JP5031275B2 - Isotope gas separation method using pressure swing adsorption method - Google Patents

Description

  The present invention relates to a method for separating an isotope gas using a pressure swing adsorption method (hereinafter referred to as “PSA method” where appropriate), and more specifically, using a plurality of adsorption towers packed with an isotope selective adsorbent. Gas molecules containing specific isotope atoms by selectively adsorbing and separating gas molecules having specific isotope atoms as constituent elements from source gases containing multiple types of isotope gases using pressure swing adsorption method The present invention relates to a method for separating and concentrating an isotope gas by changing the concentration of.

There is a technique for separating ¹³ CH ₄ that is an isotope gas from methane using an adsorbent. This separation technology is a technology that increases the concentration of ¹³ CH ₄ that has passed through the adsorbent by selectively adsorbing ¹² CH ₄ of ¹² CH ₄ and ¹³ CH ₄ , which are methane isotopes, to the adsorbent. It is.

For example, (hereinafter referred to "767 JP".) JP 2004-89767 discloses in, as an adsorbent which selectively adsorbs the ¹² CH ₄ of ¹² CH _4, ¹³ CH ₄ contained in the methane gas, Na A material obtained by heat-treating Na-A-type zeolite, in which at least a part thereof is replaced with Ca or Zn at a temperature of 650 ° C. or higher and 800 ° C. or lower, pentasil zeolite or mordenite zeolite is used.

The 767 discloses, by contacting them methane containing relatively under high pressure ¹³ CH ₄ and ¹² CH ₄ with respect to the adsorbent, together with the adsorbing primarily ¹² CH _4, flow of ¹³ CH ₄ It is said that it is suitable for separation by the PSA method in which ¹² CH ₄ is desorbed by lowering the adsorbent adsorbing ¹² CH ₄ to a relatively low pressure after recovery.

FIG. 1 is a diagram for explaining an outline of an isotope separation device described in Japanese Patent No. 767 and a separation and concentration process by the isotope separation device. The adsorption towers 31 to 33 are filled with an adsorbent that selectively adsorbs ¹² CH ₄ , and each of the adsorption towers 31 to 33 has an operation cycle of ¹² CH ₄ adsorption → cocurrent purge → decompression → countercurrent purge → pressure increase. Repeatedly. Hereinafter, according to the description in paragraphs 0029 to 0035 of No. 767, focusing on the adsorption tower 31, the separation and concentration process will be described.

First, the valve 1 is opened, and the raw material gas containing ¹² CH ₄ and ¹³ CH ₄ is supplied from the flow path 34 to the adsorption tower 31 in the cold box 30 by the blower 35. The ¹² CH ₄ contained in the raw material gas is selectively adsorbed by the adsorbent packed in the adsorption tower 31, and the gas after adsorbing ¹² CH ₄ , that is, ¹³ CH ₄ enriched gas, It is collected through the passage 38 and the blower 39. At this time, ¹² CH ₄ is desorbed by suction by the vacuum pump 37 in one of the adsorption towers 32 and 33, and the desorbed ¹² CH ₄ enriched gas is stored in the buffer tank 36.

Next, the valves 1 and 4 are closed, the valves 3 and 6 are opened, and ¹² CH ₄ enriched gas is supplied from the buffer tank 36 through the flow path 45 to the adsorption tower 31. Thus, ¹² CH ₄ portion of the enriched gas is replaced with ¹³ CH _4, which is partially adsorbed to ¹³ CH ₄ and adsorbent remaining in the adsorption tower 31, reducing the ¹³ CH ₄ concentration in the adsorption tower 31 Let The gas discharged from the adsorption tower 31 has a high ¹³ CH ₄ concentration, is refluxed to the flow path 34 through the valve 6 and the flow path 46, and is supplied to one of the adsorption towers 32 and 33.

Here, the direction of the ¹² CH ₄ enriched gas from the buffer tank 36 is the same direction as the raw material gas when adsorbing ¹² CH ₄ from the raw material gas containing ¹² CH ₄ and ¹³ CH ₄ , that is, “cocurrent purge” ". In the first operation cycle in which the ¹² CH ₄ enriched gas is not recovered in the buffer tank 36, it is preferable to supply the ¹² CH ₄ enriched gas into the buffer tank 36 in advance. May be omitted.

Next, the valve 2 of the adsorption tower 31 is opened, and the remaining valves 1 and 3 to 6 are closed. Then, the inside of the adsorption tower 31 is depressurized by the vacuum pump 37 from the time of ¹² CH ₄ adsorption, preferably 1 to 20 kPa. As a result, the ¹² CH ₄ enriched gas is desorbed and temporarily stored in the buffer tank 36 via the valve 2 and the flow path 41. The ¹² CH ₄ enriched gas in the buffer tank 36 is used for the cocurrent purge of the adsorption towers 32 and 33 different from the adsorption tower 31 through the flow path 45.

Further, the valve 5 is opened, and the gas in the countercurrent purge tank 43 is supplied to the adsorption tower 31 through the blower 44 and the flow path 42. Since this operation remarkably increases the ¹² CH ₄ concentration in the adsorption tower 31 by cocurrent purge, it is possible that removal of ¹² CH ₄ may be insufficient only by simple pressure reduction by the vacuum pump 37. Following the ¹² CH ₄ recovery by vacuum, and the direction of the raw material gas under reduced pressure by supplying a countercurrent purge gas containing no ¹² CH ₄ from the opposite direction, ¹² in the adsorption tower 31 by clogging "countercurrent purge" It is described that it is for completely removing CH ₄ (see paragraph 0034 of No. 767).

As described above, in the isotope separation device of 767, the ¹² CH ₄ enriched gas adsorbed on the adsorbent is desorbed from the adsorption tower inlet side by the vacuum pump 37, sent to the buffer tank 36, and stored. The ¹² CH ₄ enriched gas stored in 36 can be refluxed to the adsorption tower inlet side where the adsorption operation is completed. However, according to Table 3 shown as the operating conditions of Example 2 using the separation apparatus, the cocurrent purge rate R2 is 0%, and the desorption gas flows to the adsorption tower inlet side where the adsorption operation is completed. Is not refluxed and not used at all.

  A co-current reflux operation in which the gas adsorbed on the adsorbent in the adsorption tower is sucked with a vacuum pump and desorbed from the inlet side of the adsorption tower, and the desorbed gas is sent to the inlet side of the adsorption tower after the adsorption operation is completed is disclosed in Japanese Patent No. 3025653. It is also disclosed in a gazette (hereinafter referred to as “653” gazette). In Japanese Patent No. 653, each component is separated and concentrated using a mixed gas of ammonia, nitrogen, and hydrogen, a mixed gas of nitrogen, oxygen, and chlorine, or a mixed gas of nitrogen, hydrogen, and carbon monoxide as a source gas.

  As the operation, desorption gas from the adsorption tower inlet at the time of regeneration is flowed from the other adsorption tower inlet after completion of the adsorption operation in the other adsorption tower, so that the effect of higher separation and concentration can be obtained for each component. It is said that. However, it is unclear whether the technique of the 653 publication can be applied to, for example, a co-current reflux operation in the separation and concentration operation of methane isotopes, and what proportion of gas is relative to the amount of gas desorbed from the adsorbent. It is also unclear whether a higher separation and concentration effect can be obtained by refluxing the amount.

  In the meantime, as in the 767 and 653 publications, in the separation and concentration operation performed by the cocurrent reflux for sending the desorption gas from the adsorption tower inlet side to the adsorption tower, the desorption gas is sent from the adsorption tower outlet side to the adsorption tower. There are also separation and concentration operations carried out by flow reflux. The former reflux is called a cocurrent reflux operation, and the latter reflux is called a countercurrent reflux operation.

  The counter-current reflux operation is not related to the isotope gas separation and concentration operation, but is described in, for example, Japanese Patent No. 323003 (hereinafter referred to as “003”). In No. 003, air is used as a raw material gas, and oxygen is separated and concentrated using a zeolite Li-X adsorbent. Specifically, when two adsorption towers are used and the gas of one adsorption tower is desorbed from the tower entrance side by a vacuum pump, the gas discharged from the adsorption tower outlet during adsorption of the other adsorption tower is removed. It flows to the outlet of the adsorption tower that is being desorbed. And by performing this operation, it is said that higher purity oxygen can be produced at a higher recovery rate than when this operation is not performed.

JP 2004-89767 A Japanese Patent No. 3025653 Japanese Patent No. 323003

By the way, since the isotope gas separation method using the PSA method is separation using an adsorbent, the apparatus configuration and operation are simple, and this is an interesting technique from a practical viewpoint. However, in the technology of No. 767, the ¹³ CH ₄ enriched gas obtained by the separation and concentration operation is recovered as it is or is sent to a subsequent apparatus. For this reason, in order to achieve a higher separation / concentration effect than the separation / concentration effect that can be achieved by the separation / concentration operation, a subsequent apparatus must be prepared, and this increases the overall apparatus configuration. End up.

  Further, even if the technique of No. 653 is applied to the separation of isotope gas, the product gas obtained by the separation and concentration operation is taken out of the system as it is. Therefore, as in the case of the technique of No. 767, In order to achieve a high separation / concentration effect, it is necessary to prepare a subsequent apparatus, and the entire apparatus configuration becomes large.

  Further, even if the technology of 003 is applied to the separation and concentration of isotope gas, in this technology, the product gas obtained by the separation and concentration operation is refluxed to the separation and concentration device, but the reflux is performed at the outlet of the adsorption tower. This is a completely different operation from the reflux to the source gas supply side.

  The present inventors have found that these problems in the prior art can be solved while repeating various experiments on the isotope gas separation and concentration operation using the PSA method. That is, the present invention is an isotope gas separation method using the PSA method, without taking a large-scale apparatus configuration for realizing a higher separation and concentration effect as in the techniques of 767 and 653. Another object of the present invention is to provide a method for separating an isotope gas using the PSA method capable of realizing a high separation and concentration effect.

The present invention (1) is a method for separating and concentrating isotope gas using a pressure swing adsorption method using an adsorption tower packed with an isotope selective adsorbent. And
(A) After at least one isotope gas is adsorbed on the isotope-selective adsorbent of the adsorption tower from the source gas containing a plurality of kinds of isotope gases, and other isotope gases are passed through and recovered. ,
(B) recirculating other recovered isotope gas to the source gas supply side;
(C) Next, the adsorption tower is set to a pressure lower than that during adsorption, and the isotope gas adsorbed on the isotope selective adsorbent is desorbed and regenerated,
(D) The operations (a) to (c) are repeated a plurality of times.

  In the present invention (1), the raw material gas containing a plurality of types of isotope gases is a gas containing at least one of methane, ethane, ethylene, propane, butane, carbon dioxide and ammonia.

The present invention (2) is a method for separating and concentrating an isotope gas of methane from a raw material gas containing methane using a pressure swing adsorption method using an adsorption tower packed with an isotope selective adsorbent. And
(A) After adsorbing ¹² CH ₄ from methane on the isotope-selective adsorbent of the adsorption tower and allowing ¹³ CH ₄ to flow through to recover ¹³ CH ₄ enriched gas,
(B) refluxing the recovered ¹³ CH ₄ enriched gas to the source gas supply side,
(C) Next, the adsorption tower is set to a lower pressure than during adsorption, and ¹² CH ₄ adsorbed on the isotope-selective adsorbent is desorbed and regenerated,
(D) The operations (a) to (c) are repeated a plurality of times.

  The present invention (2) corresponds to the case of the present invention (1) in which the source gas containing the plurality of types of isotope gases is methane or a gas containing methane.

  In the present invention (1)-(2), the configuration of the above (b), that is, “returning the recovered other isotope gas to the raw material gas supply side” is an important configuration. It can be improved further. By the operation (b) in the present invention (1)-(2), the concentration of the isotope gas on the source gas supply side is increased, and the separation factor can be further improved. Further, by repeating the operations (a) to (c), particularly the operation (b) at least 45 times, the separation factor can be improved to the maximum.

The present invention (3) is a method for separating and concentrating isotope gas using a pressure swing adsorption method using at least one adsorption tower packed with an isotope selective adsorbent. And
(A) In one adsorbing tower, at least one isotope gas is adsorbed on an isotope selective adsorbent from a source gas containing a plurality of isotope gases, and other isotope gases are allowed to flow through. After collecting
(B) recirculating other recovered isotope gas to the source gas supply side;
(C) Immediately before regenerating the isotope-selective adsorbent of the adsorption tower at a low pressure, the isotope gas that has been desorbed in advance during regeneration and that has been stored is allowed to flow from the inlet of the adsorption tower. Perform the co-current reflux operation to return the gas discharged from the source gas side,
(D) Next, the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure,
(E) The operations (a) to (d) are repeated a plurality of times.

As one aspect of the present invention (3), when two adsorption towers of an adsorption tower A and an adsorption tower B filled with an isotope-selective adsorbent are used, and isotope gas is separated and concentrated using a pressure swing adsorption method Is performed as follows (a)-(e).
(A) In the adsorption tower A, at least one isotope gas is adsorbed on the isotope-selective adsorbent from the source gas containing a plurality of isotope gases, and another isotope gas is passed through and recovered. After
(B) recirculating other recovered isotope gas to the source gas supply side;
(C) Immediately before regenerating the isotope-selective adsorbent in the adsorption tower A at a low pressure, it is desorbed during the regeneration of the adsorption tower B, and the stored isotope gas is introduced from the inlet side of the adsorption tower A. , Perform a co-current reflux operation to return the gas discharged from the outlet side of the adsorption tower A to the raw material gas side,
(D) Next, the isotope-selective adsorbent of the adsorption tower A is regenerated at a low pressure,
(E) The operations (a) to (d) are repeated a plurality of times.

  In the present invention (3), the source gas containing a plurality of types of isotope gases is a gas containing at least one of methane, ethane, ethylene, propane, butane, carbon dioxide and ammonia.

The present invention (4) is a method for separating and concentrating an isotope gas of methane from a source gas containing methane using a pressure swing adsorption method using at least one adsorption tower packed with an isotope selective adsorbent. It is. And
(A) After adsorbing ¹² CH ₄ from methane to an isotope-selective adsorbent in a certain adsorption tower and allowing ¹³ CH ₄ to flow through and recovering ¹³ CH ₄ enriched gas,
(B) refluxing the recovered ¹³ CH ₄ enriched gas to the source gas supply side,
(C) Immediately before the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure, ¹² CH ₄ previously desorbed and stored at the time of regeneration is introduced from the entrance of the adsorption tower, so that the exit of the adsorption tower Perform the co-current reflux operation to return the gas discharged from the source gas side,
(D) Next, the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure,
(E) The operations (a) to (d) are repeated a plurality of times.

As one aspect of the present invention (4), two adsorption towers, an adsorption tower A and an adsorption tower B filled with an isotope-selective adsorbent, are used, and a methane-containing raw material gas is converted using a pressure swing adsorption method. In the case of isolating and concentrating isotope gas, it is performed as follows (a)-(e).
(A) In the adsorption tower A, ¹² CH ₄ is adsorbed from methane to the isotope selective adsorbent, and ¹³ CH ₄ enriched gas is recovered by passing ¹³ CH ₄ through,
(B) refluxing the recovered ¹³ CH ₄ enriched gas to the source gas supply side,
(C) Immediately before regenerating the isotope-selective adsorbent of the adsorption tower A at a low pressure, it is desorbed when the adsorption tower B is regenerated, and the stored ¹² CH ₄ is allowed to flow from the inlet side of the adsorption tower A. , Perform a co-current reflux operation to return the gas discharged from the outlet side of the adsorption tower A to the raw material gas side,
(D) Next, the isotope-selective adsorbent of the adsorption tower A is regenerated at a low pressure,
(E) The operations (a) to (d) are repeated a plurality of times.

  The present invention (4) corresponds to the case of the present invention (3) in which the source gas containing the plurality of kinds of isotope gases is methane or a gas containing methane.

  In the present invention (3)-(4), the configuration of the above (b), that is, “returning the recovered other isotope gas to the raw material gas supply side” is an important configuration. As in the case of 1)-(2), the separation factor can be further improved.

  Further, in the present invention (3)-(4), the constitution of (c), that is, “desorbed and stored in advance at the time of regeneration immediately before the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure. It is an important configuration to allow the isotope gas to flow from the inlet of the adsorption tower and to perform a cocurrent reflux operation to return the gas discharged from the outlet of the adsorption tower to the raw material gas side. Further improvements can be made.

  By the operations (b) and (c) in the present invention (3)-(4), the concentration of the isotope gas on the source gas supply side is increased, and the separation factor can be further improved. Further, by repeating the operations (a) to (d), particularly the operations (b) and (c) at least 30 times or more, the separation factor can be improved to the maximum.

  According to the present invention (1)-(2), the isotope-enriched gas that has flowed and recovered during adsorption by the isotope-selective adsorbent is refluxed to the source gas supply side, and this operation is repeated a plurality of times. High separation and concentration effect can be obtained.

  Also, according to the present invention (3)-(4), in addition to the present invention (1)-(2), the regeneration of the adsorption tower is performed immediately before the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure. Sometimes the desorbed and stored isotope gas is allowed to flow from the inlet of the adsorption tower, so that the gas discharged from the outlet of the adsorption tower is returned to the raw material gas side. Obtainable.

In the present invention, as the isotope-selective adsorbent, an adsorbent that selectively adsorbs a gas containing at least one isotope atom from a gas containing a plurality of isotope atoms for the elements constituting the gas is used. For example, in the case of methane, the constituent elements thereof are C and H. Of these, element C naturally has at least two isotope atoms of ¹³ C and ¹² C, and therefore methane contains ¹³ CH ₄ And methane. Two types of methane, ¹² CH _4, are included. For this reason, as an isotope selective adsorbent, an adsorbent that selectively adsorbs ¹² CH ₄ or ¹³ CH ₄ from the methane is used.

  When the source gas is a gas containing at least one of methane, ethane, ethylene, propane and butane, carbon dioxide gas or ammonia, and helium is used as the carrier gas, mordenite zeolite is effective, Of these, mordenite-type zeolite that supports ions by ion exchange is particularly effective.

  This adsorbent was previously developed by the present inventors (Japanese Patent Application No. 2005-38922, filing date = February 16, 2005). According to this adsorbent, gas isotope separation can be effectively performed not only in a low temperature range of 0 ° C. or lower, but particularly at a room temperature exceeding 0 ° C. There are various types of mordenite-type zeolite having cations, including those having H ions as cations, those having metal ions, and those having ammonium ions. These can be obtained by ion exchange of mordenite-type zeolite.

  When the raw material gas is a gas containing at least one of methane, ethane, ethylene, propane, and butane, carbon dioxide, or ammonia, activated carbon, particularly molecular sieve charcoal is also effective. This adsorbent was previously developed by some of the present inventors (Japanese Patent Application No. 2005-214093, filing date = July 25, 2005). According to this adsorbent, it is possible to effectively perform gas isotope separation by using nitrogen instead of helium as a carrier gas.

Application for Japanese Patent Application No. 2005-38922 Application for Japanese Patent Application No. 2005-214093

  Hereinafter, embodiments of the present invention will be described based on experimental examples. An apparatus having the configuration shown in FIG. 2 was used as an experimental apparatus. In this experimental apparatus, two towers of an adsorption tower A and an adsorption tower B filled with an isotope selective adsorbent are juxtaposed. The experimental examples described below also correspond to the examples of the present invention.

  In this experimental apparatus, two adsorption towers are used. However, in the separation method of the present invention, only one adsorption tower may be used, or three or more adsorption towers may be used. A smaller number of adsorption towers can reduce the amount of adsorbent and reduce the installation space of the apparatus, but the separation operation takes time. Further, if the number of adsorption towers is increased, the amount of adsorbent increases and the installation space for the apparatus increases, but the time required for the separation operation can be shortened. The number of adsorption towers can be appropriately set according to conditions such as the amount of adsorbent, the time required for operation, and the installation space of the apparatus.

As isotope selective adsorbents, Na-mordenite type zeolite and molecular sieve charcoal 4A (manufactured by Nippon Enviro Chemicals) were used to separate methane, which is an isotope gas. Na-mordenite type zeolite and molecular sieve charcoal 4A are adsorbents that selectively adsorb ¹² CH ₄ from methane composed of ¹² CH ₄ and ¹³ CH ₄ .

  In FIG. 2, the carrier gas is supplied from the carrier gas supply source 51 to the buffer tank BT1 via the valve V1 and the flow rate controller MFC1, and the methane gas is supplied from the methane gas supply source 52 to the buffer tank BT1 via the valve V2 and the flow rate controller MFC2. Supply. Then, the mixed gas of the carrier gas and methane is introduced from the buffer tank BT1 to the adsorption tower A or the adsorption tower B.

  In both the adsorption tower A and the adsorption tower B, separation and concentration operations are performed in the order of the steps of pressure increase → adsorption → collection → cocurrent reflux → regeneration. The regeneration step is performed in the other adsorption tower during the period in which one adsorption tower undergoes the steps from the pressure increase to the reflux. The pressure at the inlet of the adsorption tower A is measured with the pressure gauge P1, the pressure at the outlet of the adsorption tower A is measured with the pressure gauge P2, the pressure at the inlet of the adsorption tower B is measured with the pressure gauge P3, and the pressure at the outlet of the adsorption tower B is the pressure. Measured with a total of P4.

<Outline of each step of pressurization->adsorption->collection->reflux-> regeneration
(1) In the pressure increasing step, a carrier gas is flowed to the adsorption tower whose pressure has become lower than the atmospheric pressure during regeneration, and the pressure in the adsorption tower is increased in preparation for the next step.

  (2) In the adsorption step, raw material methane is adsorbed, and the carrier gas is exhausted through the valve V10 in the adsorption step of the adsorption tower A and through the valve V13 in the adsorption step of the adsorption tower B.

(3) In the collection step, the adsorbed CH ₄ breaks through and the gas that has become ¹³ CH ₄ enriched gas is discharged from the adsorption tower A through the valve V11 and from the adsorption tower B through the valve V14. It is stored in the product tank 55.

(4) The ¹³ CH ₄ enriched gas collected in the collection step is refluxed from the product tank 55 to the buffer tank BT1 on the raw material gas supply side. The collected ¹³ CH ₄ enriched gas always flows from the product tank 55 to the buffer tank BT1 on the raw material gas supply side through each step.

  (5) In the reflux step, the gas exhausted from the inside of the adsorption tower at the time of regeneration is transferred from the buffer tank BT2 to the inlet of the adsorption tower A through the valve V5 in the reflux step of the adsorption tower A, and through the valve V8 in the reflux step of the adsorption tower B. Each is sent to the adsorption tower B inlet. Further, in the reflux step, by flowing the gas from the adsorption tower inlet, the gas remaining near the adsorption tower outlet at the time of adsorption is discharged from the adsorption tower outlet. In the reflux step of the adsorption tower A, the adsorption is performed through the valve V15. In the reflux step of the tower B, each is sent to the buffer tank BT1 through the valve V16.

  (6) The gas sent to the buffer tank BT1 is used as a gas to be supplied to the adsorption tower inlet together with the raw material gas in the adsorption step and the collection step.

(7) In the regeneration step, ¹³ CH ₄ enriched gas remaining in the adsorption tower is desorbed by the vacuum pump 53 and exhausted to the buffer tank BT2.

  (8) Of the gas exhausted to the buffer tank BT2, the gas that is not refluxed to the adsorption tower is discharged out of the system through the needle valve NV1. In this experiment, the opening degree of the needle valve NV1 was adjusted so as to have an arbitrary co-current reflux rate.

The experimental conditions are shown in Table 1. In the case of Na-mordenite type zeolite, helium (He) was used as the carrier gas, and in the case of molecular sieve charcoal 4A, nitrogen (N ₂ ) was used as the carrier gas. As the raw material gas, methane gas having a ¹³ CH ₄ : ¹² CH ₄ ratio = 1.1: 98.9 and methane gas having a ¹³ CH ₄ : ¹² CH ₄ ratio = 9: 91 were used.

  Table 2 shows the time of each step (including the adsorption time), the valve open / close state, and the like. Hereinafter, each step in the adsorption tower A and the adsorption tower B will be described in more detail based on FIG.

<Pressurization step of adsorption tower A, regeneration step of adsorption tower B>
In the pressure increasing step of the adsorption tower A and the regeneration step of the adsorption tower B, among the valves V1 to V16, the valves V7 and V9 are opened, and the other valves are closed. Since the valve V9 is open, the carrier gas is supplied from the carrier gas supply source 51 to the adsorption tower A through the pressure regulator 54, and the pressure is increased. Further, the gas in the adsorption tower B is sucked and exhausted through the valve V7 to be regenerated, and the exhaust gas is stored in the buffer tank BT2.

<Adsorption step of adsorption tower A, regeneration step of adsorption tower B>
In the adsorption step of the adsorption tower A and the regeneration step of the adsorption tower B, among the valves V1 to V16, V1 to V3, V7, and V10 are opened, and the other valves are closed. In this state, the adsorbing tower A is supplied with a mixed gas of the carrier gas from the carrier gas supply source 51 and the methane from the methane supply source 52, and pushes out the carrier gas introduced in the pressure increasing step, while methane is adsorbed on the adsorbent. Adsorbed. The extruded carrier gas is discharged through the valve V10.

  During this time, the adsorption tower B continues to be a regeneration step. The gas in the adsorption tower B was sucked through the valve V7 by the vacuum pump 53 and exhausted and stored in the buffer tank BT2.

<Adsorption tower A collection step, adsorption tower B regeneration step>
In the collection step of the adsorption tower A and the regeneration step of the adsorption tower B, among the valves V1 to V16, V1 to V3, V7, and V11 are opened, and the other valves are closed. In this state, the adsorption tower A is continuously supplied with a mixed gas of carrier gas from the carrier gas supply source 51 and methane (= raw material gas) from the methane supply source 52. ¹² CH _{4 in} methane is selectively trapped by the adsorbent, and ¹³ CH ₄ which is not trapped is enriched in methane, that is, ¹³ CH ₄ enriched methane, which is discharged from the adsorption tower A outlet. ¹³ CH ₄ enriched methane is stored in product tank 55 through V11.

  During this time, the adsorption tower B continues to be a regeneration step. The vacuum pump 53 sucks the gas in the adsorption tower B through the valve V7 and stores it in the buffer tank BT2.

<Adsorption tower A co-current reflux step, adsorption tower B regeneration step>
In the co-current reflux step of the adsorption tower A and the regeneration step of the adsorption tower B, among the valves V1 to V16, V5, V7 and V15 are opened, and the other valves are closed. In this state, ¹² CH ₄ enriched gas desorbed and exhausted from the adsorption tower B during regeneration of the adsorption tower B and stored in the buffer tank BT2 is supplied to the adsorption tower A through the check valve CV2 and the valve V5. Is done. Since the gas is supplied to the inlet side of the adsorption tower A, the gas remaining in the vicinity of the outlet of the adsorption tower A at the adsorption step and the collection step of the adsorption tower A is discharged from the outlet side of the adsorption tower A, and the valve V15 and the check valve CV1 are opened. Then, it is sent to the buffer tank BT1. The gas sent to the buffer tank BT1 is mixed with methane (= source gas) from the methane gas supply source 52 and used as the gas supplied to the adsorption tower B in the adsorption step and the collection step.

  During this time, the adsorption tower B continues to be a regeneration step. The vacuum pump 53 sucks the gas in the adsorption tower B through the valve V7 and stores it in the buffer tank BT2.

<Adsorption tower A regeneration step, adsorption tower B pressure increase step>
In the regeneration step of the adsorption tower A and the pressure increase step of the adsorption tower B, among the valves V1 to V16, V4 and V12 are opened, and the other valves are closed. The gas in the adsorption tower A is sucked and exhausted through the valve V4 to be regenerated, and the exhaust gas is stored in the buffer tank BT2. Further, since the valve V12 is open, the carrier gas is supplied from the carrier gas supply source 51 to the adsorption tower B via the pressure regulator 54, and the pressure is increased.

<Adsorption step of adsorption tower A, adsorption step of adsorption tower B>
In the regeneration step of the adsorption tower A and the adsorption step of the adsorption tower B, among the valves V1 to V16, V1 to V2, V4, V6, and V13 are opened, and the other valves are closed. In this state, the adsorption tower A continues to be a regeneration step. The vacuum pump 53 sucks the gas in the adsorption tower A through the valve V4 and exhausts and stores it in the buffer tank BT2.

  During this time, a mixed gas of carrier gas from the carrier gas supply source 51 and methane from the methane supply source 52 is supplied to the adsorption tower B, and methane is adsorbed on the adsorbent while pushing out the carrier gas introduced in the pressure increasing step. The The extruded carrier gas is discharged through the valve V13.

<Regeneration step of adsorption tower A, collection step of adsorption tower B>
In the regeneration step of the adsorption tower A and the collection step of the adsorption tower B, among the valves V1 to V16, V1 to V2, V4, and V14 are opened, and the other valves are closed. In this state, the adsorption tower A is still a regeneration step. The vacuum pump 53 sucks the gas in the adsorption tower A through the valve V4 and stores it in the buffer tank BT2.

During this time, the mixed gas of carrier gas from the carrier gas supply source 51 and methane (= raw material gas) from the methane supply source 52 is continuously supplied to the adsorption tower B. ¹² CH _{4 in} methane is selectively trapped by the adsorbent, and ¹³ CH ₄ which is not trapped is enriched in methane, that is, ¹³ CH ₄ enriched methane, and is discharged from the adsorption tower B outlet. ¹³ CH ₄ enriched methane is stored in product tank 55 through V14.

<Regeneration step of adsorption tower A, co-current reflux step of adsorption tower B>
In the regeneration step of the adsorption tower A and the cocurrent reflux step of the adsorption tower B, among the valves V1 to V16, V4, V8, and V16 are opened, and the other valves are closed. In this state, the adsorption tower A is still a regeneration step. The vacuum pump 53 sucks the gas in the adsorption tower A through the valve V4 and stores it in the buffer tank BT2.

During this time, ¹² CH ₄ enriched gas exhausted from the adsorption tower A during regeneration of the adsorption tower A and stored in the buffer tank BT2 is supplied to the adsorption tower B through the check valve CV2 and the valve 8. Since the gas is supplied to the inlet side of the adsorption tower B, the gas remaining near the outlet of the adsorption tower B during the adsorption step and the collection step of the adsorption tower B is discharged from the outlet side of the adsorption tower B, and the valve V16 and the check valve It is sent to the buffer tank BT1 via CV1. The gas sent to the buffer tank BT1 is mixed with methane (= raw material gas) from the methane gas supply source 52 and used as the gas supplied to the adsorption tower A in the adsorption step and the collection step.

In this experiment, (a) the above-described series of separation and concentration operations is performed only once, and the ¹³ CH ₄ enriched gas discharged from the adsorption tower is not refluxed to the raw material gas supply side, and (b ) The above series of separation and concentration operations were repeated a plurality of times, and the effects of separation and concentration when ¹³ CH ₄ enriched gas discharged from the adsorption tower was refluxed to the raw material gas supply side were compared. As a result, it has been found from the conventional common sense that an unexpected effect can be obtained.

<Experimental result>
3 to 6 show the results of the above experiment. 3 to 6, the horizontal axis represents the number of repetitions of the separation and concentration operation (the scale is a logarithmic scale), and the vertical axis is the separation coefficient β ′. 3 to 6, the leftmost end is a separation coefficient β ′ in a single separation / concentration operation.

FIG. 3 shows the number of repetitions of the separation / concentration operation of the separation coefficient β ′ at a cocurrent reflux rate of 0 using Na-mordenite zeolite and He as the carrier gas. As shown in FIG. 3, the separation and concentration operation is repeated both in the case of ¹³ CH ₄ : ¹³ CH ₄ = 1.1: 98.9 and in the case of ¹³ CH ₄ : ¹³ CH ₄ = 9: 91. As the number of times increases, the separation coefficient β ′ increases. When the source gas is methane of ¹³ CH ₄ : ¹³ CH ₄ = 9: 91, the separation coefficient β ′ = 1.007 only once, whereas the separation coefficient β ′ = 1. 033, and when the number of repetitions is 10, the separation coefficient β ′ increases to 1.052. Further, when the raw material gas is methane of ¹³ CH ₄ : ¹³ CH ₄ = 1.1: 98.9, the separation coefficient β ′ = 1.016 only once, whereas the separation is performed 10 times. The coefficient β ′ increases to 1.056, and after that, although it is slightly smaller, it shows almost the same value.

FIG. 4 shows the number of repetitions of the separation / concentration operation of the separation coefficient β ′ at the cocurrent reflux rate 0 using N ₂ as the molecular sieve 4A and the carrier gas. As shown in FIG. 4, in the case of a source gas of ¹³ CH ₄ : ¹³ CH ₄ = 1.1: 98.9, the separation coefficient β ′ increases as the number of repetitions of the separation and concentration operation increases. For example, while the separation coefficient β ′ = 1.018 only once, the separation coefficient β ′ = 1.023 when the number of repetitions is 10, and the separation coefficient β ′ = 1.046 when the number of repetitions is 80. The value is shown.

  In the present invention (1)-(2), the number of operations for maximizing the separation coefficient is 10 times or more from the result of FIG. 3, and 45 times or more from the result of FIG. Therefore, the operations (a) to (c), particularly the operations (b) and (c) in the present invention (1)-(2) are preferably at least 45 times.

FIG. 5 shows the number of repetitions of the separation / concentration operation of the separation coefficient β ′ at a cocurrent reflux rate of 0.25 using Na-mordenite zeolite and He as the carrier gas. As shown in FIG. 5, the separation and concentration operation was performed for both ¹³ CH ₄ : ¹³ CH ₄ = 1.1: 98.9 source gas and ¹³ CH ₄ : ¹³ CH ₄ = 9: 91 source gas. As the number of repetitions increases, the separation coefficient β ′ increases. When the source gas is methane of ¹³ CH ₄ : ¹³ CH ₄ = 9: 91, the separation coefficient β ′ = 1.007 only once, whereas the separation coefficient β ′ = 1. 036, and when the number of repetitions is 10, the separation coefficient β ′ increases to 1.061. Further, when the raw material gas is methane of ¹³ CH ₄ : ¹³ CH ₄ = 1.1: 98.9, the separation coefficient β ′ = 1.016 only once, whereas the separation is performed 10 times. The coefficient β ′ increases to 1.064, and after that, although it is slightly smaller, it shows almost the same value.

FIG. 6 shows the number of repetitions of the separation / concentration operation of the separation coefficient β ′ at a cocurrent reflux rate of 0.1 using the molecular sieves 4A and N ₂ . As shown in FIG. 6, in the case of a source gas of ¹³ CH ₄ : ¹³ CH ₄ = 1.1: 98.9, the separation coefficient β ′ increases as the number of repetitions of the separation and concentration operation increases. For example, while the separation coefficient β ′ = 1.018 only once, the separation coefficient β ′ = 1.029 when the number of repetitions is 10, and the separation coefficient β ′ = 1.03 over when the number of repetitions is 30. Even when the number of repetitions is 100, it shows almost the same value.

  In the present invention (3)-(4), the number of operations for maximizing the separation coefficient is 10 times or more from the result of FIG. 5 and 30 times or more from the result of FIG. Therefore, the operations (a) to (d), particularly the operations (b) and (c) in the present invention (3)-(4) are preferably at least 30 times or more.

  As is apparent from FIGS. 3 to 6, it is apparent that the separation coefficient β ′ can be improved by repeatedly performing a series of separation and concentration operations. Further, as is clear from the comparison of the results of FIGS. 3 to 4 and the results of FIGS. 5 to 6, the separation coefficient β ′ can be further improved by performing cocurrent reflux together.

Prior Art: Illustration explaining the isotope separation apparatus and separation / concentration process of 767 The figure which shows the apparatus used for the experiment of this invention The figure which shows the experimental result of this invention The figure which shows the experimental result of this invention The figure which shows the experimental result of this invention The figure which shows the experimental result of this invention

Explanation of symbols

1-18 Openable and closable valves 30 Cold box 31-33 Adsorption tower 35, 39, 44 Blower 36 Buffer tank 37 Vacuum pump 34, 38, 41, 42, 45, 46 Channel 43 Counterflow purge tank A Inlet side channel B Outlet side channel C Regeneration unit D Cocurrent purge unit 51 Carrier gas supply source 52 Methane gas supply source 53 Vacuum pump 54 Pressure regulator 55 Product tank 56 Mass spectrometer BT1, BT2 Buffer tank CV1, CV2 Check valve MFC1 Carrier gas Flow controller MFC2 Methane gas flow controller P1 Adsorption tower A inlet pressure gauge P2 Adsorption tower A outlet pressure gauge P3 Adsorption tower B inlet pressure gauge P4 Adsorption tower B outlet pressure gauge V1 to V16 Valve NV1 Needle valve

Claims (4)

A method for separating and concentrating isotope gas of methane from a source gas containing methane using a pressure swing adsorption method using an adsorption tower packed with an isotope-selective adsorbent,
(A) After adsorbing ¹² CH ₄ from methane on the isotope-selective adsorbent of the adsorption tower and allowing ¹³ CH ₄ to flow through to recover ¹³ CH ₄ enriched gas,
(B) refluxing the recovered ¹³ CH ₄ enriched gas to the source gas supply side,
(C) Next, the adsorption tower is set to a lower pressure than during adsorption, and ¹² CH ₄ adsorbed on the isotope-selective adsorbent is desorbed and regenerated,
(D) And the operation of (a)-(c) is repeated at least 45 times or more, The methane isotope gas separation method characterized by the above-mentioned. The method of separating isotopes gases according to claim 1, which is a mordenite type zeolite bets - the isotope-selective adsorbents of metal ions supported by ion exchange metal. A method of separating and concentrating an isotope gas of methane from a source gas containing methane using a pressure swing adsorption method using at least one adsorption tower packed with an isotope-selective adsorbent,
(A) After adsorbing ¹² CH ₄ from methane to an isotope-selective adsorbent in a certain adsorption tower and allowing ¹³ CH ₄ to flow through and recovering ¹³ CH ₄ enriched gas,
(B) refluxing the recovered ¹³ CH ₄ enriched gas to the source gas supply side,
(C) Immediately before the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure, ¹² CH ₄ previously desorbed and stored at the time of regeneration is introduced from the entrance of the adsorption tower, so that the exit of the adsorption tower Perform the co-current reflux operation to return the gas discharged from the source gas side,
(D) Next, the isotope-selective adsorbent of the adsorption tower is regenerated at a low pressure,
(E) And the operation of (a)-(d) is repeated at least 30 times or more, and the methane isotope gas separation method characterized by the above-mentioned. The method of separating isotopes gases according to claim 3, characterized in that the mordenite zeolite bets - the isotope-selective adsorbents of metal ions supported by ion exchange metal.

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