2-hydroxy-benzonitrile by-product recovery process

Abstract

The invention belongs to the technical field of chemical production, and provides a 2-hydroxy-benzonitrile by-product recovery process which is characterized by comprising the following steps: step 1, cooling and condensing a liquid-phase crude product from a 2-hydroxy-benzonitrile synthesis reactor, then adding a sodium hydroxide solution, adjusting the pH value, stirring for 0.5-1 hour, standing for layering, and separating a water phase; step 2, dropwise adding hydrochloric acid into the water phase, adjusting the pH value, cooling to 8-10 DEG C, separating out crystals, and filtering to obtain crude phenol; and step 3, heating the crude phenol to 60-70 DEG C for melting, adding activated carbon and sodium hydrogen sulfite, stirring for 20-30 minutes, filtering while hot, and rectifying to obtain phenol. According to the method disclosed by the invention, through the synergistic effect of the process steps, high-efficiency and high-purity recovery of phenol in the 2-hydroxy-benzonitril process is realized on the premise of not introducing an organic extraction agent, the production cost is remarkably reduced, and the method has a remarkable industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, specifically relating to a process for recovering salicylates by-products. Background Technology

[0002] Salicylic acid nitrile (o-hydroxybenzonitrile) is an important pharmaceutical and pesticide intermediate, widely used in the synthesis and production of pharmaceuticals, pesticides, fragrances and liquid crystal materials.

[0003] Currently, the main production processes for salicylnitrile include salicylaldehyde oxime dehydration, salicylamide dehydration, ammonium salicylate dehydration, and methyl salicylate ammoniation dehydration. Among these, the salicylaldehyde oxime and salicylamide dehydration methods use highly toxic raw materials as dehydrating agents and generate large amounts of acidic wastewater, causing environmental pollution. Chinese patent application CN110698362A discloses a continuous process for synthesizing salicylnitrile. This process involves a mixture of methyl salicylate from a gasification chamber, steam, and ammonia, which are then introduced into a two-stage fluidized bed and reacted under the action of a vanadium-supported catalyst to produce salicylnitrile gas. This allows for rapid mixing of the reactants in the fluidized bed and timely removal of reaction heat, overcoming the uneven concentration distribution and localized overheating issues inherent in traditional reactors. It also allows for effective control of the mixing, mass transfer, and heat transfer processes of the reactants, increasing production capacity and reducing labor intensity. However, the steam treatment process increases the formation of the byproduct phenol, leading to a decrease in the yield of salicylnitrile and further increasing the difficulty of purifying it. Impurities in crude salicylnitrile mainly include unreacted methyl salicylate, byproduct salicylamide, and phenol.

[0004] Currently, the technical route for synthesizing salicylnitrile mainly focuses on optimizing the product itself, lacking a systematic and resource-oriented separation and recovery solution for the complex mixture system formed after the reaction. In particular, the increased content of phenol, a newly emerging component due to process improvements (such as continuous production), poses a significant challenge. How to economically and efficiently separate and purify this complex system and achieve its high-value utilization has become one of the key bottlenecks restricting the economic benefits and environmental performance of this process. Existing separation technologies either focus on the purification of the main product, salicylnitrile, or only perform simple and crude disposal of by-products, failing to construct a systematic process that integrates the purification of the main product with the targeted recovery, resource utilization, and harmless treatment of multiple by-products (especially phenol). Summary of the Invention

[0005] To address the technical problem of difficulty in recovering phenol, a byproduct, in the existing process of synthesizing salicylnitrile using methyl salicylate and ammonia as raw materials, this invention provides a salicylnitrile byproduct recovery process that achieves efficient recovery of the byproduct phenol.

[0006] The objective of this invention can be achieved through the following technical solutions: A process for recovering salicylates as a byproduct includes the following steps: Step 1: Cool and condense the crude liquid product from the salicylaniline synthesis reactor, then add sodium hydroxide solution to adjust the pH value, stir for 0.5-1 h, and separate the aqueous phase after standing and layering. Step 2: Add hydrochloric acid dropwise to the aqueous phase to adjust the pH value, cool down to 8-10℃, precipitate crystals, and filter to obtain crude phenol; Step 3: Heat the crude phenol to 60-70℃ to melt it, add activated carbon and sodium bisulfite, stir for 20-30 minutes, filter while hot, and obtain phenol by distillation.

[0007] As a further embodiment of the present invention, the crude liquid product in step 1 comprises salicylonitrile, methyl salicylate, salicylamide and phenol.

[0008] As a further embodiment of the present invention, the mass fraction of the sodium hydroxide solution in step 1 is 15% to 20%.

[0009] As a further aspect of the present invention, the pH value is adjusted to 12-13 in step 1. Phase separation is achieved by utilizing the specific reaction between phenol and sodium hydroxide, whereby phenol can be converted into sodium phenolate and enter the aqueous phase, thus separating it from the organic phase mixture.

[0010] As a further embodiment of the present invention, the mass fraction of hydrochloric acid in step 2 is 28% to 30%.

[0011] As a further embodiment of the present invention, the pH value is adjusted to 2-4 in step 2.

[0012] As a further embodiment of the present invention, in step 3, the amount of activated carbon used is 0.5% to 1.2% of the mass of crude phenol; the particle size of the activated carbon is 150 to 300 mesh.

[0013] As a further aspect of this invention, in step 3, the amount of sodium bisulfite used is 0.1% to 0.2% of the crude phenol mass. By reducing quinone impurities (such as salicylnitrile degradation products) in phenol with sodium bisulfite, and then further combining it with activated carbon adsorption, the problem of trace salicylnitrile residues is effectively solved.

[0014] As a further embodiment of the present invention, in step 3, a packed distillation column is used for distillation, with a theoretical plate number of 18 to 25 and a reflux ratio of 1 to 5:1.

[0015] As a further embodiment of the present invention, the distillation in step 3 is carried out under reduced pressure, with a vacuum pressure of -0.09 to -0.10 MPa.

[0016] The beneficial effects of this invention are: This invention provides a process for recovering salicylates byproducts. Through selective phase transfer, low-temperature melting and descaling, and precision fractionation, this process achieves efficient and high-purity recovery of phenol from salicylates without the introduction of organic extractants. This significantly reduces production costs and has significant industrial application value.

[0017] This invention utilizes the specific reaction between phenol and sodium hydroxide to achieve phase separation from salicylic nitrile, avoiding side reactions caused by high-temperature distillation. Then, through low-temperature melting purification and activated carbon adsorption, combined with sodium bisulfite reduction of quinone impurities in phenol, the problem of trace salicylic nitrile residue is effectively solved, further improving the content and purity of recovered phenol, and obtaining phenol with a recovery rate of ≥93.3% and a purity of ≥98.3%.

[0018] This invention provides a process for recovering salicylates byproducts. This process has the advantages of simple operation, low cost, and high purity of phenol products, and has outstanding economic and environmental benefits. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example

[0021] Example 1

[0022] This embodiment provides a process for recovering salicylates as a byproduct, including the following steps: Step 1: Cool and condense the crude liquid product (containing salicylnitrile, methyl salicylate, salicylamide and phenol) from the salicylnitrile synthesis reactor, then add sodium hydroxide solution (mass fraction of 15%), adjust the pH to 12, stir for 0.5 h, and separate the aqueous phase after standing and layering. Step 2: Add hydrochloric acid (28% by mass) dropwise to the aqueous phase to adjust the pH to 2, cool to 8°C to precipitate crystals, and filter to obtain crude phenol; Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0023] Example 2

[0024] The only difference compared to Example 1 is: Step 1: Cool and condense the crude liquid product (containing salicylnitrile, methyl salicylate, salicylamide and phenol) from the salicylnitrile synthesis reactor, then add sodium hydroxide solution (mass fraction of 20%), adjust the pH to 12, stir for 0.5 h, and separate the aqueous phase after standing and layering.

[0025] Example 3

[0026] The only difference compared to Example 1 is: Step 1: Cool and condense the crude liquid product (containing salicylnitrile, methyl salicylate, salicylamide and phenol) from the salicylnitrile synthesis reactor, then add sodium hydroxide solution (mass fraction of 15%), adjust the pH to 13, stir for 0.5 h, and separate the aqueous phase after standing and layering.

[0027] Example 4

[0028] The only difference compared to Example 1 is: Step 2: Add hydrochloric acid (30% by mass) dropwise to the aqueous phase to adjust the pH to 2, cool to 8°C, precipitate crystals, and filter to obtain crude phenol.

[0029] Example 5

[0030] The only difference compared to Example 1 is: Step 2: Add hydrochloric acid (28% by mass) dropwise to the aqueous phase to adjust the pH to 4, cool to 10℃ to precipitate crystals, and filter to obtain crude phenol.

[0031] Example 6

[0032] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 1.2% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol) and stir for 20 minutes. Filter while hot and then distill using a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. Distillation is carried out under reduced pressure (vacuum pressure -0.09 MPa) to obtain phenol.

[0033] Example 7

[0034] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (300 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0035] Example 8

[0036] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.2% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0037] Example 9

[0038] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 25 theoretical plates and a reflux ratio of 3:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0039] Comparative Example

[0040] Comparative Example 1

[0041] This comparative example provides a process for recovering salicylates as a byproduct, including the following steps: Step 1: Cool and condense the crude liquid product (containing salicylonitrile, methyl salicylate, salicylamide and phenol) from the salicylonitrile synthesis reactor, then add sodium hydroxide solution (mass fraction of 10%), adjust the pH to 12, stir for 0.5 h, and separate the aqueous phase after standing and layering. Step 2: Add hydrochloric acid (28% by mass) dropwise to the aqueous phase to adjust the pH to 2, cool to 8°C to precipitate crystals, and filter to obtain crude phenol; Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0042] Comparative Example 2

[0043] This comparative example provides a process for recovering salicylates as a byproduct, including the following steps: Step 1: Cool and condense the crude liquid product (containing salicylonitrile, methyl salicylate, salicylamide and phenol) from the salicylonitrile synthesis reactor, then add sodium hydroxide solution (mass fraction of 15%), adjust the pH to 10, stir for 0.5 h, and separate the aqueous phase after standing and layering. Step 2: Add hydrochloric acid (28% by mass) dropwise to the aqueous phase to adjust the pH to 2, cool to 8°C to precipitate crystals, and filter to obtain crude phenol; Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0044] Comparative Example 3

[0045] The only difference compared to Example 1 is: Step 2: Add hydrochloric acid (35% by mass) dropwise to the aqueous phase to adjust the pH to 2, cool to 8°C, precipitate crystals, and filter to obtain crude phenol.

[0046] Comparative Example 4

[0047] The only difference compared to Example 1 is: Step 2: Add hydrochloric acid (28% by mass) dropwise to the aqueous phase to adjust the pH to 6, cool to 8°C to precipitate crystals, and filter to obtain crude phenol.

[0048] Comparative Example 5

[0049] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.2% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol) and stir for 20 minutes. Filter while hot and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure (vacuum pressure -0.09 MPa) to obtain phenol.

[0050] Comparative Example 6

[0051] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (100 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0052] Comparative Example 7

[0053] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.3% sodium bisulfite (by mass of crude phenol), stir for 20 minutes, filter while hot, and then distill. The distillation is carried out in a packed distillation column with 18 theoretical plates and a reflux ratio of 1:1. The distillation is carried out under reduced pressure with a vacuum pressure of -0.09 MPa to obtain phenol.

[0054] Comparative Example 8

[0055] The only difference compared to Example 1 is: Step 3: Heat the crude phenol to 60℃ to melt it, add 0.5% activated carbon (150 mesh particle size) and 0.1% sodium bisulfite (by mass of crude phenol) and stir for 20 minutes. Filter while hot and then distill. The distillation is carried out in a packed distillation column with 15 theoretical plates and a reflux ratio of 0.5:1. The distillation is carried out under reduced pressure (vacuum pressure -0.09 MPa) to obtain phenol.

[0056] Performance testing

[0057] Application and performance tests were conducted on Examples 1-9 and Comparative Examples 1-8. During the production process of synthesizing salicylnitrile using methyl salicylate and ammonia as raw materials, a large amount of byproducts containing phenol were generated. The recovery rate and purity of phenol in Examples 1-9 and Comparative Examples 1-8 were determined after the reaction. The test results are shown in Table 1. Table 1

[0058] As shown in Table 1, the recovery rate and purity of phenol recovered in Example 19 were significantly higher than those in Comparative Example 18. This demonstrates that different process parameters can affect the recovery rate and yield of phenol in the salicylate byproduct recovery process. The salicylate byproduct recovery process provided by this invention can achieve efficient recovery of the byproduct phenol.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0060] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0061] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions, and all technical features and optional technical features of this application can be combined to form new technical solutions.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for recovering salicylates as a byproduct, characterized in that, Includes the following steps: Step 1: Cool and condense the crude liquid product from the salicylaniline synthesis reactor, then add sodium hydroxide solution to adjust the pH value, stir for 0.5-1 h, and separate the aqueous phase after standing and layering. Step 2: Add hydrochloric acid dropwise to the aqueous phase to adjust the pH value, cool down to 8-10℃, precipitate crystals, and filter to obtain crude phenol; Step 3: Heat the crude phenol to 60-70℃ to melt it, add activated carbon and sodium bisulfite, stir for 20-30 minutes, filter while hot, and obtain phenol by distillation.

2. The salicylaniline by-product recovery process according to claim 1, characterized in that, The crude liquid product in step 1 contains salicylonitrile, methyl salicylate, salicylamide and phenol.

3. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 1, the mass fraction of the sodium hydroxide solution is 15% to 20%.

4. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 1, adjust the pH value to 12-13.

5. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 2, the mass fraction of hydrochloric acid is 28%–30%.

6. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 2, adjust the pH value to 2-4.

7. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 3, the amount of activated carbon used is 0.5% to 1.2% of the mass of crude phenol; the particle size of the activated carbon is 150 to 300 mesh.

8. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 3, the amount of sodium bisulfite used is 0.1% to 0.2% of the mass of crude phenol.

9. The salicylnitrile by-product recovery process according to claim 1, characterized in that, In step 3, a packed distillation column is used for rectification, with a theoretical plate number of 18 to 25 and a reflux ratio of 1 to 5:

1.

10. The salicylaniline by-product recovery process according to claim 1, characterized in that, In step 3, distillation is carried out under reduced pressure, with a vacuum pressure of -0.09 to -0.10 MPa.

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