JP2003261306A - Method for separating gaseous chlorine and hydrogen chloride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for separating gaseous chlorine and hydrogen chloride capable of preventing precipitation of chlorine hydrate. <P>SOLUTION: When in a counter-flow gas-liquid contact apparatus 1 having two or more stages, hot gas comprising chlorine and hydrogen chloride is brought into contact with falling water fed from the uppermost stage 4 of the apparatus 1, whereby the gas is cooled, hydrogen chloride in the gas is dissolved in the falling water and drawn from the tower bottom 5 as hydrochloric acid and gaseous chlorine freed of hydrogen chloride is drawn from the tower top 8, part of the falling water is discharged from the bottom of the medium stage 3 under the condition of 0.1-1 MPa pressure in the apparatus 1 and this discharged water is fed into the apparatus 1 from the upper part of the medium stage 3 through piping 18. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating chlorine gas and hydrogen chloride by bringing hot gas containing chlorine and hydrogen chloride into contact with water.

[Prior art]

Chlorine is useful as an industrial raw material for vinyl chloride, phosgene and the like. Chlorine can be produced by oxidizing hydrogen chloride with oxygen. When hydrogen chloride is oxidized, a high-temperature gas containing impurities such as unreacted oxygen and unreacted hydrogen chloride in addition to chlorine is obtained, and purified chlorine is obtained by removing the impurities from this gas. Among the impurities, as a method for removing hydrogen chloride, for example, the hot gas is allowed to flow down in a countercurrent gas-liquid contactor such as a plate column or a packed tower (water flowing down in the countercurrent gas-liquid contactor). By contacting with, the gas is cooled, and hydrogen chloride in the gas is dissolved in water and extracted as hydrochloric acid from the bottom of the column,
A method of extracting chlorine gas from which hydrogen chloride has been removed from the top of the tower can be mentioned.

However, as described above, in the countercurrent gas-liquid contactor for contacting the gas containing chlorine with the flowing water, a part of chlorine is dissolved in the flowing water and exists as chlorine water. In water, chlorine hydrate (Cl ₂ .6H ₂ O or Cl
_{Sometimes 2} · 8H ₂ O) crystals are precipitated. When chlorine hydrate precipitates in the countercurrent gas-liquid contactor, it becomes a blockage to increase the pressure in the countercurrent gas-liquid contactor, and clogging of the blocker causes the spillage to flow to the top of the tower. In some cases, flooding may occur due to reverse flow.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for separating chlorine gas and hydrogen chloride which can prevent the precipitation of chlorine hydrate.

[0005]

Means for Solving the Problems In the course of intensive studies to solve the above-mentioned problems, the inventors have found that the equilibrium temperature of chlorine water and chlorine hydrate increases as the concentration of hydrogen chloride in chlorine water increases. It was found that the amount of chlorine hydrate decreased and the hydrate of chlorine was less likely to precipitate. Based on this finding, a part of the effluent (chlorine water) containing hydrogen chloride was discharged from any of the multiple stages in the countercurrent gas-liquid contactor to obtain discharged water, and this discharged water was If it is supplied into the countercurrent gas-liquid contactor from either the top of the discharged stage or the top of the column, the concentration of hydrogen chloride in the effluent increases, and the equilibrium temperature between the effluent (chlorine water) and the chlorine hydrate is increased. Therefore, the present invention has been completed by discovering a new fact that it is possible to prevent chlorine hydrate from precipitating in the column. Here, the equilibrium temperature between the flowing water (chlorine water) and the chlorine hydrate refers to the temperature at which the chlorine hydrate deposited in the chlorine water dissolves due to the temperature increase.

That is, the method for separating chlorine gas and hydrogen chloride according to the present invention uses a countercurrent gas-liquid contactor having a plurality of stages,
The hot gas containing chlorine and hydrogen chloride is cooled by bringing it into contact with the effluent supplied from the uppermost stage of the countercurrent gas-liquid contactor, and the hydrogen chloride in this gas is dissolved in the effluent to produce hydrochloric acid in the tower. When the chlorine gas withdrawn from the bottom and with hydrogen chloride removed is withdrawn from the top of the tower, the pressure in the countercurrent gas-liquid contactor is 0.1 MPa to 1 MPa.
Under the conditions of the above, the counterflow gas-liquid contactor has a plurality of stages, except for the lowest stage, to discharge a part of the flowing water to obtain discharged water, and discharge the discharged water. It is characterized in that it is supplied into the countercurrent gas-liquid contactor from either the upper part of the above stage or the top of the column.

In the above separation method of the present invention, when the concentration of hydrogen chloride in the flowing water increases, the vapor pressure of hydrogen chloride in the flowing water also increases. If such effluent water having a high hydrogen chloride vapor pressure exists near the tower top, a small amount of hydrogen chloride originating from the effluent water may be mixed in the chlorine gas extracted from the tower top.

[0008] Therefore, in order to make the chlorine gas extracted from the top of the column of higher purity, the present inventors mix the chlorine gas extracted from the top of the column with hydrogen chloride originating from the effluent. Without further, in addition to the above-mentioned separation method of the present invention, as a result of diligent study to develop a separation method of chlorine and hydrogen chloride capable of preventing the precipitation of chlorine hydrate in the tower,
Furthermore, if the concentration of hydrogen chloride in the uppermost liquid phase is set to 10% by weight or less, the vapor pressure of hydrogen chloride in the flowing water existing near the top of the tower will be kept sufficiently low, so the chlorine gas extracted from the top of the tower We have found a new fact that it is possible to prevent hydrogen chloride from being mixed in and at the same time prevent chlorine hydrate from depositing in the column.

That is, in the method for separating chlorine gas and hydrogen chloride of the present invention, in addition to the above separation method, the hydrogen chloride concentration in the uppermost liquid phase is preferably 10% by weight or less.

In the method for separating chlorine gas and hydrogen chloride of the present invention, it is more preferable that the temperature of hydrochloric acid extracted from the bottom of the column is 40 ° C. or higher. Since the solubility of chlorine gas in hydrochloric acid decreases at 40 ° C or higher, the recovery rate of chlorine gas extracted from the tower top is improved, and the purity of hydrochloric acid extracted from the tower bottom is improved.

In the method for separating chlorine gas and hydrogen chloride of the present invention, a part of the hydrochloric acid extracted from the bottom of the column is subjected to countercurrent flow from any stage located below the discharge stage after the temperature is adjusted. It can be fed into a gas-liquid contact device. In this way, when the hydrochloric acid is adjusted in temperature and then fed into the countercurrent gas-liquid contactor, the temperature of the hydrochloric acid extracted from the column bottom can be easily adjusted to, for example, 40 ° C. or higher. Further, the hydrochloric acid extracted from the bottom of the column contains a relatively high concentration of hydrogen chloride, but even if such hydrochloric acid is supplied from any of the stages below the discharge stage, it will flow down above the discharge stage. The hydrogen chloride concentration of the water is not affected and is maintained at a relatively low concentration, so that the hydrogen chloride is well absorbed by the effluent.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a countercurrent gas-liquid contactor 1 used in a method for separating chlorine gas and hydrogen chloride according to an embodiment of the present invention.
It is a schematic diagram showing (it is hereafter called "apparatus 1".).

In the present embodiment, in the apparatus 1 having a plurality of stages including the lowermost stage 2, the middle stage 3 and the uppermost stage 4 as shown in FIG. 1, under the condition that the pressure in the device 1 is 0.1 MPa to 1 MPa, The high temperature gas containing chlorine and hydrogen chloride supplied from the pipe 9 of the lower stage 2 is cooled by contacting it with the flowing water supplied from the pipe 10 of the uppermost stage 4, and the hydrogen chloride in this gas is dissolved in the flowing water. Hydrochloric acid is withdrawn from the pipe 22 at the bottom 5 of the column, and chlorine gas from which hydrogen chloride has been removed is withdrawn via the pipe 11 at the top 8. The hot gas is
300-4 obtained in the previous step of oxidizing hydrogen chloride with oxygen
It is a gas at 00 ° C. The chlorine gas extracted from the tower top 8 is sent to the next step (for example, the drying step) through the pipe 11. The lowermost stage 2 and the middle stage 3 of the apparatus 1 are provided with filling parts 6 and 7 filled with a filling material such as Raschig rings in order to efficiently bring the gas and the flowing water into contact with each other.

The temperature of the flowing water is adjusted to about 10 to 30 ° C. by the heat exchanger 16 in advance, and then the water is discharged from the pipe 10 to the apparatus 1.
And is uniformly supplied from the upper part of the filling section 7 of the middle stage 3 by the liquid distributor 20. When the temperature of the flowing water supplied from the pipe 10 is lower than 10 ° C., a portion of the apparatus 1 having a temperature lower than the equilibrium temperature is likely to be generated, and chlorine hydrate may be generated in this portion. Further, if the temperature of the flowing water supplied from the pipe 10 exceeds 30 ° C., the water vapor partial pressure near the top of the tower becomes high, and the water content of chlorine obtained increases, which is not preferable. The supplied effluent is supplied to the filling section 7
While flowing through the inside, it comes into contact with the high-temperature gas, is further supplied to the filling section 6 of the lowermost stage 2 through the chimney tray 21, and comes into contact with the high-temperature gas while flowing down through the filling section 6.

In the apparatus 1 as described above, not only hydrogen chloride is dissolved in the flowing water but also a part of chlorine gas is dissolved and exists as chlorine water, so that the chlorine in the flowing water flowing down in the apparatus 1 is chlorinated. By increasing the hydrogen concentration and lowering the equilibrium temperature between the effluent (chlorine water) and the chlorine hydrate, the temperature of the effluent is kept above the equilibrium temperature to prevent chlorine hydrate from precipitating. There is. That is, a part of the falling water in which hydrogen chloride in the high temperature gas is dissolved is discharged from the bottom of the middle stage 3 (discharging stage) by the pump 13 through the pipe 23, and the discharged water is discharged from the upper part of the middle stage 3 through the pipe 18 to the device 1 Are supplied within.

The hydrogen chloride concentration in the liquid phase of the uppermost stage 4 is preferably 10% by weight or less. If the hydrogen chloride concentration exceeds 10% by weight, the vapor pressure of hydrogen chloride in the flowing water cannot be kept sufficiently low, and thus a small amount of hydrogen chloride may be mixed in the chlorine gas extracted from the top of the column. Further, the concentration of hydrogen chloride is more preferably 2% by weight or more and 10% by weight or less, and further preferably 5% by weight or more and 10% by weight or less, from the viewpoint that the chlorine hydrate is more difficult to precipitate.

When the concentration of hydrogen chloride in the liquid phase of the uppermost stage 4 exceeds 10% by weight, the amount of the falling water supplied from the pipe 10 may be increased, for example. On the other hand, when the hydrogen chloride concentration is less than 2% by weight, for example, the supply amount of the flowing water supplied from the pipe 10 is reduced or the pipe 1
The flowing water supplied from 0 may contain hydrogen chloride. The supply amount and the hydrogen chloride concentration of the falling water supplied from these pipes 10 are determined by experiments and simulations performed in advance so that the hydrogen chloride concentration in the liquid phase of the uppermost stage 4 falls within the above range. In order to increase the concentration of hydrogen chloride in the liquid phase of the uppermost stage 4, for example, the discharged water discharged from the bottom of the middle stage 3 is added to the uppermost stage 4 (for example, near the tower top 8).
It may be supplied from.

In order to more reliably prevent the temperature of the flowing water in the apparatus 1 from falling below the equilibrium temperature, the middle stage 3
It is also possible to preliminarily adjust the temperature of the discharged water discharged from the device to a suitable temperature in the heat exchanger 15 before returning it into the device 1. The equilibrium temperature is determined by the pressure in the apparatus 1 and the concentration of hydrogen chloride in the flowing water, as shown in a test example described later.

Further, in the present embodiment, after the temperature of a part of the hydrochloric acid extracted from the pipe 22 at the bottom 5 of the column by the pump 12 is adjusted by the heat exchanger 14, it is placed below the middle stage 3 (discharging stage). It is supplied from the upper part of the lowermost stage 2 located through the pipe 17 into the apparatus 1, and the remaining hydrochloric acid is recovered through the pipe 19. The temperature of the hydrochloric acid adjusted in the heat exchanger 14 is 40 ° C.
It is adjusted so that it is above ℃. Moreover, in order to adjust the hydrogen chloride concentration of hydrochloric acid extracted from the bottom 5 of the column,
It is sufficient to adjust the supply amount of the effluent water supplied from. Also,
By using the falling water containing hydrogen chloride as the falling water supplied from the uppermost stage 4, the hydrogen chloride concentration of the hydrochloric acid extracted from the column bottom 5 can be adjusted.

According to the method for separating chlorine gas and hydrogen chloride as described above, when the concentration of hydrogen chloride in the high temperature gas supplied from the pipe 9 is, for example, about 10 to 30% by weight, it is extracted from the top 8 of the column. The concentration of hydrogen chloride in chlorine gas discharged is about 1
It is possible to reduce the concentration to ppm (weight ratio) or less, and it is possible to extract hydrochloric acid containing a small amount of impurities by adjusting the concentration from the bottom 5 of the column, and to prevent chlorine hydrate from precipitating in the apparatus 1. it can.

In the above embodiment, the case where the device 1 is provided with the filling portions 6 and 7 has been described, but the countercurrent gas-liquid contact device used in the present invention efficiently contacts gas and liquid. There is no particular limitation as long as it can be used, and for example, a packed column, a plate column, or the like can be used.

The heat exchangers 14, 15 and 16 include:
There is no particular limitation, and for example, a shell-and-tube cylindrical heat exchanger that is a partition wall heat exchanger, a plate heat exchanger, a spiral heat exchanger, or the like can be used, and the heat medium used for this is an aqueous solution of calcium chloride or sodium chloride. An aqueous solution, brine such as an aqueous solution of magnesium chloride, water, etc. can be used.

In the above embodiment, the case where the discharged water discharged from the bottom of the middle stage 3 is supplied from the upper part of the middle stage 3 has been described. However, it is supplied from the upper part of the middle stage 3, for example, the top 8 of the uppermost stage 4 or the like. You can also do it.

In the above-described embodiment, the case where the apparatus 1 having the three stages of the lowermost stage 2, the middle stage 3 and the uppermost stage 4 as shown in FIG. 1 is used is explained. The present invention can also be applied to the case of using a liquid contact device or a countercurrent gas-liquid contact device having four or more stages.

[0025]

EXAMPLES The present invention will be described in detail below with reference to test examples, but the present invention is not limited to the following test examples.

Test Example 1 Using the equilibrium temperature measuring device 34 shown in FIG. 2, the behavior of chlorine water and chlorine hydrate under normal pressure to high pressure was investigated. The equilibrium temperature measuring device 34 includes a pressure-resistant glass container 33 for containing water or hydrochloric acid, a brine bath 32 for adjusting the temperature in the container 33, and a pipe 25 for supplying chlorine gas to the container 33. , A pressure valve 29 for adjusting the pressure in the container 33, and the like. A mixture of methanol and water was used as the brine. <Experimental Method> 100 cm ³ of water was placed in the pressure resistant glass container 33 and sealed. A container 33 that opens the valve 26 and is closed through the pipe 25.
Chlorine gas was supplied to the inside, and water 24 in the container 33 was bubbled through the pipe 27. At this time, the pressure adjusting valve 29 was opened and closed to adjust the inside of the container 33 to a predetermined pressure. This pressure was measured by a pressure gauge 30. The brine 28 is circulated to circulate the water 24 in the glass container 33.
The temperature was lowered and chlorine hydrate was deposited. After the chlorine hydrate was deposited, the temperature was raised to dissolve the chlorine hydrate. The dissolution temperature at this time was defined as the equilibrium temperature between chlorine water and chlorine hydrate. This equilibrium temperature is measured by thermometer 3
1 was measured. Table 1 shows the measurement results of the equilibrium temperature at each pressure.

[Table 1]

Test Example 2 Using the equilibrium temperature measuring device 34 shown in FIG. 2, hydrochloric acid having a hydrogen chloride concentration of 0 to 20% by weight was placed in the container 33 and the pressure in the container 33 was set to 0.1 MPa. In the same manner as in Example 1, the equilibrium temperature between chlorine water and chlorine hydrate was measured.
Table 2 shows the measurement results of the equilibrium temperature at each concentration of hydrogen chloride.

[Table 2]

As shown in Table 2, it is understood that the equilibrium temperature between chlorine water and chlorine hydrate decreases as the concentration of hydrogen chloride increases.

[0029]

According to the present invention, it is possible to prevent the precipitation of chlorine hydrate in the countercurrent gas-liquid contact device.

Further, according to the present invention, when the concentration of hydrogen chloride in the uppermost liquid phase is set to 10% by weight or less, the mixing of hydrogen chloride in the chlorine gas extracted from the top of the column is suppressed, and the purity of hydrogen chloride is higher. There is an effect that a high chlorine gas can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing a countercurrent gas-liquid contactor used for separating chlorine gas and hydrogen chloride, which is an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an equilibrium temperature measuring device used in Test Examples 1 and 2 of the present invention.

[Explanation of symbols]

1 Countercurrent Gas-Liquid Contact Device 2 Bottom Stage 3 Middle Stage 4 Top Stage 5 Tower Bottom 6, 7 Packing Section 8 Tower Top 9, 10, 11, 17, 18, 19, 22, 23 Pipes 12, 13 Pumps 14, 15, 16 Heat Exchanger 20 Liquid Distributor 21 Chimney Tray

Claims (4)

[Claims] 1. A counterflow gas-liquid contactor having a plurality of stages,
The hot gas containing chlorine and hydrogen chloride is cooled by bringing it into contact with the effluent supplied from the uppermost stage of the countercurrent gas-liquid contactor, and the hydrogen chloride in this gas is dissolved in the effluent to produce hydrochloric acid in the tower. When the chlorine gas withdrawn from the bottom and with hydrogen chloride removed is withdrawn from the top of the tower, the pressure in the countercurrent gas-liquid contactor is 0.1 MPa to 1 MPa.
Under the conditions of the above, the counterflow gas-liquid contactor has a plurality of stages, except for the lowest stage, to discharge a part of the flowing water to obtain discharged water, and discharge the discharged water. A method for separating chlorine gas and hydrogen chloride, characterized in that the gas is supplied into the countercurrent gas-liquid contactor from either the upper part of the plate or the top of the column. 2. The method for separating chlorine gas from hydrogen chloride according to claim 1, wherein the concentration of hydrogen chloride in the uppermost liquid phase is 10% by weight or less. 3. The temperature of hydrochloric acid withdrawn from the bottom of the tower is 40.degree.
The method for separating chlorine gas and hydrogen chloride according to claim 1 or 2, which is as described above. 4. A part of the hydrochloric acid withdrawn from the bottom of the column is adjusted in temperature and then fed into the countercurrent gas-liquid contactor from any of the stages located below the stage from which the flowing water is discharged. The method for separating chlorine gas and hydrogen chloride according to claim 3.