JPS59102811A - Treatment by sintered metal filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Technical field of invention The present invention relates to methods of using sintered metal filters.

In particular, the present invention relates to a process for producing fumed silica using a sintered metal filter.

BACKGROUND OF THE INVENTION Methods for producing fumed silica are well known. For example, 1
Oamp <D U.S. Patent J@ dated October 5, 981
No. 308,286 describes a method for producing fumed silica by combustion of alkoxysilanes. According to this method, alkoxysilane is combusted to form heated silica particles, and then the combustion gas and fumed silica particles are passed to a heat exchanger. The combustion gases are then passed to a condenser which consists of a long series of tube connections wound at a steep angle. The purpose of this flocculator is to increase the size of fumed silica particles so that they can be separated by bag filters.

The combustion gas and the fumed silica particles are then passed through a series of cyclones to separate the fumed silica particles, and finally the combustion gas and remaining fumed silica particles are passed to a bag filter to separate the residual fumed silica particles from the combustion gas. After passing the combustion gases through the bag filter assembly, the combustion gases are discharged to the atmosphere. If the fumed silica particles collected from the cyclone and bag filter are not sufficiently dried, they are sent to a calcining furnace where the fumed silica particles are
Moisture is removed by heating to temperatures above 0.degree. C. for various times. After being removed from the kiln, the fumed silica particles have α0
It is preferred to have a moisture content in the range of 1 to 1.0% by weight.

At that point, the fumed silica particles typically have a density of 1 to 2.5 bonds/cubic foot. These particles are then desirably fed into a densifier to increase their density to 4-5 bonds/cubic foot. It is desirable for fumed silica to have a high density for most applications when used as a reinforcing filler in silicone elastomer compositions. Furthermore, a cyclone can be attached to the calcining furnace and the gases discharged from the calcining furnace can be fed into this cyclone in order to remove as much fumed silica from these gases as possible. The recovered silica can be returned to the calcining furnace to maximize the recovery rate of fumed silica particles.

The bag filters described above generally consist of several bags, each bag consisting of a Teflon matrices having small holes through which the combustion gases can pass through the bag. Gas flows through these bars and the fumed silica becomes embedded in the Teflon matrix. 1 minute depending on the specific procedure, i.e. the amount of fumed silica produced and the number of bag filters in the processing equipment.

Every 2, 3 or 4 minutes, the flow of combustion gases to the bag filter is stopped. The bag filter is then blown with an inert gas, such as nitrogen, countercurrently to the flow of combustion gases to desorb the fumed silica particles from the Teflon matrix and cause them to fall to the bottom of the filter where they are collected. Then, send it to the roasting furnace.

By using such a series of cyclones and bag filters, it is possible to provide a process in which up to 97%, preferably up to 99%, of the fumed silica formed in the burner furnace can be recovered. However, this method has many disadvantages. In particular, the use of bag filters has a number of disadvantages. It should be noted that it is desirable for the bag filter to have a series of cyclones communicating with the filter to effect proper separation of the fumed silica particles. Otherwise the bag filter will not work properly.

That is, if a cyclone is not used, an excessively large amount of fumed silica will be trapped in the bag in a short period of time, and therefore inert gas must be blown into the bag filter frequently. Furthermore, in order to separate the fumed silica particles as completely as possible, a high recovery rate of the fumed silica particles, preferably a high recovery rate of the fumed silica particles as described above, i.e. 97-
It is necessary to equip a cyclone to achieve a recovery rate of 99%. Another problem with the use of bag filters is that when the bag is filled with silica particles, cleaning the bag can be extremely difficult and requires a special cleaning process that is time consuming. Additionally, over time, the fabric of the bag tends to wear out and must be replaced.

However, in the process of producing fumed silica, the use of bag filters to separate fumed silica particles is generally not as efficient as desired.

Additionally, such methods are expensive in that they require the use of additional equipment, such as cyclones and condensers, to accomplish the separation step and that the bags in the bag filters need to be replaced periodically. It was something. C! It should be noted that the aforementioned method of producing heated silica, such as that described in U.S. Pat. However, the most common method for producing fumed silica is by combustion of chlorosilanes, such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, silicon tetrachloride, and other chlorosilanes. These chlorosilanes are very inexpensive and commonly available starting materials for the production of fumed silica. In addition to the differences described in Camp U.S. Pat. Chills in that it must be removed from the combustion gas along with other corrosive impurities. To achieve this purpose, various means are used, such as scrubbers, caustic towers, etc., i.e. after passing the combustion gases through a bag filter, these gases are then passed through a scrubber and then into a caustic column. It is described that the combustion gas is fed into a column to remove corrosive impurities from the combustion gas, after which the combustion gas is discharged to the atmosphere.

Additionally, there are other differences in the method of producing chlorosilanes and the method of burning chlorosilanes to produce heated silica that distinguish them from the method described in Camp U.S. Pat. Since it has nothing to do with the method, I will omit it here.

Sintered metal filters are known to those skilled in the art and are described, for example, in US Pat. No. 4,328,353 to 5 hah. This patent describes the use of a sintered metal filter to remove catalyst particles from the product stream in the production of chlorosilane by a direct process so that the silicon and copper catalyst particles can be recycled to the reactor. Disclosed. However, to the best of the inventor's knowledge, sintered metal filters have never been used in the process for producing fumed silica as contemplated by the present invention.

One object of the present invention is to provide an efficient method for producing heated silica that uses a sintered metal filter to separate fumed silica particles formed during the production of heated silica from combustion gases. Another object of the present invention is to recover fumed silica particles from combustion gases with a recovery rate of greater than 99.5%, preferably greater than 9999%, by using a sintered metal filter in a process for producing fumed silica. The object of the present invention is to provide an efficient method for separating fumed silica from gas.

Still another object of the present invention is to provide an optimal method for separating fumed silica particles from combustion gas, using a sintered metal filter in place of a cyclone and bag filter, and producing fumed silica by combustion of chlorosilanes. .

Furthermore, it is an object of the present invention to provide an efficient method for the production of fumed silica by combustion of alkoxysilanes, in which the separation of heated silica particles from the combustion gases is optimized by the use of sintered metal filters. It is something.

These and still other objects of the present invention are achieved by the following disclosure.

SUMMARY OF THE INVENTION In accordance with the foregoing objects, the present invention provides the following steps: (a) combusting silanes in a burner furnace to produce heated silica particles and combustion gas; (b) passing the combustion gas and heated silica particles through a sintered metal filter; A method for producing heated silica is provided which uses a sintered metal filter to separate heated silica from combustion gas, comprising the steps of: transporting the heated silica to a combustion gas to separate the fumed silica particles from the combustion gas and collecting the fumed silica particles.

The silanes used as raw materials in the present invention may also be chlorosilanes or U.S. patent application No. 50a28 of Camp.
Alkoxysilanes such as those disclosed in the specification of No. 6 may also be used.

The main condition when operating the sintered metal filter is that the temperature of the combustion gas introduced into the sintered metal filter is preferably not lower than 135°C, particularly preferably not lower than 150°C.

Still, it is preferred that the pressure drop of the combustion gases as they pass through the sintered metal filter does not exceed 1 pound per square inch. Additionally, the sintered metal filter must be well electrically grounded and that excessive static charge does not build up on the filter components. Otherwise, it may be very difficult, and in some cases impossible, for the countercurrently blown gas to desorb the fumed silica particles from the metal filter cartridge. The above and other conditions regarding the operation of sintered metal filters in the production of heated silica will be explained in more detail below. As already mentioned, the method of the present invention is not limited only to the use of two sintered metal filters in the separation of heated silica from the combustion gases when the fumed silica is produced by combustion of chlorosilanes;
Sintered metal filters can be used to separate fumed silica formed when the heated silica is produced by combustion of any silane.

The sintered metal filter used in the method of the invention consists of a metal container or nosing unit and a metal tube placed inside it. The metal tube has a matrix with small pores or small openings that allow gas to flow through but do not allow most heated silica particles or other solid materials to pass through. This filter passes a gas containing solid particles into a metal container and then through small holes in a metal tube or filter frame where the solid particles are embedded in the surface pores.
The process is such that the gas is removed through small holes in the filter frame and through the hollow filter core to other equipment in the process chain. The force required to pump the combustion gases into and out of the sintered metal filter is provided by the pressure drop from the inlet to the sintered metal filter to the outlet of the hollow filter casing. This pressure difference serves to force gas through the hollow filter and out through the central ring. Sintered metal filters are preferably constructed from an alloy such as Inconel, which is an alloy of chromium, nickel, and iron. Materials or alloys of this type are salts that may be present in the combustion gases7
Resistant to decomposition and deterioration by corrosive vapors such as arsenic or chlorine.

It should be noted that it is desirable that the sintered metal filter be operated at favorable operating conditions.

If the filter is not operated under favorable operating conditions, the small pores in the filter frame can become blocked by fumed silica particles that melt with the metal. If such a blockage occurs, it may be necessary to shut down the entire process and remove the filter from the process stream. It is then necessary to remove the sintered metal filter rod from the filter housing and clean the filter by immersing it in a bath of caustic solution, such as a solution of sodium or potassium hydroxide and water. This is because the fumed silica particles become welded or embedded in the pores of the filter and it is necessary to remove the solid particles from the filter by immersing them in a caustic solution. In any case,
After extended use, it may be necessary to clean or treat the filter as described above to maintain the sintered metal filter at peak efficiency. It should be noted that there is little maintenance required for such sintered metal filters other than periodic cleaning and replacement of the filter rods which may be necessary after various periods of use. Furthermore, during the treatment process, the process flow from the sintered metal filter is interrupted after the sintered metal filter has been operated for a period of about 1 to 3 or 4 minutes, and the flow is countercurrent to the previous combustion gas flow. It is necessary to backflow hot gas (at a temperature above the dew point of the combustion gases) to the combustion chamber. This countercurrent gas flow will blow the fumed silica particles out of the filter and cause them to be collected in a hopper at the bottom of the filter assembly.

The fumed silica is then sent to a kiln or subjected to storage or any suitable treatment. This gas back-blowing time is usually a short time on the order of minutes. This process may be carried out by backblowing operations with the process completely shut down or by switching the combustion gas flow from one series of sintered metal filters to another series, i.e. one series of sintered metal filters. The sintered metal filters (here series means - or more rows of sintered metal filters operated in parallel) can be used with any non-condensable gas to remove fumed silica from the filter tubes. Alternatively, a separate series of sintered metal filters may be operated to filter combustion gases from the combustion furnace while receiving back-blowing of inert gas. Using the latter method, the process can be carried out substantially continuously without interruptions during which the process is shut down for backblowing operations to desorb the fumed silica powder from the filter.

There are several requirements for the desired operation of sintered metal filters. A very desirable and necessary condition in the operation of the filter is the lower temperature limit at which the mixture of combustion gas and fumed silica powder is introduced into the filter. Additionally, it is generally desirable that the temperature at which the combustion gases and fumed silica are introduced into the inlet of the sintered metal filter is at least 155°C, more preferably at least 150°C or higher. The reason is that when the temperature of the combustion gas is lower than the above limit value, especially 135℃
If it is too low, the gas will cause condensation of the various vapors on the sintered metal filter, thus leading to a filling of the condensate to the rapid agglomeration of the product fumed silica onto the wet surface. Furthermore, as a result of condensation of such gases, the heated silica particles will tend to form a paste on the metal in the filter and block the openings or pores in the filter.

Although the filter can be operated at temperatures below 135°C,
Under such conditions, operation of this process step may have to be interrupted and the filter must be cleaned with a caustic solution as described above, which may shorten the effective operating time in the sintered metal filter. points must be recognized. Furthermore, the higher the temperature of the combustion gases, the less chance there will be of isolated cold spots in the filter causing vapor condensation.

Another necessary condition in the operation of sintered metal filters is that a pressure drop occur across the filter. in general,
The pressure drop should not exceed 2.5 pounds per square inch, more preferably 1.0 pounds per square inch. If the pressure drop is too large, the flow rate of gas through the filter will be very high, but the large pressure drop through the filter will cause the pores in the filter tube to collapse as the silica collides with the metal surface. will tend to become occluded and make it more difficult for heated silica particles to be blown back through the holes in the filter tube.

One requirement during operation of sintered metal filters is that the filter must be properly grounded. If the filter is not properly grounded, an excessively high electrostatic charge will build up on the filter and as a result °fumed silica particles will tend to stick on the filter, so these particles will be removed during the blowback operation. It will not be blown away and therefore will not be collected. Therefore, the sintered metal filter is preferably grounded such that the electrical ground has a ground resistance of less than 1.0 ohm, preferably less than 0.5 ohm.

If the filter is so grounded, high static electricity will not build up in the filter and any static electricity that develops will be quickly dissipated.

Therefore, there are three main conditions for efficient operation of filters, and within the general ranges described above, these conditions are such as to yield the best performance of the sintered metal filter for each particular process step. can be changed to If the desired range of these conditions is found,
It should be noted that the ground resistance preferably ranges in value from 01 to less than a5 ohms. The operating temperature of the filter should be in the range 150° to 300°C and the pressure drop should be between 0.1 and 300°C while the combustion gases pass through the filter.
Preferably it should be 1.0 bonds/in².

There are other conditions that are desirable for the filter to operate at maximum efficiency. One measure of efficiency is to measure flow velocity. The higher the flow rate without clogging the filter, the higher the efficiency. Regarding the average surface velocity of the filter, to achieve maximum efficiency
The surface velocity of the combustion gas passing through the hole in the tar frame is 1 to 6.
Preferably it is 1 foot/minute. Another way to define the flow rate is to express it by the number of branes of fumed silica removed per minute and per square foot of filtration area. Such filtration rates can vary from 20 to 120 grains of heated silica per cubic foot of filtered air per minute, depending on the particular filter type and its surface area and the number of filters in the unit.

As for the throughput of the filter, this will also vary depending on the size of the filter and, for any particular series of filters, the number of filters in the series. Therefore, for a typical series of filters, the filter capacity ranges from less than 10 grains of fumed silica per cubic foot of combustion gas to about 200 to 300 dalenes of fumed silica per cubic foot of combustion gas. It fluctuates. As already stated, the range for the surface velocity of the filter, the filtration rate in branes per square foot of surface area per minute, and the throughput of the filter in branes per cubic foot of combustion gas is: It may vary depending on the size of the filter and the number of filter rods in the filter and the number of sintered metal filters in a series of sintered metal filters.

The above numbers are for a filter rod that is 5 feet long and has an overlapping area of approximately 62.2 square feet.

However, as previously mentioned, these dimensions and capabilities may vary from filter to filter depending on how the filter is designed and the amount of lacrimal area formed therein. Furthermore, for maximum efficiency operation of the filter and for the longest period of use of the filter before it becomes necessary to clean or disassemble the filter and to clean or replace the filter rods, the measures described above occur through the filter during operation. The above-mentioned limitations apply to the pressure drop and the inlet temperature 4 of the combustion gases introduced into the filter. In addition to these two limitations, grounding the sintered metal filter is also a necessary measure.

When these three requirements are within the ranges described above for the fumed silica manufacturing process, the sintered metal filter can be operated with good efficiency with minimal downtime for cleaning or changing filter rods. Dew. This not only results in more efficient production of heated silica;
Savings in filter maintenance costs would also be achieved. Although the filter can be operated outside of the limiting ranges - or more of the above limitations, only shorter periods of operation are possible under these conditions, after which the filter must be removed from the operating line and cleaned. In some cases it may be necessary to replace it.

The deviation and degree of deviation from the above-mentioned triad characteristics, i.e. the required grounding, pressure drop and temperature of introduction of the combustion gases into the filter, will determine the degree of reduction in operating time, the frequency of cleaning required, etc. Dew.

On the other hand, within the specified ranges already mentioned, experimentation may be necessary to determine the optimum conditions for each particular heated silica manufacturing process. However, regardless of whether optimal conditions are obtained, good operating conditions will be achieved in the heated silica manufacturing process as long as the sintered metal filter is operated at conditions within the above ranges.

A preferred method of operating a sintered metal filter in the present invention will now be described. Preferably, the heated silica is formed by combusting hydrogen, natural gas, and silane with combustion air in a combustion furnace. The silane may be an alkoxysilane or other type of silane, but most preferably the silane is a chlorosilane.

Chlorsilane is monomethyltrichlorosilane, dimethyldichlorosilane, and trimethylchlorosilane.

It can be any chlorosilane, such as methylhydrogen dichlorosilane and tetrachlorosilane and other chlorosilanes. It is preferred to use tetrachlorosilane, methyltrichlorosilane, and methylhydrogendichlorosilane to produce the -C-heated silane because they are inexpensive and are the most readily available silanes. Other methylchlorosilanes and phenylchlorosilanes, as well as vinylchlorosilanes, can be used in the production of fumed silica, but are preferred for the purposes of the present invention because they are more expensive and have other uses. Not used. Furthermore, among the methylchlorosilanes, methyltrichlorosilane, methylhydrogensilane, and tetrachlorosilane have limited uses as such and are less useful in the production of heated silica than other silanes. These are preferably used for the purposes of the present invention since they are economically advantageous.

Additionally, it should be noted that alkoxysilanes and other types of silanes may also be used in the preparation of fumed silica, as described in the process of Camp US Pat. No. 308,286. However, although these methods have advantages, it is generally more expensive to use other types of silanes than chlorosilanes in the production of fumed silica, and the use of chlorosilanes, which are more readily available in the industrial market, is generally more expensive. Use is preferred.

Therefore, silanes are selected, vaporized, and then combusted in a combustion furnace with air and hydrogen gas (or some other oxidizing agent). Preferably, the chlorosilanes are first heated to a temperature above 90°C, preferably between 90°C and 150°C to vaporize them, and then they are heated to a suitable combustion temperature. In order to obtain fumed silicon particles with maximum structure and particle size, the combustion furnace
It is preferred to operate at a temperature of 1600-1900°C, more preferably 1600-1900°C. Air for cooling the combustion gases is then introduced into the bottom of the combustion furnace so that the combustion gases can be processed in a conventional heat exchanger. Combustion gas is 400-600
Preferably it is cooled to a temperature of °C. Next, huh?
The cooled gas is passed through a heat exchanger. This heat exchanger can be utilized for heating any fluid used in an operating chemical device. For example, such a heat exchanger converts water to steam, which can be used for various purposes that conventionally utilize steam. A heat exchanger is not required. Any means of cooling the combustion gases so that they can be processed in the sintered metal filter may be used, such as sufficient cooling air.

By this means the temperature of the fumed silica combustion gas is reduced to 300°C or less. There are no critical limits on this temperature either. The desired cooling temperature of the combustion gases is simply the temperature at which the combustion gases can be processed in a filter after passing through a heat exchanger or any other device. Moreover, this temperature reduction is the preferred temperature for reducing the temperature of the combustion gases after they have been quenched in the lower part of the combustion furnace. The combustion gases may then be passed to a condenser to increase the particle size of the fumed silica. however,
This is not essential to the invention.

The sintered metal filter will separate at least 995% of the silica particles even if the particle size of the fumed silica particles is not increased by a coagulator. therefore,
The present invention may eliminate the need for and expense of operating a condenser, which is another advantage of the method of the present invention.

Then, the fumed silica particles and combustion gas are usually 135
Preferably, it is delivered to the inlet of the sintered metal filter assembly at a temperature in the range from ' to 300<0>C. As already mentioned, the combustion gases should have a desired lower inlet temperature limit at the inlet of the sintered metal filter. The fumed silica particles collected in the sintered metal filter may then be stored or fed to a calcining furnace, essentially a drying oven, operated at temperatures above 700°C to remove the fumed silica particles present in the fumed silica. A treatment may be performed to remove the resulting moisture and acid. The water content of the fumed silica is preferably 0.01 to 1% by weight. If the heated silica particles need to be further densified after processing in the calciner, they can be fed to a densifier to increase the particle size and density. Such a densification device may be as simple as two rollers, either on a conveyor belt or without a conveyor belt, through which the fumed silica particle mass is squeezed to achieve its purpose. By this means, the density of fumed silica can be increased to 4-5 pounds per cubic foot. This density level is desirable for heated silica particles to be used as fillers in the manufacture of silicone elastomer compositions.

The combustion gas from the sintered metal filter containing hydrogen chloride gas can then be passed to a scrubber to separate the aqueous solution from the gas and HC, which can be used as needed in chemical equipment. On the other hand, the gas purified by the scrubber is then passed to another scrubber to further remove other impurities from the gas, including chlorine impurities.

By that point, the gas has a temperature equal to atmospheric temperature and can be vented to the atmosphere. , the σ method of the present invention described above allows silica to be removed from the combustion gas such that generally at least 995% and preferably 9999% of the fumed silica is removed from the combustion gas. Fumed silica recovered from combustion gases can be used for various filler purposes. As shown in the methods described above, the filter may consist of a single filter or a series of filters used intermittently. That is, while one filter or series of filters is being filtered, another filter or series of filters is subjected to blowback treatment, whereby the fumed silica particles retained on the filter rods are removed. Will be detached. The desorbed fumed silica particles are collected at the bottom of the filter and can be used as described above. Additionally, it should be noted that with the use of sintered metal filters, it is not necessary to use a cyclone to achieve the aforementioned recovery rates as is the case with bag filters.

Next, a preferred embodiment of a method for producing fumed silica using a sintered metal filter to recover fumed silica particles from combustion gas according to the present invention will be described with reference to FIG. 1, which schematically shows the process. Hydrogen is introduced through a tube 12, natural gas is introduced through a tube 14, and combustion air is introduced through a tube S6 into the end of the burner furnace 10 where the burner flame is present, that is, into the nozzle end. As already mentioned, the chlorosilane is preferably heated to an elevated temperature in a vaporizer 22, whereupon the heated chlorosilane is fed via tube 24 to the upper end 26 of the combustion furnace 10.

The fumed silica particles and combustion gases formed therein are then forced under pressure toward the bottom 32 of the combustion furnace 10. Cooling air is supplied via tubes 30 to the bottom 32 of the combustion furnace 10, where the temperature of the combustion gases is cooled to below 900C, preferably in the range 400-600C. However, if it is not desired to conserve heat through the use of a heat exchanger, sufficient cooling is required to reduce the temperature of the gases to 300°C or less so that the combustion gases can be treated in a sintered metal filter. Air or other means can be used. The combustion gas is preferably 400
~600°C and then the combustion furnace 10
through the bottom 32 and tubes 34 to a heat exchanger 36. Water is fed into heat exchanger 3 through pipe 40 and into pipe 4
2 and is discharged as process steam or hot water.

The gas, cooled to a temperature of 500° C. or less, but not lower than 135-150° C., is then delivered from heat exchanger 36 and passed through tube 50 to sintering, which can be carried out with a single filter or a series of filters. It is passed to the crystalline metal filter assembly 64. The collected fumed silica is then transferred to tube 6.
6 and is sent to a firing furnace 67. Calcining furnace 67 is used to reduce the water content of the heated silica to a desired level so that it can be used as a filler in silicone nidistomer compositions. Pure nitrogen or a mixture of nitrogen and air is passed through tubes 68, 69 and 70 to the kiln 67 along with water vapor to aid in the removal of moisture. Calcining furnace 67 is a rotary furnace operated at a temperature of 100° C. or higher, preferably about 700° C., to drive out moisture in the silica. The gas containing moisture and some suspended fumed silica particles is then passed through pipe 71 to cyclone 72 where it separates out most of the fumed silica particles and returns these particles to firing furnace 67 via pipe 76.

Gas from cyclone 72 exits to the atmosphere via pipe 74. Since it is undesirable for hydrogen chloride to be included in the filler, care should be taken to pass water vapor into the calciner 67 to aid in the complete expulsion of any hydrogen chloride remaining in the fumed silica particles.

The heated silica is sent from the firing furnace 67 to the densification device 76 via a tube 75. A densifier 76 increases the density of the heated silica to a range of 4 to 5 pounds per cubic foot. Densities in this range are preferred for fumed silicas to be used in silicone elastomer compositions.

The densification device 76 may consist of simply two rollers or a series of rollers disposed on a conveyor belt to force the fumed silica into small voids and increase its density, as is well known to those skilled in the art. . Fumed silica from densification device 76 is sent to a reservoir via pipe 77.

After removing almost all of the fumed silica with the sintered metal filter, the combustion gases exiting the filter are then sent to scrubber column 82 via tube 80. As already explained, the back-blown gas passes through the pipe 83 to the filter 6.
4' is sent intermittently. The gas is then washed with an aqueous Hct solution which is collected at the bottom 84 of column 82 and recycled to the top 100 of column 82 via line 85, pump 86 and lines 8B, 90, 92 and 94. When water is needed in tower 82, it is passed through pipe 102 to pipe 88. The hot aqueous solution is approximately 32% at the bottom 84 of the column 82.
After being concentrated to a concentration of HC1, tube 106 and pump 1
08 and further via tube 110 for any purpose for which it is desired to use the Hot.

Exhaust gas from column 82 is routed through tube 120 from the top 100 of the column.
and caustic scrubber 12 via blower 121
6 to the bottom 122. Blower 121 is necessary to create a pressure differential within the system to force combustion gases through the system. Caustic alkali is introduced into the top 128 of the caustic scrubber 126 via a tube, 130, which passes through the tube 120 to the top 128 of the caustic scrubber 126.
The combustion gases flow countercurrently to the combustion gases entering the bottom 122 of the combustion chamber.

The caustic solution is collected in caustic scrubber 126 for impurities such as chlorine impurities in the form of Na0C4 and other compounds and disposed of via line 140 in any suitable manner. Top 12 of caustic scrubber 126
The combustion gases exiting via 8 are then removed via pipe 150. These gases may also be passed through a filter (not shown) before being released into the atmosphere. In most sites it will not be necessary to use a filter.

As a result of using this method, it is possible to vent to the atmosphere combustion gases which have been cleaned of most impurities and are therefore suitable for release into the atmosphere. Furthermore, it is possible to recover the HCt gas and use it in any manner in processing equipment requiring an aqueous HC1 solution or even sell it if desired. In addition, as mentioned above, the use of sintered metal filters generally removes 99% from the combustion gases.
% heated silica, preferably at least 99.9% heated silica.
5% of hiemed silica can be recovered. Sintered metal filters are more economical to operate as they do not require the use of cyclones and require less maintenance than bag filters.

In order to teach those skilled in the art in detail the method of the present invention, typical operating conditions are shown in Figure 1 for the production of heated silicate forces using an apparatus similar to that shown in Figure 1 and using a sintered metal filter. Shown in the table.

The apparatus and method are similar to those described above for the preferred embodiment of FIG. These conditions listed in Table 1 are representative and illustrate the operating temperatures and pressures and filter capacity of the sintered metal filter used in the process. Of course, these are not intended to equally limit the invention.

Table 1 △ P Entrance Exit Start End Bond AI 155 120
2.5 142 170 130
0. 6 13.83
195 140. 1. 8
16.24 175 m55.
8. 7 12.65 27[
! 175 2.2 2.3
．． 11.46 225 155 1.7
2.5 11.57 260 1
40 1.5 1.5 11.
48 370 200 1.0
9 145 140. 5. 5~
．． 8 1310 150 140. 4
．． 5-. 6 14◆ 11 150 125. 6-. 9 1.8
-1.6 1412 140 130. 9-
15 1.6-2.4 1413 m40
130 2-2.5 2.8-5.5 14
1.47 88.7 60.41
．． 56 81,? 52.5
1.47 75.6 50.12
．． 46 23.1 9.42.
37 25.8 10.92.
49 24.9 10.21.4
7 102. ．． 6 69. B1.4
7 61.0 41.51.
50 77.2 51.51.
6j 70.2 45.6fi
1 75.8 45.8

[Brief explanation of the drawing]

FIG. 1 is a process diagram illustrating the preferred method of the present invention using a sintered metal filter to separate fumed silica particles from combustion gases. 1a... Combustion furnace, 12... Hydrogen introduction pipe, 14...
Natural gas introduction pipe, 16... Combustion air introduction pipe, 22.
... Silane vaporizer, 24... Silane introduction pipe, 56...
・Heat exchanger, 64...Sintered metal filter assembly, 6
7゛...Kilning furnace, 72...Cyclone, 76...
Densification device, 82...Scrubber tower, 121...Blower, 126...Caustic alkali scrubber.

Claims (1)

[Claims] 1. The following steps: (1) Burning silanes in a burner furnace to produce heated silica particles and combustion gas: (b) Passing the combustion gas and fumed silica particles to a sintered metal filter. separating the heated silica particles from the combustion gas; and (C) collecting the heated silica particles. 2. Further passing the combustion gas from the sintered metal filter to a water scrubber to remove hydrogen chloride from the combustion gas and form an aqueous stream of HCl, and removing a purified second combustion gas stream from the scrubber. The manufacturing method according to claim 1, which comprises the step of: 3. The flow of combustion gases and fumed silica particles from the burner furnace is heated to 155°C before passing through the sintered metal filter.
The manufacturing method according to claim 1, wherein the temperature is controlled to be between 300°C and 300°C. 4. The method of claim 1, wherein the combustion gas and fumed silica particles flowing through the sintered metal filter are at a temperature in the range of 155°C to 30°C. 5. The gas entering the sintered metal filter is at least 135
A method according to claim 1, wherein the temperature is between 150°C and 150°C. 6. The method of claim 1, wherein the pressure drop across the sintered metal filter does not exceed 2.5 pounds per square inch. 7. The effective electrical grounding resistance of the sintered metal filter is t
The manufacturing method according to claim 1, wherein the resistance is less than 0 ohm. 8. The manufacturing method according to claim 1, wherein the surface velocity of the combustion gas and heated silica particles passing through the sintered metal filter can vary in the range of 1 to 6 feet/min. 9. The manufacturing method according to claim 1, wherein the silane to be converted into silane by combustion in a burner furnace is a chlorosilane. 10. Chlorosilanes are methyltrichlorosilane. dimethyldichlorosilane, methylhydrogendichlorosilane,
10. The method according to claim 9, which is selected from tetrachlorosilane and mixtures thereof. 11. The manufacturing method according to claim 1, wherein the silane to be converted into fumed silica by combustion in a burner furnace is an alkoxysilane. 12. The flow of combustion gas to the sintered metal filter is interrupted, and the gas is blown countercurrently to the flow direction of the combustion gas into the filter to blow out and collect the heated silica particles from the filter rod inside the filter. The manufacturing method according to claim 1, further comprising the step of: 15. A process for producing fumed silica that includes a step of burning silanes in a burner furnace to produce fumed silica particles and combustion gas, in which the combustion gas and fumed silica particles are passed through a sintered metal filter to combust the fumed silica particles. A process for producing fumed silica from silanes, which recovers at least 99.5% of the produced fumed silica, characterized by separation from the gas and a temperature of at least 135° C. of the combustion gas and fumed silica particles entering the filter. 14. Pressure drop through sintered metal filter is 2.5
13. The method of claim 12, which is less than pounds per square inch. 15. The effective electrical ground resistance of the sintered metal filter is 1
．． Claim 18 is smaller than 0 ohm.
Manufacturing method described in section. 16. The manufacturing method according to claim 12, wherein the silane to be converted into fumed silica by combustion in a burner furnace is an alkoxysilane.