Method for preparing high-purity crystalline aluminum chloride from 1, 4-bis (4-fluorobenzoyl) benzene production wastewater

Abstract

The invention discloses a method for preparing high-purity crystalline aluminum chloride from 1, 4-bis (4-fluorobenzoyl) benzene production wastewater, which belongs to the technical field of 1, 4-bis (4-fluorobenzoyl) benzene production, and comprises the following steps: (1) introducing aluminum chloride wastewater generated in 1, 4-bis (4-fluorobenzoyl) benzene production into a triple-effect evaporator for cyclic concentration and evaporation; (2) filtering the crystallized aluminum chloride solution concentrated in the step (1), and mixing with hydrochloric acid, so that the pH value of the crystallized aluminum chloride solution is less than 2; (3) feeding the acidified crystalline aluminum chloride solution in the step (2) into a crystallizer for crystallization; and (4) feeding the material in the crystallizer in the step (3) to a centrifugal filter for filtering to obtain crystalline aluminum chloride with the purity of more than 98%, and returning the mother liquor to the crystallizer. According to the method, the aluminum chloride wastewater is treated by using the triple-effect evaporator, aluminum-containing insoluble substances generated by thermal decomposition and hydrolysis after evaporation are treated by adding hydrochloric acid, the purity of crystallized aluminum chloride is high and can be stabilized at 98% or above, and the standard of a premium grade product is met.

Description

Technical Field

[0001] The invention relates to the technical field of 1,4-bis(4-fluorobenzoyl)benzene production, and particularly to a method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater. Background Art

[0002] 1,4-bis(4-fluorobenzoyl)benzene is a key monomer used in the polyaryletherketone series of high-performance engineering plastics. The current industrial production method is to synthesize 1,4-bis(4-fluorobenzoyl)benzene from fluorobenzene and terephthaloyl chloride under the catalysis of aluminum chloride. During the post-treatment process, the reaction mixture is quenched with water as a quenching agent, forming a large amount of aluminum chloride wastewater. This wastewater contains a small amount of fluorobenzene and a large amount of crystalline aluminum chloride. If left untreated, it will not only cause serious environmental problems, but also lead to a waste of aluminum resources.

[0003] Patent CN106800346A uses activated carbon to decolorize organic wastewater produced by the Friedel-Crafts reaction, then uses toluene to extract and remove organic matter from the wastewater. Hydrogen chloride gas is introduced into the aqueous layer after extraction to saturate the aluminum chloride wastewater with hydrogen chloride gas, thereby obtaining a crystalline aluminum chloride precipitate. This method can obtain crystalline aluminum chloride, but the amount of hydrogen chloride gas used is more than 35.wt% of the wastewater mass, which wastes a large amount of hydrogen chloride gas and produces difficult-to-treat hydrogen chloride wastewater. Using a solvent to extract the organic matter from the wastewater also requires distillation, recovery, and separation of the extraction solvent, resulting in high energy consumption.

[0004] Patent CN11078691A uses diatomaceous earth, zeolite, etc. to adsorb aluminum chloride after treatment of the Friedel-Crafts reaction solution. The obtained filter cake is washed with an organic solvent and then dried. This method can remove aluminum chloride from the Friedel-Crafts reaction system. However, adsorbents such as diatomaceous earth are difficult to regenerate, and the adsorbed aluminum chloride releases a large amount of heat with water, which is highly dangerous. As a result, the filter cake can only be treated as hazardous waste.

[0005] Patent CN110330043A uses a method of adding sodium hydroxide solution to neutralize the acidic wastewater and produce polyaluminum chloride to treat the acidic aluminum-containing wastewater generated during the preparation of musk dew, while sodium chloride is produced as a by-product. The treatment conditions are mild, but the resulting products are polyaluminum chloride and sodium chloride, and the by-products have low economic value. At the same time, a large amount of sodium hydroxide is required.

[0006] Therefore, there is no method in the prior art to utilize the wastewater generated by 1,4-di(4-fluorobenzoyl)benzene with high added value.

[0007] In view of the above problems in the prior art, the present invention combines many years of design and use experience in related fields to design a method for preparing high-purity crystalline aluminum chloride from 1,4-di(4-fluorobenzoyl)benzene production wastewater to overcome the above defects. Summary of the Invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a method for preparing high-purity crystalline aluminum chloride from 1,4-di(4-fluorobenzoyl)benzene production wastewater to produce crystalline aluminum chloride with a purity greater than 98%. The method is economical and simple to operate.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a method for preparing high-purity crystalline aluminum chloride from 1,4-di(4-fluorobenzoyl)benzene production wastewater, comprising the following steps: (1) Circular evaporation: the crystalline aluminum chloride wastewater produced by the production of 1,4-di(4-fluorobenzoyl)benzene is passed into a three-effect evaporator for cyclic concentration and evaporation to obtain a concentrated crystalline aluminum chloride solution and steam condensate containing fluorobenzene. The steam condensate containing fluorobenzene enters a recovery water tank, and the water in the recovery water tank is used to quench the next Friedel-Crafts reaction; (2) Acidification: mixing the concentrated crystalline aluminum chloride solution of step (1) with a hydrochloric acid solution having a concentration of 30.wt%-37.wt% to adjust the pH of the crystalline aluminum chloride solution to less than 2; (3) crystallization, feeding the acidified crystalline aluminum chloride solution of step (2) into a crystallizer for crystallization; (4) Filtration: The material from the crystallizer in step (3) is sent to a centrifugal filter for filtration to obtain crystalline aluminum chloride with a purity greater than 98%, and the mother liquor is returned to the crystallizer.

[0010] Preferably, the three-effect evaporator in step (1) comprises a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator connected in sequence, each of the evaporators comprises a heating chamber and a separation chamber connected in sequence, the temperature of the heating chamber of the first-effect evaporator is 101-110° C., and the pressure of the separation chamber of the first-effect evaporator is 1 bar; The temperature of the heating chamber of the second-effect evaporator is 80-95°C, and the pressure of the separation chamber of the second-effect evaporator is 0.4-0.72 bar; The temperature of the heating chamber of the third-effect evaporator is 62-75° C., and the pressure of the separation chamber of the third-effect evaporator is 0.05-0.27 bar.

[0011] Preferably, the triple-effect evaporator is a triple-effect falling film evaporator; the separation chamber is made of one of the materials selected from the group consisting of glass lining, phenolic resin impregnated graphite, and silicon carbide; the height of the packing layer in the separation chamber is 0.4 m; the packing is a ceramic material; and the heating chamber is made of silicon carbide or phenolic resin impregnated graphite.

[0012] Preferably, the concentrated crystalline aluminum chloride solution is obtained from the separation chamber of the third-effect evaporator, and part of the concentrated crystalline aluminum chloride solution enters a static mixer and is mixed with a hydrochloric acid solution, wherein the volume of the hydrochloric acid solution added is 0.5%-3% of the volume of the crystalline aluminum chloride solution in the static mixer.

[0013] Preferably, the pH of the crystallized aluminum chloride solution in step (2) is less than 1, and the pH of the crystallized aluminum chloride solution is monitored by an online pH meter.

[0014] Preferably, the crystallizer in step (3) is one of a forced circulation crystallizer, an Oslo crystallizer, and a DTB crystallizer; the crystallizer temperature is 60-70°C, and the pressure is 0.01-0.1 bar.

[0015] Preferably, the crystallizer in step (3) is a DTB crystallizer.

[0016] Preferably, the centrifugal filter in step (4) is one of a spiral unloading filter centrifuge, a spiral unloading sedimentation filter, a filter centrifuge, a horizontal scraper unloading centrifuge, a horizontal piston pusher centrifuge, and a centrifugal unloading centrifuge.

[0017] Preferably, the centrifugal filter is a spiral discharge filter centrifuge.

[0018] The invention is beneficial in that: 1. The present invention adopts a triple-effect evaporator, a static mixer and a crystallizer in series to treat the crystallized aluminum chloride wastewater, thereby realizing a fully continuous treatment process and stable control; during the evaporation process of the triple-effect evaporator, steam at each stage is coupled and utilized to improve steam utilization efficiency.

[0019] 2. The present invention increases the heat transfer temperature difference between each effect and reduces the total heat exchange area of the evaporation and crystallization unit by controlling the temperature of the first-effect evaporator to be greater than the decomposition temperature of the crystalline aluminum chloride. At the same time, it ensures that the water vapor temperature of the third effect is greater than 50°C, and can use circulating water for condensation, thereby reducing operating energy consumption. By adding hydrochloric acid, insoluble matter produced by the high-temperature decomposition of the crystalline aluminum chloride and insoluble matter such as aluminum hydroxide produced by the volatilization of hydrogen chloride caused by the hydrolysis of the crystalline aluminum chloride are dissolved. At the same time, hydrochloric acid can reduce the solubility of the crystalline aluminum chloride without affecting the solubility of other impurity metal ions. The obtained crystalline aluminum chloride has high purity and can be stabilized at more than 98%.

[0020] 3. The present invention is directed to a production process for 1,4-bis(4-fluorobenzoyl)benzene. An organic matter removal device is omitted before the triple-effect evaporator, thereby reducing investment in fixed equipment. At the same time, organic corrosion-resistant equipment such as silicon carbide, glass lining, and phenolic resin-impregnated graphite are selected for evaporation and crystallization to prevent fluorobenzene from corroding the equipment. Fluorobenzene and steam condensate obtained from the triple-effect evaporator and crystallizer enter a recovery water tank. The material in the recovery water tank is recycled to the front-end process and used as a quenching agent to quench the next Friedel-Crafts reaction. DETAILED DESCRIPTION

[0021] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to specific embodiments.

[0022] A method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater comprises the following steps: (1) Circular evaporation: the crystalline aluminum chloride wastewater produced by the production of 1,4-di(4-fluorobenzoyl)benzene is passed into a three-effect evaporator for cyclic concentration and evaporation to obtain a concentrated crystalline aluminum chloride solution and steam condensate containing fluorobenzene. The steam condensate containing fluorobenzene enters a recovery water tank, and the water in the recovery water tank is used to quench the next Friedel-Crafts reaction; (2) Acidification: the concentrated crystalline aluminum chloride solution in step (1) is mixed with a hydrochloric acid solution having a concentration of 30.wt% to 37.wt% to adjust the pH of the crystalline aluminum chloride solution to less than 2. More preferably, the pH of the crystalline aluminum chloride solution is less than 1, and the pH is monitored by an online pH meter; (3) crystallization, feeding the acidified crystalline aluminum chloride solution of step (2) into a crystallizer for crystallization; (4) Filtration: The material from the crystallizer in step (3) is sent to a centrifugal filter for filtration to obtain crystalline aluminum chloride with a purity greater than 98%, and the mother liquor is returned to the crystallizer.

[0023] Since the thermal decomposition temperature of crystalline aluminum chloride is 100°C, if the triple-effect evaporation crystallization process is only operated below 100°C, the direct decomposition of crystalline aluminum chloride can be avoided. However, as the water in the raw material evaporates, the hydrolysis equilibrium of the crystalline aluminum chloride will shift to the right (aluminum chloride hydrolysis ionization equilibrium equation), and a small amount of hydrogen chloride gas will condense in the condenser together with water vapor, causing the solution to hydrolyze and generate insoluble substances such as aluminum hydroxide, affecting the purity of the product. It is also difficult to obtain high-purity crystalline aluminum chloride.

[0024] The equilibrium equation for the hydrolysis and ionization of aluminum chloride in aqueous solution In addition, the boiling point of the saturated solution in the evaporation process of the crystalline aluminum chloride solution increases by about 25°C due to the salt effect. If the three-effect evaporation process is operated below 100°C, the heat transfer temperature difference of each effect is about 8-10°C. The heat transfer temperature difference is too low, resulting in a significant increase in equipment investment costs. At the same time, during the operation, the temperature of the evaporated water vapor in the third (or first) effect is generally less than 40°C, resulting in the need to use cold salt for condensation, which results in high operating energy consumption costs.

[0025] In the present invention, crystallized aluminum chloride wastewater is first evaporated through a triple-effect evaporator to increase the content of crystallized aluminum chloride in the wastewater. The first effect of the triple-effect evaporator is atmospheric pressure evaporation, and the temperature of the first-effect evaporator is controlled to be greater than the decomposition temperature of the crystallized aluminum chloride, so as to increase the heat transfer temperature difference and reduce the total heat exchange area of the evaporation and crystallization unit. At the same time, the water vapor temperature of the third effect is ensured to be greater than 50°C, so that circulating water can be used for condensation and the operation energy consumption is reduced. Then, a hydrochloric acid solution is used to adjust the pH value of the solution, and aluminum-containing insoluble matter generated by hydrolysis and thermal decomposition in the system is converted into crystallized aluminum chloride. At the same time, the hydrochloric acid solution can reduce the solubility of the crystallized aluminum chloride in water without affecting the solubility of impurity metal ions. The impurity metal ions are enriched in the mother liquor, and the obtained solid is crystallized aluminum chloride with a purity of more than 98%, thereby reducing the operation cost of the equipment.

[0026] In the present invention, the three-effect evaporator in step (1) includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator connected in sequence, each evaporator including a heating chamber and a separation chamber connected in sequence, and the steam in the heating chamber can enter the heating chamber of the next-effect evaporator for secondary utilization, thereby improving heat utilization efficiency. The temperature of the heating chamber of the first-effect evaporator is 101-110°C, and the pressure of the separation chamber of the first-effect evaporator is 1 bar. The temperature of the heating chamber of the second-effect evaporator is 80-95°C, and the pressure of the separation chamber of the second-effect evaporator is 0.4-0.72 bar. The temperature of the heating chamber of the third-effect evaporator is 62-75°C, and the pressure of the separation chamber of the third-effect evaporator is 0.05-0.27 bar.

[0027] The triple-effect evaporator is a conventional device. Specifically, after the crystallized aluminum chloride wastewater enters the separation chamber of the first-effect evaporator, it enters the heating chamber of the first-effect evaporator through a first-effect circulation pump for heating. After being heated in the heating chamber, it returns to the separation chamber of the first-effect evaporator. The material in the separation chamber of the first-effect evaporator partially enters the separation chamber of the second-effect evaporator through the first-effect circulation pump, and then enters the heating chamber of the second-effect evaporator through the second-effect circulation pump. The remaining part circulates in the separation chamber and heating chamber of the first-effect evaporator. After that, the material in the heating chamber of the second-effect evaporator is heated and then enters the separation chamber of the second-effect evaporator. The material in the separation chamber of the second-effect evaporator partially enters the separation chamber of the third-effect evaporator through the second-effect circulation pump, and then enters the heating chamber of the third-effect evaporator through the triple-effect circulation pump. The remaining part circulates in the separation chamber and heating chamber of the second-effect evaporator. After the material is heated in the heating chamber of the third-effect evaporator, it returns to the separation chamber of the third-effect evaporator. The material in the separation chamber of the third-effect evaporator is the concentrated crystalline aluminum chloride solution. A part of it enters the separation chamber of the third-effect evaporator for circulation through the three-effect circulation pump, and the other part enters the static mixer to be mixed with the hydrochloric acid solution.

[0028] The triple-effect evaporator is a triple-effect falling film evaporator, in which the heating chamber is made of phenolic resin impregnated graphite or silicon carbide. The separation chamber is made of one of glass-lined material, phenolic resin impregnated graphite, and silicon carbide. A packing layer is provided in the separation chamber, the packing layer height is 0.4m, and the packing is a ceramic material. In the present invention, the heating chamber adopts a device containing an organic corrosion-resistant material to carry out evaporation and crystallization to prevent fluorobenzene from corroding the equipment, so that the crystallized aluminum chloride wastewater can be directly evaporated and crystallized, omitting the organic separation step and reducing the investment in fixed equipment. The fluorobenzene and steam condensate obtained by the triple-effect evaporator and crystallizer enter the recovery water tank and can be returned to the front-end process as a quenching agent to quench the next Friedel-Crafts reaction, thereby realizing the recycling of the reaction raw materials and reducing the generation of waste liquid.

[0029] Specifically, the partially concentrated crystalline aluminum chloride solution in the separation chamber of the third-effect evaporator in step (1) is introduced into a static mixer and mixed with a hydrochloric acid solution. The volume of the hydrochloric acid solution added is 0.5%-3% of the volume of the crystalline aluminum chloride solution in the static mixer. The amount of hydrochloric acid solution added is controlled to improve the purity of the crystalline aluminum chloride while avoiding the generation of difficult-to-treat high-concentration hydrochloric acid wastewater. The crystallizer is one of a forced circulation crystallizer, an Oslo crystallizer, and a DTB crystallizer. The crystallizer temperature is 60-70°C and the pressure is 0.01-0.1 bar. The DTB crystallizer is preferred.

[0030] The centrifugal filter is one of a spiral unloading filter centrifuge, a spiral unloading sedimentation filter, a filter centrifuge, a horizontal scraper unloading centrifuge, a horizontal piston pusher centrifuge, and a centrifugal unloading centrifuge, and is more preferably a spiral unloading filter centrifuge. The specific embodiments are as follows Example 1

[0031] In this embodiment, the triple-effect evaporator is a triple-effect falling film evaporator, the heating chamber is made of phenolic resin impregnated graphite, the separation chamber is made of glass-lined material, the crystallizer is a DTB crystallizer, and the centrifugal filter is a horizontal spiral discharge centrifugal filter; (1) Circulating evaporation: The crystalline aluminum chloride wastewater (mass fraction of crystalline aluminum chloride is 17.6 wt% and temperature is 30°C) produced by the production of 1,4-di(4-fluorobenzoyl)benzene enters the first-effect evaporator, whose heating chamber temperature is 106°C and the separation chamber pressure is 1 bar. The steam evaporated from the first-effect evaporator enters the second-effect evaporator for secondary use. The material in the separation chamber of the first-effect evaporator partially enters the separation chamber of the second-effect evaporator through the first-effect circulation pump, and then enters the heating chamber of the second-effect evaporator through the second-effect circulation pump. The other part circulates in the separation chamber and heating chamber of the first-effect evaporator. The mass fraction of crystalline aluminum chloride when the first-effect evaporator is discharged is 22.8 wt%. The heating chamber temperature of the second-effect evaporator is 90°C, and the separation chamber pressure of the second-effect evaporator is 0.47 bar. The steam evaporated from the second-effect evaporator enters the third-effect evaporator for secondary use. The material in the separation chamber of the second-effect evaporator is partially transferred to the separation chamber of the third-effect evaporator via a second-effect circulation pump, while the remaining material circulates through the separation chamber and heating chamber of the second-effect evaporator. The mass fraction of crystallized aluminum chloride discharged from the second-effect evaporator is 32.5 wt%. The temperature of the third-effect evaporator is 70°C, and the pressure in the separation chamber of the third-effect evaporator is 0.12 bar. The steam from the third-effect evaporator enters the third-effect condenser. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the third-effect evaporator is 50 wt%. The steam condensate containing fluorobenzene enters the recovery tank. (2) Acidification: a portion of the material in the separation chamber of the third-effect evaporator is circulated into the separation chamber of the third-effect evaporator through a three-effect circulation pump, and the other portion enters a static mixer and is mixed with a hydrochloric acid solution with a concentration of 30 wt%. The volume of hydrochloric acid added is 1% of the volume of the crystalline aluminum chloride solution in the static mixer. The pH of the solution after mixing is 1.5; (3) Crystallization: the material in step (2) enters the DTB crystallizer, the temperature of the DTB crystallizer is 70°C, the pressure is 0.09 bar, and the amount of water evaporated from the DTB crystallizer is 50% of the feed amount; (4) Filtration: The material from step (3) is fed into a horizontal spiral discharge centrifugal filter via a crystallization feed pump at a speed of 6000 r / min. The mother liquor then re-enters the DTB crystallizer. The purity of the crystalline aluminum chloride product is 98.5 wt%, with no aluminum-containing insoluble matter. Example 2

[0032] In this embodiment, the triple-effect evaporator is a triple-effect falling film evaporator, the heating chamber is made of phenolic resin impregnated graphite, the separation chamber is made of glass-lined material, the crystallizer is a DTB crystallizer, and the centrifugal filter is a horizontal spiral discharge centrifugal filter; (1) Circulating evaporation: The crystalline aluminum chloride wastewater (with a mass fraction of 10.8 wt% and a temperature of 30°C) produced by the production of 1,4-di(4-fluorobenzoyl)benzene enters the first-effect evaporator, whose heating chamber temperature is 102°C and the separation chamber pressure is 1 bar. The steam discharged from the first-effect evaporator enters the second-effect evaporator for secondary use. The material in the separation chamber of the first-effect evaporator partially enters the separation chamber of the second-effect evaporator through the first-effect circulation pump, and then enters the heating chamber of the second-effect evaporator through the second-effect circulation pump. The other part circulates in the separation chamber of the first-effect evaporator and its heating chamber. The mass fraction of crystalline aluminum chloride when discharging from the separation chamber of the first-effect evaporator is 14.9 wt%. The heating chamber temperature of the second-effect evaporator is 90°C, and the separation chamber pressure of the second-effect evaporator is 0.6 bar. The steam discharged from the second-effect evaporator enters the third-effect evaporator for secondary use. The material in the separation chamber of the second-effect evaporator is partially transferred to the separation chamber of the third-effect evaporator via a second-effect circulation pump, while the remaining material circulates within the separation chamber and the heating chamber of the second-effect evaporator. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the second-effect evaporator is 23.6 wt%. The heating chamber temperature of the third-effect evaporator is 65°C, and the pressure in the separation chamber of the third-effect evaporator is 0.15 bar. The steam from the third-effect evaporator enters a third-effect condenser. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the third-effect evaporator is 50 wt%. The steam condensate containing fluorobenzene enters the recovery tank. (2) Acidification: a portion of the material in the separation chamber of the third-effect evaporator is circulated into the separation chamber of the third-effect evaporator through a three-effect circulation pump, and the other portion enters a static mixer and is mixed with a hydrochloric acid solution with a concentration of 35 wt%. The volume of hydrochloric acid added is 1.5% of the volume of the crystalline aluminum chloride solution in the static mixer. The pH of the solution after mixing is 1.5; (3) Crystallization: the material in step (2) enters the DTB crystallizer. The temperature of the DTB crystallizer is 61°C, the pressure is 0.02 bar, and the amount of water evaporated from the DTB crystallizer is 50% of the feed amount. (4) Filtration: The material from step (3) is fed into a horizontal spiral discharge centrifugal filter via a crystallization feed pump at a centrifuge speed of 5000 r / min. The mother liquor then re-enters the DTB crystallizer. The purity of the crystalline aluminum chloride product is 98.7 wt%, with no aluminum-containing insoluble matter. Example 3

[0033] In this embodiment, the triple-effect evaporator is a triple-effect falling film evaporator, the heating chamber is made of silicon carbide, the separation chamber is made of silicon carbide, the crystallizer is an Oslo crystallizer, and the centrifugal filter is a horizontal scraper discharge centrifuge; (1) Circulating evaporation: The crystalline aluminum chloride wastewater (with a mass fraction of 21.2 wt% and a temperature of 30°C) produced by the production of 1,4-di(4-fluorobenzoyl)benzene enters the first-effect evaporator, whose heating chamber temperature is 109°C and the separation chamber pressure is 1 bar. The steam discharged from the first-effect evaporator enters the second-effect evaporator for secondary use. The material in the separation chamber of the first-effect evaporator partially enters the separation chamber of the second-effect evaporator through the first-effect circulation pump, and then enters the heating chamber of the second-effect evaporator through the second-effect circulation pump. The other part circulates in the separation chamber and heating chamber of the first-effect evaporator. The mass fraction of crystalline aluminum chloride when discharging from the separation chamber of the first-effect evaporator is 26.6 wt%. The heating chamber temperature of the second-effect evaporator is 82°C, and the separation chamber pressure of the second-effect evaporator is 0.4 bar. The steam discharged from the second-effect evaporator enters the third-effect evaporator for secondary use. The material in the separation chamber of the second-effect evaporator is partially transferred to the separation chamber of the third-effect evaporator via a second-effect circulation pump, while the remaining material circulates through the separation chamber and heating chamber of the second-effect evaporator. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the second-effect evaporator is 35.3 wt%. The temperature of the heating chamber of the third-effect evaporator is 62°C, and the pressure in the separation chamber of the third-effect evaporator is 0.10 bar. The steam from the third-effect evaporator enters the third-effect condenser. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the third-effect evaporator is 50 wt%. The steam condensate containing fluorobenzene enters the recovery tank. (2) Acidification: a portion of the material in the separation chamber of the third-effect evaporator is circulated into the separation chamber of the third-effect evaporator through a three-effect circulation pump, and the other portion enters a static mixer and is mixed with a hydrochloric acid solution with a concentration of 37 wt%. The volume of hydrochloric acid added is 2% of the volume of the crystalline aluminum chloride solution in the static mixer. The pH of the solution after mixing is 1; (3) Crystallization: the material in step (2) enters the Oslo crystallizer. The temperature of the Oslo crystallizer is 63°C, the pressure is 0.05 bar, and the amount of water evaporated from the Oslo crystallizer is 50% of the feed amount. (4) Filtration: The material from step (3) is fed into a horizontal scraper discharge centrifuge via a crystallization feed pump at a speed of 5000 r / min. The mother liquor then re-enters the Oslo crystallizer. The purity of the crystalline aluminum chloride product is 98.6 wt%, with no aluminum-containing insoluble matter. Example 4

[0034] In this embodiment, the triple-effect evaporator is a triple-effect falling film evaporator, the heating chamber is made of phenolic resin impregnated graphite, the separation chamber is made of phenolic resin impregnated graphite, the crystallizer is a forced circulation crystallizer, and the centrifugal filter is a horizontal piston pusher centrifuge; (1) Circulating evaporation: The crystalline aluminum chloride wastewater (with a mass fraction of 35.4 wt% and a temperature of 30°C) produced by the production of 1,4-di(4-fluorobenzoyl)benzene enters the first-effect evaporator, whose heating chamber temperature is 110°C and the separation chamber pressure is 1 bar. The steam discharged from the first-effect evaporator enters the second-effect evaporator for secondary use. The material in the separation chamber of the first-effect evaporator partially enters the separation chamber of the second-effect evaporator through the first-effect circulation pump, and then enters the heating chamber of the second-effect evaporator through the second-effect circulation pump. The other part circulates in the separation chamber and heating chamber of the first-effect evaporator. The mass fraction of crystalline aluminum chloride when discharging from the separation chamber of the first-effect evaporator is 39.4 wt%. The heating chamber temperature of the second-effect evaporator is 80°C, and the separation chamber pressure of the second-effect evaporator is 0.47 bar. The steam discharged from the second-effect evaporator enters the third-effect evaporator for secondary use. The material in the separation chamber of the second-effect evaporator is partially transferred to the separation chamber of the third-effect evaporator via a second-effect circulation pump, while the remaining material circulates through the separation chamber and heating chamber of the second-effect evaporator. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the second-effect evaporator is 44.3 wt%. The temperature of the heating chamber of the third-effect evaporator is 62°C, and the pressure in the separation chamber of the third-effect evaporator is 0.06 bar. The steam from the third-effect evaporator enters the third-effect condenser. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the third-effect evaporator is 50 wt%. The steam condensate containing fluorobenzene enters the recovery tank. (2) Acidification: a portion of the material in the separation chamber of the third-effect evaporator is circulated into the separation chamber of the third-effect evaporator through a three-effect circulation pump, and the other portion enters a static mixer and is mixed with a hydrochloric acid solution with a concentration of 33 wt%. The volume of hydrochloric acid added is 1.6% of the volume of the crystalline aluminum chloride solution in the static mixer. The pH of the solution after mixing is 1; (3) Crystallization: the material in step (2) enters a forced circulation crystallizer, the temperature of the forced circulation crystallizer is 62°C, the pressure is 0.02 bar, and the amount of evaporated water in the forced circulation crystallizer is 50% of the feed amount; (4) Filtration: The material from step (3) is fed into a horizontal piston pusher centrifuge via a crystallization feed pump at a speed of 5000 r / min. The mother liquor then re-enters the forced circulation crystallizer. The purity of the crystalline aluminum chloride product is 99.3 wt%, with no aluminum-containing insoluble matter. Example 5

[0035] In this embodiment, the triple-effect evaporator is a triple-effect falling film evaporator, the heating chamber is made of phenolic resin impregnated graphite, the separation chamber is made of phenolic resin impregnated graphite, the crystallizer is an Oslo crystallizer, and the centrifugal filter is a horizontal piston pusher centrifuge; (1) Circulating evaporation: The crystalline aluminum chloride wastewater (with a mass fraction of 4.7 wt% and a temperature of 30°C) produced by the production of 1,4-di(4-fluorobenzoyl)benzene enters the first-effect evaporator, whose heating chamber temperature is 101°C and the separation chamber pressure is 1 bar. The steam discharged from the first-effect evaporator enters the second-effect evaporator for secondary use. The material in the separation chamber of the first-effect evaporator partially enters the separation chamber of the second-effect evaporator through the first-effect circulation pump, and then enters the heating chamber of the second-effect evaporator through the second-effect circulation pump. The other part circulates in the separation chamber and heating chamber of the first-effect evaporator. The mass fraction of crystalline aluminum chloride when discharging from the separation chamber of the first-effect evaporator is 6.9 wt%. The heating chamber temperature of the second-effect evaporator is 95°C, and the separation chamber pressure of the second-effect evaporator is 0.72 bar. The steam discharged from the second-effect evaporator enters the third-effect evaporator for secondary use. The material in the separation chamber of the second-effect evaporator is partially transferred to the separation chamber of the third-effect evaporator via a second-effect circulation pump, while the remaining material circulates through the separation chamber and heating chamber of the second-effect evaporator. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the second-effect evaporator is 12.6 wt%. The temperature of the heating chamber of the third-effect evaporator is 75°C, and the pressure in the separation chamber of the third-effect evaporator is 0.27 bar. The steam from the third-effect evaporator enters a third-effect condenser. The mass fraction of crystallized aluminum chloride discharged from the separation chamber of the third-effect evaporator is 50 wt%. The steam condensate containing fluorobenzene enters the recovery tank. (2) Acidification: a portion of the material in the separation chamber of the third-effect evaporator is circulated into the separation chamber of the third-effect evaporator through a three-effect circulation pump, and the other portion enters a static mixer and is mixed with a hydrochloric acid solution with a concentration of 36 wt%. The volume of hydrochloric acid added is 1.8% of the volume of the crystalline aluminum chloride solution in the static mixer. The pH of the solution after mixing is 1; (3) Crystallization: the material in step (2) enters the Oslo crystallizer, the temperature of the Oslo crystallizer is 63°C, the pressure is 0.03 bar, and the amount of water evaporated from the Oslo crystallizer is 50% of the feed amount; (4) Filtration: The material from step (3) is fed into a horizontal piston pusher centrifuge via a crystallization feed pump at a speed of 5000 r / min. The mother liquor then re-enters the Oslo crystallizer. The purity of the crystalline aluminum chloride product is 99.2 wt%, with no aluminum-containing insoluble matter.

[0036] It should be understood that the purpose of these embodiments is only to illustrate the present invention and is not intended to limit the scope of protection of the present invention. In addition, it should also be understood that after reading the technical content of the present invention, those skilled in the art may make various changes, modifications and / or variations to the present invention, and all of these equivalent forms also fall within the scope of protection defined by the claims appended hereto.

Claims

1. A method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater, characterized in that: The following steps are involved: (1) Circular evaporation: the crystalline aluminum chloride wastewater produced by the production of 1,4-di(4-fluorobenzoyl)benzene is passed into a three-effect evaporator for cyclic concentration and evaporation to obtain a concentrated crystalline aluminum chloride solution and steam condensate containing fluorobenzene. The steam condensate containing fluorobenzene enters a recovery water tank, and the water in the recovery water tank is used to quench the next Friedel-Crafts reaction; (2) acidification, mixing the crystalline aluminum chloride solution concentrated in step (1) with a hydrochloric acid solution having a concentration of 30.wt%-37.wt% to adjust the pH of the crystalline aluminum chloride solution to less than 2; (3) crystallization, feeding the acidified crystalline aluminum chloride solution of step (2) into a crystallizer for crystallization; (4) Filtration: The material from the crystallizer in step (3) is sent to a centrifugal filter for filtration to obtain crystalline aluminum chloride with a purity greater than 98%, and the mother liquor is returned to the crystallizer.

2. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 1, characterized in that: The three-effect evaporator in step (1) includes a first-effect evaporator, a second-effect evaporator, and a third-effect evaporator connected in sequence, each of the evaporators includes a heating chamber and a separation chamber connected in sequence, the temperature of the heating chamber of the first-effect evaporator is 101-110° C., and the pressure of the separation chamber of the first-effect evaporator is 1 bar; The temperature of the heating chamber of the second-effect evaporator is 80-95°C, and the pressure of the separation chamber of the second-effect evaporator is 0.4-0.72 bar; The temperature of the heating chamber of the third-effect evaporator is 62-75° C., and the pressure of the separation chamber of the third-effect evaporator is 0.05-0.27 bar.

3. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 2, characterized in that: The triple-effect evaporator is a triple-effect falling film evaporator; The separation chamber is made of one of the materials selected from the group consisting of glass lining, phenolic resin impregnated graphite, and silicon carbide. The height of the packing layer in the separation chamber is 0.4 m, and the packing is made of ceramic material. The heating chamber is made of silicon carbide or phenolic resin impregnated graphite.

4. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 2, characterized in that: The concentrated crystalline aluminum chloride solution is obtained from the separation chamber of the third-effect evaporator. Part of the concentrated crystalline aluminum chloride solution enters a static mixer and is mixed with a hydrochloric acid solution. The volume of the hydrochloric acid solution added is 0.5%-3% of the volume of the crystalline aluminum chloride solution in the static mixer.

5. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 1, characterized in that: In step (2), the pH of the crystallized aluminum chloride solution is less than 1, and the pH of the crystallized aluminum chloride solution is monitored by an online pH meter.

6. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 1, characterized in that: The crystallizer in step (3) is one of a forced circulation crystallizer, an Oslo crystallizer, and a DTB crystallizer; the crystallizer temperature is 60-70° C., and the pressure is 0.01-0.1 bar.

7. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 6, characterized in that: The crystallizer is a DTB crystallizer.

8. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 1, characterized in that: The centrifugal filter in step (4) is one of a spiral unloading filter centrifuge, a spiral unloading sedimentation filter, a filter centrifuge, a horizontal scraper unloading centrifuge, a horizontal piston pusher centrifuge, and a centrifugal unloading centrifuge.

9. The method for preparing high-purity crystalline aluminum chloride from 1,4-bis(4-fluorobenzoyl)benzene production wastewater according to claim 8, characterized in that: The centrifugal filter is a spiral unloading filtering centrifuge.

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