CN114773228A - Method for refining acetonitrile by rectification-melt crystallization coupling process - Google Patents
Method for refining acetonitrile by rectification-melt crystallization coupling process Download PDFInfo
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- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 title claims abstract description 468
- 238000002425 crystallisation Methods 0.000 title claims abstract description 75
- 230000008025 crystallization Effects 0.000 title claims abstract description 73
- 238000000034 method Methods 0.000 title claims abstract description 54
- 238000010168 coupling process Methods 0.000 title claims abstract description 15
- 238000007670 refining Methods 0.000 title claims abstract description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 31
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 claims abstract description 28
- 239000012535 impurity Substances 0.000 claims abstract description 20
- FVSKHRXBFJPNKK-UHFFFAOYSA-N propionitrile Chemical compound CCC#N FVSKHRXBFJPNKK-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000000155 melt Substances 0.000 claims abstract description 8
- 239000012452 mother liquor Substances 0.000 claims abstract description 4
- 239000013078 crystal Substances 0.000 claims description 68
- 239000007788 liquid Substances 0.000 claims description 46
- RAXXELZNTBOGNW-UHFFFAOYSA-N imidazole Natural products C1=CNC=N1 RAXXELZNTBOGNW-UHFFFAOYSA-N 0.000 claims description 39
- PBCJIPOGFJYBJE-UHFFFAOYSA-N acetonitrile;hydrate Chemical compound O.CC#N PBCJIPOGFJYBJE-UHFFFAOYSA-N 0.000 claims description 26
- 239000000126 substance Substances 0.000 claims description 25
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 24
- 238000007599 discharging Methods 0.000 claims description 22
- KAKZBPTYRLMSJV-UHFFFAOYSA-N Butadiene Chemical compound C=CC=C KAKZBPTYRLMSJV-UHFFFAOYSA-N 0.000 claims description 20
- 210000004243 sweat Anatomy 0.000 claims description 19
- 238000000746 purification Methods 0.000 claims description 17
- 230000035900 sweating Effects 0.000 claims description 17
- 239000000463 material Substances 0.000 claims description 16
- 238000001816 cooling Methods 0.000 claims description 15
- ZCQWOFVYLHDMMC-UHFFFAOYSA-N Oxazole Chemical compound C1=COC=N1 ZCQWOFVYLHDMMC-UHFFFAOYSA-N 0.000 claims description 14
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 12
- 238000002844 melting Methods 0.000 claims description 11
- 230000008018 melting Effects 0.000 claims description 11
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 6
- 238000009835 boiling Methods 0.000 claims description 5
- 230000008878 coupling Effects 0.000 claims description 5
- 238000005859 coupling reaction Methods 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 4
- 239000006227 byproduct Substances 0.000 claims description 4
- 238000000605 extraction Methods 0.000 claims description 3
- HRPVXLWXLXDGHG-UHFFFAOYSA-N Acrylamide Chemical compound NC(=O)C=C HRPVXLWXLXDGHG-UHFFFAOYSA-N 0.000 claims 1
- 150000001336 alkenes Chemical class 0.000 claims 1
- 238000005576 amination reaction Methods 0.000 claims 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 claims 1
- 238000011084 recovery Methods 0.000 claims 1
- 239000002904 solvent Substances 0.000 claims 1
- 238000005265 energy consumption Methods 0.000 abstract description 10
- 238000003912 environmental pollution Methods 0.000 abstract description 4
- 150000003839 salts Chemical class 0.000 abstract description 2
- 239000012071 phase Substances 0.000 description 32
- 239000007789 gas Substances 0.000 description 31
- 230000001276 controlling effect Effects 0.000 description 25
- 239000011259 mixed solution Substances 0.000 description 25
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 14
- 239000000047 product Substances 0.000 description 14
- 239000002994 raw material Substances 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 8
- 239000007791 liquid phase Substances 0.000 description 7
- 238000005070 sampling Methods 0.000 description 6
- 238000000926 separation method Methods 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 4
- 239000003814 drug Substances 0.000 description 4
- 239000012528 membrane Substances 0.000 description 4
- 230000007547 defect Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 235000013305 food Nutrition 0.000 description 3
- 239000008204 material by function Substances 0.000 description 3
- 239000003513 alkali Substances 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 229940079593 drug Drugs 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000004128 high performance liquid chromatography Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 238000007689 inspection Methods 0.000 description 2
- 238000011031 large-scale manufacturing process Methods 0.000 description 2
- 238000005373 pervaporation Methods 0.000 description 2
- 239000010865 sewage Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 150000003863 ammonium salts Chemical class 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000004587 chromatography analysis Methods 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 239000012043 crude product Substances 0.000 description 1
- -1 cyanohydrin Chemical compound 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 229910017053 inorganic salt Inorganic materials 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000010815 organic waste Substances 0.000 description 1
- 238000000053 physical method Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C253/00—Preparation of carboxylic acid nitriles
- C07C253/32—Separation; Purification; Stabilisation; Use of additives
- C07C253/34—Separation; Purification
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Abstract
The invention discloses a method for refining acetonitrile by a rectification-melt crystallization coupling process, which comprises the steps of firstly removing high-boiling-point impurities such as salt water, acrylonitrile, propionitrile and the like from water-containing crude acetonitrile with the purity of not less than 50% through a rectification system, condensing acetonitrile steam extracted from a lateral line into acetonitrile with the purity of not less than 99.3% through a heat exchanger, and further obtaining gradient chromatographic pure acetonitrile through a melt crystallization mode. The invention adopts rectification and melt crystallization processes to be coupled to refine acetonitrile, and mother liquor generated by melt crystallization is circulated back to a rectification system, so that rectification and crystallization can be continuously carried out. The method has the advantages of simple operation, high product yield, little environmental pollution, low energy consumption and the like, and the final purity of the acetonitrile can reach more than 99.99 percent.
Description
Technical Field
The invention belongs to the technical field of chemical industry, and particularly relates to a method for producing gradient chromatographic pure acetonitrile by adopting a rectification-melt crystallization coupling process.
Background
The HPLC technology has become an important tool for researching synthetic chemistry, petrochemistry, life science, clinical chemistry and medicine at the molecular level, and is one of the essential means for environmental monitoring, food inspection, forensic inspection and the like, but the realization of the HPLC technology must rely on gradient chromatographic pure acetonitrile. At present, industrial acetonitrile is mainly produced by a method of separating acrylonitrile as a byproduct and ammoniating the acrylonitrile by acetic acid or ethanol, but the technology for preparing chromatographic pure acetonitrile by using the industrial acetonitrile has certain defects.
At present, acetonitrile is purified mainly by physical methods such as evaporation, rectification, pervaporation membrane and the like. For example, CN214496149U discloses a continuous acetonitrile separation and purification device, which removes acetone in crude acetonitrile through a pervaporation membrane, thereby purifying high-purity acetonitrile. The scheme has low universality, and acetonitrile impurities from different sources can easily reduce the separation effect of the membrane and even cause failure.
CN113372242A relates to a purification method of water-containing acetonitrile, wherein the water-containing acetonitrile is subjected to steam stripping in a stripping tower, a first material containing acetonitrile with higher concentration is obtained at the top of the tower, and the first material is subjected to water removal through a vaporization membrane to obtain an acetonitrile product. The purification method can purify the water-containing acetonitrile containing only a small amount of acetonitrile to obtain the acetonitrile product with high purity. CN213416715U realizes the chemical impurity removal of crude acetonitrile through adding ammonia water, and the formed ammonium salt can be directly incinerated. However, these methods require high energy consumption and also require a large amount of chemical reagents, and most importantly, it is difficult to obtain gradient chromatographic pure acetonitrile by using the existing methods.
The invention adopts a rectification-melt crystallization coupling method to obtain gradient chromatographic pure acetonitrile from water-containing crude acetonitrile at high yield.
Disclosure of Invention
The invention aims to provide a method for refining acetonitrile by adopting rectification-melt crystallization coupling. The rectification operation of the invention is simple and convenient, and inert gas protection is not needed: the melt crystallization overcomes the defects of large energy consumption, high production cost, low yield and the like of secondary rectification: and the rectification and crystallization coupling method is adopted, so that a large amount of energy consumption is saved, the separation operation is continuously carried out, and the requirement of industrial large-scale production can be met. The purity of the obtained pure acetonitrile reaches more than 99.99 percent, and the use requirement of the gradient chromatographic pure acetonitrile is met. Simultaneously meets the requirements of food, medicine and functional materials for production.
The object of the invention can be achieved by the following measures: the crude acetonitrile mixed solution is firstly separated by rectification, and the purpose of primary purification is achieved by utilizing the difference of azeotropic points of acetonitrile water under different conditions. Crude acetonitrile enters a rectification tower I from the middle lower part through on-line analysis, acid and alkali with stoichiometric ratio are added according to analysis data to convert impurities into inorganic salt, acetonitrile water azeotrope with proper concentration is extracted from the tower top of the tower I, water, salt and tar impurities with high boiling point are left at the bottom of a kettle, and all impurities enter a water phase discharge system of the tower kettle. Controlling the side temperature to be 63 ℃, ensuring that the concentration of the acetonitrile extracted from the side is about 87 percent, feeding the acetonitrile into a chemical treatment tank, adding activated carbon (about 20 percent of the mass of the feeding amount) into a chemical treatment tank to remove acrylonitrile, discharging acetonitrile from the bottom of a chemical treatment tank, feeding acetonitrile-water azeotrope into a rectification II tower from the middle lower part, controlling the pressure of the top of the tower to be about 0.3MPa, the temperature of the top of the tower to be 110 ℃, condensing acetonitrile steam with the purity of more than 99.3 percent from the upper part of the II tower into liquid crude acetonitrile after heat exchange by a heat exchanger, directly introducing the heat-exchanged acetonitrile crude product into a crystallizer crystallized by high-purity acetonitrile to reduce the temperature and control the crystallization temperature to be-52-50 ℃, keeping the temperature for 1-1.5h, growing crystals, returning an uncrystallized solution after a crystal layer grows to be 10-50mm to an inlet of the II tower through the heat exchanger, cutting the material of the II tower into a standby crystallizer, and performing gas phase melting on the crystallized crystallizer by using the II tower to obtain 99.99 percent of acetonitrile and then feeding the acetonitrile product into a storage tank. The cooling crystallization process is melt crystallization and comprises 4 steps: crystal forming, conveying, crystal washing and melting.
The invention applies rectification and melt crystallization process to refine acetonitrile, and the melt crystallization process is selected for recycling, so that rectification and crystallization can be continuously carried out. The method has the advantages of simple operation, small environmental pollution, low energy consumption and the like, and the final purity of the acetonitrile can reach more than 99.99 percent.
The rectification process is divided into two sections, and is firstly carried out under the reduced pressure condition, wherein the operation pressure is 20-50kPa, and preferably 25-45 kPa; controlling the temperature of a tower kettle I to be 60-80 ℃, preferably 66-76 ℃; the temperature of the top of the tower is controlled to be 50-65 ℃, preferably 58-62 ℃. Light components in the crude acetonitrile, such as acrylonitrile and acetone, are discharged from the tower top as a gas phase, and water and other heavy organic matters, including one or more heavy byproducts of propionitrile, acetone, butadiene, cyanohydrin, oxazole, imidazole and the like, are discharged from the tower bottom and enter a water treatment system. An acetonitrile-water azeotrope is drawn from the side line of the column I, which contains 87% acetonitrile and about 13% water, and contains trace heavy organics. The material flow enters a chemical treatment tank, alkali liquor is added to remove residual acrylonitrile, and then secondary rectification is carried out, wherein the operating pressure of a tower II is 260-350kPa, and preferably 310-320 kPa; controlling the temperature of the tower kettle to be 100-150 ℃, preferably 110-120 ℃; and controlling the temperature at the top of the tower to be 90-120 ℃, preferably 100-110 ℃, and obtaining a 99.3% acetonitrile material at the top of the tower.
The temperature of the materials is reduced by a heat exchanger to reach the temperature required by the melting crystallization, and the outlet temperature of the materials is-40 to-50 ℃, preferably-43 to-45 ℃. The cooling crystallization process is melt crystallization and comprises 4 steps: film forming, crystallization, sweating and melting.
The specific implementation method comprises the steps of firstly introducing liquid high-purity acetonitrile into a crystallizer at the temperature of-50 to-52 ℃ for staying for 2-8 min, then discharging acetonitrile which is not crystallized to form a film, forming an acetonitrile crystal film on the surface of the crystallizer, raising the temperature of the crystallizer to-40 to-45 ℃, introducing low boiling fraction which is subjected to heat exchange in the previous step and reaches-40 ℃, staying for 0.5-1.5 hours to grow a crystal layer, cooling to ensure that the crystal layer continues to grow for 2-6 hours after the crystal layer grows to a certain degree, wherein the cooling rate is 0.01-0.08 ℃/min, and discharging residual raw material liquid which is not crystallized after the crystallization is reduced: cutting the cooled low boiling fraction into a spare crystallizer; and then raising the temperature of the crystallizer at the speed of 0.005-0.1 ℃/min to enable the crystallization layer to sweat, wherein the sweating end point temperature is-46 to-50 ℃: after high-purity acetonitrile crystals are formed, the temperature of the crystallizer is raised to be higher than 80 ℃, crystal layers are completely melted, and high-purity acetonitrile products are collected. Wherein the thickness of the crystalline film formed in the film forming process is moderate, and is generally between 0.1 and 0.5 mm. The cooling rate is 0.01-0.08 ℃/min, preferably 0.03-0.05 ℃/min in the crystallization process, the cooling time is 2-6 hours, preferably 2-4 hours, because the acetonitrile content in the mother liquor is reduced along with the crystallization to a certain degree, the crystallization rate is reduced, the influence of the cooling on the crystallization is reduced, the temperature can be kept unchanged to a certain degree, the crystal can continue to grow to a certain thickness, and the growth thickness of the crystal layer is determined by the size of the crystallizer and the sweating operation efficiency. The temperature rise rate in the sweating process is 0.005-0.1 ℃/min, preferably 0.01-0.04 ℃/min, and the sweating end point temperature is-45-80 ℃, preferably-60-70 ℃.
The melting crystallization and the vacuum rectification processes are continuously carried out, the crude acetonitrile obtained by vacuum rectification is in a gaseous state, and the middle distillate of the melting crystallization, such as sweat and the like, is adopted to cool to the feeding temperature of the melting crystallization, so that the crude acetonitrile does not need to be separately cooled, and a large amount of cold energy is saved. Because the crystallization process needs long time, the vacuum rectification and the melt crystallization are continuously carried out, and a plurality of crystallizers can be selected for crystallization alternately. The operation process is described in detail below with reference to the accompanying drawings.
The method is characterized in that firstly, crude acetonitrile mixed solution is subjected to preliminary separation by adopting reduced pressure rectification to obtain an acetonitrile product with the content of 99.3 percent, then, the crude pure acetonitrile is refined by using melt crystallization, and a dehydration product is purified by two steps of rectification and crystallization to obtain the acetonitrile with the purity higher than 99.99 percent, so that the purity requirements of medicines and industrial products can be met, and particularly the index requirements of gradient grade chromatographic pure acetonitrile can be met. The rectification operation is simple and easy to control, the melt crystallization does not use organic solvent, and no organic waste is generated, so the method is an environment-friendly, economical and feasible separation operation. The other important substance of the invention is characterized in that the rectification and crystallization are coupled, so that the rectified steam is crystallized immediately after heat exchange, thereby saving a large amount of energy consumption, and then the rectification and crystallization can be continuously carried out by alternately crystallizing through a plurality of crystallizers, which is beneficial to large-scale continuous production and can meet the requirement of industrial production. The method has the advantages of simple operation, high product yield, little environmental pollution, low energy consumption and the like, and the final purity of the acetonitrile can reach more than 99.99 percent.
The invention adopts rectification and melt crystallization processes to be coupled to refine acetonitrile, and mother liquor generated by melt crystallization is circulated back to a rectification system, so that rectification and crystallization can be continuously carried out. The method has the advantages of simple operation, high product yield, little environmental pollution, low energy consumption and the like, and the final purity of the acetonitrile can reach more than 99.99 percent. The invention has the advantages that:
the invention aims to provide a method for refining acetonitrile by adopting rectification-melt crystallization coupling. The rectification operation of the invention is simple and direct, and does not need inert gas protection: the melt crystallization overcomes the defects of high energy consumption, high residue, easy pollution and the like of secondary removal of the mixed solvent: and a rectification and crystallization coupling method is adopted to save a large amount of energy consumption and cold energy, so that the separation operation is continuously carried out, and the requirement of industrial large-scale production can be met. The purity of the obtained pure acetonitrile reaches more than 99.99 percent, and the pure acetonitrile can meet the requirements of foods, medicines and functional materials for preparing the functional materials.
Drawings
FIG. l is a schematic diagram of a process flow for refining acetonitrile by a rectification-crystallization coupling method.
In the figure: column I; 2. a chemical treatment tank: 3, a II tower; 4. a crystallizer: 5. a residue tank; 6. an intermediate tank; 7. and (5) a product tank.
Detailed Description
As shown in figure 1, the process flow for refining acetonitrile by the rectification-crystallization coupling method comprises the following steps that crude acetonitrile enters a tower I1 from a material inlet at the middle lower part of the tower I, and in the tower I: discharging light components in the crude acetonitrile as gas phase from the top of the tower, feeding the gas phase into a light component tank, and discharging sewage and heavy components from the bottom of the tower; introducing an acetonitrile-water azeotrope led out from the side line of the tower I into a chemical treatment tank 2, and removing residual acrylonitrile in the acetonitrile-water azeotrope to obtain acetonitrile-containing fraction; then, the fraction containing acetonitrile enters a tower II from a material inlet at the middle lower part of the tower II 3 for rectification, sewage and heavy components are discharged from a tower kettle of the tower II, acetonitrile with the mass purity of more than or equal to 99 percent obtained at the tower top of the tower II enters a crystallizer 4, pure acetonitrile is collected into a product tank 7, crystallized residual liquid (entering a residual liquid tank 5) and perspiration liquid (entering an intermediate tank 6) are respectively collected, and then the crystallized residual liquid returns to the tower II for continuous rectification; the crystallized sweat is directly returned to the crystallizer for further purification.
The crude acetonitrile is water-containing acetonitrile, the rectification is double-tower rectification, namely a tower I and a tower II, the crude acetonitrile product enters the tower I from a material inlet at the middle lower part of the tower I, and the operating pressure of the tower I is 20-50kPa, preferably 25-45 kPa; the temperature of the tower kettle is controlled to be 60-85 ℃, preferably 66-76 ℃; the temperature of the top of the tower is controlled to be between 50 and 65 ℃, preferably between 58 and 62 ℃, and the temperature difference between the bottom of the tower and the top of the tower is preferably controlled as follows: 8-14 ℃, controlling the lateral line temperature to be 60-65 ℃, and preferably between 62-64 ℃; the temperature difference between the side line and the tower top is preferably controlled as follows: 2 to 4 ℃. In the tower I: discharging light components (such as one or two of acrylonitrile, butadiene and acetone) in the crude acetonitrile as gas phase from the top of the tower, and discharging water and heavy components (one or more of tar, propionitrile, cyanohydrin, oxazole, imidazole and the like) from the bottom of the tower;
leading out an acetonitrile-water azeotrope from the side line of the tower I, leading out the acetonitrile-water azeotrope from the side line of the tower I, and removing residual acrylonitrile in the acetonitrile-water azeotrope in a chemical treatment tank to obtain a fraction containing acetonitrile; then the fraction containing acetonitrile enters the II tower for rectification from the material inlet at the middle lower part of the II tower, and the operation pressure is 260-350kPa, preferably 310-320 kPa; the temperature of the tower kettle is controlled to be between 100 ℃ and 150 ℃, preferably between 110 ℃ and 120 ℃; the temperature at the top of the tower is controlled between 90-120 ℃, preferably between 100 ℃ and 110 ℃, and acetonitrile with the purity of more than or equal to 99 percent (preferably 99.1-99.5 percent of mass content) is obtained at the top of the tower.
The side line of the tower I leads out acetonitrile-water azeotrope containing acetonitrile, water, a small amount of acrylonitrile and heavy organic matters (one or more than two of cyanohydrin, oxazole, imidazole and the like), wherein the preferable content is as follows: 80-95% of acetonitrile (preferably 85-90% of mass content) and less than 5-less than 20% of water (preferably less than 10-less than 15% of mass content).
The process of removing trace acrylonitrile in the chemical treatment tank comprises the following steps: sodium hydroxide is added to the chemical treatment tank to adjust the pH of the acetonitrile-water azeotrope solution to 7-9, and/or 5-40% (preferably 15% -30%, more preferably 18% -25%) of the mass of the acetonitrile-water azeotrope feed is added to the chemical treatment tank to remove the acrylonitrile.
The specific process of carrying out melt crystallization in the crystallizer comprises the following steps: introducing pure acetonitrile into a crystallizer at the temperature of-40 to-45 ℃ to ensure that the inner surface of the crystal is opened into an acetonitrile crystal layer, and the thickness of the acetonitrile crystal layer is about: 0.1-0.5mm, then adjusting the temperature of a crystallizer to-52 to-50 ℃, introducing a II tower subjected to heat exchange by a heat exchanger to rectify more than 99% of acetonitrile fraction, controlling the temperature of the crystallizer to-40 to-45 ℃ after the gas phase temperature at the top of the heat exchange II tower is-40 to-45 ℃, keeping for 1-1.5 hours to grow a crystal layer, then reducing the temperature of the crystallizer to continue to grow the crystal layer, reducing the temperature at the rate of 0.01-0.1 ℃/min (preferably 0.02-0.04 ℃/min), discharging uncrystallized impurity liquid after the crystal layer grows to the thickness of 10-50mm, then raising the temperature to sweat the crystal, discharging sweat, raising the temperature to 75-90 ℃ (preferably 80-85 ℃) to melt the crystal and collect to obtain the high-purity acetonitrile crystal.
The rectification and crystallization processes are continuously carried out, the rectified low-boiling fraction directly enters a crystallizer for cooling crystallization after heat exchange to the inlet temperature required by the crystallization process, the process of coupling vacuum rectification and melt crystallization is carried out, and 6 crystallizers are selected for use in turn in the melt crystallization process for circulation and sequential use, so that the rectification and crystallization can be continuously carried out.
Comparative example 1
The single rectifying tower purification effect of the acetonitrile-water mixed solution is as follows: introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower, detecting that the acetonitrile contains 66% of acetonitrile, 32% of water, 1% of acrylonitrile and a small amount of other impurities (including one or more of tar, propionitrile, cyanohydrin, oxazole, imidazole and the like), heating the mixed solution to 110 ℃, rectifying under normal pressure, displaying the top temperature at 77 ℃, collecting a product at the top of the tower, and analyzing the acetonitrile concentration to be 83.5%, the water content to be 16% and the acrylonitrile content to be about 0.5%.
The result shows that acetonitrile with water content of 16 percent can not be obtained by single rectification under normal pressure.
Comparative example 2
1kg of acetonitrile having a purity of 99.5% was further purified by an atmospheric distillation column. The quality purity of raw material acetonitrile is 99.5%, water is 0.45%, acrylonitrile is 0.04% and a small amount of other impurities (including one or more than two of tar, propionitrile, cyanohydrin, oxazole, imidazole and the like) are detected, the mixed solution is heated to 110 ℃, the normal pressure secondary rectification and purification are carried out, after the temperature of the tower top is stable, fractions in different stages are collected, the purity of each fraction is detected through chromatography, and the results are shown in the following table:
| fraction number | Temperature at the top of the column | Acetonitrile content/%) | Weight/kg |
| 1 | 81.0-81.3 | 99.2 | 0.153 |
| 2 | 81.3-81.4 | 99.6 | 0.625 |
| 3 | 81.4-81.5 | 99.7 | 0.133 |
| 4 | Residual kettle | 99.3 | 0.075 |
The result shows that acetonitrile with the concentration of more than 99.99 percent can not be obtained by adopting the secondary rectification of acetonitrile containing more than 99.3 percent of water.
Example 1
Introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower of a tower I, detecting that the acetonitrile has the mass content of 60 percent, water has the mass content of 35 percent, acrylonitrile has the mass content of 2 percent and a small amount of other impurities (comprising one or more than two of tar, propionitrile, acetone, butadiene, cyanohydrin, oxazole, imidazole and the like) on line, sending the mixed solution into the rectifying tower I from a material inlet at the middle lower part of the rectifying tower I, heating the mixed solution to 75 ℃ by a reboiler, vacuumizing the rectifying tower I, controlling the pressure to be 31KPa, rectifying, displaying the temperature at the top of the tower I at 58 ℃, and controlling the side line extraction temperature to be: at 60 ℃. Cooling the gas phase at the top of the tower and sending the gas phase to a light component tank; collecting side acetonitrile-water azeotrope fraction in a chemical treatment tank (2), adding sodium hydroxide to adjust the pH value to 8, standing for 30min, discharging the lower-layer material of the chemical treatment tank, feeding the upper-layer liquid phase into a rectifying tower of a tower II from a material inlet at the middle lower part of the rectifying tower II, heating the mixed solution to 120 ℃ by a reboiler of the tower II, operating the pressure of 310kPa, displaying the temperature at the top of the tower to 110 ℃, and rectifying. And acetonitrile is extracted from the top of the rectifying tower II, and the detection concentration is 99.5%. The temperature of the crystallizer is-45 ℃, pure acetonitrile is introduced, and acetonitrile crystals grow into a film on the inner wall surface of the crystallizer: 0.1-0.3 mm. Then the temperature of the crystallizer is adjusted to-52 to-50 ℃, the gas phase at the top of the II tower is cooled to-40 ℃ by a heat exchanger and then is led into an acetonitrile crystallizer which is already coated with a film, the temperature of the crystallizer is controlled to-45 ℃, a crystal layer grows for 1.2 hours, then the temperature is reduced at the speed of 0.02 ℃/min, the crystal layer continues to grow for 3 hours, the crystallization thickness is 50mm, and the liquid (residual liquid) which is not crystallized is discharged out of the crystallizer: raising the temperature of the crystallizer at the speed of 0.01 ℃/min to enable the crystal layer to sweat and remove impurities, wherein the sweating end point temperature is-46 ℃; the molten liquid is drained. And (3) raising the temperature of the crystallizer to 80 ℃ by utilizing the gas phase of the rectifying tower II to melt the crystal layer, collecting the crystal layer, and sampling and analyzing the crystal layer. 446g of pure acetonitrile was obtained with a purity of 99.992%.
Respectively collecting the crystallized residual liquid (entering a residual liquid tank 5) and the perspiration liquid (entering an intermediate tank 6), and returning the crystallized residual liquid to the II tower for continuous rectification; the crystallized sweat is directly returned to the crystallizer for continuous purification.
Example 2
Introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower of a tower I, detecting that the acetonitrile content is 55%, water is 43%, acetone is 1.2% and a small amount of other impurities (comprising one or more than two of tar, propionitrile, acrylonitrile, butadiene, cyanohydrin, oxazole, imidazole and the like) on line, sending the mixed solution into the rectifying tower I, heating the mixed solution to 70 ℃ by a reboiler, vacuumizing the rectifying tower I, operating at 29KPa, displaying the tower top temperature of the tower I at 56 ℃, rectifying, collecting a side-line acetonitrile-water azeotrope, and controlling the temperature of a rectifying section to indicate 58 ℃; cooling the gas phase at the top of the tower, conveying the gas phase to a light component tank, adding 0.2Kg of activated carbon into a chemical treatment tank (2), treating the gas phase to be qualified, then feeding the gas phase into a rectifying tower of a tower II, standing the gas phase for 30min, discharging the activated carbon, feeding the liquid phase into the rectifying tower II, controlling the kettle temperature of the tower II to be 120 ℃ by a reboiler, rectifying the pressure in the tower to be 320kPa, displaying the temperature at the top of the tower to be 110 ℃, extracting acetonitrile at the top of the tower, detecting that the purity of the acetonitrile is 99.4 percent, controlling the temperature of the crystallizer to be-45 ℃, and introducing high-purity acetonitrile to ensure that the acetonitrile crystal grows to form a film: 0.4-0.5 mm. Then regulating the temperature of the crystallizer to-52 to-50 ℃, reducing the temperature of a gas phase of a rectifying tower II to-40 ℃ through a heat exchanger, introducing the gas phase into the crystallizer with the film formed, enabling a crystal layer to grow for 1.3 hours, controlling the temperature to be-44 ℃, reducing the temperature at the speed of 0.04 ℃/min, enabling the crystal layer to continue to grow for 3 hours, enabling the thickness of the crystal layer to be 50mm, and discharging the residual liquid which is not crystallized out of the crystallizer; raising the temperature of the crystallizer at a rate of 0.02 ℃/min to cause the crystal layer to sweat, the sweating end point temperature being-46 ℃, draining the melted sweating liquid: and raising the temperature of the crystallizer to 80 ℃ by utilizing the gas phase of the II rectifying tower, melting a crystal layer, collecting, sampling and analyzing. 486g of acetonitrile was obtained in a purity of 99.994%.
After the crystallization residual liquid and the perspiration liquid are respectively collected (enter residual liquid tanks 5 and 6), the crystallization residual liquid returns to the II tower for continuous rectification; the crystallized sweat is directly returned to the crystallizer for continuous purification.
Example 3
Introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower of a tower I, detecting that the acetonitrile content is 60%, water is 38%, acrylonitrile is 1% and a small amount of other impurities (comprising one or more than two of tar, propionitrile, acetone, butadiene, cyanohydrin, oxazole, imidazole and the like) on line, sending the mixed solution into the rectifying tower I, heating the mixed solution to 76 ℃ by a reboiler, carrying out rectification under the operation pressure of 30kPa in the tower, indicating the temperature at the top of the tower to be 60 ℃, controlling the temperature at the lateral line to be 62 ℃, collecting acetonitrile-water azeotrope at the top of the tower, and cooling the gas phase at the top of the tower to be sent to a light component tank. Collecting side-stream acetonitrile-water azeotrope fraction in a chemical treatment tank, adjusting the pH value to 8 by using sodium hydroxide, standing for 30min, discharging a lower-layer liquid phase through a drain outlet, feeding an upper-layer liquid phase into a rectifying tower of a tower II, controlling the kettle temperature of the tower II to be 120 ℃ through a reboiler, controlling the pressure in the tower to be 320kPa, and rectifying at the tower top temperature of 110 ℃. Extracting acetonitrile from the top of a rectifying tower II, detecting the concentration to be 99.5 percent, introducing high-purity acetonitrile into the rectifying tower at the temperature of-45 ℃ to ensure that acetonitrile crystals grow and form a film: 0.2-0.4 mm. Then the temperature of the crystallizer is adjusted to-52 to-50 ℃, the gas phase of the II rectifying tower is cooled to-40 ℃ through a heat exchanger and is introduced into the crystallizer with the film, the crystal layer grows for 1 hour, the temperature is controlled to be-42 ℃, then the temperature is reduced at the speed of 0.05 ℃/min, the crystal layer continues to grow for 3.5 hours, the thickness of the crystal layer is 50mm, and the residual liquid which is not crystallized is discharged out of the crystallizer: the crystallizer temperature was raised at a rate of 0.05 ℃/min to sweat the crystalline layer, the end point temperature of sweating was-46 ℃, the melted liquid was drained off: and (3) raising the temperature of the crystallizer to 80 ℃ by utilizing the gas phase of the rectifying tower II to melt the crystal layer, collecting the crystal layer, and sampling and analyzing the crystal layer. 522g of pure acetonitrile with a purity of 99.993% was obtained. After the crystallization residual liquid and the perspiration liquid are respectively collected (enter residual liquid tanks 5 and 6), the crystallization residual liquid returns to a tower II for rectification; the crystallized sweat is directly returned to the crystallizer for continuous purification.
Example 4
Introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower of a tower I, detecting that the acetonitrile content is 63 percent, water is 35 percent, butadiene is 1 percent, and a small amount of other impurities (comprising one or more than two of tar, propionitrile, acetone, acrylonitrile, cyanohydrin, oxazole, imidazole and the like) are detected, sending the mixed solution into the rectifying tower I, heating the mixed solution to 75 ℃ by the rectifying tower I through a reboiler, vacuumizing, controlling the vacuum degree to be 32kPa and the tower top temperature to be 60 ℃, performing reduced pressure rectification, controlling the side line extraction temperature to be 62 ℃, and cooling the tower top gas phase and sending the gas phase to a light component tank. Collecting acetonitrile-water azeotrope at the tower top in a chemical treatment tank, adding about 0.2Kg of active carbon for purification, standing for 30min, discharging the active carbon, allowing the liquid phase to enter a rectifying tower of a tower II, controlling the kettle temperature of the tower II to be 120 ℃, controlling the pressure in the tower to be 320kPa and the tower top temperature to be 110 ℃ by using a reboiler, and rectifying. And II, extracting acetonitrile from the top of the rectifying tower, keeping the temperature of a fraction collecting point at 110 ℃, and detecting the concentration at 99.5%. The temperature of the crystallizer is-45 ℃, and high-purity acetonitrile is introduced to ensure that acetonitrile crystals grow and form a film: 0.1-0.5 mm. Then the temperature of the crystallizer is adjusted to-52 to-50 ℃, the gas phase at the top of the heat exchanger II is cooled to-40 ℃ and then is introduced into the crystallizer with the coated film, so that the crystal layer grows for 1 hour, the temperature is controlled to-44 ℃, then the temperature is reduced at the speed of 0.04 ℃/min so that the crystal layer continues to grow for 3 hours, and the residual liquid which is not crystallized is discharged out of the crystallizer; raising the temperature of the crystallizer at the speed of 0.06 ℃/min to sweat the crystal layer, wherein the sweating end point temperature is-46 ℃, and discharging the melted sweating liquid: and (3) raising the temperature of the crystallizer to 80 ℃ by utilizing the gas phase of the rectifying tower II, melting the crystal layer, collecting, sampling and analyzing. 516g of pure acetonitrile with a purity of 99.996% was obtained.
After the crystallization residual liquid and the perspiration liquid are respectively collected (enter residual liquid tanks 5 and 6), the crystallization residual liquid returns to a tower II for rectification; the crystallized sweat is directly returned to the crystallizer for continuous purification.
Example 5
Introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower of a tower I, detecting that the acetonitrile content is 84%, water is 15%, oxazole is 1% and a small amount of other impurities (comprising one or more of tar, propionitrile, acetone, acrylonitrile, cyanohydrin, butadiene, imidazole and the like) on line, sending the mixed solution into the rectifying tower I, heating the mixed solution to 70 ℃ by a reboiler of the rectifying tower I, vacuumizing, controlling the vacuum degree to be 32kPa, carrying out reduced pressure rectification at the tower top temperature of 60 ℃, controlling the side-draw temperature to be 62 ℃, collecting side-draw acetonitrile-water azeotrope, and cooling the gas phase at the tower top to be sent to a light component tank. Adding 0.2Kg of activated carbon into the chemical treatment tank for treatment for 30min, discharging the activated carbon, feeding the liquid phase into a rectifying tower of a tower II, and rectifying by using a reboiler to control the kettle temperature of the tower II to be 120 ℃, the vacuum degree to be 320kPa and the tower top temperature to be 110 ℃. And acetonitrile is extracted from the top of the II rectifying tower, and the detection concentration is 99.5%. The temperature of a crystallizer is minus 45 ℃, and high-purity acetonitrile is introduced to ensure that acetonitrile crystals grow and form a film: 0.1-0.5 mm. Then the temperature of the crystallizer is adjusted to-52 to-50 ℃, the gas phase at the top of the II tower is cooled to-40 ℃ through a heat exchanger and then is introduced into the crystallizer with the coated film, the crystal layer grows for 1.0 hour, the temperature is controlled to be-40 ℃, then the temperature is reduced at the rate of 0.06 ℃/min, the crystal layer continues to grow for 3 hours, and the residual liquid which is not crystallized is discharged out of the crystallizer: raising the temperature of the crystallizer at the speed of 0.02 ℃/min to sweat the crystal layer, wherein the sweating end point temperature is-46 ℃, and discharging the melted sweating liquid: and (3) raising the temperature of the crystallizer to 80 ℃ by utilizing the gas phase of the rectifying tower II to melt the crystal layer, collecting the crystal layer, and sampling and analyzing the crystal layer. 446g of pure acetonitrile was obtained with a purity of 99.995%.
After the crystallization residual liquid and the perspiration liquid are respectively collected (enter residual liquid tanks 5 and 6), the crystallization residual liquid returns to a tower II for rectification and purification; the crystallized sweat is directly returned to the crystallizer for continuous purification.
Example 6
Introducing l Kg of crude acetonitrile mixed solution into a raw material tank of a rectifying tower of a tower I, detecting that the acetonitrile content is 63%, water is 35%, cyanohydrin is 1.8% and a small amount of oxazole and other impurities (comprising one or more than two of tar, propionitrile, acetone, acrylonitrile, oxazole, butadiene, imidazole and the like) on line, sending the mixed solution into the tower I of the rectifying tower, heating the mixed solution to 75 ℃ by a reboiler of the rectifying tower I, vacuumizing, controlling the vacuum degree to be 32kPa, carrying out reduced pressure rectification at the tower top temperature of 60 ℃, controlling the side-draw temperature to be 62 ℃, and cooling the gas phase at the tower top to send to a light component tank. Collecting acetonitrile-water azeotrope on the side line of the tower I in a chemical treatment tank, adding 0.2Kg of active carbon, standing for 30min, discharging the active carbon, allowing the liquid phase to enter a rectifying tower of the tower II, controlling the kettle temperature of the tower II to be 120 ℃, the vacuum degree to be 320kPa and the tower top temperature to be 110 ℃ by using a reboiler for rectification. Extracting acetonitrile from the top of a rectifying tower II, detecting the concentration to be 99.5 percent, introducing high-purity acetonitrile into the rectifying tower at the temperature of-45 ℃ to ensure that acetonitrile crystals grow and form a film: 0.1-0.5 mm. Then the temperature of the crystallizer is adjusted to-52 to-50 ℃, the gas phase at the top of the II tower is cooled to-40 ℃ by a heat exchanger and is introduced into the crystallizer with the film, the crystal layer grows for 1.5 hours, the temperature is controlled to-45 ℃, then the temperature is reduced at the speed of 0.03 ℃/min, the crystal layer continues to grow for 3 hours, and the residual liquid which is not crystallized is discharged out of the crystallizer: raising the temperature of the crystallizer at a rate of 0.02 ℃/min to cause the crystal layer to sweat, the sweating end point temperature being-46 ℃, draining the melted sweating liquid: and (3) raising the temperature of the crystallizer to 80 ℃ by utilizing the gas phase of the II rectifying tower, melting a crystal layer, collecting to obtain a crystal product, and sampling and analyzing. 458g of pure acetonitrile with a purity of 99.995% were obtained.
After the crystallization residual liquid and the perspiration liquid are respectively collected (enter residual liquid tanks 5 and 6), the crystallization residual liquid returns to a tower II for rectification and purification; the crystallized sweat returns to the crystallizer for continuous purification.
Claims (9)
1. A method for refining acetonitrile by a rectification-melt crystallization coupling process is characterized by comprising the following steps:
the crude acetonitrile with the mass purity of not less than 50 percent (more than or equal to 50 percent, usually the mass content is 50-90 percent, and the preferred mass content is 60-80 percent) is rectified to remove component impurities, so that analytically pure acetonitrile with the mass purity of more than or equal to 99 percent (the preferred mass content is 99.1-99.5 percent) is obtained, and further the analytically pure acetonitrile with the purity of 99.99 percent is obtained by melting and crystallizing in a crystallizer.
2. The method of claim 1, wherein: the crude acetonitrile having a mass purity of not less than 50% can be recovered as a by-product from a production apparatus, such as: the by-products from the production apparatus for acrylonitrile, acrylamide, etc. may be obtained from one or more of an acetonitrile apparatus for acetic acid or ethanol amination, a pharmaceutical factory, and a solvent recovery section of an olefin extraction apparatus.
3. The method of claim 1 or 2, wherein: the crude acetonitrile is water-containing acetonitrile with water content of 9.9-49.9% (preferably 19.9-39.9 wt%), and also contains one or more of tar, acrylonitrile, propionitrile, acetone, butadiene, cyanohydrin, oxazole, and imidazole, and other impurities.
4. The method of claim 1, wherein: the crude acetonitrile containing water is rectified into double-tower rectification, namely a tower I and a tower II, the crude acetonitrile enters the tower I from a material inlet at the middle lower part of the tower I, and the operating pressure of the tower I is 20-50kPa, preferably 25-45 kPa; the temperature of the tower kettle is controlled to be 60-85 ℃, preferably 66-76 ℃; the temperature at the top of the tower is controlled to be between 50 and 65 ℃, preferably between 58 and 62 ℃, the temperature at the lateral line is controlled to be between 60 and 65 ℃, preferably between 62 and 64 ℃, and the difference between the temperature at the lateral line and the temperature at the top of the tower is preferably between 2 and 4 ℃; discharging light components (such as one or two of acrylonitrile, butadiene and acetone) in the crude acetonitrile as gas phase from the top of the tower, and discharging water and heavy components (one or more of tar, propionitrile, cyanohydrin, oxazole, imidazole and the like) from the bottom of the tower; leading out an acetonitrile-water azeotrope from the side line of the tower I, and removing residual acrylonitrile in the acetonitrile-water azeotrope in a chemical treatment tank; then the fraction containing acetonitrile enters the II tower for rectification from the middle-lower material inlet of the II tower, and the operation pressure is 260-350kPa, preferably 310-320 kPa; the temperature of the tower kettle is controlled to be between 100 ℃ and 150 ℃, preferably between 110 ℃ and 120 ℃; the temperature at the top of the tower is controlled between 90-120 ℃, preferably between 100 ℃ and 110 ℃, the difference between the top of the tower and the bottom of the tower is preferably more than 10 ℃, and acetonitrile with the purity of more than or equal to 99 percent (preferably 99.1-99.5 percent by mass content) is obtained at the top of the tower.
5. The method of claim 4, wherein: after the acetonitrile-water azeotrope is sent to a chemical treatment tank to remove residual acrylonitrile, the acetonitrile-water azeotrope is rectified by a tower II;
the process of removing trace acrylonitrile in the chemical treatment tank comprises the following steps: sodium hydroxide is added to the chemical treatment tank to adjust the pH of the acetonitrile-water azeotrope solution to 7-9, and/or 5-40% (preferably 15% -30%, more preferably 18% -25%) of the mass of the acetonitrile-water azeotrope feed is added to the chemical treatment tank to remove acrylonitrile.
6. The method of claim 1, further comprising: the specific process of carrying out melt crystallization in the crystallizer comprises the following steps: introducing pure acetonitrile into a crystallizer at the temperature of-40 to-45 ℃ to ensure that the inner surface of the crystal is opened into an acetonitrile crystal layer, and the thickness of the acetonitrile crystal layer is about: 0.1-0.5mm, then adjusting the temperature of a crystallizer to-52 to-50 ℃, introducing a II tower subjected to heat exchange by a heat exchanger to rectify more than 99% of acetonitrile fraction, controlling the temperature of the crystallizer to-40 to-45 ℃ after the gas phase temperature at the top of the heat exchange II tower is-40 to-45 ℃, staying for 1-1.5 hours to enable a crystal layer to grow, then reducing the temperature of the crystallizer to enable the crystal layer to continue to grow, reducing the temperature at the rate of 0.01-0.1 ℃/min (preferably 0.02-0.04 ℃/min), discharging uncrystallized impurity liquid after the crystal layer grows to the thickness of 10-50mm, then raising the temperature to enable the crystal to sweat, discharging sweat, raising the temperature to 75-90 ℃ (preferably 80-85 ℃) to melt the crystal and collect, and obtaining the high-purity acetonitrile crystal.
7. The method of claim 6, further comprising: the sweating temperature rise rate is 0.01-0.1 ℃/min (preferably 0.02-0.06 ℃/min), and the sweating end point temperature is-50 to-46 ℃.
8. The method of claim 6, further comprising: mother liquor (impurity liquor) generated by crystallization is circulated back to the rectifying tower for purification, and the process of rectification and crystallization coupling is realized.
9. The method of claim 1, further comprising: the rectification and crystallization processes are continuously carried out, the rectified low-boiling fraction directly enters a crystallizer for cooling crystallization after being subjected to heat exchange to the inlet temperature required by the crystallization process, the process of coupling vacuum rectification and melt crystallization is carried out, and 3-8 crystallizers are selected for the melt crystallization process to be used in turn in a circulating mode, so that the rectification and crystallization can be continuously carried out.
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