Gas Separation Method

Abstract

To provide a gas separation method that reduces slipping-off phenomena in a PSA system which uses a gate type porous polymer complex, improves a gas recovery, and obtains a gas with high efficiency and high purity.SOLUTION: A gas separation method uses a gas separator that includes at least an adsorption tower in which a gate type porous polymer complex-containing gas adsorbent is filled and gas supply means which supplies a mixed gas containing multiple kinds of gases to the adsorption tower. In this method, a ratio of a partial pressure of an adsorption object gas at an inlet of the adsorption tower to an adsorption start gate pressure in the multiple kinds of gases is larger than 1.3, and is 400 or less.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a gas separation method using a porous polymer complex that exhibits a gate phenomenon (hereinafter, also simply referred to as a "gate-type porous polymer complex"). [Background technology]

[0002] Pressure swing adsorption (PSA) systems using solid adsorbents are widely used as a method for producing industrially important gases such as oxygen and nitrogen. For example, when separating two gases from a mixture, an adsorption tower is filled with solid adsorbents that have different adsorption capacities for the two gases. When the mixed gas is introduced, one gas is selectively adsorbed. As a result, a large amount of unadsorbed gas remains in the gas phase, and the pressure is reduced to recover the adsorbed gas. For this purpose, so-called porous solid adsorbents such as zeolite and activated carbon are widely used, and PSA systems for oxygen generation, nitrogen generation, and other applications are widely used (Patent Document 1).

[0003] In general, existing porous materials such as zeolites and activated carbon can be classified into the six IUPAC adsorption isotherm categories. In other words, existing porous materials have the property that their gas adsorption capacity increases as the pressure increases, and existing PSA systems are optimized for this property. However, materials that exhibit unique adsorption isotherms that cannot be classified into the six IUPAC categories have been announced. These are types of porous coordination polymers (PCPs) formed from metal ions and ligands, and are known as gate-type porous polymer complexes or flexible porous polymer complexes, and the unique gas adsorption behavior they exhibit is known as the gate phenomenon or gate adsorption.

[0004] The gate phenomenon is a phenomenon in which the amount of gas adsorbed by a gate-type porous polymer complex changes dramatically, primarily due to structural changes. At low gas pressures, the gate-type porous polymer complex barely adsorbs gas. However, once the gas pressure reaches a certain value (called the adsorption initiation gate pressure), the structure of the gate-type porous polymer complex changes (e.g., the stacking structure shifts, the interlayer space widens, etc.), and gas molecules are incorporated into the structure. This results in a rapid increase in the amount of gas adsorbed beyond the adsorption initiation gate pressure. This phenomenon is thought to be due to the fact that, below the adsorption initiation gate pressure, it is energetically more stable for the gate-type porous polymer complex and gas molecules to exist separately. However, above the adsorption initiation gate pressure, it is more energetically advantageous for the gas molecules to be incorporated into the gate-type porous polymer complex, forming a more stable inclusion complex than if the gate-type porous polymer complex and gas molecules existed separately.

[0005] The opposite phenomenon occurs during gas release. That is, when the gas pressure drops below a certain pressure (desorption initiation gate pressure), the gas molecules trapped in the gate-type porous polymer complex are released and attempt to return to the original structure of the gate-type porous polymer complex, resulting in a sudden release of gas. In other words, this gating phenomenon is based on the flexibility of the gate-type porous polymer complex structure; the gating phenomenon does not occur in existing porous materials such as zeolite and activated carbon, which do not have this flexibility. The gating phenomenon is a phenomenon unique to gate-type porous polymer complexes.

[0006] When this gate phenomenon is applied to gas separation, there are two major advantages. The first advantage is highly efficient gas separation due to the rapid adsorption and release of gas. Existing porous materials exhibit adsorption isotherms in which the gas pressure is roughly proportional to the amount of adsorption. In order to recover the entire amount of gas adsorbed by such adsorbents, large pressure fluctuations are required. In contrast, with gate-type porous polymer complexes that exhibit the gate phenomenon, gas can be recovered by fluctuating the pressure across the gate pressure, so adsorbed gas can be recovered with very small pressure fluctuations (Figure 1). Pressure fluctuations during adsorption gas recovery are directly linked to the cost of electricity used. In other words, the gate-type porous polymer complex, which can recover adsorbed gases with small pressure fluctuations, is a material that can separate gases at low cost.

[0007] The second benefit is high gas separation efficiency. As mentioned above, gas adsorption by gate-type porous polymer complexes is not a simple mechanism in which gas molecules to be adsorbed are trapped in the pores of the adsorbent, as in conventional methods. Rather, it is based on a mechanism in which the gate-type porous polymer complex and the adsorbed gas molecules form stable inclusion complexes with the gate-type porous polymer complex at a certain gas pressure (adsorption onset gate pressure) or above. With existing porous adsorbents, even if two gases have different affinities, the presence of pores makes it easy for the gas with lower affinity to be trapped in the pores, resulting in a co-adsorption phenomenon in which the gas with lower affinity is also trapped in the pores. In contrast, gate-type porous polymer complexes have the property of selectively trapping gases with higher affinity and forming more stable inclusion complexes, since the co-adsorption phenomenon reduces the stability of the inclusion complex when gas molecules with lower affinity are also trapped. Therefore, gate-type porous polymer complexes have high gas selectivity, and when applied to PSA systems, they can produce high-purity separated gases with high recovery rates and high efficiency.

[0008] However, when this gate-type porous polymer complex is actually applied to a PSA system, a problem called slipping-off occurs, which can reduce the recovery rate of the adsorbed gas. Slipping-off refers to the phenomenon in which, when gas is injected into a PSA unit, the components to be adsorbed are not adsorbed by the gate-type porous polymer complex and instead flow out of the PSA unit. This phenomenon is due to the property of the gate-type porous polymer complex, which adsorbs almost no gas when the partial pressure of the adsorbed gas is low (below the adsorption initiation gate pressure). Furthermore, even when the partial pressure of the adsorbed gas is higher than the adsorption initiation gate pressure, the recovery rate of the adsorbed gas may be low (approximately 0.4). This occurs because the partial pressure of the adsorbed gas is high (above the adsorption initiation gate pressure) near the gas inlet of the PSA unit, causing the gate adsorption phenomenon, but the adsorbed gas that is not completely adsorbed near the inlet flows toward the gas outlet. This gas that is not completely adsorbed near the inlet has a lower partial pressure than the adsorption start gate pressure, so it flows out of the PSA unit without being adsorbed near the outlet.When this slipping-off phenomenon occurs, the gas that should have been adsorbed ends up leaking out, resulting in a lower recovery rate.

[0009] To solve this slipping-off phenomenon, Patent Document 2 proposes a PSA system in which two adsorption columns are connected in series. One of the two columns is packed with a gate-type porous polymer complex, and the other is packed with a conventional porous material. In this system, gas to be adsorbed leaks from the column packed with the gate-type porous polymer complex due to slipping-off, but the gas is adsorbed by the column packed with the conventional porous material, thereby preventing gas leakage.

[0010] This system has the following problems. The first is the high equipment cost. Because two adsorption columns are required, the equipment cost is higher than that of a typical PSA system that uses a single column for adsorption.

[0011] The second issue is the shortened service life of the equipment. The two types of adsorbents have different service lives, and equipment replacement must be carried out according to the one with the shorter service life, which requires more frequent replacement than PSA systems that use a single column for adsorption. Equipment replacement requires stopping the entire production system, which is costly, and frequent replacement directly leads to reduced productivity.

[0012] The third issue is the increased energy required to desorb gases adsorbed in existing porous materials. Slipping-off is a phenomenon in which low-concentration gases below the gate pressure at which adsorption begins leak out. For this reason, existing porous materials that capture gases must have strong adsorption power. Thus, a large amount of energy is consumed to desorb gases adsorbed from adsorbents with such strong adsorption power. As a result, the energy-saving feature of PSA systems using gate-type porous polymer complexes may be lost. For this reason, a PSA system using a gate-type porous polymer complex has not yet been put to practical use, and this problem has not yet been solved. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-061244 [Patent Document 2] Japanese Patent Publication No. 2020-018995 Summary of the Invention [Problem to be solved by the invention]

[0014] An object of the present invention is to provide a gas separation method that reduces the slipping-off phenomenon in a PSA system using a gate-type porous polymer complex, improves the gas recovery rate, and produces a highly efficient, high-purity gas. [Means for solving the problem]

[0015] In order to solve the above-mentioned problems, the present inventors have investigated the following three methods to reduce the slipping-off phenomenon and improve the gas recovery rate in a PSA system using a gate-type porous polymer complex.

[0016] The first method involves recovering the gas flowing out from the gas outlet of the adsorption column of the PSA system, returning it to the inlet side, and repressurizing it to adsorb it, thereby increasing the gas recovery rate.

[0017] The gas separation device using this method has an outlet gas recycling system as shown in Figure 4. This system stores the outlet gas discharged from the adsorption column in a tank, re-compresses it with a compressor, and feeds it back to the inlet of the adsorption column to re-adsorb the target gas. This prevents the target gas from leaking from the adsorption column outlet, making it possible to improve the recovery rate of the target gas.

[0018] The gas separation system is operated by repeating steps (1) to (4) shown in Figure 5. The dotted line indicates the magnitude of the gas partial pressure of the component to be adsorbed in the adsorption column. First, in step (1), the low-concentration gas stored in the tank in step (3) of the previous cycle is compressed into the adsorption column by a compressor. During this process, gas adsorption occurs in a portion of the column (near the inlet). Note that step (1) is not performed in the first cycle. Next, in step (2), the raw gas is compressed into the column. When gas begins to leak from the outlet due to slipping off, step (3) is initiated. In step (3), this leaked gas is stored in the tank. The tank is replenished with the low-concentration gas used in step (1). When the amount of gas adsorbed in the tank reaches saturation, step (4) is initiated. Here, the column is first depressurized to atmospheric pressure, and then a vacuum pump is used to reduce the pressure in the column to below the gate pressure, allowing the gas to be desorbed. Once gas desorption is complete, step (1) is initiated again. This is a method of circulating the effluent gas, but circulating it makes the entire system more complicated.

[0019] The second method is to configure a PSA system with two adsorption columns, the first and second, containing gate-type porous polymer complexes, and appropriately control the gate pressure by keeping the first adsorption column at room temperature or heated and cooling the second adsorption column. This aims to increase adsorption by cooling the gate material of the second column and reduce the amount of outflow gas.

[0020] This gas separation system utilizes a heating and cooling system to reduce slipping-off. Figure 6 shows a system consisting of a room-temperature adsorption column A and a low-temperature, high-pressure adsorption column B. The dotted lines indicate the partial pressure of the gas to be adsorbed within the columns, with the gate pressures for columns A and B being [Pgate,A] and [Pgate,B], respectively. The gate pressure of the gate-type porous polymer complex decreases at low temperatures, resulting in [Pgate,A] > [Pgate,B]. Gases above the adsorption initiation gate pressure within the column are adsorbed; therefore, gases leaking from column A with a partial pressure lower than the gate pressure [Pgate,A] can be adsorbed in column B until the partial pressure of the gas to be adsorbed reaches [Pgate,B]. This reduces the amount of gas that slips off compared to PSA using only column A.

[0021] This method also has a system that reduces the amount of gas that escapes due to slipping-off through pressure control. In Figure 6, a compressor is installed between columns A and B, and the gas at the outlet of column A is re-pressurized and flows into column B, further reducing the amount of gas that slips off.

[0022] As explained in the aforementioned Patent Document 2, this method involves preparing two adsorption columns and filling them with adsorbents with different lifespans, which increases equipment costs and reduces the service life of the entire equipment due to the different lifespans of the materials.

[0023] The third method is to increase the partial pressure of the gas to be adsorbed at the inlet of the PSA column above the adsorption start gate pressure, thereby reducing the amount of gas that flows out relative to the total amount of gas that flows in. Using this method, the gas recovery rate unexpectedly increased.

[0024] The present invention is as follows. (1) A gas separation method using a gas separation apparatus including at least an adsorption tower packed with a gas adsorbent containing a gate-type porous polymer complex and a gas supply means for supplying a mixed gas containing a plurality of gases to the adsorption tower, A gas separation method characterized in that the ratio of the partial pressure of the gas to be adsorbed at the inlet of the adsorption tower to the adsorption start gate pressure of the gas to be adsorbed among the multiple gases is greater than 1.3 and 400 or less. (2) The gas separation method according to (1) above, wherein the pressure difference between the adsorption completion gate pressure and the desorption completion gate pressure of the gate-type porous polymer complex is 2 kPa to 8000 kPa. (3) The gas separation method according to (1) or (2), wherein the gate-type porous polymer complex is an ELM, a Kagome, an MIL, or a CID. [Effects of the Invention]

[0025] The gas separation method of the present invention solves the problem of reduced recovery rate of the adsorbed gas due to the slipping-off phenomenon that has been encountered in conventional PSA systems using gated porous polymer complexes, and achieves high efficiency, high purity, and high recovery rate of the adsorbed gas. The gas separation apparatus of the present invention can be a pressure swing adsorption (PSA) gas separation apparatus. Specifically, either vacuum swing adsorption (VSA) or pressure swing adsorption (PSA) can be suitably used. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a graph showing the relationship between gas pressure and gas adsorption amount for an existing solid adsorbent and an adsorbent made of a gate-type porous polymer complex. [Figure 2] FIG. 1 is a diagram showing the gate pressures of an adsorbent made of a gate-type porous polymer complex used in the present invention. [Figure 3] A diagram explaining gate coefficients using ELM-11 as an example. [Figure 4] Diagram of a slip-off mitigation system using outlet gas reuse. [Figure 5] How the system shown in Figure 4 is operated [Figure 6] Diagram of the slip-off mitigation system using heating and cooling. [Figure 7] 1 is a conceptual diagram of a process operation simulating the gas separation method of the present invention. [Figure 8] Adsorption isotherm equation for ELM-11 used in the examples. Adsorption and desorption isotherm model (1) for ELM-11 used in the simulation. [Figure 9] The adsorption-desorption isothermal model of ELM-11 used in the simulation (2). DETAILED DESCRIPTION OF THE INVENTION

[0027] The gate-type porous polymer complex according to the present invention is a material that exhibits a gate-type isotherm. A gate-type isotherm refers to an adsorption isotherm and a desorption isotherm that exhibit an inflection point as shown in Figure 2, mainly due to a structural change in the porous polymer complex. As shown in Figure 2, the isotherm of the gate-type porous polymer complex is defined by the adsorption initiation gate pressure, the adsorption completion gate pressure, the gate adsorption amount, the desorption initiation gate pressure, the desorption completion gate pressure, and the gate desorption amount.

[0028] The adsorption start gate pressure is the pressure at which the proportional relationship between the adsorption amount and pressure in the early stage of adsorption in the adsorption process suddenly increases (the adsorption amount increment suddenly increases with respect to the gas pressure increment). The adsorption completion gate pressure is the pressure at which the proportional relationship between the adsorption amount and pressure after the adsorption start gate pressure suddenly decreases (the desorption amount increment suddenly decreases with respect to the gas pressure increment). The gate adsorption amount is the amount of adsorption between the adsorption start gate pressure and the adsorption completion gate pressure. The desorption start gate pressure is the pressure at which the proportional relationship between the adsorption amount and pressure in the early stage of desorption in the desorption process suddenly increases (the desorption amount increment suddenly increases with respect to the gas pressure increment). The desorption completion gate pressure is the pressure at which the proportional relationship between the adsorption amount and pressure after the desorption start gate pressure suddenly decreases (the desorption amount increment suddenly decreases with respect to the gas pressure increment). The gate desorption amount is the amount of desorption from the desorption start gate pressure to the desorption completion gate pressure. Both the adsorption start gate pressure and desorption start gate pressure vary depending on the affinity between the adsorption material and the gas to be adsorbed; that is, the higher the affinity, the smaller the pressure; and the lower the affinity, the larger the pressure. Also, the lower the temperature, the higher the affinity, so the gate pressure will be lower. Therefore, since the pressures vary depending on the adsorption material, gas type, and temperature, it is not possible to determine a single pressure.

[0029] The adsorption and desorption characteristics of the gate-type porous polymer complex can be defined by the following two equations.

[0030] Equation 1: Adsorption gate coefficient = (adsorption amount at adsorption completion gate pressure - adsorption amount at adsorption start gate pressure) / (adsorption completion gate pressure - adsorption start gate pressure) Equation 2: Desorption gate coefficient = (adsorption amount at desorption start gate pressure - adsorption amount at desorption completion gate pressure) / (desorption start gate pressure - desorption completion gate pressure) Note: The adsorption amount is the amount of adsorption of the measurement gas at the measurement temperature, and the unit is m(STP)L / g. Note: Pressure is in kPa.

[0031] Currently known gate-type porous polymer complexes include ELMs (Elastic Layer-structured metal organic frameworks), Kagome complexes, MILs, CIDs, and others. The literature on these gate-type porous polymer complexes is as follows: ELMs are described in Ueshiro et al., Int. J. Mol. Sci. 2010, 11, 3803; Kagome complexes are described in Sato et al., SCIENCE (2014) 343, 167, and Zaworotko et al., Chem. Commun., 2004, 2534; and MILs are described in Ferey et al., Chem. Soc. Rev., 2009, 38, 1380. CIDs are described in Inubushi et al., Chem. Commun., 2010, 46, 9229 and Nakagawa et al., Chem. Commun., 2010, 46, 4258. Other examples are described in Kitaura et al., Angew. Chem. Int. Ed. 2003, 42, 428. Among these, ELMs, Kagome compounds, MILs, and CIDs are preferred because they have a clear gating phenomenon and are highly effective for the present invention.

[0032] The gate coefficient will be explained using Figure 3, taking ELM-11 as an example. The carbon dioxide adsorption / desorption isotherms for ELM-11 at 273 K are shown in Figure 3. The x-axis is pressure (kPa) and the y-axis is the adsorption amount (mL(STP) / g). In this case, each isotherm passes through the following points, so these isotherms can be approximated by the following formula:

[0033] Adsorption isotherm before the adsorption gate: Representative waypoint 1: x = 5.23, y = 0.188; waypoint 2: x = 27.4, y = 0.665, and the approximate equation is y = 0.022x + 0.0753. Adsorption isotherm after adsorption gate: Typical passing points 3 :x=34.2,y=23.3;passing point 4 :x=35.2, y=50.7, and the approximate equation is y=27.4x-913.

[0034] By solving the above simultaneous equations, x ("adsorption start gate pressure") = 33.4 kPa (the amount of adsorption before the gate is 1.1 mL (STP) / g). Similarly, the "adsorption completion gate pressure" calculated from the isotherm was 36.0 kPa, and the amount of adsorption at that point was 74.4 mL. From the above, the adsorption gate coefficient is calculated as (77.4-1.1) / (36.0-33.4)=29.3. Similarly, the desorption start gate pressure is 28.41 kPa (the adsorption amount is 75.2 mL (STP) / g), and the desorption completion gate pressure is 26.20 kPa (the adsorption amount is 2.71 mL (STP) / g). From the above, the desorption gate coefficient is calculated as (75.2-2.71) / (28.41-26.20)=32.8.

[0035] The gate-type porous polymer complex that can be used in the gas separation method of the present invention preferably has an adsorption gate coefficient of 0.7-75 and a desorption gate coefficient of 0.4-80. If the adsorption gate factor is less than 0.7, the change in adsorption amount with respect to pressure fluctuation is too small, resulting in no clear difference from that of general adsorbents, making it difficult to say that the adsorption behavior is gate-type. Furthermore, if the adsorption gate factor exceeds 75, the change in adsorption amount with respect to pressure fluctuation is too steep, resulting in a sudden increase in adsorption heat and a sudden change in the concentration ratio of the mixed gas due to the sudden adsorption of a specific gas, making it difficult to use (control) as a practical gas separation material. If the desorption gate factor is less than 0.4, the change in adsorption amount with respect to pressure fluctuation is too small, resulting in no clear difference from that of general adsorbents, making it difficult to say that the adsorption behavior is gate-type. Furthermore, if the desorption gate factor exceeds 80, the change in desorption amount with respect to pressure fluctuation is too steep, resulting in a sudden drop in temperature due to the sudden increase in desorption heat and a sudden change in the concentration ratio of the mixed gas due to the sudden release of a specific gas, making it difficult to use (control) as a practical gas separation material.

[0036] In the gate-type porous polymer complex that can be used in the gas separation method of the present invention, the pressure difference between the adsorption completion gate pressure and the desorption completion gate pressure is preferably 2 kPa to 8000 kPa. If the pressure difference between the adsorption completion gate pressure and the desorption completion gate pressure is less than 2 kPa, the adsorption pressure and the desorption pressure are too close to each other and cannot be fully controlled by the PSA device. On the other hand, if the pressure difference exceeds 8000 kPa, the adsorption pressure and the desorption pressure are too far apart, and recovering the gas adsorbed from such a material requires very large pressure fluctuations, which increases the power cost and operation time, eliminating the benefit of using the gating phenomenon for gas separation. Particularly preferred gate-type porous polymer complexes that can be used in the gas separation method of the present invention include ELMs, Kagomes, MILs, and CIDs.

[0037] These various gate-type porous polymer complexes have their own specific adsorption initiation gate pressures, which can vary with temperature. However, since the phenomenon of slipping-off occurs when the partial pressure of the gas to be adsorbed in the adsorption tower drops below the adsorption initiation gate pressure, the slipping-off phenomenon can be reduced by setting the partial pressure of the gas to be adsorbed at a certain level higher than the adsorption initiation gate pressure. In other words, even for materials with different adsorption initiation gate pressures, an excellent recovery rate for the gas to be adsorbed can be achieved as long as the ratio of the partial pressure of the gas to the adsorption initiation gate pressure at the inlet of the adsorption tower is greater than 1.3 and less than 400.

[0038] A device packed with the gate-type porous polymer complex of the present invention can be applied to the separation of various gases. Examples of gas species include oxygen, nitrogen, argon, carbon dioxide, carbon monoxide, hydrogen, alkanes, alkenes, and alkynes. When a device packed with the gate-type porous polymer complex of the present invention is applied to gas separation, it is possible to easily separate high-purity gases with a high recovery rate and high efficiency by utilizing the gate phenomenon.

[0039] In the gas separation device filled with the gate-type porous polymer complex according to the present invention, the shape and material of the container, the type of gas valve, etc. do not need to be particularly special devices, and those used in gas separation devices can be used. However, this does not exclude improvements to various devices, and any device used is within the technical scope of the present invention as long as it uses the gas polymer metal complex of the present invention.

[0040] The gas separation method using a gas separation device packed with a gate-type porous polymer complex according to the present invention is a separation method in which the ratio of the partial pressure of the gas to be adsorbed at the inlet of the adsorption tower to the adsorption initiation gate pressure of the gas to be adsorbed among a plurality of gases is greater than 1.3 and not greater than 400. If the partial pressure ratio of the gas to be adsorbed at the inlet to the adsorption initiation gate pressure is less than 1.3, even if gate adsorption occurs, gas separation cannot be performed due to slipping-off in the adsorption tower. On the other hand, if it exceeds 400, the mixed gas must be pressurized very high, resulting in high electricity and equipment costs. In the gas separation method of the present invention, the specific means for making the ratio of the partial pressure of the gas to be adsorbed at the inlet of the adsorption tower to the adsorption start gate pressure of the gas to be adsorbed greater than 1.3 can be any of the usual means used for controlling the gas pressure in an adsorption tower. [Example]

[0041] The ratio of the adsorbed gas partial pressure to the adsorption initiation gate pressure and the change in gas recovery rate are shown in Table 1 below. This is the result of simulating a PSA system using ELM-11 and supplying a mixture of 20% carbon dioxide and 80% nitrogen at a temperature of 25°C. Note that the adsorption isotherm model used was that proposed by Hefti et al. (Faraday Discuss (2016), pp. 153-179, Adsorption 20, 359-371 (2014)), and the kinetic model used was that used by Ko et al. (Ind. Eng. Chem. Res. 2005, 44, 21, 8084-8094).

[0042] In the case of a mixture of carbon dioxide and other gases, it has been reported in many publications that ELM-11 does not adsorb these gases, even if the gas other than carbon dioxide is one or more of oxygen, argon, helium, hydrogen, and methane. Therefore, when considering the separation of these gases from carbon dioxide, the same results as for the separation of a mixture of carbon dioxide and nitrogen can be obtained.

[0043] The ratios of adsorbed CO2 partial pressure to adsorption initiation gate pressure for Examples A to G in Table 1 were 4.87, 2.43, 1.22, 5.73, 1.72, 4.65, and 1.55, respectively, and the corresponding recovery rates were 0.863, 0.710, 0.337, 0.890, 0.574, 0.853, and 0.498, respectively. These results confirm that the recovery rate increases as the ratio of adsorbed gas partial pressure to adsorption initiation gate pressure increases. Example C was selected as a comparative example because its recovery rate was below 0.4.

[0044] [Table 1]

[0045] (Note) Capture rate: The ratio of the amount of CO2 captured to the amount of CO2 input, expressed by the following formula: [ka] Note that u [m / s] is the flow velocity at the inlet, Pi is the partial pressure of component i at the inlet [Pa], R is the gas constant [J / (kg·K)], T is the temperature at the inlet [K], the feed step is the process of introducing the raw gas into the column, and the exhaust step is the process of extracting CO2 from the column. Purity: The purity of the recovered CO2 gas, expressed by the following formula: [ka] BSF: An index showing the reciprocal of the amount of CO2 that can be treated per unit amount of adsorbent, and is expressed by the following formula: [ka] However, m PCP is the amount of adsorbent used [kg], t cycle indicates the time [days] per PSA cycle. Power Consumption: The amount of energy used to capture a unit of CO2, expressed as follows: [ka] In addition, P in is the total pressure at the column inlet [Pa], P atm is atmospheric pressure [Pa], γ is the specific heat ratio [-], R bed indicates the column radius [m].

[0046] Table 2 shows the results of simulating a PSA system supplying a mixture of 40% carbon dioxide and 60% nitrogen at a temperature of 25°C.

[0047] [Table 2]

[0048] As can be seen from Table 1, in Example A (invention example), the inlet adsorption CO2 partial pressure was set to 2.0 [10 5 Under the condition of [inlet adsorption CO2 partial pressure / adsorption start gate pressure = 4.87 Pa], it was found that the recovery rate could be improved by 2.56 times compared to Example C (comparative example) without a significant decrease in the purity of the recovered gas. In addition, the BSF (the amount of material required to recover a certain amount of CO2) could be reduced by nearly 80%. In other words, it was confirmed that a large amount of gas could be recovered, and separation efficiency was greatly improved. This indicates that slipping-off was reduced.

[0049] Gas separation, particularly CO2 separation, is often expected to be carried out on a scale of several million tons per year. This means that separation costs are high, the equipment is large, and the site area required is large. For example, the separation cost for chemical absorption using amine liquid is said to be 5,000 yen / ton-CO2, but the cost of separating 1 million tons would be as much as 5 billion yen. Therefore, if the separation efficiency of CO2 separation can be improved, significant cost reductions are expected, and if the equipment is made more compact, significant site area reductions are also expected. This technology dramatically improves recovery rates and BSF, as shown in Table 1 above, and can be said to contribute to cost reductions and site area reductions.

[0050] The simulation results shown in Table 1 were calculated as follows. Example A (invention example) Inlet adsorption CO 2 Partial pressure 4.00[10 5 Pa] In this example, we assume a process using a lab-scale single-column apparatus. The column length is 1 m, and the column tube radius is 1.1 cm. The pellet size is 3 mm, and the pellets are packed to give a porosity of 34.8%. The pellets are ELM-11 supported on cellulose, with a weight ratio of 3:1, and the weight of ELM-11 is 0.293 kg. The temperature outside the tube is 298.15 K.

[0051] The process procedure is shown in Figure 7. First, in the (a) pressurization process, the column outlet is blocked and exhaust gas is injected through the inlet. The inlet pressure is 0.25[10 5 Pa] and gradually increased pressure to 20 [10 5 The temperature of the inflowing gas is 298.15K, and the molar fraction is 20% CO2 and 80% N2. This process continues for 40 seconds. Next, in (b) the adsorption process, the column outlet is opened, and gas continues to be injected from the inlet. The gas temperature and molar fraction are the same as in (a), and the gas flow rate is 0.302 m / s. This process continues for 84.4 seconds. (c) In the depressurization process, the column outlet is closed, and the pressure is reduced and CO2 gas is recovered from the inlet. The inlet pressure is gradually reduced to 0.25 [10 5The pressure is reduced to 0.25 [10 Pa]. This process continues for 120 seconds. (d) The desorption process is 5 The reduced pressure state of [Pa] is maintained and CO2 gas is collected from the inlet. This process continues for 250 seconds. The simulation results are obtained by repeating the above operations (a) to (d) for 10 cycles.

[0052] Example B (invention example) Inlet adsorption CO 2 Divided pressure 2.00[10 5 Pa] In this example, the process is the same as in Example A, but with the following two changes to the operating conditions. The first change is the CO2 partial pressure during the pressurization and adsorption process, which is 4.00 [10 5 Pa] to 2.00 [10 5 The second point is the time taken for the adsorption process, which was changed from 84.4 seconds to 169 seconds.

[0053] Example C (comparative example) Inlet adsorption CO 2 Divided pressure 1.00[10 5 Pa] This example, like Example B, is the same process as Example A, but with modified operating conditions. The inlet adsorption CO2 partial pressure during the pressurization and adsorption process was set to 4.00 [10 5 Pa] to 1.00[10 5 Pa].

[0054] In examples D to M, similar to examples A, B, and C, simulations were performed by changing the inlet adsorption CO2 partial pressure and the temperature of the raw gas. The parameters used in the example are summarized in Table 3.

[0055] [Table 3]

[0056] The adsorption isotherm model used in the above simulation was that proposed by Joss et al. (Energy Procedia (2017), 114, 2271-2278). This method is explained below. CO2 adsorption in ELM-11 consists of two processes: adsorption around the framework and adsorption within the framework. Here, we assume that there are two hypothetical adsorption isotherms that express these adsorption behaviors. Specifically, the adsorption isotherm when all gates are closed, regardless of pressure, is defined as n L The adsorption isotherm when all gates are open regardless of pressure is n U Here, when ELM-11 performs gate adsorption, if we assume that the number of open gates increases depending on the CO2 partial pressure, the actual adsorption / desorption isotherm is n U and n L Under this assumption, the adsorption / desorption isotherm of ELM-11 is expressed as Equation 1 (Fig. 8). j is a weight that takes a value between 0 and 1 and indicates the proportion of open gates to the total number of gates.

[0057]

number

[0058] Here, j indicates whether the process is adsorption or desorption. U and n L is expressed by the Langmuir equation shown in Equation 2 and Equation 3.

[0059]

number

[0060]

number

[0061] Also, the weight function w j is expressed as Equation 4.

[0062]

number

[0063]

number

number

[0064] In addition, modeling of the change in adsorption / desorption isotherm due to the hysteresis phenomenon depending on the pressure operation conditions was performed based on the following paper (Hefti et al. Adsorption 20.2-3 (2014): 359-371). In this model, as shown in Figure 9, the adsorption amount n switch Saturation adsorption amount n sat The isothermal equation after switching is a contraction of the isothermal equation shown in Equation 1, which is the ratio of the adsorption amount to the desorption amount. ads→des , the amount of adsorption when switching from adsorption to desorption is n des→ads These are expressed by Equation 7 and Equation 8, respectively.

[0065]

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[0066]

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[0067] The dynamic model used in the simulation was the same as that used by Ko et al. for the CO2 capture process using zeolite 13X (Ind. Eng. Chem. Res. 2005, 44, 21, 8084-8094). However, the driving force q in the linear driving force model, which determines the direction and rate of adsorption and desorption, was used. * In this proposal, this is expressed as Equation 9.

[0068]

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[0069] The mode in Equation 9 is a binary variable that is 1 during the pressurization-adsorption process and 0 during the depressurization-desorption process. This is expressed in Equation 10.

[0070]

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[0071] The process used to carry out the above simulation is shown below. 1. The gas is an ideal gas. 2. Temperature, pressure, and concentration changes in the pipe diameter direction are not taken into account. 3. The adsorption rate is calculated using the linear driving force (LDF) model. 4. The physical properties of the adsorbent, such as density, do not change with temperature. 5. Pressure loss follows the Elgin formula. 6. The change in flow velocity is calculated using the total material balance equation.

Claims

1. A gas separation method using a gas separation apparatus including at least an adsorption tower packed with a gas adsorbent containing a gate-type porous polymer complex and a gas supply means for supplying a mixed gas containing a plurality of gases to the adsorption tower, the method comprising the steps of a pressurization step, an adsorption step, a depressurization step, and a desorption step in this order: In the pressurization process, a mixed gas containing the plurality of gases is injected into the adsorption tower through an inlet of the adsorption tower with the outlet of the adsorption tower closed, and the pressure at the inlet of the adsorption tower is increased until a partial pressure of the gas to be adsorbed among the plurality of gases at the inlet of the adsorption tower reaches a predetermined pressure that is higher than an adsorption start gate pressure of the gas to be adsorbed among the plurality of gases; In the adsorption process, the outlet of the adsorption tower is opened, and the mixed gas containing the plurality of gases is continuously injected into the inlet of the adsorption tower at the predetermined pressure, thereby adsorbing the adsorption target gas among the plurality of gases onto the gas adsorbent; In the depressurization step, the pressure in the adsorption tower is reduced, and in the desorption step, the reduced pressure state is maintained, and the adsorption target gas adsorbed by the gas adsorbent is recovered; A gas separation method characterized in that the ratio of the partial pressure of the gas to be adsorbed among the plurality of gases at the inlet of the adsorption tower to the adsorption start gate pressure of the gas to be adsorbed is greater than 1.3 and less than 400.

2. 2. The gas separation method according to claim 1, wherein the pressure difference between the adsorption completion gate pressure and the desorption completion gate pressure of the gate-type porous polymer complex is 2 kPa to 8000 kPa.

3. 3. The gas separation method according to claim 1, wherein the gate-type porous polymer complex is an ELM, a Kagome, an MIL, or a CID.

4. A gas separation method described in any one of claims 1 to 3, characterized in that the pressurization process, the adsorption process, the decompression process, and the desorption process are repeated.

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