus obtaining the catalyst precursor.

[0133] (6) The catalyst precursor was subjected to hydrogen reduction treatment. The reduction temperature was 400℃, the reduction time was 4h, and the hydrogen flow rate (expressed as hydrogen volume hourly space velocity, defined as the volume of hydrogen passing through a unit volume of catalyst per unit time, in ideal gas terms) was 300 h⁻¹. -1 After hydrogen reduction treatment, the finished Cu-Beta zeolite catalyst, code-named Cu3-Beta24c-1, was obtained.

[0134] Secondly, in order to understand the effectiveness of the catalyst preparation method provided by this invention from the perspective of the physicochemical properties of the catalyst, the XRD patterns and hydroxyl vibration infrared spectra of Cu3-Beta24c-1 and its dealuminized Beta zeolite support (Beta24c) were measured in parallel using XRD and FT-IR methods, as shown in the attached figures. Figure 1 and attached Figure 2 As shown. In addition, TEM images of the Cu3-Beta24c-1 catalyst and its high-temperature calcined sample (550℃×3h) were also obtained, as shown. Figure 3 and Figure 4 As shown.

[0135] from Figure 1 As can be seen, the Cu3-Beta24c-1 catalyst prepared by the improved ammonia stripping method provided by this invention retains the Beta zeolite crystal structure very well, and the relative crystallinity of the zeolite in the catalyst, calculated based on the dealuminated Beta zeolite support (Beta24c), is 79%. Figure 2 As can be seen, the Cu3-Beta24c-1 catalyst prepared according to the method of the present invention exhibits a significant decrease in the intensity of the infrared characteristic band of the zeolite hydroxyl lattice compared to the dealuminated Beta zeolite support (Beta24c), indicating that metallic copper occupies a large number of hydroxyl lattice defect sites. Furthermore, from... Figure 3 and Figure 4It is evident that the copper particles in the Cu3-Beta24c-1 catalyst exist in a highly dispersed nano- and sub-nano particle state, with an average particle size of approximately 6 nm. After calcination at 550 °C for 3 h, the copper particles exhibit good dispersion, with an average particle size of around 10 nm. These data indicate that the hydroxyl-dwelling lattice defect sites of the dealuminolite Beta zeolite support play a role in dispersing and stabilizing nano- and sub-nano copper particles.

[0136] Based on this, the catalytic performance of the Cu3-Beta24c-1 catalyst and its calcined sample at 550℃ was evaluated using the gas-solid phase hydroammoniation of caprolactone to caprolactam. The reaction was carried out in a small fixed-bed reactor with a stainless steel reaction tube inner diameter of 9 mm, employing a top-feed, bottom-discharge operation. 2 g of tableted catalyst (20-40 mesh sample after sieving) was placed in the isothermal zone of the reactor. The upper and lower spaces of the catalyst bed were filled with inert ceramic balls. The upper ceramic ball region of the reactor served as the vaporization and preheating zone for the feedstock. The isothermal zone temperature was 280℃, the reaction pressure was 1 atm, and the caprolactone feed space velocity (WHSV) was 0.6 h⁻¹. -1 For convenience, caprolactone, ammonia (analytical grade, ammonia concentration 25-28 wt.%), and deionized water were prepared into a feed solution with an ammonia-ester molar ratio of 6 and a water-ester molar ratio of 30. This feed solution was introduced into the reactor using a micro-metering pump, and hydrogen was fed in using a mass flow meter at a hydrogen-ester molar ratio of 50. The reaction products were continuously collected in a stainless steel collection tank with a cooling water jacket connected to the reactor outlet. Product liquid was collected at fixed time intervals and analyzed using a Shimadzu GC-2014 gas chromatograph (FID detector, OV-1701 column). The conversion rate of caprolactone and the selectivity of caprolactam were calculated using the internal standard method (internal standard: 1,4-dioxane). Under the above conditions, when the caprolactone hydroamination reaction was carried out continuously for 6 hours, the caprolactam yield of the Cu3-Beta24c-1 catalyst was approximately 84%; the caprolactam yield of the sample calcined at 550℃ was 81%. The above reaction results indicate that the Cu-Beta zeolite catalyst provided by this invention is a high-performance catalyst for the hydroamylation of caprolactone to caprolactam.

[0137] Comparative Example 1: This example illustrates that when Cu-Beta zeolite catalysts are prepared by loading copper using the conventional ammonia stripping method with dealubilized Beta zeolite as a support, the crystal structure of the Beta zeolite support is severely damaged. The loaded metallic copper mainly falls outside the zeolite channels, resulting in low dispersion and large copper particle size. Due to the lack of protection from the active silanol groups in the hydroxyl pockets of dealubilized Beta zeolite, the sintering resistance is poor.

[0138] Example 1 was repeated, but after the qualified dealuated Beta zeolite support (Beta24c) was prepared in the first step, copper hydroxide was deposited on the dealuated Beta zeolite support using the same conventional ammonia stripping method as published in Science 10.1126 / science.adj1962 (2023), as follows:

[0139] (1) Dissolve 1.18g Cu(NO3)2·3H2O in 515ml ammonia solution (containing 3.86g NH3·H2O, equivalent to 8.1ml 26wt.% industrial ammonia water, with a copper ion to ammonia molecule molar ratio of approximately 1:23) and stir at room temperature for 10min to prepare a copper ammonia complex aqueous solution (complex ion concentration approximately 9.5mmol / L, i.e. 9.5mM);

[0140] (2) 10g of dealuminized Beta zeolite carrier (Beta24c) was added to 515ml of copper ammonia complex solution, and ammonia stripping was performed under vigorous stirring. The ammonia stripping temperature was 80℃, and the stripping time was 6h.

[0141] (3) After the ammonia stripping is completed, the diluted and excess copper ammonia complex solution is removed by filtration. The resulting filter cake is dried, calcined and hydrogen reduced in the same way as in Example 1 to obtain Cu-Beta zeolite catalyst, designated Cu3-Beta24c-CE1 (CE = Comparative Example).

[0142] To understand the physicochemical properties of the Cu-Beta zeolite catalyst prepared by the traditional ammonia stripping method, the Beta zeolite crystal structure of the Cu3-Beta24c-CE1 catalyst was characterized by XRD and compared with its support (Beta24c). Figure 5 As shown. In addition, the Cu metal dispersion of Cu3-Beta24c-CE1 catalyst and its high-temperature calcined sample (550℃×3h) was characterized by transmission electron microscopy, and the catalytic performance of Cu3-Beta24c-CE1 catalyst and its high-temperature calcined sample was evaluated by the gas-solid phase hydroammoniation of caprolactone to caprolactam.

[0143] from Figure 5As can be seen, the Cu3-Beta24c-CE1 catalyst prepared by the traditional ammonia stripping method exhibits a high degree of damage to the Beta zeolite crystal structure, with a relative crystallinity of 62% calculated based on its support (Beta24c). According to transmission electron microscopy (TEM) characterization, the average Cu metal particle size of the Cu3-Beta24c-CE1 catalyst and its high-temperature calcined sample are 11 nm and 20 nm, respectively, indicating low Cu metal dispersion and easy sintering on the catalyst. Reaction evaluation results show that, under the same reaction conditions, the caprolactam yield of the Cu3-Beta24c-CE1 catalyst is approximately 77%; the caprolactam yield of its high-temperature calcined sample is approximately 72%. These results indicate that the Cu-Beta zeolite catalyst prepared by the traditional ammonia stripping method on a dealuminated Beta zeolite support exhibits low catalytic activity and poor resistance to sintering deactivation in the gas-solid phase hydroammoniation of caprolactone to caprolactam.

[0144] Comparative Example 2: This example is used to illustrate the use of amorphous fumed silica (white carbon black, BET specific surface area 286 m²). 2 Copper-silica catalysts prepared by loading copper with copper using the traditional ammonia stripping method with copper as a support ( / g) have poor resistance to sintering.

[0145] The conventional ammonia stripping method described in this example follows the procedure in Example 1 of US Patent 4,440,873 (1984), as follows:

[0146] (1) Dissolve 1.14 g of copper nitrate (Cu(NO3)2·3H2O) in 100 ml of water to obtain an aqueous solution containing copper ions. Then, according to a copper ion to ammonia molecule molar ratio of approximately 1:10, add 3.6 ml of concentrated ammonia solution (industrial ammonia water with NH3 content of 26 wt.% and density of 0.89 g / ml) and add 50 ml of water to obtain a dark blue solution containing copper ammonia complex with a pH value of 11-12 (complex ion concentration of approximately 30.8 mM. The purpose of adding 50 ml of water is to maintain the solution volume to silica dry basis ratio consistent with the literature).

[0147] (2) Add 10g of fumed silica (dry basis) to the copper ammonia complex solution and stir at room temperature for 2h;

[0148] (3) The reaction mixture of step (2) was heated and ammonia was removed (80℃, 6h). When the pH of the mixture dropped to 6-7, the solid was filtered and washed three times with deionized water to obtain the solid product.

[0149] (4) Dry the solid product at 120°C for 12 hours and calcine it at 450°C for 4 hours;

[0150] (5) The calcined solid product was subjected to hydrogen reduction treatment. The reduction conditions were 350℃×2h to obtain a copper-silica catalyst, designated Cu3-SiO2-CE2.

[0151] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield of the Cu3-SiO2-CE2 catalyst was 77%, while the caprolactam yield of the high-temperature calcined sample (550℃×3h) was 69%. These results indicate that the copper-based catalyst prepared using amorphous silica as a support has poor resistance to sintering, and its catalytic activity decreases significantly after high-temperature treatment.

[0152] Comparative Example 3: This example is used to further illustrate that the copper-silica catalyst prepared by copper-supported by the traditional ammonia stripping method has poor resistance to sintering.

[0153] Comparative Example 2 was repeated, but 33.3 g of silica sol (30 wt.% SiO2) was used as the precursor for the in-situ generation of 10 g of silica support. To maintain the same volume-to-dry-silica ratio as in Comparative Example 2, the water addition in step (1) was changed to 26.7 ml when preparing the copper-ammonia complex solution. The prepared copper-silica catalyst was designated Cu3-SiO2-CE3.

[0154] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield of the Cu3-SiO2-CE3 catalyst was 80%, while the caprolactam yield of the high-temperature calcined sample (550℃×3h) was 68%. These results also indicate that the copper-based catalyst prepared using amorphous silica as a support has poor resistance to sintering, and its catalytic activity decreases significantly after high-temperature treatment.

[0155] Comparative Example 4: This example illustrates that the amorphous nature of the silica support determines the poor sintering resistance of the copper-silica catalyst.

[0156] In this example, a copper-silica catalyst is prepared on a fumed silica support using the improved ammonia stripping method provided by this invention. Specifically:

[0157] Repeat Example 1, but replace 10g of dealuminized Beta zeolite carrier with 10g (dry basis) fumed silica (white carbon black, BET specific surface area 286m²). 2 / g (saturated water absorption rate 2.5ml / g), 10g of fumed silica requires 25ml of copper-ammonia complex solution. Based on a copper loading of 3wt.%, the required concentration of the copper-ammonia complex solution is approximately 0.19M. 11.9ml of the saturated copper-ammonia complex solution was diluted to 25ml with a dilute ammonia base solution, yielding 25ml of a 0.19M copper-ammonia complex solution. The prepared copper-silica catalyst is designated Cu3-SiO2-CE4.

[0158] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield of the Cu3-SiO2-CE4 catalyst was 78%; the caprolactam yield of the high-temperature calcined sample (550℃×3h) was 69%. These results also indicate that the copper-based catalyst prepared using amorphous silica as a support has poor resistance to sintering, and its catalytic activity decreases significantly after high-temperature treatment.

[0159] Example 2: This example illustrates that, according to the method provided by the present invention for preparing Cu-Beta zeolite catalysts with different copper loadings, using dealuminated Beta zeolite as a support and a modified ammonia stripping method to load copper in the zeolite channels, Cu-Beta zeolite catalysts with different copper loadings can be prepared.

[0160] Example 1 was repeated, but the copper loading in the prepared Cu-Beta zeolite catalyst was successively reduced to 1 wt.% and 2 wt.%, resulting in required copper-ammonia complex solution concentrations of approximately 0.13 M and 0.26 M, respectively. 3.9 ml and 7.8 ml of the saturated copper-ammonia complex solution were successively diluted to 12 ml with dilute ammonia solution to obtain equal-volume impregnation solutions of Cu-Beta zeolite catalysts with copper loadings of 1 wt.% and 2 wt.%. In the preparation of the Cu-Beta zeolite catalyst using the improved ammonia stripping method, the time for equal-volume impregnation of the dealuminized Beta support at room temperature was changed to 6 h, the ammonia stripping temperature and time were changed to 65 °C and 12 h, respectively, the dehydration drying temperature and time were changed to 150 °C and 3 h, respectively, the subsequent calcination temperature and time were changed to 450 °C and 6 h, respectively, the final hydrogen reduction temperature and time were changed to 350 °C and 8 h, respectively, and the hydrogen flow rate (volume hourly space velocity) was changed to 1000 h⁻¹. -1 The prepared Cu-Beta zeolite catalysts are designated as Cu1-Beta24c-2 and Cu2-Beta24c-2, respectively.

[0161] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield of Cu1-Beta24c-2 catalyst was 81%, while that of Cu2-Beta24c-2 catalyst was 82%.

[0162] Example 3: This example further illustrates that the Cu-Beta zeolite catalyst preparation method provided by this invention, which uses dealulated Beta zeolite as a support and employs an improved ammonia stripping method to load copper in the zeolite channels, can prepare Cu-Beta zeolite catalysts with varying copper loadings. However, when preparing Cu-Beta zeolite catalysts with copper loadings higher than 3 wt.%, a multi-loading scheme is preferable.

[0163] Repeating Example 1, but increasing the copper loading in the prepared Cu-Beta zeolite catalyst to 4 wt.% and 6 wt.%, respectively, the calculated required concentrations of the copper-ammonia complex solution were approximately 0.52 M and 0.79 M, respectively. Clearly, the required copper-ammonia complex concentrations both exceeded the concentration of the saturated copper-ammonia complex solution prepared with a dilute ammonia base solution. We attempted to dissolve the copper-ammonia complex using industrial ammonia instead of the dilute ammonia base solution, obtaining a maximum concentration of approximately 0.5 M. Although dissolving the copper-ammonia complex with industrial ammonia can produce a high-concentration copper-ammonia complex solution of approximately 0.5 M, this solution has an ammonia / copper ion molar ratio exceeding 24:1, is highly alkaline, and exhibits significant ammonia volatilization, which is detrimental to protecting the crystal structure of the dealubilized Beta zeolite and also hinders operation. This indicates that the modified ammonia stripping method cannot yield a high-copper-loading Cu-Beta zeolite catalyst on a dealubilized Beta zeolite support through a single equal-volume impregnation and ammonia stripping operation. Therefore, this invention uses a dilute ammonia-based solution to dilute a saturated solution of copper-ammonia complex, and prepares Cu-Beta zeolite catalysts with copper loadings increased to 4 wt.% and 6 wt.%, respectively, through multiple equal-volume impregnation and ammonia stripping operations. For the preparation of the 4 wt.% copper loading catalyst, the impregnation and ammonia stripping operations can be performed twice, such as 1 wt.% + 3 wt.%, 2 wt.% + 2 wt.%. For the preparation of the 6 wt.% copper loading catalyst, the operations can be performed twice (3 wt.% + 3 wt.%) or three times (2 wt.% + 2 wt.% + 2 wt.%). For simplicity, in this example, the preparation of Cu-Beta zeolite catalysts with copper loadings increased to 4 wt.% and 6 wt.%, respectively, is performed twice (2 wt.% + 2 wt.%, 3 wt.% + 3 wt.%). To load 2 wt.% copper onto a dealuminol Beta zeolite support using a modified ammonia stripping method, 12 ml of an impregnation solution with a copper-ammonia complex concentration of 0.26 M is required. For a single loading of 3 wt.% copper onto the dealuminol Beta zeolite support, 12 ml of an impregnation solution with a copper-ammonia complex concentration of 0.40 M is required. The 0.26 M impregnation solution is obtained by diluting 7.8 ml of a saturated copper-ammonia complex solution with a dilute ammonia base solution, while the 0.40 M impregnation solution is obtained directly from a saturated copper-ammonia complex solution. When performing equal-volume impregnation treatment on the dealuminol Beta support at room temperature, the impregnation time was changed to 6 h, the ammonia stripping temperature and time were changed to 85 °C and 3 h, respectively, the dehydration and drying temperature and time were changed to 120 °C and 5 h, respectively, the subsequent calcination temperature and time were changed to 550 °C and 2 h, respectively, and the final hydrogen reduction temperature and time were changed to 500 °C and 2 h, respectively, with a hydrogen flow rate (volume hourly space velocity) of 20 h⁻¹. -1(The feed was controlled by a mass flow meter after mixing with an appropriate amount of nitrogen). The prepared Cu-Beta zeolite catalysts were designated as Cu4-Beta24c-3 and Cu6-Beta24c-3, respectively.

[0164] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield was 80% with the Cu4-Beta24C-3 catalyst and 79% with the Cu6-Beta24C-3 catalyst.

[0165] Example 4: This example illustrates that when preparing Cu-Beta zeolite catalysts according to the improved ammonia stripping method provided by the present invention, it is permissible to use Beta zeolite matrix with different crystal sizes to prepare dealubilized Beta zeolite supports.

[0166] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 22 was synthesized using the hydrothermal crystallization method (with ammonium fluoride additive) provided in the published literature J. Mater. Sci. 41 (2006) 1861-1864 as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (80℃, 24h) and calcination to remove the template agent (600℃, 3h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size of 1μm, belonging to large-grained Beta zeolite; XRD analysis showed no impurities; and its BET specific surface area was calculated to be approximately 480 m² using its nitrogen physical adsorption data. 2 The molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) was approximately 23, as determined by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix. This Beta zeolite matrix was dealuminized with 13M concentrated nitric acid to become a large-grain dealuminized Beta zeolite support (designated Beta23c), with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3) of 748 (>700), meeting the technical requirements of this invention for the dealuminized Beta zeolite support. Based on this, copper was loaded into the zeolite channels using a modified ammonia stripping method to prepare a Cu-Beta zeolite catalyst with a copper content of 3 wt.%, designated Cu3-Beta23c-4.

[0167] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield of the Cu3-Beta23c-4 catalyst was 82%.

[0168] Example 5: This example illustrates that when preparing Cu-Beta zeolite catalysts according to the improved ammonia stripping method provided by the present invention, it is permissible to use Beta zeolite precursors with different molar ratios of silicon and aluminum oxides (molar ratio of SiO2 to Al2O3) to prepare dealuminized Beta zeolite supports.

[0169] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 60 was synthesized using the hydrothermal crystallization method provided in US Patent 3,308,069 (1967) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (170°C, 3h), and calcination to remove the template agent (500°C, 8h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size close to 100 nm, classifying it as nano-Beta zeolite. XRD analysis revealed no impurities, and its BET specific surface area was calculated to be approximately 530 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was approximately 57, as determined by XRF, which meets the technical requirements of this invention for the Beta zeolite matrix.

[0170] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminized Beta zeolite support, resulting in a dealuminized Beta zeolite support (Beta57c) with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 861 (>800). The degree of dealumination of the support met the requirements of this invention. Based on this, a Cu-Beta zeolite catalyst with a copper content of 3 wt.% was prepared using a modified ammonia stripping method. Specifically, when impregnating the support with an equal volume of a saturated solution of a copper-ammonia complex at room temperature, the impregnation time was changed to 2 h. During ammonia stripping, a slightly negative pressure was used, the stripping temperature was 50℃, and the stripping time was 48 h. When dehydrating and drying the material after ammonia stripping, the drying temperature and time were changed to 100℃ and 48 h, respectively. The subsequent calcination temperature and time were changed to 350℃ and 24 h, respectively. The final hydrogen reduction treatment temperature, time, and hydrogen flow rate (volume hourly space velocity) were changed to 300℃, 20 h, and 2000 h, respectively. -1 The catalyst designation is Cu3-Beta57c-5

[0171] Evaluation results of the gas-solid phase hydroammoniation of caprolactone to caprolactam showed that, under the same reaction conditions, the caprolactam yield of the Cu3-Beta57c-7 catalyst was 80%.

[0172] Example 6: This example is used to further illustrate that when preparing Cu-Beta zeolite catalyst according to the improved ammonia stripping method provided by the present invention, it is permissible to use Beta zeolite parent materials with different silicon-aluminum oxide molar ratios (molar ratio of SiO2 to Al2O3) to prepare dealuminized Beta zeolite supports.

[0173] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, Beta zeolite precursors with silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratios) of 40, 80, 100, 150, and 200 were synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as raw materials for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (110℃, 12h), and calcination to remove the template agent (540℃, 6h), the synthesized Beta zeolite precursors were observed by TEM to have an average grain size at the nanometer and small grain (less than 1μm) levels. The grain size increased with increasing silicon-aluminum oxide molar ratio (SiO2 to Al2O3); no impurities were observed by XRD; and the BET specific surface area calculated using nitrogen physisorption data was consistently higher than 500 m². 2 The molar ratios of silicon and aluminum oxides (SiO2 to Al2O3) measured by XRF were 38, 72, 94, 136 and 189, respectively, which meet the technical requirements of this invention for Beta zeolite matrix.

[0174] The five Beta zeolite precursors were used for dealumination with concentrated nitric acid to prepare dealuminized Beta zeolite supports, resulting in five dealuminized Beta zeolite supports: Beta38c, Beta72c, Beta94c, Beta136c, and Beta189c. Their silicon-aluminum oxide molar ratios (SiO2 to Al2O3 molar ratios) were 870, 855, 932, 1088, and 960, respectively, all meeting the technical requirements for dealuminized Beta zeolite supports. Based on this, a Cu-Beta zeolite catalyst with a copper content of 3 wt.% was prepared using a modified ammonia stripping method. Specifically, when impregnating the support with an equal volume of a saturated solution of a copper-ammonia complex at room temperature, the impregnation time was changed to 1 hour. During ammonia stripping, the stripping temperature was set at 90°C, and the stripping time was 1 hour. When dehydrating and drying the material after ammonia stripping, the drying temperature and time were changed to 200°C and 1 hour, respectively. The subsequent calcination temperature and time were changed to 550°C and 1 hour, respectively. The final hydrogen reduction treatment temperature, time, and hydrogen flow rate were changed to 550℃, 1h, and 5h, respectively. -1(The feed is controlled by a mass flow meter after mixing with an appropriate amount of nitrogen). The catalyst codes are Cu3-Beta38c-6, Cu3-Beta72c-6, Cu3-Beta94c-6, Cu3-Beta136c-6 and Cu3-Beta189c-6.

[0175] The anti-sintering deactivation properties of the above catalysts and their samples calcined at 550 °C (3 h) were evaluated using the gas-solid phase hydroammoniation of caprolactone to produce caprolactam. The results showed that, under the same reaction conditions, the catalytic activity (caprolactam yield) of the Cu3-Beta38c-6, Cu3-Beta72c-6, Cu3-Beta94c-6, Cu3-Beta136c-6, and Cu3-Beta189c-6 catalysts decreased by approximately 5%, 8%, 10%, 14%, and 17% respectively after high-temperature calcination.

[0176] Example 7: This example illustrates that when preparing Cu-Beta zeolite catalysts according to the improved ammonia stripping method provided by the present invention, it is permissible to use Beta zeolite precursors with different molar ratios of silicon and aluminum oxides (Molar ratio of SiO2 to Al2O3) to prepare dealubilized Beta zeolite supports. However, using Beta zeolite precursors with higher Molar ratios of silicon and aluminum oxides (Molar ratio of SiO2 to Al2O3) to prepare dealubilized Beta zeolite supports is suitable for preparing Cu-Beta zeolite catalysts with lower copper loadings.

[0177] Example 1 was repeated, but in the first step of preparing the dealubilized Beta zeolite support, a Beta zeolite matrix with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 100 was synthesized using the hydrothermal crystallization method provided in Chinese Invention Patent CN1108275C (application date 1999.9.10) as the raw material for preparing the dealubilized Beta zeolite support. After conventional filtration, washing, drying (200℃, 3h), and calcination to remove the template agent (500℃, 8h), the synthesized Beta zeolite matrix was observed by TEM to have an average grain size of small grains (less than 1μm). XRD analysis showed no impurities, and its BET specific surface area was calculated to be higher than 530 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was measured to be 94 by XRF, which meets the technical requirements of this invention for Beta zeolite matrix.

[0178] The Beta zeolite matrix was used for dealumination with concentrated nitric acid to prepare a dealuminated Beta zeolite support (Beta94c) with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 932 (>900). The silicon-aluminum oxide molar ratio of the support meets the technical requirements of this invention. Based on this, a Cu-Beta zeolite catalyst with a copper content of 6 wt.% was prepared by a modified ammonia stripping method, consisting of two equal-volume impregnations and two ammonia strippings. The copper-ammonia complex solution used in both equal-volume impregnations was a 0.4 M saturated copper-ammonia complex solution. The prepared catalyst is designated Cu6-Beta94c-7.

[0179] The anti-sintering deactivation properties of the catalyst and its calcined (3 h) sample were evaluated using the gas-solid phase hydroammoniation of caprolactone to caprolactam. The results showed that, under the same reaction conditions, the catalytic activity (caprolactam yield) of the Cu6-Beta94c-7 catalyst decreased by 15% after high-temperature calcination.

Claims

1. A method for the preparation of a Cu-Beta zeolite catalyst for the conversion of caprolactone to caprolactam, characterized in that, The steps are as follows: First step, preparation of dealuminated Beta zeolite support (1) Selecting Beta zeolite mother body The Beta zeolite mother phase refers to a silicon-aluminum Beta zeolite meeting the following requirements: 1) the Beta zeolite mother phase contains no impurity crystals; 2) the Beta zeolite mother phase has good crystallization, i.e. the BET specific surface area value of the Beta zeolite mother phase measured by a nitrogen physical adsorption method is ≧450 m 2 / g; 3) the silicon-alumina oxide molar ratio of the Beta zeolite mother phase, i.e. the molar ratio of SiO2 to Al2O3 is in the range of 20-100; (2) Preparation of dealuminated Beta zeolite support Dealuminated Beta zeolite support is prepared by acid dealuminating method based on Beta zeolite mother body; the molar ratio of silicon aluminum oxide, i.e. the molar ratio of SiO2 and Al2O3 of the dealuminated Beta zeolite support prepared is required to be in the range of >=700; Second step, loading copper in the pore channel of the dealuminated Beta zeolite support by improved ammonia evaporation method to prepare Cu-Beta zeolite catalyst The specific steps are as follows: (1) Preparation of dilute ammonia water base solution and saturated solution of copper ammonia complex: according to the proportion of 4.4 g of industrial ammonia water containing 25-28 wt.% of NH3 diluted into 100 ml of deionized water, dilute ammonia water base solution with pH value = 11-12 is prepared, and is sealed and stored for standby; then, according to the molar ratio of copper ion to ammonia molecule of 1:4, copper ammonia complex is synthesized by reaction of copper nitrate trihydrate as a soluble copper-containing compound with industrial ammonia water; finally, the copper ammonia complex is dissolved in dilute ammonia water base solution at room temperature to prepare a saturated solution of copper ammonia complex, which is sealed and stored for standby; the concentration of copper ammonia complex ions in the saturated solution of copper ammonia complex is 0.4 M; (2) Impregnate the zeolite support with the copper ammonia complex solution in equal volume: first, determine the saturated water absorption rate of the zeolite support, and then calculate the amount of copper ammonia complex solution required for equal volume impregnation of the zeolite support; then, according to the copper loading amount of the Cu-Beta zeolite catalyst to be prepared, calculate the concentration of the copper ammonia complex solution required; when the calculated concentration is equal to 0.4 M, directly use the saturated solution of copper ammonia complex to impregnate the zeolite support in equal volume; when the calculated concentration is lower than 0.4 M, then dilute the saturated solution of copper ammonia complex with dilute ammonia water base solution as appropriate, and then impregnate the zeolite support in equal volume; When the calculated value is higher than 0.4 M, then according to multiple equal volume impregnation, recalculate the concentration of copper ammonia complex solution for single equal volume impregnation, and prepare the copper ammonia complex solution with the required concentration by using dilute ammonia water base solution and saturated solution of copper ammonia complex for each equal volume impregnation; After each impregnation, the dealuminated Beta zeolite support is treated by ammonia evaporation; the equal volume impregnation is carried out in a sealed container at room temperature; the equal volume impregnation time is in the range of 0.5-24 h; (3) Ammonia evaporation treatment: the ammonia evaporation process is carried out at normal pressure or reduced pressure; the ammonia evaporation temperature and time are in the range of 50-100℃ and 0.5-48 h, respectively; (4) Dehydration and drying treatment after ammonia evaporation: the drying temperature and time are in the range of 100-200℃ and 0.5-48 h, respectively; (5) Calcination treatment after ammonia evaporation: the calcination is carried out in air atmosphere, and the calcination temperature and time are in the range of 350-650℃ and 0.5-24 h, respectively; After the calcination treatment, the catalyst precursor is obtained; (6) Hydrogen reduction treatment of the catalyst precursor: the reduction temperature, time and volume space velocity of hydrogen are in the ranges of 280-600°C, 0.5-20 h and 1-2000 h, respectively -1 ; and the catalyst precursor becomes a Cu-Beta zeolite catalyst after the hydrogen reduction treatment.

2. The preparation method of the Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to claim 1, characterized in that, In the first step (1), the molar ratio of silica to alumina, SiO2 / Al2O3, of the Beta zeolite precursor is in the range of 25-60.

3. The method for preparing a Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to claim 1, characterized in that, In the first step (2), the molar ratio of silica to alumina, SiO2 / Al2O3, of the dealuminated Beta zeolite support is in the range of >800.

4. The method for preparing a Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to claim 3, characterized in that, In the first step (2), the molar ratio of silica to alumina, SiO2 / Al2O3, of the dealuminated Beta zeolite support is in the range of >900.

5. The method for preparing a Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to claim 1, characterized in that, In the first step (2), the Beta zeolite precursor is subjected to acid dealumination treatment with a concentrated nitric acid aqueous solution, and the specific process is as follows: The 13 M concentrated nitric acid is used as the dealumination acid solution, and the acid solution is used in the liquid-solid ratio of 20:1, wherein the unit of the liquid-solid ratio is ml / g; the dealumination reaction is carried out at 95°C, and the dealumination reaction time is 20 h; after the dealumination reaction is completed, the solid product is recovered through solid-liquid separation, then the solid product is washed with water until the pH value is neutral, and then the solid product is subjected to drying treatment at a temperature of 80-200°C for 3-24 h and calcination treatment at a temperature of 500-600°C for 3-8 h to obtain the dealuminated Beta zeolite.

6. The method for preparing a Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to claim 1, characterized in that, In the second step (2), the equal-volume impregnation time is in the range of 1-12 h; In the second step (3), the ammonia evaporation temperature and time are in the range of 60-90°C and 1-24 h, respectively; In the second step (4), the drying temperature and time are in the range of 110-170°C and 1-24 h, respectively; In the second step (5), the calcination temperature and time are in the range of 400-600°C and 1-12 h, respectively; In the second step (6), the reduction temperature, time and hydrogen volume space velocity range from 300 to 550 °C, 1 to 15 h and 10 to 1500 h, respectively -1 .

7. The method for preparing a Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to claim 6, characterized in that, In the second step (2), the equal-volume impregnation time is in the range of 2-6 h; In the second step (3), the ammonia evaporation temperature and time are in the range of 65-85°C and 3-12 h, respectively; In the second step (4), the drying temperature and time are in the range of 120-150°C and 3-12 h, respectively; In the second step (5), the calcination temperature and time are in the range of 450-550°C and 2-6 h, respectively; In the second step (6), the reduction temperature, time and hydrogen volume space velocity range from 350 to 500°C, 2 to 8 h and 20 to 1000 h, respectively -1 .

8. The Cu-Beta zeolite catalyst prepared by the method for preparing a Cu-Beta zeolite catalyst for preparing caprolactam from caprolactone according to any one of claims 1-7 is used to catalyze the gas-solid phase hydrogenation of caprolactone to prepare caprolactam.

9. Use according to claim 8, characterized in that, The reaction conditions are as follows: The reaction temperature ranges from 120 to 350°C, the reaction pressure ranges from 0.01 to 2 atm, and the feed space velocity of the caprolactone ranges from 0.1 to 5 h -1 The molar ratios of the amine-ester, hydrogen-ester, and water-ester range from 1 to 50, 5 to 70, and 0 to 100, respectively.

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