A continuous separation process for a catalyst for the chlorination of o-chlorotoluene

Abstract

The application discloses a continuous separation method of o-chlorotoluene chlorination liquid and a catalyst, which adopts a continuous freezing treatment and filtration method, and first freezes the chlorination liquid to precipitate most of the catalyst, then removes the precipitated catalyst through filtration, and then circulates and evaporates the filtrate to a concentrated liquid, so that the content of the catalyst in the concentrated liquid is 5-10 wt%; after cooling, the concentrated liquid is mixed with the frozen chlorination liquid suspension to be filtered again. The application uses the continuous freezing and filtration method, uses the property that temperature significantly affects the solubility of the catalyst in the chlorination liquid, separates most of the catalyst from the chlorination liquid, removes the remaining catalyst which is not precipitated by freezing through evaporation of the filtrate, and realizes the continuous separation of the insoluble solid catalyst and the o-chlorotoluene chlorination liquid. The application not only avoids the defects that a large amount of waste water containing metal salts is generated in the process of removing the catalyst in the chlorination liquid through the traditional water washing and alkali washing methods, but also realizes the resource recycling of the catalyst.

Description

Technical Field

[0001] This invention relates to a separation method, specifically to a continuous separation method for o-chlorotoluene chlorination catalyst, and more particularly to a method for continuously separating the catalyst from a chlorination liquid used in the catalytic chlorination of o-chlorotoluene to produce dichlorotoluene. Background Technology

[0002] 2,3-Dichlorotoluene and 2,6-Dichlorotoluene are both important intermediates in the preparation of fungicides, insecticides, herbicides, preservatives, dyes, pigments, and photosensitive materials. Dichlorotoluene is usually obtained by reacting o-chlorotoluene with chlorine gas in the presence of a Lewis acid catalyst. The chlorination product contains 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,6-dichlorotoluene, and 3,4-dichlorotoluene.

[0003] Common Lewis acid catalysts include inorganic chlorides such as aluminum chloride, ferric chloride, and zinc chloride, which have a certain solubility in aromatic hydrocarbons. After the chlorination reaction is complete, distillation is required to separate the chlorinated aromatic hydrocarbon products. Inorganic chlorides can precipitate during distillation, causing column blockage and disrupting production; furthermore, inorganic chlorides are highly acidic and can corrode the distillation equipment. Therefore, inorganic chlorides must be removed before product distillation.

[0004] A common method for removing chlorides utilizes the high solubility of inorganic chlorides in water, employing a process of washing with water followed by alkaline washing. The purpose of washing with water first and then alkaline washing is to reduce the amount of alkali used and ensure that the chlorinated solution after alkaline washing is neutral or slightly alkaline. However, the main drawback of this method is that the water washing generates a large amount of acidic wastewater containing organic aluminum chloride. At the same time, because aluminum chloride is highly susceptible to hydrolysis, it is completely destroyed during the water washing process, turning into aluminum hydroxide, which cannot be recycled, resulting in resource waste, increased production costs, and significant environmental pressure and catalyst costs for enterprises. Therefore, process innovation is necessary. Summary of the Invention

[0005] The purpose of this invention is to solve the environmental problem of generating a large amount of wastewater during the separation of catalysts in o-chlorotoluene chlorination solution. This invention provides a continuous separation method for o-chlorotoluene chlorination catalysts. The method uses continuous freeze filtration, taking advantage of the property that temperature significantly affects the solubility of the catalyst in the chlorination solution, to separate most of the catalyst from the chlorination solution. The filtrate after the separation of most of the catalyst is then evaporated to remove the remaining unfreezed catalyst, thus achieving continuous separation of the insoluble solid catalyst from the o-chlorotoluene chlorination solution. The separated catalyst can then be recycled.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A continuous separation method for o-chlorotoluene chlorination liquid and catalyst is provided, which employs continuous freezing and filtration. First, the chlorination liquid is frozen until most of the catalyst precipitates. The precipitated catalyst is removed by filtration. The filtrate is then evaporated in a circulating manner until the catalyst content in the concentrate is about 5-10 wt%. After cooling, the concentrate is mixed with the frozen chlorination liquid suspension and filtered again.

[0008] Specifically, a continuous separation method for o-chlorotoluene chlorination catalyst includes the following steps:

[0009] Step (1), freezing: The chlorination solution is continuously fed into a freezer for freezing treatment to obtain a chlorination suspension containing solid catalyst particles;

[0010] Step (2), Filtration: The chlorination suspension is passed through the first filter to remove the precipitated catalyst. The filtrate enters the filtrate tank. When the filter cake capacity reaches the design value of the first filter, the chlorination suspension is switched to the second filter connected in parallel with the first filter for filtration. At the same time, the filtrate in the filtrate tank is used to backwash the first filter. When the filter cake capacity reaches the design value of the second filter, the chlorination suspension is switched to the first filter that has completed regeneration for filtration. At the same time, the filtrate in the filtrate tank is used to backwash the second filter. The two parallel filters are used alternately to continuously filter the chlorination suspension and obtain the filtrate.

[0011] Step (3), Concentration: The filtrate obtained in step (2) enters the evaporation kettle and is evaporated under vacuum. The evaporated gaseous material enters the distillation separation system. The material in the evaporation kettle is reboiled by the reboiler and then returned to the evaporation kettle. The evaporation kettle is circulated and concentrated until the catalyst content in the concentrate is about 5-10 wt%. After the concentrate is cooled, it is mixed with the chlorinated suspension obtained by freezing treatment and filtered to separate the concentrated catalyst.

[0012] The chlorination liquid is obtained by reacting o-chlorotoluene with chlorine gas at a temperature of 40-60°C using an inorganic chloride as a catalyst.

[0013] The catalyst is aluminum chloride, ferric chloride, or zinc chloride.

[0014] The solubility of aluminum chloride in o-chlorotoluene and dichlorotoluene is shown in Table 1.

[0015] Table 1. Solubility of aluminum chloride

[0016]

[0017] Note: In Table 1, dichlorotoluene refers to 2,4-dichlorotoluene. The solubility of aluminum chloride in other dichlorotoluene isomers is consistent with that in 2,4-dichlorotoluene.

[0018] In the catalytic chlorination of o-chlorotoluene to produce dichlorotoluene, the amount of aluminum chloride used is typically about 1 wt% of the mass of o-chlorotoluene, and the chlorination reaction temperature is usually 40–60 °C. As shown in Table 1, under the chlorination reaction conditions, aluminum chloride is completely dissolved in the reaction solution. Therefore, the conventional method for removing aluminum chloride after the catalytic chlorination of o-chlorotoluene to produce dichlorotoluene is to wash the chlorination solution with a large amount of water. However, this often generates a large amount of wastewater containing metal ions, requiring a series of environmental protection technologies and facilities for purification, such as neutralization, precipitation, and biochemical treatment, which greatly increases the environmental burden on enterprises. Furthermore, because aluminum chloride is highly susceptible to hydrolysis, it is completely destroyed during the water washing process and cannot be recycled, resulting in resource waste and increased production costs.

[0019] Table 1 shows that the solubility of aluminum chloride decreases with decreasing temperature. When the temperature drops below 8℃, the solubility of aluminum chloride is approximately 1 / 3 to 1 / 7 of its solubility at the chlorination reaction temperature. The solubility trends of ferric chloride and zinc chloride in chlorination solutions with temperature show the same pattern as those of aluminum chloride.

[0020] Therefore, this invention utilizes the property that the solubility of inorganic chlorides such as aluminum chloride varies significantly at different temperatures. The chlorination solution is first frozen to precipitate most of the dissolved aluminum chloride and other inorganic chlorides, which are then removed by filtration, reducing the burden on subsequent processing. Furthermore, this invention returns the filtered aluminum chloride and other inorganic chlorides to the catalyst preparation system, enabling catalyst recycling and significantly reducing production costs.

[0021] In step (1), the solubility of the catalyst dissolved at the chlorination reaction temperature in the chlorination liquid is reduced by freezing treatment, and most of the catalyst is precipitated, forming catalyst precipitate and chlorination liquid saturated with catalyst at freezing temperature, i.e. chlorination liquid suspension containing solid catalyst particles.

[0022] The freezing process is carried out at a temperature of 5–8°C. A chlorination suspension containing solid catalyst particles is obtained at the outlet of the freezer at a temperature of 5–8°C.

[0023] In step (2), the first filter and the second filter are both membrane filters with an average pore size of 0.1 to 0.5 μm; the materials of the first filter and the second filter are corrosion-resistant Hastelloy or polytetrafluoroethylene.

[0024] The filtration temperature is 5–8°C. The filtrate is a chlorinated solution with a saturated catalyst concentration at a freezing temperature.

[0025] The filtration pressure shall not exceed 0.5 MPa, preferably 0.3 to 0.5 MPa.

[0026] The design value of the filter cake capacity of the first filter is the filter cake capacity when the filtration pressure reaches the maximum value (0.5MPa); the design value of the filter cake capacity of the second filter is the filter cake capacity when the filtration pressure reaches the maximum value (0.5MPa).

[0027] The backwashing pressure shall not exceed 0.2 MPa, preferably 0.1 to 0.2 MPa.

[0028] The backflush liquid enters the backflush liquid clarification tank and settles naturally to separate the filter cake. The supernatant is mixed with the chlorination liquid to be treated and then frozen again. The separated filter cake is returned to the catalyst preparation system for recycling.

[0029] In step (3), the evaporation treatment temperature is 100-180°C and the vacuum degree is 95-98 kPa.

[0030] The evaporator is a forced circulation evaporator. Both the evaporator and the distillation separation system are made of carbon steel.

[0031] Typically, the weight ratio of the concentrate to the chlorination suspension is 1:5 to 1:10. The amount of concentrate is relatively small, and mixing it with the chlorination suspension obtained through freeze-treatment will not significantly affect the filtration temperature. However, to minimize the impact on the filtration temperature, the concentrate is cooled to 5–8°C before being mixed with the freeze-treated chlorination suspension and filtered again. The circulation rate of the concentrate back to the filter is determined by the catalyst content in both the filtrate and the concentrate.

[0032] The method described in this invention is applicable to any reaction system in which the solubility of the catalyst in the chlorination liquid changes significantly with temperature.

[0033] The beneficial effects of this invention are:

[0034] (1) Compared with traditional methods for separating aluminum chloride catalysts, the method of the present invention can avoid generating a large amount of wastewater, can achieve continuous operation, and realize the recycling of catalysts, which greatly reduces the cost of environmental treatment and the cost of catalysts for producing dichlorotoluene. It is a more competitive process route.

[0035] (2) The method of the present invention can avoid the metal salt mud generated by the hydrolysis of aluminum chloride due to water washing, and also avoid the corrosion of the equipment caused by the acidity generated by the water brought into the system during the subsequent product distillation. The evaporation kettle and distillation separation system of the present invention can be made of cheaper materials such as carbon steel, which can greatly reduce investment costs.

[0036] (3) The material distilled out in the evaporator of the present invention enters the subsequent distillation system in gaseous form, which can significantly save distillation energy consumption.

[0037] (4) The present invention features continuous processing with low energy consumption and low material consumption. Attached Figure Description

[0038] Figure 1 This invention relates to a continuous separation system for the o-chlorotoluene chlorination catalyst.

[0039] Figure 1 In the middle, 1-chlorination liquid storage tank, 2-chlorination liquid pump, 3-chlorination liquid freezer, 4-first filter, 5-second filter, 6-filtrate tank, 7-filtrate pump, 8-evaporator, 9-forced circulation pump, 10-reboiler, 11-evaporator cooler, 12-backflush pump, 13-backflush liquid clarification tank. Specific implementation methods

[0040] The technical solution of the present invention will be described in detail below through specific embodiments.

[0041] Example 1

[0042] like Figure 1 A continuous separation system for o-chlorotoluene chlorination catalyst includes a chlorination liquid storage tank 1, which is connected to a chlorination liquid freezer 3 via a chlorination liquid pump 2. Two parallel filters, a first filter 4 and a second filter 5, are installed at the outlet of the chlorination liquid freezer 3. The first filter 4 and the second filter 5 are switched between each other. The filtrate outlets of the first filter 4 and the second filter 5 are respectively connected to a filtrate tank 6. The outlet of the filtrate tank 6 is connected to the inlet of an evaporator 8 via a filtrate pump 7. The filtrate is evaporated under vacuum. The top of the evaporator 8... The outlet is connected to the distillation separation system to perform distillation treatment on the evaporated gaseous material. The bottom outlet of the evaporator 8 is connected to the inlet of the forced circulation pump 9. The outlet of the forced circulation pump 9 is respectively equipped with a circulation pipeline connected to the circulation inlet of the evaporator 10 and a reflux pipeline connected to the outlet pipeline of the chlorination liquid freezer 3. A reboiler 10 is provided on the circulation pipeline, and an evaporation liquid cooler 11 is provided on the reflux pipeline. The concentrated liquid obtained in the evaporator 8 is transported to the reboiler 10, and the reboiled material is returned to the evaporator 8. When the catalyst content in the concentrated liquid is about 5-10 wt%, it is cooled by the evaporation liquid cooler 28 and then mixed with the chlorination liquid suspension at the outlet of the chlorination liquid freezer 3 and enters the filter.

[0043] The backwash outlet of the filtrate tank 6 is connected to the backwash inlets of the first filter 4 and the second filter 5 via the backwash pump 12. The backwash outlets of the first filter 4 and the second filter 5 are connected to the backwash clarification tank 13. The upper outlet of the backwash clarification tank 13 is connected to the inlet of the chlorination tank 1. The supernatant of the backwash clarification tank 13 is returned to the chlorination tank 1. The bottom outlet of the backwash clarification tank 13 is connected to the o-chlorotoluene chlorination production system, returning the filter cake to the catalyst preparation system of the o-chlorotoluene chlorination production system to achieve the recycling of aluminum chloride.

[0044] The first filter 4 and the second filter 5 are both membrane filters with an average pore size of 0.5 μm; the materials of the first filter and the second filter are corrosion-resistant Hastelloy or polytetrafluoroethylene.

[0045] o-Chlorotoluene is catalytically chlorinated with aluminum chloride to obtain a chlorinated liquid to be treated. This chlorinated liquid is fed into a chlorinated liquid storage tank 1 via a feed pipe. The chlorinated liquid in storage tank 1 is then pumped into a chlorinated liquid freezer 3 via a chlorinated liquid pump 2 for freezing. At the outlet of the freezer 3, a chlorinated liquid suspension containing solid aluminum chloride particles at a temperature of 5–8°C is obtained. This suspension is filtered by a first filter 4. The resulting filtrate enters a filtrate tank 6 and is then pumped into an evaporator 8 via a filtrate pump 7. Evaporation is performed under vacuum. The material distilled from the evaporator 8 enters a distillation separation system in a gaseous state for further distillation. The material in the evaporator is then reboiled in a reboiler 10 and returned to the evaporator 8. This process is repeated until the catalyst content in the concentrate in the evaporator 8 is approximately 5–10%. The concentrate (wt%) is cooled to 5-8°C by the evaporator cooler 11 and mixed with the chlorinated suspension obtained after freezing treatment. The mixture is then filtered again to separate the catalyst. Once the amount of filter cake in the first filter 4 reaches the filter's saturation design capacity (corresponding to the filter cake capacity when the filtration pressure reaches its maximum value), the feed line to the first filter 4 is disconnected, and the chlorinated suspension is switched to the second filter 5 for filtration. Simultaneously, the backwash pump 12 is activated, pumping the filtrate in the filtrate tank 6 as backwash liquid into the first filter 4 for backwashing. This allows the filter cake in the first filter to enter the backwash liquid clarification tank 13 along with the backwash liquid. The flushing liquid settles naturally in the backflushing liquid clarification tank, and the supernatant enters the chlorination liquid storage tank 1 to mix with the chlorination liquid to be treated. The filter cake is returned to the catalyst preparation system for recycling. When the amount of filter cake in the second filter 5 reaches the filter's saturation design capacity (corresponding to the filter cake capacity when the filtration pressure reaches the maximum value), the feed pipe of the first filter 4 is opened, and the feed pipe of the second filter 5 is closed at the same time. The backflushing liquid inlet of the first filter 4 is closed, and the backflushing liquid inlet of the second filter 5 is opened to backflush the second filter 5. This allows for the switching operation between the first filter 4 and the second filter 5.

[0046] Example 2

[0047] o-chlorotoluene was used as a raw material and aluminum chloride as a catalyst. Under the action of aluminum chloride, o-chlorotoluene and chlorine gas underwent a chlorination reaction at 50°C to obtain a chlorinated liquid. The composition of the chlorinated liquid to be treated is shown in Table 2.

[0048] Table 2. Composition of chlorination solution

[0049]

[0050] Based on the continuous separation system of the o-chlorotoluene chlorination catalyst described in Example 1, aluminum chloride is continuously separated from the chlorination liquid, as follows:

[0051] The chlorinated liquid to be treated enters the chlorinated liquid storage tank 1 through the feed pipeline. The chlorinated liquid in the chlorinated liquid storage tank 1 is then transported to the chlorinated liquid freezer 3 by the chlorinated liquid pump 2. The chlorinated liquid is frozen to 5°C by the chlorinated liquid freezer 3, resulting in a chlorinated liquid suspension containing solid aluminum chloride particles (temperature 5°C). The chlorinated liquid suspension is then transported to the first filter 4 and filtered at 5°C with an initial pressure of 0.1 MPa, resulting in filtrate (temperature 5°C). The filtrate enters the filtrate tank 6. When the amount of filter cake in the first filter 4 reaches the filter's saturation design capacity, i.e., when the filtration pressure rises to 0.5 MPa, the feed pipeline of the first filter 4 is disconnected, and the chlorinated liquid suspension is switched to the second filter 5 connected in parallel with the first filter 4. Filtration is then carried out at an initial pressure of 0.1 MPa and a temperature of 5°C. Simultaneously, the backflush pump 12 is activated, and the filtrate in the filtrate tank 6 is used as backflush fluid to enter the first filter 4, where it is filtered at a pressure of 0.1 MPa. Backwashing is performed, and the filter cake in the first filter 4 enters the backwash clarification tank 13 with the backwash liquid for natural sedimentation. The upper clear liquid in the backwash clarification tank 13 is returned to the chlorination liquid storage tank 1 to mix with the chlorination liquid to be treated, and the lower filter cake is returned to the catalyst preparation system of the o-chlorotoluene chlorination production system for recycling. When the amount of filter cake in the second filter 5 reaches the filter's saturation design capacity (i.e., the filtration pressure rises to 0.5 MPa), the feed pipe of the first filter 4 is opened, and the feed pipe of the second filter 5 is closed at the same time. The backwash liquid inlet of the first filter 4 is closed, and the backwash liquid inlet of the second filter 5 is opened. The filtrate in the filtrate tank 6 is pumped into the second filter 5 by the backwash pump 12 and backwashed at a pressure of 0.1 MPa. In this way, one of the first filter 4 and the second filter 5 is used for filtration, and the other is used for backwashing, realizing the switching operation between the first filter 4 and the second filter 5. During backwashing, the amount of backwash liquid used is about 5 times the volume of the filter cake.

[0052] The composition of the filtrate in filtrate tank 6 is shown in Table 3.

[0053] Table 3. Filtrate Composition

[0054]

[0055] The filtrate in the filtrate tank 6 is pumped to the evaporator 8 by the filtrate pump 7 and evaporated at a temperature of 150 °C and a vacuum of 92 kPa. The evaporated gaseous material is discharged from the top of the evaporator 8 and transported to the subsequent distillation separation system. The material in the evaporator 8 is transported to the reboiler 10 by the forced circulation pump 9 through the circulation pipeline. The reboiled material is returned to the evaporator 8 until the concentration of aluminum chloride in the concentrate is 5.25%. The composition of the concentrate is shown in Table 4. Part of the concentrate enters the evaporator cooler 11 and is cooled to 5 °C. Then, it goes through the reflux pipeline to the outlet of the chlorination liquid freezer 3. The concentrate is mixed with the chlorination liquid suspension (5 °C) containing solid aluminum chloride particles at a weight ratio of 1:10 according to the weight ratio of concentrate to chlorination liquid suspension. Then, it enters the filter.

[0056] Table 4. Composition of Concentrate

[0057] .

Claims

1. A continuous separation method for o-chlorotoluene chlorination liquid and catalyst, characterized in that: A continuous freezing and filtration method is used. First, the chlorination solution is frozen until most of the catalyst precipitates, then the precipitated catalyst is removed by filtration. The filtrate is then evaporated in a circulating manner until the catalyst content in the concentrate is 5-10 wt%. After cooling, the concentrate is mixed with the frozen chlorination suspension and filtered again. The chlorination solution is obtained by reacting o-chlorotoluene with chlorine gas at a temperature of 40-60°C using an inorganic chloride as a catalyst. The catalyst is aluminum chloride, ferric chloride, or zinc chloride.

2. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 1, characterized in that: Includes the following steps: Step (1), freezing: The chlorination solution is continuously fed into a freezer for freezing treatment to obtain a chlorination suspension containing solid catalyst particles; Step (2), Filtration: The chlorination suspension is passed through the first filter to remove the precipitated catalyst. The filtrate enters the filtrate tank. When the filter cake capacity reaches the design value of the first filter, the chlorination suspension is switched to the second filter connected in parallel with the first filter for filtration. At the same time, the filtrate in the filtrate tank is used to backwash the first filter. When the filter cake capacity reaches the design value of the second filter, the chlorination suspension is switched to the first filter that has completed regeneration for filtration. At the same time, the filtrate in the filtrate tank is used to backwash the second filter. The two parallel filters are used alternately to continuously filter the chlorination suspension and obtain the filtrate. Step (3), Concentration: The filtrate obtained in step (2) enters the evaporation kettle and is evaporated under vacuum. The evaporated gaseous material enters the distillation separation system. The material in the evaporation kettle is reboiled by the reboiler and then returned to the evaporation kettle. The evaporation kettle is circulated and concentrated until the catalyst content in the concentrate is 5-10 wt%. After the concentrate is cooled, it is mixed with the chlorinated suspension obtained by freezing treatment and filtered to separate the concentrated catalyst.

3. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 1 or 2, characterized in that: The freezing temperature is 5–8°C.

4. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 1 or 2, characterized in that: The filtration temperature is 5–8℃.

5. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 2, characterized in that: Both the first filter and the second filter are membrane filters with an average pore size of 0.1 to 0.5 μm.

6. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 2, characterized in that: The backwashing pressure shall not exceed 0.2 MPa.

7. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 2, characterized in that: The backflush liquid enters the backflush liquid clarification tank and settles naturally to separate the filter cake. The supernatant is mixed with the chlorination liquid to be treated and then frozen again. The separated filter cake is returned to the catalyst preparation system for recycling.

8. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 1 or 2, characterized in that: The evaporation process is carried out at a temperature of 100–180°C and a vacuum degree of 95–98 kPa.

9. The continuous separation method for the o-chlorotoluene chlorination catalyst according to claim 1 or 2, characterized in that: The weight ratio of the concentrate to the chlorinated suspension is 1:5 to 1:10.

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