JP2023108363A - Method of recovering chlorosilanes - Google Patents

Abstract

To develop a method of further suppressing deposition of aluminum chloride scale in a thin film evaporation device, upon recovering chlorosilanes by feeding an aluminum chloride-containing distillation residual liquid of liquid chlorosilanes.SOLUTION: The method of recovering chlorosilanes includes cooling distillation residual liquid obtained by distillating liquid chlorosilanes containing aluminum chloride, with a liquid temperature of 50°C or higher to a liquid temperature of 40°C or lower, and subsequently feeding the cooled distillation residual liquid to a thin film evaporator such as an agitation-type thin film evaporator to evaporate and recover chlorosilanes.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for recovering chlorosilanes, more specifically, a chlorosilanes liquid containing aluminum chloride produced by reacting a gas containing chlorine or hydrogen chloride or silicon tetrachloride and hydrogen with metallurgical grade silicon. from, to a method for recovering chlorosilanes.

Chlorosilanes obtained by chlorinating or hydrochlorinating metallurgical grade silicon are obtained by chlorinating or hydrochlorinating aluminum, which is usually contained in metallurgical grade silicon in an amount of about 0.01 to 10% by weight. Therefore, it contains aluminum chloride as an impurity. Therefore, aluminum chloride becomes an unfavorable impurity in the manufacturing process of semiconductor-grade high-purity silicon and photovoltaic-grade silicon, so it is necessary to separate and remove it from chlorosilanes.

Aluminum chloride has a higher boiling point than useful chlorosilanes such as trichlorosilane (hereinafter referred to as TCS) and silicon tetrachloride (hereinafter referred to as STC). It is common to collect the chlorosilanes from the chlorosilanes liquid by distillation and separate them as a distillation residue. This distillation residue is properly withdrawn from the lower part of the distillation column and disposed of.

However, useful chlorosilanes such as TCS and STC are still contained in such a waste distillation residue, usually in an amount of about 95% by weight. Therefore, useful chlorosilanes are preferably recovered by re-evaporation, and thin-film evaporation has been proposed as an effective method (see Patent Document 1). Here, in the method using this thin film evaporation, the chlorosilanes liquid is supplied to the thin film evaporator because the distillation residue discharged from the chlorosilanes distillation column has a high temperature and is transferred as it is. , under a high liquid temperature of 55°C.

Japanese Patent Application Laid-Open No. 2001-261324

By the way, the aluminum chloride contained in the chlorosilanes liquid has the property of being easily precipitated due to concentration fluctuations. In particular, when the chlorosilanes are recovered by distillation, the concentration of the aluminum chloride in the bottom liquid becomes high due to concentration, so that the precipitation of the aluminum chloride becomes particularly severe in the distillation residue extracted from the bottom liquid. For this reason, in recovering chlorosilanes from the distillation residue by evaporating them, deposition of scale on the inner wall of the device becomes a problem. The deposition of scale inside can be considerably reduced.

This is based on the fact that even if the concentration of aluminum chloride exceeds the deposition limit of 2% by weight in the chlorosilanes solution, it is difficult for aluminum chloride to deposit as a solid matter for about 10 minutes thereafter. That is, if the chlorosilanes are evaporated by thin film evaporation, the staying time of the chlorosilanes liquid in the apparatus can be shortened, so that the effect of suppressing the deposition of aluminum chloride as scale is exhibited (Patent Document 1). [0015] [0037]).

Therefore, even in the method of applying thin film evaporation, which is highly effective in suppressing the deposition of aluminum chloride scale, the deposition suppressing effect is still insufficient from the viewpoint of implementing it on an industrial level. That is, according to the above method, the inner wall heating surface where the chlorosilanes evaporate violently in the chlorosilanes liquid, and the rotating blade surface where centrifugal force is applied in the case of a stirring type thin film evaporator, aluminum chloride scale Although the deposition of the scale was suppressed to a low level, the deposition of the scale was still not sufficiently suppressed on the adjacent lower surface of the heating zone where such thin film evaporation takes place. In particular, when the thin film evaporator is a stirring type, the bearing portion that supports the lower end of the central rotating shaft to which the rotating blades are connected is often provided with a plurality of reinforcing ribs in the radial direction. Since centrifugal force is not applied to the rib surface, scale deposits and grows more easily, and when the thin film evaporation is operated for a long time, the inner space of the apparatus is clogged.

Against the above background, the present invention develops a method for highly suppressing the deposition of aluminum chloride scale in the apparatus when the distillation residue is subjected to a thin film evaporation apparatus to recover chlorosilanes. That's what it is.

In view of the above problems, the inventors of the present invention have continued to earnestly study. As a result, the present inventors have found that the above problems can be solved by cooling the distillation residue to a liquid temperature of 40° C. or less when it is supplied to the thin film evaporator, and have completed the present invention. .

That is, the present invention relates to a distillation residue cooling liquid obtained after cooling a distillation residue having a liquid temperature of 50 ° C. or higher to a liquid temperature of 40 ° C. or lower, which is obtained by distilling a chlorosilanes liquid containing aluminum chloride. is provided to a thin film evaporator to evaporate and recover the chlorosilanes.

The present invention also provides a method for producing chlorosilanes by distilling a chlorosilanes liquid containing aluminum chloride produced by reacting a gas containing chlorine or hydrogen chloride or silicon tetrachloride and hydrogen with metallurgical grade silicon. In the above, there is also provided a method for producing chlorosilanes, characterized in that the distillation residue having a liquid temperature of 50° C. or higher obtained by the above distillation is subjected to the above method for recovering chlorosilanes.

According to the method of the present invention, it is possible to continue the thin film evaporation of the distillation residue obtained by distilling the chlorosilanes liquid containing aluminum chloride while highly suppressing scale deposition in the apparatus. . As a result, it is possible to stably recover chlorosilanes for a long period of time.

FIG. 1 is a process chart showing a representative embodiment of the method for recovering chlorosilanes of the present invention.

The chlorosilanes liquid to be subjected to the recovery method of the present invention is not limited at all as long as it contains aluminum chloride, but in general, metallurgical grade silicon with a purity of about 90 to 99%, chlorine, hydrogen chloride, or hydrogen. A representative one is obtained by condensing a chlorosilane mixed gas produced by reacting with silicon tetrachloride or the like.

In the above _{chlorosilanes} synthesis reaction, _the types _and production ratios of chlorosilanes _generated differ depending on the reaction raw materials and reaction conditions. are chloromonosilanes. In addition to these, dimeric chlorosilanes such as pentachlorodisilane (Si ₂ HCl ₅ ) and hexachlorodisilane (Si ₂ Cl ₆ ), and higher chlorosilanes may also be included.

As described above, metallurgical grade silicon usually contains about 0.01 to 10% by weight of aluminum, and aluminum chloride is added to the chlorosilane solution by chlorinating or hydrochlorinating it. contained. The aluminum chloride content varies depending on the aluminum content in the metallurgical grade silicon used, reaction conditions for producing chlorosilanes, and the like.

More specifically, the method for producing the aluminum chloride-containing chlorosilane solution used in the present invention includes the following method. For example, metallurgical grade silicon powder and a chlorine-containing gas are subjected to a chlorination reaction at 100°C or higher, generally 100 to 500°C, metallurgical grade silicon powder and a hydrogen chloride-containing gas are subjected to a chlorination reaction at 250°C or higher, generally 250 to 450°C. or a method of hydrochlorinating a mixed gas of metallurgical grade silicon powder, STC and hydrogen at a temperature of 400 ° C. or higher, generally 400 to 600 ° C., etc. are generally known. ing.

In these reactions, gases to be reacted with metallurgical grade silicon can be mixed with each other and reacted, or can be mixed with a reaction inert gas such as hydrogen or nitrogen to react. be.

The chlorosilanes liquid obtained by condensing the chlorosilanes gas thus obtained usually contains 0.01 to 2% by weight of aluminum chloride. In addition to aluminum, metallurgical grade silicon, which is a raw material for producing the chlorosilanes liquid, usually contains metal impurity components such as iron and titanium. Since these are also chlorinated, the chlorosilanes liquid may contain chlorinated products thereof (iron chloride, titanium chloride, etc.). Also, the chlorosilanes liquid may contain fine silicon powder or the like.

The details of the recovery method of the present invention using such a chlorosilane liquid containing aluminum chloride as the liquid to be treated will be described with reference to the flow of FIG.

In FIG. 1, a known distillation column can be used as the distillation column (1). That is, the distillation column trays that are commonly used can be used without restriction. For example, regular packing, packed type filled with irregular packing, bubble cap type, perforated plate type, and the like can be mentioned.

The distillation column (1) may also have a reboiler. The reboiler may be of a type in which the periphery of the bottom of the distillation column is jacketed and directly heated, or may be of a type in which a heat exchanger is installed outside the bottom of the distillation column. Also, a method of installing a heat exchanger inside the bottom of the distillation column can be adopted.

As the heat exchanger, a shell-and-tube system is generally preferably used to increase the heat transfer area, but a corrugated tube system, an electric heater, or the like can also be used. If the chlorosilanes liquid stays in the heat exchanger to which the distillation energy is applied and the aluminum chloride is highly concentrated, it causes scaling. As a method in which the liquid hardly stays, a method using convection caused by heating, or a method using a pump or the like to forcibly flow the liquid can be suitably adopted.

The distillation column (1) is connected to a feed pipe (2) for the chlorosilanes liquid containing aluminum chloride, which is the liquid to be treated in the present invention. The supply point to the distillation column (1) may be any part, but it is more preferable to supply directly to the bottom of the distillation column in order to prevent contamination of the trays.

Here, since the boiling point difference between the chlorosilanes to be purified and the impurities such as aluminum chloride to be separated and removed is quite large, the distillation can be carried out satisfactorily without performing a particularly high degree of rectification, and the distillation operation can be maintained within a range. The reflux ratio may be about 0.1 to 1. The purified chlorosilanes are discharged from a purified chlorosilanes gas distillation pipe (3) connected to the top of the distillation column (1).

In the present invention, the distillation is carried out at a bottom liquid temperature of 50°C or higher, more preferably 70 to 150°C, most preferably 80 to 120°C. By setting the temperature of the column bottom liquid to 50° C. or higher in this way, the distillation of chlorosilanes can be made highly efficient. Since the temperature of the bottom liquid is 50° C. or higher, the distillation residue extracted from the bottom of the distillation column (1) through the distillation residue discharge pipe (4) is also at a high temperature of the same liquid temperature at the beginning of discharge. presents a state.

The concentration of aluminum chloride dissolved in the bottom liquid of the distillation column (1) is adjusted to be less than the saturation solubility at the temperature of the bottom liquid, thereby preventing aluminum chloride from precipitating into the bottom of the column and keeping the solution for a long period of time. This is preferable for continuing stable operation. For example, when the temperature of the bottom liquid is 50° C. or higher, the concentration of aluminum chloride in the bottom liquid is maintained in the range of 0.1 to 5.0% by mass, preferably 0.5 to 1.2% by mass. is preferred.

The most important feature of the recovery method of the present invention is that the distillation residue with a temperature of 50° C. or higher, which is extracted to the distillation residue discharge pipe (4), is not supplied to a thin film evaporator at such a high temperature. is cooled to a liquid temperature of 40° C. or less to increase the concentration of dispersed aluminum chloride precipitates before serving. By using the distillation residue cooling liquid for thin film evaporation in this way, it is possible to highly suppress the deposition of scale in the thin film evaporator. The reason for this is not necessarily clear, but the present inventors speculate that the following effects are involved.

In other words, the Al--Cl bond is substantially polarized as Al ^{+ --Cl-} , which results in a quasi-ionic bond of Al--Cl--Al--Cl in the aluminum chloride solid. Therefore, if the pseudoionic bond is stably crystal-grown, it exhibits a certain degree of resolubility in the chlorosilanes liquid as the liquid temperature rises. However, the re-solubility in this chlorosilanes liquid is due to the fact that the quasi-ionic bond undergoes crystal growth under unstable conditions, that is, the distillation of the chlorosilanes liquid in the thin film evaporation is explosive, and the precipitate In the production under conditions in which impurity metal elements such as Fe and Ti are likely to be taken in, the ionicity of Al and Cl is disturbed and greatly impaired. Thus, in the thin-film evaporation of the distillation residue, a large amount of aluminum chloride precipitates are produced at once with the explosive removal of the chlorosilanes, leading to the problem of scale deposition. it is conceivable that.

For this reason, in the present invention, prior to the thin film evaporation, the distillation residue is cooled to the above temperature, so that a certain amount of dissolved aluminum chloride is firmly crystal-grown under the above-mentioned stability, and the re-solubility is improved. It is contained as a precipitate having That is, when the distillation residue cooling liquid obtained in this way is subjected to thin film evaporation, when the liquid temperature of the treatment liquid rises on the heating surface of the apparatus, the evaporation of the chlorosilanes proceeds rapidly, while the chloride Redissolution in the chlorosilanes liquid residue also occurs in the aluminum precipitate. It is believed that the deduction by this re-dissolution greatly suppresses the formation of the aluminum chloride precipitates, and as a result, the problem of scale deposition in the equipment is significantly reduced.

Further, according to the present invention, if the dispersion concentration of aluminum chloride precipitates in the distillation residue is increased by the pre-cooling and subjected to thin-film evaporation, the aluminum chloride precipitates are not removed from the inner wall of the device that contacts the aluminum chloride from the beginning of the supply. The precipitate acts like an abrasive grain, and an effect of scraping off deposits on the wall surface is also produced. In particular, when the thin film evaporator is of a stirring type, the scraping effect is enhanced because the stirring applies pressure to the treatment liquid. Thus, in the present invention, it is presumed that the deposition of scale in the apparatus can be greatly suppressed in addition to the scraping effect of the precipitated aluminum chloride.

In the present invention, it is more preferable that the distillation residue is cooled to a liquid temperature of 30° C. or less from the viewpoint of suppressing the deposition amount of the aluminum chloride scale to a higher degree. On the other hand, the liquid temperature is preferably 5° C. or higher, because if cooling is carried out to a too low temperature, the temperature must be raised before being supplied to the thin film evaporator, resulting in inefficiency.

By cooling the distillation residue, the coarse portion of the aluminum chloride dissolved therein is precipitated. Therefore, in the obtained distillation residue cooling liquid, the concentration of solids composed of aluminum chloride precipitates is usually 0.1 to 5.0% by mass, which is preferably the same as the concentration of aluminum chloride in the bottom liquid of the distillation column. is 0.5 to 1.2% by mass. Here, the aluminum chloride precipitate solid content concentration in the distillation residue cooling liquid is measured by an ICP emission spectrometer for the evaporation residue after evaporating chlorosilane from the cake obtained by suction filtration using a membrane filter. It can be obtained by a method of quantifying aluminum chloride using In the distillation residue cooling liquid, when the solid content concentration of the aluminum chloride precipitates reaches a high concentration range, the liquid becomes slurry, but its fluidity is well maintained.

The method for cooling the high-temperature distillation residue to a liquid temperature of 40° C. or less is not particularly limited, and the distillation residue flowing through the distillation residue discharge pipe (4) is cooled inside or outside the vessel. Although it may be carried out by passing through a known liquid cooling device that circulates a refrigerant in the cooling tank (5), the cooling tank (5) It is preferable to store and implement it in the inside.

Cooling of the distillation residue in the cooling tank (5) may be performed by air cooling, but considering the efficiency of cooling and the ease of controlling the cooling temperature, the use of an external cooler, specifically Specifically, it is preferable to forcibly cool the cooling tank by encircling the outer wall of the cooling tank with a cooling jacket or installing a refrigerant pipe in the cooling tank.

Furthermore, the cooling in the cooling tank (5) is preferably carried out with stirring from the viewpoint of increasing the homogeneity of the aluminum chloride solids dispersed in the distillation residue cooling liquid. Stirring may be carried out using a magnetic stirrer or the like, but stirring with a stirring blade is preferred. Specific examples of stirring blades include paddle type, ribbon type, anchor type, propeller type, turbine type, swept-wing type, and gate type. The number of stirring blades to be attached to the stirring shaft cannot be unconditionally determined depending on the shape, the size of the reactor, etc., but generally 1 to 4 blades are sufficient on the rotating shaft. The peripheral speed of the blade tip of the stirring blade is preferably 0.1 to 10 m/s, and the rotational speed is preferably 100 to 300 rpm.

In the present invention, the distillation residue cooling liquid formed by the cooling is subjected to thin film evaporation. As shown in the flow of FIG. 1, the residual cooling liquid discharged from the cooling tank (5) is supplied to the thin film evaporator (7) through the residual cooling liquid circulation pipe (6). Here, as the thin film evaporator, a known thin film evaporation method capable of forming a thin film of the liquid to be treated on the heating surface and evaporating the liquid component can be applied without limitation. Specifically, there is a stirring thin film evaporator in which internal blades rotate against a fixed heating surface (evaporation surface) to forcibly stir the treatment liquid to form a thin film, and a centrifugal thin film in which the heating surface rotates. Evaporators may be mentioned, and agitated thin film evaporators are particularly preferred.

The stirring type thin film evaporator can be of vertical type or horizontal type depending on the direction of the rotating shaft, fixed blade type or movable blade type depending on the mounting type of the blades on the rotating shaft, and whether the blades come into contact with the evaporation surface. It is classified into a contact blade type and a non-contact blade type according to the above, and these methods can be used in combination as appropriate. Among these, more preferable types include the vertical contact movable blade type and the vertical non-contact blade type, and these thin film evaporators are relatively excellent in the effect of suppressing scale deposition. In particular, the vertical contact movable blade type is most preferable because the blade contacts the evaporating surface and thus has the highest effect of suppressing scale deposition.

In the thin-film evaporator (7), if the evaporative gas components are accompanied by droplets due to the operating conditions, the removal rate of aluminum chloride may be lowered. In such a case, as a means of preventing entrainment of droplets in the collected chlorosilanes, a droplet collector (9) should be installed in the middle of the collection pipe (8) for the purified chlorosilanes discharged from the thin film evaporator. is an effective means. The droplet collector (9) may be of any type as long as it can collect and remove droplets. For example, a baffle plate (collision plate) type, a sintered type, and a centrifugal separation type can be used.

In addition, it is effective to interpose such a droplet collector (9) also in the middle of the distillation residue cooling liquid flow pipe (6) connecting the cooling tank (5) and the thin film evaporator (7). . The residual cooling liquid discharged from the cooling tank (5) may also be accompanied by droplets of aluminum chloride. However, it is effective in suppressing deposition of aluminum chloride in the apparatus.

When the thin-film evaporator (7) has contact movable blades, the peripheral speed of the tip of the blade is preferably 0.1 m/s or more, preferably 0.5 m/s or more, more preferably 1 m/s or more. In addition, the frequency of the blades migrating at one point on the evaporation surface is 1 time or more per second, preferably 1 time or more per 0.5 seconds, and more preferably 1 time or more per 0.3 seconds. It is preferable for exhibiting a sufficient scale suppressing effect.

On the other hand, in the case of the vertical non-contact blade type, since the blade does not contact the evaporating surface, it must be rotated at a higher speed than the blade contact type, and the peripheral speed of the blade tip is 1 m / s or more, preferably. It is 3 m/s or more, more preferably 5 m/s or more. In addition, the frequency of the blades migrating at one point on the evaporation surface is preferably 1 time or more in 0.5 seconds, preferably 1 time or more in 0.3 seconds, and more preferably 1 time or more in 0.1 seconds, Appropriate conditions may be appropriately adopted depending on the heat transfer area, blade type, and the like.

By using such a thin film evaporator, it is possible to shorten the residence time of the distillation residue cooling liquid in the apparatus, and to enhance the effect of suppressing the deposition of aluminum chloride scale in the apparatus. This effect can be further improved by selecting the structure or operating conditions of the thin film evaporator described above.

In the present invention, when the distillation residue cooling liquid is supplied to the thin film evaporator (7), the treated liquid is heated while forming a liquid film on the evaporation surface, and chlorosilanes are evaporated and aluminum chloride is concentrated. In this way, the chlorosilanes are taken out in gaseous form from the upper outlet of the evaporator (7) into the purified chlorosilanes recovery pipe (8), and from the lower outlet the concentrate of the distillation residue cooling liquid is transferred to the concentrate discharge pipe. (10) is taken out.

In this case, the residence time in the thin film evaporator (7) until the distillation residue cooling liquid is supplied and taken out as a concentrate is usually within about 1 minute or several at the longest in a vertical thin film evaporator. Usually within minutes. In the case of the horizontal type, the staying time can be adjusted to some extent, but it is preferable to adjust the staying time within 10 minutes, preferably within 5 minutes.

The operating conditions for the thin-film evaporation include the temperature of the heating medium, the operating pressure, and the like. Appropriate operating conditions can be adopted according to magnification and the like. At this time, the deposition of aluminum chloride from the distillation residue cooling liquid becomes violent when the temperature is higher than about 180 ° C., and since the aluminum chloride precipitate formed here has low re-solubility in the chlorosilane liquid as described above, thin film evaporation From the viewpoint of preventing scale deposition on the apparatus to a high degree, it is preferable to set the evaporation conditions so that the temperature of the concentrate at the lower outlet of the thin film evaporator (7) is 180° C. or lower, preferably 150° C. or lower. .

In the present invention, by taking advantage of the special behavior of aluminum chloride with respect to the bottoms cooling liquid, the concentrate obtained after evaporation is allowed to contain aluminum chloride to a very high concentration, but the concentrate does not dry up. If this occurs, the function to wash away the partially scaled substances or the solids contained from the beginning may be lost, and the scaling may become severe, making continuous treatment difficult.

Therefore, in the present invention, it is necessary to carry out the thin film evaporation under conditions in which the resulting concentrate remains liquid. In particular, a suitable upper limit for aluminum chloride concentration in the concentrate is 80% by weight, preferably 50% by weight, more preferably 40% by weight. Moreover, the lower limit is preferably 3% by weight, which has been difficult to concentrate according to the prior art, and further 10% by weight, since the effect of the present invention can be sufficiently exhibited.

In the recovery method, the chlorosilanes taken out from the refined chlorosilanes recovery pipe (8) may be effectively used as a raw material for producing semiconductor-grade high-purity silicon or photovoltaic-grade silicon. On the other hand, the concentrate discharged to the concentrate discharge pipe (10) may be properly disposed of after being supplied to a detoxification pit or the like.

EXAMPLES Hereinafter, the present invention will be described with reference to examples in order to explain the present invention in detail, but the present invention is not limited to these examples. The measurements and evaluations carried out in Examples and Comparative Examples were obtained by the following methods.

1) Measurement of Aluminum Chloride Concentration in Chlorosilanes Liquid A chlorosilanes liquid or slurry as a measurement sample is accurately weighed into a container, and an inert gas obtained by sufficiently drying the upper space of the object to be measured at 50° C. or less. The contained chlorosilanes are sufficiently removed by evaporation. Dilute hydrochloric acid is added to the evaporation residue after evaporation removal to dissolve aluminum chloride, followed by filtration. removed.

2) Measurement of Aluminum Chloride Precipitate Solid Content Concentration in Stillage Cooling Liquid A portion of the stillage cooling liquid was extracted from the stillage cooling liquid flow pipe (6), and the mass was measured and used as a measurement sample. This measurement sample is filtered by suction filtration using a membrane filter with an opening of 5 μm, and the resulting cake is subjected to evaporation of the chlorosilanes in the same manner as in “1) Measurement of aluminum chloride concentration in chlorosilanes liquid”. Aluminum chloride contained in the evaporation residue obtained by removal was quantified and divided by the mass of the measurement sample.
3) Method for evaluating scale adhesion in thin film evaporator After the operation of the thin film evaporator was finished, the device was stopped and opened. The amount of scale adhering to the inside of the apparatus was visually evaluated. The following four stages were used for evaluation.
"Severe": Severe scale deposits in the apparatus, and a large amount of scale adheres to the reinforcing ribs of the central rotating shaft bearing portion of the rotating blades, clogging the inside of the apparatus. Therefore, operation cannot be continued unless these scales are removed.
"Much": A large amount of scale deposits in the apparatus, but the amount of deposits on the reinforcing ribs in the central rotating shaft bearing portion of the rotary vane does not clog the inside of the apparatus. In order to continue operation, it is desirable to remove the scale.
"Minor": A small amount of scale is observed on the reinforcing ribs, etc., of the central rotating shaft bearing portion of the rotating blades in the apparatus, but there is no problem in continuing the operation.
"No": A state in which no scale is observed or only a very small amount is observed in the device, including the reinforcing ribs at the central rotary shaft bearing portion of the rotary blade.

Example 1
As the chlorosilanes liquid containing aluminum chloride, a chlorosilanes liquid containing 80% by mass of STC, 20% by mass of TCS, and 0.02% by mass of dissolved aluminum chloride obtained by reacting metallurgical grade silicon powder with a chlorine-containing gas is shown in FIG. 1 was subjected to treatment.

The chlorosilanes liquid is sent to the distillation column (1) at a supply rate of 60,000 kg/H from the chlorosilanes liquid supply pipe (2), and distilled at a bottom temperature of 80 ° C. in the distillation column (1). carried out. As a result, the distillation residue at 70° C. was discharged to the distillation residue discharge pipe (4) at a rate of 1,200 kg/h. This distillation residue had a composition containing 90% by mass of STC, 10% by mass of TCS, and 0.9% by mass of aluminum chloride (the sum of dissolved and supersaturated precipitates).

The distillation bottoms were fed into a cooling bath (5) and cooled to a cooling temperature of 25°C during storage. The cooling tank (5) has a structure in which the outer wall of the tank is surrounded by a cooling jacket, and a stirring blade is installed in the tank. The distillation residue was cooled by rotating at 200 rpm. As a result of this cooling, the crude aluminum chloride in the distillation residue is supersaturated and dispersed. A high dispersion of mass % aluminum chloride precipitates flowed. This distillation residue cooling liquid was supplied to the thin film evaporator (7) while maintaining the temperature of 70°C.

As the thin film evaporator (7), a contact movable blade type vertical thin film evaporator having a heat transfer area of 0.15 m ² and an inner diameter of 0.15 m was used. Thin film evaporation of the distillation residue cooling liquid using this apparatus is performed at one point on the evaporation surface under the temperature condition that the concentrate temperature at the lower outlet is 50 ° C., the peripheral speed of the rotating blade tip is 4 m / s. The rotation was performed under a rotation condition in which the frequency of the blades migrated was once every 3.3 seconds.

When the thin film evaporation was operated for 24 hours, the collected liquid obtained by condensing the gas from the purified chlorosilanes collection tube (8) was measured for the concentration of aluminum chloride and found to be 6.0% by mass. The mass of the recovered liquid was 54 kg/H, and the recovery rate of chlorosilanes in thin film evaporation was determined from this value to be 85%. On the other hand, the mass of the concentrate discharged from the concentrate discharge pipe (910) was measured and found to be 77 kg/H.

After the thin film evaporation in this state was continued for another 10 days, the adhesion of scale in the thin film evaporator was evaluated and found to be "absent".

Comparative example 1
In Example 1, without providing the cooling tank (5), the evaporation residue discharged from the distillation column (1) flows through the distillation residue discharge pipe (4) and is subjected to thin film evaporation at a temperature of 70 ° C. The chlorosilane liquid was recovered in the same manner as in Example 1 except that it was supplied to the device (7). As a result, the state of the recovered liquid from the purified chlorosilanes recovery tube (8) when thin film evaporation was operated for 24 hours was almost the same as in Example 1, but after continuing this thin film evaporation for 10 days, , When the scale adhesion in the thin film evaporator was evaluated, it was in a "strong" state.

Example 2
In Example 1, the cooling temperature of the cooling tank (5) was changed, and the residual cooling liquid flowing through the residual cooling liquid flow pipe (6) had a temperature of 35°C and an aluminum chloride precipitate solid content concentration of 3.0 mass. Chlorosilane liquid was recovered in the same manner as in Example 1, except that the chlorosilane solution was 1%. As a result, the state of the recovered liquid from the purified chlorosilanes recovery tube (8) when the thin film evaporation was operated for 24 hours was almost the same as in Example 1. When the scale adhesion property inside the evaporator was evaluated, it was in a "low" state.

1: Distillation column 2: Chlorosilanes liquid supply pipe 3: Purified chlorosilanes gas distillation pipe 4: Distillation residue discharge pipe 5: Cooling tank 6: Distillation residue cooling liquid distribution pipe 7: Thin film evaporator 8: Purified chlorosilanes recovery Tube 9: droplet collector 10: concentrate discharge tube

Claims (6)

After cooling the distillation residue with a liquid temperature of 50 ° C. or higher obtained by distilling the chlorosilanes containing aluminum chloride to a liquid temperature of 40 ° C. or less, the obtained distillation residue cooling liquid is supplied to a thin film evaporator. A method for recovering chlorosilanes, characterized in that the chlorosilanes are recovered by evaporating them. 2. The method for recovering chlorosilanes according to claim 1, wherein the thin film evaporator is a stirring thin film evaporator. 3. The chlorosilane according to claim 1 or 2, wherein the distillation residue is cooled by storing the distillation residue in a cooling tank and lowering the liquid temperature to 40° C. or lower while stirring. collection method. A method for recovering chlorosilanes, comprising circulating and feeding the chlorosilanes recovered by the method according to any one of claims 1 to 3 to distillation of a chlorosilanes liquid containing aluminum chloride. The chlorosilanes liquid containing aluminum chloride is produced by reacting a gas containing chlorine, hydrogen chloride or silicon tetrachloride and hydrogen with metallurgical grade silicon. 2. The method for recovering chlorosilanes according to claim 1. A method for producing chlorosilanes by distilling a chlorosilanes liquid containing aluminum chloride produced by reacting a gas containing chlorine or hydrogen chloride or silicon tetrachloride and hydrogen with metallurgical grade silicon, wherein the chlorosilanes are obtained by the distillation. A method for producing chlorosilanes, wherein the method for recovering chlorosilanes according to any one of claims 1 to 4 is applied to a distillation residue having a liquid temperature of 50 ° C. or higher.