KR101124824B1 - Method and apparatus for separating acetic acid from water - Google Patents

Abstract

The present invention is to produce a water crystal and acetic acid crystals by cooling the mixture of acetic acid used as a solvent in the preparation of aromatic dicarboxylic acid and water as a reaction by-product below the eutectic point to separate the water and acetic acid by the density difference It relates to a method and a separation device therefor. The separation method of the present invention can effectively separate a mixture of water and acetic acid while using less energy.

Terephthalic Acid, Acetic Acid, Separation, Dehydration Tower, Crystallization, Separation Tower

Description

Separation method of water and acetic acid and apparatus {METHOD AND APPARATUS FOR SEPARATING ACETIC ACID FROM WATER}

The present invention relates to a method for separating water and acetic acid and a separator used therein.

Aromatic dicarboxylic acid is a compound used as a raw material for a variety of products, specifically used as the main raw material of polyethylene terephthalate (PET), polyester fibers, polyester film for packaging and containers.

The aromatic dicarboxylic acid can be produced by the oxidation reaction of para xylene, which is generally used acetic acid as a solvent and cobalt (Co), manganese (Mn), bromine (Br) and the like as a catalyst In the process, water is produced as a by-product. Therefore, in order to maintain a constant concentration of water in the reactor, the produced water must be removed. At this time, the generated water is vaporized using the energy generated in the oxidation reaction and then condensed through a condenser to the outside of the reactor. Can be removed as it is discharged.

However, water and acetic acid have a boiling point difference of less than 20 ° C. and are well mixed. When water undergoes vaporization and condensation, acetic acid is also vaporized and condensed together, and it is difficult to separate water only from the condensate and discharge it out of the reactor. . Therefore, in order to recover and reuse only acetic acid in the discharged condensate, water and acetic acid are separated using a distillation column called a dehydration tower.

However, as described above, since water and acetic acid do not have a large difference in boiling point, the separation of the distillation column requires not only a large amount of energy but also a large number of stages of the distillation column.

Therefore, the azeotropic distillation method reduces the energy required for separation and reduces the number of stages of the distillation column by introducing an azeotrope which forms an azeotrope with water to increase the difference between boiling points of the acetic acid and azeotropes. Although azeotropic distillation techniques have been proposed, even azeotropic distillation techniques have limited limitations in lowering the boiling point of azeotrope, which still consumes a lot of energy. In addition, in order to separate the azeotrope that is discharged to the top of the distillation column with water and azeotropic agents to recover only the azeotropic agent, additional equipment such as a decanter is required, and due to frequent changes in process conditions, the azeotrope is not precisely formed. There is also a problem with a lot of loss.

On the other hand, in recent years, a membrane technology such as a membrane (membrane) that is not consumed for the separation of water and organic matter has been proposed, accordingly the membrane is applied to the separation of water and acetic acid. However, such a membrane technique is cumbersome to adjust the process conditions according to the ratio of water and acetic acid, and there is a limit in the life of the plant.

The present invention is to solve the above problems, to provide a separation method and a separation device of water and acetic acid that can efficiently separate the water and acetic acid using a low energy, and recover the separated water and acetic acid in high purity For that purpose.

The present invention to solve the above problems is a) supplying a mixture of water and acetic acid to the crystal bath; b) lowering said crystal bath below the eutectic temperature of said mixture to separately crystallize said water and said acetic acid; c) transferring the crystallized slurry containing water crystallization, acetic acid crystallization and water and an acetic acid mixture liquid crystallized in the crystal bath to a separation column; And d) separating the water crystals and the acetic acid crystals into the upper and lower portions of the separation column, respectively, by the difference in density in the crystal slurry in the separation column.

The present invention also provides a crystal bath for controlling the mixture of water and acetic acid below the eutectic temperature to separate and crystallize the water and the acetic acid; A separation tower separating the water crystallized and the acetic acid crystallized in the crystal tank into upper and lower portions by density differences, respectively; And a transfer line for transferring the water slurry, the acetic acid crystal, and a crystal slurry containing a mixture of water and acetic acid discharged from the crystal bath to the separation tower.

Since the separation method of water and acetic acid of the present invention and the separation device separates water and acetic acid through eutectic crystallization, only 20% or less of energy consumed when separating water and acetic acid using a conventional distillation column is used. In addition, water and acetic acid can be efficiently separated, and investment costs are also reduced by using general materials and simplifying equipment, thereby achieving economically superior effects. In addition, since the water crystal and acetic acid crystals are recovered through the impurity removal process (sweat operation) in the separation column, high purity water and acetic acid can be obtained.

Hereinafter, the present invention will be described in detail.

<Separation method of water and acetic acid>

The separation method of water and acetic acid of the present invention controls the degree of supersaturation of the crystal bath and separates the water crystals and the acetic acid crystals by the difference in density in the separation column. This separation process will be described with reference to FIG. 1.

a) step: feeding a mixture of water and acetic acid to the crystal bath

The mixture of water and acetic acid is fed to a crystal bath to separate. In this case, the mixture is preferably a by-product produced during the production of aromatic dicarboxylic acid, but is not limited thereto, and any mixture of water and acetic acid may be produced.

On the other hand, Figure 2 shows a state diagram of the mixture of water and acetic acid, water and acetic acid is a eutectic mixture and when cooled to the below-mentioned eutectic temperature -26.7 ℃ only one substance of water and acetic acid is crystallized. That is, if the acetic acid concentration in the mixture exceeds 60% by weight at the eutectic temperature, only acetic acid is crystallized up to -26.7 ° C and water is in a liquid state, and only water is up to -26.7 ° C when the acetic acid concentration is less than 60% by weight. Crystallized and acetic acid is present in the liquid state. When the mixture of water and acetic acid is cooled to below -26.7 ° C, which is a eutectic temperature, both water and acetic acid crystallize and exist in a crystalline state.

Therefore, since the order and temperature of crystallization in the crystal bath, the crystal formation amount, etc. may vary according to the acetic acid concentration in the mixture to be supplied, acetic acid is preferably mixed at an appropriate concentration. At this time, the preferred acetic acid concentration in the mixture is 60 to 80 parts by weight, more preferably 70 parts by weight based on the total weight of the mixture 100. For reference, the concentration refers to the content ratio of acetic acid mixed in the mixture.

In addition, the temperature of the mixture supplied to the crystal bath is sufficient to maintain the temperature of water and acetic acid, but considering that the concentration of acetic acid is higher than the concentration of water as shown in the state diagram of Figure 2 melting point of acetic acid Preference is given to maintaining at a level of at least 16.6 ° C.

b) step: crystallization of water and acetic acid

When a mixture of water and acetic acid is fed to a crystal bath, the temperature of the crystal bath is lowered below the eutectic temperature of the mixture to crystallize water and acetic acid, respectively. Here, the eutectic temperature refers to the lowest temperature at which the eutectic mixture melts, which is lower than the melting point of each of the mixed materials. Therefore, when the temperature of the crystal bath is lowered below the eutectic temperature of the mixture, the water and acetic acid contained in the mixture are separately crystallized. At this time, the temperature of the crystal bath (cooling temperature) may be adjusted to be below -26.7 ° C, which is a eutectic temperature of the water and acetic acid mixture, but if it is set too low, excessive crystals are generated to reduce the purity of the water and acetic acid crystals recovered. It is preferable to adjust to -26.7 ~ -36 ℃ because it can be wasted, the energy used for temperature control.

In addition, the crystallization time (cooling time) is 0.5 to 3 hours because it affects the recovery and purity of the separated water and acetic acid crystals depending on the time and speed of crystallizing water and acetic acid in the crystal bath. The speed (cooling rate) is preferably 0.1 to 5 ° C / minute.

In other words, the crystallization temperature, crystallization time and crystallization rate are the controlling factors for controlling the supersaturation of the crystallization tank. When the supersaturation is high, the crystallization rate and crystal growth rate are high, and the recovery rate of the crystallization is high. Purity of the separated crystals may be lowered. On the contrary, when the supersaturation is low, the rate of crystal nucleation and crystal growth is slowed down, and when separated, the purity is increased but the recovery rate is lowered. It is desirable to adjust.

On the other hand, when the water and acetic acid is purified in the crystal bath by adjusting the supersaturation control factor described above, the mixture of water and acetic acid supplied to the crystal bath forms a crystalline slurry that can be transferred to the separation tower later. That is, as the mixture of water and acetic acid crystallizes in a crystal bath, water crystals, acetic acid crystals, and crystalline slurries are composed of a mixed liquid in which water and acetic acid are mixed in a liquid state. Here, the amount of water crystals and acetic acid crystals contained in the crystal slurry present in the crystal bath is preferably 30 to 80 parts by weight based on the total weight of the crystal slurry 100, and particularly preferably 60 parts by weight. If the amount of water crystals and acetic acid crystals contained in the crystal slurry is less than 30 parts by weight, the recovery rate of water crystals and acetic acid crystals is lowered. If the amount of water crystals and acetic acid crystals is more than 80 parts by weight, the fluidity is lowered, so that the crystal slurry cannot be smoothly transferred to the separation tower, thereby recovering the crystals. And the purity falls.

c) step: transfer the crystal slurry to the separation column

The crystal slurry containing the crystallized water crystals and acetic acid crystals in the crystal bath is transferred to the separation column. At this time, if the crystallization capacity (cooling capacity) of the crystallization tank is insufficient, the amount of water and acetic acid crystals produced is small, and the crystallization is carried out through heat exchange without transferring some of the crystal slurry discharged from the crystallization column to the crystallizer for further crystallization. Can also be fed back into the tank.

d) step: water crystal and acetic acid crystal separation in separation column

The temperature of the separation column is controlled, and the water crystals contained in the crystal slurry are moved to the upper part of the separation column and the acetic acid crystals are moved to the lower part of the separation column by the density difference in the crystal slurry supplied to the separation column. Separate the crystals.

That is, the separation tower is controlled to a temperature higher than the crystal bath to separate the water and acetic acid crystals contained in the crystal slurry (since the crystallization is carried out in the separation column when controlled to the temperature of the crystal bath), the transfer to the separation tower As described above, the crystalline slurry is composed of a water crystal (ice), an acetic acid crystal, a mixed liquid in which water and acetic acid are mixed in a liquid state. Here, the density of the mixed liquid is greater than that of the water crystal, and the density of the acetic acid crystal is greater than that of the mixed liquid, so that the water crystal moves to the upper part of the separation column as it floats in the mixed liquid by buoyancy, and the acetic acid sinks in the mixed liquid by gravity and separates the separation column. Water crystals and acetic acid crystals separate as they move to the bottom of.

The temperature of the separation column is preferably controlled at -26.7 ~ -28 ℃, which is higher than the temperature of the crystal bath and not higher than the eutectic temperature of the water and acetic acid mixture to separate the water and acetic acid crystals contained in the crystal slurry, respectively. . In this case, the temperature of the separation tower may be specifically defined as the temperature of the center of the separation tower, which is a region where water crystals and acetic acid crystals start to separate.

In addition, if the time for separating the water and acetic acid crystals in the separation tower (operation time of the separation tower) is too short, the water and acetic acid crystals are not sufficiently separated, the recovery rate of the crystal may be reduced, if too long, the crystallization in the separation tower The separation time is preferably adjusted to 1 to 5 hours because it can proceed and the operating efficiency is also reduced.

Meanwhile, the recovery and purity of the crystals may also vary depending on the amount of water crystals and acetic acid crystals present in the separation column. Therefore, the amount of water crystals and acetic acid crystals present in the separation column is preferably 3 to 20 parts by weight, specifically 3 to 10 parts by weight based on the total weight of the crystal slurry present in the separation column. At this time, the amount of water crystals and acetic acid crystals present in the separation column may vary depending on the amount of crystals contained in the crystal slurry discharged from the crystal bath, but the amount of crystals present by adjusting the size of the separation column and the temperature of the separation column. You can also adjust

Here, the liquid water and acetic acid mixed liquid discharged without separation in the separation column is supplied back to the crystal bath and recovered as water crystals and acetic acid crystals through recrystallization and reseparation. This recycling process may be performed after the following impurity removal step.

e) step: removing impurities from the separated water and acetic acid crystals

The separation method of water and acetic acid of the present invention is a process of removing impurities present in the water and acetic acid crystals separated into the upper and lower portions of the separation column, respectively, in order to recover the water and acetic acid crystals with high purity. sweating)).

Impurities including acetic acid may be present on the surface of the water crystal separated in the upper part of the separation column, as is the surface of the acetic acid crystal separated in the lower part. Therefore, the present invention can remove impurities present in the water crystal and acetic acid crystal surface by adjusting the upper and lower portions of the separation column to the temperature near the melting point of water and acetic acid, respectively.

Here, based on the melting point of each of the water and acetic acid, if the temperature of the top and bottom of the separation column is too high than the melting point, impurities can be removed completely, but the recovery size is too small, the recovery rate is too low, too low than the melting point If the impurities are not properly removed, it is difficult to recover the crystal with high purity, so it is preferable to adjust the upper part of the separation tower to a temperature range of 0 to 5 ° C. and the lower part of the separation tower to a temperature range of 16.6 to 25 ° C.

On the other hand, it is preferable that the weight of each of the water crystals and the acetic acid crystals recovered after the impurities are removed to increase the recovery rate while completely removing the impurities is 70 to 80% of the crystal weight separated from the separation column.

<Separation device of water and acetic acid>

Separation device of water and acetic acid according to the present invention includes a crystal bath, separation tower, transfer line. 3 shows the configuration of the separation device of the present invention. Referring to FIG. 3, the separation device of the present invention will be described in detail as follows.

The crystal bath 100 controls the mixture of water and acetic acid below the eutectic temperature to separate and crystallize water and acetic acid, respectively. The crystal bath 100 may be operated only at a temperature below the eutectic temperature in order to crystallize the water and acetic acid contained in the mixture, respectively, but at -26.7 to -36 ° C to increase the operating efficiency and appropriately control the amount of crystals produced. It is preferable to operate.

Meanwhile, in order to control the temperature of the crystal bath 100 as described above, a freezer or a cooling jacket is provided outside the crystal bath 100 so that the refrigerant circulates directly outside the crystal bath or is cooled by the refrigerant. You can also configure this jacket to cycle.

Here, as the crystal bath 100 is controlled to below the eutectic temperature of the mixture by the above-mentioned freezer or cooling jacket, water and acetic acid are separately crystallized. In this case, since the wall of the crystal bath 100 is in contact with the refrigerant, Is mainly produced by accumulation on walls. Therefore, in order to promote the growth of the crystal by moving the crystal generated on the wall inside the crystal tank 100, a scraper 110 for scraping the generated crystal can be provided.

At this time, the rotational speed of the scraper 110 may affect the recovery and purity of the crystal is preferably operated at 5 ~ 50rpm. When the crystallization of the crystal bath 100 proceeds rapidly and the crystal growth rate is fast, the scraper 110 scrapes the crystal at a slow rate, and the recovery rate decreases. On the other hand, when the crystallization progresses slowly and the crystal growth rate is slow, the scraper 110. This is because scraping the crystal at a high speed lowers the purity of the separated crystal.

In addition, a heat exchanger 120 may be provided outside the crystal bath 100 so that additional cooling energy may be supplied when the cooling capacity of the crystal bath 100 is insufficient.

Separation tower 200 separates the water crystal and acetic acid crystallized in the crystal tank 100 by moving to the upper and lower, respectively, by the density difference. That is, the separation tower 200 is operated at a higher temperature than the crystal bath 100 and the water crystal and acetic acid crystal due to the density difference in the crystal slurry including the water crystal and the acetic acid crystal transferred through the transfer line 300 to be described later. To separate. At this time, the temperature of the separation tower 200 may be adjusted to a level higher than the temperature of the crystal bath 100 and not higher than the eutectic temperature of the mixture, but is preferably adjusted to -26.7 to -28 ° C in consideration of process efficiency.

The separation tower 200 includes a water crystal storage unit 210, acetic acid crystal storage unit 220, coexistence unit 230, temperature control unit 240 to control the temperature to separate and recover the crystal with high purity This is described in detail below.

The water crystal storage unit 210 is provided on the separation tower 200 to store the separated water crystals. That is, as described above, the water crystal having a lower density than the mixed liquid in the crystal slurry moves to the upper portion of the separation tower 200 by buoyancy, and the water crystal storage unit 210 stores the moved water crystal. .

Here, impurities may exist on the surface of the water crystal stored in the water crystal storage unit 210. In order to remove such impurities, the water crystal storage unit 210 is preferably maintained at a temperature in the range of 0 ~ 5 ℃. This is because if the temperature of the water crystal storage 210 is too high, the recovery rate of the crystal decreases. In addition, when the impurities are removed while maintaining the temperature range as described above, the weight of the water crystals recovered after the impurities are removed in consideration of the recovery and purity of the crystals is preferably 70 to 80% of the crystal weight at the time of separation. .

The acetic acid crystal storage unit 220 is provided under the separation column 200 to store the separated acetic acid crystals. That is, as described above, the acetic acid crystal having a higher density than the mixed liquid in the crystal slurry is moved to the lower part of the separation column 200 by gravity, and the acetic acid crystal storage unit 220 stores the acetic acid crystal thus moved. .

Here, an acetic acid crystal surface stored in the acetic acid crystal storage unit 220 may also have impurities, and in order to remove such impurities, the acetic acid crystal storage unit 220 may also be maintained at a temperature in the range of 16.6 to 25 ° C. This is because if the temperature of the acetic acid crystal storage unit 220 is too high, the recovery rate of the crystal decreases. In addition, when the impurities are removed while maintaining the temperature range as described above, it is preferable that the weight of the acetic acid crystals recovered after the impurities are removed in consideration of the recovery and purity of the crystals is 70 to 80% of the crystal weight at the time of separation. Do.

Coexistence unit 230 is provided in the center of the separation tower 200, where the water and acetic acid crystals start to move to the upper and lower portions of the separation column due to the density difference in the crystal slurry, respectively, the water and acetic acid crystals This is where the acetic acid and the water contained in the crystal slurry coexist in the liquid state. The coexistence unit 230 is preferably maintained at a temperature in the range of -26.7 ~ -28 ℃ so that the water and acetic acid crystals can be separated while suppressing the crystallization of the crystal slurry.

The temperature controller 240 adjusts the temperature of the water crystal storage 210, the acetic acid crystal storage 220 and the coexistence 230. At this time, the water crystal storage unit 210 and the acetic acid crystal storage unit 220 is a heater or heater is applied to adjust the temperature according to each zone, the coexistence unit 230 is the outside of the crystal bath 100 The freezer or cooling jacket used in the present invention may be applied.

On the other hand, the separation tower 200 is preferably used that the ratio of height / diameter is 1 ~ 10. When the ratio of height / diameter of the separation tower 200 is less than 1, the separation of water crystals and acetic acid crystals may not be properly performed because the interval in which the crystal slurry existing in the separation tower 200 may be separated by a density difference is not large. If it exceeds 10, the separation space is sufficient, so that the water crystal and acetic acid crystal separation is good, but the investment cost rises and economic efficiency is low.

In addition, the agitator 250 may be provided in the separation tower 200 so that the water crystal and the acetic acid crystal do not aggregate and exist in the form of particles.

The transfer line 300 is provided to transfer a crystal slurry containing water crystals and acetic acid crystals discharged from the crystal tank 100 to the separation tower 200.

Such a separation apparatus of the present invention can be operated in a batch or continuous manner, in which the crystallization and separation process is separated into a separate tank and a separation column to separate the mixture of water and acetic acid, respectively, the process temperature (Crystallization temperature, separation tower temperature) and the ratio of crystallization produced can be efficiently adjusted according to the crystallization and separation process, it is possible to increase the recovery rate and purity of water and acetic acid.

The above-described method and apparatus for separating water and acetic acid of the present invention can efficiently separate water and acetic acid using only 20% or less of energy consumed when water and acetic acid are separated using a conventional distillation column. have. That is, in order to separate water and acetic acid using a conventional distillation column, the amount of heat must be supplied from Reboiler as much as the heat of vaporization of water and the amount thereof is 540 kcal / kg, whereas in the present invention, a cooling means (chiller or cooling jacket) is used to crystallize water and acetic acid. This cooling means can significantly save energy because only 60% of 123 kcal / kg of water, which is the coagulation heat of water and 76 kcal / kg of acetic acid, is supplied. In addition, the present invention consists of only the configuration of the crystal tank and the separation tower is simple and the equipment can be increased as a result of the investment cost is reduced by using a general-purpose material, resulting in economic efficiency.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

Example 1 Measurement of Water and Acetic Acid Concentration According to Crystallization Temperature

A mixture of water and acetic acid having an acetic acid concentration of 60 parts by weight was supplied to a crystal bath (inner diameter of 10 cm and height of 10 cm) with a scraper rotating at 18 rpm, and the mixture was crystallized for 3 hours (cooling time) at various crystallization temperatures (cooling temperatures). Then, the mixture was transferred to a separation column (inner diameter of 10 cm and height of 40 cm) to recover a liquid and a crystal of water and acetic acid from the upper part of the separation tower, and the concentrations of water and acetic acid contained in each were measured. Table 1 shows.

[Table 1]

Crystallization temperature (℃) -31.5 -31.0 -30.0 -29.7 -29.5 -28.8 -28.5 Liquid Acetic acid concentration 53.7 51.4 48.6 45.0 41.2 42.4 41.4 Water concentration 46.3 48.6 51.4 55 58.8 57.6 58.6 Solid (part by weight) Acetic acid concentration 40.1 41.6 26.2 32.7 24.0 23.7 23.6 Water concentration 59.9 58.4 73.8 67.3 76 76.3 76.4

Referring to Table 1, it was found that the lower the crystallization temperature, the higher the concentration of acetic acid crystals (Solid) and acetic acid (Liquid) in the separation column. These results indicate that the degree of supersaturation increases with the crystallization temperature, so that acetic acid may be incorporated in the upper part of the separation column in which the water crystal is present.

Example 2 Measurement of Water and Acetic Acid Concentration According to Crystallization Time

The same separation apparatus and mixture as in Example 1 were used, and the crystallization temperature was fixed at -28 ° C., whereby a liquid and a solid mixture of water and acetic acid in the upper part of the separation column according to the crystallization time were recovered and included in each. The concentration of acetic acid and acetic acid was measured, and the results are shown in Table 2.

TABLE 2

Crystallization time (hr) 2 3 4 5 6 8 Liquid Acetic acid concentration 36.5 27.9 32.3 27.9 20.2 20.8 Water concentration 63.5 72.1 67.7 72.1 79.8 79.2 Solid (part by weight) Acetic acid concentration 29.8 22.8 24.3 19.0 10.2 19.5 Water concentration 70.2 77.2 75.7 81.0 89.8 80.5

Referring to Table 2, it can be seen that as the crystallization time increases, the concentration of acetic acid crystals (Solid) and acetic acid (Liquid) in the top of the separation column decreases to increase the purity of the water crystals. However, after 3 hours, the purity of water crystals decreased, and even at 8 hours, the purity decreased compared to 6 hours. These results indicate that as the crystallization time increases, the rate of crystallization increases, so that the acetic acid crystals move to the top of the separation column to decrease the purity of the water crystals. Therefore, the crystallization time in the crystal bath does not exceed 3 hours. The preferable thing was confirmed.

Example 3 Measurement of Water and Acetic Acid Concentration According to Separation Column Location

The same separation apparatus and mixture as in Example 1 were used, and the crystallization temperature was -28 ° C and the crystallization time was 3 hours, thereby recovering a liquid and a solid solution of water and acetic acid according to the separation column position. The concentrations of water and acetic acid contained in were measured, and the results are shown in Table 3.

[Table 3]

Height (cm) from bottom of divider 10 20 30 40 Liquid Acetic acid concentration 52 50 32 17 Water concentration 48 50 68 83 Solid (part by weight) Acetic acid concentration 87 65 47 10 Water concentration 23 35 53 90

Referring to Table 3, it was confirmed that the concentration of water crystal (Solid) and water (Liquid) is high in the upper part of the separation column, the concentration of acetic acid crystal (Solid) and acetic acid (Liquid) is high in the lower part of the separation column. This result confirms that the mixture of water and acetic acid is separated into the upper and lower portions of the separation column after crystallization.

Example 4 Relation between Cooling Temperature and Sweating Temperature

Using the same separator as in Example 1, the water and acetic acid mixture having an acetic acid concentration of 50 parts by weight was crystallized at -28.7 ° C for 3 hours, and the mixture of water and acetic acid having an acetic acid concentration of 60 parts by weight was crystallized at -29.5 ° C. After each supply to the separation tower. The water crystals supplied to the separation tower and then separated into the upper part of the separation column were removed impurities at various temperatures, and the acetic acid concentration included in the water crystals was measured. The results are shown in Table 4 below.

[Table 4]

Contained in the mixture
Acetic acid concentration (part by weight) Crystallization temperature
(℃) Concentration
(Parts by weight) Sweating temperature (℃) -15 -10 -5 0 3 50 -28.7 Acetic acid concentration 19.8 26.9 15.9 6.1 1.0 Water concentration 80.2 73.1 84.1 93.9 99.0 60 -29.5 Acetic acid concentration 59.4 48.2 31.7 19.7 3.5 Water concentration 40.6 51.8 68.3 80.3 96.5

Referring to Table 4, it can be seen that the purity of the crystal increases as the sweating temperature of the water crystal increases. At this time, when the crystallization temperature is -28.7 ° C, the crystallization and separation are better than the case where the crystallization temperature is -29.5 ° C. Even though impurities were removed from, it was found that the purity of crystals was relatively higher. In addition, the purity of the water crystal was confirmed that the higher the purity when removing impurities at 0 ℃ or more.

Example 5 Measurement of Recovery Rate According to Crystallization Temperature and Impurity Removal Temperature

Using the same separator and mixture as in Example 1, each crystallized at various crystallization temperatures for 3 hours, and then recovered the water crystals present in the upper part of the separation column to measure the weight. Then, the weight of the water crystal was measured and the impurities were removed in order to increase the temperature of the water crystal, and the weight of the water crystal was measured. Compared to the weight of the water crystal before the impurity was removed, the reduced weight change rate is shown in Table 5.

TABLE 5

Crystallization temperature (℃) Sweating temperature (℃) -15 -10 -5 0 3 -28.0 100 83 59 24 0 -28.7 100 92 80 59 0 -29.0 100 70 0 0 0 -29.5 100 68 45 26 0 -30.5 100 69 47 31 0

Referring to Table 5, as the sweating temperature increases, the amount of recovered water crystals decreases, but the crystallized temperature crystallized at -28.7 ° C crystallizes and separates well, so the water crystals recovered even when the sweating temperature increases. (When 0 ° C.), the change in weight was not large. These results indicate that by selecting the appropriate crystallization temperature, firstly growing and separating the crystals correctly and removing the impurities, crystals of high purity can be obtained without reducing the recovery rate.

Example 6 Relationship between Crystallization Temperature and Scraper Rotational Speed

The same separators and mixtures as in Example 1 were used, and the crystallization temperatures were varied for crystallization for 3 hours each. At this time, the rotation speed of the scraper in the crystal bath was fixed at 18 rpm. Thereafter, the crystals were separated by moving to a separation column, and water and acetic acid concentrations in the crystals were measured after removing the water crystals recovered therefrom at various temperatures, and the results are shown in Table 6.

TABLE 6

Crystallization temperature (℃) Concentration
(Parts by weight) Sweating temperature (℃) -15 -10 -5 0 3 -28.5 Acetic acid concentration 37.3 26.9 16.0 6.1 0.98 Water concentration 62.7 73.1 84.0 93.9 99.02 -29.0 Acetic acid concentration 36.6 32.3 14.6 3.45 - Water concentration 63.4 67.7 85.4 96.55 - -30.0 Acetic acid concentration 48.8 47.6 40.9 26.0 - Water concentration 51.2 52.4 59.1 74.0 -

Referring to Table 6, it can be seen that when the rotational speed of the scraper is 18rpm, the crystallization temperature is adjusted to -28.5 ° C to facilitate crystallization and separation, and the purity of the water crystal decreases as the crystallization temperature is lowered. Could. These results confirm that the lower the crystallization temperature should increase the rotational speed of the scraper. This is because the lower the crystallization temperature, the more crystals are formed on the walls of the crystal bath, and the more quickly scraped it out, the better the crystal growth and the better the recovery rate.

Example 7 Crystallization Ratio Measurement According to Crystallization Temperature and Time

By using the same separation apparatus and mixture as in Example 1 and varying the crystallization temperature, the crystal ratio (the amount of water crystal and acetic acid crystal contained in the crystal slurry) was measured according to the crystallization time. It is shown in Table 7 below.

TABLE 7

Crystallization temperature (℃) Crystal ratio in the separation column (parts by weight) 1 hour later 2 hours later 3 hours later 4 hours later 5 hours later -28.5 - 3 7 - - -29.5 9 12 16 19 - -30.5 - - 17 19 21 -31.5 - - 18 20 -

Referring to Table 7, it can be seen that the crystal ratio in the separation column decreases with increasing crystallization temperature and increases with increasing crystallization time.

Example 8 Measurement of Crystal Particle Size According to Crystallization Temperature and Time

The same separation apparatus and mixture as in Example 1 were used, and the crystallization temperature and crystallization time were changed to measure the size (μm) of the water crystals and the acetic acid crystals separated into the upper and lower portions of the separation column, and the results are shown in Table 8. It was.

[Table 8]

Crystallization temperature (℃) location Crystallization time 1 hours 2 hours 3 hours 4 hours 5 hours -30.0 Top (water crystal size) - 64.80 106.73 83.86 76.24 -30.5 Top (water crystal size) 95.30 104.19 - - - Lower part (acetic acid crystal size) - - 114.36 135.32 242 -31.0 Top (water crystal size) 53.37 - 68.25 129.67 122.84 Lower part (acetic acid crystal size) - - - 307.11 78.48 -31.5 Top (water crystal size) - 68.61 85.77 53.37 38.12 Lower part (acetic acid crystal size) - - 190.59 185.77 - -32.0 Top (water crystal size) 88.72 119.43 - - - Lower part (acetic acid crystal size) - 272.98 270.62 - -

Referring to Table 8, the crystal grain size was hardly affected by the crystallization temperature, but it was confirmed that the grain size increases as the crystallization time increases. At this time, since the crystal grain size is rather reduced after the crystallization time passes 4 hours or 5 hours, the crystallization time is preferably not more than 3 hours as mentioned above.

Example 9 Relationship between Crystal Ratio and Crystal Purity

Using the same separator and mixture as in Example 1, crystallization was carried out at -32 ° C in a crystal bath and transferred to the separation tower to raise the temperature of the separation tower to -27 ° C, reducing the crystal ratio at the top and bottom of the separation tower. The acetic acid concentration of the crystals present was measured twice, and the results are shown in Table 9 below.

TABLE 9

Number of times location Crystal ratio (part by weight) 50 parts by weight 35 parts by weight 15 parts by weight 7 parts by weight 3 parts by weight 1 time Top 37 32 29 27 25 bottom 62 62 63 68 76 Episode 2 Top 32 33 29 23 22 bottom 63 64 68 72 78

Referring to Table 9, when the ratio of crystals in the separation column is high (50 parts by weight), there is not enough space to separate the acetic acid crystals and water crystals. (Part by weight) of acetic acid at the top of the separation column was found to be high. On the other hand, when the crystal ratio in the separation column is 10 parts by weight or less, the concentration of acetic acid in the upper part of the separation tower was reduced to around 20% and the acetic acid concentration in the lower portion was confirmed to increase to about 80%. This point confirms that it is most preferable to set the crystal ratio in the separation column to 10 parts by weight or less.

1 is a flow chart showing a separation process of water and acetic acid of the present invention in a continuous process.

2 is a state diagram for explaining the principle of eutectic crystallization of water and acetic acid mixture.

3 is a block diagram of an apparatus for separating water and acetic acid according to the present invention.

<Brief Description of Drawings>

100: crystal

200: separation tower

300: transfer line

Claims (18)

a) feeding to a crystal bath a mixture of water and acetic acid, the mixture having an acetic acid concentration of 50 to 80 parts by weight, based on the total weight of the mixture 100; b) lowering said crystal bath below the eutectic temperature of said mixture to separately crystallize said water and said acetic acid; c) transferring the crystallized slurry containing water crystallization, acetic acid crystallization and water and an acetic acid mixture liquid crystallized in the crystal bath to a separation column; And d) separating the water crystal and the acetic acid crystal into the upper and lower portions of the separation column, respectively, by the difference in density in the crystal slurry in the separation column. The method of claim 1, The crystal bath temperature of step b) is -26.7 ~ -36 ℃ separation method of water and acetic acid, characterized in that it is adjusted. The method of claim 1, Separating method of water and acetic acid, characterized in that the time to crystallize the mixture in the crystal bath of step b) is adjusted to 0.5 to 3 hours. The method of claim 1, Separating method of water and acetic acid, characterized in that the rate of crystallization of the mixture in the crystal bath of step b) is adjusted to 0.1 ~ 5 ℃ / min. The method of claim 1, The amount of the water crystal and the acetic acid crystal produced in the crystal bath of step b) is 30 to 80 parts by weight based on the total weight of 100 of the crystal slurry present in the crystal bath. . The method of claim 1, The separation tower temperature of step d) is -26.7 ~ -28 ℃ characterized in that the separation method of water and acetic acid. The method of claim 1, Separating method of water and acetic acid, characterized in that the time for separating the water crystals and the acetic acid crystals in the separation column is adjusted to 1 to 5 hours. The method of claim 1, The amount of the water crystal and the acetic acid crystal present in the separation column of step d) is 3 to 20 parts by weight based on the total weight 100 of the crystal slurry present in the separation column. The method of claim 1, e) The temperature of the separation column is adjusted to 0 ~ 5 ℃ near the melting point of the water, the temperature of the bottom of the separation column is adjusted to 16.6 ~ 25 ℃ near the melting point of the acetic acid to the water crystal and the acetic acid Separation method of water and acetic acid, characterized in that it further comprises the step of removing impurities present in. The method according to claim 1 or 9, And re-crystallizing and re-separating the mixed solution of water and acetic acid discharged to the outside from the separation tower to the crystal bath. A mixture of water and acetic acid, the crystal bath for separating and crystallizing the water and the acetic acid, respectively, by adjusting the mixture having an acetic acid concentration of 50 to 80 parts by weight based on the total weight of the mixture to below the eutectic temperature; A separation tower separating the water crystallized and the acetic acid crystallized in the crystal tank into upper and lower portions by density differences, respectively; And And a transfer line for transferring the crystal slurry containing the water crystal, the acetic acid crystal and the mixed liquid of water and acetic acid discharged from the crystal bath to the separation tower. The method of claim 11, Separation device of water and acetic acid, characterized in that the temperature of the crystal bath is -26.7 ~ -36 ℃. The method of claim 11, And a scraper for scraping the crystallized water crystals and the acetic acid crystals into the crystal bath. The method of claim 13, Separation device of water and acetic acid, characterized in that the rotational speed of the scraper is 5 ~ 50rpm. The method of claim 11, Separation device of water and acetic acid, characterized in that the temperature of the separation column is -26.7 ~ -28 ℃. The method of claim 11, The separation tower, A water crystal storage unit disposed above the separation column to store the water crystal; An acetic acid crystal storage unit provided below the separation column to store the acetic acid crystals; A coexistence unit provided at a center of the separation tower, wherein the water and acetic acid coexist in a liquid state in the crystal slurry; And Separation device for water and acetic acid, characterized in that it comprises a temperature control unit for adjusting the temperature of the water crystal storage unit, the acetic acid crystal storage unit, the coexistence unit. The method of claim 16, The temperature of the water crystal storage unit is 0 ~ 5 ℃, the temperature of the acetic acid crystal storage unit is 16.6 ~ 25 ℃, the coexistence unit is -26.7 ~ -28 ℃ characterized in that the separation device of water and acetic acid. The method of claim 11, Separation device of water and acetic acid, characterized in that the ratio of the height / diameter of the separation column is 1 ~ 10.

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