JPH04290518A - Gas separating method - Google Patents

Abstract

PURPOSE:To provide a method for effectively separating condensable gas from inert gas containing condensable gas, sufficiently preventing its condensation. CONSTITUTION:Such inert gas as air or gaseous nitrogen which contains condensable gas is pressurized to not lower than atmospheric pressure and to not higher than condensation pressure to condensable gas in the inert gas and supplied to a gas separation membrane module. Pressure on the permeated side of the module is reduced to not higher than condensation pressure to condensable gas in the permeated gas to allow the condensable gas to selectively permeate the membrane.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a gas separation method using a gas separation membrane.
It is used to separate condensable gas from inert gas such as nitrogen gas.

0002

[Prior Art] When gases are separated using the permselectivity of a gas separation membrane, the permeation rate is determined by the solubility of the gas to be separated on the membrane surface and the diffusivity of the dissolved gas within the membrane. The permeation rate can be increased by increasing the pressure difference between the membranes.

Conventionally, gas separation membrane modules have been operated using either a pressurized-atmospheric system in which the gas supply side is pressurized and the permeate side is at normal pressure, or a pressurized-atmospheric system in which the gas supply side is at normal pressure and the permeate side is at normal pressure. A normal pressure-reduced pressure system is used to reduce the pressure on the permeate side, and when reducing the pressure on the permeate side,
Depending on the gas supply method, the supply side may be slightly pressurized due to the supply means, but this also essentially belongs to the normal pressure-pressure system.

0004

[Problem to be solved by the invention] However, normal pressure -
In a reduced pressure system, when the gas to be separated is a highly condensable gas, for example, water vapor or organic solvent vapor such as hexane or toluene, the high concentration and condensability of the gas on the permeate side of the module The gas becomes supersaturated under reduced pressure on the permeate side and tends to condense.

Furthermore, even in a pressurized-atmospheric pressure system, depending on the concentration of the condensable gas in the supply gas, it may become supersaturated and condense under the supply side pressurizing pressure.

[0006] The generation of such condensate adversely affects the separation performance of the membrane module and mechanical parts, and in particular, the deterioration of separation performance is not limited to a mere decrease in the dissolution/diffusion rate, but is also caused by the condensate of the membrane. There is also concern that the membrane performance itself may deteriorate due to contact with the membrane, which is a serious problem.

Conventionally, in the case of water vapor separation membranes, the condensed water that accumulates on the permeate side has been removed by continuously flowing a small amount of dry air, or temporarily by flowing a low-concentration gas semi-batch on the supply side. A method for removing condensed water on the permeate side has been proposed.

[0008] However, these methods cannot prevent the generation of condensate, but make condensation unavoidable.
Since the generated condensate is removed, it is unavoidable that the condensate comes into contact with the membrane, even if only temporarily, so it is difficult to completely eliminate the aforementioned deterioration in membrane performance.

Furthermore, even if the condensation phenomenon on the permeate side can be completely prevented, such as when purging the permeate side with dry air in the case of water vapor separation, the energy required for the permeate side purge is loss is unavoidable, and an increase in the power required for the separation membrane device is unavoidable.

An object of the present invention is to provide a method that can efficiently separate condensable gas from an inert gas containing condensable gas while sufficiently preventing condensation.

[0011]

[Means for Solving the Problems] The gas separation method of the present invention is to condense air containing a condensable gas or an inert gas such as nitrogen gas at a pressure higher than atmospheric pressure to the condensable gas using the inert gas. The gas separation membrane module is pressurized below the pressure.
This configuration is characterized in that the permeate side of the module is depressurized below the condensation pressure of the condensable gas in the permeate gas to selectively permeate the condensable gas.

0012

[Operation] Even if the gas supply side of the gas separation membrane module is pressurized, the pressure is limited to less than the condensation pressure of the condensable gas in the supply gas, so the condensable gas on the gas supply side Since the pressure on the permeate side is reduced below the condensation pressure of the condensable gas in the permeate gas, condensation of the condensable gas on the gas permeate side can also be prevented. Furthermore, since the condensable gas is separated by a dissolution/diffusion mechanism, the permeation rate can be increased due to the large transmembrane pressure difference based on the supply side pressurization/permeation side depressurization system.

[0013]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 shows a gas separation membrane device used in an embodiment of the present invention. In FIG. 1, S is a gas supply source. 1 is a compressor. 2 is a gas cooler, which cools the gas heated by the compressor 1 to prevent the separation performance from deteriorating (the gas permeation rate of the membrane usually decreases as the temperature increases). . 3 is a drain trap. 4 is a separation membrane module, which can be of any type such as a spiral type, hollow fiber membrane type, tubular type, or plate type. 5 is a vacuum pump installed on the permeate side of the membrane module 4;
is a capacitor.

The gas to be treated according to the present invention is air containing water vapor or organic solvent vapor such as hexane or toluene;
Inert gas such as nitrogen gas.

The compression pressure of the compressor 1 is set below the condensation pressure determined from the concentration-vapor pressure characteristic of the condensable gas in the inert gas.

To separate condensed gas from inert gas according to the invention, inert gas from gas source S is passed through compressor 1.
The inert gas is pressurized below the condensation pressure of the condensable gas in the inert gas, and then cooled in the gas cooler 2 according to the temperature rise accompanying the compression, and the cooled inert gas is transferred to the membrane module. Supply to 4. During this supply, even if the condensable gas becomes supersaturated and condenses due to fluctuations in the concentration of the condensable gas and fluctuations in the performance of the gas cooler 2, this condensate can be trapped in the drain trap 3 and the membrane module - Only gas can be supplied to the tube 4.

In the gas that has reached the membrane module 4,
The condensable gas flows through the module 4 in contact with the membrane, and during this time, the condensable gas permeates through the membrane due to the selective permselectivity of the membrane for condensable gas, and the condensable gas is concentrated in the permeate side gas. The non-permeable gas is exhausted from the non-permeable gas outlet of the module 4.

The condensable gas concentration of the permeate gas is determined by the stage cut (permeate gas flow rate/supply gas flow rate) and permeation rate, and the pressure on the permeate side is lowered by the vacuum pump 5 to below the condensation pressure for the condensed gas in the permeate gas. It has been set. Therefore, condensation of condensable gas can also be prevented on the permeate side of the membrane module 4. This condensable gas is condensed in the condenser 6, and the gas from which the condensate has been removed is released into the atmosphere.

In the above, excessive depressurization on the permeate side of the module 4 wastes the operating energy of the vacuum pump 5, so the pressure is adjusted to be suitable for the type of condensable gas to be handled and the membrane performance, that is, for the condensed gas. It is necessary to set the degree of vacuum to be below the condensation pressure of the permeated gas whose concentration has increased, and to an energy-appropriate degree of vacuum.

FIG. 2 shows a gas separation membrane device used in another embodiment of the present invention. In Figure 2, S represents a gas supply source, 1 represents a compressor, 2 represents a gas cooler, 3 represents a drain trap, 4 represents a separation membrane module, and 5 represents a vacuum pump. Reset the outlet side of pump 5.
It is connected to the inlet side of the compressor 1 through a piping 7.

In another embodiment of the present invention, the permeate gas is returned to the gas supply source, and the condensable gas is condensed by compression by the compressor 1 and cooling by the gas cooler 2. This corresponds to a method using a cloud system.

In this other embodiment, the gas supply source side S
Since the permeate gas having a high condensable gas concentration is combined with the gas from the compressor 1 and introduced into the compressor 1, the condensable gas concentration of the introduced gas is usually higher than that in the above embodiment.

In the present invention, the gas separation membrane can be used without any restriction as long as it can selectively separate a condensable gas from air or an inert gas such as nitrogen gas. For example, when the condensable gas is water vapor, , methylpentene resin type, and when the condensable gas is hexane or toluene, silicone rubber type can be used.

According to the present invention, the condensable gas in the inert gas can be separated by the gas separation membrane without being condensed, thereby eliminating deterioration in separation performance due to contact of the membrane with the condensate. can be increased, so condensable gases can be separated through the membrane at a high permeation rate. This can also be confirmed by comparing the following examples and comparative examples.

Example 1 Air with a water vapor concentration of 1 vol% and a temperature of 20° C. was used as the supply gas, and the gas separation device shown in FIG. 1 was used. Gas separation membrane module 4 has an effective membrane area of 21 m2.
A spiral type methylpentene resin membrane was used, and the stage cut was 0.07. Supply side pressure is 2.03
Atm, when water vapor was separated by setting the permeation side reduced pressure to 0.05 atm, the water vapor permeation rate was 26.4 Nm3/m
The temperature was 2 hours atm (where atm is the transmembrane pressure).

Comparative Example 1 The above water vapor-containing air was blown onto the membrane module used in Example 1 using a blower (pressure: 1.23 atm), and the pressure on the permeate side of the module was reduced to 0.05 atm using a vacuum pump. As a result, the water vapor transmission rate was 15.1Nm3/m2
hr atm, which was considerably lower than that in Example 1.

Comparative Example 2 The above water vapor-containing air was pumped to a pressure of 3.03
When the water vapor was fed under pressure to the membrane module using ATM and the permeation side of the module was maintained at substantially normal pressure (1.03 atm), the water vapor transmission rate was 13.5 Nm3/m2hr atm, which was higher than in Example 1. It was quite low.

Example 2 The supplied gas had a hexane vapor concentration of 1 vol% and a temperature of 15%.
℃ air was used, and the gas separation device shown in FIG. 1 was used. The gas separation membrane module 4 has an effective membrane area of 2
A spiral type with a 1 m2 silicone rubber membrane was used, and the stage cut was 0.2. Supply side pressure is 2.03
When hexane vapor was separated by setting the permeation side reduced pressure to 0.11 atm, the hexane vapor transmission rate was 8.6.
Nm3/m2hr atm (however, atm is transmembrane pressure)
Met.

Comparative Example 3 The above hexane vapor-containing air was blown onto the membrane module used in Example 2 using a blower (pressure: 1.05 atm).
The permeate side of the module is heated to 0.11at by a vacuum pump.
When the pressure was reduced to m, the hexane vapor transmission rate was 5.3N.
m3/m2hr atm, which was considerably lower than that in Example 2.

Comparative Example 4 The above hexane vapor-containing air was pumped to a pressure of 3
．． When the hexane vapor permeation rate was 6.0 Nm3/m2hr a, the hexane vapor permeation rate was 6.0 Nm3/m2hr a.
tm, which was considerably lower than that of Example 2.

[0031]

[Effects of the Invention] The gas separation method of the present invention has the configuration as described above, and the pressure on the gas supply side of the gas separation membrane module is limited to the condensation pressure of the condensable gas of the supply gas, and the permeation side is Since the pressure of the permeate gas is reduced below the condensation pressure of the condensable gas, condensation of the condensable gas can be prevented, contact of the membrane with the condensate can be completely eliminated, and the separation performance of the membrane can be well maintained. Furthermore, since an operating system of pressurizing the gas supply side and depressurizing the permeate side is used, the transmembrane pressure difference can be increased and the acceleration can be increased. Therefore, according to the present invention, water vapor, toluene, hexane, etc. can be efficiently separated from air containing organic solvent vapors such as water vapor, toluene, hexane, etc., and from factory exhaust gas such as nitrogen gas.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a gas separation membrane device used in the present invention.

FIG. 2 is an explanatory diagram showing another example of the gas separation membrane device used in the present invention.

[Explanation of symbols]

1 Compressor 4 Gas separation membrane module 5 Vacuum pump

Claims (1)

[Claims] Claim 1: A gas separation membrane module is produced by pressurizing an inert gas such as air or nitrogen gas containing a condensable gas above atmospheric pressure to below the condensation pressure of the condensable gas with the inert gas. A gas separation method characterized in that the permeate side of the module is depressurized below the condensation pressure of the condensable gas in the permeate gas to selectively permeate the condensable gas.