Gas separation method and method for producing refined gas

Abstract

A gas separation method in which two or more towers containing an adsorbent are switched and used, the method comprising: an adsorption step for causing a raw material gas containing an easily adsorbable gas and a hardly adsorbable gas to pass through at least one of the towers to adsorb the easily adsorbable gas by the adsorbent in the tower and to recover the hardly adsorbable gas; an inflow step for, after the adsorption step, causing the raw material gas remaining in the tower to flow into another tower and setting the pressure in the tower after the adsorption step to a negative pressure; and a desorption step for, after the inflow step, desorbing the easily adsorbable gas adsorbed by the adsorbent in the tower and recovering the easily adsorbable gas, wherein the other tower into which the raw material gas has flowed in the inflow step is subjected to the adsorption step.

Description

Gas separation method and method for producing purified gas

[0001] The present invention relates to a gas separation method and a method for producing a purified gas.

[0002] Gas separation technology is used in various industries, such as energy, environment, chemical industry, and food industry, and an appropriate separation technology is selected depending on the type of gas and purpose. One such technology, pressure swing adsorption (PSA), is well known as a method of separating gas mixtures containing two or more different components by selectively adsorbing easily adsorbed gas components onto an adsorbent and then desorbing the gas components by reducing the pressure.

[0003] For example, Patent Document 1 discloses an example of separating and purifying raw material gases of carbon monoxide and nitrogen using a pressure swing adsorption separation method. In this method, gas separation is performed by repeatedly using multiple adsorption towers and performing a pressure recovery step, an adsorption step, a pressure equalization step, a cleaning step, a desorption step, and a pressure equalization step, and switching between adsorption towers. After the adsorption step is completed, a pressure equalization step is performed in which void gas in the adsorption tower is sent to the adsorption tower after desorption is completed, and a cleaning step is performed in which a portion of the desorbed gas is sent back to the adsorption tower to wash out the void gas, thereby improving the recovery rate of the difficult-to-adsorb gas.

[0004] Japanese Unexamined Patent Publication No. 193623 / 1986

[0005] In gas separation, it is desirable to separate gas components with a high recovery rate, but there is a problem that the recovery rate decreases due to gas components remaining in void spaces. The present invention provides a gas separation method that improves the recovery rate of poorly adsorbed gases and a method for producing purified gas.

[0006] The present invention includes the following embodiments: <1> A gas separation method that switches between two or more towers containing an adsorbent, comprising: an adsorption step of passing a feed gas containing a readily adsorbable gas and a poorly adsorbable gas through at least one of the towers to adsorb the readily adsorbable gas onto the adsorbent in the tower and recovering the poorly adsorbable gas; an inflow step of flowing the feed gas remaining in the tower into another tower after the adsorption step and reducing the pressure in the tower after the adsorption step to a negative pressure; and a desorption step of desorbing the readily adsorbable gas adsorbed onto the adsorbent in the tower after the inflow step and recovering the readily adsorbable gas, wherein the other tower into which the feed gas has flowed in the inflow step is subjected to the adsorption step. <2> The gas separation method according to <1>, further comprising: a pressure reduction step of flowing out a portion of the feed gas in the tower to reduce the pressure inside the tower after the adsorption step and before the inflow step, wherein the feed gas flowed out in the pressure reduction step is subjected to the adsorption step. <3> The gas separation method according to <2>, wherein the hardly adsorbable gas is a target component, and the concentration of the target component in the feed gas discharged in the pressure reduction step is higher than the concentration of the target component in the feed gas flowed into the other tower in the inflow step. <4> The gas separation method according to <2>, wherein the column is pressurized before pressure reduction in the pressure reduction step. <5> The gas separation method according to any of <1> to <4>, further comprising a pressure recovery step of supplying the hardly adsorbable gas having a purity of 50% or more into the column after the desorption step. <6> The gas separation method according to any of <1> to <5>, wherein the feed gas is flowed into the other tower under reduced pressure in the inflow step. <7> The gas separation method according to any one of <1> to <6>, wherein three or more towers containing the adsorbent are used, and after a first tower is subjected to the adsorption step, the supply destination of the raw material gas is switched to a second tower, and after the second tower is subjected to the adsorption step, the supply destination of the raw material gas is switched to a third tower, thereby keeping the amount of the raw material gas supplied to the towers constant. <8> The gas separation method according to any one of <1> to <7>, wherein, in the inflow step, when the pressure in the tower after the adsorption step is A (kPa) and the pressure in the other tower is B (kPa), the relationship (A + B) / 2<101.3 is satisfied.<9> The gas separation method according to any one of <1> to <8>, wherein the tower has an adsorption layer, and wherein the packing rate of the adsorbent in the adsorption layer is 90% by volume or less. <10> The gas separation method according to any one of <1> to <9>, wherein the easily adsorbable gas is carbon dioxide and the poorly adsorbable gas is methane. <11> The gas separation method according to any one of <1> to <10>, wherein the adsorbent contains zeolite or activated carbon. <12> The gas separation method according to any one of <1> to <11>, wherein, when the amount of the easily adsorbable gas flowing out in the inflow step is Q2 and the amount of the easily adsorbable gas flowing out in the desorption step is Q3, the relationship Q3 > Q2 is satisfied. <13> The gas separation method according to <2>, wherein the adsorbent is zeolite, and where Q1 is the amount of the highly adsorbable gas discharged in the pressure reduction step, Q2 is the amount of the highly adsorbable gas discharged in the inflow step, and Q3 is the amount of the highly adsorbable gas discharged in the desorption step, the relationship Q3 > Q1 + Q2 is satisfied. <14> A method for producing a purified gas, comprising purifying the highly adsorbable gas and / or the weakly adsorbable gas by the gas separation method according to any one of <1> to <13>. <15> The method for producing a purified gas according to <14>, wherein the gas separation method is the gas separation method according to <3>, and at least the weakly adsorbable gas is purified.

[0007] According to the present invention, it is possible to provide a gas separation method and a method for producing a purified gas that improve the recovery rate of a gas that is difficult to adsorb.

[0008] FIG. 1 is a schematic flow diagram of a gas separation method according to this embodiment. FIG. 2 is a block diagram of a gas separation apparatus used in the gas separation method according to this embodiment. FIG. 3 is a schematic flow diagram of the gas separation method according to this embodiment. FIG. 4 is a diagram showing a schematic configuration of a gas separation apparatus 100. FIG. 5 is a diagram showing a schematic configuration of a biogas purification system 1000 in which the gas separation apparatus 100 is applied to biogas purification. FIG. 6 is a diagram showing a schematic configuration of the gas separation apparatus 100 including a sample recovery line 28. FIG. 7 is a schematic flow diagram of a gas separation method according to Comparative Example 2-4.

[0009] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The present invention is not limited to the following description, and various modifications can be made within the scope of the present invention.

[0010] [Gas Separation Method] This embodiment is a gas separation method that uses two or more towers containing an adsorbent by switching between them, the method comprising: an adsorption step (hereinafter also simply referred to as the "adsorption step") in which a feed gas containing a readily adsorbable gas and a poorly adsorbable gas is passed through at least one of the towers to adsorb the readily adsorbable gas onto the adsorbent in the tower and recover the poorly adsorbable gas; an inflow step (hereinafter also simply referred to as the "inflow step") in which the feed gas remaining in the tower after the adsorption step is introduced into another tower and the pressure in the tower after the adsorption step is reduced to a negative pressure; and a desorption step (hereinafter also simply referred to as the "desorption step") in which the readily adsorbable gas adsorbed onto the adsorbent in the tower is desorbed after the inflow step and recovers the readily adsorbable gas, the other tower into which the feed gas has been introduced in the inflow step being subjected to the adsorption step. This embodiment can provide a gas separation method and a method for producing a purified gas that improve the recovery rate of poorly adsorbable gas.

[0011] The reason why the gas separation method according to this embodiment achieves a high recovery rate of the hardly adsorbable gas is presumed to be as follows. Among the gases recovered during desorption, if we consider "gas recovered from the voids in the adsorption tower (hereinafter referred to as A)" and "gas desorbed from the adsorbent and recovered (hereinafter referred to as B)," B represents the gas desorbed from the adsorbent during the desorption process, and therefore is mainly composed of easily adsorbable gas. On the other hand, since A is filled with the raw material gas at the end of the adsorption process, it contains more easily adsorbable gas than B. Furthermore, when the pressure in the adsorption tower after inflow is made negative by the inflow process, a decrease in the gas density of A is observed according to the negative pressure, while B desorbed from the adsorbent increases significantly due to the negative pressure. "Negative pressure" means that the pressure is 101.3 kPa or less. Therefore, the amount of B relative to the amount of A increases significantly, and the easily adsorbable gas generated during desorption efficiently purges the voids in the adsorption tower, thereby improving the recovery rate of the hardly adsorbable gas. That is, when the target component is a gas that is not easily adsorbed, the recovery rate of the target component is improved. When the target component is a gas that is easily adsorbed, the purity of the target component is improved due to the improvement in the recovery rate of the gas that is not easily adsorbed.

[0012] For the reasons stated above, by making the pressure in the adsorption tower negative before desorption, the amount of difficult-to-adsorb gas contained in the desorbed gas recovered in the desorption process is reduced, and a high recovery rate of difficult-to-adsorb gas can be obtained.

[0013] The gas separation method according to this embodiment preferably further includes a pressure reduction step (hereinafter simply referred to as the "pressure reduction step") in which a portion of the raw gas in the column is discharged to reduce the pressure inside the column after the adsorption step and before the inflow step. In this case, the discharged raw gas is supplied to the adsorption step. As a result, even if the column is pressurized in the adsorption step, the pressure inside the column can be reduced before the inflow step, making it easier to make the pressure inside the column negative after the inflow step.

[0014] The gas separation method according to this embodiment preferably further includes a pressure restoration step (hereinafter also simply referred to as the "pressure restoration step") in which a poorly adsorbable gas having a purity of 50% or more is supplied into the column after the desorption step. By supplying a poorly adsorbable gas having a purity of 50% or more into the column in the pressure restoration step, the pressure is restored, which prevents the feed gas from flowing into the column too quickly at the beginning of the adsorption step, causing the highly adsorbable gas to pass through without being adsorbed by the adsorbent, and enables the recovery of a highly adsorbable gas of high purity.

[0015] In the gas separation method according to this embodiment, two or more towers containing adsorbents are used by switching between them. First, as an example, the gas separation method according to this embodiment will be described using two adsorption towers, adsorption tower a and adsorption tower b, containing adsorbents. FIG. 1 is a schematic flow diagram of the gas separation method according to this embodiment. FIG. 1 shows the processes performed in adsorption tower a and adsorption tower b. In adsorption tower a and adsorption tower b, adsorption steps and desorption steps are repeatedly performed, respectively, to separate highly adsorbable gases and weakly adsorbable gases. The adsorption step is terminated depending on the adsorption capacity of the highly adsorbable gas of the adsorbent, and in the desorption step, the highly adsorbable gas adsorbed in the adsorption step is desorbed from the adsorbent. This regenerates the adsorbent, allowing the adsorption step to be performed again. While the adsorption step is being performed in adsorption tower a, the desorption step is performed in adsorption tower b to regenerate the adsorbent. After the adsorption step in adsorption tower a is completed, the operation can be switched to perform the adsorption step in adsorption tower b.

[0016] As shown in FIG. 1 , a feed gas is supplied to adsorption tower a, and an adsorption step is performed. After the adsorption step, if the pressure in adsorption tower a has increased, a pressure reduction step may be performed. Then, in an inflow step, adsorption tower a is connected to adsorption tower b, which has been reduced in pressure by the desorption step, and the feed gas remaining in adsorption tower a is allowed to flow into adsorption tower b. It is preferable that a desorption step be performed in adsorption tower b prior to the inflow step, in which the highly adsorbable gas is desorbed from the adsorbent and reduced in pressure. Performing the desorption step following the adsorption step causes problems such as the feed gas remaining in adsorption tower a flowing into the recovery line for the highly adsorbable gas, resulting in a decrease in the purity of the highly adsorbable gas or a decrease in the recovery rate of the less adsorbable gas. However, by including the inflow step, the more adsorbable gas and the less adsorbable gas contained in the feed gas remaining in the adsorption tower after the adsorption step can be recovered without loss.

[0017] The target component of gas purification by the gas separation method according to this embodiment may be a gas that is difficult to adsorb, a gas that is easily adsorbed, or both. However, the recovery rate of the target component can be improved by making the concentration of the target component in the raw gas discharged in the pressure reduction step higher than the concentration of the target component in the raw gas that is introduced into another column in the inflow step.

[0018] After the adsorption step, when the pressure is reduced from a pressurized state to near atmospheric pressure in the pressure reduction step, the gases that move are unadsorbed gas present in the adsorption tower and gas that is desorbed from the adsorbent due to a decrease in the amount of adsorption by the adsorbent caused by the pressure reduction. When the target component is a gas that is difficult to adsorb, the former has a higher concentration of the target component, and the latter tends to have a lower concentration in accordance with the selectivity of the adsorbent.

[0019] For example, when the gas discharged in the desorption step is returned to the adsorption tower for purification or to a location upstream thereof in order to achieve a recovery rate of 90% or more of the highly adsorbable gas, the highly adsorbable gas to be separated is returned to the adsorption step process again, and therefore the highly adsorbable gas to be separated must be compressed and adsorbed multiple times, which tends to result in further economic disadvantages due to an increase in the required throughput of the compressor and a decrease in the adsorption performance of the adsorbent per unit of the highly adsorbable gas.

[0020] However, if the timing of the adsorption step is controlled and the adsorption step is terminated before complete breakthrough of the adsorbent and the pressure reduction step is started, the easily adsorbable gas present in the adsorption tower will be re-adsorbed onto the unadsorbed adsorbent. The desorbed easily adsorbable gas is re-adsorbed into the unadsorbed zone, which increases the likelihood of efficiently returning the difficultly adsorbable gas contained in the adsorption tower to the raw material in a state containing a high concentration of the difficultly adsorbable gas, which is a factor in reducing the recovery rate. Meanwhile, the difficultly adsorbable gas contained in the voids inside the adsorption tower will flow out of the adsorption tower. As a result, even when gas is circulated by reducing the pressure, the recovery rate of the difficultly adsorbable gas can be increased without significantly impairing economic efficiency.

[0021] The amount of circulated gas is preferably greater for the less adsorbable gas than for the more easily adsorbable gas. When the less adsorbable gas is the target component, it is not practical to circulate only the less adsorbable gas when re-adsorption is performed, because the purity of the less adsorbable gas is not 100%. On the other hand, if the more easily adsorbable gas that should be separated is circulated than the less adsorbable gas that is the target component, the amount of adsorbent is expected to increase by 20 to 30%.

[0022] After the above-mentioned inflow step, a desorption step is carried out in the adsorption tower a to recover the easily adsorbable gas and to regenerate the adsorbent.

[0023] While the desorption step is being performed in adsorption tower a, the adsorption step is being performed in adsorption tower b. Note that a pressure recovery step may be performed before the adsorption step. After the adsorption step in adsorption tower b is completed, if the pressure in adsorption tower b has increased, a pressure reduction step may be performed.

[0024] Thereafter, in the inflow step, adsorption tower b and adsorption tower a are connected, and the raw material gas remaining in adsorption tower b is introduced into adsorption tower a. In adsorption tower a, a pressure recovery step may be performed after the inflow step. Adsorption tower a is then subjected to the adsorption step again. Meanwhile, in adsorption tower b, after the inflow step, it is subjected to the desorption step and then to the inflow step again. By repeating the above steps, the raw material gas can be efficiently separated.

[0025] Hereinafter, each step will be described in detail using an example in which a gas separation apparatus having two or more towers containing adsorbents (hereinafter simply referred to as "adsorption towers") is used.

[0026] FIG. 2 is a block diagram of a gas separation apparatus used in the gas separation method according to this embodiment. As shown in FIG. 2, the gas separation apparatus includes two or more adsorption towers (adsorption tower a and adsorption tower b) containing an adsorbent, a raw material supply unit, a first product storage unit, a second product storage unit, and a pressure reduction device. The second product storage unit may be omitted if a highly adsorbable gas is not used. The gas separation apparatus includes a first flow path switching unit C1 and a second flow path switching unit C2, which are capable of switching between a flow path that can supply raw material gas to adsorption tower a or adsorption tower b during the adsorption process and introduces a less adsorbable gas into the first product storage unit, a flow path that connects adsorption tower a or adsorption tower b to the raw material supply unit during the pressure reduction process and supplies raw material gas remaining in the adsorption tower to the raw material supply unit, a flow path that connects adsorption tower a and adsorption tower b during the inflow process, and a flow path that can reduce the pressure in adsorption tower a or adsorption tower b using a pressure reduction device during the desorption process. The first flow path switching unit C1 and the second flow path switching unit C2 can be configured to achieve the above functions using multiple pipes, automatic valves, etc., as described below.

[0027] <Adsorption Tower> The adsorption tower is filled with an adsorbent. The two or more adsorption towers used in this embodiment may have different configurations, but it is preferable to use adsorption towers with the same configuration.

[0028] The adsorption tower is configured to allow the raw gas to be introduced and to bring the raw gas into contact with the adsorbent. In the adsorption process, the raw gas is brought into contact with the adsorbent, thereby causing easily adsorbable gases in the raw gas to be adsorbed onto the adsorbent. Since easily adsorbable gases are adsorbed in the raw gas, it is possible to extract a hardly adsorbable gas. Furthermore, after the adsorption process, the pressure in the adsorption tower is reduced in the desorption process, allowing the hardly adsorbable gas to be extracted. In this way, a purified gas of hardly adsorbable gases and a purified gas of easily adsorbable gases are obtained in the adsorption process and desorption process.

[0029] The adsorption tower has a portion filled with adsorbent (hereinafter also referred to as the "adsorption layer") and a portion not filled with adsorbent. From the viewpoint of further improving the recovery rate of the hardly adsorbed gas and from the viewpoint of reducing pressure loss, the packing rate of the adsorbent in the adsorption layer is preferably 90% by volume or less, more preferably 65 to 80% by volume, and even more preferably 67 to 70% by volume. Here, the packing rate (volume %) is calculated by the following formula: Packing rate = [volume of adsorbent] / [volume in the adsorption layer] × 100. The volume of the adsorbent represents the bulk density × mass of the adsorbent.

[0030] In the portion of the adsorption tower other than the adsorption layer, for example, in order to promote diffusion in a direction perpendicular to the gas flow, inert balls may be packed above or below the adsorption layer or in both directions.

[0031] The fewer the number of adsorption towers, the smaller the size of the separation device, which is preferable, but if the number is too small, it becomes difficult to switch between multiple adsorption towers and continuously separate gases. The number of adsorption towers is preferably 2 to 6, more preferably 2 to 4, and even more preferably 3.

[0032] (Adsorbent) As the adsorbent, it is preferable to use a solid adsorbent. More specifically, examples of the adsorbent include solid adsorbents such as zeolite, metal organic framework (MOF), carbonaceous char, activated carbon, reactivated carbon, carbon black, graphite, silica, silica gel, alumina clay, and metal oxides. Among these, it is preferable to use zeolite and activated carbon.

[0033] From the viewpoint of increasing the recovery rate of the hardly adsorbable gas, the adsorbent preferably has an adsorption selectivity, expressed as the ratio of the amount of easily adsorbable gas adsorbed to the amount of hardly adsorbable gas adsorbed, of 10 or more. The adsorption selectivity is more preferably 13 or more, and even more preferably 15 or more. The upper limit of the adsorption selectivity is not particularly limited, but is, for example, 100 or less. The amount of easily adsorbable gas adsorbed or the amount of hardly adsorbable gas adsorbed is the easily adsorbable gas adsorption capacity (cc) or the hardly adsorbable gas adsorption capacity (cc) per gram of adsorbent at 25°C. In the inflow step described below, gas moves from a high-pressure adsorption tower to a low-pressure adsorption tower. The gas moving at this time is the gas adsorbed by the adsorbent, and therefore has a high proportion of easily adsorbable gas. As this gas moves, gas with a high proportion of easily adsorbable gas washes out the voids in the adsorption tower, thereby increasing the recovery rate of the hardly adsorbable gas. This tendency becomes more pronounced as the selectivity of the adsorbent increases. When the pressure reduction step is performed, a similar washing effect is obtained, so the higher the selectivity of the adsorbent, the higher the recovery rate of the hardly adsorbable gas.

[0034] From the viewpoint of increasing the recovery rate of the hardly adsorbable gas, the adsorbent preferably has an adsorption capacity of 10 cc / g or more for a easily adsorbable gas such as carbon dioxide. The adsorption capacity of the easily adsorbable gas is preferably 20 cc / g or more, more preferably 40 cc / g or more, and even more preferably 50 cc / g or more. The upper limit of the adsorption capacity of the easily adsorbable gas is not particularly limited, but is, for example, 100 cc / g or less. As described above, in the inflow step and pressure drop step, the gas adsorbed to the adsorbent washes out the voids in the adsorption tower. Therefore, the greater the adsorption capacity, the greater the amount of gas used for washing, and the higher the recovery rate of the hardly adsorbable gas. Furthermore, when the target of separation is biogas, biogas generally contains methane and carbon dioxide. Even in cases where methane, which has high market value, is recovered as a hardly adsorbable gas and carbon dioxide, a easily adsorbable gas, is released into the atmosphere, a high recovery rate of the hardly adsorbable gas is desirable in terms of suppressing the amount of methane, which has a high greenhouse effect potential, released into the atmosphere. In addition, because the separated highly adsorbable gas, carbon dioxide, has a low methane content, it can be used as a carbon-neutral technology by combining it with technologies such as CCUS (Carbon Capture, Utilization, and Storage) as a high-purity gas. Achieving high purity and high recovery rates for highly adsorbable gases also encompasses achieving high purity and high recovery rates for highly adsorbable gases. In industrial gas utilization, meeting the purity levels required for the product and efficiently discharging it into the target gas are important not only for matching with current technologies but also with future technologies.

[0035] Examples of zeolites include CHA type zeolite, GIS type zeolite, FAU type zeolite, MWF type zeolite, LTA type zeolite, etc. Among these, GIS type zeolite or FAU type zeolite is preferred, and GIS type zeolite is more preferred.

[0036] The GIS zeolite preferably contains silica and alumina as its main components, which are components that account for 51 mass % or more.

[0037] The GIS zeolite may contain silica and alumina. The aluminum content in the GIS zeolite is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more. The silicon content in the GIS zeolite is preferably 3 mass% or more, and more preferably 5 mass% or more. The upper limit of the aluminum and silicon contents is preferably such that the SAR described below satisfies a predetermined range, and is determined by the SAR value.

[0038] The silica-alumina ratio (SiO ２ / Al ２ O ３ The SAR (representing the molar ratio of silica to alumina, hereinafter also referred to as "SAR") is preferably 3.40 or more. The lower the SAR of a GIS-type zeolite, the more hydrophilic it becomes, and the stronger its adsorption power for polar molecules such as carbon dioxide. If the SAR is low, the adsorption power is too strong, and the energy required for desorption by heating or vacuuming becomes large, so a high SAR is preferable, but if the SAR is too high, the interaction with the adsorbate becomes weak. The SAR is more preferably 4.40 to 3000, even more preferably 4.60 to 500, and even more preferably 4.80 to 100.

[0039] The phosphorus content in the GIS zeolite is preferably 4% by mass or less. The lower limit of the phosphorus content is not particularly limited, and may be 0% by mass or more.

[0040] The Zr content in the GIS zeolite is preferably 8% by mass or less. The lower limit of the Zr content is not particularly limited, and may be 0% by mass or more.

[0041] The Ti content in the GIS zeolite is preferably 8% by mass or less. The lower limit of the Ti content is not particularly limited, and may be 0% by mass or more.

[0042] From the viewpoint of further improving the selective adsorption capacity of carbon dioxide, the content of phosphorus atoms in the zeolite is more preferably 1.5 mass % or less, and particularly preferably 0 mass %.

[0043] The contents of aluminum, silicon, phosphorus, Zr, and Ti can be measured by the method described in the Examples below. The contents of aluminum, silicon, phosphorus, Zr, and Ti can be adjusted to the above-mentioned ranges, for example, by adjusting the composition ratio of the mixed gel used in synthesizing the GIS zeolite to the preferred ranges described below.

[0044] From the viewpoint of improving the selective adsorption capacity of easily adsorbable gases such as carbon dioxide, the GIS zeolite preferably contains potassium or lithium as a cation species, and more preferably contains potassium. The total content of potassium and lithium in the zeolite is calculated as the ratio (Z / T) of the total amount of potassium and lithium (Z) to the total amount of alkali metals (T) in the GIS zeolite. Z / T is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more. There is no particular upper limit to Z / T, but Z / T may be 1.00 or less. Z / T can be measured by thermally dissolving the zeolite in a sodium hydroxide aqueous solution or aqua regia and then subjecting the appropriately diluted solution to ICP-emission spectroscopy. More specifically, Z / T can be measured by the method described in the Examples below. Z / T can be adjusted by changing the ratio of potassium and lithium as cation species in the GIS zeolite.

[0045] The ratio (K / T) of the total amount of potassium (K) to the total amount of each alkali metal (T) in the GIS zeolite is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more. There is no particular upper limit to K / T, but K / T may be 1.00 or less.

[0046] From the viewpoint of the energy required for desorption, a high SAR is preferable, but it has been confirmed that when the SAR in GIS zeolite becomes high, adsorption / desorption hysteresis becomes apparent in the adsorption / desorption isotherm of the easily adsorbed gas. In GIS zeolite, the adsorption / desorption hysteresis in the adsorption / desorption isotherm of the easily adsorbed gas can be eliminated by controlling the bonding mode of Si and Al in the zeolite framework. Specifically, ２９ When the peak area intensities assigned to Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al) observed in the Si-MAS-NMR spectrum are a, b, c, and d, respectively, it is preferable that (a+d) / (b+c)≧0.192 is satisfied, more preferably 0.913≧(a+d) / (b+c)≧0.195, and even more preferably 0.519≧(a+d) / (b+c)≧0.199. ２９ Peaks such as Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al) observed in the Si-MAS-NMR spectrum represent the bonding modes of Si and Al in the zeolite framework, and the sums of the area intensities, X and Y, represent the sum of the abundances of these bonding modes, and Z represents the abundance ratio. The abundance ratio of Si and Al bonding modes affects the structural changes in the zeolite framework itself during adsorption and desorption, so by setting Z, the abundance ratio of Si and Al bonding modes in the zeolite framework, within an appropriate range, adsorption / desorption hysteresis in the adsorption / desorption isotherm can be eliminated.

[0047] ２９ For Si-MAS-NMR spectroscopy, a desiccator filled with water is prepared, and a sample tube containing zeolite is placed in the desiccator at the top and kept at room temperature (25°C) for 48 hours to perform humidity control. After that, measurements are performed using a solid-state NMR measurement device. Examples of the solid-state NMR measurement device include a JEOL "RESONANCE ECA700" (magnetic field strength: 16.44 T ( １ The resonant frequency at H is 700 MHz.

[0048] The GIS zeolite of this embodiment is ２９ The Si-MAS-NMR spectrum generally shows the following five peaks:

[0049] ​(1) Q4(0Al): Peak of Si that is not bonded to any Al through oxygen. (2) Q4(1Al): Peak of Si that is bonded to one Al through oxygen. (3) Q4(2Al): Peak of Si that is bonded to two Al through oxygen. (4) Q4(3Al): Peak of Si that is bonded to three Al through oxygen. (5) Q4(4Al): Peak of Si that is bonded to four Al through oxygen. ２９ In the Si-MAS-NMR spectrum, these peak positions generally exist between -112 ppm and -80 ppm, and can be assigned to Q4(0Al), Q4(1Al), Q4(2Al), Q4(3Al), and Q4(4Al) from the upfield side. The peak positions may vary depending on the cation species present in the zeolite framework, but generally exist in the following range:

[0050] (1) Q4(0Al): -105 ppm to -112 ppm (2) Q4(1Al): -100 ppm to -105 ppm (3) Q4(2Al): -95 ppm to -100 ppm (4) Q4(3Al): -87 ppm to -95 ppm (5) Q4(4Al): -80 ppm to -87 ppm ２９ The peak area intensity of the Si-MAS-NMR spectrum is analyzed using the analysis program dmfit (version #202000113) with Gaussian and Lorentzian functions, and the four parameters, amplitude (height of the maximum value of the spectrum), position (spectral position, ppm), width (full width at half maximum of the spectrum, ppm), and Gaussian / Lorentzian ratio (xG / (1−x)L), are calculated by optimizing them using a least-squares algorithm.

[0051] Using the area intensities of the peaks obtained by this calculation, the area intensities a, b, c, and d of the peaks assigned to Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al) can be determined.

[0052] ２９ ​More specifically, the Si-MAS-NMR spectrum can be measured by the method described in the Examples below. In order to set (a+d) / (b+c) within a predetermined range, it is possible to add a salt compound containing an alkali metal and / or an alkaline earth metal and adjust the quantitative ratio of the cation provided by the addition of the salt compound to the aluminum source, etc.

[0053] [Method for Producing Adsorbent] (Preparation Step) The above-mentioned GIS-type zeolite can be obtained by a production method including a preparation step of a mixed gel containing, for example, a silica source containing silicon, an aluminum source containing aluminum, an alkali source containing at least one selected from alkali metals (M1) and alkaline earth metals (M2), a salt compound containing at least one selected from alkali metals (M1) and alkaline earth metals (M2), a phosphorus source containing phosphorus, an organic structure-directing agent, and water.

[0054] (Hydrothermal synthesis step) The method for producing GIS zeolite preferably further includes a hydrothermal synthesis step in which the hydrothermal synthesis temperature is 80°C to 200°C. The hydrothermal synthesis temperature is preferably 100°C to 180°C. The mixed gel obtained in the preparation step is held at a predetermined temperature for a predetermined time, either stirred or left to stand, to perform hydrothermal synthesis. The hydrothermal synthesis time is not particularly limited as long as it is a commonly used time, and is preferably 3 hours to 30 days, more preferably 10 hours to 20 days, and even more preferably 24 hours to 10 days.

[0055] (Separation and drying process) After the hydrothermal synthesis process, the solid product and the aqueous liquid are separated. The separation method is not particularly limited as long as it is a common method, and examples that can be used include filtration, decantation, spray drying (rotary spraying, nozzle spraying, ultrasonic spraying, etc.), drying using a rotary evaporator, vacuum drying, freeze drying, and natural drying. Separation is usually achieved by filtration or decantation.

[0056] (Caustic Step) The method for producing GIS zeolite preferably further includes a calcination step in which the calcination temperature is 300°C to 450°C. The calcination temperature is more preferably 350°C to 420°C, and even more preferably 360°C to 400°C. The calcination time may be 0.5 hours to 10 days, 1 hour to 7 days, or 3 hours to 5 days. The calcination atmosphere is not particularly limited as long as it is a commonly used atmosphere, but typically, an air atmosphere, an inert gas such as nitrogen or argon, or an atmosphere containing oxygen is used.

[0057] (Cation Exchange Step) The method for producing GIS zeolite preferably further includes a cation exchange step. The cation exchange may be performed using, but is not limited to, carbonates such as sodium carbonate, potassium carbonate, lithium carbonate, rubidium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, or ammonium carbonate; nitrates such as sodium nitrate, potassium nitrate, lithium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, or ammonium nitrate; salts in which the carbonate ion or nitrate ion contained in the carbonate or nitrate salt is replaced with a halide ion, sulfate ion, carbonate ion, bicarbonate ion, acetate ion, phosphate ion, or hydrogen phosphate ion; or acids such as nitric acid or hydrochloric acid. The temperature for the cation exchange may be any common cation exchange temperature, but is typically from room temperature to 100° C. or less.

[0058] When separating the zeolite after cation exchange, the separation method is not particularly limited as long as it is a common method, and methods such as filtration, decantation, spray drying (rotary spraying, nozzle spraying, ultrasonic spraying, etc.), drying using a rotary evaporator, vacuum drying, freeze drying, and natural drying can be used, and separation can usually be performed by filtration or decantation.

[0059] <Feedstock supply section> The feedstock supply section refers to a feedstock gas tank or piping located upstream of the pressure booster. The feedstock supply section is filled with a feedstock gas, which is the raw material. The feedstock gas is pressurized from the feedstock supply section to a predetermined pressure by a pressure booster and flows into the adsorption tower.

[0060] <First Product Storage Section> The first product storage section is filled with a purified, hardly adsorbable gas. During the adsorption process, the hardly adsorbable gas obtained by passing through the adsorption tower is stored in the first product storage section. During the pressurization process, the hardly adsorbable gas may be flowed from the first product storage section into an adsorption tower with a lower pressure to increase the pressure in the adsorption tower. The first product storage section stores the hardly adsorbable gas obtained in the adsorption process and, during the pressurization process, flows a portion of the gas into the adsorption tower to increase the pressure. The first product storage section may be large enough to supply a sufficient amount of hardly adsorbable gas by connecting to the adsorption tower during the pressurization process (e.g., a volume equal to or greater than the volume of the adsorption tower). When the first product storage section is filled during the adsorption process, the overflowing hardly adsorbable gas may be introduced into a gas bag (not shown). When introducing the gas into a gas bag, a preferred embodiment is to provide a backpressure valve downstream of the first product storage section, which is closed until the product storage section reaches a predetermined pressure and then opens after the pressure is reached.

[0061] <Second Product Storage Section> The second product storage section is filled with the purified highly adsorbable gas. In the desorption step, the highly adsorbable gas desorbed from the adsorbent is stored in the second product storage section.

[0062] The source gas used as a raw material contains a gas that is difficult to adsorb and a gas that is easily adsorbed. The content of the easily adsorbed gas in the source gas may be 1% by volume to 99% by volume, 5% by volume to 90% by volume, 10% by volume to 80% by volume, 20% by volume to 70% by volume, or 30% by volume to 70% by volume.

[0063] <Difficult to adsorb gas> The amount of hardly adsorbed gas adsorbed to the adsorbent (cm ３ (STP)g －１) compared to the easily adsorbed gas. The "gaseous substance" means a substance that is gaseous at room temperature (25°C) and normal pressure. Examples of the hardly adsorbed gas include methane, ethane, nitrogen, argon, and dimethyl ether. Among these hardly adsorbed gases, methane, ethane, and nitrogen are preferred, methane and ethane are more preferred, and methane is even more preferred.

[0064] <Easily Adsorbable Gas> The easily adsorbable gas is measured by the amount of adsorption (cm ３ (STP)g －１ ) is higher than that of the poorly adsorbed gas. Examples of the readily adsorbed gas include carbon dioxide, nitrous oxide, nitric oxide, hydrogen, water, and ammonia. Among these readily adsorbed gases, carbon dioxide, carbon monoxide, nitrous oxide, and nitric oxide are preferred, carbon dioxide and carbon monoxide are more preferred, and carbon dioxide is even more preferred.

[0065] Each step of the gas separation method according to this embodiment will be described in detail.

[0066] <Adsorption Step> In the adsorption step, the raw material gas is passed through at least one of two or more towers to adsorb the easily adsorbable gas onto the adsorbent in the tower, and the less easily adsorbable gas is recovered.

[0067] The pressure in the adsorption step affects the purity of the hardly adsorbed gas recovered. The purity (volume %) of the hardly adsorbed gas is given by (1 - pressure at the end of the desorption step (kPa) / pressure in the adsorption step (kPa)) * 100 (Equation 1). From the viewpoint of increasing the purity of the hardly adsorbed gas, a higher pressure in the adsorption step is desirable, but if the pressure is too high, the cost required for increasing the pressure increases. Therefore, the pressure in the adsorption step is preferably 101.3 kPa or more and 700 kPa or less, and more preferably 200 kPa or more and 400 kPa or less.

[0068] If a pressure reduction step is not performed after the adsorption step, the pressure in the adsorption step affects the number of inflow steps required to achieve a negative pressure in the tower. When the pressure in the adsorption step is less than 202.6 kPa, a single inflow step will result in a negative pressure after the inflow. On the other hand, even if the pressure in the adsorption step is 202.6 kPa or higher, the pressure at the start of the desorption step can be set to a negative pressure by performing the inflow step two or more times after the adsorption step is completed. Thus, the number of inflow steps performed may be increased depending on the pressure in the adsorption step. To perform multiple inflow steps, the number of adsorption towers corresponding to the number of inflow steps is reduced and connected to the adsorption tower used in the adsorption step. When the adsorption step is operated at an internal pressure of the adsorption tower less than 202.6 kPa, a negative pressure can be achieved by a single inflow step in which the adsorption tower flows into one other adsorption tower. However, when the adsorption step is operated at a pressure of 202.6 kPa or higher and two or more inflow steps are performed without a pressure reduction step, two or more adsorption towers are required. Therefore, from the viewpoint of the size of the gas separation apparatus, it is preferable to carry out the pressure reduction step after the adsorption step and prior to the inflow step. Furthermore, if the pressure in the adsorption tower at the start of desorption is made negative in a single inflow step without carrying out the pressure reduction step, an upper limit is imposed on the pressure in the adsorption tower, and therefore an upper limit is imposed on the purity of the hardly adsorbable gas according to Equation 1. On the other hand, if the pressure reduction step is carried out after the adsorption step, the pressure in the adsorption tower at the start of desorption can be made negative in a single inflow step regardless of the pressure in the adsorption step, thereby increasing the recovery rate of the hardly adsorbable gas and increasing the purity of the hardly adsorbable gas. Therefore, from the viewpoint of freely controlling the purity of the hardly adsorbable gas, it is preferable to carry out the pressure reduction step after the adsorption step and prior to the inflow step.

[0069] <Pressure Reduction Step> In the pressure reduction step, a portion of the raw material gas in the adsorption tower is discharged to reduce the pressure inside the adsorption tower, and the raw material gas discharged in the pressure reduction step is supplied to the adsorption step. In the pressure reduction step, the adsorption tower is preferably in a pressurized state before the pressure reduction. Even if the adsorption step results in a pressurized state, the pressure inside the tower can be lowered before the inflow step, making it easier to make the pressure inside the tower negative after inflow. "Pressurized state" means that the pressure is greater than 101.3 kPa.

[0070] In the pressure reduction step, it is preferable to connect the pressurized adsorption tower to the raw material supply unit. As a portion of the gas flows from the adsorption tower to the raw material supply unit, the pressure in the adsorption tower decreases to the pressure in the raw material supply unit. That is, in the pressure reduction step, the gas in the adsorption tower moves to the raw material supply unit until the pressures in the adsorption tower and the raw material supply unit become the same.

[0071] If the pressure reduction step is performed after the adsorption step is completed, the pressure before desorption becomes negative due to the subsequent inflow step, regardless of the adsorption pressure in the adsorption step. As a result, even at high adsorption pressures, the number of adsorption towers required to achieve a negative pressure before desorption does not increase. Furthermore, even when the adsorption pressure is low and the pressure before desorption becomes negative after a single inflow operation, the pressure at the start of the desorption step can be further reduced by performing the pressure reduction step prior to the inflow operation. This further improves the recovery rate of the difficultly adsorbed gas. Thus, from the perspective of further improving the recovery rate of the difficultly adsorbed gas, it is preferable to perform the pressure reduction step after the adsorption step is completed.

[0072] During the pressure reduction step, the pressure in the adsorption tower decreases. The pressure at the start of the pressure reduction step is the pressure at the end of the adsorption step. Meanwhile, the pressure at the end of the pressure reduction step varies depending on the pressure in the raw material supply section, etc. Furthermore, in the case of a large-scale apparatus, it may take several to tens of seconds for the pressure reduction to be completed. Therefore, it is preferable to determine the pressure at the end of the pressure reduction step by determining the time until the pressure change ceases. The lower the pressure in the adsorption tower after the pressure reduction step, the lower the pressure before the desorption step will be due to the subsequent inflow step, thereby improving the recovery rate of the difficult-to-adsorb gas. The pressure after the pressure reduction step depends on the pressure in the raw material supply section, but the pressure in the raw material supply section may momentarily increase due to the gas movement during the pressure reduction step. For this reason, in terms of process management, it is assumed that the pressure reduction step will continue until the pressure stabilizes, but the time required for this depends on the size of the apparatus, the pressure in the adsorption step, etc. From the viewpoint of recovery rate of the hardly adsorbable gas, the pressure after completion of the pressure reduction step is preferably 101.3 kPa or more and 120.0 kPa or less, more preferably 101.3 kPa or more and 110.0 kPa or less, and even more preferably 101.3 kPa or more and 105.0 kPa or less.

[0073] <Inflow Process> In the inflow process, the raw material gas remaining in the adsorption tower after the adsorption process is introduced into another adsorption tower, thereby creating a negative pressure in the adsorption tower after the adsorption process. "Negative pressure" refers to a pressure less than 101.3 kPa. Specifically, the valves from the adsorption tower to the product storage section and the raw material supply section are closed to connect the adsorption tower used in the adsorption process to the other adsorption tower. When two adsorption towers are connected, gas flows from the higher-pressure adsorption tower to the lower-pressure adsorption tower, roughly equalizing the pressures of the two adsorption towers. For this reason, this operation is sometimes referred to as pressure equalization. In this way, in the inflow process, a portion of the gas in the adsorption tower is introduced by utilizing the pressure difference between the towers. For example, when an adsorption tower that has completed the adsorption process is connected to another adsorption tower that has completed the desorption process, gas flows from the adsorption tower that has completed the adsorption process to the other adsorption tower that has completed the desorption process. The tower used in the inflow process may be a tower that has completed the pressure reduction process after the adsorption process.

[0074] From the viewpoint of making the pressure inside the adsorption tower after the inflow step negative, the raw material gas is introduced from the adsorption tower after the adsorption step into another tower under reduced pressure. "Reduced pressure" means a pressure of less than 101.3 kPa. The pressure before the inflow into the other tower in the inflow step is preferably 50.0 kPa or less, more preferably 30.0 kPa or less, and even more preferably 10.0 kPa or less. There are no particular restrictions on the lower limit, but if it is too low, too much energy is required for separation, so it is preferably set to 1 kPa or more, and in practical terms, it is preferably set to 2 kPa or more.

[0075] From the viewpoint of making the pressure inside the adsorption tower after the inflow negative, when the pressure inside the adsorption tower after the adsorption step in the inflow step is A (kPa) and the pressure inside the other tower is B (kPa), it is preferable to satisfy (A+B) / 2<101.3, it is more preferable to satisfy (A+B) / 2<80.0, it is even more preferable to satisfy (A+B) / 2<60.0, and it is even more preferable to satisfy (A+B) / 2<40.0.

[0076] The following description will be given taking as an example a case where adsorption tower a is subjected to the adsorption step, adsorption tower b is subjected to the desorption step, and then the adsorption towers are subjected to the inflow step as other towers. Note that in the gas separation method according to this embodiment, there is also a case where adsorption tower b is subjected to the adsorption step, adsorption tower a is subjected to the desorption step, and then the adsorption towers are subjected to the inflow step as other towers.

[0077] At the start of the inflow step of adsorption tower a, the pressure in adsorption tower a is the pressure after the end of the adsorption step or the pressure after the end of the pressure drop step. On the other hand, the pressure at the end of the inflow step varies depending on the pressure of the connected adsorption tower b, the type of adsorbent, etc. In the inflow step, in addition to gas movement due to the pressure difference between the towers, adsorption of easily adsorbable gas occurs in the destination tower, causing a slight pressure drop in the destination tower, and gas movement occurs to equalize this between the towers. As a result, it takes about several tens of seconds for the pressure after inflow to become constant. The pressure after inflow in the inflow step means the pressure after the pressure has become constant.

[0078] The lower the pressure in adsorption tower a after the inflow step (the adsorption tower before the desorption step), the more the weakly adsorbable gas is sent to the other towers, and the lower the pressure before the start of the subsequent desorption step, thereby improving the recovery rate of the weakly adsorbable gas. On the other hand, if the pressure after the inflow step is too low, although a larger amount of the weakly adsorbable gas will be sent to the other towers in the inflow step, the amount of the weakly adsorbable gas recovered in the desorption step will decrease because the weakly adsorbable gas adsorbed on the adsorbent will be desorbed and sent.

[0079] For the above reasons, from the viewpoint of the recovery rate of the hardly adsorbable gas, the pressure in the adsorption tower after the inflow step and after the adsorption step is preferably 2 kPa or more and 80 kPa or less, more preferably 5 kPa or more and 60.0 kPa or less, and even more preferably 10 kPa or more and 40.0 kPa or less.

[0080] In the inflow step, the pressure of adsorption tower b increases after the desorption step. The pressure of adsorption tower b at the start of the inflow step may be the pressure after the desorption step. The pressure of the tower after the inflow step and the desorption step is preferably 2 kPa or more and 80 kPa or less, more preferably 5 kPa or more and 60.0 kPa or less, and even more preferably 10 kPa or more and 40.0 kPa or less. The pressures of adsorption tower a and adsorption tower b after the inflow step may be the same or different.

[0081] <Desorption Step> In the desorption step, the adsorption tower is depressurized and evacuated using a pressure reducing device. When the pressure inside the adsorption tower is reduced, the highly adsorbable gas adsorbed by the adsorbent is desorbed. In this way, the adsorbent is regenerated and the purified highly adsorbable gas is extracted.

[0082] In the desorption step, the pressure in the adsorption tower decreases. The pressure at the start of the desorption step is the pressure at the end of the inflow step. When the adsorption tower is used as "another tower" in the inflow step after the desorption step, the lower the pressure at the end of the desorption step, the lower the pressure in the tower at the end of the inflow step, thereby improving the recovery rate of the hardly adsorbable gas. Therefore, from the viewpoint of the recovery rate of the hardly adsorbable gas, the pressure at the end of the desorption step is preferably 50.0 kPa or less, more preferably 30.0 kPa or less, and even more preferably 10.0 kPa or less. Although the lower limit is not particularly limited, if it is too low, too much energy is required for separation, so it is preferably set to 1 kPa or more, and in practical terms, it is preferably set to 2 kPa or more.

[0083] <Repressurization Step> In the repressurization step, a poorly adsorbable gas having a purity of 50% or more is supplied into the column. If the adsorption step is performed without going through the repressurization step after the desorption step, or after the desorption step and the inflow step, the raw material gas is supplied into the adsorption column at a low pressure, and the velocity of the raw material gas passing through the adsorption column is too high, and the easily adsorbable gas contained in the raw material gas may not be sufficiently adsorbed by the adsorbent and may flow into the product storage section. Therefore, from the viewpoint of improving the purity of the poorly adsorbable gas, it is preferable to perform the repressurization step after the desorption step.

[0084] The purity of the hardly adsorbable gas supplied in the pressure recovery step is preferably 50% or more, more preferably 75% or more, and even more preferably 90% or more. For example, the hardly adsorbable gas recovered in the adsorption step may be flowed into the adsorption tower from the product storage section. The hardly adsorbable gas recovered in the adsorption step can be separated without decreasing the purity of the recovered hardly adsorbable gas even if it is further subjected to the adsorption step after pressure recovery. Because the gas flowing into the adsorption tower is not easily adsorbed by the adsorbent, the pressure inside the tower is increased. In this way, in the pressure recovery step, the hardly adsorbable gas is flowed into the adsorption tower and pressurized to a predetermined pressure. Although it is preferable to increase the pressure to the pressure required for the adsorption step, when pressurizing using gas flowing in from the product storage section, the pressure in the product storage section decreases as the gas flows out. Therefore, depending on the size of the product storage section relative to the adsorption tower, the pressure may not be increased to the pressure required for the adsorption step. Even a pressure increase that occurs spontaneously depending on the volume ratio between the product storage section and the adsorption tower is effective in suppressing a decrease in the purity of the hardly adsorbable gas.

[0085] In the repressurization step, the pressure in the adsorption tower increases. The pressure at the start of the repressurization step may be the pressure at the end of the desorption step or the pressure at the end of the inflow step. The pressure at the end of the repressurization step may be the pressure at the start of the adsorption step. However, the pressure at the end of the repressurization step may be lower than the pressure at the start of the adsorption step, as long as the purity of the difficult-to-adsorb gas does not decrease.

[0086] After the pressure recovery step, the adsorption tower is subjected to the adsorption step, and the hardly adsorbable gas introduced into the adsorption tower in the pressure recovery step is pushed out by the raw material gas supplied in the adsorption step and recovered as a hardly adsorbable gas.

[0087] In the gas separation method according to this embodiment, the adsorption step, pressure reduction step, inflow step, desorption step, inflow step, and pressure recovery step may be repeated depending on the amount of raw gas to be treated and the purity of the desired purified gas, and by repeating these steps, a highly pure purified gas can be obtained.

[0088] In the gas separation method according to this embodiment, three or more adsorption towers may be used for the purpose of continuously separating gases at a constant amount of raw gas. "Constant" means that the change in flow rate of the raw gas supplied from the raw material supply unit is within 10% by mass throughout the operation of each process and the point of switching to the next process. For example, when switching the supply destination of the raw material gas, the flow rate may increase or decrease instantaneously by opening or closing a valve. However, it is preferable to control the flow rate change to within 10% by mass, and more preferably within 5% by mass, throughout the switching process. By suppressing the increase or decrease in flow rate, the load on the device is stabilized, so that the device does not require a large margin of capacity. The time required for switching is not particularly limited as long as the gas flow rate is constant, but it can usually be completed in about 5 seconds.

[0089] In an example of using three or more adsorption towers, for example, three or more towers are used, and after the first tower is used for the adsorption step, the supply destination of the raw material gas is switched to the second tower, and after the second tower is used for the adsorption step, the supply destination of the raw material gas is switched to the third tower, thereby keeping the amount of raw material gas supplied to the towers constant.

[0090] 3 , the first tower is designated as adsorption tower a, the second tower as adsorption tower b, and the third tower as adsorption tower c. While the adsorption step is being performed in adsorption tower a, the desorption step is performed in adsorption tower c. After the adsorption step in adsorption tower a is completed, the supply destination of the raw gas is switched to adsorption tower b for the desorption step, a pressure reduction step is performed in adsorption tower a, an inflow step is performed in adsorption towers a and c, a desorption step is performed in adsorption tower a, and then a pressure recovery step is performed in adsorption tower c.

[0091] After the adsorption step is performed in adsorption tower b, the supply destination of the raw gas is switched to adsorption tower c, and after the pressure in adsorption tower b is reduced, an inflow step is performed in adsorption tower b and adsorption tower a, a desorption step is performed in adsorption tower b, and a pressure recovery step is performed in adsorption tower a.

[0092] After the adsorption step in adsorption tower c is completed, the supply destination of the raw material gas is switched to adsorption tower a. While the adsorption steps are being performed sequentially in adsorption tower b and adsorption tower c, adsorption tower a performs a pressure reduction step, an inflow step, a desorption step, an inflow step, and a pressure recovery step, thereby continuously purifying the raw material gas. The fewer the number of adsorption towers, the smaller the size of the separation device, so this is preferable; however, if the number is too small, it becomes difficult to switch between multiple adsorption towers and continuously separate gases. The number of adsorption towers is preferably 2 to 6, more preferably 2 to 4, and even more preferably 3.

[0093] As described above, the gas separation method of this embodiment can produce a readily adsorbable gas and / or a poorly adsorbable gas from a raw material gas. That is, the gas separation method of this embodiment can also be used as a method for producing a purified gas that purifies a readily adsorbable gas and / or a poorly adsorbable gas. For example, in a method for producing a purified gas in which the target component is a poorly adsorbable gas, at least the poorly adsorbable gas can be purified.

[0094] The gas separation device according to the embodiment and its operating mode will be described in more detail below.

[0095] [Gas Separation Apparatus 100] The schematic configuration of a gas separation apparatus 100 according to an embodiment will be described with reference to Figure 4. The gas separation apparatus 100 includes a raw material gas supply line 1, a raw material gas tank 2, a pressurizing device 3, adsorption towers 5a and 5b, a weakly adsorbable gas recovery line 7, a first product storage section 8, a depressurized gas line 10, an inlet gas line 11, a highly adsorbable gas recovery line 14, a depressurizing device 15, a restored pressure gas line 16, and a second product storage section 25. The raw material gas supply line 1 and the raw material gas tank 2 are collectively referred to as the raw material supply section.

[0096] The adsorption tower 5a has a fixed bed 20a packed with an adsorbent configured to be able to come into contact with the raw material gas introduced therein. One end of the adsorption tower 5a is connected to the raw material gas supply line 1, and the other end is connected to a hardly adsorbable gas recovery line 7. The hardly adsorbable gas recovery line 7 is equipped with an automatic valve AV6a. A first product storage section 8 is connected to the end of the hardly adsorbable gas recovery line 7.

[0097] The adsorption tower 5a is connected to a depressurized gas line 10 at an end in the same direction as the end connected to the hardly adsorbable gas recovery line 7. A raw material gas tank 2 is connected to the end of the depressurized gas line 10. The raw material gas supply line 1 may be connected to the end of the depressurized gas line 10. The depressurized gas line 10 connected to the adsorption tower 5a is equipped with an automatic valve AV9a. The depressurized gas line may be connected to an end in the opposite direction to the end connected to the hardly adsorbable gas recovery line 7.

[0098] The adsorption tower 5a is connected to a highly adsorbable gas recovery line 14 at an end thereof on the same side as the end connected to the raw gas supply line 1. The raw gas supply line 1 is equipped with a raw gas tank 2 and a pressurizing device 3. The pressurizing device 3 may be a compressor. An automatic valve AV4a is provided at the inlet of the adsorption tower 5a. Meanwhile, a pressure reducing device 15 is connected to the highly adsorbable gas recovery line 14, which is configured to be able to reduce the pressure inside the adsorption tower 5a. The pressure reducing device 15 may be a vacuum pump. The highly adsorbable gas recovery line 14 may be connected to a second product storage section 25. An automatic valve AV13a is provided on the highly adsorbable gas recovery line 14 connected to the adsorption tower 5a.

[0099] The adsorption tower 5a is connected to a pressure recovery gas line 16 at the end thereof connected to the hardly adsorbable gas recovery line 7. The pressure recovery gas line 16 is equipped with an automatic valve AV17a. The first product storage unit 8 is connected to the end of the pressure recovery gas line 16.

[0100] The adsorption tower 5b has a fixed bed 20b packed with an adsorbent configured to be able to come into contact with the raw material gas introduced therein. One end of the adsorption tower 5b is connected to the raw material gas supply line 1, and the other end is connected to the hardly adsorbable gas recovery line 7. The hardly adsorbable gas recovery line 7 is equipped with an automatic valve AV6b.

[0101] The adsorption tower 5b is connected to a depressurized gas line 10 at an end in the same direction as the end connected to the hardly adsorbable gas recovery line 7. A raw material gas tank 2 is connected to the end of the depressurized gas line 10. The raw material gas supply line 1 may be connected to the end of the depressurized gas line 10. The depressurized gas line 10 connected to the adsorption tower 5b is equipped with an automatic valve AV9b. The depressurized gas line may be connected to an end in the opposite direction to the end connected to the hardly adsorbable gas recovery line 7.

[0102] The adsorption tower 5b is connected to a highly adsorbable gas recovery line 14 at the end thereof that is in the same direction as the end connected to the raw material gas supply line 1. An automatic valve AV4b is provided at the inlet of the adsorption tower 5b. Meanwhile, a pressure reducing device 15 is connected to the highly adsorbable gas recovery line 14, so that the pressure inside the adsorption tower 5b can be reduced. In addition, an automatic valve AV13b is provided on the highly adsorbable gas recovery line 14 that is connected to the adsorption tower 5a.

[0103] The adsorption tower 5b is connected to a pressure-recovery gas line 16 at the end thereof connected to the hardly adsorbable gas recovery line 7. The pressure-recovery gas line is equipped with an automatic valve AV17b. The first product storage unit 8 is connected to the end of the pressure-recovery gas.

[0104] The adsorption towers 5a and 5b are connected by an inlet gas line 11 at an end in the same direction as the end connected to the raw gas supply line 1. The inlet gas line 11 is equipped with an automatic valve AV12. The inlet gas line 11 may connect the adsorption towers 5a and 5b at an end in the opposite direction to the end connected to the raw gas supply line 1, or may connect the adsorption towers 5a and 5b alternately at an end in the same direction as the end connected to the raw gas supply line 1 and an end in the opposite direction.

[0105] The gas separation apparatus may be equipped with pressure gauges for the purpose of measuring the pressure at each position in the apparatus. The raw material gas tank 2 may be equipped with a pressure gauge 18. The first product storage section 8 may be equipped with a pressure gauge 23. The adsorption tower 5a may be equipped with a pressure gauge 22a and a pressure gauge 21a at the top and bottom, respectively, and the adsorption tower 5b may be equipped with a pressure gauge 22b and a pressure gauge 21b at the top and bottom, respectively. The pressure gauge 19 may be equipped downstream of the pressurizing device 3, and the pressure gauge 24 may be equipped upstream of the decompression device 15.

[0106] Next, the operation of the gas separation apparatus 100 of this embodiment will be described with reference to FIG. 4 . A raw material gas is supplied to the adsorption tower 5a via the raw material gas supply line 1. Then, a highly adsorbable gas contained in the raw material gas is adsorbed by the adsorbent filled in the adsorption tower 5a, and a weakly adsorbable gas is recovered through the weakly adsorbable gas recovery line 7. That is, the adsorption tower 5a performs an adsorption process in which the raw material gas is introduced into the adsorption tower, the highly adsorbable gas is adsorbed by the adsorbent, and the weakly adsorbable gas is extracted. In the adsorption process, gas is introduced into the adsorption tower while maintaining the pressure in the adsorption tower constant at a predetermined pressure. Note that in the adsorption process, pressure loss occurs when the raw material gas flows through the adsorption tower, and a pressure difference may occur between the inlet and outlet of the adsorption tower.

[0107] After the adsorption step is completed, the gas in the adsorption tower 5a is released to the outside of the adsorption tower 5a to reduce the pressure therein. At this time, the gas in the adsorption tower 5a is recovered to the raw material supply section from the adsorption tower 5a via the pressure reduction gas line 10. At this time, as the pressure in the adsorption tower decreases, the easily adsorbable gas is desorbed from the adsorbent, and a portion of the hardly adsorbable gas remaining in the voids in the adsorption tower is replaced with the easily adsorbable gas. In other words, the pressure reduction step is performed by inflowing the gas in the adsorption tower to recover the hardly adsorbable gas.

[0108] The adsorption tower 5a is connected to the adsorption tower 5b via an inlet gas line 11, and the gas in the adsorption tower 5a is recovered in the adsorption tower 5b. At this time, as the pressure in the adsorption tower decreases, the easily adsorbable gas is desorbed from the adsorbent, and a portion of the hardly adsorbable gas remaining in the voids in the adsorption tower is further replaced by the easily adsorbable gas. In other words, an inflow step is performed in which the hardly adsorbable gas is recovered by inflowing the gas in the adsorption tower.

[0109] The adsorption tower 5a containing the adsorbent that has adsorbed the highly adsorbable gas is depressurized and evacuated by the pressure reducing device 15, thereby regenerating the adsorbent in the adsorption tower 5a and extracting the purified highly adsorbable gas. In other words, the desorption step of extracting the highly adsorbable gas is performed by depressurizing and evacuating the highly adsorbable gas from the adsorption tower 5a.

[0110] As described above, adsorption towers 5a and 5b repeatedly perform adsorption of a highly adsorbable gas by introducing a raw material gas and desorption of the highly adsorbable gas by reducing the pressure. Therefore, while adsorption tower 5a is desorbing a highly adsorbable gas, raw material gas is introduced into adsorption tower 5b to adsorb the highly adsorbable gas. After desorption of the highly adsorbable gas in adsorption tower 5a is complete, raw material gas is again introduced into adsorption tower 5a, and adsorption tower 5b is depressurized to desorb the highly adsorbable gas. This allows the adsorption and desorption of the highly adsorbable gas to be repeated in each tower, enabling continuous processing of the raw material gas.

[0111] When the adsorption tower 5a is in the adsorption process and the adsorption tower 5b is in the desorption process, the automatic valves AV4a, AV6a, and AV13b are opened from a state in which all the automatic valves are closed. By opening the automatic valve AV4a between the raw material gas tank 2 and the adsorption tower 5a, the raw material gas is introduced into the adsorption tower 5a.

[0112] A pressure reduction step may be subsequently performed. In this step, the valve from the adsorption tower 5a to the first product storage section 8 is closed, and gas inside the adsorption tower, which is in a pressurized state, is discharged to the raw material supply section. When switching from the adsorption step to the pressure reduction step in the adsorption tower 5a, the automatic valves AV6a and AV4a are closed, and the automatic valve AV9a on the pressure reduction gas line 10 is opened. During this time, the desorption step may be continued in the adsorption tower 5b.

[0113] During the inflow process, only the automatic valve AV12 provided on the inflow gas line 11 opens, and the other automatic valves close. As a result, gas transfer occurs only between the adsorption towers 5a and 5b. For example, if the adsorption tower 5a that has completed the adsorption process is connected to the adsorption tower 5b that has completed the desorption process, the pressure in the adsorption tower 5a is higher than the pressure in the adsorption tower 5b, and gas flows from the adsorption tower 5a to the adsorption tower 5b.

[0114] Next, the adsorption tower 5a undergoes a desorption process. During the desorption process, the automatic valves AV4a, AV6a, AV9a, and AV12 are closed, and the automatic valve AV13a is opened. The highly adsorbable gas in the adsorption tower 5a is introduced into the second product storage section 25 by the pressure reducing device 15.

[0115] On the other hand, after the inflow step, a pressure recovery step may be performed in the adsorption tower 5b. The automatic valve AV17b provided in the pressure recovery gas line 16 is opened, and the hardly adsorbable gas is introduced from the first product storage section 8 into the adsorption tower 5b.

[0116] The gas separation device 100 may be applied to, for example, purification of industrial exhaust gas containing carbon dioxide, biogas obtained by fermentation of organic matter, etc. Among these, it is preferable to use it for purification of biogas.

[0117] When the amount of the highly adsorbable gas discharged in the inflow step is Q2 and the amount of the highly adsorbable gas discharged in the desorption step is Q3, it is preferable to satisfy Q3 > Q2. Increasing the amount of gas originally separated using the desorbed gas in order to increase the recovery rate in the inflow step results in the highly adsorbable gas being re-adsorbed onto the adsorbent in the adsorption tower after regeneration, resulting in an apparent decrease in the amount of highly adsorbable gas adsorbed per unit adsorbent amount. By satisfying Q3 > Q2, the amount of highly adsorbable gas circulated is less than half of the total inflow gas, and the adsorbent occupancy by the inflow gas is also less than half. This eliminates the need for an excessively large adsorption tower to ensure a sufficient processing capacity, which is economically advantageous. From the above perspective, determining the pressure ranges for the adsorption step and the desorption step based on the adsorption characteristics of the adsorbent so as to satisfy Q3 > Q2 tends to enable the use of an economical device while increasing the recovery rate.

[0118] When the adsorbent is zeolite, and the amount of the highly adsorbable gas discharged in the pressure reduction step is Q1, the amount of the highly adsorbable gas discharged in the inflow step is Q2, and the amount of the highly adsorbable gas discharged in the desorption step is Q3, it is preferable that Q3 > Q1 + Q2 be satisfied. In an embodiment including a pressure reduction step, satisfying Q3 > Q1 + Q2 ensures that the selection of the adsorbent and the setting of the pressure range do not become significantly uneconomical from the viewpoint of the above-mentioned gas purification and separation.

[0119] [Biogas Refining System 1000: Example of Application to Biogas Refining] Fig. 5 is a diagram showing a schematic configuration of a biogas refining system 1000 in which the gas separation device 100 is applied to biogas refining. In this example of application to biogas refining, an example is shown in which methane, which is the main component of biogas, and carbon dioxide are separated and recovered. In the case of biogas refining, methane (CH ４ ), and the easily adsorbed gas is carbon dioxide (CO ２ )

[0120] The biogas purification system 1000 of this embodiment includes a fermenter 200, a desulfurization tower 300, a siloxane removal device 400, an oxygen removal device 500, a cooling device 600, a dehydration device 700, and a gas separation device 100.

[0121] The fermenter 200 is a tank that generates biogas (hereinafter also referred to as "raw material gas") by anaerobic fermentation of sewage sludge generated from sewage treatment plants, food waste generated from food factories and restaurants, and manure generated by dairy farms, etc. The fermenter 200 is connected to a blower 201 so that the generated biogas can be supplied to other devices.

[0122] The fermenter 200 may be connected to a desulfurization tower 300 before the biogas is introduced into the gas separation apparatus 100. The desulfurization tower 300 is an adsorption tower for removing hydrogen sulfide contained in the biogas. An example of a desulfurization agent filled in the desulfurization tower 300 is iron oxide. The iron oxide reacts with the hydrogen sulfide contained in the biogas to produce iron sulfide.

[0123] The fermenter 200 may be connected to a siloxane removal device 400 before the biogas is introduced into the gas separation device 100. The siloxane removal device 400 removes siloxanes contained in the biogas. These siloxanes are silicon oxide-containing substances contained in sewage sludge.

[0124] The fermenter 200 may be connected to an oxygen remover 500 before the biogas is introduced into the gas separation apparatus 100. The oxygen remover 500 removes oxygen contained in the biogas. By removing this oxygen, the purified methane gas can be safely transported.

[0125] The fermenter 200 may be connected to a cooling device 600 before the biogas is introduced into the gas separation device 100. The cooling device 600 removes moisture contained in the biogas by cooling the supplied biogas, thereby lowering the dew point of the biogas. As the cooling device 600, for example, a water-cooled cooler, an air-cooled cooler, an electric cooler, or the like can be used.

[0126] The fermenter 200 may be connected to a dehydration device 700 before the biogas is introduced into the gas separation device 100. The dehydration device 700 further removes moisture from the biogas from which moisture has been removed by the cooling device 600. This can further lower the dew point of the biogas. As the dehydration device 700, for example, a device filled with a dehydrating agent can be used.

[0127] Next, the operation of the biogas purification system 1000 of this embodiment will be described with reference to FIG.

[0128] First, biogas is generated by anaerobic fermentation of sewage sludge from sewage treatment plants, food waste from food factories and restaurants, and manure from dairy farms, etc., in the fermenter 200. The biogas at this stage contains hydrogen sulfide, moisture, etc.

[0129] The biogas generated in the fermenter 200 is sent to the desulfurization tower 300. In the desulfurization tower 300, hydrogen sulfide is removed so that the concentration of hydrogen sulfide contained in the biogas is at the level of several ppm by volume.

[0130] Thereafter, the biogas from which hydrogen sulfide has been removed is sent to the siloxane removal device 400. In the siloxane removal device 400, the concentration of siloxane contained in the biogas is reduced to several mg / Nm3. ３ Siloxane is removed to a level.

[0131] The biogas from which siloxane has been removed is then sent to the oxygen remover 500. In the oxygen remover 500, oxygen is removed so that the concentration of oxygen contained in the biogas is at the level of several ppm by volume.

[0132] The biogas is then sent to a cooling device 600. The cooling device 600 cools the biogas and removes moisture contained in the biogas, thereby lowering the dew point of the biogas. The biogas is then sent to a dehydration device 700. In the dehydration device 700, moisture in the biogas is further removed, reducing the moisture content to 1000 ppm by volume or less.

[0133] The biogas from which hydrogen sulfide, siloxane, and moisture have been removed is sent to the gas separation apparatus 100. The operation of the gas separation apparatus 100 is as described above for the gas separation apparatus.

[0134] According to the gas separation method of the present embodiment, high-purity methane and high-purity carbon dioxide can be efficiently recovered.

[0135] The present invention will be described in more detail below with reference to examples, but these are merely illustrative and the present invention is not limited to the following examples.

[0136] <Atomic Concentrations of Silicon, Aluminum, Phosphorus, and Potassium, and the Contents of Potassium and Lithium in Zeolite> Zeolite was dissolved in an aqueous sodium hydroxide solution, or if it was not soluble in an aqueous sodium hydroxide solution, it was thermally dissolved in aqua regia, and the solution was appropriately diluted and used to measure the concentrations of alkali metals in the zeolite by ICP-AES (hereinafter also referred to as "ICP-AES", SPS3520UV-DD: instrument name, manufactured by Hitachi High-Tech Science Corporation). The contents of potassium and lithium in the zeolite were calculated as the ratio (Z / T) of the total amount of potassium and lithium (Z) to the total amount of alkali metals (T) in the zeolite. The ratio (K / T) of the total amount of potassium (K) to the total amount of alkali metals (T) in the zeolite was also calculated in the same manner.

[0137] < ２９ Measurement of Si-MAS-NMR spectrum and SAR> The SAR of the zeolite in the zeolite molded body is ２９It can be determined by measuring Si-MAS-NMR. First, to condition the moisture of the zeolite, water was placed at the bottom of a desiccator, and the zeolite placed in a sample tube was kept above the water for 48 hours. After the moisture conditioning treatment, the zeolite was measured under the following conditions: ２９ Si-MAS-NMR measurement was carried out. Apparatus: JEOL RESONANCE ECA700 Magnetic field strength: 16.44 T ( １ H resonance frequency 700MHz) Measurement nucleus: ２９ Si Resonance frequency: 139.08 MHz NMR tube: 4 mmφ (zirconia rotor) Measurement method: DD / MAS (dipolar decoupling magic angle spinning) Pulse width: 45° Waiting time: 50 sec Number of accumulations: 800 (measurement time: approximately 22 hours) MAS: 10,000 Hz Chemical shift reference: silicone rubber (−22.34 ppm) external reference For the molded body containing GIS-type zeolite, ２９ The Si-MAS-NMR spectrum shows the following five peaks: (1) Q4(0Al): a peak of Si that is not bonded to any Al atoms via oxygen; (2) Q4(1Al): a peak of Si that is bonded to one Al atom via oxygen; (3) Q4(2Al): a peak of Si that is bonded to two Al atoms via oxygen; (4) Q4(3Al): a peak of Si that is bonded to three Al atoms via oxygen; and (5) Q4(4Al): a peak of Si that is bonded to four Al atoms via oxygen. ２９ In the Si-MAS-NMR spectrum, the peak positions are generally located between -112 ppm and -80 ppm, and can be assigned to Q4(0Al), Q4(1Al), Q4(2Al), Q4(3Al), and Q4(4Al) from the upfield side. The peak positions may vary depending on the cation species present in the zeolite framework, but generally, the peak positions are located in the following ranges: (1) Q4(0Al): -105 ppm to -112 ppm (2) Q4(1Al): -100 ppm to -105 ppm (3) Q4(2Al): -95 ppm to -100 ppm (4) Q4(3Al): -87 ppm to -95 ppm (5) Q4(4Al): -80 ppm to -87 ppm ２９The peak area intensity of the Si-MAS-NMR spectrum is analyzed using the analysis program dmfit (version #202000113) with Gaussian and Lorentzian functions, and the four parameters, amplitude (height of the maximum value of the spectrum), position (spectral position, ppm), width (full width at half maximum of the spectrum, ppm), and Gaussian / Lorentzian ratio (xG / (1−x)L), are calculated by optimizing them using a least-squares algorithm. The peak areas of Q4(0Al), Q4(1Al), Q4(2Al), Q4(3Al), and Q4(4Al) thus determined are designated as A_Q4(0Al), A_Q4(1Al), A_Q4(2Al), A_Q4(3Al), and A_Q4(4Al), and the total value of A_Q4(0Al), A_Q4(1Al), A_Q4(2Al), A_Q4(3Al), and A_Q4(4Al) is designated as A_total, and the SAR can be calculated as follows: SAR = 100 / [A_Q4(1Al) / 4 + 2 x A_Q4(2Al) / 4 + 3 x A_Q4(3Al) / 4 + 4 x A_Q4(4Al) / 4] x 2

[0138] <X-ray diffraction; crystal structure analysis> X-ray diffraction was performed according to the following procedure. (1) The zeolite (dried product) obtained in each production example was used as a sample and pulverized in an agate mortar. 10% by mass of crystalline silicon (manufactured by Rare Metallic Co., Ltd.) was then added, and the mixture was mixed in the agate mortar until uniform, to prepare a sample for structural analysis. (2) The sample (1) above was uniformly fixed on a non-reflective powder sample plate, and crystal structure analysis was performed by X-ray diffraction under the following conditions. X-ray diffractometer (XRD): Rigaku Corporation, powder X-ray diffractometer "RINT2500" (product name) X-ray source: Cu tube (40 kV, 200 mA) Measurement temperature: 25°C Measurement range: 5 to 60° (0.02° / step) Measurement speed: 0.2° / min Slit width (scattering, divergence, receiving light): 1°, 1°, 0.15 mm

[0139] Production Example 1: Method for producing a GIS-type zeolite molded body 61.93 g of water, 0.403 g of sodium hydroxide (NaOH, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and sodium nitrate (NaNO ３ , manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 3.39 g, and sodium aluminate (NaAlO ２A mixed gel was prepared by mixing 1.64 g of PEG-400 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 10.82 g of colloidal silica (Ludox AS-40, solid content concentration 40 mass%, manufactured by Grace Chemicals) and stirring for 30 minutes. The composition of the mixed gel was α = E / Al ２ O ３ =4.53, β=SiO ２ / Al ２ O ３ = 8.17, γ = Na ２ O / Al ２ O ３ = 3.99, δ = P ２ O ５ / Al ２ O ３ = 0.00, ε = H ２ O / Al ２ O ３ = 431.0, ζ = H ２ O / OH － =376.7, η=R / Al ２ O ３ = 0.00. The mixed gel was placed in a 200 mL stainless steel micro-bomb (manufactured by HIRO COMPANY) containing a fluororesin inner cylinder, and hydrothermal synthesis was carried out for 4 days at a stirring speed of 30 rpm and 135°C using a stirring thermostatic chamber (manufactured by HIRO COMPANY) that can rotate the micro-bomb up and down. The product was filtered and dried at 120°C, and then powdered zeolite was obtained. 1 g of the obtained zeolite was dissolved in potassium carbonate (K ２ CO ３ The resulting mixture was placed in 500 mL of a 0.05 N aqueous potassium carbonate solution prepared using a zeolite ion exchanger (manufactured by Nippon Soda Co., Ltd.) and stirred at 500 rpm at room temperature for 3 hours. The product was filtered and dried at 120°C to obtain a powdered zeolite in which some of the cations had been exchanged with potassium. The XRD spectrum confirmed that the resulting zeolite was a GIS-type zeolite. Furthermore, since no peaks attributable to other zeolites or amorphous silica-alumina were observed, the zeolite was evaluated as a high-purity GIS-type zeolite.

[0140] The obtained zeolite was ２９The silica-alumina ratio was calculated from the Si-MAS-NMR spectrum, and as a result, SAR was 6.90, and (a+d) / (b+c) was 0.305. The contents of potassium and lithium in the zeolite were Z / T=0.99 (=K / T). ２ The adsorption and desorption isotherms of CH were measured, and the adsorption amount at 760 mmHg was 82.2 cc / g, and q(Ad) / q(De)=0.984. ４ The adsorption isotherm was measured and the adsorption amount at 760 mmHg was 2.2 cc / g.

[0141] 40 parts by mass of GIS type zeolite powder, 1.2 parts by mass of methyl cellulose (Celander YB-132A manufactured by HighChem Co., Ltd.), 0.2 parts by mass of polyvinyl alcohol (Gohsenol N-300 manufactured by Mitsubishi Chemical Corporation), 48.2 parts by mass of alumina sol (manufactured by Nissan Chemical Industries, Ltd., alumina content: 10.5% by mass), and 10.4 parts by mass of powdered alumina hydrate were mixed. The mixture was extruded into a cylindrical shape with a diameter of 3 mm using a wet extrusion granulator MG-55 (manufactured by Dalton Co., Ltd.), and then calcined in an electric furnace at 350°C for 24 hours in an air atmosphere to produce a GIS type zeolite molded body.

[0142] In addition, commercially available 13X type zeolite molded body (Fujifilm Wako Pure Chemical Industries, Ltd., trade name "Molecular Sieves 13X", faujasite (hereinafter also referred to as "FAU")) and activated carbon CMS (Osaka Gas Chemicals Co., Ltd., trade name "3K-172" (hereinafter also referred to as "CMS")) were used.

[0143] Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-3: Gas Separation Method Using the gas separation apparatus shown in FIG. 4, a raw gas containing 60% by volume of methane and 40% by volume of carbon dioxide was separated and recovered into Gas 1 (methane) and Gas 2 (carbon dioxide). As shown in Table 1, 1 kg of the GIS-type zeolite shaped body obtained in Production Example 1, 13X, FAU, or CMS was packed into each of the adsorption towers 5a and 5b. At this time, the packing was carried out so that the packing rate of the adsorption layer (the cylindrical portion packed with the adsorbent) was 68% by volume. Before the following operation 1, the adsorption towers 5a and 5b were depressurized to 50 Pa and heated to 200°C using a heater, and the moisture contained in the adsorbent was removed.

[0144] (Operation 1) Adsorption tower 5a: Adsorption step With all automatic valves AV closed, automatic valves AV4a and AV6a were opened, and the raw material gas was supplied to adsorption tower 5a by pressure device 3 at the pressure shown in Table 1. After 2 minutes had elapsed, automatic valves AV4a and AV6a were closed. The entire amount of gas 1 (methane) that flowed out of first product storage section 8 from the time automatic valves AV4a and AV6a were opened until they were closed was recovered in a gas bag (not shown).

[0145] Adsorption Tower 5b: Desorption Step With all automatic valves AV closed, automatic valve AV13b was opened, and the pressure in the adsorption tower 5b was reduced by the pressure reducing device 15.

[0146] When skipping operation 2 and proceeding to operation 3, the pressure in adsorption tower 5b was reduced, and then automatic valve AV13b was closed after confirming that the pressure indicated by pressure gauge 22b located at the top of the adsorption tower had reached the pressure indicated in Table 1. The entire amount of gas 2 (carbon dioxide) that flowed out of adsorption tower 5b from the time automatic valve AV13b was opened until it was closed was recovered in a gas bag (not shown).

[0147] (Operation 2) Adsorption tower 5a: pressure drop step After the automatic valves AV4a and AV6a were closed in operation 1, the automatic valve AV9a was opened to allow the gas in the adsorption tower 5a to flow into the raw gas tank 2. After 10 seconds had elapsed, the automatic valve AV9a was closed.

[0148] Adsorption tower 5b: Desorption step The automatic valve was maintained in the state of Operation 1. After it was confirmed that the pressure indicated by pressure gauge 22b located at the top of the adsorption tower reached the pressure indicated in Table 1, automatic valve AV13b was closed. The entire amount of gas 2 (carbon dioxide) that flowed out of adsorption tower 5b from the time automatic valve AV13b was opened until it was closed was recovered in a gas bag (not shown).

[0149] (Operation 3) Adsorption tower 5a and adsorption tower 5b: inflow step After the automatic valves AV9a and AV13b were closed in operation 2, the automatic valve AV12 was opened to allow the gas in the adsorption tower 5a to flow into the adsorption tower 5b. After 10 seconds had elapsed, the automatic valve AV12 was closed.

[0150] (Operation 4) Adsorption Tower 5a: Desorption Step After the automatic valve AV12 was closed in Operation 3, the automatic valve AV13a was opened, and the pressure in the adsorption tower 5a was reduced by the pressure reducing device 15.

[0151] Adsorption tower 5b: Pressure recovery step After automatic valve AV12 was closed in operation 3, automatic valve AV17b was opened to allow gas to flow in from first product storage section 8. After confirming that the pressures indicated by pressure gauges 21b and 22b located above and below adsorption tower 5b had reached the pressures shown in Table 1, automatic valve AV17b was closed.

[0152] (Operation 5) Adsorption tower 5a: desorption step The automatic valve was maintained in the state of Operation 4. When proceeding to Operation 7 without performing Operation 6 described below, the pressure in the adsorption tower 5a was reduced, and then the automatic valve AV13a was closed after confirming that the pressure indicated by the pressure gauge 22a located at the top of the adsorption tower had reached the pressure shown in Table 1. The entire amount of gas 2 (carbon dioxide) that flowed out of the adsorption tower 5a from the time the automatic valve AV13a was opened until the time it was closed was recovered in a gas bag (not shown).

[0153] Adsorption tower 5b: Adsorption step After automatic valve AV17b was closed, automatic valves AV4b and AV6b were opened, and the raw material gas was supplied to adsorption tower 5b by pressure device 3 at the pressure shown in Table 1. After 2 minutes had elapsed, automatic valves AV4b and AV6b were closed. The entire amount of gas 1 (methane) that flowed out of first product storage section 8 from the time automatic valves AV4b and AV6b were opened until they were closed was recovered in a gas bag (not shown).

[0154] (Operation 6) Adsorption tower 5a: Desorption step The automatic valve was maintained in the state of Operation 5. After confirming that the pressure indicated by the pressure gauge 22a located at the top of the adsorption tower reached the pressure indicated in Table 1, the automatic valve AV13a was closed. The entire amount of gas 2 (carbon dioxide) that flowed out of the adsorption tower 5a from the time the automatic valve AV13a was opened until the time it was closed was recovered in a gas bag (not shown).

[0155] Adsorption tower 5b: Pressure drop step After automatic valves AV4b and AV6b were closed in operation 5, automatic valve AV9b was opened to allow the gas in adsorption tower 5b to flow into raw gas tank 2. After 10 seconds had elapsed, automatic valve AV9b was closed.

[0156] (Operation 7) Adsorption tower 5a and adsorption tower 5b: inflow step After the automatic valves AV13a and AV9b were closed in operation 6, the automatic valve AV12 was opened to allow the gas in the adsorption tower 5b to flow into the adsorption tower 5a. After 10 seconds had elapsed, the automatic valve AV12 was closed.

[0157] (Operation 8) Adsorption tower 5a: pressure recovery step After closing automatic valve AV12 in operation 7, automatic valve AV17a was opened to allow gas to flow in from the product storage section. After confirming that the pressures indicated by pressure gauges 21a located above and below adsorption tower 5a and pressure gauge 21a reached the pressures indicated in Table 1, automatic valve AV17a was closed.

[0158] Adsorption Tower 5b: Desorption Step After the automatic valve AV12 was closed in operation 7, the automatic valve AV13b was opened and the pressure in the adsorption tower 5b was reduced by the pressure reducing device 15.

[0159] (Operation 9) Adsorption tower 5a: Adsorption step After closing automatic valve AV17a, automatic valves AV4a and AV6a were opened, and the raw material gas was supplied to adsorption tower 5a by pressure device 3 at the pressure shown in Table 1. After 2 minutes had elapsed, automatic valves AV4a and AV6a were closed. The entire amount of gas 1 (methane) that flowed out of first product storage section 8 from the time automatic valves AV4a and AV6a were opened until they were closed was recovered in a gas bag (not shown).

[0160] Adsorption tower 5b: Desorption step The automatic valve was maintained in the state of Operation 8. After it was confirmed that the pressure indicated by the pressure gauge 22b located at the top of the adsorption tower reached the pressure indicated in Table 1, the automatic valve AV13b was closed. The entire amount of gas 2 (carbon dioxide) that flowed out of the adsorption tower 5b from the time the automatic valve AV13b was opened until it was closed was recovered in a gas bag (not shown).

[0161] Using the adsorbents shown in Table 1, in Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-3 which did not include a pressure reduction step, the above procedures 1, 3, 4, 5, 7, 8, and 9 were carried out once, and then the procedures 3, 4, 5, 7, 8, and 9 were repeated 100 times. Similarly, in Examples 1-9 to 1-14 which included a pressure reduction step, the above procedures 1, 2, 3, 4, 5, 6, 7, 8, and 9 were carried out once, and then the procedures 2, 3, 4, 5, 6, 7, 8, and 9 were repeated 100 times.

[0162] All of the obtained gas 1 (methane) and gas 2 (carbon dioxide) were recovered. The obtained methane purity and carbon dioxide purity were the values ​​shown in Table 1. The recovery rate was calculated from the amount of methane V2 (NL) recovered in gas 1 from the amount of methane V1 (NL) supplied during this period by calculating V2 / V1, and is shown in Table 1. Similarly, the recovery rate was calculated from the amount of methane V4 (NL) recovered in gas 2 from the amount of carbon dioxide V3 (NL) supplied during this period by calculating V2 / V1, and is shown in Table 1. The pressure before desorption was calculated from the average pressure (kPa) indicated by pressure gauges 21a, 22a, 21b, and 22b located above and below adsorption towers 5a and 5b after the inflow step was completed, and is shown in Table 1.

[0163]

[0164]

[0165]

[0166] A comparison of the above examples and comparative examples reveals that a negative pre-desorption pressure can increase the recovery rate of a difficult-to-adsorb gas such as methane. It also reveals that a pressure-reducing step prior to the inflow step can further increase the recovery rate of the difficult-to-adsorb gas while also increasing the purity of the difficult-to-adsorb gas.

[0167] In the above embodiment, the raw material gas is purified using two adsorption towers, but it is also possible to add one more adsorption tower of the same size and operate three towers.

[0168] For example, in Example 1-9, the adsorption time was 120 seconds, the pressure drop time was 10 seconds, the inflow time was 10 seconds, the desorption time was 160 seconds, the inflow time was 10 seconds, and the pressure recovery time was 30 seconds. Each operation was repeated to obtain a 1.0 m ３ That is, in Example 1-9, the time required for the cycle from the start of the adsorption step to the start of the next adsorption step is 340 seconds, and the adsorption steps for two reactors are performed during that time, so the raw gas is purified within 240 seconds of the cycle time of 340 seconds (corresponding to 1 / 1.42 of the cycle time).

[0169] On the other hand, if one more adsorption tower of the same size is added and the feed gas is purified using three towers, the adsorption time is 120 seconds, the pressure drop time is 10 seconds, the inflow time is 10 seconds, the desorption time is 110 seconds, the inflow time is 10 seconds, the pressure recovery time is 30 seconds, and the standby time is 70 seconds, and each operation can be repeated. In this case, the time required for the cycle from the start of the adsorption step to the start of the next adsorption step is 360 seconds, and since three adsorption steps are performed during that time, it can be seen that the feed gas is constantly purified for 360 seconds out of the 360-second cycle time. In this case, the time for purifying the gas is 1.42 times longer than in Example 1-9, and the amount of gas purified is 1.42 m ３ It can be seen that the amount of raw gas that can be treated per unit time can be increased by operating three adsorption towers.

[0170] In addition, in Example 1-9, when the adsorbent packing rate was set to 68% and gas was purified, CH ４ The recovery rate was 98.1%, but when the filling rate was 60%, CH ４ The recovery rate was 97.6%.

[0171] Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-3 Gas separation was performed while sampling a portion of the depressurized gas using the gas separation apparatus shown in Figure 6. The feed gas composition, adsorption step pressure, presence or absence of a depressurization step, and presence or absence of an inflow step were the same as in Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-3, and as shown in Table 2, the pressures before and after desorption were also approximately the same as the values ​​shown in Table 1.

[0172] The gas separation apparatus shown in Fig. 6 is the same as the apparatus shown in Fig. 4 except that a three-way solenoid valve AV26 is provided in the depressurized gas line 10 and a sample recovery line 28 branches off from it, so only the differences will be explained below. One side of the three-way solenoid valve AV26 is connected downstream of the depressurized gas line 10, and the other two sides are connected to a sample recovery line 28 connected to a gas bag (not shown) and a depressurized gas return line 27, so that the apparatus can automatically switch between sample recovery and recovery as raw gas.

[0173] In the examples including the depressurization step, the depressurization step was carried out with the three-way solenoid valve AV26 venting from the depressurized gas line 10 to the depressurized gas return line 27. However, for gas analysis, the three-way solenoid valve AV26 was connected from the depressurized gas line 10 to the sample collection line 28 every 20 times, and the entire amount of the outflowing gas 3 (depressurized gas) was collected in a gas bag (not shown). After this operation, the three-way solenoid valve AV26 was returned to the state of venting from the depressurized gas line 10 to the depressurized gas return line 27. The reason for carrying out this operation every 20 times is that it takes 20 times for the various processes in the gas separation apparatus 100 to become stable after collection of the depressurized gas, and the measurement period is not limited thereto.

[0174] The amounts q0 to q3 of the weakly adsorbable gas and the amounts Q0 to Q3 of the easily adsorbable gas are determined as follows: In this example, when the supply amount is determined to be 100, q0 is 60 and Q0 is 40 based on the distribution of the raw material gas composition.

[0175] The amount q1 of the weakly adsorbable gas and the amount Q1 of the easily adsorbable gas in the depressurized gas are values ​​expressed as a ratio to the specified amount 100 of the raw material gas supply amount, based on the measurement results of a gas bag (not shown) of the gas 3 (depressurized gas) flowing out from the depressurized gas return line 27 using a gas meter (not shown) and gas chromatography (not shown).

[0176] The amount q3 of the weakly adsorbable gas and the amount Q3 of the easily adsorbable gas in the desorption step are values ​​expressed as a ratio to the specified amount 100 of the raw material gas supply amount, based on the results of measuring gas bags (not shown) of gas 2 (carbon dioxide) flowing out from adsorption towers 5a and 5b using a gas meter (not shown) and gas chromatography (not shown).

[0177] The amount q2 of the weakly adsorbable gas and the amount Q2 of the easily adsorbable gas in the inflow step are calculated by taking a mass balance from the results of measuring q0, q1, q3 and Q0, Q1, Q3 as well as a gas bag (not shown) of gas 1 using a gas meter (not shown) and gas chromatography (not shown), and are numerical values ​​expressed as a ratio to the specified amount of raw material gas supplied, which is 100.

[0178] In Examples 2-9 to 2-14 and Comparative Example 2-4, which include a depressurization step, the amount of depressurized gas circulated is defined as (Q1+q1) / (Q0+q0).

[0179] In Examples 2-1 to 2-8 and Comparative Examples 2-1 to 2-3, which did not include a pressure-reducing step, the above-mentioned operations 1, 3, 4, 5, 7, 8, and 9 were performed once, and then operations 3, 4, 5, 7, 8, and 9 were repeated 100 times. In Examples 2-9 to 2-14, which included a pressure-reducing step, the above-mentioned operations 1, 2, 3, 4, 5, 6, 7, 8, and 9 were performed once, and then operations 2, 3, 4, 5, 6, 7, 8, and 9 were repeated 100 times. In Comparative Example 2-4, which included a pressure-reducing step, operations 1, 2', 3', 4', 5', 6', 7', 8', and 9' were performed once, and then operations 2', 3', 4', 5', 6', 7', 8', and 9' were repeated 100 times. Operation 1 was as described above, and operations 2', 3', 4', 5', 6', 7', 8', and 9' were as follows. The outline of the flow of Comparative Example 2-4 is as shown in FIG.

[0180] (Operation 2') Adsorption tower 5a and adsorption tower 5b: inflow step After the automatic valves AV4a, AV6a, and AV13b were closed in operation 1, the automatic valve AV12 was opened to allow the gas in the adsorption tower 5a to flow into the adsorption tower 5b. After 10 seconds had elapsed, the automatic valve AV12 was closed.

[0181] (Operation 3′) Adsorption tower 5a: depressurization step After operation 2′, the automatic valve AV9a was opened, and the three-way solenoid valve AV26 was in a state of venting from the depressurized gas line 10 to the depressurized gas return line 27, allowing the gas in the adsorption tower 5a to flow into the raw gas tank 2. After 10 seconds had elapsed, the automatic valve AV9a was closed.

[0182] Adsorption tower 5b: Pressure recovery step After operation 2', automatic valve AV17b was opened to allow gas to flow in from first product storage section 8.

[0183] (Operation 4′) Adsorption Tower 5a: Desorption Step After Operation 3′, the automatic valve AV13a was opened, and the pressure in the adsorption tower 5a was reduced by the pressure reducing device 15.

[0184] Adsorption tower 5b: pressure recovery step Automatic valve 17b was maintained in the state of Operation 3'. After it was confirmed that the pressures indicated by pressure gauges 21b and 22b located above and below adsorption tower 5b had reached the pressures shown in Table 2, automatic valve AV17b was closed.

[0185] (Operation 5') Adsorption tower 5a: Desorption step The automatic valve was maintained in the state of Operation 4'. After confirming that the pressure indicated by the pressure gauge 22a located at the top of the adsorption tower reached the pressure indicated in Table 2, the automatic valve AV13a was closed. The entire amount of gas 2 (carbon dioxide) that flowed out of the adsorption tower 5a from the time the automatic valve AV13a was opened to the time it was closed was recovered in a gas bag (not shown).

[0186] Adsorption tower 5b: Adsorption step After automatic valve AV17b was closed, automatic valves AV4b and AV6b were opened, and the raw material gas was supplied to adsorption tower 5b by pressure device 3 at the pressure shown in Table 2. After 2 minutes had elapsed, automatic valves AV4b and AV6b were closed. The entire amount of gas 1 (methane) that flowed out of first product storage section 8 from the time automatic valves AV4b and AV6b were opened until they were closed was recovered in a gas bag (not shown).

[0187] (Operation 6') Adsorption tower 5a and adsorption tower 5b: inflow step After operation 5', automatic valves AV4b, AV6b, and AV13a were closed, and automatic valve AV12 was opened to allow the gas in adsorption tower 5b to flow into adsorption tower 5a. After 10 seconds had elapsed, automatic valve AV12 was closed.

[0188] (Operation 7′) Adsorption tower 5a: pressure recovery step After operation 2′, the automatic valve AV17a was opened, and gas was allowed to flow in from the first product storage section 8. After confirming that the pressures indicated by the pressure gauges 21a and 22a located above and below the adsorption tower 5a had reached the pressures shown in Table 2, the automatic valve AV17a was closed.

[0189] Adsorption tower 5b: depressurization step After operation 6′, the automatic valve AV9b was opened, and the three-way solenoid valve AV26 was in a state of venting from the depressurized gas line 10 to the depressurized gas return line 27, allowing the gas in the adsorption tower 5b to flow into the raw gas tank 2. After 10 seconds had elapsed, the automatic valve AV9b was closed.

[0190] (Operation 8') Adsorption tower 5a: pressure recovery step The automatic valve AV17a was maintained in the state of Operation 7'. After confirming that the pressures indicated by the pressure gauges 21a and 22a located above and below the adsorption tower 5a had reached the pressures shown in Table 2, the automatic valve AV17a was closed.

[0191] Adsorption Tower 5b: Desorption Step After operation 7', the automatic valve AV13b was opened, and the pressure in the adsorption tower 5b was reduced by the pressure reducing device 15.

[0192] (Operation 9') Adsorption tower 5a: Adsorption step After closing automatic valve AV17a, automatic valves AV4a and AV6a were opened, and the raw material gas was supplied to adsorption tower 5a by pressure device 3 at the pressure shown in Table 2. After 2 minutes had elapsed, automatic valves AV4a and AV6a were closed. The entire amount of gas 1 (methane) that flowed out of first product storage section 8 from the time automatic valves AV4a and AV6a were opened until they were closed was recovered in a gas bag (not shown).

[0193] Adsorption tower 5b: Desorption step The automatic valve was maintained in the state of operation 8'. After it was confirmed that the pressure indicated by the pressure gauge 22b located at the top of the adsorption tower reached the pressure indicated in Table 2, the automatic valve AV13b was closed. The entire amount of gas 2 (carbon dioxide) that flowed out of the adsorption tower 5b from the time the automatic valve AV13b was opened until it was closed was recovered in a gas bag (not shown).

[0194]

[0195]

[0196]

[0197] When the pressure reduction step and the inflow step were performed in the reverse order to that of the present invention in Comparative Example 2-4, the adsorption tower did not reach a negative pressure after the inflow step. Compared with Example 2-9 of the present invention under the same pressure conditions, Example 2-9 had a recovery rate of 98% or more, while Comparative Example 2-4 had a low methane recovery rate of 97%.

[0198] The amount of highly adsorbable gas in Comparative Example 2-3 is Q2 > Q3, while the amount of highly adsorbable gas in Examples 2-1 to 2-8, which do not include a pressure reduction step, is Q3 > Q2. The amount of highly adsorbable gas adsorbed per unit adsorbent amount is determined by the properties of the adsorbent and the pressure range. To separate the highly adsorbable gas in the present technology, the highly adsorbable gas must be discharged downstream from the second product storage section 25 in the desorption step. Increasing the amount of gas originally separated by the desorption gas in the inflow step to increase the recovery rate would result in the highly adsorbable gas being re-adsorbed by the adsorbent in the adsorption tower after regeneration, resulting in an apparent decrease in the amount of highly adsorbable gas adsorbed per unit adsorbent amount. If Q2 > Q3, more than half of the highly adsorbable gas would need to be circulated again, simply requiring more than double the amount of adsorbent. In this case, the unit price of the adsorbent and the capacity of the adsorption tower filled with the adsorbent would be calculated to be twice as much as when the highly adsorbable gas is not circulated, resulting in an economic disadvantage. From the above viewpoint, the pressure range is determined based on the adsorption characteristics of the adsorbent, and the combination condition Q3>Q2 is the above condition that increases the recovery rate while not making the apparatus significantly uneconomical.

[0199] In Examples 2-9 to 2-14 including the pressure reduction step, by satisfying Q3>Q1+Q2, the selection of the adsorbent and the setting of the pressure range are within a range that is not significantly uneconomical from the viewpoint of the above-mentioned gas purification and separation.

[0200] DESCRIPTION OF SYMBOLS 1...raw material gas supply line, 2...raw material gas tank, 3...pressurizing device, 5a, 5b...adsorption tower, 7...hardly adsorbable gas recovery line, 8...first product storage section, 10...depressurized gas line, 11...inlet gas line, 14...easily adsorbable gas recovery line, 15...depressurizing device, 16...repressurized gas line, 25...second product storage section, 100...gas separation device, 200...fermenter, 300...desulfurization tower, 400...siloxane removal device, 500...oxygen removal device, 600...cooling device, 700...dehydration device, 1000...biogas purification system

Claims

1. A gas separation method in which two or more towers containing an adsorbent are used in a switching manner, the gas separation method comprising: an adsorption step in which a feed gas containing an easily adsorbable gas and a poorly adsorbable gas is passed through at least one of the towers to adsorb the easily adsorbable gas onto the adsorbent in the tower, and recover the poorly adsorbable gas; an inflow step in which, after the adsorption step, the feed gas remaining in the tower is flowed into another tower, and the pressure in the tower after the adsorption step is made negative; and a desorption step in which, after the inflow step, the easily adsorbable gas adsorbed onto the adsorbent in the tower is desorbed, and the easily adsorbable gas is recovered; and the other tower into which the feed gas was flowed in the inflow step is subjected to the adsorption step.

2. The gas separation method according to claim 1, further comprising a pressure reduction step of reducing the pressure inside the tower by discharging a portion of the raw material gas inside the tower after the adsorption step and before the inflow step, and the raw material gas discharged in the pressure reduction step is supplied to the adsorption step.

3. The gas separation method according to claim 2, wherein the poorly adsorbable gas is a target component, and the concentration of the target component in the raw gas discharged in the pressure reduction step is higher than the concentration of the target component in the raw gas flowed into the other tower in the flow-in step.

4. The gas separation method according to claim 2, wherein the inside of the column is pressurized before the pressure reduction step.

5. A gas separation method according to claim 1, further comprising a pressure recovery step of supplying the hardly adsorbed gas having a purity of 50% or more into the column after the desorption step.

6. The gas separation method according to claim 1, wherein in the inflow step, the raw material gas is introduced into the other column under reduced pressure.

7. The gas separation method according to claim 1, wherein three or more towers containing the adsorbent are used, and after a first tower is subjected to the adsorption process, the supply destination of the raw material gas is switched to a second tower, and after the second tower is subjected to the adsorption process, the supply destination of the raw material gas is switched to a third tower, and the amount of the raw material gas supplied to the towers is kept constant.

8. The gas separation method according to claim 1, wherein, in the inflow step, when the pressure in the column after the adsorption step is A (kPa) and the pressure in the other column is B (kPa), the relationship (A + B) / 2 < 101.3 is satisfied.

9. The gas separation method according to claim 1, wherein the tower has an adsorption layer, and the packing rate of the adsorbent in the adsorption layer is 90% by volume or less.

10. The gas separation method according to claim 1, wherein the easily adsorbed gas is carbon dioxide and the less easily adsorbed gas is methane.

11. The gas separation method of claim 1, wherein the adsorbent comprises zeolite or activated carbon.

12. The gas separation method according to claim 1, wherein when the amount of the highly adsorbable gas discharged in the inflow step is Q2 and the amount of the highly adsorbable gas discharged in the desorption step is Q3, the relationship Q3 > Q2 is satisfied.

13. The gas separation method according to claim 2, wherein the adsorbent is zeolite, and when the amount of the highly adsorbable gas discharged in the pressure reduction step is Q1, the amount of the highly adsorbable gas discharged in the inflow step is Q2, and the amount of the highly adsorbable gas discharged in the desorption step is Q3, the relationship Q3 > Q1 + Q2 is satisfied.

14. A method for producing a purified gas, comprising purifying the easily adsorbable gas and / or the less adsorbable gas by the gas separation method according to any one of claims 1 to 13.

15. The method for producing a purified gas according to claim 14, wherein the gas separation method is the gas separation method according to claim 3, and at least the gas that is difficult to adsorb is purified.

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