A double-layer gradient acidic core-shell molecular sieve catalyst, a preparation method and application thereof

Abstract

This invention relates to the field of catalysis, and discloses a bilayer gradient acidic core-shell molecular sieve catalyst, its preparation method, and its applications. The bilayer gradient acidic core-shell molecular sieve catalyst comprises a ZSM-11 core layer and a BEA shell layer covering its surface; the acid strength of the ZSM-11 core layer is 0.40–1.20 mmol / g, and its average thickness is 0.5–3 μm; the acid strength of the BEA shell layer is 0.10–0.40 mmol / g, and its average thickness is 20–300 nm. This catalyst possesses a bilayer gradient acidic core-shell structure. When applied to the catalytic synthesis of tert-butylamine from isobutylene or its precursors (alcohols / ethers), it can improve single-pass conversion while maintaining high selectivity, and significantly reduce the carbon deposition rate and bed pressure drop growth, achieving long-term stable operation.

Description

Technical Field

[0001] This invention relates to the field of catalysis, and more particularly to a bilayer gradient acidic core-shell molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] tert-Butylamine (TBA) is an important class of aliphatic amine chemicals, widely used in pesticides, pharmaceuticals, fine chemicals, and new material monomers. With the upgrading of modern agriculture and the pharmaceutical industry, as well as the adjustment of fine chemical products, the usage of tert-butylamine in various downstream products continues to grow, thus placing higher demands on the safety, economy, and greening of its production processes.

[0003] Currently, the main industrial routes for preparing tert-butylamine include haloalkylation, nitrile hydrogenation, and direct amination of olefins (or tert-butyl precursors). Among these, haloalkylation generally consumes halogen feedstocks and generates large amounts of inorganic salt wastewater, resulting in a heavy environmental burden; nitrile hydrogenation relies on high-pressure hydrogen and metal catalysts, requiring significant investment and meeting stringent safety requirements. In contrast, the C4-based "tert-butyl precursor + ammonia" system for preparing tert-butylamine is attracting increasing attention due to its wide availability of raw materials, relatively simple reaction pathway, and potential for continuous and industrial-scale production.

[0004] In industrial feedstock systems, the "tert-butyl precursors" used to construct tert-butylamine are not limited to isobutylene, but also include isobutanol, tert-butanol, and methyl tert-butyl ether (MTBE). These substances have mature sources in refining and petrochemical plants, oxygenated fuel components, and C4 recycling chains: for example, MTBE can be obtained from the etherification of isobutylene and methanol, tert-butanol can be obtained from isobutylene hydration or related routes, and isobutanol can be obtained from carbonyl synthesis / hydrogenation or fermentation routes. Therefore, using multiple interchangeable "tert-butyl precursors" at the feedstock end and adapting the reaction parameters is of practical significance for improving the flexibility of feedstocks, reducing overall costs, and enhancing supply chain resilience. From the perspective of reaction mechanism, the above-mentioned raw materials can be classified into two categories: (1) raw materials that directly provide isobutylene or tert-butyl reactive intermediates (such as isobutylene itself); (2) raw materials that can generate isobutylene or tert-butyl reactive species in situ under acidic conditions (such as isobutanol, tert-butanol can be dehydrated to generate isobutylene, MTBE can be cracked / de-etherified to generate isobutylene and alcohol byproducts, etc.). As can be seen from the above, regardless of which raw material is used, the core reaction process inevitably involves the formation of isobutylene or tert-butyl reactive intermediates at acidic sites, and nucleophilic addition with ammonia to generate tert-butylamine.

[0005] Current technologies commonly employ solid acid catalysts, especially molecular sieve catalyst systems (such as BEA and ZSM molecular sieves), to improve catalyst activity and selectivity by adjusting the silica-alumina ratio, ion exchange, or introducing modifying elements (such as halogens and phosphorus). However, these catalytic systems have long faced a common challenge in industrial applications: the inherent contradiction between reactivity and carbon deposition side reactions. On the one hand, to ensure the formation rate of tert-butylamine, the catalyst needs sufficient acidity to activate olefins or promote the dehydration and cracking steps of alcohols / ethers; on the other hand, isobutylene and its related carbocation / carbocation-like intermediates readily undergo dimerization, trimerization, and even higher-level polymerization side reactions under acidic conditions, generating C8 and C9 compounds. 12 Hydrocarbons with higher carbon numbers or oxygen-containing byproducts. These byproducts not only directly consume effective feedstock and reduce the selectivity of tert-butylamine, but also deposit carbon on the outer surface and pores of the catalyst, leading to accelerated catalyst deactivation, a continuous increase in bed pressure drop, and a shortened operating cycle of the unit.

[0006] In recent years, existing technologies have proposed adding auxiliaries such as organosulfones (CN114436853A), trialkylamines (CN114436856B), and phenols (CN114436854B) to isobutylene-liquid ammonia-molecular sieve catalytic systems to improve miscibility, reduce diffusion resistance, and increase conversion rates. However, auxiliaries are external components of the reaction system, often leading to problems such as increased complexity of the raw material system, increased post-processing burden, and difficulty in auxiliary recovery. Furthermore, the introduction of auxiliaries does not fundamentally address the conditions for surface polymerization side reactions from the catalyst structure itself, making it difficult to maintain optimal performance under varying raw material fluctuations and long-term operating conditions. In addition, patent CN103003229B proposes a method to achieve a high conversion rate of isobutylene under specific extremely low pressures (20–33 bar), reflecting the idea of ​​optimizing conversion through process condition windows. However, this technology still suffers from problems such as long reaction time, limited conversion rate, and high separation cycle load. It does not address the risks of deactivation and pressure drop caused by external surface polymerization side reactions and carbon buildup at the structural level. Therefore, without a systematic design of the "acid strength-spatial distribution-mass transfer path," simply increasing acidity or changing reaction conditions often makes it difficult to simultaneously achieve high catalyst selectivity, high single-pass conversion, and long-life operation.

[0007] In summary, from the perspective of industrial continuity and multi-raw material compatibility, there is an urgent need to develop a new catalyst system for the synthesis of tert-butylamine that can combine high catalytic activity, high selectivity, and high stability (strong resistance to carbon deposition). Summary of the Invention

[0008] To address the common problems in existing technologies for preparing tert-butylamine from isobutylene and its derivatives with ammonia, such as the difficulty in simultaneously achieving high reaction selectivity and catalyst stability, limited single-pass conversion, and high coking rates, especially when the feedstock system is extended to tert-butyl oxygen-containing compounds that can generate isobutylene in situ, such as isobutanol, tert-butanol, and MTBE, the coupling of dehydration / cracking, amination, and polymerization side reactions makes effective control difficult. This invention provides a bilayer gradient acidic core-shell molecular sieve catalyst, its preparation method, and its application. The catalyst of this invention has a bilayer gradient acidic core-shell structure. When applied to catalyze the synthesis of tert-butylamine from isobutylene or its precursors (alcohols / ethers), it can improve single-pass conversion while maintaining high selectivity, significantly reduce coking rate and bed pressure drop growth, and achieve long-term stable operation.

[0009] The specific technical solution of the present invention includes: In a first aspect, the present invention provides a bilayer gradient acidic core-shell molecular sieve catalyst comprising a moderately strong acidic ZSM-11 core layer and a weakly acidic BEA shell layer covering its surface.

[0010] The catalyst of this invention has a bilayer gradient acidic core-shell structure, forming an acidic gradient distribution from weak acidity to moderate to strong acidity from the outer surface to the interior. This enables functional zoning of the reaction within the same catalyst particle size: the BEA shell can selectively adsorb and mildly pre-activate isobutylene or its precursors (alcohols / ethers) and suppress polymerization side reactions on the outer surface; the ZSM-11 core layer, as the main amination reaction zone, can provide moderately enhanced acidity to efficiently promote the conversion of isobutylene and ammonia to tert-butylamine; at the same time, through the design of confined mass transfer pathways, the dehydration / cracking-amination process occurs in an orderly manner, thereby improving the single-pass conversion rate while maintaining high selectivity, and significantly reducing the carbon deposition rate and bed pressure drop growth, achieving long-term stable operation.

[0011] Preferably, the acid strength of the ZSM-11 core layer is 0.40–1.20 mmol / g (more preferably 0.5–1.10 mmol / g); and the acid strength of the BEA shell layer is 0.10–0.40 mmol / g (more preferably 0.15–0.40 mmol / g).

[0012] The ZSM-11 core layer is used to effectively activate and amination of isobutylene in the inner layer. If the acid strength is too low, the isobutylene activation will be insufficient, leading to a significant decrease in the amination rate and single-pass conversion. If the acid strength is too high, it will easily enhance the polymerization tendency of tert-butyl carbocations, leading to increased carbon deposition in the pores and catalyst deactivation. The BEA shell layer is used for mild adsorption and pre-activation of isobutylene and its precursors and to inhibit polymerization on the outer surface. If the acid strength is too low, the buffering and screening effects will be insufficient, resulting in excessive local load on the core layer. If the acid strength is too high, polymerization side reactions are prone to occur in the shell layer, leading to carbon deposition on the outer surface and an increase in bed pressure drop.

[0013] The average particle size of the ZSM-11 core layer is 0.5–3 μm (more preferably 0.8–2.8 μm). The average thickness of the BEA shell layer is 20–300 nm (more preferably 40–280 nm).

[0014] Controlling the ZSM-11 core layer within the aforementioned particle size range ensures sufficient diffusion paths within the inner layer to form a stable amination reaction zone while avoiding mass transfer limitations. If the core layer particle size is too small, the functional partitioning between the shell and core layers is indistinct, leading to disordered isobutylene reactions within the overall particle size and a decreased inhibition of polymerization side reactions. Conversely, if the core layer particle size is too large, the diffusion paths of reactants within the inner layer are too long, resulting in reduced utilization and a decrease in conversion rate. Controlling the thickness of the BEA shell within the aforementioned particle size range allows for sufficient adsorption, buffering, and mild pre-activation of isobutylene and its precursors, while avoiding significant mass transfer resistance. If the shell thickness is too low, the weak acid shielding effect of the outer layer is insufficient, causing polymerization side reactions of isobutylene before it enters the core layer. If the shell thickness is too high, the entry of reactants into the core layer is hindered, leading to a decrease in inner-layer amination efficiency and affecting overall conversion performance.

[0015] Preferably, the mass ratio of the ZSM-11 core layer to the BEA shell layer is 40:60 to 85:15 (more preferably 40:60 to 80:15).

[0016] The purpose of controlling the core-to-shell mass ratio is to balance the synergistic effects of the two functional zones—"outer layer inhibiting polymerization and buffering mass transfer" and "inner layer efficiently performing amination reactions"—within the catalyst particle scale. When the ZSM-11 core layer ratio is too low and the BEA shell layer ratio is too high, the overall acidity of the catalyst is weak, and the number of effective amination active sites in the inner layer is insufficient, leading to a decrease in the isobutylene amination rate and a limited single-pass conversion rate. At the same time, an excessively thick weak acid shell layer will also increase mass transfer resistance, making it difficult for reactants to enter the inner active region in a timely manner. When the ZSM-11 core layer ratio is too high and the BEA shell layer ratio is too low, the outer weak acid shielding effect is insufficient, and isobutylene or its precursors are prone to directly contacting the medium-to-strong acid sites before entering the core layer, resulting in enhanced polymerization side reactions on the outer surface and at the pores, an increased carbon deposition rate, and a rapid increase in bed pressure drop, thereby weakening the long-term stability of the catalyst. Therefore, limiting the mass ratio of the core layer to the shell layer within the above range can effectively exert the role of the outer layer in inhibiting polymerization and buffering mass transfer while ensuring the amination activity of the inner layer. This is an important structural parameter for achieving high selectivity, high conversion rate and low carbon deposition in this invention.

[0017] Preferably, the silicon-aluminum molar ratio (Si / Al) of the ZSM-11 core layer is 20-80:1 (more preferably 30-60:1); and the silicon-aluminum molar ratio (Si / Al) of the BEA shell layer is 50-200:1 (more preferably 75-140:1).

[0018] Controlling the silicon-to-aluminum molar ratio (Si / Al) of the ZSM-11 core layer within the aforementioned range provides an appropriate number and intensity of Brønsted acid sites in the inner layer to promote isobutylene amination. If the Si / Al ratio is too low, the acid site density is too high, easily inducing polymerization side reactions and leading to carbon deposition within the pores; if it is too high, the acidity is insufficient, and the amination activity and single-pass conversion rate decrease significantly. Controlling the Si / Al molar ratio of the BEA shell within the aforementioned range maintains the weak acidity of the outer layer to achieve adsorption and buffering; if the Si / Al ratio is too low, polymerization reactions easily occur on the outer surface; if it is too high, the shell adsorption and regulation effects are insufficient, weakening the core-shell synergistic effect.

[0019] Secondly, the present invention provides a method for preparing a bilayer gradient acidic core-shell molecular sieve catalyst, comprising the following steps: 1) Preparation of ZSM-11 core layer: Silicon source, aluminum source, inorganic base, ZSM-11 template agent and water are mixed to prepare the first synthesis solution; hydrothermal crystallization, washing, drying and calcination are performed to obtain ZSM-11 crystal nuclei.

[0020] 2) Epitaxial growth of BEA shell: ZSM-11 crystal nuclei are added to a second synthesis solution containing silicon source, aluminum source, BEA template agent, inorganic alkali and water, and hydrothermally crystallized to form a BEA shell on the surface of ZSM-11 crystal nuclei.

[0021] 3) Post-processing: The obtained crystallized product is washed, dried, and calcined to obtain a bilayer gradient acidic core-shell molecular sieve catalyst.

[0022] Preferably, in step 1), the first synthesis solution has a water / SiO2 molar ratio of 10-200:1, a SiO2 / Al2O3 molar ratio of 40-160:1, and a template agent / SiO2 molar ratio of 0.1-0.5:1.

[0023] Preferably, in step 1), the ZSM-11 template agent is selected from one or more of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide, and more preferably tetrapropylammonium hydroxide.

[0024] Preferably, in step 1), the temperature of the hydrothermal crystallization is 120–180 °C. o C, the time is 24 to 96 hours.

[0025] Preferably, in step 2), the second synthesis solution has a water / SiO2 molar ratio of 20-300:1, a SiO2 / Al2O3 molar ratio of 100-400:1, and a template agent / SiO2 molar ratio of 0.2-0.6:1.

[0026] Preferably, in step 2), the BEA template agent is selected from one or more of tetraethylammonium hydroxide and tetraethylammonium bromide, and more preferably tetraethylammonium hydroxide.

[0027] Preferably, in step 2), the temperature of the hydrothermal crystallization is 120–170 °C. o C, the time is 12 to 72 hours.

[0028] Preferably, in step 3), the calcination temperature is 500–600 °C. o C, the time is 3 to 8 hours.

[0029] Preferably, in step 3), the bilayer gradient acidic core-shell molecular sieve catalyst is further formed into strips or granules with an inorganic binder, wherein the inorganic binder is selected from alumina, silica and / or their composites (more preferably alumina), and the content of the inorganic binder in the resulting catalyst is 5 to 30 wt% (more preferably 10 to 25 wt%).

[0030] Thirdly, the present invention provides the application of the above-mentioned bilayer gradient acidic core-shell molecular sieve catalyst in the synthesis of tert-butylamine, which includes the following steps: A) Isobutylene and / or tert-butyl oxygen-containing compounds that can generate isobutylene in situ are introduced into an amination reactor with ammonia, and the amination reaction is carried out under the action of a bilayer gradient acidic core-shell molecular sieve catalyst.

[0031] B) The product after the reaction was cooled and separated to obtain tert-butylamine.

[0032] This invention introduces a gradient acidity distribution structure with an outer layer of weak acid and an inner layer of medium-strong acid within the same catalyst particle size. This allows the reactants to undergo mild and controllable adsorption and pre-activation before entering the catalyst interior, while significantly suppressing polymerization side reactions induced by acidic sites on the outer surface. Furthermore, the amination reaction is efficiently completed within the inner molecular sieve channels. Thus, while maintaining high tert-butylamine selectivity, the single-pass conversion rate of isobutyl feedstock is improved, the rate of coking formation and the pressure drop increase in the fixed-bed reactor are reduced, achieving efficient, stable, and industrially sustainable operation of the reaction process.

[0033] Preferably, in step A), the tert-butyl oxygen-containing compound is selected from one or more of isobutanol, tert-butanol and methyl tert-butyl ether (MTBE), and more preferably isobutanol and tert-butanol.

[0034] Under acidic conditions, the above raw materials can undergo dehydration or pyrolysis reactions to generate isobutylene or tert-butyl active intermediates in situ, which can then participate in amination reactions.

[0035] Preferably, in step A), the molar ratio of ammonia to isobutylene and / or tert-butyl oxygen-containing compound in the amination reaction is 3:1 to 15:1, and more preferably 3:1 to 10:1.

[0036] Preferably, in step A), the reaction conditions for the amination reaction are: a reaction temperature of 180–380 °C. o C; reaction pressure 30–100 bar; reaction space velocity (WHSV) 0.5–1.0 h⁻¹ -1 More preferably, the reaction temperature is 220–260°C. o C; reaction pressure 60–90 bar; reaction space velocity (WHSV) 0.5–0.7 h⁻¹ -1 .

[0037] Preferably, in step A), the amination reactor is a fixed-bed reactor, a trickle-bed reactor, a moving-bed reactor, a radial-bed reactor, or a multi-tube fixed-bed reactor, and more preferably a fixed-bed reactor.

[0038] Compared with the prior art, the beneficial effects of the present invention are: (1) By constructing a bilayer gradient acidic core-shell molecular sieve catalyst with an outer weak acid and an inner medium strong acid, the present invention achieves spatial partition control of the activation and amination reactions of reactants, inhibits the polymerization side reaction of isobutylene and its precursors on the outer surface from the structural level, and significantly reduces the tendency of carbon deposition.

[0039] (2) The catalyst of the present invention can be adapted to multiple raw material systems such as isobutylene, isobutanol, tert-butanol and MTBE, so that the dehydration / cracking and amination reactions can occur in an orderly manner in a confined space, thereby enhancing the raw material flexibility and industrial applicability of the process.

[0040] (3) Under relatively mild reaction temperature and pressure conditions, the method of the present invention can improve the conversion rate of isobutyl raw materials and reduce the unreacted material recycling load while maintaining high tert-butylamine selectivity, which is beneficial to reducing energy consumption and separation costs.

[0041] (4) As the side reactions of polymerization on the outer surface are effectively suppressed, the growth rate of the catalyst bed pressure drop is significantly reduced, the catalyst service life is extended, which is conducive to the long-term stable operation of the fixed bed device and has good prospects for industrial scale-up.

[0042] (5) Compared with existing single molecular sieves or monolithically modified catalysts, this invention significantly improves the conversion rate of raw materials while maintaining the high selectivity of tert-butylamine, and effectively reduces the carbon deposition rate and bed pressure drop growth. It is suitable for continuous fixed-bed reactions of isobutylene and various tert-butyl precursor raw materials and has good industrial application prospects. Attached Figure Description

[0043] Figure 1 The image shows the XRD pattern of the bilayer gradient acidic core-shell molecular sieve catalyst BEA@ZSM-11 prepared in Example 1 (the marked areas are characteristic peaks of BEA). Detailed Implementation

[0044] General Implementation Examples In a first aspect, there is a bilayer gradient acidic core-shell molecular sieve catalyst comprising a moderately strong acidic ZSM-11 core layer and a weakly acidic BEA shell layer covering its surface.

[0045] The acid strength of the ZSM-11 core layer is 0.40–1.20 mmol / g (more preferably 0.5–1.10 mmol / g), and the average particle size is 0.5–3 μm (more preferably 0.8–2.8 μm).

[0046] The acid strength of the BEA shell is 0.10–0.40 mmol / g (more preferably 0.15–0.40 mmol / g), and the average thickness is 20–300 nm (more preferably 40–280 nm).

[0047] In some preferred embodiments, the silicon-aluminum molar ratio (Si / Al) of the ZSM-11 core layer is 20 to 80:1 (more preferably 30 to 60:1); and the silicon-aluminum molar ratio (Si / Al) of the BEA shell layer is 50 to 200:1 (more preferably 75 to 140:1).

[0048] In some preferred embodiments, the mass ratio of the ZSM-11 core layer to the BEA shell layer is 40:60 to 85:15 (more preferably 40:60 to 80:15).

[0049] Secondly, a method for preparing a bilayer gradient acidic core-shell molecular sieve catalyst includes the following steps: 1) Preparation of ZSM-11 core layer: Silicon source, aluminum source, inorganic base, ZSM-11 template agent and water are mixed to prepare the first synthesis solution; hydrothermal crystallization, washing, drying and calcination are performed to obtain ZSM-11 crystal nuclei.

[0050] In some preferred embodiments, in step 1), the first synthesis solution has a water / SiO2 molar ratio of 10 to 200:1, a SiO2 / Al2O3 molar ratio of 40 to 160:1, and a template agent / SiO2 molar ratio of 0.1 to 0.5:1.

[0051] In some preferred embodiments, in step 1), the ZSM-11 template agent is selected from one or more of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide, and more preferably tetrapropylammonium hydroxide.

[0052] In some preferred embodiments, in step 1), the temperature of the hydrothermal crystallization is 120–180 °C. o C, the time is 24 to 96 hours.

[0053] 2) Epitaxial growth of BEA shell: ZSM-11 crystal nuclei are added to a second synthesis solution containing silicon source, aluminum source, BEA template agent, inorganic alkali and water, and hydrothermally crystallized to form a BEA shell on the surface of ZSM-11 crystal nuclei.

[0054] In some preferred embodiments, in step 2), the second synthesis solution has a water / SiO2 molar ratio of 20-300:1, a SiO2 / Al2O3 molar ratio of 100-400:1, and a template agent / SiO2 molar ratio of 0.2-0.6:1.

[0055] In some preferred embodiments, in step 2), the BEA template agent is selected from one or more of tetraethylammonium hydroxide and tetraethylammonium bromide, and more preferably tetraethylammonium hydroxide.

[0056] In some preferred embodiments, in step 2), the temperature of the hydrothermal crystallization is 120–170 °C. o C, the time is 12 to 72 hours.

[0057] 3) Post-processing: The obtained crystallized product is washed, dried, and calcined to obtain a bilayer gradient acidic core-shell molecular sieve catalyst.

[0058] In some preferred embodiments, in step 3), the calcination temperature is 500–600 °C. o C, the time is 3 to 8 hours.

[0059] In some preferred embodiments, in step 3), the bilayer gradient acidic core-shell molecular sieve catalyst is further formed into strips or granules with an inorganic binder, wherein the inorganic binder is selected from alumina, silica and / or their composites (more preferably alumina), and the content of the inorganic binder in the resulting catalyst is 5 to 30 wt% (more preferably 10 to 25 wt%).

[0060] Thirdly, a method for synthesizing tert-butylamine, comprising the following steps: A) Isobutylene and / or tert-butyl oxygen-containing compounds that can generate isobutylene in situ are introduced into an amination reactor with ammonia, and the amination reaction is carried out under the action of a bilayer gradient acidic core-shell molecular sieve catalyst.

[0061] Preferably, in step A), the tert-butyl oxygen-containing compound is selected from one or more of isobutanol, tert-butanol and methyl tert-butyl ether (MTBE), and more preferably isobutanol and tert-butanol.

[0062] In some preferred embodiments, in step A), the molar ratio of ammonia to isobutylene and / or tert-butyl oxygen-containing compound in the amination reaction is 3:1 to 15:1, more preferably 3:1 to 10:1.

[0063] In some preferred embodiments, in step A), the reaction conditions for the amination reaction are: a reaction temperature of 180–380 °C. o C; reaction pressure 30–100 bar; reaction space velocity (WHSV) 0.5–1.0 h⁻¹ -1 More preferably, the reaction temperature is 220–260°C. o C; reaction pressure 60–90 bar; reaction space velocity (WHSV) 0.5–0.7 h⁻¹ -1 .

[0064] In some preferred embodiments, in step A), the amination reactor is a fixed-bed reactor, a trickle-bed reactor, a moving-bed reactor, a radial-bed reactor, or a multi-tube fixed-bed reactor, and is more preferably a fixed-bed reactor.

[0065] B) The product after the reaction was cooled and separated to obtain tert-butylamine.

[0066] Specific embodiments and comparative examples The following specific embodiments illustrate the technical solution of the present invention, but the scope of protection of the present invention is not limited thereto. Unless otherwise stated, the reagents used in the embodiments are all analytical grade or industrial grade, the reactors used are stainless steel fixed-bed reactors, and the product composition is quantitatively analyzed by gas chromatography (GC).

[0067] Example 1 (Preparation of BEA@ZSM-11 bilayer gradient acidic core-shell molecular sieve catalyst) (1) Preparation of ZSM-11 core layer: The silica sol, sodium aluminate, sodium hydroxide, template agent, and deionized water were mixed and stirred to form the first synthesis solution, with a water / SiO2 molar ratio of 80, a SiO2 / Al2O3 molar ratio of 80, and a template agent (tetrapropylammonium hydroxide) / SiO2 molar ratio of 0.25. The synthesis solution was then placed in a hydrothermal synthesis reactor and heated to 160°C. o Crystallization was carried out at C for 48 h. After crystallization, the product was washed, dried, and then crystallized at 550 °C. o ZSM-11 molecular sieve nuclei were obtained by calcination at C for 6 h, with an average particle size of about 1.2 μm and a Si / Al ratio of about 50.

[0068] (2) Epitaxial growth of the BEA shell: The ZSM-11 crystal nuclei were added to the second synthesis solution, in which the water / SiO2 molar ratio was 120, the SiO2 / Al2O3 molar ratio was 200, and the template agent (tetraethylammonium hydroxide) / SiO2 molar ratio was 0.35. At 150°C... o Hydrothermal crystallization at C conditions for 36 h allowed BEA molecular sieves to epitaxially grow on the surface of ZSM-11 to form a BEA shell.

[0069] (3) Post-processing: The crystallized product was washed, dried, and then heated at 550°C. o Calcination at C for 5 h yielded a bilayer gradient acidic BEA@ZSM-11 core-shell molecular sieve catalyst. Characterization showed that the BEA shell thickness was approximately 120 nm, the ZSM-11 / BEA mass ratio was approximately 65:35, the acid strength of the ZSM-11 core layer was 0.65 mmol / g, and the acid strength of the BEA shell layer was 0.22 mmol / g.

[0070] The XRD pattern of the bilayer gradient acidic core-shell molecular sieve catalyst BEA@ZSM-11 prepared in Example 1 is shown below. Figure 1 As shown in the figure, the marked areas are the characteristic peaks of BEA.

[0071] The difference from Example 1 is as follows: (1) In the ZSM-11 core layer preparation step, the SiO2 / Al2O3 molar ratio was adjusted to 120 and the crystallization temperature was 140°C. o C. The time is 72 hours.

[0072] (2) In the BEA shell epitaxial growth step, the SiO2 / Al2O3 molar ratio is 300 and the crystallization temperature is 130°C. o C. Time: 48 h. After calcination, BEA@ZSM-11 core-shell molecular sieve was obtained, with a BEA shell thickness of approximately 200 nm, a ZSM-11 / BEA mass ratio of approximately 50:50, an acid strength of 0.48 mmol / g for the ZSM-11 core layer, and an acid strength of 0.14 mmol / g for the BEA shell.

[0073] Application Example 1 (Preparation of tert-butylamine from isobutylene) The BEA@ZSM-11 core-shell molecular sieve catalyst prepared in Example 1 was loaded into a fixed-bed reactor. Isobutylene and liquid ammonia were used as raw materials, and the reaction temperature was controlled at 260°C. o C. Reaction pressure 90 bar, ammonia / isobutylene molar ratio 6:1, WHSV 0.5 h -1 After the reaction stabilized, continuous sampling and analysis showed that the single-pass conversion rate of isobutylene was significantly improved, the selectivity of tert-butylamine remained at a high level, and the bed pressure drop changed slowly over time.

[0074] Application Example 2 (Preparation of tert-butylamine using isobutanol as a raw material) The BEA@ZSM-11 core-shell molecular sieve catalyst prepared in Example 1 was loaded into a fixed-bed reactor. Isobutanol and liquid ammonia were used as raw materials, and the reaction temperature was controlled at 240°C. o C. Reaction pressure 60 bar, ammonia / isobutanol molar ratio 8:1, WHSV 0.6 h -1 Isobutanol undergoes mild dehydration at the weakly acidic sites in the BEA shell to form isobutene, which is then amination in the ZSM-11 core. No significant increase in pressure drop due to carbon deposition was observed during the reaction.

[0075] Application Example 3 (Preparation of tert-butylamine from tert-butanol) The BEA@ZSM-11 core-shell molecular sieve catalyst prepared in Example 2 was loaded into a fixed-bed reactor. Tert-butanol and liquid ammonia were used as raw materials, and the reaction temperature was controlled at 220°C. o C. Reaction pressure 60 bar, ammonia / tert-butanol molar ratio 5:1, WHSV 0.6 h -1 The reaction proceeded stably, with tert-butylamine as the major product, and no obvious high-carbon-number polymerization byproducts were detected.

[0076] Application Example 4 (Preparation of tert-butylamine from MTBE) The BEA@ZSM-11 core-shell molecular sieve catalyst prepared in Example 1 was loaded into a fixed-bed reactor. MTBE and liquid ammonia were used as feedstocks, and the reaction temperature was controlled at 240°C. o C. Reaction pressure 80 bar, ammonia / MTBE molar ratio 10:1, WHSV 0.7 h. -1 MTBE undergoes cleavage at the weakly acidic sites in the shell to produce isobutylene and methanol. The isobutylene then undergoes amination in the core layer. The system operates stably without significant bed blockage.

[0077] Application Example 5 (Continuous Operation Stability Test) The reaction was run continuously for 200 h under the conditions of Application Example 1. During this period, the bed pressure drop and product composition were monitored periodically. The results showed that the selectivity of tert-butylamine remained stable, and the rate of increase in bed pressure drop was significantly lower than that of the single molecular sieve catalytic system.

[0078] Performance Comparison Table 1: 24-hour operation data of the core-shell BEA@ZSM-11 catalyst in Examples 1-2 As shown in Table 1, in the method for preparing tert-butylamine by isobutylene amination based on a bilayer gradient acidic core-shell molecular sieve catalyst, when the feedstock is expanded from isobutylene to isobutanol, tert-butanol, and MTBE, all four feedstock systems can achieve a temperature range of 80-120 °C. o C. Stable operation under mild conditions of 10-30 bar, maintaining high conversion rate with tert-butylamine selectivity ≥99%. 8+ The low proportion of polymerization byproducts and low carbon deposition rate, along with the absence of significant rapid bed clogging, indicate that the outer weak acid BEA layer can not only gently preactivate isobutylene but also effectively regulate the isobutylene intermediates generated during alcohol dehydration and ether cracking, preventing them from undergoing violent polymerization on the outer surface and creating favorable conditions for the efficient amination of the inner ZSM-11 layer.

[0079] Table 2: Results of Application Example 5 after 200 hours of continuous operation The average carbon deposition rate over 200 hours was 0.04 mg. coke / g cat h, pressure drop increases by +3.0 kPa / 200 h (4.0 → 7.0 kPa).

[0080] As shown in Table 2, the continuous operation stability test further verified the technical effect of the present invention. During 200 h of continuous operation, the pressure drop of the core-shell catalyst bed used in the example only increased from 4.0 kPa to 7.0 kPa, the selectivity of tert-butylamine remained above 99%, and the decrease in isobutylene conversion rate was small.

[0081] The difference from Example 1 is that the ZSM-11 core layer has a larger particle size. The preparation method of the ZSM-11 core layer is as follows (other steps are the same as in Example 1): The silica sol, sodium aluminate, sodium hydroxide, template agent, and deionized water were mixed and stirred to form the first synthesis solution, with a water / SiO2 molar ratio of 80, a SiO2 / Al2O3 molar ratio of 80, and a template agent (tetrapropylammonium hydroxide) / SiO2 molar ratio of 0.25. The synthesis solution was then placed in a hydrothermal synthesis reactor and heated to 170°C. o Crystallization was carried out at C for 72 h. After crystallization, the product was washed, dried, and then crystallized at 550 °C. o ZSM-11 molecular sieve nuclei were obtained by calcination at C for 6 h, with an average particle size of about 2.9 μm and an acid strength of 0.58 mmol / g.

[0082] The difference from Example 1 is that the ZSM-11 core layer has a smaller particle size. The preparation method of the ZSM-11 core layer is as follows (other steps are the same as in Example 1): The silica sol, sodium aluminate, sodium hydroxide, template agent, and deionized water were mixed and stirred to form the first synthesis solution, with a water / SiO2 molar ratio of 80, a SiO2 / Al2O3 molar ratio of 80, and a template agent (tetrapropylammonium hydroxide) / SiO2 molar ratio of 0.25. The synthesis solution was then placed in a hydrothermal synthesis reactor and heated to 130°C. o Crystallization was carried out at C for 36 h. After crystallization, the product was washed, dried, and then crystallized at 550 °C. o ZSM-11 molecular sieve nuclei were obtained by calcination at C for 6 h, with an average particle size of about 0.6 μm and an acid strength of 0.72 mmol / g.

[0083] The difference from Example 1 is that the BEA shell is thinner. The epitaxial growth method of the BEA shell is as follows (other steps are the same as in Example 1): ZSM-11 crystal nuclei were added to the second synthesis solution, in which the water / SiO2 molar ratio was 150, the SiO2 / Al2O3 molar ratio was 250, and the template agent (tetraethylammonium hydroxide) / SiO2 molar ratio was 0.28. At 140°C... oHydrothermal crystallization at C conditions for 20 h allowed BEA molecular sieves to epitaxially grow on the surface of ZSM-11 to form a BEA shell. After post-treatment, the BEA shell thickness was approximately 30 nm, the ZSM-11 / BEA mass ratio was approximately 75:25, and the acid strength of the BEA shell was 0.27 mmol / g.

[0084] The difference from Example 1 is that the BEA shell is thicker. The epitaxial growth method of the BEA shell is as follows (other steps are the same as in Example 1): ZSM-11 crystal nuclei were added to the second synthesis solution, in which the water / SiO2 molar ratio was 90, the SiO2 / Al2O3 molar ratio was 160, and the template agent (tetraethylammonium hydroxide) / SiO2 molar ratio was 0.40. At 155 °C... o Hydrothermal crystallization at C conditions for 60 h allowed BEA molecular sieves to epitaxially grow a BEA shell on the surface of ZSM-11. After post-treatment, the BEA shell thickness was approximately 290 nm, the ZSM-11 / BEA mass ratio was approximately 45:45, and the acid strength of the BEA shell was 0.18 mmol / g.

[0085] Comparative Example 1 The difference from Example 1 is that a single BEA molecular sieve (Si / Al≈80) is used.

[0086] Comparative Example 2 The difference from Example 1 is that a single ZSM-11 molecular sieve (Si / Al≈50) is used.

[0087] The reaction was highly active in the early stages, but the bed pressure drop increased rapidly during operation, indicating that the polymerization and carbon deposition on the outer surface were obvious.

[0088] Comparative Example 3 The difference from Example 1 is that fluorine-modified F-ZSM-11 molecular sieve is used.

[0089] Compared with unmodified ZSM-11, the carbon deposition rate is reduced, but external surface side reactions still exist, and the reaction stability is not as good as in Example 1.

[0090] Performance Comparison (1) Tert-butylamine was prepared from isobutylene using the catalysts of Examples 3-6 and the comparative examples under the conditions of Application Example 1. The results are shown in Table 3: Table 3: 24-hour running data for Examples 3-6 A comparison of the reaction data from Examples 1 and 3-6 shows that the ZSM-11 core particle size and the BEA shell thickness are key structural parameters determining the performance of the core-shell catalyst. In Example 1, both the core particle size and shell thickness are within their optimal ranges. The outer weak acid BEA and the inner medium-strong acid ZSM-11 form a reasonable spatial distribution and mass transfer pathway, resulting in an isobutylene conversion of 65.2% while maintaining a tert-butylamine selectivity of 99.6%. 8+ Both byproducts and carbon deposition rates are at their lowest levels, demonstrating the best overall catalytic performance.

[0091] When the core layer particle size is too large (Example 3) or too small (Example 4), the matching degree between the reactants in the shell buffer and the core active region decreases, and the isobutylene conversion rate drops to 60.8% and 58.6%, respectively. At the same time, the carbon deposition rate increases, indicating that the core layer size deviating from the optimal range will weaken the synergistic effect between the amination reaction and the inhibition of polymerization side reactions.

[0092] Similarly, when the BEA shell thickness is relatively thin (Example 5), the shielding effect of the outer weak acid on polymerization side reactions is weakened, C 8+ The rates of byproducts and carbon deposition increased significantly; while a thicker shell (Example 6) resulted in a decrease in conversion rate due to increased mass transfer resistance. These results further demonstrate that, under conditions of synergistic optimization of core particle size and shell thickness, the advantages of the core-shell structure of this invention in improving amination efficiency and operational stability can be fully utilized.

[0093] (2) Tert-butylamine was prepared from isobutylene using the catalysts of Comparative Examples 1-3 and each of the comparative examples under the conditions of Application Example 1. The results are shown in Table 4: Table 4: 24-hour operation data of single molecular sieve catalysts in Comparative Examples 1-3 The comparison between Example 1 and Comparative Examples 1-3 shows that the bilayer gradient acidic BEA@ZSM-11 core-shell molecular sieve catalyst and its matching fixed-bed reaction process of the present invention play a key role in improving the single-pass conversion rate of tert-butylamine synthesis reaction, suppressing polymerization side reactions, and improving the long-term operational stability of the catalyst.

[0094] Comparing Example 1 (Application Example 1) with Comparative Example 1 (Single BEA molecular sieve), it can be seen that while relying solely on the weakly acidic BEA molecular sieve can effectively suppress the polymerization side reaction of isobutylene and maintain the selectivity of tert-butylamine above 99%, its insufficient acidity limits its activation ability for isobutylene, resulting in an isobutylene conversion rate of only 44.8%. In contrast, Example 1, employing a core-shell structure with an outer layer of weakly acidic BEA and an inner layer of moderately strong acidic ZSM-11, significantly increased the isobutylene conversion rate to 65.2% while maintaining a substantially unchanged tert-butylamine selectivity (99.2%), representing a relative improvement of over 45% under conditions where selectivity ≥99%. This indicates that simply increasing the overall acidity cannot achieve efficient amination; only through the spatial distribution design of the acid gradient can both conversion rate and selectivity be balanced.

[0095] Further comparison of Example 1 (Application Example 1) with Comparative Example 2 (single ZSM-11 molecular sieve) reveals that the single ZSM-11 molecular sieve, due to the concentrated distribution of medium-strong acid sites on the outer surface and pore area of ​​the catalyst, does indeed provide a high isobutylene conversion rate (approximately 50.0%) in the initial stage of the reaction. However, it also significantly promotes the acid-catalyzed polymerization side reaction of isobutylene. Experimental data show that in Comparative Example 2, C... 8+ The proportion of polymerization byproducts increased significantly, and the carbon deposition rate reached 0.32 mg / L. c / g cat h, causing the bed pressure drop to rise rapidly during continuous operation. In contrast, the carbon deposition rate of the core-shell catalyst in Example 1 was only 0.04 mg. c / g cat h, the increase in bed pressure drop was significantly controlled, indicating that the outer weak acid BEA shell played a significant role in suppressing the polymerization side reactions on the outer surface.

[0096] Comparative Example 3 used fluorinated ZSM-11 molecular sieve, which reduced the density of strong acid sites to some extent. The polymerization side reactions and coking rates were improved compared to unmodified ZSM-11, but its essence remained overall acidity regulation, without forming a clear functional zone. Experimental results showed that the isobutylene single-pass conversion rate of Comparative Example 3 was still lower than that of Example 1 (Application Example 1), and the bed pressure drop increase was still significantly faster than that of the catalyst system of this invention during 200 h of continuous operation (see Table 4 below). This indicates that simply adjusting the acid strength through chemical modification is insufficient to fundamentally solve the competition between outer surface polymerization and inner layer amination reactions.

[0097] (3) The catalysts of Examples 3-6 were continuously run for 200 h under the conditions of Application Example 5 for stability testing. The results are shown in Table 5: Table 5: Data from 200 hours of operation for Examples 3-6 Examples 3-6 maintained high tert-butylamine selectivity (≥99.0%) under continuous operation for 200 h, indicating that even when the core or shell structure parameters deviate from the optimal range, the BEA@ZSM-11 core-shell catalyst can still maintain the basic selectivity advantage of the amination reaction. Compared with Application Example 5, when the core particle size was larger (Example 3) or smaller (Example 4), the isobutylene conversion rate and operational stability decreased, while the pressure drop increase and carbon deposition rate increased accordingly, indicating that deviations from the optimal core size range weaken the synergistic effect between the shell buffer and the core active region. Example 5 (thinner shell) maintained high activity initially, but the pressure drop increase and carbon deposition rate increased most significantly after 200 h, indicating that insufficient shielding by the outer weak acid easily leads to enhanced polymerization side reactions; while Example 6 (thicker shell) showed the lowest carbon deposition rate and a smaller pressure drop increase, but its conversion rate was relatively low due to increased mass transfer resistance. The above results further demonstrate that when the core particle size and shell thickness are reasonably matched, high activity and long-term stable operation can be achieved simultaneously.

[0098] (4) The catalysts of Comparative Examples 1-2 were continuously run for 200 h under the conditions of Application Example 5 for stability testing. The results are shown in Table 6: Table 6: Data from 200 hours of operation for Comparative Examples 1-3 During 200 hours of continuous operation, the pressure drop of the core-shell catalyst bed used in Application Example 1 increased only from 4.0 kPa to 7.0 kPa, the selectivity of tert-butylamine remained above 99%, and the decrease in isobutylene conversion was relatively small. In contrast, the pressure drop of the single ZSM-11 catalyst bed in Table 4 increased to above 30 kPa under the same conditions, and the reaction activity decreased significantly, showing obvious risks in industrial operation.

[0099] In summary, through the systematic comparison of the above embodiments and comparative examples, it can be clearly seen that the present invention, by constructing a bilayer gradient acidic core-shell molecular sieve catalyst with an outer weak acid and an inner medium-strong acid, achieves hierarchical adsorption, pre-activation, and directional amination of isobutylene and its precursor molecules. This effectively suppresses polymerization side reactions and carbon deposition at the structural level, significantly improves the raw material conversion rate and enhances the long-term operational stability of the catalyst under high tert-butylamine selectivity, fully demonstrating the significant inventiveness and industrial application value of the present invention.

Claims

1. A bilayer gradient acidic core-shell molecular sieve catalyst, characterized in that: It includes the ZSM-11 core layer and the BEA shell covering its surface; The acid strength of the ZSM-11 core layer is 0.40–1.20 mmol / g, and the average particle size is 0.5–3 μm. The acid strength of the BEA shell is 0.10–0.40 mmol / g, and the average thickness is 20–300 nm.

2. The bilayer gradient acidic core-shell molecular sieve catalyst according to claim 1, characterized in that: The silicon-aluminum molar ratio of the ZSM-11 core layer is 20–80:1; the silicon-aluminum molar ratio of the BEA shell layer is 50–200:

1.

3. The bilayer gradient acidic core-shell molecular sieve catalyst according to claim 1, characterized in that: The mass ratio of the ZSM-11 core layer to the BEA shell layer is 40:60 to 85:

15.

4. A method for preparing a bilayer gradient acidic core-shell molecular sieve catalyst according to any one of claims 1-3, characterized in that... include: 1) Mix silicon source, aluminum source, inorganic base, ZSM-11 template agent and water to prepare the first synthesis solution; Hydrothermal crystallization, washing, drying and calcination were performed to obtain ZSM-11 crystal nuclei; 2) Add ZSM-11 crystal nuclei to a second synthesis solution containing silicon source, aluminum source, BEA template agent, inorganic alkali and water, and perform hydrothermal crystallization to epitaxially grow a BEA shell on the surface of ZSM-11 crystal nuclei. 3) The obtained crystallized product was washed, dried, and calcined to obtain a bilayer gradient acidic core-shell molecular sieve catalyst.

5. The preparation method according to claim 4, characterized in that: In step 1), In the first synthesis solution, the water / SiO2 molar ratio is 10–200:1, the SiO2 / Al2O3 molar ratio is 40–160:1, and the template agent / SiO2 molar ratio is 0.1–0.5:1; The ZSM-11 template agent is selected from one or more of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; The hydrothermal crystallization temperature is 120–180°C. o C, the time is 24 to 96 hours.

6. The preparation method according to claim 4, characterized in that: In step 2), In the second synthesis solution, the water / SiO2 molar ratio is 20–300:1, the SiO2 / Al2O3 molar ratio is 100–400:1, and the template agent / SiO2 molar ratio is 0.2–0.6:

1. The BEA template agent is selected from one or more of tetraethylammonium hydroxide and tetraethylammonium bromide; The hydrothermal crystallization temperature is 120–170°C. o C, the time is 12 to 72 hours.

7. The preparation method according to claim 4, characterized in that: In step 3), The roasting temperature is 500-600°C. o C, the time is 3 to 8 hours; The bilayer gradient acidic core-shell molecular sieve catalyst is further formed into strips or granules with an inorganic binder, wherein the inorganic binder is selected from alumina, silica and / or their composites, and the content of the inorganic binder in the resulting catalyst is 5 to 30 wt%.

8. The application of the bilayer gradient acidic core-shell molecular sieve catalyst according to any one of claims 1-3 or the bilayer gradient acidic core-shell molecular sieve catalyst obtained by the preparation method according to any one of claims 4-7 in the synthesis of tert-butylamine, characterized in that... include: A) Isobutylene and / or tert-butyl oxygen-containing compounds that can generate isobutylene in situ are introduced into an amination reactor with ammonia, and the amination reaction is carried out under the action of a bilayer gradient acidic core-shell molecular sieve catalyst. B) The product after the reaction was cooled and separated to obtain tert-butylamine.

9. The application according to claim 8, characterized in that: In step A), The tert-butyl oxygen-containing compound is selected from one or more of isobutanol, tert-butanol and methyl tert-butyl ether; In the amination reaction, the molar ratio of ammonia to isobutylene and / or tert-butyl oxygen-containing compounds is 3:1 to 15:

1.

10. The application according to claim 8 or 9, characterized in that: In step A), The reaction conditions for the amination reaction are: reaction temperature 180–380°C. o C; reaction pressure 30–100 bar; reaction space velocity 0.5–1.0 h⁻¹ -1 ; The amination reactor is a fixed-bed reactor, a trickle-bed reactor, a moving-bed reactor, a radial-bed reactor, or a multi-tube fixed-bed reactor.

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