JPH0687943B2 - 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 exhaust gas industry and optoelectronics industry, arsine, phosphine, silane, diborane,
In addition, the usage of highly toxic hydrides such as hydrogen selenide is increasing.

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 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 the 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 the 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. 59-16053).
No. 5 bulletin). 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 depending on conditions, so that the use conditions are limited for industrial use.

To treat the exhaust gas containing silanes, for example, as shown in JP-A-56-84619 and JP-A-57-94323, a method of washing with an alkaline aqueous solution such as caustic soda and wet-removing is adopted. It has been. However, the wet treatment is inconvenient because the apparatus becomes large and handling of the alkaline aqueous solution is dangerous.

On the other hand, as disclosed in JP-A-58-128146, a dry absorption treatment agent has been proposed in which a solid carrier is impregnated with an aqueous solution of caustic soda alone or simultaneously with an aqueous solution of an oxidizing agent such as potassium permanganate. There is. When this treatment agent is used, it is a semi-dry type, so there is an advantage that the device can be downsized, but caustic soda and potassium permanganate are precipitated on the surface of the carrier, and the filling cylinder is repeated while repeatedly deliquescing. However, there are drawbacks such as an increase in the pressure loss of the device, a trouble of closing the device depending on the case, and a need to stop the entire semiconductor manufacturing process.

[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 (1) cupric oxide and (2) lithium,
It was found that contacting exhaust gas containing toxic components with a purifying agent containing respective hydroxides such as magnesium, calcium, strontium and barium removes these toxic components efficiently, and further research is continued. Was completed.

That is, the present invention relates to a method for purifying exhaust gas in which a gas containing one or more of arsine, phosphine, silane, 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 a purifying agent, (1) cupric oxide and (2) at least one metal hydroxide selected from the group consisting of lithium, magnesium, calcium, strontium and barium are blended, and the composition is an atom of a metal. Ratio M / (M + Cu) [wherein Cu represents the number of atoms of copper, M represents the number of atoms of Li, Mg, Ca, Sr or Ba (when two or more of these components are used, the number of those atoms is [In total]] is 0.01 to 0.7, and a molded body having a density of 1.5 to 3.5 g / ml formed by molding the composition is used, and the exhaust gas purification method is characterized.

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, silane, 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 lithium, magnesium, calcium, strontium and barium, and its composition is Atomic ratio of metal M / (M + Cu) [wherein Cu represents the number of atoms of copper, M represents the number of atoms of Li, Mg, Ca, Sr or Ba (when two or more of these components are used, those The total number of atoms is 0.01) to 0.7, preferably 0.03 to 0.55, and the composition is molded to have a density of 1.5 to 3.5 g / ml. 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, salts of copper, lithium, magnesium, calcium, strontium, barium nitrates, sulfates, chlorides, organic acid salts, caustic soda, caustic potassium, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonia. An alkali such as is added to precipitate hydroxide or basic carbonate, and the resulting precipitate is calcined to burn cupric oxide and lithium, magnesium, calcium, strontium, barium hydroxide or basic carbonate. A mixture of salts is prepared so that it has a specific composition.

Further, for example, cupric oxide powder is mixed with hydroxides of lithium, magnesium, calcium, strontium, and barium, kneaded with a kneader, and dried to obtain 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 size of the molded product is spherical, the diameter is preferably in the range of 2 mm to 12 mm, 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 3.0 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 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 fixed 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 measures 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 for the purifying agent can be installed upstream of the vacuum pump for sucking the gas to be treated. It is possible to process 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 and calcium nitrate were used in an atomic ratio of Ca / (Ca + C).
u) was mixed at a ratio of 0.1 and 0.5, and the respective mixtures were dissolved in ion-exchanged water so as to be 20% by weight. On the other hand, to obtain these hydroxides, a stoichiometric amount of caustic soda was made into a 20% by weight aqueous solution.

While stirring each nitrate mixed solution in a stirring tank,
The above caustic soda solution was added dropwise to form precipitates of copper hydroxide and calcium hydroxide.

These precipitates were filtered, washed, dried at 120 ° C. for 10 hours and calcined to obtain two kinds of mixtures having different ratios of cupric oxide and calcium hydroxide.

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 Activated Alumina (Brand Name Neo Bead D4, 6-10 mesh)
56 g (100 ml) 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 Activated Alumina (Neobead D4, 6-10 mesh, trade name)
56g (100ml) 5% by weight aqueous solution of potassium permanganate
The operation of spraying 20 g and drying at 120 ° C. was repeated 4 times to prepare an absorbent. This absorbent contained 0.025 g of manganese as a metal per 1 g of alumina. Example 1 using the obtained absorbent 1g instead of the cleaning agent 1g of Example 1
The saturated purification amount was measured in the same manner as. 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 7 Gases containing 1% of phosphine, silane, diborane or hydrogen selenide alone in nitrogen gas were flowed under the same conditions as in Example 1 to measure the amount of saturated purification. The results are shown in Table 3.

Examples 8 to 11 Cupric oxide and Li, Mg having an atomic ratio of M / (M + Cu) of 0.07, respectively, using lithium nitrate, magnesium nitrate, strontium nitrate, and barium nitrate in place of the calcium nitrate of Example 1. A mixture of Sr or Ba hydroxides was obtained.

These mixtures were tabletted into 6 mmΦ × 6 mmH pellets. The density of the obtained particles was 2.8 kg / l. The packing density was 1.8 kg / l. Crush and sift this 12
~ 28mesh was used as a cleaning agent.

The activity test was the same as in Example 1 (gas composition was N ₂ + As).
H _3). The results are shown in Table 4.

Examples 12 to 16 36 g (the filling volume of about 20 ml) of the same purifying agent as used in Examples 1 and 8 to 11 were filled in a purifying cylinder made of quartz having the same size as that of the purifying agent used in Example 1. 1 in nitrogen gas
% Arsine each 25 / hr (vacant tower linear velocity 5.3 cm / se
It passed at the superficial linear velocity of c), and the time until each gas passed through was measured. The breakthrough was detected using the following detector tube.

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

Example 17 In Example 12, 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 12 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.

Claims (1)

[Claims] 1. A method for purifying exhaust gas, which comprises contacting a gas containing at least one of arsine, phosphine, silane, diborane and hydrogen selenide as a toxic component with a purifying agent to adsorb and remove the toxic component from the gas, As a purifying agent, (1) cupric oxide, and (2) at least one metal hydroxide selected from the group consisting of lithium, magnesium, calcium, strontium, and barium are blended, and the composition has an atomic ratio of metal. M / (M + Cu) [In the formula, Cu represents the number of copper atoms, M is the number of atoms of Li, Mg, Ca, Sr or Ba (when two or more of these components are used, the total number of those atoms is used). 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.