Method and apparatus for purifying ethylene carbonate

Abstract

The invention relates to a method for purifying ethylene carbonate from a crude ethylene carbonate composition, comprising the following steps: a) subjecting a crude composition comprising ethylene carbonate to at least one distillation step to obtain a pre-purified composition comprising at least 99.5% by weight of ethylene carbonate, and b) subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition wherein in step a) a bottom divided wall distillation column is used as a distillation column (if step a) comprises one distillation step) or as a first distillation column (if step a) comprises two or more distillation steps), and a bottom partition distillation column comprising a partition wall connected to the bottom of the bottom partition distillation column and extending upward from the bottom of the bottom partition distillation column by a portion of the height of the bottom partition distillation column, whereby a bottom section of the divided wall distillation column is subdivided into a first bottom sub-section and a second bottom sub-section as viewed from a cross-section of the divided wall distillation column.

Description

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

[0002] Ethylene carbonate is an important industrial raw material which is used, for example, as a solvent or as a starting material for the synthesis of ethylene glycol, dimethyl carbonate, glycol ethers and ethanol amines. Ethylene glycol is in turn widely used as a chemical, for example as an antifreeze agent or as a monomer in the production of polyesters and polyethylene terephthalate, as a liquid coolant and as a solvent, while dimethyl carbonate is used for the manufacture of polycarbonates. Furthermore, ethylene carbonate is becoming increasingly important as an electrolyte solvent for lithium-ion batteries, which facilitates the transport of lithium ions from the cathode to the anode. Thus, ethylene carbonate contributes in a twofold manner to combating climate change. Firstly, the main route applied in the industrial synthesis of ethylene carbonate is the reaction of ethylene oxide with carbon dioxide, which enables the consumption of captured carbon dioxide as a feedstock for the production of green chemicals, and secondly, lithium-ion batteries contribute to the decarbonization of the energy industry through electrification, especially in relation to transport. However, ethylene carbonate used as an electrolyte solvent for lithium-ion batteries needs to be very pure, taking into account the detrimental effect of high contents of diols and especially water on the long-term performance of the battery, since they promote the formation of hydrogen fluoride, which in turn affects the quality of the solid-electrolyte interface. Common techniques for purifying crude ethylene carbonate are distillation, crystallization, adsorption, etc. However, these methods have at least one of the following disadvantages: low separation efficiency, for example but not limited to, low depletion factor of diols and / or water, high energy demand and subjecting ethylene carbonate to certain thermal stress so that it degrades acceleratedly and forms by-products and undesirable impurities.

[0003] In view of the foregoing, it is an object of the present invention to provide a method and a plant for purifying ethylene carbonate, which is characterized by a particularly high productivity (which is the mass of product purified per unit of time), a high recovery yield and a particularly low energy consumption, wherein the method further results in a very pure ethylene carbonate containing 50 ppm or less of impurities, such as water and diols.

[0004] According to the present invention, this object is met by providing a method for purifying ethylene carbonate from a crude ethylene carbonate composition, said method comprising the following steps: a) subjecting a crude composition containing ethylene carbonate to at least one distillation step to obtain a pre-purified composition containing at least 99.5 wt.% of ethylene carbonate, and b) subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition, wherein in step a) a bottom divided wall distillation column is used as distillation column (if step a) comprises one distillation step) or as first distillation column (if step a) comprises two or more distillation steps), which bottom divided wall distillation column comprises a dividing wall connected to the bottom of the bottom divided wall distillation column and extending from the bottom of the bottom divided wall distillation column over a part of the height of the bottom divided wall distillation column, thereby subdividing the bottom section of the bottom divided wall distillation column into a first bottom subsection and a second bottom subsection as seen in cross section of said bottom divided wall distillation column.

[0005] This solution is based on the finding that by first subjecting a crude ethylene carbonate containing composition, which can for example be derived from a reaction scheme or can be recovered from any kind of recycling stream, to one distillation step carried out in a bottom divided wall distillation column or to two or more distillation steps wherein the first distillation step is carried out in a bottom divided wall distillation column, wherein the distillation step(s) lead to a pre-purified composition containing at least 99.5 wt% of ethylene carbonate, and then subjecting the pre-purified composition to one or more melt crystallization steps, not only a very pure ethylene carbonate containing at most 50 ppm impurities or even not more than 10 ppm impurities, such as water and diols, is obtained, but the process can be carried out with a particularly low energy consumption, but a particularly high productivity and a high recovery yield. This is in particular due to the fact that the distillation step(s) can be carried out under comparatively mild conditions, as the crude ethylene carbonate composition is only purified to an ethylene carbonate content of at least 99.5 wt%. This not only enables to maintain the ethylene carbonate recovery at more than 90%, but also to maintain the energy consumption at a low level, as much more energy consuming stricter distillation conditions or further distillation steps are not needed to achieve a higher purity of ethylene carbonate, such as ethylene carbonate containing 200 to 800 ppm impurities. The energy consumption to achieve such a high purity by distillation only is 3 to 6 times higher compared to the energy consumption to carry out the distillation step under mild conditions to obtain a pre-purified composition containing at least 99.5 wt% of ethylene carbonate. Furthermore, the use of a bottom divided wall distillation column significantly reduces the energy consumption of the process, even while maintaining a particularly high productivity and a high recovery yield. This is due to the fact that the dividing wall, which subdivides the bottom section of the bottom divided wall distillation column into two separate bottom sub-sections, as seen from the cross-section of the bottom divided wall distillation column, avoids backmixing of the column bottom fractions between these two bottom sub-sections and thus allows the column bottom fraction contained in one of the bottom sub-sections to have a higher content of high boiling point compounds, meaning compounds having a higher boiling point than ethylene carbonate, such as low or medium molecular weight polymers, catalyst ionic liquids and salts, such as calcium and sodium salts, and a lower content of ethylene carbonate than the column bottom fraction contained in the other bottom sub-section. This in turn enables to increase the separation efficiency within the distillation column and to reduce the energy consumption of the process. Furthermore, this enables an especially efficient removal of high boiling point compounds from the crude ethylene carbonate composition, which leads to a reduced degradation of ethylene carbonate in the pre-purified composition in the subsequent step(s) and thus to an increase of the ethylene carbonate yield during the process of about 20%. The further purification of the pre-purified composition in one or more melt crystallization steps is then carried out according to the present invention, which leads to a purified ethylene carbonate containing at most 50 ppm or even at most 10 ppm impurities.It has been found in this invention that if a pre-purified composition containing at least 99.5% by weight of ethylene carbonate is used as the starting composition for melt crystallization, melt crystallization is characterized by high separation efficiency of ethylene carbonate from water and glycols in each crystallization stage and a very high depletion factor for glycols, significantly higher than 10. The depletion factor in this respect refers to the ratio of the concentration of the substance in the feed during the melt crystallization stage to the concentration of the product obtained as a result of the same melt crystallization stage. Even if it were possible to purify crude ethylene carbonate compositions solely through melt crystallization without any distillation steps, this would require a very large number of crystallization stages to achieve purification to an impurity content of at most 50 ppm. Such a large number of crystallization stages would result in very high operating costs due to exceptionally high energy consumption. Furthermore, this would require large-scale crystallization equipment. Therefore, one or more distillation steps a) and crystallization steps b) work together to produce a pre-purified composition containing at least 99.5% by weight of ethylene carbonate, yielding very pure ethylene carbonate containing up to 50 ppm of impurities or even no more than 10 ppm of impurities with particularly low energy consumption and particularly high productivity and recovery yield. More specifically, energy savings of 20 to 25% are achieved compared to known methods.

[0006] 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., it does not need to be so pure as to have only a low ppm impurity content. Therefore, the number of distillation steps can be kept low, and the temperature and pressure conditions during the distillation(s) can be kept moderate so that the energy requirement for distillation is relatively low. 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 content of diol impurities in the pre-purified composition is preferably 100 to 2,000 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, even 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.

[0007] In a further development of the concept 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.

[0008] As described above, step a) includes at least one distillation step. Therefore, step a) may include two or more distillation steps. However, it is preferred that step a) does not include more than two distillation steps. For example, step a) includes two successive distillation steps. In this embodiment, the crude composition is preferably fed into a first bottom-separated wall distillation column in step a) and distilled therein into a top fraction, side fraction, and bottom fraction, wherein the bottom fraction of the first bottom-separated wall distillation column is introduced into a second distillation column and distilled therein into a top fraction, side fraction, and bottom fraction, wherein the top fraction of the second distillation column is introduced as a pre-purified composition into the at least one melt crystallization step in step b). However, in this embodiment, more preferably, the crude composition is fed into a first bottom partition wall distillation column in step a) and distilled therein into a top fraction, a bottom fraction, and a side fraction, wherein the side fraction of the first bottom partition wall distillation column is introduced into a second distillation column and distilled therein into a top fraction, a bottom fraction, and a side fraction, wherein the side fraction of the second distillation column is introduced as a pre-purified composition into the at least one melt crystallization step in step b).

[0009] According to an alternative, particularly preferred embodiment of the invention, step a) includes a (only) distillation step in a bottom-separated wall distillation column, wherein the crude composition is fed into the bottom-separated wall distillation column in step a) and distilled therein into a top fraction, a bottom fraction, and preferably also into a side fraction, wherein the side fraction is preferably introduced as a pre-purified composition into the at least one melt crystallization step of step b).

[0010] Particularly good results are obtained when the partition wall extends at least substantially vertically upwards from the bottom of the bottom partition wall distillation column, thereby subdividing the bottom section of the distillation column into a first bottom sub-section and a second bottom sub-section when viewed in cross-section. The bottom section refers to the section of the distillation column extending from the uppermost to the lowermost part of the partition wall according to the invention. The first bottom sub-section is a sub-section of the bottom section located on the side of the distillation column, through which the inlet of the crude ethylene carbonate composition passes, while the second bottom sub-section is opposite to the first bottom sub-section. Finally, "at least substantially vertical" means that the angle between the partition wall and the vertical direction is at most 10°, preferably at most 5°, more preferably at most 1°, and most preferably 0°.

[0011] According to a further preferred embodiment of the invention, the partition wall of the bottom partition wall distillation column, viewed in cross-section, subdivides the bottom section of the bottom partition wall distillation column into two equal-sized or two different-sized bottom sub-sections. Therefore, preferably, one of the first and second bottom sub-sections covers at least 50%, more preferably at least 55%, even more preferably at least 60%, and most preferably 65 to 70% of the total cross-sectional area of ​​the bottom section of the partition wall distillation column, while the other of the first and second bottom sub-sections covers up to 100% of the remaining portion of the total cross-sectional area of ​​the bottom section of the partition wall distillation column. For example, one bottom sub-section covers 43% of the total cross-sectional area and the other 57%, or each of the two bottom sub-sections covers exactly 50% of the total cross-sectional area. If the total cross-sectional area of ​​the bottom section varies along its axial length, the above values ​​relate to the average total cross-sectional area of ​​the bottom section.

[0012] Particularly good results are obtained when the partition wall of the bottom partition wall distillation column extends from its bottom by 1 to 30%, and preferably 5 to 20%, of the height of the bottom partition wall distillation column.

[0013] According to a further particularly preferred embodiment of the invention, a second bottom subsection of the bottom-divided-wall distillation column includes an outlet line, and the bottom-divided-wall distillation column includes an inlet line within or above the first bottom subsection, both connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is connected to a first reboiler. The first reboiler may include two or more heat exchangers connected in series. The first reboiler includes one or two vapor outlet lines (or gas outlet lines, respectively) and a liquid outlet line. The liquid outlet line serves as an outlet line for high-boiling compounds, via which the liquid fraction having a high content of high-boiling compounds is discharged from the method, while one of the one or two vapor outlet lines is connected to a condenser and downstream thereto to the inlet line leading into the bottom-divided-wall distillation column within or above the first bottom subsection. More specifically, the recirculated bottom fraction is partially evaporated in the first reboiler to obtain a vapor fraction with a reduced content of high-boiling-point compounds, and then recirculated via the aforementioned inlet line to the bottom partial partition wall distillation column, where a liquid fraction with an increased content of high-boiling-point compounds is obtained in the first reboiler, which is then removed from the method. When the first reboiler is a scraped-film evaporator, falling-film evaporator, or short-path evaporator, it is more preferable that the first reboiler is a scraped-film evaporator or a short-path evaporator, and most preferably that the first reboiler is a scraped-film evaporator, particularly good results are obtained.

[0014] Similarly, it is also preferred that the first bottom sub-section includes an outlet line, and the bottom partition wall distillation column includes an inlet line within or above the second bottom sub-section, both connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is connected to a second reboiler. Particularly good results are obtained when the second reboiler is a falling film evaporator.

[0015] Preferably, the two embodiments described above are combined, wherein the second bottom sub-section includes the aforementioned recirculation line (which leads from the second bottom sub-section via the first reboiler and its vapor outlet line and subsequently the condenser to the first bottom sub-section of the bottom partition wall distillation column), wherein the first reboiler is preferably a scraped film evaporator, a falling film evaporator, or a short-path evaporator, and the first bottom sub-section includes the aforementioned recirculation line leading from the first bottom sub-section via the second reboiler to the second bottom sub-section of the bottom partition wall distillation column, wherein the second reboiler is preferably a falling film evaporator. Particularly preferred in this embodiment is that the first reboiler (more preferably a scraped film evaporator or a short-path evaporator) operates at an operating pressure at least 25%, preferably 40%, and even more preferably 50% lower than the operating pressure of the second reboiler. This implementation scheme enables the particularly efficient utilization of the volatility differences of individual components in the crude ethylene carbonate composition, thereby efficiently separating low-boiling-point compounds (compounds with boiling points below ethylene carbonate) and high-boiling-point compounds (compounds with boiling points above ethylene carbonate, such as low or medium molecular weight polymers, catalyst ionic liquids, and salts, such as calcium and sodium salts) from ethylene carbonate with low energy consumption. In addition to the fact that the partition wall prevents backmixing of the bottom fraction between the two bottom sub-sections of the bottom partition wall distillation column, the two aforementioned recirculation lines, each connected to a reboiler, enable the operation of a first reboiler, preferably a scraped-film evaporator or a short-path evaporator, to achieve a very low residence time of the composition, preferably 3 to 15 seconds, in the first reboiler. This low residence time contributes to the low energy consumption of the method. Furthermore, the partial evaporation of the bottom fraction within the first reboiler results in a reduction in the content of high-boiling-point compounds in the vapor fraction obtained in the first reboiler and recirculated to the first bottom sub-section of the bottom partition wall distillation column.

[0016] In addition to the aforementioned dividing wall, the bottom dividing wall distillation column preferably further includes a partition wall, which preferably comprises at least a first portion extending substantially vertically downward and a second portion connected to the upper part of the first portion of the partition wall and extending into the inner wall of the bottom dividing wall distillation column, wherein the first portion of the partition wall extends above and / or at least partially within the second bottom sub-section of the bottom dividing wall distillation column. In this embodiment, the preferred inlet line of the bottom dividing wall distillation column connected to the second reboiler is preferably located below the second portion of the partition wall and connected to the wall of the bottom dividing wall distillation column at a position between the upper and lower ends of the first portion of the partition wall, and the second reboiler is connected to the outlet line of the first bottom sub-section. The second portion of the partition wall may extend obliquely relative to the horizontal plane, for example, at an angle greater than 10° to 40° relative to the horizontal plane, or may extend at least substantially horizontally, wherein "at least substantially horizontally" means that the angle between the second portion of the partition wall and the horizontal plane is at most 10°, preferably at most 5°, more preferably at most 1°, and most preferably 0°. The second section of the partition wall is preferably in close fluid contact with the inner wall of the bottom partition wall distillation column, meaning that neither the descending liquid nor the rising vapor can pass through the second section of the partition wall. The terms "partition wall" and "spacer wall" each refer to any kind of wall, with "partition" and "spacer" used only to easily distinguish between the two walls.

[0017] According to a further particularly preferred embodiment of the invention, the bottom-separated wall distillation column includes a side-stage outlet and, more preferably, a separation wall. The term "separation wall" also refers to any type of wall, where "separation" is used only to readily distinguish the wall from the aforementioned partition wall and the aforementioned spacer wall. The separation wall includes at least a first portion extending substantially vertically downward and a second portion connected to the upper part of the first portion of the separation wall and extending into the inner wall of the bottom-separated wall distillation column. The first portion of the separation wall extends above and / or at least partially within a first bottom sub-section of the bottom-separated wall distillation column, while a preferred inlet line of the bottom-separated wall distillation column connected to a first reboiler is preferably located below the second portion of the separation wall and connected to the wall of the bottom-separated wall distillation column at a position between the upper and lower ends of the first portion of the separation wall, the first reboiler being connected to the outlet line of a second bottom sub-section. Furthermore, it is preferred that the highest point of the second portion of the separation wall is located below the side-stage outlet of the bottom-separated wall distillation column. The second portion of the partition wall may extend at an angle relative to the horizontal plane, for example, at an angle greater than 10° to 40°, or may extend at least substantially horizontally, where "at least substantially horizontally" means that the angle between the second portion of the partition wall and the horizontal plane is at most 10°, preferably at most 5°, more preferably at most 1°, and most preferably 0°. The second portion of the partition wall is preferably in close fluid contact with the inner wall of the bottom partition wall distillation column, meaning that neither the descending liquid nor the rising vapor can pass through the second portion of the partition wall. The side stage outlet is located between the top and bottom, and preferably at 40 to 90%, and more preferably 60 to 90%, of the height of the bottom partition wall distillation column when viewed from the bottom to the top.

[0018] In a further development of the concept of the invention, it is preferred that the top of the bottom-partitioned distillation column includes an outlet line and an inlet line, both of which are connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is respectively connected to a top condenser or cold trap, the top condenser or cold trap being connected to a liquid line leading to the recirculation line and to a gas line.

[0019] Particularly good results are obtained when the sidewall of the bottom partition wall distillation column includes an outlet line and an inlet line, both of which are connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is connected to a side condenser, the side condenser is connected to a liquid line leading to the recirculation line and to a gas line, wherein the liquid line is returned to the bottom partition wall distillation column.

[0020] To minimize energy consumption during the process, it is further proposed to perform one or more distillation steps to allow for thermal integration. For example, distillation is carried out in at least one distillation step to achieve a condensation temperature of at least 100°C, preferably 110 to 150°C, and more preferably 115 to 125°C at the top of the column. This allows for the generation of a heat transfer medium stream in the top condenser at a temperature of at least 80°C, preferably 90 to 130°C, and more preferably 95 to 105°C. This heat transfer medium can then be used to drive another step, such as the sweating and / or melting of ethylene carbonate crystals obtained in at least one melt crystallization step described further below. Compared to a corresponding system without any thermal integration, this can reduce total energy consumption by up to 25%.

[0021] Furthermore, it is preferred that the distillation column(s) used in step a) comprises one or more internals, such as one or more structured packed beds, one or more random packed beds, or one or more trays. This results in particularly efficient mass and heat transfer between the descending liquid phase and the rising gas phase. More preferably, the distillation column(s) used in step a) comprises one or more structured packed beds, for example, 1 to 5, and preferably 2 to 4, structured packed beds. When each structured packing has a density of 100 to 750 m³... 2 / m 3 And more preferably 150 to 500 m 2 / m 3 When the specific surface area is high, particularly good results are obtained. In the bottom-partitioned distillation column used according to the invention, the partition wall may extend to touch or even penetrate the structured packed bed. However, it is preferred that the partition wall of the bottom-partitioned distillation column does not extend to touch or even penetrate the structured packed bed.

[0022] The present invention does not impose any particular limitation on the type or number of at least one melt crystallization stage. Particularly favorable results are obtained when the at least one melt crystallization step b) includes at least one melt crystallization stage selected from falling film crystallization, static crystallization, or suspension crystallization. Falling film crystallization also refers to dynamic crystallization. Each of the above crystallization techniques may include 1 to 5, preferably 1 to 4, more preferably 1 to 3, and most preferably 1 to 2 melt crystallization stages.

[0023] According to a particularly preferred embodiment of the invention, the at least one melt crystallization step b) includes at least one falling film crystallization stage. During the falling film crystallization stage, the melt to be crystallized flows downwards along a cooling surface (e.g., along the inside of a cooling tube), enabling crystals to fall film from the melt onto the inner surface of the tube, which is cooled by a falling film of coolant flowing in parallel on the outer surface of the tube. High and highly reproducible transport rates are achieved on both sides of the tube, where shear generated at the crystal / liquid interface rapidly transports impurities into the bulk of the melt. Preferably, the falling film crystallizer for crystallization stage (one or more) b) comprises multiple vertical tubes (where crystal layers grow as cylindrical shells), a collection container below the tubes, and a circulation pump. Before the crystallization stage begins, the collection container is filled with a batch of melt to be crystallized. The circulation pump is then started to wet the tubes and initiate crystallization at a certain temperature level, while a coolant temperature ramping begins. The melt circulation rate is adjusted to a high value compared to the crystal deposition rate to ensure that the temperature and composition conditions are substantially uniform along the length of the tube. The temperature decreases at a constant rate until the liquid level in the collection container drops to a preset value. At this point, melt circulation stops.

[0024] When step b) includes 1 to 5, preferably 1 to 4, more preferably 1 to 3, and most preferably 1 to 2 falling film crystallization stages, particularly good results are obtained.

[0025] Preferably, the pre-purified composition obtained in step a) and subjected to at least one melt crystallization step in step b) is fed to the first of the 2 to 5 falling film crystallization stages to produce a first ethylene carbonate enriched crystallization fraction and a residue fraction, wherein the first ethylene carbonate enriched crystallization fraction is fed to the second of the 2 to 5 falling film crystallization stages, wherein in the second and optionally the third to fifth falling film crystallization stages, an ethylene carbonate enriched crystallization fraction and a residue fraction are produced, wherein each of the ethylene carbonate enriched crystallization fractions produced in the second and optionally the third to fourth falling film crystallization stages is fed to a downstream ethylene carbonate crystallization stage, and each of the residue fractions produced in the second and optionally the third to fifth falling film crystallization stages is fed to an upstream falling film crystallization stage, wherein the ethylene carbonate enriched crystallization fraction obtained at the very downstream of the falling film crystallization stage is a purified ethylene carbonate composition.

[0026] Furthermore, preferably, the generation of ethylene carbonate enriched crystal fraction and residual fraction in the crystallization stage includes the following steps: removing the remaining liquid from the crystallization stage as a residual fraction after crystallization is terminated in the crystallization stage, melting the crystal layer obtained in the crystallization stage, and removing the obtained crystal melt as ethylene carbonate enriched crystal fraction from the crystallization stage.

[0027] In a further development of the invention, it is proposed to perform one or more sweating steps on the crystal layer before melting the crystal layer obtained in the crystallization stage to obtain one or more sweating fractions and a purified crystal layer, wherein preferably at least a portion of the first sweating fraction obtained therefrom is fed into the remaining liquid that has been removed as a residual fraction. Sweating is achieved by raising the temperature of the crystals to just below the melting point of ethylene carbonate, for example, 0.1 to 2°C below the melting point of ethylene carbonate, to liquefy impurities and facilitate further drainage.

[0028] Particularly good results are obtained when at least one, and preferably all, of the melt crystallization steps are carried out at a temperature of -10°C to 70°C, preferably at a temperature of -5°C to 65°C, and more preferably at a temperature of 0°C to 60°C.

[0029] According to a particularly preferred embodiment of the invention, the purified ethylene carbonate composition contains 50 ppm or less, and preferably 10 ppm or less, impurities.

[0030] In another aspect, the present invention relates to an apparatus for purifying ethylene carbonate from a crude ethylene carbonate composition, wherein the apparatus comprises at least one distillation column and at least one crystallizer, wherein the distillation column (if the apparatus comprises one distillation column) or a first distillation column (if the apparatus comprises two or more distillation columns) is a bottom partition wall distillation column, comprising a partition wall connected to the bottom of the bottom partition wall distillation column and extending upward from the bottom of the bottom partition wall distillation column to a portion of the height of the bottom partition wall distillation column, thereby subdividing the bottom section of the partition wall distillation column into a first bottom sub-section and a second bottom sub-section in cross-section, wherein the bottom partition wall distillation column further comprises an inlet line for the crude composition containing ethylene carbonate, a top outlet line, a bottom outlet line, and a side outlet line, wherein the at least one crystallizer comprises an inlet line for a pre-purified composition and an outlet line for purifying the ethylene carbonate composition, wherein the side outlet line of the bottom partition wall distillation column is connected to the inlet line of the at least one crystallizer for the pre-purified composition. "The side outlet line of the bottom partition wall distillation column is connected to the inlet line of the at least one crystallizer for pre-purifying the composition" means that the side outlet line of the bottom partition wall distillation column is directly or indirectly connected to the inlet line of the at least one crystallizer for pre-purifying the composition. Indirect connection specifically refers to the side outlet line of the bottom partition wall distillation column serving as a feed line into a second distillation column, which includes a top outlet line, a side outlet line, and a bottom outlet line, wherein preferably the side outlet line is directly connected to the inlet line of the at least one crystallizer for pre-purifying the composition.

[0031] Preferably, the partition wall extends at least substantially vertically upward from the bottom of the bottom partition wall distillation column to a portion of the height of the bottom partition wall distillation column, wherein “at least substantially vertical” means that the angle between the at least one partition wall (16) and the vertical direction is at most 10°, preferably at most 5°, more preferably at most 1°, and most preferably 0°.

[0032] Particularly good results are obtained when the partition wall extends from its bottom in the distillation column by 1 to 30, preferably 5 to 20%, of the height of the distillation column.

[0033] Furthermore, preferably, when viewed from the cross-section of the partition wall distillation column, the partition wall subdivides the bottom section of the partition wall distillation column into a first bottom sub-section covering at least 30%, more preferably at least 40%, even more preferably at least 45%, and most preferably 50% of the total cross-sectional area of ​​the bottom section of the partition wall distillation column, while the other part of the first and second bottom sub-sections covers the remaining portion covering up to 100% of the total cross-sectional area of ​​the bottom section of the partition wall distillation column.

[0034] According to a further particularly preferred embodiment of the invention, the bottom partition wall distillation column further includes a partition wall comprising at least a first portion extending substantially vertically downward and a second portion connected to the upper portion of the first portion of the partition wall and extending into the inner wall of the bottom partition wall distillation column, wherein the first portion of the partition wall extends above and / or at least partially within a second bottom sub-section of the bottom partition wall distillation column.

[0035] According to a further particularly preferred embodiment of the invention, the bottom partition wall distillation column includes a side-stage outlet and further includes a separation wall comprising at least a first portion extending substantially vertically downward and a second portion connected to the upper portion of the first portion of the separation wall and extending into the inner wall of the bottom partition wall distillation column, wherein the first portion of the separation wall extends above and / or at least partially within a first bottom sub-section of the bottom partition wall distillation column.

[0036] In a further development of the invention, it is proposed that a second bottom sub-section of the bottom-divided-wall distillation column include an outlet line, and that the bottom-divided-wall distillation column includes an inlet line within or above the first bottom sub-section, both connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is connected to a first reboiler. The first reboiler may include two or more heat exchangers connected in series. The first reboiler preferably includes one or two vapor outlet lines and a liquid outlet line. The liquid outlet line serves as an outlet line for high-boiling-point compounds, via which a liquid fraction with a high content of high-boiling-point compounds is discharged from the device. One of the one or two vapor outlet lines is connected to a condenser, and its downstream end is connected to an inlet line leading into the bottom-divided-wall distillation column within or above the first bottom sub-section. If the bottom partition wall distillation column includes a partition wall in the first bottom sub-section, preferably, the inlet line connected to the first reboiler is below the second portion of the partition wall and connected to the wall of the bottom partition wall distillation column at a position between the upper and lower ends of the first portion of the partition wall, and the first reboiler is connected to the outlet line of the second bottom sub-section. This embodiment yields particularly good results when the first reboiler is a wiped-film evaporator, falling-film evaporator, or short-path evaporator, more preferably a wiped-film evaporator or short-path evaporator, and most preferably a wiped-film evaporator.

[0037] According to a further particularly preferred embodiment of the invention, a first bottom sub-section of the bottom-partitioned distillation column includes an outlet line, and the bottom-partitioned distillation column includes an inlet line within or above a second bottom sub-section, both connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is connected to a second reboiler. If the bottom-partitioned distillation column includes a partition wall in the second bottom sub-section, preferably, the inlet line connected to the second reboiler is below a second portion of the partition wall and connected to the bottom-partitioned distillation column at a location between the upper and lower ends of a first portion of the partition wall, the second reboiler being connected to the outlet line of the first bottom sub-section, wherein the highest point of the second portion of the partition wall is located below the side-stage outlet. In this embodiment, preferably, the second reboiler is a falling film evaporator.

[0038] Good results are particularly obtained when the at least one crystallizer includes 1 to 5, preferably 1 to 4, more preferably 1 to 3, and most preferably 1 to 2 falling film crystallization stages.

[0039] The invention is explained in more detail below with reference to the accompanying drawings, in which: Figure 1 The illustration schematically shows an apparatus for purifying ethylene carbonate from a crude ethylene carbonate composition according to one embodiment of the invention.

[0040] Figure 2The illustration schematically shows an apparatus for purifying ethylene carbonate from a crude ethylene carbonate composition according to another embodiment of the invention.

[0041] Figure 3 Schematic display Figure 1 and 2 The bottom section of an alternative bottom-separated wall distillation column that can be used in the apparatus shown.

[0042] Figure 1 The apparatus 10 shown for purifying ethylene carbonate from a crude ethylene carbonate composition includes a distillation column 12 and a crystallizer 14. More specifically, the distillation column 12 is a bottom-partitioned distillation column 12, which includes a partition wall 16 connected to the bottom of the distillation column 12 and extending vertically upward from the bottom of the distillation column 12 for a portion of the height of the distillation column 12, thereby subdividing the bottom section of the partition wall distillation column 12 into a first bottom sub-section 18 and a second bottom sub-section 20 when viewed in cross-section. The partition wall 16 extends from its bottom for approximately 10% of the height of the distillation column 12. Furthermore, the bottom-partitioned distillation column 12 includes an inlet line 22 for the crude composition containing ethylene carbonate, a top outlet line 24, two bottom outlet lines 26, 26', and a side outlet line 28 for introducing the pre-purified composition into the crystallizer. Furthermore, the bottom partition wall distillation column 12 includes a partition wall 32 comprising a first portion 34 extending vertically downward and a second portion 36 connected to the uppermost portion of the first portion 34 and extending to the inner wall of the bottom partition wall distillation column 12. The first portion 34 of the partition wall 32 extends above and partially within the second bottom sub-section 20 of the bottom partition wall distillation column 12. Additionally, the bottom partition wall distillation column 12 includes a partition wall 38 comprising a first portion 40 extending vertically downward and a second portion 42 connected to the upper part of the first portion 40 and extending to the inner wall of the bottom partition wall distillation column 12, wherein the first portion 40 of the partition wall 38 extends above and at least partially within the first bottom sub-section 18.

[0043] The bottom partition wall distillation column 12 further includes an inlet line 44 connected to a recirculation line 46 leading from the outlet line 26' of the second bottom sub-section 20 to the inlet line 44, which leads into the first bottom sub-section 18 of the bottom partition wall distillation column 12. The recirculation line 46 is connected to a first reboiler 48, wherein the first reboiler 48 is preferably a scraped film evaporator.

[0044] The first reboiler 48 includes a liquid outlet line 49 for high-boiling-point compounds (heavy substances), which is essentially a take-off line drawn from the device 10. Additionally, the first reboiler 48 includes a vapor outlet line 63 for low-boiling-point compounds (light substances) and a vapor outlet line that is part of a recirculation line 46 and connected to a condenser (not shown) and downstream of it to an inlet line 44. Since the first reboiler 48 typically operates below the bottom partition wall distillation column 12, the vapor cannot flow directly to the storage tank of the bottom partition wall distillation column 12; instead, it first condenses, and the resulting liquid flows by gravity into the bottom partition wall distillation column 12 via the inlet line 44. Similarly, the outlet line 26 of the first bottom sub-section 18 is also connected to a recirculation line 50 leading from the outlet line 26' to the inlet line 52, which leads into the second bottom sub-section 20 of the bottom partition wall distillation column 12. The recirculation line 50 is connected to a second reboiler 54, which is preferably a falling film evaporator. Furthermore, the bottom-partitioned distillation column 12 includes two structured packed beds 56, 56', one of which 56 is arranged above the side outlet line 28, and the other 56' is arranged below the side outlet line 28 and above the partition wall 38. Additionally, the outlet line 24 at the top of the bottom-partitioned distillation column 12 is connected to the recirculation line 58, which in turn is connected to the inlet line 60 leading into the top portion of the bottom-partitioned distillation column 12. The recirculation line 58 is further connected to the top condenser 62, which is also connected to the outlet line 63 for light materials.

[0045] The crystallizer 14 includes three falling film crystallization stages, an outlet line 64 for pure ethylene carbonate, and an outlet line 66 for residues. Furthermore, the crystallizer 14 is connected to a heater 68 and a cooler 70, which, together with the condenser 62, form a thermal integration system 72.

[0046] Figure 2 The device shown corresponds to Figure 1 The apparatus further includes a second distillation column 74 arranged between the bottom partition wall distillation column 12 and the crystallizer 14. More specifically, the second distillation column 74 includes three structured packed beds 76, 76', 76'', with connecting lines 78 leading from the side outlet of the bottom partition wall distillation column 12 to the second distillation column 74 and entering the second distillation column 74 at a position between the highest and intermediate structured packed beds 76, 76'. The second distillation column 74 also includes a top outlet 80, a bottom outlet 82, and further includes a recirculation line 84 equipped with a reboiler 86 and leading back to the bottom portion of the second distillation column 74 from the bottom outlet line 82. Similarly, the second distillation column 74 further includes a recirculation line 88 equipped with a condenser 90 and leading back to the top portion of the second distillation column 74 from the top outlet line 80.

[0047] Figure 3 This shows an alternative bottom section of the bottom partition wall distillation column 12, which can replace... Figure 1 and 2 The usage shown is illustrated. Figure 3 The bottom partition wall distillation column 12 shown corresponds to Figure 1 and 2 As shown, the only difference is that the shape of the isolation wall 38 is slightly different.

[0048] Figure Labels 10 Equipment 12 (Bottom partition wall) Distillation column 14 Crystallizer 16. Dividing wall 18. First bottom subsection of the bottom partition wall distillation column 20. Second bottom subsection of the bottom partition wall distillation column 22. Inlet piping of the bottom partition wall distillation column 24. Top outlet pipeline of the bottom-partitioned distillation column 26, 26' Bottom outlet pipeline of the bottom partition wall distillation column 28. Side outlet line for the pre-purified composition 32. Partition wall 34. The first part of the partition wall 36. The second part of the partition wall 38. Separation wall 40. The first part of the isolation wall 42. The second part of the isolation wall 44 Inlet Pipeline 46 Recirculation Line 48 First Reboiler 49 Liquid outlet lines for high-boiling-point compounds 50 Recirculation Line 52 Inlet Pipeline 54 Second Reboiler 56,56' Structured Packing Bed 58 Recirculation Line 60 Inlet Pipeline 62. Top Condenser 63. Outlet pipeline for low-boiling-point compounds 64. Outlet pipeline for pure ethylene carbonate 66. Outlet pipeline for residues 68 heaters 70 Cooler 72 Thermal Integration System 74 Second Distillation Column 76,76',76'' Structured packed bed of the second distillation column 78 Connecting pipes 80. Top outlet pipeline of the second distillation column 82. Bottom outlet pipeline of the second distillation column 84 Recirculation Line 86 Reboiler 88 Recirculation Line 90 Condenser 94 Containers 96 pipelines.

Claims

1. A method for purifying ethylene carbonate from a crude ethylene carbonate composition, comprising the following steps: a) 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, and b) Subject the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition. In step a), a bottom partition wall distillation column (12) is used, which is a distillation column if step a) includes one distillation step, or a first distillation column if step a) includes two or more distillation steps. The bottom partition wall distillation column (12) includes a partition wall (16) connected to the bottom of the bottom partition wall distillation column (12) and extending upward from the bottom of the bottom partition wall distillation column (12) to a certain height of the bottom partition wall distillation column (12), thereby subdividing the bottom section of the partition wall distillation column (12) into a first bottom sub-section (18) and a second bottom sub-section (20) when viewed in cross-section.

2. The method according to claim 1, wherein the crude composition is fed into a first bottom partition wall distillation column (12) in step a) and distilled therein into a top fraction, a bottom fraction and a side fraction, wherein the side fraction of the first bottom partition wall distillation column (12) is introduced into a second distillation column (74) and distilled therein into a top fraction, a bottom fraction and a side fraction, wherein the side fraction of the second distillation column (74) is introduced as the pre-purified composition into at least one melt crystallization step in step b).

3. The method according to claim 1 or 2, wherein the partition wall (16) extends at least substantially vertically upward from the bottom of the bottom partition wall distillation column (12) to a portion of the height of the bottom partition wall distillation column (12), wherein "at least substantially vertical" means that the angle between the at least one partition wall (16) and the vertical direction is at most 10°, preferably at most 5°, more preferably at most 1° and most preferably 0°.

4. The method according to any one of the preceding claims, wherein the partition wall (16) extends from its bottom in the bottom partition wall distillation column (12) for 1 to 30%, and preferably 5 to 20%, of the height of the bottom partition wall distillation column (12), and wherein, viewed from the cross-section of the partition wall distillation column, the partition wall (16) subdivides the bottom section of the bottom partition wall distillation column into a first bottom sub-section (18) covering at least 50%, more preferably at least 55%, even more preferably at least 60%, and most preferably 65 to 70% of the total cross-sectional area of ​​the bottom section of the bottom partition wall distillation column (12), and the other portion of the first and second bottom sub-sections (20) covers up to 100% of the total cross-sectional area of ​​the bottom section of the partition wall distillation column (12).

5. The method according to any one of the preceding claims, wherein the second bottom subsection (20) of the bottom partition wall distillation column (12) includes an outlet line (26'), and the bottom partition wall distillation column (12) includes an inlet line (44) within or above the first bottom subsection (18), both connected to a recirculation line (46) leading from the outlet line (26') to the inlet line (44), wherein the recirculation line (46) is connected to a first reboiler (48), the first reboiler (48) including a liquid outlet line (49) and one or two vapor outlet lines (44, 63), one of which (44) is connected to the condenser and downstream of the inlet line (44), wherein the first bottom subsection (18) includes an outlet line (26), and the bottom partition wall distillation column (12) includes an inlet line (52) within or above the second bottom subsection (20), both of which are connected to a recirculation line (50) leading from the outlet line (26) to the inlet line (52), wherein the recirculation line (50) is connected to a second reboiler (54), wherein the first reboiler (48) is preferably a scraped film evaporator, a falling film evaporator, or a short-path evaporator, and the second reboiler (54) is a falling film evaporator.

6. The method according to any one of the preceding claims, wherein the top of the bottom partition wall distillation column (12) includes an outlet line (24) and an inlet line (60), both connected to a recirculation line (58) leading from the outlet line (24) to the inlet line (60), wherein the recirculation line (58) is connected to a top condenser (62), the top condenser (62) being connected to a liquid line leading to the recirculation line (58) and to a gas line.

7. The method according to any one of the preceding claims, wherein the sidewall of the bottom partition wall distillation column (12) includes an outlet line and an inlet line, both connected to a recirculation line leading from the outlet line to the inlet line, wherein the recirculation line is connected to a side condenser, the side condenser is connected to a liquid line and a gas line, wherein the liquid line leads into the bottom partition wall distillation column (12).

8. The method according to any one of the preceding claims, wherein the at least one melt crystallization step b) comprises at least one melt crystallization stage selected from falling film crystallization stage, static crystallization stage and suspension crystallization stage, and preferably comprises at least one falling film crystallization stage.

9. The method according to any one of the preceding claims, wherein step b) comprises 1 to 5, preferably 1 to 4, more preferably 1 to 3, and most preferably 1 to 2 falling film crystallization stages.

10. The method of claim 9, wherein the pre-purified composition obtained in step a) and subjected to at least one melt crystallization step in step b) is fed to the first of the 2 to 5 falling film crystallization stages to produce a first ethylene carbonate enriched crystallization fraction and a residue fraction, wherein the first ethylene carbonate enriched crystallization fraction is fed to the second of the 2 to 5 falling film crystallization stages, wherein in any one of the second and optionally the third to fifth falling film crystallization stages, an ethylene carbonate enriched crystallization fraction and a residue fraction are produced, wherein each of the ethylene carbonate enriched crystallization fractions produced in the second and optionally the third to fourth falling film crystallization stages is fed to a downstream ethylene carbonate crystallization stage, and each of the residue fractions produced in the second and optionally the third to fifth falling film crystallization stages is fed to an upstream falling film crystallization stage, wherein the most downstream ethylene carbonate enriched crystallization fraction of the falling film crystallization stage is the purified ethylene carbonate composition.

11. The method of claim 10, wherein generating the ethylene carbonate enriched crystal fraction and the residue fraction in the crystallization stage comprises the steps of: removing the remaining liquid from the crystallization stage as a residue fraction after crystallization is terminated in the crystallization stage, melting the crystal layer obtained in the crystallization stage, and removing the resulting crystal melt as the ethylene carbonate enriched crystal fraction from the crystallization stage, wherein one or more sweating steps of the crystal layer are performed before melting the crystal layer obtained in the crystallization stage to obtain one or more sweating fractions and a purified crystal layer.

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

13. An apparatus (10) for purifying ethylene carbonate from a crude ethylene carbonate composition, wherein the apparatus (10) comprises at least one distillation column (12, 74) and at least one crystallizer (14), wherein if the apparatus (10) comprises one distillation column, then the distillation column (12), or if the apparatus (10) comprises two or more distillation columns, then the first distillation column is a bottom partition wall distillation column (12), which includes a partition wall (16) connected to the bottom of the bottom partition wall distillation column (12) and extending upward from the bottom of the bottom partition wall distillation column (12) to a portion of the height of the bottom partition wall distillation column (12), thereby allowing the ethylene carbonate to be purified from a cross-section of the partition wall distillation column (12). The bottom section of the partition wall distillation column (12) is subdivided into a first bottom sub-section (18) and a second bottom sub-section (20), wherein the bottom partition wall distillation column (12) further includes an inlet line (22) for a crude composition containing ethylene carbonate, a top outlet line (24), a bottom outlet line (26, 26') and a side outlet line (28), wherein at least one crystallizer (14) includes an inlet line for a pre-purified composition and an outlet line (64) for purifying the ethylene carbonate composition, wherein the side outlet line (28) of the bottom partition wall distillation column is directly or indirectly connected to the inlet line of the at least one crystallizer (14) for the pre-purified composition.

14. The apparatus (10) according to claim 13, wherein the partition wall (16) extends at least substantially vertically upward from the bottom of the bottom partition wall distillation column (12) to a portion of the height of the bottom partition wall distillation column (12), wherein "at least substantially vertically" means that the angle between the at least one partition wall (16) and the vertical direction is at most 10°, preferably at most 5°, more preferably at most 1°, and most preferably 0°.

15. The apparatus (10) according to claim 13 or 14, wherein the bottom partition wall distillation column (12) further comprises a partition wall (32) comprising at least a first portion (34) extending substantially vertically downward and a second portion (36) connected to the upper portion of the first portion (34) of the partition wall (32) and extending to the inner wall of the bottom partition wall distillation column (12), wherein the first portion (34) of the partition wall extends above and / or at least partially within a second bottom sub-section (20) of the bottom partition wall distillation column (12).

16. The apparatus according to any one of claims 13 to 15, wherein the bottom partition wall distillation column (12) includes a side-stage outlet (28) and further includes a partition wall (38) comprising at least a first portion (40) extending substantially vertically downward and a second portion (42) connected to the upper portion of the first portion (40) of the partition wall (38) and extending to the inner wall of the bottom partition wall distillation column (12), wherein the first portion (40) of the partition wall (38) extends above and / or at least partially within a first bottom sub-section (18) of the bottom partition wall distillation column (12).

17. The apparatus according to any one of claims 13 to 16, wherein the second bottom subsection (20) of the bottom partition wall distillation column (12) includes an outlet line (26'), and the bottom partition wall distillation column (12) includes an inlet line (44) within or above the first bottom subsection (18), both connected to a recirculation line (46) leading from the outlet line (26') to the inlet line (44), wherein the recirculation line (46) is connected to a first reboiler (48), the first reboiler (48) including a liquid outlet line (49) and one or two vapor outlet lines (4... 4,63), one of which (44) is connected to the condenser and downstream thereto to the inlet line (44), wherein preferably, the inlet line (44) connected to the first reboiler (48) is below the second part (42) of the partition wall (38) and is connected to the wall of the bottom partition wall distillation column (12) at a position between the upper and lower ends of the first part (40) of the partition wall (38), the first reboiler (48) being connected to the outlet line (26') of the second bottom subsection (20), wherein preferably the first reboiler (48) is a scraped film evaporator, a falling film evaporator or a short-path evaporator.

18. The apparatus according to any one of claims 13 to 17, wherein the first bottom subsection (18) of the bottom partition wall distillation column (12) includes an outlet line (26), and the bottom partition wall distillation column (12) includes an inlet line (52) within or above the second bottom subsection (20), both connected to a recirculation line (50) leading from the outlet line (26) to the inlet line (52), wherein the recirculation line (50) is connected to a second reboiler (54), wherein preferably, it is connected to the second reboiler (54). The inlet line (52) is connected to the bottom partition wall distillation column (12) below the second part (36) of the partition wall (32) and at a position between the upper and lower ends of the first part (34) of the partition wall (32). The second reboiler (54) is connected to the outlet line (26) of the first bottom sub-section (18), wherein the highest point of the second part (36) of the partition wall (32) is located below the side stage outlet (28). Preferably, the second reboiler (54) is a falling film evaporator.

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