Process for preparing high-purity alkyl orthosilicate and silicon dioxide from carbonate and waste silicon dioxide

Abstract

The invention discloses a process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide, comprising the following steps: S1, mixing a catalyst with waste silicon dioxide; S2, putting the mixture into a reactor, heating and putting carbonate into the reactor for reaction; S3, separating the products after the reaction, obtaining crude alkyl orthosilicate, carbon dioxide and catalyst, recovering the catalyst, and recycling it as the raw material in step S1; S4, separating and purifying the crude alkyl orthosilicate to obtain pure alkyl orthosilicate; S5, reacting the pure alkyl orthosilicate with deionized water to generate pure silicon dioxide and alkyl alcohol; S6, reacting the alkyl alcohol with the carbon dioxide obtained in step S3 to prepare carbonate, which is recycled as the raw material in step S2. The high-purity silicate and silicon dioxide prepared by the invention have very broad application prospects in semiconductors, high-purity quartz, high-end coatings and the like.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of alkyl orthosilicate and silicon dioxide, and in particular to a process for preparing high-purity alkyl orthosilicate and silicon dioxide by utilizing carbonate and waste silicon dioxide. Background Art

[0002] Alkyl orthosilicate (tetraalkoxysilane, referred to as silicate) is an important organosilicon compound with excellent stability and chemical inertness. It is widely used in the preparation of various organosilicon compounds, resin materials, insulating materials for the electronics industry, and corrosion-resistant paint preparation. High-purity silicate can be used to prepare high-purity quartz, catalyst carriers, etc.

[0003] The traditional method for synthesizing silicate esters is to react silicon tetrachloride and methanol. A large amount of hydrogen chloride gas will be produced during the reaction, which aggravates the corrosion of pipelines and equipment. It not only poses a great safety hazard, but also causes environmental pollution and other problems. In addition, as the reaction proceeds, the increase in hydrogen chloride content will inhibit the forward reaction, resulting in more side reactions and a lower yield of silicate esters. The silicate ester product obtained by this reaction has a high chloride ion content, which limits its application in high-end fields, such as the high-purity quartz required in the photovoltaic field.

[0004] The main application of silicates is the preparation of silicon dioxide. Silicon dioxide is the raw material for the manufacture of quartz glass, water glass, optical fiber, and refractory materials, which are important components of the electronics industry. It is also an important material for scientific research. The high-end field has very strict standards for the purity and impurity content of silicon dioxide. For example, the content of impurities such as chloride ions and metal ions is required to be ppm or even ppb level. The product obtained by the traditional method of preparing silicon dioxide by hydrolyzing silicon tetrachloride contains a large amount of impurities, such as metal ions and chloride ions, which is not applicable to the semiconductor and photovoltaic fields that require very high purity.

[0005] High-purity quartz crucibles are widely used in the photovoltaic and semiconductor fields. However, quartz crucibles will transform into silicon dioxide crystals (cristobalite) at high temperatures, which is called recrystallization, also known as "devitrification" or "crystallization". Crystallization causes the inner layer of the crucible to be destroyed, causing the structure of the growing silicon crystals to change and unable to grow normally; the thickness of the crucible is accelerated to thin, and then deformation occurs, so the crucible is scrapped and cannot be reused. For this type of discarded silicon dioxide, the industry currently hopes to recover silicon dioxide that has not undergone structural changes through separation and purification, but it is extremely difficult and difficult to achieve, and usually can only be treated as waste in the end.

[0006] Therefore, it is necessary to improve the existing technology to provide a more reliable solution. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a process for preparing high-purity alkyl orthosilicate and silicon dioxide by using carbonate and waste silicon dioxide in view of the above-mentioned deficiencies in the prior art.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide, comprising the following steps:

[0009] S1. mixing a catalyst with waste silicon dioxide, wherein the catalyst is an inorganic compound containing at least one Group IA alkali metal ion;

[0010] S2, putting the mixture obtained in step S1 into a reactor, heating it to a reaction temperature under the protection of an inert gas, and adding a carbonate to react;

[0011] S3, after the reaction is completed, the products are separated to obtain crude alkyl orthosilicate, carbon dioxide and catalyst, and the catalyst is recovered and recycled as a raw material in step S1;

[0012] S4, separating and purifying the crude alkyl orthosilicate to obtain a pure alkyl orthosilicate;

[0013] S5, pure alkyl orthosilicate reacts with deionized water to generate pure silicon dioxide and alkyl alcohol;

[0014] S6. The alkyl alcohol reacts with the carbon dioxide obtained in step S3 to prepare a carbonate ester, which is recycled as a raw material in step S2.

[0015] Preferably, the mixing method in step S1 can be to dissolve the catalyst in a solvent and then impregnate it on the waste silica, or the two can be directly mechanically mixed after grinding.

[0016] Preferably, the silicon dioxide contained in the waste silicon dioxide is amorphous silicon dioxide (such as white carbon black, etc.) or silicon dioxide crystals (such as cristobalite, quartz) or a mixture of multiple crystal forms.

[0017] Preferably, the catalyst is represented by A x B y , x=1-2, y=1; A is a Group IA alkali metal ion selected from Li + 、Na + , K + , Rb + , Cs + At least one of; B is selected from F - , Cl - Br - OH - 、SiO3 2- 、NO3 - 、CO32- 、HCO3 - 、SO4 2- At least one of .

[0018] Preferably, the mass ratio of the catalyst to the waste silica in step S1 is 0.05-20:1, and more preferably, the ratio is 3-10.

[0019] Preferably, when the silicon dioxide contained in the waste silicon dioxide is amorphous silicon dioxide, a lower reaction temperature can be used, and the reaction temperature in step S2 is 200-500° C.;

[0020] When the silicon dioxide contained in the waste silicon dioxide is silicon dioxide crystals, a higher reaction temperature is required, and the reaction temperature in step S2 is 400-550°C.

[0021] Preferably, the molecular formula of the carbonate is CO(OR)2, wherein R includes but is not limited to methyl, ethyl, etc. The carbonate in step S2 is at least one of dimethyl carbonate, diethyl carbonate, and dipropyl carbonate; the method of adding the carbonate into the reactor is to introduce the carbonate into the reactor in the form of gas phase, or to introduce the carbonate into the reactor using an inert gas as a carrier gas (at this time, the carbonate concentration is not less than 2wt%).

[0022] Preferably, the molar ratio of carbonate to waste silica in step S2 is 2-20:1.

[0023] Preferably, the inert gas in step S2 is at least one of helium, nitrogen and argon, and the pressure of the inert gas during the reaction is 0.1-0.5 MPa.

[0024] Preferably, the product in step S3 is separated by distillation or rectification. The tail gas at the outlet of the reactor is condensed to obtain a liquid product and carbon dioxide, wherein carbon dioxide is a non-condensable gas in the gas phase, and the catalyst is a product at the bottom of the reactor. The liquid product contains alkyl orthosilicate, a small amount of unreacted carbonate and ether substances (derived from the thermal decomposition of carbonate), and the liquid product is separated by distillation or rectification, and the carbonate is recovered and reused. The selectivity of alkyl orthosilicate is above 90%, more preferably above 97%, and other heavy products containing silicon do not exceed 5%, more preferably not more than 3%.

[0025] The silicate obtained by separation and purification reacts with water to obtain high-purity silicon dioxide and corresponding alcohol. Preferably, the alkyl orthosilicate is methyl orthosilicate or ethyl orthosilicate, and when the alkyl orthosilicate is methyl orthosilicate, the alkyl alcohol in step S5 is methanol; when the alkyl orthosilicate is ethyl orthosilicate, the alkyl alcohol in step S5 is ethanol.

[0026] Preferably, the high-purity alkyl orthosilicate prepared in the present invention can be used to prepare materials such as organosilicon compounds, high-purity quartz, optical fibers, etc. The high-purity silicon dioxide finally prepared can be used in semiconductors, high-purity quartz, high-end coatings, catalyst carriers, etc.

[0027] The present invention provides a new process for preparing high-purity silicate and silicon dioxide using waste silicon dioxide as raw material and carbonate as circulating medium. The overall process principle is:

[0028] Waste silicon dioxide and carbonate generate silicate, carbon dioxide and a small amount of ether substances under the action of inorganic salt (alkali) catalyst; since the waste silicon dioxide raw material is generally only impure in configuration but has extremely high chemical purity, the obtained product can be purified by distillation or rectification to obtain high-purity silicate, without introducing impurities such as metal ions and chloride ions as in traditional methods.

[0029] High-purity silicates can be hydrolyzed to obtain high-purity silicon dioxide and corresponding alcohols. High-purity silicon dioxide can be subsequently applied to fields such as semiconductors and photovoltaics to generate high value-added products. Alcohols can be synthesized with carbon dioxide in the presence of a catalyst to synthesize carbonates, thus achieving the recycling of carbonates and greatly reducing production costs.

[0030] After high-purity silicate is hydrolyzed, high-purity silicon dioxide and corresponding alcohol can be directly obtained. These high-purity silicon dioxide can be further processed according to the requirements of different application fields to enhance its value. The alcohol obtained by hydrolysis of silicate can react with carbon dioxide under the action of catalyst to form carbonate, thus realizing the recycling of carbonate.

[0031] Among them, the main reactions involved are as follows:

[0032] SiO2+2CO(OR)2=Si(OR)4+2CO2 (1)

[0033] Si(OR)4+2H2O=SiO2+4ROH (2)

[0034] 2ROH+CO2=CO(OR)2+H2O (3)

[0035] It can be seen that through the above reaction, high-purity silicate and silicon dioxide are prepared using waste silicon dioxide as raw material and carbonate as circulating medium, thus realizing waste utilization; and it has the advantages of simple process, low cost and high product purity.

[0036] The beneficial effects of the present invention are:

[0037] (1) The present invention provides a process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide. The present invention uses cheap silicon dioxide as raw material and carbonate as circulating medium, generates high-purity silicate and carbon dioxide under the action of inorganic salt (alkali) catalyst, and then uses silicate to hydrolyze to generate high-purity silicon dioxide and realizes the recycling of carbonate and catalyst. The high-purity silicate and silicon dioxide prepared by the present invention have very broad application prospects in semiconductors, high-purity quartz, high-end coatings and the like.

[0038] (2) The semiconductor and photovoltaic industries generate a large amount of waste silicon dioxide, which has no good way to be utilized. The process of the present invention can realize waste utilization and turn waste into treasure.

[0039] (3) The catalyst used in the present invention is cheap, readily available, low-cost, and can be recycled.

[0040] (4) The silicate prepared by the present invention has high purity and does not contain impurity ions such as metal ions and chloride ions.

[0041] (5) The raw material carbonate in the present invention can be recycled, thereby reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a flow chart of a process for preparing high-purity alkyl orthosilicate and silicon dioxide by using carbonate and waste silicon dioxide.

[0043] Figure 2 It is a gas chromatogram (GC spectrum) of the liquid product obtained in step S3 in Example 1 of the present invention.

[0044] Description of reference numerals:

[0045] 100 - mixer; 101 - silicate preparation reactor; 102 - distillation tower; 103 - hydrolysis reactor; 104 - carbonate preparation reactor. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0047] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0048] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially. Example

[0049] Reference Figure 1 This embodiment provides a process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide, comprising the following steps:

[0050] S1. Grind the catalyst and waste silicon dioxide and mix them evenly in a mixer 100, wherein the mass ratio of waste silicon dioxide to catalyst is 100:10, the waste silicon dioxide is provided by a domestic semiconductor company, and is a waste quartz crucible after crystal transformation, the main chemical component is silicon dioxide, and the crystal form is a mixture of cristobalite and amorphous silicon dioxide, and the catalyst is lithium carbonate (purity> 99%, Aladdin reagent);

[0051] S2. The mixture obtained in step S1 is placed in a silicate preparation reactor 101 and heated to 420°C under the protection of an inert gas (nitrogen, pressure of 0.1 MPa). o C and adding carbonate (specifically dimethyl carbonate, introduced in the form of gas phase) to react;

[0052] S3. After the reaction is completed, the tail gas at the outlet of the silicate preparation reactor is condensed to obtain a liquid product (i.e., crude alkyl orthosilicate) and carbon dioxide. The bottom product of the silicate preparation reactor is a catalyst, which is recycled and used as a raw material in step S1;

[0053] S4, the liquid product is purified by distillation separation in the distillation tower 102 to obtain a pure alkyl orthosilicate (specifically methyl orthosilicate), and the carbonate obtained by distillation separation can be recycled;

[0054] S5. At 30° C., methyl orthosilicate and deionized water are added into a hydrolysis reactor 103 in a molar ratio of 1:5 to react to generate high-purity silicon dioxide and an alkyl alcohol (specifically methanol);

[0055] S6. Methanol and the carbon dioxide obtained in step S3 are put into a carbonate preparation reactor 104 (fixed bed reactor) for reaction. The reaction is carried out at 120° C. and 1.2 MPa pressure under the action of a Cu-Ni-V2O5-SiO2 catalyst to prepare carbonate (specifically dimethyl carbonate), thereby realizing the circulation of dimethyl carbonate as a raw material in step S2.

[0056] Combination Figure 1 The materials and their proportions in each stage of the process of this embodiment are summarized in the following Table 1:

[0057] Table 1

[0058]

[0059] The catalyst in material 3 includes newly added catalyst (0.01 kg / h) and recycled catalyst; the dimethyl carbonate in material 9 includes newly added dimethyl carbonate (64.1 kg / h) and recycled dimethyl carbonate.

[0060] Referring to Table 2, which is the element detection result of the methyl orthosilicate finally prepared in step S4 of this embodiment, it can be seen that only sodium and titanium with a concentration of less than 100 ppb are detected in the methyl orthosilicate, which can be used in the semiconductor and photovoltaic fields with extremely high purity requirements.

[0061] Table 2

[0062]

[0063] Note: MDL means method detection limit, ND means not detected.

[0064] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide, characterized in that: The following steps are involved: S1. mixing a catalyst with waste silicon dioxide, wherein the catalyst is an inorganic compound containing at least one Group IA alkali metal ion; S2, putting the mixture obtained in step S1 into a reactor, heating it to a reaction temperature under the protection of an inert gas, and adding a carbonate to react; S3, after the reaction is completed, the products are separated to obtain crude alkyl orthosilicate, carbon dioxide and catalyst, and the catalyst is recovered and recycled as a raw material in step S1; S4, separating and purifying the crude alkyl orthosilicate to obtain a pure alkyl orthosilicate; S5, pure alkyl orthosilicate reacts with deionized water to generate pure silicon dioxide and alkyl alcohol; S6, the alkyl alcohol reacts with the carbon dioxide obtained in step S3 to prepare a carbonate ester, and the carbonate ester is recycled as a raw material in step S2; The carbonate in step S2 is at least one of dimethyl carbonate, diethyl carbonate and dipropyl carbonate; the method of adding the carbonate into the reactor is to introduce the carbonate into the reactor in the form of gas phase, or to introduce the carbonate into the reactor using an inert gas as a carrier gas; The alkyl orthosilicate is methyl orthosilicate or ethyl orthosilicate. When the alkyl orthosilicate is methyl orthosilicate, the alkyl alcohol in step S5 is methanol; when the alkyl orthosilicate is ethyl orthosilicate, the alkyl alcohol in step S5 is ethanol.

2. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 1, characterized in that: The silicon dioxide contained in the waste silicon dioxide is amorphous silicon dioxide or silicon dioxide crystals or a mixture of multiple crystal forms.

3. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 1, characterized in that: The catalyst is represented by A x B y , x=1-2, y=1; A is a Group IA alkali metal ion selected from Li + 、Na + , K + , Rb + , Cs + At least one of; B is selected from F - , Cl - Br - OH - 、SiO3 2- 、NO3 - 、CO3 2- 、HCO3 - 、SO4 2- At least one of .

4. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 3, characterized in that: The mass ratio of the catalyst to the waste silicon dioxide in step S1 is 0.05-20:

1.

5. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 2, characterized in that: When the silicon dioxide contained in the waste silicon dioxide is amorphous silicon dioxide, the reaction temperature in step S2 is 200-500° C.; When the silicon dioxide contained in the waste silicon dioxide is silicon dioxide crystals, the reaction temperature in step S2 is 400-550°C.

6. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 1, characterized in that: The molar ratio of carbonate to waste silicon dioxide in step S2 is 2-20:

1.

7. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 6, characterized in that: The inert gas in step S2 is at least one of helium, nitrogen and argon, and the pressure of the inert gas during the reaction is 0.1-0.5 MPa.

8. The process for preparing high-purity alkyl orthosilicate and silicon dioxide using carbonate and waste silicon dioxide according to claim 1, characterized in that: The product in step S3 is separated by distillation or rectification.

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