JPH11253741A - Method for treating silanes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decompose silanes stably with a silanes decomposing liquid such as water and an alkaline solution. SOLUTION: When silanes such as an exhaust gas or a waste liquid containing silanes which is generated in the distillation/purification process of chlorosilanes and a process in which the purified silanes are heat-decomposed and deposited are brought into contact with a decomposition liquid in a reactor to decompose the silanes, a flowing liquid layer is formed on the surface of a member existing in the gas phase of the reactor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a silane-containing waste gas or a liquor which is generated in a step of purifying chlorosilanes by distillation or a step of heating and decomposing and separating silanes purified by distillation. The present invention relates to a treatment method capable of stably decomposing silanes with a decomposition solution such as water or an alkaline solution for a long period of time.

[0002]

2. Description of the Related Art Silane waste generated in a process of producing high-purity silicon is generated in a replacement operation for opening a container or the like, or a pressure in a distillation column or a storage container is regulated. There are gaseous silanes released from valves and the like, and liquid silanes containing impurities concentrated in the distillation purification step. These silanes are silane (SiH ₄ ) and various chlorosilanes, which react with water in gaseous or liquid form to react with silicon dioxide (S
iO ₂ ).

Heretofore, as a simple method for detoxifying such silanes, decomposition using a decomposition solution such as water or an alkaline solution has been generally performed, and various methods have been proposed. For example, a method in which calcium hydroxide suspension water is brought into gas-liquid contact with silanes while adjusting the pH to about 10 as an alkaline solution (Japanese Patent Laid-Open No. 63-214321), or a method of decomposing with water and treating with an alkaline solution (particularly, No. 4-124011).

As described above, gaseous or liquid silanes are generally decomposed and detoxified by contact with a decomposition solution, but chlorosilanes other than silane have extremely strong corrosiveness. In addition, it not only has a strong pungent odor, but also emits a large amount of heat of reaction and hydrochloric acid gas when reacting with the decomposition solution, and in some cases generates hydrogen gas. It is customary to use a container having a structure that does not make contact. For example, a method in which a lime particle slurry is filled in a pressurized vessel and a silane waste liquid is directly flowed into the slurry (Japanese Patent Laid-Open No. 62-2750)
No. 13) has been proposed.

[0005]

However, even if the treatment is performed by various proposed methods, it is difficult to prevent the generation of mist and vapor of unreacted silanes. Subsequently, in the member present in the gas phase of the container into which the accompanying gas or the reaction liquid flows, the moisture adhering or adsorbed to the member reacts with unreacted silanes to generate silicon dioxide, and the silanes As the decomposition reaction continues to increase in size as long as the decomposition reaction is continued, the container is eventually closed, and the treatment must be interrupted to perform open cleaning.

[0006] The time until such blockage depends on the size and shape of the container, the processing method and the processing speed, but is several days, and in some cases, several hours. It will be a very inconvenient trouble.

Accordingly, an object of the present invention is to prevent silicon dioxide from adhering and depositing on members existing in the gas phase of a decomposition vessel for decomposing silanes with a decomposition solution such as water or an alkaline solution,
It is an object of the present invention to provide a method for treating a silane-containing liquid capable of stably performing industrially continuous treatment.

[0008]

Means for Solving the Problems The present inventors have intensively studied a method for preventing mist or vapor of silanes from adhering as silicon dioxide on the surface of a member existing in a gas phase portion of a reaction vessel. As a result, silicon dioxide produced by the decomposition of silanes is fine particles in the initial stage of its production, and the particles can be easily removed with a liquid at a low flow rate before growth, and Thus, it was found that the particles hardly grew if the flow of the liquid was maintained. As a result of further study based on this knowledge, it was found that by forming a liquid layer having a flow on the surface of the member existing in the gas phase portion of the reaction vessel, the phenomenon of silicon dioxide adhering and growing on the member surface was extremely reliably prevented. Find out what they can do,
The present invention has been proposed.

That is, according to the present invention, when a silane-containing liquid and a decomposition solution are brought into contact with each other in a reaction vessel to decompose the silanes, the surface of a member existing in a gas phase portion of the reaction vessel has a flow. A method for treating a silane-containing liquid, which comprises forming a liquid layer.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, silanes include silane (SiH ₄ ), monochlorosilane (SiH ₃ Cl),
Silanes such as dichlorosilane (SiH ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ), silicon tetrachloride (SiCl ₄ ), and polychlorosilanes (chlorosilanes having at least one Si—Si bond) alone or as a mixture It is a generic term for gas or liquid contained as.

In the present invention, the silanes are generally supplied to the reaction vessel in a gaseous or liquid state, but may be supplied in a state of being dissolved or suspended in a solvent or the like.

In the present invention, the decomposition solution may be
Any liquid capable of decomposing such silanes may be used. Generally, water or an aqueous solution or suspension of an alkali such as a hydroxide of an alkali metal or an alkaline earth metal, an alkali metal or an alkaline earth metal oxide is industrially used. It is preferably used. Specifically, water, aqueous sodium hydroxide,
An aqueous solution of potassium hydroxide, an aqueous solution of calcium hydroxide, a suspension of calcium oxide and the like can be mentioned.

In the present invention, the reaction vessel for bringing the silane and the decomposition solution into contact with each other includes a means for supplying the silane,
It basically consists of means for filling and / or supplying the decomposition solution. For example, FIGS. 1 and 2 show typical embodiments of a reaction vessel that can be suitably used for carrying out the method of the present invention. That is, FIG. 1 shows an embodiment in which a filling layer 2 is provided inside, and a silane supply nozzle 3 and decomposition solution supply nozzles 11 and 12 are provided above the filling layer 2. In such an embodiment, it is preferable that the decomposed liquid is stored in the lower part of the reaction vessel 1 after contact with the silanes, and at least a part thereof is circulated through a line provided with the pump 6 and the cooler 7. In addition, in order to replenish the consumption of the decomposition solution,
Is supplied through a control valve 5 as needed. Further, a part of the decomposed liquid after contact with the silanes stored in the lower part of the reaction vessel 1 is extracted from the liquid outlet 13 by overflow.

FIG. 2 shows an embodiment in which a silane supply nozzle 3 and a decomposition solution supply nozzle 4 are inserted into a liquid phase composed of a decomposition solution, in which a stirrer 7 is provided instead of the above packed bed.
The supply amount of the decomposition solution to the liquid phase can be adjusted by the valve 5 depending on the pH of the decomposition solution circulating in the reaction vessel. Of course, the pH of the liquid phase may be directly measured to control the supply amount of the decomposition solution.

In the present invention, it is extremely important to form a liquid layer having a flow on the surface of the member existing in the gas phase of the reaction vessel in order to prevent silicon dioxide from adhering to the surface of the member.

That is, in the reaction vessel having the gas phase as described above, the water adhering or adsorbing to the surface of the member existing in the gas phase reacts with the mist or vapor silanes and is consumed. However, in the case of the conventional method in which carbon dioxide is generated but a liquid layer having a flow on the surface of the member is not formed, the generated silicon dioxide reaches the container member and the silicon dioxide adheres strongly to the member surface. , Which triggers the deposition of silicon dioxide. The silicon dioxide, which once adhered to the surface of the member and began to grow, cannot be removed without strong cleaning, and a decomposition solution for decomposing silanes exists in the reaction vessel. Therefore, water vapor is inevitably generated, and this water vapor is adsorbed on the surface of silicon dioxide adhering to the surface of the container, which causes the formation of new silicon dioxide. In this way, the silicon dioxide rapidly enlarges on the surface of the member existing in the gas phase of the reaction vessel, and eventually reaches blockage.

On the other hand, in the present invention, by forming a liquid layer having a flow on the surface of the member existing in the gas phase portion of the reaction vessel, it is possible to prevent the initial adhesion of the generated silicon dioxide particles. Growth can be prevented very effectively.

In the present invention, the gas phase portion of the reaction vessel
A gas phase portion in which mist or vapor silanes substantially exist. Therefore, in the embodiment in which the packed layer shown in FIG. 1 is provided, the mist or vapor silanes are often substantially not present in the gaseous phase portion below the packed layer. There is no need to particularly form a liquid layer having the above-mentioned flow on the existing member surface such as a wall surface. Of course, even in this case, it is possible to provide the liquid layer in view of safety, and the present invention does not exclude such an embodiment.

Since the flow speed in the liquid layer varies depending on the degree of finishing and the material of the inner wall of the reaction vessel, it is desirable to appropriately determine the optimum speed in advance by experiments.
Generally, 0.01 m / sec or more, preferably 0.05 to
It is determined from the speed of 50 m / sec. Flow velocity 0.01m /
If the time is shorter than seconds, the generated silicon dioxide has a high probability of reaching and adhering to the members of the reaction vessel before being washed out, and may start growing.

In the present invention, the member present in the gas phase of the reaction vessel, which forms the liquid layer, is a gas phase in which mist or vapor of unreacted silane is present in the reaction between the silane and the decomposing agent. Is a member that is in contact with. Specific examples include the wall surface of a reaction vessel, the surface of a nozzle for supplying silanes and a decomposing agent, and the like. It is recommended that a liquid layer be continuously present on the entire surface of the member existing in the gas phase.

In the present invention, the liquid for forming the liquid layer having a flow is used to physically prevent particles from adhering due to the flow of the liquid layer formed on the member surface by the liquid layer having the flow. Since it does not significantly inhibit the decomposition reaction of silanes, it may be one that reacts with silanes, one that dissolves silanes, or one that does not react with silanes. There may be. When the silanes are liquid, they may be the silanes themselves. Among them, water or alkaline liquid is industrially preferable. When an alkaline solution is used as the decomposition solution, the decomposition solution is most preferably used in consideration of the loss due to dilution.

Further, in the present invention, the method for forming a liquid layer having a flow is not particularly limited, but a mode in which the liquid is supplied to the surface of the member existing in the gas phase by spraying is the most reliable. It is preferably used. That is, when the spray is used, a liquid layer having a relatively uniform flow is formed even when the arrangement of the spray and the direction of the spray are appropriately set, even for the dead space and the complicated surface of the gas phase portion of the container. be able to.

In FIG. 1, for forming a liquid layer, liquid layer forming nozzles 8, 9 and 10 are provided, and a part of the decomposed liquid is supplied to the nozzle from the circulating line of the decomposed liquid and supplied to the surface of the member. This is done by:

The structure of the liquid layer forming nozzle 8 is set so that a liquid layer is formed on the inner wall of the upper part of the reaction vessel and the surface of the silane supply nozzle and the line leading to the nozzle. The structures 9 and 10 are set so that a liquid layer is formed mainly on the inner wall surface of the reaction vessel below the position.

In FIG. 2, spray nozzles 14 for forming a liquid layer are formed of the inner wall of the reaction vessel, the line leading to the silane supply nozzle, and the line leading to the decomposition solution supply nozzle in the gas phase. The structure is determined so as to form a liquid layer on the surface.

In any of the embodiments shown in FIGS. 1 and 2, when the internal shape of the reaction vessel is a simple cylindrical or conical shape, the swirling flow is caused by flowing water that releases liquid tangentially to the inner wall of the member. Is also an effective method.

In the embodiment shown in FIG. 2, the liquid supplied to the nozzle circulates the decomposition liquid present in the liquid phase of the reaction vessel by the pump 6 through the cooler 7. A part of the circulating liquid is discharged from the line 13 while adjusting an appropriate amount with the valve 15 as necessary.

In the embodiment shown in FIG. 2, in order to reduce the area of the members in the gas phase as much as possible, the silane supply nozzle and the decomposition solution are not substantially passed through the gas phase but from the side of the reaction vessel. An embodiment in which the supply nozzle is formed directly in the liquid phase is also suitable.

Further, there is a possibility that a gas containing unreacted silanes may pass through the exhaust gas line 16, and the line may be blocked by the generation of silicon dioxide. In order to prevent this phenomenon, it is preferable to use the exhaust gas lines alternately as two lines or to install the exhaust gas lines via an absorption tower for silanes.

When there is a portion in the gas phase portion of the reaction vessel that is so narrow that liquid spray cannot be used, the mist or vapor of unreacted silanes exists in such a portion. A mode in which a curtain of liquid is formed so as to block the space from the phase portion, a mode in which a filler, a baffle plate, or the like is arranged in the space and a liquid flows in from the side opposite to the side in contact with the atmosphere. Etc. are preferred. In particular, in a mode in which a filler or a baffle plate is arranged in a space, the space can be effectively shut off with a small amount of liquid.

In the method of the present invention, by forming a flowing liquid layer on the surface of the member, a liquid film is formed on the surface of the member, and mist or vapor of silanes is brought into contact with the surface of the flowing liquid layer. Even if silicon dioxide is generated as a result, it is assumed that the silicon dioxide flows down without contacting the member because the silicon dioxide is separated from the member by the liquid film.

[0032]

As will be understood from the above description, according to the present invention, in a reaction vessel for decomposing waste containing silanes using water or an aqueous solution, the reaction is carried out in the gas phase of the vessel. It is possible to prevent the deposition of silicon dioxide on the surfaces of the members in contact with each other, and it is possible to stably and continuously continue the treatment reaction industrially, and the effect is enormous.

[0033]

EXAMPLES The present invention will be described specifically with reference to Examples and Comparative Examples below, but the present invention is not limited to these Examples.

Example 1 A gas containing silanes was treated using a reaction vessel as shown in FIG. The straight body of the reaction vessel 1 has an inner diameter of 1
25mm and 3m long, about 2m below the straight body
Is filled. The upper portion of the reaction vessel has a conical shape with a top angle of about 60 degrees, and a nozzle 3 for supplying silane waste gas is inserted from the center of the tip of the cone.

The decomposition solution is replenished with about 10% by weight aqueous sodium hydroxide from the decomposition solution supply port 4, and the replenishing amount is adjusted by the control valve 5 so as to maintain the pH of the treatment reaction solution at 12 to 14. did.

On the other hand, the liquid outlet 1 located at the lower part of the reaction vessel
From 3, a part of the processing solution was discharged by overflow together with the supplied gas and the gas generated by the decomposition reaction.

The decomposition solution is supplied by a circulation pump 6 from a supply nozzle 8 near the top of the cone at the top of the reaction vessel to about 1 m ³ /
A spray nozzle 11 located approximately 50 m below the top of the reaction vessel straight body, with a flow rate of about 3 m ³ / H from nozzles 9 and 10 near the boundary between the straight body and the cone at a flow rate of H From No. 12, a total amount of about 2 m ³ / H was fed into the reaction vessel.

At this time, the nozzle 8 and the nozzles 9 and 1
From 0, the decomposed liquid was supplied tangentially inside the reaction vessel so that a liquid layer having a homogeneous flow was formed inside the conical portion and the cylindrical portion.

At this time, the liquid layer having the slowest flow rate was the outer peripheral portion of the silane supply nozzle 3 and had a flow rate of about 0.05 m / sec.

In this way, a liquid layer having a flow over substantially the entire surface of the members existing in the gas phase of the reaction vessel was formed.

Since the decomposition reaction is an exothermic reaction, the circulating liquid is cooled by the cooler 7 to prevent overheating. The composition of the waste gas to be treated is about 15 mol% dichlorosilane, about 5 mol% trichlorosilane, about 3 mol% silicon tetrachloride, and about 77 mol% nitrogen.
Met. This waste gas was supplied to the reaction vessel at a rate of about 30 Nm ³ / H.

After the treatment of the silane waste gas under the above conditions for 30 consecutive days, the reaction vessel was stopped and the inside was inspected. No trace of silicon dioxide deposited and grown to such an extent as to hinder was observed.

Comparative Example 1 Using the same reaction vessel as in Example 1, nitrogen was supplied at a flow rate of about 20 Nm ³ / H instead of the decomposition solution supplied from the conical upper nozzle 8. In addition, the supply of the decomposition solution supplied from the nozzle 8 was stopped, and the flow rate of the decomposition solution supplied from the nozzles 11 and 12 was increased accordingly.

Other conditions were the same as in Example 1, and as a result of starting the treatment of the silane waste gas, about one day later, a large amount of silicon dioxide was deposited on the upper part of the reaction vessel, and the treatment was continued. It became impossible.

Example 2 Using a reaction vessel as shown in FIG. 2, waste liquid containing silanes was treated. The inner diameter of the reaction vessel 1 is about 50 c
m, the capacity is about 200 liters. The decomposition solution is supplied from the decomposition solution supply port 4 with an aqueous solution of about 10% by weight of sodium hydroxide.
The supply amount was adjusted by the control valve 5 so as to be maintained at １４14. On the other hand, the liquid was discharged through the liquid level control valve 15 so that the amount of liquid held in the container was maintained at about 100 liters.

The decomposition liquid in the reaction vessel was supplied to the spray nozzle 14 by the pump 6 in order to form a liquid layer having a flow on the surface of the member existing in the gas phase portion of the reaction vessel. The spray nozzle was arranged so as to jet toward the upper part of the gas phase part of the container, and was jetted in a filled conical pattern, and released the decomposition solution at a flow rate of about 5 m ³ / H.

Since the decomposition reaction is an exothermic reaction, the decomposition solution circulated by the pump was cooled by passing through the cooler 7.

In this manner, a liquid layer having a flow was formed on substantially the entire surface of the members existing in the gas phase of the reaction vessel.

The composition of the waste liquid to be treated is about 65% by weight of silicon tetrachloride, about 33% by weight of disilicon hexachloride (Si ₂ Cl ₆ ), and about 2% by weight of other high boiling polychlorosilanes.
% By weight. The waste liquid was flowed at a flow rate of about 30 L / H directly into the decomposition reaction vessel through the silane waste liquid supply nozzle 3 for treatment.

According to the above conditions, the treatment of the silane waste liquid is
After performing the test for 0 consecutive days, the reaction vessel was opened and the interior was inspected. There was almost no adhesion of silicon dioxide, and no trace of silicon dioxide deposition and growth was observed to such an extent as to hinder the treatment. Was not done.

Comparative Example 2 In the same reaction vessel as used in Example 2,
The spray nozzle 14 disposed inside the reaction vessel was removed, and the entire amount of the decomposition solution from the pump was directly returned to the decomposition solution in the container. Other conditions were the same as in Example 1, and the treatment of the silane waste liquid was continuously performed. After 5 days, the reaction vessel was opened and the inside was inspected. as a result,
There was a large amount of silicon dioxide deposits that grew to a considerable size on the wall surfaces of the members existing in the gas phase inside the reaction vessel. This trouble is inherently serious.

That is, blocking in the reaction vessel is caused by
This is because the treatment reaction must be stopped.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a typical embodiment of a reaction vessel used in the method of the present invention.

FIG. 2 is a schematic diagram showing another typical embodiment of the reaction vessel used in the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction container 2 Packing layer 3 Silane supply nozzle 4 Decomposition liquid supply port 5 Control valve 6 Decomposition liquid circulation nozzle 7 Cooler 8 Liquid layer formation nozzle 9 Liquid layer formation nozzle 10 Liquid layer formation nozzle 11 Decomposition liquid supply nozzle 12 Decomposition liquid Supply nozzle 13 Liquid outlet 14 Spray nozzle 15 Valve 16 Exhaust gas line 17 Stirrer

Claims (3)

[Claims] When a silane and a decomposition solution are brought into contact with each other in a reaction vessel to decompose the silane, a liquid layer having a flow is formed on a surface of a member existing in a gas phase portion of the reaction vessel. A method for treating a silane-containing liquid. 2. The method according to claim 1, wherein the liquid forming the liquid layer is a decomposition liquid. 3. The method according to claim 1, wherein the decomposition solution is an aqueous alkali hydroxide solution.