Hexamethyldisiloxane preparation method capable of purifying raw materials

Abstract

The invention discloses a hexamethyldisiloxane preparation method capable of purifying a raw material, and relates to the technical field of chemical preparation, the hexamethyldisiloxane preparation method capable of purifying the raw material comprises the following steps: S1, raw material preparation: cooling deionized water through a cooling system, and maintaining the temperature to be less than or equal to 10 DEG C, then injecting part of the cooled deionized water into a tubular reactor, pumping trimethylchlorosilane and methylbenzene into a premixing tank according to a proportion, and uniformly stirring and mixing; s2, catalytic promotion: injecting diluted hydrochloric acid into the tubular reactor, uniformly mixing the diluted hydrochloric acid with deionized water, and maintaining the pH value to 2-3; according to the hexamethyldisiloxane preparation method capable of purifying the raw materials, redundant steps such as catalyst recovery and repeated washing can be omitted through the hydrolysis reaction, the method is suitable for continuous production, meanwhile, the process of the hydrolysis reaction is optimized by changing the use steps and the input method of the deionized water, and the stability in the preparation process is further maintained.

Description

Technical Field

[0001] The invention relates to the technical field of chemical preparation, in particular to a method for preparing hexamethyldisiloxane capable of purifying raw materials. Background Art

[0002] Hexamethyldisiloxane (HMDSO) is an important organic silicon compound, commonly used in silicone resins, silicone oils, coatings, the electronics industry, and in the preparation of other silicon compounds. There are various methods for its synthesis, most commonly through the reaction of metallic silicon with alkyl halides or through the reaction of silicon hydrides with alkyl halides.

[0003] Patent publication number CN103951692B relates to a method for preparing high-purity, high-quality hexamethyldisiloxane. The method comprises the following steps: (1) adding trimethylchlorosilane dropwise to a hydrolysis reactor pre-filled with water and a condensation catalyst, and heating and refluxing; (2) after the hydrolysis reaction is complete, transferring the product into a separator for separation, wherein the bottom layer is the condensation catalyst, which can be separated and reused; the middle layer is concentrated acid water, which can be used to recover hydrogen chloride through a hydrochloric acid separation process; the hydrolyzate in the upper layer is washed with water, neutralized with a carbonate solution to neutrality, and washed with water multiple times to separate the oil phase; (3) removing water from the oil phase separated in step (2) with a dehydrating agent, stirring and filtering; and (4) fractionating, collecting the fraction at 99-102°C, to obtain hexamethyldisiloxane with a purity greater than 99.9% (mass fraction). This patented preparation method has a fast reaction speed, high utilization of trimethylchlorosilane, high yield of hexamethyldisiloxane, and superior quality.

[0004] In the above patent, the utilization rate of trimethylchlorosilane is increased by separating and reusing the condensation catalyst, and the yield of hexamethyldisiloxane is high and the quality is superior. However, additional catalyst input is required, and subsequent separation and reuse require additional steps and costs. Therefore, a method for preparing hexamethyldisiloxane with better preparation effect and the ability to purify the raw materials is designed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing hexamethyldisiloxane that can purify the raw materials, thereby solving the problems raised in the above-mentioned background technology.

[0006] To achieve the above objectives, the present invention is implemented by the following technical solution: a method for preparing hexamethyldisiloxane that can purify raw materials, comprising the following steps: S1. Raw material preparation: cool deionized water through a cooling system and maintain the temperature ≤ 10°C. Then, inject part of the cooled deionized water into a tubular reactor. Then, pump trimethylchlorosilane and toluene into a premixing tank in proportion and stir to mix them evenly. S2, catalytic promotion: inject dilute hydrochloric acid mixed uniformly with deionized water in a tubular reactor, maintain PH to 2-3; S3, hydrolysis reaction: the mixed solution enters the tubular reactor through a static mixer, while the remaining deionized water is injected in proportion, after reaction, the material enters a gas-liquid separator to release HCl gas, reducing the risk of reverse reaction, and the main product HMDSO is selectively increased to more than 95%; S4, neutralization and layering: continuously add sodium carbonate solution to the reaction liquid to adjust the pH to 6-7 to neutralize residual HCl, then the mixed solution enters a centrifugal separator to separate the organic phase and the aqueous phase at high speed, and the wastewater is adsorbed by activated carbon before entering the wastewater treatment system; S5, organic phase water washing and drying: the organic phase passes through a countercurrent water washing tower to remove residual salt and trace alkali, and passes through a 3Å molecular sieve adsorption tower to dehydrate to water content ≤50ppm, and reduced pressure rectification (50-100mmHg, 80-85℃) to ensure that the main fraction of HMDSO has a purity of ≥99.5%; S6, rectification purification: the dried organic liquid enters an atmospheric distillation column to recover toluene for recycling, while the remaining material is pumped into a reduced pressure rectification column to collect the main fraction of HMDSO, and the residue at the bottom is discharged periodically for byproduct treatment; S7, tail gas and wastewater treatment: HCl gas generated during the reaction stage is absorbed by an alkali spray tower to form a NaCl solution, and the salt-containing wastewater is evaporated and crystallized to recover NaCl.

[0007] The present application provides a method for preparing hexamethyldisiloxane which can purify raw materials. It has the following advantages:

[0008] (1) The method for preparing hexamethyldisiloxane which can purify raw materials can save the steps of catalyst recovery and multiple water washing through hydrolysis reaction, which is suitable for continuous production. By changing the use steps and input method of deionized water, the hydrolysis reaction process is optimized, the effect of hydrolysis reaction is improved, and the stability during preparation is further maintained by maintaining the deionized water below 10℃.

[0009] (2) The method for preparing hexamethyldisiloxane which can purify raw materials can batch process the byproduct dilute hydrochloric acid produced during preparation, part of which can be used as raw material for subsequent preparation, and the other part can be further concentrated to industrial grade as byproduct for sale, reducing the cost of waste liquid treatment. At the same time, hydrochloric acid can be used as an acidic catalyst to crack the byproduct oligomeric siloxane into cyclic siloxane, which can also be sold as a raw material for silicone rubber, increasing the added value of byproducts and greatly reducing the preparation cost. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1This is a flow chart for the preparation of hexamethyldisiloxane according to the present invention. DETAILED DESCRIPTION

[0011] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0012] See also Figure 1-Figure 1 One embodiment of the present invention is: a method for preparing hexamethyldisiloxane that can purify raw materials, the steps of which are as follows: S1. Raw material preparation: cool deionized water through a cooling system and maintain the temperature ≤ 10°C. Then, inject part of the cooled deionized water into a tubular reactor. Then, pump trimethylchlorosilane and toluene into a premixing tank in proportion and stir to mix them evenly. S2. Catalytic promotion: inject dilute hydrochloric acid and deionized water into the tubular reactor and mix them evenly, maintaining the pH at 2-3; S3, hydrolysis reaction: the mixed liquid enters the tubular reactor through the static mixer, and the remaining deionized water is injected in proportion. After the reaction, the material enters the gas-liquid separator to release HCl gas; S4, neutralization and separation: Sodium carbonate solution is continuously added to the reaction solution to adjust the pH to 6-7 to neutralize the residual HCl. The mixed solution then enters a centrifugal separator to separate the organic phase and the aqueous phase at high speed. The wastewater is adsorbed by activated carbon and then enters the sewage treatment system; S5. Washing and drying of the organic phase: The organic phase passes through a countercurrent water washing tower to remove residual salt and trace alkali solution, and then passes through a 3Å molecular sieve adsorption tower to dehydrate the organic phase to a moisture content of ≤50ppm. S6, distillation purification: The dried organic liquid enters the atmospheric distillation tower to recover toluene and recycle it. At the same time, the remaining material is pumped into the vacuum distillation tower to collect the main HMDSO fraction. At the same time, the bottom residue is regularly discharged and can be treated as a by-product. S7. Tail gas and wastewater treatment: During the reaction stage, HCl gas is absorbed by an alkali solution spray tower to generate NaCl solution, and the salt-containing wastewater is evaporated and crystallized to recover NaCl.

[0013] In S1, an automatic feeding system and a stirring system are equipped. First, 50% to 60% of the measured deionized water is injected into the tubular reactor, and the temperature of the deionized water is controlled at ≤10°C. This can effectively slow down the hydrolysis rate of trimethylchlorosilane and avoid runaway due to violent heat release. The reaction conversion rate is stabilized at more than 90%. Subsequently, the mixed liquid is injected into the tubular reactor, and the remaining water is continuously injected at a slow rate. The tubular reactor is combined with a static mixer to achieve rapid mass and heat transfer, avoid local overheating or uneven concentration, and inhibit the formation of by-products such as oligosiloxanes.

[0014] In S1, the ratio of trimethylsilyl chloride to toluene is 1:1 to 1:1.5. Toluene is used as an inert solvent to dilute the reactants and reduce the self-polymerization side reaction. The molar ratio of water to trimethylsilyl chloride in the deionized water is controlled at 0.45 to 0.5:1.

[0015] In S4, a pH monitoring system and a temperature detection system are provided to record the status of the mixed solution in real time, and coordinate with the automatic feeding system and the stirring system for synchronous adjustment. By setting up the feeding system, the input rate of deionized water can be effectively maintained, further maintaining the stability of the reaction.

[0016] In S5, the water used in the countercurrent water washing tower is deionized water, the boiling point of toluene is 110°C, the vacuum degree in the vacuum distillation tower is set at 50-100 mmHg, and the tower top temperature is controlled at 80-85°C. High-speed centrifugation is used to quickly separate the organic phase and the aqueous phase, and countercurrent water washing is used to remove residual salts, and the purity of the organic phase reaches more than 99%.

[0017] In S6, the main component of the bottom residue is oligosiloxane, and a regeneration system is provided to crack the oligosiloxane into cyclic siloxane by an acidic catalyst. The oligosiloxane is cracked into cyclic siloxane (such as D4 / D5) by an acidic catalyst and used as a raw material for silicone oil or sealant. The comprehensive utilization rate of by-products is increased to more than 80%.

[0018] In S7, a hydrochloric acid production system is set up to further concentrate the dilute hydrochloric acid in the HCl absorption tower to industrial grade, generating NaCl solution. After concentration, industrial grade hydrochloric acid is recovered, reducing the cost of hazardous waste treatment, recovering NaCl solids, and increasing the wastewater reuse rate by 50%, achieving near-zero emissions. At the same time, part of the hydrochloric acid can be extracted in this process as a catalyst in S2, thereby improving the utilization rate of hydrochloric acid.

[0019] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing hexamethyldisiloxane that can purify raw materials, characterized in that: The following steps are described: S1. Raw material preparation: cool deionized water through a cooling system and maintain the temperature ≤ 10°C. Then, inject part of the cooled deionized water into a tubular reactor. Then, pump trimethylchlorosilane and toluene into a premixing tank in proportion and stir to mix them evenly. S2. Catalytic promotion: inject dilute hydrochloric acid and deionized water into the tubular reactor and mix them evenly, maintaining the pH at 2-3; S3, hydrolysis reaction: the mixed liquid enters the tubular reactor through the static mixer, and the remaining deionized water is injected in proportion. After the reaction, the material enters the gas-liquid separator to release HCl gas; S4, neutralization and separation: Sodium carbonate solution is continuously added to the reaction solution to adjust the pH to 6-7 to neutralize the residual HCl. The mixed solution then enters a centrifugal separator to separate the organic phase and the aqueous phase at high speed. The wastewater is adsorbed by activated carbon and then enters the sewage treatment system; S5. Washing and drying of the organic phase: The organic phase passes through a countercurrent water washing tower to remove residual salt and trace alkali solution, and then passes through a 3Å molecular sieve adsorption tower to dehydrate the organic phase to a moisture content of ≤50ppm. S6, distillation purification: The dried organic liquid enters the atmospheric distillation tower to recover toluene and recycle it. At the same time, the remaining material is pumped into the vacuum distillation tower to collect the main HMDSO fraction. At the same time, the bottom residue is regularly discharged and can be treated as a by-product. S7. Tail gas and wastewater treatment: During the reaction stage, HCl gas is absorbed by an alkali solution spray tower to generate NaCl solution, and the salt-containing wastewater is evaporated and crystallized to recover NaCl.

2. A method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, characterized in that: In S1, an automatic feeding system and a stirring system are provided. First, 50% to 60% of the measured deionized water is injected into the tubular reactor, and then the mixed liquid is injected into the tubular reactor, and then the remaining water is continuously injected at a slow rate.

3. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S1, the ratio of trimethylsilyl chloride to toluene is 1:1 to 1:1.5, and the molar ratio of water to trimethylsilyl chloride in the deionized water is controlled to be 0.45 to 0.5:

1.

4. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S2, dilute hydrochloric acid is injected so that the molar ratio of hydrochloric acid to water is controlled at 0.1 to 0.

5.

5. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S4, the concentration of the sodium carbonate solution is 10%, the organic phase contains HMDSO and toluene, and the aqueous phase contains NaCl and residual alkali solution.

6. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S4, a pH monitoring system and a temperature detection system are provided to record the status of the mixed solution in real time, and coordinate with the automatic feeding system and the stirring system for synchronous adjustment.

7. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S5, the water used in the countercurrent water washing tower is deionized water, the boiling point of toluene is 110°C, the vacuum degree in the vacuum distillation tower is set at 50-100 mmHg, and the tower top temperature is controlled at 80-85°C.

8. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S6, the main component of the bottom residue is oligosiloxane, and a regeneration system is provided to crack the oligosiloxane into cyclic siloxane by an acidic catalyst.

9. The method for preparing hexamethyldisiloxane capable of purifying raw materials according to claim 1, wherein: In S7, a hydrochloric acid production system is provided to further concentrate the dilute hydrochloric acid in the HCl absorption tower to industrial grade.

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