JP2011230035A - Gas separation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas separation method for separating a gaseous mixture including a hydride gas while keeping a high recovery rate and condensing the hydride gas to high purity.SOLUTION: The gas separation method comprises: a first process of closing an unpermeated gas discharge port of a closed vessel in which a gas separation membrane is stored, supplying the gaseous mixture into the closed vessel by opening a gas supply port and charging pressure while a permeated gas discharge port is opened; a second process of closing the gas supply port to stop the supply of the gaseous mixture when a predetermined time elapses from the start of supplying the gaseous mixture or the inside of the closed vessel reaches a predetermined pressure, and maintaining the state; a third process of opening the unpermeated gas discharge port to recover the hydride gas when a predetermined time elapses from the start of retaining state or the inside of the closed vessel reaches a predetermined pressure; and a fourth process of closing the unpermeated gas discharge port when a predetermined time elapses from the start of recovery or the inside of the closed vessel reaches a predetermined pressure. The first to fourth processes are continuously repeated.

Description

  The present invention relates to a gas separation method.

  Currently, there are various types of special gases used in the semiconductor field, typically hydride gases such as monosilane, monogermane, arsine, phosphine, and hydrogen selenide. Of these gases, monosilane, monogermane, arsine, phosphine, hydrogen selenide and the like are highly toxic and flammable gases and are very difficult to handle.

  In particular, the hydride-based gas is used as a high purity gas by itself, but is also widely used as a mixed gas diluted with a gas such as hydrogen or helium.

  Here, for example, a mixed gas diluted with hydrogen or the like can be safely used by separating it into hydrogen and special gas in the immediate vicinity of the equipment using the mixed gas, and sending only the special gas to the gas using equipment. Are known.

Generally, special gas is filled in a cylinder (cylinder), but depending on the type of special gas, it is known that the special gas itself may have a larger filling amount than the pure gas that is not diluted. ing.
When returning a used cylinder filled with a diluted mixed gas, the cylinder is generally returned as a residual gas while leaving some gas in the cylinder. By separating and recovering the residual gas into a diluting gas and a special gas, the expensive special gas can be reused, and the processing cost of the residual gas can be reduced.

  On the other hand, gas separation technologies include gas separation methods using adsorption and reaction with adsorbents and metal catalysts, separation methods using phase change by rectification (liquefaction purification) and solidification purification, and molecular diameters by gas separation membranes. There are separation methods that use the differences.

  Among these separation methods, a gas separation technique using a gas separation membrane is attracting attention as an excellent energy-saving separation technique.

  Gas separation technology using gas separation membranes is about a compressor for boosting as basic power, and its energy-saving performance is PSA (gas separation method using adsorption or reaction), rectification (phase change). Compared to the separation method used, this can be expected. In addition, gas separation technology using a gas separation membrane can perform the separation operation by pulling the permeate side of the separation membrane to a vacuum, so it can handle low vapor pressure gas, which is difficult to obtain a sufficient supply pressure, and is pyrophoric. Gas and self-decomposable gas can also be safely separated, and it is possible to cope with gas that is easily decomposed by the catalytic action of metal or gas that easily reacts with metal. In addition, there are advantages such that there are few driving devices, no trouble is required, maintenance is unnecessary, and it is not necessary to add an operation such as regeneration in the PSA even when high-concentration impurities are separated.

  As a gas separation technique using a gas separation membrane, a gas separation technique using a polyimide membrane or a polyaramid membrane (see Patent Documents 1 to 4), a gas separation technique using a polysulfone membrane (see Patent Document 5), Examples include gas separation technology using a special silica membrane or alumina membrane (see Patent Document 6), gas separation technology using a distillation membrane or a pervaporation membrane (see Patent Document 7), and the like.

  Further, as a gas separation technique using a gas separation membrane, a gas separation technique using a carbon membrane (see Patent Document 8) is known, and a technique related to a carbon membrane manufacturing method is also disclosed (Patent Document). 9-11).

JP-A-7-171330 JP 2002-308608 A JP 2005-154203 A JP 2003-37104 A Japanese Patent No. 2615265 Japanese Patent No. 3477517 JP 2005-60225 A JP 2008-238357 A Patent No. 2914972 JP-A-10-52629 JP 2006-231095 A

  However, the gas separation technique using the carbon membrane exemplified in Patent Document 8 is for the purpose of purification using the carbon membrane to remove trace level impurities at the ppm level, and is known to have a high recovery rate. However, a method for separating a special gas such as a hydride-based gas from a diluted gas is not shown. Furthermore, when these special gases are used as semiconductor materials, it has been required to concentrate them to a concentration higher than the concentration of the special gas in the diluted and mixed gas.

  The present invention separates a mixed gas containing a hydride-based gas, which is a highly reactive and highly corrosive semiconductor material gas, into a hydride-based gas and a dilution gas, and maintains a high recovery rate while maintaining a high recovery rate. An object of the present invention is to provide a gas separation method capable of concentrating gas with high purity.

The invention according to claim 1 uses the gas separation membrane having a molecular sieving action to separate the dilution gas from a mixed gas of a dilution gas having a molecular diameter of 3 mm or less and a hydride-based gas, and the hydride A gas separation method for concentrating a system gas,
Close the non-permeate gas outlet provided in the sealed container containing the gas separation membrane so as to communicate with the space on the non-permeate side of the gas separation membrane, and communicate with the space on the permeate side of the gas separation membrane. In a state where the permeated gas discharge port provided to open is opened, the first step of opening the gas supply port, supplying the mixed gas into the sealed container, and charging it,
When a predetermined time has elapsed from the start of the supply of the mixed gas or when the inside of the sealed container reaches a predetermined pressure, the gas supply port is closed to stop the supply of the mixed gas, and the state is maintained. The second process,
When a predetermined time has elapsed from the start of the holding state or when the inside of the sealed container has reached a predetermined pressure, the non-permeate gas discharge port is opened and the hydride gas is recovered from the non-permeate gas discharge port. A third process to
A fourth step of closing the non-permeated gas discharge port when a predetermined time has elapsed from the start of recovery or when the inside of the sealed container has reached a predetermined pressure,
The gas separation method is characterized in that the first to fourth steps are continuously repeated.

The invention according to claim 2 is the gas separation method according to claim 1, wherein the gas separation membrane is a hollow fiber-like or tubular carbon membrane.
The invention described in claim 3 is characterized in that the hydride-based gas is any one of arsine, phosphine, hydrogen selenide, monosilane, and monogermane. This is a gas separation method.

  According to the gas separation method of the present invention, using a gas separation membrane having a molecular sieving action, it is possible to maintain a high recovery rate and to make a hydride gas higher in purity or concentrated in a higher concentration than in the past. It becomes possible.

It is a schematic sectional drawing which shows the carbon membrane module which is an example of the gas separation membrane used for the gas separation method of this invention. It is A-A 'sectional drawing in the carbon membrane module shown in FIG. It is a figure which shows an example of the timing chart of batch operation in the gas separation method of this invention.

  Hereinafter, the case where a carbon membrane is used as a gas separation membrane will be described in detail with reference to FIGS.

  The carbon membrane module which is an example of the gas separation membrane module used for the gas separation method of this invention was shown in FIG.1 and FIG.2. In FIG. 1, reference numeral 1 denotes a carbon membrane module. The carbon membrane module 1 is generally composed of a sealed container 6 and a carbon membrane unit 2 provided in the sealed container 6.

  The sealed container 6 has a hollow cylindrical shape, and the carbon membrane unit 2 is accommodated in an internal space. A gas supply port 3 is provided at one end in the longitudinal direction of the sealed container 6, and an unpermeated gas discharge port 5 is provided at the other end. Further, a permeate gas discharge port 4 and a sweep gas supply port 8 are provided on the peripheral surface of the sealed container 6.

The carbon membrane unit 2 is composed of a large number of hollow fiber-like carbon membranes (gas separation membranes) 2a, and a pair of resin walls 7 that bind and fix both ends of the hollow fiber-like carbon membranes 2a. The resin wall 7 is hermetically fixed to the inner wall of the sealed container 6 using an adhesive or the like.
FIG. 2 is a cross-sectional view taken along the line AA ′ in the carbon membrane module 1 shown in FIG. 1, and illustrates the surface structure of the resin wall 7 in the sealed container 6. The resin wall 7 is formed with openings of hollow fiber-like carbon membranes 2a.

  The inside of the sealed container 6 is divided into three spaces of a first space 11, a second space 12, and a third space 13 by a pair of resin walls 7. The first space 11 is a space between one end of the sealed container 6 provided with the gas supply port 3 and the resin wall 7, and the second space 12 is paired with the peripheral surface of the sealed container 6. The third space 13 is a space between the resin wall 7 and the resin wall 7. The third space 13 is a space between the other end of the sealed container 6 provided with the non-permeated gas discharge port 5 and the resin wall 7.

  The gas supply port 3 is provided so as to communicate with the first space 11 in the sealed container 6. The gas supply port 3 is provided with an open / close valve 3a. Then, by opening the on-off valve 3a, the mixed gas can be supplied into the first space 11 from the outside of the sealed container 6 through the gas supply port 3.

  The non-permeated gas discharge port 5 is provided so as to communicate with the third space 13 in the sealed container 6. Further, an opening / closing valve 5 a is provided at the non-permeated gas discharge port 5. Then, by opening the on-off valve 5a, the non-permeated gas can be discharged from the third space 13 to the outside of the sealed container 6 through the non-permeated gas discharge port 5.

  The permeate gas discharge port 4 and the sweep gas supply port 8 are provided so as to communicate with the second space 12 in the sealed container 6. The permeate gas discharge port 4 is provided with an open / close valve 4a, and the sweep gas supply port 8 is provided with an open / close valve 8a. Then, by opening the on-off valve 4a, the permeated gas can be discharged from the second space 12 to the outside of the sealed container 6 through the permeated gas discharge port 4. On the other hand, by opening the on-off valve 8a, the sweep gas can be supplied to the second space 12 from the outside of the sealed container 6 through the sweep gas supply port 8.

  One end of the hollow fiber-like carbon membrane 2a... Is fixed to one resin wall 7 and opened, and the other end is fixed to the other resin wall 7 and opened. Thereby, in the part where hollow fiber-like carbon membrane 2a ... is fixed by one resin wall 7, one opening part of hollow fiber-like carbon membrane 2a ... is connected with the 1st space 11, and the other opening part is It communicates with the third space 13. Thereby, the 1st space 11 and the 3rd space 13 are connected via the internal space of hollow fiber-like carbon membrane 2a .... On the other hand, the first space 11 and the second space 12 communicate with each other via the carbon membrane unit 2.

  The hollow fiber-like carbon film 2a is formed by forming an organic polymer film and then sintering it. For example, a film-forming stock solution is prepared by dissolving polyimide, which is an organic polymer, in an arbitrary solvent, and a solvent that is insoluble in polyimide is prepared by mixing with the solvent of the film-forming stock solution. Next, the film-forming stock solution is extruded from the circumferential annular port of the hollow fiber spinning nozzle having a double-pipe structure, and the solvent is simultaneously extruded into the coagulating liquid from the central circular port of the spinning nozzle to form a hollow fiber shape. Manufacturing organic polymer membranes. Next, the obtained organic polymer film is carbonized after being infusibilized to form a carbon film.

  The carbon membrane is used by selecting an optimal form such as a carbon membrane coated only on a porous support and a carbon membrane coated on a gas separation membrane other than the carbon membrane. Examples of the porous support include ceramic-based alumina, silica, zirconia, magnesia, zeolite, and metal-based filters. Application to the support has effects such as improvement of mechanical strength and simplification of carbon film production.

  In particular, in the present invention, a gas separation membrane that normally performs a separation operation in a steady state is used with a pressure swing as in PSA described later. Therefore, the gas separation membrane is required to have good stability against pressure swing, that is, mechanical strength is superior to the conventional one. Therefore, in the present invention, it is preferable to use an inorganic gas separation membrane such as a silica membrane, a zeolite membrane or a carbon membrane rather than a general polymer membrane gas separation membrane.

  The organic polymer used as the raw material for the carbon film includes polyimide (aromatic polyimide), polyphenylene oxide (PPO), polyamide (aromatic polyamide), polypropylene, polyfurfuryl alcohol, polyvinylidene chloride (PVDC), phenol resin, Examples thereof include cellulose, lignin, polyetherimide, and cellulose acetate.

  Among the above carbon film materials, polyimide (aromatic polyimide), cellulose acetate, and polyphenylene oxide (PPO) can be easily formed into a hollow fiber carbon film. Polyimide (aromatic polyimide) and polyphenylene oxide (PPO) have particularly high separation performance. Furthermore, polyphenylene oxide (PPO) is less expensive than polyimide (aromatic polyimide).

  Next, a gas separation method using the carbon membrane module 1 shown in FIG. 1 will be described. Here, the molecular sieving action is an action in which a gas having a small molecular diameter and a gas having a large molecular diameter are separated according to the molecular diameter of the gas and the pore diameter of the gas separation membrane.

  The gas separation method of the present invention separates a dilution gas and a hydride gas from a mixed gas of a dilution gas and a hydride gas using a carbon membrane having a molecular sieving action, and concentrates the hydride gas. This is a gas separation method.

  The mixed gas to be separated and concentrated is a mixture of two or more gas components having a small molecular diameter and gas components having a large molecular diameter. Any combination of gas components may be used as long as there is a difference in molecular diameter between these gas components. The greater the difference between these molecular diameters, the shorter the processing time for the separation operation.

  The dilution gas in the mixed gas is often a gas component having a small molecular diameter. For example, it is preferable to use a gas component having a molecular diameter of 3 mm or less, such as hydrogen or helium. On the other hand, the hydride gas in the mixed gas is often a gas component having a large molecular diameter. For example, the molecular diameter of arsine, phosphine, hydrogen selenide, monosilane, monogermane is larger than 3 mm. The gas component is large, preferably 4 mm or more, more preferably 5 mm or more.

  The mixed gas is not limited to the two-component system, and may be a mixture of a plurality of gas components. However, in order to sufficiently separate each gas component on either the permeation side or the non-permeation side of the carbon membrane, the molecular diameter It is preferable that the gas component group is largely classified into a gas component group having a large molecular weight and a gas component group having a small molecular diameter. The pore diameter of the carbon film may be between the molecular diameter of the gas component group having a large molecular diameter and the molecular diameter of the gas component group having a small molecular diameter. The pore diameter of the carbon film can be adjusted by changing the firing temperature during carbonization.

  Specifically, the gas separation method of the present invention is characterized in that operations of the following first to fourth steps are continuously repeated.

(First process)
First, in the supply process which is the first process, the non-permeation provided so as to communicate with the third space 13 (the space on the non-permeate side of the carbon film) of the sealed container 6 in which the carbon film unit 2 is accommodated. With the open / close valve 5a of the permeate gas exhaust port 4 provided so as to communicate with the second space 12 (the space on the permeation side of the carbon membrane) being closed, the open / close valve 5a of the gas exhaust port 5 is closed. The open / close valve 3a of the supply port 3 is opened, and the mixed gas is supplied into the sealed container 6 to be charged.

As shown in FIG. 3, in the first process, the mixed gas is supplied from the gas supply port 3 into the sealed container 6 at a constant flow rate. Here, since the non-permeate gas discharge port 5 on the non-permeate side of the sealed container 6 is closed, the pressure (supply pressure) of the first space 11 rises when the mixed gas is supplied at a constant flow rate. Accordingly, the pressure (non-permeation pressure) in the third space 13 on the non-permeation side of the carbon membrane unit 2 in the sealed container 6 also increases.
On the other hand, since the permeate gas discharge port 4 on the permeate side of the sealed container 6 is open, the pressure (permeate pressure) in the second space 12 does not change. Further, since the dilution gas in the mixed gas passes through the carbon membrane unit 2 and moves to the second space 12 and is discharged from the permeated gas discharge port 4, the permeate flow rate becomes constant after increasing temporarily.

The time required for the first process (T ₁ ) is not particularly limited, and the volume (V) of the sealed container 6, the performance of the carbon membrane unit 2 (P, S), the supply flow rate of the mixed gas ( F) and filling pressure and the like (A) can be selected as appropriate.

  If the volume (V) of the sealed container 6 is increased, the amount of mixed gas supplied to the sealed container 6 is increased, and the time required for the first process is increased unless the supply flow rate of the mixed gas is changed. Further, since the amount of gas mixture to be supplied increases, the recovered amount after separation increases.

  If the filling pressure (A) is increased, the amount of mixed gas supplied to the sealed container 6 increases and the time required for the first process becomes longer if the supply flow rate of the mixed gas does not change. Further, since the amount of gas mixture to be supplied increases, the recovered amount after separation increases. However, if the filling pressure is too high, the carbon membrane unit 2 may be damaged or the like. Furthermore, in the case of the hydride gas which is the separation object of the present invention, it is preferable not to raise the pressure so much in terms of safety, so that it is more preferably 0.5 MPaG or less, and 0.2 MPaG or less. Further preferred.

  The performance (permeation rate of permeation component) (P) of the carbon membrane unit 2 represents the permeation rate of the component that permeates the carbon membrane 2a. For example, when the permeation component is hydrogen and the non-permeation component is monosilane, the required time becomes longer if the hydrogen permeation rate is high. This is because hydrogen escapes at the same time as charging, and therefore it must be charged with monosilane, which is an impermeable component.

  The performance (separation performance) (S) of the carbon membrane unit 2 represents the performance of separation into a component that permeates the carbon membrane 2a and a component that does not permeate (residual component). For example, when the permeation component is hydrogen and the residual component is monosilane, the required time is shortened if the separation performance for hydrogen and monosilane is excellent. This is because the monosilane remains without permeating the carbon film 2a, that is, the permeation rate of the monosilane is small, so that the pressure is increased as much as possible.

  If the supply flow rate (F) of the mixed gas is large, the required time is shortened. However, since there is a risk of damage to the carbon membrane unit 2, it is preferable to supply at a linear velocity of 10 cm / sec or less. : 1 cm / sec or less is more preferable. However, this is not the case when a resistance plate or a diffusion plate is introduced so that the gas flow does not directly hit the carbon film 2a.

From the above-described conditions, the required time (T ₁ ) of the first process is related as shown in the following formula (1).
T ₁ ∝ (V × A × P) / (S × F) (1)

For example, the membrane area 1114 cm ² (membrane performance: hydrogen permeation rate = 5 × 10 ⁻⁵ cm ³ (STP) / cm ² / sec / cmHg, (hydrogen / monosilane separation factor) = approximately shown in the examples described later. In the case of a closed container in which the carbon membrane unit 2 of 5000) is sufficiently dense, when a mixed gas of 10% monosilane and 90% hydrogen is supplied at a flow rate of 150 sccm, the filling pressure is 0 in about 7 minutes. .2 MPaG will be reached.

(Second process)
Next, in the separation process, which is the second process, when a predetermined time has elapsed since the start of the supply of the mixed gas, or when the pressure in the sealed container 6 (supply pressure or non-permeation pressure) reaches a predetermined pressure, The open / close valve 3a of the gas supply port 3 is closed to stop the supply of the mixed gas, and this state is maintained.
As a result, from the mixed gas supplied to the non-permeate side (first and third spaces 11 and 13) of the carbon membrane unit 2, only the dilution gas that is a gas component having a small molecular diameter is selectively and preferentially carbonized. It is possible to allow the hydride gas, which is a gas component having a large molecular diameter, to remain on the non-permeating side while allowing the membrane unit 2 to pass through to the low pressure side (second space 12).

As shown in FIG. 3, in the second process, since the supply of the mixed gas from the gas supply port 3 into the sealed container 6 is stopped, the supply flow rate becomes zero. At this time, the open / close valves 3a and 5a of the gas supply port 3 and the non-permeate gas discharge port 5 on the non-permeate side of the sealed container 6 are closed, but the permeate gas discharge port 4 is open and is in the mixed gas. Gas passes through the carbon membrane unit 2 and is discharged from the permeate gas discharge port 4, so that the pressure in the first space 11 (supply pressure) and the pressure in the third space 13 (non-permeation pressure) gradually descend.
On the other hand, the permeate gas outlet 4 on the permeate side of the sealed container 6 is open, and the pressure (permeate pressure) in the second space 12 does not change. However, the permeate flow rate of the dilution gas discharged from the permeate gas discharge port 4 gradually decreases.

The time required for the second process (T ₂ ) is not particularly limited, and the volume (V) of the sealed container 6, the filling pressure (A), the predetermined pressure at the end of separation (also referred to as discharge pressure, B), can be appropriately selected according to the performance (P, S) of the carbon membrane unit 2 and the composition (Z) of the supply gas.

  Here, the volume (V), the filling pressure (A), and the performance (separation performance) (S) of the carbon membrane unit 2 are as described in the first step.

  The performance of the carbon membrane unit 2 (permeation rate of the permeation component) (P) is shorter when the permeation rate is higher, for example, when the permeation component is hydrogen. This is because hydrogen escapes quickly.

  If the discharge pressure (B) is high, the time required for the second process is shortened. However, if the pressure is higher than the ideal discharge pressure, the pressure is not sufficiently separated, and the purity of the recovered gas does not become high purity or high concentration.

  The composition (Z) of the supply gas is an index representing the gas composition and is the amount of permeated gas component / the amount of residual gas component.

From the above-described conditions, the time required for the second process (T ₂ ) is related as shown in the following formula (2).
T ₂ ∝ (V × A) / (B × P × S) (2)

Further, the discharge pressure (B) is related as shown in the following formula (3).
Discharge pressure (B) ∝1 / (F × Z) (3)

Here, if the supply flow rate (F) of the mixed gas is large, the discharge pressure (B) becomes smaller than the equation (3). This means that if the supply flow rate (F) of the mixed gas is large, the filling pressure is reached sooner, so that the ratio of separation in the first process becomes small, and most of the separation is separated in the second process.
On the other hand, if the supply flow rate (F) of the mixed gas is small, the discharge pressure (B) increases. This is because the mixed gas supply flow rate (F) is small, so that it is sufficiently separated in the first process and almost reaches the filling pressure with the residual gas component, so the filling pressure (A) and the discharge pressure (B). This means that the difference between and becomes smaller.

  When this index (Z) is large, the partial pressure of the permeate gas component is small, so the discharge pressure (B) is small.

For example, the membrane area 1114 cm ² (membrane performance: hydrogen permeation rate = 5 × 10 ⁻⁵ cm ³ (STP) / cm ² / sec / cmHg, (hydrogen / monosilane separation factor) = approximately shown in the examples described later. When a gas mixture of 10% monosilane and 90% hydrogen is charged in a sealed container having a carbon membrane unit 2 of 5000) sufficiently densely at a filling pressure of 0.2 MPaG, the discharge pressure is reduced to 0 in about 5 minutes. It will reach 12 MPaG.

(Third process)
Next, in the discharging process, which is the third process, when a predetermined time has elapsed from the start of the holding state, or the inside of the sealed container 6 (that is, the first space 11 and the third space 13 on the non-permeable side) is predetermined. When this pressure is reached, the on-off valve 5a of the non-permeate gas discharge port 5 is opened, and the mixed gas containing the hydride-based gas is discharged from the non-permeate gas discharge port 5 and recovered.
As a result, a mixed gas containing a hydride-based gas concentrated (purified) than the hydride-based gas concentration in the mixed gas supplied to the carbon membrane module 1 is obtained.

As shown in FIG. 3, in the third process, the non-permeate flow rate increases simultaneously with the opening of the opening / closing valve 5 a of the non-permeate gas discharge port 5. At the same time, the supply pressure and the non-permeation pressure of the first and third spaces 11 and 13 that are the non-transmission side space gradually decrease.
On the other hand, there is no change in the pressure (permeation pressure) in the second space 12, and the value of the permeate flow rate of the dilution gas from the permeate gas discharge port 4 is very small.

The time required for the third process (T ₃ ) is not particularly limited, and the volume (V), discharge pressure (B), and exhaust gas flow rate (also referred to as discharge flow rate, G) of the sealed container 6 is not limited. It can be selected as appropriate according to the conditions.
Here, the volume (V) of the sealed container 6 is as described in the first step.

  The higher the discharge pressure (B), the longer the time required for the third process. This is because the amount of residual gas components is increasing.

  If the discharge flow rate (G) is large, the time required for the third process is shortened, but the carbon membrane unit 2 may be damaged. For this reason, the linear velocity is preferably supplied at 10 cm / sec or less, and more preferably at a linear velocity of 1 cm / sec or less. However, this is not the case when a resistance plate or a diffusion plate is introduced so that the gas flow does not directly hit the carbon film 2a.

From the above-described conditions, the time required for the third process (T ₃ ) is related as shown in the following formula (4).
T ₃ ∝ (V × B) / (G) (4)

For example, the membrane area 1114 cm ² (membrane performance: hydrogen permeation rate = 5 × 10 ⁻⁵ cm ³ (STP) / cm ² / sec / cmHg, (hydrogen / monosilane separation factor) = approximately shown in the examples described later. In the case of discharging from a discharge pressure of 0.12 MPaG to about 100 sccm in a closed container provided with a carbon film unit 2 of 5000), the pressure reaches 0 MPaG in about 2 minutes.

(Fourth process)
Next, when a predetermined time has elapsed from the start of the recovery of the mixed gas containing the hydride-based gas, or the inside of the sealed container 6 (that is, the first space 11 and the third space 13 on the non-permeate side) is maintained at a predetermined pressure. When reaching, the open / close valve 5a of the non-permeate gas outlet 5 is closed. As a result, the state immediately before the start of the first process is restored.

The gas separation method of the present invention is characterized by continuously repeating such separation operations in the first to fourth steps (hereinafter referred to as “batch operation”) (such a method is referred to as “batch method”). It is said.
By such batch operation, the hydride gas having a large molecular diameter is concentrated and separated on the high pressure side (carbon membrane non-permeation side) of the carbon membrane unit 2 in the first and second processes, and in the third process. Collected. On the other hand, dilution gases such as hydrogen and helium having a small molecular diameter are continuously recovered in the first to fourth processes from the low-pressure side (carbon membrane permeation side) of the carbon membrane unit 2.

In addition, when the time (T) required for one cycle in the gas separation method of the present invention is expressed by the time required for each process described above, it can be expressed as the following formula (5).
T = T ₁ + T ₂ + T ₃ (5)

  By the way, in the conventional gas separation method, for example, when a mixed gas of 90% hydrogen having a small molecular diameter and 10% monosilane having a large molecular diameter is continuously supplied to a carbon membrane as a gas separation membrane (continuous gas separation method). On the permeate side, hydrogen was almost 100%, and on the non-permeate side, monosilane was about 60% (hydrogen 40%).

  On the other hand, according to the batch type gas separation method of the present invention, the separation operation is performed with a separation performance of about 100% hydrogen on the permeate side and about 90% or more monohydrogen (10% or less hydrogen) on the non-permeate side. be able to.

In addition, when a normal polymer membrane is used as the gas separation membrane, a certain degree of permeation occurs even if the molecular diameter is about 4 mm or more. However, in the case of the carbon membrane used in the gas separation method of the present invention, it hardly penetrates when the molecular diameter is about 4 mm or more, and further does not permeate when the molecular diameter becomes larger. Thus, a carbon film can be expected to have an effect of molecular sieving rather than a polymer film.
In addition, the carbon membrane has better chemical resistance than other zeolite membranes and silica membranes having molecular sieving action, and is suitable for the separation of special gases used in the highly corrosive semiconductor field.
Furthermore, by forming the carbon membrane into a hollow fiber shape, the membrane module can be designed more compactly than a flat membrane shape or a spiral wound shape.

  In the batch type gas separation method of the present invention, the temperature at which the separation operation is performed (operation temperature) is not particularly limited, and can be appropriately set according to the required separation performance of the gas separation membrane. The operating temperature here is assumed to be the ambient temperature of the carbon membrane module 1, and a temperature range of −20 ° C. to 120 ° C. is appropriate. When the operation temperature is increased, the permeate flow rate can be increased and the processing time of the batch operation can be shortened.

  In the batch type gas separation method of the present invention, the pressure (operating pressure) (on the high pressure side of the carbon membrane unit 2) is not particularly limited, and is appropriately set according to the required separation performance of the gas separation membrane. Is possible. Specifically, the pressure of the gas supplied to the carbon membrane module 1 can be set to 1 MPaG or more if a support is used, and normally a pressure of about 0.5 MPaG is maintained. This support is a member that prevents the hollow fiber-like carbon membrane 2a ... from being crushed. If the operation pressure is increased, the permeate flow rate can be increased, and the processing time of the batch operation can be shortened.

In order to control the pressure, in the conventional continuous gas separation method, a back pressure valve or the like is installed at the non-permeated gas discharge port 5.
On the other hand, in the batch type gas separation method of the present invention, it is not necessary to provide a back pressure valve in order to control the operation pressure. In the example shown in FIG. 1, the operating pressure can be controlled by closing the open / close valve 5 a of the non-permeated gas discharge port 5. When the non-permeated gas held on the non-permeate side is taken out, if the opening / closing valve 5a of the non-permeate gas discharge port 5 is opened at once (at a time), there is a possibility that the carbon membrane as the gas separation membrane may be seriously damaged. is there. For this reason, it is preferable to provide a flow meter 9 or the like at the non-permeate gas outlet 5 and take out the non-permeate gas at a constant flow rate.

  Moreover, in the carbon membrane module 1 shown in FIG. 1, it is preferable that the 2nd space 12 which is the low voltage | pressure side (permeation | transmission side) of the carbon membrane unit 2 is evacuated. Pulling the second space 12 to a vacuum also has the effect of increasing the pressure difference between the high-pressure side (non-permeation side) of the carbon membrane unit 2 and the low-pressure side (permeation side) of the carbon membrane unit 2. The pressure ratio between the high pressure side (non-permeation side) of the unit 2 and the low pressure side (permeation side) of the carbon membrane unit 2 can be particularly increased. Note that both the pressure difference and the pressure ratio are preferably large for the separation performance by the gas separation membrane, but the pressure ratio has an influence on the separation performance.

Further, in the carbon membrane module 1 shown in FIG. 1, flowing a sweeping gas to the low pressure side (permeation side) of the carbon membrane unit 2 can provide the same effect as that of drawing a vacuum. The open / close valve of the sweep gas supply port 8 is opened, and the sweep gas is supplied into the second space 12 at a predetermined flow rate.
The sweep gas is the same component as the permeate gas (that is, a diluted component of the mixed gas), so that the gas on the permeate side can be efficiently recovered. Further, a part of the permeated gas recovered from the permeated gas discharge port 4 may be used as the sweep gas.

  In the batch type gas separation method of the present invention, as a supply form of the mixed gas to the carbon membrane module 1, for example, in the case of the hollow fiber shape as described above, a high-pressure gas is supplied into the hollow fiber carbon membrane. Two patterns are conceivable: the case (core side supply) and the case of supplying high pressure gas around the hollow fiber carbon membrane (outside supply), but the core side supply is separated as shown in FIG. It is preferable because it can be operated with improved performance.

  In the batch type gas separation method of the present invention, in order to increase the gas throughput per one carbon membrane module 1, the membrane area is increased (in the case of a hollow fiber-like carbon membrane, the number is increased), the second space 12. Reduce the volume of the. In the latter case, it is necessary to devise the structure in the space or add a mixer in order to bring the gas and the carbon film into sufficient contact.

  Specific examples are shown below. However, the present invention is not limited to the following examples.

Example 1
Batch-type gas separation was performed using the carbon membrane module shown in FIG.

The mixed gas was supplied batchwise to the carbon membrane module under the following conditions, and three cycles were performed. As a result, the discharge pressure was 0.12 MPaG. The breakdown of the time required for one cycle was about 7 minutes for the first process (supply process), about 5 minutes for the second process (separation process), and about 2 minutes for the third process (discharge process). Moreover, the gas composition of the non-permeation | transmission side and the permeation | transmission side was measured, respectively. In addition, the gas concentration (GC-TCD) provided with a thermal conductivity detector was used for the volume concentration measurement. The results are shown in Table 1.
(Carbon membrane module)
-Hollow fiber carbon membrane tube-Total surface area of the tube: 1114 cm ²
・ Hold at 25 ℃ (mixed gas)
-Gas composition: Monosilane 10.3% by volume
: Hydrogen 89.7% by volume
(Operating conditions)
-Supply gas flow rate: about 150 sccm of the mixed gas
-Filling pressure: 0.2 MPaG
-Permeation side pressure: -0.088 MPaG (using vacuum pump or vacuum generator, etc.)
・ Exhaust gas flow rate: Approximately 100 sccm

(Comparative Example 1)
Continuous gas separation was performed using the carbon membrane module shown in FIG.

The mixed gas was continuously supplied to the carbon membrane module under the following conditions, and the gas composition on the non-permeation side and the permeation side was measured. In addition, the gas concentration (GC-TCD) provided with a thermal conductivity detector was used for the volume concentration measurement. The results are shown in Table 1.
(Carbon membrane module)
-Hollow fiber carbon membrane tube-Total surface area of the tube: 1114 cm ²
・ Hold at 25 ℃ (mixed gas)
-Gas composition: Monosilane 10.3% by volume
: Hydrogen 89.7% by volume
(Operating conditions)
-Supply gas flow rate: about 150 sccm of the mixed gas
・ Discharge pressure: 0.2MPaG (use back pressure valve instead of flow meter 9)
-Permeation side pressure: -0.088 MPaG (using vacuum pump or vacuum generator, etc.)
・ Exhaust gas flow rate: Approximately 100 sccm

(Example 2)
-Gas separation by batch operation was performed under the same conditions as in Example 1 except that the supply flow rate was about 200 sccm. The results are shown in Table 1.

(Example 3)
-Gas separation by batch operation was performed under the same conditions as in Example 1 except that the supply flow rate was about 100 sccm. The results are shown in Table 1.

Example 4
-Gas separation by batch operation was performed under the same conditions as in Example 1 except that the filling pressure was 0.1 MPaG. The results are shown in Table 1.

(Example 5)
-Gas separation by batch operation was performed under the conditions of Example 1 so that the second step was about 4 minutes. The results are shown in Table 1.

  As shown in Table 1, when Examples 1 to 5 and Comparative Example 1 are compared, Examples 1 to 5 in which batch-type gas separation is performed are less than Comparative Example 1 in which continuous gas separation is performed. The monosilane concentration in the permeate gas composition could be increased.

  When Example 1 and Example 5 were compared, the monosilane concentration in the non-permeated gas composition could be increased in Example 1 in which the time of the second process was sufficiently taken.

  When Example 1 was compared with Example 2, Example 3, and Example 4, the monosilane concentration in the unpermeated gas composition could be increased to the same extent. However, there was a difference in the amount of unpermeated gas recovered and the time required for one cycle. Most preferably, the time required is short, the amount recovered is large, and the monosilane concentration in the unpermeated gas is high. However, it is desirable to optimize each condition in consideration of the trade-off relationship between the required time and the collected amount.

As shown above, if concentration by continuous gas separation is compared with concentration by batch gas separation, it is confirmed that concentration by batch gas separation can be concentrated to a higher concentration than concentration by continuous gas separation. did.
Further, according to the time required for the first process of batch gas separation, the gas separation is optimized to optimize the gas separation conditions so that the time required for the second process is sufficient. I confirmed that I was able to.

  INDUSTRIAL APPLICABILITY The present invention can be applied to an apparatus and equipment for separating a hydride gas for semiconductor manufacturing using a gas separation membrane having a molecular sieving action. In particular, the present invention can be applied to an apparatus and equipment for separating a gas component having a large molecular diameter such as a hydride-based gas and a gas component having a small molecular diameter such as hydrogen or helium.

1. Carbon membrane module (separation membrane module)
2. Carbon membrane unit (separation membrane unit)
2a: hollow fiber carbon membrane (gas separation membrane)
DESCRIPTION OF SYMBOLS 3 ... Gas supply port 3a ... Open / close valve 4 ... Permeate gas discharge port 4a ... Open / close valve 5 ... Non-permeate gas discharge port 5a ... Open / close valve 6 ... Sealed container 7 ... Resin wall 8 ... Sweep gas supply port 8a ... Open / close valve 9 ... Flow meter 11 ... first space 12 ... second space 13 ... third space

Claims (3)

A gas separation method using a gas separation membrane having a molecular sieving action to separate the dilution gas from a mixed gas of a dilution gas having a molecular diameter of 3 mm or less and a hydride gas, and concentrate the hydride gas. There,
Close the non-permeate gas outlet provided in the sealed container containing the gas separation membrane so as to communicate with the space on the non-permeate side of the gas separation membrane, and communicate with the space on the permeate side of the gas separation membrane. In a state where the permeated gas discharge port provided to open is opened, the first step of opening the gas supply port, supplying the mixed gas into the sealed container, and charging it,
When a predetermined time has elapsed from the start of the supply of the mixed gas or when the inside of the sealed container reaches a predetermined pressure, the gas supply port is closed to stop the supply of the mixed gas, and the state is maintained. The second process,
When a predetermined time has elapsed from the start of the holding state or when the inside of the sealed container has reached a predetermined pressure, the non-permeate gas discharge port is opened and the hydride gas is recovered from the non-permeate gas discharge port. A third process to
A fourth step of closing the non-permeated gas discharge port when a predetermined time has elapsed from the start of recovery or when the inside of the sealed container has reached a predetermined pressure,
A gas separation method, wherein the first to fourth steps are continuously repeated.   The gas separation method according to claim 1, wherein the gas separation membrane is a hollow fiber-like or tubular carbon membrane.   The gas separation method according to claim 1 or 2, wherein the hydride gas is any one of arsine, phosphine, hydrogen selenide, monosilane, and monogermane.

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