KR100713141B1 - Separation of dimethylcarbonate by layer melt crystallization - Google Patents

Abstract

The present invention relates to a method for separating dimethyl carbonate by film-melt crystallization, and more particularly, the cost of energy and the complexity of the process when operating at a boiling point much higher than the melting point, which is a problem of known dimethyl carbonate separation and purification methods. Solving the problem of recovery of solvent and exposure of volatile substances by using excess solvent, adopting film-type melt-crystallization method that can be separated at melting point without using solvent at all and prevents transesterification of alkylene carbonate and methanol. A method for separating 99 wt% or more of high purity dimethyl carbonate from 85 wt% or more of dimethyl carbonate raw material obtained.

Film Melt Crystallization, Dimethyl Carbonate, Separation, High Purity

Description

Separation of dimethylcarbonate by layer melt crystallization

Figure 1 shows the calibration curve between the actual purity of dimethyl carbonate mixture (reactant material) and the purity on gas chromatography (GC).

Figure 2 shows the temperature at which crystals are first formed according to the initial concentration of the mixture at a constant cooling rate (0.1 ℃ / min).

The present invention relates to a method for separating dimethyl carbonate by film-melt crystallization, and more particularly, the cost of energy and the complexity of the process when operating at a boiling point much higher than the melting point, which is a problem of known dimethyl carbonate separation and purification methods. Solving the problem of recovery of solvent and exposure of volatile substances by using excess solvent, adopting film-type melt-crystallization method that can be separated at melting point without using solvent at all and prevents transesterification of alkylene carbonate and methanol. A method for separating 99 wt% or more of high purity dimethyl carbonate from 85 wt% or more of dimethyl carbonate raw material obtained.

Dimethyl carbonate is colorless, odorless and has no toxicity to humans. In recent years, dimethyl carbonate has been used as a substitute for phosgene, an intermediate raw material of polycarbonate, additives for improving the octane number of automobiles, electrolytes for various solvents and secondary batteries. Purity of at least% by weight is applied.

When ethylene carbonate, which is an alkylene carbonate, is reacted in the presence of a transesterification catalyst, methanol is produced as dimethyl carbonate and an unreacted product. Distillation can be considered because dimethyl carbonate has a boiling point of 90-91 ° C. and methanol has a boiling point of 65 ° C., but an azeotrope mixture is prepared at a composition of 95%: 5% of dimethyl carbonate and methanol. Since the separation is not possible by a conventional distillation method, various methods have been proposed as a means to solve this problem. For example, US Pat. No. 4,458,645 and Japanese Patent Laid-Open No. 60-106505 describe a method for adsorptive separation of dimethyl carbonate using hydrophobic zeolite. However, such an adsorption separation method is a method of removing impurities in ppm units, which requires a costly adsorbent in order to remove methanol in which 5% or more is present in dimethyl carbonate. In addition, Japanese Patent Laid-Open Publication No. 54-41820, Japanese Patent Laid-Open Publication No. 63-205101, and Japanese Patent Laid-Open No. 2-212456 describe azeotropic distillation by adding an azeotrope that forms an azeotrope with methanol. In addition, Japanese Patent Laid-Open No. 2-212456, Japanese Patent Laid-Open No. 2-128741, Japanese Patent Laid-Open No. 6-228026, etc., combine two or more distillation columns or selectively discharge dimethyl carbonate from the middle of the tower, or excess solvent. Extractive distillation methods used in the art are known. However, these methods require additional distillation and absorption towers, such as distillation towers and absorption towers, to remove additional extractants such as o-xylene and azeotropic destructive substances. Phosphorus energy consumption has a big problem. In US Pat. No. 55289696 and Japanese paper Lagaku Kogaku Ronbunshu, 23 (5), 7330737 (1997), a separation method by pervaporation membrane separation is known. However, the membrane separation method is a separation method based on the permeation characteristics of the hydrophobic membrane, and the permeation separation efficiency by the membrane is low, and the continuous operation of the membrane is prevented due to contamination due to the material of the membrane, and the degradation is remarkably reduced with the durability time. Without.

Thus, the inventors of the present invention, in order to solve the known problems in the separation and purification of dimethyl carbonate, the melting point (melting point) of the dimethyl carbonate, which is the material to be purified, is a material having crystallinity of 2 to 4 ℃, including In view of the fact that trace impurities such as methanol, which is a major impurity, is an amorphous material, such an amorphous material can be efficiently removed from a crystal, it is a simpler device than a conventional purification device without using a separate solvent. 85% by weight or more of dimethyl carbonate-containing mixture obtained from transesterification reaction of alkylene carbonate and methanol by applying a film-type melt crystallization method in which a crystal is formed in a double-cylindrical structure purifier to grow crystals on the inner film. High purity dimethyl carbonate The present invention has been completed by developing a separation method.

Accordingly, an object of the present invention is to provide a method for separating at least 99% by weight of high purity dimethyl carbonate from a raw material containing at least 85% by weight of dimethyl carbonate obtained from transesterification of alkylene carbonate with methanol without using a solvent. .

The present invention is crystallized under solvent-free conditions by cooling the raw material containing more than 85% by weight of dimethyl carbonate obtained from the transesterification of alkylene carbonate and methanol at -5 ~ -25 ℃ at a cooling rate of 0.05 ~ 0.7 ℃ / min at room temperature In the post-treatment operation, the crystals were heated to 0.1-0.5 ° C / min at -10 to 20 ° C, and partially melted to remove impurities contained in the crystal layer in the form of a solution. It is characterized by a method of separating dimethyl carbonate.

The present invention will be described in more detail as follows.

The present invention addresses the problem of cost of energy and complexity of the process when operating at boiling points far higher than the melting point of the known separation and purification methods of dimethyl carbonate, recovery of solvents due to the use of excess solvents, and exposure of volatile substances. By adopting a film-type melt crystallization method that can be separated at the melting point without using any solvent, high purity dimethyl carbonate of 99% by weight or more can be obtained from 85% by weight or more of dimethyl carbonate raw material obtained from transesterification of alkylene carbonate and methanol. It is about how to separate.

The raw material used in the present invention is a dimethyl carbonate mixture containing 85 to 95% by weight of dimethyl carbonate and 5 to 15% by weight of methanol. Preferably dimethyl carbonate having a purity of 85 to 95% by weight is used.

In general, unlike recrystallization method in which a crystal is formed by cooling in a solution state using a solvent, a crystallization method that separates impurities in a molten state without adding a solvent, is classified into molten crystallization. Crystallization by forming crystals on the surface of the crystallization and growing the crystallization method has the advantage that the apparatus is very simple compared to the recrystallization method in which an excessive amount of solvent is crystallized by injecting an excessive amount of solvent in a crystallizer including a stirrer which is a crystallization method . That is, this method can be separated because the melting points of the mixture to be separated from each other, it is characterized in that separation occurs easily when forming an eutectic system on the phase diagram (phase diagram). In other words, if the mixture is maintained at a melting point or higher and melted, and then the temperature is lowered to the metastable zone of phase equilibrium, phase separation occurs, where a relatively large crystallinity is determined. And the remainder can be separated from the crystal with the remaining liquid. Therefore, when the temperature is lowered to the inside of the metastable region, it is very important to control the supersaturation including the cooling rate, the appropriate cooling temperature, and the like so that impurities do not exist in the crystal. That is, when crystals are formed too quickly and packed into a large form such as ice of crystals, it becomes very difficult to remove remaining impurities from the formed crystals.

In addition, the cooling rate and the final subcooling temperature during the crystallization is a major variable in the crystallization, the cooling rate is possible in the range of 0.05 ℃ / min to 0.7 ℃ / min, preferably 0.1 ℃ / min to 0.5 ℃ / min range proper. That is, if the cooling rate is too fast, the temperature at the point where the crystal is formed becomes too low, and the crystal is formed rapidly, making it difficult to remove impurities present in the crystal. In addition, when too slow, there is a problem that it is difficult to adjust to such a low cooling rate commercially and takes too much time. In addition, the final subcooling temperature can be a temperature range of -0 ℃ to -30 ℃ based on the initial temperature of the dimethyl carbonate raw material having a purity of 85% by weight, more preferably -5 ℃ to -25 ℃ proper. In other words, the supercooling temperature is directly related to the yield and purity of the crystal. If the supercooling temperature is too small, the yield of the crystal is low when the initial temperature is too small. One problem is that purification rarely occurs.

In addition, when a crystal is rapidly formed and grown at a certain moment, a substance in which the crystal is not formed is contained in the crystal, and it is difficult to separate it by crystallization. In this case, impurities are difficult to escape out of the crystal even after the post-treatment operation. This phenomenon is difficult to control only by the variables of cooling rate and supercooling temperature, so to solve this problem, at some point, an appropriate amount of seed is added to the crystallizer, and nuclei are formed from the seed and crystal grains grow large. Operation is required. As a seed, dimethyl carbonate in a solid state is suitable. The dimethyl carbonate should be administered in a solid state by maintaining it at a temperature of 2 to -2 ° C below the melting point of the dimethyl carbonate. If other materials were used as seeds, these materials, which were used as seeds in the final purified dimethyl carbonate, would remain as impurities and degrade the final purity. The amount of seed injected is about 0.02 to 1.5% by weight based on the total amount of raw material injected. If too small an amount is used as the seed, crystals cannot be formed from the seed, whereas too much In this case, crystals are rapidly formed and crystals may rapidly pack in the crystallizer. The seed timing is usually advantageous at the point where the crystal is first formed. That is, the temperature at which the crystal is formed varies depending on the initial injection concentration of dimethyl carbonate and the cooling rate. The timing of seed administration is shown in FIG. 1 when the cooling rate is 0.1 K / min and the initial mixture concentration is 85%. As such, for example, when seed is added based on -6 to -4 ° C, which is a temperature at which crystals are initially formed during cooling, it is effective, and yield and purity can be improved. If the input temperature is too low, crystals are already formed and the effect of seed injection cannot be exerted. If the input temperature is too high, crystal formation does not occur at all.

Usually, in order to further improve the purification efficiency in melt crystallization, a post-treatment operation after a crystallization operation is performed. As a post-treatment method, partial melting, washing, and migration methods are applied. In the case of a mixture containing dimethyl carbonate, the method of partial melting is considered to be appropriate because methanol, which is an amorphous substance, is contained as an impurity. This partial melting operation is to raise the crystals again based on the final temperature at which crystallization is completed, and to further remove residual impurities contained in the crystals. The temperature is variable. In other words, the heating rate for raising the temperature of the crystallizer is appropriate from about 0.1 ℃ / min to 0.5 ℃ / min, if the lower than this there is a problem that the yield of the crystal is lowered, conversely if too fast There is a problem that the purity is lowered. In addition, the final heating temperature is mainly related to the yield, it is possible to -10 ~ 20 ℃ based on the final heating temperature during crystallization, and more preferably -5 ~ 5 ℃. At this time, if the heating temperature is too low, there is a problem that the yield is increased, but impurities are not removed from the crystal, if too high, the crystal easily melts the crystal and the yield is sharply dropped.

By removing the impurities through the crystallization step and the partial melting step, an excessive amount of solvent due to extraction and azeotropic distillation, which is a problem in the separation and purification of dimethyl carbonate, is used in excess, or an increase in device cost when purification by a multi-stage distillation unit is performed. It is possible to separate and purify high purity dimethyl carbonate of more than 99% by weight while solving problems such as the complexity and the use of excessive energy operating at high temperature.

For reference, in the present invention, purity analysis uses gas chromatography (GC), a detector uses a flame ion detector, a GC column is 25 m long, 0.53 mm diameter, BP20 1.0 UM (SGE), The temperature was analyzed while raising the temperature from 60 ° C. to 150 ° C. at 10 ° C./min. Since the actual concentration of dimethyl carbonate and methanol was mixed with the analyzed result on GC, the mixture was mixed at a constant concentration to obtain a calibration curve between the actual concentration and the concentration analyzed at GC as shown in FIG. 1. Using this, the concentration of the actual purified sample was calculated.

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited to these Examples.

Example 1

120 g of a dimethyl carbonate mixture (raw material) having a purity of 85% by weight was injected into the cylindrical duramel crystallizer at room temperature, and crystallization was performed while lowering the temperature of the crystallizer jacket to a constant cooling rate of 0.1 ° C / min. The first nuclei were crystallized from these seeds by administering 0.12 g of seed (0.1% by weight of the total amount of the material) near −6 ° C. as the crystallization temperature of the crystallizer indicated in FIG. 1. As the temperature was continuously lowered, crystals slowly grew in the crystallizer and formed as a whole. When the final crystallization temperature reached -20 ° C, crystallization was stopped to open the bottom valve of the crystallizer to remove residual liquid which did not form into crystals. The yield was calculated by the difference in the amount of the residual liquid based on the amount of the mixed liquid initially injected, yielding a yield of about 75% by weight. Subsequently, in order to further increase the purity, the crystallizer temperature was gradually raised to 0.1 ° C / min for partial melting operation based on the temperature after crystallization, -20 ° C, and the temperature was raised to 0 ° C. Part of the crystals were melted by partial melting, and impurities contained in the crystals were removed into the crystals in solution. The samples were taken, and the purity was measured using gas chromatography, which was 95.7% by weight. The purity confirmed by was 99.2% by weight.

Comparative Example 1

In Example 1, the crystallization operation was performed in the same manner, and partial melting was not performed by the post-treatment operation. The final dimethyl carbonate had a purity of 98.2 wt%.

Examples 2-4 and Comparative Example 2

When the crystallization in the conditions of Example 1, the cooling rate is 0.2 ℃ / min (Example 2), 0.3 ℃ / min (Example 3), 0.5 ℃ / min (Example 4) and 1.0 ℃ / min (Comparative Example 2 And the respective conditions were the same as in Example 1. The purity of Comparative Example 2 was 99% by weight or less, and the yield was also very low, 15% by weight. Final purity and yield of the dimethyl carbonate obtained under each condition and the results of Comparative Example 2 are shown in Table 1.

division Example 2 Example 3 Example 4 Comparative Example 2 Cooling rate (℃ / min) 0.2 0.3 0.5 1.0 Purity (% by weight) 99.7 99.5 99.2 98.1 Yield (% by weight) 58 52 38 15

Examples 5 to 7 and Comparative Example 3

Example 5 (-10 ° C), Example 6 (-15 ° C), Example 7 (-25) based on the room temperature which is the holding temperature of the initial solution state of the crystal when crystallization under the conditions of Example 1 ℃) and Comparative Example 3 (-35 ℃) were carried out respectively, and the other conditions are the same as in Example 1. Final purity and yield of the dimethyl carbonate obtained under each condition and the results of Comparative Example 3 are shown in Table 2.

division Example 5 Example 6 Example 7 Comparative Example 3 Final Cooling Temperature (℃) -10 -15 -25 -35 Purity (% by weight) 99.9 99.7 99.1 97.2 Yield (% by weight) 62 60 51 22

Examples 8-10 and Comparative Example 4

The heating rate of partial melting after crystallization under the conditions of Example 1 was determined in Example 8 (0.2 ° C / min), Example 9 (0.3 ° C / min), Example 10 (0.5 ° C / min) and Comparative Example 4 (1.0). ° C / min) was carried out by changing, respectively, and other conditions are the same as in Example 1. Final purity and yield of the dimethyl carbonate obtained under each condition and the results of Comparative Example 4 are shown in Table 3.

division Example 8 Example 9 Example 10 Comparative Example 4 Heating rate during partial melting (℃ / min) 0.2 0.3 0.5 1.0 Purity (% by weight) 99.7 99.6 99.2 98.4 Yield (% by weight) 63 57 38 18

Examples 11 to 13 and Comparative Example 5

The final heating temperature of partial melting after crystallization under the conditions of Example 1 was changed to Example 11 (-5 ° C), Example 12 (-3 ° C), Example 13 (5 ° C) and Comparative Example 5 (15 ° C). The change was carried out respectively, and the other conditions are the same as in Example 1. Final purity and yield of the dimethyl carbonate obtained under each condition and the results of Comparative Example 5 are shown in Table 4.

division Example 11 Example 12 Example 13 Comparative Example 5 Final heating temperature at partial melting (℃) -5 -3 5 15 Purity (% by weight) 99.9 99.8 99.4 97.3 Yield (% by weight) 66 61 43 12

Examples 14-15 and Comparative Example 6

The amount of seed to be injected during crystallization under the conditions of Example 1 was determined in Example 14 (0.6 g, 0.5% by weight of raw material), Example 15 (1.2 g, 1% by weight of raw material) and Comparative Example 6 (0.012 g, raw material). 0.01 wt%), and the other conditions were the same as in Example 1. Final purity and yield of the dimethyl carbonate obtained under each condition and the results of Comparative Example 6 are shown in Table 5.

division Example 14 Example 15 Comparative Example 6 Seed injection amount (g) 0.6 1.2 0.012 Purity (% by weight) 99.5 99.8 97.3 Yield (% by weight) 62 61 60

As described above, the present invention uses an excessive amount of a solvent due to extraction and azeotropic distillation, which is a problem in the separation and purification of dimethyl carbonate, or increases the apparatus cost in the purification by a multi-stage distillation apparatus, complexity of the process and high In order to solve problems such as the use of excessive energy operated at temperature, methanol as an impurity can be separated from dimethyl carbonate by a film-melt crystallization method which can be operated in a simple apparatus without using any solvent, and also in the post-treatment process. It is possible to separate and purify high purity dimethyl carbonate of more than 99% by weight by gradually increasing the temperature of the crystal at a constant rate of partial sweating operation to dissolve a portion of the crystal and removing impurities contained in the crystal. .

Claims (3)

The raw material containing more than 85% by weight of dimethyl carbonate obtained from the transesterification of alkylene carbonate and methanol is cooled to -5 to -25 ℃ at a cooling rate of 0.05 ~ 0.7 ℃ / min at room temperature to crystallize under solvent-free conditions. , A method of separating 99% by weight or more of high-purity dimethyl carbonate by removing impurities contained in the crystal layer while heating the crystal again to -10 to 20 ° C. at a heating rate of 0.1 to 0.5 ° C./min by a post-treatment operation. The method of claim 1, wherein the raw material comprises 85 to 95% by weight of dimethyl carbonate and 5 to 15% by weight of methanol. The method of claim 1, wherein in the crystallization step, a seed of 0.02 to 1.5% by weight based on the weight of the raw material is added.

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