Gas separation method, method for producing refined gas, and gas separation device

Abstract

Provided is a gas separation method for separating carbon dioxide and a gaseous substance (A) different from the carbon dioxide from a mixed gas containing the carbon dioxide and the gaseous substance (A) using an adsorption tower filled with an adsorbent, the gas separation method comprising: an adsorption step for adsorbing the carbon dioxide and the gaseous substance (A); introducing the mixed gas into the adsorption tower, adsorbing carbon dioxide on the adsorbent, and taking out a gaseous substance A; a cleaning step in which carbon dioxide is introduced into the adsorption tower, the gaseous substance A in the adsorption tower is discharged, and the interior of the adsorption tower is cleaned; and a desorption step in which the carbon dioxide is removed from the adsorbent by decompressing and exhausting the carbon dioxide from the adsorption tower, and the amount Q [NL] of the carbon dioxide introduced into the adsorption tower in the cleaning step satisfies Q < = 5.5 x, where x [L] is the volume of the adsorbent filled in the adsorption tower.

Description

Technical Field

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

[0002] In recent years, the demand for carbon dioxide separation has been growing in order to reduce carbon dioxide emissions. There are several methods for separating carbon dioxide, one of which is separation methods using adsorbents. Among these methods, there are pressure swing adsorption (PSA), where the pressure during gas desorption is lower than the pressure during adsorption, and gas separation is performed using the difference between the adsorption amount at high pressure and the adsorption amount at low pressure; and temperature swing adsorption (TSA), where the temperature during gas desorption is higher than the temperature during adsorption, and gas separation is performed using the difference between the adsorption amount at low temperature and the adsorption amount at high temperature. There is also a combination of these methods, pressure swing and temperature swing adsorption (PTSA).

[0003] For example, as a method for producing carbon dioxide that can extract high-purity methane and high-purity carbon dioxide from biogas, a method for producing carbon dioxide that separates methane and carbon dioxide from biogas by pressure swing adsorption using an adsorption tower filled with an adsorbent has been disclosed (Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-67504 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] As a method for producing higher-purity carbon dioxide, there is the following method: after circulating biogas through an adsorption tower, a cleaning operation is performed by circulating carbon dioxide through the adsorption tower to flush out methane remaining in the space and methane adhering to the adsorbent. After reducing the methane in the adsorption tower as much as possible, vacuuming is performed to recover the carbon dioxide.

[0009] While washing can produce high-purity carbon dioxide and improve methane recovery, the adsorbent absorbs large amounts of carbon dioxide. When using porous materials such as zeolite and activated carbon as adsorbents, the adsorption of large amounts of carbon dioxide causes the porous material to expand. Adsorbent molded bodies formed using a binder have the potential to rupture or pulverize due to this expansion, increasing the likelihood of the adsorbent becoming brittle, such as pulverization.

[0010] The present invention relates to a gas separation method, a method for producing a purified gas, and a gas separation apparatus for separating carbon dioxide from a gaseous substance A, which are capable of suppressing pulverization of an adsorbent even when obtaining high-purity carbon dioxide.

[0011] Means for solving problems

[0012] The present inventors have found that by using a porous body that has a low carbon dioxide adsorption capacity as an adsorbent during the cleaning operation, it is possible to suppress the occurrence of pulverization of the adsorbent even when obtaining high-purity carbon dioxide.

[0013] The present invention includes the following embodiments.

[0014] <1>

[0015] A gas separation method is a gas separation method for separating carbon dioxide and the gas substance A from a mixed gas containing carbon dioxide and a gas substance A different from carbon dioxide using an adsorption tower filled with an adsorbent, wherein:

[0016] The method comprises the following steps:

[0017] Adsorption step, introducing the mixed gas into the adsorption tower, allowing carbon dioxide to be adsorbed on the adsorbent, and removing gaseous substance A;

[0018] a cleaning step of introducing carbon dioxide into the adsorption tower, discharging the gaseous substance A in the adsorption tower, and cleaning the adsorption tower; and

[0019] The desorption step is to decompress and exhaust the carbon dioxide from the adsorption tower, thereby removing the carbon dioxide from the adsorbent.

[0020] When the volume of the adsorbent filled in the adsorption tower is defined as x [L], the amount Q [NL] of carbon dioxide introduced into the adsorption tower in the cleaning step satisfies Q ≤ 5.5x.

[0021] <2>

[0022] like <1> The gas separation method, wherein the carbon dioxide adsorption amount per 1g of the above-mentioned adsorbent under the conditions of a temperature of 35°C and 40kPa is set to V1, and the carbon dioxide adsorption amount per 1g of the above-mentioned adsorbent under the conditions of a temperature of 35°C and 100kPa is set to V2, the above-mentioned adsorbent in the above-mentioned adsorption process satisfies (V2-V1) / V1≤0.160.

[0023] <3>

[0024] like <1> or <2> The gas separation method, wherein:

[0025] In the adsorption step, the adsorption tower is pressurized.

[0026] When the amount of carbon dioxide adsorbed per 1 g of the adsorbent at a temperature of 35° C. and 100 kPa is defined as V2, and the amount of carbon dioxide adsorbed per 1 g of the adsorbent at a temperature of 35° C. and 200 kPa is defined as V3, the adsorbent satisfies (V3−V2) / V2≤0.155.

[0027] The method includes:

[0028] The depressurization step is to reduce the pressure in the adsorption tower after the adsorption step and before the cleaning step.

[0029] <4>

[0030] like <1> ~ <3> In any one of the gas separation methods, the recovery rate of the gaseous substance A is 90% or higher relative to the total amount of the gaseous substance A in the mixed gas introduced into the adsorption tower in the adsorption step.

[0031] <5>

[0032] like <1> ~ <4> The gas separation method according to any one of the preceding claims, wherein the carbon dioxide is introduced into the adsorption tower in the cleaning step using the exhaust pressure of a vacuum pump that decompresses and exhausts the carbon dioxide from the adsorption tower in the desorption step.

[0033] <6>

[0034] like <1> ~ <5> In any one of the gas separation methods, the amount Q[NL] of carbon dioxide introduced into the adsorption tower in the cleaning step satisfies Q>0.10x.

[0035] <7>

[0036] like <1> ~ <6> The gas separation method according to any one of the preceding claims, wherein in the cleaning step, the start or end of the introduction of carbon dioxide into the adsorption tower is performed by time control.

[0037] <8>

[0038] like <1> ~ <7> The gas separation method according to any one of the preceding claims, wherein the purity of the recovered gaseous substance A is 90% by volume or higher.

[0039] <9>

[0040] like <1> ~ <8> The gas separation method according to any one of the preceding claims, wherein the purity of the recovered carbon dioxide is 90% by volume or higher.

[0041] <10>

[0042] like <1> ~ <9> The gas separation method according to any one of the preceding claims, wherein the V1 in the adsorbent satisfies V1≥20 cc / g.

[0043] <11>

[0044] like <1> ~ <10> The gas separation method according to any one of the preceding claims, wherein the adsorbent is zeolite.

[0045] <12>

[0046] like <11> In the gas separation method, the adsorbent is GIS type zeolite.

[0047] <13>

[0048] like <1> ~ <12> The gas separation method according to any one of the preceding claims, wherein the average temperature in the adsorption step is 0° C. or higher.

[0049] <14>

[0050] like <1> ~ <13> The gas separation method according to any one of the preceding claims, wherein the final pressure P in the desorption step is b Below 30kPa.

[0051] <15>

[0052] like <1> ~ <14> The gas separation method according to any one of the preceding claims, wherein the average temperature in the desorption step is 150° C. or lower.

[0053] <16>

[0054] like <1> ~ <15> The gas separation method according to any one of the preceding claims, wherein the water content of the mixed gas is 1000 ppm by volume or less.

[0055] <17>

[0056] like <1> ~ <16> The gas separation method according to any one of the preceding claims, wherein the gas substance A is at least one selected from the group consisting of methane, ethane, nitrogen, carbon monoxide, hydrogen, argon and dimethyl ether.

[0057] <18>

[0058] A method for producing a purified gas, wherein <1> ~ <17> Any one of the gas separation methods described above can produce purified gaseous substance A or purified carbon dioxide.

[0059] <19>

[0060] A gas separation device is a gas separation device for separating carbon dioxide and a gas substance A different from carbon dioxide from a mixed gas containing the carbon dioxide and the gas substance A, wherein:

[0061] The gas separation device has:

[0062] an adsorption tower filled with an adsorbent for adsorbing carbon dioxide,

[0063] a gaseous substance A recovery line, which takes out the gaseous substance A from the above-mentioned adsorption tower;

[0064] a carbon dioxide recovery line having a pressure reducing device for removing carbon dioxide from the adsorption tower;

[0065] a carbon dioxide storage tank for storing carbon dioxide sent from the carbon dioxide recovery pipeline; and

[0066] a carbon dioxide purge line that supplies carbon dioxide from the carbon dioxide storage tank to the adsorption tower;

[0067] When the carbon dioxide adsorption amount per 1g of the adsorbent at 35°C and 40kPa is V1 and the carbon dioxide adsorption amount per 1g of the adsorbent at 35°C and 100kPa is V2, the adsorbent satisfies (V2-V1) / V1≤0.160.

[0068] Effects of the Invention

[0069] According to the present invention, a gas separation method, a method for producing a purified gas, and a gas separation apparatus for separating carbon dioxide from a gaseous substance A can be provided, which can suppress pulverization of an adsorbent even when obtaining high-purity carbon dioxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 1 is a diagram showing a schematic configuration of the gas separation device 100 .

[0071] Figure 2 Schematic diagram showing temporal changes in pressure fluctuations in the carbon dioxide adsorption tower 3 a and the carbon dioxide adsorption tower 3 b due to the operation of the gas separation device 100 .

[0072] Figure 3 1 is a diagram showing a schematic configuration of a biogas refining system 1000 in which the gas separation device 100 is applied to biogas refining. DETAILED DESCRIPTION

[0073] Hereinafter, a specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail. The present invention is not limited to the following description, and various modifications can be made within the scope of the gist of the invention.

[0074] [Gas separation method]

[0075] The gas separation method of this embodiment is a gas separation method for separating carbon dioxide and the gas substance A from a mixed gas containing carbon dioxide and a gas substance A different from carbon dioxide using an adsorption tower filled with an adsorbent, wherein the method includes the following steps:

[0076] Adsorption step, introducing the mixed gas into the adsorption tower, allowing carbon dioxide to be adsorbed on the adsorbent, and removing gaseous substance A;

[0077] a cleaning step of introducing carbon dioxide into the adsorption tower, discharging the gaseous substance A in the adsorption tower, and cleaning the adsorption tower; and

[0078] The desorption step is to decompress and exhaust the carbon dioxide from the adsorption tower, thereby removing the carbon dioxide from the adsorbent.

[0079] When the volume of the adsorbent filled in the adsorption tower is defined as x[NL], the amount Q[L] of carbon dioxide introduced into the adsorption tower in the cleaning step satisfies Q<5.5×x.

[0080] According to the above-mentioned structure, a gas separation method, a method for producing a purified gas and a gas separation device for separating carbon dioxide from gaseous substance A can be provided, which can suppress the occurrence of adsorbent rupture or pulverization even when the recovery rate of gaseous substance A (such as methane) is improved or high-purity carbon dioxide is obtained.

[0081] The amount of carbon dioxide used in cleaning is related to improving the recovery rate of the gas substance A to be recovered until it reaches a certain level. However, it will cause an increase in the maximum expansion amount due to the adsorption of the adsorbent to the saturated adsorption amount or an amount close to it, and therefore has a tendency to cause the adsorbent to break and pulverize.

[0082] The adsorption of gas is an equilibrium state of adsorption and desorption. If more carbon dioxide than the amount required for cleaning is circulated, the adsorption and desorption of carbon dioxide will be excessive, and expansion and contraction will be repeated, especially at the interface of particles with adsorption sites where carbon dioxide molecules can easily flow, and the possibility of cracking will be high. Therefore, it is preferred that the amount of carbon dioxide circulated during cleaning is small. The inventors have found that the purpose of using carbon dioxide for cleaning is to wash away the gas substance A remaining in the gap, and the amount of cleaning gas that can be fully cleaned without the adsorbent cracking or pulverizing can be defined based on the volume of the adsorbent filled in the adsorption tower.

[0083] In the gas separation method of the present embodiment, it is preferred that the purity of the carbon dioxide extracted through one desorption step is 90% by volume or higher.

[0084] The above configuration enables efficient separation of high-purity carbon dioxide and gaseous substance A. In the gas separation method of this embodiment, carbon dioxide and gaseous substance A are obtained as purified gases. In the gas separation method of this embodiment, the adsorption step, the cleaning step, and the desorption step can be repeated depending on the purity of the target purified gas. By repeating these steps, a high-purity purified gas can be obtained.

[0085] It should be noted that the recovery rate of gaseous substance A removed through the first adsorption step refers to the recovery rate after the second cycle in the pressure fluctuation cycle. During the initial pressure fluctuation cycle (at startup), the adsorbent is in a state where almost no carbon dioxide is adsorbed. However, after the second cycle in the pressure fluctuation cycle, the adsorption step begins after a predetermined amount of carbon dioxide has been adsorbed. Therefore, the recovery rate after the second cycle is considered the recovery rate of gaseous substance A removed through the first adsorption step.

[0086] “One adsorption step”, “one cleaning step” and “one desorption step” refer to one pressure fluctuation cycle of the adsorption tower based on the adsorption step, the cleaning step and the desorption step.

[0087] <Gaseous substance A>

[0088] The gaseous substance A may be any gaseous substance other than carbon dioxide. "Gaseous substance" refers to a substance that is gaseous at room temperature (25°C) and normal pressure. Examples of the gaseous substance A include methane, ethane, nitrogen, carbon monoxide, hydrogen, argon, and dimethyl ether. Of these gaseous substances A, methane, ethane, and nitrogen are preferred, methane and ethane are more preferred, and methane is even more preferred.

[0089] <Mixed gas>

[0090] The mixed gas used as a raw material contains carbon dioxide and gaseous substance A.

[0091] The carbon dioxide content in the mixed gas may be 1% by volume or more, 5% by volume or more, 10% by volume or more, 20% by volume or more, or 30% by volume or more. Alternatively, the carbon dioxide content in the mixed gas may be 99% by volume or less, 90% by volume or less, 80% by volume or less, or 70% by volume or less.

[0092] The content of the gaseous substance A in the mixed gas may be 1% by volume or more, 5% by volume or more, 10% by volume or more, 20% by volume or more, or 30% by volume or more. Alternatively, the gaseous substance A in the mixed gas may be 99% by volume or less, 90% by volume or less, 80% by volume or less, or 70% by volume or less.

[0093] The water content of the mixed gas is preferably 1000 ppm by volume or less, more preferably 500 ppm by volume or less, and even more preferably 100 ppm by volume or less. A water content within this range allows the adsorbent to exhibit high adsorption performance. The water content of the mixed gas can be measured, for example, using a dew point meter and can be converted to water content using the method described in JIS Z8806:2001.

[0094] <Adsorption process>

[0095] The adsorption tower is filled with an adsorbent. The tower is configured to allow the introduction of a mixed gas and contact of the adsorbent with the mixed gas. The adsorption process allows the mixed gas and adsorbent to contact each other, causing carbon dioxide in the mixed gas to be adsorbed by the adsorbent. The adsorption of carbon dioxide in the mixed gas allows the removal of gaseous substance A.

[0096] As described in detail below, the adsorbent in the adsorption tower uses inorganic porous materials such as zeolite, silica, and alumina. When the adsorbent is an inorganic porous material such as zeolite, silica, and alumina, the bulk density is 0.9 to 1.3 g / cc. When the adsorbent is cylindrical or spherical, the diameter is 1 to 10 mm and the length is about 3 to 20 mm. In addition to such shapes, there are also honeycomb structures, rings, macaroni shapes, etc. Regardless of the shape, the adsorbent filling rate (the proportion of the adsorbent in the volume of the fixed bed) when filled in the adsorption tower is 60 to 90 vol%, and the porosity (the proportion of the gaps between adsorbents. Although the adsorbent is porous, the volume of the pores inside the adsorbent is not included) is 10 to 40 vol%.

[0097] Adsorption pressure P in the adsorption process a It is preferably 50 to 3000 kPa, more preferably 60 to 2500 kPa or less, and even more preferably 70 to 2000 kPa or less. aIt refers to the pressure near the inlet of the adsorption tower where the mixed gas is introduced.

[0098] In the adsorption process, the adsorption tower can be pressurized. The pressurized state refers to a pressure exceeding 101.3 kPa. In the case of the pressurized state, the adsorption pressure P in the adsorption process is a It is preferably 102 to 3000 kPa, more preferably 150 to 2500 kPa or less, and even more preferably 200 to 2000 kPa or less.

[0099] Carbon dioxide partial pressure P in the adsorption process a-CO2 It is preferably 1 to 500 kPa, more preferably 10 to 400 kPa, and even more preferably 20 to 400 kPa. CO2 This can be adjusted by adjusting the pressure of the mixed gas and the concentration of carbon dioxide in the mixed gas.

[0100] From the perspective of improving the desorption efficiency of carbon dioxide in the subsequent desorption step and reducing the power per unit amount of the mixed gas to be treated, the average temperature during the adsorption step is preferably 0°C or higher, preferably 10°C or higher, and more preferably 25°C or higher. Furthermore, the average temperature during the adsorption step is preferably 400°C or lower, more preferably 300°C or lower, and even more preferably 200°C or lower. The average temperature during the adsorption step refers to the average temperature of the gas near the outlet of the adsorption tower during the adsorption step.

[0101] <Pressure Reduction Process>

[0102] If the pressure in the adsorption process is higher than the pressure in the cleaning process, a pressure reduction step may be included before the cleaning process to reduce the pressure in the adsorption tower to the pressure of the cleaning process (e.g., atmospheric pressure). By recycling the gas released during the pressure reduction as the raw gas, the recovery rate of the gaseous substance A can be increased. However, increasing the amount of gas to be recycled increases the power used by the compression pump and vacuum pump, so it is preferable to balance the target recovery rate and power costs when setting the pressure reduction step.

[0103] Preferably, in the adsorption step, the interior of the adsorption tower is pressurized.

[0104] When the amount of carbon dioxide adsorbed per 1 g of the adsorbent at a temperature of 35° C. and 100 kPa is defined as V2 and the amount of carbon dioxide adsorbed per 1 g of the adsorbent at a temperature of 35° C. and 200 kPa is defined as V3, the adsorbent satisfies (V3−V2) / V2≤0.155.

[0105] The method includes a pressure reducing step of reducing the pressure in the adsorption tower after the adsorption step and before the cleaning step.

[0106] A higher carbon dioxide adsorption capacity allows for more efficient carbon dioxide separation and recovery using a smaller amount of adsorbent, making this a preferred method. However, a higher carbon dioxide adsorption capacity during the purge process increases the amount of carbon dioxide required for purge. This not only increases the electricity cost for circulating the carbon dioxide, but also increases the amount of carbon dioxide contained in the adsorbent and the maximum expansion of the adsorbent, increasing the likelihood of pulverization, making this undesirable. Specifically, a smaller slope of the adsorption isotherm is preferred, preferably satisfying (V3 - V2) / V2 ≤ 0.155. Within the preferred range of (V3 - V2) / V2, while the likelihood of pulverization is reduced, the purge process incurs electricity costs for introducing the carbon dioxide used for purge. Therefore, by including a pressure reduction step, the carbon dioxide adsorbed on the adsorbent is desorbed and can be used as part of the carbon dioxide used for purge, thus suppressing increases in electricity costs. In other words, by satisfying this condition, even when the pressure during the adsorption process is higher than that during the purge process, pulverization of the adsorbent can be suppressed, and increases in electricity costs can be minimized.

[0107] <Cleaning process>

[0108] By performing a cleaning step after the adsorption step, namely, introducing carbon dioxide into the adsorption tower, discharging the gaseous substance A in the adsorption tower, and cleaning the adsorption tower, the purity of the purified carbon dioxide obtained in the desorption step described later can be improved, and the recovery rate of the gaseous substance A can be increased. In the cleaning step, carbon dioxide is circulated within the adsorption tower, replacing a portion of the gaseous substance A adsorbed on the adsorbent with carbon dioxide, and flushing away the gaseous substance A remaining in the air, thereby increasing the carbon dioxide concentration within the adsorption tower.

[0109] The cleaning step is a step of flowing recovered carbon dioxide or previously prepared carbon dioxide through the adsorption tower that has completed the adsorption step to flush the gaseous substance A adsorbed in the voids and adsorbent in the adsorption tower and expel it from the adsorption tower.

[0110] The inventors have discovered that the amount of carbon dioxide used in cleaning is correlated with an increase in the recovery rate of the desired gas substance A until it reaches a certain level. However, adsorption of the adsorbent to or near the saturated adsorption amount causes an increase in the maximum expansion amount, which tends to cause the adsorbent to break and pulverize.

[0111] When the recovered carbon dioxide is used, the larger the amount of gas introduced during cleaning, the larger the amount of gas to be recycled, and the higher the electricity cost.

[0112] Research into conditions for achieving a sufficient cleaning effect without causing adsorbent breakage or pulverization has shown that the amount of carbon dioxide used for cleaning, Q[NL], preferably satisfies Q≤x×5.5. More preferably, Q[NL] satisfies Q≤x×5.3, and even more preferably, Q≤x×5.0.

[0113] When the adsorbent is an inorganic porous material such as zeolite, silica, or alumina, the maximum gas adsorption capacity is 20 to 110 times the adsorbent volume. However, repeated adsorption and desorption require a high vacuum to completely desorb the adsorbed gas. Therefore, it is preferable to set the actual adsorption capacity to 5 to 40 times the volume, rather than performing complete desorption and regeneration. Despite this, the adsorbent can also adsorb gas volumes far greater than the volume of the adsorbent. Considering the actual adsorption capacity, the above range is preferred.

[0114] The inventors of this application believe that, based on the properties of the adsorbent, the pores within the adsorbent accommodate a much larger number of gas molecules than the volume of the adsorbent itself, maintaining equilibrium even under saturation. Therefore, despite the entry and exit of gas molecules, regardless of the type or shape of the adsorbent, the amount of carbon dioxide introduced during the cleaning process should be considered to be at least the amount required to expel the gas from the pores, that is, the amount of gas equivalent to the volume of the pores. Therefore, assuming the volume of the adsorbent filled in the adsorption tower is x [L], the amount of carbon dioxide introduced into the adsorption tower during the cleaning process, Q [NL], preferably satisfies Q > 0.10 × x, more preferably Q > 0.12 × x, and even more preferably Q > 0.16 × x.

[0115] The volume of the adsorbent is determined by adding the adsorbent to a graduated cylinder filled with paraffin wax. The volume per unit mass of the adsorbent is calculated based on the rise in the liquid level and the mass of the adsorbent added. The volume of the adsorbent loaded into the adsorption tower can be determined based on the mass of the adsorbent loaded and the volume per unit mass calculated using the above method.

[0116] Increasing the amount of carbon dioxide used in cleaning increases the amount of carbon dioxide circulating within the adsorption tower, which in turn increases the amount of carbon dioxide exposed to the adsorbent. Adsorption is essentially a state of equilibrium in which adsorption and desorption repeat. Increasing the amount of carbon dioxide exposed to the adsorbent increases the number of adsorption and desorption cycles, leading to increased expansion and contraction, and thus increasing the likelihood of cracking or pulverization of the adsorbent. Therefore, by adjusting the amount of carbon dioxide used in cleaning, cracking and pulverization can be prevented while maintaining a high recovery rate.

[0117] Regarding the pressure P in the adsorption tower during the cleaning process c In order to fully replace the gas substance A adsorbed on the adsorbent with carbon dioxide, the pressure P is preferably cOn the other hand, if the pressure is high, additional energy for pressurization will be required. Therefore, in order to reduce energy costs such as electricity, it is preferred to have a low pressure. From these aspects, the pressure Pc is preferably 50 to 500 kPa, more preferably 70 to 450 kPa, and even more preferably 85 to 400 kPa. It should be noted that, from the same aspect, the carbon dioxide partial pressure P in the cleaning process is c-CO2 It is preferably 50 to 300 kPa, more preferably 70 to 200 kPa, and even more preferably 85 to 130 kPa.

[0118] Alternatively, the carbon dioxide can be introduced into the adsorption tower in the cleaning step by utilizing the exhaust pressure of the vacuum pump that decompresses and exhausts the carbon dioxide from the adsorption tower in the desorption step. This configuration can save energy required for the gas separation method.

[0119] From the perspective of improving the desorption efficiency of carbon dioxide in the subsequent desorption process and reducing the power per unit amount of the mixed gas to be treated, the average temperature in the cleaning process is preferably above 0°C, preferably above 10°C, and more preferably above 25°C. In addition, the average temperature in the cleaning process is preferably below 200°C, more preferably below 120°C, and more preferably below 90°C. The average temperature in the cleaning process refers to the average temperature of the gas near the outlet of the adsorption tower in the cleaning process. The higher the temperature of the cleaning process, the more it can promote the desorption of carbon dioxide in the subsequent desorption process, and therefore it is preferred, but it is necessary to preheat the gas used in the cleaning, etc., and additional equipment is required. Therefore, a temperature that can be used for cleaning without heating the gas is preferred.

[0120] <Desorption Process>

[0121] After the adsorption step, the carbon dioxide can be removed by reducing the pressure in the adsorption tower in the desorption step. Thus, purified gas of the gaseous substance A and purified gas of carbon dioxide are obtained through the adsorption and desorption steps.

[0122] Final pressure P in the desorption process b It is preferably 50 kPa or less, more preferably 30 kPa or less, further preferably 20 kPa or less, further preferably 15 kPa or less, further preferably 12 kPa or less, further preferably 10 kPa or less, further preferably 9 kPa or less. Final pressure P b This refers to the pressure near the exhaust outlet of an adsorption tower filled with adsorbent when the decompression exhaust is carried out.

[0123] From the perspective of improving the desorption efficiency of carbon dioxide and reducing the power of the mixed gas to be treated per unit amount, the average temperature in the desorption process is preferably above 0°C, more preferably above 10°C, and further preferably above 25°C. In addition, the average temperature in the desorption process is preferably below 200°C, more preferably below 120°C, and further preferably below 90°C. The average temperature in the desorption process refers to the average temperature of the desorbed gas (carbon dioxide) near the outlet of the adsorption tower in the desorption process. The higher the desorption temperature, the more it promotes the desorption of carbon dioxide, and therefore it is preferred. However, if the temperature of the adsorbent is high, the amount of carbon dioxide adsorbed in the subsequent adsorption process will decrease, so it is preferred to perform desorption within an appropriate temperature range.

[0124] The purity of carbon dioxide extracted in one desorption step is preferably 90% by volume or higher, more preferably 92% by volume or higher, further preferably 93% by volume or higher, and even more preferably 94% by volume or higher.

[0125] In the gas separation method of this embodiment, the purity of the gas substance A extracted through a single adsorption step is preferably 93% by volume or more, more preferably 94% by volume or more, and even more preferably 95% by volume or more. In order to extract the gas substance A of the preferred purity, it is preferable to use an adsorbent with a strong adsorption capacity for carbon dioxide. When a mixed gas of carbon dioxide and gas substance A is circulated in an adsorption tower, if an adsorbent with a strong adsorption capacity for carbon dioxide is used, the adsorbed carbon dioxide is less likely to desorb and leak out, and less likely to be mixed into the extracted gas substance A, thereby increasing the purity of the gas substance A. For adsorbents with a strong adsorption capacity for carbon dioxide, the adsorption capacity quickly reaches a saturation adsorption capacity at a low carbon dioxide partial pressure. The strength of the adsorption capacity is also expressed as V1 and V2. When V1 reaches a value close to V2, it means that the adsorption capacity is close to that at 100 kPa even under 40 kPa conditions, and can be simply evaluated as the value of (V2-V1) / V1. From this viewpoint, the preferred ratio (V2-V1) / V1 is preferably 0.160 or less, more preferably 0.155 or less, and even more preferably 0.150 or less.

[0126] The recovery rate of carbon dioxide removed through one adsorption process and one desorption process is preferably 90% or more, more preferably 93% or more, and further preferably 95% or more relative to the total amount of carbon dioxide in the mixed gas introduced into the adsorption tower through one adsorption process. It should be noted that the recovery rate of carbon dioxide removed through one adsorption process and one desorption process refers to the recovery rate after the second cycle in the pressure change cycle. The adsorbent at the first time of the pressure change cycle (at the time of startup) is in a state where carbon dioxide is almost not adsorbed, but after the second cycle in the pressure change cycle, the adsorption process is started in a state where a specified amount of carbon dioxide has been adsorbed in the previous cycle. Therefore, the recovery rate after the second cycle is taken as the recovery rate of carbon dioxide removed through one adsorption process and one desorption process.

[0127] According to this embodiment, carbon dioxide and gaseous substance A (methane in this embodiment) can be separated and recovered, and pulverization can be suppressed on the basis of the respective purity and recovery rate becoming appropriate conditions, thereby achieving durable separation and recovery of carbon dioxide and gaseous substance A.

[0128] The purity of the gaseous substance A recovered by this embodiment varies depending on the location of implementation and how the gaseous substance A is used, but is preferably 90% by volume or greater, more preferably 92% by volume or greater, even more preferably 93% by volume or greater, and even more preferably 95% by volume or greater. If the gaseous substance A is methane, a purity of 90% by volume or greater is preferred because it has a sufficient calorific value for use as a fuel. Furthermore, high-purity methane is more preferred because it can be used as a natural gas substitute and has a higher calorific value.

[0129] A higher recovery rate of gaseous substance A is preferred because the production of gaseous substance A per unit amount of raw material increases, leading to cost reduction. The recovery rate of gaseous substance A is preferably 90% or higher, more preferably 92% or higher, even more preferably 93% or higher, and even more preferably 95% or higher.

[0130] The purity of the carbon dioxide recovered by this embodiment is preferably 90% by volume or higher, more preferably 92% by volume or higher, even more preferably 93% by volume or higher, and even more preferably 94.0% by volume or higher. Regarding the purity of carbon dioxide, when used as a raw material for carbonic acid gas or dry ice or when compressed for transportation, a high purity is preferred because it can reduce electricity costs, etc.

[0131] A higher carbon dioxide recovery rate is preferred because the production of carbon dioxide and gaseous substance A per unit amount of raw material increases, leading to cost reduction. The carbon dioxide recovery rate is preferably 90% or higher, more preferably 92% or higher, even more preferably 93% or higher, and even more preferably 96% or higher.

[0132] <Adsorbent>

[0133] The adsorbent preferably has a high carbon dioxide adsorption capacity at the carbon dioxide partial pressure when the mixed gas is introduced during the adsorption step, and does not adsorb more carbon dioxide even when a higher carbon dioxide partial pressure is introduced. Since the carbon dioxide concentration in exhaust gas and the peak carbon dioxide concentration in biogas are often 40% by volume, it is preferable to have a high adsorption capacity V1 at a carbon dioxide partial pressure of 40 kPa. The adsorption capacity V1 is preferably 10 cc / g or greater, more preferably 15 cc / g or greater, and even more preferably 20 cc / g or greater. Because porous materials such as zeolite adsorb the adsorbent within the pores within the crystals, a greater adsorption capacity leads to greater expansion. Therefore, in the case of saturated adsorption, that is, when the difference V2 - V1 between the adsorption capacity V2 and V1 at a carbon dioxide partial pressure of 100 kPa is small, the amount of carbon dioxide adsorbed during the cleaning step after the adsorption step is reduced. A smaller V2 - V1 ratio can reduce the amount of carbon dioxide used in cleaning, reduce electricity costs for carbon dioxide recovery, and further reduce expansion of the adsorbent caused by carbon dioxide adsorption. Regarding V2-V1, since it changes when diluted with the carrier amount, etc., it can be standardized by dividing V2-V1 by V1. That is, if (V2-V1) / V1 is within the preferred range, the amount of carbon dioxide required in the cleaning process can be reduced, and expansion during cleaning can be suppressed. Therefore, even if the adsorbent material is brittle, cracking and powdering can be reduced, and carbon dioxide can be separated and recovered without reducing the durability of the adsorbent. If (V2-V1) / V1 is not within the preferred range, if the amount of carbon dioxide used in cleaning can be increased within the range that satisfies Q≤x×5.5, the purity of the recovered carbon dioxide can be improved while suppressing the powdering of the adsorbent.

[0134] Using an adsorbent that satisfies (V2 - V1) / V1 ≤ 0.160 can improve the recovery rate of gaseous substance A, such as methane. When using an adsorbent with a (V2 - V1) / V1 ratio exceeding 0.160, a large amount of carbon dioxide introduced for cleaning is adsorbed by the adsorbent. This tends to prevent the gaseous substance A remaining in the adsorption tower from being expelled from the adsorption tower. If the carbon dioxide is desorbed and recovered in this state, gaseous substance A is also recovered along with the carbon dioxide, reducing the purity of the recovered carbon dioxide and the recovery rate of gaseous substance A.

[0135] (V2-V1) / V1 is preferably less than 0.160, more preferably less than 0.155, and further preferably less than 0.150. In order to obtain an adsorbent within this range, it is preferred to use a porous body with high adsorption energy. If the adsorption energy is high, adsorption can be achieved even at a low carbon dioxide partial pressure, and the adsorption saturation state can be approached more quickly. Therefore, the adsorption amount V1 becomes larger and the adsorption amount V2 becomes smaller, and an adsorbent with a preferred (V2-V1) / V1 can be obtained. As materials with high carbon dioxide adsorption energy, hydrophilic zeolites such as LTA zeolite, FAU zeolite, GIS zeolite, and CHA zeolite with a low silica-alumina ratio can be cited.

[0136] When the mixed gas is introduced at a higher pressure during the adsorption step than during the purge step, some of the carbon dioxide adsorbed on the adsorbent is released when the gas pressure in the adsorption column is reduced during the depressurization step. Therefore, in addition to adsorbents having the preferred ratio (V2 - V1) / V1, a method has been discovered that satisfies Q ≤ x × 5.5, suppressing pulverization and improving the recovery rate of gaseous substance A. Specifically, assuming the carbon dioxide adsorption per gram of adsorbent at 35°C and 200 kPa is V3, an adsorbent that satisfies (V3 - V2) / V2 ≤ 0.155 can be used. (V3 - V2) / V2 represents the slope of the carbon dioxide adsorption isotherm at pressures above 100 kPa. A larger (V3 - V2) increases the amount of carbon dioxide released before purge, reducing the amount of carbon dioxide required for purge. However, a larger V3 results in a higher maximum carbon dioxide absorption, which increases the maximum expansion during the adsorption step and increases the likelihood of cracking and pulverization. Furthermore, a larger (V3 - V2) ratio increases the difference in carbon dioxide adsorption between the adsorption and purging steps, i.e., the greater the shrinkage, the greater the strain on the adsorbent, and the greater the likelihood of cracking and pulverization. Using an adsorbent with (V3 - V2) / V2 ≤ 0.155 can reduce the difference in expansion and contraction between the adsorption and purging steps, preventing adsorbent pulverization. A more preferred (V2 - V1) / V1 ratio is 0.150 or less, even more preferably 0.140 or less, and even more preferably 0.135 or less.

[0137] The adsorbent preferably has an adsorption selectivity of carbon dioxide to gaseous substance A of 10 or greater. By using an adsorbent having a high adsorption selectivity of carbon dioxide to gaseous substance A, the recovery rate of gaseous substance A removed in a single adsorption step and the purity of carbon dioxide removed in a single desorption step can be improved.

[0138] Regarding the adsorption selectivity, q(CO2) / q(GMA) was taken as the adsorption selectivity when the equilibrium adsorption amounts of carbon dioxide and gaseous substance A at 760 mmHg obtained by measuring the adsorption isotherm were defined as q(CO2) and q(GMA), respectively.

[0139] The adsorption selectivity of the adsorbent for carbon dioxide / gas substance A is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more.

[0140] As the adsorbent, a solid adsorbent is preferably used. More specifically, examples of the adsorbent include zeolite, metal organic framework (MOF), carbonaceous coke, activated carbon, regenerated activated carbon, carbon black, graphite, silicon oxide, silica gel, alumina clay, and metal oxides. Among these, zeolite is preferably used.

[0141] Examples of zeolite include CHA zeolite, GIS zeolite, FAU zeolite, MWF zeolite, and LTA zeolite. Among these, GIS zeolite is preferred.

[0142] In GIS type zeolite, silicon oxide and aluminum oxide are preferably the main components. The main component refers to a component that accounts for 51% by mass or more.

[0143] GIS zeolite may contain silicon oxide and aluminum oxide. The aluminum content in the GIS zeolite is preferably 1% by mass or greater, more preferably 3% by mass or greater, and even more preferably 5% by mass or greater. The silicon content in the GIS zeolite is preferably 3% by mass or greater, more preferably 5% by mass or greater. The upper limits of the aluminum and silicon contents are preferably such that the SAR (Special Acid Reduction) values, described below, fall within the specified ranges, and are determined based on these SAR values.

[0144] The silica-alumina ratio (indicates the molar ratio of silica to alumina expressed as SiO2 / Al2O3, hereinafter also referred to as "SAR") in GIS zeolite is preferably 3.40 or greater. The lower the SAR of the GIS zeolite, the more hydrophilic it is, and the stronger the adsorption force for polar molecules such as carbon dioxide. If the SAR is low, the adsorption force is too strong, and the energy required for desorption by heating or vacuuming increases, so a high SAR is preferably used. The SAR is more preferably 4.40 or greater, and even more preferably 4.80 or greater. There is no particular upper limit to the SAR, but if the SAR is too high, the interaction with the adsorbate is reduced, so the SAR is preferably 3000 or less, more preferably 500 or less, and even more preferably 100 or less.

[0145] The phosphorus content in the GIS zeolite is preferably 4% by mass or less. The lower limit of the phosphorus content is not particularly limited, and may be 0% by mass or more.

[0146] The Zr content in the GIS-type zeolite is preferably 8% by mass or less. The lower limit of the Zr content is not particularly limited, and may be 0% by mass or more.

[0147] The Ti content in the GIS-type zeolite is preferably 8% by mass or less. The lower limit of the Ti content is not particularly limited, and may be 0% by mass or more.

[0148] From the viewpoint of further improving the selective adsorption capacity of carbon dioxide, the phosphorus atom content in the zeolite is more preferably 1.5% by mass or less, and particularly preferably 0% by mass.

[0149] The contents of aluminum, silicon, phosphorus, Zr, and Ti can be measured by the methods described in the Examples below. Furthermore, the contents of aluminum, silicon, phosphorus, Zr, and Ti can be adjusted to the above-mentioned ranges by, for example, adjusting the composition ratio of the mixed gel used in the synthesis of the GIS-type zeolite to the preferred ranges described below.

[0150] From the perspective of improving the selective adsorption capacity of carbon dioxide, the cationic species in the GIS type zeolite preferably contains potassium or lithium, and more preferably contains potassium. In addition, the total content of potassium and lithium in the zeolite is calculated as the ratio (Z / T) of the total amount of potassium and lithium in the GIS type zeolite (Z) to the total amount of alkali metal (T). Z / T is preferably 0.05 or more, more preferably 0.10 or more, and further preferably 0.15 or more. There is no particular limit to the upper limit of Z / T, and Z / T can be 1.00 or less. Z / T can be measured by thermally dissolving the zeolite with sodium hydroxide aqueous solution or aqua regia and performing ICP-emission spectrometry using an appropriately diluted liquid. Z / T can be measured in more detail by the method described in the examples described later. Z / T can be adjusted by changing the ratio of potassium and lithium in the cationic species of the GIS type zeolite.

[0151] The ratio (K / T) of the total amount of potassium (K) to the total amount of each alkali metal (T) in the GIS zeolite is preferably 0.05 or greater, more preferably 0.10 or greater, and even more preferably 0.15 or greater. The upper limit of K / T is not particularly limited, and K / T may be 1.00 or less.

[0152] [Method for producing adsorbent]

[0153] (Preparation process)

[0154] The above-mentioned GIS type zeolite is obtained, for example, by a manufacturing method including a preparation step of a mixed gel, wherein the mixed gel contains a silicon oxide source containing silicon, an aluminum source containing aluminum, an alkali source containing at least one selected from alkali metals (M1) and alkaline earth metals (M2), a salt compound containing at least one selected from alkali metals (M1) and alkaline earth metals (M2), a phosphorus source containing phosphorus, an organic structure directing agent and water.

[0155] (Hydrothermal Synthesis Process)

[0156] The method for producing GIS-type zeolite preferably further includes a hydrothermal synthesis step at a hydrothermal synthesis temperature of 80°C to 200°C. The hydrothermal synthesis temperature is preferably 100°C to 180°C. The hydrothermal synthesis is performed by maintaining the mixed gel obtained in the preparation step at a predetermined temperature for a predetermined time while stirring or standing. The hydrothermal synthesis time is not particularly limited as long as it is a commonly used time, but is preferably 3 hours to 30 days, more preferably 10 hours to 20 days, and even more preferably 24 hours to 10 days.

[0157] (Separation-Drying Process)

[0158] After the hydrothermal synthesis step, the solid product and the liquid containing water are separated. The separation method is not particularly limited as long as it is a common method. Filtration, decantation, spray drying (rotary spray, nozzle spray and ultrasonic spray, etc.), drying using a rotary evaporator, vacuum drying, freeze drying or natural drying can be used. Separation can usually be carried out by filtration or decantation.

[0159] (Firing process)

[0160] The method for producing GIS zeolite preferably further includes a calcination step at a temperature of 300°C to 650°C. The calcination temperature is more preferably 350°C to 620°C, and even more preferably 360°C to 600°C or lower. The calcination time can be 0.5 hours to 10 days, 1 hour to 7 days, or 3 hours to 5 days. The calcination atmosphere is not particularly limited as long as it is a commonly used atmosphere; air, an inert gas such as nitrogen or argon, or an atmosphere containing oxygen is generally used.

[0161] (Cation Exchange Process)

[0162] The method for producing GIS zeolite preferably further includes a cation exchange step. Cation exchange can be performed using, but is not limited to, carbonates such as sodium carbonate, potassium carbonate, lithium carbonate, rubidium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, and ammonium carbonate; or nitrates such as sodium nitrate, potassium nitrate, lithium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, and ammonium nitrate; or salts obtained by replacing the carbonate ions or nitrate ions contained in the above carbonates or nitrates with halide ions, sulfate ions, carbonate ions, bicarbonate ions, acetate ions, phosphate ions, or hydrogenphosphate ions; or acids such as nitric acid and hydrochloric acid. The cation exchange temperature is not particularly limited as long as it is a typical cation exchange temperature, but is typically between room temperature and below 100°C.

[0163] When separating the zeolite after cation exchange, the separation method is not particularly limited as long as it is a common method. Filtration, decantation, spray drying (rotary spray, nozzle spray and ultrasonic spray, etc.), drying using a rotary evaporator, vacuum drying, freeze drying or natural drying, etc. can be used. Separation can usually be carried out by filtration or decantation.

[0164] [Gas separation device]

[0165] Reference Figure 1 The schematic structure of the gas separation device 100 of the first embodiment will be described. The gas separation device 100 includes a mixed gas supply line 1, carbon dioxide adsorption towers 3a and 3b, a carbon dioxide recovery line 5, a gaseous substance A recovery line 7, and a decompression device 9.

[0166] The carbon dioxide adsorption tower 3a includes a fixed bed 31a filled with an adsorbent, configured to allow contact with the mixed gas introduced therein. One end of the carbon dioxide adsorption tower 3a is connected to the mixed gas supply line 1, and the other end is connected to the gaseous substance A recovery line 7. The gaseous substance A recovery line 7 is equipped with an automatic valve AV3. The gaseous substance A recovery line 7 is equipped with a flow meter 71, a moisture meter 72, and a component analyzer 73. The component analyzer can be any analyzer capable of measuring the concentrations of carbon dioxide and gaseous substance A.

[0167] The carbon dioxide adsorption tower 3a is connected to the carbon dioxide recovery line 5 at the end in the same direction as the end connected to the mixed gas supply line 1. The mixed gas supply line 1 is equipped with a blower 14, a flowmeter 11, a moisture meter 12, and a component analyzer 13. It should be noted that when a pressurized mixed gas is fed into the adsorption tower, the blower 14 can also serve as a compression pump. An automatic valve AV1 is provided at the inlet of the carbon dioxide adsorption tower 3a. Meanwhile, a pressure reducing device 9 is connected to the carbon dioxide recovery line 5, enabling the interior of the carbon dioxide adsorption tower 3a to be depressurized. It should be noted that the pressure reducing device 9 can also be a vacuum pump. Furthermore, the carbon dioxide recovery line 5 connected to the carbon dioxide adsorption tower 3a is equipped with an automatic valve AV5 and a pressure gauge 53a. Furthermore, the carbon dioxide recovery line 5 is equipped with a flowmeter 51, a moisture meter 52, and a component analyzer 53.

[0168] The carbon dioxide adsorption tower 3b includes a fixed bed 31b containing an adsorbent, configured to contact the mixed gas introduced into the tower. An automatic valve AV2 is provided at the entrance of the carbon dioxide adsorption tower 3b. One end of the carbon dioxide adsorption tower 3b is connected to the mixed gas supply line 1, and the other end is connected to the gaseous substance A recovery line 7. The carbon dioxide adsorption tower 3b is also connected to the carbon dioxide recovery line 5 at the same end as the end connected to the mixed gas supply line 1. Furthermore, the carbon dioxide recovery line 5 connected to the carbon dioxide adsorption tower 3b is equipped with an automatic valve AV6 and a pressure gauge 53b.

[0169] The carbon dioxide recovery line 5 is connected to the carbon dioxide tank 2 and can temporarily store the separated and recovered high-purity carbon dioxide. If temporary storage is not required, the carbon dioxide tank 2 can be omitted and the carbon dioxide can be directly exposed to the atmosphere, or a device for incinerating residual combustible gases can be connected. The carbon dioxide tank 2 is connected to a purge line 8, which is further connected to a blower 10 and a flowmeter 81. The system is configured to allow the carbon dioxide temporarily stored in the carbon dioxide tank 2 to circulate through the carbon dioxide adsorption towers 3a and 3b during the cleaning process. When the exhaust pressure of the vacuum pump used for the pressure reducing device 9 is used for cleaning, the blower 10 is not required. Using the exhaust pressure reduces the equipment cost of the blower and reduces electricity consumption, making it economically preferable. By connecting the exhaust pressure of the pressure reducing device 9 to the carbon dioxide tank 2 or the piping 8, carbon dioxide can be introduced into the adsorption tower during the cleaning process without using the blower 10. The pipeline connected to the carbon dioxide adsorption tower 3a is equipped with an automatic valve AV7, and the pipeline connected to the carbon dioxide adsorption tower 3b is equipped with an automatic valve AV8 to switch the adsorption tower to be cleaned.

[0170] Then refer to Figure 1The operation of the gas separation device 100 of this embodiment will be described. A mixed gas is supplied to the carbon dioxide adsorption tower 3a via the mixed gas supply line 1. The carbon dioxide (CO2) contained in the mixed gas is adsorbed by the adsorbent filled within the carbon dioxide adsorption tower 3a, and gaseous substances A, such as methane (CH4), are recovered via the gaseous substance A recovery line 7. Specifically, the carbon dioxide adsorption tower 3a performs the following adsorption process: the mixed gas is introduced into the adsorption tower, carbon dioxide is adsorbed by the adsorbent, and gaseous substances A are removed.

[0171] Carbon dioxide is supplied from the carbon dioxide tank 2 via the purge line 8 to the carbon dioxide adsorption tower 3a containing an adsorbent adsorbed with carbon dioxide. As a result, the gas containing a large amount of gaseous substance A such as methane remaining in the space in the adsorption tower is flushed into the gaseous substance A recovery line 7, and the gaseous substance A adsorbed on the adsorbent is replaced with carbon dioxide, so that the gaseous substance is desorbed and flushed away, thereby improving the recovery rate of the gaseous substance A. The switching of the adsorption tower for cleaning and the opening and closing of the automatic valves AV7 and AV8 for the start and end of cleaning can be controlled by performing the operation when the carbon dioxide concentration in the adsorption tower for cleaning, the amount of gas introduced during cleaning, the concentration of gaseous substance A in the gas containing a large amount of gaseous substance A flushed away by cleaning, and the concentration of carbon dioxide reach a certain value, or by time control. By performing time control, the number of sensors can be reduced, the cost of equipment can be reduced, and a high-responsiveness control can be performed, which is preferred.

[0172] The carbon dioxide adsorption tower 3a, which contains an adsorbent containing adsorbed carbon dioxide, is decompressed and exhausted by the decompression device 9 to regenerate the carbon dioxide adsorption tower 3a and remove the purified carbon dioxide. In other words, a carbon dioxide desorption process is performed in which the carbon dioxide is removed by decompressing and exhausting the carbon dioxide from the adsorption tower.

[0173] As described above, carbon dioxide adsorption tower 3a and carbon dioxide adsorption tower 3b repeatedly perform carbon dioxide adsorption by introducing a mixed gas and carbon dioxide desorption by reducing pressure. Therefore, while carbon dioxide adsorption tower 3a is desorbing carbon dioxide, the mixed gas is introduced into carbon dioxide adsorption tower 3b to adsorb carbon dioxide and perform a cleaning process. After carbon dioxide adsorption tower 3a completes carbon dioxide desorption, the mixed gas is again introduced into carbon dioxide adsorption tower 3a, and the pressure in carbon dioxide adsorption tower 3b is reduced to continue desorbing carbon dioxide. This repeats carbon dioxide adsorption and desorption in each tower, enabling continuous treatment of the mixed gas.

[0174] More specifically, it works as follows. Figure 2Schematic diagram showing the temporal change of the pressure fluctuations in the carbon dioxide adsorption tower 3a and the carbon dioxide adsorption tower 3b due to the operation of the gas separation device 100. Figure 2 Time T 1a , open the automatic valves AV1 and AV3 from the closed state of the automatic valves AV1 to AV8, check the flowmeter 11 so that the mixed gas supply line 1 reaches the specified flow rate, and adjust the mixed gas to the adsorption pressure P a (e.g. 105 kPa) is supplied to the carbon dioxide adsorption tower 3a. When the carbon dioxide concentration in the component analyzer 73 exceeds 5% by volume (e.g. Figure 2 Time T 1b ), the automatic valve AV1 can be closed and the automatic valve AV7 can be opened at the same time to supply carbon dioxide from the carbon dioxide tank 2 to clean the carbon dioxide adsorption tower 3a. When the carbon dioxide concentration in the component analyzer 73 exceeds 8% by volume (for example Figure 2 Time T 1c ), the automatic valves AV7 and AV3 can be closed, while the automatic valves AV2 and AV4 are opened, thereby switching the supply of the mixed gas from the carbon dioxide adsorption tower 3a to the carbon dioxide adsorption tower 3b. Furthermore, in the carbon dioxide adsorption tower 3a, by opening the automatic valve AV5 while the automatic valve AV3 is closed and reducing the pressure using the pressure reducing device 9, the pressure inside the carbon dioxide adsorption tower 3a is reduced, and the pressure in the carbon dioxide adsorption tower 3a reaches the final pressure P b (e.g. 2 kPa) to perform desorption operation, thereby recovering carbon dioxide from the carbon dioxide adsorption tower 3a. b The moment is T 1d Since the carbon dioxide adsorbed on the adsorbent in the carbon dioxide adsorption tower 3a is desorbed, the adsorbent is regenerated while the carbon dioxide is recovered.

[0175] Next, when the carbon dioxide concentration of the gas flowing out of the carbon dioxide adsorption tower 3b exceeds 5% by volume, the automatic valve AV2 can be closed and the automatic valve AV8 can be opened simultaneously to supply carbon dioxide from the carbon dioxide tank 2 to clean the carbon dioxide adsorption tower 3b. When the carbon dioxide concentration in the component analyzer 73 exceeds 8% by volume, the automatic valves AV8 and AV4 can be closed and the automatic valves AV1 and AV3 can be opened simultaneously to switch the supply of the mixed gas from the carbon dioxide adsorption tower 3b to 3a (this time is referred to as T 1e ). In addition, in the carbon dioxide adsorption tower 3b, the pressure of the carbon dioxide adsorption tower 3b is reduced to 2kPa by opening the automatic valve AV6 and using the decompression device 9 to perform a desorption operation, thereby recovering carbon dioxide from the carbon dioxide adsorption tower 3b. The time T shown above 1a ~T 1eThe series of operations described so far constitutes one cycle C1 of pressure fluctuation in the carbon dioxide adsorption tower 3a. This cycle C1 of pressure fluctuation includes one adsorption step and one desorption step. By repeating the same operations, the adsorption and desorption steps can be repeated in a second cycle C2 and a third cycle C3 of pressure fluctuation.

[0176] The gas separation device 100 can be applied to, for example, purification of industrial waste gas containing carbon dioxide, biogas obtained by fermentation of organic matter, etc. Among these, the gas separation device 100 is preferably used for purification of biogas.

[0177] [Biogas Refining System 1000; Application Examples in Biogas Refining]

[0178] Figure 3 This diagram shows the schematic configuration of a biogas refining system 1000 in which a gas separation device 100 is applied to biogas refining. In the biogas refining application example, the system separates and recovers methane and carbon dioxide, the main components of biogas. In biogas refining, gaseous substance A is typically methane (CH4).

[0179] The biogas purification system 1000 of the present embodiment includes a fermentation tank 200 , a desulfurization tower 300 , a siloxane removal device 400 , an oxygen removal device 500 , a cooling device 600 , a dehydration device 700 , and a gas separation device 100 .

[0180] Fermentation tank 200 produces biogas (hereinafter referred to as "mixed gas") by anaerobic fermentation of sewage sludge from sewage treatment plants, food waste from food factories and restaurants, and feces and urine from dairy farms. Fermentation tank 200 is connected to desulfurization tower 300 to supply the generated biogas.

[0181] The fermentation tank 200 can be connected to a desulfurization tower 300 before the biogas is introduced into the gas separation device 100. The desulfurization tower 300 is an adsorption tower for removing hydrogen sulfide contained in the biogas. An example of a desulfurizing agent filled in the desulfurization tower 300 is iron oxide. Iron oxide reacts with hydrogen sulfide contained in the biogas to produce iron sulfide.

[0182] The fermentation tank 200 may be connected to a siloxane removal device 400 before the biogas is introduced into the gas separation device 100. The siloxane removal device 400 removes siloxane contained in the biogas. Siloxane is a substance containing silicon oxide contained in sewage sludge.

[0183] The fermentation tank 200 may be connected to an oxygen removal device 500 before the biogas is introduced into the gas separation device 100. The oxygen removal device 500 removes oxygen contained in the biogas. By removing the oxygen, the purified methane gas can be safely transported.

[0184] The fermentation tank 200 can be connected to a cooling device 600 before the biogas is introduced into the gas separation device 100. The cooling device 600 cools the supplied biogas to remove moisture from the biogas. This lowers the dew point of the biogas. Cooling device 600 can be, for example, a water-cooled cooler, an air-cooled cooler, or an electric cooler.

[0185] The fermentation tank 200 can be connected to a dehydration device 700 before the biogas is introduced into the gas separation device 100. The dehydration device 700 further removes moisture from the biogas after the moisture has been removed by the cooling device 600. This further lowers the dew point of the biogas. For example, a device filled with a dehydrating agent can be used as the dehydration device 700.

[0186] Then refer to Figure 3 The operation of the biogas purification system 1000 according to this embodiment will be described.

[0187] First, biogas is generated by anaerobic fermentation of sewage sludge from sewage treatment plants, food waste from food factories and restaurants, and feces and urine from dairy farms in a fermentation tank 200. The biogas at this stage contains hydrogen sulfide, water, etc.

[0188] The biogas generated in the fermentation tank 200 is sent to the desulfurization tower 300. In the desulfurization tower 300, hydrogen sulfide is removed to a concentration of approximately several ppm by volume. The fermentation tank 200 is connected to a blower 201 to supply the generated biogas to other equipment.

[0189] Thereafter, the biogas from which hydrogen sulfide has been removed is sent to the siloxane removal device 400. In the siloxane removal device 400, the biogas is heated to a concentration of several mg / Nm 3 Remove the silicone in a horizontal manner.

[0190] Thereafter, the biogas from which siloxane has been removed is sent to the oxygen removal device 500. In the oxygen removal device 500, oxygen is removed so that the concentration of oxygen contained in the biogas becomes a level of approximately several ppm by volume.

[0191] The biogas is then sent to a cooling device 600. This cools the biogas, removing moisture from it and lowering its dew point. The biogas is then sent to a dehydration device 700. Dehydration device 700 further removes moisture from the biogas, reducing its water content to below 1000 ppm by volume.

[0192] The biogas from which hydrogen sulfide, siloxane and moisture have been removed is sent to the gas separation device 100. The operation of the gas separation device 100 is the same as that of the gas separation device described above.

[0193] The gas separation method of this embodiment can be implemented by performing the following steps: an adsorption step in which a mixed gas is introduced into an adsorption tower, where carbon dioxide is adsorbed onto an adsorbent and gaseous substance A is removed; a subsequent cleaning step in which carbon dioxide is introduced into the adsorption tower and gaseous substance A is discharged to clean the interior of the tower; and a carbon dioxide desorption step in which carbon dioxide is removed by decompressing and exhausting the adsorption tower. This allows for efficient recovery of high-purity methane and high-purity carbon dioxide. The gas separation method of this embodiment is less susceptible to problems such as clogging due to adsorbent pulverization and can also reduce the amount of carbon dioxide used in cleaning, thereby reducing recovery costs.

[0194] Example

[0195] The present embodiment will be described in further detail below with reference to Examples and the like. However, these are merely illustrative examples, and the present embodiment is not limited to the following Examples.

[0196] <Measurement of Carbon Dioxide Adsorption Amount (V1, V2)>

[0197] The amount of carbon dioxide adsorption was determined by the following procedure.

[0198] (1) 0.2 g of adsorbent was added to a 12 mm sample cell (manufactured by Micro Meritics).

[0199] (2) The sample placed in the sample cell in (1) above was placed in a gas adsorption measuring device "3-Flex" (trade name) manufactured by Micro Meritics and subjected to a heating vacuum degassing treatment at 250°C and 0.001 mmHg or less for 12 hours.

[0200] (3) The sample added to the sample cell after the treatment in (2) above is placed in constant temperature circulating water at 25°C. After the sample temperature reaches 25±0.2°C, measurement is performed using liquefied carbon dioxide gas (manufactured by Sumitomo Seika Co., Ltd., purity 99.9% by mass volume or more) at an absolute pressure of 0.03 to a maximum of 100 kPa. It should be noted that in the above measurement, the pressure is measured over time, and the saturated adsorption amount is determined to have been reached when the pressure fluctuation reaches 0.001% by volume / 10 seconds or less. The carbon dioxide adsorption amount under 40 kPa is defined as V1 (cc / g), and the carbon dioxide adsorption amount under 100 kPa is defined as V2 (cc / g), and (V2-V1) / V1 is calculated.

[0201] Similarly, for the second component gas, a gas with a purity of 99.9 mass / volume % or more is also used, and the measurement is carried out at an absolute pressure of 0.03 to a maximum of 100 kPa. As the adsorption selectivity, when the equilibrium adsorption amounts (cc / g) of carbon dioxide and gas substance A under the condition of 100 kPa obtained by the measurement of the adsorption isotherm are set as q(CO2) and q(GMA), respectively, q(CO2) / q(GMA) is taken as the adsorption selectivity.

[0202] <Measurement of Carbon Dioxide Adsorption Amount (V3)>

[0203] The carbon dioxide adsorption amount under pressure is obtained by the following steps.

[0204] (1) Add 0.2 g of the adsorbent to a 12-mm sample cell (manufactured by Micro Meritics).

[0205] (2) Set the sample added to the sample cell in step (1) in a gas adsorption measurement device "BELSORP-HP" (trade name) manufactured by Microtrac BEL, and perform a heating vacuum degassing treatment at 250 °C and under 0.001 mmHg or less for 12 hours.

[0206] (3) Place the sample in the sample cell after the treatment in step (2) in a constant temperature circulating water at 25 °C. After the temperature of the sample reaches 25 ± 0.2 °C, use liquefied carbon dioxide gas (manufactured by Sumitomo Seika Chemicals Co., Ltd., with a purity of 99.9 mass / volume % or more) to carry out the measurement at an absolute pressure of 0.03 to a maximum of 300 kPa. It should be noted that in the above measurement, the pressure is measured over time, and when the pressure change reaches 0.001 volume % / 10 sec or less, it is determined that the saturated adsorption amount has been reached. Let the carbon dioxide adsorption amount under the condition of 200 kPa be V3 (cc / g), and use the carbon dioxide adsorption amount V2 (cc / g) under the condition of 100 kPa obtained by the above method to calculate (V3 - V2) / V2.

[0207] <X-ray Diffraction; Crystal Structure Analysis>

[0208] X-ray diffraction is carried out by the following steps.

[0209] (1) Use the zeolite (dry product) obtained in each production example as a sample, and crush it with an agate mortar. Further add 10 mass % of crystalline silicon (manufactured by Rare Metallic Co., Ltd.), and mix it with the agate mortar until it is uniform. The obtained mixture is used as the sample for structure analysis.

[0210] (2) The sample of (1) above was uniformly fixed on a non-reflective sample plate for powder, and the crystal structure was analyzed by X-ray diffraction under the following conditions.

[0211] X-ray diffractometer (XRD): Powder X-ray diffractometer "RINT2500" (trade name) manufactured by Rigaku Corporation

[0212] X-ray source: Cu tube (40kV, 200mA)

[0213] Measurement temperature: 25°C

[0214] Measuring range: 5 to 60° (0.02° / step)

[0215] Measuring speed: 0.2° / min

[0216] Slit width (scattering, divergence, light receiving): 1°, 1°, 0.15mm

[0217] < 29 Si-MAS-NMR spectroscopy, SAR determination>

[0218] The SAR of zeolite in the zeolite molded body can be measured by 29 First, as a zeolite humidity control, the bottom of the desiccator was filled with water, and the zeolite placed in the test tube was kept at the top for 48 hours. After the humidity control, the zeolite was tested under the following conditions. 29 Determination of Si-MAS-NMR.

[0219] Device: JEOL RESONANCE ECA700

[0220] Magnetic field strength: 16.44T (1H resonance frequency 700MHz)

[0221] Determination of nucleus: 29 Si

[0222] Resonant frequency: 139.08MHz

[0223] NMR tube: 4mm Ø (zirconia rotor)

[0224] Measurement method: DD / MAS (dipolar decoupling magic angle spinning)

[0225] Pulse width: 45°

[0226] Waiting time: 50 seconds

[0227] Integration times: 800 times (measurement time: about 22 hours)

[0228] MAS: 10,000Hz

[0229] Chemical shift standard: Silicone rubber (-22.34ppm) external standard

[0230] In the molded body comprising GIS type zeolite, 29 The Si-MAS-NMR spectrum showed the following five peaks.

[0231] (1) Q4 (0Al): Peak of Si that is not bonded to Al via oxygen

[0232] (2) Q4(1Al): Peak of Si bonded to one Al via oxygen

[0233] (3) Q4 (2Al): Peak of Si bonded to two Al atoms via oxygen

[0234] (4) Q4 (3Al): Peak of Si bonded to three Al atoms via oxygen

[0235] (5) Q4 (4Al): Peak of Si bonded to four Al atoms via oxygen

[0236] In addition, 29 In Si-MAS-NMR spectra, these peaks are typically located between -112 ppm and -80 ppm, and can be assigned to Q4(0Al), Q4(1Al), Q4(2Al), Q4(3Al), and Q4(4Al) from the high magnetic field side. The peak positions may vary depending on the cationic species present in the zeolite framework, but are typically within the following ranges.

[0237] (1) Q4(0Al): -105ppm to -112ppm

[0238] (2) Q4(1Al): -100ppm to -105ppm

[0239] (3) Q4 (2Al): -95ppm to -100ppm

[0240] (4) Q4 (3Al): -87ppm to -95ppm

[0241] (5) Q4 (4Al): -80 ppm to -87 ppm

[0242] about 29The peak area intensity of the Si-MAS-NMR spectrum was analyzed using the analysis program dmfit (version #202000113) using Gaussian and Lorentzian functions. Four parameters, namely amplitude (height of the spectrum maximum), position (spectral position, ppm), width (spectral full width at half maximum, ppm), and Gaussian / Lorentzian ratio (xG / (1-x)L), were optimized and calculated using the least squares algorithm. The peak areas of Q4(0Al), Q4(1Al), Q4(2Al), Q4(3Al), and Q4(4Al, obtained in this way, were designated A_Q4(0Al), A_Q4(1Al), A_Q4(2Al), A_Q4(3Al), and A_Q4(4Al), and the total value of A_Q4(0Al), A_Q4(1Al), A_Q4(2Al), A_Q4(3Al), and A_Q4(4Al) was designated A_total. SAR can be calculated as follows.

[0243] SAR=100 / [A_Q4(1Al) / 4+2×A_Q4(2Al) / 4+3×A_Q4(3Al) / 4+4×A_Q4(4Al) / 4]×2

[0244] <Evaluation of Powdering Rate of Adsorbent>

[0245] After separation and recovery of carbon dioxide and methane, the zeolite molded body used as an adsorbent was recovered and its pulverization rate was measured. The pulverization rate was evaluated by the following procedure.

[0246] (1) Before carbon dioxide separation and recovery, 100 g of the zeolite molded body was weighed, and the short diameter of the zeolite molded body was measured. The average value of the short diameter of the zeolite molded body was defined as ds.

[0247] (2) A sieve having a maximum mesh size smaller than ds is selected and prepared according to the mesh size disclosed in JIS Z 8801-1.

[0248] (3) The mass W1 of the zeolite molded body filled in the adsorption tower is measured.

[0249] (4) All the zeolite molded bodies after separation and recovery of carbon dioxide and methane are recovered, and sieved to recover the zeolite molded bodies that have passed through the sieve. The mass W2 of the zeolite molded bodies that have passed through the sieve is measured.

[0250] (3) The value calculated using equation (1) based on the mass W1 of the zeolite molded body packed in the adsorption tower is defined as the pulverization rate (mass %) of the zeolite molded body. The lower the pulverization rate, the more effective the gas separation method is while suppressing pulverization of the adsorbent. Since some powder is generated during filling or recovery, a value of 0.5 (mass %) or less is considered to be sufficient in suppressing pulverization.

[0251] Powdering rate [mass %] = (W2 [g]) / (W1 [g]) × 100 Formula (1)

[0252] The acceptance threshold for the pulverization rate was set at 0.5 [mass %] or less based on experimental results confirming that the pulverized powder is less likely to clog the adsorption tower or piping or cause pump failure, and can be sufficiently captured by filters, etc., without affecting the biogas purification device.

[0253] Production Example 1: Method for producing a GIS-type zeolite molded body

[0254] 61.93 g of water, 0.403 g of sodium hydroxide (NaOH, manufactured by Fujifilm-Wako Pure Chemical Industries, Ltd.), 3.39 g of sodium nitrate (NaNO3, manufactured by Fujifilm-Wako Pure Chemical Industries, Ltd.), 1.64 g of sodium aluminate (NaAlO2, manufactured by Fujifilm-Wako Pure Chemical Industries, Ltd.), and 10.82 g of colloidal silica (Ludox AS-40, solid content concentration 40% by mass, manufactured by Grace Co., Ltd.) were mixed and stirred for 30 minutes to prepare a hybrid gel. The composition of the hybrid gel was: α = SiO2 / Al2O3 = 7.21, β = Na2O / Al2O3 = 3.47, γ = P2O5 / Al2O3 = 0.00, δ = H2O / Al2O3 = 380.1, ε = H2O / OH -=377.3, ζ=R / Al2O3=0.00. The mixed gel was put into a 200 mL stainless steel micro-storage bottle (manufactured by HIRO COMPANY) with a fluororesin inner cylinder, and hydrothermal synthesis was carried out for 4 days at a stirring speed of 30 rpm and 135°C using a stirring thermostatic bath (manufactured by HIRO COMPANY) that can rotate up and down along the micro-storage bottle. The product was filtered out and dried at 120°C to obtain a powdered zeolite. 1 g of the obtained zeolite was added to 500 mL of a 0.05N potassium carbonate aqueous solution prepared using potassium carbonate (K2CO3, manufactured by Nippon Soda Co., Ltd.) and stirred at 500 rpm for 3 hours at room temperature. The product was filtered out and dried at 120°C to obtain a powdered zeolite in which part of the cations were exchanged for potassium. The XRD spectrum confirmed that the obtained zeolite was a GIS type zeolite. In addition, since no peaks derived from other zeolites, amorphous silica-alumina, etc. were observed, it was evaluated as a high-purity GIS type zeolite. 29 The silicon oxide-aluminum oxide ratio was calculated from the Si-MAS-NMR spectrum and found to be SAR=6.90.

[0255] 40 parts by mass of GIS-type zeolite powder, 1.2 parts by mass of methylcellulose (Serander YB-132A, manufactured by Highchem Co., Ltd.), 0.2 parts by mass of polyvinyl alcohol (Gohsenol N-300, manufactured by Mitsubishi Chemical Corporation), and 48.2 parts by mass of alumina sol (manufactured by Nissan Chemical Co., Ltd., alumina content: 10.5% by mass) were mixed with 10.4 parts by mass of powdered alumina hydrate. The mixture was extruded into a cylindrical shape with a diameter of 3 mm using a wet extrusion granulator MG-55 (manufactured by Dalton Co., Ltd.), and then calcined in an electric furnace at 350°C in an air atmosphere for 24 hours to produce a GIS-type zeolite molded body.

[0256] The adsorption isotherms of CO2 and CH4 for the resulting GIS zeolite were measured, and the adsorption capacity V1 was 42.4 cc / g, the adsorption capacity V2 was 46.9 cc / g, and the adsorption capacity V3 was 47.1 cc / g. Furthermore, (V2-V1) / V1=0.106 and (V3-V2) / V2=0.004. Furthermore, the adsorption capacities of CO2 and CH4 at 100 kPa were CO2:46.9 cm / g, and V3:47.1 cc / g, respectively. 3 / g, CH4: 3.5cm 3 / g, and the adsorption selectivity (CO2 / CH4) was 13.4, confirming that it had sufficient performance as an adsorbent.

[0257] Production Example 2: Method for producing a GIS-type zeolite molded body

[0258] A zeolite molded body was obtained by the same method as in Production Example 1, except that the firing temperature and time of the GIS type zeolite molded body were 570°C and 32 hours. The adsorption isotherm of CO2 of the obtained GIS type zeolite molded body was measured, and the adsorption amount V1 was 35.6cc / g, the adsorption amount V2 was 41.2cc / g, and the adsorption amount V3 was 47.1cc / g. In addition, (V2-V1) / V1=0.157, (V3-V2) / V2=0.143. In addition, the adsorption amounts of CO2 and CH4 under 100kPa conditions were CO2:41.2cm 3 / g, CH4: 3.1cm 3 / g, and the adsorption selectivity (CO2 / CH4) was 13.3, confirming that it had sufficient performance as an adsorbent.

[0259] Production Example 3: Method for producing a GIS-type zeolite molded body

[0260] A zeolite molded body was obtained by the same method as in Production Example 1, except that the firing temperature and time of the GIS type zeolite molded body were set to 600°C and 32 hours. The adsorption isotherm of CO2 of the obtained GIS type zeolite molded body was measured, and the adsorption amount V1 was 34.0cc / g, the adsorption amount V2 was 39.7cc / g, and the adsorption amount V3 was 46.1cc / g. In addition, (V2-V1) / V1=0.168, (V3-V2) / V2=0.161. In addition, the adsorption amounts of CO2 and CH4 under 100kPa conditions were CO2: 39.7cm / g, and CH4: 46.1cc / g, respectively. 3 / g, CH4: 3.0cm 3 / g, and the adsorption selectivity (CO2 / CH4) was 13.2, confirming that it had sufficient performance as an adsorbent.

[0261] Production Example 4: Method for producing a GIS-type zeolite molded body

[0262] 62.20 g of water, 0.35 g of sodium hydroxide (NaOH, manufactured by Fujifilm-Wako Pure Chemical Industries, Ltd.), 5.20 g of sodium sulfate (Na2SO4, manufactured by Fujifilm-Wako Pure Chemical Industries, Ltd.), 1.6 g of sodium aluminate (NaAlO2, manufactured by Fujifilm-Wako Pure Chemical Industries, Ltd.), and 11.50 g of colloidal silica (Ludox AS-40, solid content concentration 40% by mass, manufactured by Grace Co., Ltd.) were mixed and stirred for 30 minutes to prepare a hybrid gel. The composition of the hybrid gel was: α = SiO2 / Al2O3 = 8.98, β = Na2O / Al2O3 = 5.80, γ = P2O5 / Al2O3 = 0.00, δ = H2O / Al2O3 = 449.7, ε = H2O / OH -=438.7, ζ=R / Al2O3=0.00. The mixed gel was put into a 200 mL stainless steel micro-storage bottle (manufactured by HIRO COMPANY) with a fluororesin inner cylinder, and hydrothermal synthesis was carried out for 4 days at a stirring speed of 30 rpm and 135°C using a stirring thermostatic bath (manufactured by HIRO COMPANY) that can rotate up and down along the micro-storage bottle. The product was filtered out and dried at 120°C to obtain a powdered zeolite. 1 g of the obtained zeolite was added to 500 mL of a 0.05N potassium carbonate aqueous solution prepared using potassium carbonate (K2CO3, manufactured by Nippon Soda Co., Ltd.) and stirred at 500 rpm for 3 hours at room temperature. The product was filtered out and dried at 120°C to obtain a powdered zeolite in which part of the cations were exchanged for potassium. The XRD spectrum confirmed that the obtained zeolite was a GIS type zeolite. In addition, since no peaks derived from other zeolites, amorphous silica-alumina, etc. were observed, it was evaluated as a high-purity GIS type zeolite. 29 The silicon oxide-aluminum oxide ratio was calculated from the Si-MAS-NMR spectrum and the result was SAR=7.15.

[0263] 40 parts by mass of GIS-type zeolite powder, 1.2 parts by mass of methylcellulose (Serander YB-132A, manufactured by Highchem Co., Ltd.), 0.2 parts by mass of polyvinyl alcohol (Gohsenol N-300, manufactured by Mitsubishi Chemical Corporation), and 48.2 parts by mass of alumina sol (manufactured by Nissan Chemical Co., Ltd., alumina content: 10.5% by mass) were mixed with 10.4 parts by mass of powdered alumina hydrate. The mixture was extruded into a cylindrical shape with a diameter of 3 mm using a wet extrusion granulator MG-55 (manufactured by Dalton Co., Ltd.), and then calcined in an electric furnace at 375°C in an air atmosphere for 24 hours to produce a GIS-type zeolite molded body.

[0264] The adsorption isotherms of CO2 and CH4 for the resulting GIS zeolite were measured, and the adsorption capacity V1 was 35.0 cc / g, the adsorption capacity V2 was 40.5 cc / g, and the adsorption capacity V3 was 47.2 cc / g. Furthermore, (V2-V1) / V1=0.157 and (V3-V2) / V2=0.165. Furthermore, the adsorption capacities of CO2 and CH4 at 100 kPa were CO2:40.5 cm / g, respectively. 3 / g, CH4: 3.4cm 3 / g, and the adsorption selectivity (CO2 / CH4) was 11.9, confirming that it had sufficient performance as an adsorbent.

[0265] Production Example 5: Method for producing a GIS-type zeolite molded body

[0266] A zeolite molded body was obtained by the same method as in Preparation Example 4, except that the firing temperature and time of the GIS type zeolite molded body were 580°C and 30 hours. The adsorption isotherm of CO2 of the obtained GIS type zeolite molded body was measured, and the adsorption amount V1 was 33.1cc / g, the adsorption amount V2 was 39.3cc / g, and the adsorption amount V3 was 44.5cc / g. In addition, (V2-V1) / V1=0.187, (V3-V2) / V2=0.132. In addition, the adsorption amounts of CO2 and CH4 under 100kPa conditions were CO2: 39.3cm / g, and CH4: 44.5cc / g, respectively. 3 / g, CH4: 3.3cm 3 / g, and the adsorption selectivity (CO2 / CH4) was 11.9, confirming that it had sufficient performance as an adsorbent.

[0267] Example 1: Gas Separation Method

[0268] use Figure 1 The gas separation device shown separates a mixed gas containing methane and carbon dioxide into gas 1 (methane) and gas 2 (carbon dioxide) for separation and recovery.

[0269] A system was used in which carbon dioxide adsorption towers 3a and 3b each had a volume of 1 L and were filled with the GIS-type zeolite molded body of Production Example 1 as an adsorbent. The volume x of the adsorbent filled in the towers was 0.69 L, and the porosity was 31%. Therefore, as indicators of the amount Q of carbon dioxide used in cleaning, 5.5x was 3.80 NL, and 0.10x was 0.069 NL.

[0270] A mixed gas containing 60% by volume of methane and 40% by volume of carbon dioxide was used. The water content in the mixed gas was 98 ppm by volume.

[0271] (Operation 1)

[0272] With all automatic valves AV1 to AV6 closed, automatic valves AV1 and AV3 are opened, and while the flow rate in pipe 1 is monitored using flowmeter 11 to maintain a constant flow rate of 8.0 NL / min, a mixed gas at 25°C is supplied to carbon dioxide adsorption tower 3a at 101 kPa. When the carbon dioxide concentration in component analyzer 73 exceeds 5% by volume, automatic valve AV1 is closed, and automatic valve AV7 is opened simultaneously, allowing carbon dioxide to flow from carbon dioxide tank 2 into adsorption tower 3a, flushing out the gas containing a large amount of methane in adsorption tower 3a. When the carbon dioxide concentration in component analyzer 73 exceeds 8% by volume, automatic valves AV3 and AV7 are closed, and automatic valves AV2 and AV4 are opened simultaneously, switching the feed gas supply from carbon dioxide adsorption tower 3a to 3b. All gas flowing out of carbon dioxide adsorption tower 3a before the switch is recovered. (The resulting gas is referred to as Gas 1 (methane).) Furthermore, a desorption operation was performed on the carbon dioxide adsorption tower 3a by opening automatic valve AV5 and reducing the pressure in the carbon dioxide adsorption tower to 2 kPa using the decompression device 9. Gas was recovered from the carbon dioxide adsorption tower 3a. (The resulting gas is referred to as Gas 2 (carbon dioxide).) The average temperature of the desorbed gas was 35°C. The operations up to this point are referred to as Operation 1.

[0273] (Operation 2)

[0274] Next, when the carbon dioxide concentration of the gas flowing out of the carbon dioxide adsorption tower 3b exceeds 5% by volume, automatic valve AV2 is closed and automatic valve AV8 is opened simultaneously, allowing carbon dioxide to flow from the carbon dioxide tank 2 into the adsorption tower 3b, flushing out the gas containing a large amount of methane within the adsorption tower 3b. When the carbon dioxide concentration in the component analyzer 73 exceeds 8% by volume, automatic valves AV4 and AV8 are closed, while automatic valves AV1 and AV3 are opened simultaneously, switching the supply of raw gas from the carbon dioxide adsorption tower 3b to the carbon dioxide adsorption tower 3a. At this time, the amount Q of carbon dioxide used for cleaning is 3.06 NL, which is within the preferred range. Furthermore, a desorption operation is performed on the carbon dioxide adsorption tower 3b by opening automatic valve AV6 and reducing the pressure in the carbon dioxide adsorption tower 3b to 2 kPa using the decompression device 9, thereby recovering gas from the carbon dioxide adsorption tower 3b. The operations up to this point are referred to as Operation 2.

[0275] The above operations 1 and 2 were repeated 10,000 times, followed by operation 1 again. The resulting methane concentration in Gas 1 was 97.7% by volume (the purity of gaseous substance A removed through the first adsorption step was 97.7% by volume), and the carbon dioxide concentration in Gas 2 was 96.5% by volume (the purity of carbon dioxide removed through the first desorption step was 96.5% by volume). Furthermore, the methane recovery rate in Gas 1 after the first adsorption step was 97.7%, and the carbon dioxide recovery rate in Gas 2 after the first desorption step was 96.5%. The powdering rate in Example 1 was 0.10% by mass, indicating that powdering of the adsorbent was suppressed.

[0276] Example 2

[0277] The pressure of the mixed gas was set to 300 kPa. After the mixed gas was supplied to the adsorption tower 3a, the automatic valve AV1 was closed and the automatic valve AV3 was opened before the carbon dioxide flowed from the carbon dioxide tank 2 to the adsorption tower 3a. The gas flow path was connected to the raw gas through the flow path control valve 41, and the gas pressure in the adsorption tower was reduced to normal pressure (101 kPa). The released gas was returned to the raw material. After the mixed gas was supplied to the adsorption tower 3b, the automatic valve AV2 was closed and the automatic valve AV4 was opened. The gas flow path was connected to the raw gas through the flow path control valve 41. The gas pressure in the adsorption tower was reduced to normal pressure (101 kPa). The released gas was returned to the raw material. After that, the carbon dioxide was flowed from the carbon dioxide tank 2 to the adsorption tower to perform the cleaning process. The amount Q of carbon dioxide used in the cleaning was 3.32 NL, which is within the preferred range. The same operation as in Example 1 was performed except for these. The methane concentration in the obtained gas 1 was 97.6% by volume, and the carbon dioxide concentration in the gas 2 was 96.5% by volume. The methane recovery rate in Gas 1 obtained through a single adsorption step was 97.7%, and the carbon dioxide recovery rate in Gas 2 obtained through a single desorption step was 96.6%. The powdering rate was 0.14% by mass, indicating that powdering of the adsorbent was suppressed.

[0278] Example 3

[0279] Carbon dioxide adsorption columns 3a and 3b were filled with the GIS-type zeolite molded article of Production Example 1. The carbon dioxide and methane mixture was separated and recovered using the same method as in Example 1, except that the amount of carbon dioxide used for cleaning, Q, was set to 0.50 NL. After separation and recovery, the pulverization rate was measured and found to be 0.08% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 97.6% by volume, with a methane recovery rate of 95.2%. The carbon dioxide concentration in Gas 2 was 94.9% by volume, with a recovery rate of 96.3%.

[0280] Example 4

[0281] Carbon dioxide adsorption towers 3a and 3b were filled with the GIS-type zeolite molded body of Production Example 2. Carbon dioxide and methane were separated and recovered from the mixed gas of carbon dioxide and methane using the same method as in Example 1, except that the amount of carbon dioxide used for cleaning, Q, was set to 3.22 NL. The volume x of the adsorbent filled was 0.68 L, and the porosity was 32%. Therefore, as an indicator of the amount of carbon dioxide used for cleaning, Q, 5.5x was 3.74 NL, and 0.1x was 0.068 NL. After separation and recovery, the pulverization rate was measured and found to be 0.19% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 97.2% by volume, with a methane recovery rate of 94.6%. The carbon dioxide concentration in Gas 2 was 94.3% by volume, with a recovery rate of 96.5%.

[0282] Example 5

[0283] Carbon dioxide adsorption columns 3a and 3b were filled with the GIS-type zeolite molded article of Production Example 2. Carbon dioxide and methane were separated and recovered from the mixed gas of carbon dioxide and methane using the same method as in Example 2, except that the amount of carbon dioxide used for cleaning, Q, was set to 3.55 NL. The pulverization rate after separation and recovery was measured and found to be 0.21% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 97.2% by volume, with a methane recovery rate of 94.8%. The carbon dioxide concentration in Gas 2 was 94.8% by volume, with a recovery rate of 96.3%.

[0284] Example 6

[0285] Carbon dioxide adsorption towers 3a and 3b were filled with the GIS-type zeolite molded body of Production Example 3. Carbon dioxide and methane were separated and recovered from a mixed gas of carbon dioxide and methane using the same method as in Example 1, except that the amount of carbon dioxide used for cleaning, Q, was set to 3.60 NL. The volume x of the adsorbent filled was 0.70 L, and the porosity was 30%. Therefore, as indicators of the amount of carbon dioxide used for cleaning, Q, 5.5x was 3.85 NL, and 0.10x was 0.070 NL. After separation and recovery, the pulverization rate was measured and found to be 0.31% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 95.8% by volume, with a methane recovery rate of 93.4%. The carbon dioxide concentration in Gas 2 was 93.6% by volume, with a recovery rate of 95.2%.

[0286] Example 7

[0287] Carbon dioxide adsorption columns 3a and 3b were filled with the GIS-type zeolite molded article of Production Example 3. The carbon dioxide and methane mixture was separated and recovered using the same method as in Example 2, except that the amount of carbon dioxide used for cleaning, Q, was set to 3.76 NL. The pulverization rate after separation and recovery was measured and found to be 0.38% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 95.8% by volume, with a methane recovery rate of 94.1%. The carbon dioxide concentration in Gas 2 was 93.9% by volume, with a recovery rate of 95.1%.

[0288] Example 8

[0289] Carbon dioxide adsorption towers 3a and 3b were filled with the GIS-type zeolite molded body of Production Example 4. Carbon dioxide and methane were separated and recovered from a mixed gas of carbon dioxide and methane using the same method as in Example 1, except that the amount of carbon dioxide used for cleaning, Q, was set to 3.60 NL. The volume x of the adsorbent filled was 0.68 L, and the porosity was 32%. Therefore, as indicators of the amount of carbon dioxide used for cleaning, Q, 5.5x was 3.74 NL, and 0.10x was 0.068 NL. After separation and recovery, the pulverization rate was measured and found to be 0.38% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 95.6% by volume, with a methane recovery rate of 93.1%. The carbon dioxide concentration in Gas 2 was 95.2% by volume, with a recovery rate of 95.0%.

[0290] Example 9

[0291] Carbon dioxide adsorption towers 3a and 3b were filled with the GIS-type zeolite molded body of Production Example 5. Carbon dioxide and methane were separated and recovered from a mixed gas of carbon dioxide and methane using the same method as in Example 2, except that the amount of carbon dioxide used for cleaning, Q, was set to 3.70 NL. The volume x of the adsorbent filled was 0.68 L, and the porosity was 32%. Therefore, as indicators of the amount of carbon dioxide used for cleaning, Q, 5.5x was 3.74 NL, and 0.10x was 0.068 NL. After separation and recovery, the pulverization rate was measured and found to be 0.41% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 95.7% by volume, with a methane recovery rate of 93.3%. The carbon dioxide concentration in Gas 2 was 93.6% by volume, with a recovery rate of 95.1%.

[0292] Comparative Example 1

[0293] Carbon dioxide and methane were separated and recovered from the mixed gas of carbon dioxide and methane using the same method as in Example 1, except that the amount of carbon dioxide used for cleaning, Q, was set to 11.5 NL. The pulverization rate after separation and recovery was measured and found to be 2.12% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 97.7% by volume, with a methane recovery rate of 97.9%. The carbon dioxide concentration in Gas 2 was 97.0% by volume, with a recovery rate of 96.9%.

[0294] Comparative Example 2

[0295] Carbon dioxide and methane were separated and recovered from the mixed gas of carbon dioxide and methane using the same method as in Example 2, except that the amount of carbon dioxide used for cleaning, Q, was set to 12.3 NL. The pulverization rate after separation and recovery was measured and found to be 2.54% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 97.7% by volume, with a methane recovery rate of 97.8%. The carbon dioxide concentration in Gas 2 was 97.0% by volume, with a recovery rate of 97.0%.

[0296] Comparative Example 3

[0297] Carbon dioxide and methane were separated and recovered from the mixed gas of carbon dioxide and methane using the same method as in Example 6, except that the amount of carbon dioxide used for cleaning, Q, was set to 6.01 NL. The pulverization rate after separation and recovery was measured and found to be 1.88% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 95.8% by volume, with a methane recovery rate of 94.9%. The carbon dioxide concentration in Gas 2 was 95.2% by volume, with a recovery rate of 95.3%.

[0298] Comparative Example 4

[0299] Carbon dioxide and methane were separated and recovered from the mixed gas of carbon dioxide and methane using the same method as in Example 7, except that the amount of carbon dioxide used for cleaning, Q, was set to 6.13 NL. The pulverization rate after separation and recovery was measured and found to be 2.02% by mass, indicating that pulverization of the adsorbent was suppressed. The resulting methane concentration in Gas 1 was 95.9% by volume, with a methane recovery rate of 95.1%. The carbon dioxide concentration in Gas 2 was 95.3% by volume, with a recovery rate of 95.3%.

[0300]

[0301] Industrial Applicability

[0302] The gas separation method and gas separation device of the present invention can recover carbon dioxide from, for example, biogas and simultaneously produce purified methane gas, and have industrial applicability.

[0303] Explanation of symbols

[0304] 100 Gas Separation Device

[0305] 1 Mixed gas supply line

[0306] 11 Flow meter

[0307] 12 Moisture Meter

[0308] 13. Composition Analyzer

[0309] 14 Blower

[0310] 2: Carbon dioxide tank

[0311] 3a, 3b carbon dioxide adsorption tower

[0312] 31a, 31b fixed bed

[0313] 41 Flow control valve

[0314] 5 Carbon dioxide recovery pipeline

[0315] 53a, 53b pressure gauge

[0316] 51 Flow Meter

[0317] 52 Moisture Meter

[0318] 54 Composition Analyzer

[0319] 7 Gas material A recovery pipeline

[0320] 71 flow meter

[0321] 72 Moisture Meter

[0322] 73 Composition Analyzer

[0323] 8 Purge lines

[0324] 81 flow meter

[0325] 9 Pressure relief device

[0326] 10 Blower

[0327] AV1,AV2,AV3,AV4,AV5,AV6,AV7,AV8 automatic valve

[0328] 1000 Biogas Refining System

[0329] 200 fermentation tanks

[0330] 300 Desulfurization Tower

[0331] 400 Siloxane Removal Device

[0332] 500 Oxygen Removal Device

[0333] 600 Cooling Unit

[0334] 700 Dehydration Unit

Claims

1. A gas separation method, comprising separating carbon dioxide and a gaseous substance A different from carbon dioxide from a mixed gas containing carbon dioxide using an adsorption tower filled with an adsorbent, wherein: The method comprises the following steps: an adsorption step, introducing the mixed gas into the adsorption tower, allowing carbon dioxide to be adsorbed on the adsorbent, and removing gaseous substance A; a cleaning step of introducing carbon dioxide into the adsorption tower, discharging the gaseous substance A in the adsorption tower, and cleaning the adsorption tower; and The desorption process is to decompress and exhaust the carbon dioxide from the adsorption tower, thereby removing the carbon dioxide from the adsorbent. When the volume of the adsorbent filled in the adsorption tower is defined as x [L], the amount Q [NL] of carbon dioxide introduced into the adsorption tower in the cleaning step satisfies Q ≤ 5.5x.

2. The gas separation method according to claim 1, wherein: When the carbon dioxide adsorption amount per 1g of the adsorbent at a temperature of 35°C and 40kPa is V1 and the carbon dioxide adsorption amount per 1g of the adsorbent at a temperature of 35°C and 100kPa is V2, the adsorbent in the adsorption step satisfies (V2-V1) / V1≤0.

160.

3. The gas separation method according to claim 1, wherein: In the adsorption step, the adsorption tower is pressurized. When the amount of carbon dioxide adsorbed per 1 g of the adsorbent at a temperature of 35° C. and 100 kPa is defined as V2 and the amount of carbon dioxide adsorbed per 1 g of the adsorbent at a temperature of 35° C. and 200 kPa is defined as V3, the adsorbent satisfies (V3−V2) / V2≤0.

155. The method includes: The depressurization step is to reduce the pressure in the adsorption tower after the adsorption step and before the cleaning step.

4. The gas separation method according to claim 1, wherein: The recovery rate of the gaseous substance A relative to the total amount of the gaseous substance A in the mixed gas introduced into the adsorption tower in the adsorption step is 90% or more.

5. The gas separation method according to claim 1, wherein: The carbon dioxide is introduced into the adsorption tower in the cleaning step by utilizing the exhaust pressure of the vacuum pump used to decompress and exhaust the carbon dioxide from the adsorption tower in the desorption step.

6. The gas separation method according to claim 1, wherein: The amount Q[NL] of carbon dioxide introduced into the adsorption tower in the cleaning step satisfies Q>0.10x.

7. The gas separation method according to claim 1, wherein: In the cleaning step, the start or end of the introduction of carbon dioxide into the adsorption tower is performed by time control.

8. The gas separation method according to claim 1, wherein: The purity of the recovered gaseous substance A is 90% by volume or more.

9. The gas separation method according to claim 1, wherein: The purity of the recovered carbon dioxide is 90% by volume or more.

10. The gas separation method according to claim 1, wherein: The V1 in the adsorbent is V1≥20cc / g.

11. The gas separation method according to claim 1, wherein: The adsorbent is zeolite.

12. The gas separation method according to claim 11, wherein: The adsorbent is GIS type zeolite.

13. The gas separation method according to claim 1, wherein: The average temperature in the adsorption step is 0° C. or higher.

14. The gas separation method according to claim 1, wherein: The final pressure P in the desorption process b Below 30kPa.

15. The gas separation method according to claim 1, wherein: The average temperature in the desorption step is 150° C. or lower.

16. The gas separation method according to claim 1, wherein: The water content of the mixed gas is less than 1000 volume ppm.

17. The gas separation method according to claim 1, wherein: The gas substance A is at least one selected from methane, ethane, nitrogen, carbon monoxide, hydrogen, argon and dimethyl ether.

18. A method for producing a purified gas, wherein: The gas separation method according to any one of claims 1 to 17 can produce a purified gaseous substance A or purified carbon dioxide.

19. A gas separation device for separating carbon dioxide and a gaseous substance A different from carbon dioxide from a mixed gas containing the carbon dioxide and the gaseous substance A, wherein: The gas separation device has: an adsorption tower filled with an adsorbent for adsorbing carbon dioxide; a gaseous substance A recovery pipeline, which takes out the gaseous substance A from the adsorption tower; a carbon dioxide recovery pipeline having a pressure reducing device for taking out carbon dioxide from the adsorption tower; a carbon dioxide storage tank for storing carbon dioxide sent from the carbon dioxide recovery pipeline; and a carbon dioxide purge line, which supplies carbon dioxide from the carbon dioxide storage tank to the adsorption tower, When the carbon dioxide adsorption amount per 1 g of the adsorbent at 35° C. and 40 kPa is V1 and the carbon dioxide adsorption amount per 1 g of the adsorbent at 35° C. and 100 kPa is V2, the adsorbent satisfies (V2−V1) / V1≤0.160.

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