A method for purifying trichlorosilane

Abstract

The application provides a trichlorosilane purification method. The trichlorosilane purification method comprises the following steps: reacting a treating agent with trichlorosilane crude product; the treating agent is a silicon-based phosphate; and a preparation method of the trichlorosilane crude product comprises the following steps: reacting metal silicon with hydrogen chloride to obtain trichlorosilane crude product. The purification method can efficiently and at low cost treat metal and nonmetal impurities such as iron, calcium, magnesium, aluminum and boron in the trichlorosilane crude product, meets the manufacturing requirements of solar-grade polysilicon raw materials in the photovoltaic industry, and removes light and impurities in a multi-stage distillation process.

Description

Technical Field

[0001] This invention relates to the field of organosilicon monomer synthesis technology, and more specifically, to a method for purifying trichlorosilane. Background Technology

[0002] Trichlorosilane is an important raw material in the organosilicon industry for synthesizing functional silanes, silicone oils, silicone rubbers, and other products. It is also a crucial raw material for the photovoltaic and semiconductor industries. Industry-grade trichlorosilane is categorized into organosilicon grade, photovoltaic grade, and electronic grade. Photovoltaic grade trichlorosilane has specific requirements regarding metallic and non-metallic impurities and total carbon content, especially for impurities such as boron, phosphorus, iron, and aluminum. Electronic grade trichlorosilane, used as a raw material for semiconductor epitaxial wafer fabrication, has even higher requirements for the content of these impurities.

[0003] In existing technologies, crude trichlorosilane is typically prepared in factories by reacting metallic silicon with hydrogen chloride. This crude trichlorosilane is then purified to obtain various grades of trichlorosilane. The main component of metallic silicon is silicon, and impurities include iron, aluminum, and calcium. When metallic silicon reacts with hydrogen chloride, the resulting crude trichlorosilane will also contain these impurities. Even in extremely small amounts, these metallic impurities can significantly affect the properties of the obtained trichlorosilane.

[0004] Current purification methods for crude trichlorosilane typically employ distillation, but this method is ineffective at removing impurities, consumes high energy, is difficult to control, and results in inconsistent product quality. The higher the quality of the trichlorosilane product (i.e., the lower its impurity content), the higher the cost of purification using this method. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for removing impurities from trichlorosilane. The trichlorosilane obtained by this method has stable quality. Compared with the prior art, the purification method provided by this invention effectively reduces production costs while ensuring product performance.

[0006] The present invention provides a purification method for trichlorosilane, which includes the following steps: reacting a treatment agent with crude trichlorosilane;

[0007] The treatment agent is a silicon-based phosphate ester;

[0008] The preparation method of the crude trichlorosilane includes the following steps: reacting metallic silicon with hydrogen chloride to obtain crude trichlorosilane.

[0009] In a preferred embodiment of the present invention, the amount of the treatment agent added is 1-3 wt% of the crude trichlorosilane.

[0010] In a preferred embodiment of the present invention, the treatment agent includes, but is not limited to, one or more of the following: tris[(dimethylethyl)silyl] phosphate, tris[(dimethylphenyl)silyl] phosphate, tris[(dimethylvinyl)silyl] phosphate, tris[2-(perfluorodecyl)ethyl] phosphate, bis(trimethylsilyl) ethyl phosphate, tris(trimethylsilyl) phosphate, and tris[(2,2,2-trifluoroethyl)silyl] phosphate, preferably tris(trimethylsilyl) phosphate (also known as tris(trimethylsilyl) phosphate). The treatment agent used in the present invention can be commercially available or prepared in-house.

[0011] In another preferred embodiment of the present invention, the preparation method of the treatment agent includes the following steps: under nitrogen protection and micro-reflux, phosphoric acid is added dropwise to trialkylchlorosilane, maintaining the reaction solution temperature at no more than 100°C. After the addition is complete, the reaction is carried out at 80-90°C for 2-4 hours. After the reaction is completed, impurities are removed at -0.05 to -0.01 MPa (removing low-boiling-point substances until no hydrogen chloride gas is emitted), followed by atmospheric distillation to remove impurities. The dropping rate of phosphoric acid should not be too fast, preferably completed within 4-5 hours. The molar ratio of trialkylchlorosilane to phosphoric acid is preferably (3-4):1, more preferably (3.2-3.6):1. The trialkylchlorosilane can be one or more of trimethylchlorosilane, triethylchlorosilane, dimethylvinylchlorosilane, dimethylisopropylchlorosilane, dimethylchloropropylchlorosilane, dimethyloctylchlorosilane, and dimethyl-dodecylchlorosilane (preferably trimethylchlorosilane), or it can be a byproduct of the production process of organosilicon intermediates.

[0012] Another key aspect of this invention is that it utilizes silanyl phosphate esters, obtained by reacting chlorosilanes (a byproduct of the production of organosilicon intermediates) with phosphoric acid, as the processing agent. This method efficiently utilizes byproducts, saving on the cost of external complexing agents and multi-stage distillation columns, and reducing equipment wear and tear.

[0013] In one specific embodiment of the present invention, the purification method for trichlorosilane provided by the present invention includes the following steps: mixing crude trichlorosilane with a treatment agent, and reacting at 80-90°C for 2 hours under a pressure of 0.05-0.1 MPa. The preferred reaction pressure for reacting the treatment agent with the crude trichlorosilane is 0.05-0.1 MPa. The preferred reaction temperature is 80-90°C, and the preferred reaction time is 1-2 hours.

[0014] In one specific embodiment of the present invention, the purification method for trichlorosilane provided by the present invention includes the following steps: after the reaction is completed, the pressure is released under nitrogen protection, cooled at normal pressure, and then distilled (to collect the trichlorosilane) to obtain the product. In this specific embodiment of the present invention, ice-salt water is typically used for cooling at normal pressure. The distillation pressure is approximately 0.04–0.05 MPa, and the distillation temperature is 58–62°C. Under these conditions, the trichlorosilane is collected to obtain the target product.

[0015] In a specific embodiment of the present invention, the crude trichlorosilane is an industrially produced crude trichlorosilane, which is well known in the art. Specifically, the crude trichlorosilane is obtained by reacting metallic silicon with hydrogen chloride. In existing industrial processes, the reaction conditions for this reaction are typically a pressure difference of 35-60 kPa and a reaction temperature of 300-400 °C. In the prior art, because metallic silicon contains other metallic impurities, the obtained crude trichlorosilane requires multi-stage dust removal and multi-stage distillation, resulting in numerous steps, a large number of pieces of equipment, and low efficiency. The purification method of the present invention can effectively reduce the number of steps, the number of pieces of equipment used, and the complexity of the process, achieving high efficiency and effectively reducing costs.

[0016] The purification method provided by this invention can obtain trichlorosilane with fewer impurities at low cost, and the resulting product can be directly used as a raw material for manufacturing solar-grade polysilicon in the photovoltaic industry. In this field, due to the rapid development of the photovoltaic industry, higher requirements have been placed on the quality of the raw material trichlorosilane. The national standard for trichlorosilane (GB 28654-2012) is no longer applicable compared to the standards and testing ranges of various polysilicon companies. However, this method allows us to obtain the trichlorosilane quality required by leading polysilicon companies. Taking a leading domestic polysilicon company as an example, its trichlorosilane specifications are: trichlorosilane purity ≥99.5%, total carbon ≤50ppb, boron ≤20ppb, phosphorus ≤50ppb, iron ≤20ppb, aluminum ≤20ppb, calcium ≤20ppb, magnesium ≤20ppb, copper ≤20ppb, titanium ≤20ppb, and arsenic ≤20ppb.

[0017] The purification method provided by this invention can efficiently and cost-effectively treat metallic and non-metallic impurities such as boron, phosphorus, iron, aluminum, calcium, and magnesium, meeting the manufacturing requirements of polycrystalline silicon raw materials for the photovoltaic industry and saving the need for multi-stage distillation to remove light and impurities. In a preferred embodiment, a silicon-containing phosphate ester can be prepared from the trialkylchlorosilane byproduct of organosilicon intermediate synthesis to treat metal ions, thereby reducing metallic impurities in trichlorosilane at a lower cost and higher efficiency. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] The preparation method of crude trichlorosilane in this embodiment of the invention includes the following steps: metallic silicon powder and dry hydrogen chloride are reacted in a synthesis furnace at 45-50 kPa and 340-360 °C. The synthesized crude trichlorosilane is then passed through a cyclone dust collector and a bag filter to remove silica ash and unreacted silicon powder impurities. Then, it is subjected to wet dust removal using the existing crude product as the spray liquid in a wet dust collector. Finally, the crude trichlorosilane is obtained through a water cooling and salt cooling device.

[0020] The specific quality indicators of the obtained crude trichlorosilane are as follows: air 0.015%, hydrogen chloride 0.026%, dichlorosilane 0.327%, trichlorosilane 77.772%, silicon tetrachloride 20.623%, methyltrichlorosilane 0.642%, hexachlorobissilane 0.427%, and octachlorotrisilane 0.168%.

[0021] Example 1

[0022] 1) Synthesis of treatment agent

[0023] Phosphoric acid was pre-treated under reduced pressure to remove moisture, with the moisture content controlled below 3000 ppm. Under nitrogen protection, 195.5 g of trimethylchlorosilane was added to a three-necked flask, and the mixture was heated to allow slight reflux. 49 g of dehydrated phosphoric acid was added dropwise, maintaining the reaction temperature below 100 °C for 4.5 ± 0.5 h. The reaction was then maintained at 80–90 °C for 2 h. After removing low-boiling point at -0.05–-0.01 MPa until no more hydrogen chloride was emitted, the temperature was slowly raised to 120 °C, and impurities were removed under normal pressure to obtain the treated agent.

[0024] 2) Specific purification steps

[0025] In an enamel-lined reactor, 1200g of crude trichlorosilane and 24g of the treatment agent obtained in step 1) were reacted at 0.07-0.08 MPa and 85±5℃ for 2 hours. After depressurization under nitrogen protection, the mixture was cooled with atmospheric pressure ice-salt water. After distillation in a first enamel-lined distillation column with an inner diameter of 30mm and a height of 80cm, the mixture was transferred to a second enamel-lined distillation column with an inner diameter of 30mm and a height of 120cm for further distillation. The pressure was controlled at 0.04-0.05 MPa and the temperature at 58-62℃ during the distillation process. The trichlorosilane was collected, cooled, and tested.

[0026] In this embodiment, the trichlorosilane obtained has a total carbon content of 16.43 ppb and a CG content of 99.86%. ICPMS analysis revealed the following metal elements: boron 1.24 ppb, phosphorus 4.37 ppb, iron 9.82 ppb, aluminum 2.78 ppb, calcium 4.88 ppb, magnesium 4.52 ppb, copper 3.42 ppb, and titanium 1.34 ppb. 、 Arsenic 0.76 ppb was used to obtain trichlorosilane, which meets the requirements for trichlorosilane used in photovoltaics.

[0027] Example 2

[0028] The raw materials and methods provided in this embodiment are the same as those in Example 1, except that the treatment agent is commercially available trimethylsilyl phosphate.

[0029] The trichlorosilane obtained in this embodiment has a total carbon content of 18.64 ppb and a CG content of 99.82%. ICPMS analysis showed the following metal elements: boron 1.89 ppb, phosphorus 4.21 ppb, iron 8.73 ppb, aluminum 3.92 ppb, calcium 3.95 ppb, magnesium 4.52 ppb, copper 3.66 ppb, titanium 1.57 ppb, and arsenic 0.85 ppb. The obtained trichlorosilane meets the requirements for photovoltaic trichlorosilane.

[0030] Example 3

[0031] The raw materials and methods provided in this embodiment are the same as those in Example 1, except that dimethylvinylchlorosilane, a byproduct of the synthesis of methylvinylchlorosilane, is used instead of trimethylchlorosilane in the treatment agent.

[0032] The trichlorosilane obtained in this embodiment has a total carbon content of 17.98 ppb and a CG content of 99.87%. ICPMS analysis showed the following metal elements: boron 2.36 ppb, phosphorus 3.67 ppb, iron 6.35 ppb, aluminum 2.97 ppb, calcium 5.36 ppb, magnesium 5.27 ppb, copper 4.42 ppb, titanium 1.88 ppb, and arsenic 0.81 ppb. The obtained trichlorosilane meets the requirements for photovoltaic trichlorosilane.

[0033] Example 4

[0034] The raw materials and methods provided in this embodiment are the same as those in Example 1. The only difference is that dimethylisopropylchlorosilane, a byproduct of the synthesis of methylisopropyldichlorosilane, is used instead of trimethylchlorosilane in the treatment agent.

[0035] The trichlorosilane obtained in this embodiment has a total carbon content of 22.64 ppb and a CG content of 99.81%. ICPMS analysis showed the following metal elements: boron 2.36 ppb, phosphorus 5.17 ppb, iron 8.47 ppb, aluminum 4.73 ppb, calcium 7.53 ppb, magnesium 6.92 ppb, copper 5.24 ppb, titanium 2.36 ppb, and arsenic 0.87 ppb. The obtained trichlorosilane meets the requirements for photovoltaic trichlorosilane.

[0036] Example 5

[0037] The raw materials and methods provided in this embodiment are the same as those in Example 1. The only difference is that dimethylchloropropylchlorosilane, a byproduct of the synthesis of methylchloropropyldichlorosilane, is used instead of trimethylchlorosilane in the treatment agent.

[0038] The trichlorosilane obtained in this embodiment has a total carbon content of 25.78 ppb and a CG content of 99.77%. ICPMS analysis showed the following metal elements: boron 5.36 ppb, phosphorus 6.17 ppb, iron 11.35 ppb, aluminum 6.95 ppb, calcium 8.46 ppb, magnesium 7.74 ppb, copper 4.82 ppb, titanium 2.69 ppb, and arsenic 2.11 ppb. The obtained trichlorosilane meets the requirements for photovoltaic trichlorosilane.

[0039] Example 6

[0040] The raw materials and methods provided in this embodiment are the same as those in Example 1, except that dimethyloctylchlorosilane is used instead of trimethylchlorosilane in the treatment agent.

[0041] The trichlorosilane obtained in this embodiment has a total carbon content of 25.64 ppb and a CG content of 99.83%. ICPMS testing showed the following metal elements: boron 8.74 ppb, phosphorus 8.33 ppb, iron 13.21 ppb, aluminum 8.34 ppb, calcium 9.42 ppb, magnesium 9.44 ppb, copper 5.93 ppb, titanium 2.83 ppb, and arsenic 2.05 ppb. The obtained trichlorosilane meets the requirements for photovoltaic trichlorosilane.

[0042] Example 7

[0043] The raw materials and methods provided in this embodiment are the same as those in Example 1, except that dimethyl n-dodecylchlorosilane is used instead of trimethylmonochlorosilane in the treatment agent.

[0044] The trichlorosilane obtained in this embodiment has a total carbon content of 28.21 ppb and a CG content of 99.85%. ICPMS analysis showed the following metal elements: boron 10.36 ppb, phosphorus 12.36 ppb, iron 16.36 ppb, aluminum 13.95 ppb, calcium 12.46 ppb, magnesium 14.77 ppb, copper 8.82 ppb, titanium 4.88 ppb, and arsenic 2.23 ppb. The obtained trichlorosilane meets the requirements for photovoltaic trichlorosilane.

[0045] Finally, the method of this invention is merely a preferred embodiment and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for purifying trichlorosilane, characterized in that, Includes the following steps: The treatment agent is reacted with crude trichlorosilane; the reaction conditions for the treatment agent and crude trichlorosilane are: 0.05-0.1 MPa, 80-90℃, reaction time 1-2 h. The treatment agent is a silicon-based phosphate ester; The preparation method of the crude trichlorosilane includes the following steps: reacting metallic silicon with hydrogen chloride to obtain crude trichlorosilane; The amount of the treatment agent added is 1-3 wt% of the crude trichlorosilane. The preparation method of the treatment agent includes the following steps: Under nitrogen protection and micro-reflux, phosphoric acid was added dropwise to trialkylchlorosilane, maintaining the reaction solution temperature at no more than 100°C. After the addition was complete, the reaction was carried out at 80~90°C for 2~4 hours. After impurity removal at -0.05~-0.01MPa, the mixture was then distilled at atmospheric pressure to remove impurities. The trialkylchlorosilane is trimethylmonochlorosilane, dimethylvinylchlorosilane, dimethylisopropylchlorosilane, dimethylchloropropylchlorosilane, dimethyloctylchlorosilane, or dimethyl-dodecylchlorosilane.

2. The purification method according to claim 1, characterized in that, The trialkylchlorosilane is a byproduct of the production process of organosilicon intermediates.

3. The purification method according to claim 1, characterized in that, The trialkylchlorosilane is trimethylchlorosilane.

4. The purification method according to claim 1, characterized in that, The molar ratio of the trialkylchlorosilane to phosphoric acid is (3~4):

1.

5. The purification method according to claim 4, characterized in that, The molar ratio of the trialkylchlorosilane to phosphoric acid is (3.2~3.6):

1.

6. The purification method according to any one of claims 1 to 5, characterized in that, The process also includes the following steps: after the reaction between the treatment agent and crude trichlorosilane is completed, the pressure is released under nitrogen protection, the mixture is cooled at atmospheric pressure, and then distilled to obtain the final product.