Process for removing chlorine from orthosilicates

Abstract

The application discloses a method for removing chlorine from orthosilicate. The method comprises the following steps: providing a crude silicate product containing orthosilicate and chloro-orthosilicate; contacting the crude silicate product with a fluorinated salt to make the chloro-orthosilicate undergo a nucleophilic substitution reaction with the fluorinated salt and be converted into fluoro-orthosilicate; and separating the orthosilicate and fluoro-orthosilicate through rectification to obtain a pure orthosilicate product. The method provided by the application can convert chloro-orthosilicate into fluoro-orthosilicate through a substitution reaction with a soluble inorganic fluorinated salt, and convert organic chlorine into inorganic chloride, thus achieving good chlorine removal effect. The newly generated fluoro-orthosilicate has a large difference in boiling point from the product, which is very beneficial to subsequent rectification, and can obtain a pure orthosilicate product with a semiconductor-grade chlorine content. The method does not need to use a large amount of alcohol solvent and flammable treatment agent, is easy to operate, and can reuse the chlorine removal agent, is safe and controllable, has low cost, and is easy to scale up for industrial production.

Description

Technical Field

[0001] This invention relates to the field of orthosilicate purification technology, and more particularly to a method for removing chlorine from orthosilicates. Background Technology

[0002] Orthosilicates have a wide range of applications, with the most representative including methyl orthosilicate (TMOS, also known as tetramethoxysilane), ethyl orthosilicate (TEOS, also known as tetraethoxysilane), and propyl orthosilicate (TPOS, also known as tetrapropoxysilane). They are primarily used as electrical insulation materials, optical glass treatment agents, heat-resistant and chemically resistant coatings, refractory fillers, and binders for pigments. They are also used as intermediates in organic synthesis, organosilicon solvents, and crosslinking agents in silicone sealants. Additionally, they can serve as a silicon source, being important raw materials for abrasive particles in high-purity silica, quartz, aerogels, and chemical mechanical polishing (CMP) slurries for integrated circuits.

[0003] There are two main methods for synthesizing methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate: the silicon powder method and the silicon tetrachloride method. The silicon powder method involves reacting silicon powder with methanol, ethanol, or propanol in a chlorine-containing catalytic system to obtain methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate, with hydrogen gas as a byproduct. The silicon tetrachloride method involves reacting silicon tetrachloride with methanol or ethanol to obtain methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate, with hydrogen chloride as a byproduct.

[0004] For example, the reaction formula for the preparation of methyl silicate is shown below:

[0005] SiCl4+CH3OH→CH3OSiCl3+HCl↑(1);

[0006] CH3OSiCl3+CH3OH→(CH3O)2SiCl2+HCl↑(2);

[0007] (CH3O)2SiCl2+CH3OH→(CH3O)3SiCl+HCl↑(3);

[0008] (CH3O)3SiCl+CH3OH→(CH3O)4Si+HCl↑(4);

[0009] If the silicon tetrachloride process is incomplete, unsubstituted chlorine functional groups may remain in the product, such as methanol, ethanol, or propanol, resulting in the presence of chlorine-containing compounds. Similarly, the silica powder process uses chlorine-containing catalysts, therefore the product also contains chlorine-containing compounds.

[0010] The presence of these chlorine-containing compounds causes methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate to corrode metals and cause yellowing when used in coatings. When used as precursors for SiO2 thin films in CVD, the high-temperature reaction conditions generate free chloride ions from organic chlorides, corroding metal equipment and affecting the quality of the deposited SiO2 film. When used as precursors for high-purity silica sol, hydrolysis releases HCl, affecting the precise control of SiO2 synthesis and even leading to residual chloride ions in subsequent CMP applications, corroding silicon wafers and affecting planarization. Therefore, chlorine-containing methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate are unsuitable for subsequent high-purity applications, especially in the high-end semiconductor industry.

[0011] Existing purification processes for methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate primarily involve adsorption and distillation. Current distillation techniques mainly remove metallic impurities and impurities with significantly different boiling points. For organochlorine compounds with boiling points close to the product, distillation is insufficient for removal. For example, ethyl orthosilicate has a boiling point of 165.5°C, while triethoxychlorosilane has a boiling point of 156.0°C, a difference of less than 10°C, making effective separation by distillation difficult.

[0012] Chinese invention patent CN110498811A proposes a method for mixing crude tetraethyl orthosilicate with a sodium ethoxide ethanol solution, reacting the mixture first at a temperature not exceeding 60°C, and then continuing the reaction at 80°C–140°C to obtain the reacted material. The reacted material is then filtered to obtain a liquid phase, which is further purified by distillation to remove light and heavy components, yielding the tetraethyl orthosilicate product. This invention solves the problem of excessively high chlorine content in tetraethyl orthosilicate, effectively removing both free chloride ions and organic chlorine, reducing the chlorine content to below 50 ppb.

[0013] However, the preparation of sodium ethoxide in the aforementioned prior art requires metallic sodium and anhydrous ethanol. Metallic sodium is classified as a Class 1 flammable substance in contact with water (hazardous substances category GB 4.3), exhibiting strong chemical reactivity and reacting violently with water, posing a risk of combustion and explosion. The reaction between metallic sodium and ethanol produces hydrogen gas as a byproduct, making this process highly risky, and requiring inert gas protection throughout the preparation of sodium ethoxide. Even if commercially purchased sodium ethoxide is used directly, its highly flammable, strong alkali, and highly corrosive nature still poses significant safety risks. Furthermore, the large amount of ethanol solvent used in its purification process, which is used as a fore-distillate during distillation, still requires further safety or recovery treatment, leading to a cumbersome process and a sharp increase in costs. Summary of the Invention

[0014] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for removing chlorine from orthosilicates.

[0015] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0016] This invention provides a method for removing chlorine from orthosilicates, comprising:

[0017] A crude silicate product is provided, wherein the crude silicate product comprises orthosilicate and chloro-orthosilicate;

[0018] The crude silicate product is contacted with a soluble fluoride salt to allow the chloro-orthosilicate to undergo a nucleophilic substitution reaction with the fluoride salt at high temperature, converting it into a fluoro-orthosilicate.

[0019] The orthosilicate and fluoroorthosilicate are separated by distillation to obtain pure orthosilicate.

[0020] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0021] The dechlorination method provided by this invention involves a substitution reaction between inorganic fluoride salts and chloro orthosilicates to convert them into fluoro orthosilicates, and converts organic chlorine into inorganic chloride salts, resulting in a good dechlorination effect. The newly generated fluoro orthosilicates have a boiling point that differs greatly from that of the product, which is very beneficial for subsequent distillation and can obtain pure orthosilicates with a chlorine content reaching semiconductor grade.

[0022] The dechlorination method provided by this invention does not require the use of large amounts of alcohol solvents, sodium alkoxide solutions, and flammable treatment agents. It is highly operable, and the dechlorination agent can be reused, is safe and controllable, has low cost, and is easy to scale up for industrial production.

[0023] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below. Detailed Implementation

[0024] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0026] This invention provides a method for dechlorinating orthosilicates, comprising the following steps:

[0027] A crude silicate product is provided, wherein the crude silicate product comprises orthosilicate and chloro-orthosilicate.

[0028] The crude silicate is contacted with a soluble fluoride salt to allow the chloro-orthosilicate to undergo a nucleophilic substitution reaction with the fluoride salt at high temperature, converting it into a fluoro-orthosilicate.

[0029] The orthosilicate and fluoroorthosilicate are separated by distillation to obtain pure orthosilicate.

[0030] As some typical representative implementation cases, the dechlorination method provided in the embodiments of the present invention adopts the form of heating and mixing soluble inorganic fluoride salts with crude silicate esters to replace organic chlorides with fluorides, thereby increasing the boiling point difference between impurities and products. Then, light and heavy components are removed by distillation to obtain a pure product with low chlorine.

[0031] The principle behind the above technical solution is that Si-F (bond energy 560.6 kJ / mol) is more stable than Si-Cl (bond energy 368.2 kJ / mol). Fluoride ions, at high temperatures, replace Cl via an SN2 nucleophilic substitution reaction, forming an inorganic chloride salt. Due to the superior stability of Si-F, the newly formed fluorine-containing compound is more stable than the chlorine-containing compound, and its boiling point differs more significantly from the product. For example:

[0032] compound Boiling point (bp) Tetraethyl orthosilicate 165.5℃ Triethoxychlorosilane 156.0℃ Triethoxyfluorosilane 132.4℃

[0033] Triethoxychlorosilane has a boiling point of 156.0℃, while tetraethyl orthosilicate has a boiling point of 165.5℃. The difference in their boiling points is less than 10℃, making separation by distillation difficult. However, after fluorination, the boiling point of triethoxyfluorosilane decreases to 132.4℃, a difference of 33.1℃ from that of tetraethyl orthosilicate. This significantly facilitates their separation by distillation.

[0034] By utilizing the aforementioned difference in boiling points, the removal of chlorine impurities and the purification of orthosilicates were achieved.

[0035] Regarding the specific selection of orthosilicate, in some embodiments, the orthosilicate includes any one or a combination of two or more of methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate.

[0036] Correspondingly, in some embodiments, the chlorinated orthosilicate comprises the orthosilicate substituted with 1 to 3 chlorine atoms.

[0037] Regarding the specific reaction conditions, in some embodiments, the nucleophilic substitution reaction is carried out at a temperature of 60–200°C for a time of 1–20 h.

[0038] In some embodiments, the stirring rate is maintained at no less than 30 rpm during the nucleophilic substitution reaction.

[0039] More specifically, in some embodiments, when the orthosilicate is selected from methyl orthosilicate, the temperature of the nucleophilic substitution reaction is controlled at 60–120°C, in some preferred embodiments at 70–115°C, and in some further preferred embodiments at 80–110°C.

[0040] Alternatively, in some embodiments, when the orthosilicate is selected from tetraethyl orthosilicate, the temperature of the nucleophilic substitution reaction is 60–160°C, in some preferred embodiments it is 80–140°C, and in some further preferred embodiments it is 90–130°C.

[0041] Alternatively, in some embodiments, when the orthosilicate is selected from propyl orthosilicate, the temperature of the nucleophilic substitution reaction is 70–200°C, in some preferred embodiments it is 100–180°C, and in some further preferred embodiments it is 110–150°C.

[0042] Different orthosilicates have different preferred temperature ranges. As the molecular weight increases, the boiling points of orthosilicates and their corresponding chlorides gradually increase. It is necessary to optimize the nucleophilic substitution reactivity within the preferred temperature range to achieve a more complete fluorine substitution reaction, thereby obtaining a higher purity orthosilicate.

[0043] Regarding the reactant ratio, in some embodiments, the mass ratio of the fluoride salt to the crude silicate is greater than 1:1000.

[0044] More specifically, in some embodiments, the mass ratio of the fluoride salt to the crude silicate is 1:1000 to 1:1.

[0045] In addition to the above, the choice of soluble fluoride salt is also crucial. In some embodiments, the fluoride salt is selected from alkali metal fluorides to ensure the reaction proceeds. Of course, the range of options is not limited to this; other fluoride salts capable of achieving fluorine substitution reactions can also be used.

[0046] Specific choices include, for example, in some embodiments, potassium fluoride and / or sodium fluoride.

[0047] Furthermore, regarding more specific implementation details, in some implementations, the fluoride salt is subjected to a dehydration and drying treatment before contacting the crude silicate with the fluoride salt to ensure that no moisture is introduced.

[0048] In some embodiments, the receiving ratio of the fore-distillate, middle-distillate, and residue of the distillation is (5-30):(10-80):(5-20); the pure orthosilicate is obtained from the middle-distillate.

[0049] As some typical application examples of the above technical solutions, the soluble inorganic fluoride salt and orthosilicate can be mixed at a mass ratio of 1:1 to 1:1000. The dechlorination reaction temperature of methyl orthosilicate should be controlled at 60-120℃, preferably 70-115℃, and most preferably 80-110℃; the dechlorination reaction temperature of ethyl orthosilicate should be controlled at 60-160℃, preferably 80-140℃, and most preferably 90-130℃; the dechlorination reaction temperature of propyl orthosilicate should be controlled at 70-200℃, preferably 100-180℃, and more preferably 110-150℃.

[0050] Afterwards, continue heating and stirring for 1 to 20 hours, and finally distillation is carried out. The middle fraction is the low-chlorine, high-purity product.

[0051] Furthermore, the technical method provided by this invention can also realize the recycling of the dechlorination agent, and the operation is relatively simple. The reactor residue is directly mixed with new crude orthosilicate to form a new mixed reaction system, and the reaction is repeated. Of course, a more complex implementation method, such as evaporating and crystallizing the reactor residue to extract new independent fluoride salts, is also within the scope of this invention.

[0052] Regarding the chlorine content in the crude and pure products, in some embodiments, the chlorine content in the crude silicate is above 700 ppb.

[0053] In some embodiments, the chlorine content in the orthosilicate ester is below 50 ppb.

[0054] The technical solution of the present invention will be further described in detail below through several embodiments. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0055] Example 1

[0056] This embodiment illustrates the dechlorination and purification process of methyl orthosilicate, as detailed below:

[0057] Step 1: Sodium fluoride water removal treatment

[0058] 500g of sodium fluoride was calcined at 500℃ for 3 hours, cooled to room temperature, and then stored in a desiccator.

[0059] Step 2: Treat chlorine-containing methyl silicate with sodium fluoride.

[0060] 20g of dehydrated sodium fluoride and 1kg of methyl orthosilicate were added to a 2L flask equipped with a stirrer and a reflux condenser. The mixture was gradually heated to 100°C and refluxed for 2 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, the mixture was heated to the boiling point of methyl orthosilicate. The fractions were collected at a weight ratio of 20:60:20 for the fore-distillate, middle-distillate, and still-residue.

[0061] Step 3: Detect the chlorine content of methyl orthosilicate before and after treatment.

[0062] 100g of the middle fraction of methyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 1.

[0063] Table 1

[0064] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 860 31 <![CDATA[F - ]]> ND ND

[0065] Comparative Example 1-1

[0066] The dechlorination purification process of methyl orthosilicate in this comparative example is shown below:

[0067] Step 1: Sodium fluoride water removal treatment

[0068] 500g of sodium fluoride was calcined at 500℃ for 3 hours, cooled to room temperature, and then stored in a desiccator.

[0069] Step 2: Treat chlorine-containing methyl silicate with sodium fluoride.

[0070] 100g of dehydrated sodium fluoride and 1kg of methyl orthosilicate were added to a 2L flask equipped with a stirrer and a reflux condenser. The mixture was gradually heated to 50°C and refluxed for 2 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, it was heated to the boiling point of methyl orthosilicate. The fractions were collected in a weight ratio of 20:60:20 for the fore-distillate, middle-distillate, and still residue.

[0071] Step 3: Detect the chlorine content of methyl orthosilicate before and after treatment.

[0072] 100g of the middle fraction of methyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 2.

[0073] Table 2

[0074] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 860 843 <![CDATA[F - ]]> ND ND

[0075] The above comparative cases show that insufficient temperature during nucleophilic substitution reactions can lead to incomplete reactions, leaving a large amount of chloride residue that fails to meet semiconductor-grade purity requirements.

[0076] Example 2

[0077] This embodiment illustrates the dechlorination and purification process of tetraethyl orthosilicate, as detailed below:

[0078] Step 1: Potassium fluoride water removal treatment

[0079] 500g of potassium fluoride was vacuum-treated at -80kPa and high temperature at 150℃ for 8 hours. After cooling to room temperature, it was stored in a desiccator.

[0080] Step 2: Treat chlorine-containing ethyl silicate with potassium fluoride.

[0081] Add 20g of dehydrated potassium fluoride and 1kg of tetraethyl orthosilicate to a 2L flask equipped with a stirrer and a reflux condenser. Gradually heat the mixture to 120°C and reflux for 2 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, heat to the boiling point of tetraethyl orthosilicate. Collect the fractions at a weight ratio of 20:60:20 for the fore-distillate, middle-distillate, and still residue.

[0082] Step 3: Detect the chlorine content of tetraethyl orthosilicate before and after treatment.

[0083] 100g of the middle fraction of tetraethyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 3.

[0084] Table 3

[0085] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 752 26 <![CDATA[F - ]]> ND ND

[0086] Comparative Example 2-1

[0087] The dechlorination purification process of tetraethyl orthosilicate in this comparative example is shown below:

[0088] Step 1: Potassium fluoride water removal treatment

[0089] 500g of potassium fluoride was vacuum-treated at -80kPa and high temperature at 150℃ for 8 hours. After cooling to room temperature, it was stored in a desiccator.

[0090] Step 2: Treat chlorine-containing ethyl silicate with potassium fluoride.

[0091] Add 20g of dehydrated potassium fluoride and 1kg of tetraethyl orthosilicate to a 2L flask equipped with a stirrer and a reflux condenser. Gradually heat the mixture to 50°C and reflux for 10 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, heat to the boiling point of tetraethyl orthosilicate and collect the fractions at a weight ratio of 20:60:20 for the fore-distillate, middle-distillate, and still-residue.

[0092] Step 3: Detect the chlorine content of tetraethyl orthosilicate before and after treatment.

[0093] 100g of the middle fraction of tetraethyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 4.

[0094] Table 4

[0095] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 752 727 <![CDATA[F - ]]> ND ND

[0096] The above comparative cases show that insufficient temperature during nucleophilic substitution reactions can lead to incomplete reactions, leaving a large amount of chloride residue that fails to meet semiconductor-grade purity requirements.

[0097] Comparative Example 2-2

[0098] The dechlorination purification process of tetraethyl orthosilicate in this comparative example is shown below:

[0099] Step 1: Potassium fluoride water removal treatment

[0100] 500g of potassium fluoride was vacuum-treated at -80kPa and high temperature at 150℃ for 8 hours. After cooling to room temperature, it was stored in a desiccator.

[0101] Step 2: Treat chlorine-containing ethyl silicate with potassium fluoride.

[0102] Add 0.5g of dehydrated potassium fluoride and 1kg of tetraethyl orthosilicate to a 2L flask equipped with a stirrer and a reflux condenser. Gradually heat the mixture to 120°C and reflux for 2 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, heat to the boiling point of tetraethyl orthosilicate. Collect the fractions at a weight ratio of 20:60:20 for the fore-distillate, middle-distillate, and still residue.

[0103] Step 3: Detect the chlorine content of tetraethyl orthosilicate before and after treatment.

[0104] 100g of the middle fraction of tetraethyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 5.

[0105] Table 5

[0106] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 752 620 <![CDATA[F - ]]> ND ND

[0107] The above comparative cases show that when carrying out nucleophilic substitution reactions, insufficient concentration of fluoride ions will lead to incomplete reaction, leaving a large amount of chloride residue, which cannot meet the purity requirements of semiconductors.

[0108] Comparative Examples 2-3

[0109] The dechlorination purification process of tetraethyl orthosilicate in this comparative example is shown below:

[0110] Step 1: Calcium fluoride dewatering treatment

[0111] 500g of calcium fluoride was vacuum-treated at -80kPa and high temperature at 150℃ for 8 hours. After cooling to room temperature, it was stored in a desiccator.

[0112] Step 2: Treat chlorine-containing ethyl silicate with calcium fluoride.

[0113] 100g of dehydrated calcium fluoride and 1kg of tetraethyl orthosilicate were added to a 2L flask equipped with a stirrer and a reflux condenser. The mixture was gradually heated to 120°C and refluxed for 2 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, the mixture was heated to the boiling point of tetraethyl orthosilicate. The fractions were collected in a weight ratio of 20:60:20 for the fore-distillate, middle-distillate, and still residue.

[0114] Step 3: Detect the chlorine content of tetraethyl orthosilicate before and after treatment.

[0115] 100g of the middle fraction of tetraethyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 6.

[0116] Table 6

[0117] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 752 748 <![CDATA[F - ]]> ND ND

[0118] The above comparative cases show that when carrying out nucleophilic substitution reactions, it is necessary to select fluoride salts with sufficient solubility. Using calcium fluoride with insufficient solubility will result in the reaction not proceeding completely, leaving a large amount of chloride residue, which will not meet the purity requirements of semiconductors.

[0119] Example 3

[0120] This embodiment illustrates the dechlorination and purification process of propyl orthosilicate, as detailed below:

[0121] Step 1: Sodium fluoride water removal treatment

[0122] 500g of sodium fluoride was calcined at 500℃ for 3 hours, cooled to room temperature, and then stored in a desiccator.

[0123] Step 2: Treat chlorine-containing propyl silicate with sodium fluoride.

[0124] Add 20g of dehydrated sodium fluoride and 1kg of propyl orthosilicate to a 2L flask equipped with a stirrer and a reflux condenser. Gradually heat the mixture to 120°C and reflux for 2 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, heat to the boiling point of propyl orthosilicate. Collect the fractions at a weight ratio of 15:70:15 for the fore-distillate, middle-distillate, and still residue.

[0125] Step 3: Detect the chlorine content of propyl orthosilicate before and after treatment.

[0126] 100g of the middle fraction of propyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 7.

[0127] Table 7

[0128] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 792 27 <![CDATA[F - ]]> ND ND

[0129] Comparative Example 3-1

[0130] The dechlorination purification process of propyl orthosilicate in this comparative example is shown below:

[0131] Step 1: Sodium fluoride water removal treatment

[0132] 500g of sodium fluoride was calcined at 500℃ for 3 hours, cooled to room temperature, and then stored in a desiccator.

[0133] Step 2: Treat chlorine-containing propyl silicate with sodium fluoride.

[0134] 100g of dehydrated sodium fluoride and 1kg of propyl orthosilicate were added to a 2L flask equipped with a stirrer and a reflux condenser. The mixture was gradually heated to 60°C and refluxed for 5 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, the mixture was heated to the boiling point of propyl orthosilicate. The fractions were collected at a weight ratio of 15:70:15 for the fore-distillate, middle-distillate, and still residue.

[0135] Step 3: Detect the chlorine content of propyl orthosilicate before and after treatment.

[0136] 100g of the middle fraction of propyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 8.

[0137] Table 8

[0138] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 792 736 <![CDATA[F - ]]> ND ND

[0139] The above comparative cases show that insufficient temperature during nucleophilic substitution reactions can lead to incomplete reactions, leaving a large amount of chloride residue that fails to meet semiconductor-grade purity requirements.

[0140] Comparative Example 3-2

[0141] The dechlorination purification process of propyl orthosilicate in this comparative example is shown below:

[0142] Step 1: Sodium fluoride water removal treatment

[0143] 500g of sodium fluoride was calcined at 500℃ for 3 hours, cooled to room temperature, and then stored in a desiccator.

[0144] Step 2: Treat chlorine-containing propyl silicate with sodium fluoride.

[0145] Add 0.5g of dehydrated sodium fluoride and 1kg of propyl orthosilicate to a 2L flask equipped with a stirrer and a reflux condenser. Gradually heat the mixture to 120°C and reflux for 5 hours with a stirring speed of 60r / min. Then, while maintaining a constant stirring speed, heat to the boiling point of propyl orthosilicate. Collect the fractions at a weight ratio of 15:70:15 for the fore-distillate, middle-distillate, and still residue.

[0146] Step 3: Detect the chlorine content of propyl orthosilicate before and after treatment.

[0147] 100g of the middle fraction of propyl orthosilicate before and after treatment was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 9.

[0148] Table 9

[0149] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 792 685 <![CDATA[F - ]]> ND ND

[0150] The above comparative cases show that when carrying out nucleophilic substitution reactions, insufficient concentration of fluoride ions will lead to incomplete reaction, leaving a large amount of chloride residue, which cannot meet the purity requirements of semiconductors.

[0151] Example 4

[0152] This example demonstrates the dechlorination and purification of methyl orthosilicate, showing the reuse of the dechlorination agent as detailed below:

[0153] Step 1: In Example 1, the reactor residue contained 200g of methyl orthosilicate and 20g of sodium fluoride. 800g of chlorinated methyl orthosilicate raw material was added to the reactor.

[0154] Step 2: Treat chlorine-containing methyl silicate with sodium fluoride.

[0155] The mixture from step one is gradually heated to 100°C and refluxed for 2 hours at a stirring speed of 60 r / min. Then, while maintaining the stirring speed, it is heated to the boiling point of methyl orthosilicate and collected according to the weight ratio of the fore-distillate, middle-distillate, and residue in the still is 20:60:20.

[0156] Step 3: Detect the chlorine content of methyl orthosilicate before and after treatment.

[0157] 100g of the middle fraction of methyl orthosilicate before and after heating and reflux was mixed with 100g of deionized water at room temperature and stirred for 30min, then allowed to stand for 30min. The upper aqueous phase was collected and subjected to anion exchange chromatography to analyze the chloride ion content. The analytical results are listed in Table 10.

[0158] Table 10

[0159] Before processing (ppb) After processing (ppb) <![CDATA[Cl - ]]> 702 23 <![CDATA[F - ]]> ND ND

[0160] This example illustrates that soluble fluoride salts can still achieve good dechlorination even after repeated use. Inorganic chlorine (sodium chloride or potassium chloride) is present in the residue in the reactor, and the middle fraction is a qualified low-chlorine product.

[0161] Based on the above embodiments and comparative examples, it is clear that the dechlorination method provided by the embodiments of the present invention converts inorganic fluoride salts into fluorosilicates through a substitution reaction with chlorosilicates, and converts organic chlorine into inorganic chlorides, resulting in good dechlorination effect. The boiling point of the newly generated fluorosilicates differs greatly from that of the product, which is very beneficial for subsequent distillation, and can obtain pure silicates with a chlorine content reaching semiconductor grade. It does not require the use of large amounts of alcohol solvents and flammable treatment agents, is highly operable, the dechlorination agent can be reused, it is safe and controllable, low in cost, and easy to scale up for industrial production.

[0162] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for removing chlorine from orthosilicates, characterized in that, include: A crude silicate product is provided, wherein the crude silicate product comprises orthosilicate and chloro-orthosilicate, wherein the orthosilicate is selected from any one or a combination of two or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate, and the chloro-orthosilicate is selected from the orthosilicate substituted with 1 to 3 chlorine atoms. The crude silicate ester is contacted with a fluoride salt to cause the chloro-orthosilicate to undergo a nucleophilic substitution reaction with the fluoride salt, converting it into a fluorinated orthosilicate ester. The mass ratio of the fluoride salt to the crude silicate ester is 1:1000 to 1:

1. The fluoride salt is selected from alkali metal fluorides. The temperature of the nucleophilic substitution reaction is 60 to 200°C, and the time is 1 to 20 hours. The orthosilicate and fluoroorthosilicate are separated by distillation to obtain pure orthosilicate.

2. The dechlorination method according to claim 1, characterized in that, During the nucleophilic substitution reaction, the stirring rate should be kept at no less than 30 rpm.

3. The dechlorination method according to claim 1, characterized in that, When the orthosilicate is selected from methyl orthosilicate, the temperature of the nucleophilic substitution reaction is 60~120℃; When the orthosilicate is selected from tetraethyl orthosilicate, the temperature of the nucleophilic substitution reaction is 60~160℃; When the orthosilicate is selected from propyl orthosilicate, the temperature of the nucleophilic substitution reaction is 70~200℃.

4. The dechlorination method according to claim 3, characterized in that, When the orthosilicate is selected from methyl orthosilicate, the temperature of the nucleophilic substitution reaction is 70~115℃; When the orthosilicate is selected from tetraethyl orthosilicate, the temperature of the nucleophilic substitution reaction is 80~140℃; When the orthosilicate is selected from propyl orthosilicate, the temperature of the nucleophilic substitution reaction is 100~180℃.

5. The dechlorination method according to claim 4, characterized in that, When the orthosilicate is selected from methyl orthosilicate, the temperature of the nucleophilic substitution reaction is 80~110℃; When the orthosilicate is selected from tetraethyl orthosilicate, the temperature of the nucleophilic substitution reaction is 90~130℃; When the orthosilicate is selected from propyl orthosilicate, the temperature of the nucleophilic substitution reaction is 110~150℃.

6. The dechlorination method according to claim 1, characterized in that, The fluoride salt is selected from potassium fluoride and / or sodium fluoride.

7. The dechlorination method according to claim 1, characterized in that, Before contacting the crude silicate with the fluoride salt, the fluoride salt is subjected to a dehydration and drying process.

8. The dechlorination method according to claim 1, characterized in that, The receiving ratio of the fore-distillate, middle-distillate, and residue in the distillation is (5-30):(10-80):(5-20). The pure orthosilicate is obtained from the middle fraction.

9. The dechlorination method according to claim 1, characterized in that, The crude silicate has a chlorine content of more than 700 ppb, while the pure orthosilicate has a chlorine content of less than 50 ppb.