A closed loop process for simultaneous high value of silicon, fluorine components in silicon tetrafluoride

Abstract

The application discloses a closed loop process for synchronously increasing the value of silicon and fluorine components in silicon tetrafluoride, and belongs to the technical field of fluorine-containing silicon byproduct resource utilization. The steps are as follows: 1) mixing anhydrous alcohol with triethylamine, and introducing silicon tetrafluoride gas at 0-30 DEG C to generate alkyl orthosilicate and triethylamine monohydrofluoride; 2) distilling the reaction liquid to recover alcohol, performing vacuum rectification to obtain alkyl orthosilicate product, and separating to obtain triethylamine monohydrofluoride; 3) adding triethylamine monohydrofluoride into water, and performing heating reflux reaction with inorganic alkali or basic oxide to separate to obtain triethylamine crude product and fluorinated metal salt; 4) after dehydration rectification, the triethylamine crude product is recycled to step 1) with recovered alcohol; and the fluorinated metal salt is post-treated to obtain high-purity fluorinated metal salt. The process has low reaction temperature, high alkyl orthosilicate yield, recyclable triethylamine, all fluorine solidified into high-value-added products, no three-waste emissions, and can be continuously industrialized.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization technology of fluorinated silicon by-products, specifically involving a closed-loop process for the simultaneous high-value utilization of silicon and fluorine components in silicon tetrafluoride. Background Technology

[0002] Silicon tetrafluoride (SiF4) is a toxic and harmful byproduct generated in large quantities during phosphate rock beneficiation, phosphoric acid production, photovoltaic etching, and fluorochemical processes. It is highly corrosive and toxic. However, silicon tetrafluoride is also an important fluorine and silicon resource, and how to achieve its resource utilization has been a long-standing concern for related industries. Currently, the traditional mainstream treatment method is the wet absorption process, using water as the absorbent to react silicon tetrafluoride with water to produce fluorosilicic acid and, as a byproduct, silica. The obtained fluorosilicic acid can be further processed by concentrated sulfuric acid pyrolysis and distillation to produce anhydrous hydrogen fluoride. However, these processes suffer from low silicon resource utilization, low product added value, difficulty in treating fluorine-containing wastewater, high safety risks, and the inability to simultaneously utilize silicon and fluorine resources at high value, making it difficult to meet the requirements of modern chemical industry development for safety, greenness, efficiency, and high value.

[0003] Therefore, developing a safe, closed-loop, low-cost, and high-value-added co-production process to simultaneously increase the value of silicon and fluorine components in silicon tetrafluoride is of great industrial significance and application potential. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a closed-loop process for the simultaneous high-value utilization of silicon and fluorine components in silicon tetrafluoride. This process is a silicon tetrafluoride resource utilization process that features mild reaction, high yield of orthosilicate, recyclable triethylamine, complete curing of fluorine into high-value-added products, and zero emissions of waste.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A closed-loop process for simultaneously increasing the silicon and fluorine content in silicon tetrafluoride includes the following steps: 1) Synthesis reaction: Anhydrous alcohol and triethylamine are mixed and silicon tetrafluoride gas is introduced at 0-30°C. The reaction produces alkyl orthosilicate and triethylamine monohydrofluoride. 2) Distillation and separation: The alcohol in the reaction solution of step 1) is recovered by distillation, and the product of orthosilicate is obtained by vacuum distillation, and triethylamine monohydrofluoride is obtained by separation. 3) Aqueous phase regeneration: The triethylamine monohydrofluoride obtained in step 2) is added to water and reacted with an inorganic base or basic oxide under reflux to separate crude triethylamine and fluorinated metal salt. 4) Purification and recycling: The crude triethylamine obtained in step 3) is dehydrated and distilled, and then recycled with the alcohol recovered in step 2) to step 1); the fluorinated metal salt is then processed to obtain high-purity fluorinated metal salt.

[0006] The main reactions involved in the above process are as follows, with ethanol and Mg(OH)2 as examples: Main reaction 1: SiF4 + 4C2H5OH + 4Et3N = Si(OC2H5)4 + 4Et3N•HF Main reaction 2: 2Et3N•HF + Mg(OH)2 = 2Et3N + MgF2↓ + 2H2O According to the above scheme, the silicon tetrafluoride gas is pure silicon tetrafluoride gas or resource tail gas containing silicon tetrafluoride.

[0007] According to the above scheme, in step 1), the molar ratio of SiF4 to triethylamine is 1:4 to 4.05; the molar ratio of SiF4 to alcohol is 1:20 to 80.

[0008] According to the above scheme, in step 1), the anhydrous alcohol is methanol, ethanol, propanol or isopropanol.

[0009] According to the above scheme, in step 1), the alkyl orthosilicate is methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate or isopropyl orthosilicate; the specific product is determined based on the type of alcohol.

[0010] According to the above scheme, in step 1), when the system pH reaches 6.5~7.5 and tends to stabilize, stop the aeration and continue stirring for 0.5~2h to make the reaction complete.

[0011] According to the above scheme, in step 3), the molar ratio of silicon tetrafluoride to inorganic alkali or basic oxide is 1:4.04-4.4; wherein the alkali is in the form of OH groups. - In terms of molar quantity, basic oxides are determined by the amount of OH- they can provide upon complete hydration. - A measure of the amount of substance.

[0012] According to the above scheme, in step 3), the inorganic base is magnesium hydroxide, sodium hydroxide, or calcium hydroxide; the basic oxide is calcium oxide.

[0013] According to the above scheme, in step 3), the reflux reaction temperature is 80-100℃ and the reflux time is 1-3 h.

[0014] According to the above scheme, in step 4), triethylamine is dehydrated using solid KOH / NaOH and then subjected to atmospheric distillation.

[0015] According to the above scheme, the post-treatment of the fluorinated metal salt in step 4) specifically includes: When magnesium hydroxide is reacted with triethylamine monohydrofluoride, magnesium fluoride is obtained. The magnesium fluoride is filtered, acid-washed with a weak acid, washed with water, and dried to obtain high-purity magnesium fluoride. Preferably, the magnesium fluoride is ≥99%. Preferably, the weak acid is 0.8~1.2% dilute hydrochloric acid or dilute sulfuric acid.

[0016] When sodium hydroxide is reacted with triethylamine monohydrofluoride, sodium fluoride is obtained. The sodium fluoride product is obtained by concentrating the aqueous solution of sodium fluoride. When calcium hydroxide or calcium oxide is reacted with triethylamine monohydrofluoride, calcium fluoride is obtained. Calcium fluoride is then filtered, washed with water, and dried to obtain calcium fluoride. Alternatively, the dried calcium fluoride can be reacted with concentrated sulfuric acid to prepare anhydrous hydrogen fluoride. The anhydrous hydrogen fluoride then reacts with the triethylamine monohydrofluorate obtained in step 2) under anhydrous conditions to obtain triethylamine trihydrofluorate. At this point, the triethylamine monohydrofluorate obtained in step 2) is divided into two parts for reaction: one part reacts with calcium hydroxide or calcium oxide, and the remainder reacts with anhydrous hydrogen fluoride. The two parts of triethylamine monohydrofluorate are distributed according to the stoichiometric ratio of the reactions.

[0017] Preferably, the molar ratio of calcium fluoride to concentrated sulfuric acid is 1:1.1 to 1.3.

[0018] Preferably, calcium fluoride reacts with concentrated sulfuric acid at 120–160°C for 1–3 hours to generate hydrogen fluoride gas, which is then condensed through multiple stages to obtain anhydrous hydrogen fluoride.

[0019] Preferably, triethylamine trihydrofluoride is synthesized from anhydrous hydrogen fluoride and triethylamine monohydrofluoride under low temperature, closed, and anhydrous conditions of 0-25°C, and the product has a water content of <0.1%.

[0020] According to the above scheme, the yield of tetraethyl orthosilicate is ≥95%, the recovery rate of triethylamine is ≥89%, and the purity of fluorinated metal salt is ≥99%.

[0021] Alkyl orthosilicates are key raw materials in the fields of organosilicon, electronic materials, ceramic coatings, and sol-gels, with stable market demand. Traditionally synthesized using silicon tetrachloride, they suffer from significant equipment corrosion and high hydrogen chloride treatment costs. Using silicon tetrafluoride as a raw material to prepare alkyl orthosilicates offers advantages in raw material cost and atom economy; however, current technologies struggle to achieve high-purity recovery of silicon atoms from silicon tetrafluoride, limiting their industrial-scale application.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a closed-loop process for the simultaneous high-value extraction of silicon and fluorine components from silicon tetrafluoride. A gas containing silicon tetrafluoride is passed into a mixture of anhydrous alcohol and triethylamine, resulting in alcoholysis and acid-binding reactions to generate alkyl orthosilicates and triethylamine monohydrofluorate. The alcohol is recovered, and the alkyl orthosilicate product and triethylamine monohydrofluorate are separated. The triethylamine monohydrofluorate is then reacted with an alkaline substance to release triethylamine and generate a fluoride metal salt. The recovered alcohol and triethylamine can be recycled for further alcoholysis and acid-binding reactions, simultaneously yielding high-value orthosilicate. Alkyl ester products and fluorinated metal salts; the entire process achieves full resource utilization of Si, F, triethylamine, and alcohol, with a yield of ethyl orthosilicate ≥95%, a triethylamine recovery rate ≥89%, and a purity of fluorinated metal salts ≥99%; the reaction conditions are mild, with no fluorine-containing waste generated, and triethylamine and alcohol can be recycled, forming a closed-loop process that is green, environmentally friendly, low-cost, and suitable for continuous industrial production. It is applicable to the high-value utilization of silicon tetrafluoride byproducts in phosphorus chemicals, fluorine chemicals, and photovoltaics, as well as the industrial production of orthosilicates and high-purity magnesium fluoride, and has significant industrial application value.

[0023] 2. Furthermore, when triethylamine monohydrofluoride reacts with calcium hydroxide or calcium oxide, fluoride ions are completely separated in the form of calcium fluoride precipitate. Calcium fluoride is then reacted with concentrated sulfuric acid to produce anhydrous hydrogen fluoride, which is then reacted with triethylamine monohydrofluoride under anhydrous conditions to synthesize triethylamine trihydrofluoride. This achieves the simultaneous high-value utilization of both fluorine and silicon elements in silicon tetrafluoride, and the dual production of ethyl silicate and triethylamine trihydrofluoride, which has significant application value. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of an embodiment of the present invention, taking magnesium hydroxide as an example. Detailed Implementation

[0025] The present invention will be further illustrated below using ethanol as a specific example, but this is not intended to limit the scope of the invention.

[0026] Figure 1 This is a process flow diagram of an embodiment of the present invention, taking magnesium hydroxide as an example, wherein the material flow direction is as follows: Silicon tetrafluoride, anhydrous corresponding alcohol, and triethylamine are fed into a synthesis reactor for reaction; the reaction solution is fed into a distillation unit to recover the corresponding alcohol and is recycled; the alcohol-free solution is fed into a rectification unit to obtain orthosilicate products; the triethylamine monohydrofluoride from the bottom of the rectification reactor is fed into an aqueous phase regeneration reactor to react with magnesium hydroxide; the reaction solution is fed into a separation tank, the upper layer of crude triethylamine is fed into a triethylamine purification unit, purified and recycled back to the synthesis reactor; the lower layer of magnesium fluoride suspension is fed into a filtration and drying unit to obtain high-purity magnesium fluoride products.

[0027] Example 1 A closed-loop process for simultaneously increasing the silicon and fluorine content in silicon tetrafluoride is provided, comprising the following steps: 1) Add 4000g of anhydrous ethanol and 1050g of triethylamine to a 10L reactor equipped with a stirrer, condenser and tail gas absorption device. Stir and cool to 10℃. Introduce 270g of silicon tetrafluoride over 2 hours, controlling the introduce rate to keep the reaction temperature ≤25℃, until the pH of the reaction system is maintained at 6.5-7.5 and tends to stabilize. Stop the gas introduction and continue stirring for 1 hour to make the reaction complete, and obtain a mixed system of tetraethyl orthosilicate and triethylamine monohydrofluoride.

[0028] 2) The reaction solution obtained in step 1) was distilled to obtain anhydrous ethanol with a recovery rate of 98%, which can be directly reused in the alcoholysis reaction in step 1); the fraction at 75-85℃ was collected by vacuum distillation (-0.09MP) to obtain 532g of tetraethyl orthosilicate with a yield of 98.5%, and triethylamine monohydrofluoride was separated.

[0029] 3) Add the triethylamine monohydrofluoride obtained in step 2) to a 10L reactor, add 4L of water, add 317g of magnesium hydroxide (based on the theoretical amount of triethylamine monohydrofluoride produced, magnesium hydroxide is in excess by 5%), and reflux at 98℃ for 2.5h.

[0030] 4) The reaction solution obtained in step 3) is cooled and separated into organic phases of triethylamine and magnesium fluoride. The triethylamine is dehydrated with solid KOH / NaOH to obtain 952g of crude product, which is then distilled at atmospheric pressure to obtain 948g, with a recovery rate of 90.3%, and can be directly reused in the alcoholysis reaction in step 1). The magnesium fluoride is acid-washed with 1% dilute hydrochloric acid, washed with water, and dried at 110℃ to obtain 320g, with a fluorine curing rate of nearly 100% and a purity of 99.5%.

[0031] Example 2 A closed-loop process for the simultaneous high-value extraction of silicon and fluorine components in silicon tetrafluoride is provided. The specific steps are the same as in Example 1, except that the synthesis temperature in step 1) is increased to 25°C. Specifically, the yield of tetraethyl orthosilicate is 98.2%, the recovery rate of triethylamine is 89.7%, the purity of magnesium fluoride is 99.5%, and the fluorine curing rate is nearly 100%.

[0032] Example 3 A closed-loop process for the simultaneous high-value extraction of silicon and fluorine components in silicon tetrafluoride is provided. The specific steps are the same as in Example 1, except that in step 3), 332g of magnesium hydroxide is added, which is equivalent to a 10% excess of magnesium hydroxide based on the theoretical production of triethylamine monohydrofluoride. Specifically, the yield of tetraethyl orthosilicate is 98%, the triethylamine recovery rate is 91.2%, the purity of magnesium fluoride is 99.2%, and the fluorine curing rate is nearly 100%.

[0033] Example 4 A closed-loop process for simultaneously increasing the silicon and fluorine content in silicon tetrafluoride includes the following steps: 1) In a 1000mL four-necked reaction flask equipped with a stirrer, condenser, and exhaust gas absorber, add 600mL of anhydrous ethanol and 80g of triethylamine. Turn on the stirrer and cool to 12℃. Slowly introduce 20.6g of silicon tetrafluoride gas, controlling the introduction rate to keep the reaction temperature below 25℃, until the pH of the reaction system is maintained at 6.5-7.0. Stop the gas introduction and continue stirring for 30min to ensure the reaction is complete, producing a mixed system of tetraethyl orthosilicate and triethylamine monohydrofluoride.

[0034] 2) The reaction solution obtained in step 1) is distilled to obtain anhydrous ethanol, which can be directly reused in the alcoholysis reaction in step 1); the fraction at 75-85℃ is collected by vacuum distillation (-0.09MP) to obtain tetraethyl orthosilicate product with a yield of 95.2% and a purity of 99.1%, and triethylamine monohydrofluoride residue is also obtained.

[0035] 3) Add the residual triethylamine monohydrofluoride to the reactor, add 400 mL of water, and add 33.6 g of sodium hydroxide (based on the theoretical amount of triethylamine monohydrofluoride produced, sodium hydroxide is in excess by 5%). Reflux and stir at 98 °C for 60 min.

[0036] 4) The reaction solution obtained in step 3) is separated into two phases: an organic phase of triethylamine and an aqueous phase of sodium fluoride. The triethylamine is simply dehydrated and then distilled, and can be directly reused in the alcoholysis reaction in step 1), with a reuse rate of 94.5%. The sodium fluoride aqueous solution is concentrated to obtain sodium fluoride product, with a fluorine recovery rate of 96.8% and a purity of 99.5%.

[0037] Example 5 A closed-loop process for simultaneously increasing the silicon and fluorine content in silicon tetrafluoride is provided, with specific steps similar to those in Example 4, wherein: Add 620 mL of anhydrous ethanol and 82 g of a mixed alkali (fresh triethylamine and recycled triethylamine in a 1:1 mass ratio) to a 1000 mL reaction flask. Stir and cool to 12 °C, then start introducing 21 g of silicon tetrafluoride. Control the reaction temperature to not exceed 28 °C. Continue the reaction until the pH of the reaction system is maintained at 6.5–7.0 and tends to stabilize. After the system no longer releases heat significantly, stop the gas flow and continue stirring for 30 min.

[0038] Tetraethyl orthosilicate was obtained with a yield of 94.9% and a purity of 99.0%. The byproduct triethylamine monohydrofluoride was neutralized with sodium hydroxide (5% excess alkali) after being added to water. The mixture was then refluxed at 98°C for 60 min with stirring. After separation and post-treatment, triethylamine and sodium fluoride were obtained. The triethylamine recovery rate was 93.8%, the fluorine recovery rate was 96.5%, and the purity of sodium fluoride was 99.3%.

[0039] Example 6 A closed-loop process for simultaneously increasing the silicon and fluorine content in silicon tetrafluoride includes the following steps: 1) Add 750 mL of ethanol and 100 g of triethylamine to a dry reaction vessel, stir and cool to 20 °C, slowly introduce 25.8 g of silicon tetrafluoride gas, control the reaction temperature to not exceed 30 °C, and react until the pH of the system is maintained at 6.5-7.5 and tends to stabilize. Stop the gas supply and continue stirring for 40 min to make the reaction complete, and generate a mixed system of ethyl silicate and triethylamine monohydrofluoride.

[0040] 2) The reaction solution obtained in step 1) is distilled to obtain ethanol, which can be directly reused in the alcoholysis reaction in step 1); then vacuum distillation is carried out, and the fraction at 75-85℃ is collected to obtain ethyl silicate product with a yield of 96% and a purity of ≥99.0%, and triethylamine monohydrofluoride is separated.

[0041] 3) Add the triethylamine monohydrofluoride obtained in step 2) of 2 / 3 to the reactor, add 330 mL of water and calcium oxide. Based on the theoretical amount of triethylamine monohydrofluoride produced, the molar ratio of triethylamine monohydrofluoride to calcium oxide is 2:1.05 (calcium oxide in excess of 5%). Reflux and stir at 98°C for 1.5 h to generate calcium fluoride precipitate and release triethylamine organic phase.

[0042] 4) The reaction liquid obtained in step 3) is centrifuged and filtered to achieve solid-liquid separation, resulting in calcium fluoride filter cake and triethylamine organic phase. The triethylamine is dehydrated by distillation and returned to step 1) as raw material for recycling, with a recovery rate of 95%.

[0043] 5) After washing the calcium fluoride filter cake obtained in step 4), dry it at 105°C to constant weight, mix it with concentrated sulfuric acid at a molar ratio of 1:1.2, heat it to 130°C and react for 2 hours. The generated hydrogen fluoride gas is then purified through multi-stage condensation to obtain anhydrous liquid hydrogen fluoride.

[0044] 6) Pass the anhydrous hydrogen fluoride obtained in step 5) into the remaining 1 / 3 of the triethylamine monohydrofluoride and react it under low temperature, closed and anhydrous conditions at 15°C to obtain triethylamine trihydrofluoride. The product has a water content of <0.1%.

[0045] The specific reaction process in this embodiment is as follows: (1) Fluorosilicone separation and amination reaction SiF4+ 4C2H5OH + 4Et3N → Si(OEt)4+ 4Et3N·HF (2) Calcium oxide neutralization and defluorination 2Et3N·HF + CaO → CaF2↓ + 2Et3N + H2O (3) Preparation of anhydrous hydrogen fluoride CaF2 + H2SO4(conc.) → 2HF↑ + CaSO4 (4) Synthesis of triethylamine trihydrofluoride Et3N·HF + 2HF → Et3N·3HF It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A closed-loop process for simultaneously increasing the value of silicon and fluorine components in silicon tetrafluoride, characterized in that, Includes the following steps: 1) Anhydrous alcohol and triethylamine are mixed, and silicon tetrafluoride gas is introduced at 0-30°C to react and produce alkyl orthosilicate and triethylamine monohydrofluoride; wherein the molar ratio of silicon tetrafluoride and triethylamine is 1:4-4.05; 2) The reaction solution from step 1) was distilled to recover the alcohol, and the product was obtained by vacuum distillation to obtain alkyl orthosilicate, and then triethylamine monohydrofluoride was separated. 3) Add the triethylamine monohydrofluoride obtained in step 2) to water, and react it with an inorganic base or basic oxide under reflux to separate crude triethylamine and fluorinated metal salt. 4) The crude triethylamine obtained in step 3) is dehydrated and distilled, then recycled with the recovered alcohol from step 2) to step 1); the fluorinated metal salt is then processed to obtain a high-purity fluorinated metal salt; wherein: Tetraethyl orthosilicate yield ≥95%, triethylamine recovery ≥89%, and fluorinated metal salt purity ≥99%.

2. The closed-loop process according to claim 1, characterized in that, In step 1), the molar ratio of SiF4 to alcohol is 1:20 to 80.

3. The closed-loop process according to claim 1, characterized in that, In step 1), the anhydrous alcohol is methanol, ethanol, propanol or isopropanol.

4. The closed-loop process according to claim 1, characterized in that, In step 1), when the system pH reaches 6.5-7.5 and tends to stabilize, stop the aeration and continue stirring for 0.5-2 hours to ensure the reaction is complete.

5. The closed-loop process according to claim 1, characterized in that, In step 3), the molar ratio of silicon tetrafluoride to an inorganic alkali or basic oxide is 1:4.04–4.4; wherein the alkali is in the form of OH groups. - In terms of molar quantity, basic oxides are determined by the amount of OH- they can provide upon complete hydration. - A measure of the amount of substance.

6. The closed-loop process according to claim 1, characterized in that, In step 3), the reflux reaction temperature is 80–100°C and the reflux time is 1–3 h.

7. The closed-loop process according to claim 1, characterized in that, In step 3), the inorganic base is magnesium hydroxide, sodium hydroxide, or calcium hydroxide; the basic oxide is calcium oxide.

8. The closed-loop process according to claim 7, characterized in that, In step 4), the post-treatment of the fluorinated metal salt specifically involves: When magnesium hydroxide is reacted with triethylamine monohydrofluoride, magnesium fluoride is obtained. After filtration, acid washing with a weak acid, water washing, and drying, high-purity magnesium fluoride is obtained. When sodium hydroxide is reacted with triethylamine monohydrofluoride, sodium fluoride is obtained. The sodium fluoride product is obtained by concentrating the aqueous solution of sodium fluoride. When calcium hydroxide or calcium oxide is reacted with triethylamine monohydrofluoride, calcium fluoride is obtained. Calcium fluoride is then filtered, washed with water, and dried to obtain calcium fluoride. Alternatively, the dried calcium fluoride can be reacted with concentrated sulfuric acid to prepare anhydrous hydrogen fluoride; the anhydrous hydrogen fluoride reacts with the triethylamine monohydrofluorate obtained in step 2) under anhydrous conditions to obtain triethylamine trihydrofluorate; at this time, the triethylamine monohydrofluorate obtained in step 2) is divided into two parts for reaction, one part reacts with calcium hydroxide or calcium oxide, and the remainder reacts with anhydrous hydrogen fluoride.

9. The closed-loop process according to claim 8, characterized in that, The molar ratio of calcium fluoride to concentrated sulfuric acid is 1:1.1 to 1.3; calcium fluoride and concentrated sulfuric acid react at 120 to 160°C for 1 to 3 hours to produce hydrogen fluoride gas, which is then condensed through multiple stages to obtain anhydrous hydrogen fluoride; anhydrous hydrogen fluoride is then reacted with triethylamine monohydrofluoride at 0 to 25°C under low temperature, closed, and anhydrous conditions to synthesize triethylamine trihydrofluoride with a water content of <0.1%.

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