A process for reducing siloxane impurities in hydrochloric acid produced by hydrolysis of dimethyldichlorosilane

Abstract

The invention provides a process for reducing siloxane impurities in hydrogen chloride by hydrolyzing dimethyldichlorosilane. The dimethyldichlorosilane is fully mixed with water in a static mixer for reaction, and then enters a packed washing tower for acid washing. The internal structure of the washing tower is a ball ring packing, and saturated hydrochloric acid cooled by a 35°C refrigerant is used for spray washing from the top of the tower; then the hydrogen chloride gas enters a gas-liquid separation tank and a hydrogen chloride cooler for deep condensation and dehydration to achieve gas-liquid two-phase separation, and then the dried hydrogen chloride gas is passed into the bottom of a demister. The adsorption medium of the inner layer of the demister is a special glass fiber, and its composition is a FRP+glass fiber mixed material. Droplets with a diameter greater than 1 micron can be directly intercepted. When these impurities in the form of droplets accumulate to the point where their own gravity exceeds the combined force of the gas rise force and the liquid surface tension, they will separate and fall, thereby achieving the purpose of further removing the siloxane impurities.

Description

Technical Field

[0001] The invention relates to the technical field of chemical process, and in particular to a process for reducing siloxane impurities in hydrogen chloride produced by hydrolysis of dimethyldichlorosilane. Background Art

[0002] Organic silicon has the properties of both inorganic and organic materials, and has excellent characteristics such as high and low temperature resistance, electrical insulation, oxidation stability, corrosion resistance, non-toxicity, tastelessness, and physiological inertness. It is widely used in aerospace, electrical and electronic, construction, transportation, chemical, textile, medical and other industries. Most of its organic silicon products are processed from polydimethylsiloxane obtained by hydrolysis of dimethyldichlorosilane (abbreviated as dimethyl) and other additives. Therefore, dimethyl hydrolysis is one of the important links in the upstream industrial production of organic silicon.

[0003] At present, the industrial hydrolysis process adopts the low-energy concentrated acid hydrolysis process to produce oligosiloxane (dimethyl hydrolyzate) and release hydrogen chloride gas. However, due to the complexity of the process, the generated hydrogen chloride gas carries a small amount of incompletely reacted chlorosilane monomers, volatile small molecular siloxane impurities and water. Among them, siloxane impurities are very unstable in acidic media, and condensation reactions are easy to occur between hydroxyl groups. Its short-chain siloxane polymerizes into long chains over time, undergoes cross-linking reactions to form colloids and sticks to the wall. These siloxane impurities often exist in the form of droplets with a diameter of less than 1 micron, and the continuous accumulation leads to the blockage of pipeline equipment, shortening the start-up cycle, which is not conducive to safe and stable production. In addition, the presence of siloxane impurities will also restrict the synthesis of methyl chloride in the next loop, affecting its reaction efficiency and product purity. Therefore, the adsorption and removal of siloxane impurities in hydrogen chloride gas is of great significance to the safe and stable production of silicone enterprises and the healthy development of the industrial economy. Summary of the invention

[0004] In order to solve the problem that the content of siloxane impurities in the hydrogen chloride gas produced by the hydrolysis of dimethylsilane is high, which leads to serious equipment loss, high maintenance frequency and low methyl chloride synthesis efficiency, the present invention provides a process system for reducing siloxane impurities in the hydrogen chloride produced by the hydrolysis of dimethyldichlorosilane, so as to improve the recovery rate of hydrogen chloride and the purity of the product, increase the economic value of the enterprise and reduce the discharge of waste acid.

[0005] The invention discloses a process system for reducing siloxane impurities in hydrogen chloride by hydrolyzing dimethyldichlorosilane, comprising the following process flow: dimethyldichlorosilane is fully mixed with water in a static mixer to react, and hydrogen chloride gas carrying siloxane impurities is released, and the hydrogen chloride gas first enters a packing-type washing tower for acid washing, wherein the internal structure of the washing tower is a ball ring packing, so that gas-liquid two phases can be fully and continuously contacted on the surface of the packing and gas-liquid mass transfer can be performed, and saturated hydrochloric acid cooled by a -35 DEG C refrigerant is sprayed from the top of the tower for washing, so that the siloxane impurities in the hydrogen chloride gas are absorbed by the supercooled saturated hydrochloric acid and condensed back, so as to remove part of the siloxane impurities; and the temperature of the cooled saturated hydrochloric acid is -1 DEG C to -25 DEG C.

[0006] Then the hydrogen chloride gas enters the gas-liquid separation tank and the hydrogen chloride cooler (-35℃ refrigerant) for deep condensation and dehydration to achieve gas-liquid two-phase separation, and the hydrogen chloride is deeply cooled to -10℃~-25℃. Then the dried hydrogen chloride gas is passed into the bottom of the demister. The adsorption medium of the inner layer of the demister is a special glass fiber, which is composed of FRP + glass fiber mixed materials. The droplets with a diameter greater than 1 micron can be directly intercepted. When the droplets are very fine, they will be collided with the surrounding gas molecules to produce irregular Brownian diffusion movement, and this movement will increase with the reduction of fog particles, greatly increasing the probability of fiber capturing fog particles. Therefore, this special adsorption medium can adsorb siloxane impurities with a diameter less than 1 micron on the fiber layer at 1 / 2 of the filter element, and impurities with a diameter less than 0.3 microns are adsorbed and fixed by the finer filter layer. When these impurities in the form of droplets accumulate to the point where their own gravity exceeds the combined force of the gas's rising force and the liquid's surface tension, they will separate and fall, thereby achieving the purpose of further removing siloxane impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The invention discloses a process for reducing siloxane impurities in hydrogen chloride, a product of dimethyldichlorosilane hydrolysate, wherein 1 is a hydrogen chloride gas washing tower, 2 is a gas-liquid separation tank, 3-1 is a hydrogen chloride cooler, 3-2 is a hydrochloric acid cooler, 4 is a demister, and 5 is a demister. DETAILED DESCRIPTION

[0008] Example 1 like Figure 1 As shown, Figure 1 As shown, a system for reducing siloxane impurities in the hydrolysis of dimethyldichlorosilane into hydrogen chloride, The top outlet of the hydrogen chloride gas washing tower 1 is connected to the inlet of the gas-liquid separation tank 2 through a pipeline, the top outlet of the gas-liquid separation tank 2 is connected to the hydrogen chloride cooler 3 - 1 , and the hydrogen chloride cooler 3 - 1 is connected to the demister 4 .

[0009] The middle part of the hydrogen chloride gas washing tower 1 is connected to the circulation pump through a pipeline, and the circulation pump is connected to the hydrochloric acid cooler 3-2. The refrigerant pipeline of the hydrochloric acid cooler 3-2 extends deep into the upper part of the hydrogen chloride gas washing tower 1 and is provided with a nozzle to achieve refrigerant spray washing from the top of the tower to remove part of the siloxane impurities and achieve circulation.

[0010] The top outlet of the hydrogen chloride gas washing tower 1 is also connected to the demister 4 through a pipeline.

[0011] The outlets of the gas-liquid separation tank 2, the hydrogen chloride cooler 3-1 and the demister 4 are connected to the separator 5 through pipelines.

[0012] The bottom outlet of the hydrogen chloride gas scrubbing tower 1 is connected to the separator 5 through a pipeline.

[0013] After the hydrolysis of dimethylbenzene, the hydrogen chloride gas with siloxane impurities is released and enters the packed scrubber 1 through pipeline a for acid washing. The internal structure of the scrubber is ball ring packing, which can make the gas and liquid phases fully and continuously contact on the packing surface and carry out gas-liquid mass transfer. At the same time, saturated hydrochloric acid cooled by -35℃ refrigerant is used for spray washing from the top of the tower, so that the siloxane impurities in the hydrogen chloride gas are absorbed by the supercooled saturated hydrochloric acid and condensed back to remove part of the siloxane impurities. At this time, the temperature of the hydrogen chloride gas is reduced to -1.7℃; then the hydrogen chloride gas enters the gas-liquid separation tank 2 and the hydrogen chloride cooler 3-1 (-35℃ refrigerant) in turn to be deeply condensed to -15.2℃ for dehydration, and then the dried hydrogen chloride gas is passed from pipeline e to the bottom of the demister 4. The adsorption medium of the filter layer is special glass fiber, which is composed of FRP + glass fiber mixed material. Droplets with a diameter greater than 1 micron can be directly intercepted. When the droplets are very fine, they will be collided with the surrounding gas molecules to produce irregular Brownian diffusion motion, and this motion increases with the reduction of fog particles, greatly increasing the probability of fiber capturing fog particles. Therefore, this special adsorption medium can adsorb siloxane impurities with a diameter less than 1 micron on the fiber layer at 1 / 2 of the filter element, and impurities with a diameter less than 0.3 microns are adsorbed and fixed by the finer filter layer. When these impurities in the form of droplets accumulate to the point where their own gravity exceeds the combined force of the gas's rising force and the liquid's surface tension, they will separate and fall, thereby achieving the purpose of further removing siloxane impurities.

[0014] Table 1 Impurity removal effect of hydrogen chloride gas

[0015] Example 2 like Figure 1As shown, after the hydrolysis of dimethylformamide, the hydrogen chloride gas containing siloxane impurities is released and enters the packed scrubber 1 through pipeline a for acid washing. The internal structure of the scrubber is ball ring packing, which can make the gas-liquid two phases fully and continuously contact on the packing surface and carry out gas-liquid mass transfer. At the same time, saturated hydrochloric acid cooled by -35℃ refrigerant is sprayed from the top of the tower for washing, so that the siloxane impurities in the hydrogen chloride gas are absorbed by the supercooled saturated hydrochloric acid and condensed back to remove part of the siloxane impurities. At this time, the temperature of the hydrogen chloride gas is reduced to -3.4℃; then the hydrogen chloride gas enters the gas-liquid separation tank 2 and the hydrogen chloride cooler 3-1 (-35℃ refrigerant) from pipelines c and d in turn, and is deeply condensed to -17.2℃ for dehydration, and then the dried hydrogen chloride gas is passed from pipeline e to the bottom of the demister 4 The adsorption medium of the inner layer of the demister is special glass fiber, which is composed of FRP + glass fiber mixed material. The fog droplets with a diameter greater than 1 micron can be directly intercepted. When the fog droplets are very fine, they will be collided with the surrounding gas molecules to produce irregular Brownian diffusion motion, and this motion increases with the reduction of fog particles, greatly increasing the probability of fiber capturing fog particles. Therefore, this special adsorption medium can adsorb siloxane impurities with a diameter less than 1 micron on the fiber layer at 1 / 2 of the filter element, and impurities with a diameter less than 0.3 micron are adsorbed and fixed by the finer filter layer. When these impurities in the form of fog droplets accumulate to the point where their own gravity exceeds the combined force of the gas's rising force and the liquid's surface tension, they will separate and fall, thereby achieving the purpose of further removing siloxane impurities.

[0016] Table 2 Impurity removal effect of hydrogen chloride gas

[0017] Example 3 like Figure 1As shown, after the hydrolysis of dimethylformamide, the hydrogen chloride gas containing siloxane impurities is released and enters the packed washing tower 1 for acid washing through pipeline a. The internal structure of the washing tower is ball ring packing, which can make the gas-liquid two phases fully and continuously contact on the packing surface and carry out gas-liquid mass transfer. At the same time, saturated hydrochloric acid cooled by -35℃ refrigerant is sprayed from the top of the tower for washing, so that the siloxane impurities in the hydrogen chloride gas are absorbed by the supercooled saturated hydrochloric acid and condensed back to remove part of the siloxane impurities. At this time, the temperature of the hydrogen chloride gas is reduced to 0.8℃; then the hydrogen chloride gas enters the gas-liquid separation tank 2 and the hydrogen chloride cooler 3-1 (-35℃ refrigerant) from pipelines c and d in turn, and is deeply condensed to -14.6℃ for dehydration, and then the dried hydrogen chloride gas is passed from pipeline e to the bottom of the demister 4 The adsorption medium of the inner layer of the demister is a special glass fiber, which is composed of a mixed material of FRP + glass fiber. The fog droplets with a diameter greater than 1 micron can be directly intercepted. When the fog droplets are very fine, they will be collided with the surrounding gas molecules to produce irregular Brownian diffusion motion, and this motion increases with the reduction of fog particles, greatly increasing the probability of fiber capturing fog particles. Therefore, this special adsorption medium can adsorb siloxane impurities with a diameter less than 1 micron on the fiber layer at 1 / 2 of the filter element, and impurities with a diameter less than 0.3 microns are adsorbed and fixed by the finer filter layer. When these impurities in the form of fog droplets accumulate to the point where their own gravity exceeds the combined force of the gas's rising force and the liquid's surface tension, they will separate and fall, thereby achieving the purpose of further removing siloxane impurities.

[0018] Table 3 Impurity removal effect of hydrogen chloride gas .

Claims

1. A process for reducing siloxane impurities in hydrogen chloride by hydrolysis of dimethyldichlorosilane, characterized in that: The following steps are involved: (1) Dimethyldichlorosilane is hydrolyzed to release hydrogen chloride gas containing siloxane impurities, which is then passed into a scrubbing tower for acid washing to remove some of the siloxane impurities; (2) subjecting the hydrogen chloride gas mixture obtained in step (1) from which part of the siloxane impurities have been removed to gas-liquid separation and deep condensation of hydrogen chloride to remove water; (3) The condensed and dehydrated hydrogen chloride gas obtained in step (2) is passed to the bottom of a demister to further remove siloxane impurities.

2. A process for reducing siloxane impurities in hydrochloric acid from dimethyldichlorosilane as claimed in claim 1, characterized in that: The internal structure of the washing tower in step (1) adopts ball ring packing to make the gas-liquid two phases contact fully and continuously to carry out gas-liquid mass transfer and purify the hydrogen chloride gas.

3. A process for reducing siloxane impurities in hydrogen chloride by hydrolysis of dimethyldichlorosilane as claimed in claim 1, characterized in that: In the step (1), the washing tower uses saturated hydrochloric acid cooled by -35°C refrigerant to spray and wash from the top of the tower to remove some siloxane impurities.

4. A process for reducing siloxane impurities in hydrochloric acid from dimethyldichlorosilane as claimed in claim 3, characterized in that: The temperature of the cooled saturated hydrochloric acid is -1°C to -25°C.

5. A process for reducing siloxane impurities in hydrogen chloride by hydrolysis of dimethyldichlorosilane as claimed in claim 1, characterized in that: In the step (2), the hydrogen chloride-35°C refrigerant is subjected to deep condensation to remove water.

6. A process for reducing siloxane impurities in hydrogen chloride by hydrolysis of dimethyldichlorosilane as claimed in claim 5, characterized in that: Hydrogen chloride is deeply cooled to -10℃~-25℃.

7. A process for reducing siloxane impurities in hydrogen chloride by hydrolysis of dimethyldichlorosilane as claimed in claim 1, characterized in that: The adsorption medium used in the defoamer in step (3) is a special glass fiber, whose composition is FRP+glass fiber, which further removes siloxane impurities.

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