JP7499640B2 - Method for treating waste gas containing hydrophobic silica - Google Patents

Description

The present invention relates to a method for treating waste gas containing hydrophobic silica. More specifically, the present invention provides a method for easily treating waste gas containing hydrophobic silica by burning the waste gas with a burner and then contacting the waste gas with water.

Dry silica is generally used as an additive to impart thickening and thixotropy effects and reinforcing effects to resins, etc. In order to obtain these desired application properties, hydrophilic silica or hydrophobic silica with the surface of hydrophilic silica hydrophobized is appropriately selected depending on the type of resin, etc. used.

Hydrophobicity is generally imparted to hydrophilic silica by treating the surface of the hydrophilic silica with an organosilicon compound such as hexamethyldisilazane or cyclic dimethylsiloxane (see Patent Documents 1 and 2, etc.).
In the surface treatment process of hydrophilic silica, it is necessary to discharge the gas introduced for the surface treatment outside the system. In this case, hydrophobic silica is generally entrained in the gas discharged, so a process for treating the waste gas containing hydrophobic silica that is generated is required. This is particularly noticeable in the surface treatment of fumed silica, which has a small particle size and bulk density and is easily entrained in gas.

One possible method for treating waste gas containing fine particles such as silica is to bring the gas into contact with water to remove the fine particles by suspending them in the water. However, in the case of hydrophobic silica, the problem is that it is difficult to suspend the silica because it is inherently poorly compatible with water.

When the fine particles contained in the waste gas are hydrophobic silica, one method is to treat the liquid with which the gas comes into contact with an organic solvent in which hydrophobic fine particles are easily suspended. However, this is not economically viable when treating large amounts of hydrophobic silica, as it requires costs for the organic solvent used and for treating the organic solvent waste liquid.

Japanese Patent Application Laid-Open No. 8-259216 JP 2004-352606 A

Therefore, the object of the present invention is to provide a method for easily treating waste gas containing hydrophobic silica.

The inventors conducted extensive research to develop a method for efficiently treating waste gases containing hydrophobic silica. As a result, they discovered that by burning hydrophobic silica with a burner that creates a flame, the organic matter that gives the silica its hydrophobicity is burned and removed, and the silica becomes hydrophilic, making it possible to suspend it in water, which led to the completion of the present invention.

That is, the present invention is a method for treating a waste gas containing hydrophobic silica, which comprises a step of combusting the waste gas in a combustion furnace having a burner and a combustion chamber provided below the burner, and then contacting the waste gas with water , characterized in that the combustion treatment is carried out in a state where a swirling flow is generated in the combustion chamber .

The waste gas treatment method of the present invention makes it possible to efficiently treat waste gas containing hydrophobic silica, which is difficult to treat using conventional methods, without using organic solvents, etc., making it extremely useful as a waste treatment method.

The waste gas may contain organosilicon compounds, in which case the organosilicon compounds can be treated to produce hydrophilic silica by combustion.

1 is a schematic cross-sectional view showing one embodiment of a combustion furnace used in the waste gas treatment method of the present invention. FIG. 2 is a schematic top view showing one embodiment of a method for injecting swirling air into a combustion chamber in the present invention.

In the present invention, the cause of the generation of waste gas containing hydrophobic silica to be treated is not particularly limited, but typical examples of the generation causes are as follows:

Gases discharged from processes that use hydrophobic silica as a raw material, specifically gases discharged from flue gas desulfurization equipment when hydrophobic silica is used as an anti-caking agent for desulfurization components in the equipment, and gases discharged in the process of compounding and kneading hydrophobic silica as a filler during the manufacture of silicone materials or other resin compositions (more specifically, intake gas in vacuum processing, for example).

Furthermore, gases discharged from the process of producing hydrophobic silica, specifically gases containing hydrophobic silica dispersed during recovery of untreated surface treatment agents in a process of surface treating silica with a silane coupling agent, etc., can be mentioned. Such gases include organosilicon compounds used in the surface treatment, specifically chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, tert-butyldimethylchlorosilane, and vinyltrichlorosilane, as well as tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, iso-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, and phenyltriethoxysilane. , diphenyldiethoxysilane, iso-butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and other alkoxysilanes; hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahexyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, dimethyltetravinyldisilazane, and other silazanes, and derivatives thereof (compounds generated by hydrolysis or thermal cleavage, and further condensates thereof, etc.), are generally included.

Or gas generated during the suction recovery of hydrophobic silica that has been dispersed as dust during the packaging process.

There are no particular limitations on the hydrophobic silica contained, and any type of silica may be used, but it is preferable to use hydrophobic fumed silica, which has a small particle size and bulk density and is easily entrained in gas.

The present invention for treating waste gas containing hydrophobic silica produced as described above will be explained in more detail below with reference to the attached drawings, but the present invention is not limited to these drawings.

The processing equipment used in the processing method of the present invention (see FIG. 1) is composed of a combustion furnace 8 having a burner 1 and a combustion chamber 2. Furthermore, the combustion furnace 8 generally includes a cooling chamber 3 for cooling the high-temperature gas and silica generated by the combustion process.

In order to facilitate smooth movement of the burned silica through the furnace, this type of combustion furnace is designed with a combustion chamber 2 below the burner 1, and a cooling chamber 3 below that.

A flame is formed in burner 1 by introducing fuel gas and oxygen or air. There are no particular restrictions on the fuel gas used, but it is preferable to use hydrogen from the standpoint of ease of handling.

In the waste gas containing hydrophobic silica, the organic groups (derived from the surface treatment agent) of the hydrophobic silica are burned by the flame formed by burner 1, becoming carbon dioxide and water, etc., which leave the silica, and the groups present on the silica surface are converted to silanol groups (which are further dehydrated and condensed), turning it into hydrophilic silica. The flame temperature may be set within a range in which such a combustion reaction occurs, but is generally 1,000°C or higher.

In the embodiment shown in FIG. 1, the waste gas inlet 4 for introducing waste gas into the combustion furnace 8 is provided inside the burner, but it may also be provided on the ceiling or side wall of the combustion chamber 2 as long as a flow can be formed in which the introduced waste gas comes into contact with the burner flame.

As mentioned above, waste gas containing hydrophobic silica often contains the organosilicon compound or its derivatives used to make the silica hydrophobic. Since such organosilicon compounds also usually produce silica when burned, when the waste gas is burned with a burner flame as described above, the organosilicon compound also becomes silica (hydrophilic silica). The hydrophilic silica produced by the combustion of organosilicon compounds in this way can be treated as the same as the hydrophilic silica produced by the combustion process from the hydrophobic silica contained in the waste gas.

In other words, by subjecting the waste gas to combustion treatment, hydrophobic silica can be converted to hydrophilic silica, and the organosilicon compounds in the gas can be rendered harmless by the combustion treatment, eliminating the need for an additional process for treating the organosilicon compounds.

Naturally, flammable substances other than organosilicon compounds will also burn at the same time, and if the combustion products are harmless, they can be rendered harmless in this process. For example, if the surface treatment is performed using a wet method that uses an organic solvent, the organic solvent may be discharged during the drying process after treatment, but many organic solvents can be rendered harmless by combustion.

The hydrophilic silica produced by the combustion process in burner 1 tends to adhere to the inner walls of the combustion furnace as it passes through the furnace. This makes it easy for the inside of the furnace to become clogged due to silica accumulation, necessitating frequent maintenance of the equipment. Therefore, in order to perform the combustion process continuously, it is preferable to employ technology that prevents silica from adhering and accumulating on the inner walls of the combustion furnace.

One example of this technology is a method of preventing silica from adhering to and accumulating on the combustion chamber walls by introducing swirling gas from swirling gas outlets 6 provided on the wall surface of the combustion chamber 2 and performing combustion processing while generating a swirling flow on the combustion chamber walls.

The swirling gas introduced is usually an inert gas or air, with nitrogen and air being preferred from an economical standpoint.

There are no particular limitations on the method for generating the swirling flow, but one method is to provide a swirling gas outlet 6 on the combustion chamber wall and introduce the swirling gas from there.

This method will be described with reference to FIG. 2. In this method, it is preferable to provide the swirling gas outlets 6 in at least four directions, 0°, 90°, 180°, and 270°, as viewed from above. In addition, in order to generate a swirling flow throughout the entire height of the combustion chamber 2, it is preferable to provide multiple swirling gas outlets at different positions in the height direction. It is also preferable to avoid interference between the swirling gases introduced from different swirling gas outlets. In order to achieve these simultaneously, it is particularly preferable to provide adjacent swirling gas outlets at positions in different height directions. For example, in an embodiment in which swirling gas outlets are provided in the four directions described above, it is preferable to provide the 0° and 180° inlets and the 90° and 270° inlets at different positions in the height direction.

The angle θ of the swirling gas outlet 6 relative to the tangent of the outer wall of the combustion chamber may be set appropriately within a range that allows a swirling flow to be generated within the combustion furnace, but if the angle θ is too large, it is difficult to generate a swirling flow near the wall of the combustion chamber, and the effect of preventing silica adhesion to the wall of the combustion chamber is weakened. Therefore, the angle θ of the swirling gas outlet 6 is preferably 10 to 40°, and more preferably 20 to 30°.

The flow rate of the gas introduced into the combustion chamber from the swirling gas outlet 6 may be set appropriately depending on the amount of hydrophobic silica contained in the exhaust gas and its adhesion. However, if the gas linear velocity is slow, the effect of preventing silica adhesion to the combustion chamber inner wall will be weakened, and if the gas linear velocity is fast, wear of the combustion chamber inner wall will progress, so the gas flow rate is preferably about 60 to 90 Nm/s.

The inner diameter of the swirling gas outlet 6 and the number of gas swirling gas outlets may be set appropriately depending on the inner diameter, height, etc. of the combustion chamber.

In the present invention, high-temperature gas is generated by the combustion treatment as described above. As mentioned above, such high-temperature gas is generally cooled in the cooling chamber 3, but in the treatment method of the present invention, the silica contained in the waste gas adheres to the inner wall of this cooling chamber 3, which may cause operational problems.

Therefore, it is preferable to carry out the treatment method of the present invention while forming wet walls by fluidizing the water on the wall surface of the cooling chamber 3. By forming wet walls, silica adhesion to the inner wall of the cooling chamber is prevented, and at the same time, the fluidized water cools the silica and waste gas that have been combusted. The use of wet walls also has the effect of protecting the inner wall of the cooling chamber.

The amount of water to be added to the wetted wall should be the amount necessary to cool the silica and gases produced by the combustion process to a temperature that takes into account the design temperature of the equipment, etc.

In addition to the method using a wetted wall, methods such as scrubbers, plate towers, and packed towers are known as methods for contacting waste gas after combustion treatment with water, and these may be used alone or in appropriate combination.

When the waste gas containing silica that has been subjected to the calcination treatment as described above is brought into contact with water, the silica that has been rendered hydrophilic by calcination is suspended in the water to produce a silica slurry. The silica slurry is sent to a tank or the like, and then subjected to solid-liquid separation and dehydration treatment using a dehydrator such as a filter press to produce a silica cake. At this time, additional water may be added from the combustion furnace outlet or the like as needed to send the liquid to the tank or the like. The resulting silica cake can be disposed of by any known method as appropriate.

On the other hand, combustible substances such as organosilicon compounds have been removed from waste gas that has been combusted, and solids such as silica have also been removed by contact with water as described above. However, depending on the source of the waste gas, it may still contain various substances, and it may not be possible to release it directly into the atmosphere. In such cases, it is sufficient to carry out further detoxification treatment depending on the substances contained before releasing it into the atmosphere.

Based on the above-mentioned principle, the present invention also provides a method for disposing of hydrophobic silica. For example, hydrophobic silica to be disposed of may be generated for various reasons, such as cleaning of manufacturing equipment or switching of manufacturing items. In this case, the disposed hydrophobic silica is temporarily stored in a hopper or the like, but if the hydrophobic silica is transported using air or nitrogen for powder transportation, the gas can be treated as the same as the above-mentioned "waste gas containing hydrophobic silica". Therefore, if this is sent to burner 1 and subjected to the same treatment as the above-mentioned method, the hydrophobic silica to be disposed of can be made into silica cake. Silica cake containing water is much easier to handle than powdered hydrophobic silica, making subsequent treatment easier.

The above-mentioned principle of the present invention can also be applied to the treatment of gaseous organosilicon compounds. That is, if the waste gas does not contain hydrophobic silica but does contain organosilicon compounds, the hydrophobic silica will not be hydrophilized by combustion, but all other phenomena such as the combustion of the organosilicon compounds may occur, and the gas can be finally detoxified and silica cake can be obtained by similar treatment. Examples of such gases include unreacted organosilicon compounds used in the surface treatment of silica and purge gases from containers filled with organosilicon compounds (which do not actually contain hydrophobic silica). Specific examples of organosilicon compounds are the same as those mentioned above.

Furthermore, it can be applied to various waste gases, including organometallic compounds that produce oxides when burned, in addition to organosilicon compounds.

1: Burner 2: Combustion chamber 3: Cooling chamber 4: Waste gas inlet 5: Swirling gas inlet 6: Swirling gas outlet 7: Cooling water inlet 8: Combustion furnace

Claims (5)

A method for treating waste gas containing hydrophobic silica, comprising a step of combusting the waste gas in a combustion furnace having a burner and a combustion chamber provided below the burner, and then contacting the waste gas with water, characterized in that the combustion treatment is carried out while generating a swirling flow in the combustion chamber . 2. The method for treating said exhaust gas according to claim 1, further comprising the step of: providing a cooling chamber below said combustion chamber; and causing water to flow down along the wall surface of said cooling chamber to carry out the combustion treatment. 3. The method for treating said waste gas according to claim 1, wherein said waste gas contains an organosilicon compound. 4. The method for treating said waste gas according to claim 1, wherein said hydrophobic silica is fumed silica. 1. A method for disposing of hydrophobic silica, comprising the steps of:
A step of pneumatically transporting the hydrophobic silica to be disposed of in a combustion furnace having a burner and a combustion chamber provided below the burner, and combusting the hydrophobic silica in the furnace;
a step of contacting the silica-containing gas subjected to the combustion treatment with water to suspend the silica in the water to obtain a slurry; and a step of subjecting the silica slurry to solid-liquid separation to obtain a silica cake.
and performing a combustion treatment in a state where a swirling flow is generated in the combustion chamber .

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