A process for the preparation of salicylonitrile from salicylamide

Abstract

The application discloses a method for preparing salicylonitrile from salicylamide, and belongs to the technical field of chemical synthesis. The method adopts a fixed-bed continuous reaction process, a modified catalyst is filled in a fixed-bed reactor, ammonia gas is preheated, the preheated salicylamide solution in p-xylene is introduced into the reactor together with the ammonia gas to perform a gas-phase catalytic dehydration reaction, and reaction effluent is collected after cooling to obtain salicylonitrile. The application adopts a step-by-step modified catalyst, amino functionalization is performed on 3A molecular sieves by using an amino silane coupling agent to effectively anchor ZnO active components and improve the dispersity of active sites; a moderate hydrophobic interface is constructed by using n-octyl triethoxysilane to accelerate the desorption of water vapor, inhibit side reactions and promote the forward progress of the dehydration reaction; and finally, a synergistic catalytic system is formed by compounding the modified catalyst with a boron phosphate active matrix. The application effectively solves the problem of low conversion rate and selectivity in the traditional process, has the advantages of high catalytic activity and few side reactions, and is suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a method for preparing salicylnitrile from salicylamide. Background Technology

[0002] Salicylic nitrile (o-hydroxybenzonitrile) is an important intermediate in the synthesis of pharmaceuticals, pesticides, and fine chemicals, and is particularly widely used in the preparation of highly effective fungicides such as pyraclostrobin. Currently, the main synthetic routes for salicylic nitrile include the salicylaldehyde oxime dehydration method, the ammonium salicylate catalytic dehydration method, and the salicylamide catalytic dehydration method. Among these, the preparation of salicylic nitrile from salicylamide via dehydration reaction has attracted considerable attention due to the readily available raw materials and fewer reaction steps.

[0003] However, existing methods for preparing salicylates from salicylamide generally suffer from low conversion rates and poor selectivity. Specifically: Firstly, when using stoichiometric dehydrating agents such as phosgene and thionyl chloride, although the dehydration capacity is strong, the reaction is violent and there are many side reactions. It is easy to generate byproducts such as benzoxazole and dimers, resulting in low selectivity of salicylnitrile, which is highly toxic and corrosive, and requires high-end equipment.

[0004] Secondly, while solid acid catalysts developed in recent years avoid the use of highly toxic dehydrating agents, they suffer from problems such as easy loss of active components, uneven distribution of acidic sites, and sensitivity to water. In fixed-bed continuous reactions, they have low conversion rates and selectivity, and short catalyst lifespans, which cannot meet the requirements for long-term industrial operation.

[0005] Third, in traditional batch reactor processes, the water generated during the reaction cannot be removed in time, which inhibits the positive shift of the dehydration equilibrium, further reducing the conversion rate and selectivity, and also results in low production efficiency and poor batch-to-batch repeatability.

[0006] Therefore, there is an urgent industrial need to develop a new method that can significantly improve the conversion rate and selectivity of salicylamide dehydration to prepare salicylnitrile, while achieving continuous and long-term stable operation. Summary of the Invention

[0007] This invention provides a method for preparing salicylnitrile from salicylamide, which can solve the problems of low conversion rate and selectivity in the existing methods for preparing salicylnitrile from salicylamide by dehydration.

[0008] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for preparing salicylnitrile from salicylamide, comprising the following steps: The catalyst was packed into a fixed-bed reactor and preheated to the reaction temperature by ammonia gas. A solution of salicylamide in p-xylene and ammonia gas was preheated and then introduced into the fixed-bed reactor to carry out the reaction at the reaction temperature. The reaction effluent was collected after cooling to obtain salicylnitrile.

[0009] Furthermore, the concentration of the salicylamide in the p-xylene solution is 0.08-0.12 g / mL, preferably 0.1 g / mL.

[0010] Furthermore, the temperature at which the salicylamide solution in p-xylene and ammonia are preheated is 150°C.

[0011] Furthermore, the molar ratio of ammonia to salicylamide is (20-40):1.

[0012] Furthermore, the specific parameters for the reaction at the specified reaction temperature are: reaction temperature 360-380℃, and liquid hourly space velocity (LISH) of 0.2-0.5 h⁻¹. -1 .

[0013] Furthermore, the catalyst is prepared by the following method: S1. Add 3A molecular sieve to an ethanol aqueous solution, then add aminosilane coupling agent, stir, wash, and dry to obtain NH2-3A; S2. Add NH2-3A to deionized water, then add zinc nitrate hexahydrate, stir, let stand, dry, and calcine to obtain ZnO / NH2-3A; S3. Add ZnO / NH2-3A to an aqueous ethanol solution, then add n-octyltriethoxysilane, stir, wash, and dry to obtain modified 3A molecular sieve; S4. Add boric acid, phosphoric acid, and stearic acid to deionized water, stir, then add modified 3A molecular sieve, stir, heat to dry, dry, and calcine to obtain the catalyst.

[0014] Further, in step S1, the ratio of the amount of the 3A molecular sieve, the aqueous ethanol solution, and the aminosilane coupling agent is 1g:10-12mL:0.1-0.2g; the volume fraction of the aqueous ethanol solution is 60%-70%.

[0015] Further, in step S1, the aminosilane coupling agent includes any one or more of aminopropyltriethoxysilane, aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0016] Furthermore, in step S1, the stirring temperature is 60-70℃ and the stirring time is 1-2 hours.

[0017] Further, in step S2, the ratio of NH2-3A, deionized water, and zinc nitrate hexahydrate is 1g:10-20mL:0.2-0.4g.

[0018] Further, in step S2, the stirring time is 2-3 hours; the standing time is 1-2 hours; the drying temperature is 100°C and the time is 10-12 hours; the calcination temperature is 380-420°C and the time is 4-6 hours.

[0019] Further, in step S3, the ratio of ZnO / NH2-3A, ethanol aqueous solution, and n-octyltriethoxysilane is 1g:10-12mL:0.04-0.06g; the volume fraction of the ethanol aqueous solution is 60%-70%.

[0020] Furthermore, in step S3, the stirring time is 1-2 hours.

[0021] Further, in step S4, the ratio of boric acid, phosphoric acid, stearic acid, deionized water, and modified 3A molecular sieve is 20g:37g:1.2-1.4g:130-150mL:12-14g.

[0022] Furthermore, in step S4, the calcination temperature is 300-400℃ and the time is 6-8h.

[0023] The beneficial effects of this invention are: 1. This invention employs a fixed-bed continuous operation. By loading the catalyst into a fixed-bed reactor and preheating it with ammonia gas, ammonia serves as both a reactant and a carrier gas, promoting the vaporization and mass transfer of salicylamide. Furthermore, the alkaline environment of ammonia helps suppress side reactions and improve reaction selectivity. Preheating the paraxylene solution of salicylamide and ammonia gas separately before introducing them into the reactor avoids the impact of cold materials on the reaction temperature, ensuring stable temperature in the reaction zone and facilitating stable catalyst activity. The effluent after reaction can be efficiently collected by cooling. The overall process is simple to operate, allows for continuous production, significantly improves production efficiency and product quality stability, and is suitable for industrial applications.

[0024] 2. The catalyst used in this invention undergoes multi-step functionalization modification. First, an amino group is introduced onto the surface of the 3A molecular sieve using an aminosilane coupling agent, enhancing its coordination and anchoring ability for the active component zinc ions, resulting in uniform ZnO loading and exposure of abundant Lewis acid sites. Subsequently, hydrophobic modification is performed using n-octyltriethoxysilane, constructing a hydrophobic surface layer while maintaining the pores of the molecular sieve. This facilitates rapid desorption of water generated during the reaction, suppresses side reactions, and promotes a positive shift in the dehydration equilibrium. Finally, the modified molecular sieve is combined with boric acid, phosphoric acid, and stearic acid to form a stable synergistic catalytic system of boron phosphate active centers and the molecular sieve support. This catalyst exhibits advantages such as uniform dispersion of active components, tunable surface acid sites, suitable hydrophobic environment, and good structural stability. When used for continuous dehydration of salicylamide in a fixed bed to prepare salicylnitrile, it can significantly improve conversion and selectivity and extend catalyst life. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0026] This invention provides a method for preparing salicylnitrile from salicylamide, comprising the following steps: The catalyst was packed into a fixed-bed reactor and preheated to the reaction temperature by ammonia gas. A solution of salicylamide in p-xylene and ammonia gas was preheated and then introduced into the fixed-bed reactor to carry out the reaction at the reaction temperature. The reaction effluent was collected after cooling to obtain salicylnitrile.

[0027] In this step, ammonia acts as both a reactant in the dehydration reaction and a carrier gas to promote the vaporization of salicylamide and its uniform distribution in the catalyst bed. Its alkaline environment effectively suppresses side reactions and significantly improves the selectivity of salicylnitrile. p-Xylene, a high-boiling-point inert solvent, stably dissolves salicylamide and forms a homogeneous reaction liquid. It is preheated together with ammonia and salicylamide before entering the reactor, avoiding the impact of cold materials on the temperature field of the reaction zone and ensuring the activity and stability of the catalyst. The catalyst packed in the fixed-bed reactor enables continuous catalytic dehydration. After cooling, the salicylnitrile condenses and separates from the gas phase. The operation is simple and easy to scale up for continuous production, achieving a balance between high conversion rate, high selectivity, and industrial operability.

[0028] In some embodiments, the concentration of the salicylamide in the p-xylene solution is 0.08-0.12 g / mL, preferably 0.1 g / mL. This concentration range ensures that the salicylamide is fully dissolved and stably fed into the fixed-bed reactor, while maintaining suitable material viscosity and gasification efficiency. Too low a concentration will reduce the reactor capacity per unit volume and increase the solvent recovery load, while too high a concentration may lead to salicylamide precipitation or poor atomization, thereby causing catalyst carbon buildup and bed blockage.

[0029] In some embodiments, the preheating temperature of the salicylamide p-xylene solution and ammonia gas is 150°C. Preheating to 150°C ensures that the materials reach a state close to the reaction temperature before entering the reactor, preventing cold materials from impacting the catalyst bed and ensuring stable temperature in the reaction zone. Too low a preheating temperature will cause a sharp drop in the reactor inlet temperature, affecting the stability of the conversion rate; too high a preheating temperature may cause premature thermal decomposition of salicylamide or excessive vaporization of p-xylene, leading to a deviation of the feed composition from the set value.

[0030] In some embodiments, the molar ratio of ammonia to salicylamide is (20-40):1. This molar ratio range provides sufficient ammonia to promote the forward dehydration reaction and suppress side reactions, while avoiding excessive ammonia dilution of the reactant concentration. A molar ratio that is too low will result in insufficient ammonia, incomplete reaction, and increased byproducts, while a molar ratio that is too high will excessively dilute the salicylamide vapor, reduce the processing efficiency per unit volume of reactor, and increase the burden on tail gas recovery.

[0031] In some embodiments, the specific parameters for carrying out the reaction at the reaction temperature are: reaction temperature 360-380℃, and liquid hourly space velocity (LISH) of 0.2-0.5 h⁻¹. -1 This allows salicylamide to obtain sufficient residence time in the catalyst bed to achieve high conversion rates, while preventing high-temperature side reactions. Too low a reaction temperature or too high a liquid hourly space velocity (LISH) will lead to a significant decrease in conversion rates. Too high a reaction temperature will exacerbate carbon deposition and catalyst deactivation, while too low a LISH will result in low production capacity, which is not conducive to industrial economics.

[0032] 3A molecular sieves possess a regular microporous structure and a high specific surface area, enabling them to selectively adsorb water molecules and provide a dispersion carrier for active components. However, their anchoring ability for metal ions is weak, and their strong hydrophilicity easily leads to water adsorption inhibiting dehydration reactions. Therefore, the present invention makes the following improvements.

[0033] In some embodiments, the catalyst is prepared by: S1. Add 3A molecular sieve to an ethanol aqueous solution, then add aminosilane coupling agent, stir, wash, and dry to obtain NH2-3A; In the above steps, 3A molecular sieve is added to an ethanol-water solution, along with an aminosilane coupling agent. The ethoxy groups in the coupling agent undergo a condensation reaction with the silanol groups on the molecular sieve surface via hydrolysis, covalently grafting the amino groups onto the molecular sieve surface. This step introduces abundant amino groups onto the molecular sieve surface, providing a chemical anchor for subsequent coordination and anchoring of metal ions, while preserving the microporous structure of the molecular sieve and ensuring the adsorption and mass transfer performance of the support.

[0034] S2. Add NH2-3A to deionized water, then add zinc nitrate hexahydrate, stir, let stand, dry, and calcine to obtain ZnO / NH2-3A; The above steps disperse NH2-3A in water, add zinc nitrate hexahydrate, and Zn 2+ ZnO nanoparticles are uniformly anchored by coordination with surface amino groups, and after drying and calcination, highly dispersed ZnO nanoparticles are generated in situ. This step constructs abundant and uniform Lewis acid sites on the surface of the molecular sieve, significantly enhancing the catalyst's activation ability for salicylamide active sites, while effectively inhibiting the aggregation of ZnO particles and improving the utilization efficiency of the active components.

[0035] S3. Add ZnO / NH2-3A to an aqueous ethanol solution, then add n-octyltriethoxysilane, stir, wash, and dry to obtain modified 3A molecular sieve; In the above steps, ZnO / NH2-3A is added to an ethanol-water solution, followed by the addition of n-octyltriethoxysilane. The ethoxy groups in n-octyltriethoxysilane hydrolyze and then condense with the residual silanol groups on the molecular sieve surface, covalently grafting the octyl group onto the catalyst surface. This step, while maintaining the pores of the molecular sieve, constructs a hydrophobic surface layer, which facilitates the rapid desorption of water generated in the reaction, inhibits the poisoning of active sites by water molecules and the occurrence of side reactions, and simultaneously promotes a positive shift in the dehydration equilibrium, thereby improving the selectivity of salicylnitrile.

[0036] S4. Add boric acid, phosphoric acid, and stearic acid to deionized water, stir, then add modified 3A molecular sieve, stir, heat to dry, dry, and calcine to obtain the catalyst.

[0037] The above steps involve dissolving boric acid, phosphoric acid, and stearic acid in water, adding modified 3A molecular sieve, and stirring and heating to evaporate to dryness. This allows boric acid and phosphoric acid to condense in situ to form boron phosphate. Stearic acid, acting as a pore-forming agent, decomposes during calcination to form a mesoporous structure. Simultaneously, the hydrophobic surface of the modified molecular sieve and the acidic centers of boron phosphate synergistically construct an acid-hydrophobic bifunctional interface. This step achieves uniform loading of the boron phosphate active phase on the molecular sieve support. The introduction of stearic acid optimizes the pore structure. The catalyst obtained after calcination possesses strong Brønsted acid sites (from boron phosphate), strong Lewis acid sites (from ZnO), and a hydrophobic microenvironment. The synergistic effect of these three factors significantly improves the conversion rate of salicylamide and the selectivity of salicylate.

[0038] In some embodiments, in step S1, the ratio of the 3A molecular sieve, the ethanol aqueous solution, and the aminosilane coupling agent is 1g:10-12mL:0.1-0.2g; the volume fraction of the ethanol aqueous solution is 60%-70%. This ratio range ensures uniform monolayer grafting of aminosilane on the surface of the molecular sieve. An ethanol concentration of 60%-70% promotes silane hydrolysis and inhibits its self-condensation. Too little coupling agent will result in insufficient grafting density and fewer anchoring points, while too much will lead to multilayer adsorption or blockage of pores. If the ethanol concentration is too low, the silane will hydrolyze too quickly and easily agglomerate; if it is too high, the hydrolysis will be insufficient and the grafting efficiency will be low.

[0039] In some embodiments, in step S1, the aminosilane coupling agent includes any one or more of aminopropyltriethoxysilane, aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. These aminosilane coupling agents all contain hydrolyzable alkoxy groups (ethoxy or methoxy) and terminal amino groups, which can be covalently grafted onto the surface of the molecular sieve via a condensation reaction. The introduced amino groups can serve as highly efficient coordination anchors for subsequent metal ions, significantly improving the uniformity and stability of the loading of the active component.

[0040] In some embodiments, in step S1, the stirring temperature is 60-70°C and the stirring time is 1-2 hours. This allows the silane to fully react with the hydroxyl groups on the surface of the molecular sieve and avoids excessive self-condensation of the silane due to high temperature; if the temperature is too low or the time is too short, the reaction will be incomplete, while if the temperature is too high or the time is too long, it may damage the molecular sieve structure or trigger side reactions.

[0041] In some embodiments, in step S2, the ratio of NH2-3A, deionized water, and zinc nitrate hexahydrate is 1g:10-20mL:0.2-0.4g. This ratio ensures that zinc ions are fully coordinated and anchored to amino groups without producing free precipitates; too little zinc salt results in insufficient active sites for ZnO, while too much leads to zinc species agglomeration, pore blockage, and coarse grains after calcination.

[0042] In some embodiments, in step S2, the stirring time is 2-3 hours; the settling time is 1-2 hours; the drying temperature is 100°C for 10-12 hours; and the calcination temperature is 380-420°C for 4-6 hours. Stirring for 2-3 hours ensures adsorption equilibrium, and settling for 1-2 hours allows Zn to... 2+ The ZnO crystallizes fully into the vicinity of the pores. It is then dried at 100℃ for 10-12 hours to completely remove physical water. Finally, it is calcined at 380-420℃ for 4-6 hours to ensure complete ZnO crystallization without damaging the molecular sieve framework. If the time is too short or the temperature is too low, the ZnO crystallization will be insufficient. If the time is too long or the temperature is too high, the ZnO crystals will grow and the molecular sieve channels will collapse.

[0043] In some embodiments, in step S3, the ratio of ZnO / NH2-3A, ethanol aqueous solution, and n-octyltriethoxysilane is 1g:10-12mL:0.04-0.06g; the volume fraction of the ethanol aqueous solution is 60%-70%. This ratio allows for controllable grafting of hydrophobic groups, avoiding over-coating; too little silane results in insufficient hydrophobic effect, while too much will form multiple hydrophobic layers that block pores or cover active sites, and deviations in ethanol concentration will lead to uneven grafting.

[0044] In some embodiments, the stirring time in step S3 is 1-2 hours. This is sufficient to allow the hydrophobic silane to be uniformly grafted; if the time is too short, the grafting will be insufficient, and if the time is too long, self-condensation or excessive physical adsorption of silane may occur, making it difficult to elute.

[0045] In some embodiments, in step S4, the ratio of boric acid, phosphoric acid, stearic acid, deionized water, and modified 3A molecular sieve is 20g:37g:1.2-1.4g:130-150mL:12-14g. This ratio achieves optimal matching between the boron phosphate loading and the molecular sieve carrier, with stearic acid introduced in appropriate amounts as a pore-forming agent. Too little phosphoric acid or boric acid results in insufficient active phase, while too much leads to free acid corrosion of the equipment or blockage of the pores. Too little stearic acid results in small pore volume and poor mass transfer, while too much results in excessively thin pore walls and reduced strength after calcination.

[0046] In some embodiments, in step S4, the calcination temperature is 300-400℃ and the time is 6-8 hours. This allows boric acid and phosphoric acid to fully condense to form boron phosphate, while stearic acid is completely decomposed to create pores and the molecular sieve framework remains intact. If the temperature is too low, the boron phosphate crystals incompletely and has low activity; if the temperature is too high, the molecular sieve channels collapse and the specific surface area decreases sharply. If the time is too short, the reaction is insufficient; if the time is too long, energy consumption is high and it may lead to the sintering of the active components.

[0047] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0048] Preparation Example 1 The catalyst in this preparation example is prepared by the following method: S1. Add 1g of 3A molecular sieve to 10mL of 60% ethanol aqueous solution, then add 0.1g of aminopropyltriethoxysilane, stir at 60℃ for 1h, wash, and dry to obtain NH2-3A; S2. Add 1g NH2-3A to 10mL of deionized water, then add 0.2g zinc nitrate hexahydrate, stir for 2h, let stand for 1h, dry at 100℃ for 10h, and calcine at 380℃ for 4h to obtain ZnO / NH2-3A. S3. Add 1g ZnO / NH2-3A to 10mL of 60% ethanol aqueous solution, then add 0.04g n-octyltriethoxysilane, stir for 1h, wash, and dry to obtain modified 3A molecular sieve. S4. Add 20g boric acid, 37g phosphoric acid, and 1.2g stearic acid to 130mL of deionized water, stir, then add 12g modified 3A molecular sieve, stir, heat to dry, dry, and calcine at 300℃ for 6h to obtain the catalyst.

[0049] Preparation Example 2 The catalyst in this preparation example is prepared by the following method: S1. Add 1g of 3A molecular sieve to 11mL of 65% ethanol aqueous solution, then add 0.15g of aminopropyltriethoxysilane, stir at 65℃ for 1.5h, wash, and dry to obtain NH2-3A. S2. Add 1g of NH2-3A to 15mL of deionized water, then add 0.3g of zinc nitrate hexahydrate, stir for 2.5h, let stand for 1.5h, dry at 100℃ for 11h, and calcine at 400℃ for 5h to obtain ZnO / NH2-3A. S3. Add 1g ZnO / NH2-3A to 11mL of 65% ethanol aqueous solution, then add 0.05g n-octyltriethoxysilane, stir for 1.5h, wash, and dry to obtain modified 3A molecular sieve. S4. Add 20g boric acid, 37g phosphoric acid, and 1.3g stearic acid to 140mL of deionized water, stir, then add 13g modified 3A molecular sieve, stir, heat to dry, dry, and calcine at 350℃ for 7h to obtain the catalyst.

[0050] Preparation Example 3 The catalyst in this preparation example is prepared by the following method: S1. Add 1g of 3A molecular sieve to 12mL of 70% ethanol aqueous solution, then add 0.2g of aminopropyltriethoxysilane, stir at 70℃ for 2h, wash, and dry to obtain NH2-3A; S2. Add 1g of NH2-3A to 20mL of deionized water, then add 0.4g of zinc nitrate hexahydrate, stir for 3h, let stand for 2h, dry at 100℃ for 12h, and calcine at 420℃ for 6h to obtain ZnO / NH2-3A. S3. Add 1g ZnO / NH2-3A to 12mL of 70% ethanol aqueous solution, then add 0.06g n-octyltriethoxysilane, stir for 2h, wash, and dry to obtain modified 3A molecular sieve. S4. Add 20g boric acid, 37g phosphoric acid, and 1.4g stearic acid to 150mL of deionized water, stir, then add 14g modified 3A molecular sieve, stir, heat to dry, dry, and calcine at 400℃ for 8h to obtain the catalyst.

[0051] Compare with Example 1 The only difference between this comparative example and preparation example 1 is that step S3 is omitted. Specifically: S1. Add 1g of 3A molecular sieve to 10mL of 60% ethanol aqueous solution, then add 0.1g of aminopropyltriethoxysilane, stir at 60℃ for 1h, wash, and dry to obtain NH2-3A; S2. Add 1g NH2-3A to 10mL of deionized water, then add 0.2g zinc nitrate hexahydrate, stir for 2h, let stand for 1h, dry at 100℃ for 10h, and calcine at 380℃ for 4h to obtain ZnO / NH2-3A. S4. Add 20g boric acid, 37g phosphoric acid, and 1.2g stearic acid to 130mL of deionized water, stir, then add 12g ZnO / NH2-3A, stir, heat to dry, dry, and calcine at 300℃ for 6h to obtain the catalyst.

[0052] Compare with Example 2 The only difference between this comparative example and preparation example 1 is that step S1 is omitted. Specifically: S2. Add 1g of 3A molecular sieve to 10mL of deionized water, then add 0.2g of zinc nitrate hexahydrate, stir for 2h, let stand for 1h, dry at 100℃ for 10h, and calcine at 380℃ for 4h to obtain ZnO / 3A. S3. Add 1g ZnO / 3A to 10mL of 60% ethanol aqueous solution, then add 0.04g n-octyltriethoxysilane, stir for 1h, wash, and dry to obtain modified 3A molecular sieve. S4. Add 20g boric acid, 37g phosphoric acid, and 1.2g stearic acid to 130mL of deionized water, stir, then add 12g modified 3A molecular sieve, stir, heat to dry, dry, and calcine at 300℃ for 6h to obtain the catalyst.

[0053] Compare with Example 3 The only difference between this comparative example and preparation example 1 is that steps S3 and S2 are omitted. Specifically: S1. Add 1g of 3A molecular sieve to 10mL of 60% ethanol aqueous solution, then add 0.1g of aminopropyltriethoxysilane, stir at 60℃ for 1h, wash, and dry to obtain NH2-3A; S4. Add 20g boric acid, 37g phosphoric acid, and 1.2g stearic acid to 130mL of deionized water, stir, then add 12g NH2-3A, stir, heat to dry, dry, and calcine at 300℃ for 6h to obtain the catalyst.

[0054] Compare with Example 4 This comparative example directly uses 3A molecular sieve, specifically: 20g boric acid, 37g phosphoric acid, and 1.2g stearic acid were added to 130mL of deionized water and stirred. Then, 12g of 3A molecular sieve was added, stirred, heated, evaporated to dryness, dried, and calcined at 300℃ for 6h to obtain the catalyst.

[0055] Example 1 This embodiment provides a method for preparing salicylnitrile from salicylamide, including the following steps: 10 mL of the catalyst obtained in Preparation Example 1 was packed into a fixed-bed reactor, and ammonia gas was introduced to preheat the reactor to 360°C. A 0.1 g / mL salicylamide solution in p-xylene and ammonia gas, preheated to 150°C, were then introduced into the fixed-bed reactor, and the liquid hourly space velocity (LHSV) of the reaction was controlled at 0.2 h⁻¹. -1 The reaction was carried out at 360°C with a molar ratio of ammonia to salicylamide of 20:1. The effluent was collected after cooling to obtain salicylnitrile.

[0056] Example 2 This embodiment provides a method for preparing salicylnitrile from salicylamide, including the following steps: 10 mL of the catalyst obtained in Preparation Example 1 was packed into a fixed-bed reactor and preheated to 370°C by introducing ammonia gas. A 0.1 g / mL solution of salicylamide in p-xylene and ammonia gas, preheated to 150°C, were then introduced into the fixed-bed reactor, and the liquid hourly space velocity (LHSV) of the reaction was controlled at 0.3 h⁻¹. -1 The reaction was carried out at 370°C with a molar ratio of ammonia to salicylamide of 30:1. The effluent was collected after cooling to obtain salicylonitrile.

[0057] Example 3 This embodiment provides a method for preparing salicylnitrile from salicylamide, including the following steps: 10 mL of the catalyst obtained in Preparation Example 1 was packed into a fixed-bed reactor, and ammonia gas was introduced to preheat the reactor to 380°C. A 0.1 g / mL solution of salicylamide in p-xylene and ammonia gas were preheated to 150°C and then introduced into the fixed-bed reactor, with the liquid hourly space velocity (LHSV) controlled at 0.5 h⁻¹. -1 The reaction was carried out at 380°C with a molar ratio of ammonia to salicylamide of 40:1. The effluent was collected after cooling to obtain salicylnitrile.

[0058] Example 4 The only difference between this embodiment and Example 3 is that the catalyst obtained in Example 1 is replaced with an equal amount of the catalyst obtained in Example 2.

[0059] Example 5 The only difference between this embodiment and Example 3 is that the catalyst obtained in Example 1 is replaced with an equal amount of the catalyst obtained in Example 3.

[0060] Comparative Example 1 The only difference between this comparative example and Example 1 is that the catalyst obtained in Preparation Example 1 was replaced with an equal amount of the catalyst obtained in Control Example 1.

[0061] Comparative Example 2 The only difference between this comparative example and Example 1 is that the catalyst obtained in Preparation Example 1 was replaced with an equal amount of the catalyst obtained in Control Example 2.

[0062] Comparative Example 3 The only difference between this comparative example and Example 1 is that the catalyst obtained in Preparation Example 1 was replaced with an equal amount of the catalyst obtained in Control Example 3.

[0063] Comparative Example 4 The only difference between this comparative example and Example 1 is that the catalyst obtained in Preparation Example 1 was replaced with an equal amount of the catalyst obtained in Control Example 4.

[0064] The conversion rates of salicylamide and the selectivity of salicylate in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1 below: Table 1

[0065] As can be seen from the experimental results in Table 1, the catalysts of the embodiments of the present invention exhibit high conversion rates and selectivity in the dehydration of salicylamide to prepare salicylnitrile in a fixed-bed reactor, and their performance is stable. Compared with the embodiments, the catalytic performance of each comparative example is significantly reduced: Comparative example 1, lacking hydrophobic modification, shows a decrease in both conversion rate and selectivity, indicating that the hydrophobic surface layer plays an important role in suppressing side reactions and promoting water desorption; Comparative example 2, lacking amino grafting, further decreases in conversion rate and selectivity due to the inability of ZnO to be uniformly anchored, resulting in fewer active sites; Comparative example 3, retaining only amino grafting but lacking ZnO loading and hydrophobic modification, has a severe shortage of active centers and poor catalytic performance; Comparative example 4, using unmodified molecular sieve directly, has almost no catalytic activity and the worst performance. The above results indicate that the present invention significantly improves the catalytic performance of the catalyst through a multi-step synergistic modification strategy of amino grafting, ZnO loading, hydrophobic modification, and boron phosphate composite, and each step is indispensable.

[0066] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing salicylamide from salicylnitrile, characterized in that, Includes the following steps: The catalyst was packed into a fixed-bed reactor and preheated to the reaction temperature by ammonia gas. A solution of salicylamide in p-xylene and ammonia gas was preheated and then introduced into the fixed-bed reactor to carry out the reaction at the reaction temperature. The reaction effluent was collected after cooling to obtain salicylnitrile.

2. The method for preparing salicylnitrile from salicylamide as described in claim 1, characterized in that, The concentration of the salicylamide in the p-xylene solution is 0.08-0.12 g / mL.

3. The method for preparing salicylnitrile from salicylamide as described in claim 1, characterized in that, The temperature at which the salicylamide solution and ammonia are preheated is 150°C.

4. The method for preparing salicylnitrile from salicylamide as described in claim 1, characterized in that, The molar ratio of ammonia to salicylamide is (20-40):

1.

5. The method for preparing salicylnitrile from salicylamide as described in claim 1, characterized in that, The specific parameters for the reaction at the specified reaction temperature are: reaction temperature 360-380℃, and liquid hourly space velocity (LISH) 0.2-0.5 h⁻¹. -1 .

6. The method for preparing salicylnitrile from salicylamide as described in claim 1, characterized in that, The catalyst is prepared by: S1. Add 3A molecular sieve to an ethanol aqueous solution, then add aminosilane coupling agent, stir, wash, and dry to obtain NH2-3A; S2. Add NH2-3A to deionized water, then add zinc nitrate hexahydrate, stir, let stand, dry, and calcine to obtain ZnO / NH2-3A; S3. Add ZnO / NH2-3A to an aqueous ethanol solution, then add n-octyltriethoxysilane, stir, wash, and dry to obtain modified 3A molecular sieve; S4. Add boric acid, phosphoric acid, and stearic acid to deionized water, stir, then add modified 3A molecular sieve, stir, heat to dry, dry, and calcine to obtain the catalyst.

7. The method for preparing salicylnitrile from salicylamide as described in claim 6, characterized in that, In step S1, the ratio of the 3A molecular sieve, the ethanol aqueous solution, and the aminosilane coupling agent is 1g:10-12mL:0.1-0.2g; the volume fraction of the ethanol aqueous solution is 60%-70%. In step S1, the aminosilane coupling agent includes any one or more of aminopropyltriethoxysilane, aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. In step S1, the stirring temperature is 60-70℃ and the stirring time is 1-2 hours.

8. The method for preparing salicylnitrile from salicylamide as described in claim 6, characterized in that, In step S2, the ratio of NH2-3A, deionized water, and zinc nitrate hexahydrate is 1g: 10-20mL: 0.2-0.4g; In step S2, the stirring time is 2-3 hours; the standing time is 1-2 hours; the drying temperature is 100°C and the time is 10-12 hours; the calcination temperature is 380-420°C and the time is 4-6 hours.

9. The method for preparing salicylnitrile from salicylamide as described in claim 6, characterized in that, In step S3, the ratio of ZnO / NH2-3A, ethanol aqueous solution, and n-octyltriethoxysilane is 1g:10-12mL:0.04-0.06g; the volume fraction of the ethanol aqueous solution is 60%-70%. In step S3, the stirring time is 1-2 hours.

10. The method for preparing salicylnitrile from salicylamide as described in claim 6, characterized in that, In step S4, the ratio of boric acid, phosphoric acid, stearic acid, deionized water, and modified 3A molecular sieve is 20g:37g:1.2-1.4g:130-150mL:12-14g; In step S4, the calcination temperature is 300-400℃ and the time is 6-8h.

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