JPH0356114A - Method for treating exhaust gas of organic solvent storage vessel - Google Patents

Abstract

PURPOSE:To achieve prevention of pollution of the atmosphere and recovery of solvents with high efficiencies by separating an exhaust gas from an organic solvent storage vessel into a nonpermeative gas B of low solvent concentration and a permeative gas C of high solvent concentration by means of a permselective membrane to discharge the gas B and by returning the gas C to said storage vessel. CONSTITUTION:A gas mixed with organic solvent vapor in the upper space of an organic solvent storage vessel 1 is discharged through a discharge pipe 6 to adjust the internal pressure of the vessel 1. The gas thus discharged is separated into a nonpermeative gas B of low solvent concentration and a permeative gas C of high solvent concentration by means of a permselective membrane 8, whereby the gas B is exhausted through an exhaust pipe 9, while the gas C is returned to the vessel 1 through a return pipe 12. As a result, the concentration of the organic solvent in the gas to be vented to atmosphere can be reduced to as low as 0.005% or lower, thereby raising the recovery efficiency of solvent to as high as 99.9% or higher.

Description

[Detailed Description of the Invention] Industrial Field in Icheon> The present invention relates to a method for treating ILR gas when the gas in the upper space of an organic solvent storage container is discharged in order to adjust the internal pressure of the container. ．． BACKGROUND TECHNOLOGY When storing organic solvents, the space above the liquid level in the storage container is often filled with a non-volatile gas such as N3 gas. In this case, to adjust the internal pressure of the storage container, when the internal pressure increases and reaches the upper limit pressure, the above gas is discharged from the container, and when the internal pressure decreases and reaches the lower limit pressure, inert gas is pumped out. However, the upper space inside the container is saturated with organic solvent, and the inert gas discharged from the storage container contains a large amount of organic solvent vapor. Therefore, as shown in FIG. 4, if the gas inside the container is directly released into the atmosphere through the exhaust pipe 6', depending on the amount released, it may cause air pollution that is difficult to ignore. This results in solvent loss. <Problem to be Solved> Conventionally, as shown in FIG. 5, the organic solvent in the exhaust gas is adsorbed and removed from the exhaust gas in the organic solvent storage container 1' using an adsorbent packed tower 13'. It has been proposed to release the clean gas of 1977-
No. 413515). However, due to the high concentration of organic solvent in the gas before adsorption, the adsorbent is not suitable for storage vessel exhaust gas loading conditions {'t. There is little margin to accommodate fluctuations in (concentration, processing time, processing amount, etc.)
Since the amount of heat generated during adsorption is greater than the amount of heat generated during adsorption, there is a high possibility that an operating point will occur that exceeds the equilibrium saturation of the adsorbent, and organic solvent vapor may be released into the atmosphere without being adsorbed. obtain. Therefore, even in the method shown in FIG. 5, the overall concentration of solvent in the exhaust gas is high, and therefore,
The solvent recovery rate is also far from sufficient. The purpose of the present invention is to reduce the concentration of organic solvent in the gas released into the atmosphere to a significantly low concentration (0.005% or less),
Significant solvent recovery <+fli efficiency (>99.9%)
The goal is to provide ways that can be done. <Means for Solving the Problems> How to treat the exhaust gas of the 1ltl drug storage container according to the present invention? In the method of discharging the organic solvent vapor mixed gas in the upper space of the container in order to control the internal administration of the container, the discharged gas is selected and treated with a low solvent concentration film using a V<S-permeable membrane. The permeated gas and the high solvent concentration permeated gas are separated, the low solvent concentration non-permeated gas is exhausted, and the high solvent concentration permeated gas is
This method is characterized by returning the solvent to the T machine solvent storage container.

The above-mentioned 1a78 agents include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ketones, alcohols, and carboxylic acid esters. Normally, an inviscid gas such as N2 gas is used to fill the container, but air may also be used. A selectively permeable membrane, that is, a membrane that allows solvent vapor to pass through but hardly allows MJ for inert gas or air, is selected depending on the solvent. Composite membranes formed on porous supports nIi, polyamide, polyvinylidene fluoride, or polysulfone can be used. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, 1 is an organic solvent storage container, 2 is an organic solvent supply pipe, 3 is an organic solvent take-out pipe, 4 is a take-out pump, 5 is a gas inflow pipe, and 6 is a gas discharge pipe. A shows the equipment added to carry out the present invention. 7 is a blower connected to the exhaust pipe. 8 is an i1 permeable module, in which a membrane separates the primary side (l1ll) and the secondary side (permeation side), and the primary side is communicated with the outlet 1-1 pipe of the air blower a7.9 is a non-permeable gas discharge pipe provided on the primary side, and has a pressure regulating valve IO. 11 is a vacuum suction machine, whose suction side is connected to the secondary side of the module 8, and its discharge side is connected by a return pipe l2. It is connected to an organic solvent storage container.The vapor of the storage solvent reaches a saturated state under a reduced pressure of several hundred millimeters! Inert gas containing solvent vapor (solvent concentration is l
When the internal pressure of this container increases, the blower 7 and the vacuum suction device 11 are driven. In this case, the primary pressure of the module 8 is set to 100-10
00m+a■, 0 (gauge pressure), secondary pressure 10~3
The pressure regulating valve 10 is set to 00 torr (absolute pressure).
, operates the blower 7 and the vacuum suction machine l1. Blower 7
, by driving the vacuum suction Ia11, the solvent vapor mixed inert gas in the container l is sent to the primary 01 of the module 8,
Due to the selective permselectivity of the membrane, under the differential pressure between the primary side and the secondary side, solvent vapor permeates well through the 11 ta, while inert gas hardly permeates. The high solvent vapor concentration on the side is separated from the non-oily gas. The inert gas with low solvent vapor concentration is released into the atmosphere through the exhaust pipe. The solvent vapor temperature of this gas is usually 0.005% or less, so there is virtually no problem with environmental pollution or solvent loss. The permeate gas on the secondary side of the module has a high solvent concentration, but module 8 and vacuum suction machine I! The pressure is low at 10 to 300 torr, and the temperature after 1 liter of vacuum suction machine is heated to 30 to 80°C, so in any section, the solvent vapor mixed inert gas is It is below the saturation point. This solvent vapor mixed inert gas flows into the upper space of the solvent storage container l through the return pipe 12, and since this space is in a saturated state, the inflow causes supersaturation and condensation, and non-condensable gas is again subjected to the above treatment together with the gas in the container L. Below, this is vf4
1! Repeat this process until the pressure inside the container drops to normal pressure. , stop the vacuum suction machine l1. Normally, the above operations involve driving and
A ratio switch for operating the stop is provided on the solvent storage container for automatic operation.

In the above exhaust gas treatment, the inert gas with high solvent vapor concentration leaving the vacuum suction machine 11 is directly returned to the solvent storage container 1.
3 (For example, recovery by absorption method, condensation method, activated carbon adsorption method, etc.) The solvent in the gas may be recovered, and the recovered gas may be returned to the solvent storage container 1 through the return pipe 12.14 is a recovered solvent extraction pipe.Furthermore, as shown in the third picture, any of the above treatment methods may be selected by operating valves 15, 16, etc. In the present invention, the pressure inside the container is reduced by releasing tJr of the solvent vapor mixed inert gas in the a-containing solvent storage container. is discharged into the atmosphere, and the permeated gas is circulated in the module, and the solvent concentration in the discharged gas can be significantly lowered due to the selective permselectivity of the membrane (0.00
5% or less), can prevent air pollution and efficiently recover solvents. This is also clear from the comparison between the following example and comparative example. Examples n-hexane (saturated vapor pressure at 25°C: 160 mlg) was used as the organic solvent, and N2 gas was used as the inert gas. N of the space inside the container. The concentration of solvent in the gas is 21'/
It was V%. Using the device shown in Figure 1, the module has a membrane area of approximately 20 m! A spiral membrane module was used, and a silicone cross-linked polyimide membrane was used for the membrane.
The discharge pressure of the blower is 100 mml {to (gauge pressure), and the degree of vacuum of the vacuum suction machine is 150 torr (
absolute pressure), and the gas feed rate is On3/l{r and 1 2
Intermittent feed of m'/H r and average flow rate of 5 m'/H
It was set as r. Comparative Example 1 (Direct tJ air method) The apparatus shown in FIG. 4 was used, and the same solvent, inert gas, and container as in the example were used. The gas output amount tJi is Om'/Ilr and 1 2 m3/H r, and the average flow rate is 5 m3/tlr.

Comparative Example 2 (viscous carbon adsorption method) In the above Comparative Example 1 (iiT. open exhaust method), an activated carbon adsorber (approximately 200 particles of viscous carbon of 4 to 8 mesh) was installed in the exhaust pipe.
The procedure was the same as that of Comparative Example 1 above, except that filling i) was installed. In each of these examples and comparative examples, the solvent vapor concentration (average) in the exhaust gas was measured, and the solvent recovery rate was calculated from the measured value. It is clear that the melting concentration can be significantly lowered and the solvent can be recovered efficiently.

[Brief explanation of drawings]

Claims (2)

[Claims] (1) In a method of discharging a mixed gas of organic solvent vapor in the upper space of an organic solvent storage container in order to adjust the internal pressure of the container, the exhaust gas is separated by a selectively permeable membrane into a non-permeable gas with a low solvent concentration and a non-permeable gas with a high solvent concentration. A method for treating exhaust gas from an organic solvent storage container, which comprises separating the gas from the permeated gas, exhausting the non-permeated gas with a low solvent concentration, and returning the permeated gas with a high solvent concentration to the organic solvent storage container. (2) A method for treating exhaust gas from an organic solvent storage container according to claim (1), characterized in that the high solvent concentration permeated gas is introduced into a solvent recovery device and the solvent is recovered in a liquid phase before being returned to the organic solvent storage container.