A method for concentrating and separating organic matter in high-salinity wastewater and separating salt by synchronous freezing and crystallization

Abstract

The present invention relates to the technical field of waste salt resource utilization and freezing crystallization, and specifically to a method for concentrated separation of organic matter in high-salt wastewater and simultaneous freezing crystallization salt separation. It can treat wastewater containing high-concentration organic matter and salt, and add the wastewater to a hot molten stabilizer for pretreatment; then cool and concentrate the high-salt wastewater solution containing the stabilizer to obtain an organic concentrate, obtain a dissolved stabilizer solution after solvent extraction and distillation, and recover the organic waste liquid; the salt water removed from the organic matter is subjected to low-temperature freezing treatment to form ice crystals and a concentrate; the concentrate is subjected to gradient freezing crystallization to produce ice crystals and high-purity saturated brine; and pure salt is prepared after centrifugal drying treatment. Beneficial effects: This method can not only achieve efficient impurity removal of organic matter in waste salt, but also simultaneously achieve crystallization and salt separation of waste salt, and has the advantages of simple processing procedures, short processing cycles, and modularization.

Description

Technical Field

[0001] The invention relates to the technical field of waste salt resource utilization and freezing crystallization, and specifically to a method for concentrating and separating organic matter in high-salt wastewater and performing synchronous freezing crystallization salt separation. Background Art

[0002] A large amount of high-salt organic wastewater is generated during the production process of various industries such as chemical, pharmaceutical, petroleum, papermaking, dairy processing, and food canning. The COD concentration in the wastewater is above 5g / L, and the salt content is higher than 1.5%, mostly sodium or potassium salts, including sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, etc. After the conventional process is used to treat high-salt organic wastewater or waste liquid, a large amount of complex waste salt containing organic matter will be generated, and it belongs to the category of hazardous waste, which makes it impossible to be effectively utilized. It has become a key technical problem that needs to be solved urgently in the industry. Although the multi-effect evaporation technology can improve the salt separation efficiency of waste salt in wastewater to a certain extent, the investment cost of this technology is high, and it is difficult to improve the recovery quality of salt. In recent years, the combination of membrane filtration technology and freeze crystallization technology has been considered to be an effective high-salt wastewater treatment process. However, this combined process is susceptible to organic contamination, and the operation is cumbersome. It has high requirements for the freezing crystallizer, resulting in unsatisfactory salt separation effect. Therefore, in order to solve the above problems, a method for high-salt wastewater organic concentration separation and synchronous freeze crystallization salt separation is designed. Summary of the invention

[0003] The object of the present invention is to provide a method for concentrating and separating organic matter in high-salinity wastewater and separating salt by synchronous freezing and crystallization, so as to solve the problems raised in the above-mentioned background technology.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for concentrating and separating organic matter in high-salinity wastewater and performing simultaneous freezing and crystallization to separate salt, comprising the following steps:

[0006] S1: adding organic high-salt wastewater to the hot-melted extraction stabilizer for mixed pretreatment to obtain organic high-salt wastewater pretreatment material;

[0007] S2: pumping the organic high-salt wastewater pretreatment material obtained in S1 into a low-temperature crystallization tank for stirring to obtain organic concentrated crystals and high-salt water;

[0008] S3: hot-melting the organic concentrated crystals obtained in S2, purifying them by combining reverse extraction and distillation processes, and returning the purified solvent to the wastewater pretreatment unit for reuse; and recovering the organic waste liquid;

[0009] S4: pumping the high-salt water obtained in S2 into a low-temperature freezing crystallizer for primary low-temperature freezing crystallization to obtain salt concentrate and secondary crystallized salt, and produce pure ice crystals;

[0010] S5: The salt concentrate obtained in S4 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization to obtain secondary crystallized salt; the primary crystallized salt and the secondary crystallized salt are post-processed to obtain pure salt.

[0011] More optimally: the organic high-salt wastewater in step S1 contains one or both of sodium sulfate or potassium sulfate, with a salt content of 1.5% to 10.0%, and an initial COD concentration of 0.5 g / L to 4 g / L.

[0012] More optimally: the extraction stabilizer in step S1 is dimethyl sulfoxide (DMSO), and the volume ratio of the extraction stabilizer to the wastewater is 1-5:200-300; the hot melting temperature in step S1 is 30-60°C.

[0013] More optimally: the temperature of the low-temperature crystallization tank in step S2 is 10-25°C; the speed of the pump in step S2 is 0.1L / min-5L / min; and the stirring speed in step S2 is 30-50r / min.

[0014] More optimally: the hot melting temperature in step S3 is 30-60°C; the reagent used for reverse extraction is N,N-dimethylformamide (DMF); the parameters of the distillation process in step S3 are: temperature 80-120°C, pressure -0.2~-0.1MPa.

[0015] More optimally: the low-temperature freezing crystallizer in step S4 is an OSLO horizontal continuous cooling crystallizer, and its parameters are: the length of the external cooler is 80.00cm~150.00cm, and the diameter is 10.00cm~35.00cm; the speed of the pump in step S4 is 0.1L / min~5L / min, and the material is driven by an axial flow circulation pump.

[0016] More optimally: the primary low-temperature freezing crystallization adopts three-step gradient cooling, and its specific process is: the first step is cooling to 10~20℃, the speed is 5~10℃ / min; the second step is cooling to -5~10℃, the speed is 10~20℃ / min; the third step is cooling to -15~-5℃, the speed is 2.0-5.0℃ / min.

[0017] More optimally: the secondary low-temperature freezing crystallization in step S5 is the same as the primary low-temperature freezing crystallization process.

[0018] More optimally: the post-treatment process of step S5 is: centrifuging the primary crystallized salt and the secondary crystallized salt at low temperature, washing with alcohol and then vacuum low-temperature drying; the parameters of the low-temperature centrifugation are: temperature 0~5°C, centrifugal speed 500~3000r / min; the alcohol for the alcohol washing is methanol or ethanol; the parameters of the vacuum low-temperature drying are: temperature -20~10°C, vacuum degree 20~100Pa, and drying time 2~6h.

[0019] The invention is based on the low-temperature recrystallization characteristics of DMSO and DMF. By adding an extraction stabilizer into high-salt wastewater, the organic matter in the wastewater can be concentrated and separated under low-temperature cooling conditions. The extraction stabilizer can be purified through reverse extraction and distillation processes and can be recycled for wastewater pretreatment. The collected high-salt water is subjected to gradient freezing crystallization in an OSLO horizontal continuous cooling crystallizer to remove the residual stabilizer, generate salt concentrate and crystallized salt, and discharge clean ice crystals (water) at the same time. Finally, the salt concentrate is subjected to secondary freezing crystallization and centrifugal drying to obtain high-purity salt.

[0020] Beneficial effects:

[0021] (1) The present invention innovatively uses DMSO solvent to wash and extract organic matter in high-salt organic wastewater, which can effectively stabilize the organic matter in the DMSO medium; after cooling and crystallization, the organic matter in the wastewater can be efficiently concentrated. This process has high impurity removal efficiency for organic matter in wastewater, is simple to operate, and is easy to modularize.

[0022] (2) In the method described in the present invention, the extraction stabilizer DMSO is reversely extracted with DMF, and then distilled, separated and recycled. This process has high organic matter removal efficiency and can save costs.

[0023] (3) In the method described in the present invention, after the high-salt water is subjected to a two-step gradient freezing crystallization treatment in an OSLO horizontal continuous cooling crystallizer, ice crystals (water), crystallized salt and salt concentrate can be obtained respectively. This process has high wastewater treatment efficiency, low energy consumption and high cold capacity utilization.

[0024] (4) In the method of the present invention, methanol or ethanol is used for alcohol washing and drying of the crystallized salt, which can improve the purity of the crystallized salt, and has good dehydration efficiency. The salt obtained after drying has high purity. The purity of sodium sulfate is >80%; the purity of potassium sulfate is >85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 This is the process flow of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1: A method for concentrating and separating organic matter in high-salinity wastewater and performing simultaneous freezing and crystallization to separate salt: wherein the initial contents of the components in the high-salinity wastewater are as shown in Table 1, and the method comprises the following steps:

[0029] S1: Add wastewater containing 0.5 g / L COD and 1.5% sodium sulfate into 30°C DMSO, mix and pretreat at a volume ratio of 1:200, and stir evenly;

[0030] S2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 25°C at a pumping speed of 0.1L / min, and the organic matter is concentrated and crystallized under a stirring condition of 30r / min, and the wastewater containing sodium sulfate is separated and collected;

[0031] S3: After the organic concentrated crystals collected in step S2 are melted at 30° C., DMSO is reversely extracted using DMF, and then the DMSO is purified and separated by distillation technology at 80° C. and a distillation pressure of -0.2 MPa, and the purified solvent is refluxed to the wastewater pretreatment unit for reuse; finally, the remaining organic waste liquid is recovered;

[0032] S4: The sodium sulfate-containing wastewater collected in step S2 is pumped into an OSLO horizontal continuous cooling crystallizer at a pumping rate of 5 L / min, and the cooler is 80 cm long and 10 cm in diameter; three-step gradient cooling is used to remove residual DMSO, the first step cooling rate is 5°C / min, cooling to 10°C; the second step cooling rate is 10°C / min, cooling to -5°C; the third step cooling rate is 2.0°C / min, cooling to -15°C; sodium sulfate concentrate and sodium sulfate crystal salt are prepared, and pure ice crystals (water) are produced;

[0033] S5: The concentrated solution collected in step S4 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization, and all the sodium sulfate crystals are subjected to low-temperature centrifugation. The sodium sulfate crystals are washed with ethanol and then dried at -20°C vacuum low temperature with a vacuum degree of 20 Pa. After drying for 2 hours, pure sodium sulfate salt is obtained.

[0034] Example 2: A method for concentrating and separating organic matter in high-salinity wastewater and performing simultaneous freezing and crystallization to separate salt: wherein the initial contents of the components in the high-salinity wastewater are as shown in Table 1, and the method comprises the following steps:

[0035] S1: Add wastewater containing 1.5 g / L COD and 5% potassium sulfate into 30°C DMSO, mix and pretreat at a volume ratio of 1:300, and stir evenly;

[0036] S2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 10°C at a pumping rate of 5L / min, and the organic matter is concentrated and crystallized under a stirring condition of 50r / min, and the wastewater containing potassium sulfate is separated and collected;

[0037] S3: After the organic concentrated crystals collected in step S2 are melted at 60° C., DMSO is reversely extracted using DMF, and then the DMSO is purified and separated using a distillation process at 120° C. and a distillation pressure of -0.2 MPa. The purified solvent is refluxed to the wastewater pretreatment unit for reuse; and the remaining organic waste liquid is recovered;

[0038] S4: The potassium sulfate-containing wastewater collected in step S2 is pumped into an OSLO horizontal continuous cooling crystallizer at a pumping rate of 0.1 L / min, and the cooler is 150 cm long and 10 cm in diameter; the residual DMSO is removed by three-step gradient cooling, wherein the first step is a cooling rate of 20°C / min, cooling to 10°C; the second step is a cooling rate of 10°C / min, cooling to -5°C; the third step is a cooling rate of 2.0°C / min, cooling to -15°C; potassium sulfate concentrate and potassium sulfate crystal salt are prepared, and pure ice crystals (water) are produced;

[0039] S5: The concentrated solution collected in step S4 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization, and all potassium sulfate crystals are subjected to low-temperature centrifugation. The potassium sulfate crystals are washed with ethanol and then vacuum-dried at -20°C with a vacuum degree of 100 Pa. Pure potassium sulfate salt is obtained after drying for 2 hours.

[0040] Example 3: A method for concentrating and separating organic matter in high-salinity wastewater and performing simultaneous freezing and crystallization for salt separation: wherein the initial contents of the components in the high-salinity wastewater are as shown in Table 1, and the method comprises the following steps:

[0041] S1: Add wastewater containing 4.0 g / L COD, 5% sodium sulfate, and 2.5% potassium sulfate into 40°C DMSO, mix and pretreat at a volume ratio of 1:100, and stir evenly;

[0042] S2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 10°C at a pumping rate of 0.5L / min, and the organic matter is concentrated and crystallized under a stirring condition of 30r / min, and the wastewater containing sodium sulfate and potassium sulfate is separated and collected;

[0043] S3: After the organic concentrated crystals collected in step S2 are melted at 40° C., DMSO is reversely extracted using DMF, and then the DMSO is purified and separated by distillation technology at 80° C. and a distillation pressure of -0.1 MPa, and the purified solvent is refluxed to the wastewater pretreatment unit for reuse; finally, the remaining organic waste liquid is recovered;

[0044] S4: The wastewater containing potassium sulfate and sodium sulfate collected in step S2 is pumped into an OSLO horizontal continuous cooling crystallizer at a pumping rate of 0.5 L / min, and the cooler is 80 cm long and 20 cm in diameter; the residual DMSO is removed by three-step gradient cooling, the first step is a cooling rate of 10°C / min, cooling to 15°C; the second step is a cooling rate of 15°C / min, cooling to 0°C; the third step is a cooling rate of 5.0°C / min, cooling to -5°C; potassium sulfate and sodium sulfate concentrates and potassium sulfate and sodium sulfate crystal salts are prepared, and pure ice crystals (water) are produced;

[0045] S5: The concentrated solution collected in step S4 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization, and all potassium sulfate and sodium sulfate crystal salts are subjected to low-temperature centrifugation. The crystal salts are washed with ethanol and then vacuum-dried at -20°C with a vacuum degree of 60 Pa. After drying for 2 hours, pure potassium sulfate and sodium sulfate salts are obtained.

[0046] Comparative Example 1: No extraction stabilizer DMSO was added, and no back extraction was performed subsequently. The rest was the same as in Example 3, as follows:

[0047] S1: Pre-treat wastewater containing 4.0 g / L COD, 5% sodium sulfate, and 2.5% potassium sulfate;

[0048] S2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 10°C at a pumping rate of 0.5L / min, and the organic matter is concentrated and crystallized under a stirring condition of 30r / min, and the wastewater containing potassium sulfate and sodium sulfate is separated and collected;

[0049] S3: The wastewater containing potassium sulfate and sodium sulfate collected in step S2 is pumped into an OSLO horizontal continuous cooling crystallizer at a pumping rate of 0.5 L / min, and the cooler is 80 cm long and 20 cm in diameter; the residual DMSO is removed by three-step gradient cooling, wherein the first step is cooled at a rate of 10°C / min to 15°C; the second step is cooled at a rate of 15°C / min to 0°C; the third step is cooled at a rate of 5.0°C / min to -5°C; potassium sulfate and sodium sulfate concentrates and potassium sulfate and sodium sulfate crystal salts are prepared, and pure ice crystals (water) are produced;

[0050] S4: The concentrated solution collected in step S3 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization, and all potassium sulfate and sodium sulfate crystal salts are subjected to low-temperature centrifugation. The crystal salts are washed with ethanol and then vacuum-dried at -20°C with a vacuum degree of 60 Pa. After drying for 2 hours, pure potassium sulfate and sodium sulfate salts are obtained.

[0051] Comparative Example 2: A triple-effect evaporator was used for evaporation and concentration, followed by brine separation, instead of cryogenic freezing and crystallization. The rest was the same as in Example 3, as follows:

[0052] S1: Add wastewater containing 4.0 g / L COD, 5% sodium sulfate, and 2.5% potassium sulfate into 40°C DMSO, mix and pretreat at a volume ratio of 1:100, and stir evenly;

[0053] S2: The pretreated organic wastewater is pumped into a low-temperature crystallization tank at 10°C at a pumping rate of 0.5L / min, and the organic matter is concentrated and crystallized under a stirring condition of 30r / min, and the wastewater containing sodium sulfate and potassium sulfate is separated and collected;

[0054] S3: After the organic concentrated crystals collected in step S2 are melted at 40° C., DMSO is reversely extracted using DMF, and then the DMSO is purified and separated by distillation technology at 80° C. and a distillation pressure of -0.1 MPa, and the purified solvent is refluxed to the wastewater pretreatment unit for reuse; finally, the remaining organic waste liquid is recovered;

[0055] S4: The wastewater containing potassium sulfate and sodium sulfate collected in step S2 is evaporated by a triple-effect evaporator at a temperature of 120° C. to obtain a first steam and a wastewater concentrate, and the evaporation time is 5 hours; then the wastewater concentrate is evaporated at 160° C. to obtain a second steam and a residual liquid I, and the total evaporation time is 5 hours; the residual liquid I is evaporated at 260° C. to obtain a third steam and a residual liquid II, and the total evaporation time is 3 hours; the total pressure in the evaporation step of the triple-effect evaporator is 9 MPa, and potassium sulfate and sodium sulfate concentrates are obtained, and then brine separation is performed to obtain potassium sulfate and sodium sulfate crystal salts, and the crystal salts are washed with ethanol and then dried at -20° C. vacuum low temperature, with a vacuum degree of 60 Pa, and potassium sulfate and sodium sulfate pure salts are obtained after drying for 2 hours.

[0056] Example Brine Type Salt content (%) COD (g / L) Example 1 Sodium sulfate wastewater 1.5% 0.5 Example 2 Potassium sulfate wastewater 5% 1.5 Example 3 Sodium sulfate-potassium sulfate wastewater Sodium sulfate 5%, potassium sulfate 2.5% 4 Comparative Example 1 Sodium sulfate-potassium sulfate wastewater Sodium sulfate 5%, potassium sulfate 2.5% 4 Comparative Example 2 Sodium sulfate-potassium sulfate wastewater Sodium sulfate 5%, potassium sulfate 2.5% 4

[0057] Table 1

[0058] Detection: The purity of the pure salt obtained in the embodiment and the comparative example and the concentration ratio of COD were calculated to obtain the following data:

[0059] Example Crystalline salt purity (%) COD concentration ratio (%) Example 1 >80% >80 Example 2 >85% >85 Example 3 Sodium sulfate>90%, potassium sulfate>80% >83 Comparative Example 1 Sodium sulfate>76%, potassium sulfate>70% >72 Comparative Example 2 Sodium sulfate>78%, potassium sulfate>73% >76

[0060] Table 2

[0061] Conclusion: The methods of Examples 1-3 can achieve efficient concentration of more than 80% of organic matter, and the purity of waste salt can reach more than 80%; Comparative Example 1 does not add the extraction stabilizer DMSO compared with Example 3, and the performance is reduced; Comparative Example 2 uses a multi-effect evaporator for evaporation concentration treatment, and then separates the brine instead of low-temperature freezing crystallization. Compared with Example 3, the operation is complicated, and the concentration ratio of organic matter and the purity of crystallized salt are reduced. Therefore, the method of the present invention not only meets the requirements of concentrated collection of organic matter in wastewater, but also can simultaneously realize the separation and purification of salt in wastewater. At the same time, the method has high wastewater treatment efficiency, low energy consumption, and high cold utilization rate.

[0062] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0063] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for concentrating and separating organic matter in high-salinity wastewater and performing simultaneous freezing and crystallization to separate salt, characterized in that: The following steps are involved: S1: adding organic high-salt wastewater to the hot-melted extraction stabilizer for mixed pretreatment to obtain organic high-salt wastewater pretreatment material; S2: pumping the organic high-salt wastewater pretreatment material obtained in S1 into a low-temperature crystallization tank for stirring to obtain organic concentrated crystals and high-salt water; S3: hot-melting the organic concentrated crystals obtained in S2, purifying the solvent by combining reverse extraction and distillation processes, and returning the purified solvent to the wastewater pretreatment unit for reuse; and recycling of organic waste liquid; S4: pumping the high-salt water obtained in S2 into a low-temperature freezing crystallizer for primary low-temperature freezing crystallization to obtain a salt concentrate and a primary crystallized salt, and produce pure ice crystals; the primary low-temperature freezing crystallization adopts a three-step gradient cooling process, and its specific process is: the first step is cooling to 10~20℃, the speed is 5~10℃ / min; the second step is cooling to -5~10℃, the speed is 10~20℃ / min; the third step is cooling to -15~-5℃, the speed is 2.0-5.0℃ / min; S5: The salt concentrate obtained in S4 is pumped into a low-temperature freezing crystallizer for secondary low-temperature freezing crystallization to obtain secondary crystallized salt; the primary crystallized salt and the secondary crystallized salt are post-processed to obtain pure salt.

2. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The organic high-salt wastewater in step S1 contains one or both of sodium sulfate and potassium sulfate, with a salt content of 1.5% to 10.0%, and an initial COD concentration of 0.5 g / L to 4 g / L.

3. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The extraction stabilizer in step S1 is dimethyl sulfoxide, and the volume ratio of the extraction stabilizer to the wastewater is 1-5:200-300; the temperature of the hot melting in step S1 is 30-60°C.

4. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The temperature of the low-temperature crystallization tank in step S2 is 10-25° C.; the speed of the pump in step S2 is 0.1 L / min-5 L / min; and the stirring speed in step S2 is 30-50 r / min.

5. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The hot melting temperature in step S3 is 30-60°C; the reagent used for reverse extraction is N,N-dimethylformamide; the parameters of the distillation process in step S3 are: temperature 80-120°C, pressure -0.2-0.1MPa.

6. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The low-temperature freezing crystallizer in step S4 is an OSLO horizontal continuous cooling crystallizer, and its parameters are: the length of the external cooler is 80.00cm~150.00cm, and the diameter is 10.00cm~35.00cm; the speed of the pump in step S4 is 0.1L / min~5L / min, and the material is driven by an axial flow circulation pump.

7. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The secondary low-temperature freezing crystallization in step S5 is the same as the primary low-temperature freezing crystallization process.

8. The method for concentration and separation of organic matter in high-salinity wastewater and simultaneous freezing and crystallization salt separation according to claim 1, characterized in that: The post-treatment process of step S5 is: centrifuging the primary crystallized salt and the secondary crystallized salt at low temperature, washing with alcohol and then vacuum low-temperature drying; the parameters of the low-temperature centrifugation are: temperature 0~5°C, centrifugal speed 500~3000r / min; the alcohol for the alcohol washing is methanol or ethanol; the parameters of the vacuum low-temperature drying are: temperature -20~10°C, vacuum degree 20~100Pa, and drying time 2~6h.

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