JPH0771614B2 - 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 exhaust gas industry and the optoelectronics industry, the use amount of highly toxic hydrides such as arsine, phosphine, diborane, and hydrogen selenide is increasing.

These toxic components are substances that are indeterminate 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 process or the optical fiber manufacturing process. Each of these components is extremely toxic to living organisms and must be removed prior to gas emissions to avoid environmental damage.

[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. Generally, the wet method has a drawback that the maintenance of the apparatus is expensive because it is difficult to be corroded by the absorbing solution and post-treated.

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). Issue) 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 by utilizing the adsorption power of this activated carbon and further adding various substances thereto. For example, activated carbon is used alone, and 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, if the adsorbent is exposed to air, heat is generated and activated carbon may be ignited under some conditions, so that the industrial use conditions are limited.

[Means for solving problems]

As a result of diligent studies to compensate for these drawbacks of the prior art, the present inventors have found that a toxic component is added to a purifying agent containing (1) cupric oxide and (2) respective oxides such as vanadium, molybdenum, and tungsten. It was found that these toxic components can be efficiently removed by contacting the contained exhaust gas, and further research was conducted to complete the present invention.

That is, the present invention is a method for purifying an exhaust gas in which a gas containing one or more 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. (1) cupric oxide, and (2) at least one metal oxide selected from the group consisting of vanadium, molybdenum, and tungsten are mixed as an agent, and the composition thereof has an atomic ratio of metal M / (M + Cu) [ In the formula, Cu represents the number of atoms of copper, M represents the number of atoms of vanadium, molybdenum, or tungsten (when two or more of these components are used, the total number of atoms thereof) is 0.01 to 0.7. In addition, the method for purifying exhaust gas is characterized by using a molded body having a density of 1.5 to 3.5 g / ml obtained by molding the composition.

The purifying agent used in the present invention can remove toxic components in completely dry gas without any trouble, so that the moistening treatment is not required and the merit thereof is great.

Further, the cleaning agent used in the present invention has an advantage that the removal amount and the removal rate of the toxic component per unit weight of the cleaning agent are significantly higher than those of the conventional cleaning agents.

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

Further, the purifying agent of the present invention is highly safe because it does not ignite even though the purifying agent after use may generate heat by contact with air.

The present invention is applicable to a gas containing nitrogen gas, hydrogen gas or air and one or more hydrides such as arsine, phosphine, diborane and hydrogen selenide.

The purifying agent used in the present invention comprises (1) cupric oxide, and (2) at least one metal oxide selected from the group consisting of vanadium, molybdenum, and tungsten, and the composition thereof has an atomic ratio of metal. M / (M + Cu) [In the formula, Cu represents the number of atoms of copper, and M represents the number of atoms of vanadium, molybdenum or tungsten (when two or more of these components are used, the total number of those atoms)] And 0.01-0.7, preferably 0.03-0.55, and a density of 1.5-3.5 g / ml obtained by molding the composition. If the atomic ratio is less than 0.01, not only the amount of saturated purification is small, but also molding cannot be performed. When it is larger than 0.7, the amount of saturated purification becomes small.

In this specification, the saturated purification amount is the maximum purification capacity of the purifying agent (the maximum amount of toxic gas that can be removed) divided by the weight or volume of the purifying agent.

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

For example, copper nitrates, sulfates, chlorides, organic acid salts, etc. are added with alkalis such as caustic soda, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonia to form oxide intermediates. Allow to settle.

The precipitate obtained by adding an alkali to a metal salt is preferably a hydroxide or a basic carbonate. The obtained slurry of copper hydroxide or basic copper carbonate and an aqueous solution of ammonium metavanadate, ammonium molybdate, and ammonium tungstate are kneaded with a kneader, dried and fired to have a specific composition.

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. In addition, a small amount of water, a lubricant or the like may be used in the molding, if necessary.

The shape of the molded body is not particularly limited, but typical examples include spherical, cylindrical, and tubular shapes.

If the shape of the molded product is spherical, the diameter is preferably in the range of 2 mm to 12 mm, and if it is cylindrical, the diameter is in the range of 2 mm to 12 mm, and the height is also suitable in the range of 2 mm to 12 mm. Generally, it is said that the filling cylinder needs to have a particle diameter smaller than about 1/10 of the cylinder diameter, so that it is convenient in that range because there is no drift. The particle density of the purifying agent used in the present invention is 1.5 to 3.5 g / ml,
It is preferably in the range of 2 to 3.5 g / ml.

In the present specification, the density means a value obtained by dividing the weight of a molded product (grain) by the geometric volume of the molded product. Density is 1.5g / ml
When it is smaller than the above, not only the density of the molded body is weakened, but also the purification amount per volume is reduced. Further, when the density is higher than 3.5 g / ml, the amount of purification per weight, which is considered to be due to the decrease in pore volume, decreases.

It is surprising that such a heavy cleaning agent has a greater cleaning capacity even at low temperatures. This is probably because the reaction between the purifying agent and the hydride is not a catalytic dehydrogenation reaction but a reaction that produces water. This suggests that the active hydrogen generated from the hydride reacts with the lattice oxygen of the oxide, and the purifying agent has sufficiently large pores so that it can reach the inside of the molded body.

The cleaning agent used in the present invention is packed in a cleaning column and used as a solid bed. However, it can also be used as a moving bed or a solid bed. Gas containing harmful components (hereinafter,
A gas to be treated) is flown into the purifying cylinder and brought into contact with the purifying agent, whereby various hydrides which are toxic components are removed and purified.

There are no particular restrictions on the concentration of hydride in the gas to be treated and the gas flow rate to which the purification method of the present invention is applied. Generally, the higher the concentration, the smaller the flow rate. That is, the empty cylinder linear velocity at which exhaust gas passes through the purification cylinder is a cm / sec,
When the concentration of the toxic component is b vol%, the operation parameter is y, and it is preferable to operate in the range of the following formula.

0.0005 <y <200 However, under the condition that y = axby is less than 0.0005, the size of the purification column becomes too large, which is economically disadvantageous. When it exceeds 200, the amount of heat generated becomes large. Therefore, it becomes necessary to use a cooler or the like.

For example, when the gas to be treated is hydrogen-based, if the concentration of the toxic gas contained is 10% or more and the flow rate is 20 cm / sec or more, heat will cause the reduction of the cleaning agent by hydrogen and the activity will be lost. Therefore, in such a case, it is preferable to operate by taking a treatment such as cooling the purifying cylinder.

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 cleaning agent is 15
It is 0 ° C or lower, preferably 0 to 100 ° C. In particular, when hydrogen is used as a gas base (atmosphere gas), the temperature is preferably 100 ° C. or lower. Usually, the temperature may be from room temperature to room temperature, and 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
The range is up to 10 Kg / cm ² abs.

In the present invention, since the moistening treatment (the treatment by the bubbler usually provided before the purifying cylinder) is unnecessary, the purifying cylinder of the present purifying agent can be installed on the upstream side of the vacuum pump for sucking the gas to be treated. Can be processed under reduced pressure.
By doing so, the toxic gas is removed before it passes through the vacuum pump, and the oil in the pump is not contaminated by the toxic gas, thus facilitating maintenance.

According to the purification method of the present invention, it is possible to efficiently purify a gas containing various hydrides, which are discharged from a semiconductor manufacturing process, as a toxic component in a dry state.

〔Example〕

Examples 1 and 2 Copper nitrate was dissolved in ion-exchanged water so as to be 20% by weight. On the other hand, a stoichiometric amount of caustic soda was made into a 20% by weight aqueous solution.

While the nitrate solution was being stirred in the stirrer, the caustic soda solution was added dropwise to form a copper hydroxide precipitate.

The precipitate was filtered, washed, added with a 10% ammonium metavanadate aqueous solution, kneaded with a kneader to form a uniform solution, which was dried at 120 ° C for 10 hours and then calcined at 350 ° C for 5 hours to oxidize. Two types of mixtures with different ratios of cupric and vanadium pentoxide were obtained.

Each of these mixtures was tablet-molded into pellets of 6 mmΦ × 6 mmH. The grain density of this product was 2.8 g / ml. The packing density of this product was 1.8 Kg / l. Crush this,
It was sifted and 12-28 mesh was used as a cleaning agent.

A purifying cylinder made of hard polyvinyl chloride with an inner diameter of 13 mmΦX200 mmH was filled with about 1 g of the above-mentioned purifying agent (filling height of about 4 mm), and this purifying cylinder contained 1 vol% arsine as a gas to be treated at 20 ° C, 1 atm Nitrogen gas of 3 / hr (vacuum tower linear velocity 0.63c
The flow rate was set to m / sec), and the saturated purification amount was measured when each purifying agent was filled.

The results are shown in Table 1.

Comparative Example 1 56 g (100 ml) of activated alumina (trade name: Neobead D4, 6 to 10 mesh) was sprayed with 20 g of a 20 wt% aqueous solution of ferric chloride to give an absorbent as it was. This absorbent contained 0.025 g of iron as a metal per 1 g of alumina.
The saturated purification amount was measured in the same manner as in Example 1 except that 1 g of the obtained absorbent was used instead of 1 g of the purification agent of Example 1. The results are shown in Table 1.

Comparative Example 2 4 g of activated alumina (trade name: Neobead D4, 6 to 10 mesh) 56 g (100 ml) was sprayed with 20 g of a 5 wt% aqueous solution of potassium permanganate and dried at 120 ° C.
The absorbent was prepared by repeating the process. This absorbent is alumina
The content of manganese was 0.025 g per 1 g of metal. The saturated purification amount was measured in the same manner as in Example 1 except that 1 g of the obtained absorbent was used instead of 1 g of the purification agent of Example 1. The results are shown in Table 1.

Example 3 Under the same conditions as used in Example 1, nitrogen gas was changed to hydrogen gas and the saturated purification amount of arsine was measured. The results are shown in Table 2.

Examples 4 to 6 Gases each containing 1% of phosphine, silane, diborane or hydrogen selenide alone in nitrogen gas were passed under the same conditions as in Examples, and the saturated purification amount was measured.
The results are shown in Table 3.

Examples 7 to 8 Purifying agents were prepared in the same manner as in Example 1 using ammonium molybdate or ammonium tungstate in place of ammonium metavanadate, and the activity was investigated (gas composition N ₂ + AsH ₃ ).

The results are shown in Table 4.

Examples 9 to 11 The same purifying agent as used in Examples 1, 7 and 8 was filled with 36 g (a filling volume of about 20 ml) in a purifying cylinder made of quartz having the same size as that of the purifying agent used in Example 1. 1% arsine in nitrogen gas at 25 / hr each (superficial linear velocity 5.3 cm / s
ec), and the time until each gas breaks through was measured. The breakthrough was detected using the following detector tube.

Arsine: No. 19L manufactured by Gastec Co., lower limit of detection 0.05ppm The results are shown in Table 5.

Example 12 In Example 9, the concentration of arsine was 100 ppm in nitrogen gas.
And the other conditions were the same, and the time to breakthrough was measured. The results are shown in Table 6.

Comparative Example 3 16-24 mesh activated carbon was sequentially impregnated with an aqueous solution of copper nitrate and an aqueous solution of potassium hydroxide, dried, and dried in nitrogen gas at 300
An adsorbent was prepared by firing at 30 ° C. for 30 minutes.

The prepared adsorbent contained 0.063 copper as a metal per 1 g of activated carbon.
It contained 0.078 g of g and potassium. The time required to break through 12 g of this impregnated carbon (filling volume of about 20 ml) under the same reaction conditions as in Example 9 was measured. The results are shown in Table 7.

Comparative Example 4 15 g of absorbent prepared in the same manner as Comparative Example 1 (filling volume of about 2
The breakthrough time was measured under the same conditions as in Comparative Example 3. The results are shown in Table 7.

Comparative Example 5 15 g of absorbent prepared in the same manner as Comparative Example 2 (filling volume of about 2
The breakthrough time was measured under the same conditions as in Comparative Example 3. The results are shown in Table 7.

[Effect of the present invention] The purification method of the present invention has the following excellent features and is industrially very useful.

(1) The removal amount and removal rate of the toxic component per unit volume of the cleaning agent are large.

(2) Various hydrides can be completely removed regardless of their concentration.

(3) The purification operation can be performed at room temperature to room temperature, and heating or cooling is not particularly required.

(4) Since the purifying agent contains substantially no water or the like, stable purifying performance can always be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01J 20/06 B01D 53/34 ZAB

Claims (1)

[Claims] 1. A method for purifying an exhaust gas, wherein a gas containing one or more 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. As (1) cupric oxide, and (2) at least one kind of metal oxide selected from the group consisting of vanadium, molybdenum, and tungsten are mixed, and the composition has an atomic ratio of metal M / (M + Cu) [formula Where Cu represents the number of atoms of copper, M represents the number of atoms of vanadium, molybdenum or tungsten (the total number of atoms when two or more of these components are used)] and 0.01 to 0.7, And a method of purifying exhaust gas, characterized by using a molded body having a density of 1.5 to 3.5 g / ml obtained by molding the composition