WO2021179638A1 - Purification method for electronic-grade ethylene carbonate, and purification apparatus - Google Patents

Abstract

Disclosed are a purification method for electronic-grade ethylene carbonate, and a purification apparatus thereof. The method comprises the following steps: S1: seeding ethylene carbonate having a purity of 99.90%-99.98%; S2: heating to 36-37℃ after the seeding ends, and then maintaining a constant temperature for 0.5-3 h; S3: carrying out cooling and crystallization after the temperature maintenance ends; S4: carrying out heating and sweating on crystals in a gradual heating manner, and carrying out a next round of crystallization on an obtained sweating liquid; S5: after the sweating ends, heating to melt the crystals subjected to sweating to obtain a first product having a purity of 99.995% or more; and S6: rectifying a non-crystallized mother liquor twice to obtain a second product having a purity of 99.990% or more.

Description

Purification method and purification device of electronic grade ethylene carbonate

METHOD AND DEVICE OF PURIFYING ELECTRONIC GRADE ETHYLENE CARBONATE

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on March 11, 2020, the application number is 202010164468.X, and the invention title is "Electronic Grade Ethylene Carbonate Purification Method and Purification Device", and its entire content Incorporated in this application by reference.

Technical field

This application relates to the technical field of preparation of electronic grade reagents, in particular to a purification method of electronic grade ethylene carbonate and a purification device thereof.

Background technique

Ethylene carbonate, also known as 1,3-dioxolane-2 ketone, ethylene carbonate, and ethylene glycol carbonate, has a molecular formula of C ₃ H ₄ O ₃ and abbreviated as EC. Ethylene carbonate is an organic solvent and organic synthesis intermediate with excellent performance, which can be used in various fields such as spinning, medicine, and plastic processing. In the capacitor battery industry, the mixed solution of ethylene carbonate and propylene carbonate has a high dielectric constant and can be used as an electrolyte for lithium ion batteries.

In recent years, with the vigorous development of the new energy industry and the continuous advancement of electronic component technology, high-purity ethylene carbonate has become an important organic solvent in the electronics industry, especially in the production of lithium battery electrolyte. Since the electrolyte is the key material of lithium batteries, the performance of the electrolyte depends on the quality of various solvents in the formulation. The purity of high-purity ethylene carbonate, total alcohol content, water content, metal ion content and other single impurity components will be Directly affect the performance of the electrolyte product, and then affect the battery indicators. Therefore, the quality requirements for high-purity ethylene carbonate are getting higher and higher.

Chinese patent application CN107629030A provides a method for preparing electronic grade ethylene carbonate by falling film crystallization. The ethylene carbonate raw material is added from the top of the crystallizer and circulates between the crystallizer and the ethylene carbonate raw material storage tank at a certain flow rate. The crystallization is carried out in a gradual cooling mode, and the uncrystallized ethylene carbonate residual liquid is discharged and transported to the recovery device. The crystal layer is melted by a step-by-step heating and sweating method, and the sweating liquid is cut in a certain proportion, and the sweating liquid and the residual liquid are recovered and sent back to the crystallizer. The molten material liquid is returned to the raw material storage tank, and the second falling film crystallization is repeated to obtain electronic grade ethylene carbonate. This method can prepare ethylene carbonate with a purity higher than 99.99%, but requires secondary falling film crystallization, high energy consumption, high perspiration cutting ratio, and low yield after primary crystallization.

Chinese patent application CN107501230A provides a device and method for preparing electronic grade ethylene carbonate by coupling crystallization and distillation. The medium is cooled and crystallized to a certain thickness of the crystal layer, feeding is stopped, and the temperature is raised to sweat. The sweated liquid after crystallization is collected and transported to the rectification tower. The top product enters the second product tank, and the bottom product is recycled back to the crystallization raw material tank. After sweating is over The crystals are melted and transported to the first product tank as a liquid. This application realizes the recycling of the raw material liquid, and finally obtains the electronic grade ethylene carbonate product with a content of more than 99.99%. The method enters the crystallizer to separate and purify impurities with a low removal rate. In order to obtain high-purity products, the amount of residual liquid and sweating liquid is large, resulting in a low yield of one crystallization, and the obtained sweating liquid and residual liquid need to be repeatedly crystallized , High energy consumption. At the same time, due to the low impurity removal rate during the reaction process, it is easy to change color under oxygen and high temperature conditions. When entering the electrolyte product, the capacity of the battery will decrease and the cycle life will be reduced.

Summary of the invention

In view of the shortcomings of the prior art, this application provides a purification method and a purification device for electronic grade ethylene carbonate. The specific solutions are as follows:

A purification method of electronic grade ethylene carbonate includes the following steps:

S1: Seed ethylene carbonate with a purity of 99.90%～99.98% at 20～28℃, and finish seeding when the material temperature drops to 31～32℃;

S2: After seeding, the temperature is raised to 36～37℃ and then the temperature is kept constant. The time from the temperature rise to the end of the constant temperature is 25～30min;

S3: Cool down and crystallize after the end of the constant temperature, and keep the temperature constant for 0.5 to 3 hours after the completion of the cooling and crystallization, to obtain the crystalline and non-crystallized mother liquor, and separate the obtained crystalline and non-crystallized mother liquor;

S4: The crystallization of step S3 is gradually raised to heat and sweat, and the obtained sweat is subjected to the next round of crystallization;

S5: After the sweating is over, the temperature is raised to melt the crystals after sweating to obtain the first product with a purity greater than 99.995%;

S6: The uncrystallized mother liquor in step S3 is subjected to two rectifications to obtain a second product with a purity greater than 99.990%.

In some embodiments of the present application, the cooling rate of cooling crystallization in step S3 is 0.25-1.0° C./h, the end temperature is 32-34° C., and the crystallization time is 5-20 h.

In some embodiments of the present application, the heating rate of heating and sweating in step S4 is 3 to 5°C/h, and the end temperature is 34 to 36.5°C.

In some embodiments of the present application, the crystal melting temperature in step S5 is 40-50°C.

In some embodiments of the present application, the material feed rate during seeding in step S1 is 1.0 t/h to 5.0 t/h.

In some embodiments of the present application, the vacuum degree during the two rectifications in the step S6 is -99.9 to -99.0 KPa, and the temperature is 140 to 150° C., respectively.

This application also provides the purification device used in the above-mentioned purification method, including a falling film crystallizer, a sweating liquid tank, a mother liquor tank, a first product tank, a second product tank, a third rectification tower, and a second rectification tower;

The falling film crystallizer is respectively connected to the inlets of the sweating liquid tank, the mother liquid tank and the first product tank through the first discharge pipeline;

The sweat tank is connected to the feed port of the falling film crystallizer through a circulating pipeline;

The mother liquor tank is connected to the third rectification tower through a second discharge line;

The mother liquor tank, the third rectification tower, the second rectification tower and the second product tank are connected in sequence;

When working, the raw material ethylene carbonate is first seeded and crystallized in a falling film crystallizer to obtain crystalline and uncrystallized ethylene carbonate. The uncrystallized ethylene carbonate enters the mother liquor tank through the first discharge line, and the uncrystallized in the mother liquor tank Ethylene carbonate enters the third rectification tank and the second rectification tank through the second discharge line in turn for rectification into the second product tank; the crystallization is heated and sweated in the falling film crystallizer, and the sweat obtained passes through the first outlet The feed pipeline enters the sweat tank, and the sweat in the sweat tank enters the falling film crystallizer through the circulation pipeline; the remaining crystal after sweating melts and enters the first product tank.

In some embodiments of the present application, a crystallization tube, a material circulation pump and a cooling system are installed inside the falling film crystallizer.

In some embodiments of the application, it further includes a first rectification tower, and the first rectification tower is connected to the falling film crystallizer.

Compared with the prior art, this application has achieved the following technical effects:

The method for purifying electronic grade ethylene carbonate provided in this application is to seed crystals before cooling down and crystallize to provide seed crystals for crystallization, so that crystallization is easy to proceed, and the crystals are coated with fewer impurities, thereby improving the performance of electronic grade ethylene carbonate. Purity and yield. After seeding, cooling and crystallization are performed, and the difference in melting point is used to remove substances with boiling points similar to ethylene carbonate, azeotropes and heat-sensitive substances, which can effectively remove trace impurities, so that the impurity removal rate is high, and the single impurity content ≤5ppm, to obtain high-purity ethylene carbonate, thereby effectively improving the performance of the electrolyte. According to the comparison between Example 2 and Comparative Example 2, the primary crystallization yield of the purification method provided by the present application is 5% higher than that of Comparative Example 2, and the sweat output is small, so that the number of cycles of sweating is less and energy consumption is reduced. At the same time, the electronic grade ethylene carbonate prepared by the present application has less impurity content and small discoloration of the electronic grade ethylene carbonate, so that the battery life can be improved. After cooling and crystallization, the uncrystallized mother liquor is enriched with a variety of impurities such as organic alcohols, aldehydes, ketones, which are close to the boiling point and properties of ethylene carbonate. In this application, the uncrystallized mother liquor after cooling and crystallization is subjected to two rectifications, and impurities are further removed through rectification, and a second product with a purity greater than 99.99% is obtained from the second rectification tower. At the same time, the perspiration liquid is returned to the falling film crystallizer to recycle the raw material liquid and increase the total yield.

Description of the drawings

FIG. 1 is a schematic flow chart of a method for purifying electronic grade ethylene carbonate according to an embodiment of this application;

2 is a schematic diagram of the structure of a purification device according to an embodiment of this application;

FIG. 3 is a schematic structural diagram of a purification device according to another embodiment of this application;

1. The first distillation tower; 2. The second distillation tower; 3. The falling film crystallizer; 31. The first discharge pipeline; 311, the first route; 312, the second route; 313, the third route; 4. Sweat tank; 41. Circulation pipeline; 5. Mother liquor tank; 51. Second discharge pipeline; 6. Third rectification tower; 7. First product tank; 8. Second product tank; 9. Buffer tank .

Detailed ways

The technical solution of the present application will be described in detail below in combination with specific embodiments. However, it should be understood that without further description, elements, structures and features in one embodiment can also be beneficially combined into other embodiments.

It should be understood that although the drawings may show a specific order of method steps, the order of steps may be different from the order depicted. In addition, two or more steps may be performed simultaneously or partially simultaneously. Such variants will depend on the software and hardware chosen and the designer's choice. All such variations are within the scope of this disclosure.

In the description of this application, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. . Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of these features.

In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral Ground connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood under specific circumstances.

The described implementations are merely descriptions of the preferred implementations of the application, and are not intended to limit the scope of the application. Without departing from the design spirit of the application, various modifications made by those of ordinary skill in the art to the technical solutions of the application All improvements and improvements shall fall within the scope of protection determined by the claims of this application.

As shown in Fig. 1, a purification method of electronic grade ethylene carbonate according to an embodiment of this application includes the following steps:

S1: seeding ethylene carbonate with a purity of 99.90% to 99.98% under environmental conditions of 20 to 28°C, and ending the seeding when the temperature of the material drops to 31 to 32°C;

S2: After seeding, the temperature is raised to 36～37℃ and then the temperature is kept constant. The time from the temperature rise to the end of the constant temperature is 25～30min;

S3: Cool down and crystallize after the end of the constant temperature, and keep the temperature constant for 0.5 to 3 hours after the completion of the cooling and crystallization, to obtain the crystalline and non-crystallized mother liquor, and separate the obtained crystalline and non-crystallized mother liquor;

S4: The crystallization of step S3 is gradually raised to heat and sweat, and the obtained sweat is subjected to the next round of crystallization;

S5: After the sweating is over, the temperature is raised to melt the crystals after sweating to obtain the first product with a purity greater than 99.995%;

S6: The uncrystallized mother liquor in step S3 is subjected to two rectifications to obtain a second product with a purity greater than 99.990%.

In this application, ethylene carbonate with a purity of 99.90% to 99.98% is seeded at 20-28°C, and the seeding is terminated when the temperature of the material drops to 31-32°C. When the temperature of the material drops to 31～32℃ and crystallizes out, the heat of solidification will be released and the temperature will rebound. This rebound temperature is the final cooling temperature, and the seeding ends. In this embodiment, the source of the ethylene carbonate having a purity of 99.90% to 99.98% is not particularly limited. For example, the ethylene carbonate with a purity of 99.90% to 99.98% is prepared by the addition reaction of ethylene oxide and carbon dioxide as raw materials to obtain crude ethylene carbonate, and the crude product is flashed out of unreacted carbon dioxide through a flash tank. Then it enters the thin film evaporator, the gas phase is condensed and then enters the first rectification tower for rectification. In this embodiment, the feed rate during seeding is preferably 1.0 t/h to 5.0 t/h, more preferably 2.0 t/h. In this embodiment, the seeding temperature is preferably 25°C. In this embodiment, the quenching method is used for seeding under the condition of 20-28° C. to form seed crystals in the crystallizer, which is beneficial for the crystallization process to proceed on the seed crystals.

After seeding is completed, the temperature is raised to 36-37°C and then the temperature is kept constant. The time from the temperature rise to the end of the constant temperature is 25-30 minutes. In this embodiment, seeding can crystallize the crude ethylene carbonate as the raw material. After the crystals are obtained, the temperature is raised to 36-37° C. to melt the excess crystals, and a small amount of crystals are retained as seed crystals. Since the melting temperature of impurities is lower than the melting temperature of ethylene carbonate, the impurities melt faster in the process of melting the excess crystals, reducing the coating of impurities in the seed crystals, thereby improving the purity of the seed crystals and improving the purity of the seed crystals. Thereby the crystal purity is improved, and finally the purity of the first product is improved.

After the end of the constant temperature, cooling crystallization is performed, and after the cooling and crystallization is completed, the temperature is kept constant for 0.5 to 3 hours, and the obtained crystalline and uncrystallized mother liquor are separated. In this embodiment, the cooling rate of the cooling crystallization is preferably 0.25-1.0°C/h, more preferably 0.5°C/h; the end temperature is preferably 32-34°C, more preferably 32°C; the crystallization time is preferably 5 ~20h, more preferably 10h; the constant temperature time is preferably 1h.

After the crystals are obtained, the crystals are heated and sweated by gradually increasing the temperature, and the obtained sweating liquid is subjected to the next round of crystallization, that is, the cooling crystallization in step S3 is performed. In this embodiment, the temperature increase rate of the temperature increase perspiration is preferably 3 to 5°C/h, more preferably 4°C/h; the end temperature is preferably 34 to 36.5°C, more preferably 35°C. In this embodiment, the purity of the sweat liquid obtained is 99.9910% to 99.9920%. In this embodiment, the next round of crystallization of the sweating fluid can make the material recycled and improve the utilization rate of the raw material.

After the sweating is over, the temperature is raised to melt the remaining crystals after sweating, and the first product with a purity greater than 99.995% is obtained. In the present invention, the melting temperature of the crystal is preferably 40-50°C, more preferably 45°C.

After cooling and crystallization to obtain crystalline and uncrystallized mother liquor, the uncrystallized mother liquor is subjected to two rectifications to obtain a second product with a purity greater than 99.99%. In this embodiment, the purity of the mother liquor obtained after cooling and crystallization is 99.97 to 99.98%. In the present invention, the degree of vacuum during the two rectifications is preferably -99.9 to -99.0 KPa, more preferably -99.9 Kpa, and the temperature is preferably 140 to 150°C, more preferably 145°C.

In this embodiment, the judgment standard of the electronic grade ethylene carbonate adopts HG/T5391-2018 for evaluation.

As shown in Figure 2, another embodiment of the present application provides a purification device used in the above-mentioned purification method, including a falling film crystallizer 3, a sweating liquid tank 4, a mother liquor tank 5, a first product tank 7, and a second product. Tank 8, the third rectification tower 6 and the second rectification tower 2;

The falling film crystallizer 3 is respectively connected to the inlets of the sweating liquid tank 4, the mother liquor tank 5 and the first product tank 7 through the first discharge line 31;

The sweat tank 4 is connected to the feed port of the falling film crystallizer 3 through a circulating pipeline 41;

The mother liquor tank 5 is connected to the third rectification tower 6 through the second discharge line 51;

The mother liquor tank 5, the third rectification tower 6, the second rectification tower 2 and the second product tank 8 are connected in sequence;

When working, the raw material ethylene carbonate is first seeded and crystallized in the falling film crystallizer 3 to obtain crystallized and uncrystallized ethylene carbonate. The uncrystallized ethylene carbonate enters the mother liquor tank 5 through the first discharge line 31. The mother liquor tank The uncrystallized ethylene carbonate in 5 then enters the third rectification tower 6 and the second rectification tower 2 through the second discharge line 51 in turn for rectification and enters the second product tank 8; the crystallization is carried out in the falling film crystallizer 3. Heat up and sweat, and the obtained sweat liquid enters the sweat liquid tank 4 through the first discharge line 31, and the sweat liquid in the sweat liquid tank 4 enters the falling film crystallizer 3 through the circulation line 41; the remaining crystal after sweating melts and enters the second A product tank 7.

In this embodiment, the inside of the falling film crystallizer 3 is preferably installed with a crystallization tube, a plate heat exchanger, a material circulation pump and a cooling system. In this embodiment, the discharge pipeline of the falling film crystallizer 3 is preferably divided into three paths, the first path 311 is connected to the first product tank 7, the second path 312 is connected to the mother liquor tank 5, and the third path 313 is connected to The sweat tank 4 is connected.

In this embodiment, the purification device preferably further includes a first rectification tower 1, and the first rectification tower 1 is connected to the falling film crystallizer 3, so that the ethylene carbonate obtained by the rectification of the first rectification tower 1 The crude product is fed from the side line of the first rectification tower 1 and fed from the top of the falling film crystallizer 3 for cooling and crystallization. In this embodiment, it is preferable to use inert gas protection when adding raw materials to the falling film crystallizer 3.

As shown in FIG. 3, in this embodiment, the purification device preferably further includes a buffer tank 9. The buffer tank 9 is respectively connected to the falling film crystallizer 3 and the first product tank 7. The product obtained after the crystallization of the sweating is melted is output from the falling film crystallizer 3 and preferably enters the buffer tank 9 for buffering, and then enters The first product tank 7. In this embodiment, the first purpose of setting up the buffer tank is to ensure that the crystalline product is qualified before entering the product tank, avoiding the product index fluctuations caused by unstable operation and polluting the product tank, and at the same time, the product after crystallization is injected into the buffer at one time The tank, after passing the test, is transferred to the product tank through the pump, which saves the total operating time of the crystallization process.

In this embodiment, the falling film crystallizer 3, the sweating liquid tank 4, the mother liquor tank 5, the first product tank 7, the second product tank 8, the third rectification tower 6, the second rectification tower 2 and the second rectification tower The inlet and outlet pipelines of a rectification tower 1 are all provided with valves for controlling the inlet and outlet of materials.

In order to further explain the present application, the technical solutions provided by the present application will be described in detail below in conjunction with embodiments, but they should not be understood as limiting the protection scope of the present application.

Example 1

In this embodiment, the ethylene carbonate with a purity of 99.90% to 99.98% is prepared by the addition reaction of ethylene oxide and carbon dioxide as raw materials to obtain a crude ethylene carbonate product, and the crude product is flashed out by a flash tank The unreacted carbon dioxide enters the thin film evaporator, the gas phase is condensed, and then enters the first distillation tower for rectification.

(1) Seeding and cooling crystallization: Under the protection of inert gas, take the crude ethylene carbonate produced from the side line of the first rectification tower (the crude ethylene carbonate with a mass fraction of 99.98%) and add it from the top of the falling film crystallizer. The feed rate is 1.5t/h. After the feed is completed, the material circulation pump is turned on, the cooling system is turned on, and the cooling source at 20°C is used to stimulate the material to crystallize. When the temperature of the material drops to 31～32°C, it rebounds. The rebound temperature is After cooling to the final temperature, seeding is over. After seeding, the temperature control plate heat exchanger is switched, and the circulating water is quickly heated to 36°C by steaming, and the temperature is kept constant after the temperature is raised to 36°C. The crystal is partially melted, leaving a small amount of crystal on the surface of the heat exchange tube as a seed crystal). After the end of the constant temperature, the material is crystallized in a crystallization tube with a gradual cooling method, and a crystal layer is formed on the wall of the crystallizer. The cooling rate is 0.25°C/h, the end temperature of the cooling crystallization is 32°C, and the crystallization time is 16h. It takes 1h to obtain crystallized and uncrystallized ethylene carbonate mother liquor (the purity of the uncrystallized ethylene carbonate mother liquor is 99.97%); the uncrystallized ethylene carbonate mother liquor is discharged from the crystallizer outlet and transported to the mother liquor tank as The raw materials enter the third distillation tower.

(2) Warming up sweating: Melting the crystals of step (1) in a stepwise warming up sweating manner, the heating rate is 3°C/h, the end point temperature of sweating is 36°C, and the sweating liquid (purity of sweating liquid is 99.9910%) is discharged to Sweat in a tank.

(3) Crystal melting: After sweating, continue to increase the temperature to melt all the crystals remaining after sweating into liquid (the temperature during crystal melting is 40°C), and the product is discharged from the bottom of the falling film crystallizer into the buffer tank , And then transported to the first product tank.

(4) Distillation: using continuous distillation operation under reduced pressure, the material in the mother liquor tank is transported to the third rectification tower, the pressure inside the tower is -99.9Kpa, the temperature at the bottom of the tower is 145°C, and the light components are removed from the top of the tower. Impurities, heavy component impurities are removed from the bottom of the tower, and ethylene carbonate with a mass fraction of 99.97% is extracted from the side line and transported to the second rectification tower for rectification (the internal pressure is -99.9Kpa, and the bottom temperature is 145°C), the side line The second product is obtained and sent to the second product tank.

Gas chromatography was used to determine the purity, impurity type and content, and yield of the products in the first product tank and the second product tank. The specific detection conditions are shown in Table 1, and the specific results are shown in Table 2.

Table 1 Gas Chromatography Test Conditions

Column model	DB-1701, 30m*0.53mm*0.5um
Inlet	260°C
Detector	300°C
Oven temperature program	90℃(0mim)→10℃/min→190℃(0min)→20℃/min→220℃(6min)
Column flow	1ml/min
Split ratio	50:1

Table 2 Product quality evaluation results of the first and second product cans in Example 1

To	purity(%)	Ethylene glycol (ppm)	Diethylene glycol (ppm)	Yield (%)
First product	99.99693	3.1	0	70

Second product

99.99110

5.0

15.0

75

Further, after the sweat liquid is returned to the falling film crystallizer again for cyclic cooling and crystallization, the total yield of the entire purification method is determined to be 99%.

Example 2

In this embodiment, the ethylene carbonate with a purity of 99.90% to 99.98% is prepared by the addition reaction of ethylene oxide and carbon dioxide as raw materials to obtain a crude ethylene carbonate product, and the crude product is flashed out by a flash tank The unreacted carbon dioxide enters the thin film evaporator, the gas phase is condensed, and then enters the first distillation tower for rectification.

(1) Seeding and cooling crystallization: Under the protection of inert gas, take the crude ethylene carbonate produced from the side line of the first rectification tower (the crude ethylene carbonate with a mass fraction of 99.95%) and add it from the top of the falling film crystallizer. The material rate is 2.0t/h. After the feeding is completed, the material circulation pump is turned on, the cooling system is turned on, and the 25℃ cold source is used to stimulate the material to crystallize. When the material temperature reaches 31～32℃, the seeding will stop when the temperature rebounds. After seeding is over, switch the temperature control plate heat exchanger, and steam the circulating water to quickly heat up to 36.5°C, and then keep the temperature at 36.5°C (the time from the temperature rise to the end of the constant temperature is 25min. The excess crystals are partially melted, leaving a small amount of crystals on the surface of the heat exchange tube as seed crystals). After the end of the constant temperature, the material is crystallized in a crystallization tube with a gradual cooling method, and a crystal layer is formed on the wall of the crystallizer. The cooling rate is 0.5°C/h, the end temperature of the cooling crystallization is 32°C, the crystallization time is 9h, and then the constant temperature is performed. It takes 2h to obtain crystallized and uncrystallized ethylene carbonate mother liquor (the purity of the uncrystallized ethylene carbonate mother liquor is 99.98%); the uncrystallized ethylene carbonate mother liquor is discharged from the crystallizer outlet and transported to the mother liquor tank as The raw materials enter the third distillation tower.

(2) Warming up sweating: Melting the crystals of step (1) in a stepwise warming up sweating manner, the heating rate is 4°C/h, the end point temperature of sweating is 36.5°C, and the sweating fluid (purity of sweating fluid is 99.9920%) is discharged to Sweat in a tank.

(3) Crystal melting: After sweating, continue to increase the temperature to melt all the crystals remaining after sweating into liquid (the temperature during crystal melting is 45°C), and the product is discharged from the bottom of the falling film crystallizer into the buffer tank , And then transported to the first product tank. The purity of ethylene carbonate in the first product tank is 99.9961%, ethylene glycol 3.0ppm, and diethylene glycol 2.5ppm.

(4) Distillation: using continuous distillation operation under reduced pressure, the material in the mother liquor tank is transported to the third rectification tower, the pressure inside the tower is -99.5Kpa, the temperature at the bottom of the tower is 147°C, and the light components are removed from the top of the tower. Impurities, heavy component impurities are removed from the bottom of the tower, and ethylene carbonate with a mass fraction of 99.96% is extracted from the side line and transported to the second rectification tower (internal pressure is -99.5Kpa, and the bottom temperature is 147°C). The second product is sent to the second product tank.

The purity, impurity type and content, and yield of the products in the first product tank and the second product tank were determined by gas chromatography.

Table 3 Evaluation results of product quality in the first and second product cans of Example 2

To	purity(%)	Ethylene glycol (ppm)	Diethylene glycol (ppm)	Yield (%)
First product	99.99610	3.0	2.5	68
Second product	99.99100	6.0	13.0	73

Further, after the sweating liquid was returned to the falling film crystallizer again for cyclic cooling and crystallization, the total yield of the entire purification method was determined to be 98%.

Example 3

In this embodiment, the ethylene carbonate with a purity of 99.90% to 99.98% is prepared by the addition reaction of ethylene oxide and carbon dioxide as raw materials to obtain a crude ethylene carbonate product, and the crude product is flashed out by a flash tank The unreacted carbon dioxide enters the thin film evaporator, the gas phase is condensed, and then enters the first distillation tower for rectification.

(1) Seeding and cooling crystallization: Under the protection of inert gas, take part of the crude ethylene carbonate produced from the side line of the first rectification tower (the crude ethylene carbonate with a mass fraction of 99.90%) and add it from the top of the falling film crystallizer. The feed rate is 5.0t/h. After the feed is completed, turn on the material circulation pump and turn on the cooling system. Use a 28°C cold source to stimulate the material to crystallize for 60 minutes. When the material temperature reaches 31-32°C, stop when the temperature rebounds. After crystal seeding is finished, switch the temperature control plate heat exchanger, and steam the circulating water to quickly heat up the circulating water to 36°C. After the temperature is raised to 36°C, it will be kept at a constant temperature. Part of the excess crystals melted, leaving a small amount of crystals on the surface of the heat exchange tube as seed crystals). After the end of the constant temperature, the material is crystallized in a crystallization tube with a gradual cooling method, and a crystal layer is formed on the wall of the crystallizer. The cooling rate is 0.75°C/h, the end temperature of the cooling crystallization is 32°C, the crystallization time is 5.3h, and then the constant temperature is performed. The constant temperature time is 3h to obtain crystallized and uncrystallized ethylene carbonate mother liquor (the purity of the uncrystallized ethylene carbonate mother liquor is 99.97%); the uncrystallized ethylene carbonate mother liquor is discharged from the crystallizer outlet and transported to the mother liquor tank, It enters the third distillation tower as a raw material.

(2) Sweating at elevated temperature: Melt the crystals of step (1) by gradually heating up perspiration at a heating rate of 5°C/h and a sweating end temperature of 36.5°C. The sweating fluid (purity of sweating fluid is 99.9910%) is discharged to Sweat in a tank.

(3) Crystal melting: After sweating, continue to increase the temperature to melt all the crystals remaining after sweating into liquid (the temperature during crystal melting is 50°C), and the product is discharged from the bottom of the falling film crystallizer into the buffer tank , And then transported to the first product tank.

(4) Distillation: using continuous distillation operation under reduced pressure, the material in the mother liquor tank is transported to the third rectification tower, the pressure inside the tower is -99.5Kpa, the temperature at the bottom of the tower is 148°C, and the light components are removed from the top of the tower. Impurities, heavy component impurities are removed from the bottom of the tower, and ethylene carbonate with a mass fraction of 99.98% is extracted from the side line and transported to the second rectification tower for rectification (internal pressure is -99.5Kpa, and the bottom temperature is 148°C), side line The second product is obtained and sent to the second product tank.

The purity, impurity type and content, and yield of the products in the first product tank and the second product tank were determined by gas chromatography. The specific detection conditions were the same as those shown in Table 1 of Example 1, and the specific results were shown in Table 4.

Table 4 Evaluation results of product quality in the first and second product cans of Example 3

To	purity(%)	Ethylene glycol (ppm)	Diethylene glycol (ppm)	Yield (%)
First product	99.99550	5.0	4.0	72
Second product	99.99200	6.0	13.0	73

Further, after the sweat liquid is returned to the falling film crystallizer again for cyclic cooling and crystallization, the total yield of the entire purification method is determined to be 97%.

Example 4

In this embodiment, the ethylene carbonate with a purity of 99.90% to 99.98% is prepared by the addition reaction of ethylene oxide and carbon dioxide as raw materials to obtain a crude ethylene carbonate product, and the crude product is flashed out by a flash tank The unreacted carbon dioxide enters the thin film evaporator, the gas phase is condensed, and then enters the first distillation tower for rectification.

(1) Seeding and cooling crystallization: Under the protection of inert gas, take the crude ethylene carbonate produced from the side line of the first rectification tower (the crude ethylene carbonate with a mass fraction of 99.98%) and add it from the top of the falling film crystallizer. The material rate is 1.0t/h. After the material is fed, the material circulation pump is turned on, the cooling system is turned on, and the 20℃ cold source is used to stimulate the material to crystallize. When the material temperature drops to 31～32℃, it rebounds. The rebound temperature is After cooling to the final temperature, seeding is over. After seeding is finished, switch the temperature control plate heat exchanger, and steam the circulating water to quickly heat up the circulating water to 37°C. After the temperature is raised to 37°C, the temperature will be kept constant (the time from the temperature rise to the end of the constant temperature is 30 minutes, and the explosion will cause excess The crystal is partially melted, leaving a small amount of crystal on the surface of the heat exchange tube as a seed crystal). After the end of the constant temperature, the material is crystallized in a crystallization tube with a step-by-step cooling method, and a crystal layer is formed on the wall of the crystallizer. The cooling rate is 0.25°C/h, the end temperature of the cooling crystallization is 33°C, the crystallization time is 16h, and then the constant temperature is performed. Time 0.5h to obtain crystallized and uncrystallized ethylene carbonate mother liquor (the purity of the uncrystallized ethylene carbonate mother liquor is 99.975%); discharge the uncrystallized ethylene carbonate mother liquor from the crystallizer outlet and transport it to the mother liquor tank, It enters the third distillation tower as a raw material.

(2) Warming up sweating: Melting the crystals of step (1) in a stepwise warming up and sweating manner, the heating rate is 3°C/h, the end point temperature of sweating is 34°C, and the sweating fluid (purity of sweating fluid is 99.9912%) is discharged to Sweat in a tank.

(3) Crystal melting: After sweating, continue to increase the temperature to melt all the crystals remaining after sweating into liquid (the temperature during crystal melting is 40°C), and the product is discharged from the bottom of the falling film crystallizer into the buffer tank , And then transported to the first product tank.

(4) Distillation: using continuous distillation operation under reduced pressure, the material in the mother liquor tank is transported to the third rectification tower, the pressure inside the tower is -99.0Kpa, the temperature at the bottom of the tower is 140°C, and the light components are removed from the top of the tower. Impurities, heavy component impurities are removed from the bottom of the tower, and ethylene carbonate with a mass fraction of 99.98% is extracted from the side line and transported to the second rectification tower for rectification (internal pressure is -99.0Kpa, and the temperature at the bottom of the tower is 150°C). The second product is obtained and sent to the second product tank.

The purity, impurity type and content, and yield of the products in the first product tank and the second product tank were determined by gas chromatography. The specific detection conditions were the same as those shown in Table 1 of Example 1, and the specific results were shown in Table 5.

Table 5 Evaluation results of product quality in the first and second product cans of Example 4

To	purity(%)	Ethylene glycol (ppm)	Diethylene glycol (ppm)	Yield (%)
First product	99.99600	5.0	4.0	70
Second product	99.99250	8.0	13.0	73

Further, after the sweat liquid is returned to the falling film crystallizer again for cyclic cooling and crystallization, the total yield of the entire purification method is determined to be 97.5%.

Comparative example 1

Except for the operations of non-seeding and crystal seeding and melting, the other operation steps are exactly the same as those in the second embodiment.

The purity, impurity type and content, and yield of the products in the first product tank and the second product tank were determined by gas chromatography. The specific detection conditions were the same as those shown in Table 1 of Example 1, and the specific results were shown in Table 6.

Table 6 The quality assessment results of the first and second product cans of Comparative Example 1

To	purity(%)	Ethylene glycol (ppm)	Diethylene glycol (ppm)	Yield (%)
First product	99.99410	4.5	6.7	65
Second product	99.99100	6.0	13.0	73

Further, after the sweat liquid is returned to the falling film crystallizer again for cyclic cooling and crystallization, the total yield of the entire purification method is determined to be 96%;

From the comparison of Example 2 and Comparative Example 1, it can be seen that the purification method provided by the present invention can reduce the coating of impurities in the crystal, reduce the content of each impurity, and increase the purity of the seed crystal, thereby increasing the purity of the crystal. , Improve product purity and yield.

Comparative example 2

The raw materials to be purified are exactly the same as in Example 2, and they are all crude ethylene carbonate (crude ethylene carbonate with a mass fraction of 99.95%) produced from the side line of the first rectification tower. Purification is carried out using the operating method and conditions of Example 4 in patent CN107501230A. After rectification, the ethylene carbonate solution obtained at the bottom of the rectification tower is returned to the raw material tank and then the purification is stopped. Rate. At this time, the purity and yield of the products in the first product tank and the second product tank were determined by gas chromatography. The specific detection conditions were the same as those shown in Table 1 of Example 1, and the specific results were shown in Table 7.

Table 7 The quality evaluation results of the first and second product cans of Comparative Example 2

To	purity(%)	Ethylene glycol (ppm)	Diethylene glycol (ppm)	Yield (%)
First product	99.9921	8.2	9.5	63
Second product	99.9910	6.0	13.0	73

Among them, in Examples 1 to 4 and Comparative Examples 1 to 2:

The yield of the first product (%) = the mass of the first product after crystallization/the amount of feed;

Second product yield (%) = quality of rectified product/feed amount

Total yield = total product quality/total feed.

From the comparison of Example 2 and Comparative Example 2, it can be seen that the purification method provided by the present invention has a 5% higher yield than that of Comparative Example 2 during a single crystallization. Energy consumption, less impurity content, higher purity.

Example 5

The crystalline product in the first product tank in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 was mixed with the lithium battery electrolyte, and after mixing uniformly, it was transferred to a 60°C incubator for storage, and the color was measured for 24 hours. Spend. Among them, the chromaticity detection adopts the colorimeter detection method, Pt-Co color number. The specific results are shown in Table 8.

Table 8 Discoloration reaction results

To	Chroma
Example 1	＜5(Does not change color)
Example 2	＜5(Does not change color)
Example 3	＜5(Does not change color)
Example 4	＜5(Does not change color)
Comparative example 1	15-20 (light pink)
Comparative example 2	20 (light pink)

It can be seen from Table 8 that the electronic grade ethylene carbonate purified by the present invention has little discoloration. The results show that the purified ethylene carbonate of the present invention has high purity and low impurity content, thereby improving battery life.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also It should be regarded as the protection scope of the present invention.

Claims (10)

1. The purification method of electronic grade ethylene carbonate is characterized in that it comprises the following steps:

   S1: Seed ethylene carbonate with a purity of 99.90%～99.98% at 20～28℃, and finish seeding when the material temperature drops to 31～32℃;

   S2: After seeding, the temperature is raised to 36～37℃ and then the temperature is kept constant. The time from the temperature rise to the end of the constant temperature is 25～30min;

   S3: Cool down and crystallize after the end of the constant temperature, and keep the temperature constant for 0.5 to 3 hours after the completion of the cooling and crystallization, to obtain the crystalline and non-crystallized mother liquor, and separate the obtained crystalline and non-crystallized mother liquor;

   S4: The crystallization of step S3 is gradually raised to heat and sweat, and the obtained sweat is subjected to the next round of crystallization;

   S5: After the sweating is over, the temperature is raised to melt the crystals after sweating to obtain the first product with a purity greater than 99.995%;

   S6: The uncrystallized mother liquor in step S3 is subjected to two rectifications to obtain a second product with a purity greater than 99.990%.
2. The purification method according to claim 1, wherein the cooling rate of the cooling crystallization in step S3 is 0.25-1.0°C/h, the end temperature is 32-34°C, and the crystallization time is 5-20h.
3. The purification method according to claim 1, characterized in that the heating rate of heating and sweating in step S4 is 3 to 5°C/h, and the end temperature is 34 to 36.5°C.
4. The purification method according to claim 1, wherein the temperature of crystal melting in the step S5 is 40-50°C.
5. The purification method according to claim 1, wherein the feeding rate during seeding in the step S1 is 1.0 t/h to 5.0 t/h.
6. The purification method according to claim 1, wherein the vacuum degree during the two rectifications in the step S6 is -99.9~-99.0KPa, and the temperature is 140~150°C, respectively.
7. The purification device of the purification method according to any one of claims 1 to 6, characterized in that it comprises a falling film crystallizer, a sweating liquid tank, a mother liquor tank, a first product tank, a second product tank, a third rectification tower and The second distillation tower;

   The falling film crystallizer is respectively connected to the inlets of the sweating liquid tank, the mother liquid tank and the first product tank through the first discharge pipeline;

   The sweat tank is connected to the feed port of the falling film crystallizer through a circulating pipeline;

   The mother liquor tank is connected to the third rectification tower through a second discharge line;

   The mother liquor tank, the third rectification tower, the second rectification tower and the second product tank are connected in sequence;

   When working, the raw material ethylene carbonate is first seeded and crystallized in the falling film crystallizer to obtain crystallized and uncrystallized ethylene carbonate. The uncrystallized ethylene carbonate enters the mother liquor tank through the first discharge line, and the uncrystallized in the mother liquor tank Ethylene carbonate then enters the third rectification tower and the second rectification tower in turn through the second discharge line for rectification into the second product tank; the crystallization is heated and sweated in the falling film crystallizer, and the sweat obtained passes through the first The discharge pipeline enters the sweating liquid tank, and the sweating liquid in the sweating liquid tank enters the falling film crystallizer through the circulation pipeline; the remaining crystal after sweating melts and enters the first product tank.
8. The purification device according to claim 7, characterized in that, a crystallization tube, a material circulation pump and a cooling system are installed inside the falling film crystallizer.
9. 8. The purification device according to claim 7, further comprising a first rectification tower connected to the falling film crystallizer.
10. The purification device according to claim 7, wherein the discharge pipeline of the falling film crystallizer is preferably divided into three paths, the first path is connected to the first product tank, and the second path is connected to the mother liquor tank. Connected, and the third way is connected to the sweat tank.

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