In-situ conversion treatment process for synthesizing silicon slurry by methyl chlorosilane monomer

Abstract

The invention discloses an in-situ conversion treatment process for methyl chlorosilane synthetic silicon slurry, which comprises the following steps of: flashing the methyl chlorosilane synthetic silicon slurry, cooling in a cooling tank, slowly pressing the silicon slurry into a plate-and-frame filter press by utilizing nitrogen, enabling solid slag after plate-and-frame filter pressing to enter double-screw equipment to be mixed and reacted with alkali, enabling liquid-phase high-boiling residues discharged from the plate-and-frame filter press to enter a storage tank, and enabling the liquid-phase high-boiling residues to enter the storage tank. And separating by using a rectifying tower, and cracking a high-boiling-point substance obtained at the top of the rectifying tower to produce a chlorosilane or silicone oil product. High-boiling-point substances containing silicon powder and copper powder and obtained in the tower kettle are subjected to backwashing in a plate-and-frame filter press. And the solid-liquid mixture is delivered to a twin-screw device after back flushing, and inactivated solid slag is obtained at an outlet of the twin-screw device. The method is simple in process, silicon slurry can be subjected to inactivation treatment on site, the silicon slurry transfer link is reduced, the silicon slurry treatment capacity and treatment difficulty are greatly reduced, and remarkable economic benefits and safe and environment-friendly benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of organosilicon production, and specifically relates to a process for in-situ conversion treatment of methylchlorosilane monomer synthesized silicon slurry. Background Art

[0002] Silicone slurry is a viscous semi-solid or solid paste obtained by wet dust removal process in the synthesis process of methylchlorosilane monomer, and its color is mostly dark gray, black or brown. Silicon slurry is generally dense and complex in composition, containing solid silicon powder of different particle sizes, metal catalyst particles, methylchlorosilane monomer, high boiling point, oligomers, etc. The solid content in silicon slurry is about 10-50%, and its fluidity is poor. Due to its viscous state and the presence of solid particles, silicon slurry is difficult to flow in the natural state and needs to be transported and handled with the help of external force. The solid particles in silicon slurry are extremely active and prone to spontaneous combustion. The liquid in silicon slurry will continue to undergo hydrolysis, condensation and other reactions, and release hydrogen chloride gas. The composition and characteristics of silicon slurry make the chemical properties very complex and difficult to handle. If not properly handled, it will cause serious pollution to the environment, and harmful substances may penetrate into the soil and water, causing damage to soil quality, water quality and ecological environment. At the same time, the stacking of silicon slurry will also occupy a large amount of land resources and bring safety and environmental accidents.

[0003] By the end of 2022, my country's organosilicon methyl monomer production capacity has reached 5 million tons, accounting for about 67% of the world's total organosilicon methyl monomer production capacity. The organosilicon methyl monomer production capacity in my country will reach 7.5 million tons / year, accounting for more than 75% of the world's total organosilicon methyl monomer production capacity. The output of silicone slurry accounts for 1-3% of the output of silicone monomer, so there are 75,000 tons to 225,000 tons of silicone slurry per year. Silicone slurry has certain resource recovery potential. For example, the organosilicon monomer, metal and other resources can be recovered through appropriate treatment methods to achieve resource reuse and reduce pressure on the environment. The following are some common technologies for silicone slurry treatment and recycling.

[0004] High temperature cracking method: Under high temperature conditions, the silicon-silicon bond in the silicon slurry is broken to generate silane monomers. It can break the silicon-silicon bond in the silicon slurry to generate silane monomers, realize the efficient recovery of valuable silane monomers, and create economic value. The requirements for raw materials are relatively loose, and silicon slurries of different compositions can be processed. It is not necessary to remove some solid impurities in high-boiling products, and a variety of silanes can be cracked. However, this method has a high reaction temperature and serious carbon deposition.

[0005] The silicon slurry is separated into solid and liquid, and the high-boiling substances in the liquid phase are hydrolyzed or alcoholyzed to prepare high-boiling silicone oil, silicone waterproofing agent, defoaming agent, release agent, silicone resin, ceramics, etc. The production cost is relatively low, and the raw material source is abundant, which realizes the effective utilization of resources and reduces waste emissions. The high-boiling substances are catalytically cracked to obtain silicone monomers.

[0006] Domestic technology hydrolyzes silicon slurry to improve safety. The slurry residue is transported to the hydrolysis kettle, which avoids close contact between operators and slurry residue, high boiling substances and toxic and harmful gases during the manual slag removal process, reducing potential risks such as fire, flash explosion, and personal injury. Reduce environmental pollution: effectively prevent the high boiling chlorosilane in the slurry residue from hydrolyzing with moisture in the air to produce hydrochloric acid mist, reducing corrosion to metal equipment and damage to the respiratory tract and skin of operators, while also reducing pollution to the environment. The hydrolyzed slurry residue can be further treated for copper extraction or transfer, realizing the comprehensive utilization of resources. Domestic technology incinerates the slurry residue. Under high temperature conditions of 1100℃, the substances in the slurry residue are oxidized and pyrolyzed and destroyed, which can effectively remove harmful substances in the organosilicon slurry residue and achieve thorough harmless treatment. A large amount of heat will be released during the incineration of slurry residue, which can be recycled and utilized through appropriate equipment and technology, such as for power generation or heating, to improve energy utilization efficiency. The hydrolysis and incineration technologies have a large processing volume and are suitable for large-scale silicone slurry treatment. They can meet the processing needs of large silicone production companies. Targeted measures need to be taken in equipment material selection, dust and exhaust gas treatment, etc. to continuously improve the treatment effect and safety.

[0007] The above technologies have become mature in China and have achieved large-scale production. The generally accepted method is to transport the silicon slurry synthesized from the monomers in barrels or cans to the silicon slurry treatment plant for device treatment. First, the construction cost is high, and it is necessary to consider the storage and stacking facilities of the silicon slurry and the process treatment facilities of the silicon slurry. Due to the high liquid content in the silicon slurry, the scale of the device construction is large, and the investment and safety risks are high. In practical applications, it is necessary to select appropriate treatment technologies based on the composition, properties and treatment requirements of the silicon slurry, and optimize and improve them to improve the treatment efficiency and product quality. At the same time, it is also necessary to consider factors such as safety, environmental protection and economy during the treatment process. Summary of the invention The present invention studies the technology of on-site treatment and conversion of silicon slurry. In the monomer synthesis device where silicon slurry is produced, a certain process flow and equipment are used on-site to separate the liquid phase methylchlorosilane, high-boiling substances and solids in the slurry residue, so as to obtain a solid phase with a low high-boiling content. On the one hand, the efficiency of the recovery of high-boiling substances can be improved, and on the other hand, the subsequent treatment of the solid is simpler and more efficient, such as further hydrolysis treatment or recovery, transfer, etc., which is conducive to the maximization of resource utilization and safe and environmentally friendly production. Through solid-liquid separation, the liquid and solid in the slurry residue are treated separately, which reduces the complexity and difficulty caused by the mixed state of the slurry residue in the subsequent treatment process, helps to adopt more appropriate treatment methods and processes for materials in different phases, and improves the treatment effect and economy. The device system is closed, which avoids the occurrence of spontaneous combustion of silicon slurry in the process of transportation, unloading, and manual tanking of silicon slurry. It is environmentally friendly, can realize unmanned operation, and has a high level of automation and mechanization.

[0008] The specific steps are as follows: (1) The silicon slurry after flash evaporation is cooled and filtered to separate the solid and liquid; (2) After the liquid phase separated in step (1) is distilled, the organic silicon monomer and high boiling products with a boiling point below 165°C are obtained at the top of the tower, and the high boiling products with a boiling point greater than 165°C containing fine silicon powder and catalyst are obtained at the bottom of the tower. The high boiling products with a boiling point below 165°C can be used to crack the organic silicon monomer or produce high boiling silicone oil.

[0009] (3) The high-boiling substances with a boiling point greater than 165° C. containing fine silicon powder and catalyst obtained in step (2) are used as backwashing liquid in the plate and frame filter press (2). The solid-liquid mixture after backwashing is passed through a pipeline to the feed port of the twin-screw device (4) to react with the solid phase and alkali obtained by the filter press in step (1) to obtain a deactivated solid waste mixture. The mixture is weakly alkaline with a pH value of 7-10.

[0010] In some specific embodiments, the present invention passes the organic silicon monomer synthesis gas through a scrubber wet dust removal, discharges the silicon slurry from the scrubber reboiler to a flash tank for flash recovery of part of the monomers and high boiling products, and then discharges the silicon slurry to a cooling tank for cooling to below 60°C (in the preferred embodiment, the cooling by circulating cooling water is 25°C-60°C), and the cooling tank is provided with an agitator to prevent solid deposition and blockage, and the cooling jacket is passed through circulating water. After cooling, the silicon slurry is pressed from the cooling tank to a plate and frame filter press by nitrogen, and the flow rate is controlled during the process, and solid-liquid separation is achieved by plate and frame filter pressing. The liquid phase flows to the storage tank through a sealed pipeline, and the liquid content in the obtained solid phase is less than 20%, and the solid phase is sent to a twin-screw conveying device through a sealed connecting pipeline. The high boiling products in the storage tank are sent to the distillation tower by power transmission and flow regulation to separate the high boiling products. After condensation, part of the top material is refluxed, and part of the high boiling products are taken out for subsequent cracking or production of high boiling silicone oil. The high-boiling substances with a certain amount of solids obtained in the bottom of the tower are pumped to the plate and frame filter press as backwashing liquid, and finally enter the twin-screw conveying equipment. The twin-screw conveying equipment simultaneously puts alkali solution or alkaline powder into the silicon slurry and high boiling point for mixing reaction, and the inactivated weak alkaline solid slag mixture is obtained at the tail of the screw equipment for packaging.

[0011] The present invention adopts methylchlorosilane slurry with a solid content of 10%-50%, and the solid includes silicon, copper, iron, aluminum, carbon and other particles with a particle size of less than 20um; the content of monosilane and high boiling substances with a boiling range of 72-130°C in the methylchlorosilane slurry liquid is less than 5%, the content of high boiling substances with a boiling point greater than 130°C-165°C is 70%-90%, and the content of high boiling substances with a boiling point greater than 165°C is 5%-20%. The high boiling substances contain chlorine-containing organic compounds such as Si-Si bonds, Si-O-Si bonds, Si=Si, Si-C-Si bonds, and Si-C bonds.

[0012] The flow control of silicon slurry from cooling tank to plate and frame filter press can be carried out by weight loss method, liquid level reduction method and flow meter measurement method, among which electromagnetic flow meter and ultrasonic flow meter are preferred. To prevent spontaneous combustion of silicon slurry, the plate and frame filter press system adopts a closed structure, uses nitrogen positive pressure protection, pressure 1-10kpa, and leads the tail gas to a safe place for absorption and treatment.

[0013] The liquid content of the solid phase after plate and frame filter press separation is controlled to be less than 20%, more preferably less than 10%, and more preferably less than 5%. The solid phase is fine silicon powder, catalyst and high boiling point. The lower the liquid content, the higher the recovery rate of high boiling point, the less solid residue discharge, and the lower the alkali consumption. The liquid phase separated by plate and frame filter press is mostly high boiling point, which contains a small amount of fine silicon powder and catalyst that are not filtered out by the plate and frame.

[0014] The heat source at the bottom of the distillation tower is the reaction heat of methylchlorosilane synthesis. The distillation tower can be operated at negative pressure or positive pressure, preferably slightly positive pressure. The working pressure in the distillation tower is -50~50kpa, and the working temperature is 80-250℃, so as to achieve the separation of high boiling products in the tower.

[0015] The twin-screw equipment is provided with an external cooling jacket, and a 5-10°C refrigerant is used for cooling, and the temperature of the material in the twin screw is controlled to be lower than 50°C, and it is further preferred to control the temperature of the material in the twin screw to be 15-40°C. The twin-screw equipment is provided with a solid phase feed port, a high-boiling feed port for the distillation tower kettle, an alkali feed port, a nitrogen inlet, and a vent port. Two alkali feed ports are provided, namely the top and the middle of the twin-screw equipment. The alkali feed in the middle is added according to the results of the sampling in the middle, and a small flow of nitrogen is added to the screw equipment to maintain the internal nitrogen protection environment, and the pressure range is 1-10kpa; the vent port is connected to the exhaust system to lead the tail gas to the tail gas absorption device.

[0016] The silicon slurry pipeline of the self-monomer synthesis flash tank of the device of the present invention is connected to the top of the cooling tank, the bottom of the cooling tank is connected to the inlet of the plate and frame filter press, the liquid phase outlet of the frame filter press is connected to the storage tank, and the solid phase outlet is connected to the inlet of the twin-screw device. The storage tank is connected to the distillation tower through moving equipment and pipelines. The device has a high level of automation, and is equipped with automatic monitoring, adjustment, and control instruments such as temperature, pressure, liquid level, regulating valve, flow meter, and switch valve.

[0017] The process of the present invention is simple, and the silicon slurry can be deactivated on site, thereby reducing the silicon slurry transportation link and greatly reducing the silicon slurry treatment volume and treatment difficulty, thereby having significant economic benefits and safety and environmental protection benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a process flow chart of the present invention, wherein: 1. cooling tank; 2. plate and frame filter press; 3. storage tank; 4. twin-screw equipment; 5. distillation tower. DETAILED DESCRIPTION

[0019] Example 1 The device for in-situ conversion of methylchlorosilane monomer synthesis silicon slurry, the silicon slurry pipeline from the monomer synthesis flash tank is connected to the top of the cooling tank 1, the bottom of the cooling tank 1 is connected to the inlet of the plate and frame filter press 2, the liquid phase outlet of the frame filter press is connected to the storage tank 3, and the solid phase outlet is connected to the inlet of the twin screw equipment 4. The storage tank 3 is connected to the distillation tower 5 through the moving equipment and pipeline. The storage tank adopts an agitator to prevent solid deposition, and the outer jacket is passed through circulating water to cool the material. The plate and frame filter press system adopts a closed structure, uses nitrogen positive pressure protection, and the pressure is 3-10kpa. The twin screw is equipped with a cooling water jacket, and the cooling water is passed through to cool the system. The twin screw equipment is equipped with a vent, and the acidic gas of the system is extracted to the tail gas absorption system by an exhaust fan. The device has a high level of automation. Each device is equipped with temperature, pressure, liquid level and other instrument monitoring facilities as needed. The pipeline is equipped with regulating and control instruments such as regulating valves, flow meters, and switch valves. There is no manual operation on site.

[0020] Example 2 The usual process for treating silicon slurry in a methylchlorosilane synthesis unit is that the synthesis gas is wet-dusted by a scrubber, and the silicon slurry is discharged from the scrubber reboiler to a flash tank for flash recovery of some monomers and high-boiling products, and then the silicon slurry is discharged to a cooling tank for cooling to 40°C. After cooling, the silicon slurry is discharged to a mobile tank or iron barrel and transported to a silicon slurry treatment unit inside or outside the factory for hydrolysis or incineration. Taking a 150,000 tons / year methylchlorosilane monomer synthesis unit as an example, the silicon slurry yield is 2%, the solid content is 30%, and 3,000 tons of silicon slurry are transferred each year. Among them, 2,100 tons of high-boiling products are hydrolyzed or incinerated to produce a large amount of waste hydrochloric acid and silica hazardous waste, and the operating cost of the unit is high.

[0021] Example 3 Taking a 150,000 tons / year methylchlorosilane synthesis unit as an example, the silicon slurry yield is 2%, and 3,000 tons of silicon slurry with a solid content of 30% will be produced each year (the solid contains silicon, copper, iron, aluminum, carbon and other particles with a particle size less than 20um. The content of monosilane and high boiling points with a low boiling point range of 72-130°C in the liquid in the silicon slurry is 4-5%, and the content of high boiling points with a boiling point greater than 130°C-165°C is 80%-90%. The rest are high boiling points with a boiling point greater than 165°C, mostly organic compounds with Si=Si bonds, Si-O-Si bonds, and Si-C-Si bonds). After the silicon slurry is cooled to 60°C, nitrogen is used to press it from the cooling tank to the plate and frame filter press 2, and it enters the plate and frame filter press at a rate of 0.5 tons / hour. The plate and frame filter press system adopts a closed structure and uses nitrogen positive pressure protection with a pressure of 5kpa to achieve solid-liquid separation through plate and frame filter press. The liquid phase flows to the storage tank 3 through a sealed pipeline, and a solid phase of 0.176 tons / hour is obtained, in which the liquid content is about 15%, and the solid phase is sent to the twin-screw conveying device 4 through a sealed connecting pipeline. The high-boiling substances in the storage tank 3 are sent to the distillation tower 5 by power transmission and flow adjustment at about 0.33 tons / hour. The distillation tower 5 has a working pressure of 10kpa, a working temperature of 125-145℃ at the top of the tower, and a working temperature of 180-230℃ at the bottom of the tower to separate the high-boiling substances. After condensation, part of the top material is refluxed, and part is taken out for subsequent cracking or production of high-boiling silicone oil. The extraction flow rate is about 0.25 tons / hour. The high-boiling with a certain solid content in the bottom of the tower is about 0.03 tons / hour as the backwashing liquid of the plate and frame filter press, and finally enters the twin-screw conveying equipment for neutralization reaction. The twin-screw conveying equipment 4 simultaneously puts a certain amount of 32% liquid alkali and silicon slurry into the internal mixing reaction, and obtains a deactivated neutral solid slag mixture at the tail of the screw equipment for packaging, with a packaging volume of about 0.22 tons / hour. 1,900 tons of high-boiling materials are recovered annually, and about 1,200 tons of solid slag are transferred. Compared with the existing process, 1,800 tons of waste transfer and treatment are reduced, and high-boiling materials are recycled. The transferred solid slag has been deactivated, the storage safety of the conveyor is improved, and the effective components inside are retained, which can continue to be used for copper extraction.

[0022] Example 4 Taking a 200,000 tons / year methylchlorosilane synthesis unit as an example, the silicon slurry yield is 1.6%, and 3,200 tons of silicon slurry with a solid content of 20% will be produced each year (the solid contains silicon, copper, iron, aluminum, carbon and other particles with a particle size less than 20um. The content of monosilane and high boiling points with a low boiling point range of 72-130°C in the liquid in the silicon slurry is 4-5%, and the content of high boiling points with a boiling point greater than 130°C-165°C is 80%-90%. The rest are high boiling points with a boiling point greater than 165°C, mostly organic compounds with Si=Si bonds, Si-O-Si bonds, and Si-C-Si bonds). After the silicon slurry is cooled to 55°C, nitrogen is used to press it from the cooling tank to the plate and frame filter press 2, and it enters the plate and frame filter press at a rate of 0.45 tons / hour. The plate and frame filter press system adopts a closed structure and uses nitrogen positive pressure protection with a pressure of 1-3kpa to achieve solid-liquid separation through plate and frame filter press. The liquid phase flows to the storage tank 3 through a sealed pipeline, and a solid phase of 0.1 tons / hour is obtained, in which the liquid content is about 10%, and the solid phase is sent to the twin screw conveying device 4 through a sealed connecting pipeline. The high-boiling substances in the storage tank 3 are sent to the distillation tower 5 by power transmission and flow adjustment at about 0.35 tons / hour. The distillation tower 5 has a working pressure of 30kpa, a working temperature of 125-135℃ at the top of the tower, and a working temperature of 190-220℃ in the bottom of the tower to separate the high-boiling substances. After condensation, part of the top material is refluxed, and part is taken out for subsequent cracking or production of high-boiling silicone oil. The extraction flow rate is about 0.33 tons / hour. The high-boiling substance with a certain solid content obtained in the bottom of the tower is about 0.02 tons / hour, which is pumped to the plate and frame filter press as a backwashing liquid. The twin screw conveying equipment 4 evenly puts lime powder and silicon slurry into the internal mixing reaction, removes the reaction heat in time through the cooling water jacket, controls the screw conveying temperature within 40°C, and vacuumizes the screw to absorb the reaction gas in time. The deactivated alkaline or neutral solid slag mixture is packaged at the tail of the screw equipment, and the packaging volume is about 0.15 tons / hour. 2,376 tons of high boiling materials are recovered and about 1,080 tons of solid slag are transferred each year. Compared with the existing process, 2,120 tons of waste transfer and treatment are reduced. The transportation and storage of hazardous waste are greatly reduced, and resources are used efficiently.

Claims

1. A process for in-situ conversion of methylchlorosilane monomer into silicon slurry, characterized in that: The following steps are involved: (1) The silicon slurry after flash evaporation is cooled and filtered to separate the solid and liquid; (2) After the liquid phase separated in step (1) is distilled, the organic silicon monomer and high boiling products with a boiling point below 165° C. are obtained at the top of the tower, and the high boiling products with a boiling point greater than 165° C. containing fine silicon powder and catalyst are obtained at the bottom of the tower; (3) The high-boiling point of the fine silicon powder and the catalyst obtained in step (2) with a boiling point greater than 165°C is cooled to below 60°C and sent to the plate and frame filter press as backwashing liquid. The solid-liquid mixture after backwashing enters the feed port of the twin-screw equipment through a pipeline, and reacts with the solid phase and alkali obtained by the filter press in step (1) to obtain a deactivated solid waste mixture. The mixture is weakly alkaline with a pH value of 7-10.

2. The process for in-situ conversion treatment of methylchlorosilane synthetic silicon slurry according to claim 1, characterized in that: The solid content of methylchlorosilane synthetic silicon slurry is 10%-50%, and the solids include silicon, copper, iron, aluminum, and carbon particles; the content of monosilane and high-boiling substances with a boiling range of 72-130°C in the methylchlorosilane silicon slurry liquid is less than 5%, the content of high-boiling substances with a boiling point greater than 130°C-165°C is 70%-90%, and the content of high-boiling substances with a boiling point greater than 165°C is 5%-20%.

3. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 1 is characterized in that: The silicon slurry is cooled to below 60°C, preferably cooled to 25°C-60°C by circulating cooling water.

4. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 3 is characterized in that: After the silicon slurry is cooled, it enters the plate and frame filter press system at a uniform speed for filtration. The plate and frame filter press system adopts nitrogen positive pressure protection with a pressure range of 1-10kpa.

5. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 1 is characterized in that: The working pressure of the distillation tower is -50~50kpa, and the working temperature is 80~250℃, which can realize the separation of high boiling substances in the tower.

6. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 1, characterized in that: The liquid content in the solid phase after plate and frame filtration is less than 20%, and it enters the twin-screw equipment to react with alkali to obtain solid waste for on-site packaging.

7. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 1 is characterized in that: The twin-screw equipment is equipped with an external cooling jacket, which uses a 5~10℃ refrigerant for cooling and controls the material temperature inside the twin-screw to be below 50℃.

8. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 7, characterized in that: Use refrigerant cooling to control the material temperature in the twin screw to 15~40℃.

9. The in-situ conversion treatment process of methylchlorosilane synthetic silicon slurry according to claim 8, characterized in that: Nitrogen is introduced during the operation of the twin-screw equipment to maintain the internal nitrogen protection environment and control the internal pressure range of the equipment to be 1-10kpa.

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