JPS643139B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for removing fluorine gas from a gas containing a relatively low concentration of elemental fluorine gas (hereinafter abbreviated as fluorine gas). Currently, fluorine gas is frequently used for surface fluorination of plastics, synthesis of various fluorides, and excimer lasers, but the waste gas after use is inert gas such as N ₂ , Ar, He, Ne, etc. Fluorine is often in the form of diluted fluorine gas, and it is necessary to remove it to a safe low concentration (tolerable concentration of 1 ppm or less), and the present invention provides a method for its removal. Conventional technology Conventionally, methods for removing fluorine gas include a dry method in which waste gas containing fluorine gas is passed through a fixed bed filled with soda lime, activated alumina, etc. (hereinafter referred to as a neutralizing agent) at room temperature, and a KOH method. and NaOH
There was a wet method to remove fluoride by passing fluorine gas-containing waste gas through an alkaline scrubber using an aqueous solution. Among these various methods, when attempting to treat fluorine gas-containing waste gas at room temperature using a fixed bed filled with a neutralizing agent, if the fluorine concentration in the waste gas is high, the neutralizing agent and the Because the reaction easily occurs,
It was possible to reduce the fluorine gas concentration in the exhaust gas after treatment to 1 ppm or less. However, as the fluorine gas concentration in the waste gas becomes lower than 30vol%, the inert gas (N ₂ , He, Ar, Ne, etc.) in the waste gas decreases.
This results in a relative increase in fluorine gas and insufficient reaction with low-concentration fluorine gas, so if 1 ppm or more of unreacted fluorine gas remains in the exhaust gas and the exhaust gas is released into the outside air, it may cause air pollution. It was inevitable that it would happen. On the other hand, although the alkaline scrubber type can treat waste gas containing various concentrations of fluorine gas to below the permissible concentration, the gas linear velocity can only be set to a small value of several cm/sec, making the equipment large and the removal system It is not possible to maintain a vacuum inside, and it is only effective when the pressure is either partially pressurized or slightly reduced, and the absorbent must be handled as a solution, which is extremely inconvenient in terms of handling. Problems to be Solved by the Invention The present invention solves the problems of the low removal efficiency in the dry method and the inconvenience of handling in the wet method in the removal of fluorine gas, which is contained in waste gas at a relatively low concentration. This solves the problem of increasing the size of the Means for Solving the Problems The present inventors discovered that in a dry method, the absorption rate of low concentration fluorine gas into a neutralizing agent strongly depends on temperature, and the present invention was achieved based on this finding. . In other words, when attempting to treat fluorine-containing waste gas with a fixed bed filled with a neutralizing agent, the fluorine concentration in exhaust gas is determined by the fluorine concentration, gas linear velocity, bed thickness of the neutralizing agent, and neutralization. It is thought that the temperature of the neutralizing agent is a function of the temperature of the neutralizing agent, and it has been found that the temperature of the neutralizing agent in particular strongly controls the fluorine gas removal reaction. The application temperature of the neutralizer in the present invention is 70 to 600℃
Preferably, the temperature is in the range of 100 to 300°C; if the temperature exceeds 600°C, the desorption of fluorine adsorbed on the neutralizer tends to proceed slightly, and the fluorine concentration in the exhaust gas is lowered.
It is undesirable because it becomes extremely difficult to maintain the concentration below 1 ppm, and at the same time, the neutralizing agent caking occurs and internal corrosion of the equipment progresses. Furthermore, at temperatures below 70°C, fluorine gas is not removed sufficiently, making it difficult to reduce the temperature to 1 ppm or less. In the present invention, the neutralizing agent used is soda lime, activated alumina, Ca(CH) ₂ , CaO, etc.
The shape is preferably granular, but powder can also be used. Further, in order to remove adhering moisture, it is advantageous to use the neutralizer after heating and vacuum drying at 100° C. or higher for several hours to remove adhering moisture. In the present invention, the composition of the applied fluorine gas-containing waste gas includes He, O ₂ , N ₂ , CO ₂ , Ar, Ne, and chemically inert gaseous fluorides, such as
Mixed gases such as C _o F _2o+2 and SF ₆ are common;
It is particularly useful for waste gas with a fluorine gas concentration of 30 vol% or less. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 A fixed bed with an inner diameter of 2.5 cm and a length of 60 cm filled with 5 to 15 meshes of granular soda lime 175 gr prepared by diluting fluorine gas with helium gas to various concentrations and heating and vacuum drying the gas at 120°C for 120 minutes. From the top of the vertical reactor, an absorption linear velocity of 4 m/sec and room temperature (25
°C) under atmospheric pressure. Table 1 shows the results of analyzing the fluorine gas concentration in the gas after treatment.

[Table] Example 2 Gas 100 prepared by diluting fluorine gas with helium gas to 1 Vol% was heated to various temperatures using the same reactor and neutralizing agent as in Example 1 while heating the outside of the reactor with a heater. It was adjusted and fed under atmospheric pressure. The analytical values of the obtained gas are shown in Table 2.

[Table] Example 3 Using the same reactor and neutralizing agent as in Example 1, dilute fluorine gas with helium gas to various concentrations and adjust the gas temperature to 200 °C while heating the outside of the reactor with a heater. The reactor was supplied at a linear velocity of 5.0 m/sec under atmospheric pressure while maintaining the temperature at °C. The analytical values of the obtained gas are shown in Table 3.

[Table] Example 4 Using the same reactor and neutralizing agent as in Example 1, gas 1 prepared by diluting fluorine gas with helium gas to 1 vol% was heated to 250°C while heating the outside of the reactor with a heater. A vacuum pump was used to supply each under reduced pressure. The analytical values of the obtained gas are shown in Table 4.

[Table] Example 5 Using the same reactor and neutralizing agent as in Example 1, the temperature was raised to 200°C while heating the outside of the reactor with a heater. It was supplied under atmospheric pressure while adjusting the linear velocity to various values. The analytical values of the obtained gas are shown in Table 5.

[Table] Example 6 Fluorine gas was diluted to 1 Vol% with helium gas and 1 to 100 mesh of each neutralizing agent was added to the gas.
Using the same reactor as in Example 1, which was filled with 200g of the product that had been heated and vacuum dried at 120°C for 120 minutes, the reactor was supplied under atmospheric pressure while heating the outside of the reactor with a heater and maintaining the temperature at 250°C. The analytical values of the obtained gas are shown in Table 6.

[Table] Example 7 Fluorine gas diluted to 1 Vol% with chemically inert gaseous fluoride (CF ₄ , SF ₆ ) 100
Using the same reactor and neutralizing agent as in Example 1,
While heating the outside of the reactor with a heater, raise the temperature to 200℃.
It was supplied under atmospheric pressure while being maintained at ℃. Table 7 shows the analytical values of the obtained gas.

[Table] Effects of the Invention The method for removing fluorine gas of the present invention is effective for removing fluorine gas at low concentrations, especially
It is extremely effective in treating waste gas containing fluorine gas of 30 Vol% or less, and can reliably reduce the fluorine gas concentration in the exhaust gas after treatment to 0.1 ppm or less. Furthermore, in applications that require raw material gas to be used in a vacuum system, the oil in the vacuum pump is denatured by fluorine gas, so it must be removed before the vacuum pump is used, but it can be removed sufficiently even in a vacuum. It has the ability.

Claims (1)

[Claims] 1 When separating and removing fluorine content in waste gas containing 30 vol% or less of fluorine gas, use a solid neutralizing agent at 70% by volume.
A method for removing fluorine gas, which comprises bringing the gas into contact with these while heating the gas to a temperature above 0.degree.