Preparation process of 2-hydroxy-benzonitril

Abstract

The invention discloses a preparation process of 2-hydroxy-benzonitrile, which belongs to the field of organic chemical industry, and comprises the following steps: dissolving salicylamide in a solvent to obtain a salicylamide solution, introducing the salicylamide solution into a continuous reactor together with ammonia gas, reacting at 350-400 DEG C at the reaction space velocity of 0.1-1.5 h <-1 >, cooling effluent steam, collecting, filtering, and recrystallizing with toluene to obtain the 2-hydroxy-benzonitrile, the continuous reactor is filled with a modified alpha-ZrP-based catalyst. According to the method, the modified alpha-ZrP-based catalyst is taken as a core, and the continuous reaction and the ammonia atmosphere are combined, so that high-efficiency and environment-friendly dehydration of salicylamide is realized to prepare the 2-hydroxy-benzonitrile.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic chemical industry, in particular to a preparation process of salicylonitrile. BACKGROUND

[0002] Salicylonitrile is an important organic chemical intermediate, which is widely used in the fields of medicine, pesticide, dye and polymer material. For example, it is a key precursor for the synthesis of some antibiotics, herbicides and liquid crystal compounds.

[0003] At present, the synthesis process routes of salicylonitrile mainly include the following: dehydration method taking salicylaldehyde oxime as raw material, direct catalysis method taking ammonium salt of salicylic acid as raw material, and catalytic dehydration method taking salicylamide as raw material. Among them, the catalytic dehydration path taking salicylamide as raw material is considered to have good industrialization potential because of its clear reaction route and relatively simple process flow. However, the dehydrating agent used in the current salicylamide catalytic dehydration method is generally phosgene, thionyl chloride and the like, which is not only expensive and highly toxic but also easy to pollute the environment.

[0004] In addition to dehydration by dehydrating agent, solid catalyst can also be used. The solid catalyst is in different phase with salicylamide, and the separation operation is easy and can be recycled. However, the existing catalytic process for preparing salicylonitrile by dehydration of salicylamide still has some problems, such as insufficient activity and selectivity of the catalyst. Dehydration reaction is essentially a process of acid and base site cooperative catalysis. Single type of active site is difficult to simultaneously activate the carbonyl group and N-H bond of amide group efficiently, resulting in that the reaction conversion rate and selectivity are difficult to be considered together, and the by-products increase. In addition, the dehydration reaction of salicylamide is usually carried out in an organic solvent. If the surface of the catalyst is hydrophilic, it is difficult to disperse well in the reaction medium, and it also hinders the diffusion of hydrophobic reactant molecules to the active sites inside the catalyst. This mass transfer limitation will significantly reduce the reaction rate.

[0005] Therefore, it is necessary to develop a new type of heterogeneous catalyst with high efficiency, high selectivity, good stability and strong adaptability to reaction system, and a matching process. SUMMARY

[0006] The present application aims to provide a preparation process of salicylonitrile, and to develop a preparation process of salicylonitrile with simple operation and high amide conversion rate.

[0007] The present application provides a preparation process of salicylonitrile, which comprises the following steps: The salicylamide is dissolved in a solvent to obtain a salicylamide solution, which is introduced into a continuous reactor together with ammonia gas, and the reaction is carried out at 350-400℃, with a space velocity of 0.1-1.5h -1 After cooling, the effluent gas is collected and filtered, and recrystallized with toluene to obtain salicylonitrile. The continuous reactor is filled with a modified α-ZrP-based catalyst.

[0008] By employing the above-mentioned technical solution, using a modified α-ZrP-based catalyst as the core, and combining continuous reaction with an ammonia-inert atmosphere, a highly efficient and environmentally friendly dehydration process to prepare salicylnitrile from salicylamide was achieved. α-ZrP, as a natural layered inorganic material, possesses a regular layered structure and abundant surface hydroxyl groups, exhibiting not only good chemical and thermal stability, but also providing a structural basis for subsequent modification through its interlayer exchangeable sites. Organic amine intercalation modification of α-ZrP not only disrupts strong interlayer hydrogen bonds, expanding the interlayer distance and increasing the specific surface area, thus exposing more active sites, but also alters the surface hydrophilicity of α-ZrP by utilizing the hydrophobic long chains in the organic amine molecule, enabling it to form good compatibility with hydrophobic reaction solvents, preventing catalyst aggregation, and eliminating mass transfer barriers for reactant molecules to diffuse to active sites. More importantly, quaternary ammonium groups in the organic amine molecule can provide weakly basic sites, which can extract hydrogen protons from the NH bonds in the salicylamide molecule, creating conditions for subsequent dehydration reactions. Then, zinc ions are loaded. Zinc ions can form stable coordination bonds with hydroxyl groups on the surface of α-ZrP and be uniformly dispersed on the surface and between layers of the support, forming a high density of weak Lewis acid active sites. These sites can activate the carbonyl group in the salicylamide molecule and reduce the activation energy of the dehydration reaction. At this time, the catalyst forms a synergistic system of weak Lewis acid sites, weak basic sites and surface hydroxyl groups. The weak basic sites provided by the organic amine extract NH hydrogen, zinc ions activate the carbonyl group, and surface hydroxyl groups assist in proton transfer. The three work together to efficiently break the NH bond and remove water molecules, ultimately converting the amide group into a cyano group.

[0009] Meanwhile, the use of a continuous reactor enables the continuous feeding of salicylamide solution, the integration of catalytic reaction and product separation, and the catalyst is fixedly packed in the reactor, eliminating the need for repeated separation and recovery, making operation simpler. The introduced ammonia gas serves two purposes: firstly, it acts as an inert protective atmosphere to suppress the oxidation side reaction of salicylamide at high temperatures; secondly, it can promptly remove the water molecules generated in the reaction, detach them from the reaction system, and promote the positive shift of the dehydration equilibrium, further improving the conversion rate of salicylamide. Moreover, the acetonitrile solvent has good compatibility with the reaction solvent and will not introduce new impurities.

[0010] Preferably, the catalyst is prepared by the following method: S1. Dissolve ZrOCl2·8H2O in phosphoric acid solution, stir well and add to the reaction vessel. Heat at 180-200℃ for 20-24h, centrifuge, wash and dry to obtain α-ZrP; S2. Dissolve α-ZrP and organic amine in phosphoric acid solution, stir evenly, add to reaction vessel, heat at 180-200℃ for 20-24h, centrifuge, wash, and dry to obtain organic amine intercalated α-ZrP; S3. Disperse the organic amine intercalated α-ZrP in a mixed solvent of ethanol and water, add zinc acetate, and react at 60-80℃ for 4-8 hours. Centrifuge, wash, and dry to obtain the final product.

[0011] Preferably, in step S1, the ratio of ZrOCl2·8H2O to phosphoric acid solution is 1g: (8-12)mL.

[0012] Preferably, the concentration of the phosphoric acid solution is 3M.

[0013] Preferably, in step S2, the molar ratio of α-ZrP to organic amine is 1:(0.03 to 0.1).

[0014] Preferably, in step S2, the organic amine includes hexadecyltrimethylammonium bromide and tetrabutylammonium hydroxide.

[0015] Preferably, in step S3, the mass ratio of organic amine intercalated α-ZrP to zinc acetate is 1:(0.1~0.5).

[0016] Preferably, the concentration of the salicylamide solution is 0.05–0.3 g / mL.

[0017] Preferably, the molar ratio of ammonia to salicylamide is 1:(0.1-20).

[0018] Preferably, the solvent includes one or a mixture of several of toluene, mesitylene, and dioxane.

[0019] Preferably, the continuous reactor includes a fixed-bed reactor and a fluidized-bed reactor.

[0020] The beneficial effects of this invention are: 1. This invention abandons the highly toxic and polluting dehydrating agents such as phosgene and thionyl chloride used in traditional processes, and uses a heterogeneous modified α-ZrP-based catalyst to achieve catalytic dehydration. The catalyst can be recycled and regenerated. Ammonia gas is introduced during the reaction, which can not only inhibit the oxidation side reaction of salicylamide, but also remove the water molecules generated in the reaction in time, and promote the positive shift of the dehydration equilibrium.

[0021] 2. This invention employs a dual modification of α-ZrP through organic amine intercalation and zinc ion loading to construct a catalytic system characterized by interlayer confinement and acid-base synergy. Specifically, organic amine intercalation disrupts the interlayer hydrogen bonds of α-ZrP, expanding the interlayer distance and specific surface area, significantly increasing the exposure of active sites. Zinc ions are stably loaded onto the hydroxyl groups of α-ZrP through coordination, forming a high-density Lewis acid sites that can efficiently activate the carbonyl groups of amide groups and lower the activation energy of the reaction. The surface hydroxyl groups of α-ZrP itself provide weakly acidic sites, which synergistically work with the Lewis acid sites to achieve selective NH bond cleavage, avoiding side reactions caused by a single active site.

[0022] 3. The introduction of hydrophobic groups into the surface and interlayer of α-ZrP by organic amine intercalating agents enhances its hydrophobicity and forms good compatibility with hydrophobic solvents such as toluene and mesitylene, thus avoiding catalyst aggregation. At the same time, the expanded interlayer spacing provides unobstructed diffusion channels for reactant / product molecules, solving the mass transfer limitation problem of traditional hydrophilic catalysts. Detailed Implementation

[0023] 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.

[0024] A process for preparing salicylnitrile includes the following steps: Salicylic amide was dissolved in a solvent to obtain a salicylic amide solution, which was then introduced into a continuous reactor along with ammonia gas. The reaction was carried out at 350–400°C with a reaction space velocity of 0.1–1.5 h⁻¹. -1 The outflowing vapor is collected and filtered after cooling, and then recrystallized with toluene to obtain the final product. The continuous reactor is filled with a modified α-ZrP-based catalyst.

[0025] By employing the above-mentioned technical solution, using a modified α-ZrP-based catalyst as the core, and combining continuous reaction with an ammonia-inert atmosphere, a highly efficient and environmentally friendly dehydration process to prepare salicylnitrile from salicylamide was achieved. α-ZrP, as a natural layered inorganic material, possesses a regular layered structure and abundant surface hydroxyl groups, exhibiting not only good chemical and thermal stability, but also providing a structural basis for subsequent modification through its interlayer exchangeable sites. Organic amine intercalation modification of α-ZrP not only disrupts strong interlayer hydrogen bonds, expanding the interlayer distance and increasing the specific surface area, thus exposing more active sites, but also alters the surface hydrophilicity of α-ZrP by utilizing the hydrophobic long chains in the organic amine molecule, enabling it to form good compatibility with hydrophobic reaction solvents, preventing catalyst aggregation, and eliminating mass transfer barriers for reactant molecules to diffuse to active sites. More importantly, quaternary ammonium groups in the organic amine molecule can provide weakly basic sites, which can extract hydrogen protons from the NH bonds in the salicylamide molecule, creating conditions for subsequent dehydration reactions. Then, zinc ions are loaded. Zinc ions can form stable coordination bonds with hydroxyl groups on the surface of α-ZrP and be uniformly dispersed on the surface and between layers of the support, forming a high density of weak Lewis acid active sites. These sites can activate the carbonyl group in the salicylamide molecule and reduce the activation energy of the dehydration reaction. At this time, the catalyst forms a synergistic system of weak Lewis acid sites, weak basic sites and surface hydroxyl groups. The weak basic sites provided by the organic amine extract NH hydrogen, zinc ions activate the carbonyl group, and surface hydroxyl groups assist in proton transfer. The three work together to efficiently break the NH bond and remove water molecules, ultimately converting the amide group into a cyano group.

[0026] Meanwhile, the use of a continuous reactor can realize the continuous feeding of salicylamide solution, the catalytic reaction and product separation in one integrated manner, and the catalyst is fixedly filled in the reactor, eliminating the need for repeated separation and recovery, making the operation simpler; the introduced ammonia gas can serve as an inert gas protective atmosphere to suppress the oxidation side reaction of salicylamide at high temperature, and can also promptly remove the water molecules generated in the reaction, remove them from the reaction system, promote the positive shift of the dehydration equilibrium, and further improve the conversion rate of salicylamide.

[0027] In some embodiments, the catalyst is prepared by the following method: S1. Dissolve ZrOCl2·8H2O in phosphoric acid solution, stir well and add to the reaction vessel. Heat at 180-200℃ for 20-24h, centrifuge, wash and dry to obtain α-ZrP; S2. Dissolve α-ZrP and organic amine in phosphoric acid solution, stir evenly, add to reaction vessel, heat at 180-200℃ for 20-24h, centrifuge, wash, and dry to obtain organic amine intercalated α-ZrP; S3. Disperse the organic amine intercalated α-ZrP in a mixed solvent of ethanol and water, add zinc acetate, and react at 60-80℃ for 4-8 hours. Centrifuge, wash, and dry to obtain the final product.

[0028] By adopting the above technical solution, step S1 involves preparing α-ZrP layered support via a hydrothermal method, with excess phosphoric acid ensuring the Zr content is maintained. 4+ Complete conversion avoids impurity generation; Step S2 expands the α-ZrP interlayer spacing and improves hydrophobicity through organic amine intercalation, while the basicity of organic amine can extract NH protons, which is beneficial to the dehydration process of salicylamide. In addition, organic amine has high thermal stability and can remain stable at the dehydration reaction temperature; Step S3 achieves uniform loading of zinc ions through ethanol dispersion and heating, forming stable Lewis acid active sites, thereby enabling the large-scale preparation of high-performance catalysts.

[0029] In some embodiments, in step S1, the ratio of ZrOCl2·8H2O to phosphoric acid solution is 1 g: (8-12) mL; the concentration of phosphoric acid solution is 3M; the 3M phosphoric acid solution not only serves as a phosphorus source but also provides an acidic environment to inhibit Zr. 4+ Hydrolysis, with a dosage ratio of 1g:(8-12)mL, can ensure the generation of pure-phase α-ZrP, avoiding the blockage of α-ZrP channels and the shadow intercalation effect caused by too much or too little.

[0030] In some embodiments, in step S2, the molar ratio of α-ZrP to organic amine is 1:(0.03~0.1). When organic amine is used as an intercalating agent, its dosage directly affects the interlayer spacing and hydrophobicity of α-ZrP. When the molar ratio is less than 0.03, the organic amine intercalation is insufficient, the interlayer spacing is limited, the improvement in hydrophobicity is not obvious, and the mass transfer efficiency is low. When the molar ratio is greater than 0.1, the excess organic amine will aggregate on the surface of α-ZrP, block the pores, and cause the active sites to be covered, resulting in a decrease in selectivity.

[0031] In some embodiments, in step S2, the organic amine includes hexadecyltrimethylammonium bromide and tetrabutylammonium hydroxide. The long-chain alkyl group of hexadecyltrimethylammonium bromide can significantly improve the hydrophobicity of the α-ZrP surface, and the quaternary ammonium group has a strong electrostatic interaction with the interlayer anions of α-ZrP, resulting in high intercalation stability. The short-chain quaternary ammonium group of tetrabutylammonium hydroxide has moderate steric hindrance, so it will not block the pores after intercalation, and the ammonium hydroxide group can form hydrogen bonds with the hydroxyl groups on the α-ZrP surface, further stabilizing the intercalation structure. Both organic amines can effectively disrupt the interlayer hydrogen bonds of α-ZrP, expand the interlayer spacing, and are widely available and inexpensive, making them suitable for industrial applications.

[0032] In some embodiments, in step S3, the mass ratio of organic amine intercalated α-ZrP to zinc acetate is 1:(0.1–0.5). Zinc acetate serves as the zinc source, achieving loading through the coordination of zinc ions with hydroxyl groups on the α-ZrP surface, forming Lewis acid active sites. When the mass ratio is below 0.1, the zinc ion loading is insufficient, resulting in few active sites and low salicylamide conversion. When the mass ratio is above 0.5, excessive zinc ions aggregate to form ZnO particles, leading to excessively strong Lewis acid, which triggers the hydrolysis of salicylamide to generate phenolic byproducts, reducing selectivity. A mass ratio of 1:(0.1–0.5) allows zinc ions to exist in a monodisperse state on the α-ZrP surface, forming Lewis acid sites of moderate strength, ensuring high activity and high selectivity.

[0033] In some embodiments, the concentration of the salicylamide solution is 0.05–0.3 g / mL; when the concentration is too low, the salicylamide content per unit volume of solution is low, resulting in low production efficiency and difficulty in achieving a space velocity of 0.1 h⁻¹. -1 The above points are relevant; when the concentration is too high, salicylamide will not dissolve fully in the solvent, and solids will easily precipitate out and block the reactor pipeline, causing fluctuations in reaction pressure and affecting the stability of continuous operation.

[0034] In some embodiments, the molar ratio of ammonia to salicylamide is 1:(0.1–20). Ammonia not only inhibits the oxidation side reaction of salicylamide but also promptly removes water molecules generated in the reaction, allowing them to leave the reaction system and promoting a forward shift in the dehydration equilibrium. When the molar ratio is below 0.1, there is insufficient ammonia, resulting in an inadequate forward shift of the dehydration equilibrium; when the molar ratio is above 20, excess ammonia may clog the catalyst, causing a decrease in mass transfer efficiency and a slowdown in the reaction rate.

[0035] In some embodiments, the solvent includes one or a mixture of toluene, mesitylene, and dioxane. Toluene is highly hydrophobic, which is compatible with the hydrophobicity of the modified α-ZrP catalyst, resulting in high mass transfer efficiency. It also has a moderate boiling point, facilitating subsequent separation. Mesitylene has a high boiling point and is less volatile under reaction conditions of 350–400°C, reducing solvent loss and making it suitable for long-term continuous operation. Dioxane has moderate polarity, which can improve the solubility of salicylamide. When used in combination with toluene or mesitylene, it can adjust the solubility and viscosity of the solution, further optimizing mass transfer efficiency. All three solvents are commonly used organic solvents, widely available, and low in toxicity, meeting the requirements of green chemistry.

[0036] In some embodiments, the continuous reactor includes a fixed-bed reactor and a fluidized-bed reactor. The fixed-bed reactor has a simple structure and is easy to operate. The catalyst is filled in the bed, and the reactant solution flows from top to bottom through the catalyst bed to react. The product flows out continuously, which is suitable for large-scale continuous production. Moreover, the catalyst wear is small and the service life is long. In the fluidized-bed reactor, the catalyst particles are fluidized under the combined action of gas and liquid, which allows for more complete contact with the reactants and higher mass transfer efficiency. It is suitable for high-space-velocity operation and can further improve production efficiency.

[0037] 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.

[0038] Preparation Example

[0039] Preparation Example 1: A modified α-ZrP-based catalyst was obtained by the following preparation method: S1. Dissolve 1g ZrOCl2·8H2O in 10mL of 3M phosphoric acid solution, stir well and add to the reaction vessel. Heat at 200℃ for 20h, centrifuge, wash until pH value is 7, and vacuum dry at 80℃ to obtain α-ZrP. S2. Dissolve 1g of α-ZrP and tetrabutylammonium hydroxide in 10mL of 3M phosphoric acid solution, stir well, and then add to a reaction vessel. Heat at 200℃ for 20h, centrifuge, wash until pH is 7, and dry at 80℃ to obtain organic amine intercalated α-ZrP; wherein the molar ratio of α-ZrP to tetrabutylammonium hydroxide is 1:0.05. S3. Disperse 1g of organic amine intercalated α-ZrP in a mixed solvent of ethanol and water, add 0.15g of zinc acetate, react at 80℃ for 5h, centrifuge, wash with ethanol 5 times, and dry at 60℃ to obtain a modified α-ZrP-based catalyst.

[0040] Preparation Example 2, a modified α-ZrP-based catalyst, differs from Preparation Example 1 only in that hexadecyltrimethylammonium bromide is used instead of tetrabutylammonium hydroxide, wherein the molar ratio of α-ZrP to hexadecyltrimethylammonium bromide is 1:0.05.

[0041] Preparation Example 3: A modified α-ZrP-based catalyst was obtained by the following preparation method: S1. Dissolve 1g ZrOCl2·8H2O in 10mL of 3M phosphoric acid solution, stir well and add to the reaction vessel. Heat at 200℃ for 20h, centrifuge, wash until pH value is 7, and vacuum dry at 80℃ to obtain α-ZrP. S3. Disperse 1g of α-ZrP in a mixed solvent of ethanol and water with a volume ratio of 1:1, add 0.15g of zinc acetate, react at 80℃ for 5h, centrifuge, wash with ethanol 5 times, and dry at 60℃ to obtain a modified α-ZrP-based catalyst.

[0042] Preparation Example 4: A modified α-ZrP-based catalyst was obtained by the following preparation method: S1. Dissolve 1g ZrOCl2·8H2O in 10mL of 3M phosphoric acid solution, stir well and add to the reaction vessel. Heat at 200℃ for 20h, centrifuge, wash until pH value is 7, and vacuum dry at 80℃ to obtain α-ZrP. S2. Dissolve 1g of α-ZrP and tetrabutylammonium hydroxide in 10mL of 3M phosphoric acid solution, stir well and add to the reaction vessel, heat at 200℃ for 20h, centrifuge, wash until pH value is 7, dry at 80℃ to obtain organic amine intercalated α-ZrP; wherein the molar ratio of α-ZrP to tetrabutylammonium hydroxide is 1:0.05.

[0043] Example

[0044] Example 1: A preparation process for salicylnitrile, comprising the following steps: 10 mL of the modified α-ZrP-based catalyst prepared in Preparation Example 1 was loaded into a fixed-bed reactor and preheated to 350 °C. A toluene solution of salicylamide with a concentration of 0.12 g / mL was preheated to 100 °C and then introduced into the reactor. The reaction space velocity of the reaction solution was 0.5 h⁻¹. -1The molar ratio of ammonia to salicylamide was 15, and the reaction was carried out at 350°C. The outflowing vapor was collected after cooling and filtered, and recrystallized with toluene to obtain a salicylic nitrile. The conversion rate of salicylamide was 98%, and the selectivity of salicylic nitrile was 98%.

[0045] Example 2, a preparation process for salicylanilide, differs from Example 1 only in that the modified α-ZrP-based catalyst prepared in Example 2 is used instead of the modified α-ZrP-based catalyst in Example 1. The conversion rate of salicylamide was 98% and the selectivity of salicylanilide was 95%.

[0046] Comparative Example

[0047] Comparative Example 1, a preparation process for salicylanilide, differs from Example 1 only in that the modified α-ZrP-based catalyst prepared in Example 3 is used instead of the modified α-ZrP-based catalyst in Example 1. The conversion rate of salicylamide was 67% and the selectivity of salicylanilide was 78%.

[0048] Comparative Example 2, a preparation process for salicylanilide, differs from Example 1 only in that the modified α-ZrP-based catalyst prepared in Example 4 is used instead of the modified α-ZrP-based catalyst in Example 1. The conversion rate of salicylamide was 63% and the selectivity of salicylanilide was 72%.

[0049] Comparative Example 3, a preparation process for salicylaniline, differs from Example 1 only in that ammonia gas is not introduced. The conversion rate of salicylamide was tested to be 89%, and the selectivity of salicylaniline was 91%.

[0050] A comparison of Example 1 and Comparative Example 1 shows that without intercalation modification of α-ZrP, the catalyst layers are relatively compact, resulting in a small specific surface area. This leads to insufficient exposure of active sites and a lack of weakly basic sites provided by organic amines, preventing synergistic interaction with the Lewis acid sites of zinc ions. Furthermore, the strong hydrophilicity of the surface results in poor compatibility with hydrophobic solvents, hindering mass transfer and reducing the conversion and selectivity of salicylamide. A comparison of Example 1 and Comparative Example 2 shows that without zinc ion loading, the catalyst only possesses weakly basic sites provided by organic amines and hydroxyl groups on the α-ZrP surface. The lack of Lewis acid sites to activate the carbonyl group in the salicylamide molecule means it lacks the synergistic dehydration process of carbonyl activation, NH4+ extraction, and proton transfer, making the reaction difficult to proceed efficiently. A comparison of Example 1 and Comparative Example 3 shows that without ammonia gas, salicylamide undergoes a slight oxidation side reaction at 350°C, leading to a decrease in the selectivity of salicylnitrile. On the other hand, the generated water molecules cannot leave the reaction system in time, resulting in insufficient forward shift of the dehydration equilibrium and a decrease in the conversion rate of salicylamide.

[0051] 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 process for the preparation of salicylonitrile, characterized in that, The method comprises the following steps: The salicylamide is dissolved in a solvent to obtain a salicylamide solution, which is introduced into a continuous reactor together with ammonia gas and reacted at 350-400°C at a space velocity of 0.1-1.5h -1 The effluent gas is collected after cooling, filtered and recrystallized from toluene to obtain the product. The continuous reactor is filled with a modified alpha-ZrP-based catalyst.

2. A process for the preparation of salicylanilide according to claim 1, characterized in that, The catalyst is prepared by the following method: S1, dissolving ZrOCl2·8H2O in a phosphoric acid solution, stirring uniformly, and then adding into a reaction kettle, heating at 180-200℃ for 20-24h, centrifuging, washing, and drying to obtain alpha-ZrP; S2, dissolving alpha-ZrP and an organic amine in a phosphoric acid solution, stirring uniformly, and then adding into a reaction kettle, heating at 180-200℃ for 20-24h, centrifuging, washing, and drying to obtain an organic amine intercalated alpha-ZrP; S3, dispersing the organic amine intercalated alpha-ZrP into a mixed solvent of ethanol and water, adding zinc acetate, and reacting at 60-80℃ for 4-8h, centrifuging, washing, and drying to obtain the catalyst.

3. A process for the preparation of salicylanilide according to claim 2, characterized in that, In step S1, the amount ratio of ZrOCl2·8H2O to the phosphoric acid solution is 1g:(8-12)mL.

4. The process for the preparation of salicylanilide according to claim 2, characterized in that, In step S2, the molar ratio of alpha-ZrP to the organic amine is 1:(0.03-0.1).

5. The process for the preparation of salicylanilide according to claim 2, characterized in that, In step S2, the organic amine includes cetyltrimethylammonium bromide and tetrabutylammonium hydroxide.

6. The process for the preparation of salicylanilide according to claim 2, wherein, In step S3, the mass ratio of the organic amine intercalated alpha-ZrP to zinc acetate is 1:(0.1-0.5).

7. The process for the preparation of salicylanilide according to claim 1, characterized in that, The concentration of the salicylamide solution is 0.05-0.3g / mL.

8. The process for the preparation of salicylanilide according to claim 1, characterized in that, The molar ratio of the ammonia gas to salicylamide is 1:(0.1-20).

9. The process for the preparation of salicylanilide according to claim 1, characterized in that, The solvent includes one or a mixture of several of toluene, mesitylene, and dioxane.

10. The process for the preparation of salicylanilide according to claim 1, characterized in that, The continuous reactor includes a fixed bed reactor and a fluidized bed reactor.