JP6837023B2 - Gas separation method - Google Patents

Description

The present invention relates to a gas separation method.

At steelworks, gas called by-product gas is generated from equipment such as coke ovens, blast furnaces, and converters. This by-product gas is used as a fuel for hydrogen (hereinafter, _{also referred to as "H 2} "), carbon monoxide (hereinafter, also referred to as "CO"), and methane (hereinafter, also referred to as _{"CH 4").} In addition to the possible components, nitrogen (hereinafter, _{also referred to as "N 2} ") and carbon dioxide (hereinafter, _{also referred to as "CO 2} ") are contained. In particular, the blast furnace gas discharged from the top of the blast furnace accounts for 80% of the by-product gas discharged from the steelworks in terms of volume, and about 40% of the _{CO 2 discharged from the steelworks is included here.} ..

In response to recent demands for reduction of CO _{2 emissions, technologies for separating and recovering CO 2} have been developed in various fields, and various methods have been proposed, including the chemical absorption method. Among them, the pressure swing adsorption method (hereinafter, also referred to as "PSA method") requires relatively small power for separation and recovery, and unlike the method using a chemical reaction, it can often be operated at room temperature. It is one of the useful techniques because it can process gas on a relatively large scale of about several thousand Nm ^{3 per hour (see, for example, Patent Document 1).}

The PSA method is relatively easy to adsorb to the adsorbent by introducing the raw material gas into an adsorption tower filled with materials (adsorbents) that have different adsorption performances for the above gas components such as activated carbon and zeolite. This is a method of separating a gas component (usually a plurality of gas types) and a gas component (which is also usually a plurality of gas types) that are relatively difficult to adsorb. Normally, by introducing the raw material gas for a predetermined time, the easily adsorbed gas component in the raw material gas is adsorbed on the adsorbent (hereinafter referred to as "adsorption step"), and then from the time of introducing the above gas. By depressurizing the inside of the adsorption tower to desorb and recover the adsorbed gas component, and to regenerate the gas adsorption performance of the adsorbent (hereinafter referred to as "desorption step"), the gas separation operation is performed. It can be repeated.

Here, when there is not much difference in the adsorption performance of the gas component contained in the raw material gas to be separated to the adsorbent, for example, when the adsorption amount at the same gas partial pressure is only about several tens of times different, the gas is separated. As described above, the gas is often a mixed gas containing a plurality of types of gas components. Therefore, when the blast furnace gas is separated into gas components using activated carbon or zeolite as an adsorbent, it is separated into a gas containing CO ₂ as a main component and a _{small amount of CO and N 2} and other gases.

Therefore, between the adsorption step and the desorption step, a part of the gas having a high _{CO 2} gas concentration obtained in the desorption step is introduced into the adsorption tower to desorb the _{CO and N 2 adsorbed on the adsorbent.} A step of reducing these components (hereinafter referred to as "cleaning step") may be performed.

Japanese Patent No. 5069087

By the way, since the blast furnace gas discharged from the top of the blast furnace contains dust and the like, wet dust removal is performed on the blast furnace gas to remove the dust and the like. Therefore, the dust-removed blast furnace gas contains a large amount of water, and its humidity is almost 100% (dew point = gas temperature).

However, _{when a zeolite having a high ability to adsorb CO 2} is used as an adsorbent, the ability of the zeolite _{to adsorb CO 2} is often reduced by water. Therefore, in the conventional gas separation method, a high degree of dehumidification (for example, dew point: −60 ° C.) is performed prior to introducing the blast furnace gas into the adsorption tower.

The power required for dehumidifying the blast furnace gas accounts for a relatively large proportion of the power required for the entire gas separation, and its reduction is an issue. As described above, the advanced dehumidification of the raw material gas is to prevent the zeolite from decreasing its ability to adsorb _{CO 2 due to the inclusion of water.} On the other hand, the degree of dehumidification is reduced to reduce power, which reduces the _{ability of zeolite to adsorb CO 2} , resulting in _{PSA performance such as CO 2} concentration and amount (recovery amount) of desorbed gas and required power. It is not desirable to decrease.

Therefore, an object of the present invention is to propose a gas separation method that can alleviate the degree of dehumidification and at the same time maintain the performance as PSA.

The gist structure of the present invention for solving the above problems is as follows. That is,
(1) A mixed gas containing water and composed of at least two types of gas components is introduced into an adsorption tower filled with an adsorbent, and a predetermined gas component contained in the mixed gas is adsorbed on the adsorbent. It is composed of a plurality of steps including a predetermined gas adsorption step and a predetermined gas desorption step of desorbing a predetermined gas component adsorbed on the adsorbent by reducing the pressure in the adsorption tower as compared with the predetermined gas adsorption step. At the same time, the adsorbent reduces the water adsorption isotherm measured by increasing the water partial pressure of the gas phase and the water partial pressure of the gas phase in the measurement of the adsorption isotherm of water at a predetermined temperature. In the mixed gas separation method, which is an adsorbent having hysteresis between the measured moisture desorption isotherm and the temperature line.
The amount of water in the mixed gas is controlled to be equal to or less than the water partial pressure in the water adsorption isotherm, which corresponds to the amount of water adsorbed when the water partial pressure is reduced to zero in the water desorption isotherm. A method for separating a mixed gas, which comprises.

(2) The gas separation method according to (1) above, wherein the lower limit of the ultimate pressure in the adsorption tower in the predetermined gas desorption step is 5 kPa.

(3) The gas separation method according to (1) or (2) above, wherein the adsorbent is zeolite.

(4) The gas separation method according to (3) above, wherein in the predetermined gas adsorption step, a raw material gas having a partial pressure of water of 0.06 kPa or more and 0.16 kPa or less is introduced into the adsorption tower.

(5) The gas separation method according to (4) above, wherein in the predetermined gas adsorption step, a raw material gas having a partial pressure of water of 0.06 kPa or more and 0.15 kPa or less is introduced into the adsorption tower.

According to the present invention, in a method of separating a raw material gas containing water using an adsorbent affected by water, it is possible to reduce the dehumidifying power of the raw material gas water without lowering the efficiency for separating a predetermined gas. it can.

It is a figure which shows the relationship between the pressure of a gas in an adsorption tower, and the amount of a gas component adsorbed on an adsorbent. It is a figure which shows the relationship between the pressure of a gas in an adsorption tower, and the amount of a gas component adsorbed on an adsorbent. It is a figure which shows the relationship between the amount of water adsorbed by _{an adsorbent and the amount of CO 2 adsorbed by an adsorbent.} It is a figure which shows the relationship between the amount of water adsorbed by _{an adsorbent and the amount of N 2 adsorbed by an adsorbent.} It is a figure which shows the relationship between the amount _{of water adsorbed to the adsorbent and the effective adsorbed amount of CO 2} and N ₂ when the pressure of the gas in the adsorption process is 101 kPa and the pressure of the gas in a desorption step is 0 kPa. It is a figure which shows the relationship between the amount _{of water adsorbed to the adsorbent and the effective adsorbed amount of CO 2} and N ₂ when the pressure of the gas in the adsorption process is 101 kPa and the pressure of the gas in a desorption step is 5 kPa. It is a figure which shows the amount of moisture adsorbed to an adsorbent, the CO ₂ concentration of a desorption gas, and _{the recovery rate of CO 2 by a desorption gas.} It is a figure which shows the relationship between the partial pressure of water, and the amount of water adsorbed on an adsorbent. It is a figure which shows the gas separation test apparatus used in an Example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the gas separation method according to the present invention, a mixed gas containing water and composed of at least two types of gas components is introduced into an adsorption tower filled with an adsorbent to adsorb a predetermined gas component contained in the mixed gas. A plurality of steps including a predetermined gas adsorption step of adsorbing to the agent and a predetermined gas desorption step of desorbing a predetermined gas component adsorbed on the adsorbent by reducing the pressure in the adsorption tower as compared with the above-mentioned predetermined gas adsorption step. The adsorbent is composed of a water adsorption isotherm measured by increasing the water partial pressure of the gas phase in the measurement of the adsorption and desorption isotherm of water at a predetermined temperature, and the water partial pressure of the gas phase. It is a mixed gas separation method which is an adsorbent having hysteresis between it and the moisture desorption isotherm measured by reducing it. Here, the amount of water in the mixed gas is controlled to be equal to or less than the water partial pressure in the water adsorption isotherm, which corresponds to the amount of water adsorbed when the water partial pressure is reduced to zero in the water desorption isotherm. It is characterized by that.

The present inventors investigated in detail the effect of the amount of water adsorbed on the adsorbent on gas separation while investigating ways to reduce the power required for gas separation. As a result, even if the adsorbent (for example, zeolite) is conventionally considered to be sensitive to water, by appropriately controlling the amount of water adsorbed, the degree of dehumidification of the raw material gas containing water can be suppressed and the degree of dehumidification can be suppressed. It was discovered that the gas separation performance can be maintained. The findings that led to this discovery will be described below.

First, FIG. 1 _{shows the relationship between the gas pressure of each single component of CO 2} and N ₂ and the amount of the gas component adsorbed on the adsorbent (zeolite). The amount of the gas component adsorbed on the adsorbent is a value with respect to 1 g of the adsorbent. As shown in this figure, the _{amount of CO 2} adsorbed on the adsorbent increases sharply with the increase in pressure from 0 kPa, and after adsorbing to some extent, the _{amount of CO 2} adsorbed is not so large even if the pressure increases further. Does not increase. From these facts, it is considered that zeolite has a _{site where CO 2} is easily adsorbed (hereinafter, also referred to as “strong adsorption site”) and a site where CO 2 is hard to be adsorbed (hereinafter, also referred to as “weak adsorption site”). ..

On the other hand, the _{amount of N 2} adsorbed on the adsorbent increases almost in proportion to the pressure (see also FIG. 4), and is extremely small compared to _{CO 2.} For example, when the gas pressure is 100 kPa, the _{amount of CO 2} adsorbed on the adsorbent is 5.5 mmol, whereas the _{amount of N 2} adsorbed is 0.4 mmol. As a result, in the adsorption step, for example, the pressure in the adsorption tower in the adsorption step is increased to 101 kPa _{to adsorb CO 2} and N ₂ to the adsorbent, and in the desorption step, the pressure in the adsorption tower is reduced to 0 kPa to reduce CO. _{When 2} and N ₂ are desorbed from the adsorbent, the CO ₂ concentration of the desorbed gas is assumed to be 5.5 / (5.5 + 0.4) = 93.2% by simple calculation from the adsorption isotherm of a single component. To.

By the way, in the desorption step, in order to reduce the pressure in the adsorption tower to near 0 kPa as described above, an extremely large amount of power and time are required. Therefore, in actual gas separation, the pressure reduction is often limited to several kPa (for example, 5 kPa). For example, when CO ₂ and N ₂ are adsorbed on an adsorbent at a pressure of 101 kPa in the adsorption step, and the inside of the adsorption tower is reduced to 5 kPa in the desorption step to desorb CO ₂ gas and N ₂ gas, the adsorbent is used. As shown in FIG. 2, the adsorption amount of CO ₂ gas is 2.6 mmol and that of N ₂ gas is 0.4 mmol. The difference between the amount of gas adsorbed at the pressure of the gas in the adsorption step and the amount of gas adsorbed at the pressure of the gas in the depressurization step, which is used in the actual separation step, is called "effective adsorption amount". In the above case, the CO ₂ concentration of the exhausted desorbed gas is 2.6 / (2.6 + 0.4) = 86.7%.

By the way, as described above, when the raw material gas contains water and the adsorbent used is a so-called "moisture-sensitive" adsorbent such as zeolite, the raw material gas must be dehumidified. In order to determine the degree of dehumidification, it is necessary to confirm the effect of water on the adsorbent.

3 and 4 show the relationship between the partial pressure of _{CO 2} and N ₂ and the amount of adsorption of the zeolite on which water is adsorbed. Moisture adsorption to the adsorbent is performed by introducing a dry adsorbent into the adsorption tower and introducing a gas containing water vapor into the adsorption tower to increase the weight ratio of the dry adsorbent before and after water adsorption. The amount of water adsorbed was used.

As is clear from FIGS. 3 and 4, as the amount of adsorbed water increases, the amount of CO ₂ and N ₂ adsorbed decreases. FIG. 5 shows the water content to the adsorbent when the gas pressure in the adsorption step is 101 kPa and the gas pressure in the desorption step is 0 kPa (hereinafter, also referred to as “pressure swing pressure range is 0 to 101 kPa”). The relationship between the adsorption amount and the effective adsorption amount of CO ₂ and N _{2 is shown.} As is clear from this figure _{, in both cases of CO 2} and N ₂ , the effective adsorption amount decreases with the amount of water adsorbed on the adsorbent.

_{However, as a result of detailed examination of the amount of CO 2} adsorbed shown in FIG. 3, the present inventors did not reduce the pressure in the adsorption tower to 0 kPa in the desorption step, but as described above, for example, reduced the pressure to 5 kPa. It was found that the effective adsorption amount of CO ₂ does not change so much even if the water adsorption amount increases. When the pressure of the gas in the adsorption step is 101 kPa and the pressure of the gas in the desorption step is 5 kPa (hereinafter, also referred to as "the pressure range of the pressure swing is 5 to 101 kPa"), CO _{The effective adsorption amount of 2} does not change even if the water adsorption amount increases and is almost constant, whereas _{the effective adsorption amount of N 2} decreases as the water adsorption amount increases.

Therefore, the present inventors performed a PSA operation using an adsorbent that adsorbed water, and conducted a gas separation test from a mixed gas that imitated a blast furnace gas at a steel mill. The detailed conditions of the test will be described later.

FIG. 7 shows the amount of water adsorbed on the adsorbent, the CO ₂ concentration of the desorbed gas, and the CO ₂ recovery rate of the desorbed gas. Zeolite is used as the adsorbent, and the pressure range of the pressure swing is 5 to 101 kPa. As shown in this figure, when the amount of water adsorbed on the adsorbent exceeds 0 g / g-adsorbent and reaches 0.14 g / g-adsorbent, the desorbing gas is compared with the case where the adsorbent does not contain water. It can be seen that the CO _{2 concentration of is high.} When the amount of water adsorbed on the adsorbent is 0.3 g / g-adsorbent or more and 0.14 g / g-adsorbent _{, not only the CO 2} concentration of the desorbed gas exceeds 91%, but also the adsorbent. _{It can be seen that the CO 2} recovery rate is also improved as compared with the case where the gas does not contain water.

As described above, conventionally, since the _{amount of CO 2} adsorbed is reduced by the water contained in the zeolite, it is considered that the smaller the water contained in the zeolite, the better, and the raw material gas has been highly dehumidified. However, as a result of detailed studies by the present inventors, in the desorption step, when the pressure in the adsorption tower is not reduced to 0 kPa, but is limited to, for example, 5 kPa, _{the effective adsorption amount of CO 2 is} the adsorption amount of water. It was found that the amount did not change even when the amount increased and became almost constant, and that _{the effective adsorption amount of N 2} decreased as the amount of water adsorbed increased. As a result, when separating the raw material gas containing water, the degree of dehumidification of the raw material gas is controlled within an appropriate range to alleviate the dehumidification and at the same time maintain the separation performance such as _{CO 2} concentration and CO _{2 recovery rate.} It turned out that it was possible to do so.

_{The mechanism by which the CO 2} concentration is improved by controlling the amount of water adsorbed on the adsorbent within an appropriate range is not necessarily clear, but the present inventors consider it as follows. That is, FIG. 8 shows the relationship (adsorption / desorption curve) between the partial pressure of water in the gas phase and the amount of water adsorbed on the adsorbent. The measurement temperature was 25 ° C., and zeolite was used as the adsorbent.

Looking at the amount of water adsorbed at the water adsorption stage (solid line) in FIG. 8, as with CO ₂ , the amount of water adsorbed rapidly increases in the region where the pressure of water is low, and when water is adsorbed to some extent, the amount of water adsorbed even if the pressure is increased. It can be seen that does not increase much. On the other hand, looking at the amount of water adsorbed at the water desorption stage (dotted line), it can be seen that the amount of water adsorbed does not decrease much even if the pressure is lowered in the region where the partial pressure of water is high, but it decreases sharply when the pressure approaches 0 kPa. .. However, it can be seen that even if the pressure is reduced to near 0 kPa, all the water is not completely desorbed and remains in the adsorbent.

The present inventors considered that the water remaining in the adsorbent at the water desorption stage was the water adsorbed on the strong adsorption site of the adsorbent. Since this water is strongly adsorbed on the site, it inhibits _{CO 2 adsorption in the low pressure region shown in FIG.} On the other hand, when the pressure swing range is 5 to 101 kPa in the gas separation operation, the _{site used for CO 2} adsorption / desorption is considered to be a rather weak adsorption site as described above. That is, it is considered that if the adsorption of water remains at the strong adsorption site, the _{effect on the adsorption and desorption of CO 2} at 5 to 101 kPa is small, and the effective adsorption amount does not change.

In the adsorption / desorption isotherm shown in FIG. 8, the amount of water adsorbed W at 0 Pa (average reached depressurization of the vacuum pump used in the adsorption / desorption measuring device) in the moisture desorption isotherm is relative to 1 g of the adsorbent. It is 0.14 g, and the corresponding water partial pressure P of the water adsorption isotherm is 0.18 kPa. Therefore, when the adsorbent is zeolite, the influence on the adsorption and desorption _{of CO 2} at 5 to 101 kPa should be reduced by setting the partial pressure of the water contained in the raw material gas to 0.18 kPa or less in the adsorption step. Can be done.

_{Although the separation of CO 2} using zeolite as an adsorbent has been described above as an example, the present invention is not limited to this, and an adsorbent having the hysteresis shown in FIG. 8 is used for adsorbing water. It is clear that the gas separation that was present can also be expanded. Therefore, the adsorbent is not limited to zeolite, and for example, alumina, silica gel, activated carbon, or the like can be used. When the raw material gas is a by-product gas of a steel mill such as a blast furnace gas, it is preferable to use zeolite as an adsorbent, which has a relatively large difference in the amount of adsorption between _{CO 2 and other gases.}

When the blast furnace gas is used as the raw material mixed gas and zeolite (eg, Na-13X type zeolite) is used as the adsorbent, the raw material mixed gas is dehumidified before being distributed to the adsorption tower filled with the adsorbent and contained in the gas. The partial pressure of the water is preferably in the range of 0.01 kPa (corresponding to the dew point −45 ° C.) to 0.6 kPa (corresponding to the dew point 0 ° C.). The dehumidification method is not particularly specified, but a combination of a method of condensation by gas cooling with cooling water or the like and a method of adsorption by an agent that adsorbs water is preferable. When the partial pressure is 0.01 kPa, the power required for dehumidification increases, and a dehumidifying device with higher dehumidifying capacity is required. Further, when the partial pressure is 0.6 kPa or more, the influence of water adsorbed on the adsorbent becomes large, and the target CO ₂ adsorption is hindered.

The dehumidified raw material mixed gas is circulated in an adsorption tower filled with an adsorbent to adsorb components such as _{CO 2.} In this case, the pressure in the adsorption tower is preferably 101 kPa to 200 kPa. When the pressure is lower than 101 kPa, CO ₂ adsorption to the adsorbent is reduced and the efficiency is lowered. On the other hand, even if the pressure is increased above 200 kPa, the _{amount of CO 2} adsorbed does not increase so much even though the required power increases.

_{To desorb CO 2} adsorbed on the adsorbent, use an exhaust means such as a vacuum pump to reduce the pressure inside the adsorption tower. The ultimate pressure for decompression is preferably in the range of 5 kPa to 20 kPa. If the ultimate pressure is lower than 5 kPa, more power is required. On the other hand, if it does not reach 20 kPa, the _{amount of CO 2} desorbed becomes small and it is not efficient.

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

(Invention Examples 1 to 5)
Using the gas separation test apparatus shown in FIG. 9, a test was conducted in which _{CO 2 gas was separated and recovered from a simulated blast furnace gas that imitated the blast furnace gas.} Specifically, first, 100 g of an adsorbent (NaX-type zeolite, manufactured by Tosoh Corporation, trade name: Zeolam) was filled in the adsorption tower 160 of the gas separation test apparatus. Next, the gas from the nitrogen gas cylinder 114 is branched into two, and one gas is bubbling in ion-exchanged water (not shown) in the washing bottle 140 placed in the hot bath of the temperature-controlled water bath 130. , Moisture was added. The nitrogen gas to which this moisture is added and the dry nitrogen gas that has not been bubbled are mixed, the moisture content of the humidified nitrogen gas is adjusted by the flow rate regulators 124 and 125, and the gas is distributed to the adsorption tower 160, and the moisture content is added to the adsorbent. Was adsorbed. The amount of water adsorbed on the adsorbent was 0.03 g (Invention Example 1), 0.06 g (Invention Example 2), 0.09 g (Invention Example 3), 0.12 g (Invention Example 4), per 1 g of the adsorbent. It was 0.14 g (Invention Example 5).

Subsequently, a simulated blast furnace gas imitating the blast furnace gas was prepared by a flow control meters 121 to 124 connected to the hydrogen gas cylinder 111, the carbon monoxide gas cylinder 112, the carbon dioxide gas cylinder and the nitrogen gas cylinder 114. The composition of this simulated blast furnace gas was CO ₂ : 22% by volume, CO: 23% by volume, N ₂ : 52% by volume, and H ₂ : 3% by volume, excluding water. The simulated blast furnace gas was ventilated to the adsorbent filled in the adsorption tower 10 through the automatic valves 151 and 152. At that time, the flow rate of the simulated blast furnace gas was 8 NL / min, the back pressure valve 170 was set to 150 kPa, and the gas (off gas) not adsorbed by the adsorbent was collected through the automatic valve 154 and the back pressure valve 170. It was sent to an analyzer (not shown).

After venting the simulated blast furnace gas for 100 seconds, the automatic valves 152 and 154 are temporarily closed, and the inside of the adsorption tower 160 is depressurized by the vacuum pump 180 through the automatic valve 152 for a decompression time of 100 seconds to desorb the gas adsorbed on the adsorbent. It was. At that time, the ultimate pressure in the adsorption tower at the time of depressurization was set to 6 kPa. The desorbed gas was exhausted from the adsorption tower 160 and sent to a gas collecting / analyzing device (not shown).

The above-mentioned humidification gas ventilation and decompression by a vacuum pump were repeated at regular intervals, _{and the CO 2} concentration of the desorbed gas and the CO ₂ recovery rate of the desorbed gas were analyzed. The results obtained are shown in Table 1. Further, the CO _{2 concentration of the desorbed gas analyzed and the CO 2} recovery rate of the desorbed gas are shown in FIG. 7.

(Comparative Examples 1 and 2)
Similar to Invention Example 1, the gas separation test apparatus shown in FIG. 9 was used to separate and recover the _{CO 2 gas from the simulated gas simulating the blast furnace gas.} However, the amount of water adsorbed on the adsorbent was set to the case where water was not adsorbed (Comparative Example 1), and the amount of water adsorbed was set to 0.15 g per 1 g of the adsorbent (Comparative Example 2). Other conditions are all the same as in Invention Example 1. The CO ₂ concentration of the desorbed gas and the CO ₂ recovery rate of the desorbed gas were analyzed. The results obtained are shown in Table 1. Further, the CO _{2 concentration of the desorbed gas analyzed and the CO 2} recovery rate of the desorbed gas are shown in FIG. 7.

<Evaluation of CO ₂ concentration and CO ₂ recovery rate of desorbed gas>
As is clear from Table 1 and FIG. 7, the CO ₂ concentration of the desorbed gas was higher than that of the comparative example in all of Invention Examples 1 to 5. Further, in Invention Examples 1 to 4, _{the recovery rate of CO 2 in} the desorbed gas was also higher than that in Comparative Examples 1 and 2. From this result, if the water content of the raw material mixed gas is controlled so that the amount of water adsorbed by the adsorbent does not exceed 0.14 g per 1 g of the adsorbent (0.18 kPa at partial pressure of water = -15 ° C at dew point), CO ₂ It turned out that there is no problem in terms of separation performance.

According to the present invention, when a specific gas component is separated from the raw material gas and recovered, the power can be reduced, which is useful in the steelmaking industry.

111 Hydrogen gas cylinder 112 Carbon monoxide gas cylinder 113 Carbon monoxide gas cylinder 114 Nitrogen gas cylinder 121-125 Flow controller 130 Water bath 140 Cleaning bin 151-154 Automatic valve 160 Suction tower 170 Back pressure valve 180 Vacuum pump

Claims (4)

Predetermined gas adsorption in which a mixed gas containing water and composed of at least two types of gas components is introduced into an adsorption tower filled with an adsorbent to adsorb a predetermined gas component contained in the mixed gas to the adsorbent. It is composed of a plurality of steps including a step and a predetermined gas desorption step of desorbing a predetermined gas component adsorbed on the adsorbent by reducing the pressure in the adsorption tower as compared with the predetermined gas adsorption step. The adsorbent is a water adsorption isotherm measured by increasing the water partial pressure of the gas phase in the measurement of the adsorption / desorption isotherm of water at a predetermined temperature, and the water content measured by reducing the water partial pressure of the gas phase. In the mixed gas separation method, which is an adsorbent having hysteresis between the desorption isotherm and the desorption isotherm.
The amount of water in the mixed gas is controlled to be equal to or less than the water adsorption amount in the water adsorption isotherm, which corresponds to the water adsorption amount when the water partial pressure is reduced to zero in the water desorption isotherm.
The upper limit of the pressure in the adsorption tower in the predetermined gas adsorption step is 101 kPa or more and 200 kPa or less, and the lower limit of the pressure in the adsorption tower in the predetermined gas desorption step is 5 kPa or more and 20 kPa or less . Method of separating mixed gas. The adsorbent is a zeolite, a gas separation method according to claim 1. The gas separation method according to claim 2 , wherein in the predetermined gas adsorption step, a raw material gas having a partial pressure of water of 0.06 kPa or more and 0.16 kPa or less is introduced into the adsorption tower. The gas separation method according to claim 3 , wherein in the predetermined gas adsorption step, a raw material gas having a partial pressure of water of 0.06 kPa or more and 0.15 kPa or less is introduced into the adsorption tower.

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