Production process flow of polysilicon-trichlorosilane


Time:

2023-01-20

Introduction: Trichlorosilane, the English scientific name of trichlorosilane, is numbered 10025-78-2 in CAS (International Journal of Chemical Abstracts). Its common molecular formula is SiHCl3, molecular weight is 135.45, common melting point is mp-126.5 ° C, common boiling point is bp760 31.8 ° C, also reported as 36.5 ° C, and common density is d40 0.001383 g/cm3. It is a compound composed of Cl 78.52%, H 0.74%, and Si 20.73%.

Chinese name: trichlorosilane
English name: Trichlorosilane
Chemical formula: SiHCl3
Composition: Cl 78.52%, H 0.74%, Si 20.73%
Relative molecular weight: 135.45
Relative density: d40 0.001383 g/cm3; d420 1.3417 kg/m3;  d425 1.3313 kg/m3
Melting point: mp - 126.5 ° C
Boiling point: bp760 31.8 ° C, also reported as 36.5 ° C
Refractive index: nD20 1.4020; nD25 1.3983
CAS : 10025-78-2
Introduction: Trichlorosilane, the English scientific name of trichlorosilane, is numbered 10025-78-2 in CAS (International Journal of Chemical Abstracts). Its common molecular formula is SiHCl3, molecular weight is 135.45, common melting point is mp-126.5 ° C, common boiling point is bp760 31.8 ° C, also reported as 36.5 ° C, and common density is d40 0.001383 g/cm3. It is a compound composed of Cl 78.52%, H 0.74%, and Si 20.73%.
1. Main uses of trichlorosilane
Trichlorosilane (HSiCl3) is a kind of organosilicon monomer with a wide range of uses. It is an important raw material for the production of semiconductor silicon, monocrystalline silicon and polycrystalline silicon. It is also the most basic monomer for the synthesis of organosilane and alkyl, aryl and organic functional group chlorosilane. With the development of polysilicon and organosilane coupling agent industry, especially the rapid development of fine chemical industry, organosilicon industry, electronic products, optical fiber communication and other industries, it provides a huge market space and opportunities for the production of trichlorosilane and the development of downstream products. For chlor-alkali enterprises, trichlorosilane is still a product with high output value and development prospects that can be planned, with small investment, quick effect, good economic benefits and great market development potential.
2. Market demand of trichlorosilane
Trichlorosilane is mainly used as the intermediate of silane coupling agents and polysilicon. At present, there is a strong demand for silane coupling agents and polysilicon products in China.
The polysilicon production technology in the world (including China) mainly adopts the improved Siemens method, that is, synthesis of hydrogen chloride (or purchased hydrogen chloride) from chlorine and hydrogen, synthesis of trichlorosilane from hydrogen chloride and industrial silicon powder at a certain temperature, followed by separation, distillation and purification of trichlorosilane, and production of polysilicon from purified trichlorosilane through CVD reaction in the hydrogen reduction furnace. This shows that manufacturers can produce polysilicon in other regions as long as they purchase the core raw materials for polysilicon production, such as trichlorosilane. According to our investigation, most polysilicon manufacturers are basically outsourcing raw materials.
3. Chenguang Academy trichlorosilane technical advantages
Trichlorosilane is produced in a fluidized bed reactor with silicon powder and hydrogen chloride gas, which consumes a large amount of chlorine and hydrogen in production. It is a good chlorine balance product for chlor-alkali enterprises to improve economic benefits.
Trichlorosilane, also known as silicochloroform, has the molecular formula of SiHCl3, a trichloride of silane. It is a colorless liquid that flows easily, with a density of 1.34 g/cm; It is soluble in benzene, chloroform and carbon disulfide.
It is used for the synthesis of organosilane and alkyl, aryl and organic functional group chlorosilane. It is the most basic monomer in organosilane coupling agent, and also the raw material for the production of semiconductor silicon and monocrystalline silicon. With the development of organosilane coupling agent industry, the supply is in short supply, and the production volume is increasing.
Trichlorosilane is a colorless liquid that is easy to flow, volatile and deliquescent. It reacts in the air to produce white smoke and emit a strong odor. It decomposes in water and is easily soluble in organic solvents such as benzene, ether, chloroform and carbon disulfide. The melting point is - 126.5 ℃, the boiling point is 31.8 ℃, and the flash point is - 13.9 ℃. It is a Class I flammable and explosive material in wet conditions, with a spontaneous combustion temperature of 185 ℃, a relative density of 4.7 when the air density is 1, and an explosion limit of 1.2~90.5% (volume fraction) in the air. React with water to produce hydrogen chloride gas; It reacts strongly with oxidant and burns or explodes in case of open fire and high heat. Its fire hazard is Class A and B.
Refer to the Report on China's trichlorosilane market competition research and development trend forecast in the 13th Five-Year Plan issued by China Report Network
The production of trichlorosilane mainly includes three processes: trichlorosilane synthesis, trichlorosilane rectification and tail gas treatment.
1. Synthesis and production process of trichlorosilane
The silicon powder is added into the silicon powder dryer manually, heated to a certain temperature by steam, then pressed into the silicon powder metering tank by nitrogen and level difference, and finally sent into the trichlorosilane boiling furnace by the silicon powder feeder, which reacts with the hydrogen chloride gas at a certain temperature; The generated gas passes through the gravity settler, bag filter, high boiling matter remover and two-stage condenser to obtain the crude trichlorosilane; The crude trichlorosilane is put into the chlorinated material storage tank through the metering tank.
In the actual production process of this process, the following seven situations occur: the silicon powder adding pipeline is easy to be blocked, and it often needs to be knocked manually, which increases the labor intensity of workers, and is easy to cause unstable pressure in the furnace, affecting the yield of trichlorosilane synthesis; The seal of the silicon powder feeder is not good, resulting in the leakage of the top gas of the fluidized bed furnace, which is a great potential safety hazard; The hydrogen chloride gas has high water content, shortens the service life of the equipment, and frequently overhauls, and the device cannot reach the design capacity; The amount of crude products condensed by the two-stage condenser is small, the amount of system tail gas is large, and the hydrolysate in the tail gas absorption tank is too much; The cooling water volume is not easy to control, especially when the boiler is just started, it is easy to cause boiler shutdown; The water cooler is easy to block, and the continuous production of the production unit is not guaranteed; The system pressure is unstable, which leads to the unstable amount of hydrogen chloride entering the furnace, which is easy to cause boiler shutdown.
2. Trichlorosilane rectification process flow
The trichlorosilane in the crude product storage tank is pumped into the distillation tower kettle by rotameter; Use steam regulating valve to control the temperature in the kettle; The trichlorosilane gas flows out from the tower top, condenses through the tower top condenser, and then enters the product metering tank. After passing the analysis, it enters the finished product storage tank, and the other part returns to the tower top; Silicon tetrachloride is stored at the bottom of the distillation tower and sent to the silicon tetrachloride storage tank through the metering control valve.
Process flow chart of trichlorosilane production before technical transformation

  

 

(1) 1st stage cooler;
(2) 2nd stage cooler;
(3) Hydrogen chloride trap;
(4) Hydrogen chloride buffer tank;
(5) Silica powder dryer;
(6) Silicon powder silo;
(7) Silicon powder metering tank;
(8) Silicon powder feeder;
(9) Fluidized bed furnace;
(10) Gravity settler;
(11) Bag filter;
(12) High boiling substance remover;
(13) Water cooler;
(14) Cryogenic cooler;
(15) Chlorine metering tank;
(16) Warm water cooler;
(17) Warm water storage tank;
(18) Tail gas absorption tower
Source: sorting out public data
Process flow diagram of trichlorosilane rectification

  

 

(1) Chlorinated material storage tank;
(2) Chlorination feed pump;
(3) Tower 1 reboiler;
(4) 1 Distillation tower;
(5) Tower 1 overhead condenser;
(6) Surge tank of overhead condenser of tower 1;
(7) Low-boiler metering tank;
(8) Tower 2 reboiler;
(9) 2 Distillation tower;
(10) 2 Tower overhead condenser;
(11) 2. Surge tank of overhead condenser;
(12) High boiling substance metering tank;
(13) Product metering tank
Source: sorting out public data
The key points of operation of this process are the temperature of tower top and bottom, the amount of incoming and outgoing materials and the reflux ratio. Once the temperature of tower top and bottom is not well controlled, the product purity will be affected, resulting in the generation of unqualified products; Stable feed and discharge is a necessary and sufficient condition for stable distillation operation; The reflux ratio is related to the product quality and energy consumption.
3. Tail gas treatment
The main components of tail gas are trichlorosilane, hydrogen chloride and hydrogen. The treatment method of tail gas in the original process is mainly hydrolysis by water washing tower to generate insoluble silica and hydrochloric acid. This treatment method not only wastes trichlorosilane, increases the production cost of trichlorosilane, and the pipeline is easy to be blocked. Moreover, the cleaning of hydrolysates increases the labor intensity of workers, and the treatment of acid water increases the cost of sewage treatment.
Future transformation direction
(1) The boiling furnace is cooled by warm water instead of heat transfer oil, which further stabilizes the reaction temperature of the boiling furnace and prolongs the service life of the equipment. At the same time, the heat of the heat transfer oil is used to heat the silicon powder and preheat the incoming hydrogen chloride. The by-product low-pressure steam is used for trichlorosilane rectification, thus further reducing steam consumption and improving the yield of trichlorosilane synthesis.
(2) Improve the drying system of silicon powder, increase the drying temperature of silicon powder from 100e to about 200e, further reduce the water content in silicon powder, and further improve the yield of trichlorosilane.
(3) The tail gas system will be equipped with pressurized condensation and pressure swing adsorption facilities to further recover trichlorosilane in the tail gas, and at the same time, the hydrogen chloride and hydrogen in the tail gas will be reused, which will not only solve the "three wastes" problem, but also greatly reduce the production cost of trichlorosilane.