Separation and recovery method of mixed solution

Abstract

The invention belongs to the technical field of organic chemistry, and particularly relates to a separation and recovery method of a mixed solution. In order to solve the problem of high energy consumption of a rectification separation mode in the prior art, the invention provides a separation and recovery method of a mixed solution, which comprises the following steps: transferring the mixed solution containing tetrachloroethylene, hexachloroethane, hexachlorobutadiene and hexachlorobenzene into a melt crystallizer, and carrying out programmed cooling by using the melt crystallizer until the temperature of the mixed solution is 25-100 DEG C, so as to obtain a mixed solution containing tetrachloroethylene, hexachloroethane, hexachlorobutadiene and hexachlorobenzene; solidifying the high-melting-point substance in the mixture onto a crystallizer to obtain a product crystal; transferring the liquid phase as residual liquid into a residual liquid tank; raising the temperature to 185-190 DEG C to sublimate and condense hexachloroethane to form hexachloroethane crystals; heating the remaining product crystals to 220-230 DEG C for melting, and discharging the remaining product crystals into a product tank to obtain a hexachlorobenzene solution; and carrying out rectification separation on the residual liquid to obtain a tower top light component tetrachloroethylene product and a tower bottom heavy component hexachlorobutadiene product. The highest operation temperature is 250 DEG C or below, and the energy consumption is low.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of organic chemistry, and particularly relates to a separation and recovery method of a mixed solution. BACKGROUND

[0002] In the process of treating waste containing chlorine, mixed waste liquid mainly containing tetrachloroethylene (20%), hexachloroethane (29%), hexachlorobutadiene (22%) and hexachlorobenzene (29%) is generated. Tetrachloroethylene and hexachlorobutadiene in the mixed waste liquid have high economic value. The boiling point of tetrachloroethylene is 121℃, and the melting point is -22℃; the sublimation point of hexachloroethane is 186℃, and the melting point is 184℃ (white crystalline powder); the boiling point of hexachlorobutadiene is 213℃, and the melting point is -19℃; the boiling point of hexachlorobenzene is 324.5℃, and the melting point is 226℃; under the action of a solvent and high temperature, the mixture is in a liquid state. Hexachloroethane and hexachlorobenzene are white crystalline powder at normal temperature and pressure, and can be dissolved in tetrachloroethylene and hexachlorobutadiene at a high concentration under high temperature conditions.

[0003] In the prior art, the above four kinds of mixed substances are usually separated by rectification, but the separation process of rectification for separating the four substances is complex, and the energy consumption is large, and the recovery cost is extremely high.

[0004] In the patent application with the publication number "CN103787823A", a method for recovering organic chlorides from the distillation residues of methane chlorides and / or tetrachloroethylene is provided. Specifically, the distillation residues of methane chlorides and tetrachloroethylene are evaporated in an evaporator, the volatilized components are condensed into liquid and then introduced into a trap, and the residues are transferred into a sublimator; part of the light component mixture is separated into chloroform, carbon tetrachloride and tetrachloroethylene by a tetrachloroethylene distillation system; at the same time, the residues in the sublimator are sublimated at 240-250℃, and hexachloroethane is obtained by cooling in a condenser; the light component mixture is introduced into a refining pot, and hexachloroethane is added, then hexachloroethane is dissolved, and after dissolution, it is transferred to a crystallization pot for crystallization; after crystallization, filtration is performed, and the filter cake and filtrate are collected, the filter cake is dried to obtain hexachloroethane product, and the filtrate is introduced into an evaporator for continuous circulation. However, the method does not involve how to recover hexachlorobutadiene and hexachlorobenzene, and the sublimation residues and the crystallization mother liquor both contain a large amount of hexachlorobutadiene and hexachlorobenzene.

[0005] In the invention patent application with publication number "CN105384598A", a method for separating chlorides from high chlorides is provided. Specifically, high chloride waste is added to an evaporator, and the evaporated gas phase is sent to a tetrachloroethylene rectification system to separate carbon tetrachloride and tetrachloroethylene; the evaporation residue is transferred to a sublimation kettle, water is added and heated to boiling, while hot nitrogen gas is introduced; the sublimated hexachloroethane is dissolved in a chloroform dissolving tank, then heated and filtered, and the filtrate is cooled and crystallized, centrifuged, and the crystals are dried to obtain hexachloroethane product; the sublimation kettle liquid is added to tetrachloroethylene for heating and dissolution, and then heated and filtered, and the filtrate is cooled and crystallized, centrifuged to obtain hexachlorobenzene crude product. This method does not involve how to recover hexachlorobutadiene, and the sublimation kettle liquid and the crystallization mother liquor both contain a large amount of hexachlorobutadiene. At the same time, this process introduces a new solvent, chloroform.

[0006] In the invention patent with publication number "CN110540486B", a separation system and method for byproduct high-boiling substances in tetrachloroethylene production are provided. Specifically, tetrachloroethylene is removed by vacuum flash evaporation, and then hexachloroethane gas is sublimated by heating the flash evaporation kettle liquid, and after condensing into a solid, a solvent is added, and after cooling and crystallization, solid-liquid separation is performed to obtain hexachloroethane crystals; the sublimation kettle liquid is added to a solvent, and after cooling and crystallization, solid-liquid separation is performed to obtain hexachlorobenzene crystals; the mother liquor from the two solid-liquid separations is separated by multiple distillations to obtain hexachlorobutadiene. This method involves multiple distillations, which is energy-intensive; the tetrachloroethylene evaporated by flash evaporation has not been subjected to a distillation system, and there is a lot of hexachloroethane in the tetrachloroethylene; at the same time, this process introduces a new solvent. SUMMARY

[0007] The purpose of the present invention is to provide a method for separating and recovering a mixed solution to solve the above problems.

[0008] To achieve the above-mentioned purpose, the following technical solutions are adopted in the present invention:

[0009] A method for separating and recovering a mixed solution, comprising the following steps:

[0010] Step one: transfer the mixed solution containing tetrachloroethylene, hexachloroethane, hexachlorobutadiene, and hexachlorobenzene to a melt crystallizer, and use the melt crystallizer for programmed cooling until the temperature of the mixed solution is 25-100°C, the high-melting-point substances in the mixture are solidified onto the crystallizer, and the product crystals are obtained;

[0011] Step two: transfer the liquid phase to a residue tank as residue;

[0012] Step three: warm the product crystals obtained in step one to 185-190°C to sublimate the hexachloroethane and form hexachloroethane crystals;

[0013] Step four: melt the remaining product crystals at 220-230℃ and discharge into the product tank to obtain a hexachlorobenzene solution;

[0014] Step five: separate the residual liquid in step two by rectification to obtain light component tetrachloroethylene product and heavy component hexachlorobutadiene product.

[0015] In the above-mentioned separation and recovery method of a mixed solution, the melt crystallizer in step one is a falling film crystallizer, a suspension crystallizer or a combination of a falling film crystallizer and a suspension crystallizer.

[0016] In the above-mentioned separation and recovery method of a mixed solution, the mixed solution in step one is cooled to 120-150℃ to start the programmed cooling step, which is: preliminary cooling at a cooling rate of 10-25℃ / h to 90-100℃, and then cooling crystallization at a cooling rate of 5-8℃ / h to 65-75℃.

[0017] In the above-mentioned separation and recovery method of a mixed solution, it further comprises a sweating step: heating the product crystals prepared in step one to 100-150℃ and discharging the sweating liquid.

[0018] In the above-mentioned separation and recovery method of a mixed solution, the heating rate in the sweating step is 0.5-20℃ / h.

[0019] In the above-mentioned separation and recovery method of a mixed solution, the heating rate in step three is 50-60℃ / h.

[0020] In the above-mentioned separation and recovery method of a mixed solution, the heating rate in step four is 40-45℃ / h.

[0021] In the above-mentioned separation and recovery method of a mixed solution, the rectification column in step five is a packed column, a plate column or a combination of a packed column and a plate column.

[0022] In the above-mentioned separation and recovery method of a mixed solution, tetrachloroethylene and hexachlorobutadiene are separated by vacuum fractionation in step five.

[0023] In the above-mentioned separation and recovery method of a mixed solution, the temperature of vacuum fractionation is 75-85℃ and the pressure is 0.1 atm.

[0024] Compared with the prior art, the advantages of the present application are:

[0025] 1. The distillation separation method used in the prior art has a highest operating temperature above 325℃, high energy consumption, and material vaporization, which is prone to leakage and other risks, and has safety hazards. In the present application, hexachloroethane and hexachlorobenzene are separated by crystallization, the highest operating temperature is below 250℃, the energy consumption is low, and the material in the crystallization process is more stable in solid and liquid state, without gasification, low operating pressure and low leakage risk.

[0026] 2. The present application also has a sweating step after crystallization, which effectively improves the product purity of the prepared hexachloroethane and hexachlorobenzene.

[0027] 3. The operating temperature of the tower bottom in the prior art is high, and organic matter is prone to coking to produce polymers. In order to ensure stable operation of the tower, the equipment needs to be cleaned regularly to discharge solid waste, waste liquid, etc. The separation method of the present application can better avoid this problem. DETAILED DESCRIPTION

[0028] The present application will be further described in detail below in combination with specific embodiments.

[0029] Example 1

[0030] The present embodiment provides a separation and recovery method of a mixed solution, comprising the following steps:

[0031] Step one: 1000 kg of a mixed solution containing 20.0% tetrachloroethylene, 29.0% hexachloroethane, 22.0% hexachlorobutadiene and 29.0% hexachlorobenzene is transferred to a falling film crystallizer, the mixed solution is cooled to 120℃, the programmed cooling step is started, the initial cooling is carried out at a cooling rate of 10℃ / h, the temperature is cooled to 90℃, and the cooling crystallization is carried out at a cooling rate of 5℃ / h, the temperature is cooled to 65℃, the high melting point substances in the mixture are solidified on the crystallizer to obtain product crystals;

[0032] Step two: the liquid phase is transferred to a residual liquid tank as residual liquid;

[0033] Step three: the product crystals prepared in step one are heated to 100℃ at a heating rate of 0.5℃ / h, and the sweating liquid is discharged, then the temperature is increased to 185℃ at a heating rate of 50℃ / h to make hexachloroethane sublimate and condense to form hexachloroethane crystals;

[0034] Step four: the remaining product crystals are heated to 220℃ at a heating rate of 40℃ / h to melt, and are discharged into a product tank to obtain a hexachlorobenzene solution;

[0035] Step five: the residual liquid in step two is subjected to vacuum fractionation by using a packed column, the temperature of vacuum fractionation is 75℃, and the pressure is 0.1 atm, to obtain tetrachloroethylene product as light component on the top of the column and hexachlorobutadiene product as heavy component at the bottom of the column.

[0036] The total recovery rate of the recovered hexachloroethane and hexachlorobenzene crystals was 99.0%, and the content of other components in the recovered hexachloroethane was 0.09%, and the content of other components in the hexachlorobenzene was 0.07%.

[0037] Example 2

[0038] The present embodiment provides a separation and recovery method of a mixed solution, comprising the following steps:

[0039] Step one: 1000 kg of a mixed solution containing 20.0% tetrachloroethylene, 29.0% hexachloroethane, 22.0% hexachlorobutadiene, and 29.0% hexachlorobenzene is transferred to a suspension crystallizer, and the mixed solution is cooled to 150°C, and the programmed cooling step is started, and the initial cooling is carried out at a cooling rate of 25°C / h, and the temperature is cooled to 100°C, and the cooling crystallization is carried out at a cooling rate of 8°C / h, and the temperature is cooled to 75°C, and the high-melting-point substances in the mixture are solidified on the crystallizer to obtain product crystals;

[0040] Step two: the liquid phase is transferred to a residual liquid tank as residual liquid;

[0041] Step three: the product crystals prepared in step one are heated to 150°C at a heating rate of 20°C / h, and the sweating liquid is discharged, and then the temperature is increased to 190°C at a heating rate of 60°C / h to make the hexachloroethane sublimate and condense to form hexachloroethane crystals;

[0042] Step four: the remaining product crystals are heated to 230°C at a heating rate of 45°C / h to melt, and are discharged to a product tank to obtain a hexachlorobenzene solution;

[0043] Step five: the residual liquid in step two is subjected to vacuum fractional distillation by using a plate column, and the temperature of the vacuum fractional distillation is 85°C, and the pressure is 0.1 atm, and the top light component tetrachloroethylene product and the bottom heavy component hexachlorobutadiene product are obtained.

[0044] The total recovery rate of the recovered hexachloroethane and hexachlorobenzene crystals was 99.2%, and the content of other components in the recovered hexachloroethane was 0.08%, and the content of other components in the hexachlorobenzene was 0.08%.

[0045] Example 3

[0046] The present embodiment provides a separation and recovery method of a mixed solution, comprising the following steps:

[0047] Step one: transfer 1000 kg of mixed solution containing 15.5% tetrachloroethylene, 29.0% hexachloroethane, 21.6% hexachlorobutadiene and 33.9% hexachlorobenzene into a falling film crystallizer, and start the programmed cooling step when the mixed solution is cooled to 128℃, and carry out preliminary cooling at a cooling rate of 15℃ / h, and then cool to 95℃, and then carry out cooling crystallization at a cooling rate of 5.5℃ / h, and then cool to 68℃, and the high melting point substances in the mixture are solidified on the crystallizer to obtain product crystals;

[0048] Step two: transfer the liquid phase into a residual liquid tank as residual liquid;

[0049] Step three: heat the product crystals obtained in step one to 125℃ at a heating rate of 10℃ / h, and discharge the sweat, and then heat to 186℃ at a heating rate of 58℃ / h to make hexachloroethane sublimate and condense to form hexachloroethane crystals;

[0050] Step four: heat the remaining product crystals to 225℃ at a heating rate of 44℃ / h to melt, and discharge into a product tank to obtain a hexachlorobenzene solution;

[0051] Step five: carry out vacuum fractional distillation on the residual liquid in step two by using a packed column, and the temperature of the vacuum fractional distillation is 80℃, and the pressure is 0.1 atm, to obtain tetrachloroethylene product as the light component on the top of the column and hexachlorobutadiene product as the heavy component at the bottom of the column.

[0052] It is measured that the total recovery rate of the recovered hexachloroethane and hexachlorobenzene crystals is 99.3%, the content of other components in the recovered hexachloroethane is 0.07%, and the content of other components in the hexachlorobenzene is 0.06%.

[0053] Example 4

[0054] The present embodiment provides a method for separating and recovering a mixed solution, which comprises the following steps:

[0055] Step one: transfer 1000 kg of mixed solution containing 19.5% tetrachloroethylene, 30.1% hexachloroethane, 22.1% hexachlorobutadiene and 28.3% hexachlorobenzene into a falling film crystallizer, and start the programmed cooling step when the mixed solution is cooled to 149℃, and carry out preliminary cooling at a cooling rate of 22℃ / h, and then cool to 95℃, and then carry out cooling crystallization at a cooling rate of 6℃ / h, and then cool to 71℃, and the high melting point substances in the mixture are solidified on the crystallizer to obtain product crystals;

[0056] Step two: transfer the liquid phase into a residual liquid tank as residual liquid;

[0057] Step three: the product crystals prepared in step one are heated to 125°C at a heating rate of 10°C / h, and the sweat is discharged, and then heated to 189°C at a heating rate of 59°C / h to make the hexachloroethane sublimate and condense to form hexachloroethane crystals;

[0058] Step four: the remaining product crystals are heated to 225°C at a heating rate of 41°C / h to melt, and discharged into a product tank to obtain a hexachlorobenzene solution;

[0059] Step five: the residual liquid in step two is subjected to vacuum fractional distillation using a packed column, and the temperature of the vacuum fractional distillation is 80°C and the pressure is 0.1 atm, to obtain a light component tetra-chloroethylene product on the top of the column and a heavy component hexachlorobutadiene product at the bottom of the column.

[0060] The total recovery rate of the recovered hexachloroethane and hexachlorobenzene crystals is 99.4%, and the content of other components in the recovered hexachloroethane is 0.05%, and the content of other components in the hexachlorobenzene is 0.07%.

[0061] Comparative Example 1

[0062] The present comparative example provides a separation and recovery method of a mixed solution, comprising the following steps:

[0063] Step one: 1000 kg of a mixed solution containing 19.5% tetra-chloroethylene, 30.1% hexachloroethane, 22.1% hexachlorobutadiene and 28.3% hexachlorobenzene is transferred to a falling film crystallizer, and the mixed solution is cooled to 149°C, and then a programmed cooling step is started, and the initial cooling is performed at a cooling rate of 22°C / h, and the temperature is cooled to 95°C, and then the cooling and crystallization are performed at a cooling rate of 6°C / h, and the temperature is cooled to 71°C, and the high-melting-point substances in the mixture are solidified on the crystallizer to obtain product crystals;

[0064] Step two: the liquid phase is transferred to a residual liquid tank as a residual liquid;

[0065] Step three: the product crystals prepared in step one are heated to 189°C at a heating rate of 59°C / h to make the hexachloroethane sublimate and condense to form hexachloroethane crystals;

[0066] Step four: the remaining product crystals are heated to 225°C at a heating rate of 41°C / h to melt, and discharged into a product tank to obtain a hexachlorobenzene solution;

[0067] Step five: the residual liquid in step two is subjected to vacuum fractional distillation using a packed column, and the temperature of the vacuum fractional distillation is 80°C and the pressure is 0.1 atm, to obtain a light component tetra-chloroethylene product on the top of the column and a heavy component hexachlorobutadiene product at the bottom of the column.

[0068] The total recovery rate of the recovered hexachloroethane and hexachlorobenzene crystals was 99.5%, and the content of other components in the recovered hexachloroethane was 0.21%, and the content of other components in the hexachlorobenzene was 0.28%.

[0069] The specific embodiments described herein are merely illustrative of the principles of this application. Numerous modifications or adaptations will be readily apparent to those skilled in the art of this application without departing from the spirit or scope of the application as defined by the following claims.

Claims

1. A method for separating and recovering a mixed solution, characterized by comprising: The method comprises the following steps: Step 1: transferring a mixed solution containing tetrachloroethylene, hexachloroethane, hexachlorobutadiene and hexachlorobenzene into a melt crystallizer, and performing programmed cooling by using the melt crystallizer until the temperature of the mixed solution is 25-100℃, and the high-melting-point substances in the mixture are solidified on the crystallizer to obtain product crystals; Step 2: transferring the liquid phase into a residual liquid tank as residual liquid; Step 3: heating the product crystals obtained in Step 1 to 185-190℃ to make hexachloroethane sublimate and condense to form hexachloroethane crystals; Step 4: heating the remaining product crystals to 220-230℃ to melt, and discharging into a product tank to obtain a hexachlorobenzene solution; Step 5: performing rectification separation on the residual liquid in Step 2 to obtain tetrachloroethylene product as light component on the top of the column and hexachlorobutadiene product as heavy component at the bottom of the column.

2. The method of claim 1, wherein: The melt crystallizer in Step 1 is a falling film crystallizer, a suspension crystallizer or a combination of a falling film crystallizer and a suspension crystallizer.

3. The method of claim 1, wherein: In Step 1, the mixed solution is cooled to 120-150℃, and then the programmed cooling step is started, which comprises: preliminary cooling at a cooling rate of 10-25℃ / h until the temperature is 90-100℃, and then cooling crystallization at a cooling rate of 5-8℃ / h until the temperature is 65-75℃.

4. The method of claim 1, wherein: The method further comprises a sweating step: heating the product crystals obtained in Step 1 to 100-150℃, and discharging the sweating liquid.

5. The method of claim 4, wherein: The heating rate in the sweating step is 0.5-20℃ / h.

6. The method of claim 1, wherein: The heating rate in Step 3 is 50-60℃ / h.

7. The method of claim 1, wherein: The heating rate in Step 4 is 40-45℃ / h.

8. The method of claim 1, wherein: The rectification column in Step 5 is a packed column, a plate column or a combination of a packed column and a plate column.

9. The method of claim 1, wherein: In Step 5, the tetrachloroethylene and hexachlorobutadiene are separated by vacuum fractionation.

10. The method of claim 9, wherein: The temperature of the vacuum fractionation is 75-85℃, and the pressure is 0.1 atm.