Gas capturing agent, semi-clathrate hydrate, and gas capturing method and gas separation method using them

Abstract

To provide a gas capturing agent which forms semi-clathrate hydrate and can contain much gas.SOLUTION: A gas capturing agent contains an ionic substance and water, and captures target gas. The ionic substance includes one or more cations of tri-n-butyl, n-hexyl ammonium cation, tri-n-butyl, n-pentyl phosphonium cation, tri-n-butyl, n-hexyl phosphonium cation, tri-iso-butyl and n-hexyl ammonium cation, and one or more anions of bromide ion, chlorine ion, fluorine ion and hydroxyl group ion.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to gas scavenger agents for trapping gases, and in particular to semiclathrate hydrate-type gas scavenger agents. [Background technology]

[0002] Gas hydrates, such as methane hydrate, which is formed when water and methane crystallize, are known to exist stably in large quantities on the seabed and elsewhere. In response to this, studies are underway to artificially create gas hydrates and use them to separate, store, and transport natural gas and other gases. In other words, gas hydrates solidify by trapping gas within a cage-like structure formed by water crystals, allowing the gas to be separated. Furthermore, at temperatures below -20°C, the decomposition of gas hydrates is suppressed even under atmospheric pressure (self-preservation effect). For this reason, gas hydrates can be stored for long periods of time, such as several months, making them suitable for transporting and storing gases.

[0003] However, to utilize the self-preserving effect, it is necessary to produce gas hydrate by compressing and removing unreacted water. Performing these steps under low-temperature, high-pressure conditions is technically and cost-effective. Therefore, efforts were made to facilitate the production of gas hydrate by adding additives to water. This gas hydrate is formed by trapping gas within a crystalline cage structure formed from water and additives. Known additives include tetrahydrofuran (THF), which forms structure II hydrate. The addition of such additives results in the loss of the self-preserving effect of gas hydrate. However, this gas hydrate is highly stable even without the self-preserving effect, allowing it to preserve gas at the same temperature range of approximately -20°C.

[0004] Semiclathrate hydrates (quasi-clathrate hydrates) are also used as gas collectors. Clathrate hydrates are crystals in which guest molecules are enclosed within a cage-like structure formed by water molecules through hydrogen bonds. Semiclathrate hydrates are a type of clathrate hydrate. Semiclathrate hydrates are crystalline substances in which anions are incorporated into part of the cage-like structure formed by water molecules, and can be produced from aqueous solutions of ionic substances. Although not an ionic substance, tri-n-butylphosphine oxide (TBPO) is also known to form semiclathrate hydrates. These semiclathrate hydrates can encapsulate gases in part of the cage-like structure in a gas atmosphere such as methane, carbon dioxide, nitrogen, oxygen, hydrogen, or rare gases, and can be used as gas collectors.

[0005] Patent Document 1 describes a gas separating agent made of a clathrate hydrate having a hollow cage-like crystal structure containing an alkylammonium salt as a guest molecule. More specifically, Patent Document 1 discloses experimental data on the separation of a mixed gas of methane and hydrogen sulfide and a mixed gas of methane and propane by a semiclathrate hydrate formed using tetra-n-butylammonium bromide (TBAB).

[0006] Patent Document 2 describes a gas collector containing a clathrate hydrate that has the property of collecting gases. That is, Patent Document 2 describes how argon or carbon dioxide is collected in a clathrate hydrate by cooling an aqueous solution containing tetraisopentylammonium bromide (TiPAB) and / or triisopentyl-n-butylammonium bromide (TiPBAB) as solutes. Furthermore, Non-Patent Document 1 discloses experimental results of methane gas collection by a semiclathrate hydrate using an aqueous solution of tri-n-butylphosphine oxide (TBPO). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2003-138281

Patent document 2

Non-licensed literature

[0008] [Non-licensed document 1] TV Rodionova et al., “Semiclathrate Hydrates in Tri-n-butylphosphine Oxide (TBPO)-Water and TBPO-Water-Methane Systems”, J. Phys. Chem. B, 121, (2017), pp.4900-4908 [Non-licensed document 2] N. Ye et al., "Phase Equilibrium Conditions and Carbon Dioxide Separation Efficiency of Tetra-n-Butylphosphoniumbromide Hydrate", Journal of Chemical & Engineering Data, 59(9), (2014), pp.2920-2926 [Non-licensed document 3] ED Sloan Jr. et al., "Clathrate Hydrates of Natural Gases 3rd ed.", CRC Press, Boca Raton, 2007, pp.241-242

Non-licensed Document 4

[0009] Structure II hydrates using THF and other compounds have a relatively large number of voids (cages) in the hydrogen-bonded network of water molecules that can trap gases, resulting in a large gas storage capacity. To generate structure II hydrates, substances such as THF, cyclopentane, or dioxolane are required. However, these substances have been reported to be harmful to living organisms. Furthermore, these substances are volatile and flammable, requiring careful handling during gas separation, storage, and transportation. Semiclathrate hydrates formed from aqueous TBPO solutions have a relatively large methane gas storage capacity. However, TBPO is known to be a corrosive substance, requiring careful handling.

[0010] Aqueous solutions of ionic substances form semiclathrate hydrates, which are gas hydrates with the ionic substance as a guest. As disclosed in Patent Document 1 or Patent Document 2, quaternary ammonium salts such as tetra-n-butylammonium are ionic substances that form semiclathrate hydrates. Theoretically, the number of cages in which these ions can trap gas, supporting the hydrogen-bonded network of water molecules, is smaller than the number of cages in which gas hydrates made of pure water and structure II hydrates can trap gas.

[0011] However, quaternary ammonium salts and the like are expected to be non-volatile and non-flammable even when mixed with water, and to have low harmfulness to living organisms. Therefore, quaternary ammonium salts and the like have the potential to become practical gas collectors. Until now, the actual gas storage capacity estimated from the structure has been extremely small. The present disclosure aims to provide a gas collector that can store a large amount of gas by forming semiclathrate hydrates. [Means for solving the problem]

[0012] A gas collector according to one embodiment of the present disclosure is a gas collector that comprises an ionic substance and water and that collects a target gas, wherein the ionic substance comprises one or more cations selected from the group consisting of tri-n-butyl,n-hexylammonium cation, tri-n-butyl,n-pentylphosphonium cation, tri-n-butyl,n-hexylphosphonium cation, and tri-isobutyl,n-hexylammonium cation, and one or more anions selected from the group consisting of bromide ions, chloride ions, fluoride ions, and hydroxyl ions. [Effects of the Invention]

[0013] The gas collector and semiclathrate hydrate of the present disclosure contain a predetermined ionic substance. Therefore, according to the present disclosure, a semiclathrate hydrate with a large gas storage capacity can be obtained. The gas collection method of the present disclosure causes the gas collector of the present disclosure to collect a target gas. Therefore, according to the present disclosure, a large number of target gases can be collected. The gas separation method of the present disclosure uses the gas collector of the present disclosure, which collects different amounts of gas depending on the gas. Therefore, according to the present disclosure, the content ratio of a predetermined component in a mixed gas can be increased. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view of an SCH generating device according to an embodiment. [Figure 2] 2 is a graph showing the phase equilibrium temperature and pressure conditions for CO2 of the gas collectors of Example 1, Example 2, and the comparative example. [Figure 3] 2 is a graph showing the phase equilibrium temperature and pressure conditions for CH4 of the gas collectors of Example 1, Example 2, and the comparative example. [Figure 4] 2 is a graph showing the results of a CO 2 gas absorption test for the gas collectors of Example 1, Example 2, and a comparative example. [Figure 5] 2 is a graph showing the results of a CH4 gas absorption test for the gas collectors of Example 1, Example 2, and a comparative example. [Figure 6] 1 is a powder X-ray diffraction chart of SCH formed by the gas collector of Example 2 and the target gas. [Figure 7] 2 is a graph showing the results of a CO2 occlusion selectivity test for the gas traps of Example 1, Example 2, and a comparative example. [Figure 8] 1 is a graph showing the results of a CO2 separation performance test of the gas collectors of Example 1, Example 2, and the comparative example on a mixed gas of CH4 and CO2. [Figure 9] 2 is a graph showing the results of a CO2 separation performance test of the gas collectors of Example 1, Example 2, and the comparative example on a mixed gas of N2 and CO2. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present disclosure will be described in detail below based on embodiments and examples. However, the present disclosure is not limited to the descriptions of the embodiments and examples. Note that duplicated explanations will be omitted as appropriate. In this application, when a range between two numerical values ​​is expressed using "to", these two numerical values ​​are also included in this range. Furthermore, when the upper and lower limits of a numerical value are each stated in stages, the upper and lower limits of the numerical range can be any combination of these staged numerical values.

[0016] (Gas Scavenger and Semiclathrate Hydrate) The gas collector of the embodiment captures a target gas. The terms "encapsulate" or "take in" may be used instead of "capture," but these terms have the same meaning. The gas collector comprises an ionic substance and water. An ionic substance is a substance in which a cation and an anion are bound by an ionic bond. Ionic substances are also sometimes referred to as "ionic compounds" or "ionic compounds." The target gas is captured by the gas collector by forming semi-clathrate hydrate (SCH) with the gas collector at a predetermined temperature and pressure. In other words, the ionic substance and water crystallize with the target gas at a predetermined temperature and pressure to generate SCH. The hydrate of the ionic substance and the target gas form SCH in a crystalline state. In other words, SCH comprises the ionic substance, water, and target gas.

[0017] In this disclosure, the target gas encapsulated in SCH will be referred to as "gas" or "gas" regardless of the state change of the substance in SCH. SCH can also be generated by crystallizing an ionic substance and water without containing the target gas. In this case, SCH contains an ionic substance and water. From the perspective of forming SCH, the ionic substance can also be considered an additive to water. The target gas may be encapsulated in this SCH to form SCH encapsulating the target gas. A method for encapsulating a target gas in SCH containing an ionic substance and water will be described later. The formation of SCH can be confirmed by X-ray crystal structure analysis.

[0018] Examples of cations include one or more of the tri-n-butyl, n-hexylammonium (N4446) cation, the tri-n-butyl, n-pentylphosphonium (P4445) cation, the tri-n-butyl, n-hexylphosphonium (P4446) cation, and the tri-isobutyl, n-hexylammonium (Ni5i5i56) cation. The alternative name for tri-n-butyl, n-hexylammonium, "N4446," refers to a single nitrogen (N) bonded to three n-butyl groups (444) with four carbon atoms and one n-hexyl group (6) with six carbon atoms. The same applies to P4445, P4446, and Ni5i5i56. Because SCH encapsulates a large amount of the target gas, the N4446 cation is preferred.

[0019] It is known that when N4444 or P4444 is the cation, the melting point of the hydrate of an ionic substance at atmospheric pressure varies significantly depending on the choice of anion. The melting point of the hydrate of an ionic substance is highest when the anion is OH or F, followed by Cl, and lowest by Br. Even when the hydrate of an ionic substance forms SCH and encapsulates a gas, the melting point relationship at atmospheric pressure basically holds, especially in the low-pressure region where the influence of the gas is small. In other words, when the cation is the same, the phase equilibrium temperature under pressure with a certain target gas is thought to be highest when the anion is OH or F, next highest when the anion is Cl, and lowest when the anion is Br.

[0020] For this reason, it is estimated that the phase equilibrium temperature of a hydrate of an ionic substance having OH or F as the anion will be equal to or higher than the phase equilibrium temperature of a hydrate of an ionic substance having Br or Cl as the anion. Therefore, examples of the anion include one or more of bromide ions, chloride ions, fluoride ions, and hydroxyl ions. Among these, bromide ions or chloride ions are preferred as the anion, as they have little effect on the SCH generator.

[0021] As long as SCH can be formed, there is no particular restriction on the content of ionic substances in the gas collector. The content of ionic substances in the gas collector is, for example, 20 to 40 mass %, which is a level at which SCH can be easily formed. As long as SCH can be formed, there is no particular restriction on the content of water in the gas collector. The content of water in the gas collector is, for example, 60 to 80 mass %, which is a level at which SCH can be easily formed. The content of water in the gas collector is preferably close to the content of water in the hydrate of the ionic substance. There are no particular restrictions on the water contained in the gas collector, and ion-exchanged water, ultrapure water, etc. can be used. There is no particular restriction on the melting point of the gas collector, but a melting point closer to room temperature can save energy in generating SCH.

[0022] The temperature and pressure for generating SCH are not particularly limited, but are preferably 0 to 20°C and 0.2 to 10 MPa, respectively, and more preferably 5 to 10°C and 0.5 to 3 MPa. Examples of target gases include carbon dioxide (CO2), methane (CH4), hydrogen (H2), hydrogen sulfide, sulfur dioxide, argon, krypton, and xenon. The target gas may also be an isotope of any of these. Because SCH has a large storage capacity, the target gas is preferably at least one of carbon dioxide and methane.

[0023] The inventors first conceived the usefulness of the N4446 cation as follows. After successfully synthesizing N4446Br and N4446Cl, they measured the phase equilibrium temperature and pressure of these aqueous solutions and compared them with the phase equilibrium temperature and pressure of tetra-n-butylammonium bromide (TBAB) aqueous solution reported in the literature. Furthermore, the inventors performed single-crystal X-ray crystal structure analysis of SCH formed from N4446Cl aqueous solution and CH4, and discovered that this SCH has a unique crystal structure. This SCH has the same framework as the previously known orthorhombic structure, but is found to have a more symmetrical hexagonal structure.

[0024] Next, we came up with the idea that the Ni5i5i56 cation, a variant of the N4446 cation, would also have similar properties. The size and shape of the butyl group (4) and the isopentyl group (i5) are known to be highly compatible with the conventional SCH structure (Non-Patent Document 6). However, neither the N4444 cation nor the Ni5i5i5i5 cation led to the formation of the SCH structure obtained with the N4446 cation. This is thought to be because the butyl group (4) and the isopentyl group (i5) were too small to stabilize the hexahedral cage in a well-ordered shape. However, a new SCH structure was obtained by N4446, in which one side chain of N4444 was replaced with a hexyl group.

[0025] In the SCH structure of N4446, the hexyl groups stabilized the decahedral cage in a well-ordered configuration. In contrast, the butyl groups occupied both the tetradecahedral and decahedral cages. This cage occupancy of the butyl groups is no different from the cage occupancy previously observed for butyl and isopentyl groups. Therefore, Ni5i5i56, in which the butyl groups in N4446 are replaced with isopentyl groups, is expected to conform to this SCH structure and exhibit similar properties to N4446. Furthermore, since the phase equilibrium temperature of Ni5i5i5i5 aqueous solution is higher than that of N4444 aqueous solution, it can be inferred that the phase equilibrium temperature of SCH obtained from Ni5i5i56 aqueous solution is higher than that of SCH obtained from N4446 aqueous solution.

[0026] Furthermore, the inventors conceived the idea that the P4445 cation or P4446 cation, another variant of the N4446 cation, would also have similar properties, as follows. Non-Patent Document 5 discloses powder X-ray diffraction experimental data for variations in the alkyl group R in tri-n-butylalkylphosphonium bromide (P444RBr). The inventors of the present application found that the crystal structure analysis data for P4445Br, which exhibits a unique structure among these, is similar to that of SCH, which is formed by an aqueous solution of N4446Cl and CH4.

[0027] Therefore, the crystal structure of SCH obtained from P4445 in aqueous solution in P444R is thought to be similar to that of SCH obtained from N4446 in aqueous solution. Furthermore, as an extension of P4445, P4446 is thought to conform to a similar SCH structure and exhibit similar properties. Therefore, SCH obtained from P4445 aqueous solution and SCH obtained from P4446 aqueous solution are thought to exhibit properties similar to those of SCH obtained from N4446 aqueous solution.

[0028] (SCH generator) 1 is a schematic cross-sectional view of an SCH generator A according to an embodiment. The SCH generator A includes a gas supply unit 1, a vacuum pump 2, a thermostatic water bath agitator 3, a cooler 4, a thermostatic water bath 5, a pressure gauge 6, a reaction vessel 7, which is a high-pressure autoclave, an agitator 8 inside the reaction vessel, a gas sampling vessel 9, a recorder 10, a temperature-controlled heater 11, a thermometer 12, and multiple valves V1 to V9. Water is contained in the thermostatic water bath 5. The reaction vessel 7 is placed in this water. The temperature inside the reaction vessel 7 can be adjusted by the thermostatic water bath agitator 3, the cooler 4, and the temperature-controlled heater 11.

[0029] The reaction vessel 7 is an airtight metal vessel that can be opened and closed, for example, by a flange that is tightened with bolts. The reaction vessel 7 is filled with a gas collector 13 so that a predetermined space is formed. The pressure inside the reaction vessel 7 is monitored by a pressure gauge 6. The temperature of the water in the constant temperature water bath 5 is monitored by a thermometer 12. The readings of the pressure gauge 6 and the thermometer 12 are recorded by a recorder 10. The reaction vessel 7 is connected to a vacuum pump 2 via valves V1, V2, and V3 and piping, so that the gas inside the reaction vessel 7 can be discharged. The reaction vessel 7 is also connected to a gas supply unit 1 via valves V1, V2, V4, and V5 and piping, so that the target gas can be supplied at a predetermined pressure.

[0030] The gas supply unit 1 is, for example, a gas cylinder with a regulator that holds the target gas. A reactor agitator 8 is provided inside the reactor 7 to agitate the gas collector 13 to promote the formation of SCH when the target gas is supplied to form SCH. Furthermore, a gas sampling vessel 9 is connected via valves V6 and V7 and piping to monitor the residual gas in the reaction vessel 7 after gas collection is complete. By connecting the gas sampling vessel 9 to a separate gas chromatography device or the like, the type and concentration of the gas remaining in the reaction vessel 7 can be measured. Valves V8 and V9 are used to purge the gas in the piping.

[0031] An example of SCH production using SCH generator A is described below. A raw aqueous solution, which is a liquid gas trap, is injected into reactor 7, and the target gas is supplied up to a predetermined pressure. The reactor 7 is cooled, and as needed, operations such as stirring, shaking, or removing supercooling are performed to generate SCH containing the target gas. As the target gas is encapsulated in the SCH, the pressure inside reactor 7 decreases. Additional target gas may be supplied to compensate for the pressure drop. Once the required amount of SCH has been produced, a slurry of SCH, a mixture of the raw aqueous solution and SCH, is discharged through a slurry discharge line (not shown). If necessary, the liquid component of the raw aqueous solution may be removed using a filter or compressor to increase the SCH content in the slurry. These processes, which involve contacting a gas with a liquid to form SCH, can be defined as a "gas-liquid contact method."

[0032] The discharged raw material aqueous solution can be re-injected into the reaction vessel 7 and the above steps repeated to continuously produce SCH. The method for producing SCH is not limited to the above. SCH may be produced continuously in a pipe or the like, or SCH may be produced directly in a container for transportation and storage. When the produced SCH is to be transported and stored under atmospheric pressure, it is cooled to about -20°C or below and then depressurized to atmospheric pressure. If necessary, SCH may be formed into pellets or the like.

[0033] Alternatively, SCH that does not encapsulate the target gas may be produced in advance, and the target gas may be introduced into this SCH to produce SCH encapsulating the target gas. An example of the production of such SCH will be described below. An aqueous solution of an ionic substance (hereinafter sometimes referred to as "ionic substance aqueous solution") is prepared. There are no particular restrictions on the concentration of this ionic substance aqueous solution, and it does not have to have a composition close to that of the ionic substance hydrate. The ionic substance aqueous solution is cooled under atmospheric pressure or reduced pressure to produce SCH. The cooling temperature at this time is a temperature lower than the melting point of the ionic substance hydrate under atmospheric pressure. There are no particular restrictions on the degree of supercooling (difference from the melting point), and it is desirable that it be 5°C or higher.

[0034] If necessary, any remaining aqueous ionic substance solution is removed. The resulting SCH can be stored for long periods of time at temperatures below its melting point at atmospheric pressure. However, there is a risk of hydrate decomposition due to water sublimation. If necessary, the SCH is crushed or classified and transferred to a pressure-resistant vessel at a temperature below the SCH's melting point at atmospheric pressure. The target gas is supplied to this pressure-resistant vessel to set the pressure, and the pressure vessel is maintained at a temperature lower than the phase equilibrium temperature at this set pressure. This temperature may be higher than the SCH's melting point at atmospheric pressure. If necessary, the vessel may be stirred. When the target gas is recovered, the temperature inside the pressure-resistant vessel is raised. These processes can be defined as a "gas-solid contact method" because the gas is brought into contact with the solid SCH, causing the SCH to encapsulate the gas.

[0035] (Gas collection method) A gas collection method according to an embodiment involves causing a gas collector according to an embodiment to collect a target gas. This gas collection method includes a collection step. In the collection step, SCH containing the gas collector and the target gas is formed, and the target gas is collected in the SCH. More specifically, in the collection step, the target gas is brought into contact with the liquid gas collector while the temperature of the gas collector is lowered, thereby obtaining a slurry of SCH encapsulating the target gas (gas-liquid contact method). Note that in the collection step, the target gas may be collected in SCH by the gas-solid contact method described below. This gas collection method may also be performed using an SCH generator A. Another embodiment of the gas collection method, in which a target gas is collected by the gas collector according to an embodiment, includes an SCH generation step and an encapsulation step. In the SCH generation step, the temperature of the liquid gas collector is lowered to generate SCH. In the encapsulation process, the target gas is brought into contact with the SCH to obtain SCH encapsulating the target gas (gas-solid contact method).

[0036] (Gas separation method) The simplest way to use a gas scavenger is to form SCH from a gas scavenger and a single gas, such as CO2, and encapsulate this single gas in the SCH. However, when a gas mixture containing two or more gases is brought into contact with the gas scavenger, the amount of each gas encapsulated in the SCH (encapsulation composition ratio) varies depending on the temperature, pressure, and composition of the mixture. This property can be used to concentrate specific gases in SCH.

[0037] That is, after discharging the gas not captured in the SCH or the remaining gas captured in small amounts in the SCH, the temperature is raised to melt the SCH, and the specific gas captured in large amounts in the SCH is recovered, thereby obtaining a concentrated specific gas. In other words, in this disclosure, the gas collector functions as a gas separating agent or a gas concentrator depending on the application. Furthermore, the ionic substance aqueous solution that serves as the gas collector exists in liquid form at temperatures and pressures that do not form SCH, and in solid form as SCH at certain temperatures and pressures. Therefore, the gas collector of this disclosure includes both the liquid state of the aqueous solution and the solid state of SCH.

[0038] A gas separation method according to an embodiment utilizes a gas collector according to an embodiment. This gas separation method includes a first preparation step, a first collection step, and a first separation step. In the first preparation step, a first mixed gas containing a first gas and a second gas is prepared as a target gas. In the first collection step, a first SCH containing the gas collector and the target gas is formed, and a portion of the first gas and a portion of the second gas are collected in the first SCH. In the first separation step, the first SCH is melted to obtain a second mixed gas having a different content ratio of the first gas to the second gas from that of the first mixed gas.

[0039] The gas separation method may further include a second preparation step, a second collection step, and a second separation step. In the second preparation step, a second mixed gas is prepared as a target gas. In the second collection step, a second SCH containing a gas collection agent and the target gas is formed, and a portion of the first gas and a portion of the second gas are collected in the second SCH. In the second separation step, the second SCH is melted to obtain a third mixed gas having a different content ratio of the first gas to the second gas from that of the second mixed gas. The first mixed gas, the second mixed gas, and the third mixed gas may be mixed gases of three or more components containing gases other than the first gas and the second gas.

[0040] In the first collection step, the first gas mixture may be collected in a first SCH by gas-liquid contact or gas-solid contact. CO2, CH4, or N2 differs in the ease with which it is taken up by the gas collection agent of the embodiment. CO2 is more easily taken up by the gas collection agent of the embodiment than CH4 or N2. Therefore, when the first gas is CO2 and the second gas is CH4 or N2, the content ratio of CO2 in the second gas mixture will be higher than the content ratio of CO2 in the first gas mixture.

[0041] In another embodiment, a gas separation method obtains a second gas mixture containing the first gas and the second gas, the first gas and the second gas being contained in a different ratio from that of the first gas mixture. This gas separation method includes a collection step I, a removal step I, and a separation step I. In the collection step I, the first gas mixture is brought into contact with a liquid gas collector while the temperature of the gas collector is lowered to obtain a slurry of SCH. In the removal step I, liquid components are removed from the SCH slurry that has undergone the collection step I to obtain SCH. In the separation step I, the SCH that has undergone the removal step I is melted to obtain a second gas mixture.

[0042] This gas separation method may further include a collection step II, a removal step II, and a separation step II. In the collection step II, a liquid gas collector is brought into contact with the second mixed gas while the temperature of the gas collector is lowered to obtain a slurry of SCH. In the removal step II, the liquid is removed from the SCH slurry that has undergone the collection step II to obtain SCH. In the separation step II, the SCH that has undergone the removal step II is melted to obtain a third mixed gas. These steps may be repeated to obtain a mixed gas containing a larger amount of a specific gas component.

[0043] An example of a gas separation method using SCH generator A will be described. In this example, it is assumed that gas component G in the mixed gas is more easily incorporated into SCH than other gas components. An ionic substance aqueous solution, which is the raw aqueous solution, is injected into reactor vessel 7, and the target gas, the mixed gas, is supplied up to a predetermined pressure. The reactor vessel 7 is cooled, and operations such as stirring, shaking, or removing supercooling are performed as necessary to generate SCH containing the mixed gas. Additional mixed gas may be supplied to compensate for the pressure drop. Once a predetermined amount of SCH has been generated, a mixed slurry of the raw aqueous solution and SCH is discharged from a slurry discharge line (not shown).

[0044] If necessary, the liquid component of the raw aqueous solution can be removed using a filter or compressor to increase the SCH content in the slurry. SCH can be continuously produced by re-injecting a raw aqueous solution equivalent to the discharged raw aqueous solution into the reaction vessel 7 and repeating these steps. Furthermore, continuous gas separation can be achieved by occasionally releasing a portion of the gas mixture that remains uncaptured in the SCH and adding more gas mixture. The content of gas component G in the released gas mixture is lower than the content of gas component G in the initial gas mixture. The SCH is transferred to a decomposition device, where the SCH is decomposed by increasing the temperature or reducing the pressure to release the gas. The ratio of gas component G to the other gas components in this released gas is higher than the ratio of gas component G to the other gas components in the initial gas mixture.

[0045] The above steps are described using the "gas-liquid contact method" as an example, in which a gas is brought into contact with a liquid to form SCH. As mentioned above, the gas separation method may also be performed using the "gas-solid contact method." Furthermore, the above gas separation method has been described on the premise that a specific gas is concentrated in SCH. However, because the relationship between the gas phase and the SCH phase is complementary, the gas separation method of the present disclosure can also be used as a gas separation method that focuses on one of the gas components that is less likely to be captured in SCH and remains in the gas phase. [Example]

[0046] Example 1 The properties of the N4446Br aqueous solution as a gas capture agent were evaluated by forming SCH from N4446Br aqueous solution and the target gases CO2 or CH4. More specifically, measurements of phase equilibrium temperature and pressure, gas absorption tests for CO2 and CH4, and CO2 occlusion selectivity tests and CO2 separation performance tests using CH4 and CO2 mixed gases and N2 and CO2 mixed gases were conducted.

[0047] (Synthesis of N4446Br and preparation of N4446Br aqueous solution) The raw materials, 46 g of tri-n-butylamine (Tokyo Chemical Industry Co., Ltd.) and 49 g of hexyl bromide (Tokyo Chemical Industry Co., Ltd.), and 94 g of the solvent, nitrobenzene (Fujifilm Wako Pure Chemical Industries Co., Ltd.), were added to a sealed glass container (Sansho, vacuum tube). The molar ratio of tri-n-butylamine to hexyl bromide was 1:1. After replacing the remaining air in the sealed glass container with nitrogen, the sealed glass container was evacuated and the mixture was reacted for 66 hours at 80°C in a silicone oil bath while stirring with a magnetic stirrer. After the reaction was complete, heating was stopped and the product was extracted with water.

[0048] After repeating the product extraction three or more times, the resulting aqueous solution was placed in an evaporator to remove water, yielding tri-n-butyl, n-hexylammonium bromide (N4446Br). An N4446Br aqueous solution, a gas scavenger, containing 30% by mass of N4446Br and 70% by mass of water was prepared. Note that this N4446Br aqueous solution containing 30% by mass of N4446Br and 70% by mass of water is sometimes referred to as "N4446Br aqueous solution (30% by mass)." The same applies to aqueous solutions of other ionic substances.

[0049] (Measurement of phase equilibrium temperature and pressure) Using SCH generator A equipped with a pressure gauge (Kyowa Electronics, PGR-100KA-P), a thermometer (Chino, CAB-F201B), and a platinum resistance temperature sensor (Chino, NRHS1-0), the phase equilibrium temperature and pressure of SCH formed by the gas collector and the target gas were measured using the following procedure. Note that, under atmospheric pressure (1 atom = 0.1013 MPa), SCH was not formed from an N4446Br aqueous solution at temperatures above -5°C. For this reason, the melting point of SCH was measured in a gas atmosphere above 1 MPa.

[0050] Internal volume 113cm 3A reaction vessel 7 (hereinafter sometimes referred to simply as the "vessel") was filled with an N4446Br aqueous solution (30% by mass) to form a predetermined space. After evacuating the remaining air in the vessel, the target gas, CO2 or CH4, was supplied until the test pressure was reached. The vessel was cooled to a temperature at which SCH was generated, and SCH was generated while stirring with an agitator 8. As SCH was generated, the target gas was encapsulated in SCH, causing the pressure in the vessel to decrease. The temperature was then raised in 0.1°C increments to reach each measurement temperature. As the temperature increased, the target gas was released due to the decomposition of SCH, causing the pressure to increase. At each measurement temperature, the vessel was stirred until the pressure increase subsided, and the pressure was recorded. The waiting time at each measurement temperature was at least one hour.

[0051] The measured temperature one step before the temperature at which the solid matter in the container, i.e., SCH, disappeared, was taken as the melting point of SCH. Also, since the pressure stops increasing when SCH disappears, it is possible to confirm whether SCH is present in the container by recording the pressure between the measured temperatures. The melting point of SCH obtained by measurement and the pressure at that time were taken as the phase equilibrium temperature and pressure. For example, if the solid matter disappears at 2.0°C and no pressure increase due to temperature increase is observed, the measured temperature one step before, 1.9°C, and the pressure at that time were taken as the phase equilibrium temperature and pressure. The phase equilibrium temperature and pressure conditions are a representation of the phase equilibrium temperature and pressure at various temperatures and pressures.

[0052] Figure 2 shows the phase equilibrium temperature and pressure conditions for an N4446Br aqueous solution with respect to CO2. Figure 3 shows the phase equilibrium temperature and pressure conditions for an N4446Br aqueous solution with respect to CH4. Figures 2 and 3 show the three-phase equilibrium temperature and pressure conditions (gas, liquid, and SCH) and also show the melting point of SCH at a certain pressure. This means that at that pressure, the gas trap is a liquid (N4446Br aqueous solution) below the melting point and a solid (SCH encapsulating the target gas) above the melting point.

[0053] For comparison, the CO2 vapor-liquid equilibrium conditions are also shown in Figure 2. These CO2 vapor-liquid equilibrium conditions were determined using REFPROP version 10 (hereinafter sometimes referred to as "REFPROP"), a standard physical property calculation software from the US NIST. As shown in the CO2 vapor-liquid equilibrium conditions in Figure 2, when the pressure exceeds approximately 4 MPa, CO2 gas liquefies in the range of 5 to 20°C. When CO2 liquefies, SCH cannot be formed. For comparison, Figure 2 also shows the phase equilibrium temperature and pressure conditions for a TBAB aqueous solution cited from Non-Patent Document 2.

[0054] It is known that for gas hydrates in the broad sense, the slope of the phase equilibrium temperature-pressure conditions indicates the gas storage capacity of the hydrate, with a smaller slope indicating a larger gas storage capacity (Non-Patent Document 3). As shown in Figure 2, the slope of the N4446Br aqueous solution was smaller than that of the TBAB aqueous solution. Therefore, it is thought that the N4446Br aqueous solution can store a large amount of CO2 gas when it forms SCH with CO2.

[0055] For comparison, Figure 3 also shows the phase equilibrium temperature and pressure conditions for a TBAB aqueous solution cited from Non-Patent Document 4. Note that because CH4 does not liquefy within the temperature and pressure range shown in Figure 3, the CH4 vapor-liquid equilibrium conditions are not shown in Figure 3. As shown in Figure 3, the slope of the N4446Br aqueous solution was smaller than that of the TBAB aqueous solution. Therefore, it is thought that the N4446Br aqueous solution can encapsulate a large amount of CH4 gas when it forms SCH with CH4.

[0056] (Gas absorption test) Using SCH generator A, a gas absorption test was conducted using an aqueous solution of N4446Br, which is a gas collector. The gas capacity of SCH depends on the temperature and pressure at the time of SCH generation and the concentration of ionic substances in the gas collector, i.e., the aqueous solution concentration. Generally, the higher the pressure, the higher the gas capacity. Furthermore, it is thought that the gas capacity of SCH generated from an aqueous solution and gas will be maximum when the aqueous solution concentration has the same composition as SCH (eutectic composition). For this reason, a gas absorption test was conducted with an aqueous solution concentration that matched the eutectic composition of SCH.

[0057] Internal volume 113cm 3 The vessel was filled with an N4446Br aqueous solution (33% by mass) to form a predetermined space. After evacuating the remaining air in the vessel, the target gas, CO2 or CH4, was supplied until the test pressure was reached. The degree of supercooling (the difference between the phase equilibrium temperature and the test temperature) during SCH generation was set to 5°C. When SCH was generated while stirring with the agitator 8, the target gas was encapsulated in the SCH, causing the pressure in the vessel to decrease. Once the pressure decreased, the target gas was again supplied up to the test pressure, and this supply was repeated until the target gas was no longer encapsulated in the SCH. Using REFPROP, the encapsulation density (% by mass) of the target gas was calculated from the test pressure and the SCH generation temperature.

[0058] CO2 was supplied to the N4446Br aqueous solution at 1 MPa, 2 MPa, and 3 MPa. The encapsulation densities of CO2 in SCH were 5.4 mass%, 5.9 mass%, and 6.5 mass%, respectively. These values, expressed as a percentage, represent the mass fractions of CO2 gas when encapsulating CO2 in SCH. These values ​​are 0.054, 0.059, and 0.065 at 1 MPa, 2 MPa, and 3 MPa, respectively. Figure 4 shows the results. Similarly, CH4 was supplied to the N4446Br aqueous solution at 1 MPa, 3 MPa, 5 MPa, and 10 MPa. The mass fractions of CH4 gas when encapsulating CH4 in SCH were 0.009, 0.027, 0.0028, and 0.037, respectively. Figure 5 shows the results.

[0059] (CO2 storage selectivity test and CO2 separation performance test) Using SCH generator A, CO2 encapsulation selectivity tests and CO2 separation performance tests were carried out for a mixture of CH4 and CO2 (CH4 + CO2 mixture) with a CO2 molar fraction of approximately 0.5, and a mixture of N2 and CO2 (N2 + CO2 mixture) with a CO2 molar fraction of approximately 0.15. The internal volume was 113 cm3. 3The vessel was filled with an N4446Br aqueous solution (33% by mass) to form a predetermined space. After evacuating the remaining air in the vessel, the mixed gas was supplied until the test pressure was reached. The test pressure for the CO2 encapsulation selectivity test was 3 MPa, and the test pressures for the CO2 separation performance test were 1 MPa, 3 MPa, and 5 MPa. The degree of supercooling (the difference between the phase equilibrium temperature and the test temperature) during SCH generation was 5°C.

[0060] When SCH was generated while stirring with the stirrer 8, the gas in the container was encapsulated in the SCH, causing the pressure in the container to decrease. Even when the pressure decreased, no additional mixed gas was supplied. The gas in the container before and after the generation of SCH was measured in a volume of approximately 10 cm. 3 The gas was collected in a gas sampling vessel 9 and its composition was analyzed using a gas chromatograph (Shimadzu GC-2014, TCD detector, Shinwa Chemical Co., Ltd. packed column ShinCarbon-ST). The gas density was calculated using REFPROP based on the temperature, pressure, and gas composition before and after SCH generation, and the amount of gas present in the gas phase in the vessel before and after SCH generation was calculated. The difference in the amount of gas before and after SCH generation was taken as the amount of gas encapsulated in SCH, and the composition of the gas encapsulated in SCH was calculated.

[0061] Figure 7 shows the relationship between the CO2 mole fraction in the initial gas phase and the CO2 mole fraction of the gas components in SCH, indicating CO2 occlusion selectivity. The initial gas phase on the horizontal axis of Figure 7 is the gas phase in the vessel before SCH is generated. The gas components in SCH on the vertical axis of Figure 7 are the gas components occluded in SCH. Figures 8 and 9 show the relationship between the initial pressure of the mixed gas and the amount of CO2 occluded in SCH, indicating CO2 separation efficiency. The initial pressure on the horizontal axis of Figures 8 and 9 is the pressure in the vessel before SCH is generated. The CO2 occlusion amount on the vertical axis of Figures 8 and 9 is the absolute amount of CO2.

[0062] The amounts of CO2 supplied before SCH generation at initial pressures of 1 MPa, 3 MPa, and 5 MPa in Figure 8 were estimated to be 18.6 mmol, 58.9 mmol, and 114.6 mmol, respectively. As an example of the experimental data in Figure 8, it can be understood that at 1 MPa, 18.6 mmol of CO2 supplied before SCH generation resulted in 12.6 mmol being encapsulated in SCH (a recovery rate of approximately 68%). The amounts of CO2 supplied before SCH generation at initial pressures of 1 MPa, 3 MPa, and 5 MPa in Figure 9 were estimated to be 5.6 mmol, 16.8 mmol, and 33.2 mmol, respectively.

[0063] <Example 2> The properties of the N4446Cl aqueous solution as a gas collector were evaluated in the same manner as in Example 1. More specifically, phase equilibrium temperature and pressure measurements, CO2 gas absorption tests, CH4 gas absorption tests, and CO2 occlusion selectivity tests and CO2 separation gas separation tests using a CO2 and CH4 mixed gas or a CO2 and N2 mixed gas were performed. In addition, the structural stability of the SCH formed from the N4446Cl aqueous solution and the target gas was evaluated. The following will mainly explain the differences from Example 1.

[0064] (Preparation of N4446Cl aqueous solution) The N4446Br aqueous solution of Example 1 was passed through an anion exchange resin (IRA402BL(CL) manufactured by Oregano Co.) to exchange Br ions for Cl ions, yielding an N4446Cl aqueous solution. Ion chromatography confirmed that the Br ion concentration in this N4446Cl aqueous solution was less than 0.1% by mass.

[0065] (Measurement of phase equilibrium temperature and pressure) The phase equilibrium temperature and pressure of SCH formed by an N4446Cl aqueous solution (25 mass%) with CO2 or CH4 were measured using a method similar to that used in Example 1. The phase equilibrium temperature and pressure conditions for an N4446Br aqueous solution (25 mass%) with CO2 and CH4 are shown in Figures 2 and 3, respectively. As shown in Figures 2 and 3, regardless of whether the target gas is CO2 or CH4, under the same pressure conditions, an N4446Cl aqueous solution can generate SCH at a temperature about 3°C ​​higher than an N4446Br aqueous solution.

[0066] (Evaluation of SCH structural stability) The structural stability of SCH formed from an N4446Cl aqueous solution (30 mass%) and the target gases CO2 and CH4 was evaluated. Using SCH generator A, CO2 was supplied to an N4446Cl aqueous solution (30 mass%) and a slurry of SCH was generated in the N4446Cl aqueous solution under the conditions of 3 MPa and 10°C. Similarly, CH4 was supplied to an N4446Cl aqueous solution (30 mass%) and a slurry of SCH was generated in the N4446Cl aqueous solution under the conditions of 3 MPa and 13°C.

[0067] The N4446Cl aqueous solution was removed from the slurry to obtain a crystalline sample, SCH. This SCH was powdered in a liquid nitrogen atmosphere and heated to approximately 200 K to sublimate the dry ice. Powder X-ray diffraction measurements (PXRD) were then performed by increasing the temperature between 93 and 277 K in 15 K increments. PXRD measurements were performed over a 110-minute period, with a 10-minute wait after each set temperature. The powder sample holding area was maintained at approximately 40 kPa absolute pressure using a vacuum pump. Figure 6(a) shows the powder X-ray diffraction pattern when the target gas was CO2. The crystalline structure was maintained even at 268 K (-5 °C). Powder X-ray diffraction patterns at temperatures between 93 K and 243 K were omitted because no significant changes were observed. Figure 6(b) shows the powder X-ray diffraction pattern when the target gas was CH4. The crystalline structure was maintained even at 258 K (-15 °C).

[0068] Thus, by using the SCH of Example 2 containing an ionic substance, it is possible to store the target gas at -15 to -5°C, even if the self-preservation effect of SCH composed of ionic substance-free water and the target gas is lost. This temperature range is also compatible with existing cold chains such as refrigerated transportation. Therefore, gases can be transported using the SCH of the present disclosure. Furthermore, PXRD was performed while holding SCH at a pressure of approximately 40 kPa, which is lower than atmospheric pressure. This indicates that once SCH is generated, the structure of SCH is stable even when the environmental pressure is reduced.

[0069] (Gas absorption test) A gas absorption test was conducted in the same manner as in Example 1, except that the N4446Br aqueous solution (33 mass%) was replaced with an N4446Cl aqueous solution (30 mass%). CO2 was supplied to the N4446Cl aqueous solution at 1 MPa and 3 MPa. The mass fractions of CO2 gas when CO2 was encapsulated in SCH were 0.041 and 0.062, respectively. Figure 4 shows the results. Similarly, CH4 was supplied to the N4446Cl aqueous solution at 1 MPa, 3 MPa, 5 MPa, and 10 MPa, respectively. The mass fractions of CH4 gas when CH4 was encapsulated in SCH were 0.014, 0.027, 0.030, and 0.033, respectively. Figure 5 shows the results.

[0070] (CO2 storage selectivity test and CO2 separation performance test) A CO2 encapsulation selectivity test and a CO2 separation performance test were carried out in the same manner as in Example 1, except that the N4446Br aqueous solution (33 mass%) was replaced with the N4446Cl aqueous solution (30 mass%) used in Example 2. The results are shown in Figures 7 to 9.

[0071] <Comparative Example> An aqueous TBAB solution (32% by mass) was prepared using tetra-n-butylammonium bromide (TBAB) (manufactured by Merck Co., Ltd.) This comparative TBAB aqueous solution was compared with the N4446Br aqueous solution of Example 1 and the N4446Cl aqueous solution of Example 2.

[0072] (Measurement of phase equilibrium temperature and pressure) The phase equilibrium temperature and pressure of SCH formed by a TBAB aqueous solution (32 mass%) and CO or CH was measured using the same method as in Example 1. The phase equilibrium temperature and pressure conditions for a TBAB aqueous solution (32 mass%) with CO and CH are shown in Figures 2 and 3, respectively.

[0073] (Gas absorption test) A gas absorption test was conducted in the same manner as in Example 1, except that the N4446Br aqueous solution (33 mass%) was replaced with a TBAB aqueous solution (32 mass%). CO2 was supplied to the TBAB aqueous solution at 1 MPa and 3 MPa. The mass fractions of CO2 gas when CO2 was encapsulated in SCH were 0.026 and 0.035, respectively. Figure 4 shows the results. Similarly, CH4 was supplied to the TBAB aqueous solution at 1 MPa, 3 MPa, 5 MPa, and 10 MPa, respectively. The mass fractions of CH4 gas when CH4 was encapsulated in SCH were 0.01, 0.015, 0.018, and 0.020, respectively. Figure 5 shows the results.

[0074] (CO2 storage selectivity test and CO2 separation performance test) Except for changing the N4446Br aqueous solution (33 mass%) to the TBAB aqueous solution (32 mass%) of the comparative example, a CO2 encapsulation selectivity test and a CO2 separation performance test were carried out in the same manner as in Example 1. The results are shown in Figures 7 to 9.

[0075] <Analysis> Table 1 shows the gas encapsulation properties of the SCH formed by the gas collection agents and target gases of Example 1, Example 2, and Comparative Example based on the above-mentioned various evaluation results. The gas encapsulation density in SCH is an important performance index for transporting and storing gases.

[0076] [Table 1]

[0077] As shown in Table 1, the CO2 occlusion densities of the N4446Br and N4446Cl aqueous solutions were approximately 1.9 and 1.8 times, respectively, that of the TBAB aqueous solution. The CH4 occlusion densities of the N4446Br and N4446Cl aqueous solutions were approximately 1.8 and 1.7 times, respectively, that of the TBAB aqueous solution. For both target gases, the occlusion densities of the N4446Br aqueous solution were slightly higher than those of the N4446Cl aqueous solution. Furthermore, for both gas traps, the CO2 occlusion densities were more than 1.7 times higher than those of the CH4. These properties of the gas traps make them suitable for adsorbing CO2 in a CO2 / CH4 mixture, such as fermentation biogas, and separating CH4 from the mixture.

[0078] The "Water / Gas (molar ratio)" in Table 1 indicates the number of moles of water that make up the SCH required to encapsulate 1 mole of gas in SCH. The "Water / Gas (molar ratio)" (number of moles of water (Nw) / number of moles of target gas (Ng)) is calculated using the following formula from the gas encapsulation density X, the concentration of the ionic substance in the aqueous solution (aqueous solution concentration) W, the molecular weight of the target gas Mg, and the molecular weight of water Mw. Nw / Ng={(1-X)×(1-W) / Mw} / (X / Mg)

[0079] Nw / Ng corresponds to the hydration number for a gas. The lower the Nw / Ng, the less water is needed to capture the gas. For both target gases, the Nw / Ng of the N4446Br and N4446Cl aqueous solutions was approximately half that of the TBAB aqueous solution. This shows that the N4446Br and N4446Cl aqueous solutions can store CO2 and CH4 with less water than the TBAB aqueous solution.

[0080] The "Gas / Ionic Substance (Molar Ratio)" in Table 1 indicates the number of moles of gas encapsulated in one mole of ionic substance. The "Gas / Ionic Substance (Molar Ratio)" (number of moles of target gas (Ng) / number of moles of ionic substance (Na)) is calculated using the following formula from the gas encapsulation density X, the concentration of the ionic substance in the aqueous solution (aqueous solution concentration) W, the molecular weight of the target gas Mg, and the molecular weight of the ionic substance Ma. Ng / Na = (X / Mg) / {(1-X) × W / Ma}

[0081] A higher Ng / Na indicates that the gas can be captured with fewer additives. For both target gases, the Ng / Na of the N4446Br and N4446Cl aqueous solutions was higher than that of the TBAB aqueous solution. This shows that the N4446Br and N4446Cl aqueous solutions can store CO2 and CH4 with fewer additives than the TBAB aqueous solution.

[0082] 4 shows the generation pressure dependence of the mass fraction of CO2 gas for the gas collectors of Examples 1 and 2, and the comparative example. The mass fraction of CO2 gas on the vertical axis is a value calculated by assuming that all of the ionic substance aqueous solution filled in the container is converted to SCH, and dividing the mass of CO2 gas encapsulated in SCH by the mass of the ionic substance aqueous solution filled in the container + the mass of CO2 gas encapsulated in SCH.

[0083] Furthermore, when CO2 gas was supplied into the vessel at the set pressure, a pressure drop occurred due to the CO2 gas being encapsulated in the SCH, so CO2 gas was repeatedly supplied to compensate for this pressure drop. For this reason, the horizontal axis represents "generation pressure." At generation pressures of 1 to 3 MPa, the mass fractions of CO2 gas in the N4446Br and N4446Cl aqueous solutions were higher than the mass fraction of CO2 gas in the TBAB aqueous solution. This indicates that CO2 is more easily encapsulated in the N4446Br and N4446Cl aqueous solutions than in the TBAB aqueous solution.

[0084] Figure 5 shows the generation pressure dependence of the mass fraction of CH gas for the gas collectors of Examples 1 and 2, and the Comparative Example. The mass fraction of CH gas on the vertical axis is a value calculated in the same manner as the mass fraction of CO gas in Figure 4. At generation pressures of 3 to 10 MPa, the mass fractions of CH gas in the N4446Br and N4446Cl aqueous solutions were higher than the mass fraction of CH gas in the TBAB aqueous solution. This shows that the N4446Br and N4446Cl aqueous solutions have a higher CH absorption capacity than the TBAB aqueous solution.

[0085] The results in Table 1, Figures 4, and 5 show that the N4446Br and N4446Cl aqueous solutions significantly improved the low gas encapsulation capacity of conventional TBAB aqueous solutions. Furthermore, the gas encapsulation capacity of the N4446Br aqueous solution was slightly higher than that of the N4446Cl aqueous solution. Additives added to water to form gas hydrates with water and target gases must prioritize low risk of biological toxicity, flammability, and corrosivity over performance factors such as the gas encapsulation capacity of the gas hydrate. Furthermore, for ease of handling, it is desirable for these additives to be nonvolatile and / or water-soluble. The N4446Br and N4446Cl contained in the gas scavenger of the present disclosure are the additives with the highest performance among those that meet these requirements.

[0086] Figure 7 shows the relationship between the CO2 composition in the gas phase before SCH formation and the CO2 composition of the gas components in SCH after SCH formation. If the CO2 composition in SCH is higher than that in the initial gas phase, CO2 is selectively encapsulated in SCH relative to other gases in the mixed gas. The values ​​of 0.15 and 0.5 on the horizontal axis of Figure 7 indicate that an N2 + CO2 mixed gas containing 15 mol% CO2 or a CH4 + CO2 mixed gas containing 50 mol% CO2 was respectively supplied into the vessel as the initial gas phase before SCH formation.

[0087] The vertical axis in Figure 7 represents the CO2 composition of the gas components present in SCH when an N2+CO2 gas mixture or a CH4+CO2 gas mixture is encapsulated in SCH. The greater the deviation of the value on the vertical axis in Figure 7 from the dashed line indicating the initial composition, the more concentrated the CO2 is. In Figure 7, the magnitude of the deviation is represented by the length of the double-headed arrow. Using an N4446Br aqueous solution, the CO2 composition of the N2+CO2 gas mixture could be enriched from approximately 15 mol% to approximately 39 mol%. Furthermore, using an N4446Br aqueous solution, the CO2 composition of the CH4+CO2 gas mixture could be enriched from approximately 50 mol% to approximately 62 mol%.

[0088] Although not particularly limited, an N2+CO2 mixed gas is assumed to be an example of the composition of high-concentration CO2 exhaust gas released from a thermal power plant or the like. The gas collectors of Examples 1 and 2 can be used to selectively store or concentrate CO2 from high-concentration CO2 exhaust gas. To further increase the concentration of CO2, the process of encapsulating high-concentration CO2 exhaust gas in the gas collector and the process of releasing the encapsulated gas from the SCH can be repeated multiple times. Although not particularly limited, a CH4+CO2 mixed gas is assumed to be an example of the composition of biogas. The gas collectors of Examples 1 and 2 can be used to purify or concentrate CH4 from biogas.

[0089] Figure 8 shows the results of a gas separation test, i.e., the CO2 occlusion amount in SCH formed from the gas collector of Example 1, Example 2, or Comparative Example and a mixed gas of CH4 (50 mol%) and CO2 (50 mol%). At initial pressures of 1 to 5 MPa, the CO2 occlusion amount of SCH formed using the gas collectors of Examples 1 and 2 was greater than the CO2 occlusion amount of SCH formed using the gas collector of Comparative Example. Note that there was almost no difference in the CO2 occlusion amount between the gas collectors of Example 1 and Example 2.

[0090] 9 shows the CO2 occluded amounts in SCH formed from the gas collectors of Example 1, Example 2, or Comparative Example and a mixed gas of N2 (85 mol%) and CO2 (15 mol%). At initial pressures of 1 to 5 MPa, the CO2 occluded amounts in SCH formed using the gas collectors of Example 1 and Example 2 were greater than the CO2 occluded amounts in SCH formed using the gas collector of Comparative Example. Furthermore, at initial pressures of 3 to 5 MPa, the CO2 occluded amounts in SCH formed using the gas collector of Example 1 were greater than the CO2 occluded amounts in SCH formed using the gas collector of Example 2.

[0091] The results in Figures 7 to 9 show that the SCH formed using N4446Br or N4446Cl aqueous solutions had the same CO2 occlusion selectivity and a larger CO2 occlusion capacity than the SCH formed using the conventional TBAB aqueous solution. The larger CO2 occlusion capacity was consistent with the tendency for the mass fraction of CO2 gas to be higher in the gas absorption tests.

[0092] Some examples of the inventions that have been understood from the above disclosure are as follows. [Configuration 1] A gas collector that contains an ionic substance and water and that collects a target gas, wherein the ionic substance comprises one or more cations selected from the group consisting of tri-n-butyl, n-hexylammonium cation, tri-n-butyl, n-pentylphosphonium cation, tri-n-butyl, n-hexylphosphonium cation, and tri-isobutyl, n-hexylammonium cation, and one or more anions selected from the group consisting of bromide ions, chloride ions, fluoride ions, and hydroxyl ions.

[0093] [Configuration 2] The gas collector according to configuration 1, wherein the cation is a tri-n-butyl, n-hexylammonium cation and the anion is a bromide ion or a chloride ion. [Configuration 3] The gas collector according to Configuration 1 or 2, in which the ionic substance and water crystallize together with the target gas to form SCH. [Configuration 4] The gas collector according to any one of Configurations 1 to 3, wherein the target gas is at least one of carbon dioxide and methane.

[0094] [Configuration 5] An SCH comprising an ionic substance having one or more cations selected from the group consisting of tri-n-butyl, n-hexylammonium cation, tri-n-butyl, n-pentylphosphonium cation, tri-n-butyl, n-hexylphosphonium cation, and tri-isobutyl, n-hexylammonium cation, and one or more anions selected from the group consisting of bromide ion, chloride ion, fluoride ion, and hydroxyl ion, and water.

[0095] [Configuration 6] The SCH according to Configuration 5, further comprising a target gas, wherein the ionic substance, water, and the target gas are crystallized. [Configuration 7] A gas collection method for collecting a target gas using the gas collection agent according to any one of Configurations 1 to 4, the gas collection method including a collection step of forming an SCH containing the gas collection agent and the target gas, and collecting the target gas in the SCH. [Configuration 8] The gas collection method according to Configuration 7, wherein the collection step involves collecting the target gas in the SCH by a gas-liquid contact method or a gas-solid contact method.

[0096] [Configuration 9] A gas separation method using the gas collector according to any one of Configurations 1 to 3, comprising: a first preparation step of preparing a first mixed gas containing a first gas and a second gas as a target gas; a first collection step of forming a first SCH containing the gas collector and the target gas and collecting a portion of the first gas and a portion of the second gas in the first SCH; and a first separation step of melting the first SCH to obtain a second mixed gas having a content ratio of the first gas to the second gas different from that of the first mixed gas.

[0097] [Configuration 10] The gas separation method according to Configuration 9, further comprising a second preparation step of preparing a second mixed gas as a target gas, a second collection step of forming a second SCH containing a gas collector and the target gas and collecting a portion of the first gas and a portion of the second gas in the second SCH, and a second separation step of melting the second SCH to obtain a third mixed gas having a content ratio of the first gas to the second gas different from that of the second mixed gas.

[0098] [Configuration 11] A gas separation method according to Configuration 9 or 10, wherein in the first capture step, a first mixed gas is captured in a first SCH by gas-liquid contacting or gas-solid contacting, the first gas being CO2, the second gas being CH4 or N2, and the content ratio of the first gas in the second mixed gas being higher than the content ratio of the first gas in the first mixed gas. [Explanation of symbols]

[0099] A SCH generator 1 Gas supply section 2. Vacuum pump 3 Constant temperature water bath agitator 4 Cooler 5. Constant temperature water bath 6. Pressure gauge 7 Reaction vessel 8. Reaction vessel agitator 9 Gas sampling vessel 10 Recorder 11 Temperature Controlled Heater 12 Thermometer 13 Gas collector V1~V9 valves

Claims

1. A gas collecting agent having an ionic substance and water, which collects a target gas, The gas scavenger, wherein the ionic substance comprises one or more cations selected from the group consisting of tri-n-butyl, n-hexylammonium cation, tri-n-butyl, n-pentylphosphonium cation, tri-n-butyl, n-hexylphosphonium cation, and tri-isobutyl, n-hexylammonium cation, and one or more anions selected from the group consisting of bromide ions, chloride ions, fluoride ions, and hydroxyl ions.

2. the cation is a tri-n-butyl, n-hexylammonium cation, 2. The gas scavenger according to claim 1, wherein the anion is a bromide ion or a chloride ion.

3. 2. The gas collector according to claim 1, wherein the ionic substance and the water crystallize with the target gas to form a semiclathrate hydrate.

4. 4. The gas collector according to claim 3, wherein the target gas is at least one of carbon dioxide and methane.

5. an ionic substance comprising one or more cations selected from the group consisting of tri-n-butyl, n-hexylammonium cation, tri-n-butyl, n-pentylphosphonium cation, tri-n-butyl, n-hexylphosphonium cation, and tri-isobutyl, n-hexylammonium cation, and one or more anions selected from the group consisting of bromide ion, chloride ion, fluoride ion, and hydroxyl ion; Water and Semiclathrate hydrate having

6. Further, it has a target gas, The semiclathrate hydrate according to claim 5 , wherein the ionic substance, the water, and the target gas are crystallized.

7. A gas collection method for collecting a target gas using the gas collection agent according to any one of claims 1 to 4, comprising: A gas collection method including a collection step of forming a semiclathrate hydrate containing the gas collection agent and the target gas, and collecting the target gas in the semiclathrate hydrate.

8. The gas collection method according to claim 7 , wherein in the collection step, the target gas is captured in the semiclathrate hydrate by a gas-liquid contact method or a gas-solid contact method.

9. A gas separation method using the gas collector according to any one of claims 1 to 3, a first preparation step of preparing a first mixed gas containing a first gas and a second gas as the target gas; a first collection step of forming a first semiclathrate hydrate containing the gas collector and the target gas, and collecting a portion of the first gas and a portion of the second gas in the first semiclathrate hydrate; a first separation step of melting the first semiclathrate hydrate to obtain a second mixed gas having a content ratio of the first gas to the second gas different from that of the first mixed gas; A gas separation method comprising:

10. a second preparation step of preparing the second mixed gas as the target gas; a second collection step of forming a second semiclathrate hydrate containing the gas collector and the target gas, and collecting a portion of the first gas and a portion of the second gas in the second semiclathrate hydrate; a second separation step of melting the second semiclathrate hydrate to obtain a third mixed gas having a content ratio of the first gas to the second gas different from that of the second mixed gas; 10. The gas separation method of claim 9, further comprising:

11. In the first capture step, the first mixed gas is captured in the first semiclathrate hydrate by a gas-liquid contact method or a gas-solid contact method; the first gas is carbon dioxide and the second gas is methane or nitrogen; 10. The gas separation method according to claim 9, wherein the content ratio of the first gas in the second gas mixture is higher than the content ratio of the first gas in the first gas mixture.

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