A method for preparing tetramethyl silicate

Abstract

The application discloses a preparation method of tetramethyl silicate, which comprises the following steps: adding silicon powder, methanol and alkali metal carbonate into a reactor, and reacting under the conditions of 150-190 DEG C of temperature and 2-3 Mpa of pressure for 160-200 min; and then separating and purifying the product to obtain the tetramethyl silicate. The application can efficiently promote the reaction of the silicon powder and the methanol to generate the tetramethyl silicate by using high temperature and high pressure and combining the alkali metal carbonate as a catalyst, the utilization rate of the silicon powder and the yield of the tetramethyl silicate are both above 97%, and the conversion rate of the silicon powder and the generation rate of the tetramethyl silicate are greatly improved. The process flow is simple and convenient to operate, the alkali metal carbonate is used as the catalyst, the cost is lower than that of the traditional copper-based oxide catalyst, the side reaction is less, the environment is not polluted, and the large-scale production is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and particularly relates to a preparation method of tetramethyl silicate. BACKGROUND

[0002] Tetramethyl silicate (tetramethoxysilane) is an organic compound, which is mainly used as an insulating material in the electronic industry, an optical glass processing agent and a condensing agent, and can also be used for the synthesis of organosilicon compounds.

[0003] At present, there are many methods for preparing tetramethyl silicate in theory, but the methods that can realize industrial production mainly include a silicon tetrachloride method and a silicon powder method. The silicon tetrachloride method is a classical method for preparing tetramethyl silicate, in which silicon tetrachloride and methanol are reacted at normal temperature and pressure to generate tetramethyl silicate and a large amount of hydrochloric acid gas. However, the method has great disadvantages, such as high raw material consumption, long production cycle, low yield, unstable product quality, and great environmental pollution caused by the generated HCl gas. The silicon powder method is more environmentally friendly and cleaner than the silicon tetrachloride method, and is gradually favored by people. However, the existing silicon powder method for preparing tetramethyl silicate all has a pretreatment process. One is that a catalyst is pretreated with silicon powder and then reacted with methanol, and the other is that the catalyst is composed of multiple substances and needs to be pretreated before being added to silicon powder and methanol for reaction, so that the preparation process is complicated. In addition, the existing silicon powder method for preparing tetramethyl silicate mostly uses copper oxides or alkali metal alcoholates as catalysts, which are high in cost and great in pollution, and thus cannot be applied on a large scale.

[0004] CN107216348A discloses a method for preparing tetramethoxysilane, which comprises the following steps: (1) weighing silicon powder and a catalyst, mixing and stirring, and then putting into a pulverizer for pulverization; (2) pouring the pulverized silicon powder and catalyst mixture into a fixed bed reactor, combining the device, and putting the reactor device into a tubular heating furnace; (3) first introducing nitrogen into the fixed bed reactor, performing programmed heating on the tubular furnace, heating to 240 DEG C, and keeping 240 DEG C for 2 h; (4) reducing the internal temperature of the fixed bed reactor to 220 DEG C, starting to replace methanol, starting to count the reaction time after 0.5 h, and performing the reaction, and the reaction product is tetramethoxysilane. Although the technical scheme uses silicon powder and methanol as raw materials to synthesize tetramethoxysilane in one step, the yield of tetramethoxysilane is low, the silicon powder and the catalyst need to be pulverized before mixing, and N2 needs to be introduced for protection before adding methanol, so that the operation steps are complicated. In addition, the catalyst used is copper oxide, which is high in cost and great in pollution, and is not conducive to large-scale application. SUMMARY

[0005] In view of the above-mentioned deficiencies of the prior art, the present application aims to provide a preparation method of tetramethyl silicate, which solves the problems of the prior art, such as low generation rate of tetramethyl silicate, complicated process, high cost of catalyst, and serious pollution, etc.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of tetramethyl silicate, wherein silicon powder, methanol and alkali metal carbonate are added into a reactor, and then reacted under the conditions of a temperature of 150-190 DEG C and a pressure of 2-3 Mpa for 160-200 min, and then the tetramethyl silicate is obtained by separation and purification after the reaction is completed.

[0008] Principle: The present application can efficiently promote the forward reaction of silicon powder and methanol by using high temperature and high pressure and combining alkali metal carbonate as a catalyst, thereby improving the generation rate of tetramethyl silicate. The reaction temperature is controlled at 150-190 DEG C, because if the temperature is too low, the reaction cannot proceed normally, and if the temperature is too high, the methanol participating in the reaction will be vaporized, and the local reaction temperature of the silicon powder and the catalyst in the reactor will be too high, so that the reaction cannot proceed normally. Meanwhile, the pressure is controlled at 2-3 Mpa, because if the pressure is lower than 2 Mpa, the methanol may boil inside, resulting in a large amount of volatilization with the gas flow, and finally leading to the failure of the reaction, and if the pressure is too high, it is not convenient for the forward reaction, which will reduce the conversion rate of the silicon powder and the generation rate of the tetramethyl silicate. Meanwhile, if the pressure is too high, it also indicates that hydrogen gas is generated in the reactor, so the hydrogen gas should be discharged in time to avoid excessive pressure.

[0009] In addition, the present application uses alkali metal carbonate as a catalyst, which has lower cost, fewer side reactions and is more environmentally friendly compared with the traditional copper-based oxide catalyst. Meanwhile, the present inventors have found that the alkali metal carbonate needs to be under the high temperature and high pressure conditions of the present application to have good catalytic effect on the reaction of the present application, and it cannot be simply replaced under any conditions.

[0010] Further, the mass ratio of the silicon powder, the methanol and the alkali metal carbonate is 20-50:200-300:0.5-10. Under this mass ratio range, the yield of the tetramethyl silicate can reach the maximum value.

[0011] Further, the alkali metal carbonate is potassium carbonate or sodium carbonate. Potassium carbonate and sodium carbonate are easy to obtain and have a reasonable price.

[0012] Further, the reactor is a high-pressure reaction kettle. Using a high-pressure reaction kettle can add methanol at one time, thereby avoiding the backflow of methanol vapor in the reactor to the bottom of the reactor during the process of dropping normal-temperature methanol, reducing the energy consumption required for heating and cooling for backflow, and therefore the high-pressure reaction has obvious advantages. In addition, under high-pressure conditions, the distance between gas molecules is small, and the collision frequency of the reaction is increased, further promoting the progress of the reaction and improving the generation rate of tetramethyl orthosilicate.

[0013] Further, the rotation speed of the reactor is 200 rpm to 450 rpm. If the rotation speed is too low, the catalyst, silicon powder and methanol cannot be better contacted for reaction; and if the rotation speed is too fast, the catalyst and silicon powder will splash to the wall of the reaction kettle, resulting in a decrease in the silicon powder and catalyst participating in the reaction, and finally a decrease in the reaction rate and the conversion rate of the silicon powder.

[0014] Further, the particle size of the silicon powder is 300 mesh to 500 mesh. The present application uses silicon powder with a larger mesh number to participate in the reaction, because the larger mesh number of the silicon powder increases the active interface of the silicon powder, and is more conducive to the reaction. The larger the mesh number of the silicon powder, the more sufficient the reaction.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] 1. The present application uses high temperature and high pressure in combination with an alkali metal carbonate as a catalyst to efficiently promote the reaction of silicon powder and methanol to generate tetramethyl orthosilicate, and the utilization rate of silicon powder and the yield of tetramethyl orthosilicate are both above 97%, greatly improving the conversion rate of silicon powder and the generation rate of tetramethyl orthosilicate.

[0017] 2. The present application generates tetramethyl orthosilicate by one-step method, without pretreatment of the silicon powder and the catalyst, and has a simple process, a short production cycle and is easy to popularize and apply. In addition, the present application uses an alkali metal carbonate as a catalyst, which has a lower cost and fewer side reactions than the traditional copper-based oxide catalyst, and does not cause environmental pollution, which is conducive to large-scale production.

[0018] 3. The present application directly adds reaction raw materials in a high-pressure reaction kettle for reaction, and under high-pressure conditions, it is not easy to cause moisture in the air to enter, so that the tetramethyl orthosilicate generated in the reaction process will not become gel after being contacted with water, thereby greatly reducing the reaction rate. Compared with a fixed bed reactor, the present application increases the contact surface of the silicon powder and the catalyst, the reaction is more complete, the operation is easier, the required reaction temperature is lower, the cleaning of the reaction container after the reaction is more convenient, and the present application is more suitable for large-scale application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Figure 1 is a schematic diagram of a device for preparing and separating and purifying tetramethyl orthosilicate according to the present application;

[0020] Figure 2 Gas chromatogram of the distillate obtained in Example 1 of the present application at 64-90°C;

[0021] Figure 3 Gas chromatogram of the liquid left in the distillation flask obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described in conjunction with the following specific examples.

[0023] The numerical ranges recited herein are inclusive of the recited endpoints and all intermediate values. Ranges of intermediate values are included in the present application even if explicitly recited endpoints are not listed. The endpoints of the ranges and any intermediate value are understood to be included in the present application unless otherwise indicated. Any smaller range that falls within the recited ranges are included in the present application.

[0024] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not an admission that it is prior art with respect to the present application. With respect to the words "comprise", "comprises", "comprising", "include", "includes", "including", "contain", "contains", "containing", and the like, these words are used in an open-ended way to mean including, but not limited to.

[0025] The experimental methods used in the present application are conventional unless otherwise specified.

[0026] The materials, reagents and the like used in the present application can be purchased or synthesized by known methods unless otherwise specified.

[0027] The quantitative tests in the present application are set up with three repeated experiments, and the results are averaged.

[0028] Reference is made to Figure 1 The present application provides a preparation method of tetramethyl silicate, and the preparation process flow is as follows:

[0029]

[0030] In the formula, the catalyst is an alkali metal carbonate, preferably sodium carbonate or potassium carbonate.

[0031] The mass ratio of the silicon powder, methanol, and alkali metal carbonate is 20-50:200-300:0.5-10. In a specific implementation, the mass ratio of the silicon powder, methanol, and alkali metal carbonate can be any ratio within the range, for example, 20-40:200-250:0.5-5, 30-50:230-300:4-10, 30:250:1, 20:200:0.5, or 50:300:10.

[0032] Example 1

[0033] A method for preparing tetramethyl silicate, comprising the following steps:

[0034] (1) 30 g of silicon powder (300 mesh), 250 g of methanol (moisture content less than 0.1%), and 1 g of sodium carbonate were added to a high-pressure reaction kettle, a magnetic stirrer was placed in the kettle, and a cover was screwed on. Then the high-pressure reaction kettle was placed in a stirring heating jacket, the temperature of the heating jacket was set to 180°C, the heating time was 160 min, the rotation speed was 450 rpm, the pressure of the high-pressure reaction kettle was adjusted to 2 MPa, and then the temperature was raised for reaction. After the reaction was completed, the methanol and methyl ester were distilled out of the reaction kettle, and the water circulation was turned on. When the pressure dropped to 0 MPa, the water circulation was turned off, and the distillate and silicon residue in the reaction kettle were collected.

[0035] (2) The collected distillate was distilled, and the distillate at 64-90°C and the remaining liquid in the distillation flask were collected. The two liquids were analyzed by gas chromatography, and the results are shown in Figure 2 and Figure 3 The silicon residue was washed with alcohol twice and with water twice. After each washing, centrifugation was performed at a rotation speed of 8000 rpm. The obtained silicon residue was dried by blowing air at 120°C to obtain dried silicon residue, and the weight was recorded.

[0036] The distillate at 64-90°C was collected to preliminarily separate the distillate and facilitate the collection of methanol that did not participate in the reaction for use in the next experiment. The remaining liquid in the distillation flask was collected to obtain the product tetramethyl silicate.

[0037] Experimental results: The mass of the remaining liquid in the distillation flask was 130.93 g; the mass of the distillate at 64-90°C was 87.08 g; and the mass of the dried silicon residue was 0.4 g.

[0038] Result analysis: As shown in Tables 1-2 and Figures 2-3 .

[0039] Table 1 Composition analysis table of the distillate at 64-90°C obtained in Example 1

[0040]

[0041]

[0042] Table 2 Composition analysis of the liquid left in the distillation flask of Example 1

[0043]

[0044] (1) Silicon powder consumption: 30-0.4=29.6g; theoretical silicon powder conversion rate: 98.7%.

[0045] (2) From Table 1 and Figure 2 It can be seen that the methanol content in the distillate of 64-90°C is 37.1%, the tetramethyl orthosilicate content is 57.75%, and there are 5.2% of other impurities.

[0046] (3) From Table 2 and Figure 3 It can be seen that the methanol content in the liquid left in the distillation flask is 7.3%, the tetramethyl orthosilicate content is 84.7%, and the remaining 8% may be dimers or polymers.

[0047] The total tetramethyl orthosilicate is 130.93*84.7%+87.08*57.7%=161.15g, and the tetramethyl orthosilicate yield is 98.8%.

[0048] Among them, the tetramethyl orthosilicate yield = the actual mass of tetramethyl orthosilicate generated / the mass of silicon powder completely reacted to produce tetramethyl orthosilicate theoretically.

[0049] Example 2

[0050] A method for preparing tetramethyl orthosilicate, comprising the following steps:

[0051] (1) 20g of silicon powder (300 mesh) is added to a high-pressure reaction kettle, 200g of methanol (methanol moisture less than 0.1%), 0.5g of sodium carbonate, a magnetic stirrer is put in, and the cover is screwed tightly. Then the high-pressure reaction kettle is placed in a stirring heating jacket, the heating jacket temperature is set to 170°C, the heating time is 180min, the rotation speed is 200rpm, and the pressure of the high-pressure reaction kettle is adjusted to 2.8Mpa, then the temperature rising reaction is started. After the reaction is completed, the methanol and methyl ester are distilled out of the reaction kettle, and the water circulation is opened. When the pressure drops to 0MPa, the circulating water is turned off, and the distillate and silicon residue in the reaction kettle are collected.

[0052] (2) The collected distillate is distilled, the distillate of 64-90°C and the liquid left in the distillation flask are collected, and the two liquids are analyzed by gas chromatography; the silicon residue is washed with alcohol for 3 times and washed with water for 3 times, centrifugation is carried out at a rotation speed of 9000rpm after each cleaning, the obtained silicon residue is dried by blowing air at 120°C, and the dried silicon residue is weighed and recorded.

[0053] After analysis (as in Example 1), the tetramethyl silicate yield of this example was 97.1%.

[0054] Example 3

[0055] A method for preparing tetramethyl silicate, comprising the following steps:

[0056] (1) 50 g of silicon powder (500 mesh), 300 g of methanol (moisture content less than 0.1%), and 10 g of sodium carbonate were added to a high-pressure reaction kettle, a magnetic stirrer was placed in the kettle, and the cover was screwed tightly. Then the high-pressure reaction kettle was placed in a stirring heating jacket, the temperature of the heating jacket was set to 190°C, the heating time was 200 min, the rotation speed was 300 rpm, and the pressure of the high-pressure reaction kettle was adjusted to 3 MPa, and then the temperature was raised for reaction. After the reaction was completed, the methanol and methyl ester were distilled out of the reaction kettle, and the water circulation was turned on. When the pressure dropped to 0 MPa, the water circulation was turned off, and the distillate and silicon residue in the reaction kettle were collected.

[0057] (2) The collected distillate was distilled, and the distillate collected at 64-90°C and the remaining liquid in the distillation flask were collected and analyzed by gas chromatography. The silicon residue was washed with alcohol 5 times and with water 5 times. After each washing, centrifugation was performed at a rotation speed of 10,000 rpm. The obtained silicon residue was dried by blowing air at 120°C to obtain dried silicon residue, which was weighed and recorded.

[0058] The tetramethyl silicate yield of this example was 98.9% by gas chromatography analysis.

[0059] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the technical solutions. Those of ordinary skill in the art should understand that modifications or equivalent replacements to the technical solutions of the present application without departing from the spirit and scope of the technical solutions should be covered within the scope of the claims of the present application.

Claims

1. A process for the preparation of tetramethyl silicate, characterized in that, The silicon powder, methanol and alkali metal carbonate are added into a reactor, and reacted at a temperature of 150-190 DEG C and a pressure of 2-3 MPa for 160-200 min, and then the tetramethyl orthosilicate is obtained by separation and purification after the reaction; the alkali metal carbonate is sodium carbonate.

2. The method for preparing tetramethyl silicate according to claim 1, characterized in that, The mass ratio of the silicon powder, methanol and alkali metal carbonate is 20-50:200-300:0.5-10.

3. The method of claim 1, wherein the tetramethyl silicate is prepared by the steps of: The reactor is a high-pressure reaction kettle. ​ 4. The method of claim 1, wherein the tetramethyl silicate is prepared by the steps of: The rotation speed of the reactor is 200-450 rpm. ​ 5. The method for preparing tetramethyl silicate according to claim 1, characterized in that, The particle size of the silicon powder is 300-500 mesh.

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