JP2909253B2 - How to concentrate chlorine gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for concentrating chlorine using a pressure swing adsorption method.

[0002]

BACKGROUND OF THE INVENTION Chlorine is a very important industrial intermediate and is used in many chemical industries, and there are facilities for chlorine separation in various places. Conventionally, to separate chlorine from gas containing chlorine, pressurizing and cooling the gas to form liquid chlorine and separating it from the gas, or by stripping the solvent in which chlorine is absorbed by a chlorine-based organic solvent Methods for separating chlorine are known.

However, the former method uses a high-pressure gas, and therefore requires a gas compressor and a refrigeration facility which are expensive and troublesome for maintenance. Particularly, when separating chlorine from a gas having a relatively low chlorine concentration, Operation at very high pressure or cryogenic temperature increases equipment costs. In the latter method, carbon tetrachloride is usually used as a solvent. However, the use of carbon tetrachloride has been banned due to environmental problems due to the recent chlorofluorocarbon gas, and cannot be said to be an effective method in the future.

[0004]

One of the methods for separating chlorine from a chlorine-containing gas is a pressure swing adsorption method (hereinafter abbreviated as PSA method). However, this separation method has the following problems. (1) Since the gas supply is stopped before the adsorption tower reaches the equilibrium adsorption state with chlorine, a part of the adsorbent on the upper part of the adsorption tower remains unused. (2) Since the gas supply is stopped before the adsorption tower reaches the equilibrium adsorption state with chlorine, another component gas is adsorbed by the non-adsorbed adsorbent in the upper part of the adsorption tower, and the chlorine concentration decreases. (3) Chlorine leaks slightly from the outlet side of the adsorption tower. An object of the present invention is to provide a method for efficiently separating and concentrating chlorine from a gas containing chlorine without the above problems.

[0005]

Means for Solving the Problems The present inventors have intensively studied a method for concentrating chlorine gas which does not have the above-mentioned problems, and cascade-connected an adsorption tower filled with an adsorbent capable of adsorbing chlorine to form a chlorine gas. Is introduced until the first adsorption tower reaches the equilibrium adsorption state with chlorine to adsorb the chlorine, while the second adsorption tower is a gas containing a small amount of chlorine flowing out from the outlet of the first adsorption tower. By adsorbing the chlorine inside, it is adsorbed without getting chlorine from the adsorption tower in the adsorption process,
After desorption, it was found that a high concentration of chlorine could be concentrated, and the present invention was achieved.

That is, according to the present invention , an adsorption tower filled with an adsorbent capable of adsorbing chlorine is connected in cascade, and a chlorine-containing raw material gas is introduced until the first adsorption tower reaches an equilibrium adsorption state with chlorine. Adsorption, during which the second adsorption tower
By adsorbing chlorine in the gas containing a small amount of chlorine flowing out from the outlet of the adsorption tower, it was adsorbed without receiving chlorine from the adsorption tower in the adsorption step , and the first adsorption tower reached an equilibrium adsorption state with chlorine. After the introduction of gas is stopped, desorption is performed at a pressure lower than that at the time of gas introduction, a gas having a chlorine concentration higher than the chlorine concentration of the introduced gas is obtained, and the adsorbent is regenerated, and the chlorine gas concentrating method is characterized in that is there.

The chlorine-containing gas to which the method of the present invention is applied may include oxygen, nitrogen, carbon dioxide, carbon monoxide, hydrogen, hydrocarbons such as argon and methane as gases other than chlorine. However, in order to separate chlorine from gases containing them by the pressure swing adsorption method, it is necessary to select one having a sufficiently different adsorption affinity between these gases and the adsorbent as compared with chlorine.

Accordingly, as the chlorine adsorbent used in the method of the present invention, a carbonaceous adsorbent such as synthetic and natural zeolites, non-zeolitic porous acidic oxides, activated carbon and molecular sieve carbon is selected. For example, the zeolite includes A-type, X-type, Y-type, L-type, ZSM-type, natural mordenite, etc., and preferably X-type, Y-type
Type, L type and ZSM type, and particularly preferably a zeolite containing high silicon. Examples of the non-zeolitic porous acidic oxide include alumina, silica, silica alumina, titania, magnesia and the like. As the activated carbon, fruit shell activated carbon is preferred.

[0009] Since chlorine has a stronger affinity for these adsorbents than the above-mentioned gases, when chlorine-containing gas is introduced into an adsorption tower filled with these adsorbents, chlorine is reduced. Because it is adsorbed preferentially over other gases,
At the gas outlet side of the adsorption tower, a gas having a low chlorine concentration is obtained to such an extent that it is sometimes hardly detected.

The method of the present invention covers the disadvantages of the PSA method in the following points. In the conventional chlorine concentration by the PSA method, the adsorption of chlorine to the adsorption tower progresses, and the supply of the chlorine-containing raw material gas to the adsorption tower is stopped before the equilibrium adsorption state is established. This is because if the raw material gas is supplied to the adsorption tower until it approaches the equilibrium adsorption state, the chlorine will break through from the outlet side of the adsorption tower, and equipment such as a removal tower to collect the chlorine that breaks down at this time will be newly installed. This is because it is necessary. In the adsorption tower where the supply of the raw material gas is stopped before the equilibrium adsorption state, a void portion in which chlorine is not adsorbed is generated, and other gas remains in this portion. Therefore, chlorine obtained at the time of regeneration does not become a sufficient concentration due to the residual gas.

On the other hand, in the method of the present invention, the adsorption towers are connected in cascade, and chlorine is adsorbed until the first adsorption tower is in an equilibrium state.
Adsorb in the adsorption tower. Therefore, there is no fear that chlorine leaks out of the system in the adsorption step. Further, in the first adsorption tower, since the raw material gas is supplied until the state of equilibrium adsorption with chlorine is reached, voids are eliminated in the adsorption tower, and the amount of gas other than chlorine remains small, and the chlorine obtained during regeneration has a high concentration. . By performing equilibrium adsorption, the unadsorbed portion of the adsorbent is eliminated, and the adsorbent can be used effectively.

A feature of the method of the present invention is a pressure swing adsorption method utilizing an equilibrium adsorption state. The term "equilibrium adsorption state" as used herein means that the gas adsorption to the adsorbent progresses and the adsorbed amount is reached after reaching the equilibrium concentration. This is a state in which the amount of adsorption is constant without increasing, and the amount of equilibrium adsorption under a certain adsorption temperature and pressure condition is constant depending on the adsorbent (see FIG. 1).

The chlorine concentration of the gas containing chlorine to be adsorbed by the adsorbent is not particularly limited, but usually a chlorine concentration of 5 to 80% is applied. When the chlorine concentration is low, the adsorption time until the regeneration operation by desorption can be long. The operation pressure of this adsorption operation is set to be higher than that of the subsequent chlorine desorption operation. The operating temperature is determined by the type of zeolite to be filled, the type of gas other than chlorine contained in the introduced gas, and economical problems. For example, when Y-type zeolite is used as an adsorbent and carbon dioxide is mixed in the accompanying gas, sufficient chlorine adsorption can be performed even at around normal temperature. On the other hand, in order to prevent the deterioration of the packing material and the material of the equipment, the moisture in the raw material gas is preferably low, and is preferably 1000 ppm or less.

The adsorption step is performed in two columns, a first adsorption column and a second adsorption column. When the adsorption of chlorine to the first adsorption tower progresses and reaches an equilibrium adsorption state, the supply of the gas containing chlorine as a raw material gas to the adsorption tower is stopped. During this time, the second adsorption tower adsorbs chlorine in the gas containing a small amount of chlorine flowing out from the outlet side of the first adsorption tower, so that the adsorption and separation can be performed without receiving chlorine from the adsorption step. Subsequently, the operating pressure of the first adsorption tower is lowered to desorb the adsorbed chlorine and other gases. At this time, the operation pressure is set to be equal to or lower than the pressure at the time of adsorption, and if necessary, it is also effective to set the pressure to equal to or lower than the atmospheric pressure by using a vacuum pump. The raw material gas is continuously introduced into the second adsorption tower that has slightly adsorbed chlorine, and the supply is stopped when the equilibrium adsorption state is reached with chlorine. During this period, the third adsorption tower, which has completed the pressure raising step, adsorbs the chlorine in the gas containing a small amount of chlorine flowing out from the outlet side of the second adsorption tower. The operating temperature is optional, but it is basically more economical to set the temperature at the time of adsorption. Of course, if economically effective, a so-called thermal swing method can be used.

Further, it is a preferable embodiment that a small amount of an inert gas, preferably nitrogen gas, is passed during the desorption operation because the desorption of chlorine gas from the adsorbent is promoted. By this desorption operation, a gas having a higher chlorine concentration than the introduced gas can be obtained, and the adsorbent that has adsorbed chlorine can be regenerated by dechlorination, and the next adsorption operation can be performed again.

Next, the state of implementation in a more specific form on an industrial scale will be described. FIG. 2 shows the form.

In FIG. 2, the raw material gas containing chlorine is a pipe 1
After being sent to the gas compressor 2 where the pressure is increased to a predetermined adsorption pressure, the gas is passed through the switching valve 3 to the four adsorption towers 4 a and 4.
b, 4c and 4d are sent to the first adsorption tower 4a. Each of the four adsorption towers 4a, 4b, 4c, and 4d is filled with an adsorbent that preferentially adsorbs the above-mentioned chlorine, and preferentially adsorbs chlorine in the source gas introduced in a pressurized state. At the outlet of the adsorption tower 4a, a gas having a low chlorine content, and sometimes a gas having a chlorine concentration low enough to be hardly detectable (hereinafter referred to as a treated gas) is obtained. The treated gas is sent to the second adsorption tower 4b via the switching valves 25 and 26, and a gas having a chlorine concentration low enough to detect and detect the chlorine in the treated gas (hereinafter referred to as exhaust gas) is obtained. This exhaust gas is sent to the blower 7 via the switching valve 15 and the valve 6, and is discharged (adsorption step).

At this time, in the third adsorption tower 4c, a part of the exhaust gas discharged from the second adsorption tower 4b is introduced into the third adsorption tower 4c via the flow rate control mechanism 8 and the switching valve 16, and this column In the fourth adsorption tower 4d, the inside of the fourth adsorption tower 4d and the vacuum pump 10 are connected via the switching valves 23 and 12a, and the adsorbent in this tower is A regeneration step of performing a regeneration process under reduced pressure is performed. The adsorption tower 4a that has reached the equilibrium adsorption state by adsorbing a predetermined amount of chlorine stops the introduction of the raw material gas by switching the switching valve 3 and exhausts the inside of the tower by the vacuum pump 10 by switching the switching valve 13. Then, the pressure is reduced, the chlorine adsorbed on the adsorbent is desorbed, and the adsorbent is regenerated (regeneration step). In this regeneration step, a gas having a high chlorine concentration as a product can be obtained from the discharge port of the vacuum pump 10, and the gas containing a high concentration of chlorine is sent to a downstream consumption step.

At this time, in the second adsorption tower 4b, after the introduction of the treated gas from the adsorption tower 4a is completed, the raw material gas is introduced via the switching valve 14, and the treated gas is obtained from the outlet of this tower.
The treated gas passes through the switching valves 27 and 28 and passes through the third adsorption tower 4
c, the chlorine in the treated gas is adsorbed,
Exhaust gas having a chlorine concentration low enough to be undetectable is obtained at the outlet side of c. This exhaust gas is sent to the blower 7 via the switching valve 18 and the valve 6, and is discharged. In the fourth adsorption tower 4d, a part of the exhaust gas discharged from the third adsorption tower 4c is introduced through the flow rate control mechanism 8 and the switching valve 23, and the pressure in the column is increased by the exhaust gas. It has been implemented.

Thereafter, in the third adsorption tower 4c, the adsorption tower 4b
After the introduction of the treated gas from the column, the raw material gas is introduced through the switching valve 17, and the treated gas is obtained from the outlet of this column. This treated gas is sent to the fourth adsorption tower 4d via the switching valves 29 and 30, and the chlorine in the treated gas is adsorbed, and an exhaust gas having a chlorine concentration low enough to be undetectable is obtained at the outlet side of the adsorption tower 4d. Can be This exhaust gas is sent to the blower 7 via the switching valve 24 and the valve 6, and is discharged. Also, the first adsorption tower 4a
In the method, a part of the exhaust gas discharged from the fourth adsorption tower 4d is introduced through the flow rate adjusting mechanism 8 and the switching valve 19, and a pressure step of increasing the pressure in the tower by the exhaust gas is performed.

In the adsorption tower 4b which has reached the equilibrium adsorption state by adsorbing chlorine in the raw material gas, the introduction of the raw material gas is stopped by switching the switching valve 14, and the vacuum pump in the tower is switched by switching the switching valve 20. The gas is exhausted at 10 to be in a reduced pressure state, the chlorine adsorbed by the adsorbent is desorbed, and the adsorbent is regenerated.

Similarly, by repeating this series of operations alternately for the four adsorption towers 4a, 4b, 4c, and 4d, chlorine is separated from the chlorine-containing raw material gas, and the chlorine concentration in the raw material gas is increased. A gas having a chlorine concentration can be continuously obtained.

[0023]

Next, the present invention will be described in more detail with reference to examples. Example 1 20 g each of synthetic Y-type zeolite (manufactured by ZEOCHEM)
The first of the four packed stainless steel adsorption towers
Chlorine (5%), carbon dioxide (15%) at 5-30 ° C
A source gas having a composition of helium (80%) was adjusted to a pressure of 5 atm and aerated at 200 ml / min for 34 minutes until the composition of the treated gas on the exit side of the first adsorption tower became the same as that of the source gas. During this time, the treated gas is passed through the second adsorption tower, and the exhaust gas on the outlet side of the second adsorption tower was subjected to gas chromatographic analysis to analyze the gas composition. As a result, no chlorine gas was detected. After the completion of the aeration, the supply of the raw material gas to the first adsorption tower was stopped, and the adsorption tower was moved to 60 mmHg ab by a vacuum pump.
s. At a pressure of 5 minutes to desorb chlorine gas. Analysis of the desorbed gas revealed a chlorine concentration of 86%. After passing the treated gas from the first adsorption tower through the second adsorption tower, the raw material gas is continuously passed through the second adsorption tower, and the treated gas at the outlet side of the second adsorption tower is passed for 20 minutes until the composition of the treated gas becomes the same as the source gas. did. During this time, the treated gas is passed through the third adsorption tower,
Gas chromatographic analysis of the exhaust gas on the exit side of the third adsorption tower was performed to analyze the gas composition, and no chlorine gas was detected. After the completion of the ventilation, the supply of the raw material gas to the second adsorption tower was stopped, and the adsorption tower was evacuated to 60 mmHg abs. At a pressure of 5 minutes to desorb chlorine gas. Analysis of the desorbed gas revealed a chlorine concentration of 86%.

Example 2 Synthetic 13X type zeolite (manufactured by Fuji Devison) was used for 20 samples each.
The raw material gas having a composition of chlorine (5%), carbon dioxide (15%) and helium (80%) is adjusted to a pressure of 5 atm at 60 ° C. in the first adsorption tower among the four stainless steel adsorption towers filled with g. Then, air was passed at 200 ml / min for 17 minutes until the composition of the treated gas on the exit side of the first adsorption tower became the same as that of the raw material gas. During this time, the treated gas is passed through the second adsorption tower, and the exhaust gas on the outlet side of the second adsorption tower was subjected to gas chromatographic analysis to analyze the gas composition. As a result, no chlorine gas was detected. After the completion of the ventilation, the supply of the raw material gas to the first adsorption tower was stopped, and the adsorption tower was operated at 60 mmHg abs.
At a pressure of 5 minutes to desorb chlorine gas. Analysis of the desorbed gas revealed a chlorine concentration of 80%. After passing the treated gas from the first adsorption tower through the second adsorption tower, the source gas is continuously passed through the second adsorption tower, and the composition of the treated gas on the exit side of the second adsorption tower becomes the same as the source gas for 10 minutes. did.
During this time, the treated gas is passed through the third adsorption tower.
Gas chromatograph analysis of the exhaust gas on the exit side of the adsorption tower was performed to analyze the gas composition, and no chlorine gas was detected. After the completion of the ventilation, the supply of the raw material gas to the second adsorption tower was stopped, and the adsorption tower was evacuated to 60 mmHg abs. At a pressure of 5 minutes to desorb chlorine gas. When the desorbed gas was analyzed, the chlorine concentration was 80%.

Example 3 10 g each of gas-adsorbed activated carbon PCB (manufactured by Toyo Argon)
In the first of four packed stainless steel adsorption towers, 6
A raw gas having a composition of chlorine (5%), carbon dioxide (15%) and helium (80%) is adjusted to a pressure of 5 atm at 0 ° C., and the treated gas on the exit side of the first adsorption tower is adjusted at 200 ml / min. Until the composition became the same as that of the source gas. During this time, the adsorbed gas is passed through the second adsorption tower,
Gas chromatographic analysis of the exhaust gas on the exit side of the second adsorption tower was performed to analyze the gas composition, and no chlorine gas was detected. After the completion of the ventilation, the supply of the raw material gas to the first adsorption tower was stopped, and the adsorption tower was operated at 60 mmHg abs. At a pressure of 5 minutes to desorb chlorine gas. When the desorbed gas was analyzed, the chlorine concentration was 80%. After passing the treated gas from the first adsorption tower through the second adsorption tower which has been completely ventilated, the source gas is passed continuously, and the composition of the treated gas on the exit side of the second adsorption tower becomes the same as the source gas for 10 minutes. Ventilated.
During this time, the treated gas is passed through the third adsorption tower.
Gas chromatographic analysis of the exhaust gas on the exit side of the adsorption tower was performed to analyze the gas composition, and no chlorine gas was detected.
After the completion of the aeration, the supply of the raw material gas to the second adsorption tower is stopped,
Using a vacuum pump, set the adsorption tower at 60 mmHg abs. At a pressure of 5 minutes to desorb chlorine gas. Analysis of the desorbed gas revealed a chlorine concentration of 80%.

Example 4 10 g each of molecular sieve carbon MSC (manufactured by Takeda Pharmaceutical Co., Ltd.)
In the first of four packed stainless steel adsorption towers, 6
A raw gas having a composition of chlorine (5%), carbon dioxide (15%) and helium (80%) is adjusted to a pressure of 5 atm at 0 ° C., and the treated gas on the exit side of the first adsorption tower is adjusted at 200 ml / min. Until the composition became the same as that of the source gas. During this time, the treated gas is passed through the second adsorption tower,
Gas chromatographic analysis of the exhaust gas on the exit side of the second adsorption tower was performed to analyze the gas composition, and no chlorine gas was detected. After the completion of the ventilation, the supply of the raw material gas to the first adsorption tower was stopped, and the adsorption tower was operated at 60 mmHg abs. At a pressure of 5 minutes to desorb chlorine gas. When the desorbed gas was analyzed, the chlorine concentration was 83%. The raw material gas is continuously passed through the second adsorption tower where the passage of the treated gas from the first adsorption tower is completed, and the composition of the treated gas on the exit side of the second adsorption tower becomes the same as that of the source gas. Aerated for minutes.
During this time, the treated gas is passed through the third adsorption tower.
Gas chromatographic analysis of the exhaust gas on the exit side of the adsorption tower and analysis of the gas composition revealed that chlorine gas was not detected. After the completion of the ventilation, the supply of the raw material gas to the second adsorption tower was stopped, and the adsorption tower was evacuated to 60 mmHg abs. At a pressure of 5 minutes to desorb chlorine gas. When the desorbed gas was analyzed, the chlorine concentration was 83%.

Comparative Example 1 20 g each of synthetic Y-type zeolites (manufactured by ZEOCHEM)
The first of three packed stainless steel adsorption towers has 2
Chlorine (5%), carbon dioxide (15%) at 5-30 ° C
A gas having a composition of helium (80%) was adjusted to a pressure of 5 atm and aerated at 200 ml / min for 13 minutes from the outlet side of the first adsorption tower until chlorine passed. During this time, the gas flowing out of the column was analyzed by gas chromatography to analyze the gas composition. As a result, 100 to 300 ppm of chlorine gas was detected. After the completion of the aeration, the supply of the raw material gas to the first adsorption tower was stopped, and the first adsorption tower was moved to 60 mmHg a by a vacuum pump.
bs. At a pressure of 5 minutes to desorb chlorine gas. Analysis of the desorbed gas revealed a chlorine concentration of 55%.
When a gas having the same composition as the first gas was again passed through the first adsorption tower after the desorption under the same conditions, the chlorine concentration of the gas flowing out for 13 minutes was 100 to 300 ppm.

[0028]

The present invention provides a method for improving the pressure swing adsorption method so that chlorine is not taken out of the system from the chlorine-containing gas, is concentrated to a high concentration, and the adsorbent is effectively used. The industrial value is very large.

[Brief description of the drawings]

FIG. 1 is an adsorption curve graph of each adsorbent.

FIG. 2 is a schematic view of an installation using a plurality of adsorption towers for performing the present invention particularly continuously.

[Explanation of symbols]

1. Source gas supply pipe 2. Compressor 4a. 4b. 4c. Adsorption tower 6. Valve 7. Blower 8. Flow control mechanism 10. Vacuum pump 3,5,9,11,12a, 12b, 13-32 Switching valve

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Ito 30 Asamuta-cho, Omuta-shi, Fukuoka Prefecture Inside Mitsui Toatsu Chemicals Co., Ltd. Examiner Noriko Suzuki (58) Field surveyed (Int.Cl. ⁶ , DB name) C01B 7/01 C01B 7/07 B01D 53/04

Claims (5)

(57) [Claims] 1. An adsorption tower filled with an adsorbent capable of adsorbing chlorine is connected in cascade, and a chlorine-containing raw material gas is converted into a first gas.
The adsorption tower introduces chlorine until it reaches an equilibrium adsorption state with chlorine to adsorb chlorine, while the second adsorption tower adsorbs chlorine in the gas containing a small amount of chlorine flowing out from the outlet of the first adsorption tower, Adsorption is performed without obtaining chlorine from the adsorption tower in the adsorption step. After the first adsorption tower reaches an equilibrium adsorption state with chlorine, the introduction of gas is stopped, and desorption is performed at a lower pressure than when introducing the gas. A method for concentrating chlorine gas, comprising obtaining a gas having a chlorine concentration higher than the chlorine concentration and regenerating the adsorbent. 2. The method according to claim 1, wherein the adsorbent capable of adsorbing chlorine is zeolite. 3. The method according to claim 1, wherein the adsorbent capable of adsorbing chlorine is a non-zeolitic porous acidic oxide. 4. The method according to claim 1, wherein the adsorbent capable of adsorbing chlorine is activated carbon. 5. The method according to claim 4, wherein the activated carbon is molecular sieve carbon.