System and process for preparing 2,4-dichlorophenol by four-stage series chlorination with optimization of in-kettle packing

Abstract

The present application relates to the technical fields of pesticide intermediate synthesis, in particular to a system and process for preparing 2,4-dichlorophenol by in-kettle packing optimized four-stage series chlorination, the system comprising a dosing unit, a four-stage series chlorination unit, a tail chlorine absorption unit, a rectification unit and a hydrochloric acid absorption unit; the process uses phenol as raw material, diphenyl sulfide-sbcl3 composite catalysis, four-stage series gradient chlorination, in-kettle wire mesh packing mass transfer enhancement, tail chlorine recycling absorption, vacuum rectification purification, continuous preparation of high-purity 2,4-dichlorophenol, the beneficial effect is: the present application solves the technical problems of long reaction time, low chlorine utilization rate, poor product purity, high impurity content in traditional single-kettle process, realizes complete conversion of phenol, 2,4-dichlorophenol purity reaches 90%~92%, o-chlorophenol <1.2%; reaction time is shortened to 7.5~10 hours, chlorine utilization rate is greater than or equal to 85%, has the advantages of high efficiency, low consumption, environmental protection and continuous stability, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of pesticide intermediate synthesis technology, specifically to a system and process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing. Background Technology

[0002] 2,4-Dichlorophenol is the core intermediate in the synthesis of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Its purity directly determines the quality, efficacy, and subsequent processing stability of the 2,4-D technical material. Currently, the industrial preparation of 2,4-dichlorophenol mainly employs the direct chlorination method and the catalytic chlorination method, with the catalytic chlorination method being the most widely used due to its relatively high selectivity.

[0003] Current mainstream technologies mostly employ single-reactor batch chlorination processes, which have significant technical drawbacks: First, the reaction efficiency is extremely low, with the overall reaction time between chlorine and phenol generally exceeding 36 hours, resulting in high energy consumption and limited production capacity, making it difficult to meet the needs of large-scale production. Second, the chlorine utilization rate is low, only 45%~55%, with a large amount of unreacted chlorine being converted into hydrogen chloride waste gas, leading to serious resource waste and significant environmental pressure. Third, the reaction selectivity is poor, easily generating byproducts such as 2,6-dichlorophenol, 2,4,6-trichlorophenol, and o-chlorophenol, resulting in product purity of only 83%~87%, with o-chlorophenol impurity content ≥2.0%, making subsequent distillation purification difficult and resulting in high losses. Fourth, the temperature and chlorine concentration distribution within the single reactor are uneven, and local overheating can easily trigger side reactions, leading to large batch-to-batch variations in product quality and poor stability.

[0004] To address the limitations of single-reactor processes, some studies have explored the use of single-reactor circulating chlorination or microchannel reaction processes. Single-reactor circulating chlorination only enhances local mixing within the reactor, which cannot achieve precise control of the reaction gradient. The content of by-products remains high, and the reaction time still needs to be more than 18 hours. Although microchannel reactors can enhance mass transfer, they have high equipment investment, small processing capacity, and are difficult to scale up industrially, and large-scale stable production has not yet been achieved.

[0005] However, the limited application of multi-stage cascade chlorination technology to the synthesis of chlorinated paraffins and pyridine compounds has not been reported for a continuous process integrating four-stage gradient chlorination, in-reactor packing for enhanced mass transfer, and tail chlorine recycling for 2,4-dichlorophenol. Furthermore, existing multi-stage processes lack clear gradient conversion rate control, resulting in poor impurity control and low product purity.

[0006] In summary, existing technologies suffer from drawbacks such as low reaction efficiency, poor chlorine utilization, low product purity, high impurity content, large emissions of waste gas, wastewater, and solid waste, and difficulty in achieving continuous large-scale production. Therefore, developing a highly efficient, highly selective, low-energy-consumption, environmentally friendly, and continuous 2,4-dichlorophenol production system and process is of great significance for improving product quality, reducing production costs, minimizing waste emissions, and promoting the green development of the industry. Summary of the Invention

[0007] To address the problems in the prior art, this invention provides a system and process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing.

[0008] The technical solution adopted by this invention to solve its technical problem is: a system for preparing 2,4-dichlorophenol by optimizing the packing material inside the reactor through four-stage tandem chlorination, comprising: The batching unit includes a phenol catalyst batching kettle, a phenol catalyst storage tank, a sodium chloroacetate preparation kettle, and a sodium chloroacetate storage tank; the discharge end of the phenol catalyst batching kettle is connected to the inlet end of the phenol catalyst storage tank, and the discharge end of the phenol catalyst storage tank is connected to the inlet end of the four-stage chlorination unit; the discharge end of the sodium chloroacetate preparation kettle is connected to the inlet end of the sodium chloroacetate storage tank via a filter. The four-stage chlorination unit consists of a primary chlorination reactor, a secondary chlorination reactor, a tertiary chlorination reactor, and a quaternary chlorination reactor connected in series. The feed end of the primary chlorination reactor is connected to the discharge end of the batching unit, the discharge end of the primary chlorination reactor is connected to the feed end of the secondary chlorination reactor, the discharge end of the secondary chlorination reactor is connected to the feed end of the tertiary chlorination reactor, and the discharge end of the tertiary chlorination reactor is connected to the feed end of the quaternary chlorination reactor. Each chlorination reactor is equipped with a circulating pump, a circulating cooler, and a chlorine distribution pipe. The inlet and outlet of the circulating pump are connected to the bottom and top of the corresponding chlorination reactor, respectively, and the circulating cooler is connected in series on the circulating pump pipeline. The chlorine distribution pipe is located at the bottom of the chlorination reactor and connected to the chlorine source. The quaternary chlorination reactor is filled with corrugated metal mesh packing, and its discharge end is connected to the intermediate chlorination tank. Tail chlorine absorption unit: includes tail chlorine absorption tower; the bottom air inlet of the tail chlorine absorption tower is connected to the tail gas outlet at the top of each stage of chlorination reactor, the spray port in the middle of the tower is connected to the outlet pipeline of the circulating pump of the first stage chlorination reactor, and the air outlet at the top of the tower is connected to the hydrochloric acid absorption unit. Distillation unit: includes feed preheater, flash tank, light component removal tower, product tower, and recovery tower; the outlet of the intermediate chlorination tank is connected to the feed end of the feed preheater, the outlet of the preheater is connected to the feed end of the flash tank, the liquid phase outlet of the flash tank is connected to the feed inlet of the light component removal tower; the bottom outlet of the light component removal tower is connected to the feed inlet of the product tower, and the bottom outlet of the product tower is connected to the feed inlet of the recovery tower; Hydrochloric acid absorption unit: includes a primary absorption tower, a secondary absorption tower, and a tail gas absorption tower; the top outlet of the tail gas absorption tower is connected in sequence to the inlets of the primary and secondary absorption towers, and the outlet of the secondary absorption tower is connected to the inlet of the tail gas absorption tower.

[0009] Specifically, the light-light-removal tower, product tower, and recovery tower are all vacuum distillation towers, each equipped with a reboiler, condenser, distillation tank, and reflux device.

[0010] Specifically, the tail chlorine absorption tower is a sieve plate tower with 6 to 10 plates and a circulating liquid spray density of 8 to 15 m³ per hour.

[0011] The process for preparing 2,4-dichlorophenol using an optimized four-stage cascade chlorination reactor includes the following steps: S1. Solid ingredients: Add diphenyl sulfide and antimony trichloride to the phenol catalyst mixing tank, add phenol and stir to dissolve, and prepare phenol-catalyst solution, which is then pumped into the phenol catalyst storage tank; add chloroacetic acid and sodium carbonate to the sodium chloroacetate preparation tank, add process water and stir until pH=6.5~7.5, filter and pump into the sodium chloroacetate storage tank. S2, Primary Chlorination: Phenol-catalyst solution is pumped into the primary chlorination reactor to a liquid level of 75%~85%, the circulation pump and cooler are started, the temperature is controlled at 50~60℃, and chlorine gas is introduced to circulate the reaction until the phenol conversion rate reaches 65%~75%; S3, Secondary Chlorination: The primary chlorination reactor continuously discharges material into the secondary chlorination reactor until the liquid level reaches 75%~85%. Chlorine gas is circulated and reacted at the same temperature until the phenol conversion rate is ≥85%. S4, Tertiary Chlorination: The secondary chlorination reactor continuously discharges material to the tertiary chlorination reactor until the liquid level reaches 75%~85%. Chlorine gas is circulated and reacted at the same temperature until phenol is completely converted and the 2,4-dichlorophenol content is 35%~50%. S5, Quaternary Chlorination: The material is continuously discharged from the tertiary chlorination reactor to the quaternary chlorination reactor until the liquid level reaches 75%~85%. Chlorine gas is circulated and reacted at the same temperature until the 2,4-dichlorophenol content is 90%~92% and the o-chlorophenol content is <1.2%. The material is then continuously discharged to the intermediate chlorination tank. S6. Tail gas treatment: The tail gas from each chlorination reactor enters the tail chlorine absorption tower, where the residual chlorine is absorbed countercurrently by the primary chlorination liquid. The hydrogen chloride enters the hydrochloric acid absorption unit, and the circulating water absorbs 28%~30% hydrochloric acid. The acidic tail gas is then washed with alkali and adsorbed by activated carbon to meet emission standards. S7. Distillation and purification: The chlorinated liquid is preheated and flash evaporated to remove hydrogen chloride. Light components are removed by vacuum distillation in the light component removal tower. 2,4-Dichlorophenol is obtained by vacuum distillation in the product tower. The active ingredient is recovered in the recovery tower. The residual liquid is treated as hazardous waste.

[0012] Specifically, in step S1, the mass ratio of phenol, diphenyl sulfide, and antimony trichloride is 3 tons: 5 kg: 5 kg; the mass ratio of chloroacetic acid, sodium carbonate, and process water is 2 tons: 1 ton: 2.5 tons.

[0013] Specifically, in steps S2-5, the circulating flow rate of the reaction liquid in each chlorination reactor is 1.5 to 2.5 times the reactor volume per hour, and the total amount of chlorine gas introduced is 2.0 to 2.3 times the molar amount of phenol.

[0014] Specifically, in step S7, the vacuum degree of the light component removal tower is -0.07 to -0.09 MPa, and the tower bottom temperature is 115 to 135°C; the vacuum degree of the product tower is -0.08 to -0.095 MPa, and the tower bottom temperature is 135 to 155°C; the vacuum degree of the recovery tower is -0.075 to -0.09 MPa, and the tower bottom temperature is 125 to 145°C.

[0015] Specifically, the mass ratio of diphenyl sulfide to antimony trichloride in the composite catalyst is 1:1, and the total mass of the catalyst is 0.3% to 0.6% of the mass of phenol.

[0016] Specifically, the metal corrugated wire mesh packing in the four-stage chlorination reactor has a porosity of 85%~95%, which is used to enhance gas-liquid contact and prolong the residence time of chlorine-activated molecules.

[0017] Specifically, the residual chlorine absorption rate of the tail chlorine absorption tower is ≥85%, and the absorption liquid is recycled back to the primary chlorination reactor for reuse.

[0018] The beneficial effects of the system and process for preparing 2,4-dichlorophenol by optimizing the packing material inside the reactor as described in this invention are as follows: 1. Significantly improves production efficiency: This invention uses a four-stage series gradient chlorination combined with wire mesh packing inside the reactor to enhance mass transfer, accurately control the reaction process at each stage, effectively shorten the overall reaction time, significantly improve the production capacity compared with traditional processes, achieve efficient continuous production, and greatly improve the efficiency of industrial production.

[0019] 2. Improve raw material utilization and reduce costs: Through tail chlorine recycling and forced circulation mass transfer design, chlorine utilization is significantly improved, reducing raw material loss; the amount of composite catalyst is reasonable, and by-product hydrochloric acid can be recycled, resulting in a significant reduction in overall raw material consumption and production costs, making it economically viable.

[0020] 3. Improve product quality and reduce impurities: The four-stage gradient temperature control and composite catalysis work together to directionally enhance the selectivity of the target reaction. The purity of 2,4-dichloro is stable at 90%~92%, and the content of impurities such as o-chlorophenol is controlled within 1.2%, significantly improving the purity and quality stability of the product.

[0021] 4. Stable production and easy to scale up: The entire process is continuous and the parameters are precisely controllable, avoiding batch fluctuations in intermittent processes; the equipment layout is reasonable and the operation is simple. The process is adapted to large-scale industrial production, and the operation is stable and reliable, adaptable to continuous operation under different working conditions.

[0022] 5. Energy saving and environmental protection, and reduced emissions: The tail chlorine is recycled and hydrogen chloride is recovered to produce hydrochloric acid, which greatly reduces the amount of waste gas, wastewater, and solid waste. The reaction is mild and the energy consumption is lower, which is in line with the concept of green chemical industry. The environmental benefits are significant and the environmental treatment pressure is reduced. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 The flowchart shows the system and process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing provided by this invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] like Figure 1 As shown, the present invention provides the following technical solution: An optimized four-stage cascade chlorination system for the preparation of 2,4-dichlorophenol was developed, including: The batching unit includes a phenol catalyst batching vessel, a phenol catalyst storage tank, a sodium chloroacetate preparation vessel, and a sodium chloroacetate storage tank. The phenol catalyst batching vessel is connected to a diphenyl sulfide feeding hopper and a antimony trichloride feeding hopper, used to mix and dissolve phenol with the diphenyl sulfide-antimony trichloride composite catalyst to obtain a homogeneous and stable phenol-catalyst solution. The sodium chloroacetate preparation vessel is connected to a chloroacetic acid hopper and a sodium carbonate hopper, used to react chloroacetic acid and sodium carbonate in process water to obtain a sodium chloroacetate aqueous solution with a pH of 7, providing raw materials for subsequent condensation processes. The prepared solutions are pumped to their respective storage tanks for temporary storage, achieving precise metering, stable delivery, and continuous feeding of raw materials.

[0027] The four-stage chlorination unit consists of a primary chlorination reactor, a secondary chlorination reactor, a tertiary chlorination reactor, and a quaternary chlorination reactor connected in series. Each chlorination reactor has the same specifications and is equipped with a circulating pump, a circulating cooler, a chlorine distribution pipe, and corrugated metal mesh packing. The circulating pump drives the reaction liquid to circulate between the chlorination reactor and the circulating cooler, enhancing material mixing and heat transfer within the reactor and preventing localized overheating. The circulating cooler uses a jacket + external cooler dual temperature control to ensure the reaction temperature remains stable at 50~60℃. The chlorine distribution pipe is evenly distributed at the bottom of the reactor, introducing chlorine gas into the reaction liquid in the form of microbubbles, increasing the gas-liquid two-phase contact area. The reactor is filled with corrugated metal mesh packing with a porosity of 90%~95%, simulating a microchannel reaction environment, prolonging the contact time between chlorine-activated molecules and phenol, enhancing mass transfer efficiency, and improving reaction selectivity. The discharge end of the quaternary chlorination reactor is connected to the intermediate chlorination tank to achieve continuous delivery of the reaction liquid.

[0028] Tail chlorine absorption unit: This includes a tail chlorine absorption tower with a sieve plate structure, consisting of 8-10 plates. The bottom inlet connects to the tail gas outlet of each stage of the chlorination reactor, the spray nozzle in the middle of the tower connects to the circulating liquid from the primary chlorination reactor, and the top outlet connects to the hydrochloric acid absorption unit. The tail chlorine absorption tower uses the circulating liquid from the primary chlorination reactor as the absorbent, contacting the chlorinated tail gas countercurrently to efficiently absorb unreacted residual chlorine in the tail gas, with a residual chlorine absorption rate ≥95%. The liquid after chlorine absorption is returned to the primary chlorination reactor for recycling, achieving zero residual chlorine discharge. Hydrogen chloride gas is discharged from the top of the tower and enters the hydrochloric acid absorption unit, achieving resource recovery.

[0029] Distillation unit: includes feed preheater, flash tank, light component removal tower, product tower, and recovery tower. The chlorination liquid is preheated to 80-90°C by the feed preheater and then enters the flash tank to remove dissolved hydrogen chloride gas. The chlorinated liquid after hydrogen chloride removal enters the light component removal tower, where it is distilled under reduced pressure at a vacuum of -0.08 to -0.09 MPa and a bottom temperature of 120-130°C to separate light components such as hydrogen chloride and monochlorophenol. The bottom material of the light component removal tower enters the product tower, where it is distilled under reduced pressure at a vacuum of -0.09 to -0.095 MPa and a bottom temperature of 140-150°C to obtain high-purity 2,4-dichlorophenol at the top of the tower. The heavy components at the bottom of the product tower enter the recovery tower, where they are distilled under reduced pressure at a vacuum of -0.085 to -0.09 MPa and a bottom temperature of 130-140°C to recover the entrained 2,4-dichlorophenol, which is then returned to the product tower for recycling and purification. The high-boiling-point residue and catalyst heavy components at the bottom of the recovery tower are sent to the residue tank and periodically drummed for hazardous waste disposal.

[0030] The hydrochloric acid absorption unit includes a primary absorption tower, a secondary absorption tower, and a tail gas absorption tower. Hydrogen chloride gas discharged from the tail gas absorption tower sequentially enters the primary and secondary absorption towers, where it is absorbed counter-currently by circulating spray water, generating 30% hydrochloric acid as a byproduct, which is then pumped into a hydrochloric acid storage tank for temporary storage. The acidic tail gas after absorption enters the tail gas absorption tower, where residual acidic gases are absorbed by spraying with dilute alkaline water. After alkaline washing, the tail gas undergoes secondary activated carbon adsorption to remove trace amounts of organic matter before being discharged in compliance with emission standards, achieving compliant treatment of waste gas, wastewater, and solid waste.

[0031] The process for preparing 2,4-dichlorophenol using an optimized four-stage cascade chlorination reactor includes the following steps: S1. Solid Ingredients: Add 5 kg of barrelled liquid diphenyl sulfide to the diphenyl sulfide feeding hopper and 5 kg of bagged solid antimony trichloride to the antimony trichloride feeding hopper; turn on the phenol feeding pump and pump 3 tons of phenol from the intermediate phenol tank into the phenol catalyst mixing tank. After starting the stirring (speed 60 r / min), add the diphenyl sulfide and antimony trichloride and stir for 30 min until the antimony trichloride is completely dissolved to obtain the phenol-catalyst solution. Turn on the mixing tank discharge pump to send the solution to the phenol catalyst storage tank for storage. Turn on the chloroacetic acid feeding device and pump 2 tons of chloroacetic acid (in ton bags) into the chloroacetic acid hopper; turn on the sodium carbonate feeding device and pump 1 ton of sodium carbonate (in ton bags) into the sodium carbonate hopper; add 2.5 tons of process water to the sodium chloroacetate preparation vessel, start stirring (speed 50 r / min) and then add chloroacetic acid evenly. After the chloroacetic acid is completely dissolved, slowly add sodium carbonate, adjust the pH value in the vessel to 7, and stop adding alkali; after preparation, filter through the sodium chloroacetate filter and pump into the sodium chloroacetate storage tank for storage.

[0032] S2, Primary Chlorination: Start the phenol catalyst feed pump to pump the phenol-catalyst solution into the primary chlorination reactor until the liquid level in the reactor reaches 80%, then stop feeding. Start the primary chlorination circulation pump to drive the reaction liquid to circulate between the reactor and the circulating cooler at a circulation flow rate of 2.5 times the reactor volume per hour. Simultaneously, introduce chlorine gas into the chlorine distribution pipe in the reactor and control the chlorine flow rate using a flow meter. Utilize the jacketed cooling water and the circulating cooler for dual temperature control to stabilize the reaction temperature at 50~60℃. Circulate the reaction until the phenol conversion rate in the reactor reaches 70%~80%, completing the primary chlorination.

[0033] S3, Secondary Chlorination: The primary chlorination reactor continuously discharges the reaction liquid, which is then transported to the secondary chlorination reactor at a flow rate of 4 m³ / h. Feeding is stopped when the liquid level in the secondary chlorination reactor reaches 80%. The secondary chlorination circulation pump is started, and chlorine gas is introduced for circulation reaction at the same temperature (50~60℃), with the chlorine gas flow rate slightly higher than that of the primary chlorination reactor. The circulation reaction continues until the phenol conversion rate in the reactor is ≥90%, completing the secondary chlorination.

[0034] S4. Tertiary chlorination: The reaction liquid is continuously discharged from the secondary chlorination reactor and transported to the tertiary chlorination reactor at a flow rate of 4 m³ / h. Feeding is stopped when the liquid level in the tertiary chlorination reactor reaches 80%. The tertiary chlorination circulation pump is started, and chlorine gas is introduced into the reactor at the same temperature (50~60℃) for circulation reaction. The chlorine gas flow rate is slightly higher than that of the secondary chlorination. The circulation reaction continues until the phenol in the reactor is completely converted and the 2,4-dichlorophenol content reaches 40%~50%, thus completing the tertiary chlorination.

[0035] S5, Quaternary Chlorination: The reaction liquid is continuously discharged from the tertiary chlorination reactor and transported to the quaternary chlorination reactor at a flow rate of 4 m³ / h. Feeding is stopped when the liquid level in the quaternary chlorination reactor reaches 80%. The quaternary chlorination circulation pump is started, and chlorine gas is introduced for circulation reaction at the same temperature (50~60℃), with the chlorine gas flow rate slightly higher than that of the tertiary chlorination. The circulation reaction continues until the 2,4-dichlorophenol content in the reactor reaches 90%~93% and the o-chlorophenol impurity content is <1%. After the standard is met, the phenol catalyst feeding pump is started for continuous feeding, and at the same time, the chlorination reactor is continuously discharged through the liquid level regulating valve to transport the chlorinated liquid to the intermediate chlorination tank to complete the chlorination reaction.

[0036] S6. Tail Gas Treatment: Hydrogen chloride gas and unreacted trace amounts of chlorine gas generated in each stage of the chlorination reactor are combined through the tail gas pipeline and enter the lower part of the tail chlorine absorption tower. They come into countercurrent contact with the primary chlorination liquid overflowing from the tower plate, efficiently absorbing the unreacted residual chlorine in the tail gas. The liquid after chlorine absorption is returned to the primary chlorination reactor for recycling. Hydrogen chloride gas is discharged from the top of the tower and enters the hydrochloric acid absorption unit. The acidic tail gas after hydrochloric acid absorption enters the tail gas absorption tower and is sprayed with dilute alkaline water to absorb the residual acidic gas. The tail gas after alkaline washing is adsorbed by secondary activated carbon to remove trace organic matter before being discharged in compliance with standards.

[0037] S7. Distillation and Purification: The chlorinated liquid in the intermediate tank is pumped to the feed preheater via a chlorinated liquid feed pump. After preheating to 80-90°C, it enters the feed flash tank to remove dissolved hydrogen chloride gas. The flash-evaporated chlorinated liquid flows into the middle of the light component removal tower and is distilled under reduced pressure. Light components such as hydrogen chloride and monochlorophenol are separated at the top of the tower. After condensation, part of the condensate is refluxed, and the remainder is returned to the tertiary chlorination reactor for recycling. The bottom material of the light component removal tower is fed to the product tower. The product tower is distilled under reduced pressure, and 2,4-dichlorophenol is separated at the top of the tower. After condensation, part of the condensate is refluxed, and the remainder is sent to the dichlorophenol storage tank. The bottom material of the product tower is fed to the recovery tower. The recovery tower is distilled under reduced pressure, and the entrained 2,4-dichlorophenol is recovered at the top of the tower and sent back to the product tower for recycling and purification. The high-boiling-point substances and catalyst weights at the bottom of the tower are separated and sent to the residual liquid tank for periodic hazardous waste treatment.

[0038] Example 1: Four-stage series + wire mesh packing + 55℃ medium-temperature process System Configuration: A four-stage cascade chlorination system for preparing 2,4-dichlorophenol is optimized using in-vessel packing. Each chlorination vessel has a volume of 10 m³, a circulating pump flow rate of 25 m³ / h, a circulating cooler heat exchange area of ​​20 m², a chlorine distribution pipe with an opening diameter of 2 mm, and an in-vessel corrugated wire mesh packing with a porosity of 92%. The diameters of the light chlorine removal tower, product tower, and recovery tower are 1.2 m, 1.0 m, and 0.8 m, respectively, and their heights are 8 m, 10 m, and 6 m, respectively. The tail chlorine absorption tower has a diameter of 1.0 m, a height of 6 m, and 8 sieve plates. The hydrochloric acid absorption unit and tail gas treatment unit are configured as described in the invention.

[0039] Process operation: S1. Solid ingredients: Phenol: diphenyl sulfide: antimony trichloride = 3 tons: 5 kg: 5 kg by mass ratio. Add diphenyl sulfide and antimony trichloride to the phenol catalyst mixing vessel, add 3 tons of phenol, stir at 60 r / min for 30 min until completely dissolved, and obtain phenol-catalyst solution, which is then pumped into the phenol catalyst storage tank. The ratio of chloroacetic acid: sodium carbonate: process water is 2 tons: 1 ton: 2.5 tons. Add 2.5 tons of process water to the sodium chloroacetate preparation vessel, stir at a speed of 50 r / min, add 2 tons of chloroacetic acid evenly, and after dissolving, slowly add 1 ton of sodium carbonate. Adjust the pH to 7, filter, and pump into the sodium chloroacetate storage tank.

[0040] S2, Primary chlorination: Phenol-catalyst solution is pumped into the primary chlorination reactor until the liquid level reaches 80% (8m³) and then the feed is stopped; the circulation pump is started at a flow rate of 25m³ / h, the circulation cooler is turned on and the temperature is controlled at 55℃; chlorine gas is introduced at a flow rate of 120kg / h, the reaction is circulated for 2h, and the phenol conversion rate is measured to be 75%, thus completing the primary chlorination.

[0041] S3, Secondary Chlorination: The primary chlorination reactor continuously discharges material at a flow rate of 4 m³ / h, which is then transported to the secondary chlorination reactor. The material is stopped when the liquid level reaches 80%. The circulation pump is started, the temperature is controlled at 55℃, and the chlorine gas flow rate is 130 kg / h. The reaction is carried out for 2 hours, and a sample is taken to test the phenol conversion rate, which is 92%, thus completing the secondary chlorination.

[0042] S4. Tertiary chlorination: The secondary chlorination reactor continuously discharges material at a flow rate of 4 m³ / h, which is then transported to the tertiary chlorination reactor. The material is stopped when the liquid level reaches 80%. The circulation pump is started, the temperature is controlled at 55℃, and the chlorine gas flow rate is 140 kg / h. The reaction is carried out for 2 hours. A sample is taken to test whether the phenol is completely converted and whether the 2,4-dichlorophenol content is 45%. The tertiary chlorination is then completed.

[0043] S5, Quaternary Chlorination: The tertiary chlorination reactor continuously discharges material at a flow rate of 4 m³ / h, which is then transported to the quaternary chlorination reactor. The material is stopped when the liquid level reaches 80%. The circulation pump is started, the temperature is controlled at 55℃, and the chlorine gas flow rate is 150 kg / h. The reaction is carried out for 2.5 hours. Samples are taken to test the content of 2,4-dichlorophenol (92%) and o-chlorophenol (0.8%). After the standards are met, the material is continuously discharged at a flow rate of 4 m³ / h and sent to the intermediate chlorination tank.

[0044] S6. Tail gas treatment: The tail gas from each stage of the chlorination reactor enters the tail chlorine absorption tower and is absorbed by primary chlorination liquid spraying at a density of 12 m³ / (m²・h) with a residual chlorine absorption rate of 96%. Hydrogen chloride enters the hydrochloric acid absorption unit, where circulating water absorbs 30% hydrochloric acid at a flow rate of 1.2 t / h. Acidic tail gas is sprayed with dilute alkaline water and adsorbed by secondary activated carbon to meet emission standards.

[0045] S7. Distillation and purification: The chlorination solution is preheated to 85℃, and hydrogen chloride is removed by flash evaporation; the light component is separated by vacuum of -0.085MPa and bottom temperature of 125℃ in the light component removal column; the product column is obtained by vacuum of -0.092MPa and bottom temperature of 145℃, yielding 2,4-dichlorophenol at the top with a purity of 92.5%; the recovery column is obtained by vacuum of -0.088MPa and bottom temperature of 135℃, recovering 2,4-dichlorophenol with a recovery rate of 96%.

[0046] Comparison with Example 1: Traditional single-reactor batch chlorination, without circulation or packing material. A traditional 10m³ single-bottle chlorination reactor is used, without a circulating cooler or wire mesh packing, and only jacket temperature control is used; the tail gas is directly absorbed by water to produce hydrochloric acid, and there is no tail chlorine circulation absorption device; the distillation unit is the same as in Example 1.

[0047] Process: Add 3 tons of phenol, 5 kg of diphenyl sulfide, and 5 kg of antimony trichloride to a single reactor and stir to dissolve. Control the temperature in the jacket at 55°C, introduce chlorine gas at a flow rate of 120 kg / h, and stir intermittently for 42 hours. Take samples to test the content of 2,4-dichlorophenol, which is 86%, and o-chlorophenol, which is 2.5%. Stop the chlorination. The tail gas is directly absorbed by water, with a residual chlorine absorption rate of 45%. 30% hydrochloric acid is produced as a byproduct with a flow rate of 0.6 t / h. The acidic tail gas is directly discharged. The chlorinated liquid is subjected to three-stage vacuum distillation, and the operation is the same as in Example 1.

[0048] Compare with Example 2, single-reactor circulating chlorination, without four stages and without packing material. A 10m³ single-bottle circulating chlorination reactor is used, equipped with a circulating pump and a circulating cooler, without wire mesh packing; the tail gas treatment and distillation units are the same as in Example 1.

[0049] Process: Add 3 tons of phenol, 5 kg of diphenyl sulfide, and 5 kg of antimony trichloride to a single reactor and stir to dissolve; start the circulation pump at a flow rate of 25 m³ / h, control the temperature at 55℃, and pass chlorine gas at a flow rate of 120 kg / h. Circulate the reaction for 20 hours, take samples to test the content of 2,4-dichlorophenol (88%) and o-chlorophenol (1.8%), and stop passing chlorine; tail gas treatment and distillation purification are the same as in Example 1.

[0050] Comparative Example 3: Four-stage cascade chlorination, without wire mesh packing, otherwise the same as in Example 1. The system configuration and process operation are the same as in Example 1, except that the metal corrugated wire mesh packing in each stage of the chlorination reactor is removed, and the other parameters remain unchanged.

[0051] Comparison table of data between Example 1 and Control Example: Total reaction time (h) 8.5 42.0 20.0 14.0 Chlorine utilization rate (%) 92.0 48.0 75.0 82.0 2,4-Dichlorophenol purity (%) 92.5 85.8 87.5 89.1 o-Chlorophenol content (%) 0.8 2.6 1.9 1.5 Product yield (%) 91.0 78.0 83.0 86.2 Example 2: Four-stage series + wire mesh packing + 50℃ low-temperature process System Configuration: A four-stage cascade chlorination system for preparing 2,4-dichlorophenol was optimized using in-vessel packing. Each chlorination vessel had a volume of 10 m³, a circulation pump flow rate of 25 m³ / h, a circulating cooler heat exchange area of ​​20 m², a chlorine distribution pipe with an opening diameter of 2 mm, and in-vessel corrugated metal mesh packing with a porosity of 90%. The distillation unit and tail gas treatment unit were configured the same as in Example 1.

[0052] Process operation: S1. Solid ingredients: Phenol: diphenyl sulfide: antimony trichloride = 3 tons: 5 kg: 5 kg by mass ratio, and the operation is the same as in Example 1 to prepare phenol-catalyst solution and sodium chloroacetate aqueous solution.

[0053] S2, Primary chlorination: The solution is pumped into the primary chlorination reactor to 80% of the liquid level. The circulation pump is started, the temperature is controlled at 50℃, the chlorine gas flow rate is 110 kg / h, and the circulation reaction is carried out for 2.5 hours. The phenol conversion rate is 72%, and the primary chlorination is completed.

[0054] S3, Secondary Chlorination: The primary discharge flow rate is 4 m³ / h, the secondary chlorination reactor temperature is controlled at 50℃, the chlorine gas flow rate is 120 kg / h, the cyclic reaction is carried out for 2.5 h, the phenol conversion rate is 91%, and the secondary chlorination is completed.

[0055] S4, Tertiary Chlorination: Secondary discharge flow rate is 4 m³ / h, tertiary chlorination reactor temperature is controlled at 50℃, chlorine gas flow rate is 130 kg / h, cyclic reaction is carried out for 2.5 h, phenol is completely converted, 2,4-dichlorophenol content is 42%, and tertiary chlorination is completed.

[0056] S5, Quaternary Chlorination: The discharge flow rate of the tertiary stage is 4 m³ / h, the temperature of the quaternary chlorination reactor is controlled at 50℃, the chlorine gas flow rate is 140 kg / h, the cyclic reaction is carried out for 3 hours, the content of 2,4-dichlorophenol is 91%, and the content of o-chlorophenol is 0.7%. After the standard is met, the material is continuously discharged.

[0057] S6. Exhaust gas treatment: The operation is the same as in Example 1, with a residual chlorine absorption rate of 95%, a flow rate of 1.1t / h for the by-product 30% hydrochloric acid, and exhaust gas emissions meeting standards.

[0058] S7. Distillation and purification: The chlorination liquid is preheated to 80°C. The vacuum degree of the light component removal tower is -0.08MPa and the bottom temperature is 120°C. The vacuum degree of the product tower is -0.09MPa and the bottom temperature is 140°C. The vacuum degree of the recovery tower is -0.085MPa and the bottom temperature is 130°C. The operation is the same as in Example 1.

[0059] Comparison with Example 1: Traditional single-reactor intermittent chlorination at 50°C. It adopts a traditional 10m³ single-stage chlorination reactor, without circulation or packing, and with jacket temperature control at 50℃; Process: Add 3 tons of phenol, 5 kg of diphenyl sulfide, and 5 kg of antimony trichloride to a single reactor and stir to dissolve. Control the temperature in the jacket at 55°C, introduce chlorine gas at a flow rate of 120 kg / h, and stir intermittently for 42 hours. Take samples to test the content of 2,4-dichlorophenol, which is 86%, and o-chlorophenol, which is 2.5%. Stop the chlorination. The tail gas is directly absorbed by water, with a residual chlorine absorption rate of 45%. 30% hydrochloric acid is produced as a byproduct with a flow rate of 0.6 t / h. The acidic tail gas is directly discharged. The chlorinated liquid is subjected to three-stage vacuum distillation, with the same operation as in Example 1, and the reaction is carried out for 45 hours.

[0060] Comparative Example 2: Single-reactor circulating chlorination, 50°C low temperature, no packing material. A 10m³ single-reactor circulating chlorination reactor is used, equipped with a circulating pump and cooler, without packing material; Process: Add 3 tons of phenol, 5 kg of diphenyl sulfide, and 5 kg of antimony trichloride to a single reactor and stir to dissolve; start the circulation pump at a flow rate of 25 m³ / h, control the temperature at 55℃, and pass chlorine gas at a flow rate of 120 kg / h. Circulate the reaction for 20 hours, take samples to test the content of 2,4-dichlorophenol (88%) and o-chlorophenol (1.8%), and stop passing chlorine; treat the tail gas and distill it in the same way as in Example 1, and react for 22 hours.

[0061] Comparative Example 3: Four-stage cascade chlorination, low temperature 50°C, no packing material, no tail chlorine recirculation. The system configuration is the same as in Example 2, except that the wire mesh packing is removed, the tail chlorine is directly discharged, and the other parameters remain unchanged.

[0062] Comparison table of data between Example 2 and the control example: Total reaction time (h) 10.0 45.0 22.0 16.0 Chlorine utilization rate (%) 90.0 45.0 72.0 79.0 2,4-Dichlorophenol purity (%) 91.2 84.7 86.4 88.3 o-Chlorophenol content (%) 0.7 2.9 2.1 1.7 Product yield (%) 89.5 75.3 81.2 84.5 Example 3: Four-stage series + wire mesh packing + 60℃ high-temperature process System Configuration: A four-stage cascade chlorination system for preparing 2,4-dichlorophenol was optimized using in-vessel packing. Each chlorination vessel had a volume of 10 m³, a circulation pump flow rate of 25 m³ / h, a circulating cooler heat exchange area of ​​20 m², a chlorine distribution pipe with an opening diameter of 2 mm, and in-vessel corrugated metal mesh packing with a porosity of 95%. The distillation unit and tail gas treatment unit were configured the same as in Example 1.

[0063] Process operation: S1. Solid ingredients: Phenol: diphenyl sulfide: antimony trichloride = 3 tons: 5 kg: 5 kg by mass ratio, and the operation is the same as in Example 1 to prepare phenol-catalyst solution and sodium chloroacetate aqueous solution.

[0064] S2, Primary chlorination: The solution is pumped into the primary chlorination reactor to 80% of the liquid level, the circulation pump is started, the temperature is controlled at 60℃, the chlorine gas flow rate is 130kg / h, the circulation reaction is carried out for 1.5h, the phenol conversion rate is 78%, and the primary chlorination is completed.

[0065] S3, Secondary Chlorination: The primary discharge flow rate is 4 m³ / h, the secondary chlorination reactor temperature is controlled at 60℃, the chlorine gas flow rate is 140 kg / h, the cyclic reaction is carried out for 1.5 h, the phenol conversion rate is 93%, and the secondary chlorination is completed.

[0066] S4, Tertiary Chlorination: Secondary discharge flow rate is 4 m³ / h, tertiary chlorination reactor temperature is controlled at 60℃, chlorine gas flow rate is 150 kg / h, cyclic reaction is carried out for 1.5 h, phenol is completely converted, 2,4-dichlorophenol content is 48%, and tertiary chlorination is completed.

[0067] S5, Quaternary Chlorination: The discharge flow rate of the tertiary stage is 4 m³ / h, the temperature of the tertiary chlorination reactor is controlled at 60℃, the chlorine gas flow rate is 160 kg / h, the cyclic reaction is carried out for 2 hours, the content of 2,4-dichlorophenol is 92.8%, and the content of o-chlorophenol is 0.9%. After the standard is met, the material is continuously discharged.

[0068] S6. Exhaust gas treatment: The operation is the same as in Example 1, with a residual chlorine absorption rate of 97%, a flow rate of 1.3t / h for the by-product 30% hydrochloric acid, and exhaust gas emissions meeting standards.

[0069] S7. Distillation and purification: The chlorination liquid is preheated to 90°C. The vacuum degree of the light component removal tower is -0.09MPa and the bottom temperature is 130°C. The vacuum degree of the product tower is -0.095MPa and the bottom temperature is 150°C. The vacuum degree of the recovery tower is -0.09MPa and the bottom temperature is 140°C. The operation is the same as in Example 1.

[0070] Comparative Example 1: Single-reactor circulating chlorination, 60°C high temperature, no packing material. A 10m³ single-reactor circulating chlorination reactor is used, equipped with a circulating pump and cooler, without packing material; Process: Add 3 tons of phenol, 5 kg of diphenyl sulfide, and 5 kg of antimony trichloride to a single reactor and stir to dissolve; start the circulation pump at a flow rate of 25 m³ / h, control the temperature at 55℃, and pass chlorine gas at a flow rate of 120 kg / h. Circulate the reaction for 20 hours, take samples to test the content of 2,4-dichlorophenol (88%) and o-chlorophenol (1.8%), and stop passing chlorine; treat the tail gas and distill it in the same way as in Example 1, and react for 18 hours.

[0071] Comparative Example 2: Four-stage cascade chlorination, 60°C high temperature, no wire mesh packing. The system configuration and process operation are the same as in Example 3, except that the metal corrugated wire mesh packing in each stage of the chlorination reactor is removed, and the other parameters remain unchanged.

[0072] Comparison table of data between Example 2 and the control example: Total reaction time (h) 7.5 18.0 12.5 Chlorine utilization rate (%) 93.0 78.0 85.0 2,4-Dichlorophenol purity (%) 92.8 88.1 90.2 o-Chlorophenol content (%) 0.9 1.8 1.3 Product yield (%) 92.0 84.7 87.8 As can be seen from the comparison of the above-mentioned embodiments and control examples, the four-stage series circulating chlorination process of the present invention significantly shortens the reaction time, improves the chlorine utilization rate, enhances product purity, and reduces impurity content and waste emissions through four-stage gradient chlorination, enhanced mass transfer by wire mesh packing in the reactor, composite catalysis, and tail chlorine recycling absorption.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A system for preparing 2,4-dichlorophenol using a four-stage cascade chlorination process with optimized internal packing, characterized in that: include: The batching unit includes a phenol catalyst batching kettle, a phenol catalyst storage tank, a sodium chloroacetate preparation kettle, and a sodium chloroacetate storage tank; the discharge end of the phenol catalyst batching kettle is connected to the inlet end of the phenol catalyst storage tank, and the discharge end of the phenol catalyst storage tank is connected to the inlet end of the four-stage chlorination unit; the discharge end of the sodium chloroacetate preparation kettle is connected to the inlet end of the sodium chloroacetate storage tank via a filter. The four-stage chlorination unit consists of a primary chlorination reactor, a secondary chlorination reactor, a tertiary chlorination reactor, and a quaternary chlorination reactor connected in series. The feed end of the primary chlorination reactor is connected to the discharge end of the batching unit, the discharge end of the primary chlorination reactor is connected to the feed end of the secondary chlorination reactor, the discharge end of the secondary chlorination reactor is connected to the feed end of the tertiary chlorination reactor, and the discharge end of the tertiary chlorination reactor is connected to the feed end of the quaternary chlorination reactor. Each chlorination reactor is equipped with a circulating pump, a circulating cooler, and a chlorine distribution pipe. The inlet and outlet of the circulating pump are connected to the bottom and top of the corresponding chlorination reactor, respectively, and the circulating cooler is connected in series on the circulating pump pipeline. The chlorine distribution pipe is located at the bottom of the chlorination reactor and connected to the chlorine source. The quaternary chlorination reactor is filled with corrugated metal mesh packing, and its discharge end is connected to the intermediate chlorination tank. Tail chlorine absorption unit: includes tail chlorine absorption tower; the bottom air inlet of the tail chlorine absorption tower is connected to the tail gas outlet at the top of each stage of chlorination reactor, the spray port in the middle of the tower is connected to the outlet pipeline of the circulating pump of the first stage chlorination reactor, and the air outlet at the top of the tower is connected to the hydrochloric acid absorption unit. Distillation unit: includes feed preheater, flash tank, light component removal column, product column, and recovery column; The discharge end of the intermediate chlorination tank is connected to the feed end of the feed preheater, the discharge end of the preheater is connected to the feed end of the flash tank, and the liquid phase outlet of the flash tank is connected to the feed inlet of the middle section of the light-light removal tower; the bottom outlet of the light-light removal tower is connected to the feed inlet of the product tower, and the bottom outlet of the product tower is connected to the feed inlet of the recovery tower. Hydrochloric acid absorption unit: includes a primary absorption tower, a secondary absorption tower, and a tail gas absorption tower; the top outlet of the tail gas absorption tower is connected in sequence to the inlets of the primary and secondary absorption towers, and the outlet of the secondary absorption tower is connected to the inlet of the tail gas absorption tower.

2. The system for preparing 2,4-dichlorophenol using optimized four-stage cascade chlorination with in-reactor packing as described in claim 1, characterized in that: The light-light-removal tower, product tower, and recovery tower are all vacuum distillation towers, each equipped with a reboiler, condenser, distillation tank, and reflux device.

3. The system for preparing 2,4-dichlorophenol using optimized four-stage cascade chlorination with in-reactor packing as described in claim 1, characterized in that: The tail chlorine absorption tower is a sieve plate tower with 6 to 10 plates and a circulating liquid spray density of 8 to 15 m³ per hour.

4. An optimized four-stage tandem chlorination process for the preparation of 2,4-dichlorophenol, characterized in that: Includes the following steps: S1. Solid ingredients: Add diphenyl sulfide and antimony trichloride to the phenol catalyst mixing tank, add phenol and stir to dissolve, and prepare phenol-catalyst solution, which is then pumped into the phenol catalyst storage tank; add chloroacetic acid and sodium carbonate to the sodium chloroacetate preparation tank, add process water and stir until pH=6.5~7.5, filter and pump into the sodium chloroacetate storage tank. S2, Primary Chlorination: Phenol-catalyst solution is pumped into the primary chlorination reactor to a liquid level of 75%~85%, the circulation pump and cooler are started, the temperature is controlled at 50~60℃, and chlorine gas is introduced to circulate the reaction until the phenol conversion rate reaches 65%~75%; S3, Secondary Chlorination: The primary chlorination reactor continuously discharges material into the secondary chlorination reactor until the liquid level reaches 75%~85%. Chlorine gas is circulated and reacted at the same temperature until the phenol conversion rate is ≥85%. S4, Tertiary Chlorination: The secondary chlorination reactor continuously discharges material to the tertiary chlorination reactor until the liquid level reaches 75%~85%. Chlorine gas is circulated and reacted at the same temperature until phenol is completely converted and the 2,4-dichlorophenol content is 35%~50%. S5, Quaternary Chlorination: The material is continuously discharged from the tertiary chlorination reactor to the quaternary chlorination reactor until the liquid level reaches 75%~85%. Chlorine gas is circulated and reacted at the same temperature until the 2,4-dichlorophenol content is 90%~92% and the o-chlorophenol content is <1.2%. The material is then continuously discharged to the intermediate chlorination tank. S6. Tail gas treatment: The tail gas from each chlorination reactor enters the tail chlorine absorption tower, where the residual chlorine is absorbed countercurrently by the primary chlorination liquid. The hydrogen chloride enters the hydrochloric acid absorption unit, and the circulating water absorbs 28%~30% hydrochloric acid. The acidic tail gas is then washed with alkali and adsorbed by activated carbon to meet emission standards. S7. Distillation and purification: The chlorinated liquid is preheated and flash evaporated to remove hydrogen chloride. Light components are removed by vacuum distillation in the light component removal tower. 2,4-Dichlorophenol is obtained by vacuum distillation in the product tower. The active ingredient is recovered in the recovery tower. The residual liquid is treated as hazardous waste.

5. The process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing as described in claim 4, characterized in that: In step S1, the mass ratio of phenol, diphenyl sulfide, and antimony trichloride is 3 tons: 5 kg: 5 kg; the mass ratio of chloroacetic acid, sodium carbonate, and process water is 2 tons: 1 ton: 2.5 tons.

6. The process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing as described in claim 4, characterized in that: In steps S2-5, the circulating flow rate of the reaction liquid in each chlorination reactor is 1.5 to 2.5 times the reactor volume per hour, and the total amount of chlorine gas introduced is 2.0 to 2.3 times the molar amount of phenol.

7. The process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing as described in claim 4, characterized in that: In step S7, the vacuum degree of the light component removal tower is -0.07 to -0.09 MPa and the bottom temperature is 115 to 135°C; the vacuum degree of the product tower is -0.08 to -0.095 MPa and the bottom temperature is 135 to 155°C; and the vacuum degree of the recovery tower is -0.075 to -0.09 MPa and the bottom temperature is 125 to 145°C.

8. The process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing as described in claim 4, characterized in that: In the composite catalyst, the mass ratio of diphenyl sulfide to antimony trichloride is 1:1, and the total mass of the catalyst is 0.3% to 0.6% of the mass of phenol.

9. The process for preparing 2,4-dichlorophenol using optimized four-stage tandem chlorination with in-reactor packing as described in claim 4, characterized in that: The corrugated metal mesh packing inside the four-stage chlorination reactor has a porosity of 85%~95%, which is used to enhance gas-liquid contact and prolong the residence time of chlorine-activated molecules.

10. The process for preparing 2,4-dichlorophenol by optimizing the four-stage tandem chlorination in the reactor according to claim 4, characterized in that: The residual chlorine absorption rate of the tail chlorine absorption tower is ≥85%, and the absorption liquid is recycled back to the primary chlorination reactor.

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