JPS5843131B2 - Gas separation and concentration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and concentrating gas using a porous polymer membrane.

In recent years, research has been conducted into methods of separating and concentrating gases using membranes, and this has been applied to artificial organs such as artificial lungs and the enrichment of uranium.

For example, in oxygenators, what is generally called a homogeneous membrane with an average pore diameter of 50 Å or less is used, and in uranium enrichment, a membrane made of sintered material of Vycor glass and aluminum with an average pore diameter of 500 Å or less is used. A diaphragm is used.

The gas separation mechanism using a homogeneous membrane is a so-called diffusion mechanism that utilizes the difference in the dissolution rate and diffusion rate of gaseous molecules into the membrane, so the membrane material should be selected depending on the type of target gas. is extremely important.

Further, the gas separation mechanism using the uranium enrichment diaphragm is a free molecular flow mechanism as described later.

However, these have a permeability coefficient of, for example, 10'' to 1 for a polystyrene homogeneous membrane at room temperature for oxygen gas.
0-14(cc-crn/ see-cd-cr
rtHg), 10-7 to 10 for dimethylsiloxane membranes.
-8(cc -crrt/ see -ctrt -c
llLHg), 10-(e
c -cIrL/sec -cd -mHg), which was extremely low and unsuitable for industrially separating and concentrating a large amount of gas.

The present inventors worked on developing a method for industrially separating and concentrating a large amount of gas using a membrane, which had never been attempted before, and as a result of intensive studies from various viewpoints, surprisingly, a specific The inventors have investigated the fact that the permeability coefficient can be significantly improved by using a porous polymer membrane having a structure, and have completed the present invention.

The gist of the present invention is that when separating and concentrating gas using a porous polymer membrane, the average pore diameter (γ) is 0.01μ.
Using a gas separation device equipped with a porous polymer membrane having the above properties and a pore diameter ratio (α) of the front surface and the back surface of 1/2 or less, the surface pressure of the porous polymer membrane is set to 1.40 (1,5-a). )/(r-
o, o O5) At a pressure of 5 mmHg or less, gas is continuously introduced to the surface side of the porous polymer membrane to create a gas flow along the membrane surface, and the gas that has passed through the porous polymer membrane and the gas that has not passed through the porous membrane. This is a gas separation and concentration method characterized by supplying each gas to a separate system of porous polymer membranes and repeating gas separation to concentrate each component.

In general, free molecular flow refers to a flow of gaseous molecules that does not collide with each other, and is said to occur when gas is passed through a membrane with small pores in a region of low pressure. It has been theoretically clarified that when used for separation, the separation coefficient is inversely proportional to the 1/2 power of the molecular weight of the gaseous molecule.

However, since the operating pressure and permeability coefficient are extremely low, the permeation rate is slow, and it was considered impossible to use it for general industrial purposes except for special uses such as uranium enrichment.

The present invention has succeeded in producing such free molecular flow at a high permeation rate that can be used industrially by using a porous polymer membrane with a specific structure.

According to the present invention, the transmission coefficient is 10-4 to 1o-2 (CC-
crrL/sec-cd-CIrLHg), and combined with the ability to increase the operating pressure, significantly increases the permeation rate.Also, since it is a free molecular flow mechanism, the membrane material used is similar to the diffusion mechanism. There is no need to select anything.

Furthermore, since a polymer is used as the material for the membrane, it is extremely easy to manufacture porous membranes, and those with tensile elongation at break of 5% or more and 20% or more can be manufactured if necessary, making them easy to handle. The operability is extremely good.

The porous polymer membrane used in the present invention is made of materials such as silicone, polyethylene, polyamide, Teflon, cellulose, and derivatives thereof, either singly or as a composite.

Next, as for its structure, the average pore diameter must first be 0.01μ or more, preferably 0.05 to 1.5μ, and more preferably 0.1 to 0.3μ.

When the average pore diameter is 0.01 μm or less, gas separation is performed by a diffusion mechanism, resulting in a significant decrease in gas permeability coefficient.

Further, the pore diameter distribution is preferably sharp without cutting in the large pore diameter region, and the ratio of r4/r3 expressed by the following formula is preferably 1.5, preferably 1.3.

However, N(7'l is a function representing the pore size distribution, and is defined as the number of pores whose pore diameters range from γ to γ+dγ as given by N(γ)dγ.

Furthermore, it is necessary that the pore diameter on the front surface be 1/2 or less, preferably 1/3 or less of the pore diameter on the back surface, and this pore diameter ratio is the most important feature of the porous polymer membrane used in the present invention.
This is the basis for generating free molecular flow at a high permeation rate that can be used industrially.

In other words, because the pore size ratio between the front and back surfaces is as large as 1/2 or less, a concentration gradient of gaseous molecules occurs in the pores, and even though molecules collide with each other near the front entrance, the concentration of gaseous molecules decreases near the back exit. The flow changes to a free molecular flow without mutual collision between molecules. Therefore, the operating pressure and average pore size can be increased, and the pore size ratio between the front and back surfaces is 1/2.
Due to the following structure, the porosity can be significantly increased, and these factors combine to dramatically increase the permeation rate.

Here, the porosity is preferably 30 to 90%, preferably 70 to 80%; if it is less than 30%, the permeability coefficient will decrease, and if it is more than 90%, the mechanical strength will decrease and the operating pressure cannot be increased, which is not preferable.

Next, the film thickness should be 0.02 or more, preferably 0.05 to 0.3
mm is appropriate.

If it is made too thin, the mechanical strength will decrease, and the flow of free molecules may not be sufficiently changed in the gas separation mechanism of the present invention, which may result in a decrease in the separation coefficient, which is not preferable.

Also, if the thickness is too large, the permeation rate will decrease.

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 illustrates the basic configuration of the method of the present invention, in which a porous polymer membrane 4 having the configuration described above is attached to a separation device A-1, and the front side is connected to the high pressure section 2, and the back side is connected to the high pressure section 2. The side is defined as the low pressure section 3.

The porous polymer membrane 4 is supported by a support 8.

The crude gas to be separated is introduced from the conduit 1, compressed by the compressor 5 in front of the inlet of the high pressure section 2, and sent to the separation device A-1.
will be introduced in

This crude gas is divided in this separator A into two streams.

One of them is a flow that passes through the porous polymer membrane 4 and flows into the low pressure section 3 and is discharged from the discharge lower, and the other flow does not pass through the porous polymer membrane 4 and is discharged from the discharge port 6 of the high pressure section 2. This is the flow discharged from the

Here, the pressure of the high pressure section 2, that is, the operating pressure is the porous polymer membrane 4.
Let α be the pore diameter ratio of the front and back surfaces, and γ be the average pore diameter, then 1.4
It is necessary to set the pressure to 0(1,5-α)/(γ-0,005)5 mmHg or less, preferably 10 mmHg or less from this pressure.

If the operating pressure is higher than this, the flow of free molecules will be inhibited and gas separation will become impossible.

Further, it is preferable that the pressure difference between the high pressure section 2 and the low pressure section 3 is large. In particular, it is effective to set the pressure of the low pressure section 3 to 100 mmHg or less, preferably 50iiHg or less, to generate a free molecular flow.

Furthermore, it is preferable to increase the gas temperature in the high pressure section 2 (and lower the gas temperature in the low pressure section 3 to increase the temperature difference) because the separation coefficient increases.

Usually the high pressure part 2 is 40 to 80 degrees Celsius, preferably 50 to 70 degrees Celsius,
The temperature of the low pressure part 3 is 0 to 30°C, preferably o-io°C.

In the present invention, a separation apparatus A-1 as shown in FIG.
As shown in FIG. 2, gases can be efficiently separated and concentrated by combining four combinations.

That is, crude gas is introduced through conduit 1, compressed by compressor 5-1, introduced into high-pressure section 2 of separator A-2, and reduced to the 1/2 power of the molecular weight by a free molecular flow mechanism in porous polymer membrane 4. A gas separated and concentrated in an inversely proportional ratio (hereinafter referred to as pass-through gas) is obtained from the low pressure section 3.

A diluted gas (hereinafter referred to as non-passing gas) is obtained from the high pressure section 2.

The passing gas is then compressed by compressors 5-2 and '5-3 and introduced into the high pressure section 2 of the separator B-2.The passing gas is discharged from the low pressure section 3 and the non-passing gas is discharged from the high pressure section 2. is further introduced into the high pressure section 2 of the separator C-2 by the compressor 5-4, 5-5, and the non-passed gas is refluxed into the crude gas by the compressor 5-6.

On the other hand, the gas that does not pass through the separator A-2 is supplied to the compressor 5-7.
5-8 into the high pressure section 2 of the separator F-2, the passing gas is discharged from the low pressure section and the non-passing gas is discharged from the high pressure section 2, and the passing gas is refluxed into the crude gas by the compressor 5-9. , the non-passing gas is introduced into the high pressure section 2 of the separation device (,-2) by the compressor 5-10.5-11.

In this way, in the present invention, the X region (separation devices A2 to E2)
In this case, the passing gas is introduced into the next separator according to the arrows shown, and the non-passing gas is refluxed.

Further, in the Y region (separators F-2 to F-1-2), the passing gas is refluxed according to the arrows in the figure, as described above, and the non-passing gas is introduced to the next separating device.

By repeating the above process in each region, a gas containing many components with a small molecular weight is obtained in the X region, and a gas containing many components with a large molecular weight is obtained in the Y region.

The combination of separators can be selected as appropriate depending on the type of gas, the separation capacity of the separator, etc. For example,
Some examples of these are Figure 2, Figure 3, Figure 4, Figure 5.
There are various modifications and embodiments as shown in the figure.

Here, the gas flow in the high-pressure part and the gas flow in the low-pressure part of the separator are, for example, T-shaped 6-1, co-current type 6-2, and counter-current type 6-3, as shown in Fig. 6. A countercurrent type is preferable because it improves the separation coefficient.

9 in the figure is a gas inlet port of the low pressure section.

The method for producing the porous polymer membrane used in the present invention is as follows:
For example, there may be mentioned a film forming method using a solvent evaporation method as described in Japanese Patent Publication No. 48-40050 filed by the present applicant.

Further, the shape thereof includes a sheet shape, a hollow fiber shape, a bag shape, etc., which may be appropriately selected according to the need, but a hollow fiber shape having a large surface area and high strength is preferable.

FIG. 7 shows a separation device A-7 equipped with a hollow fiber-like porous polymer membrane 10. Gas to be separated is introduced from the inlet 1, passed through the hollow fiber-like porous polymer membrane 10, and passed through. Gas is led out from the discharge lower, and non-passing gas is led out from the discharge port 6.

Further, the reflux gas is introduced from the inlet 9.

The hollow fiber porous membrane 10 is supported by a support 8.

FIG. 8 is an explanatory diagram schematically showing the method for producing the hollow fiber porous polymer membrane.

When the material is acetate, for example, a spinning stock solution 11 consisting of cellulose acetate/acetone/methanol/cyclohexanol/CaCl2.2H20 is extruded from a hollow nozzle 12, and at the same time, spinning is carried out while constantly flowing methanol, which is a non-solvent, from another nozzle 13. After drying (14), the membrane is passed through water (15), and further passed through a methanol bath (16) and dried (17) to obtain a hollow fiber-like porous polymer membrane.

The inner diameter of the hollow fiber is 102-105μ, preferably 102-1
The outer diameter is preferably 10 to 1000 microns, preferably 50 to 150 microns larger than the inner diameter.

103 to 104 such hollow fibers are bundled together,
Harden both ends with silicone rubber, etc., and place the device (
to support.

The inside of the hollow fiber is defined as a high pressure side, and the outside thereof is defined as a low pressure side, and as described above, crude gas is introduced through the inlet 1 and passed through the hollow fiber 10 for gas separation.

Fig. 9 shows a laminated type separator A-9**, in which sheet-like porous polymer membranes 4 are laminated and attached to a container 21 at predetermined intervals, and high-pressure parts 22 and low-pressure parts 23 are alternately connected. established,
Correspondingly, the high pressure section inlet 25, the discharge port 26, the low pressure section outlet 27. The introduction ports 28 are provided alternately as shown.

29 is support.

The gases to be separated flow through the aforementioned paths and the separation action takes place.

The present invention will be explained below with reference to Examples.

In addition, the average pore diameter, pore diameter distribution, pore diameter ratio of front and back surfaces, porosity,
The permeability coefficient was measured by the following method.

The average pore diameter was determined by measuring the surface pore diameter using a transmission or scanning electron microscope, and the arithmetic mean thereof was used, and the pore diameter distribution was determined by statistical processing.

The pore diameter ratio between the front and back surfaces was also determined by measuring the pore diameters on the front and back surfaces using an electron microscope.

The porosity was determined by the following formula using the apparent density (ρa) and the material density (ρf).

The permeability coefficient is calculated by using a gas permeation device consisting of a high-pressure part and a low-pressure part gas reservoir, and measuring the change in pressure in the low-pressure part gas reservoir over time.The relationship is expressed as h(t), and the following formula is used, where T is the temperature (0
K), ■ is the volume of the low pressure gas reservoir (c4), A is the effective permeation area (cJ), l is the membrane thickness (cIrL), Pl is the high pressure gas reservoir pressure, h(t) is the low pressure gas reservoir pressure , pl
-h(t) is the time change in the high pressure gas reservoir pressure, dh(t
)/at is the time change in the low pressure gas reservoir pressure.

Example 1 Cellulose acetate 25 with a degree of acetylation of 54% and an average degree of polymerization of 205
1 was dissolved in 100 ml of acetone, and then a solution containing 80% by weight of calcium chloride based on cellulose acetate and 60% by weight of methanol based on acetone (at 25°C) was cast onto a glass plate, and the solution was cast at room temperature. The solvent was evaporated to form a film.

The obtained film was devitrified, and the film was washed with methanol for 1 hour and then dried to obtain a porous membrane used in the method of the present invention.

The properties of this were measured according to the above-mentioned measuring method, and the results shown in Table 1 were obtained.

Gas separation of 0□ and CO2 was carried out using this porous membrane and a polystyrene homogeneous membrane and Vycor glass (#7930 manufactured by Gorning) under the following conditions.

The results are shown in Table 1. From Table 1, it can be seen that the porous membrane of the present invention has a significantly higher permeability coefficient than the conventional membrane.

Next, the porous polymer membrane of the present invention was attached to a permeation device as shown in FIG.

Note that the volumes of the high pressure part and the low pressure part are 50 cd, and the effective permeation area is 10 cd.

Combination 02:C of such a transmission device is shown in FIG.
A mixed gas having a molar ratio of 02=l:1 was gas-separated at 25° C. under the following conditions.

(Operating conditions) The gas compositions obtained from the low-pressure outlet of permeation device B and the high-pressure portion outlet of permeation device F were measured by gas chromatography, and the molar ratio of 0□/Co□ was 1.37/1. ．．
It was 0.1.0/1.12.

As described above, in the present invention, a gas containing a large amount of oxygen having a small molecular weight can be obtained in the X region, and a gas containing a large amount of carbon dioxide gas having a large molecular weight can be obtained in the Y region.

Example 2 The permeation apparatus used in Example 1 was used to separate and concentrate oxygen gas from combined air (N2:02=4:1) as shown in FIG.

In addition, the air passes through a calcium chloride pipe and is pre-filtered.
The test was carried out at 25° C. under the following conditions.

(Operating conditions) However, 1. The permeability coefficient of N2 and 02 by the porous polymer membrane of the present invention (cc - cm/see -ctd ocII
LHg) is)N2=1.176X10-3.02=
It was 1.10XI O-3.

The gas composition obtained from the high pressure part outlet of permeation device C is N21
The ratio of 0□ was 3.69/1.0.

As is clear from the above examples, according to the present invention, the permeation coefficient and operating pressure are extremely large compared to gas separation using conventional membranes, so the permeation rate is high, and the membrane material is limited depending on the type of gas. The range of applications is wide, and gas separation on an industrial scale using membranes, which was previously thought to be impossible, becomes possible.

Furthermore, by supplying the gas that has passed through the porous polymer membrane and the gas that has not passed through the porous polymer membrane to separate permeation devices, it is possible to separate the gases into each component according to their molecular weight, which has great industrial significance. be.

[Brief explanation of the drawing]

The drawings are explanatory diagrams illustrating embodiments of the method of the present invention, in which Figure 1 illustrates a separation apparatus equipped with the porous polymer membrane of the present invention, and Figures 2 to 5 illustrate a separation apparatus. This is an example of how to combine devices. Figure 6 illustrates the gas flow in the high pressure section and low pressure section of the separator, where 6-1 is T-shaped, 6-2 is parallel flow type, and 6-2 is T-shaped.
-3 is a countercurrent type. FIG. 7 is a perspective model diagram of a separation device using a hollow fiber porous polymer membrane, and FIG. 8 shows a method for manufacturing the hollow fiber porous polymer membrane. FIG. 9 is a needle-view model diagram showing a laminated type transmission device. In the figure, A-1 to I-2 are separation devices, 1 is a gas inlet, 2 is a high pressure section, 3 is a low pressure section, 4 is a porous polymer membrane, 5.5-1.
5-2...... is a compressor, 6 is a gas discharge port,
7 is a gas outlet of the low pressure section, 8 is a membrane support, 9 is a gas inlet, 10 is a hollow fiber porous polymer membrane, 11 is a spinning dope, 12.13 is a nozzle, 15° and 16 are a coagulation bath, and 21 is a Container of the laminated type separation device, 22 is a high pressure section, 23 is a low pressure section, 24 is a sheet-like porous membrane, 25 is an inlet for the high pressure section, 26
is the same outlet, 27 is the low pressure part outlet, 28 is the same inlet,
29 is support.

Claims (1)

[Claims] 1. When separating and concentrating gas using a porous polymer membrane,
Using a gas separation device equipped with a porous polymer membrane having an average pore diameter (γ) of 0.01 μ or more and a pore size ratio (α) of the front surface and the back surface of 1/2 or less, the surface pressure of the porous polymer membrane is reduced. 1.4
0 (1,5-α)/(γ-0,005)5mm Hg
As follows, gas is continuously introduced to the surface side of the porous polymer membrane to create a gas flow along the membrane surface, and
A method for separating and concentrating gas, characterized in that the gas that has passed through the porous polymer membrane and the gas that has not passed through the porous polymer membrane are each supplied to separate systems of porous polymer membranes, and gas separation is repeated to concentrate each component. 2. The gas separation and concentration method according to claim 1, wherein the porous polymer membrane has a porosity of 30 to 90%. 3. The gas separation and concentration method according to claim 1, wherein the porous polymer membrane has a thickness of 0.05 to 0.3 mm. 4 The pore size distribution of the porous polymer membrane is r4/
The method for separating and concentrating gas according to claim 1, wherein the ratio of r3 is 1.5. 5. The gas separation and concentration method according to claim 1, wherein the pressure on the back surface of the porous polymer membrane is 100 mmHg or less. 6 The gas temperature on the surface side of the porous polymer membrane is 40 to 80°C,
The method for separating and concentrating a gas according to claim 1, wherein the gas temperature on the back side is 0 to 30°C. 7. The gas separation and concentration method according to claim 1, wherein the gas flow on the front side of the porous polymer membrane and the gas flow on the back side are countercurrent.