Process for preparing alkyl orthosilicate and silicon dioxide from elemental silicon powder with the aid of carbonate

Abstract

The present invention discloses a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder. The present invention uses elemental silicon powder as a raw material and carbonate as a circulating medium, and forms alkyl orthosilicate (referred to as silicate) and carbon monoxide under the action of a solid catalyst. The silicate is hydrolyzed to obtain silicon dioxide and corresponding alcohol. The alcohol, carbon monoxide and oxygen are reacted with the catalyst to obtain carbonate, thereby forming a carbonate cycle. The high-purity silicate (and the corresponding silica) prepared by the present invention has broad application prospects in high-purity quartz glass, high-purity aerogel, high-end silica and catalyst carriers. The high-purity silica prepared by silicate hydrolysis can be used in semiconductors, photovoltaics, catalysts, silicon-based aerogels and other applications. The process of the present invention can convert waste elemental silicon powder into high-purity silica, and the raw materials consumed are oxygen and elemental silicon powder, with high atomic utilization, low raw material cost and process energy consumption.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of alkyl orthosilicate and silicon dioxide, and in particular to a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide by using elemental silicon powder. Background Art

[0002] Alkyl orthosilicate (tetraalkoxysilane), referred to as silicate, is an important organosilicon compound. Common ones include methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, etc. It can be widely used in resin synthesis, aerogel preparation, electronic component adhesive, precision castings, and heat-resistant and corrosion-resistant paint preparation. High-purity silicate also has many applications in silicon-based electronic chemicals, high-purity quartz, aerogel, catalyst carriers, etc.

[0003] The traditional synthesis method of alkyl orthosilicate is the liquid phase reaction of silicon tetrachloride with methanol or ethanol. Although the reaction temperature is not high, a large amount of hydrogen chloride gas will be produced as a by-product, which will cause great corrosion to equipment and pipelines, and the hydrochloric acid formed needs to be treated or recycled, which poses a great safety hazard and environmental pollution problem. In addition, a large amount of hydrogen chloride exists in the reaction system, which will inhibit the hydrolysis reaction of silicate in the later stage of the reaction, resulting in more side reactions and a low yield of alkyl orthosilicate. The product alkyl orthosilicate inevitably contains a large amount of chloride ions, which limits its application in high-end fields, such as the semiconductor industry and the field of high-purity silica.

[0004] Another method of producing silicates is to use silicon powder and alkyl alcohol as raw materials, add nano copper catalysts in the process, and synthesize alkyl orthosilicate in one step, with hydrogen as a by-product. Hydrogen can be recycled or directly burned to produce steam. Compared with the silicon tetrachloride route, this process route is more environmentally friendly, but it requires the use of expensive nano copper powder catalysts, and the nano copper powder catalyst forms a silicon copper alloy with silicon powder, which is difficult to separate and recycle, resulting in high costs. The product contains hydrogen, which poses a safety hazard.

[0005] The main application of silicate is to obtain silicon dioxide through hydrolysis. Silicon dioxide is widely used and is the main component of quartz, silica aerogel, and white carbon black. It has a wide range of uses in optics, semiconductors, photovoltaics, daily chemicals, coatings, construction, plastics and other fields. Among them, high-end silicon dioxide has very strict requirements on the purity and impurities of raw materials, such as metal ions, chloride ions and hydrogen content. High-end silicon dioxide requires at least ppm level or even ppb level for the above impurities.

[0006] In the field of optical glass, the use of high-purity silicates can improve the transparency and refractive index of glass, thereby improving optical properties. Due to the inertness of the formation of silica, silicates are also widely used in chemical-resistant coatings and heat-resistant coatings to enhance the durability and stability of the coatings. In terms of adhesives, the excellent properties of silicates make them a highly efficient adhesive, which is widely used in the bonding of various materials and can be used in the fields of refractory adhesives and precision casting. Of course, silicates can also be used as raw materials for the synthesis of organosilicon intermediates. For example, methyl silicate is a typical organosilicon reagent. Silicates can also be used as crosslinking agents for room temperature vulcanized silicone rubber. Through their unique reaction properties, silicone rubber has better vulcanization performance and stability.

[0007] The hydrolysis products of silicate esters can also be used to make phosphors. Phosphors are an important luminescent material widely used in display technology, lighting and other fields. This characteristic of silicate esters makes it also have certain application value in the field of phosphor manufacturing.

[0008] In the field of construction, silicates are also widely used. They can react with natural stones or other building materials to form silica sol inorganic substances (SiO 2 ), thereby enhancing the strength of the substrate. In addition, silicates can also be used in glass and plastic lens materials to provide them with ultra-hard anti-scratch coatings, effectively protecting the lens surface from damage.

[0009] Silicate ester is the raw material for preparing titanium silicon molecular sieve. However, the purity of the raw material of silicate ester is very important. Ethyl silicate is commonly used, and methyl silicate can also be used. Under the same quality, the latter can produce 40% more products than the former.

[0010] When silicon dioxide is prepared from silicon tetrachloride or water glass (sodium silicate) as raw materials, the product has a high impurity content, such as metal ions and chloride ions, and can only be used for low-end applications, and cannot be used in fields such as semiconductors and photovoltaics that require high raw material purity. When silicates are prepared by reacting elemental silicon powder with alcohols, expensive nano-copper powder catalysts are required, and there are problems such as catalyst recycling and safety in fluidized bed reactors. Although the prepared silicates have a high purity, the production cost is high, which is not conducive to large-scale production.

[0011] Therefore, it is necessary to improve the existing technology to provide a more reliable solution. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder in view of the above-mentioned deficiencies in the prior art.

[0013] In order to solve the above technical problems, the technical solution adopted by the present invention is: a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder, comprising the following steps:

[0014] S1. Mixing a first catalyst with elemental silicon powder, wherein the first catalyst is an inorganic compound containing at least one alkali metal ion or alkaline earth metal ion;

[0015] S2, putting the mixture obtained in step S1 into a reactor, introducing gas for purging, heating to the reaction temperature and adding carbonate for reaction;

[0016] S3. After the reaction is completed, the products are separated to obtain a crude alkyl orthosilicate, carbon monoxide and a first catalyst, and the first catalyst is recovered and recycled as a raw material in step S1;

[0017] S4, separating and purifying the crude alkyl orthosilicate to obtain a pure alkyl orthosilicate;

[0018] S5, pure alkyl orthosilicate reacts with deionized water to generate pure silicon dioxide and alkyl alcohol;

[0019] S6, the alkyl alcohol reacts with oxygen and the carbon monoxide obtained in step S3 under the action of a second catalyst to prepare a carbonate ester, which is recycled as a raw material in step S2.

[0020] Preferably, the first catalyst is represented by A x B y , x=1-2, y=1-2; A is selected from at least one of the positive ions corresponding to the following elements: Li, Na, K, Be, Mg, Ca, Sr, Ba; B is selected from F - , Cl - Br - ,I - OH - 、SiO 3 2- 、NO 3 - , CO 3 2- , HCO 3 - 、SO 4 2- At least one of .

[0021] Preferably, the first catalyst is a powdered solid catalyst or a catalyst solution formed by dissolving a solid catalyst in water, and the concentration of the first catalyst in the catalyst solution is 0.1 wt% to 20 wt%.

[0022] Preferably, the elemental silicon powder is waste elemental silicon powder, such as waste elemental silicon powder from cutting photovoltaic silicon wafers.

[0023] Preferably, the mass ratio of the first catalyst to the elemental silicon powder is 0.001-10.

[0024] Preferably, in step S2, the purge gas is at least one of helium, nitrogen, hydrogen and argon, and the purge gas pressure is 0.1-5 bar.

[0025] Preferably, in step S2, the reaction temperature is 200-600°C, more preferably 250-500°C.

[0026] Preferably, the carbonate in step S2 is at least one of dimethyl carbonate, diethyl carbonate and dipropyl carbonate; the method of introducing the carbonate into the reactor is to evaporate the carbonate to form superheated steam and introduce it into the reactor, or to use a purge gas as a carrier gas to introduce the carbonate into the reactor.

[0027] Preferably, the molar ratio of carbonate to elemental silicon powder in step S2 is 2 to 20:1.

[0028] Preferably, the product in step S3 is separated by distillation or rectification. In step S3, the tail gas at the outlet of the reactor is condensed to obtain a liquid product and carbon monoxide, wherein carbon monoxide is a non-condensable gas in the gas phase, and the first 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 monoorthosilicate is above 80%, more preferably above 98%, and the others are heavy products containing silicon, the proportion of which does not exceed 10%, more preferably not more than 2%.

[0029] Preferably, the carbonate has the molecular formula CO(OR) 2 , wherein R can be methyl, ethyl, propyl or butyl, etc.; more preferably, 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.

[0030] Preferably, in step S6, the molar ratio of alkyl alcohol: oxygen: carbon monoxide is 4:1:2, the second catalyst is a copper catalyst, and the mass ratio of the added amount of the second catalyst to the alkyl alcohol is 1 to 5:20.

[0031] Preferably, the high-purity alkyl orthosilicate prepared in the present invention can be used to prepare materials such as silicon aerogel, high-purity quartz, optical fiber, etc. The high-purity silicon dioxide finally prepared can be used in semiconductors, high-purity quartz, high-end coatings, catalyst carriers, etc.

[0032] The present invention provides a new process for producing high-purity silicate and silicon dioxide using carbonate (dimethyl carbonate, diethyl carbonate, etc.) as a circulating medium and elemental silicon powder as a raw material. The overall process principle is:

[0033] The present invention uses cheap inorganic salt (alkali) catalysts to react cheap elemental silicon powder (such as waste elemental silicon powder from photovoltaic silicon wafer cutting) with carbonate to generate silicate, carbon monoxide and a small amount of ether by-products. After simple separation and purification of the product, high-purity silicate (without impurities such as metal ions and chloride ions) can be obtained.

[0034] 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 be combined with carbon monoxide and oxygen under the action of copper catalyst to form carbonate, thus realizing the recycling of carbonate.

[0035] The relevant reactions are as follows:

[0036] Si+2CO(OR) 2 =Si(OR) 4 +2CO (1)

[0037] Si(OR) 4 +2H 2 O=SiO 2 +4ROH (2)

[0038] 4ROH+2CO+O 2 =2CO(OR) 4 +2H 2 O (3)

[0039] (1)+(2)+(3) gives the net reaction:

[0040] Si+O 2 =SiO 2 (4)

[0041] It can be seen that through the above reaction, carbonate can be used as a circulating medium, and with the assistance of a cheap catalyst, cheap waste silicon powder can be converted into high-purity silicate and silicon dioxide, thus turning waste into treasure. The entire process is highly efficient, has the advantages of low production cost, high product purity, and easy large-scale production.

[0042] The beneficial effects of the present invention are:

[0043] (1) The present invention provides a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder, wherein elemental silicon powder is used as a raw material and carbonate is used as a circulating medium, and an alkyl orthosilicate (referred to as silicate) and carbon monoxide are formed under the action of a solid catalyst, and silicate is hydrolyzed to obtain silicon dioxide and a corresponding alcohol, and alcohol, carbon monoxide and oxygen are reacted with the catalyst to obtain carbonate, thereby forming a carbonate cycle; the high-purity silicate (and the corresponding silicon dioxide) prepared by the present invention has broad application prospects in high-purity quartz glass, high-purity aerogel, high-end silicon dioxide and catalyst carriers, and the high-purity silicon dioxide prepared by hydrolysis of silicate can be used in semiconductors, photovoltaics, catalysts, silicon-based aerogels and other applications;

[0044] (2) The present invention can obtain high-purity silicate, which does not contain impurities such as metal ions and chloride ions;

[0045] (3) The present invention uses an inexpensive inorganic salt catalyst, which is low in cost, easily soluble in water, can be recycled, and does not form a compound with elemental silicon powder;

[0046] (4) In the whole process of the present invention, the carbonate can be recycled, which can greatly reduce the consumption of reactants;

[0047] (5) The process of the present invention can convert waste silicon powder into high-purity silicon dioxide. The raw materials consumed are oxygen and silicon powder. The atomic utilization rate is high, and the raw material cost and process energy consumption are low. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The present invention is a flow chart of a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder;

[0049] Figure 2 It is a gas chromatogram (GC spectrum, the horizontal axis is retention time, and the vertical axis is signal intensity) of the liquid product obtained in step S3 in Example 1 of the present invention.

[0050] Description of reference numerals:

[0051] 100 - mixer; 101 - silicate preparation reactor; 102 - distillation tower; 103 - hydrolysis reactor; 104 - carbonate preparation reactor. DETAILED DESCRIPTION

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Example 1

[0056] Reference Figure 1 This embodiment provides a carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder, comprising the following steps:

[0057] S1. Put the first catalyst and elemental silicon powder into a mixer 100 for mixing, wherein the mass ratio of elemental silicon powder to catalyst is 100:20, the first catalyst is sodium chloride (purity>99%, Sinopharm reagent), the elemental silicon powder is provided by a domestic semiconductor company, is waste silicon plate, and the main chemical component is elemental silicon;

[0058] S2, putting the mixture obtained in step S1 into a silicate preparation reactor 101, introducing gas (nitrogen, pressure of 0.1 MPa) for purging, heating to 300° C., and adding carbonate (specifically dimethyl carbonate DMC, introduced in the form of gas phase) for reaction;

[0059] S3, after the reaction is completed, the products are separated, and the tail gas at the outlet of the silicate preparation reactor 101 is condensed to obtain a liquid product (i.e., crude alkyl orthosilicate) and carbon dioxide, and the bottom product of the silicate preparation reactor is the first catalyst and unreacted elemental silicon powder, which are recovered and recycled as the raw materials in step S1;

[0060] S4, the crude alkyl orthosilicate is distilled and separated and purified by a distillation tower 102 to obtain a pure alkyl orthosilicate (specifically methyl orthosilicate TMOS), and the carbonate obtained by distillation and separation can be recycled;

[0061] S5, methyl orthosilicate and deionized water are put into a hydrolysis reactor 103 to react, and high-purity silicon dioxide and alkyl alcohol (specifically methanol) are generated through hydrolysis;

[0062] S6, methanol, oxygen, and carbon monoxide obtained in step S3 are fed into carbonate preparation reactor 104 (fixed bed reactor), and a second catalyst (specifically Cu-Ni-V 2 O 5 -SiO 2The catalyst is reacted under the action of 120° C. and 1.2 MPa pressure to prepare dimethyl carbonate, which is recycled as the raw material in step S2 to achieve the recycling of dimethyl carbonate.

[0063] Combination Figure 1 The materials and their proportions in each stage of the process of this embodiment are summarized in the following Table 1:

[0064] Table 1

[0065]

[0066] 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 there is basically no detection of visible metal ions in the prepared methyl orthosilicate, only trace amounts of sodium, titanium and aluminum, and the concentrations are all less than 100 ppb, which can be used in high-end fields such as semiconductors and photovoltaics that have extremely high purity requirements.

[0067] Table 2

[0068]

[0069] Note: MDL means method detection limit, ND means not detected.

[0070] Figure 2 This is a gas chromatogram of the liquid product obtained in step S3 in Example 1 of the present invention. The substances corresponding to each peak time in the figure are as follows:

[0071] 2min: dimethyl ether; 2.7min: dimethyl carbonate; 4.6min: tetramethyl silicate; 12.9min: dimerized methyl silicate.

[0072] Example 2

[0073] The other conditions are the same as those in Example 1. The first catalyst used in step S1 is replaced. The conversion rate of elemental silicon powder and the selectivity of methyl orthosilicate caused by the catalytic reaction are shown in Table 3.

[0074] Table 3

[0075]

[0076]

[0077] It can be seen that the above catalysts can catalyze the reaction of waste silicon dioxide and dimethyl carbonate to produce methyl orthosilicate, but the silicon dioxide conversion rate and methyl orthosilicate selectivity are different. The sodium chloride in Example 1 or the above LiCl, KCl, LiOH, Li 2 CO 3 、Na 2 CO3 When used as the first catalyst, relatively high conversion rate and selectivity can be obtained.

[0078] 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 carbonate-assisted process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder, characterized in that: The following steps are involved: S1. Mixing a first catalyst with elemental silicon powder, wherein the first catalyst is an inorganic compound containing at least one alkali metal ion or alkaline earth metal ion; S2, putting the mixture obtained in step S1 into a reactor, introducing gas for purging, heating to the reaction temperature and adding carbonate for reaction; S3. After the reaction is completed, the products are separated to obtain a crude alkyl orthosilicate, carbon monoxide and a first catalyst, and the first 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 oxygen and the carbon monoxide obtained in step S3 under the action of a second catalyst to prepare a carbonate ester, which is recycled as a raw material in step S2.

2. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 1, characterized in that: The first catalyst is denoted as A x B y , x=1-2, y=1-2; A is selected from at least one of the positive ions corresponding to the following elements: Li, Na, K, Be, Mg, Ca, Sr, Ba; B is selected from F - , Cl - Br - ,I - OH - 、SiO3 2- 、NO3 - 、CO3 2- 、HCO3 - 、SO4 2- At least one of .

3. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 2, characterized in that: The first catalyst is a powdered solid catalyst or a catalyst solution formed by dissolving a solid catalyst in water. The concentration of the first catalyst in the catalyst solution is 0.1wt% to 20wt%.

4. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 3, characterized in that: The mass ratio of the first catalyst to the elemental silicon powder is 0.001-10.

5. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 1, characterized in that: In step S2, the purge gas is at least one of helium, nitrogen, hydrogen and argon, and the purge gas pressure is 0.1-5 bar; In step S2, the reaction temperature is 200-600 o C.

6. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 1, characterized in that: The carbonate in step S2 is at least one of dimethyl carbonate, diethyl carbonate, and dipropyl carbonate; the method of introducing the carbonate into the reactor is to evaporate the carbonate to form superheated steam and introduce it into the reactor, or to use a purge gas as a carrier gas to introduce the carbonate into the reactor.

7. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 6, characterized in that: The molar ratio of carbonate to elemental silicon powder in step S2 is 2-20:

1.

8. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 1, characterized in that: The product in step S3 is separated by distillation or rectification.

9. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to any one of claims 1 to 8, characterized in that: 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.

10. The process for preparing alkyl orthosilicate and silicon dioxide using elemental silicon powder with the aid of carbonate according to claim 1, characterized in that: In step S6, the molar ratio of alkyl alcohol: oxygen: carbon monoxide is 4:1:2, the second catalyst is a copper-containing catalyst, and the mass ratio of the added amount of the second catalyst to the alkyl alcohol is 1-5:20.

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