Environment-friendly production process of biphenyl dichloro-benzyl through solvent closed-loop circulation

Abstract

The invention discloses a solvent closed-loop circulation type green production process for benzyl dichloride, and relates to the technical field of fine chemical synthesis, high selectivity and conversion rate of reaction are ensured by accurately controlling key parameters such as temperature, pressure, material ratio and reaction time of each reaction stage, and in a chloromethylation reaction section, the yield of chloromethylation reaction is increased. A two-section temperature control program heating mode is adopted, generation of by-products is inhibited at a low-temperature section firstly, then the main reaction rate is increased at a medium-temperature section, the biphenyl conversion rate can reach 98% or above, meanwhile, an accurate temperature control system and a stirring device are arranged, it is ensured that the temperature of a reaction system is uniform, materials are fully mixed, the situation of local overheating or incomplete reaction is avoided, and the reaction efficiency is improved. Therefore, the product quality and the production efficiency are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of fine chemical synthesis technology, specifically to a green production process for biphenyl dichlorobenzyl using a closed-loop solvent recycling system. Background Technology

[0002] With increasing global awareness of sustainable development and environmental protection, the chemical industry faces an urgent need to reduce waste emissions, improve resource utilization efficiency, and lower production costs. Biphenyl dichlorobenzyl, as an important organic synthesis intermediate, has wide applications in pharmaceuticals, pesticides, dyes, and many other fields.

[0003] The traditional biphenyl dichlorobenzyl process suffers from several drawbacks: First, it suffers from low resource utilization efficiency. Solvents and raw materials are often used only once during production, making effective recycling and reuse impossible, leading to high production costs and severe environmental pollution. Second, the production process conditions are not precisely controlled, resulting in poor reaction selectivity and numerous byproducts, which not only affect product quality but also increase the difficulty of subsequent separation and purification. Third, it generates large amounts of waste, particularly waste liquids and gases containing hazardous substances, which are costly to treat and place significant pressure on the environment. For example, solvents such as calcium chloride are typically discharged as waste liquids after use, wasting resources and polluting the environment. Furthermore, the traditional process also has significant shortcomings in terms of production efficiency and product quality stability, making it difficult to meet the high standards required for modern chemical production.

[0004] To address the problems of low resource utilization efficiency, imprecise control of production conditions, large waste emissions, and insufficient production efficiency and product quality stability in traditional biphenyl dichlorobenzyl production processes, it is particularly important to develop a green production process for biphenyl dichlorobenzyl with a closed-loop solvent cycle. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a green production process for biphenyl dichlorobenzyl with a closed-loop solvent cycle. This process can significantly reduce production costs and environmental pollution, and greatly improve product quality and production efficiency by precisely controlling reaction conditions, achieving efficient recovery and reuse of solvents and raw materials, and reducing waste emissions.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a green production process for biphenyl dichlorobenzyl using a closed-loop solvent recycling system, the specific steps of which are as follows: S1. Hydrochloric acid analysis section: 30% hydrochloric acid and calcium chloride solution are mixed in proportion and reacted under heating conditions to prepare dry hydrogen chloride gas. The reaction residue is concentrated by flash evaporation to obtain a high-concentration calcium chloride solution, which is then reused for the dehydration reaction in this section to form a closed-loop cycle of calcium chloride. S2, Chloromethylation Reaction Section: Using biphenyl and paraformaldehyde as raw materials, zinc chloride as a single catalyst, and cyclohexane as a reaction solvent, hydrogen chloride gas prepared in S1 is introduced, and the reaction is first carried out in a low temperature section of 10-15℃ for 1-3 hours, and then the temperature is raised to a medium temperature section of 38-41℃ for 6-10 hours. After the reaction, the upper organic phase is distilled to recover cyclohexane and reused in the reaction, and the lower alkaline washing wastewater is concentrated by two-stage evaporation, and the condensate is reused in the water washing process to form a dual-circulation washing system. S3. Tail Gas Co-treatment Section: Collects the small amount of hydrogen chloride gas emitted from the hydrochloric acid desorption section and the tail gas generated from the chloromethylation reaction section, and introduces it into a two-stage alkaline absorption tower. The first-stage absorbent uses a 10%-15% sodium hydroxide solution to absorb and generate a sodium chloride solution, which is then concentrated by distillation to recover sodium chloride crystals. The second-stage absorbent uses a 5%-8% sodium bicarbonate solution to deeply purify the residual acidic components in the tail gas. The absorbent is periodically introduced into the alkaline washing process of the chloromethylation reaction section for recycling. S4. Refining and Purification Section: Toluene is added to the reaction product as a solvent. After standing and separating into layers, the upper organic phase is distilled to recover toluene for material washing. The lower aqueous phase is transferred to a crystallization kettle, first cooled to 25°C by circulating water, and then cooled to 5-10°C by refrigerated brine for gradient crystallization. The crystallized product is centrifuged, filtered, and vacuum dried to obtain biphenyl dichlorobenzyl product. The mother liquor is recycled to the chloromethylation reaction section for reuse.

[0007] Furthermore, in step S1, the volume ratio of 30% hydrochloric acid to calcium chloride solution is 1:0.8-1.2, and the mass concentration of the calcium chloride solution is 32%-38%. The reaction is carried out at 80-100℃ under normal pressure. During the reaction, the pH value of the system is monitored in real time by an online pH meter to maintain the pH value between 1.5 and 2.5, ensuring the stable generation of hydrogen chloride gas. The flash evaporation concentration process adopts a reduced pressure flash evaporation method with a flash pressure of -0.06~-0.08MPa and a flash temperature of 110-130℃. After the calcium chloride concentration in the reaction residue is restored to 32%-38% by distillation concentration, it is directly pumped into the hydrochloric acid desorption reaction system for recycling. The single recycling rate of calcium chloride is ≥98%, and the cumulative number of recycling times is not less than 15 times. During the recycling process, a small amount of fresh calcium chloride solution is added to maintain the stability of the system concentration, effectively avoiding the discharge of calcium chloride waste liquid and resource waste in traditional processes.

[0008] Furthermore, the hydrochloric acid desorption section in S1 also includes a raw material pretreatment step: before use, 30% hydrochloric acid is filtered by a precision filter to remove solid impurities with a filtration accuracy of 0.5μm to prevent impurities from affecting the purity of hydrogen chloride gas; the calcium chloride solution is prepared using industrial-grade calcium chloride, and after preparation, it is treated by activated carbon adsorption to remove organic impurities, ensuring that no pollutants are introduced during recycling; after the hydrogen chloride gas is generated, it is cooled to 20-30℃ by a cooler, and then further dehydrated by a dryer filled with silica gel desiccant to ensure that the water content of the hydrogen chloride gas is ≤0.05%, preventing water from entering the chloromethylation reaction system and affecting the catalyst activity and reaction effect; the entire hydrochloric acid desorption section is equipped with a gas buffer tank with a volume 1.5 times that of the reactor to ensure a stable supply of hydrogen chloride gas and prevent pressure fluctuations from affecting subsequent reactions.

[0009] Furthermore, in step S2, the molar ratio of biphenyl to paraformaldehyde is 1:2.0-2.3, the degree of polymerization of paraformaldehyde is 8-10, and the mass fraction of formaldehyde is ≥92%, ensuring the effective release and conversion of formaldehyde during the reaction. The amount of zinc chloride catalyst used is 5%-8% of the mass of biphenyl, the purity of zinc chloride is ≥98.5%, and it is free of water of crystallization impurities, avoiding the reduction of catalyst activity due to the introduction of moisture. The mass ratio of cyclohexane to biphenyl is 1.5-2.0:1, the purity of cyclohexane is ≥99.0%, and it is free of benzene and hexene impurities, preventing impurities from participating in the reaction and generating by-products. During the reaction, the hydrogen chloride gas is introduced at a rate of 0.5-1.0 L / (min·L reaction system) through a constant pressure dripping device, ensuring sufficient contact between hydrogen chloride gas and reactants, avoiding the aggravation of side reactions caused by excessively high local concentrations, and improving the selectivity and conversion rate of the reaction.

[0010] Furthermore, the two-stage temperature control of the chloromethylation reaction section in S2 adopts a programmed temperature rise method. The low-temperature section is 10-15℃, and the reaction lasts for 1.5-2.5 hours. In this stage, the hydrolysis and deactivation of the zinc chloride catalyst are inhibited by the low-temperature environment, and the formation of the highly toxic byproduct dichloromethyl ether is blocked. The amount of dichloromethyl ether formed in this stage is less than 0.01%. After the low-temperature section reaction is completed, the temperature is raised to the medium-temperature section of 38-41℃ at a rate of 1-2℃ / min, and the reaction lasts for 7-9 hours. This stage significantly improves the main chloromethylation reaction rate and ensures that the reaction is fully carried out. The reactor adopts a jacketed heat exchange structure and is equipped with a precise temperature control system with a temperature control accuracy of ±0.5℃. At the same time, a stirring device is set up with a stirring rate of 60-100r / min to ensure that the reaction system temperature is uniform and the materials are fully mixed, avoiding local overheating or incomplete reaction.

[0011] Furthermore, the dual-cycle washing system in S2 specifically includes a cyclohexane recovery cycle and an alkaline washing wastewater reuse cycle: In the cyclohexane recovery cycle, the upper organic phase after the reaction is distilled in a distillation tower at a temperature of 80-82℃ under normal pressure. The recovered cyclohexane has a purity of ≥99.0% and is directly reused in the next batch of chloromethylation reaction. The single-batch recovery rate of cyclohexane is ≥97%, and the total loss rate is ≤2%. In the alkaline washing wastewater reuse cycle, the lower alkaline washing wastewater is first pretreated to remove suspended impurities and then sent to a two-stage evaporator for evaporation and concentration. The first-stage evaporation pressure is -0.07MPa and the temperature is 80-90℃, and the second-stage evaporation pressure is -0.09MPa and the temperature is 60-70℃. After two-stage evaporation, the COD value of the condensate is ≤50mg / L and the conductivity is ≤100μS / cm. It is directly reused in the water washing process. The wastewater reuse rate is ≥95%, which reduces the wastewater discharge by more than 60% compared with the traditional process.

[0012] Furthermore, the two-stage alkaline absorption tower in S3 adopts a packed tower structure with polytetrafluoroethylene (PTFE) packing material and a packing height of 3-5m. The mass concentration of sodium hydroxide solution in the first-stage absorption tower is 12%-14%, the empty tower gas velocity is controlled at 0.8-1.0 m / s, and the absorption temperature is 20-25℃. Through countercurrent absorption, the absorption rate of hydrogen chloride in the tail gas is ≥98%. After the generated sodium chloride solution reaches a concentration of 18%-22%, it is sent to a vacuum distillation unit for distillation and concentration under conditions of -0.05~-0.07 MPa and 105-115℃ to recover sodium chloride crystals with a purity ≥98%, which can be supplied externally as a chemical raw material. The mass concentration of sodium bicarbonate solution in the second-stage absorption tower is 6%-7%, the empty tower gas velocity is 1.0-1.2 m / s, and the absorption temperature is 25-30℃. This deeply purifies the residual hydrogen chloride gas in the tail gas, ensuring that the hydrogen chloride emission concentration in the tail gas is ≤10 mg / m³. 3 When the pH value of the secondary absorbent drops to 7.5-8.5, it is introduced into the alkaline washing process of the chloromethylation reaction section to replace the fresh alkaline solution, thereby realizing the recycling of the absorbent and eliminating the need for additional wastewater discharge.

[0013] Furthermore, in step S4, the mass ratio of toluene to the reaction product is 1.2-1.8:1, the purity of toluene is ≥99.0%, and the water content is ≤0.1%, ensuring effective extraction and purification of impurities in the reaction product. The static separation process is carried out under normal temperature and pressure conditions, with a separation time of 1.5-2.5 hours. The upper organic phase and the lower aqueous phase are separated by a separating funnel. The upper organic phase is sent to a distillation column for distillation and recovery. The distillation column has 15-20 theoretical plates, and the top temperature is... The temperature is controlled at 110-112℃, the reflux ratio is 2-3:1, and the purity of the recovered toluene is ≥99.0%, which can be directly reused in the material washing process. After the lower aqueous phase is transferred into the crystallization kettle, it is first cooled to 25℃ by circulating water at a cooling rate of 2-5℃ / h, kept at this temperature for 1-2h, and then cooled to 5-10℃ by passing chilled brine at a cooling rate of 1-3℃ / h. Crystallization is carried out at this constant temperature for 4-6h. The gradient cooling method allows the biphenyl dichlorobenzyl crystals to grow uniformly, improving the product purity and crystallization yield.

[0014] Furthermore, in step S4, the centrifugal filtration employs a horizontal spiral sedimentation centrifuge with a centrifugation speed of 3000-4000 r / min, a centrifugation time of 15-20 min, and a filtration accuracy of 1 μm, effectively separating crystals from the mother liquor. The filter cake is washed 1-2 times with recovered toluene, with each wash using 0.3-0.5 times the mass of the filter cake at a washing temperature of 10-15℃. This washing removes a small amount of impurities adhering to the crystal surface, further improving product purity. The vacuum drying process involves a drying temperature of 70-80℃, a vacuum degree of -0.08~-0.09 MPa, and a drying time of 4-6 h. During the drying process, the product moisture content is monitored in real time using an online moisture analyzer to ensure that the finished product moisture content is ≤0.5%. Before the mother liquor is recovered to the chloromethylation reaction section, it is distilled and concentrated to remove some solvent, increasing the concentration of effective components in the mother liquor to 2-3 times the original concentration before being added to the reaction. This ensures full utilization of unreacted raw materials in the mother liquor and improves the overall utilization rate of raw materials.

[0015] Furthermore, the entire production process also includes process monitoring and quality control steps: the hydrochloric acid desorption section periodically tests the purity of hydrogen chloride gas, requiring a purity ≥99.5%; the chloromethylation reaction section monitors the reaction progress in real time using a gas chromatograph, stopping the reaction when the biphenyl conversion rate ≥98%; the tail gas treatment section periodically tests the tail gas emission concentration to ensure that the hydrogen chloride emission concentration ≤10mg / m³. 3 The refining and purification section uses high-performance liquid chromatography to test the purity of the products, requiring the finished product biphenyl dichlorobenzyl to have a purity of ≥95% and an impurity content of ≤5%. At the same time, a quality traceability system for raw materials, intermediate products, and finished products is established, and the production parameters and test data of each batch of products are recorded and archived to ensure the stability and traceability of product quality and meet the quality control requirements of industrial production.

[0016] Compared with existing technologies, this green production process for biphenyl dichlorobenzyl has the following advantages: I. This process ensures high selectivity and conversion rate by precisely controlling key parameters such as temperature, pressure, material ratio, and reaction time at each reaction stage. In the chloromethylation reaction section, a two-stage temperature control program is used to first suppress the formation of by-products in the low-temperature section and then increase the main reaction rate in the medium-temperature section, achieving a biphenyl conversion rate of over 98%. At the same time, a precise temperature control system and stirring device are provided to ensure uniform temperature of the reaction system and thorough mixing of materials, avoiding local overheating or incomplete reaction, thereby significantly improving product quality and production efficiency.

[0017] Second, this process achieves efficient recovery and reuse of various solvents and raw materials, such as calcium chloride, cyclohexane, and toluene, through a closed-loop solvent recycling system. For example, calcium chloride forms a closed-loop cycle in the hydrochloric acid desorption section, with a single-cycle utilization rate of up to 98% and a cumulative recycling count of no less than 15 times. This effectively avoids the discharge of calcium chloride waste liquid and resource waste in traditional processes. At the same time, the recovery rates of cyclohexane and toluene also reach 97% and nearly 100%, respectively, significantly reducing production costs and environmental pollution.

[0018] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 This is a flow chart of a green production process for biphenyl dichlorobenzyl in a closed-loop solvent cycle. Figure 2 A detailed flow chart of the hydrochloric acid analysis section (S1) of a green production process for biphenyl dichlorobenzyl in a closed-loop solvent cycle. Figure 3 This is a flow chart of a chloromethylation dual-cycle washing system for a green production process of biphenyl dichlorobenzyl in a closed-loop solvent cycle. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0022] Example 1 First, the raw materials are pretreated: 30% industrial-grade hydrochloric acid is filtered through a precision filter with a filtration accuracy of 0.5μm to remove solid impurities. A 35% (w / w) calcium chloride solution is prepared using industrial-grade calcium chloride, and then treated with activated carbon to remove organic impurities. The pretreated 30% hydrochloric acid and calcium chloride solution are added to the reactor at a 1:1 volume ratio. The actual temperature is controlled at 90℃ within a reaction temperature range of 80-100℃ under normal pressure, and the reaction is initiated to produce hydrogen chloride gas. During the reaction, the pH value of the system is monitored in real time using an online pH meter and maintained between 1.5 and 2.5. The generated hydrogen chloride gas is cooled to 25℃ by a cooler and then further dehydrated in a dryer filled with silica gel desiccant. A gas buffer tank with a volume 1.5 times that of the reactor is installed in the entire hydrochloric acid analysis section to stabilize the gas flow. After the reaction is complete, the reaction residue is sent to a vacuum flash evaporator for concentration at a flash pressure of -0.07 MPa and a flash temperature of 120°C, restoring the calcium chloride concentration in the residue to 35%. The residue is then directly pumped back into the reaction system of this section for recycling. The single-cycle utilization rate of calcium chloride in this section is ≥98%, and the cumulative number of cycles is no less than 15. During the recycling process, a small amount of fresh calcium chloride solution is added to maintain a stable system concentration.

[0023] 100 kg of biphenyl and a corresponding amount of paraformaldehyde were weighed at a molar ratio of 1:2.1 and added to a reaction vessel. Zinc chloride (6% of the biphenyl mass) was added as a single catalyst, and cyclohexane (1.8:1 mass ratio to biphenyl) was added as a reaction solvent. Dry hydrogen chloride gas prepared in step S1 was introduced into the reaction system through a constant-pressure dropping device at a rate of 0.8 L / (min·L reaction system) to ensure sufficient contact between the hydrogen chloride and the reactants. The reaction temperature was controlled using a programmed temperature ramp: the reaction was initially carried out at a low temperature of 12℃ for 2 hours. After the low temperature ramp, the temperature was increased to a medium temperature of 40℃ at a ramp rate of 1.5℃ / min, and the reaction continued for 8 hours.

[0024] The reactor adopts a jacketed heat exchange structure and is equipped with a precise temperature control system with a temperature control accuracy of ±0.5℃. Simultaneously, the stirring device is activated, and the stirring rate is set to 80 r / min. After the reaction, the system is divided into upper and lower layers. The upper organic phase is sent to a distillation column for distillation and recovery of cyclohexane under atmospheric pressure and a temperature of 81℃. The recovered cyclohexane has a purity ≥99.0% and is directly reused in the next batch of reaction, with a single batch recovery rate ≥97% and a total loss rate ≤2%. The lower alkaline washing wastewater is pretreated to remove suspended impurities before being sent to a two-stage evaporator for evaporation and concentration. The first-stage evaporation pressure is -0.07 MPa and the temperature is 85℃, and the second-stage evaporation pressure is -0.09 MPa and the temperature is 65℃. After two-stage evaporation, the COD value of the condensate is ≤50 mg / L and the conductivity is ≤100 μS / cm, which is directly reused in the water washing process, forming a dual-circulation washing system.

[0025] The small amount of hydrogen chloride gas escaping from the hydrochloric acid desorption section and the tail gas generated from the chloromethylation reaction section are collected and treated in a two-stage alkaline absorption tower. Both absorption towers are packed towers with PTFE packing material and a packing height of 4m. The first-stage absorption tower is filled with a 13% sodium hydroxide solution, with the empty gas velocity controlled at 0.9 m / s and the absorption temperature at 22℃. Countercurrent absorption is used to ensure that the hydrogen chloride absorption rate in the tail gas is ≥98%. When the concentration of the generated sodium chloride solution reaches 20%, it is sent to a vacuum distillation unit for distillation and concentration at -0.06 MPa and 110℃ to recover sodium chloride crystals with a purity ≥98%, which are supplied as chemical raw materials. The second-stage absorption tower is filled with a 6.5% sodium bicarbonate solution, with the empty gas velocity controlled at 1.1 m / s and the absorption temperature at 28℃. This deeply purifies the residual acidic components in the tail gas, ensuring that the hydrogen chloride emission concentration in the tail gas is ≤10 mg / m³. 3 When the pH of the secondary absorbent drops to 8.0, it is periodically introduced into the alkaline washing process of the chloromethylation reaction section to replace the fresh alkaline solution for recycling.

[0026] Toluene was added as a solvent to the product after the chloromethylation reaction, with a toluene-to-product mass ratio of 1.5:1. The toluene used had a purity ≥99.0% and a moisture content ≤0.1%. The mixture was allowed to stand for 2 hours at room temperature and pressure to separate into an upper organic phase and a lower aqueous phase using a separatory funnel. The upper organic phase was sent to a distillation column for distillation recovery. The distillation column had 18 theoretical plates, a top temperature controlled at 111℃, and a reflux ratio of 2.5:1. The recovered toluene had a purity ≥99.0% and was directly reused in the material washing process. The lower aqueous phase was transferred to a crystallization vessel, first cooled to 25℃ at a rate of 3℃ / h using circulating water, and held at this temperature for 1.5 hours. Then, it was cooled to 8℃ at a rate of 2℃ / h using chilled brine, and held at this temperature for 5 hours to allow for uniform crystal growth of biphenyl dichlorobenzyl crystals.

[0027] The crystallized product was centrifuged and filtered using a horizontal spiral sedimentation centrifuge at 3500 r / min for 20 min, achieving a filtration accuracy of 1 μm, effectively separating the crystals from the mother liquor. The filter cake was washed twice with recovered toluene, each time using 0.4 times the mass of the filter cake at 12℃, removing minor impurities adhering to the crystal surface. The washed filter cake was then sent to a vacuum drying device at 75℃ and a vacuum of -0.085 MPa for 4 h, with the moisture content monitored in real-time using an online moisture analyzer. Before being recycled to the chloromethylation reaction section, the mother liquor after centrifugation and filtration was distilled and concentrated to remove some solvent, increasing the concentration of effective components in the mother liquor to 2.5 times its original concentration before being added to the reaction.

[0028] The hydrochloric acid analysis section regularly tests the purity of hydrogen chloride gas to ensure it is ≥99.5%; the chloromethylation reaction section monitors the reaction progress in real time using a gas chromatograph, and stops the reaction when the biphenyl conversion rate is ≥98%; the tail gas treatment section regularly tests the tail gas emission concentration to ensure the hydrogen chloride emission concentration is ≤10mg / m³. 3 The refining and purification section uses high-performance liquid chromatography (HPLC) to test the purity of the product. The final product, biphenyl dichlorobenzyl, has a purity of ≥95% and an impurity content of ≤5%. Simultaneously, a quality traceability system for raw materials, intermediate products, and finished products is established, and all production parameters and testing data for this batch of products are recorded and archived in detail.

[0029] Example 2 Raw material pretreatment stage: Before use, 30% hydrochloric acid is filtered through a precision filter with an accuracy of 0.5μm to remove solid impurities. A 33% (w / w) calcium chloride solution is prepared using industrial-grade calcium chloride, and then treated with activated carbon to remove organic impurities. The pretreated 30% hydrochloric acid and calcium chloride solution are mixed at a volume ratio of 1:0.9 and added to the reactor. The reaction is carried out at atmospheric pressure and a reaction temperature of 85℃ to produce hydrogen chloride gas. During the reaction, the pH value of the system is monitored in real time using an online pH meter and maintained between 1.5 and 2.5. The generated hydrogen chloride gas is cooled to 22℃ by a cooler and then further dehydrated by a dryer filled with silica gel desiccant. A gas buffer tank with a volume 1.5 times that of the reactor is installed in the process section to stabilize the gas flow. The reaction residue is sent to a vacuum flash evaporator and concentrated under flash pressure of -0.06MPa and flash temperature of 115℃ until the calcium chloride concentration in the residue is restored to 33%. The concentrate is then directly pumped into the hydrochloric acid desorption reaction system for recycling. In this section, the single-cycle utilization rate of calcium chloride is ≥98%, and the cumulative number of cycles is not less than 15. During the cycle, a small amount of fresh calcium chloride solution is added to maintain the stability of the system concentration.

[0030] 200 kg of biphenyl and the corresponding amount of paraformaldehyde were weighed at a molar ratio of 1:2.2 and added to the reactor. Zinc chloride (5.5% of the biphenyl mass) was added as a catalyst, and cyclohexane (1.6:1 of the biphenyl mass) was added as a reaction solvent. The hydrogen chloride gas was introduced at a rate of 0.6 L / (min·L reaction system) using a constant pressure dropping device to ensure sufficient contact between the hydrogen chloride gas and the reactants. The reaction temperature was controlled using a programmed temperature rise method: the reaction was initially carried out at a low temperature of 11℃ for 1.5 h. After the low temperature reaction was completed, the temperature was increased to a medium temperature of 39℃ at a rate of 1℃ / min, and the reaction continued for 7.5 h. The reactor adopted a jacketed heat exchange structure and was equipped with a precise temperature control system with a temperature control accuracy of ±0.5℃. Simultaneously, the stirring device was activated, and the stirring speed was set to 70 r / min. After the reaction, the upper organic phase is distilled in a distillation column at atmospheric pressure and 80℃ to recover cyclohexane. The purity of the recovered cyclohexane is ≥99.0%, the single-batch recovery rate is ≥97%, and the total loss rate is ≤2%. It is directly reused in the next batch reaction. The lower alkaline washing wastewater is first pretreated to remove suspended impurities, and then sent to a two-stage evaporator. The first-stage evaporation pressure is -0.07MPa and the temperature is 80℃, and the second-stage evaporation pressure is -0.09MPa and the temperature is 60℃. After two-stage evaporation, the COD value of the condensate is ≤50mg / L and the conductivity is ≤100μS / cm. It is directly reused in the water washing process, forming a dual-circulation washing system.

[0031] The tail gas from the hydrochloric acid desorption section and the chloromethylation reaction section is collected and treated in a two-stage packed tower. The packing material of the tower is polytetrafluoroethylene, and the packing height is 3.5m. In the first-stage absorption tower, a 12% sodium hydroxide solution is used as the absorbent, with the empty tower gas velocity controlled at 0.8m / s and the absorption temperature at 20℃. Countercurrent absorption is used to achieve an absorption rate of ≥98% for hydrogen chloride in the tail gas. When the concentration of the generated sodium chloride solution reaches 18%, it is sent to a vacuum distillation unit for distillation and concentration at -0.05MPa and 105℃ to recover sodium chloride crystals with a purity of ≥98%, which are supplied externally as chemical raw materials. In the second-stage absorption tower, a 6% sodium bicarbonate solution is used as the absorbent, with the empty tower gas velocity controlled at 1.0m / s and the absorption temperature at 25℃. This deeply purifies the residual acidic components in the tail gas, ensuring that the hydrogen chloride emission concentration in the tail gas is ≤10mg / m³. 3 When the pH of the secondary absorbent drops to 7.8, it is introduced into the alkaline washing process of the chloromethylation reaction section to replace the fresh alkaline solution for recycling.

[0032] Toluene was added to the reaction products as a solvent at a mass ratio of 1.3:1. The toluene used had a purity ≥99.0% and a moisture content ≤0.1%. The mixture was allowed to stand for 1.5 hours at room temperature and pressure to separate the upper organic phase and the lower aqueous phase using a separatory funnel. The upper organic phase was sent to a distillation column for distillation recovery. The column had 16 theoretical plates, a top temperature controlled at 110℃, and a reflux ratio of 2:1. The recovered toluene had a purity ≥99.0% and was directly reused in the material washing process. The lower aqueous phase was transferred to a crystallization vessel. It was first cooled to 25℃ using circulating water at a rate of 2℃ / h, held at this temperature for 1 hour, and then cooled to 6℃ using chilled brine at a rate of 1℃ / h. Crystallization was carried out at this constant temperature for 4 hours, promoting uniform crystal growth of biphenyl dichlorobenzyl crystals through a gradient cooling method.

[0033] The crystallized product was centrifuged and filtered using a horizontal spiral sedimentation centrifuge at 3000 r / min for 18 min, achieving a filtration accuracy of 1 μm, effectively separating the crystals from the mother liquor. The filter cake was washed once with recovered toluene at 10°C (0.3 times the mass of the filter cake) to remove minor impurities adhering to the crystal surface. The washed filter cake was then sent to a vacuum dryer at 70°C and -0.08 MPa for 5 h, with the moisture content monitored in real-time using an online moisture analyzer. The mother liquor from centrifugation and filtration was concentrated by distillation to remove some solvent, increasing the concentration of effective components to twice the original concentration before being recycled to the chloromethylation reaction section.

[0034] The hydrochloric acid analysis section regularly tests the purity of hydrogen chloride gas to ensure it reaches ≥99.5%; the chloromethylation reaction section monitors the reaction progress in real time using gas chromatography, and stops the reaction when the biphenyl conversion rate is ≥98%; the tail gas treatment section regularly tests the tail gas emission concentration to ensure that the hydrogen chloride emission concentration is ≤10mg / m³. 3 The refining and purification section uses high-performance liquid chromatography (HPLC) to test the purity of the product. The final product, biphenyl dichlorobenzyl, has a purity of ≥95% and an impurity content of ≤5%. A comprehensive quality traceability system is established to fully record and archive raw material inspection data, process parameters of each section, intermediate product test results, and finished product quality indicators during the production process of this batch.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A green production process for biphenyl dichlorobenzyl with a closed-loop solvent cycle, characterized in that, The specific steps of this process are as follows: S1. Hydrochloric acid analysis section: 30% hydrochloric acid and calcium chloride solution are mixed in proportion and reacted under heating conditions to prepare dry hydrogen chloride gas. The reaction residue is concentrated by flash evaporation to obtain a high-concentration calcium chloride solution, which is then reused for the dehydration reaction in this section to form a closed-loop cycle of calcium chloride. S2, Chloromethylation Reaction Section: Using biphenyl and paraformaldehyde as raw materials, zinc chloride as a single catalyst, and cyclohexane as a reaction solvent, hydrogen chloride gas prepared in S1 is introduced, and the reaction is first carried out in a low temperature section of 10-15℃ for 1-3 hours, and then the temperature is raised to a medium temperature section of 38-41℃ for 6-10 hours. After the reaction, the upper organic phase is distilled to recover cyclohexane and reused in the reaction, and the lower alkaline washing wastewater is concentrated by two-stage evaporation, and the condensate is reused in the water washing process to form a dual-circulation washing system. S3. Tail Gas Co-treatment Section: Collects the small amount of hydrogen chloride gas emitted from the hydrochloric acid desorption section and the tail gas generated from the chloromethylation reaction section, and introduces it into a two-stage alkaline absorption tower. The first-stage absorbent uses a 10%-15% sodium hydroxide solution to absorb and generate a sodium chloride solution, which is then concentrated by distillation to recover sodium chloride crystals. The second-stage absorbent uses a 5%-8% sodium bicarbonate solution to deeply purify the residual acidic components in the tail gas. The absorbent is periodically introduced into the alkaline washing process of the chloromethylation reaction section for recycling. S4. Refining and Purification Section: Toluene is added to the reaction product as a solvent. After standing and separating into layers, the upper organic phase is distilled to recover toluene for material washing. The lower aqueous phase is transferred to a crystallization kettle, first cooled to 25°C by circulating water, and then cooled to 5-10°C by refrigerated brine for gradient crystallization. The crystallized product is centrifuged, filtered, and vacuum dried to obtain biphenyl dichlorobenzyl product. The mother liquor is recycled to the chloromethylation reaction section for reuse.

2. The green production process of biphenyl dichlorobenzyl in a closed-loop solvent cycle according to claim 1, characterized in that, In step S1, the volume ratio of 30% hydrochloric acid to calcium chloride solution is 1:0.8-1.2, and the mass concentration of the calcium chloride solution is 32%-38%. The reaction is carried out at 80-100℃ under normal pressure. During the reaction, the pH value of the system is monitored in real time by an online pH meter and maintained between 1.5 and 2.

5. The flash evaporation concentration process adopts a reduced pressure flash evaporation method with a flash pressure of -0.06~-0.08MPa and a flash temperature of 110-130℃. After the calcium chloride concentration in the reaction residue is restored to 32%-38% by distillation concentration, it is directly pumped into the hydrochloric acid desorption reaction system for recycling. The single recycling rate of calcium chloride is ≥98%, and the cumulative number of recycling times is not less than 15 times. During the recycling process, a small amount of fresh calcium chloride solution is added to maintain the stability of the system concentration.

3. The green production process for biphenyl dichlorobenzyl chloride with closed-loop solvent recycling according to claim 1, characterized in that, The hydrochloric acid analysis section in S1 also includes a raw material pretreatment step: 30% hydrochloric acid is filtered by a precision filtration device to remove solid impurities before use, with a filtration accuracy of 0.5μm; The calcium chloride solution is prepared using industrial-grade calcium chloride. After preparation, it is treated with activated carbon adsorption to remove organic impurities. After the hydrogen chloride gas is generated, it is cooled to 20-30℃ by a cooler and then further dehydrated by a dryer filled with silica gel desiccant. The entire hydrochloric acid desorption section is equipped with a gas buffer tank, the volume of which is 1.5 times that of the reaction vessel.

4. The green production process of biphenyl dichlorobenzyl according to claim 1, characterized in that, In step S2, the molar ratio of biphenyl to paraformaldehyde is 1:2.0-2.3, the degree of polymerization of paraformaldehyde is 8-10, and the mass fraction of formaldehyde is ≥92%. The amount of zinc chloride catalyst is 5%-8% of the mass of biphenyl, the purity of zinc chloride is ≥98.5%, and it is free of water of crystallization impurities. The mass ratio of cyclohexane to biphenyl is 1.5-2.0:1, the purity of cyclohexane is ≥99.0%, and it is free of benzene and hexene impurities. During the reaction, the hydrogen chloride gas is introduced at a rate of 0.5-1.0 L / (min·L reaction system) through a constant pressure dripping device to ensure that the hydrogen chloride gas is in full contact with the reactants.

5. The green production process for biphenyl dichlorobenzyl chloride with closed-loop solvent recycling according to claim 1, characterized in that, The two-stage temperature control of the chloromethylation reaction section in S2 adopts a programmed temperature rise method. The low-temperature section is 10-15℃, and the reaction lasts for 1.5-2.5 hours. After the low-temperature section reaction is completed, the temperature is raised to the medium-temperature section of 38-41℃ at a rate of 1-2℃ / min, and the reaction lasts for 7-9 hours. The reactor adopts a jacketed heat exchange structure and is equipped with a precise temperature control system with a temperature control accuracy of ±0.5℃. At the same time, a stirring device is set up with a stirring rate of 60-100r / min.

6. The green production process for biphenyl dichlorobenzyl chloride with closed-loop solvent recycling according to claim 1, characterized in that, The dual-cycle washing system in S2 specifically includes a cyclohexane recovery cycle and an alkaline washing wastewater reuse cycle: In the cyclohexane recovery cycle, the upper organic phase after the reaction is distilled in a distillation tower at a temperature of 80-82℃ under normal pressure. The recovered cyclohexane has a purity of ≥99.0% and is directly reused in the next batch of chloromethylation reaction. The single-batch recovery rate of cyclohexane is ≥97%, and the total loss rate is ≤2%. In the alkaline washing wastewater reuse cycle, the lower alkaline washing wastewater is first pretreated to remove suspended impurities and then sent to a two-stage evaporator for evaporation and concentration. The first-stage evaporation pressure is -0.07MPa and the temperature is 80-90℃, and the second-stage evaporation pressure is -0.09MPa and the temperature is 60-70℃. After two-stage evaporation, the COD value of the condensate is ≤50mg / L and the conductivity is ≤100μS / cm. It is directly reused in the water washing process.

7. The green production process for biphenyl dichlorobenzyl chloride with closed-loop solvent recycling according to claim 1, characterized in that, The two-stage alkaline absorption tower in S3 adopts a packed tower structure with polytetrafluoroethylene (PTFE) packing material and a packing height of 3-5m. In the first-stage absorption tower, the mass concentration of sodium hydroxide solution is 12%-14%, the empty tower gas velocity is controlled at 0.8-1.0 m / s, and the absorption temperature is 20-25℃. Through countercurrent absorption, the absorption rate of hydrogen chloride in the tail gas is ≥98%. After the generated sodium chloride solution reaches a concentration of 18%-22%, it is sent to a vacuum distillation unit for distillation and concentration under conditions of -0.05~-0.07 MPa and 105-115℃ to recover sodium chloride crystals with a purity ≥98%, which can be supplied externally as a chemical raw material. In the second-stage absorption tower, the mass concentration of sodium bicarbonate solution is 6%-7%, the empty tower gas velocity is 1.0-1.2 m / s, and the absorption temperature is 25-30℃. This deeply purifies the residual hydrogen chloride gas in the tail gas, ensuring that the hydrogen chloride emission concentration in the tail gas is ≤10 mg / m³. 3 When the pH of the secondary absorbent drops to 7.5-8.5, it is introduced into the alkaline washing process of the chloromethylation reaction section to replace the fresh alkaline solution.

8. The green production process for biphenyl dichlorobenzyl chloride with closed-loop solvent recycling according to claim 1, characterized in that, In step S4, the mass ratio of toluene to the reaction product is 1.2-1.8:1, the purity of toluene is ≥99.0%, and the moisture content is ≤0.1%. The static stratification process is carried out under normal temperature and pressure conditions, with a stratification time of 1.5-2.5 hours. The upper organic phase and the lower aqueous phase are separated by a separating funnel. The upper organic phase is sent to a distillation column for distillation and recovery. The distillation column has 15-20 theoretical plates, the top temperature is controlled at 110-112℃, the reflux ratio is 2-3:1, and the purity of the recovered toluene is ≥99.0%, which can be directly reused in the material washing process. After the lower aqueous phase is transferred to the crystallization kettle, it is first cooled to 25℃ by circulating water at a cooling rate of 2-5℃ / h, kept at this temperature for 1-2 hours, and then cooled to 5-10℃ by passing chilled brine at a cooling rate of 1-3℃ / h. Crystallization is carried out at this constant temperature for 4-6 hours, and the biphenyl dichlorobenzyl crystals grow uniformly through a gradient cooling method.

9. The green production process of biphenyl dichlorobenzyl in a closed-loop solvent cycle according to claim 1, characterized in that, In step S4, a horizontal spiral sedimentation centrifuge is used for centrifugal filtration. The centrifugation speed is 3000-4000 r / min, the centrifugation time is 15-20 min, and the filtration accuracy is 1 μm, effectively separating crystals from mother liquor. The filter cake is washed 1-2 times with recovered toluene, with the amount of toluene used each time being 0.3-0.5 times the mass of the filter cake. The washing temperature is 10-15℃, which removes a small amount of impurities attached to the crystal surface. The vacuum drying process is carried out at a drying temperature of 70-80℃, a vacuum degree of -0.08~-0.09 MPa, and a drying time of 4-6 h. During the drying process, the moisture content of the product is monitored in real time using an online moisture analyzer. Before the mother liquor is recovered to the chloromethylation reaction section, it is distilled and concentrated to remove some of the solvent, increasing the concentration of the effective components in the mother liquor to 2-3 times the original concentration before being added to the reaction.

10. The green production process of biphenyl dichlorobenzyl in a closed-loop solvent cycle according to claim 1, characterized in that, The entire production process also includes process monitoring and quality control steps: the hydrochloric acid desorption section regularly tests the purity of hydrogen chloride gas, requiring a purity of ≥99.5%; The chloromethylation reaction section monitors the reaction progress in real time using gas chromatography, and stops the reaction when the biphenyl conversion rate is ≥98%. The tail gas treatment section regularly monitors the tail gas emission concentration to ensure that the hydrogen chloride emission concentration is ≤10mg / m³. 3 The refining and purification section uses high-performance liquid chromatography to test the purity of the products, requiring the finished product to have a purity of ≥95% and an impurity content of ≤5%. At the same time, a quality traceability system for raw materials, intermediate products, and finished products is established, and the production parameters and test data of each batch of products are recorded and archived.

Images