A continuous process for the preparation of p-chloro-o-cresol with low isomer content

Abstract

This application relates to the field of chemical synthesis technology and discloses a continuous preparation process for p-chloro-o-cresol with low isomer content. The process involves preparing a catalyst mother liquor by constant-temperature stirring of anhydrous ferric chloride, a thioether ligand, and 1,2-dichloroethane solvent. The catalyst mother liquor, o-cresol, and 1,2-dichloroethane solvent are added to a reaction vessel with controlled initial temperature. Thionyl chloride is added dropwise in three stages using variable frequency technology. In the third stage, external circulation is activated, and the reaction solution, after cooling and pressurization, flows into a Venturi jet injector, where it undergoes shear mixing with the thioether chloride and is then refluxed. The reaction solution is then sent to a degassing vessel for bottom heating and gas purging, while the top is washed with a countercurrent spray of 1,2-dichloroethane. The discharged mixed gas is then subjected to high-silica hydrophobic H-ZSM-5 molecular sieve to retain organic solvent, and the crude product is purified by vacuum distillation. This invention utilizes the steric hindrance effect of the thioether ligand to improve para-selectivity, combined with Venturi jet injection to eliminate local overheating, reduce isomer content, and minimize solvent loss.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, specifically to a continuous preparation process for p-chloro-o-cresol with low isomer content. Background Technology

[0002] p-Chlorocresol is an important intermediate in organic synthesis and fine chemicals, and is widely used in pharmaceuticals, pesticides, dyes and fungicides. It is often used as a core raw material for the synthesis of herbicides such as 2-methyl-4-chloropropionic acid and 2-methyl-4-chlorobutyric acid.

[0003] Currently, the main synthetic routes for p-chloro-o-cresol include condensation and direct chlorination. The former involves a high-temperature reaction of p-chlorobenzoic acid with o-cresol under a condensation catalyst, or synthesis in a redox system and alkaline environment. However, these processes often suffer from harsh reaction conditions and low conversion rates of the target product. Therefore, the direct chlorination process is commonly used industrially, where o-cresol undergoes electrophilic substitution with the chlorinating agent under the catalysis of common Lewis acids such as copper chloride and aluminum chloride.

[0004] However, conventional chlorination processes are characterized by rapid exothermic reactions. In traditional reactors, with the addition of chlorinating agents, it is difficult to maintain uniform local temperatures and material concentrations. Due to the lack of effective steric hindrance guidance in conventional catalysts, the chlorinating agents randomly attack multiple active sites on the o-cresol benzene ring, leading to decreased reaction selectivity. This generates positional isomers such as 6-chloro-2-methylphenol and triggers over-chlorination reactions in areas of high local concentration, producing a mixture of 4,6-dichloro-2-methylphenol, increasing the energy consumption and operational difficulty of subsequent distillation purification. Furthermore, the chlorination reaction is accompanied by the generation of large amounts of acidic waste gas. During high-temperature degassing and discharge treatment in existing processes, the mixed gas stream easily carries away large amounts of organic solvents from the reaction system, causing unnecessary material losses.

[0005] Therefore, this invention proposes a continuous preparation process for p-chloro-o-cresol with low isomer content to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a continuous preparation process for p-chloro-o-cresol with low isomer content, which solves the problems of increased side reactions due to heat accumulation in the reaction zone, high isomer content, and material loss caused by solvent entrainment in the tail gas in existing p-chloro-o-cresol preparation processes.

[0007] To achieve the above objectives, the present invention provides a continuous preparation process for p-chloro-o-cresol with low isomer content, the specific steps of which are as follows: S1: Anhydrous ferric chloride, sulfide ligand and 1,2-dichloroethane solvent are added to a preparation tank with a temperature control jacket and pre-activated by constant temperature stirring to obtain a homogeneous complex catalyst mother liquor. S2: The homogeneous complex catalyst mother liquor obtained in step S1, together with o-cresol and the remaining 1,2-dichloroethane solvent, is added to a reactor with a cooling jacket to cool down and control the initial reaction temperature of the reaction system. S3: At the initial reaction temperature, a three-stage variable frequency dropwise addition of thiocyanate chloride is performed in the reactor; wherein, in the third stage, the external circulation bypass at the bottom of the reactor is opened, so that the reaction liquid is successively cooled and pressurized by a gas-liquid multiphase flow centrifugal pump and flows into the Venturi ejector; and the remaining thiocyanate chloride is injected into the Venturi ejector to shear and mix with the reaction liquid, and then flows back into the reactor; S4: After the reaction is completed, the reaction solution is sent to the degassing vessel and degassing is performed under the conditions of heating the bottom of the degassing vessel and gas purging. At the same time, 1,2-dichloroethane is extracted as a spray solvent and sprayed countercurrently from the top of the degassing vessel to perform latent heat exchange washing with the mixed gas discharged from the degassing vessel. S5: The mixed gas discharged from the top of the degassing vessel is condensed and then passed into an adsorption tower filled with high-silica hydrophobic H-ZSM-5 molecular sieve to retain organic solvents; after the degassing operation is completed, the crude product at the bottom of the degassing vessel is pumped into a vacuum distillation tower for distillation, and the top fraction is collected to obtain pure p-chloro-o-cresol.

[0008] The core of this process lies in utilizing thioether ligands to modulate the electron cloud and spatially occupy the iron center, combined with a Venturi mass transfer system, to achieve highly efficient and selective para-chlorination of o-cresol. The main reaction in the above process involves the electrophilic substitution of o-cresol with thioyl chloride under catalytic conditions, generating the target product and accompanied by the release of acidic gas. The specific synthetic route of p-chloro-o-cresol in this invention is as follows: ; The specific working principle of this process to achieve high selectivity and low side reactions for the above synthetic route is explained as follows: At the catalytic system construction level, the thioether molecule coordinates with the empty orbitals of the iron atom in anhydrous ferric chloride via the lone pair electrons of its sulfur atom. Because the sterically hindered side chain groups of the thioether ligand spatially cover a specific orientation of the catalytic center, this shielding effect significantly impedes the physical movement of the ortho and meta positions of the benzene ring in the o-cresol molecule as it approaches the catalytic center. The combined effect of electronegativity and steric hindrance guides the chlorinating agent to preferentially attack the para carbon atom, which has a higher degree of spatial freedom, thereby reducing the probability of formation of the ortho-chloro isomer at the molecular source.

[0009] To achieve heat balance and concentration control during the reaction process, this invention utilizes a Venturi jet system to achieve instantaneous dispersion at the microscale. Under the high-speed fluid shearing action at the Venturi throat, thioyl chloride transforms from macroscopic droplets into a micron-sized dispersed phase, increasing the phase interface area and eliminating localized concentration extremes that are common in conventional reactors. Simultaneously, since the material has been pre-cooled before entering the jet injector, the instantaneous heat of reaction generated during jet mixing is effectively absorbed by the heat capacity of the circulating liquid, avoiding dichlorination side reactions caused by localized overheating.

[0010] For exhaust gas treatment and solvent recovery, the countercurrent washing process at the top of the degassing reactor utilizes the temperature difference between the cold solvent and the rising high-temperature gas for mass transfer. During this process, high-boiling-point components in the gas phase condense and reflux, achieving on-site material capture. The high-silica hydrophobic H-ZSM-5 molecular sieve adsorption tower at the end utilizes its specific pore size distribution and hydrophobic framework to allow the discharge of inorganic gases such as sulfur dioxide while retaining 1,2-dichloroethane through capillary condensation, ensuring the system's material balance.

[0011] Regarding the optimization of the catalyst formulation, this invention further specifies that the sulfide ligand is diphenyl sulfide or diisobutyl sulfide, and the molar ratio of anhydrous ferric chloride to the sulfide ligand is 1:1.2 to 1:1.5.

[0012] The large steric hindrance of these ligands is highly compatible with the geometry of the o-cresol benzene ring, providing sufficient steric coverage. Maintaining a constant preparation temperature of 20℃~25℃ and stirring for 10min~20min ensures that the coordination reaction reaches thermodynamic equilibrium, guarantees that the iron atom is completely encapsulated by the ligand, and avoids non-selective side reactions caused by free ferric chloride.

[0013] Regarding temperature control in the initial stage of the reaction, the initial reaction temperature was set at 5℃~15℃, mainly to counteract the strong exothermic shock during the initial decomposition of thiocyanate. A slight excess molar ratio of 1.01:1~1.05:1 was used to ensure both the conversion depth of o-cresol and to control the instantaneous concentration of the chlorinating agent within a reasonable range.

[0014] Considering the kinetic characteristics of the later stage of the reaction, the present invention makes a fine distinction in the dripping flow rate of step 3: the first and second stages adopt dripping from the top of the vessel, and the flow rate of the second stage is lower than that of the first stage; the third stage switches to a Venturi jet injector and limits the flow rate to 0.5 kg / min to 1.5 kg / min.

[0015] This gradient-down design follows the principle of gradually decreasing substrate concentration. Especially at the end of the reaction, the high turbulence intensity of the Venturi jet can powerfully drive collisions between extremely low concentrations of substrate and chlorinating reagent, completely completing the terminal conversion without increasing the risk of isomerization.

[0016] The stability of the external circulation system is ensured by the anti-vortex guide baffle and the vertical static pressure subcooling pipe. The anti-vortex design prevents cavitation at the pump inlet, while the subcooling pipe precools the fluid to 2℃~5℃. Combined with the throat flow velocity of 15m / s~25m / s, a high-throughput, low-temperature-sensitive reaction environment is created.

[0017] During the product refining stage, a temperature of 100℃~110℃ in the degassing vessel, combined with nitrogen purging at 0.1vvm~0.5vvm, can completely remove the acidic gases in the dissolved equilibrium state within 1.0h~2.0h. The temperature of the sprayed solvent is controlled at 5℃~10℃, and its mass flow rate is set to 0.5 to 1.5 times the exhaust volume. This ratio, calculated based on thermal balance, is sufficient to cover all the latent heat carried by the exhaust.

[0018] To optimize the performance of the molecular sieve adsorption tower, the H-ZSM-5 molecular sieve selected in this invention has a micropore size of 0.51 nm to 0.56 nm and a specific surface area of ​​350 m². 2 / g~400m 2 / g, the actual silicon-aluminum molar ratio is 100:1 to 300:1.

[0019] It is prepared by a nitric acid dealumination process, and the high silicon-to-aluminum ratio effectively reduces surface polarity, preventing the chemical adsorption of acidic gases within the pores. This pore size range is precisely matched to the molecular cross-sectional size of 1,2-dichloroethane, resulting in strong physical retention when it passes through the adsorption layer.

[0020] The final vacuum distillation process controls the absolute pressure at 100Pa to 500Pa and the reboiler temperature at 120℃ to 140℃.

[0021] Under deep vacuum conditions, the boiling point of p-chloro-o-cresol decreases significantly, allowing the separation process to avoid the product's heat-sensitive range, preventing oxidation, discoloration, or condensation, and ensuring the color and purity of the final product.

[0022] This invention provides a continuous preparation process for p-chloro-o-cresol with low isomer content. It has the following beneficial effects: 1. This invention constructs a homogeneous complex catalytic system of anhydrous ferric chloride and a thioether ligand, utilizing the steric hindrance effect of the side chain groups of the thioether ligand to physically hinder the ortho and meta positions of the o-cresol molecule. This steric occupancy guides the chlorinating agent produced by the decomposition of thioyl chloride to preferentially undergo para substitution, suppressing the occurrence of ortho substitution side reactions from the source of reaction kinetics, effectively reducing the isomer content in the crude product, and improving the target selectivity for o-chlorocresol.

[0023] 2. This invention introduces an external circulation cooling and Venturi jet mixing device into the reaction process. The reaction liquid, cooled by a vertical hydrostatic subcooling tube, enters the Venturi jet injector, where the added thioyl chloride is dispersed into tiny droplets by the fluid shearing action at the throat. This fluid control structure significantly increases the phase interface area, eliminates local concentration extremes within the reactor, and utilizes the heat capacity of the pre-cooled circulating liquid to absorb the instantaneously released heat of reaction, preventing the formation of local hot spots and thus inhibiting the thermodynamic pathway of excessive chlorination of the substrate to form dichlorocresol.

[0024] 3. This invention adds an adsorption unit filled with a high-silica hydrophobic H-ZSM-5 molecular sieve after the degassing and washing process. After the mixed gas generated during degassing is washed countercurrently with a cold solvent, the residual gas enters the molecular sieve bed. Due to the high silica-to-alumina ratio and specific micropore size of this molecular sieve framework, it allows inorganic acidic gases such as sulfur dioxide and hydrogen chloride to permeate while adsorbing entrained 1,2-dichloroethane molecules through physical retention within the pores. This reduces the loss of organic solvents with the gas during the process and lowers overall material loss. Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation process of the present invention; Figure 2 This is a UV-Vis in-situ monitoring curve of the coordination process of the complex in this invention; Figure 3 This is a hydrodynamic monitoring curve of the multiphase flow centrifugal pump of the present invention; wherein, Figure 3 (a) is the curve showing the change of effective net positive suction head (NPSH) at the inlet of the centrifugal pump with operating time. Figure 3 (b) is the curve showing the change of pump body axial vibration intensity with operating time; Figure 4 This is a schematic diagram of the gas phase interception monitoring curve for the degassing process of the present invention; wherein, Figure 4 (a) is the curve showing the change in exhaust temperature of the degassing vessel with degassing time. Figure 4 (b) is the curve showing the change in the residual concentration of diphenyl sulfide in the gas phase condensate with degassing time; Figure 5 This is a test chart showing the purity of the product and the distribution of by-products in the process group of this invention. Figure 5 (a) shows the data distribution curves of target product purity and o-cresol conversion rate in different experimental groups. Figure 5 (b) Curves showing the content changes of overchlorination byproducts and isosubstituted isomers in different experimental groups; Figure 6 These are fluid stability test curves for different process groups of the present invention, wherein... Figure 6 (a) is the data distribution curve of the maximum fault-free continuous operation time on the logarithmic coordinate axis. Figure 6(b) The curves showing the change in the effluent flow rate volatility for each group before shutdown or before the end of the test; Figure 7 This is a schematic diagram of the catalyst consumption test distribution of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0027] like Figure 1 As shown, the present invention provides a continuous preparation process for p-chloro-o-cresol with low isomer content. The overall process mainly includes five steps: preparation, reaction, degassing, adsorption, and distillation. In the preparation process, anhydrous ferric chloride and sulfide ligands are added to a preparation tank containing solvent and complexed by constant temperature stirring to form a catalyst mother liquor; subsequently, the catalyst mother liquor, o-cresol, and 1,2-dichloroethane are added together to a batch reactor.

[0028] In the reaction process, pure sulfuryl chloride is added to the system through a three-stage variable frequency dripping method. The material flowing out from the bottom of the reactor is locally cooled and pressurized by an anti-vortex guide baffle and a vertical static pressure subcooling pipe. Then, it is pressurized and pumped to a Venturi jet pump by a gas-liquid multiphase flow centrifugal pump, where it is strongly sheared and mixed with the dripping sulfuryl chloride and then flows back into the reactor to form an external circulation loop.

[0029] In the degassing and separation process, all reaction liquid is transferred to the degassing vessel, where nitrogen is introduced into the bottom for purging and heating to generate an upward airflow. Simultaneously, the desorbed and recovered 1,2-dichloroethane is pre-cooled to 5°C to 10°C by a cryogenic buffer and metering pump, and then countercurrently sprayed from the structured packing washing and condensation section at the top of the degassing vessel. The rising high-temperature mixed gas and the descending cold solvent undergo latent heat exchange in the packing layer, causing the heavy components to locally drop below their dew point and condense back into the degassing vessel.

[0030] In the tail gas and crude product treatment process, the mixed gas discharged from the structured packing washing and condensation section passes through the initial condenser and is then introduced into the H-ZSM-5 molecular sieve adsorption tower to retain organic solvents. The inorganic acidic gas that passes through enters the tail gas absorption and liquefaction recovery system, producing hydrochloric acid and liquid sulfur dioxide as byproducts. The crude product at the bottom of the degassing vessel is pumped into a vacuum distillation tower for separation, and finally collected from the top of the tower to obtain pure p-chloro-o-cresol.

[0031] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0032] o-Cresol, chemically known as 2-methylphenol, has the molecular formula C7H8O, CAS number 95-48-7, and a purity greater than or equal to 99.0%.

[0033] Thionyl chloride, with the molecular formula SO2Cl2 and CAS number 7791-25-5, has a purity greater than or equal to 99.0%.

[0034] 1,2-Dichloroethane, with the molecular formula C2H4Cl2 and CAS number 107-06-2, has a purity greater than or equal to 99.5%.

[0035] Anhydrous ferric chloride, with the molecular formula FeCl3 and CAS number 7705-08-0, has a purity greater than or equal to 98.0%.

[0036] Diphenyl sulfide, with the molecular formula C 12 H 10 S, CAS number 139-66-2, purity greater than or equal to 99.0%.

[0037] Diisobutyl sulfide, with the molecular formula C8H 18 S, CAS number 592-65-4, purity greater than or equal to 98.0%.

[0038] Na-ZSM-5 molecular sieve, with an initial silica-alumina molar ratio of 50:1, crystallinity greater than or equal to 95%, and a specific surface area of ​​350 m². 2 / g to 400m 2 / g, with micropore sizes ranging from 0.51nm to 0.56nm.

[0039] Preparation Example 1-1: This preparation example provides a method for preparing a homogeneous complex catalyst, including the following steps: 10 kg of 1,2-dichloroethane was added to a preparation tank equipped with a temperature-controlled jacket as a complexing solvent. The stirrer was turned on and the speed was set to 150 r / min. 0.2 kg of anhydrous ferric chloride and 0.299 kg of diphenyl sulfide (the molar ratio of anhydrous ferric chloride to diphenyl sulfide was 1:1.3) were added sequentially. The temperature in the preparation tank was adjusted and kept constant at 25°C. The mixture was stirred at a constant temperature for 15 minutes to obtain a high-concentration homogeneous complexing catalyst mother liquor.

[0040] Preparation Examples 1-2: This preparation example provides a method for preparing a homogeneous complex catalyst, including the following steps: 10 kg of 1,2-dichloroethane was added to a preparation tank equipped with a temperature-controlled jacket as a complexing solvent. The stirrer was turned on and the speed was set to 150 r / min. 0.2 kg of anhydrous ferric chloride and 0.276 kg of diphenyl sulfide (the molar ratio of anhydrous ferric chloride to diphenyl sulfide was 1:1.2) were added sequentially. The temperature in the preparation tank was adjusted and kept constant at 20 °C. The mixture was stirred at a constant temperature for 20 minutes to obtain a high-concentration homogeneous complexing catalyst mother liquor.

[0041] Preparation Examples 1-3: These preparation examples provide a method for preparing homogeneous complex catalysts, including the following steps: 10 kg of 1,2-dichloroethane was added to a preparation tank equipped with a temperature-controlled jacket as a complexing solvent. The stirrer was turned on and the speed was set to 150 r / min. 0.2 kg of anhydrous ferric chloride and 0.345 kg of diphenyl sulfide (the molar ratio of anhydrous ferric chloride to diphenyl sulfide was 1:1.5) were added sequentially. The temperature inside the preparation tank was adjusted and kept constant at 25°C. The mixture was stirred at a constant temperature for 10 minutes to obtain a high-concentration homogeneous complexing catalyst mother liquor.

[0042] Preparation Examples 1-4: These preparation examples provide a method for preparing homogeneous complex catalysts, including the following steps: 10 kg of 1,2-dichloroethane was added to a preparation tank equipped with a temperature-controlled jacket as a complexing solvent. The stirrer was turned on and the speed was set to 150 r / min. 0.2 kg of anhydrous ferric chloride and 0.235 kg of diisobutyl sulfide (the molar ratio of anhydrous ferric chloride to diisobutyl sulfide was 1:1.3) were added sequentially. The temperature in the preparation tank was adjusted and kept constant at 25°C. The mixture was stirred at a constant temperature for 15 minutes to obtain a high-concentration homogeneous complexing catalyst mother liquor.

[0043] Preparation Example 2-1: This preparation example provides a method for preparing a high-silica hydrophobic ZSM-5 molecular sieve, including the following steps: Take 1 kg of Na-ZSM-5 molecular sieve with an initial silicon-to-aluminum molar ratio of 50:1, add it to 10 L of 0.8 mol / L nitric acid aqueous solution, and reflux and stir at 85 °C for 3 hours to perform dealuminization. Wash the treated molecular sieve with deionized water until the pH of the eluent is 7.0, filter it, and dry it in a drying oven at 110 °C for 10 hours. Then place it in a muffle furnace and calcine it at 520 °C for 5 hours to obtain a high-silica hydrophobic H-ZSM-5 molecular sieve with a silicon-to-aluminum molar ratio of 200:1.

[0044] Preparation Example 2-2: This preparation example provides a method for preparing a high-silica hydrophobic ZSM-5 molecular sieve, including the following steps: Take 1 kg of Na-ZSM-5 molecular sieve with an initial silicon-to-aluminum molar ratio of 50:1, add it to 10 L of 0.5 mol / L nitric acid aqueous solution, and reflux and stir at 80 °C for 2 hours to perform dealuminization. Wash the treated molecular sieve with deionized water until the pH of the eluent is 7.0, filter it, and dry it in a drying oven at 110 °C for 12 hours. Then place it in a muffle furnace and calcine it at 500 °C for 4 hours to obtain a high-silica hydrophobic H-ZSM-5 molecular sieve with a silicon-to-aluminum molar ratio of 100:1.

[0045] Preparation Example 2-3: This preparation example provides a method for preparing a high-silica hydrophobic ZSM-5 molecular sieve, including the following steps: Take 1 kg of Na-ZSM-5 molecular sieve with an initial silicon-to-aluminum molar ratio of 50:1, add it to 10 L of 1.0 mol / L nitric acid aqueous solution, and reflux and stir at 90 °C for 4 hours to perform dealuminization. Wash the treated molecular sieve with deionized water until the pH of the eluent is 7.0, filter it, and dry it in a drying oven at 110 °C for 8 hours. Then place it in a muffle furnace and calcine it at 550 °C for 6 hours to obtain a high-silica hydrophobic H-ZSM-5 molecular sieve with a silicon-to-aluminum molar ratio of 300:1.

[0046] Characterized by BET and BJH tests, the molecular sieves prepared in Examples 2-1 to 2-3 had micropore sizes between 0.51 nm and 0.56 nm, and specific surface areas between 350 m² / m³. 2 / g~400m 2 Between / g.

[0047] Example 1: This example provides a continuous preparation process for p-chloro-o-cresol with low isomer content, including the following steps: (1) Add 140 kg of 1,2-dichloroethane and 100 kg of o-cresol to a batch reactor with a refrigerated brine jacket, turn on the stirrer and set the speed to 200 r / min. Then pump all the high-concentration homogeneous complex catalyst mother liquor prepared in Preparation Example 1-1 into the reactor, turn on the jacket refrigeration cycle, and lower the temperature of the reaction system to 10 °C and lock it precisely.

[0048] (2) At a reaction temperature of 10°C, a three-stage frequency-controlled dropping operation was performed using a programmable logic controller to add a total of 128.5 kg of pure sulfuryl chloride (molar ratio of o-cresol to 1.03:1). First stage: 90.0 kg of pure sulfuryl chloride is added dropwise from the top of the reactor at a flow rate of 10.0 kg / min; Second stage: Continue to add 25.7 kg of pure sulfuryl chloride, with the dripping rate automatically adjusted to 3.5 kg / min; Phase 3: The external circulation bypass at the bottom of the reactor is activated. The reaction liquid flows through the anti-vortex guide baffle and enters the vertical static pressure subcooling pipe. Cooling medium is introduced to control the local fluid temperature in the static pressure subcooling pipe at 3°C. The fluid then enters the gas-liquid multiphase flow centrifugal pump for pressurization and flows into the Venturi ejector. The remaining 12.8 kg of pure sulfuryl chloride is targeted and injected into the Venturi ejector at a drip rate limited to 1.0 kg / min. The pressure difference across the ejector is monitored using a differential pressure transmitter, and the frequency of the multiphase flow centrifugal pump is adjusted to maintain the flow velocity at the throat of the ejector at 20 m / s.

[0049] (3) After the reaction is complete, pump all the reaction liquid into the degassing vessel. Turn on the steam jacket and raise the temperature of the degassing vessel to 105°C. Purge with nitrogen gas from the bottom of the vessel at a flow rate of 0.3 vvm for 1.5 hours. At the same time, pre-cool the recovered high-purity 1,2-dichloroethane to 7°C and spray it down from the top of the degassing vessel by a metering pump above the structured packing washing and condensation section. The spray mass flow rate is set to 1.0 times the exhaust mass flow rate of the degassing vessel.

[0050] (4) After initial condensation at 25°C, the mixed gas discharged from the degassing vessel is passed into an adsorption tower filled with the high-silica hydrophobic H-ZSM-5 molecular sieve prepared in Preparation Example 2-1 to retain the organic solvent. The permeated inorganic acidic gas is sent to the tail gas system to recover hydrochloric acid and liquid sulfur dioxide respectively. The crude product at the bottom of the degassing vessel after degassing is pumped into a vacuum distillation column and distilled under the conditions of an absolute pressure of 300 Pa and a column bottom temperature of 130°C. The top fraction is collected to obtain pure p-chloro-o-cresol.

[0051] Example 2: This example provides a continuous preparation process for p-chloro-o-cresol with low isomer content, including the following steps: (1) Add 90 kg of 1,2-dichloroethane and 100 kg of o-cresol to a batch reactor with a refrigerated brine jacket, turn on the stirrer and set the speed to 150 r / min. Then pump all the high-concentration homogeneous complex catalyst mother liquor prepared in Preparation Examples 1-2 into the reactor, turn on the jacket refrigeration cycle, and lower the temperature of the reaction system to 5 °C and lock it precisely.

[0052] (2) At a reaction temperature of 5°C, a three-stage frequency-controlled dropping operation was performed using a programmable logic controller to add a total of 126.1 kg of pure sulfuryl chloride (molar ratio of o-cresol to 1.01:1). First stage: 88.3 kg of pure sulfuryl chloride was added dropwise from the top of the reactor at a flow rate of 6.0 kg / min; Second stage: Continue to add 25.2 kg of pure sulfuryl chloride, with the dripping rate automatically adjusted to 2.0 kg / min; Third stage: The external circulation bypass at the bottom of the reactor is opened. After the reaction liquid flows through the anti-vortex guide baffle, it enters the vertical static pressure subcooling pipe. Cooling medium is introduced to lower the local fluid temperature in the static pressure subcooling pipe to 2℃. The fluid then enters the gas-liquid multiphase flow centrifugal pump for pressurization and flows into the Venturi ejector. The remaining 12.6 kg of pure sulfuryl chloride is targeted and injected into the Venturi ejector at a drip rate limited to 0.5 kg / min. The pressure difference across the ejector is monitored by a differential pressure transmitter, and the frequency of the multiphase flow centrifugal pump is adjusted to maintain the flow velocity at the throat of the ejector at 15 m / s.

[0053] (3) After the reaction is complete, pump all the reaction liquid into the degassing vessel. Turn on the steam jacket and raise the temperature of the degassing vessel to 100°C. Purge with nitrogen gas from the bottom of the vessel at a flow rate of 0.1 vvm for 1.0 hour. At the same time, pre-cool the recovered high-purity 1,2-dichloroethane to 5°C and spray it down from the top of the degassing vessel above the structured packing washing and condensation section using a metering pump. The spray flow rate is set to 0.5 times the exhaust flow rate of the degassing vessel.

[0054] (4) After initial condensation at 20°C, the mixed gas discharged from the degassing vessel is passed into an adsorption tower filled with the high-silica hydrophobic H-ZSM-5 molecular sieve prepared in Preparation Example 2-2 to retain the organic solvent. The permeated inorganic acidic gas is sent to the tail gas system to recover hydrochloric acid and liquid sulfur dioxide respectively. The crude product at the bottom of the degassing vessel after degassing is pumped into a vacuum distillation column and distilled under the conditions of an absolute pressure of 100 Pa and a column bottom temperature of 120°C. The top fraction is collected to obtain pure p-chloro-o-cresol.

[0055] Example 3: This example provides a continuous preparation process for p-chloro-o-cresol with low isomer content, including the following steps: (1) 290 kg of 1,2-dichloroethane and 100 kg of o-cresol were added to a batch reactor with a refrigerated brine jacket. The stirrer was turned on and the speed was set to 250 r / min. Then all the high-concentration homogeneous complex catalyst mother liquor prepared in Preparation Examples 1-3 was pumped into the reactor. The jacket refrigeration cycle was turned on to lower the temperature of the reaction system to 15 °C and lock it precisely.

[0056] (2) At a reaction temperature of 15°C, a three-stage frequency-controlled dropping operation was performed using a programmable logic controller to add a total of 131.0 kg of pure thiocyanate chloride (molar ratio of o-cresol to 1.05:1). First stage: 91.7 kg of pure sulfuryl chloride was added dropwise from the top of the reactor at a flow rate of 15.0 kg / min; Second stage: Continue to add 26.2 kg of pure sulfuryl chloride, with the dripping rate automatically adjusted to 5.0 kg / min; Phase 3: The external circulation bypass at the bottom of the reactor is activated. The reaction liquid flows through the anti-vortex guide baffle and into the vertical static pressure subcooling pipe. Cooling medium is introduced to lower the local fluid temperature in the static pressure subcooling pipe to 5°C. The fluid then enters the gas-liquid multiphase flow centrifugal pump for pressurization and flows into the Venturi ejector. The remaining 13.1 kg of pure sulfuryl chloride is targeted and injected into the Venturi ejector at a drip rate limited to 1.5 kg / min. The pressure difference across the ejector is monitored using a differential pressure transmitter, and the frequency of the multiphase flow centrifugal pump is adjusted to maintain the flow velocity at the ejector throat at 25 m / s.

[0057] (3) After the reaction is complete, pump all the reaction liquid into the degassing vessel. Turn on the steam jacket and raise the temperature of the degassing vessel to 110°C. Purge with nitrogen gas from the bottom of the vessel at a flow rate of 0.5 vvm for 2.0 hours. At the same time, pre-cool the recovered high-purity 1,2-dichloroethane to 10°C and spray it down from the top of the degassing vessel above the structured packing washing and condensation section using a metering pump. The spray mass flow rate is set to 1.5 times the exhaust mass flow rate of the degassing vessel.

[0058] (4) After initial condensation at 30°C, the mixed gas discharged from the degassing vessel is passed into an adsorption tower filled with the high-silica hydrophobic H-ZSM-5 molecular sieve prepared in Preparation Example 2-3 to retain the organic solvent. The permeated inorganic acidic gas is sent to the tail gas system to recover hydrochloric acid and liquid sulfur dioxide respectively. The crude product at the bottom of the degassing vessel after degassing is pumped into a vacuum distillation column and distilled under the conditions of an absolute pressure of 500 Pa and a bottom temperature of 140°C. The top fraction is collected to obtain pure p-chloro-o-cresol.

[0059] Example 4: This example provides a continuous preparation process for p-chloro-o-cresol with low isomer content, including the following steps: (1) Add 140 kg of 1,2-dichloroethane and 100 kg of o-cresol to a batch reactor with a refrigerated brine jacket, turn on the stirrer and set the speed to 200 r / min. Then pump all the high-concentration homogeneous complex catalyst mother liquor prepared in Preparation Examples 1-4 into the reactor, turn on the jacket refrigeration cycle, and lower the temperature of the reaction system to 10 °C and lock it precisely.

[0060] (2) At a reaction temperature of 10°C, a three-stage frequency-controlled dripping operation was performed using a programmable logic controller to add a total of 128.5 kg of pure sulfuryl chloride: First stage: 90.0 kg of pure sulfuryl chloride is added dropwise from the top of the reactor at a flow rate of 10.0 kg / min; Second stage: Continue to add 25.7 kg of pure sulfuryl chloride, with the dripping rate automatically adjusted to 3.5 kg / min; Third stage: The external circulation bypass at the bottom of the reactor is activated. The reaction liquid flows through the anti-vortex guide baffle and enters the vertical static pressure subcooling pipe. Cooling medium is introduced to lower the local fluid temperature in the static pressure subcooling pipe to 3°C. The fluid then enters the gas-liquid multiphase flow centrifugal pump for pressurization and flows into the Venturi ejector. The remaining 12.8 kg of pure sulfuryl chloride is targeted and injected into the Venturi ejector at a drip rate limited to 1.0 kg / min. The pressure difference across the ejector is monitored using a differential pressure transmitter, and the frequency of the multiphase flow centrifugal pump is adjusted to maintain the flow velocity at the throat of the ejector at 20 m / s.

[0061] (3) After the reaction is complete, pump all the reaction liquid into the degassing vessel. Turn on the steam jacket and raise the temperature of the degassing vessel to 105°C. Purge with nitrogen gas from the bottom of the vessel at a flow rate of 0.3 vvm for 1.5 hours. At the same time, pre-cool the recovered high-purity 1,2-dichloroethane to 7°C and spray it down from the top of the degassing vessel by a metering pump above the structured packing washing and condensation section. The spray mass flow rate is set to 1.0 times the exhaust mass flow rate of the degassing vessel.

[0062] (4) After initial condensation at 25°C, the mixed gas discharged from the degassing vessel is passed into an adsorption tower filled with the high-silica hydrophobic H-ZSM-5 molecular sieve prepared in Preparation Example 2-2 to retain the organic solvent. The permeated inorganic acidic gas is sent to the tail gas system to recover hydrochloric acid and liquid sulfur dioxide respectively. The crude product at the bottom of the degassing vessel after degassing is pumped into a vacuum distillation column and distilled under the conditions of an absolute pressure of 300 Pa and a column bottom temperature of 130°C. The top fraction is collected to obtain pure p-chloro-o-cresol.

[0063] Comparative Example 1: Compared with Example 1, the difference is that the thermodynamic pre-activation step of the catalyst at 20°C to 25°C was omitted. Specifically, instead of using the homogeneous complex catalyst mother liquor prepared in Preparation Example 1-1, in step (1), 0.2 kg of anhydrous ferric chloride and 0.299 kg of diphenyl sulfide were added sequentially to a batch reactor (containing 1,2-dichloroethane and o-cresol) at 10°C, and the rest were the same.

[0064] Comparative Example 2: Compared with Example 1, the difference is that the third stage of turbulent dissipation control (Da number control) is cancelled. Specifically, in the third stage of step (2), the external circulation bypass, multiphase pump and Venturi jet are not turned on. Instead, the remaining 12.8 kg of pure sulfuryl chloride is directly added dropwise from the top of the reactor to the liquid surface of the reactor under conventional stirring at a flow rate of 1.0 kg / min. Everything else is the same.

[0065] Comparative Example 3: Compared with Example 1, the difference is that the thermodynamic phase lock of the external circulation system is cancelled. Specifically, in the third stage of step (2), the vertical static pressure subcooling pipe in the external circulation system is removed, and the fluid at the bottom of the reactor does not undergo a local cooling treatment of 3°C, but directly enters the gas-liquid multiphase flow centrifugal pump in its original state at 10°C. All other aspects are the same.

[0066] Comparative Example 4: Compared with Example 1, the difference is that the countercurrent mass transfer interception in the degassing process is cancelled. Specifically, in step (3) degassing operation, only heating at 105°C and nitrogen purging at the bottom at 0.3 vvm are maintained, and the high-purity 1,2-dichloroethane cold washing spray at the top of the degassing vessel at 7°C is turned off, and the rest are the same.

[0067] Comparative Example 5: Compared with Example 1, the difference is that the conventional microchannel continuous flow process of the prior art is used instead of the semi-continuous external circulation process of the present invention. Specifically, the substrate mixture in Example 1 and 128.5 kg of pure sulfuryl chloride are pumped into a silicon carbide microchannel reactor maintained at 10°C at a set equivalence ratio flow rate for continuous mixing reaction. After the reaction liquid flows out, it directly enters the degassing vessel in step (3), and the rest is the same.

[0068] Test Example 1: Test objective: To verify the coordination kinetics between sterically hindered ligands and Lewis acid metal centers under different temperature conditions, and to explore the influence of the room temperature pretreatment stage on overcoming the coordination energy barrier.

[0069] The experimental steps are as follows: An ultraviolet-visible spectrometer based on an in-situ flow cell was bypassed into the liquid circulation pipeline of the preparation tank and the reaction vessel with a temperature control jacket. The optical path of the flow cell was set to 1 mm, and the test wavelength was set at 435 nm, which is the characteristic absorption band of the metal ligand charge transfer of the ferric chloride-diphenyl sulfide complex.

[0070] The homogeneous complex catalyst mother liquor at a constant temperature of 25°C in Preparation Example 1-1 and the reaction system at 10°C in Comparative Example 1 were used as monitoring objects, and pure 1,2-dichloroethane was used as the baseline reference for spectral scanning.

[0071] Automatic online sampling and scanning were performed at 2, 5, 8, 12, 15, 20, 30, 45 and 60 minutes after anhydrous ferric chloride and diphenyl sulfide were mixed and contacted. The absorbance at 435 nm was recorded at each time point. Each sampling measurement was performed three times and the arithmetic mean was calculated.

[0072] The experimental results are shown in Table 1: Table 1: Data on the change of absorbance of characteristic absorption peaks of complexes over time under different temperature conditions.

[0073] in conclusion: Based on the data in Table 1 and the appendix Figure 2 As shown, the absorbance of Preparation Example 1-1 at 25℃ showed an increasing trend in the first 15 minutes, and then plateaued after reaching 1.238, exhibiting apparent first-order reaction kinetics, indicating that the ligands in the system coordinated with the metal center. Comparative Example 1 showed a slower increase in absorbance at 10℃, with an absorbance of 0.105 after 60 minutes of stirring, corresponding to an effective complexation conversion rate of approximately 8.4%. Diphenyl sulfide molecules have a large spatial volume and exhibit stereorepulsion when near ferric chloride. The molecular thermal kinetic energy provided by the 10℃ environment is insufficient to overcome this potential barrier, and most sulfide molecules exist in a free state in the solvent. Introducing thioyl chloride in this state causes the free sulfide groups to preferentially react with the chlorinating agent, leading to the destruction of the catalyst's spatial shielding structure and thus reducing the regioselectivity of the reaction system for para-substitution. The above monitoring results verify the effectiveness of the room-temperature pretreatment design, and the 25℃ thermal activation operation provides the corresponding catalytic morphology basis for the subsequent low-temperature chlorination reaction.

[0074] Test Example 2: Test objective: To verify the effect of static pressure subcooling pipe on cavitation at the inlet of centrifugal pump and to explore the hydrodynamic effects of local cooling and static pressure changes in continuous external circulation reaction.

[0075] The experimental steps are as follows: The monitoring objects were the third-stage reaction external circulation pipeline equipped with a vertical static pressure subcooling pipe and locally cooled to 3°C in Example 1, and the external circulation pipeline without a subcooling pipe in Comparative Example 3, in which the fluid was directly introduced into the pump at 10°C.

[0076] At the inlet flanges of the gas-liquid multiphase flow centrifugal pumps in the two processes, absolute pressure transmitters are respectively attached to the flanges, and high-frequency piezoelectric accelerometers are magnetically fixed at the pump body bearing seats to collect the absolute pressure at the pump inlet and the axial vibration intensity parameters of the pump body in real time.

[0077] Based on the measured fluid temperature, the saturated vapor pressure of the mixture under the corresponding conditions is calculated. Combined with the measured inlet absolute pressure, the effective net positive suction head (NPSH) parameter is deduced. The required NPSH rating of the centrifugal pump used is 1.20 meters.

[0078] After the frequency conversion dripping operation begins, record various operating parameters with a data acquisition cycle of 5 minutes, and continue monitoring until the dripping ends after 45 minutes, or until the equipment is shut down due to excessive vibration intensity triggering a safety interlock.

[0079] The experimental results are shown in Table 2: Table 2: Data on the variation of pump inlet NPSH and vibration intensity over time under different pipeline structures

[0080] in conclusion: Based on the data in Table 2 and the appendix Figure 3 As shown, in Example 1, the effective net positive suction head (NPSH) at the centrifugal pump inlet remained between 4.65 m and 4.85 m during a 45-minute operating cycle, and the pump body axial vibration intensity was below 1.21 mm / s, indicating stable equipment operation. In Comparative Example 3, the NPSH dropped to 1.32 m after 15 minutes of operation, subsequently falling below the required critical NPSH value of 1.20 m. Along with the decrease in NPSH, the pump body vibration intensity increased, reaching 11.23 mm / s at 45 minutes and triggering equipment shutdown. As the droplet reaction proceeded, the accumulated hydrogen chloride and sulfur dioxide in the system caused the gas supersaturation of the reaction liquid to continuously rise. When the material entered the low-pressure zone of the centrifugal pump impeller inlet, gas desorption and solvent flashing were easily triggered by the pressure drop. Bubbles were generated in the impeller flow channel and collapsed as the fluid entered the high-pressure zone, generating mechanical impact and flow channel resistance. Example 1 incorporates a vertical hydrostatic subcooling pipe, utilizing a column of static water to increase the initial pressure of the fluid entering the pump inlet and reducing the saturated vapor pressure of the mixture through localized cooling. This combined fluid dynamics and thermodynamics control method retains the supersaturated inorganic gas in the liquid phase, widening the cavitation safety margin at the pump inlet, reducing cavitation phenomena, and providing an engineering basis for the stable transport of multiphase materials in continuous preparation processes.

[0081] Test Example 3: Test objective: To verify the effect of cold solvent countercurrent washing on the entrainment of heavy components in the degassing operation, and to explore the separation and retention effect of substances in the cross-system heat exchange process.

[0082] The experimental steps are as follows: The gas phase outlet of the degassing vessel in Example 1, which was washed and sprayed with high-purity 1,2-dichloroethane at 7°C, and the gas phase outlet of the degassing vessel in Comparative Example 4, which was heated at 105°C and purged with nitrogen but without cold washing, were selected as monitoring objects.

[0083] A gas phase condensation trapping probe and an online thermocouple temperature sensor are installed at the gas outlet above the packing section at the top of the degassing reactor to record the exhaust temperature.

[0084] Condensate samples were extracted from the gas phase condensation trap probe at 15, 30, 45, 60, 75, and 90 minutes after the degassing operation was started.

[0085] The obtained trapping liquid samples were quantitatively analyzed using high performance liquid chromatography. The mobile phase was prepared in a specific ratio, and the residual concentration of diphenyl sulfide ligands in the samples was determined by external standard method.

[0086] The experimental results are shown in Table 3: Table 3: Data on the variation of gas phase outlet temperature of the degassing reactor and the concentration of diphenyl sulfide in the condensate over time.

[0087] in conclusion: Based on the data in Table 3 and the appendix Figure 4 As shown, in Comparative Example 4, the gas phase outlet temperature of the degassing reactor was maintained between 104 and 105°C. The concentration of diphenyl sulfide in the condensate increased over time, reaching 1850 ppm at 60 minutes. High-temperature degassing processes are typically accompanied by the entrainment and loss of high-boiling-point solutes. The turbulent interface formed by the 105°C bottom heating and nitrogen bubbling provides thermodynamic conditions for the mass transfer of heavy components such as diphenyl sulfide to the gas phase. In Example 1, high-purity 1,2-dichloroethane at 7°C was introduced at the top of the degassing reactor for washing the structured packing. The gas phase outlet temperature dropped to the range of 21 to 24°C, and the diphenyl sulfide concentration remained within the range of 2.8 to 4.2 ppm. The rising high-temperature mixed gas and the descending cold liquid film came into countercurrent contact on the packing surface. After absorbing the sensible heat of the gas phase, the cold solvent partially underwent phase change vaporization. When the large diphenyl sulfide molecules entrained in the gas phase contacted the low-temperature liquid phase interface, the local temperature dropped below the dew point, condensing from the gas phase and flowing back to the bottom system along the packing. The mass transfer process based on the exchange of latent and sensible heat between hot and cold fluids alters the phase equilibrium state of the exhaust system, controlling the thermal entrainment loss of the catalyst under high-temperature purging conditions and reducing the consumption of coordinating components in continuous production operations. Furthermore, the 1,2-dichloroethane solvent vapor that enters the gas phase through latent heat exchange during vaporization is recycled after being recovered by ZSM-5 molecular sieves in subsequent systems, achieving cascade utilization of cooling capacity and materials throughout the system and a non-destructive closed-loop system.

[0088] Test Example 4: Test objective: To verify the influence of pre-activated coordination mechanism and micro-jet mixing on the regioselectivity of para-chlorination reaction, and to explore the intervention effect of different process conditions on the distribution of polychlorinated derivatives and isosubstituted isomer byproducts.

[0089] The experimental steps are as follows: Collect the crude reaction products of Examples 1 to 4 and Comparative Examples 1 and 2 after degassing treatment after the completion of the complete reaction cycle as test samples, and extract 10 ml of each sample and seal them in a sampling bottle for testing.

[0090] The components of the sample were determined by gas chromatography with a flame ionization detector. A weakly polar capillary column was selected. The injection port temperature was set to 250℃, the split ratio was set to 50:1, and the temperature program was controlled to start at 80℃ and increase to 240℃ at a rate of 10℃ per minute.

[0091] Quantitative analysis was performed using the area normalization method combined with internal standards. The peak area of ​​1,2-dichloroethane solvent was subtracted during chromatographic processing. The conversion rate of o-cresol in each group, as well as the mass percentage of the target product p-chloro-o-cresol, the overchlorinated byproduct 4,6-dichloro-o-cresol, and other isosubstituted isomers in the total product were calculated and recorded.

[0092] The experimental results are shown in Table 4: Table 4: Test results of product purity and by-product distribution

[0093] in conclusion: Based on the data in Table 4 and the appendix Figure 5 As shown, the purity of p-chloro-o-cresol in Examples 1 to 4 ranged from 99.41% to 99.72%, and the conversion rate of o-cresol remained in the range of 99.18% to 99.81%. The proportion of overchlorination byproducts and isosubstituted isomers was at a low level. The content of isosubstituted isomers in Comparative Example 1 was determined to be 11.62%, and the purity of the target product decreased to 82.37%. In the reaction material preparation stage, if the 25°C pre-activation operation is omitted and the mixture is directly mixed at 10°C, the sterically hindered sulfide ligands will have their coordination process hindered due to steric hindrance. The free sulfide molecules present in the system preferentially react with the subsequently added thioyl chloride, thereby damaging the steric shielding structure of the catalyst. The lack of steric constraint reduces the selectivity of the chlorinating reagent on the aromatic ring, increasing the proportion of ortho- or meta-substitution side reactions. The proportion of the overchlorination byproduct 4,6-dichloro-o-cresol in Comparative Example 2 was determined to be 6.83%. This process group did not utilize a jet shear mixing structure. In the later stages of the reaction, as the viscosity of the reaction solution increased, conventional mechanical stirring became insufficient to eliminate microscopic mixing dead zones within the reactor. These dead zones resulted in localized supersaturation of the thiocyanate reagent (i.e., microscopic mixing time exceeding the chemical reaction time, with a Darmquerel number Da>1), prompting the already formed monochloro derivative to undergo further secondary chlorination. The example, through a combination of pre-activation complexation and jet hydrodynamic shearing, maintained the microscopic mass transfer environment of the reaction system, reduced the incidence of side reactions, improved product purity, and lessened the separation load on subsequent distillation processes.

[0094] Test Example 5: Test objective: To verify the engineering role of multiphase flow phase-locking design in extending continuous operation cycles, and to evaluate the impact of gas phase control strategies on reducing system hydraulic fluctuations and preventing equipment failures.

[0095] The experimental steps are as follows: The external circulation continuous reaction system equipped with jet micro-mixing and static pressure subcooling tube in Examples 1 and 3 was used as the experimental object. At the same time, the external circulation system without subcooling device in Comparative Example 3 and the continuous flow system based on conventional microchannel reactor in Comparative Example 5 were introduced as reference groups.

[0096] The initial feed flow rate and system back pressure of each group under rated operating conditions are uniformly set. A Coriolis mass flow meter is installed at the end of the product discharge pipeline to record the real-time flow rate, and absolute pressure transmitters are configured at the pump outlet and both ends of the microchannel to monitor the pressure drop.

[0097] Initiate continuous operation testing, setting the maximum fault-free continuous operation time to an upper limit of 720 hours. Record the actual operating time from material feeding start-up to equipment shutdown triggered by excessive vibration, excessive pressure drop, or other safety interlocks.

[0098] Ten minutes before system shutdown or ten minutes before the end of the 720-hour planned cycle, the mass flow meter readings are extracted at 1-second sampling intervals. The ratio of the standard deviation of the flow rate to the average value within the time window is calculated to obtain the outlet flow rate fluctuation rate. After shutdown, the on-site fault phenomena and control system alarm logs are recorded.

[0099] The experimental results are shown in Table 5: Table 5: Fluid stability and continuous operation test results for different process groups

[0100] in conclusion: Based on the data in Table 5 and the appendix Figure 6As shown, in Examples 1 and 3, no equipment safety interlocks were triggered during the 720-hour test period, and the fluctuation rate of the outlet flow rate remained at 1.23% and 0.92%, respectively. The system in Comparative Example 3 shut down after 0.78 hours due to excessive pump vibration, with a flow rate fluctuation rate of 18.55% before shutdown. The conventional microchannel continuous flow process used in Comparative Example 5 experienced gas resistance within the channel after 2.42 hours of operation, causing the system pressure drop to exceed the limit and triggering depressurization; the flow rate fluctuation test value was 35.12%. During the chlorination reaction, the system continuously generates inorganic acid gas, and the volume ratio of the gas and liquid phases increases with the increase in conversion rate. The microchannel reactor, limited by its internal channel volume, cannot accommodate the increased gas phase volume in the later stages of the reaction. Bubbles rapidly coalesce within the narrow channels, causing the flow pattern to deteriorate from bubbly flow to slug flow or annular flow, forming a continuous gas column. This gas-liquid separation state interferes with the regular flow of the liquid phase material, leading to uneven local material residence time distribution and increased system friction loss. Comparative Example 3 employed an external circulation mode in the reactor to alleviate the system pressure buildup caused by the increase in gas volume, but no thermodynamic intervention was implemented before the material entered the centrifugal pump. The supersaturated gas dissolved in the solvent underwent desorption and flash evaporation in the low-pressure zone at the pump inlet. Gas-liquid separation prevented the impeller from establishing a stable liquid column head, resulting in reduced transport efficiency and mechanical vibration. In the Example group, a static pressure subcooling pipe was added to the external circulation loop, utilizing localized cooling and the superposition of a static water column to create a phase-locked environment. The combined cooling and pressurization operation retained the inorganic gas in the liquid solvent, ensuring the hydrodynamic stability of the pump body and pipelines. Combined with gas-liquid dispersion achieved by a jet mixer, the synergistic control of hydraulics and thermodynamics reduced the interference of gas resistance and flow deviation on continuous mass transfer, providing a foundation for the long-term industrial operation of the multiphase reaction system.

[0101] Test Example 6: Test objective: To verify the role of cold solvent countercurrent washing mechanism in controlling the loss of high-boiling-point ligands, and to assess the material consumption level of the process by calculating the catalyst consumption per unit product.

[0102] The experimental steps are as follows: Example 1, Example 3 and Comparative Example 4 were selected as monitoring objects. After each group entered a stable operating state, a continuous operation sampling cycle of 120 hours was started.

[0103] Sampling points were set at the gas phase outlet condenser end of the degassing process, the tail gas collection tank of the vacuum system, and the temporary storage tank for the recovered solvent, and samples of the mixed discharge liquid were collected every 24 hours.

[0104] Record the total mass of qualified p-chloro-o-cresol products produced by each group during the testing period, and uniformly measure all collected waste liquids and recovered solvents.

[0105] The samples were analyzed using high performance liquid chromatography, and the concentration of diphenyl sulfide ligands in each emission stream was quantitatively analyzed using the standard curve method.

[0106] The total mass of ligands lost is calculated based on the total amount and concentration of waste liquid, and then divided by the corresponding finished product output to obtain the mass of catalyst consumed per ton of product.

[0107] The experimental results are shown in Table 6: Table 6: Catalyst Consumption Calculation Data

[0108] in conclusion: Based on the data in Table 6 and the appendix Figure 7 As shown, the catalyst consumption in Examples 1 and 3 was maintained at 18.50 g / ton and 15.25 g / ton, respectively. The catalyst consumption in Comparative Example 4, which used a conventional high-temperature gas-phase purging process, was measured at 984.97 g / ton, showing a difference in ligand consumption between the different groups. In the aromatic ring chlorination reaction system, diphenyl sulfide ligands have high boiling points. Under a degassing temperature of 105°C and a large amount of nitrogen bubbling operation, the vapor pressure on the material surface fluctuates with local turbulence, causing catalyst components to be easily physically entrained by the gas flow. The process in the examples incorporated a countercurrent washing section composed of a 7°C cold solvent at the top of the degassing vessel, altering the material equilibrium state at the gas phase outlet. When the high-temperature mixed gas carrying entrained components passed through the packing layer, the cold solvent absorbed heat from the gas phase, undergoing local phase change vaporization. This latent heat exchange process lowered the gas flow temperature. After contacting the low-temperature liquid film interface, the partial pressure of the diphenyl sulfide molecules in the mixed gas dropped below the saturated vapor pressure, causing condensation and returning to the reactor with the washing liquid. The cross-system heat and mass exchange design suppressed ligand thermal entrainment losses and reduced auxiliary material consumption. Example 3 optimized the jet mixing effect, resulting in more uniform mass transfer in the reaction liquid, reducing ligand degradation caused by local overheating, and exhibiting lower ligand consumption. The degassing process, based on a combination of hydrodynamic interception and thermodynamic condensation, controlled catalyst loss during continuous preparation operations, reduced auxiliary catalysis costs, and decreased the proportion of high-boiling-point organic matter entering the subsequent tail gas absorption system, thus improving the process's operational economy.

[0109] 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 continuous preparation process for p-chloro-o-cresol with low isomer content, characterized in that, Includes the following steps: S1: Anhydrous ferric chloride, sulfide ligand and 1,2-dichloroethane solvent are added to a preparation tank with a temperature control jacket and pre-activated by constant temperature stirring to obtain a homogeneous complex catalyst mother liquor. S2: The homogeneous complex catalyst mother liquor obtained in step S1, together with o-cresol and the remaining 1,2-dichloroethane solvent, is added to a reactor with a cooling jacket to cool down and control the initial reaction temperature of the reaction system. S3: At the initial reaction temperature, a three-stage variable frequency dropwise addition of thiocyanate chloride is performed in the reactor; wherein, in the third stage, the external circulation bypass at the bottom of the reactor is opened, so that the reaction liquid is successively cooled and pressurized by a gas-liquid multiphase flow centrifugal pump and flows into the Venturi ejector; and the remaining thiocyanate chloride is injected into the Venturi ejector to shear and mix with the reaction liquid, and then flows back into the reactor; S4: After the reaction is completed, the reaction solution is sent to the degassing vessel and degassing is performed under the conditions of heating the bottom of the degassing vessel and gas purging. At the same time, cold 1,2-dichloroethane is introduced as a spray solvent and sprayed countercurrently from the top of the degassing vessel to perform latent heat exchange washing with the mixed gas discharged from the degassing vessel. S5: The mixed gas discharged from the top of the degassing vessel is condensed and then passed into an adsorption tower filled with high-silica hydrophobic H-ZSM-5 molecular sieve to retain organic solvents; after the degassing operation is completed, the crude product at the bottom of the degassing vessel is pumped into a vacuum distillation tower for distillation, and the top fraction is collected to obtain pure p-chloro-o-cresol.

2. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S1, the thioether ligand is diphenyl sulfide or diisobutyl sulfide; the molar ratio of anhydrous ferric chloride to the thioether ligand is 1:1.2 to 1:1.

5.

3. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S1, the pre-activation process parameters are: adjusting and maintaining the temperature in the preparation tank within the range of 20℃ to 25℃, and continuously stirring at a constant temperature for 10 min to 20 min.

4. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S2, the initial reaction temperature is controlled between 5°C and 15°C; in step S3, the total molar ratio of the added thioyl chloride to the o-cresol is 1.01:1 to 1.05:

1.

5. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S3, the flow rate control rules for the three-stage variable frequency dropwise addition of thiocyanate chloride are as follows: In both the first and second stages, sulfuryl chloride is added dropwise from the top of the reactor, and the dropwise flow rate set in the second stage is lower than that in the first stage; in the third stage, the dropwise flow rate of sulfuryl chloride injected into the Venturi ejector is limited to 0.5 kg / min to 1.5 kg / min.

6. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S3, the operating parameters in the outer loop bypass are: The reaction liquid flows through the anti-vortex guide baffle and then enters the vertical static pressure subcooling pipe. The temperature of the fluid in the vertical static pressure subcooling pipe is reduced to 2℃~5℃ by introducing a refrigerant. The flow velocity at the throat of the Venturi jet is maintained at 15m / s~25m / s by adjusting the frequency of the gas-liquid multiphase flow centrifugal pump.

7. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S4, the process parameters for degassing and washing are as follows: The temperature inside the degassing vessel is controlled at 100℃~110℃, and the gas used for gas purging is nitrogen, with a nitrogen flow rate of 0.1vvm~0.5vvm, and degassing is carried out continuously for 1.0h~2.0h; The temperature of 1,2-dichloroethane, used as the spraying solvent, is controlled between 5°C and 10°C. It is sprayed down from above the structured packing washing and condensation section at the top of the degassing vessel by a metering pump. The spraying mass flow rate is set to 0.5 to 1.5 times the mass flow rate of the exhaust gas from the degassing vessel.

8. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S5, the high-silica hydrophobic H-ZSM-5 molecular sieve has the following characteristic parameters: micropore size of 0.51 nm to 0.56 nm, specific surface area of 350 m 2 / g to 400 m 2 / g, and actual silicon-aluminum molar ratio of 100:1 to 300:

1.

9. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 8, characterized in that, The preparation method of the high-silica hydrophobic H-ZSM-5 molecular sieve includes: taking Na-ZSM-5 molecular sieve with an initial silicon-to-aluminum molar ratio of 50:1, adding it to a nitric acid aqueous solution with a concentration of 0.5 mol / L to 1.0 mol / L, and performing a dealuminization operation by refluxing and stirring at 80℃ to 90℃ for 2 to 4 hours; washing the molecular sieve after the dealuminization operation with deionized water until the pH value is 7.0, filtering and drying it, and then calcining it in a muffle furnace at 500℃ to 550℃ for 4 to 6 hours to obtain the final product.

10. The continuous preparation process of p-chloro-o-cresol with low isomer content according to claim 1, characterized in that, In step S5, the distillation process parameters of the vacuum distillation column are: the absolute pressure is controlled between 100 Pa and 500 Pa, and the column bottom temperature is controlled between 120°C and 140°C.

Images