JPH0622654B2 - Method for adsorption removal of halogenated hydrocarbon gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a halogenated hydrocarbon-based gas (hereinafter referred to as Hal-CH) from a mixed gas containing the halogenated hydrocarbon-based gas.
Gas) is efficiently adsorbed and removed.

[Prior Art] A frequent problem in the industry dealing with organic solvents is a health hazard caused by volatile solvents to workers. For this reason, recently, it is obligatory to complete the exhaust duct when constructing a building that handles organic solvents, and it is also required to install a solvent adsorption / removal facility to prevent the emission of solvent vapor into the atmosphere.
The most widely used adsorbent for such solvent adsorption removal is activated carbon. Normally, two or more adsorbing towers installed side by side are filled with activated carbon, and adsorption and detachment regeneration are alternately performed by valve operation. The solvent is continuously removed by adsorption by repeating.

[Problems to be Solved by the Invention] However, Hal-CH gas having a low boiling point (especially a boiling point of 100 ° C. or less) represented by Freon (trade name, manufactured by DuPont, USA), methylene chloride, carbon tetrachloride, chloroform, etc. There is a problem that the adsorptivity to the adsorbent is poor, and a large amount of Hal-CH gas is released without being adsorbed to cause a work atmosphere and air pollution.

That is, the Hal-CH gas as described above has a wide range of uses as a refrigerant, a solvent, an extractant, an aerosol propellant, and the like, and also has the advantage that it has no flammability, and thus has a wide range of applications. However, since it is rich in volatility, it is apt to cause atmospheric pollution, and its adsorbability for various adsorbents is poor, so that it is difficult to remove it.

Under such circumstances, the present invention aims to provide a method capable of efficiently adsorbing and removing the Hal-CH gas from a mixed gas containing the Hal-CH gas.

[Means for Solving Problems] The structure of the adsorption removal method according to the present invention is a method of adsorbing and removing the Hal-CH gas in a mixed gas containing Hal-CH gas by activated carbon prior to adsorption treatment. The gist is that the relative humidity is set to 50% or less by subjecting the mixed gas to heat treatment.

[Operation] As is well known, it is said that Hal-CH gas is difficult to be adsorbed and removed by an adsorbent, and this tendency is not an exception even when activated carbon having an excellent adsorbing power is used as the adsorbent.
Then, while various experiments were repeated to clarify the reason why the Hal-CH gas was not easily adsorbed by the activated carbon, the following facts became clear. That is, activated carbon has an excellent adsorption capacity for moisture, and moisture and Hal-CH gas act antagonistically as far as activated carbon adsorption is concerned. Moreover, generally, there is a tendency that water is more easily adsorbed. Therefore, once water is adsorbed on the activated carbon, not only the adsorbing ability of the activated carbon to the Hal-CH gas is lowered but also the affinity between the water and the Hal-CH gas is poor.
The ability to adsorb H gas becomes even poorer, and Hal-C
The purpose of H gas adsorption removal cannot be fulfilled. In particular, Japan has a warm and humid climate, and because it is surrounded by the sea on all sides, it is said that the humidity is extremely high, and indoor and outdoor humidity is almost 60% or more throughout the year. Therefore, a considerable amount of moisture is mixed in the gas to be treated, and it is considered that this moisture preferentially adsorbs to the activated carbon and inhibits the adsorption of the Hal-CH gas.

Therefore, the present inventors have made various studies on the adsorption equilibrium of Hal-CH gas and water with respect to activated carbon, and have proceeded with research on means for utilizing these differences. As a result, it was confirmed that the Hal-CH gas can be adsorbed and removed very efficiently if the mixed gas is heat-treated until the relative humidity becomes 50% or less and then adsorbed on the activated carbon.

By the way, in FIG. 1, the adsorbability of Hal-CH gas exceeds that of water, and as the former, Freon 113 (CCl ₂ F-
CClF ₂ ) gas is selected and an adsorption experiment with activated carbon is performed to determine how the relative humidity of the Hal-CH gas-containing mixed gas (the balance gas is air) affects the equilibrium adsorption amount of Freon 113 and water. The results are shown below, and the experimental method is as follows.

<Experimental method> (1) As shown in FIG. 2, 100 of a transparent closed container V was charged with a saturated aqueous solution S of the following inorganic salt, and the humidity control (at2
5 ° C).

K ₂ CO ₃ saturated aqueous: 40% NH ₄ NO ₃ saturated aqueous: 61 to 64% (NH _{4) 2} SO ₄ saturated solution: a 81 to 83% (2) absolute dry condition (after 120 ° C. × 3 hr further processing) Activated carbon (about 2 g) AC is put into the closed container V and adsorbed until the saturated moisture content is reached.

(3) After the activated carbon AC reaches the saturated moisture content, 7.8 g / 100 of Freon 113 is injected into the closed container V and stirred by the stirrer I to disperse the Freon 113 uniformly in the container V (freon concentration (10,300 ppm) and leave for about 1 hour.

(4) Thereafter, the relative humidity in the sealed container V and the Freon 113
The concentration was measured, and the stabilized concentration when the concentration was reduced from the initial concentration and stabilized was subtracted to obtain the adsorption amount on the activated carbon AC.

(5) For comparison, the relationship between relative humidity and equilibrium adsorption amount of toluene was similarly investigated.

As is clear from FIG. 1, when the relative humidity is 50% or less, the Ha-CH gas is preferentially adsorbed on the activated carbon rather than the moisture, but when the relative humidity exceeds 50%, the amount of adsorbed water becomes large. As the amount of Hal-CH gas adsorbed increases rapidly, the amount of Hal-CH gas adsorbed decreases sharply. As is clear from these tendencies, the Hal-CH gas does not necessarily have a poor adsorption capacity for activated carbon, and it is considered that the adsorption capacity for activated carbon is drastically reduced by the presence of a certain amount of water or more. In other words, if the Hal-CH gas mixed gas is preheated to lower the relative humidity and then adsorbed with activated carbon, the Hal-CH gas can be effectively adsorbed and removed. As for toluene, it can be seen that the decreasing tendency of the adsorption amount due to relative humidity is very small.

The present invention is based on these findings.
The mixed gas containing al-CH gas is characterized in that the mixed gas is heated prior to being adsorbed and removed by the activated carbon. The degree of heating depends on the experimental results shown in FIG. Based on the relative humidity of 50% at which the amount of adsorbed water of the above rapidly increased, the value was determined to be below this value (more preferably 40% or less).

[Example] Using the experimental apparatus shown in FIG. 3, the Freon 113 concentration and the relative humidity in the gas supplied to the activated carbon packed tower were variously changed, and the adsorption gas was passed through the activated carbon packed tower for a predetermined time. The change in the Freon 113 concentration was investigated. That is, as shown in FIG. 3, the Freon 113 is placed in the evaporation dish 6 installed on the heat 5 in the simulated gas generator 4 to heat and evaporate, and the vapor is admitted with the air through the line 8 and the fan 9 to the adsorption tower 1a. (Or 1b). At this time, the supply gas is heated through the heater 11 and the air whose relative humidity is changed through the humidity controller 10 is merged to change the relative humidity of the supply gas in various ways, and the temperature of the gas on the inlet side of the adsorption tower is changed. The temperature and relative humidity of the supply gas are adjusted by opening and closing the valve of the heater 11 while detecting TCA and humidity by HC respectively. Then, the Freon 113 concentration in the gas before and after passing through the adsorption tower 1a (or 1b) was examined under each condition with a hydrocarbon meter XI. The experimental conditions were as follows.

<Experimental conditions> Atmospheric conditions: 28 ° C, 90% Freon 113 concentration in source gas: 50,000 ppm Source gas feed rate: 14.4 Nm ³ / min Processing temperature: 35 to 40 ° C Figure 4 shows at the end of the first batch 3 shows the Freon 113 concentration in the gas passing through the adsorption tower and the Freon 113 concentration in the same gas at the end of the fifth batch in Table 1. From these results, it can be considered as follows.

(1) When the relative humidity of the supply gas exceeds 50%, the freon adsorption activity of the activated carbon decreases with a small number of treatments not only when the freon 113 concentration is high but also when the freon 113 concentration is low, and the freon 113 in the outlet gas is reduced. The concentration is significantly higher.

(2) On the other hand, when the relative humidity of the supply gas is reduced to 50% or less, the Freon 113 concentration in the outlet gas becomes lower after performing the adsorption treatment 5 times than in the initial adsorption treatment. There is. That is, this experiment was conducted in an outside air atmosphere of about 65% RH, and under such conditions, it is considered that the activated carbon in the adsorption tower is slightly absorbing moisture. Although it exerts a slightly lower adsorption activity due to the influence, when the relative humidity of the feed gas is set to 50% or less, the adsorbed water content of the activated carbon filled in the adsorption tower is reversely released by the passage of the feed gas. It is considered that the Freon 113 adsorption activity of the activated carbon was increased and the Freon 113 adsorption removal efficiency was improved rather than the initial adsorption treatment. In any case, the relative humidity of the supply gas is 50%
By setting the following, the Freon 113 in the supply gas can be adsorbed and removed extremely efficiently.

EFFECTS OF THE INVENTION The present invention is configured as described above, but in short, Hal
By preheating a mixed gas containing -CH gas so that its relative humidity is 50% or less, Hal-of activated carbon-
CH gas adsorption performance can be maximized and H
The al-CH gas can be efficiently adsorbed and removed.

[Brief description of drawings]

FIG. 1 is a graph showing the results of investigating the influence of the relative humidity of mixed gas on the adsorption activity of freon or toluene.
FIG. 3 is an explanatory diagram showing the adsorption activity test method, FIG. 3 is an explanatory diagram showing the apparatus used in the examples, and FIG. 4 is a graph showing changes in the relative humidity of the supply gas and the Freon concentration of the gas at the adsorption tower outlet. 1a, 1b ... Activated carbon packed tower 4 ... Simulated gas generation device, 5 ... Heater 6 ... Evaporation dish, 10 ... Humidity control device

Claims (1)

[Claims] 1. A method of adsorbing and removing the halogenated hydrocarbon-based gas in a mixed gas containing a halogenated hydrocarbon-based gas with activated carbon, wherein the mixed gas is subjected to a heat treatment prior to the adsorption treatment to obtain a relative humidity. Is 50% or less, a method for adsorbing and removing a halogenated hydrocarbon gas.