Gas separation method and purified gas production method

Abstract

The present invention addresses the problem of providing a gas separation method and a purified gas production method wherein it is possible to suppress pulverization of an adsorbent while obtaining a high recovery rate of a difficult-to-adsorb gas. The present invention solves this problem with a gas separation method for switching between and using two or more adsorption columns in which an adsorbent that includes zeolite is accommodated, said gas separation method having: an adsorption step in which a source material gas including an easy-to-adsorb gas and a difficult-to-adsorb gas is made to pass through the interior of at least one of the adsorption columns, the easy-to-adsorb gas is made to adsorb to the adsorbent within said adsorption column, and the difficult-to-adsorb gas is recovered; an inflow step in which, after the adsorption step, a residual gas in said adsorption column is made to move to another column having a lower pressure than the pressure in said adsorption column; and a desorption step in which, after the inflow step, the easy-to-adsorb gas that has adsorbed to the adsorbent within said adsorption column is made to desorb, and the easy-to-adsorb gas is recovered, wherein the other adsorption column into which the residual gas flows during the inflow step is subjected to the adsorption step, and the inflow gas quantity Vi per unit weight of the adsorbent during the inflow step is 0.40 mol / kg or less.

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 purified gas.

[0002] Gas separation technology is used in various fields such as energy, environment, chemical industry, and food industry, and the appropriate separation technology is selected according to the type of gas and purpose. One such method, pressure swing adsorption (PSA), is well known as a method in which easily adsorbed gas components from a gas mixture containing two or more components are selectively adsorbed onto an adsorbent, and then desorbed by reducing the pressure to separate the gas.

[0003] For example, Patent Document 1 shows an example of separating and purifying carbon monoxide and nitrogen raw material gases using a pressure swing type adsorption separation method. In this method, gas separation is performed by repeatedly going through a repressurization process, adsorption process, pressure equalization process, washing process, desorption process, and pressure equalization process using multiple adsorption towers and switching between adsorption towers. After the adsorption process is completed, an inflow process is performed in which the void gas in the adsorption tower is sent to the adsorption tower after desorption is complete, and a washing process is performed in which a portion of the desorbed gas is sent back to the adsorption tower to wash away the void gas, thereby improving the recovery rate of gases that are difficult to adsorb.

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

[0005] In a gas separation method using an adsorbent containing zeolite, gas separation is achieved by bringing a raw material gas containing easily adsorbed and poorly adsorbed gases into contact with the zeolite. This adsorption process allows for the adsorption of easily adsorbed gases and the recovery of poorly adsorbed gases. When the zeolite reaches its adsorption capacity, it can no longer capture the easily adsorbed gases. Therefore, a desorption process can be performed, such as by placing the zeolite under reduced pressure, to desorb and recover the easily adsorbed gases, and further restore the zeolite's adsorption capacity.

[0006] In gas separation, it is desirable to separate gas components with a high recovery rate, but there is a problem in that the recovery rate is reduced by gas components remaining in the voids. Therefore, it is desirable to increase the gas recovery rate by moving the gas present in the adsorption tower after the adsorption process to another adsorption tower with a lower pressure than the adsorption tower used after the adsorption process, and subjecting it to the adsorption process again. However, in order to achieve a high recovery rate for difficult-to-adsorb gases, this gas movement presents the problem that the adsorbent in the adsorption tower receiving the moving gas flows and turns into powder.

[0007] Therefore, the present invention aims to provide a gas separation method and a method for producing purified gas that can suppress the powdering of the adsorbent while obtaining a high recovery rate of poorly adsorbed gases.

[0008] The inventors have found that, in an inflow process after the adsorption process in which the gas in the adsorption tower is flowed into an adsorption tower with lower pressure, the gas present in the adsorption tower is released from the adsorption tower using the pressure difference between the adsorption towers as a propulsion force, and the amount of gas Vi per unit weight of adsorbent flowing into the adsorption tower in the inflow process is set to a predetermined value, and the gas discharged in the inflow process is moved to another adsorption tower, thereby enabling a high recovery rate of difficult-to-adsorb gases while suppressing the pulverization of the adsorbent.

[0009] [1] A gas separation method comprising switching between two or more adsorption towers containing an adsorbent containing zeolite, the method comprising: an adsorption step of passing a raw material gas containing an easily adsorbable gas and a poorly adsorbable gas through at least one of the adsorption towers to adsorb the easily adsorbable gas onto the adsorbent in the adsorption tower and recover the poorly adsorbable gas; an inflow step of moving the residual gas in the adsorption tower to another adsorption tower with a pressure lower than that of the adsorption tower after the adsorption step; and a desorption step of desorbing the easily adsorbable gas adsorbed onto the adsorbent in the adsorption tower after the inflow step and recovering the easily adsorbable gas, wherein the other adsorption tower into which the residual gas was introduced in the inflow step is used for the adsorption step, and the amount of gas flowing per unit weight of the adsorbent in the inflow step, Vi, is 0.40 mol / kg or less. [2] The gas separation method according to [1] above, wherein the adsorption time ta of the adsorption step and the adsorption time t0 at which the derivative obtained from d [concentration of easily adsorbable gas at the outlet of the adsorption tower (volume %)] / d [time (s)] reaches 0.1 when the raw material gas is introduced under the same conditions as the adsorption step, ta / t0 is 0.80 to 1.40. [3] The gas separation method according to [1] or [2] above, wherein the amount of inflow gas Vi of the inflow step / the amount of gas introduced Vf of the adsorption step is 0.30 or less. [4] The gas separation method according to any one of [1] to [3] above, wherein in the inflow step, the inflow gas is introduced into the other adsorption tower in a direction parallel to the supply direction of the raw material gas of the adsorption step. [5] The gas separation method according to any one of [1] to [4] above, further comprising a pressure reduction step, after the adsorption step and before the inflow step, in which a portion of the raw material gas in the adsorption tower is discharged in a direction parallel to the supply direction of the raw material gas to reduce the pressure in the adsorption tower, and a recycling step, in which the discharged raw material gas is supplied to the adsorption step. [6] The gas separation method according to any one of [1] to [5] above, wherein in the inflow step, the pressure difference between the adsorption tower from which the inflow gas discharges and the adsorption tower into which the inflow gas flows is 300 kPa or less. [7] The gas separation method according to any one of [1] to [6] above, wherein the ratio (L / D) of the length L in the supply direction of the raw material gas to the diameter D at the adsorbent-filled portion of the adsorption tower is 50 or less.[8] The gas separation method according to any one of [1] to [7] above, wherein the relationship between the gas linear velocity u [m / s] of the raw material gas in the adsorption step and the differential heat of adsorption Q [kJ / mol] of the easily adsorbable gas to the adsorbent is u / Q, and u / Q is 0.0001 to 0.003. [9] The gas separation method according to any one of [1] to [8] above, wherein the pressure in the adsorption tower in the adsorption step is 100 to 500 kPa.

[10] The gas separation method according to any one of [1] to [9] above, wherein the amount of the poorly adsorbable gas contained in the gas flowing in the inflow step is 40 volume% or less.

[11] The gas separation method according to any one of [1] to

[10] above, further comprising a repressurization step in which the pressure in the adsorption tower is restored using the purified poorly adsorbable gas before the adsorption step.

[12] The gas separation method according to any one of [1] to

[11] above, wherein, when a raw material gas is introduced under the same conditions as in the adsorption step, the relationship between the adsorption time t0 at which the derivative obtained from d [concentration of easily adsorbed gas at the outlet of the adsorption tower (volume %)] / d [time (s)] reaches 0.1, the adsorption time t1 at which the derivative reaches 0.3, and the adsorption time t2 at which the derivative reaches a maximum and then again becomes 0.3, is such that (t1-t0) / (t2-t0) is 0.40 to 0.98.

[13] The gas separation method according to any one of [1] to

[12] above, wherein the ratio of the adsorption tower volume to the apparent volume of the adsorbent in the adsorption tower is 4.0 or less.

[14] The gas separation method according to any one of [1] to

[13] above, wherein a gas separation apparatus is used in which the apparatus volume to the adsorption tower volume is 4.0 or less.

[15] The gas separation method according to any one of [1] to

[14] above, using a gas separation apparatus in which the apparatus dead space / apparatus volume is 0.9 or less.

[16] The gas separation method according to any one of [1] to

[15] above, using a gas separation apparatus in which the dead space / apparatus volume of the inflow process is 0.6 or less.

[17] The gas separation method according to any one of [1] to

[16] above, using a gas separation apparatus in which the dead space / apparatus volume of the desorption process is 0.6 or less.

[18] The gas separation method according to any one of [1] to

[17] above, wherein the easily adsorbable gas is carbon dioxide and the poorly adsorbable gas is methane.

[19] The gas separation method according to any one of [1] to

[18] above, wherein the adsorption selectivity of the zeolite for the easily adsorbed gas / the poorly adsorbed gas is 5 or more.

[20] The gas separation method according to any one of [1] to

[19] above, wherein the differential heat of adsorption of the easily adsorbed gas to the zeolite is 30 kJ / mol or more.

[21] The gas separation method according to any one of [1] to

[20] above, wherein the zeolite includes at least one selected from the group consisting of GIS, FAU, LTA, and CHA.

[22] A gas separation method according to any one of [1] to

[21] above, comprising: an adsorption step of separating the poorly adsorbed gas from the raw material gas by supplying the raw material gas to an adsorption tower having a dehumidifying layer containing a desiccant and an adsorption layer containing a carbon dioxide adsorbent, and adsorbing the water and carbon dioxide onto the desiccant and the adsorbent; and a desorption step of desorbing the water and carbon dioxide by reducing the pressure inside the adsorption tower from the inlet side of the raw material gas, wherein the raw material gas comes into contact with the dehumidifying layer and the adsorption layer in this order inside the adsorption tower.

[23] A gas separation method according to

[22] above, wherein the desiccant contains at least one selected from the group consisting of activated alumina, silica gel, and activated carbon.

[24] A method for producing purified gas, comprising purifying and recovering the easily adsorbed gas and / or the poorly adsorbed gas by the gas separation method according to any one of [1] to

[23] above.

[0010] According to the present invention, it is possible to provide a gas separation method and a method for producing purified gas that can suppress the pulverization of the adsorbent packed in the adsorption tower while obtaining a high recovery rate of poorly adsorbed gases.

[0011] The following shows the schematic process flow of the gas separation method according to this embodiment. The schematic configuration of the gas separation apparatus 100 according to the first embodiment is shown. The schematic configuration of the gas separation apparatus 101 according to the second embodiment is shown. The schematic configuration of the biogas purification system 1000 is shown. The schematic configuration of the gas separation apparatus 100' used in the comparative example is shown. The schematic configuration of the gas separation apparatus 100 according to this embodiment is shown. The schematic process flow of the gas separation method according to this embodiment is shown.

[0012] The following describes in detail an embodiment for carrying out the present invention (hereinafter referred to as "this embodiment"). The present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist. This embodiment will be described with reference to the accompanying drawings. (Note that in each drawing, components denoted by the same reference numerals have the same or similar configuration.)

[0013] [Gas Separation Method] This embodiment relates to a gas separation method that uses two or more adsorption towers containing an adsorbent containing zeolite, and comprises: an adsorption step in which a raw material gas containing an easily adsorbable gas and a poorly adsorbable gas is passed through at least one of the adsorption towers to adsorb the easily adsorbable gas onto the adsorbent in the adsorption tower and recover the poorly adsorbable gas; an inflow step in which, after the adsorption step, the residual gas in the adsorption tower is moved to another adsorption tower with a pressure lower than that of the adsorption tower; and a desorption step in which, after the inflow step, the easily adsorbable gas adsorbed onto the adsorbent in the adsorption tower is desorbed and the easily adsorbable gas is recovered, wherein the other adsorption tower into which the residual gas was introduced in the inflow step is used for the adsorption step, and the amount of gas flowing per unit weight of the adsorbent in the inflow step, Vi, is 0.40 mol / kg or less.

[0014] The gas separation method according to this embodiment may include a pressurization step of pressurizing the raw material gas to be used in the adsorption step, a pressure reduction step of releasing a portion of the raw material gas from the adsorption tower to reduce the pressure inside the adsorption tower, and a recycling step of sending the gas released in the pressure reduction step to the pressurization step.

[0015] The gas separation method according to this embodiment may further include a pressure reduction step, which reduces the pressure inside the adsorption tower by allowing a portion of the raw material gas in the adsorption tower to flow out in a direction parallel to the raw material gas supply direction after the adsorption step and before the inflow step, and a recycling step, which supplies the discharged raw material gas to the adsorption step.

[0016] The gas separation method according to this embodiment may include a repressurization step after the desorption step and before the adsorption step in which the pressure of the adsorption tower is restored using purified poorly adsorbed gas (for example, poorly adsorbed gas with a purity of 50% by volume or higher). In the repressurization step, purified poorly adsorbed gas (for example, poorly adsorbed gas with a purity of 50% by volume or higher) is supplied into the adsorption tower. By restoring the pressure through the repressurization step by supplying purified poorly adsorbed gas (for example, poorly adsorbed gas with a purity of 50% by volume or higher) into the adsorption tower, it is possible to prevent the raw material gas from rapidly flowing into the tower at the beginning of the adsorption step, which would cause easily adsorbed gas to pass through without being adsorbed by the adsorbent, and to recover high-purity easily adsorbed gas.

[0017] In the gas separation method according to this embodiment, two or more adsorption towers containing adsorbents are used in a switching manner. To begin with, as an example, the gas separation method according to this embodiment will be described using the case where two adsorption towers, adsorption tower a and adsorption tower b, containing adsorbents, are used. Figure 1 is a schematic flow diagram of the gas separation method according to this embodiment. Figure 1 shows the processes carried out in adsorption tower a and adsorption tower b, respectively. In adsorption tower a and adsorption tower b, an adsorption process and a desorption process are repeatedly performed to separate easily adsorbed gases from poorly adsorbed gases. The adsorption process ends according to the adsorption capacity of the adsorbent for easily adsorbed gases, and the adsorbed easily adsorbed gases are desorbed in the desorption process. This regenerates the adsorbent, and the adsorption process can be performed again. If the adsorption process is performed in adsorption tower a while the desorption process is performed in adsorption tower b to regenerate the adsorbent, the operation can be switched so that the adsorption process is performed in adsorption tower b after the adsorption process in adsorption tower a is completed.

[0018] As shown in Figure 1, the raw material gas is first supplied to adsorption tower a to perform the adsorption process. At this time, the raw material gas may be supplied to adsorption tower a in a pressurized state by a pressurizing device. After the adsorption process is completed, if the pressure inside adsorption tower a has risen, a pressure reduction process may be performed. The pressure-reduced gas discharged in the pressure reduction process is sent to the pressurizing device and used again in the pressurizing process (recycling process).

[0019] Subsequently, in the inflow process, adsorption tower a and adsorption tower b, which has been reduced in pressure by the desorption process, are connected, and the raw material gas remaining in adsorption tower a is allowed to flow into adsorption tower b. It is preferable that the desorption process is performed in adsorption tower b prior to the inflow process to desorb easily adsorbed gases from the adsorbent and reduce the pressure. If the desorption process is performed immediately after the adsorption process, the raw material gas remaining in adsorption tower a flows into the recovery line for easily adsorbed gases, leading to problems such as a decrease in the purity of easily adsorbed gases or a decrease in the recovery rate of poorly adsorbed gases. However, by having an inflow process, it is possible to recover both easily adsorbed and poorly adsorbed gases contained in the raw material gas remaining in the adsorption tower after the adsorption process without loss.

[0020] After the aforementioned inflow process, a desorption process is performed in adsorption tower a to recover easily adsorbed gases and regenerate the adsorbent.

[0021] While the desorption process is performed in adsorption tower a, the adsorption process is performed in adsorption tower b. A repressurization process may be performed before the adsorption process. If the pressure inside adsorption tower b has risen after the adsorption process is completed, a pressure reduction process may be performed.

[0022] Subsequently, in the inflow process, 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 repressurization process may be performed after the inflow process. Adsorption tower a is then subjected to the adsorption process again. Meanwhile, in adsorption tower b, after the inflow process, it is subjected to a desorption process and then subjected to the inflow process again. By repeating the above process, the raw material gas can be efficiently separated.

[0023] The following describes each process in detail, using as an example a gas separation apparatus having two or more towers containing adsorbents (hereinafter also simply referred to as "adsorption towers").

[0024] <Adsorption Process> In the adsorption process, the raw material gas is supplied to at least one of two or more adsorption towers filled with adsorbent, the easily adsorbed gas is adsorbed by the adsorbent, and the purified, difficult-to-adsorb gas is recovered. Details of the adsorbent, adsorption towers, etc. will be described later.

[0025] Vf is the amount of raw material gas supplied in the adsorption process (unit: mol / kg). Vf is the amount of raw material gas supplied per cycle of the adsorption process. The amount of raw material gas supplied is the value obtained by dividing the integrated value of the gas flow rate in one adsorption process (unit: NL) measured by a volumetric flow meter by the molar volume of the gas at standard conditions and the mass of the adsorbent packed in the adsorption tower. Vf is set according to the adsorption capacity of the adsorbent used in the adsorption process. Depending on the gas separation method and the target purity of the difficult-to-adsorb gas to be recovered, the adsorption process can be terminated, for example, when the concentration of easily adsorbable gas in the gas at the outlet of the adsorption tower reaches 5.0 volume%. The concentration of easily adsorbable gas in the gas at the outlet of the adsorption tower at which the adsorption process is terminated is preferably 5.0 volume% or less, more preferably 4.0 volume% or less, and even more preferably 3.0 volume% or less. The target purity of the recovered non-adsorbent gas can be set as appropriate, for example, 90% by volume or higher, 95% by volume or higher, or 98% by volume or higher.

[0026] Vf is preferably 0.01 to 10 mol / kg, more preferably 0.1 to 5.0 mol / kg, and even more preferably 1.0 to 2.5 mol / kg. Vf is determined according to the composition of the raw material gas, the linear velocity of the raw material gas, the adsorption capacity of the adsorbent, the adsorption rate of the adsorbent, etc.

[0027] Pressure P inside the adsorption tower during the adsorption process Ａ From the viewpoint of reducing the amount of easily adsorbable gas flowing out of the adsorption tower during the inflow process while increasing the recovery rate of poorly adsorbable gas, the pressure is preferably 100 to 500 kPa, more preferably 100 to 400 kPa, and even more preferably 100 to 300 kPa. In this specification, the unit of pressure kPa refers to absolute pressure.

[0028] The recovery rate of the purified poorly adsorbed gas is preferably 85% by volume or more, more preferably 90% by volume or more, even more preferably 95% by volume or more, and even more preferably 98% by volume or more.

[0029] <Depressurization Process> In the depressurization process, the supply of raw material gas is stopped, and the gas present in the adsorption tower is allowed to flow out of the adsorption tower, thereby reducing the pressure inside the adsorption tower.

[0030] The pressure-reduced gas contains poorly adsorbed gases. By subjecting it to a pressurization process and then to an adsorption process again, the recovery rate of poorly adsorbed gases in the raw material gas can be increased. The pressure-reduced gas may be released into the atmosphere.

[0031] In the pressure reduction process, it is preferable to discharge the gas present in the adsorption tower in a direction parallel to the supply direction of the raw material gas, from the viewpoint of reducing the amount of poorly adsorbed gas remaining in the adsorption tower and further reducing the amount of gas moved in the inflow process. In the pressure reduction process, from the viewpoint of sufficiently lowering the pressure inside the adsorption tower before the inflow process and further reducing the amount of gas moved in the inflow process, it is preferable that the relationship between the time of the pressure reduction process per cycle and the time of one cycle, [time of pressure reduction process per cycle] / [time of one cycle], is 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. Furthermore, from the viewpoint of efficiently producing purified gas, it is preferable that it be 0.5 or less. The time of one cycle is the time from the start of the adsorption process to the start of the next adsorption process in one adsorption tower. The execution time of the pressure reduction process means from the start to the end of the gas discharge from inside the adsorption tower. Specifically, the execution time of the pressure reduction process is, for example, the time from opening to closing the valve for discharging gas from the adsorption tower.

[0032] The gas discharged in the pressure drop process preferably contains 50% or more by volume of poorly adsorbed gas. The concentration of poorly adsorbed gas in the gas discharged in the pressure drop process is more preferably more than 50% by volume, even more preferably 60% or more by volume, even more preferably 70% or more by volume, even more preferably 80% or more by volume, and even more preferably 90% or more by volume. By sufficiently reducing the amount of poorly adsorbed gas that will not be re-adsorbed by the adsorbent in the inflow process from within the adsorption tower in the pressure drop process, the amount of gas moved in the inflow process can be reduced. In addition, by setting the pressure drop process to have a concentration of poorly adsorbed gas within the above range, a relatively high concentration of poorly adsorbed gas is maintained near the outlet of the adsorption tower, and the adsorbent can transition to the inflow process with remaining adsorption capacity. As a result, a portion of the easily adsorbed gas that moves in the inflow process can be re-adsorbed by the adsorbent, and the amount of gas that moves to another tower in the inflow process can be reduced.

[0033] Pressure P inside the adsorption tower after pressure reduction in the pressure reduction process Ｆ From the viewpoint of reducing pressure loss in the inflow or detachment process carried out following the pressure reduction process, the pressure is preferably 100 to 200 kPa, more preferably 100 to 150 kPa, and even more preferably 100 to 120 kPa.

[0034] Pressure P Ａ and pressure P Ｆ The difference (P Ａ -P Ｆ From the viewpoint of improving the recovery rate and purity of poorly adsorbed gases, the pressure is preferably 50 kPa or higher, more preferably 100 kPa or higher, and even more preferably 150 to 400 kPa.

[0035] <Inflow Process> In the inflow process, the raw material gas remaining in the adsorption tower after the adsorption process is flowed into another adsorption tower to reduce the amount of poorly adsorbed gas that flows out of the equipment during the desorption process. Specifically, the valves from the adsorption tower to the product storage section and the raw material supply section are closed, and the adsorption tower used in the adsorption process is connected to another adsorption tower. When two adsorption towers are connected, gas flows from the adsorption tower with higher pressure to the adsorption tower with lower pressure, and the pressures in the two adsorption towers become roughly equal. For this reason, this operation is sometimes called pressure equalization. In this way, in the inflow process, a portion of the gas in the adsorption tower is flowed in using 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 completing the adsorption process.

[0036] In the inflow process, from the viewpoint of improving the purity of the poorly adsorbed gas, it is preferable to introduce the incoming gas into the other adsorption tower in a direction parallel to the supply direction of the raw material gas for the adsorption process.

[0037] The pressure difference between the two towers connected in the inflow process (an adsorption tower from which the inflowing gas flows out and an adsorption tower into which the inflowing gas flows) is preferably 300 kPa or less, more preferably 10 kPa to 300 kPa, even more preferably 50 kPa to 200 kPa, and particularly preferably 80 to 100 kPa, from the viewpoint of increasing the recovery rate of poorly adsorbed gases while reducing the amount of inflowing gas.

[0038] The amount of poorly adsorbed gas in the gas discharged in the inflow process is preferably 50% by volume or less, more preferably 40% by volume or less, and even more preferably 30% by volume or less. A low concentration of poorly adsorbed gas in the gas discharged in the inflow process reduces the amount of gas that flows downstream without being readsorbed by the adsorbent in the adsorption tower that receives the inflow gas, thereby further suppressing the flow of the adsorbent and lowering the pulverization rate.

[0039] <Pressurization Process> In the pressurization process, the raw material gas containing easily adsorbable and poorly adsorbable gases is pressurized. The raw material gas may be supplied from an external source, but it may also contain pressure-reduced gas. The method of pressurization is not particularly limited, and any pressurizing device may be used.

[0040] <Recycling Process> In the recycling process, the gas exhausted in the pressure reduction process is used in the pressurization process. The gas exhausted in the pressure reduction process may be directly introduced into the pressurization device, or it may be temporarily stored in a storage container such as a raw material gas tank before being introduced into the pressurization device. This process allows easily adsorbed gases in the gas exhausted in the pressure reduction process to be treated again in the adsorption tower.

[0041] <Vi> In this embodiment, the amount of influent gas Vi per unit weight of the adsorbent is 0.40 mol / kg or less. By setting Vi to 0.40 mol / kg or less, the powdering of the adsorbent can be suppressed. Also, from the same viewpoint, Vi is preferably 0.30 mol / kg or less, more preferably 0.25 mol / kg or less, and even more preferably 0.20 mol / kg or less. The lower limit of Vi is preferably 0.01 mol / kg or more, more preferably 0.05 mol / kg or more, and even more preferably 0.10 mol / kg or more, from the viewpoint of increasing the recovery rate of poorly adsorbed gases.

[0042] Vi is the amount (unit: mol / kg) of gas flowing into the low-pressure adsorption tower during the inflow process (hereinafter also referred to as "inflow gas"). The amount of inflow gas is calculated by measuring the volume (unit: NL) of the inflow gas with an integrated volume meter and dividing that value by the molar volume of the gas at standard conditions and the mass of the adsorbent packed into the adsorption tower into which the gas flows. In the adsorption process, easily adsorbable gases are adsorbed from the adsorbent located on the side where the raw material gas is supplied (upstream) until the adsorption capacity is reached, and then easily adsorbable gases are adsorbed sequentially from the adsorbent on the downstream side. Therefore, if the amount of raw material gas supplied is less than the adsorption capacity of the adsorbent packed into the adsorption tower, the adsorbent located on the downstream side can be in a state where the adsorption capacity of easily adsorbable gases is less than the adsorption capacity. When gas is discharged in the inflow process, easily adsorbable gases are sequentially desorbed from the adsorbent located downstream of the flow of the discharged gas, but the easily adsorbable gases that flowed from upstream are re-adsorbed onto the adsorbent on the downstream side. In the adsorption process, by including an adsorbent with a low adsorption capacity for easily adsorbed gases, the downstream adsorbent can more easily re-adsorb the easily adsorbed gases in the inflow process. On the other hand, high concentrations of poorly adsorbed gases are present in the voids surrounding the adsorbent, which has a low adsorption capacity for easily adsorbed gases in the adsorption process. Since poorly adsorbed gases are not re-adsorbed in the inflow process and flow out, this leads to an increase in the inflow rate of the inflowing gas. Therefore, by setting the amount of adsorbent with a low adsorption capacity for easily adsorbed gases within an appropriate range in the adsorption process, it is possible to suppress the outflow of easily adsorbed gases due to re-adsorption while minimizing the movement of poorly adsorbed gases. In this way, Vi can be adjusted by reducing the inflow rate of the inflowing gas. Vi can also be controlled by adjusting the gas linear velocity, as described later, according to the differential heat of adsorption of easily adsorbed gases to the adsorbent.

[0043] <Vi / Vf> The ratio of the amount of gas flowing in the inflow process Vi to the amount of gas introduced in the adsorption process Vf (hereinafter also referred to as "Vi / Vf") is preferably 0.30 or less. By setting Vi / Vf to 0.30 or less, a sufficient amount of poorly adsorbed gas can be purified per cycle, and while recovering high-purity poorly adsorbed gas at a lower purification cost, the pulverization of the adsorbent in the inflow process can be suppressed. Also, from the same viewpoint, Vi / Vf is preferably 0.18 or less, more preferably 0.16 or less, and even more preferably 0.12 or less. The lower limit of Vi / Vf is not particularly limited, but for example, it may be 0.01 or more, or 0.02 or more. Vf is determined, for example, by the adsorption capacity of the adsorbent at the adsorption pressure, the supply rate of the raw material gas, the composition of the raw material gas, the temperature inside the adsorption tower, etc., and can be adjusted within a range where the amount of poorly adsorbed gas remaining in the adsorption tower during the adsorption process does not become too large, and the concentration of easily adsorbed gas at the outlet of the adsorption tower during the adsorption process does not become too high.

[0044] In this way, Vi / Vf can be adjusted. Vf can also be controlled by adjusting the gas linear velocity, as described later, according to the differential heat of adsorption of the easily adsorbed gas to the adsorbent.

[0045] Furthermore, the above-mentioned Vi and Vi / Vf can also be adjusted from the following perspectives.

[0046] In the relationship between the linear velocity u [m / s] of the raw material gas in the adsorption process and the differential heat of adsorption Q [kJ / mol] of the easily adsorbable gas on the adsorbent, it is preferable that u / Q is between 0.0001 and 0.003. When u / Q is within this range, the adsorbent packed in the adsorption tower can adsorb the easily adsorbable gas from the upstream side of the raw material gas supply, making it easier to leave adsorbent without adsorbed easily adsorbable gas on the downstream side at the end of the adsorption process, thus facilitating a reduction in the volume of incoming gas. From a similar viewpoint, u / Q is preferably between 0.0001 and 0.0025, more preferably between 0.0005 and 0.0020, and even more preferably between 0.001 and 0.0018. The linear velocity of the gas is the gas intake volume [m] of the pressurizing device. ３ [ / s] is obtained from the cross-sectional area [m²] of the adsorption tower's inner diameter. ２It is determined by dividing by [ ]. The differential heat of adsorption of an easily adsorbed gas to an adsorbent is determined by adsorption isotherms at different measurement temperatures and the Clausius-Clapeyron equation. The method for measuring the differential heat of adsorption is described in more detail by the method described in the examples.

[0047] When the raw material gas is introduced under the same conditions as the adsorption process, the relationship between the adsorption time t0, where the derivative calculated from d [concentration of easily adsorbable gas at the outlet of the adsorption tower (volume %)] / d [time (s)] begins to increase and reaches 0.1, the adsorption time t1, where the derivative reaches 0.3, and the adsorption time t2, where the derivative reaches a maximum and then returns to 0.3, is (t1-t0) / (t2-t0) between 0.40 and 0.98. When (t1-t0) / (t2-t0) is within this range, the adsorption process is completed with the adsorption capacity of the adsorbent remaining. Therefore, it becomes possible to adsorb easily adsorbable gas in the gas remaining in the adsorption tower during the inflow process, thereby reducing the volume of the inflow gas. "Adsorption time" refers to the flow time when the raw material gas is supplied at a constant flow rate. (t1-t0) / (t2-t0) is more preferably 0.50 to 0.90, and even more preferably 0.60 to 0.80.

[0048] In the relationship between the adsorption time ta in the adsorption process and t0, ta / t0 is preferably 0.80 to 1.40, more preferably 0.90 to 1.30, and more preferably 0.95 to 1.20. When ta / t0 is 0.80 or higher, it is possible to suppress the amount of poorly adsorbed gas remaining in the voids within the adsorption tower during the adsorption process, making it easier to reduce the volume of incoming gas. When ta / t0 is 1.40 or lower, it is possible to suppress the excessive mixing of easily adsorbed gas with the purified poorly adsorbed gas product during the adsorption process, making it possible to recover high-purity poorly adsorbed gas.

[0049] The adsorption tower is not particularly limited, but the ratio of the length L to the diameter D in the supply direction of the raw gas at the adsorbent-filled section of the adsorption tower (L / D) is preferably 50 or less, more preferably 0.1 to 30, even more preferably 0.3 to 20, and even more preferably 0.5 to 10. Having an L / D ratio within this range increases the efficiency of contact between the influent gas and the adsorbent, allowing for the adsorption of more influent gas within the time of the inflow process, thereby reducing the volume of gas discharged from the tower.

[0050] <Desorption Process> In the desorption process, the adsorption tower is evacuated under reduced pressure using a depressurization device. When the pressure inside the adsorption tower is reduced, the easily adsorbed gases adsorbed on the adsorbent are desorbed. In this way, the adsorbent is regenerated and the purified easily adsorbed gases are extracted.

[0051] During the desorption process, the pressure in the adsorption tower decreases. The pressure at the start of the desorption process becomes the pressure at the end of the inflow process. When the adsorption tower is used as "another tower" in the inflow process after the completion of the desorption process, the greater the pressure difference between the two towers, the better the recovery rate of poorly adsorbed gases. Therefore, from the viewpoint of increasing the recovery rate of poorly adsorbed gases, the pressure at the end of the desorption process is preferably 50.0 kPa or less, more preferably 30.0 kPa or less, and even more preferably 10.0 kPa or less. If the pressure in the desorption process is too low, the amount of gas moving in the inflow process becomes too large, causing the adsorbent to flow and increasing the pulverization rate. Therefore, a pressure of 2 kPa or more is preferred, and 5 kPa or more is more preferred.

[0052] In the desorption process, the recovery rate of easily adsorbable gas is preferably 50 volume% or more per cycle, more preferably 70 volume% or more, and even more preferably 80 volume% or more. When the recovery rate of easily adsorbable gas is 50 volume% or more, the gas that flows into the adsorption tower in the inflow process is re-adsorbed to the adsorbent near the piping that introduces the inflow gas, and the amount of gas flowing downstream in the adsorption tower that receives the inflow gas can be reduced, thereby further suppressing the flow of the adsorbent and reducing the pulverization rate. The recovery rate of easily adsorbable gas can be calculated using the following formula.

[0053] Recovery rate of easily adsorbed gas (in volume %) = Volume of easily adsorbed gas recovered in the desorption process (in NL) / (Volume of easily adsorbed gas introduced in the adsorption process (in NL) + Volume of easily adsorbed gas flowed in in the inflow process (in NL) - Volume of easily adsorbed gas flowed out of the adsorption tower in the adsorption process (in NL)) × 100

[0054] The purity of the purified easily adsorbable gas recovered in one desorption step is preferably 90% by volume or more, more preferably 95% by volume or more, and even more preferably 97% by volume or more. The purified easily adsorbable gas is preferably purified carbon dioxide. The purity of the easily adsorbable gas can be achieved by increasing the adsorption selectivity of the zeolite for easily adsorbable gases / poorly adsorbable gases.

[0055] <Raw Material Gas> The raw material gas used as a raw material includes poorly adsorbed gases and easily adsorbed gases. The content of easily adsorbed gases in the raw material gas is preferably 1% to 99% by volume, more preferably 5% to 90% by volume, even more preferably 10% to 80% by volume, even more preferably 20% to 70% by volume, and even more preferably 30% to 70% by volume.

[0056] (Easily Adsorbable Gases) Easily adsorbable gases are any gaseous substances that have a larger adsorption capacity (mol / kg) to the adsorbent compared to poorly adsorbable gases. "Gaseous substance" means a substance that is a gas at room temperature (25°C) and atmospheric pressure. Examples of easily adsorbable gases include carbon dioxide, nitrous oxide, hydrogen, water, and ammonia. Among these easily adsorbable 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.

[0057] (Poorly Adsorbed Gases) Poorly adsorbed gases are gaseous substances whose adsorption capacity (mol / kg) to the adsorbent is less than that of easily adsorbed gases. Examples of poorly adsorbed gases include methane, ethane, nitrogen, argon, and dimethyl ether. Among these poorly adsorbed gases, methane, ethane, and nitrogen are preferred, methane and ethane are more preferred, and methane is even more preferred.

[0058] The raw material gas is preferably biogas containing carbon dioxide and methane.

[0059] <Adsorbent> The adsorbent includes zeolite. The adsorbent may also include other adsorbents other than zeolite. Examples of other adsorbents include solid adsorbents such as metal-organic frameworks (MOFs), carbonaceous char, activated carbon, reactivated carbon, carbon black, graphite, silica, silica gel, alumina clay, and metal oxides.

[0060] The differential heat of adsorption of the easily adsorbed gas to the zeolite is preferably 30 kJ / mol or more, more preferably 35 kJ / mol or more, and even more preferably 40 kJ / mol or more. The upper limit of the differential heat of adsorption of the easily adsorbed gas to the zeolite is not particularly limited, but for example, it is 80 kJ / mol or less. The method for measuring the differential heat of adsorption is as described above.

[0061] The adsorption selectivity of zeolite for easily adsorbed gases / difficult-to-adsorb gases is preferably 5 or higher, more preferably 10 or higher, even more preferably 13 or higher, and even more preferably 15 or higher, from the viewpoint of increasing the recovery rate of difficult-to-adsorb gases. The upper limit of the adsorption selectivity is not particularly limited, but for example, it is 100 or less. The adsorption selectivity for easily adsorbed gases / difficult-to-adsorb gases is a selectivity expressed as the adsorption capacity of easily adsorbed gases / the adsorption capacity of difficult-to-adsorb gases. The adsorption capacity of easily adsorbed gases or difficult-to-adsorb gases is the adsorption capacity (mol / kg) of easily adsorbed gases or the adsorption capacity (mol / kg) of difficult-to-adsorb gases per 1 kg of adsorbent at 25°C and 101.3 kPa (pressure of each gas individually).

[0062] From the viewpoint of increasing the recovery rate of poorly adsorbed gases, the adsorption capacity of the adsorbent is preferably 0.4 mol / kg or more, more preferably 0.8 mol / kg or more, even more preferably 1.7 mol / kg or more, and even more preferably 2.2 mol / kg or more, relative to the easily adsorbed gas at a pressure of 101.3 kPa (pressure of the easily adsorbed gas alone). The adsorption capacity of the easily adsorbed gas is not particularly limited to an upper limit, but for example, it is 9.0 mol / kg or less.

[0063] The difference between the adsorption capacity at the pressure in the adsorption process of the adsorbent and the adsorption capacity at the pressure in the desorption process (hereinafter also referred to as "working capacity", "WC") is preferably 0.5 mol / kg or more, more preferably 0.8 mol / kg or more, still more preferably 1.0 mol / kg or more, and even more preferably 2.0 mol / kg or more for easily adsorbable gases. The upper limit of the WC of the adsorbent is not particularly limited, but for easily adsorbable gases, it is, for example, 10.0 mol / kg or less. The working capacity, that is, the adsorption capacity of the adsorbent, is measured by changing the pressure of the adsorbent over time from an absolute pressure of 0.25 to 900 mmHg using a target gas (easily adsorbable gas or hardly adsorbable gas) with a purity of 99.9 mass% or more, and obtaining the adsorption capacity at the pressure in the adsorption process and the adsorption capacity at the pressure in the desorption process.

[0064] The zeolite preferably contains at least one selected from the group consisting of GIS, FAU, LTA, and CHA. Among these, the zeolite preferably contains GIS or FAU, and more preferably contains GIS (hereinafter also referred to as "GIS-type zeolite").

[0065] The GIS-type zeolite preferably has silica and alumina as the main components. The main component is a component that occupies 51 mass% or more.

[0066] The GIS-type zeolite may contain silica and alumina. The content of aluminum (Al) in the GIS-type zeolite is preferably 1 mass% or more, more preferably 3 mass% or more, and still more preferably 5 mass% or more. The content of silicon (Si) in the GIS-type zeolite is preferably 3 mass% or more, more preferably 5 mass% or more. The upper limit of the contents of aluminum (Al) and silicon (Si) is preferably such that the SAR described below satisfies a predetermined range, and is determined by the value of the SAR.

[0067] The silica-alumina ratio (SiO ２ / Al ２ O ３The molar ratio of silica to alumina, expressed as , (hereinafter also referred to as "SAR"), is preferably 3.40 or higher. The lower the SAR of a GIS-type zeolite, the more hydrophilic it becomes and the stronger its adsorption capacity for polar molecules such as carbon dioxide. If the SAR is too low, the adsorption capacity is too strong, requiring more energy to desorb by heating or vacuuming, so a higher SAR is preferable. However, 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.

[0068] The phosphorus (P) content in GIS-type zeolite is preferably 4% by mass or less. The lower limit of the phosphorus (P) content is not particularly limited and may be 0% by mass or more.

[0069] The zirconium (Zr) content in GIS-type zeolite is preferably 8% by mass or less. The lower limit of the zirconium (Zr) content is not particularly limited and may be 0% by mass or more.

[0070] The titanium (Ti) content in GIS-type zeolite is preferably 8% by mass or less. The lower limit of the titanium (Ti) content is not particularly limited and may be 0% by mass or more.

[0071] From the viewpoint of further improving the selective adsorption capacity of carbon dioxide, it is more preferable that the phosphorus (P) atom content in the zeolite be 1.5% by mass or less, and particularly preferable that it be 0% by mass.

[0072] Furthermore, the content of aluminum (Al), silicon (Si), phosphorus (P), zirconium (Zr), and titanium (Ti) can be measured by the method described in the examples below. The content of aluminum (Al), silicon (Si), phosphorus (P), zirconium (Zr), and titanium (Ti) can also be adjusted to the above-mentioned range by, for example, adjusting the composition ratio of the mixed gel used in the synthesis of the GIS-type zeolite to a preferred range described below.

[0073] From the viewpoint of improving the selective adsorption capacity of easily adsorbed gases such as carbon dioxide, it is preferable, and more preferable, for potassium to be included as the cation species in the GIS-type zeolite. The total content of potassium and lithium in the zeolite is calculated as the ratio (Z / T) of the total amount of substance of potassium and lithium to the total amount of substance of alkali metals (T) in the GIS-type zeolite. Z / T is preferably 0.05 or higher, more preferably 0.10 or higher, and even more preferably 0.15 or higher. There is no particular upper limit to Z / T, but Z / T may be 1.00 or lower. Z / T can be measured by thermally dissolving the zeolite in an aqueous sodium hydroxide solution or aqua regia and performing ICP-emission spectroscopy analysis using a solution that has been appropriately diluted. 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-type zeolite.

[0074] The ratio (K / T) of the total amount of potassium to the total amount of each alkali metal (T) in the GIS-type zeolite is preferably 0.05 or higher, more preferably 0.10 or higher, and even more preferably 0.15 or higher. There is no particular upper limit to K / T, but K / T may be 1.00 or lower.

[0075] From the perspective of the energy required for desorption, a higher SAR is preferable. However, in GIS-type zeolites, it has been confirmed that when the SAR is high, adsorption-desorption hysteresis becomes apparent in the adsorption-desorption isotherm of easily adsorbable gases. In GIS-type zeolites, adsorption-desorption hysteresis in the adsorption-desorption isotherm of easily adsorbable gases can be eliminated by controlling the bonding mode of Si and Al in the zeolite framework. Specifically, ２９When the peak area intensities attributed 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, 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 within the zeolite framework. The sums of their area intensities, a+d and b+c, represent the sum of the abundances of these bonding modes, and (a+d) / (b+c) represents the relative abundance. Since the relative abundance of Si and Al bonding modes affects the structural changes of the zeolite framework itself during adsorption and desorption, setting the relative abundance of Si and Al bonding modes in the zeolite framework, (a+d) / (b+c), within an appropriate range can eliminate adsorption / desorption hysteresis in the adsorption / desorption isotherm.

[0076] ２９ Si-MAS-NMR spectra are prepared by preparing a desiccator with water at the bottom and keeping the zeolite sample tube in the upper part of the desiccator at room temperature (25°C) for 48 hours to control humidity, after which measurements are taken using a solid-state NMR measuring device. Examples of solid-state NMR measuring devices include the JEOL "RESONANCE ECA700" (magnetic field strength: 16.44 T). １ One example is the resonance frequency of 700 MHz at H.

[0077] The GIS-type zeolite of this embodiment is ２９ In Si-MAS-NMR spectra, the following five peaks are generally observed.

[0078] ​(1) Q4(0Al): Peak of Si that is not bonded to Al at all via oxygen (2) Q4(1Al): Peak of Si bonded to one Al via oxygen (3) Q4(2Al): Peak of Si bonded to two Al via oxygen (4) Q4(3Al): Peak of Si bonded to three Al via oxygen (5) Q4(4Al): Peak of Si bonded to four Al via oxygen Also, ２９ In the Si-MAS-NMR spectrum, these peaks are generally located between -112 ppm and -80 ppm and can be attributed to Q4(0Al), Q4(1Al), Q4(2Al), Q4(3Al), and Q4(4Al) from the high-field side. The peak positions may vary depending on the cation species present in the zeolite framework, but generally the peaks are located within the following range.

[0079] (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 obtained by analyzing it using the analysis program dmfit (version #202000113) with Gaussian and Lorentz functions, and optimizing 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 Gauss / Lorentz ratio (xG / (1-x)L)—using the least squares algorithm.

[0080] Using the peak area intensities obtained from this calculation, the peak area intensities a, b, c, and d assigned to Q4(3Al), Q4(2Al), Q4(1Al), and Q4(0Al) can be determined.

[0081] ２９ ​The Si-MAS-NMR spectrum can be measured in more detail by the method described in the examples below. 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 ratio of the cations resulting from the addition of the salt compound to the aluminum source.

[0082] [Method for producing the adsorbent] (Preparation step) The above-mentioned GIS-type zeolite can be obtained by a production method that includes, for example, a preparation step of a mixed gel containing a silica source containing silicon, an aluminum source containing aluminum (Al), an alkali source (not a salt) containing at least one selected from alkali metals (M1) and alkaline earth metals (M2), an alkali salt compound containing at least one selected from alkali metals (M1) and alkaline earth metals (M2), a phosphorus source containing phosphorus, an organic structure-defining agent, and water.

[0083] (Hydrothermal Synthesis Process) In the method for producing GIS-type zeolite, it is preferable to further include a hydrothermal synthesis process 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 process is subjected to hydrothermal synthesis by holding it at a predetermined temperature for a predetermined time, either by stirring or standing. The time for hydrothermal synthesis is not particularly limited as long as it is a commonly used time, but is preferably 3 hours to 30 days, more preferably 10 hours to 20 days, and even more preferably 24 hours to 10 days.

[0084] (Separation and Drying Process) After the hydrothermal synthesis process, the solid product and the liquid containing water are separated. The separation method is not particularly limited as long as it is a general method, and methods such as filtration, decantation, spray drying (rotary spray, nozzle spray, ultrasonic spray, etc.), drying using a rotary evaporator, vacuum drying, freeze-drying, or natural drying can be used, and separation can usually be achieved by filtration or decantation.

[0085] (Casturing process) In the method for producing GIS-type zeolite, it is preferable to further include a calcination process 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 or lower. 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 usually an air atmosphere, an inert gas such as nitrogen or argon, or an atmosphere with added oxygen is used.

[0086] (Cation Exchange Step) In a method for producing GIS-type zeolite, it is preferable to further include a cation exchange step. The cation exchange can 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, and ammonium carbonate; nitrates such as sodium nitrate, potassium nitrate, lithium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, and ammonium nitrate; salts obtained by changing the carbonate ions and nitrate ions contained in the carbonates and nitrates to halide ions, sulfate ions, carbonate ions, bicarbonate ions, acetate ions, phosphate ions, or hydrogen phosphate ions; or acids such as nitric acid and hydrochloric acid. The temperature for cation exchange is not particularly limited as long as it is a general cation exchange temperature, but is usually from room temperature to 100°C or below.

[0087] When separating zeolite after cation exchange, the separation method is not particularly limited as long as it is a general method, and methods such as filtration, decantation, spray drying (rotary spray, nozzle spray, ultrasonic spray, etc.), drying using a rotary evaporator, vacuum drying, freeze-drying, or natural drying can be used, and separation can usually be achieved by filtration or decantation.

[0088] <Adsorption Tower> The adsorption tower is filled with an adsorbent. The adsorption tower is configured to allow the introduction of a raw material gas and bring the adsorbent into contact with the raw material gas. In the adsorption process, the easily adsorbable gases in the raw material gas are adsorbed onto the adsorbent by bringing the raw material gas into contact with the adsorbent. Since the easily adsorbable gases in the raw material gas are adsorbed, the difficult-to-adsorb gases can be extracted. Furthermore, in the desorption process after the adsorption process, the difficult-to-adsorb gases can be extracted by reducing the pressure in the adsorption tower. In this way, purified gas of difficult-to-adsorb gases and purified gas of easily adsorbable gases are obtained in the adsorption and desorption processes.

[0089] An adsorption tower has a portion filled with adsorbent (hereinafter also referred to as the "adsorption layer") and a portion that is not filled with adsorbent. From the viewpoint of further improving the recovery rate of poorly adsorbed gases and 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 (by volume %) is calculated by the following formula: Packing rate = [Volume of adsorbent] / [Volume in the absorption layer] × 100 Note that the volume of the adsorbent is expressed as bulk density × mass of adsorbent.

[0090] In the portion of the adsorption tower other than the adsorption layer, inert balls may be packed, for example, above or below the adsorption layer, or in both directions, to promote diffusion perpendicular to the gas flow.

[0091] <Gas Separation Apparatus> The gas separation apparatus used in this embodiment preferably includes an adsorption tower filled with an adsorbent and a pressurizing device for pressurizing the raw material gas. It may also include a tank for storing the raw material gas and the pressure-reduced gas. In this case, the raw material gas in the tank is sent to the pressurizing device, pressurized, and then introduced into the adsorption tower.

[0092] The ratio of the adsorption tower volume to the apparent volume of the adsorbent in the adsorption tower is preferably 4.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less. The "adsorption tower volume" is the volume obtained by adding the volume of the adsorption tower body and the volume of all piping connected to the adsorption tower from the connection point to the adsorption tower to the first valve installed in the piping, and then subtracting the volume of the adsorbent filled in the adsorption tower. The volume of the adsorption tower body is obtained by multiplying the length of the adsorption tower body by the cross-sectional area calculated from the inner diameter of the adsorption tower body. The volume from the connection point to the first valve in the piping connected to the adsorption tower is obtained by multiplying the length of the piping by the cross-sectional area calculated from the inner diameter of the piping. The volume of the adsorbent filled in the adsorption tower is obtained by dividing the amount of adsorbent filled by the apparent density of the adsorbent. The apparent density of the adsorbent can be measured in the same way as the apparent density of the adsorbent described later. The "apparent volume of the adsorbent" is the weight of the filled adsorbent divided by the apparent density. The apparent density of the adsorbent can be measured by the following method. The first valve refers to the valve installed closest to the adsorption tower in each pipe connected to the adsorption tower.

[0093] <Apparent density d ａ Measurement of the apparent density d of the adsorbent ａ The procedure is as follows: (1) Add 100 mL of liquid paraffin to a 250 mL graduated cylinder and measure the initial liquid level. (2) Measure the mass W (g) of approximately 80 mL of adsorbent molded body. (3) Measure the water content u (unit: mass%) of the adsorbent molded body using the Kett Scientific Research Institute's infrared moisture meter "FD-660" (product name). (4) Place the weighed adsorbent molded body into the liquid paraffin in the graduated cylinder, and after 10 minutes, determine the volume V of the added adsorbent molded body from the amount the liquid level of the liquid paraffin rises. ａ (cm ３ Calculate the mass W (g) and volume V of the adsorbent molded body that was put in. ａ (cm ３ ) The apparent density d is obtained from the following equation ａ Calculate d ａ =(W-W×u / 100) / V ａ (g / cm ３ )

[0094] The gas separation apparatus used in this embodiment has an apparatus volume / adsorption tower volume ratio of preferably 4.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less.

[0095] "Device volume" refers to the volume of the adsorption tower [cm³]. ３ ] and the volume of the piping from the first valve to the pressure reducing device [cm³ ３ ] and the volume of the piping from the first valve to the pressurizing device [cm³ ３ ] and the volume of the piping from the first valve to the non-adsorbent gas containment section [cm³ ３ This refers to the value obtained by adding ] and . The volume of a pipe can be determined by multiplying the cross-sectional area, which is obtained from the inner diameter of the pipe, by the length of the pipe.

[0096] The equipment dead space / equipment volume of the gas separation apparatus used in this embodiment is preferably 0.9 or less, more preferably 0.6 or less, and even more preferably 0.4 or less. "Equipment dead space" refers to the equipment volume [cm³]. ３ ] and the volume of the piping from the first valve to the pressure reducing device [cm³ ３ ] and the packed bed volume of the adsorbent [cm³ ３ The difference between the value obtained by adding ] and . The packed bed volume of the adsorbent is the weight [g] of the adsorbent packed into the adsorption tower and the bulk density d of the adsorbent. ｂ [g / cm ３ This is the volume calculated by dividing by [ ]. The bulk density of the adsorbent can be measured by the following method.

[0097] <Bulk density d ｂ Measurement of the bulk density d of the adsorbent molded body ｂ The measurement was performed using the following procedure: (1) Approximately 800 mL of adsorbent molded material was filled into a 1000 mL graduated cylinder. During filling, the molded material was hammered with a rubber hammer every 50 mL until the filling height of the molded material no longer changed. (2) The filling volume V of the adsorbent molded material. ｂ (cm ３(3) The mass W (g) of the filled adsorbent molded body was read from the scale line of the graduated cylinder. (4) The water content u (unit: mass%) of the adsorbent molded body was measured using an infrared moisture meter "FD-660" (product name) manufactured by Kett Scientific Research Institute. (5) The mass W and water content u measured in (3) and (4) above and the filled volume V read in (2) above ｂ Therefore, the bulk density d can be calculated from the following formula. ｂ (g / cm ３ ) was decided. d ｂ =(W-W×u / 100) / V ｂ (g / cm ３ )

[0098] The dead space / device volume in the inlet process of the gas separation apparatus used in this embodiment is preferably 0.6 or less, more preferably 0.5 or less, and even more preferably 0.4 or less, from the viewpoint of increasing the recovery rate of the poorly adsorbed gas to be purified. From the viewpoint of not making the pressure loss in the gas flow during the pressure reduction process excessive, it is preferably 0.05 or more, and 0.1 or more.

[0099] "Dead space in the inflow process" refers to the volume of voids in the gas flow path during the inflow process in two or more adsorption towers where the inflow process takes place, from the closed valve closest to the adsorption tower that discharges the inflow gas to the closed valve closest to the adsorption tower that receives the inflow gas, for each pipe connected to the adsorption towers. The volume of the voids is determined from the difference between the volume obtained from the inner diameter and length and the volume of the packing material. For the purpose of reducing voids inside the adsorption tower and / or for the purpose of assisting gas diffusion, the upper and lower parts of the adsorption tower 5a, the interlayers of the dehumidifying layer 31 and the adsorption layer 32, or all of these, may be filled with inert balls that hardly adsorb raw gas components.

[0100] The dead space / device volume of the desorption process in the gas separation apparatus used in this embodiment is preferably 0.6 or less, more preferably 0.5 or less, and even more preferably 0.4 or less, from the viewpoint of increasing the purity of the poorly adsorbed gas to be purified. From the viewpoint of not making the power load on the depressurization device excessive, it is preferably 0.05 or more, and more preferably 0.1 or more. The "dead space in the desorption process" refers to the volume of voids in the path through which the gas depressurized in the desorption process flows, from the closed valve closest to the adsorption tower to the depressurization device, for each pipe connected to the adsorption tower where the desorption process is performed.

[0101] The adsorption tower system uses two or more adsorption towers, each containing an adsorbent, which are switched between. While fewer towers are preferable because they reduce the amount of void space, using too few towers makes it difficult to switch between multiple towers and continuously separate the gas. Three or more adsorption towers may be used to continuously separate the gas while maintaining a constant amount of raw material gas. "Constant" means that the flow rate of the raw material gas supplied from the raw material supply unit remains within 10% by mass throughout the operation of each process and at the time of switching to the next process. For example, the flow rate may instantaneously increase or decrease due to the opening and closing of valves when switching the raw material gas supply destination. It is preferable to control the flow rate change so that it remains within 10% by mass, and more preferably within 5% by mass, throughout the switching process. Suppressing fluctuations in flow rate stabilizes the load on the equipment, thus reducing the required capacity margin. The time required for switching is not particularly limited as long as the gas flow rate remains constant, but it can usually be completed in about 5 seconds.

[0102] An example of using three or more adsorption towers is to use three or more towers, and after the first tower is used for the adsorption process, switch the supply destination of the raw material gas to the second tower, and after the second tower is used for the adsorption process, switch the supply destination of the raw material gas to the third tower, thereby maintaining a constant supply rate of raw material gas to each tower.

[0103] The gas separation apparatus and its operating mode according to the embodiment will be described in more detail below.

[0104] [Gas separation equipment]

[0105] Referring to Figure 2, the schematic configuration of the gas separation apparatus 100 according to the first embodiment will be described. The gas separation apparatus 100 has two adsorption towers, and by operating them alternately, gas separation can be performed continuously.

[0106] 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 non-adsorbable gas recovery line 7, a first product storage section 8, a pressure drop gas line 10, an inflow gas line 11, an easily adsorbable gas recovery line 14, a pressure reducing device 15, a repressurizing 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.

[0107] The adsorption tower 5a has a fixed bed 20a filled with an adsorbent configured to come into contact with the raw material gas introduced inside. One end of the adsorption tower 5a is connected to the raw material gas supply line 1, and the other end is connected to the difficult-to-adsorb gas recovery line 7. The difficult-to-adsorb gas recovery line 7 is equipped with an automatic valve AV6a. A first product storage section 8 is connected to the end of the difficult-to-adsorb gas recovery line 7.

[0108] The adsorption tower 5a is connected to the pressure-reducing gas line 10 at the end in the same direction as the end connected to the poorly adsorbed gas recovery line 7. The raw material gas tank 2 is connected to the end of the pressure-reducing gas line 10. The raw material gas supply line 1 may also be connected to the end of the pressure-reducing gas line 10. An automatic valve AV9a is provided in the pressure-reducing gas line 10 connected to the adsorption tower 5a. The pressure-reducing gas line may also be connected to the end in the opposite direction from the end connected to the poorly adsorbed gas recovery line 7.

[0109] The adsorption tower 5a is connected to the easily adsorbable gas recovery line 14 at the end in the same direction as the end connected to the raw material gas supply line 1. The raw material gas supply line 1 is equipped with a raw material 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. On the other hand, a depressurizing device 15 is connected to the easily adsorbable gas recovery line 14, and is configured to reduce the pressure inside the adsorption tower 5a. The depressurizing device 15 may be a vacuum pump. The easily adsorbable gas recovery line 14 may also be connected to the second product storage section 25. Furthermore, an automatic valve AV13a is provided in the easily adsorbable gas recovery line 14 connected to the adsorption tower 5a.

[0110] The adsorption tower 5a is connected to the repressurization gas line 16 at the end in the same direction as the end connected to the poorly adsorbed gas recovery line 7. The repressurization gas line 16 is equipped with an automatic valve AV 17a. The end of the repressurization gas line 16 is connected to the first product storage section 8.

[0111] The adsorption tower 5b has a fixed bed 20b filled with an adsorbent configured to come into contact with the raw material gas introduced inside. 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 difficult-to-adsorb gas recovery line 7. The difficult-to-adsorb gas recovery line 7 is equipped with an automatic valve AV6b.

[0112] The adsorption tower 5b is connected to the pressure drop gas line 10 at the end in the same direction as the end connected to the poorly adsorbed gas recovery line 7. The raw material gas tank 2 is connected to the end of the pressure drop gas line 10. The raw material gas supply line 1 may also be connected to the end of the pressure drop gas line 10. An automatic valve AV9b is provided in the pressure drop gas line 10 connected to the adsorption tower 5b. The pressure drop gas line may also be connected to the end in the opposite direction from the end connected to the poorly adsorbed gas recovery line 7.

[0113] Adsorption tower 5b is connected to the easily adsorbable gas recovery line 14 at the end in the same direction as the end connected to the raw gas supply line 1. An automatic valve AV4b is provided at the inlet of adsorption tower 5b. Meanwhile, a depressurization device 15 is connected to the easily adsorbable gas recovery line 14, allowing for depressurization inside adsorption tower 5b. An automatic valve AV13b is also provided at the easily adsorbable gas recovery line 14 connected to adsorption tower 5a.

[0114] The adsorption tower 5b is connected to the repressurization gas line 16 at the end in the same direction as the end connected to the poorly adsorbed gas recovery line 7. The repressurization gas line is equipped with an automatic valve AV17b. The end of the repressurization gas is connected to the first product storage section 8.

[0115] Adsorption towers 5a and 5b are connected by an inflow gas line 11 at the end in the same direction as the end connected to the raw material gas supply line 1. An automatic valve AV 12 is provided in the inflow gas line 11. The inflow gas line 11 may also connect adsorption towers 5a and 5b at the end opposite to the end connected to the raw material gas supply line 1, or it may connect adsorption towers 5a and 5b alternately at the end in the same direction as the end connected to the raw material gas supply line 1 and the end opposite to it.

[0116] The gas separation apparatus may be equipped with pressure gauges for measuring the pressure at each position of the apparatus. The raw 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. Pressure gauges 22a and 21a may be provided above and below the adsorption tower 5a, respectively, and pressure gauges 22b and 21b may be provided above and below the adsorption tower 5b, respectively. A pressure gauge 19 may be provided downstream of the pressurizing device 3, and a pressure gauge 24 may be provided upstream of the depressurizing device 15.

[0117] The adsorption tower 5a is supplied with raw material gas via the raw material gas supply line 1. Easily adsorbable gases contained in the raw material gas are adsorbed by the adsorbent packed inside the adsorption tower 5a, and the difficult-to-adsorb gases are recovered from the difficult-to-adsorb gas recovery line 7. In other words, the adsorption tower 5a performs an adsorption process in which raw material gas is introduced into the adsorption tower, easily adsorbable gases are adsorbed by the adsorbent, and difficult-to-adsorb gases are extracted. During the adsorption process, the gas is introduced while maintaining a constant pressure in the adsorption tower at a predetermined pressure. Note that during the adsorption process, pressure loss occurs as the raw material gas flows through the adsorption tower, which may result in a pressure difference between the inlet and outlet of the adsorption tower.

[0118] After the adsorption process is complete, the gas inside the adsorption tower 5a is released to the outside of the tower in order to reduce the pressure inside the tower. At this time, the gas inside the adsorption tower 5a is recovered to the raw material supply section via the pressure drop gas line 10. As the pressure inside the adsorption tower decreases, easily adsorbed gases are released from the adsorbent, and some of the poorly adsorbed gases remaining in the voids inside the adsorption tower are replaced by easily adsorbed gases. In other words, a pressure drop process is performed to recover poorly adsorbed gases by allowing gases from inside the adsorption tower to flow in.

[0119] By connecting the adsorption tower 5a and the adsorption tower 5b via the inflow gas line 11, the gas inside the adsorption tower 5a is recovered into the adsorption tower 5b. At this time, as the pressure inside the adsorption tower decreases, easily adsorbed gases are desorbed from the adsorbent, and some of the poorly adsorbed gases remaining in the voids inside the adsorption tower are further replaced by easily adsorbed gases. In other words, an inflow process is performed to recover poorly adsorbed gases by introducing gas from inside the adsorption tower.

[0120] The adsorption tower 5a, which contains an adsorbent that has adsorbed easily adsorbed gas, is decomposed by a vacuum device 15 to remove the easily adsorbed gas from the adsorption tower 5a under reduced pressure. This regenerates the adsorbent in the adsorption tower 5a and extracts the purified easily adsorbed gas. In other words, the easily adsorbed gas desorption process is performed by decomposing the easily adsorbed gas from the adsorption tower under reduced pressure.

[0121] As described above, adsorption towers 5a and 5b repeatedly perform adsorption of easily adsorbable gases by introducing raw material gas and desorption of poorly adsorbable gases by reducing pressure. Therefore, while adsorption tower 5a is desorbing easily adsorbable gases, raw material gas is introduced into adsorption tower 5b to adsorb easily adsorbable gases. After the desorption of carbon dioxide in adsorption tower 5a is complete, raw material gas is introduced into adsorption tower 5a again, and adsorption tower 5b is reduced in pressure to desorb easily adsorbable gases. In this way, carbon dioxide adsorption and desorption are repeatedly performed in each tower, and the raw material gas can be processed continuously.

[0122] When adsorption tower 5a is in the adsorption process and adsorption tower 5b is in the desorption process, automatic valves AV4a, AV6a, and AV13b are opened from the closed state. By opening automatic valve AV4a, which is located between the raw material gas tank 2 and the adsorption tower 5a, the raw material gas is introduced into the adsorption tower 5a.

[0123] Next, a pressure reduction process may be provided. In the pressure reduction process, the valve from the adsorption tower 5a to the first product storage section 8 is closed, and the gas inside the tower is released from the pressurized adsorption tower to the raw material supply section. When switching from the adsorption process to the pressure reduction process in the adsorption tower 5a, automatic valves AV6a and AV4a are closed, and automatic valve AV9a in the pressure reduction gas line 10 is opened. During this time, the desorption process may continue in the adsorption tower 5b.

[0124] In the inflow process, only the automatic valve AV12 installed in the inflow gas line 11 opens, and the other automatic valves close. As a result, gas movement occurs only between the adsorption tower 5a and the adsorption tower 5b. For example, when the adsorption tower 5a, which has finished the adsorption process, is connected to the adsorption tower 5b, the pressure in the adsorption tower 5a is higher than the pressure in the adsorption tower 5b, so gas flows from the adsorption tower 5a to the adsorption tower 5b.

[0125] Next, a desorption process is performed in the adsorption tower 5a. In the desorption process, automatic valves AV4a, AV6a, AV9a, and AV12 are closed, and automatic valve AV13a is opened. The easily adsorbable gas in the adsorption tower 5a is introduced into the second product storage section 25 by the depressurization device 15.

[0126] On the other hand, after the inflow process, a repressurization process may be performed in the adsorption tower 5b. The automatic valve AV17b provided in the repressurization gas line 16 is opened, and the poorly adsorbed gas is introduced from the first product containment section 8 into the adsorption tower 5b.

[0127] Pressure gauges 22b and 21b may be provided above and below the adsorption tower 5b, respectively.

[0128] Next, with reference to Figure 3, the schematic configuration of the gas separation apparatus 101 of the second embodiment will be described. In the second embodiment, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. The gas separation apparatus 101 has an inflow gas line 11up connecting the upper parts of the adsorption tower 5a and the adsorption tower 5b, an inflow gas line 11un connecting the lower parts of the adsorption tower 5a and the adsorption tower 5b, and an inflow gas line 11in connecting the inflow gas lines 11up and 11un. An automatic valve AV26a is provided between the upper outlet of the adsorption tower 5a and the connection between the inflow gas line 11up and the inflow gas line 11in. An automatic valve AV26b is provided between the upper outlet of the adsorption tower 5b and the connection between the inflow gas line 11up and the inflow gas line 11in. An automatic valve AV12a is provided between the lower inlet of the adsorption tower 5a and the connection between the inflow gas line 11un and the inflow gas line 11in. An automatic valve AV12b is provided between the lower inlet of the adsorption tower 5b and the connection between the inflow gas line 11un and the inflow gas line 11in. With this configuration, the connection direction of the adsorption towers 5a and 5b can be freely set during the inflow process, and the outflow direction of residual gas from the outflow side adsorption tower and the inflow method to the receiving side adsorption tower can be changed.

[0129] Next, with reference to Figure 3, the operation of the gas separation apparatus 101 of the second embodiment will be described. In the second embodiment, descriptions of processes common to the first embodiment will be omitted, except for the inflow process.

[0130] After the adsorption process in adsorption tower 5a and the desorption process in adsorption tower 5b, the gas is subjected to the inflow process. In the inflow process, automatic valves AV12b and AV26a provided in the inflow gas line 11 are opened, and the other automatic valves are closed. This causes the gas to move from the top of adsorption tower 5a to the bottom of adsorption tower 5b. For example, when adsorption tower 5a, which has completed the adsorption process, is connected to adsorption tower 5b, the pressure in adsorption tower 5a is higher than the pressure in adsorption tower 5b, so gas flows from adsorption tower 5a to adsorption tower 5b. Subsequently, the desorption process is performed in adsorption tower 5a.

[0131] The gas separation devices 100 and 101 may be applied, for example, to the purification of industrial exhaust gas containing carbon dioxide, or biogas obtained by the fermentation of organic matter. Among these applications, their use in the purification of biogas is particularly preferred.

[0132] [Biogas Purification System 1000; Example of Application to Biogas Purification] Figure 4 shows a schematic configuration of the biogas purification system 1000, which applies the gas separation device 100 to biogas purification. The example of application to biogas purification shows an example of separating and recovering methane, the main component of biogas, and carbon dioxide. In the case of biogas purification, the poorly adsorbed gas is usually methane (CH4). ４ ) and easily adsorbed gases include carbon dioxide (CO2). ２ )

[0133] The biogas purification system 1000 of this embodiment includes a fermentation tank 200, a desulfurization tower 300, a siloxane removal device 400, an oxygen removal device 500, a cooling device 600, a dewatering device 700, and a gas separation device 100.

[0134] The fermentation tank 200 is a tank that generates biogas (hereinafter also referred to as "raw material gas") by fermenting sewage sludge from sewage treatment plants, food waste from food factories and restaurants, and manure from dairy farmers, etc., under anaerobic conditions. The fermentation tank 200 is connected to a blower 201 so that the generated biogas can be supplied to other equipment.

[0135] The fermentation tank 200 may be connected to the desulfurization tower 300 before the biogas is introduced into the gas separation unit 100. The desulfurization tower 300 is an adsorption tower for removing hydrogen sulfide contained in the biogas. An example of a desulfurizing agent packed into the desulfurization tower 300 is iron oxide. Iron oxide reacts with hydrogen sulfide contained in the biogas to produce iron sulfide.

[0136] The fermentation tank 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 dioxide-containing substances found in sewage sludge.

[0137] The fermentation tank 200 may be connected to an oxygen removal device 500 before the biogas is introduced into the gas separation device 100. The oxygen removal device 500 removes oxygen contained in the biogas. By removing this oxygen, the purified methane gas can be safely transported.

[0138] The fermentation tank 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. This lowers the dew point of the biogas. As the cooling device 600, for example, a water-cooled cooler, an air-cooled cooler, an electric cooler, etc., can be used.

[0139] The fermentation tank 200 may be connected to a dehydration unit 700 before the biogas is introduced into the gas separation unit 100. The dehydration unit 700 further removes moisture from the biogas from which moisture has been removed by the cooling unit 600. This further lowers the dew point of the biogas. As the dehydration unit 700, for example, a device filled with a dehydrating agent can be used.

[0140] Next, with reference to Figure 4, the operation of the biogas purification system 1000 of this embodiment will be described.

[0141] First, biogas is generated in the fermentation tank 200 by fermenting sewage sludge from sewage treatment plants, food waste from food factories and restaurants, and manure from dairy farmers, etc., under anaerobic conditions. The biogas at this stage contains hydrogen sulfide, water, and other substances.

[0142] The biogas generated in the fermentation tank 200 is sent to the desulfurization tower 300. In the desulfurization tower 300, hydrogen sulfide is removed from the biogas so that its concentration is at the level of several volumes ppm.

[0143] Subsequently, the biogas from which hydrogen sulfide has been removed is sent to the siloxane removal unit 400. In the siloxane removal unit 400, the concentration of siloxane contained in the biogas is reduced to several mg / Nm³. ３ Remove siloxane to achieve a level of saturation.

[0144] Subsequently, the biogas from which siloxane has been removed is sent to an oxygen removal device 500. In the oxygen removal device 500, oxygen is removed so that the oxygen concentration in the biogas is at the level of several volumes ppm.

[0145] Next, the biogas is sent to a cooling device 600. The cooling device 600 cools the biogas and removes the water contained in it, thereby lowering the dew point of the biogas. After that, the biogas is sent to a dewatering device 700. In the dewatering device 700, the water content of the biogas is further removed, and the water content is reduced to 1000 ppm by volume or less.

[0146] The biogas, from which hydrogen sulfide, siloxane, and water have been removed, is sent to the gas separation unit 100. The operation of the gas separation unit 100 is as described above.

[0147] In addition, the biogas purification system 1000 may use a gas separation device 101 instead of a gas separation device 100.

[0148] According to the gas separation method of this embodiment, high-purity methane and high-purity carbon dioxide can be efficiently recovered.

[0149] The gas separation apparatus shown in Figure 6 may be the same as the apparatus shown in Figure 2, except that the adsorption towers 5a and 5b have dehumidifying layers 31a and 31b containing a desiccant and adsorption layers 32a and 32b containing a carbon dioxide adsorbent. The dehumidifying layers 31a and 31b and the adsorption layers 32a and 32b are arranged in this order from the raw gas supply line 1 side so that the raw gas comes into contact with the dehumidifying layers 31a and 31b and the adsorption layers 32a and 32b in that order within the adsorption towers 5a and 5b. For example, the apparatus shown in Figure 6 is suitable when purifying gas that contains carbon dioxide and water in addition to methane to be recovered, such as biogas.

[0150] In the adsorption process, a raw material gas containing water, carbon dioxide, and a poorly adsorbed gas is supplied to the adsorption towers 5a and 5b, and the poorly adsorbed gas is separated from the raw material gas by adsorbing the water and carbon dioxide onto the desiccant and adsorbent. As a result, of the water, carbon dioxide, and poorly adsorbed gas contained in the raw material gas, water and carbon dioxide are adsorbed and removed within the adsorption tower, and the poorly adsorbed gas flows out from the outlet of the adsorption tower. The raw material gas comes into contact with the desiccant layer and the adsorption layer in that order within the adsorption tower. Adsorption towers 5a and 5b preferably have isolation plates between the desiccant layers 31a and 31b and the adsorption layers 32a and 32b in order to prevent the movement of the desiccant and carbon dioxide adsorbent due to gas flow. The isolation plates may be provided on the upper and lower sides of the adsorption layers 32a and 32b, or between the layers if two or more types of adsorbents are packed in the tower, or they may be provided above and below and between the layers in a manner that does not obstruct gas flow and does not mix the adsorbents.

[0151] The dehumidifying layers 31a and 31b are filled with a desiccant that has the function of adsorbing water in the raw material gas and desorbs water when the pressure is reduced relative to the adsorption pressure. In the desorption process, water and carbon dioxide are desorbed from the adsorbent in the adsorption tower by reducing the pressure inside the adsorption tower. Alternatively, in the desorption process, water and carbon dioxide may be desorbed from the adsorbent by reducing the pressure inside the adsorption tower from the inlet side of the raw material gas. Examples of desiccant include activated alumina, silica gel, zeolite, and activated carbon. Among these, activated carbon or activated alumina is preferred as the desiccant from the viewpoint of resistance to liquid water, and activated alumina is more preferred. When the raw material gas contains 0.1 volume% or more of water, and the raw material gas is supplied under pressure, there is a possibility that water will condense and liquid water will be generated, so a desiccant that does not easily reduce the strength of the desiccant molded body even when immersed in water is suitable.

[0152] The water adsorption capacity of the desiccant is preferably 2.37 mol / kg or more, and more preferably 2.77 mol / kg or more, under conditions of a partial pressure of water of 1 kPa and a temperature of 35°C. The water adsorption capacity of the desiccant is preferably 1.98 mol / kg or less, and more preferably 0.59 mol / kg or less, under conditions of a partial pressure of water of 0.01 kPa and a temperature of 35°C, in order to quickly desorb water during desorption. The water adsorption capacity of the desiccant is measured by introducing saturated water vapor of water at the measurement temperature of 35°C into the desiccant to measure the absolute pressure from 0.01 to 5.4 kPa. During the measurement, the pressure is measured over time, and when the pressure fluctuation becomes 0.3% / 300 sec or less, it is determined that the saturated adsorption amount has been reached, and this is taken as the adsorption capacity at 35°C (unit: mol / kg). Furthermore, the adsorption capacity at partial pressures of water of 1 kPa and 0.01 kPa is determined by creating an adsorption isotherm that shows the relationship between the change in pressure over time and the adsorption capacity from the measurement results used to determine the adsorption capacity, and then using the adsorption capacity at each pressure as read from the adsorption isotherm.

[0153] To minimize the loss rate of poorly adsorbed gases, it is preferable for dehumidifiers to have a low adsorption capacity for poorly adsorbed gases. Furthermore, while dehumidifiers may have adsorption properties for components other than water and poorly adsorbed gases in the source gas, if the source gas contains a gas with a greater adsorption capacity than water at the same partial pressure, this may impair the dehumidification performance. Therefore, it is preferable to select the type of dehumidifier by considering the components contained in the source gas and the components that the dehumidifier exhibits adsorption capacity for.

[0154] From the viewpoint of reducing the loss rate of poorly adsorbed gases and improving contact with the gas, the shape of the desiccant is preferably spherical (including approximately spherical) or cylindrical (including approximately cylindrical). Such a shape allows for a high packing density. The average particle diameter of the desiccant is preferably 10 mm or less. The average particle diameter of the desiccant is preferably 1 mm or more. It is preferable that the desiccant be within the range of the above average particle diameter so that when the desiccant moves or shakes with the movement of the gas, the desiccant particles do not collide or rub against each other and cause powdering. Note that the average particle diameter of the desiccant is the average particle diameter when it is spherical, and when it is cylindrical, it is the average diameter of the top or bottom surface. The average particle diameter of a desiccant refers to the number-average particle diameter obtained by simply averaging the diameters of each individual particle of the desiccant. Specifically, for example, 30 desiccant particles without cracks or chips are randomly selected, and for each particle, the diameter is measured using calipers if it is spherical, or the diameter of the base if it is cylindrical. These measurements are then averaged, and the resulting value is considered the average particle diameter.

[0155] As shown in Figure 7, in the gas separation method according to this embodiment, focusing on the adsorption tower 5a, the adsorption tower 5a may have an adsorption process, an inflow process, a desorption process, an inflow process, and a repressurization process in this order. In the gas separation method according to this embodiment, focusing on the adsorption tower 5b, the adsorption tower 5b may have an adsorption process, an inflow process, a desorption process, an inflow process, and a repressurization process in this order. However, from the viewpoint of efficiently performing the adsorption process by switching between adsorption towers 5a and 5b, the switching operation can be efficiently performed by performing the desorption process in the other adsorption tower while the adsorption process is being performed in one adsorption tower.

[0156] Layer thickness L in the direction of raw material gas flow in the dehumidification layer ｄ (m) is 0.05 to 0.30 m, from the viewpoint of sufficiently adsorbing and removing water in the adsorption process and keeping the loss rate of poorly adsorbed gases low. ｄ A value of 0.05 or higher ensures that the desiccant layer thickness is greater than the length of the water adsorption zone formed due to the adsorption rate when water contained in the raw material gas flowing in during the adsorption process is adsorbed onto the desiccant, thereby suppressing the decrease in carbon dioxide adsorption capacity caused by water penetrating the adsorption layer and being adsorbed onto the adsorbent. ｄ By setting the ratio to 0.30 or less, the void portion of the dehumidifying layer with little or no carbon dioxide adsorption capacity is reduced, thereby reducing the amount of poorly adsorbed gases discharged outside the system along with carbon dioxide during the desorption process, and keeping the loss rate of poorly adsorbed gases low. ｄ From the above viewpoint, the length is preferably 0.06 to 0.25 m, more preferably 0.08 to 0.20 m, and even more preferably 0.10 to 0.15 m.

[0157] Layer thickness L of the adsorption layer relative to the raw material gas flow direction. ａ (m) is preferably 0.7 to 1.5 m, more preferably 0.8 to 1.3 m, and even more preferably 0.85 to 1.05 m, from the viewpoint of preventing excessive pressure loss during the adsorption and depressurization processes at the upper limit and preventing excessive increase in the column diameter at the lower limit.

[0158] L in the gas separation apparatus of this embodiment ａ / L ｄ L is preferably 3 to 17, more preferably 5 to 13, and even more preferably 7 to 10. ａ / L ｄ By setting the thickness of the dehumidifying layer and the adsorption layer in such a way, a sufficient amount of dry carbon dioxide gas passes through the dehumidifying layer during the adsorption process, allowing the moisture adsorbed on the dehumidifying layer to be desorbed and the desiccant to be easily regenerated.

[0159] In this embodiment, Q / L ｄ is 4.4 (Nm ３It is preferable that Q is greater than or equal to ( / m). Q is the amount of carbon dioxide (Nm³) per cycle discharged outside the adsorption tower in the countercurrent direction to the raw material gas flow in the adsorption process (i.e., opposite to the direction of D in Figure 1). ３ ) For example, in the desorption process, the amount of carbon dioxide discharged outside the tower during depressurization is added to Q. In addition, in the pressure drop process, if gas is discharged outside the tower from the opposite direction to D, the amount of carbon dioxide discharged by that process is added to Q.

[0160] Dehumidifying layer thickness L ｄ (m) is the amount of carbon dioxide exhausted in the countercurrent direction from the adsorption tower system to the raw material gas introduced during the adsorption process and the adsorption tower system during one cycle from one adsorption process to the next. ３ When Q / L is set as follows, ｄ However, 4.4 (Nm ３ Set it to be greater than or equal to / m. Therefore, layer thickness L ｄ (m) will increase or decrease in the appropriate range depending on the adsorption performance of the adsorbent. This is set with the view that water adsorbed on the dehumidifying layer will be sufficiently desorbed in the desorption process. Generally, dehumidifiers have an adsorption capacity of about 0.40 mol / kg of water even at low partial pressures of around 0.01 kPa at room temperature. Therefore, water is easily adsorbed during adsorption, but desorption does not proceed even if the pressure in the system is reduced to a few kPa, making repeated use difficult in many cases. To overcome this, in addition to lowering the total pressure when reducing the pressure in the system, one measure is to lower the gas phase moisture pressure near the adsorbent by flowing a purge gas different from water, thereby promoting desorption. In a multilayer system in which dehumidifier and carbon dioxide adsorbent are packed in layers, the raw material gas introduced during the adsorption process and the carbon dioxide passing countercurrently through the adsorption tower act as purge gases, promoting the desorption of water from the dehumidifying layer. If the amount of moisture adsorbed and removed in one cycle is constant, then a larger amount of purge gas is desirable to sufficiently desorb the moisture contained in the desiccant during the desorption process, and at the same time, a lower limit is considered to exist. On the other hand, if the raw material gas introduced during the adsorption process and Q (i.e., the amount of gas that can be used as purge gas) passing through the adsorption tower in the countercurrent are constant in one cycle, then the flow path L, which removes water in the gas phase as purge gas, is considered to be constant. ｄTherefore, it is desirable that the distance the purge gas travels while containing water in the gas phase is short. For this reason, Q should be set to L. ｄ Q / L divided by ｄ > 4.4 Nm ３ By having a density of / m, it is possible to obtain poorly adsorbed gases with a low dew point and low loss rate.

[0161] This embodiment is suitable when the raw material gas contains water, carbon dioxide, and poorly adsorbed gases. Specific examples of such raw material gases include blast furnace gas and biogas. The concentration of water in the raw material gas introduced into the adsorption tower is not particularly limited, but from the viewpoint of sufficient dehumidification in the adsorption tower, it is preferably 2% by volume or less, more preferably 1.5% by volume or less, and even more preferably 1.0% by volume or less. However, when the raw material gas is pressurized, water condenses and is removed from the raw material gas, so it is often 2% by volume or less at the stage of introduction into the adsorption tower. On the other hand, in the VSA range where the raw material gas is introduced at approximately atmospheric pressure, it is preferable to keep it at 2% by volume or less. The concentration of water in the raw material gas introduced into the adsorption tower is not particularly limited, but it may be 0.03% by volume or more, 0.1% by volume or more, or 0.8% by volume or more.

[0162] From the viewpoint of making the adsorption tower compact, the concentration of carbon dioxide in the raw material gas is preferably 20 to 70% by volume, and more preferably 30 to 70% by volume. Since the carbon dioxide adsorption capacity per unit weight of a typical carbon dioxide adsorbent tends to increase monotonically in the range of 0 to 30%, the higher the carbon dioxide concentration of the raw material gas, the higher the Q / L. ｄ > 4.4 Nm ３ This is because the amount of carbon dioxide adsorbent required to ensure Q that satisfies / m becomes smaller.

[0163] Q / L in at least one adsorption tower (preferably all towers) ｄHowever, by satisfying the specified range, it is possible to obtain poorly adsorbed gases from raw material gases containing water, carbon dioxide, and poorly adsorbed gases with a low dew point and low loss rate. In other words, when two or more adsorption towers are used, Q represents the amount of carbon dioxide discharged out of the adsorption tower per cycle in the countercurrent to the raw material gas flow in the adsorption process in one tower. ｄ This is the thickness of the dehumidifying layer in the tower with respect to the direction of the raw material gas flow.

[0164] In a single tower, the above-described process may be repeated for one or more cycles. One cycle refers to the period from the adsorption step to just before the next adsorption step, within the repeated process of adsorption, inflow, desorption, inflow, and repressurization. The number of cycles in the gas separation method according to this embodiment may be two or more, three or more, five or more, ten or more, fifty or more, or 100 or more.

[0165] The apparatus shown in Figure 6 is equipped with an inlet gas line 11 having an automatic valve AV12, and a repressurization gas line 16 having automatic valves 17a and 17b. The inlet gas line 11 is connected to the inlet on the raw material gas supply side of the adsorption towers 5a and 5b. The repressurization gas line 16 is connected to the first product storage section 8 and the adsorption towers 5a and 5b.

[0166] With all automatic valves closed and the pressurizing device 3 activated, the automatic valves AV4a and AV6a are released, and the adsorption process is performed in the adsorption tower 5a. Subsequently, the automatic valves AV4a and AV6a are closed, and the automatic valve AV12 is released, connecting to the adsorption tower 5b, which has been pre-pressurized, and the inflow process is performed. Subsequently, the automatic valve AV12 is closed, and with the depressurizing device 15 activated, the automatic valve AV13a is released, and the desorption process is performed in the adsorption tower 5a. After the inflow process described above, that is, after the automatic valve AV12 is closed, the automatic valve 17b is released, and the repressurization process is performed in the adsorption tower 5b. After the repressurization process, the automatic valves AV4b and AV6b are released, and the adsorption process is performed in the adsorption tower 5b. The automatic valves AV4b, AV6b, and AV13a are closed, and the automatic valve AV12 is released, connecting to the adsorption towers 5a and 5b, and the inflow process is performed.

[0167] In the inflow process, the exhaust direction of the gas in the adsorption tower after the adsorption process may be counter-current to the raw material gas flow in the adsorption process (opposite direction D in Figure 6) or parallel to the raw material gas flow in the adsorption process (direction D in Figure 6), but it is preferable that it be counter-current to the raw material gas flow in the adsorption process. When the gas is exhausted counter-current to the raw material gas flow in the adsorption process, the amount of carbon dioxide contained in the exhaust from the inflow process is added to Q. In other words, the gas exhausted in the pressure drop process desorbs the gas adsorbed on the dehumidifying layer and the adsorption layer, and the desiccant and carbon dioxide adsorbent are regenerated.

[0168] The inflow process reduces proportional costs because it lowers the pressure inside the adsorption tower without using the power required for a pressure reducing device that demands a large amount of power. In addition, it is a useful process from the standpoint of further reducing the loss rate of difficult-to-adsorb gases. Since there is no adsorbent in the voids and piping inside the adsorption tower, these spaces naturally do not have the ability to separate the raw material gas. Therefore, at the end of the adsorption process, the raw material gas remains in these spaces. If the process were to proceed directly to the desorption process, the difficult-to-adsorb gases contained in the remaining raw material gas would move to the recovered carbon dioxide gas side, resulting in loss and a decrease in the recovery rate of difficult-to-adsorb gases. In the inflow process, the gas remaining in the adsorption tower after the adsorption process is supplied to other towers that will perform the next adsorption process, thus reducing the loss rate of difficult-to-adsorb gases.

[0169] This embodiment also provides a method for producing purified gas, which involves purifying and recovering easily adsorbable and / or poorly adsorbable gases using the gas separation method according to this embodiment.

[0170] The present invention will be described in more detail below with reference to examples, but these are illustrative examples and the present invention is not limited to the following examples.

[0171] [Adsorption Selectivity] Adsorption selectivity (CO ２ / CH ４The selectivity was determined by the following procedure: (1) 0.2 g of adsorbent was placed in a 12 mm cell (manufactured by Micro Meritics). (2) The sample in the cell from (1) was placed in a Micro Meritics gas adsorption analyzer "3-Flex" (product name) and subjected to heating and vacuum degassing treatment at 250°C and 0.001 mmHg or less for 12 hours. (3) The sample in the cell after the treatment from (2) was placed in constant temperature circulating water at 25°C, and after the sample temperature reached 25 ± 0.2°C, the absolute pressure was measured from 0.25 to 760 mmHg using liquefied carbon dioxide (manufactured by Sumitomo Seika Co., Ltd., purity 99.9% by mass or higher). During the above measurement, the pressure was measured over time, and it was determined that the saturation adsorption amount had been reached when the pressure fluctuation became 0.001% by volume / 10 sec or less. Similarly, for gaseous substance A, measurements were taken using a gas with a purity of 99.9% by volume or higher, from an absolute pressure of 0.25 to 760 mmHg. The adsorption selectivity was defined as the equilibrium adsorption amounts of carbon dioxide and gaseous substance A at 760 mmHg, obtained by measuring the adsorption isotherm, respectively, q(CO₂). ２ ), when q(GMA), q(CO ２ The adsorption selectivity is defined as ) / q(GMA).

[0172] [Differential heat of adsorption] The differential heat of adsorption was determined by the following procedure: (1) 0.2 g of adsorbent was placed in a cell (manufactured by Micro-Trac-Bel). (2) The sample in the cell from (1) was heated and vacuum-degassed at 250°C and 10 Pa or less for 5 hours. (3) The cell after the treatment from (2) was placed in a Micro-Trac-Bel gas adsorption measuring device "BERSORP MAX II", placed in constant temperature circulating water at 35°C, and the absolute pressure was measured from 0.25 to 900 mmHg using liquefied carbon dioxide (manufactured by Sumitomo Seika Co., Ltd., purity 99.9% by mass or higher), and the 35°C adsorption isotherm was used. During the above measurement, the pressure was measured over time, and it was determined that the saturation adsorption amount had been reached when the pressure fluctuation became 0.001 volume% / 10 sec or less. (4) Measurements were taken in the same manner as when the temperature was 35°C, except that the temperature of the constant-temperature circulating water was set to 20°C or 50°C, and the adsorption isotherms for 20°C and 50°C were used, respectively. (5) Using the analysis software "BELMaster" manufactured by Microtrac-Bel, the differential heat of adsorption at the pressure of the adsorption process and the pressure of the desorption process were determined from the adsorption isotherms at 20°C, 35°C, and 50°C and the Clausius-Clapeyron equation. (6) The differential heat of adsorption of the adsorbent was determined by averaging the differential heat of adsorption of the two points obtained in (5) above.

[0173] [CO ２ Adsorption capacity, working capacity (WC), and hysteresis amount; gas adsorption / desorption isotherm measurement] Gas adsorption / desorption isotherm measurement was performed using the following procedure: (1) 0.2 g of the dried adsorbent was placed in a 12 mm cell (manufactured by Micro Meritics) as a sample. (2) The sample in the cell from (1) was placed in a Micro Meritics gas adsorption analyzer "3-Flex" (product name) and subjected to heating and vacuum degassing treatment at 250°C and 0.001 mmHg or less for 12 hours. (3) The sample in the cell after the treatment from (2) was placed in constant temperature circulating water at 25°C, and after the sample temperature reached 25 ± 0.2°C, the absolute pressure was measured from 0.25 to 900 mmHg using liquefied carbon dioxide (manufactured by Sumitomo Seika Co., Ltd., purity 99.9% by mass or higher). During the above measurement, the pressure was measured over time, and it was determined that the saturation adsorption amount had been reached when the pressure fluctuation became 0.001% / 10sec or less. ２The adsorption capacity (unit: mol / kg) was used. (4) Following the measurement in (3), a pressure reduction treatment was performed over time from an absolute pressure of 900 to 0.25 mmHg to measure the desorption isotherm of carbon dioxide. As for the equilibrium judgment, similar to (3), the measurement was carried out with the pressure fluctuation being 0.001% / 10 sec or less. (5) From the adsorption and desorption isotherms of carbon dioxide, the difference between the CO ２ adsorption capacity and the CO at the pressure in the desorption process ２ adsorption capacity was calculated. In Table 1, the pressure in the adsorption process was 120 kPa and the pressure in the desorption process was 6 kPa. (6) As an index indicating the amount of hysteresis in the adsorption and desorption isotherm of carbon dioxide, when the equilibrium adsorption amounts at 75 mmHg of the adsorption isotherm measured in (3) and the equilibrium adsorption amounts at 75 mmHg of the desorption isotherm measured in (4) were respectively denoted as q(Ad) and q(De), q(Ad) / q(De) was used as the index indicating the amount of hysteresis. When q(Ad) / q(De) = 1.00, it indicates that there is no hysteresis, and the smaller q(Ad) / q(De) is, the greater the state of hysteresis.

[0174] 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 Corporation), 3.39 g of sodium nitrate (NaN ３ 3, manufactured by Fujifilm Wako Pure Chemical Corporation), 1.64 g of sodium aluminate (NaAlO ２ 2, manufactured by Fujifilm Wako Pure Chemical Corporation), and 10.82 g of colloidal silica (Ludox AS-40, solid content concentration 40% by mass, manufactured by Grace) were mixed and stirred for 30 minutes to prepare a mixed gel. The composition of the mixed gel was α = E / Al ２ 2 ３ = 4.53, β = SiO ２ 2 ２ / Al ３ 2 ２ = 8.17, γ = Na ２ 2 ３ O / Al ２ 2 ５ = 3.99, δ = P ２ 2 ３ O / Al ２ 2 ２ O３ = 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 microcylinder (manufactured by HIRO COMPANY) containing a fluororesin inner cylinder, and hydrothermally synthesized for 4 days at a stirring speed of 30 rpm and 135°C in a stirring-type constant temperature bath (manufactured by HIRO COMPANY) that can rotate in the vertical direction of the microcylinder. The product was filtered and dried at 120°C to obtain powdered zeolite. 1 g of the obtained zeolite was treated with potassium carbonate (K ２ CO ３ The mixture was placed in 500 mL of a 0.05 N potassium carbonate aqueous solution prepared using (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 were replaced with potassium. XRD spectroscopy confirmed that the obtained zeolite was a GIS-type zeolite. Furthermore, since no peaks originating from other zeolites or amorphous silica-alumina were observed, it was evaluated as a high-purity GIS-type zeolite.

[0175] Regarding the obtained zeolite, ２９ From the Si-MAS-NMR spectrum, the silica-alumina ratio was calculated to be SAR = 6.90, and (a+d) / (b+c) = 0.305. Furthermore, the potassium and lithium content in the zeolite was Z / T = 0.99 (= K / T). The obtained GIS-type zeolite CO ２ When the adsorption and desorption isotherms were measured, the adsorption capacity at 760 mmHg was 3.7 mol / kg, and q(Ad) / q(De) = 0.984. Similarly, CH ４ When the adsorption isotherm was measured, the adsorption capacity at 760 mmHg was found to be 0.09 mol / kg.

[0176] 40 parts by mass of GIS-type zeolite powder, 1.2 parts by mass of methylcellulose (Selander YB-132A, manufactured by Hi-Chem Co., Ltd.), 0.2 parts by mass of polyvinyl alcohol (Gosenol N-300, manufactured by Mitsubishi Chemical Corporation), 48.2 parts by mass of alumina sol (manufactured by Nissan Chemical Corporation, alumina content: 10.5% by mass), and 10.4 parts by mass of powdered alumina hydrate were mixed. The above 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 fired in an electric furnace at 350°C for 24 hours under an air atmosphere to produce a GIS-type zeolite molded body (hereinafter also referred to as "GIS").

[0177] Manufacturing Example 2: Method for Manufacturing CHA-type Zeolite Molded Body A CHA-type zeolite molded body was manufactured in the same manner as the GIS-type zeolite molded body in Manufacturing Example 1, except that the GIS-type zeolite powder was replaced with chabasite-type zeolite powder (manufactured by ACS Material, trade name "SSZ-13", hereinafter also referred to as "CHA").

[0178] In addition, the following commercially available products were used: 13X type zeolite molded body (Fujifilm Wako Pure Chemical Industries, Ltd., product name "Molecular Sieves 13X", faujasite (hereinafter also referred to as "FAU")) LTA type zeolite (Fujifilm Wako Pure Chemical Industries, Ltd., product name "Molecular Sieves 5A", hereinafter also referred to as "LTA") Activated carbon (Osaka Gas Chemical Co., Ltd., product name "3K-172" (hereinafter also referred to as "CMS"))

[0179] The various physical properties of the zeolite used were measured using the method described above and are shown in Table 1 below.

[0180]

[0181] Example 1: Gas Separation Method Using the gas separation apparatus shown in Figure 2, a raw material gas containing 60% methane and 40% carbon dioxide was separated and recovered as a poorly adsorbed gas (methane) and an easily adsorbed gas (carbon dioxide). As shown in Tables 2 and 3, 1.3 kg each of GIS1, a GIS-type zeolite molded body obtained in Production Example 1, was packed into the inside of adsorption towers 5a and 5b as an adsorbent. At this time, the ratio of the length L to the diameter D of the adsorption layer (the cylindrical part filled with adsorbent) (L / D) was set to 10, and the adsorption tower volume / apparent adsorbent volume was packed to 2.0. The apparatus dead space / apparatus volume was set to the values ​​shown in Tables 2 and 3. Before the following operation 1, the adsorption towers 5a and 5b were reduced to 50 Pa and heated to 250°C to remove moisture contained in the adsorbent.

[0182] (Operation 1) Adsorption tower 5a: With all automatic valves AV for the adsorption process closed, automatic valves AV4a and AV6a were opened, and the raw material gas was supplied to the adsorption tower 5a at the pressure shown in Table 1 by the pressurizer 3. After 2 minutes, automatic valves AV4a and AV6a were closed. The gas 1 (methane) that flowed out from the first product storage section 8 between the opening and closing of automatic valves AV4a and AV6a was entirely recovered in a gas bag (not shown).

[0183] Adsorption tower 5b: Simultaneously with the release of automatic valves AV4a and AV6a in the desorption process, automatic valve AV13b was opened, and the pressure in the adsorption tower 5b was reduced by the depressurization device 15.

[0184] (Operation 2) Adsorption tower 5a: After closing automatic valves AV4a and AV6a in the pressure drop process operation 1, automatic valve AV9a was opened to allow the gas from the adsorption tower 5a to flow into the raw material gas tank 2. After 10 seconds, automatic valve AV9a was closed.

[0185] Adsorption tower 5b: The automatic valve for the desorption process maintained the state of operation 1. After confirming that the pressure indicated by the pressure gauge 22b located at the top of the adsorption tower 5b reached the desorption process pressure shown in Table 1, the automatic valve AV13b was closed. From the time the automatic valve AV13b was opened until it was closed, all of the gas 2 (carbon dioxide) that flowed out of the adsorption tower 5b was recovered in a gas bag (not shown).

[0186] (Operation 3) Adsorption towers 5a and 5b: After closing automatic valves AV9a and AV13b in inflow process operation 2, automatic valve AV12 was opened to allow the gas from adsorption tower 5a to flow into adsorption tower 5b. After 10 seconds, automatic valve AV12 was closed.

[0187] (Operation 4) Adsorption tower 5a: After closing the automatic valve AV12 in the desorption process operation 3, the automatic valve AV13a was opened and the adsorption tower 5a was depressurized by the depressurization device 15.

[0188] Adsorption tower 5b: After closing automatic valve AV12 in the repressurization process operation 3, automatic valve AV17b was opened and gas was introduced from the first product containment section 8. After confirming that the pressures indicated by pressure gauges 21b and 22b located above and below the adsorption tower 5b reached the repressurization process pressure shown in Table 1, automatic valve AV17b was closed.

[0189] (Operation 5) Adsorption tower 5a: The automatic valve for the desorption process maintained the state from Operation 4.

[0190] Adsorption tower 5b: The automatic valve AV17b for the adsorption process was closed, and then the automatic valves AV4b and AV6b were opened, and the raw material gas was supplied to the adsorption tower 5b at the adsorption process pressure shown in Table 1 by the pressurizing device 3. After 2 minutes, the automatic valves AV4b and AV6b were closed. The gas 1 (methane) that flowed out from the first product storage section 8 between the opening and closing of the automatic valves AV4b and AV6b was entirely recovered in a gas bag (not shown).

[0191] (Operation 6) Adsorption tower 5a: The automatic valve for the desorption process maintained the state of Operation 5. After confirming that the pressure indicated by the pressure gauge 22a located at the top of the adsorption tower 5a reached the desorption process pressure shown in Table 1, the automatic valve AV13a was closed. From the time the automatic valve AV13a was opened until it was closed, the gas 2 (carbon dioxide) that had flowed out of the adsorption tower 5a was fully recovered in a gas bag (not shown).

[0192] Adsorption tower 5b: After closing automatic valves AV4b and AV6b in the pressure drop process operation 5, automatic valve AV9b was opened to allow the gas from adsorption tower 5b to flow into the raw material gas tank 2. After 10 seconds, automatic valve AV9b was closed.

[0193] (Operation 7) Adsorption towers 5a and 5b: After closing automatic valves AV13a and AV9b in inflow process operation 6, automatic valve AV12 was opened to allow the gas from adsorption tower 5b to flow into adsorption tower 5a. After 10 seconds, automatic valve AV12 was closed.

[0194] (Operation 8) Adsorption tower 5a: After closing the automatic valve AV12 in the repressurization process operation 7, the automatic valve AV17a was opened and gas was allowed to flow in from the product containment section. After confirming that the pressure gauges 21a located above and below the adsorption tower 5a and the pressure indicated by the pressure gauge 21a reached the repressurization process pressure shown in Table 1, the automatic valve AV17a was closed.

[0195] Adsorption tower 5b: After closing the automatic valve AV12 in the desorption process operation 7, the automatic valve AV13b was opened, and the adsorption tower 5b was depressurized by the depressurization device 15.

[0196] (Operation 9) Adsorption tower 5a: After closing automatic valve AV17a in adsorption process operation 8, automatic valves AV4a and AV6a were opened, and the raw material gas was supplied to the adsorption tower 5a at the pressure shown in Table 1 by the pressurizing device 3. After 2 minutes, automatic valves AV4a and AV6a were closed. The gas 1 (methane) that flowed out from the first product storage section 8 between the opening and closing of automatic valves AV4a and AV6a was entirely recovered in a gas bag (not shown).

[0197] Adsorption tower 5b: The automatic valve for the desorption process maintained the state of operation 8. After confirming that the pressure indicated by the pressure gauge 22b located at the top of the adsorption tower 5b reached the desorption process pressure shown in Table 1, the automatic valve AV13b was closed. From the time the automatic valve AV13b was opened until it was closed, all of the gas 2 (carbon dioxide) that had flowed out of the adsorption tower 5b was recovered in a gas bag (not shown).

[0198] After performing operations 1, 2, 3, 4, 5, 6, 7, 8, and 9 once, operations 2, 3, 4, 5, 6, 7, 8, and 9 were repeated 100 times.

[0199] All of the obtained poorly adsorbed gas (methane) and easily adsorbed gas (carbon dioxide) were recovered. The obtained methane purity and carbon dioxide purity were as shown in Table 3. The recovery rate was calculated from the amount of methane V1 (NL) supplied during this period to the amount of methane V2 (NL) recovered in gas 1, and is shown in Table 3. After repeating operations 2, 3, 4, 5, 6, 7, 8, and 9 100 times, in the 101st cycle, after the completion of operation 2, the adsorption tower 5a was heated to 250°C with a heater while the pressure was reduced to 50 Pa, and the gas discharged from the adsorption tower 5a was recovered in a gas bag. After performing operations 1, 2, 3, 4, 5, 6, 7, 8, and 9 once again, operations 2, 3, 4, 5, 6, 7, 8, and 9 were repeated 100 times. Subsequently, in the 101st cycle, after the completion of operation 3, the adsorption tower 5a was heated to 250°C while the pressure was reduced to 50 Pa, and all the gas discharged from the adsorption tower 5a was recovered into a gas bag. The volume of each recovered gas was measured using an integrated flow meter, and the difference was taken as the amount of gas flowing into the inflow process. The gas composition was calculated from the difference in the amount of substance by analyzing 100 μL of gas from each gas bag using gas chromatography. Subsequently, the adsorption tower 5b was heated to 250°C while the pressure was reduced to 50 Pa, and the gas inside the adsorption tower was discharged. After performing operations 1, 2, 3, 4, 5, 6, 7, 8, and 9 once more, operations 2, 3, 4, 5, 6, 7, 8, and 9 100 times, the raw material gas was introduced into the adsorption tower 5a again in the same manner as in operation 1, and the adsorption operation was carried out until the gas concentration at the outlet of the adsorption tower became equal to the raw material gas concentration. When the derivative was calculated from d [concentration of easily adsorbed gas at the outlet of the adsorption tower (volume %)] / d [time (s)], the adsorption time t0 when the derivative began to increase and reached 0.1, the adsorption time t1 when the derivative reached 0.3, and the adsorption time t2 when the derivative reached a maximum and then returned to 0.3 were determined, and (t1 - t0) / (t2 - t0) are shown in Table 3.

[0200] [Powdering Rate] The powdering rate of the adsorbent was evaluated using the following procedure: (1) After the gas separation operation described above was completed, the entire amount of adsorbent was withdrawn from adsorption towers 5a and 5b, and the mass W1 was measured. (2) 100 g of the withdrawn adsorbent was weighed, and the short diameter of the adsorbent was measured using a caliper, with the average value of the short diameter of the adsorbent being taken as ds. For this measurement, a caliper with a minimum reading of 0.1 mm or less was used. A sieve with a mesh opening smaller than ds and the largest mesh opening was selected and prepared from the publicly available mesh openings of JIS Z 8801-1, and all of the withdrawn adsorbent was passed through this sieve. (3) The mass W2 of the adsorbent that passed through the sieve was measured. The value calculated using formula (1) was defined as the powdering rate of the adsorbent [mass %]. The results are shown in Tables 2 and 3.

[0201]

[0202] Examples 2-4, 20: Gas Separation Methods The gas separation methods of Examples 2-4 were carried out in the same manner as in Example 1, except that 1.3 kg of the zeolite shown in Table 2 was packed inside the adsorption towers 5a and 5b as an adsorbent, and the conditions were changed as shown in Tables 2 and 3. The results are shown in Tables 2 and 3.

[0203] Examples 5-14, 19, 21: Gas separation method. The gas separation methods of Examples 5-15 were carried out in the same manner as in Example 1, except that the adsorption conditions were changed as shown in Tables 2 and 3. The results are shown in Tables 2 and 3.

[0204] Example 15 The gas separation method was carried out in the same manner as in Example 1, except that 13 kg of zeolite was packed into adsorption towers 5a and 5b, and the adsorption conditions were changed as shown in Tables 2 and 3. The results are shown in Tables 2 and 3.

[0205] Example 16 Using the gas separation apparatus shown in Figure 3, the gas separation method was carried out in the same manner as in Example 1, except that automatic valves AV26a and AV12b were opened during the inflow process of adsorption tower 5a, and automatic valves AV26b and AV12a were opened during the inflow process of adsorption tower 5b, to move the incoming gas from the outlet to the inlet of the adsorption tower. The results are shown in Tables 2 and 3.

[0206] Examples 17-18: Gas Separation Method The gas separation method was carried out in the same manner as in Example 1, except that the adsorption conditions were as shown in Tables 2 and 3, and the process proceeded to the inflow process without performing a pressure drop process after the adsorption process. The results are shown in Tables 2 and 3.

[0207] In this embodiment, in operation 1, after depressurizing the adsorption tower 5b, the automatic valve AV13b was closed after confirming that the pressure indicated by the pressure gauge 22b located at the top of the adsorption tower 5b reached the desorption process pressure shown in Table 1. From the time the automatic valve AV13b was opened until it was closed, the gas 2 (carbon dioxide) that flowed out of the adsorption tower 5b was fully recovered in a gas bag (not shown).

[0208] In operation 5, after depressurizing the adsorption tower 5a, 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 reached the desorption process pressure shown in Table 1. From the time the automatic valve AV13a was opened until it was closed, the gas 2 (carbon dioxide) that flowed out of the adsorption tower 5a was fully recovered in a gas bag (not shown).

[0209] Comparative Examples 1-4: Gas Separation Methods The gas separation methods of Comparative Examples 1-4 were carried out in the same manner as in Example 1, except that the conditions in the adsorption process were changed as shown in Tables 2 and 3 so that Vi exceeded 0.40. The results are shown in Tables 2 and 3.

[0210] Comparative Example 5: Gas Separation Method As shown in Figure 5, a device 100' equipped with automatic valves AV9a' and AV9b', and a pressure drop gas line 10' used for the pressure drop process, was installed on the raw material gas supply side of the adsorption towers 5a and 5b. The gas separation method of Comparative Example 5 was carried out in the same manner as in Example 1, except that in the pressure drop process of each adsorption tower, automatic valve AV9a' was opened in adsorption tower 5a and automatic valve AV9b' was opened in adsorption tower 5b to allow the gas in the adsorption tower to flow into the raw material gas tank 2. In this comparative example, in the pressure drop process, the gas present in adsorption tower 5a or 5b was discharged from adsorption tower 5a or 5b in the convection direction relative to the raw material gas supply direction. The results are shown in Tables 2 and 3.

[0211] Examples 22-30: Gas Separation Method Using the gas separation apparatus shown in Figure 6, the gas separation method was carried out in the same manner as in Example 1, except that the inflow process was performed without performing a pressure drop process after the adsorption process. The results are shown in Table 4.

[0212]

[0213]

[0214]

[0215] This application claims priority to Japanese Patent Application No. 2024-231086 and Japanese Patent Application No. 2024-230928, both filed on 26 December 2024, and the entire contents of those applications are deemed to be part of the disclosure of this application and are incorporated herein by reference.

[0216] 1... Raw material gas supply line, 2... Raw material gas tank, 3... Pressurization device, 5... Easily adsorbable gas recovery line, 5a, 5b... Adsorption tower, 7... Difficult-to-adsorb gas recovery line, 8... First product storage section, 10, 10'... Drop pressure gas line, 11... Inflow gas line, 14... Easily adsorbable gas recovery line, 15... Pressure reducing device, 16... Restoration gas line, 18... Pressure gauge, 19... Pressure gauge, 20a, 20b... Fixed floor, 21a, 21b, 22a, 22b, 23, 24... Pressure gauge, 25... Second product storage section, 100, 100', 101... Gas separation device, 200... Fermentation tank, 300... Desulfurization tower, 400... Siloxane removal device, 500... Oxygen removal device, 600... Cooling device, 700... Dehydration device, 1000... Biogas purification system, AV4a, AV4b, AV6a, AV6b, AV9a, AV9a', AV9b, AV12, AV13a, AV13b, AV17b... Automatic valve

Claims

A gas separation method that involves switching between two or more adsorption towers containing an adsorbent containing zeolite, An adsorption step is performed by passing a raw material gas containing an easily adsorbable gas and a poorly adsorbable gas through at least one of the adsorption towers, thereby adsorbing the easily adsorbable gas onto the adsorbent in the adsorption tower and recovering the poorly adsorbable gas. After the adsorption process, an inflow process is performed to move the residual gas in the adsorption tower to another adsorption tower with a pressure lower than that of the adsorption tower. The process includes a desorption step, after the inflow step, in which the easily adsorbed gas adsorbed on the adsorbent in the adsorption tower is desorbed and the easily adsorbed gas is recovered. The other adsorption tower into which the residual gas was introduced in the aforementioned inflow process is then used for the adsorption process. A gas separation method wherein the amount of incoming gas Vi per unit weight of the adsorbent in the inflow step is 0.40 mol / kg or less. 　 The adsorption time ta of the adsorption process, When the raw material gas is introduced under the same conditions as in the adsorption process, at the adsorption time t0 when the derivative calculated from d[concentration of easily adsorbable gas at the outlet of the adsorption tower (volume %)] / d[time (s)] reaches 0.1, The gas separation method according to claim 1, wherein ta / t0 is 0.80 to 1.

40. The gas separation method according to claim 1, wherein the amount of gas flowing in the inflow step Vi / the amount of gas introduced in the adsorption step Vf is 0.30 or less. 　 The gas separation method according to claim 1, wherein in the inflow step, the inflow gas is introduced into the other adsorption tower in a direction parallel to the supply direction of the raw material gas for the adsorption step. 　 A pressure reduction step is performed after the adsorption step and before the inflow step, in which a portion of the raw material gas in the adsorption tower is discharged in a direction parallel to the supply direction of the raw material gas to reduce the pressure inside the adsorption tower. The gas separation method according to claim 1, further comprising a recycling step of providing the released raw material gas to the adsorption step. 　 The gas separation method according to claim 1, wherein in the inflow step, the pressure difference between the adsorption tower from which the inflow gas flows out and the adsorption tower into which the inflow gas flows is 300 kPa or less. 　 The gas separation method according to claim 1, wherein the ratio (L / D) of the length L in the supply direction of the raw material gas to the diameter D in the adsorbent-filled portion of the adsorption tower is 50 or less. 　 The gas separation method according to claim 1, wherein the relationship between the gas linear velocity u [m / s] of the raw material gas in the adsorption step and the differential heat of adsorption Q [kJ / mol] of the easily adsorbable gas to the adsorbent is such that u / Q is 0.0001 to 0.

003. The gas separation method according to claim 1, wherein the pressure inside the adsorption tower in the adsorption step is 100 to 500 kPa. 　 The gas separation method according to claim 1, wherein the amount of the poorly adsorbed gas contained in the gas flowing in during the inflow step is 40% by volume or less. 　 The gas separation method according to claim 1, further comprising a repressurization step of restoring the pressure of the adsorption tower using purified poorly adsorbed gas before the adsorption step. 　 When the raw material gas is introduced under the same conditions as in the adsorption process described above, in the relationship between the adsorption time t0 at which the derivative calculated from d[concentration of easily adsorbable gas at the outlet of the adsorption tower (volume %)] / d[time (s)] reaches 0.1, the adsorption time t1 at which the derivative reaches 0.3, and the adsorption time t2 at which the derivative reaches a maximum and then returns to 0.3, The gas separation method according to claim 1, wherein (t1-t0) / (t2-t0) is 0.40 to 0.

98. The gas separation method according to claim 1, wherein the ratio of the volume of the adsorption tower to the apparent volume of the adsorbent in the adsorption tower is 4.0 or less. 　 The gas separation method according to claim 1, wherein a gas separation apparatus is used in which the apparatus volume / adsorption tower volume is 4.0 or less. 　 The gas separation method according to claim 1, wherein a gas separation apparatus is used in which the apparatus dead space / apparatus volume is 0.9 or less. 　 The gas separation method according to claim 1, wherein a gas separation apparatus is used in which the dead space / equipment volume of the inflow process is 0.6 or less. 　 The gas separation method according to claim 1, wherein a gas separation apparatus is used in which the dead space / device volume of the aforementioned attachment / detachment process is 0.6 or less. 　 The gas separation method according to claim 1, wherein the easily adsorbable gas is carbon dioxide and the poorly adsorbable gas is methane. 　 The gas separation method according to claim 1, wherein the adsorption selectivity of the zeolite for the easily adsorbed gas / the poorly adsorbed gas is 5 or more. 　 The gas separation method according to claim 1, wherein the differential heat of adsorption of the easily adsorbable gas to the zeolite is 30 kJ / mol or more. 　 The gas separation method according to claim 1, wherein the zeolite comprises at least one selected from the group consisting of GIS, FAU, LTA, and CHA. 　 The raw material gas contains water, carbon dioxide, and the poorly adsorbed gas, and the raw material gas is supplied to an adsorption tower having a dehumidifying layer containing a desiccant and an adsorption layer containing a carbon dioxide adsorbent, and the water and carbon dioxide are adsorbed by the desiccant and the adsorbent, thereby separating the poorly adsorbed gas from the raw material gas. The process includes a desorption step of desorbing the water and carbon dioxide by reducing the pressure inside the adsorption tower from the inlet side of the raw material gas, The gas separation method according to claim 1, wherein the raw material gas comes into contact with the dehumidifying layer and the adsorption layer in this order within the adsorption tower. 　 The gas separation method according to claim 22, wherein the desiccant comprises at least one selected from the group consisting of activated alumina, silica gel, and activated carbon. 　 A method for producing purified gas, comprising purifying and recovering the easily adsorbed gas and / or the poorly adsorbed gas by the gas separation method described in any one of claims 1 to 23.

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