JPH0829229B2 - Gas separation and concentration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses a natural zeolite, which is an inorganic porous material, as a permeable material and has a relatively small molecular weight (molecular weight of about 2 to 80) in a mixed gas, such as hydrogen and helium. Separates gases such as oxygen
It relates to a method of concentrating.

(Prior Art) In recent years, hydrogen has been extremely used as a reducing atmosphere in the electronics industry, as a carrier gas for vapor phase growth, or as a raw material for C ₁ chemistry such as ammonia and alcohol synthesis, or for removing sulfur compounds by hydrogen in petroleum refining. Many demands for hydrogen will continue to increase. Furthermore, a large amount of hydrogen is also used in the fuel cell process. And now that depletion of petroleum resources is called, hydrogen gas is drawing attention as a clean alternative energy. While the demand for hydrogen has increased in this way, petrochemical plants and the like still emit a large amount of mixed gas containing hydrogen gas as exhaust gas. This is because the hydrogen gas concentration is simply low, and it can be used for various purposes by separating and concentrating it into high-concentration hydrogen gas, and it will be very useful from the viewpoint of resource saving and cost saving. . Therefore, a technology that can separate and concentrate a large amount of hydrogen at low cost is required. Current,
Various gas separation methods have been devised and implemented, and cryogenic separation method and adsorption separation method are famous. The former cools the mixed gas
After liquefying, it is a method of separating by utilizing the difference in boiling point, and a large power is required for cooling. The latter is a method in which an adsorbent is used and a mixed gas is adsorbed and separated using a difference in gas adsorption equilibrium under a high-pressure group.

(Problems to be Solved by the Invention) In the above-mentioned conventional methods, large power is required for cooling or under high-pressure conditions, or an adsorbent matched to the gas is required. Not only there is room for improvement, but the cryogenic separation method requires cooling / distillation, and the adsorption / separation method requires two processes, adsorption / desorption, which complicates the structure of the device, resulting in costs for equipment, operation, maintenance, etc. Considering the above, it can be said that it is not suitable for the separation and recovery of low-concentration hydrogen gas, which is premised on resource saving and cost reduction.

(Means for Solving the Problem) Therefore, attention was paid to a separation method using a permeable material. The method according to the present invention is a method in which a mixed gas containing a gas having a relatively small molecular weight is permeated through an inorganic porous material by a Knudsen flow to separate / concentrate the gas. Using processed natural zeolite,
It is a gas separation / concentration method in which a mixed gas is passed through the inside or outside of a cylinder to permeate an inorganic porous material to obtain a mixed gas in which the gas is concentrated from the inside or outside.

The permeable material includes a homogeneous material that utilizes its chemical properties and a porous material that utilizes the pores of the permeable material. The former separation mechanism generally utilizes the difference between the dissolution rate and the diffusion rate, and the concentration ratio by one permeation is high, and the permeation coefficient used in the production of ultra-high purity hydrogen gas is very small, which is enormous. A large transparent area is required. On the other hand, the latter utilizes the Knudsen flow that occurs when the pores become smaller than the mean free path of gas. In the Knudsen flow, the diffusion rate of the gas in the pores is inversely proportional to the square root of the molecular weight of the gas, so that the gas can be separated, which is suitable for the separation of a mixed gas of two or more kinds having a large difference in molecular weight. That is, it can be said that it is suitable for separating a gas having a particularly small molecular weight such as hydrogen and helium from a gas having a molecular weight of about 30 or more. Generally, when the operating pressure is increased, the flow changes from Knudsen flow to viscous flow,
The separation, which is a function of the pressure difference, no longer takes place. Therefore, particularly in the case of a mixed gas of two or more kinds having large differences in molecular weight as described above, the operating pressure becomes relatively small, the required power is small, and the apparatus becomes simple. And the gas permeation rate of the inorganic porous permeable material is 1000 ~ compared with the homogeneous permeable material of the same thickness.
Since it has a value of 10000, it is considered to be very advantageous for the aforementioned industrial use. Furthermore, it can be said that it can be sufficiently put into practical use for the recovery of hydrogen from the exhaust gas of 200 to 650 ° C. emitted from the fuel cell process because of the heat resistance of the inorganic porous material.

(Example) In the example, tuff was used. Tuff is a natural zeolite from Itaya, and the results of X-ray analysis using Q200J type manufactured by Link are shown in FIG. Itaya's natural zeolite contains a large amount of Si and Al because it is a tuff composed mainly of SiO ₂ and Al ₂ O ₃ , and it is also composed of Na, Ti, Fe, etc. Confirmed from the X-ray analysis results. FIG. 2 shows the pore size distribution of natural zeolite. It can be seen from the figure that the distribution of pore size is mainly in the range of 50 to 450Å. This pore size distribution is the mean free path of gas, H ₂ = 1123Å, He = 1798 Å, N ₂ ＝ 600 Å, O ₂ ＝ 647 Å, CO
Considering ₂ = 397Å, it can be said that it is more suitable for hydrogen separation using Knudsen flow that occurs when the pore size is smaller than the mean free path of gas. In addition to hydrogen, it can be applied to the separation of expensive helium, which is difficult to collect in Japan. FIG. 3 shows that the permeation flow rates of hydrogen and nitrogen were actually measured and that the permeation material for gas separation can be used. As can be seen from the figure, both hydrogen and nitrogen show a good linear relationship. Linearly approximate each measurement point using the least squares method,
When the flow rate ratio was calculated from each slope, it showed a value extremely close to the square root ratio of the molecular weight. In other words, it is considered that the gas permeates through the pores of the permeable material due to the Knudsen flow,
It was suggested that it could be used as a permeable material for gas separation.

To facilitate understanding of the present invention, the constitutional principle of the present invention will be described below with reference to specific examples of the present invention, but the present invention is not limited thereto.

FIG. 4 is an outline of the experimental apparatus of the present invention. The solid line shows the gas line and the broken line shows the measurement line. Each gas is supplied from a cylinder through a regulator, and the flow rate is adjusted by the valve 1. For the measurement of the flow rate, a brass orifice flow meter 2 is used, the differential pressure is converted into a voltage by a pressure conversion element, amplified by an amplifier 3, and then taken into the computer 11 via the A / D converter 10 for data processing. went. After passing through the orifice flow meter, the two kinds of gas become mixed gas and are sent to the separation column 6. The mixed gas supplied to the column 6 is separated into a gas separated and concentrated by the separation / permeable material 7 and an exhaust gas. When measuring the hydrogen composition on the supply side, the mixed gas is sent to the gas chromatograph 9 by the three-way cock 4, and when measuring the hydrogen composition of the permeated gas, the valve 8 is opened and the mixed gas is stored in the gas chromatograph 9. Sent. The differential pressure in the column can be adjusted by opening and closing valve 1 and opening and closing valve 2, and the gauge pressure is converted to a voltage by a gauge pressure conversion element and amplified by amplifier 5 before A / D.
Measurements were taken in the computer 11 via the converter 10. FIG. 5 is an outline of the permeable material 7 and the column 6 and corresponds to 7 and 6 in FIG. The transparent material 7 has an inner diameter d = 4 mm and an outer diameter
The permeable material is a tuff processed into a cylindrical shape having D1 = 18 mm and length L1 = 80 mm, and the permeable material 7 is held between holders 15 and 16 pivotally attached to both ends in the column 6. Holder 1
Holes 19 and 20 are formed at the centers of the holes 5 and 16, respectively.
A gas supply pipe 13 and a first discharge pipe 14 are fitted in the respective 20. A gap 17 is formed between the column 6 and the permeable material 7, and a second discharge pipe 18 is attached to the column 6 so as to communicate with the gap 17. The length L2 of the column 6 including the holders 15 and 16 is 145 mm, and the outer diameter D2 of the column 6 is 35 m.
It was m.

In the separator shown in FIG. 5, the case where the single component gas is used to permeate the inside of the permeation material 7 to the outer periphery 17 and the gap 17
Comparing the case of permeation from 17 to the center of the cylinder, it was found that the relationship between the permeation flow rate and the pressure difference was exactly the same.

Next, one specific example of the permeation separation characteristics of the permeation material when using a hydrogen-nitrogen mixed gas is shown. Separation characteristics are shown using separation coefficient α (= {Y / (1-Y)} / {X / (1-X)}), and transmission characteristics are shown using stage cut θ (= Q _P / Q _F ). . Supply flow rate Q _F = 240 cc (STP) / min, and supply side hydrogen composition X ₁ = 21 to 71%, pressure difference Δ
Table 1 shows the measurement results of transmission and separation characteristics with P.
-1 to Table-1-6. It can be seen that the stage cut θ indicating the transmission characteristic is in direct proportion to the increase in the pressure difference for any composition. When the hydrogen composition on the supply side is increased from 21% to 71%, the value of (θ / ΔP) tends to increase for each composition. In other words, it can be seen from the permeation characteristics that the larger the pressure difference ΔP is and the higher the hydrogen content on the supply side is, the better the permeation characteristics are. However, from the standpoint of separation characteristics, the higher the hydrogen composition on the supply side, the better the pressure difference.However, as the pressure difference is represented by a convex curve with a peak of about 100 KPa, an excessive increase in pressure difference rather hinders the separation. is there. In other words, the pressure difference ΔP = 100 KPa is considered to be optimal if the separation characteristics are considered first for both the transmission and separation characteristics.

Therefore, the pressure difference ΔP was kept constant at 100 KPa, and the permeation / separation characteristics were examined by changing the hydrogen composition X ₁ on the supply side to 20 to 71%.
The results are shown in Table-2-1 to Table-2-5. Also, the transmission characteristics will be described. When the pressure difference is constant,
If the hydrogen composition on the supply side is also constant, the permeation flow rate Q _P shows a substantially constant value regardless of the supply flow rate Q _F. That is, when the supply flow rate is reduced, the permeation flow rate is constant, and thus the stage cut θ increases. Further, the permeation flow rate increases as the supply-side hydrogen composition increases, and if the supply flow rate is constant, the stage-cut θ increases as the supply-side hydrogen composition increases, and superior permeation characteristics are exhibited. Regarding the separation characteristics, no significant change was observed in the separation coefficient even if the hydrogen composition on the supply side was changed, and it can be said that there is almost no effect of the composition. On the other hand, when the supply flow rate is increased, the separation coefficient increases proportionally up to a certain value. However, supply flow rate Q _F = 150cc (STP) / min
It peaks near and then shows a constant value. This is because if the supply flow rate is too small, the difference from the permeation flow rate that is uniquely determined by the operating pressure difference becomes small, that is, the supplied gas almost permeates. Therefore, in the case of the results shown in Table 2, when θ = 0.3 or more, the separation characteristics are significantly affected, and the separation coefficient is reduced. If the emphasis is on separation characteristics, it seems that some sacrifice in transmission characteristics is unavoidable. In actual industrial use, the supply flow rate should be determined by finding the optimum stage cut and separation coefficient values for the operating pressure difference.

Tables 3-1 to 3-5 show the effects of permeation / separation characteristics on the hydrogen composition on the supply side when the pressure difference ΔP ≈ 100 KPa and the supply flow rate Q _F ≈ 240 cc (STP) / min. . Regarding the separation characteristics, there was no significant effect of the hydrogen composition on the supply side, and it was around 1.5 to 1.6. However, regarding the permeation characteristics, the permeation flow rate increases and the stage cut also increases as the hydrogen composition on the supply side increases. About 2.8 when the hydrogen composition on the supply side is X ₁ ≈ 4% and when X ₁ ≈ 93%
The difference in double stage cutting is recognized. The fact that the hydrogen composition on the supply side is high means that the hydrogen concentration is high, and it is considered that this occurs because hydrogen has a longer mean free path and is easier to permeate than nitrogen.

FIG. 6 is a flow system diagram in the case of multiple stages. Several cylindrical permeation materials are installed in one column, and this is made into one. In the example of FIG. 6, the supply flow rate Q _F = 1000 cc / min, the hydrogen composition of the supply gas is X ₁ = 30%, the separation coefficient α = 1.6, and the stage cut θ = 0.45. After the flow became steady state, Q _p = 121.096cc / mi from the column of c.
It is possible to obtain n, the hydrogen composition X ₂ of the permeated gas = 64.46%, which means that the concentration of 34.46% has been achieved. Also
The flow rate and hydrogen composition of each gas discharged as exhaust gas from the e and f columns are 166.375cc / min, 8.53% and 77.88cc.
/ min, 13.47%.

FIGS. 7 (A) and 7 (B) show one column 6A in which a plurality of permeation materials 7 are arranged in parallel, 13 is a gas supply pipe, and 14 and 18
Are the first and second discharge pipes, respectively, which have a large gas content and a small gas content.

When carrying out the present invention, the inorganic porous material (permeable material) processed into the cylindrical shape has an inner diameter of 2 to 130 mm and an outer diameter of 5 to 1
When the length is 50 mm and the length is 20 to 500 mm, there is an advantage that a transparent material can be easily obtained in actual processing.

(Effect of the invention) According to claim 1, natural zeolite is used as the permeable material,
The Knudsen flow that occurs when the pores of the permeable material become smaller than the mean free path of the gas is used to separate the gas. The operating pressure is low, the required power is low, and the device is simple. Further, in the present invention, since a natural zeolite is used, a permeable material can be obtained by processing with a machine tool, so that pretreatment such as pulverization or firing performed by the adsorption separation method is not required. The transparent material can be obtained inexpensively and easily. In addition, compared to porous glass that has been used conventionally,
A material using natural zeolite ore can easily obtain a material having a permeation coefficient of 50 times, high separation efficiency, and highly efficient separation and recovery work.

Further, since the cylindrical material is used as the transmissive material, a small transmissive material having a wide transmissive area can be used, and efficient separation is possible.

According to the second aspect, there is an advantage that a transparent material can be practically obtained.

According to the third aspect, more efficient separation is achieved by using the aggregated permeable material.

[Brief description of drawings]

FIG. 1 shows X of natural zeolite rough stone used in the present invention.
Fig. 2 is an output waveform diagram showing the results of the line analysis, Fig. 2 is a pore size distribution diagram of natural zeolite, Fig. 3 is a diagram showing the relationship between the pressure difference of the permeable material and the permeation flow rate for hydrogen gas and nitrogen gas, and Fig. 4 is Configuration diagram showing an example of an experimental apparatus used in the present invention,
5 (A), (B) and (C) are respectively a plan sectional view, a plan view and a view seen from the axial direction showing an example of the separator used in the present invention, and FIG. 6 shows a combination of the separators in multiple stages. An example system diagram and FIGS. 7 (A) and 7 (B) are a horizontal cross-sectional view and a vertical cross-sectional view of a separator in which a plurality of permeation materials are put in one column, respectively.

Front page continued (72) Inventor Kazuhiro Koami 1 No. 304, Negishi, Takahata-cho, Higashiokitama-gun, Yamagata Pref. Shinno Electronics Co., Ltd. (56) Reference JP-A-63-185429 (JP, A) JP-A-61 -107902 (JP, A) JP-A-63-291809 (JP, A)

Claims (3)

[Claims] 1. A method for permeating a mixed gas containing a gas having a molecular weight of 2-80 through an inorganic porous material by a Knudsen flow to separate and concentrate the gas, wherein the inorganic porous material has a cylindrical shape. A method for separating and concentrating a gas using a processed natural zeolite that allows a mixed gas to flow through the inside or outside of a cylinder to permeate an inorganic porous material to obtain a mixed gas in which a gas having a smaller molecular weight is concentrated than the outside or inside. 2. The method for separating and concentrating gas according to claim 1, wherein the inorganic porous material processed into the cylindrical shape has an inner diameter of 2 to 130 mm, an outer diameter of 5 to 150 mm, and a length of 20 to 500 mm. 3. The gas according to claim 1, wherein the plurality of cylindrical inorganic porous materials are combined into one column to form a separator, and the separator is used for gas separation and concentration. Separation and concentration method.