JPH0966217A - Gas separation method - Google Patents

Abstract

PURPOSE: To provide a gas separation method in which a film having a large transmission coefficient and a film having a relatively small transmission coefficient are used together without deteriorating the merits of both, and a specified component concentrated gas in which a specified gas component is concentrated from a mixed gas of three or more components and a specified component diluted gas in which the specified component is diluted can be separated at high purification efficiency. CONSTITUTION: Multistage separation with the use of gas separation modules 3, 4 with films having different transmission coefficients and others.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a case where a specific component concentrated gas in which one specific gas component is concentrated and a specific component dilution gas in which the specific gas component is diluted are separated from a mixed gas of three or more components. The present invention relates to a gas separation method used in.

[0002]

2. Description of the Related Art Recently, when a specific gas component is concentrated and separated from a mixed gas, in order to achieve low energy operation, simplification of operation, reduction of installation space, etc., the conventional absorption separation method, Membrane separation methods are being developed in place of adsorption separation methods or distillation separation methods. For example, petroleum chemical components such as gasoline and C _{2 to} C ₅ fractions obtained from naphtha after petroleum refining contain raw material components for chemical products such as polymer resins and rubbers. Separation / purification treatment is required to remove impurities and improve the purity, and the use of membrane separation for this treatment is being considered.

As is well known, in gas membrane separation, gas molecules are dissolved at the membrane interface, and the dissolved gas molecules diffuse in the membrane and are desorbed from the membrane at the other end. We are taking advantage of the difference. In the conventional gas membrane separation, one kind of membrane having a high permeation rate is used to increase the processing flow rate and to downsize the gas separation membrane module.

[0004]

When a specific gas component, such as isoprene-enriched specific component enriched gas, is separated from the light fraction of naphtha, the permeation characteristics of the light fraction of naphtha are similar to that of isoprene. Since the components (isopentane, n-pentane, methylbutenes) are contained at a concentration close to the isoprene concentration and the ratio of the permeation coefficient between these components and isoprene, that is, the separation coefficient is small, isoprene and isopentane, n-pentane, methylbutenes Is difficult to separate. Generally, a membrane with a large separation coefficient has a small permeation coefficient (and therefore a small permeation rate and a small processing flow rate), and it is assumed that a gas separation membrane module of one kind of membrane is used for separating one specific gas component. According to the conventional method described above, a membrane having a large separation coefficient inevitably requires an increase in the size of the module for industrial use in which the processing flow rate is large.

An object of the present invention is to combine a membrane having a large permeation coefficient with a membrane having a relatively small permeation coefficient so that one specific gas component can be obtained from a mixed gas of three or more components while having the advantages of both. It is an object of the present invention to provide a gas separation method capable of separating a concentrated concentrated gas of a specific component and a diluted gas of a specific component diluted with the same gas component with sufficient purification efficiency.

[0006]

A gas separation method according to the present invention is a specific component concentrated gas in which one specific gas component is concentrated and a specific component in which the specific gas component is diluted from a mixed gas of three or more components. In the method for separating a diluent gas, the gas separation membrane module having a different permeation coefficient of the membrane is characterized by a multi-stage separation, the mixed gas to be separated is a naphtha light fraction, one specific gas component When is isoprene gas, a crosslinked silicone-based gas separation membrane module and a fluorine-containing polyimide-based gas separation membrane module can be used as the gas separation membrane module. It is also possible to use the condensation separation method, the absorption separation method, the adsorption separation method or the distillation separation method together.

The structure of the present invention will be described below with reference to the drawings. FIG. 1A is an explanatory diagram showing an example of the basic configuration of the gas separation method according to the present invention. In FIG. 1A, reference numeral 21 denotes a gas supply source of a mixed gas of three or more components to be separated, which is a specific gas component A to be separated, A ′ which is similar in permeation characteristic to this gas component, and other It consists of gas residual components B ₁ , ... Bn. Reference numeral 3 denotes a first-stage gas separation membrane module, in which the specific gas component A has a large permeability coefficient for the membrane, but the gas residual components B ₁ , ... Bn have a larger permeability coefficient, The specific gas component A is concentrated on the non-permeate side (hereinafter, this gas separation membrane module is referred to as a gas separation membrane module having selective non-permeability with respect to the specific gas component). The permeate side gas in which the concentration of the specific gas component A is diluted is returned to the gas supply source and circulated. The gas 'substantially equal to the permeability coefficient A'f ₁ with permeability coefficient Af ₁ of the specific gas component A, A' component A to flow to the non-permeate side is not performed hardly to separate the A.

Reference numeral 4 denotes a gas separation membrane module of the second stage, which has a small permeation coefficient of the specific gas component A to the membrane, but is larger than the permeation coefficient of the gas residual components B ₁ , ... Bn, The specific gas component A is concentrated on the permeate side (hereinafter,
This gas separation membrane module is referred to as a gas separation membrane module having selective permeability for specific gas components). Therefore, the specific component dilution gas in which the specific gas component is diluted and the gas residual components B ₁ , ... Bn are concentrated is taken out from the outlet 31 on the non-permeate side. In the second-stage gas separation membrane module 4, even if the permeation coefficient Af ₂ of the specific gas component A is small, this Af ₂ and the second-stage gas separation membrane module 4
The ratio of the gas component A ′ to the permeation coefficient A′f ₂ , that is, the separation coefficient is sufficiently large (Af ₂ / A′f ₂ ≧ 1),
Therefore, A and A ′ are sufficiently separated, and the concentrated gas of the specific component where the concentration of A ′ is sufficiently reduced and the concentration of A is correspondingly increased is taken out from the outlet 32 on the permeate side. Go.

FIG. 1B is an explanatory view showing another example of the basic constitution of the gas separation method according to the present invention. (B) of FIG.
In the gas separation membrane module of the first stage 3, the permeability coefficient of the specific gas component A to the membrane is small,
The permeation coefficient of which is larger than the permeation coefficient of the residual gas components B ₁ , ... Bn (a gas separation membrane module having selective permeability for a specific gas component) is used, and the specific gas component A is on the permeation side. Will be concentrated in. The non-permeate side gas in which the concentration of the specific gas component A is diluted is taken out from the outlet 31 as the specific component dilution gas. In the first-stage gas separation membrane module 3, even if the permeation coefficient Af ₁ of the specific gas component A is small, this Af ₁ and the first-stage gas separation membrane module 3
The ratio of the gas component A ′ to the permeation coefficient A′f ₁ , that is, the separation coefficient is sufficiently large (Af ₁ / A′f ₁ ≧ 1),
Therefore, A and A ′ are sufficiently separated, the concentration of A ′ is reduced from the permeation side, and the concentration of A is increased accordingly.

In the second-stage gas separation membrane module 4, the specific gas component A has a large permeation coefficient with respect to the membrane, but the gas residual components B ₁ , ... Bn have a larger permeation coefficient. (A gas separation membrane module having a selective non-permeability with respect to a specific gas component) is used, and the specific gas component A is further concentrated on the non-permeate side to obtain a specific component concentrated gas as an outlet 3
It is taken out from 2. Second stage gas separation membrane module
The permeate side gas in which the concentration of the specific gas component A in the module 4 is diluted is returned to the supply side of the second stage gas separation membrane module 4 and circulated. This second stage gas separation membrane module
In Le 4, the transmission coefficient Af ₂ and the second stage gas separation membrane module of a specific gas component A - the ratio between the permeability coefficient A'f ₂ of the gas component A 'of Le, i.e. separation factor, a small Yes, and therefore the separation of A and A ′ is substantially not achieved, but the first
Since the separation has already been sufficiently performed in the stage gas separation membrane module 3, the concentration of the A ′ gas component of the specific component concentrated gas taken out from the outlet 32 is sufficiently low.

2 to 6 are used according to the present invention to separate a specific component, for example, a specific component concentrated gas in which isoprene gas is concentrated and a specific component diluted gas in which the same gas component is diluted, from a naphtha light fraction. 2 shows a different gas separation device, which incorporates a condenser for condensing and liquefying heavy components. In the gas separation device shown in FIG. 2, 3 is a first-stage gas separation membrane module having selective non-permeability with respect to a specific gas component, and a blower 6 separates a mixed gas 21 to be separated.
Is supplied to the gas separation membrane module 3 and mainly heavy components are liquefied and separated in the condenser 2, and the permeate side gas is returned to the separated gas supply source side by the vacuum pump 7. Reference numeral 4 denotes a second-stage gas separation membrane module having a selective permeability for a specific gas component, and a first-stage gas separation membrane module 3
Pressure regulating valve 1 for the specific gas component concentrated gas 23 on the non-permeation side of
1 to the second stage gas separation membrane module 4 to further concentrate the specific gas component on the permeate side,
6 is guided to the condenser 5 under suction by the vacuum pump 8,
The heavy component is liquefied and separated, and then the specific component concentrated gas is taken out from the outlet 32, and the second stage gas separation membrane module 4 is also used.
The specific component dilution gas is taken out from the outlet 31 on the non-permeation side. 33 is a condensate outlet. In FIG. 2, the transmembrane pressure difference of the first-stage gas separation membrane module 3 is generated by a vacuum pump 7, and the transmembrane pressure difference of the second-stage gas separation membrane module 4 is generated by a vacuum pump 8. ing.

In the gas separation device shown in FIG. 3, the first
The transmembrane pressure difference of the second stage gas separation membrane module 3 and the transmembrane pressure difference of the second stage gas separation membrane module 4 are generated by operating the compressor 1 and the pressure control valves 11 and 12. Other configurations and operations are substantially the same as those shown in FIG.

In the gas separation device shown in FIG. 4, a gas separation membrane module having a selective permeability for a specific gas component is used as the first stage gas separation membrane module 3, and the second stage gas separation membrane module 3 is used. As the eye gas separation membrane module 4, a gas separation membrane module having selective non-permeability with respect to a specific gas component is used.
The permeate side gas 26 of the stage gas separation membrane module 4 is returned to the supply side of the same gas separation membrane module 4, the specific component concentrated gas is taken out from the outlet 32, and the specific component diluted gas is taken out from the outlet 31. . 4, 1 and 9 are compressors, 11 and 12 are pressure regulating valves, 5 is a condenser,
Reference numerals 3 respectively indicate condensate outlets.

In the gas separation apparatus shown in FIG. 5, 3 is a first-stage gas separation membrane module having selective non-permeability with respect to specific gas components.
1 is supplied to the gas separation membrane module 3 and mainly heavy components are liquefied and separated in the condenser 2, and the permeate side gas 24 is returned to the separated gas supply source 21 side. Reference numeral 4 is a second-stage gas separation membrane module having a selective permeability for a specific gas component, and regulates the pressure of the specific gas component concentrated gas 23 on the non-permeate side of the first-stage gas separation membrane module 3. It is supplied to the second-stage gas separation membrane module 4 through the valve 11, the specific gas component is further concentrated on the permeate side, and the specific component dilution gas is taken out from the non-permeate side via the outlet 31. First stage gas separation membrane module 3 and second stage gas separation membrane module
The transmembrane pressure difference of the valve 4 is generated by operating the compressor 1 and the pressure control valves 11 and 12. Reference numeral 10 is a gas separation membrane module at the third stage having selective non-permeability with respect to a specific gas component, and a transmembrane gas in which the transmembrane pressure is generated by the vacuum pump 8 and the specific gas component is further diluted. To the condenser 5, mainly liquefying and separating heavy components, and then returning to the supply side of the third stage gas separation membrane module 10, and the non-permeate side of the third stage gas separation membrane module 10. The further concentrated specific component concentrated gas is taken out from the outlet 32. The condensate is taken out from the outlet 33.

In the gas separation device shown in FIG. 6, the first
A gas separation membrane module having a selective impermeability to a specific gas component is used for the second stage gas separation membrane module 3, and a second gas separation membrane module 4 for a specific gas component is used. A gas separation membrane module having selective permeability is used, and a distillation apparatus 51 is provided between the first-stage gas separation membrane module 3 and the second-stage gas separation membrane module 4, Concentrated gas 23 of specific component on the non-permeate side of the stage gas separation membrane module 3
To the distillation apparatus 51 to remove heavy components and improve the degree of purification of light components, and further supply the concentrated gas of the specific component, which is the fraction, to the second-stage gas separation membrane module 4, The further concentrated specific component concentrated gas 25 on the permeate side is taken out from the outlet 32, and the specific component diluted gas 26 on the non-permeate side is taken out from the outlet 31. 1st stage gas separation membrane module
The gas 24 in which the specific gas component of the gas 3 is diluted is liquefied to remove heavy components in the condenser 2, and then the mixed gas supply source 21 for separation is separated.
Back to the side. In FIG. 6, 1 and 11 are compressors and pressure regulating valves for generating transmembrane pressure difference in the first stage gas separation membrane module 3, and 9 and 12 are second stage gas separation membrane modules. 4, a compressor for generating a transmembrane pressure difference and a pressure regulating valve, 5 is a condenser for reflux of the distillation apparatus,
33 is a condensate outlet. In the gas separation device shown in FIG. 6, instead of the distillation device 51, an adsorption separation device that separates a specific gas component by adsorption, or an extraction separation device that separates a specific gas component by absorption with an extraction liquid can be used.

In the above, when the specific gas component is isoprene, the gas separation membrane module having selective non-permeability with respect to the specific gas component is a crosslinked silicone-based gas separation membrane module. For the gas separation membrane module having selective permeability, a fluorine-containing polyimide gas separation membrane module can be used. The types of modules are spiral type, tubular type, hollow fiber membrane type, plate &
A known method such as a frame type can be used. In the present invention, it is desired to prevent the impure component and the third component from being mixed into the gas mixture to be separated in the equipment to be used, and a dry positive-displacement type is used for the vacuum pump and the blower, and the condenser is used. It is preferable to use an indirect heat exchange type.

[0017]

In a gas separation membrane module with a membrane having a large permeation coefficient, the permeation rate is large, the membrane area can be made small, and the module can be made compact, but the separation coefficient is small and the specific gas component When the gas mixture to be separated containing A contains a component A ′ that is similar in permeation characteristics to the specific gas component, it is practically impossible to separate A and A ′, and the A yield is high. It is difficult to separate by rate. On the other hand, in a gas separation membrane module having a membrane with a small permeation coefficient, it is necessary to increase the membrane area, which necessitates an increase in the size of the module, but the separation coefficient is large and the specific gas component A is separated. Even if the gas to be separated to be separated contains a component A ′ that is similar in permeation characteristics to the specific gas component, A and A ′ can be well separated, and A
Can be separated in high yield. In the gas separation method according to the present invention, a gas separation membrane module having a membrane having a large permeability coefficient for a specific gas component and a gas separation membrane module having a membrane having a small permeability coefficient are separated in multiple stages. The specific gas component A can be well separated from the gas component A ′ by sufficiently reducing the membrane area of the entire gas separation membrane module and can be separated with a sufficient yield. Therefore, when separating the gas enriched with isoprene and the gas diluted with isoprene from the naphtha light fraction, the naphtha light fraction contains isopentane, n-pentane, and methylbutene fruits whose permeation characteristics are similar to that of isoprene. Nevertheless, the isoprene gas can be separated at a high yield by the multi-stage separation using the crosslinked silicone gas separation membrane module and the fluorine-containing polyimide gas separation membrane module.

[0018]

[Example] Separation was carried out from the light fraction of naphtha (C ₅ ) shown in the table using the gas separator shown in FIG. 5 for the purpose of recovering isoprene. In FIG. 5, the compressor 1 has an air flow of 10
m ³ / min, discharge rate 7 kg / cm ² · G, motor 75
A kw dry positive displacement compressor was used for the first stage gas separation membrane module 3 having an effective membrane area of 21 m ² and a cross-linked silicone type spiral type gas separation membrane module [manufactured by Nitto Denko Corporation,
NTGS-2200-S8] is a second stage gas separation membrane module 4 having an effective membrane area of 840 m ² , a fluorine-containing polyimide spiral type gas separation membrane module [manufactured by Nitto Denko Corporation, NTGS
-3300-S8X] for the third stage gas separation membrane module 10 having an effective membrane area of 21 m ² and a cross-linked silicone-based spiral type gas separation membrane module [Nitto Denko Corporation, NTGS-2200]. -
S8] were used respectively. Gas to be separated (pressure 1.05a
tm) supply flow rate is 100 Nm ³ / hr, operating temperature is 40 ° C.
And The flow rate of the separated gas at the outlet 32 is 48 Nm ³ / hr,
The flow rate of the separated gas at the outlet 31 is 36 Nm ³ / hr, the outlet 33
The condensate flow rate was 16 Nm ³ / hr, and the composition of each separated gas and the condensate was as shown in the table. The yield of isoprene in the separated gas at the outlet 32 is 93% [100 (48 × 2
9.3) / (100 × 15.2)], and a gas with a high isoprene yield could be separated.

[0019]

[Table 1]

Although the above examples are examples of separation of isoprene in a C ₅ fraction, the present invention is directed to separation of butadiene in a C ₄ fraction, separation of propylene in a C ₃ fraction, and C ₂ fraction. It can also be applied to the separation of ethylene inside.

[0021]

EFFECTS OF THE INVENTION According to the present invention, from a mixed gas of three or more components, a specific component concentrated gas in which one specific gas component is concentrated and a specific component dilution gas in which the specific gas component is diluted are separated by a gas separation membrane. In the case of multi-stage separation with a module, the total membrane area of all gas separation membrane modules can be made sufficiently small and the yield of the specific component gas can be increased.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a basic configuration of a gas separation method according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a separation device used in the gas separation method according to the present invention.

FIG. 3 is an explanatory view showing an example different from the above of the separation device used in the gas separation method according to the present invention.

FIG. 4 is an explanatory view showing an example different from the above of the separation device used in the gas separation method according to the present invention.

FIG. 5 is an explanatory view showing an example different from the above of the separation device used in the gas separation method according to the present invention.

FIG. 6 is an explanatory view showing an example different from the above of the separation device used in the gas separation method according to the present invention.

[Explanation of symbols]

 21 Source of mixed gas to be separated 3 First stage gas separation membrane module 4 Second stage gas separation membrane module 10 Third stage gas separation membrane module 31 Specific component diluted gas outlet 32 Specific component concentrated gas Exit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01D 71/64 B01D 71/64 71/70 500 71/70 500 // C10L 3/00 6958-4H C10L 3/00 Z

Claims (3)

[Claims] 1. A method of separating a specific component enriched gas in which one specific gas component is concentrated and a specific component dilution gas in which the specific gas component is diluted from a mixed gas of three or more components, wherein a permeation coefficient of a membrane is obtained. A gas separation method, characterized in that multi-stage separation is performed using gas separation membrane modules having different temperatures. 2. A mixed gas is a naphtha light fraction, one specific gas component is isoprene gas, and a gas separation membrane module has a crosslinked silicone-based gas separation membrane module and a fluorine-containing polyimide-based gas. The gas separation method according to claim 1, wherein a separation membrane module is used. 3. The gas separation method according to claim 1, wherein a condensation separation method, an absorption separation method, an adsorption separation method or a distillation separation method is used in combination.