Tail gas treatment method for electronic grade polysilicon

Abstract

The invention discloses a method for treating tail gas of electronic grade polysilicon, wherein the tail gas is eluted with an eluent in an eluent tower, the eluent includes an organic amine, and a separation gas and a separation liquid are obtained, the separation gas is discharged from the top of the eluent tower, the separation gas includes hydrogen, and the separation liquid includes trichlorosilane, silicon tetrachloride, organic amine and chloramine; the separation liquid is input into a reactor from the eluent tower, so that the separation liquid reacts with a high boiling point introduced into the reactor to obtain a liquid to be rectified, the liquid to be rectified includes an organic amine, trichlorosilane and silicon tetrachloride, and the high boiling point includes at least one of Si2Cl6 and Si3Cl8; the liquid to be rectified is rectified in a distillation tower to obtain a rectified gas and a mixed liquid after distillation, the rectified gas includes trichlorosilane and silicon tetrachloride, and the mixed liquid after distillation includes an organic amine. The method has high production efficiency and low cost, and can effectively remove impurities in the tail gas of electronic grade polysilicon.

Description

Technical Field

[0001] The invention belongs to the technical field of polysilicon, and in particular relates to a method for treating tail gas of electronic-grade polysilicon. Background Art

[0002] Electronic-grade polysilicon usually adopts the modified Siemens process, and reduction is the core link of its production of polysilicon rods. At a temperature of about 1100℃, high-purity polysilicon is produced by heterogeneous chemical deposition of trichlorosilane and hydrogen. However, the reaction is relatively complex and will produce a large number of by-products. At the same time, trichlorosilane itself cannot react completely, so the composition of the reduction tail gas is relatively complex, usually containing trichlorosilane, silicon tetrachloride, hydrogen chloride, hydrogen, etc. It is usually treated by the CDI process, but there is a lot of energy loss in this process. At the same time, the removal rate of hydrogen chloride and other impurities in the tail gas is not particularly outstanding, and there is still room for improvement.

[0003] In view of the above problems, the present invention provides a new tail gas treatment method, which solves the above problems and can treat the reduced tail gas at a low cost. Summary of the invention

[0004] The present invention aims to solve one of the above technical problems at least to a certain extent.

[0005] The present invention provides a method for treating tail gas of electronic grade polysilicon, wherein the tail gas comprises trichlorosilane, silicon tetrachloride, hydrogen chloride and hydrogen, and the method comprises: eluting the tail gas with an eluent in a elution tower, wherein the eluent comprises an organic amine, to obtain a separation gas and a separation liquid, wherein the separation gas is discharged from the top of the elution tower, the separation gas comprises the hydrogen, and the separation liquid comprises the trichlorosilane, the silicon tetrachloride, the organic amine and ammonium chloride;

[0006] The separated liquid is fed into the reactor from the leaching tower, so that the separated liquid reacts with the high boiling point introduced into the reactor to obtain a liquid to be distilled, wherein the liquid to be distilled includes the organic amine, the trichlorosilane and the silicon tetrachloride, wherein the high boiling point includes at least one of Si2Cl6 and Si3Cl8; the liquid to be distilled is distilled in the distillation tower to obtain a distillation gas and a mixed liquid after distillation, wherein the distillation gas includes the trichlorosilane and the silicon tetrachloride, and the mixed liquid after distillation includes the organic amine. Thus, the method has high production efficiency and low cost, and can effectively remove impurities in the tail gas of electronic-grade polysilicon.

[0007] According to an embodiment of the present invention, the elution temperature is -20°C to -5°C, and / or the pressure of the elution tower is 1 barg to 2.5 barg.

[0008] According to an embodiment of the present invention, during the elution process, the hydrogen chloride and the organic amine are complexed to form the ammonium chloride; in the presence of the organic amine, the high boiling point reacts with the ammonium chloride to form the trichlorosilane and the silicon tetrachloride.

[0009] According to an embodiment of the present invention, the pressure of the reactor is 1.5 barg to 3 barg, and the reaction temperature is 40° C. to 60° C.

[0010] According to an embodiment of the present invention, the high boiling substances come from a cold hydrogenation device.

[0011] According to an embodiment of the present invention, the distillation tower includes 50 to 80 theoretical plates, the pressure of the distillation tower is 1.5 barg to 5 barg, and the top temperature of the distillation tower is 60° C. to 115° C.

[0012] According to an embodiment of the present invention, the mixed liquid after distillation further includes the silicon tetrachloride.

[0013] According to an embodiment of the present invention, the separated gas further comprises at least one of trichlorosilane and silicon tetrachloride, and the tail gas treatment method further comprises: cooling the separated gas, and the cooling temperature is -25°C to -15°C.

[0014] According to an embodiment of the present invention, the tail gas further includes metal impurities, and the ammonium chloride is complexed with the metal impurities to generate organic salts.

[0015] According to an embodiment of the present invention, the mixed liquid after distillation is input from the distillation tower into the elution tower to perform the elution on the tail gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0017] Figure 1 A schematic flow chart of a method for treating tail gas of electronic-grade polysilicon according to an embodiment of the present invention;

[0018] Figure 2 The present invention is a flow chart of a method for treating tail gas of electronic-grade polysilicon according to an embodiment of the present invention.

[0019] Description of reference numerals:

[0020] 10: elution tower; 20: reactor; 30: distillation tower. DETAILED DESCRIPTION

[0021] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0022] The following describes the tail gas treatment method of electronic grade polysilicon proposed in the embodiment of the present invention with reference to the accompanying drawings. First, the tail gas treatment method of electronic grade polysilicon will be described with reference to the accompanying drawings.

[0023] Reference Figure 1 and Figure 2 The electronic grade polysilicon tail gas treatment method comprises the following steps:

[0024] Step S100: using an eluent to elute the tail gas in the eluent tower 10, the eluent comprising an organic amine, to obtain a separation gas and a separation liquid, the separation gas being discharged from the top of the eluent tower 10, the separation gas comprising hydrogen, and the separation liquid comprising trichlorosilane, silicon tetrachloride, organic amine and ammonium chloride.

[0025] According to an embodiment of the present invention, the tail gas is eluted with an eluent in the elution tower 10, wherein the tail gas includes trichlorosilane (TCS), silicon tetrachloride (STC), hydrogen chloride and hydrogen, and the eluent includes an organic amine, which may be at least one of dibutylamine, dioctylamine, N, N-dimethylaniline, aniline, cyclohexylamine, benzylamine, trimethylamine, triethylamine and tripropylamine. During the elution process, the separation gas containing hydrogen is discharged from the top of the elution tower 10, and the organic amine can efficiently absorb hydrogen chloride under low temperature conditions, that is, hydrogen chloride and the organic amine are complexed to form ammonium chloride, and the hydrogen chloride impurities in the tail gas are removed, so the separation liquid after elution includes at least trichlorosilane, silicon tetrachloride, organic amine and ammonium chloride.

[0026] According to an embodiment of the present invention, the elution temperature is -20°C to -5°C, such as -20°C, -15°C, -10°C, and -5°C, and the pressure of the elution tower is 1 barg to 2.5 barg, such as 1 barg, 1.5 barg, 2 barg, and 2.5 barg. Therefore, during the elution process, the organic amine can efficiently absorb hydrogen chloride under the above conditions, thereby achieving a better hydrogen chloride absorption effect.

[0027] There are no special requirements for the specific type of the elution tower 10 , and those skilled in the art can flexibly select a suitable elution tower 10 according to actual production requirements.

[0028] According to an embodiment of the present invention, in an actual production process, it is difficult to obtain a separated gas purely containing hydrogen only by eluting, so the separated gas usually also includes at least one of trichlorosilane and silicon tetrachloride chlorosilane gas. In order to further purify the hydrogen in the present invention, the tail gas treatment method of the present invention may further include: cooling the separated gas, the cooling temperature is -25°C to -15°C, such as -25°C, -22°C, -20°C, -18°C, -15°C. Thus, trichlorosilane and silicon tetrachloride can be liquefied at the above cooling temperature, separated from hydrogen, and relatively pure hydrogen can be obtained. The obtained pure hydrogen can be recycled for the production of polysilicon. Among them, there are no special requirements for the cooler used for cooling treatment, as long as the cooling temperature required by the present invention can be reached.

[0029] Step S200: The separated liquid is input into the reactor 20 from the elution tower 10, so that the separated liquid reacts with the high boiling point substances introduced into the reactor 20 to obtain a liquid to be distilled, wherein the liquid to be distilled comprises organic amines, trichlorosilane and silicon tetrachloride, wherein the high boiling point substances comprise at least one of Si2Cl6 and Si3Cl8.

[0030] According to an embodiment of the present invention, the separation liquid is input from the elution tower 10 into the reactor 20. In the reactor 20, in the presence of an organic amine, chloramine reacts with the high-boiling substances introduced into the reactor 20 to generate trichlorosilane and silicon tetrachloride. The reaction in the reactor 20 obtains a liquid to be distilled. Therefore, the liquid to be distilled includes organic amine, trichlorosilane and silicon tetrachloride.

[0031] The high boiling point includes at least one of Si2Cl6 and Si3Cl8. Thus, Si2Cl6 and Si3Cl8 can react effectively with ammonium chloride to further convert the ammonium chloride in the separated liquid into trichlorosilane and silicon tetrachloride.

[0032] In some embodiments, high boiling products may be derived from high boiling products such as Si2Cl6 and Si3Cl8 produced by side reactions in the process of converting silicon tetrachloride, silicon powder and hydrogen into trichlorosilane in the cold hydrogenation device, so that the recycling of raw materials can be achieved. In other embodiments, high boiling product reagents such as Si2Cl6 and Si3Cl8 can be directly introduced into the reactor 20, so that the high boiling products do not contain other impurities, which can ensure the good purity of trichlorosilane and silicon tetrachloride obtained later.

[0033] According to an embodiment of the present invention, the pressure of the reactor 20 is 1.5 barg to 3 barg, such as 1.5 barg, 2 barg, 2.5 barg, and 3 barg, and the reaction temperature is 40° C. to 60° C., such as 40° C., 45° C., 50° C., 55° C., and 60° C. Therefore, under the above pressure and reaction temperature range of the reactor 20, the conversion efficiency of the above conversion reaction of the present invention can be improved, thereby improving the tail gas impurity removal efficiency.

[0034] Wherein, the reaction time of the reactor has no special requirements, and those skilled in the art can flexibly select according to actual conditions, and no restriction is made here. In addition, the specific type of the reactor 20 has no special requirements, and those skilled in the art can flexibly select a suitable reactor 20 according to actual production requirements.

[0035] According to an embodiment of the present invention, the tail gas also includes metal impurities. In the reactor, ammonium chloride is complexed with the metal impurities to generate an organic salt, which is soluble in an organic solvent but insoluble in water, thereby effectively removing the metal impurities entrained in the tail gas, and having a good effect on improving the overall purity of the system. Among them, the metal impurities can be metals such as iron, chromium, nickel, copper, zinc, and sodium.

[0036] Step S300: distilling the liquid to be distilled in the distillation tower 30 to obtain a distillation gas and a distilled mixed liquid, wherein the distillation gas includes trichlorosilane and silicon tetrachloride, and the distilled mixed liquid includes an organic amine.

[0037] According to an embodiment of the present invention, a liquid to be distilled containing organic amine, trichlorosilane and silicon tetrachloride is distilled in a distillation tower 30, and the distillation gas includes trichlorosilane and silicon tetrachloride. The mixed liquid after distillation includes organic amine, and the distillation gas trichlorosilane (boiling point is 32 to 34°C) and silicon tetrachloride (boiling point is 57.6°C) are extracted from the top of the distillation tower 30. The top temperature of the distillation tower 30 is 60°C to 115°C, such as 60°C, 70°C, 80°C, 90°C, 100°C, and 115°C. Therefore, at the above temperature, trichlorosilane and silicon tetrachloride can be efficiently extracted from the top of the distillation tower 30, and subsequently incorporated into the system for continued use, so that the materials can be recycled and the production cost can be effectively reduced.

[0038] According to an embodiment of the present invention, the distillation tower 30 includes 50 to 80 theoretical plates, such as 50, 60, 70, and 80 theoretical plates, and the pressure of the distillation tower 30 is 1.5 barg to 5 barg, such as 1.5 barg, 2 barg, 2.5 barg, 3 barg, 3.5 barg, 4 barg, 4.5 barg, and 5 barg. Therefore, under the above distillation conditions, trichlorosilane and silicon tetrachloride can be effectively extracted, thereby improving the efficiency of tail gas impurity removal.

[0039] According to the embodiment of the present invention, as described above, the top temperature of the distillation tower 30 is 60°C to 115°C. If a relatively low top temperature of 60°C to 80°C is used, this temperature is close to the boiling point of silicon tetrachloride (STC), and some silicon tetrachloride cannot be completely distilled out. Therefore, in addition to the organic amine, the mixed liquid after distillation will also contain a certain amount of silicon tetrachloride. If a relatively high top temperature of 80°C to 115°C is used, a large part or all of the silicon tetrachloride (STC) can be separated out, and the mixed liquid after distillation may contain very little or no silicon tetrachloride.

[0040] Further, see Figure 1 As shown, the mixed solution after distillation containing organic amine or containing organic amine and silicon tetrachloride can be input from the distillation tower 30 to the elution tower 10 to elute the tail gas. In this way, the materials can be recycled and the production cost is effectively reduced.

[0041] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0042] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for treating tail gas of electronic grade polysilicon, wherein the tail gas comprises trichlorosilane, silicon tetrachloride, hydrogen chloride and hydrogen, characterized in that: include: The tail gas is eluted with an eluent in an eluent tower, wherein the eluent includes an organic amine, to obtain a separation gas and a separation liquid, wherein the separation gas is discharged from the top of the eluent tower, the separation gas includes the hydrogen, and the separation liquid includes the trichlorosilane, the silicon tetrachloride, the organic amine and ammonium chloride; The separated liquid is introduced into the reactor from the elution tower, so that the separated liquid reacts with the high boiling point product introduced into the reactor to obtain a liquid to be distilled, wherein the liquid to be distilled comprises the organic amine, the trichlorosilane and the silicon tetrachloride, wherein the high boiling point product comprises at least one of Si2Cl6 and Si3Cl8; The liquid to be rectified is subjected to rectification treatment in a rectification tower to obtain a rectification gas and a rectification mixed liquid, wherein the rectification gas comprises the trichlorosilane and the silicon tetrachloride, and the rectification mixed liquid comprises the organic amine, During the elution process, the hydrogen chloride and the organic amine are complexed to form the ammonium chloride; in the presence of the organic amine, the high boiling point reacts with the ammonium chloride to form the trichlorosilane and the silicon tetrachloride.

2. The method according to claim 1, characterized in that: The elution temperature is -20°C to -5°C, and / or the elution tower pressure is 1 barg to 2.5 barg.

3. The method according to claim 1, characterized in that The pressure of the reactor is 1.5 barg to 3 barg, and the reaction temperature is 40°C to 60°C.

4. The method according to claim 1, characterized in that: The high boilers come from the cold hydrogenation unit.

5. The method according to claim 1, characterized in that The distillation tower comprises 50 to 80 theoretical plates, the pressure of the distillation tower is 1.5 barg to 5 barg, and the top temperature of the distillation tower is 60° C. to 115° C.

6. The method according to claim 5, characterized in that The mixed liquid after distillation also includes the silicon tetrachloride.

7. The method according to any one of claims 1 to 6, characterized in that: The separated gas also includes at least one of trichlorosilane and silicon tetrachloride, and the tail gas treatment method further includes: cooling the separated gas, and the cooling temperature is -25°C to -15°C.

8. The method according to any one of claims 1 to 6, characterized in that: The tail gas also includes metal impurities, and the ammonium chloride is complexed with the metal impurities to generate organic salts.

9. The method according to any one of claims 1 to 6, characterized in that: The mixed liquid after distillation is input into the elution tower from the distillation tower to perform the elution on the tail gas.

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