Carbon dioxide circulation system and adsorbent for gas drying

Abstract

To provide a technique that suppresses gas from decreasing in carbon dioxide content with respect to an adsorbent for gas drying which adsorbs moisture included in the gas to dry the gas.SOLUTION: A adsorbent for gas drying has zeolite which includes a magnesium ion as a cation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adsorbent for drying gases, a gas dryer, and a carbon dioxide circulation system. [Background technology]

[0002] Gas drying adsorbents that dry gas by adsorbing moisture contained in the gas have been known for some time. For example, Patent Document 1 discloses a methane production apparatus that includes a gas drying adsorbent that dries exhaust gas from methane (CH4) combustion, and that produces methane using carbon dioxide in the exhaust gas from which water vapor has been removed by the gas drying adsorbent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-142806 Summary of the Invention [Problem to be solved by the invention]

[0004] In the methane production apparatus of Patent Document 1, a carbon dioxide recovery vessel filled with zeolite 13X is used to recover carbon dioxide from flue gas from which water vapor has been removed. Because zeolite 13X adsorbs water vapor, the flue gas must be sufficiently dried. In the methane production apparatus of Patent Document 1, a gas dryer filled with NaY-type zeolite, which contains sodium ions as cations, is installed upstream of the carbon dioxide recovery vessel. However, because NaY-type zeolite adsorbs a certain amount of carbon dioxide in the flue gas along with water vapor, drying the flue gas reduces the carbon dioxide content of the flue gas. A reduction in the carbon dioxide content in the flue gas also reduces the methane production efficiency in the methane production apparatus.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a technology for suppressing a decrease in the carbon dioxide content of a gas in a gas drying adsorbent that dries a gas containing carbon dioxide. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided an adsorbent for drying a gas, which adsorbs moisture contained in the gas to dry the gas. The adsorbent for drying the gas includes zeolite containing magnesium ions as cations.

[0008] According to this configuration, the gas drying adsorbent includes zeolite containing magnesium ions as cations. Zeolite containing magnesium ions has almost the same moisture absorption capacity as zeolite containing sodium ions as cations, but has a lower carbon dioxide absorption capacity. As a result, when drying a gas containing carbon dioxide, adsorption of carbon dioxide is suppressed, and a decrease in the carbon dioxide content of the gas to be dried can be suppressed.

[0009] (2) In the gas drying adsorbent of the above embodiment, the molar ratio of magnesium ions to cations contained in the zeolite may be 0.8 or more. According to this configuration, the molar ratio of magnesium ions to cations contained in the zeolite is 0.8 or more. By setting the ratio of magnesium ions to cations to 0.8 or more, the carbon dioxide absorption performance of the gas drying adsorbent can be further reduced. Therefore, when drying a gas containing carbon dioxide, a decrease in the carbon dioxide content of the gas to be dried can be further suppressed.

[0010] (3) In the adsorbent for drying gas of the above embodiment, the zeolite may contain a composite oxide of aluminum and silicon, and the composition ratio of silicon to aluminum in the composite oxide may be 2 or more and 5 or less. According to this configuration, the zeolite contains a composite oxide of aluminum and silicon, and the composition ratio of silicon to aluminum in the composite oxide is 2 or more and 5 or less. This increases the ion exchange capacity of the zeolite, allowing the zeolite to contain more magnesium ions. Therefore, when drying a gas containing carbon dioxide, adsorption of carbon dioxide is further suppressed, and a decrease in the carbon dioxide content of the gas to be dried can be further suppressed.

[0011] (4) In the gas drying adsorbent of the above embodiment, the zeolite may be Y-type zeolite, and the silicon to aluminum composition ratio in the composite oxide may be 2.75. According to this configuration, the zeolite is Y-type zeolite having pores large enough to allow magnesium ions to pass through, and therefore the zeolite is more likely to contain magnesium ions as cations. This further suppresses carbon dioxide adsorption when drying a gas containing carbon dioxide, thereby further suppressing a decrease in the carbon dioxide content of the gas being dried.

[0012] (5) In the gas drying adsorbent of the above embodiment, the zeolite is Mg y Na (6.4-2y) Al 6.4 Si 17.6 O 48The Y-type zeolite has a composition of 2.75, where y may be greater than 2.23. According to this configuration, the Y-type zeolite, which has a silicon to aluminum composition ratio of 2.75, has pores large enough to allow magnesium ions to pass through, and contains more magnesium ions as cations than sodium ions. This allows the carbon dioxide absorption capacity to be further reduced without substantially changing the moisture absorption capacity compared to zeolites containing sodium ions as cations. Therefore, when drying a gas containing carbon dioxide, it is possible to suppress a decrease in the carbon dioxide content of the gas to be dried.

[0013] (6) According to another aspect of the present invention, there is provided a gas dryer. The gas dryer includes the above-described gas drying adsorbent and a container that accommodates the gas drying adsorbent. According to this configuration, the gas dryer includes the above-described gas drying adsorbent. As a result, the gas dried by the gas dryer contains a relatively large amount of carbon dioxide, and therefore, carbon dioxide can be efficiently utilized in a system that utilizes carbon dioxide.

[0014] (7) According to yet another aspect of the present invention, there is provided a carbon dioxide circulation system. The carbon dioxide circulation system includes the above-mentioned gas dryer, which dries a mixed gas containing carbon dioxide and moisture supplied from an external gas generation unit by adsorbing moisture in the mixed gas onto the gas drying adsorbent; a carbon dioxide capture unit that captures carbon dioxide from the mixed gas dried in the gas dryer; and a hydrocarbon production unit that generates hydrocarbon compounds using the carbon dioxide captured in the carbon dioxide capture unit and supplies the hydrocarbon compounds to the external gas generation unit. According to this configuration, in the carbon dioxide circulation system, the mixed gas supplied from the gas generation unit is dried in the gas dryer. At this time, the above-mentioned gas drying adsorbent provided in the gas dryer adsorbs moisture but does not adsorb much carbon dioxide, so that the mixed gas sent from the gas dryer to the carbon dioxide capture unit contains a relatively large amount of carbon dioxide. The carbon dioxide captured from the mixed gas sent to the carbon dioxide capture unit serves as a raw material for hydrocarbon compounds produced in the hydrocarbon production unit. The produced hydrocarbon compounds are supplied to the external gas generation unit. In the gas generation unit, for example, thermal energy is extracted by combustion of a hydrocarbon compound, and a mixed gas containing carbon dioxide and moisture is generated. This generated mixed gas is dried again in a gas dryer, and carbon dioxide is then recovered as a raw material for the hydrocarbon compound in a carbon dioxide recovery unit. In this way, the carbon dioxide circulation system configured as described above can extract energy such as combustion heat while circulating carbon between the gas generation unit and the carbon dioxide recovery unit. In this carbon dioxide circulation system, a regeneration process is performed in the gas dryer, in which moisture adsorbed on the gas drying adsorbent is desorbed from the gas drying adsorbent by heating or the like and discharged outside the system. The above-mentioned gas drying adsorbent is less likely to adsorb carbon dioxide than, for example, zeolite containing sodium ions as cations, and therefore less carbon dioxide is discharged outside the system together with moisture in the regeneration process. This allows the carbon circulation rate throughout the system to be improved when carbon is circulated between the gas generation unit and the carbon dioxide circulation system.

[0015] The present invention can be realized in various forms, such as a control method for a gas dryer and a carbon dioxide circulation system, a computer program for causing a gas dryer and a carbon dioxide circulation system to adsorb and recover moisture, a server device for distributing the computer program, and a non-transitory storage medium on which the computer program is stored. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a carbon dioxide circulation system according to a first embodiment. [Figure 2] FIG. 1 is a conceptual diagram illustrating the distribution of adsorbed H2O in a gas dryer. [Figure 3] FIG. 1 is a diagram illustrating the CO2 loss rate in a gas dryer. [Figure 4] FIG. 1 is a diagram showing the relationship between the proportion of unused adsorbent and the amount of CO2 loss. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment FIG. 1 is an explanatory diagram showing a schematic configuration of a carbon dioxide circulation system 1 according to a first embodiment. The carbon dioxide circulation system 1 includes a gas dryer 10, a carbon dioxide separation unit 20, a mixed gas supply channel 30, a hydrogen supply source 41, a hydrogen supply channel 42, a reactor 50, a raw material gas channel 60, a reactant gas channel 70, a heat transfer medium channel 80, and a control unit 90. The carbon dioxide circulation system 1 is used in conjunction with a mixed gas supply source 5 that supplies a mixed gas containing carbon dioxide (CO). The mixed gas supply source 5 may be, for example, a combustion furnace in a factory. The mixed gas contains oxygen (O), nitrogen (N), moisture (H), and the like in addition to CO. The moisture contained in the mixed gas includes gaseous moisture (water vapor) and liquid moisture (e.g., liquid droplets). The carbon dioxide circulation system 1 circulates carbon by using CO contained in the mixed gas supplied from the mixed gas supply source 5 to generate methane (CH), which is used for combustion by the mixed gas supply source 5. In this embodiment, the carbon dioxide circulation system 1 is described as producing CH4, but it is also capable of producing hydrocarbon compounds other than CH4. The carbon dioxide circulation system 1 is also applicable to the production of hydrocarbon compounds composed of carbon and hydrogen, such as ethane (C2H6) and propane (C3H8), and hydrocarbon compounds composed mainly of carbon and hydrogen, such as methanol (CH3OH). The mixed gas supply source 5 corresponds to the "gas generating section" in the claims.

[0018] The gas dryer 10 is a device for separating HO from a mixed gas and includes a container 12 containing a gas drying adsorbent 11. The gas drying adsorbent 11 is a material capable of absorbing HO. In this embodiment, Y-type zeolite containing magnesium ions as cations is used. The gas drying adsorbent 11 can desorb and regenerate the adsorbed HO by utilizing the heat of a heat medium flowing through a heat medium flow path 80 (described later) or the heat of a heater (not shown). The HO desorbed from the gas drying adsorbent 11 is released to the outside of the system via a discharge valve 14 from a discharge flow path 13 by a purge gas supplied by a purge gas supply unit (not shown). Features of the gas drying adsorbent 11 will be described later.

[0019] The carbon dioxide separation unit 20 includes a first CO2 separator 21 and a second CO2 separator 22. The carbon dioxide separation unit 20 is a device for separating and capturing CO2 from the mixed gas. The carbon dioxide separation unit 20 corresponds to the "carbon dioxide capture unit" in the claims.

[0020] The first CO2 separator 21 contains a CO2 adsorbent 21a, such as zeolite, activated carbon, or silica gel, that has CO2 storage properties. The first CO2 separator 21 is provided with a hydrogen injection unit 21b that injects hydrogen supplied from a hydrogen supply line 42 into the first CO2 separator 21. The first CO2 separator 21 is connected to a mixed gas supply line 30, a raw gas line 60, and a first exhaust line 21c. The CO2 contained in the mixed gas supplied from the mixed gas supply line 30 is absorbed in the CO2 adsorbent 21a, and the remaining components in the mixed gas are released from the first exhaust line 21c to the outside of the system via a first exhaust valve 21d. The CO2 desorbed from the CO2 adsorbent 21a is purged with H2 injected from the hydrogen injection unit 21b and sent to the raw gas line 60 together with H2.

[0021] The second CO2 separator 22 has the same shape and capacity as the first CO2 separator 21 and contains a CO2 adsorbent 22a. Like the CO2 adsorbent 21a, the CO2 adsorbent 22a is a material capable of absorbing CO2 and has absorption performance comparable to that of the CO2 adsorbent 21a. The second CO2 separator 22 is provided with a hydrogen injection unit 22b that injects hydrogen supplied from the hydrogen supply passage 42 into the second CO2 separator 22. The second CO2 separator 22 is connected to a mixed gas supply passage 30, a raw material gas passage 60, and a second exhaust passage 22c. CO2 contained in the mixed gas supplied from the mixed gas supply passage 30 is absorbed in the CO2 adsorbent 22a, and the remaining components of the mixed gas are released from the second exhaust passage 22c via a second exhaust valve 22d to the outside of the system. The CO2 desorbed from the CO2 adsorbent 22a is purged by H2 injected from the hydrogen injection part 22b and is sent to the raw material gas flow path 60 together with H2.

[0022] The mixed gas supply flow path 30 is a gas flow path for supplying the mixed gas supplied from the mixed gas supply source 5 to the carbon dioxide separation unit 20 via the gas dryer 10, and is configured to include multiple gas pipes. The mixed gas supply flow path 30 is provided with a first mixed gas supply valve 31 and a second mixed gas supply valve 32. The mixed gas supplied from the mixed gas supply source 5 is dried in the gas dryer 10 and then supplied to the first CO2 separator 21 via the first mixed gas supply valve 31. The mixed gas supplied from the mixed gas supply source 5 is supplied to the second CO2 separator 22 via the second mixed gas supply valve 32. The first mixed gas supply valve 31 and the second mixed gas supply valve 32 are each controlled to open and close by a control unit 90. The mixed gas supply flow path 30 is provided with a temperature sensor, a flow rate sensor, and a CO2 concentration sensor (not shown) for measuring the temperature, flow rate, and CO2 concentration of the mixed gas supplied to the first CO2 separator 21 and the second CO2 separator 22.

[0023] The hydrogen supply source 41 is, for example, a water electrolysis device or a hydrogen tank, and will be described here as a water electrolysis device. The hydrogen supply source 41 generates H2 to be supplied to the first CO2 separator 21 and the second CO2 separator 22.

[0024] The hydrogen supply flow path 42 is a gas flow path for supplying H2 generated in the hydrogen supply source 41 to the first CO2 separator 21, the second CO2 separator 22, and the raw material gas flow path 60, and is configured to include multiple gas pipes. The hydrogen supply flow path 42 is provided with a first hydrogen supply valve 43, a second hydrogen supply valve 44, and a third hydrogen supply valve 45. When the first hydrogen supply valve 43 is opened, H2 generated in the hydrogen supply source 41 is injected into the first CO2 separator 21. When the second hydrogen supply valve 44 is opened, H2 generated in the hydrogen supply source 41 is injected into the second CO2 separator 22. When the third hydrogen supply valve 45 is opened, H2 is added from a hydrogen addition unit 46 to the raw material gas flowing through the raw material gas flow path 60. The opening and closing of the first hydrogen supply valve 43, the second hydrogen supply valve 44, and the third hydrogen supply valve 45 are each controlled by a control unit 90. The hydrogen supply passage 42 is provided with a temperature sensor and a flow rate sensor (not shown) for measuring the temperature and flow rate of the H2 gas supplied to the first CO2 separator 21, the second CO2 separator 22, and the raw material gas passage 60.

[0025] The reactor 50 is a container for producing CH4 through a methanation reaction therein, and contains a catalyst 51. The catalyst 51 contains a metal having methanation properties, such as Ru or Ni. A raw material gas passage 60 and a reaction gas passage 70 are connected to the reactor 50. The reactor 50 produces CH4 through a methanation reaction using a raw material gas containing CO2 and H2 supplied through the raw material gas passage 60. The reactor 50 corresponds to the "hydrocarbon production section" in the claims.

[0026] The raw material gas flow path 60 is a gas flow path for supplying the raw material gas containing H and CO sent from the first CO separator 21 and the second CO separator 22 to the reactor 50, and is configured to include multiple gas pipes. The raw material gas flow path 60 is provided with a first raw material gas valve 61 and a second raw material gas valve 62. The first raw material gas valve 61 and the second raw material gas valve 62 are each controlled to open and close by the control unit 90. Specifically, when the raw material gas inside the first CO separator 21 is to be supplied to the reactor 50, the first raw material gas valve 61 is controlled to be in an open state, and the second raw material gas valve 62 is controlled to be in a closed state. When the raw material gas inside the second CO separator 22 is to be supplied to the reactor 50, the first raw material gas valve 61 is controlled to be in a closed state, and the second raw material gas valve 62 is controlled to be in an open state. The raw material gas flow path 60 is provided with a temperature sensor, a flow rate sensor, and a CO2 concentration sensor (not shown) for measuring the temperature, flow rate, and CO2 concentration of the flowing raw material gas.

[0027] The reaction gas flow path 70 is a gas flow path for supplying CH4 generated in the reactor 50 to the mixed gas supply source 5, and is configured to include a plurality of gas pipes. A heat exchanger 71 is provided in the reaction gas flow path 70. The reaction mixed gas containing CH4 discharged from the reactor 50 is first supplied to the heat exchanger 71. In the heat exchanger 71, H2O is separated from the reaction mixed gas. The H2O separated from the reaction mixed gas is discharged to the outside of the system via an H2O discharge flow path 72. The reaction gas containing CH4 from which H2O has been separated is supplied to the mixed gas supply source 5 via the reaction gas flow path 70.

[0028] The heat medium flow path 80 is a flow path through which a heat medium (thermal fluid) such as oil flows, and supplies heat generated in the reactor 50 by the methanation reaction to the carbon dioxide separation unit 20. The heat medium flow path 80 is provided with a first flow path switching valve 81 and a second flow path switching valve 82. The heat medium flow path 80 includes three flow paths (a first heat medium flow path 83, a second heat medium flow path 84, and a third heat medium flow path 85) separated by these two valves. The first heat medium flow path 83 supplies the heat medium to the first CO2 separator 21. The second heat medium flow path 84 supplies the heat medium to the second CO2 separator 22. The third heat medium flow path 85 is provided with a pump 86 and a temperature adjustment unit 87. The heat medium in the third heat medium flow path 85 flows through the first heat medium flow path 83 or the second heat medium flow path 84 by driving the pump 86, and then returns to the third heat medium flow path 85 to be circulated. The temperature adjustment unit 87 is a device that adjusts the temperature of the heat medium, and when the temperature of the heat medium heated in the reactor 50 or the heat exchange unit 71 is higher than the set temperature, it adjusts the temperature by adding a heat medium at room temperature. Also, when the temperature of the heat medium is lower than the set temperature, in addition to adjusting the flow rate, it heats the heat medium to the set temperature using a heater or the like. The pump 86 and the temperature adjustment unit 87 are controlled by the control unit 90.

[0029] The first flow path switching valve 81 is a three-way valve for switching the destination (first heat medium flow path 83 or second heat medium flow path 84) of the heat medium sent out from the third heat medium flow path 85 by the pump 86. The second flow path switching valve 82 is linked to the switching of the first flow path switching valve 81, and is a three-way valve for switching the source (first heat medium flow path 83 or second heat medium flow path 84) of the heat medium returning to the third heat medium flow path 85. The switching of the first flow path switching valve 81 and the second flow path switching valve 82 is each controlled by a control unit 90.

[0030] The first heat medium flow path 83 includes a flow path that passes through the inside of the first CO2 separator 21, and is configured to supply heat of the heat medium to the CO2 adsorbent 21a. The first CO2 separator 21 is configured with a double pipe, and a flow path for the heat medium is formed between the outer pipe and the inner pipe.

[0031] The second heat medium flow path 84 includes a flow path that passes through the inside of the second CO2 separator 22, and is configured to supply heat from the heat medium to the CO2 adsorbent 22a. The second CO2 separator 22 is configured with a double pipe, and a flow path for the heat medium is formed between the outer pipe and the inner pipe.

[0032] The third heat medium flow path 85 includes a flow path passing through the inside of the reactor 50, and is configured so that heat generated by the methanation reaction inside the reactor 50 can be transferred to the heat medium. Here, the reactor 50 is configured with a double pipe, a catalyst 51 is disposed in the inner pipe, and a heat medium flow path is formed between the outer pipe and the inner pipe.

[0033] The control unit 90 is a computer including a ROM, a RAM, and a CPU, and performs overall control of the carbon dioxide circulation system 1. The control unit 90 is electrically connected to the valves and sensors (temperature sensors, flow rate sensors, concentration sensors, etc.) provided in each of the above-mentioned flow paths, as well as to the pump 86 and temperature adjustment unit 87, and controls the various valves, pump 86, temperature adjustment unit 87, etc. based on the measured values of the sensors, etc.

[0034] In the carbon dioxide circulation system 1, the mixed gas supplied from the mixed gas supply source 5 is dried in the gas dryer 10 by adsorbing and removing H2O. The dried mixed gas is sent to the carbon dioxide separation unit 20. In the carbon dioxide separation unit 20, the dried mixed gas is supplied to either the first CO2 separator 21 or the second CO2 separator 22. The CO2 separator to which the dried mixed gas is supplied adsorbs and recovers CO2 in the mixed gas. At this time, in the other of the first CO2 separator 21 or the second CO2 separator 22, H2 is supplied from the hydrogen supply source 41, causing the CO2 adsorbed in the CO2 adsorbent to be desorbed from the CO2 adsorbent, and the raw material gas containing CO2 and H2 is sent to the reactor 50. In this way, in the carbon dioxide separation unit 20, while either the first CO2 separator 21 or the second CO2 separator 22 is adsorbing CO2 from the mixed gas, the other of the first CO2 separator 21 or the second CO2 separator 22 supplies the raw material gas to the reactor 50. This allows the raw material gas containing CO2 and H2 to be supplied to the reactor 50 without interruption.

[0035] In the reactor 50, CH4 is produced using the raw material gas supplied from the carbon dioxide separation unit 20. The produced CH4 is discharged from the reactor 50 as a reaction mixture gas together with HO, a by-product. HO contained in the reaction mixture gas is removed from the reaction mixture gas in the heat exchange unit 71. The reaction gas from which HO has been removed is supplied to the mixture gas supply source 5 via the reaction gas flow path 70. In this embodiment, the mixture gas supply source 5 generates thermal energy by combusting CH4, and the generated thermal energy is used to generate electricity and drive various devices. The mixture gas containing CO2 produced by the combustion of CH4 in the mixture gas supply source 5 is supplied to the gas dryer 10. As a result, by using the mixture gas supply source 5 in combination with the carbon dioxide circulation system 1, thermal energy can be obtained in a circulated state without discharging carbon outside the system.

[0036] In the carbon dioxide circulation system 1, the gas drying adsorbent 11 that has adsorbed HO is heated in the gas dryer 10, thereby desorbing the adsorbed HO and regenerating the gas drying adsorbent 11. When the gas drying adsorbent 11 is regenerated, gas components other than HO adsorbed in the gas drying adsorbent 11 are also desorbed from the gas drying adsorbent 11. The gas components desorbed from the gas drying adsorbent 11, including HO, are discharged to the outside of the system by a purge gas. Note that the method for regenerating the gas drying adsorbent 11 that has adsorbed HO is not limited to the above-described method, and may be performed using only a purge gas.

[0037] Next, the gas drying adsorbent 11 will be described. The gas drying adsorbent 11 is a zeolite containing magnesium ions as cations. Specifically, the gas drying adsorbent 11 contains Mg 2.8 Na 0.8 Al 6.4 Si 17.6 O 48 The gas drying adsorbent 11 of this embodiment contains a composite oxide of aluminum and silicon, and the composition ratio of silicon to aluminum in this composite oxide is 2.75. Furthermore, the molar ratio of magnesium ions to cations contained in the Y zeolite is 0.78.

[0038] The ratio of magnesium ions to cations contained in the gas drying adsorbent 11 is measured by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, a solution is prepared by dissolving a certain amount of the gas drying adsorbent 11, and the amounts of cations and magnesium contained in the certain amount of the gas drying adsorbent 11 are measured. Next, the ratio of the amount of magnesium to the measured amount of cations is calculated, and the molar ratio of magnesium ions to cations contained in the Y-type zeolite is calculated. Alternatively, the ratio of magnesium ions to cations contained in the gas drying adsorbent 11 may be measured by energy dispersive X-ray spectroscopy (EDX). Specifically, the gas drying adsorbent 11 is polished to form a sample with an exposed cross section. The cross section of this sample is observed by EDX, and the total number of observed cation atoms and the total number of magnesium atoms within a predetermined range are counted. The ratio of the number of magnesium atoms to the total number of counted cation atoms is defined as the molar ratio of magnesium ions to cations contained in the Y-type zeolite. Furthermore, the proportion of magnesium ions in the cations contained in the gas drying adsorbent 11 may be measured using atomic absorption spectrometry (AAS).

[0039] The composition ratio of silicon to aluminum in the composite oxide contained in the Y-type zeolite is measured using ICP-AES or AAS. The type of zeolite contained in the gas drying adsorbent 11 is identified based on the measurement results obtained by X-ray diffraction (XRD).

[0040] Next, a method for producing the gas drying adsorbent 11 will be described. First, 10 g of zeolite pellets (NaY-type zeolite, Tosoh Corporation's HSZ-320NAD1C, Si / Al ratio = 2.75, composition Na: 6.4, Al: 6.4, Si: 17.6, O: 48) were immersed in 50 mL of 2 mol / L magnesium nitrate solution and allowed to stand overnight at 60°C with occasional stirring. After standing overnight, the sample was cooled to room temperature, filtered, and washed three times with 500 mL of ion-exchanged water. The washed sample was again immersed in 50 mL of fresh 2 mol / L magnesium nitrate solution and allowed to stand overnight at 60°C, followed by similar washing. The immersion, standing, and washing series was repeated once more, followed by drying, to obtain the zeolite for the gas drying adsorbent 11. This production method allows the cations of the zeolite to be exchanged from sodium ions to magnesium ions, thereby making it possible to achieve a cation exchange rate of 80% or more based on the number of ion exchange sites in the zeolite.

[0041] Next, the characteristics of the gas drying adsorbent 11 of this embodiment will be described using the performance of a gas dryer 10 equipped with the gas drying adsorbent 11. Here, the performance of the gas dryer 10 of this embodiment will be described in comparison with the performance of a gas dryer equipped with a comparative gas drying adsorbent. Here, the comparative gas drying adsorbent is a Y-type zeolite containing sodium ions as cations, and is a zeolite prepared before immersion in a magnesium nitrate solution in the above-mentioned production method. Hereinafter, the gas drying adsorbent 11 of this embodiment will be referred to as "MgY-type zeolite," and the comparative gas drying adsorbent will be referred to as "NaY-type zeolite."

[0042] Prior to evaluating the performance of the gas dryer, adsorption isotherms for CO2 and HO were prepared for MgY-type zeolite and NaY-type zeolite, respectively. The CO2 adsorption isotherm was prepared by pretreating 1 g of gas drying adsorbent in a vacuum at 150 °C and then measuring the amount of CO2 adsorbed at 30 °C using a volumetric fully automatic adsorption analyzer (BELSORP-MAX, manufactured by Microtrack Bell). The HO adsorption isotherm was prepared by pretreating 0.1 g of gas drying adsorbent in a vacuum at 150 °C and then measuring the amount of HO adsorbed at 25 °C using the volumetric fully automatic adsorption analyzer, as in the case of CO2.

[0043] In the performance evaluation test of the gas dryer, the conditions for the mixed gas and the gas dryer were set as follows in an experiment to dry a mixed gas containing CO2 and H2O. Mixed gas Flow rate: 6m 3 / h Dew point: 25℃ (H2O concentration: 3%) CO2 concentration: 10% As a result, the weight of H2O flowing into the gas dryer is 0.145 kg per hour. H2O The weight of CO2 flowing into the gas dryer is 1.18 kg per hour. CO2 This becomes: Gas dryer Internal volume: 0.26m 3 Packing weight of gas drying adsorbent: 1.82 kg ads (bulk density: 0.7 kg / L)

[0044] In the gas dryer, the adsorbent for gas drying is brought into contact with the mixed gas for 2.5 hours (adsorption step), and then the adsorbent for gas drying is regenerated (regeneration step). In this case, to adsorb all of the HO flowing into the gas dryer, 1 kg of HO per hour is required. ads It is necessary to adsorb 0.08 kg of H2O by the gas drying adsorbent. Therefore, in one adsorption process, the amount of H2O required for the adsorbent is 0.2 kg. H2O / kg ads This becomes:

[0045] From the H2O adsorption isotherms of MgY-type zeolite and NaY-type zeolite, the saturated H2O adsorption capacity of MgY-type zeolite and NaY-type zeolite was 0.3 kg / s. H2O / kg ads Therefore, there is no difference in the HO adsorption performance, i.e., the mixed gas drying capacity, between MgY-type zeolite and NaY-type zeolite. Therefore, even if MgY-type zeolite is used instead of NaY-type zeolite, the drying performance of the gas dryer does not change. In the performance evaluation test of the gas dryer described above, both MgY-type zeolite and NaY-type zeolite have sufficient capacity to adsorb HO, so the regeneration cycle (2.5 hours) can be extended (for example, to 3.5 hours). However, to maintain system redundancy, the regeneration timing of the gas drying adsorbent was maintained at 2.5 hours.

[0046] Figure 2 is a conceptual diagram illustrating the distribution of adsorbed HO within a gas dryer. Under the conditions described above, approximately 30% of the adsorbent packed in the gas dryer is not used to adsorb HO. As shown in Figure 2, when the mixed gas flows from one side of the gas dryer to the other (the direction indicated by the white arrow in Figure 2), the HO contained in the mixed gas is adsorbed by the gas drying adsorbent packed upstream of the mixed gas in the gas dryer. Therefore, the gas drying adsorbent downstream of the mixed gas in the gas dryer is not used to adsorb HO. Because the mixed gas from which HO has been removed passes through this unused adsorbent (the "HO non-adsorbed portion" in Figure 2), CO contained in the mixed gas is adsorbed. In other words, in this evaluation test, CO is adsorbed by 0.61 kg of gas drying adsorbent in one adsorption process.

[0047] Figure 3 illustrates the CO2 loss rate in the gas dryer. As mentioned above, when the CO2 concentration in the mixed gas is 10%, the total amount of CO2 flowing into the gas dryer during one adsorption process is 2.95 kg. Based on the CO2 adsorption isotherms for MgY-type zeolite and NaY-type zeolite, the "CO2 adsorption amount per unit weight" at a CO2 partial pressure of 10 kPa is 0.031 kg for MgY-type zeolite and 0.059 kg for NaY-type zeolite. Therefore, the "CO2 adsorption amount in the unused adsorbent" is 0.019 kg for MgY-type zeolite and 0.036 kg for NaY-type zeolite. The CO2 adsorbed by this "unused adsorbent" is the amount of CO2 lost and discharged outside the system during the regeneration process. The ratio of CO2 released outside the system in the regeneration process ("CO2 loss rate") to the total amount of CO2 flowing into the gas dryer in one adsorption process is smaller for MgY zeolite (0.65%) than for NaY zeolite (1.21%), so MgY zeolite can reduce the amount of CO2 released outside the system. In other words, MgY zeolite can suppress the decrease in the carbon dioxide content of the mixed gas more effectively than NaY zeolite.

[0048] In addition, the gas dryer included in the carbon dioxide circulation system is repeatedly regenerated by operating the carbon dioxide circulation system for a long period of time. Therefore, the CO2 emitted outside the system during the regeneration process cannot be used to produce hydrocarbon compounds in the carbon dioxide circulation system. As mentioned above, MgY-type zeolite can suppress the decrease in the carbon dioxide content of the mixed gas, so more carbon dioxide can be supplied to the carbon dioxide separation section in the subsequent stage than NaY-type zeolite. This improves the carbon circulation rate throughout the carbon dioxide circulation system.

[0049] Figure 4 shows the relationship between the ratio of unused adsorbent and the amount of CO2 loss. As described above, the amount of CO2 discharged outside the system during the regeneration process of the adsorbent for gas drying, that is, the amount of CO2 loss, is determined by the ratio of the unused adsorbent (the "unadsorbed H2O part" in Fig. 2) in the gas dryer. Therefore, the relationship between the ratio of the unused adsorbent in the gas dryer (the ratio to the total weight of the adsorbent for gas drying) and the CO2 loss rate was compared for each of MgY-type zeolite and NaY-type zeolite. The results are shown in Fig. 4.

[0050] The horizontal axis of Fig. 4 indicates the ratio of the unused adsorbent in the gas dryer. Specifically, the ratio of the unused adsorbent is represented by the ratio of the total weight of H2O flowing into the gas dryer to the weight of H2O that can be adsorbed by the adsorbent filled in the gas dryer. If the total weight of H2O flowing into the gas dryer is α (kg / hour) per unit time and the time for one cycle is β (hours), it can be expressed as α×β (kg). Also, if the weight of the adsorbent for gas drying filled in the gas dryer is γ (kg) and the weight of H2O that can be adsorbed by the adsorbent for gas drying per unit weight is Wsat (kg / kg), it can be expressed as γ×Wsat (kg). Since (α×β) / (γ×Wsat), that is, the ratio of α×β to γ×Wsat, is the ratio of the weight of the used adsorbent for gas drying when all the H2O flowing into the gas dryer is adsorbed by the adsorbent for gas drying to the total weight of the adsorbent for gas drying filled in the gas dryer, {1 - (α×β) / (γ×Wsat)} is the ratio of the adsorbent for gas drying that is not used for H2O adsorption among the adsorbent for gas drying filled in the gas dryer. That is, the larger {1 - (α×β) / (γ×Wsat)} is, the larger the proportion of the unused adsorbent filled in the gas dryer. Note that for the gas dryer during actual use, it is necessary that α×β / γ < Wsat. If α×β / γ > Wsat, there will be no adsorbent for gas drying that is not used for H2O adsorption. The vertical axis of Fig. 4 indicates the "CO2 loss rate" shown in Fig. 3.

[0051] As shown in Figure 4, comparing MgY-type zeolite (solid line L1 in Figure 4) and NaY-type zeolite (dashed line L2 in Figure 4), the difference in CO2 loss rate increases as the unused adsorbent fraction (horizontal axis) increases. Here, when the unused adsorbent fraction is less than 0.3, the difference in CO2 loss rate between MgY-type zeolite and NaY-type zeolite decreases, but the redundancy of the HO storage performance of the gas dryer decreases, and there is a risk of HO leakage from the gas dryer due to sudden fluctuations in gas flow rate. Furthermore, when the unused adsorbent fraction is greater than 0.6, the CO2 loss rate of MgY-type zeolite is less than half that of NaY-type zeolite, resulting in a significant reduction in CO2 loss rate. However, as the unused adsorbent fraction increases, the utilization rate of the gas drying adsorbent when adsorbing HO from the mixed gas decreases. Furthermore, if the ratio of unused adsorbent is greater than 0.6, excess gas drying adsorbent will be present, which will lead to an increase in the energy required to desorb HO by thermal regeneration (e.g., sensible heat loss). Therefore, the range of the ratio of unused adsorbent is preferably 0.3≦{1−(α×β) / (γ×Wsat)}≦0.6 (the range indicated by the double-ended arrow A1 in Figure 4).

[0052] As described above, the gas drying adsorbent 11 of this embodiment includes zeolite containing magnesium ions as cations. Zeolite containing magnesium ions has almost the same HO storage performance as zeolite containing sodium ions as cations, but has a lower CO storage performance. This suppresses CO adsorption when drying a mixed gas containing CO, thereby suppressing a decrease in the carbon dioxide content of the mixed gas discharged from the gas dryer 10.

[0053] In addition, according to the gas drying adsorbent 11 of this embodiment, the gas drying adsorbent 11 contains Mg 2.8 Na 0.8 Al 6.4 Si 17.6 O 48The gas drying adsorbent 11 contains Y-type zeolite having a composition of 2.75. That is, the aluminum to silicon composition ratio in the aluminum-silicon composite oxide is 2.75. This increases the ion exchange capacity of the zeolite, and the zeolite has pores large enough to allow magnesium ions to pass through, allowing the zeolite to contain a larger amount of magnesium ions. Therefore, compared to zeolites containing sodium ions as cations, the gas drying adsorbent 11 can reduce the CO2 storage capacity without significantly changing the HO storage capacity, thereby preventing a decrease in the carbon dioxide content of the mixed gas when drying the mixed gas containing CO2.

[0054] Furthermore, in the gas drying adsorbent 11 of this embodiment, the aluminum to silicon composition ratio in the aluminum-silicon composite oxide is 2 to 5, with a relatively high aluminum content. This improves the hydrophilicity of the zeolite, making it more likely to adsorb moisture. This can improve the dryness of the mixed gas discharged from the gas dryer 10.

[0055] Furthermore, according to the carbon dioxide circulation system 1 of this embodiment, the mixed gas discharged from the mixed gas supply source 5 is dried in the gas dryer 10. At this time, the gas drying adsorbent 11 provided in the gas dryer 10 adsorbs H2O but does not adsorb much CO2, so the mixed gas sent from the gas dryer 10 to the carbon dioxide separation unit 20 contains a relatively large amount of CO2. CO2 recovered from the mixed gas sent to the carbon dioxide separation unit 20 becomes a raw material for CH4 generated in the reactor 50. This generated CH4 is supplied to the mixed gas supply source 5. In the mixed gas supply source 5, thermal energy is extracted by combustion of CH4, and a mixed gas containing CO2 and H2O is generated. This generated mixed gas is dried again in the gas dryer 10, and then CO2 is recovered as a raw material for CH4 in the carbon dioxide separation unit 20. In this way, the carbon dioxide circulation system 1 can extract energy such as combustion heat while circulating carbon between the mixed gas supply source 5 and the carbon dioxide circulation system 1. In the carbon dioxide circulation system 1, when the gas drying adsorbent 11 adsorbs HO in the gas dryer 10, a regeneration process is performed in which the HO is desorbed from the gas drying adsorbent 11 by heating or the like and discharged outside the system. The gas drying adsorbent 11 is less likely to adsorb CO than, for example, zeolite containing sodium ions as cations, and therefore less CO is discharged outside the system together with HO in the regeneration process. This makes it possible to improve the carbon circulation rate throughout the system when carbon is circulated between the mixed gas supply source 5 and the carbon dioxide circulation system 1.

[0056] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0057] [Variation 1] In the above-described embodiment, the gas drying adsorbent 11 is used in the gas dryer 10 included in the carbon dioxide circulation system 1. However, the application field of the gas drying adsorbent 11 is not limited to this. For example, since a gas containing CO2 and H2O can be separated into CO2 and H2O with high accuracy, the separated CO2 and H2O can each be used for different purposes.

[0058] [Variation 2] In the above embodiment, the gas drying adsorbent 11 is made of Mg zeolite with a molar ratio of magnesium ions to cations of 0.78. 2.8 Na 0.8 Al 6.4 Si 17.6 O 48 The adsorbent contains a Y-type zeolite having a composition of the formula: In this Y-type zeolite, the molar ratio of magnesium ions to cations is 0.78, but the molar ratio of magnesium ions to cations is preferably 0.8 or more. This further reduces the CO2 absorption capacity of the gas drying adsorbent. Therefore, when drying a gas containing carbon dioxide, it is possible to further suppress a decrease in the carbon dioxide content of the gas. In the above-mentioned production method, by further repeating the series of steps of immersion, standing, and washing, it is possible to obtain a zeolite having a molar ratio of magnesium ions to cations of 0.8 or more.

[0059] [Variation 3] In the above-described embodiment, the zeolite contained in the gas drying adsorbent 11 is Y-type zeolite, in which the silicon to aluminum composition ratio in the composite oxide is 2.75. However, the silicon to aluminum composition ratio is not limited to this and may be 2 or more and 5 or less. When the silicon to aluminum composition ratio is 2 or more and 5 or less, the ion exchange capacity of the zeolite can be increased, and therefore, the zeolite can contain more magnesium ions.

[0060] [Variation 4] In the above-described embodiment, the carbon dioxide circulation system 1 includes the gas dryer 10, the carbon dioxide separation unit 20, the hydrogen supply source 41, the reactor 50, and the like. However, the configuration of the carbon dioxide circulation system 1 is not limited to this. For example, the carbon dioxide separation unit 20 does not need to include two CO2 separators; even if it includes only one, it can supply a raw material gas containing CO2 and H2 to the reactor 50 by switching between a CO2 adsorption step and a CO2 desorption step.

[0061] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0062] 1...Carbon dioxide circulation system 5...Mixed gas supply source 10...Gas dryer 11...Gas drying adsorbent 12...Storage container 20...Carbon dioxide separation section 41...Hydrogen source 50...Reactor

Claims

1. 1. A carbon dioxide circulation system comprising: a gas dryer including a gas drying adsorbent including zeolite containing magnesium ions as cations and a container for accommodating the gas drying adsorbent, the gas dryer drying the mixed gas containing carbon dioxide and moisture by adsorbing the moisture in the mixed gas supplied from an external gas generating unit to the gas drying adsorbent; a carbon dioxide recovery unit that recovers carbon dioxide from the mixed gas dried in the gas dryer; a hydrocarbon production unit that produces hydrocarbon compounds using the carbon dioxide recovered in the carbon dioxide recovery unit and supplies the hydrocarbon compounds to the external gas generation unit, Carbon dioxide circulation system.

2. 2. The carbon dioxide circulation system according to claim 1, The gas drying adsorbent has a molar ratio of magnesium ions to cations contained in the zeolite of 0.8 or more. Carbon dioxide circulation system.

3. The carbon dioxide circulation system according to claim 1 or 2, The zeolite contains a composite oxide of aluminum and silicon, the composition ratio of silicon to aluminum in the composite oxide is 2 or more and 5 or less; Carbon dioxide circulation system.

4. 4. The carbon dioxide circulation system according to claim 3, The zeolite is a Y-type zeolite, The composition ratio of silicon to aluminum in the composite oxide is 2.

75. Carbon dioxide circulation system.

5. 2. The carbon dioxide circulation system according to claim 1, The zeolite contains Mg y Na (6.4-2y) Al 6.4 Si 17.6 O 48 is a Y-type zeolite having a composition y is equal to or greater than 2.23; Carbon dioxide circulation system.

6. An adsorbent for drying gas that dries the gas by adsorbing moisture contained in the gas, comprising: Zeolite containing magnesium ions as cations, The zeolite is a Y-type zeolite having a composition of Mg y Na (6.4-2y) Al 6.4 Si 17.6 O 48 , y is equal to or greater than 2.23; Adsorbent for gas drying.

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