Method and plant for purifying ethylene carbonate

Abstract

The present invention relates to a method for purifying ethylene carbonate from a crude ethylene carbonate composition, and this method is a) A step of subjecting a crude composition containing ethylene carbonate to at least one distillation step to obtain a pre-purified composition containing at least 99.5% by weight of ethylene carbonate, b) A step of subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition. Includes, This method is carried out in a plant comprising at least one distillation column, one vessel, at least one crystallizer, and a supply line for a crude composition containing ethylene carbonate, wherein if the plant comprises one distillation column, the distillation column, or if the plant comprises two or more distillation columns, the first distillation column, comprises a top discharge line, a bottom discharge line, and a side discharge line, and at least one crystallizer comprises an inflow line for a pre-purified composition and a discharge line for the purified ethylene carbonate composition, and the side discharge line of the distillation column is directly or indirectly connected to the inflow line for the pre-purified composition of at least one crystallizer. i) The vessel is connected to a supply line and an inlet line for a crude composition containing ethylene carbonate, the inlet line being connected to the gas outlet of a first reboiler, the first reboiler being further connected to a bottom discharge line of a distillation column, the vessel further comprising a discharge line leading to the inlet line of the distillation column via a second reboiler, the bottom fraction of the distillation column being taken out of the distillation column via the bottom discharge line being partially evaporated in the first reboiler to obtain a gaseous fraction and a liquid fraction, or, ii) A feed line for the crude composition containing ethylene carbonate leads to a distillation column, the bottom discharge line of the distillation column leads to a vessel via a first reboiler, the vessel has a gas outlet connected to the inlet line of the distillation column, the vessel has a liquid outlet connected to a line leading to a second reboiler, the second reboiler has a gas outlet connected to the inlet line of the distillation column, the bottom fraction of the distillation column taken out of the distillation column via the bottom discharge line is partially evaporated in the first reboiler, and at least a portion of the gaseous fraction obtained in the first reboiler is recirculated into the distillation column via the inlet line.

Description

Technical Field

[0001] The present invention relates to a method for purifying ethylene carbonate and a purification plant.

Background Art

[0002] Ethylene carbonate is an important industrial raw material and is used, for example, as a solvent or starting material for the synthesis of ethylene glycol, dimethyl carbonate, ethylene glycol ether, and ethanolamine. Subsequently, ethylene glycol is widely used, for example, as an antifreeze, or as a chemical such as a monomer, a liquid coolant, and a solvent in the production of polyester and polyethylene terephthalate, while dimethyl carbonate is used in the production of polycarbonate. Furthermore, ethylene carbonate is becoming increasingly important as an electrolyte solvent for lithium-ion batteries that promotes the transport of lithium ions from the positive electrode to the negative electrode. Thereby, ethylene carbonate makes a twofold contribution to climate change countermeasures. First, the main route applied to the industrial synthesis of ethylene carbonate is the reaction of ethylene oxide and carbon dioxide, whereby the recovered carbon dioxide can be consumed as a raw material for environmentally friendly chemical production. Second, lithium-ion batteries contribute to the decarbonization of the energy sector through electrification, particularly in the transport-related area. However, considering that the production of hydrogen fluoride is promoted and the quality of the solid electrode interface is affected when the content of glycol, especially water, is high, which has an adverse effect on the long-term performance of the battery, ethylene carbonate used as an electrolyte solvent for lithium-ion batteries needs to be very highly pure. General techniques for purifying crude ethylene carbonate are distillation, crystallization, absorption, and the like. However, these methods have at least one drawback, including a low separation efficiency, a high energy requirement, and the promotion of decomposition and the generation of by-products and undesirable impurities when ethylene carbonate is exposed to some thermal stress, such as a low removal coefficient of glycol and / or water, although not limited thereto.

Summary of the Invention

[0003] With that in mind, the fundamental objective of the present invention is to provide a method for purifying ethylene carbonate and a purification plant characterized by particularly high productivity (amount of purified product per unit time), high recovery yield, and particularly low energy consumption, wherein the method further yields high-purity ethylene carbonate with impurities such as water and glycol at a concentration of 50 ppm or less. [Means for solving the problem]

[0004] According to the present invention, this objective is satisfied by a method for purifying ethylene carbonate from a crude ethylene carbonate composition, and this method is a) A step of subjecting a crude composition containing ethylene carbonate to at least one distillation step to obtain a pre-purified composition containing at least 99.5% by weight of ethylene carbonate, b) A step of subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition. Includes, This method is carried out in a plant comprising at least one distillation column, one vessel, at least one crystallizer, and a supply line for a crude composition containing ethylene carbonate, wherein if the plant comprises one distillation column, the distillation column, or if the plant comprises two or more distillation columns, the first distillation column, comprises a top discharge line, a bottom discharge line, and a side discharge line, and at least one crystallizer comprises an inflow line for a pre-purified composition and a discharge line for the purified ethylene carbonate composition, and the side discharge line of the distillation column is directly or indirectly connected to the inflow line for the pre-purified composition of at least one crystallizer. i) The vessel is connected to a supply line and an inlet line for a crude composition containing ethylene carbonate, the inlet line being connected to the gas outlet of a first reboiler, the first reboiler being further connected to a bottom discharge line of a distillation column, the vessel further comprising a discharge line leading to the inlet line of the distillation column via a second reboiler, the bottom fraction of the distillation column being taken out of the distillation column via the bottom discharge line being partially evaporated in the first reboiler to obtain a gaseous fraction and a liquid fraction, or, ii) A feed line for the crude composition containing ethylene carbonate leads to a distillation column, the bottom discharge line of the distillation column leads to a vessel via a first reboiler, the vessel has a gas outlet connected to the inlet line of the distillation column, the vessel has a liquid outlet connected to a line leading to a second reboiler, the second reboiler has a gas outlet connected to the inlet line of the distillation column, the bottom fraction of the distillation column taken out of the distillation column via the bottom discharge line is partially evaporated in the first reboiler, and at least a portion of the gaseous fraction obtained in the first reboiler is recirculated into the distillation column via the inlet line.

[0005] This solution is based on the finding that a very high-purity ethylene carbonate containing only up to 50 ppm, and even less than 10 ppm, of impurities such as water and glycol can be obtained by subjecting a crude ethylene carbonate-containing composition, which may originate from a reaction pathway or be recovered from any type of recirculation flow, to a single distillation step carried out in a distillation column, or to two or more distillation steps carried out in two or more distillation columns, thereby obtaining a pre-purified composition containing at least 99.5% by weight of ethylene carbonate, and then subjecting the pre-purified composition to one or more melt crystallization steps, not only is obtained, but this method can also be carried out with particularly low energy consumption, and nevertheless with particularly high productivity and high recovery yield. This is particularly due to the fact that the distillation step can be carried out under relatively mild conditions, since the crude ethylene carbonate composition is only purified there to an ethylene carbonate content of at least 99.5% by weight. This not only allows for maintaining an ethylene carbonate recovery rate of over 90%, but also keeps energy consumption low by eliminating the need for harsher distillation conditions and further distillation steps that consume significantly more energy to obtain higher-purity ethylene carbonate, such as ethylene carbonate containing 200-800 ppm of impurities. Such high purity can only be achieved by distilling at an energy consumption 3-6 times higher than that of a distillation step performed under mild conditions to obtain a pre-purified composition containing at least 99.5% by weight of ethylene carbonate. Furthermore, by passing the bottom fraction of the distillation column through a reboiler, where it is partially evaporated, and then leading at least a portion of the resulting gaseous or liquid fraction to another reboiler, and then recirculating at least a portion of the gaseous fraction obtained in the second reboiler back into the distillation column, process energy consumption is significantly reduced while maintaining particularly high productivity and recovery rates.This is because the bottom fraction, which is removed via the bottom discharge line, is separated into a fraction with a higher content of high-boiling-point compounds (compounds with higher boiling points than ethylene carbonate, meaning low or medium molecular weight polymers, catalytic ionic liquids and salts, e.g., calcium salts and sodium salts) and a fraction with a lower content of ethylene carbonate. The fraction with a high content of high-boiling-point compounds and a low content of ethylene carbonate is removed from the bottom, while the other fraction with a low content of high-boiling-point compounds and a high content of ethylene carbonate is recycled directly or indirectly to the distillation column. Thus, backmixing of the two fractions is avoided, separation efficiency in the distillation column is improved, and process energy consumption is reduced. In addition, this achieves efficient removal of high-boiling-point compounds in particular from the crude ethylene carbonate composition, thereby reducing the decomposition of ethylene carbonate in the pre-purified composition in subsequent steps, and thus increasing the yield of ethylene carbonate in the process by approximately 20%. Next, the pre-purified composition is further purified by one or more melt crystallization steps according to the present invention, thereby obtaining purified ethylene carbonate containing up to 50 ppm, and even up to 10 ppm, of impurities. In the present invention, it has been found that melt crystallization is characterized by high separation efficiency of ethylene carbonate from water and glycol in each crystallization stage, and by a very high removal factor significantly higher than 10 for glycol, when a pre-purified composition containing at least 99.5% by weight of ethylene carbonate is used as the starting composition for melt crystallization. In this regard, the removal factor means the ratio of the concentration of a substance in the feedstock of the melt crystallization stage divided by the concentration of the product obtained as a result of the same melt crystallization stage. Even if it were possible to purify the crude ethylene carbonate composition by melt crystallization alone without a distillation step, this would require a very large number of crystallization stages to purify the impurity content to a maximum of 50 ppm. With such a large number of crystallization stages, energy consumption is particularly high, resulting in very high operating costs. Furthermore, this requires a fairly large crystallization apparatus.Therefore, the distillation step a) and crystallization step b) that yield a pre-purified composition containing at least 99.5% by weight of ethylene carbonate work synergistically to produce very high-purity ethylene carbonate containing up to 50 ppm of impurities, and even less than 10 ppm of impurities, with particularly high productivity and high recovery yield, especially with low energy consumption. More specifically, the energy savings compared to known methods are 20-25%.

[0006] The connection of the side discharge line of the distillation column to the inflow line for the pre-purified composition of at least one crystallizer means a direct or indirect connection between the side discharge line of the distillation column and the inflow line for the pre-purified composition of at least one crystallizer. An indirect connection means, in particular, that the side discharge line of the distillation column leads as a supply line to a second distillation column including a top discharge line, a side discharge line, and a bottom discharge line, and preferably the side discharge line is directly connected to the inflow line for the pre-purified composition of at least one crystallizer.

[0007] As described above, step a) is intentionally performed to obtain a pre-purified composition containing at least 99.5% by weight of ethylene carbonate, i.e., a composition that does not need to be so pure that it contains only low ppm of impurities. This allows for a small number of distillation steps and enables the temperature and pressure conditions during the distillation step(s) to be kept moderate, thus significantly reducing the energy required for distillation. Particularly good results are obtained when at least one distillation step is performed in step a) to obtain a pre-purified composition containing 99.5 to 99.9% by weight of ethylene carbonate. The glycol impurity content in the pre-purified composition is preferably 100 to 2000 ppm. More preferably, at least one distillation step is performed in step a) to obtain a pre-purified composition containing 99.6 to 99.9% by weight, more preferably 99.7 to 99.9% by weight, even more preferably 99.8 to 99.9% by weight, and most preferably 99.85 to 99.90% by weight of ethylene carbonate.

[0008] As a further development of the present invention, it is suggested that the crude composition used in step a) contains 10 to 99% by weight, preferably 50 to 99% by weight, more preferably 70 to 99% by weight, and most preferably 95 to 99% by weight of ethylene carbonate.

[0009] As described above, step a) includes at least one distillation step. Therefore, step a) may include two or more distillation steps. However, it is preferable that step a) does not include more than two distillation steps. For example, step a) includes two subsequent distillation steps. In this embodiment, it is preferable that the crude composition is fed into a first distillation column in step a), where it is distilled into a top fraction, a side fraction, and a bottom fraction, the bottom fraction of the first distillation column is led to a second distillation column, where it is distilled into a top fraction, a side fraction, and a bottom fraction, and the top fraction of the second distillation column is led to at least one melt crystallization step in step b) as a pre-purified composition. However, in this embodiment, it is more preferable that the crude composition is supplied to a first distillation column in step a), where it is distilled into a top fraction, a bottom fraction, and a side fraction, the side fraction of the first distillation column is led to a second distillation column, where it is distilled into a top fraction, a bottom fraction, and a side fraction, and the side fraction of the second distillation column is led as a pre-purified composition to at least one melt crystallization step in step b).

[0010] According to another particularly preferred embodiment of the present invention, step a) comprises one (only) distillation step carried out in a distillation column connected to the above-described vessel and two reboilers, wherein the crude composition is fed into the distillation column in step a), where it is distilled to a top fraction, a bottom fraction, and preferably a side fraction, which preferably leads to at least one melt crystallization step of step b) as a pre-purified composition.

[0011] According to option i) of the present invention, the vessel is connected to a supply line and an inflow line for a crude composition containing ethylene carbonate, the inflow line being connected to a gas outlet of a first reboiler, the first reboiler being further connected to a bottom discharge line of a distillation column, and the vessel further includes a discharge line connected to the inflow line of the distillation column via a second reboiler. The bottom fraction of the distillation column, taken out of the distillation column via the bottom discharge line, is partially evaporated in the first reboiler to obtain a gaseous fraction and a liquid fraction, and at least a portion of the gaseous fraction is led into the vessel via an inflow line connected to the gas outlet of the first reboiler. In this embodiment, it is even more preferable that the first reboiler includes a liquid discharge line through which the liquid fraction obtained in the first reboiler is taken out of the process. The first reboiler may also include a further gas outlet through which a fraction containing low-boiling point compounds is taken out of the process. In this embodiment, particularly good results are obtained when the first reboiler is a wiped film evaporator, a drop film evaporator, or a short-pass evaporator, more preferably when the first reboiler is a wiped film evaporator or a short-pass evaporator, and most preferably when the first reboiler is a wiped film evaporator. The first reboiler may also be equipped with two or more heat exchangers in series. The second reboiler is preferably a drop film evaporator.

[0012] As a further development of the present invention, in this embodiment, the vessel is further connected to the discharge line of the distillation column, and the distillation column further comprises one or more structural packing layers, with a collector having a recovery line connected to the discharge line located below the bottom layer of structural packing. Instead of, or in addition to, one or more structural packing layers, the distillation column may comprise one or more random packing layers and / or one or more trays.

[0013] According to option ii) of the present invention, a supply line for a crude composition containing ethylene carbonate leads to a distillation column, the bottom discharge line of the distillation column leads to a vessel via a first reboiler, the vessel has a gas outlet connected to the inlet line of the distillation column, the vessel has a liquid outlet connected to a line leading to a second reboiler, the second reboiler has a gas outlet connected to the inlet line of the distillation column, the bottom fraction of the distillation column taken out of the distillation column via the bottom discharge line is partially evaporated in the first reboiler, and at least a portion of the gaseous fraction obtained in the first reboiler is recirculated to the distillation column via the inlet line. In this embodiment, it is even more preferable that the liquid fraction obtained in the vessel is partially evaporated in the second reboiler, and at least a portion of the gaseous fraction obtained in the second reboiler is recirculated to the distillation column via the gas outlet of the second reboiler and the inlet line of the distillation column connected thereto. In this embodiment, it is preferable that the second reboiler further comprises a liquid discharge line for high-boiling-point compounds and a gas discharge line for low-boiling-point compounds. In this embodiment, particularly good results are obtained when the first reboiler is a drop film evaporator, but it is preferable that the second reboiler is a wiped film evaporator, a drop film evaporator, or a short-pass evaporator, and more preferably that the second reboiler is a wiped film evaporator or a short-pass evaporator, most preferably that the second reboiler is a wiped film evaporator. The second reboiler may also comprise two or more heat exchangers in series.

[0014] As a further development of the present invention, the top of the distillation column is provided with an outlet line and an inlet line, both of which are connected to a recirculation line that runs from the outlet line to the inlet line, the recirculation line being connected to an outlet condenser or a cold trap, respectively, and further connected to a gas-liquid separator downstream of the outlet condenser, the gas-liquid separator being connected to a liquid line connected to the recirculation line, and the gas-liquid separator being connected to a gas line, which is preferable.

[0015] The side walls of the distillation column are equipped with discharge and inlet lines, both of which are connected to a recirculation line that runs from the discharge line to the inlet line. The recirculation line is connected to a side condenser, which is connected to a gas-liquid separator downstream of the side condenser. The gas-liquid separator is connected to a liquid line that is connected to the recirculation line. The gas-liquid separator is connected to a gas line, and the liquid line returns to the distillation column.

[0016] To minimize energy consumption in the method, it is further proposed to perform distillation steps(s) to enable thermal integration. For example, distillation is performed in at least one distillation step such that the condensation temperature of the top fraction is at least 100°C, preferably 110–150°C, more preferably 115–125°C. This makes it possible to generate a flow of thermal fluid in the top condenser having a temperature of at least 80°C, preferably 90–130°C, more preferably 95–105°C. This thermal fluid can be used to drive other steps, such as sweating and / or melting of ethylene carbonate crystals obtained in at least one melt crystallization step, as will be further described later. This can reduce overall energy consumption by up to 25% compared to each system without thermal integration.

[0017] Furthermore, the distillation column(s) used in step a) preferably comprises one or more internal structures, such as one or more structural packing layers, one or more random packing layers, or one or more trays. This enables particularly efficient transfer of matter and heat between the descending liquid phase and the rising gas phase. More preferably, the distillation column(s) used in step a) comprises one or more structural packing layers, for example, 1 to 5 layers, preferably 2 to 4 layers. Each of the structural packing layers is 100 to 750 m 2 / m 3 , comfortable 150~500m 2 / m 3 Particularly good results can be obtained when the specific surface area is such that...

[0018] The present invention is not particularly limited with respect to the type or number of the at least one melt crystallization step. Particularly good results are obtained when the at least one melt crystallization step b) includes at least one melt crystallization step selected from the group consisting of falling film crystallization steps, static crystallization steps, and suspension crystallization steps. Falling film crystallization also means dynamic crystallization. Each of the crystallization techniques described above may include 1 to 5 melt crystallization steps, preferably 1 to 4 steps, more preferably 1 to 3 steps, and most preferably 1 to 2 steps.

[0019] According to a particularly preferred embodiment of the present invention, at least one melt crystallization step b) includes at least one drop film crystallization step. During the drop film crystallization step, the molten material to be crystallized flows downward along a cooled surface, such as along the inside of a cooled tube, thereby enabling crystals to grow from the drop film of molten material onto the inner surface of the tube, which is cooled by a drop film of coolant flowing parallel to the outer surface of the tube. Very high and highly repeatable migration velocities are achieved on both sides of the tube, and the resulting shear at the crystal / liquid interface rapidly transfers impurities into the bulk of the molten material. Preferably, the drop film crystallization apparatus used in crystallization step(s) b) includes a plurality of vertical tubes on which the crystallized layer grows as a cylindrical shell, a collection container below the tube, and a circulation pump. Before the start of the crystallization step, the collection container is filled with a batch of molten material to be crystallized. The circulation pump is then started to wet the tube and begin crystallization at a specific temperature level, while simultaneously initiating a stepwise operation of the coolant temperature. The circulation rate of the molten material is adjusted to a value higher than the crystal precipitation rate so that the temperature and composition conditions are nearly uniform throughout the entire length of the tube. The temperature is lowered at a constant rate until the liquid level in the recovery container drops to a predetermined value. At this point, the circulation of the molten material is stopped.

[0020] Step b) yields particularly good results when it includes 1 to 5 stages, preferably 1 to 4 stages, more preferably 1 to 3 stages, and most preferably 1 to 2 stages of falling film crystallization.

[0021] Preferably, the preliminary purification composition obtained in step a) and subjected to at least one melt crystallization step in step b) is fed to the first of 2 to 5 falling film crystallization stages to produce a first ethylene carbonate concentrated crystallization fraction and a residual fraction. The first ethylene carbonate concentrated crystallization fraction is fed to the second of 2 to 5 falling film crystallization stages, and in any of the second and optional third to fifth falling film crystallization stages, an ethylene carbonate concentrated crystallization fraction and a residual fraction are produced. Each of the ethylene carbonate concentrated crystallization fractions produced in the second and optional third to fourth falling film crystallization stages is fed to a downstream ethylene carbonate crystallization stage, and each of the residual fractions produced in the second and optional third to fifth falling film crystallization stages is fed to an upstream falling film crystallization stage. The ethylene carbonate concentrated crystallization fraction obtained at the far downstream of the falling film crystallization stage is a purified ethylene carbonate composition.

[0022] Further, the production of the ethylene carbonate concentrated crystallization fraction and the residual fraction in the crystallization stage preferably includes a step of removing the residual liquid from the crystallization stage as the residual fraction after the completion of crystallization in the crystallization stage, a step of melting the crystal layer obtained in the crystallization stage, and a step of taking out the obtained crystal melt from the crystallization stage as the ethylene carbonate concentrated crystallization fraction.

[0023] As a further development of the present invention, it is proposed that before melting the crystal layer obtained in the crystallization stage, one or more sweating steps of the crystal layer are carried out to obtain one or more sweating fractions and a purified crystal layer. Preferably, at least a part of the first sweating fraction obtained thereby is fed to the remaining liquid removed as the residual fraction. Sweating is achieved by raising the temperature of the crystals to just below the melting point of ethylene carbonate, for example a value 0.1 to 2 °C lower than the melting point of ethylene carbonate, in order to liquefy impurities and promote further discharge.

[0024] Particularly good results are obtained when at least one, preferably all, of the melt crystallization steps are carried out at a temperature of -10°C to 70°C, preferably -5°C to 65°C, more preferably 0°C to 60°C.

[0025] According to a particularly preferred embodiment of the present invention, the purified ethylene carbonate composition contains impurities of 50 ppm or less, preferably 10 ppm or less.

[0026] In a further aspect, the present invention is a plant for purifying ethylene carbonate from a crude ethylene carbonate composition, The plant comprises at least one distillation column, one vessel, at least one crystallization device, and a supply line for the crude composition containing ethylene carbonate. When the plant comprises one distillation column, the distillation column has, or when the plant comprises two or more distillation columns, the first distillation column has, a top discharge line, a bottom discharge line, and a side discharge line. At least one crystallization device has an inlet line for the preliminary purification composition and a discharge line for the purified ethylene carbonate composition. The side discharge line of the first distillation column is directly or indirectly connected to the inlet line for the preliminary purification composition of at least one crystallization device, <0101 i) The vessel is connected to a supply line for the crude composition containing ethylene carbonate and an inlet line. The inlet line is connected to the gas outlet of a first reboiler. The first reboiler is further connected to the bottom discharge line of the distillation column. The vessel further comprises a discharge line leading to the inlet line of the distillation column via a second reboiler, or, ii) The supply line for the crude composition containing ethylene carbonate leads to the distillation column. The bottom discharge line of the distillation column leads to the vessel via a first reboiler. The vessel has a gas outlet connected to the inlet line of the distillation column. The vessel has a liquid outlet connected to a line leading to a second reboiler. The second reboiler has a gas outlet connected to the inlet line of the distillation column. It relates to a plant.

[0027] Particularly good results are obtained with respect to option i) if the vessel is further connected to the discharge line of the distillation column, and the second reboiler further comprises a liquid discharge line for high-boiling point compounds and a gas discharge line for low-boiling point compounds.

[0028] As a further development of the present invention, it is proposed that the distillation column further comprises one or more structural packing layers, and below the lowest layer (56') of the structural packing, a collector having a recovery line connected to a discharge line is positioned. Instead of, or in addition to, one or more structural packing layers, the distillation column may comprise one or more random packing layers and / or one or more trays.

[0029] According to a more preferred embodiment of the present invention, in the embodiment of option ii), the second reboiler preferably further comprises a liquid discharge line for high-boiling-point compounds and a gas discharge line for low-boiling-point compounds.

[0030] Preferably, the plant comprises two distillation columns, the second distillation column comprising a top discharge line, a bottom discharge line, and a side discharge line, the side discharge line of the second distillation column being directly connected to an inflow line for pre-purified compositions of at least one distillation column, and the side outlet of the first distillation column being connected to the inlet of the second distillation column by a connecting line.

[0031] Particularly good results are obtained when at least one crystallization apparatus is equipped with 1 to 5 stages, preferably 1 to 4 stages, more preferably 1 to 3 stages, and most preferably 1 to 2 stages of falling film crystallization.

[0032] The present invention will be described in more detail below with reference to the drawings. [Brief explanation of the drawing]

[0033] [Figure 1] A schematic diagram of a plant for purifying ethylene carbonate from a crude ethylene carbonate composition according to one embodiment of the present invention is shown. [Figure 2]A schematic diagram of a plant for purifying ethylene carbonate from a crude ethylene carbonate composition, according to another embodiment of the present invention, is shown. [Figure 3] A schematic diagram of a plant for purifying ethylene carbonate from a crude ethylene carbonate composition, according to another embodiment of the present invention, is shown. [Modes for carrying out the invention]

[0034] The plant 10 for purifying ethylene carbonate from a crude ethylene carbonate composition shown in Figure 1 comprises a distillation column 12, a vessel 94, and a crystallizer 14. More specifically, the plant 10 includes an inlet line 22 for the crude composition containing ethylene carbonate, and the distillation column 12 includes a top discharge line 24, a bottom discharge line 26, and a side discharge line 28 for the pre-purified composition, which are connected to the crystallizer 14. Furthermore, the crystallizer 14 includes an inlet line for the pre-purified composition and a discharge line 64 for the purified ethylene carbonate composition, and the side discharge line 28 of the distillation column 12 is directly connected to the inlet line for the pre-purified composition of the crystallizer 14. Next, the vessel 94 is connected to a supply line 22 and an inlet line 44 for the crude composition containing ethylene carbonate, and the inlet line 44 is connected to the gas outlet of a first reboiler 48. The first reboiler 48 is further connected to the bottom discharge line 26 of the distillation column 12, and the vessel 94 further comprises a discharge line 50 which connects to the inlet line 52 of the distillation column 12 via a second reboiler 54. The vessel 94 is also further connected to the discharge line 96 of the distillation column 12, and the first reboiler 48 further comprises a liquid discharge line 49 for high-boiling point compounds and a gas discharge line 63 for low-boiling point compounds. In fact, the liquid discharge line 49 of the first reboiler 48 for high-boiling point compounds is the take-out line leading from the plant 10. Furthermore, the distillation column 12 comprises two structural packing layers 56, 56', one of which 56 is located above the side discharge line 28 and the other 56' is located below the side discharge line 28. Below the lower layer 56' of the structural packing is a collector 98 having a recovery line 100 connected to the discharge line 96 of the distillation column 12. A portion of the liquid descending through the lower layer 56' of the structured packing via the recovery line 100 flows into the discharge line 96, while the remainder descends further to the bottom section of the distillation column 12, from where it flows into the bottom discharge line 26. Additionally, the discharge line 24 at the top of the distillation column 12 is connected to the recirculation line 58, which in turn connects to the inflow line 60 leading to the top of the distillation column 12.Next, the recirculation line 58 is connected to the top condenser 62, which is further connected to the discharge line 63 for the light fraction.

[0035] The crystallization apparatus 14 includes three drop film crystallization stages, a discharge line 64 for high-purity ethylene carbonate, and a discharge line 66 for residue. Furthermore, the crystallization apparatus 14 is connected to a heater 68 and a cooler 70, which together with a condenser 62 form a thermal integration system 72.

[0036] During the operation, the crude composition containing ethylene carbonate is supplied as feed to a container 94 via the inlet line 22, where it is mixed with the liquid fraction recovered by the collector 98, from which a portion is withdrawn via the discharge line 96 and led to the container 94. The remaining portion of the liquid fraction descends further to the bottom section of the distillation column 12, from which it flows into the bottom discharge line 26 and from which it leads to the first reboiler 48. In the first reboiler 48, the liquid fraction is partially evaporated to obtain a vapor fraction with a reduced content of high-boiling-point compounds, a portion of which is introduced to the container 94 via line 44, and another portion of which is withdrawn from the process via the discharge line 63 for low-boiling-point compounds. Furthermore, a liquid fraction with an increased content of high-boiling-point compounds is obtained in the first reboiler 48, which is withdrawn from the process via the liquid discharge line 49 for high-boiling-point compounds. The mixture obtained in container 94 is supplied to a second reboiler 54 via line 50, where it is evaporated and then led to the bottom section of the distillation column 12 via inflow line 52. The vapor generated during distillation is removed from the distillation column via top discharge line 24 and then partially condensed in top condenser 62, from which the liquid portion is refluxed to the distillation column 12 via recirculation line 58, while the vapor portion obtained in top condenser 62 is removed from the process via discharge line 63 for low-boiling-point compounds. Furthermore, a side fraction from the distillation column 12 is removed via a side discharge line for a pre-purified composition with an ethylene carbonate content of 99.5-99.9% by weight, which is supplied to a crystallizer 14 where the pre-purified composition is further purified. The purified ethylene carbonate is removed from the process via discharge line 64 for high-purity ethylene carbonate, while the residue obtained during crystallization is removed from the process via discharge line 68 for residue.

[0037] The plant shown in Figure 2 corresponds to the plant in Figure 1, except that it further comprises a second distillation column 74 positioned between the first distillation column 12 and the crystallizer 14. More specifically, the second distillation column 74 comprises three structural packing layers 76, 76', and 76'', and a connecting line 78 runs from the side outlet of the first distillation column 12 to the second distillation column 74, entering the second distillation column 74 at a position between the uppermost structural packing layer 76 and the intermediate structural packing layer 76'. The second distillation column 74 also comprises a top outlet 80 and a bottom outlet 82, and further comprises a recirculation line 84, which comprises a reboiler 86 and returns to the bottom of the second distillation column 74 from the bottom discharge line 82. Similarly, the second distillation column 74 further includes a recirculation line 88, which includes a condenser 90 and returns to the top of the second distillation column 74 from the top discharge line 80.

[0038] Figure 3 shows an alternative embodiment of the plant according to option ii). In the embodiment shown in Figure 3, the inlet line 22 is not connected to the vessel 94 as in the embodiment shown in Figure 2, but is directly connected to the first distillation column 12. Furthermore, the first distillation column 12 does not have a collector 98 or a recovery line 100 as in the embodiment shown in Figure 2. Rather, the bottom discharge line 26 of the distillation column 12 leads to the vessel 94 via the first reboiler 48, and the vessel 94 has a gas outlet connected to the inlet line 52 of the distillation column 12, and the vessel 94 further has a liquid outlet connected to a line 46 that leads to a second reboiler 54. The second reboiler 54 has a gas outlet connected to the inlet line 44 of the distillation column 12, and another gas outlet connected to a gas discharge line 63 for low-boiling point compounds and a liquid discharge line 49 for high-boiling point compounds. [Explanation of symbols]

[0039] 10 Plants 12 (First) distillation column 14. Crystallization apparatus 22 Distillation column inflow line 24. Discharge line at the top of the distillation column 26. Bottom discharge line of the distillation column 28 Side discharge line for pre-purified composition 44 Inflow Line 46 lines 48. First Reboiler 49. Liquid discharge line for high-boiling point compounds 50 Discharge Line 52 Inflow Line 54. Second Reboiler 56, 56' structural filling layer 58 Recirculation Line 60 Inflow Line 62. Capacitor at the top of the tower 63 Discharge line for low boiling point compounds 64. Discharge line for high-purity ethylene carbonate 66 Residue discharge line 68 Heater 70 Cooler 72 Thermal Integration System 74 Second distillation column 76, 76', 76" Structural packing layer of the second distillation column 78 connection lines 80. Top discharge line of the second distillation column 82 Bottom discharge line of the second distillation column 84 Recirculation Line 86 Reboiler 88 Recirculation Line 90 Capacitors 94 Container 96 lines 98 Collector 100 Recovery Line

Claims

1. A method for purifying ethylene carbonate from a crude ethylene carbonate composition, a) A step of subjecting a crude composition containing ethylene carbonate to at least one distillation step to obtain a pre-purified composition containing at least 99.5% by weight of ethylene carbonate, b) A step of subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition. Includes, The method is carried out in a plant (10) comprising at least one distillation column (12, 74), one vessel (94), at least one crystallizer (14), and a supply line (22) for a crude composition containing ethylene carbonate, wherein if the plant (10) comprises one distillation column (12), the distillation column (12), or if the plant (10) comprises two or more distillation columns (12, 74), the first distillation column (12), comprises a top discharge line (24), a bottom discharge line (26), and a side discharge line (28), the at least one crystallizer (14) comprises an inflow line for a pre-purified composition and a discharge line (64) for a purified ethylene carbonate composition, and the side discharge line (28) of the distillation column (12) is directly or indirectly connected to the inflow line for the pre-purified composition of the at least one crystallizer (14). i) The container (94) is connected to the supply line (22) for the crude composition containing ethylene carbonate and to an inflow line (44), the inflow line (44) is connected to the gas outlet of a first reboiler (48), the first reboiler (48) is further connected to the bottom discharge line (26) of the distillation column (12), the container (94) further comprises a discharge line (50) leading to the inflow line (52) of the distillation column (12) via a second reboiler (54), the bottom fraction of the distillation column (12) taken out of the distillation column (12) via the bottom discharge line (26) is partially evaporated in the first reboiler (48) to obtain a gaseous fraction and a liquid fraction, or, ii) The supply line (22) for the crude composition containing ethylene carbonate leads to the distillation column (12), the bottom discharge line (26) of the distillation column (12) leads to the vessel (94) via a first reboiler (48), the vessel (94) has a gas outlet connected to the inlet line (52) of the distillation column (12), and the vessel (94) has a liquid outlet connected to a line (46) leading to a second reboiler (54). The method further comprises the second reboiler (54) having a gas outlet connected to the inlet line (44) of the distillation column (12), the bottom fraction of the distillation column (12) being removed from the distillation column (12) via the bottom discharge line (26) being partially evaporated in the first reboiler (48), and at least a portion of the gaseous fraction obtained in the first reboiler (48) being recirculated into the distillation column (12) via the inlet line (52).

2. The method according to claim 1, wherein the crude composition is supplied to the first distillation column (12) in step a), distilled in the first distillation column (12) into a top fraction, a bottom fraction, and a side fraction, the side fraction of the first distillation column (12) is led to a second distillation column (74), distilled in the second distillation column (74) into a top fraction, a bottom fraction, and a side fraction, the side fraction of the second distillation column (74) is led as the pre-purified composition to the at least one crystallizer (14), and the at least one melt crystallization step of step b) is carried out in the at least one crystallizer (14).

3. The method according to claim 1 or 2, wherein, in option i), the vessel (94) is further connected to the discharge line (96) of the distillation column (12), the first reboiler (48) further comprises a liquid discharge line (49) for high-boiling-point compounds and a gas discharge line (63) for low-boiling-point compounds, the distillation column (12) further comprises one or more structural packing layers (56), and below the lowest layer (56') of the structural packing is a collector (98) having a recovery line (100) connected to the discharge line (96).

4. The method according to any one of claims 1 to 3, wherein the top of the first distillation column (12) comprises the discharge line (24) and the inflow line (60), the discharge line (24) and the inflow line (60) are connected to a recirculation line (58) that runs from the discharge line (24) to the inflow line (60), the recirculation line (58) is connected to a top condenser (62), and downstream of the top condenser (62) is connected to a gas-liquid separator, the gas-liquid separator is connected to a liquid line connected to the recirculation line (58), and the gas-liquid separator is connected to a gas line.

5. The method according to any one of claims 1 to 4, wherein the side wall of the first distillation column (12) is provided with a discharge line and an inlet line, the discharge line and the inlet line are connected to a recirculation line that runs from the discharge line to the inlet line, the recirculation line is connected to a side condenser, and downstream of the side condenser, it is connected to a gas-liquid separator, the gas-liquid separator is connected to a liquid line and a gas line, and the liquid line runs to the first distillation column (12).

6. The method according to any one of claims 1 to 5, wherein the at least one melt crystallization step b) includes at least one melt crystallization step selected from the group consisting of a falling film crystallization step, a static crystallization step, and a suspension crystallization step, preferably including at least one falling film crystallization step.

7. The method according to any one of claims 1 to 6, wherein step b) includes 1 to 5, preferably 1 to 4, more preferably 1 to 3, and most preferably 1 to 2, drop film crystallization steps.

8. The pre-purified composition obtained in step a) and subjected to at least one melt crystallization step in step b) is supplied to the first of two to five drop film crystallization steps to produce a first ethylene carbonate concentrated crystallized fraction and a residual fraction, the first ethylene carbonate concentrated crystallized fraction is supplied to the second of the two to five drop film crystallization steps, and in the second and any of the third to fifth drop film crystallization steps, the ethylene carbonate concentrated crystallized fraction and the residual fraction The method according to claim 7, wherein a is generated, each of the ethylene carbonate concentrated crystallized fractions generated in the second and optionally third to fourth drop film crystallization stages is supplied to a downstream ethylene carbonate crystallization stage, each of the residual fractions generated in the second and optionally third to fifth drop film crystallization stages is supplied to an upstream drop film crystallization stage, and the ethylene carbonate concentrated crystallized fraction at the downstream end of the drop film crystallization stage is a purified ethylene carbonate composition.

9. The method according to claim 8, wherein the generation of ethylene carbonate concentrated crystallized fraction and residual fraction in the crystallization step includes the steps of removing residual liquid as residual fraction from the crystallization step after the completion of crystallization in the crystallization step, melting the crystal layer obtained in the crystallization step, and removing the obtained crystalline molten material from the crystallization step as ethylene carbonate concentrated crystallized fraction, wherein one or more sweating steps of the crystal layer are performed before melting the crystal layer obtained in the crystallization step to obtain one or more sweating fractions and a purified crystal layer.

10. The method according to any one of claims 1 to 9, wherein the purified ethylene carbonate composition contains impurities of 50 ppm or less, preferably 10 ppm or less.

11. A plant (10) for purifying ethylene carbonate from a crude ethylene carbonate composition, The plant (10) comprises at least one distillation column (12, 74), one vessel (94), at least one crystallizer (14), and a supply line (22) for a crude composition containing ethylene carbonate, wherein if the plant (10) comprises one distillation column (12), the distillation column (12), or if the plant (10) comprises two or more distillation columns (12, 74), the first distillation column (12), comprises a top discharge line (24), a bottom discharge line (26), and side discharge lines (28, 78), wherein the at least one crystallizer (14) comprises an inflow line for a pre-purified composition and a discharge line (64) for a purified ethylene carbonate composition, and the side discharge line (28) of the first distillation column (12) is directly or indirectly connected to the inflow line for the pre-purified composition of the at least one crystallizer (14). i) The container (94) is connected to the supply line (22) for the crude composition containing ethylene carbonate and to an inflow line (44), the inflow line (44) is connected to the gas outlet of a first reboiler (48), the first reboiler (48) is further connected to the bottom discharge line (26) of the distillation column (12), and the container (94) further comprises a discharge line (50) leading to the inflow line (52) of the distillation column (12) via a second reboiler (54), or, ii) Plant (10), wherein the supply line (22) for a crude composition containing ethylene carbonate leads to the distillation column (12), the bottom discharge line (26) of the distillation column (12) leads to the vessel (94) via a first reboiler (48), the vessel (94) has a gas outlet connected to an inlet line (52) of the distillation column (12), the vessel (94) has a liquid outlet connected to a line (46) leading to a second reboiler (54), the second reboiler (54) has a gas outlet connected to an inlet line (44) of the distillation column (12).

12. The plant (10) according to claim 11, wherein, in option i), the vessel (94) is further connected to the discharge line (96) of the distillation column (12), and the first reboiler (48) further comprises a liquid discharge line (49) for high-boiling-point compounds and a gas discharge line (63) for low-boiling-point compounds.

13. The plant (10) according to claim 11, wherein the distillation column (12) further comprises one or more structural packing layers (56), and below the lowest layer (56') of the structural packing is a collector (98) having a recovery line (100) connected to the discharge line (96).

14. The plant (10) according to claim 11, wherein the second reboiler (54) further comprises a liquid discharge line (49) for high-boiling-point compounds and a gas discharge line (63) for low-boiling-point compounds.

15. Plant (10) according to any one of claims 11 to 14, comprising two distillation columns (12, 74), the second distillation column (74) comprising a top discharge line (80), a bottom discharge line (82), and a side discharge line (28), wherein the side discharge line (28) of the second distillation column (74) is directly connected to the inflow line for the pre-purified composition of at least one of the distillation columns (12, 74), and the side outlet of the first distillation column (12) is connected to the inlet of the second distillation column (74) by a connecting line (78).

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