JPH074506B2 - Exhaust gas purification method - Google Patents

Description

The present invention relates to a method for purifying exhaust gas, and more particularly to a method for purifying exhaust gas containing a toxic component discharged from a semiconductor manufacturing process or the like.

In recent years, with the development of the semiconductor industry and the optoelectronics industry, the use amount of extremely toxic hydrides such as arsine, phosphine, diborane, and hydrogen selenide has increased.

These toxic components are indispensable substances as raw materials or doping gases in the silicon semiconductor and compound semiconductor manufacturing industry, the optical fiber manufacturing industry and the like.

In many cases, unreacted toxic components are contained in the exhaust gas discharged from the semiconductor manufacturing process or the optical fiber manufacturing process. Each of these components is extremely toxic to living organisms and must be removed prior to gas emission in order not to destroy the environment.

[Prior art and problems to be solved]

As a method of removing these toxic components, a wet method of absorbing and decomposing with a scrubber and a dry method of flowing and removing the toxic component by flowing through a filling cylinder filled with a purifying agent such as an adsorbent or an oxidizer are known. In general, the wet method has a drawback in that maintenance of the apparatus is expensive because it is difficult to corrode the absorbent and post-treat it.

Further, as a method of using a purifying agent, one in which a nitrate such as silver nitrate is supported on a porous carrier, or one in which a metal chloride such as ferric chloride is impregnated in a porous carrier is used as an adsorbent, A method for oxidatively removing phosphine and arsine (JP-A-56-89837) is known. However, this method solves various drawbacks as in the wet method, but has a drawback that the apparatus becomes complicated because it is necessary to pre-wet the exhaust gas in a CVD (chemical vapor deposition) process or the like.

Furthermore, a method of treating arsine, phosphine, etc. with three kinds of absorbents in which an inorganic silicate is impregnated with an alkaline aqueous solution, an oxidizing agent aqueous solution or an alkaline and oxidizing agent aqueous solution (Japanese Patent Publication No. 59-49822). Is also proposed. Similar to the above-mentioned method, this method is also a treatment in a wet state and has the same drawbacks as the wet method.

In chemical warfare, a gas mask filled with activated carbon was used as a method for removing arsine by dry method. There are many attempts to improve the performance of the activated carbon by utilizing the adsorption power of the activated carbon and further adhering various substances thereto. For example, using activated carbon as a carrier, on which a copper compound and an alkali metal compound,
Alkaline earth compounds and Al, Ti, V, Cr, Mn, Fe, C
An arsine adsorbent containing one or more compounds of o, Ni, Zn, Cd, and Pb has also been filed (Japanese Patent Laid-Open No. 59-1605).
35 publication). This method is advantageous because it can be carried out completely dry, but it has the disadvantage that the removal capacity for arsine is relatively low. Further, after adsorbing arsine, when the adsorbent is exposed to air, heat is generated, and activated carbon may be ignited depending on the conditions, so that the use conditions are limited for industrial use.

In order to solve these problems of the prior art, the present inventors first (1) cupric oxide and (2) silicon oxide,
A method for purifying exhaust gas using a purifying agent formed by blending and molding at least one metal oxide selected from the group consisting of aluminum oxide and zinc oxide has been disclosed (Japanese Patent Laid-Open Publication No. Sho.
61-209030).

The purifying agent of the present invention has an advantage over the conventional purifying agents in that the maximum amount of toxic components removed per unit weight and unit volume of the purifying agent (hereinafter, referred to as saturated purification amount) is remarkably large.

However, it has been found that, although the purifying agent has a large amount of saturated purification, when it is used at a low temperature of, for example, 10 ° C. or lower, a sufficient removal rate cannot be obtained depending on the conditions. That is, when the purification column filled with this purifying agent is used outdoors in winter, when it is used at a low temperature and under a high load condition, the purification column breaks through in a relatively short time, and at the outlet of the purification column, a low concentration of There is a problem that toxic components are detected.

The permissible concentration of these toxic components is 0.05 ppm for arsine,
Since the concentrations of phosphine are as low as 0.3 ppm, diborane is 0.1 ppm, and hydrogen selenide is 0.05 ppm, it is required that these toxic components be reliably below the permissible concentration at the exit of the abatement system.

[Means and actions for solving problems]

The present inventors have conducted extensive studies to compensate for the problems of these conventional techniques, and by further adding manganese dioxide to cupric oxide and respective oxides of silicon, aluminum, zinc, and the like, It was found that these toxic components were efficiently removed even at low temperature, and further research was conducted to complete the present invention.

That is, the present invention is a method for purifying exhaust gas, wherein a gas containing at least one of arsine, phosphine, diborane and hydrogen selenide as a toxic component is contacted with a purifying agent to adsorb and remove the toxic component from the gas, Molded body of composition of (1) cupric oxide, (2) manganese dioxide, and (3) at least one metal oxide selected from the group consisting of silicon oxide, aluminum oxide and zinc oxide as a purifying agent Is a method of purifying exhaust gas.

According to the purifying agent of the present invention, unlike mere adsorption or absorption, the toxic component is removed from the exhaust gas by reacting with the purifying agent and being fixed to the purifying agent.

Further, this purifying agent is highly safe since it does not ignite even though the purifying agent after use may generate heat by touching the air.

Further, this purifying agent has a sufficient removing ability for toxic components contained in the gas even at a low temperature such as 10 ° C. or lower.

The present invention is applied to a gas containing one or more of arsine, phosphine, diborane and hydrogen selenide as a toxic component in nitrogen, hydrogen, argon, helium, air and the like.

The purifying agent used in the present invention has a composition of (1) cupric oxide, (2) manganese dioxide, and (3) at least one metal oxide selected from the group consisting of silicon dioxide, aluminum oxide and zinc oxide. It is a molded product.

Its composition is the atomic ratio of metal M / (M + Cu + Mn) , Usually 0.02-0.7, preferably 0.03-0.55,
In addition, the ratio of copper to manganese is the atomic ratio of metal Cu / (Cu + M
Expressed by n), it is usually in the range of 0.1 to 0.9, and preferably in the range of 0.2 to 0.8. Atomic ratio of metal M / (M + Cu
If + Mn) is smaller than 0.02, it becomes difficult to mold, and if it is larger than 0.7, the maximum removal amount of the toxic component per unit amount of the purifying agent, that is, the saturated purification amount decreases. Moreover, when the atomic ratio Cu / (Cu + Mn) of the metal is smaller than 0.1, that is, when the proportion of copper is small, the amount of saturated purification decreases. On the other hand, when it is larger than 0.9, that is, the proportion of manganese is small, purification at low temperature The speed decreases, the time to breakthrough becomes short in either case, and there is a fear that the predetermined purification efficiency may not be obtained depending on load conditions.

Various methods can be applied as a method for preparing the purifying agent.

For copper or zinc, the respective nitrates, sulfates,
Obtained by adding an alkali such as sodium hydroxide, caustic potassium, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, or ammonia to metal salts such as chlorides and organic acid salts to precipitate oxide intermediates. The oxide obtained by baking the precipitate may be mixed with other metal oxides to have a specific composition and molded, but a hydroxide or a base which is a precipitate obtained by adding an alkali to a metal salt. It is preferable that the cupric oxide or zinc oxide is obtained by mixing with another metal oxide so as to have a specific composition at the stage of the acidic carbonate, and calcining in a molded state. Among them, it is most preferable to use a basic carbonate obtained by using sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate as the alkali.

Further, as the oxides of aluminum and silicon, for example, alumina sol and silica sol are used. These are sodium salts of mineral acid produced by neutralizing an aqueous solution of sodium aluminate or sodium silicate with mineral acid by electrodialysis. Can be obtained or a method of treating an aqueous solution of sodium aluminate and sodium silicate with a cation exchange resin.

Further, regarding manganese dioxide, various methods such as a method of decomposing potassium permanganate in nitric acid, a method of oxidizing manganese sulfate with potassium permanganate, and a method of treating inactive manganese dioxide with hot concentrated nitric acid are available. Can be used.

In addition, cupric oxide, basic copper carbonate, manganese dioxide, zinc oxide, basic lead carbonate, alumina sol and silica sol are commercially available in various varieties, so use one appropriately selected from them. Good.

As the purifying agent used in the present invention, a composition obtained by molding the composition into pellets or the like is used, or the molding is crushed to an appropriate size and used.

As a molding method, a dry method or a wet method can be used. Further, when molding, a small amount of water, a lubricant, etc. may be used if necessary.

The shape of the molded product is not particularly limited, but typical examples thereof include a spherical shape, a cylindrical shape, and a cylindrical shape.

If the shape of the molded product is spherical, the diameter is preferably in the range of 1 mm to 12 mm, and if it is cylindrical, the diameter is 1 mm to 12 mm, and the height is from 2 mm to
A range of 12 mm is suitable. Since it is said from a chemical engineering point of view that it is necessary for the packed cylinder to have a particle size smaller than about 1/10 of the cylinder diameter, if it is within this range, there will be no drift and it is convenient. The purifying agent used in the present invention has a particle density of about 0.6 to 1.5 g / ml, and a packing density of about 0.4 to 1.0 g / ml is preferable. If the packing density is less than 0.4 g / ml, not only the strength of the molded product will be weakened, but also the amount of saturated purification will be reduced. If the packing density is higher than 1.0 g / ml, the purification rate at low temperature may decrease.

The purifying agent used in the present invention is packed in a purifying cylinder and used as a fixed bed. However, it can also be used as a moving bed or a fluidized bed. A gas containing a toxic component (hereinafter referred to as a gas to be treated) is caused to flow in the purifying cylinder and brought into contact with a purifying agent, whereby various hydride-based gases which are the toxic components are removed and purified.

There is no particular limitation on the concentration of the hydride gas and the gas flow rate in the gas to be treated to which the purification method of the present invention is applied, but it is generally preferable to decrease the flow rate as the concentration increases.
In practice, when the concentration of hydride-based gas is 10%, the cylinder linear velocity is 1 cm / sec or less, 1% is 5 cm / sec or less, and 0.1% is 3
It is preferably 0 cm / sec or less.

The gas to be treated to which the purification method of the present invention can be applied is usually in a dry state, but even if it is in a wet state, it does not have to be wet enough to cause dew condensation in the purification cylinder.

The contact temperature (inlet gas temperature) between the gas to be treated and the purifying agent is usually set to −20 to 100 ° C. Since such a wide range of excellent purifying ability can be obtained, heating or cooling is not particularly required.

The pressure of the gas to be treated may be any of normal pressure, reduced pressure and increased pressure, but is usually 20 Kg / cm ² abs or less, preferably 0.001 to
It is in the range of 10 kg / cm ² abs.

〔Example〕

Examples 1 to 13 Each component used in the cleaning agent was prepared by the following method to prepare the cleaning agent.

Basic copper carbonate; 20 wt% aqueous solution of copper sulfate and 20 of sodium carbonate
A wt% aqueous solution was added until the pH reached 9 to 10 to precipitate crystals of basic copper carbonate. Repeatedly wash and wash this crystal,
Basic copper carbonate was obtained.

Manganese dioxide: A 10 wt% aqueous solution of barium chlorate was mixed with a 10 wt% aqueous solution of manganese sulfate in a stoichiometric amount. After removing the precipitated barium sulfate by filtration, the solution is
Evaporation at 50 ° C. for 10 hours gave crude manganese dioxide. The crude manganese dioxide was stirred in hot concentrated nitric acid for 5 hours, washed with ion-exchanged water, and then dried at 120 ° C. for 5 hours to obtain active manganese dioxide.

Alumina sol; Cataloid-AS- manufactured by Catalyst Chemical Industry Co., Ltd.
2 was used.

Silica sol: Snowtex manufactured by Nissan Kagaku Co., Ltd. was used.

Zinc oxide; 20 wt% aqueous solution of zinc sulfate and 20 wt% of sodium carbonate
% Aqueous solution was added until the pH reached 9 to 10 to precipitate crystals of basic zinc carbonate. The crystals were filtered and washed to obtain basic zinc carbonate.

Thus prepared, (1) basic copper carbonate, (2)
Manganese dioxide, (3) alumina sol, silica sol, and basic zinc carbonate are each used in a predetermined metal atom ratio M / (M
+ Cu + Mn) and Cu / (Cu + Mn),
After kneading with a kneader, extrusion molding, and then firing at 250 ° C for 2 hours to convert copper and zinc salts into oxides, forming pellets with a diameter of 2 mm and a length of 3 to 10 mm and a packing density of 0.6 to 0.7 g / ml of various cleaning agents were prepared.

For each of the obtained purifying agents, a quartz purifying cylinder (inner diameter 19 mm, length) installed in the chamber kept at 5 ° C
400mm) filled with purifying agent (filling length 200mm, filling volume 56ml)
10% hydrogen or nitrogen containing 1% of marsine, phosphine, diborane or hydrogen selenide as a toxic component.
The gas was passed through at 0 l / hr (empty cylinder linear velocity: 10 cm / sec), the purifying cylinder outlet gas was monitored, and the time until breakthrough was measured. The detection of breakthrough was confirmed by a spectrophotometer (HD-1 manufactured by Nippon Oxygen Co., Ltd.) based on the principle of cold atomic absorption of mercury, and the toxic components were clearly confirmed, and the concentration, that is, 25 ppb for arsine, phosphine 31ppb and 27ppb for diborane were used as breakthrough control points. As for hydrogen selenide, since the standard is not specified by the above measuring instrument, it was detected by the color change of the detection agent (detection sensitivity 50 ppb) containing basic copper carbonate as the color change component.

The results obtained in Examples 1 to 13 are as shown in Table 1, and the purification was possible for a long time despite the low contact temperature of the cleaning agent and the gas of 5 ° C.

Comparative Examples 1 to 3 In the same manner as in the examples, a purifying agent containing no manganese dioxide as a component (Comparative Examples 1 to 2) and a purifying agent not containing cupric oxide (Comparative Example 3) were used. It was flown and the time to breakthrough was measured. The results are shown in Table 1, and in all cases, the time to breakthrough was remarkably short compared to the examples, and was about 1/2.

[Advantages of the Invention] The purification method of the present invention not only has a large removal amount of the toxic components contained in the gas, but is also excellent at low temperatures such as 10 ° C. or less which could not be sufficiently treated by the conventional method. Since it has a purification ability, it can be used with confidence even under low temperature conditions such as winter.

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Claims (1)

[Claims] 1. A method for purifying an exhaust gas, wherein a gas containing at least one of arsine, phosphine, diborane and hydrogen selenide as a toxic component is brought into contact with a purifying agent to adsorb and remove the toxic component from the gas. A molded article of a composition of (1) cupric oxide, (2) manganese dioxide, and (3) at least one metal oxide selected from the group consisting of silicon dioxide, aluminum oxide and zinc oxide as an agent. A method for purifying exhaust gas, which is characterized by being used.