System and method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride

Abstract

A system and method for separating aluminum trichloride from cold-hydrogenated silicon tetrachloride includes a pressure-reducing tank, a condenser, a first extraction tank, a second extraction tank, a clear liquid filter, and a clear liquid tank. The system is characterized by: a silicon tetrachloride inlet pipe at the top of the pressure-reducing tank; the bottom of the pressure-reducing tank being connected to the first and second extraction tanks via pipes; the bottoms of the first and second extraction tanks being connected to a dryer via pipes; the side walls of the first and second extraction tanks being connected to the clear liquid filter via pipes; the tops of the first and second extraction tanks being connected to the condenser via pipes; the bottom of the condenser having a liquid outlet pipe connected to the top of the clear liquid tank; and the bottom of the clear liquid tank having a silicon tetrachloride recovery pipe; and the clear liquid filter being connected to the liquid outlet pipe via a pipe. This invention improves the clogging situation of the entire cold hydrogenation system, solves the problem of long-term operation of the cold hydrogenation system, and reduces the equipment failure rate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of separating aluminum trichloride from silicon tetrachloride, and particularly relates to a system and method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride. BACKGROUND

[0002] After the cold hydrogenation reaction, the silicon tetrachloride liquid still contains a small amount of trichlorosilane and dichlorosilane, polychlorosilane (all in liquid state), and a small amount of solid impurities such as silicon powder and aluminum trichloride. In particular, the aluminum trichloride impurities are prone to fouling on the inner wall of the pipeline in the system, causing blockage, greatly shortening the operation cycle of the cold hydrogenation, so this part must be discharged to the outside of the system for treatment.

[0003] The previous disposal method of aluminum trichloride in the cold hydrogenated silicon tetrachloride produced by the polysilicon production device mainly has the following two methods:

[0004] The first method: directly discharge the cold hydrogenated silicon tetrachloride from the system for hydrolysis treatment to remove aluminum trichloride. The disadvantages of this treatment are: ① a large amount of heat is released when silicon tetrachloride reacts with water, which requires a large amount of water for cooling, resulting in a large water consumption; ② the waste liquid produced by hydrolysis is acidic, which requires a large amount of lime milk or lye for neutralization, increasing the additional treatment cost; ③ a large amount of silicon dioxide is produced by hydrolysis of a large amount of silicon tetrachloride, increasing the solid waste; ④ a large amount of silicon tetrachloride cannot be recycled, causing great waste. This method is gradually eliminated.

[0005] The second method: first flash the cold hydrogenated silicon tetrachloride, recover a small amount of silicon tetrachloride liquid, then discharge the silicon tetrachloride containing impurities into a drying machine for concentration, and then hydrolyze the concentrated solid-liquid mixture to remove aluminum trichloride. The disadvantages of this process are: ① a large amount of silicon tetrachloride enters the drying machine, the packing of the drying machine is prone to leakage, and the drying machine needs to be frequently repaired; ② a large amount of silicon tetrachloride needs to be evaporated, and the drying machine has limited processing capacity, so if the cold hydrogenated aluminum trichloride treatment requirements are to be fully met, the equipment investment needs to be increased; ③ the drying machine needs to be operated for a long time, resulting in high power consumption and steam consumption. SUMMARY

[0006] In view of the technical problems existing in the background art, the system and method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride provided by the present application improve the blockage of the entire cold hydrogenation system, solve the long-period operation of the cold hydrogenation system, and reduce the equipment failure rate.

[0007] In order to solve the above technical problems, the present application adopts the following technical solutions to achieve:

[0008] A system for separating aluminum trichloride from cold hydrogenated silicon tetrachloride includes a pressure reducing tank, a condenser, a first extraction tank, a second extraction tank, a clear liquid filter, and a clear liquid tank. The pressure reducing tank has a silicon tetrachloride inlet pipe at its top, and its bottom is connected to the first and second extraction tanks via pipes. The bottoms of the first and second extraction tanks are connected to a dryer via pipes. The sidewalls of the first and second extraction tanks are connected to the clear liquid filter via pipes. The tops of the first and second extraction tanks are connected to the condenser via pipes. The condenser has a liquid outlet pipe at its bottom, which is connected to the top of the clear liquid tank. The clear liquid tank has a silicon tetrachloride recovery pipe at its bottom. The clear liquid filter is connected to the liquid outlet pipe via a pipe.

[0009] Preferably, the top of the pressure reducing tank is connected to the top of the condenser via a pipe.

[0010] Preferably, the first and second extraction tanks are equipped with magnetic stirrers. The pressure reducing tank also has a magnetic stirrer.

[0011] Preferably, the outer walls of the pressure reducing tank, the first extraction tank, and the second extraction tank are all equipped with jackets, and the jacket of the pressure reducing tank is cooled by a circulating water system; the jackets of the first extraction tank and the second extraction tank are cooled by 7-degree water.

[0012] Preferably, the separation method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride includes the following steps:

[0013] Step 1: The high-temperature and high-pressure (3.0 MPa, 100℃) silicon tetrachloride slurry from cold hydrogenation enters the pressure reducing tank. 30℃ circulating water is introduced into the jacket half-pipe of the pressure reducing tank to cool and depressurize the silicon tetrachloride. The pressure in the pressure reducing tank is controlled at 0.1 MPa-0.15 MPa, and the temperature is controlled at 20-60℃.

[0014] Step 2: During the cooling and depressurization process in the pressure reducing tank, the volatilized gaseous silicon tetrachloride is discharged from the top of the pressure reducing tank, enters the condenser for condensation, and is then recovered into the clear liquid tank.

[0015] Step 3: When the liquid level in the pressure reducing tank reaches 50-60%, pressurize the pressure reducing tank with nitrogen to 0.2 MPa, and force the silicon tetrachloride liquid into the extraction tank from the bottom; the extraction tank includes a first extraction tank and a second extraction tank;

[0016] Step 4: After silicon tetrachloride enters the extraction tank, start the magnetic stirrer and pass 7-degree water into the jacket half-tube to crystallize aluminum trichloride and adsorb silicon powder to increase its weight. Stir for 1-2 hours to fully crystallize and adsorb, and then let it stand for 6-8 hours to settle.

[0017] Step 5: During the cooling and settling process in the extraction tank, a layer of silicon powder is adsorbed on the surface of the solid aluminum trichloride, increasing its weight and causing it to settle to the bottom of the extraction tank; the upper layer of the extraction tank is a clear liquid of silicon tetrachloride, which no longer contains aluminum trichloride impurities. The upper clear liquid is drawn out, filtered through a clear liquid filter, and then discharged into a clear liquid tank;

[0018] Step 6: The upper 90% of the clear liquid in the extraction tank is recycled to the clear liquid tank, and the lower 10% of the impurities containing aluminum trichloride and silicon tetrachloride is discharged into the dryer for treatment.

[0019] Step 7: The liquid silicon tetrachloride recovered in the clear liquid tank is sent back to the cold hydrogenation recycling system.

[0020] This patent can achieve the following beneficial effects:

[0021] 1. By optimizing the equipment and processes, the emission requirements for aluminum trichloride impurities in cold hydrogenated silicon tetrachloride were met, the blockage situation of the entire cold hydrogenation system was improved, the long-cycle operation of the cold hydrogenation system was solved, and the equipment failure rate was reduced.

[0022] 2. The extraction of silicon tetrachloride can be recycled and reused, generating significant economic benefits and saving production costs.

[0023] 3. The problem of impurities in aluminum trichloride, a raw material for cold hydrogenation, has been solved, resulting in improved conversion rate;

[0024] 4. Reduced blockages and malfunctions in cold hydrogenation pipelines and equipment, extending the start-up and operation cycle by more than 2 months;

[0025] 5. It reduces the amount of silicon tetrachloride hydrolysis, thereby reducing the amount of water used and the amount of lime slurry or alkali solution used, as well as reducing the amount of solid waste generated.

[0026] 6. More than 95% of silicon tetrachloride is recycled, reducing production costs. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0028] Figure 1 This is a system structure diagram of the present invention.

[0029] In the diagram: 1. Pressure reducing tank; 2. Condenser; 3. First extraction tank; 4. Second extraction tank; 5. Clarified liquid filter; 6. Clarified liquid tank. Detailed Implementation

[0030] Example 1:

[0031] Preferred solutions include Figure 1As shown, a system for separating aluminum trichloride from cold hydrogenated silicon tetrachloride includes a pressure-reducing tank 1, a condenser 2, a first extraction tank 3, a second extraction tank 4, a clear liquid filter 5, and a clear liquid tank 6. The pressure-reducing tank 1 is equipped with a silicon tetrachloride inlet pipe at its top, and its bottom is connected to the first extraction tank 3 and the second extraction tank 4 via pipes. The bottoms of the first extraction tank 3 and the second extraction tank 4 are connected to a dryer via pipes. The side walls of the first extraction tank 3 and the second extraction tank 4 are connected to the clear liquid filter 5 via pipes. The tops of the first extraction tank 3 and the second extraction tank 4 are connected to the condenser 2 via pipes. The bottom of the condenser 2 is equipped with a liquid outlet pipe, which is connected to the top of the clear liquid tank 6. The bottom of the clear liquid tank 6 is equipped with a silicon tetrachloride recovery pipe. The clear liquid filter 5 is connected to the liquid outlet pipe via a pipe.

[0032] The top of the pressure reducing tank 1 is connected to the top of the condenser 2 via a pipe.

[0033] Magnetic stirrers are installed in the first extraction tank 3 and the second extraction tank 4.

[0034] The outer walls of the pressure reducing tank 1, the first extraction tank 3, and the second extraction tank 4 are all equipped with jackets. The jacket of the pressure reducing tank 1 is cooled by a circulating water system; the jackets of the first extraction tank 3 and the second extraction tank 4 are cooled by 7-degree water.

[0035] The clear liquid filter 5 is a precision filter with a stainless steel filter element.

[0036] Preferably, the separation method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride includes the following steps:

[0037] Step 1: High-temperature and high-pressure (3.0 MPa, 100℃) silicon tetrachloride slurry from cold hydrogenation enters the pressure reducing tank. 30℃ circulating water is circulated through the jacketed half-pipe of the pressure reducing tank to cool and depressurize the silicon tetrachloride. The pressure in the pressure reducing tank is controlled at 0.1 MPa-0.15 MPa, and the temperature is controlled at 20-60℃. The cold hydrogenation discharge of silicon tetrachloride is a high-pressure discharge, and the discharge pipeline is not easily blocked.

[0038] Step 2: During the cooling and depressurization process in the pressure reducing tank, the volatilized gaseous silicon tetrachloride is discharged from the top of the pressure reducing tank, enters the condenser for condensation, and is then recovered into the clear liquid tank.

[0039] Step 3: When the liquid level in the pressure reducing tank reaches 50-60%, pressurize the pressure reducing tank with nitrogen to 0.2 MPa, and force the silicon tetrachloride liquid into the extraction tank from the bottom; the extraction tank includes a first extraction tank and a second extraction tank;

[0040] Step 4: After silicon tetrachloride enters the extraction tank, start the magnetic stirrer and pass 7-degree water into the jacket half-tube to crystallize aluminum trichloride and adsorb silicon powder to increase its weight. Stir for 1-2 hours to fully crystallize and adsorb, and then let it stand for 6-8 hours to settle.

[0041] Step 5: During the cooling and settling process in the extraction tank, a layer of silica powder is adsorbed on the surface of the solid aluminum trichloride, increasing its weight and causing it to settle to the bottom of the extraction tank. The upper layer of the extraction tank is a clear liquid containing silicon tetrachloride, which no longer contains aluminum trichloride impurities. The upper clear liquid is drawn out, filtered through a clear liquid filter, and discharged into a clear liquid tank. The removal of aluminum trichloride impurities is completely solved through cooling, crystallization, and adsorption.

[0042] Step 6: The upper 90% of the clear liquid in the extraction tank is recycled to the clear liquid tank, and the lower 10% of the impurities containing aluminum trichloride and silicon tetrachloride is discharged into the dryer for treatment.

[0043] Step 7: The liquid silicon tetrachloride recovered in the clear liquid tank is sent back to the cold hydrogenation recycling system.

[0044] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride, characterized in that: A system for separating aluminum trichloride from cold hydrogenated silicon tetrachloride is employed. The system includes a pressure reducing tank (1), a condenser (2), a first extraction tank (3), a second extraction tank (4), a clear liquid filter (5), and a clear liquid tank (6). The system is characterized in that: the top of the pressure reducing tank (1) is provided with a silicon tetrachloride inlet pipe, and the bottom of the pressure reducing tank (1) is connected to the first extraction tank (3) and the second extraction tank (4) respectively through pipes. The bottoms of the first extraction tank (3) and the second extraction tank (4) are connected to a dryer through pipes. The side walls of the first extraction tank (3) and the second extraction tank (4) are connected to the clear liquid filter (5) through pipes. The tops of the first extraction tank (3) and the second extraction tank (4) are connected to the condenser (2) through pipes. The bottom of the condenser (2) is provided with a liquid outlet pipe, which is connected to the top of the clear liquid tank (6). The bottom of the clear liquid tank (6) is provided with a silicon tetrachloride recovery pipe. The clear liquid filter (5) is connected to the liquid outlet pipe through a pipe. The separation method includes the following steps: Step 1: The high-temperature and high-pressure silicon tetrachloride slurry from cold hydrogenation enters the pressure reducing tank. 30°C circulating water is introduced into the jacket half-pipe of the pressure reducing tank to cool and depressurize the silicon tetrachloride. The pressure in the pressure reducing tank is controlled at 0.1Mpa-0.15Mpa, and the temperature is controlled at 20-60°C. Step 2: During the cooling and depressurization process in the pressure reducing tank, the volatilized gaseous silicon tetrachloride is discharged from the top of the pressure reducing tank, enters the condenser for condensation, and is then recovered into the clear liquid tank. Step 3: When the liquid level in the pressure reducing tank reaches 50-60%, pressurize the pressure reducing tank with nitrogen to 0.2 MPa, and force the silicon tetrachloride liquid into the extraction tank from the bottom; the extraction tank includes a first extraction tank and a second extraction tank; Step 4: After silicon tetrachloride enters the extraction tank, start the magnetic stirrer and pass 7-degree water into the jacket half-tube to crystallize aluminum trichloride and adsorb silicon powder to increase its weight. Stir for 1-2 hours to fully crystallize and adsorb, and then let it stand for 6-8 hours to settle. Step 5: During the cooling and settling process in the extraction tank, a layer of silicon powder is adsorbed on the surface of the solid aluminum trichloride, which increases its weight and causes it to settle to the bottom of the extraction tank; the upper layer of the extraction tank is a clear liquid of silicon tetrachloride, which no longer contains aluminum trichloride impurities; the upper clear liquid is drawn out, filtered through a clear liquid filter, and discharged into a clear liquid tank. Step 6: The upper 90% of the clear liquid in the extraction tank is recycled to the clear liquid tank, and the lower 10% of the impurities containing aluminum trichloride and silicon tetrachloride is discharged into the dryer for treatment. Step 7: The liquid silicon tetrachloride recovered in the clear liquid tank is sent back to the cold hydrogenation recycling system.

2. The method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride according to claim 1, characterized in that: The top of the pressure reducing tank (1) is connected to the top of the condenser (2) via a pipe.

3. The method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride according to claim 1, characterized in that: The first extraction tank (3) and the second extraction tank (4) are equipped with magnetic stirrers.

4. The method for separating aluminum trichloride from cold hydrogenated silicon tetrachloride according to claim 1, characterized in that: The outer walls of the pressure reducing tank (1), the first extraction tank (3), and the second extraction tank (4) are all equipped with jackets. The pressure reducing tank (1) is cooled by a circulating water system inside the jacket; the jackets of the first extraction tank (3) and the second extraction tank (4) are cooled by 7-degree water.

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