A two-stage hydrolysis reaction process of dimethyldichlorosilane concentrated acid

Abstract

The present application belongs to the field of dimethyldichlorosilane concentrated acid hydrolysis reaction in the organic silicon industry, and particularly relates to a dimethyldichlorosilane concentrated acid two-stage hydrolysis reaction process. The process comprises the following specific steps: dimethyldichlorosilane is subjected to a first-stage hydrolysis reaction with recycled saturated hydrochloric acid and water, and an additive is added; purification and drying are performed, and the purified siloxane is subjected to a second-stage reaction in a second-stage reactor; after the second-stage reaction is completed, the mixture is subjected to oil-water separation, and the hydrolyzate is subjected to a washing section to obtain a final product. The dimethyldichlorosilane provided by the present application is subjected to two-stage hydrolysis reaction, the content of chlorine-terminated groups in the generated hydrolyzate is greatly reduced, the acid content is low, and the quality of the hydrolysis product is high. The new process provided by the present application adopts a two-stage reaction system, solves the problems of high chlorine-terminated group content, hydrogen chloride gas containing dimethyl and hydrolyzate, and obtains high-quality hydrolyzate, and the reaction system maintains a slight positive pressure, which does not inhibit the dimethyl hydrolysis reaction.

Description

Technical Field

[0001] This invention belongs to the field of concentrated acid hydrolysis reaction of dimethyldichlorosilane in the organosilicon industry, and specifically relates to a reaction process for two-stage hydrolysis of dimethyldichlorosilane with concentrated acid. Background Technology

[0002] Dimethyl chloride (DMC) hydrolysis mainly involves two processes: azeotropic acid hydrolysis and concentrated acid hydrolysis. Azeotropic acid hydrolysis produces hydrogen chloride that dissolves in water, which is then delivered to the user via boiling, consuming a large amount of energy and resulting in low chloride ion utilization. Concentrated acid hydrolysis, on the other hand, directly produces HCl gas, significantly reducing the energy required for hydrogen chloride removal. This process has gradually become the preferred choice in the organosilicon industry, replacing the energy-intensive azeotropic acid hydrolysis process.

[0003] Currently, concentrated acid hydrolysis mostly adopts single-stage pressure hydrolysis. Due to the relatively high reaction pressure and acid concentration, the amount of water required for the reaction is insufficient, resulting in incomplete reaction of dimethyldichlorosilane and a large amount of chlorine-terminated material in the production line. At the same time, the hydrogen chloride gas contains a small amount of dimethyldichlorosilane and oil droplets, which are difficult to clean completely, directly affecting the operating quality of subsequent units. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a two-stage hydrolysis process for dimethyldichlorosilane using concentrated acid. This process improves the hydrolysis efficiency of dimethyldichlorosilane by implementing a two-stage hydrolysis. The first-stage reaction mainly generates short chains, while the second-stage reaction converts both chlorine-terminated linear groups and short-chain linear groups into hydroxyl-terminated long-chain linear groups or cyclic groups, eliminating the influence of end-chlorine groups. Simultaneously, the first-stage concentrated acid hydrolysis utilizes a low-pressure system, facilitating the removal of hydrogen chloride from the reaction system and reducing the entrainment of hydrogen chloride mist.

[0005] To achieve the above-mentioned technology, the specific technical solution adopted by the present invention is as follows:

[0006] This invention provides a reaction process for the two-stage hydrolysis of dimethyldichlorosilane with concentrated acid, comprising the following steps:

[0007] (1) Dimethyldichlorosilane is hydrolyzed in a primary reactor with circulating saturated hydrochloric acid and water containing chemical equivalents, while additives are added intermittently. The reaction products enter the hydrogen chloride purification tower in the form of liquid-gas mixture, and are purified and dried in the upper part of the hydrogen chloride purification tower.

[0008] (2) The purified siloxane and saturated acid flow out from the lower tower of the hydrogen chloride purification tower and enter the primary phase separator for oil-water separation. The separated saturated hydrochloric acid is fed as the reaction circulating acid and warm acid washing after passing through the circulating acid heater. The siloxane enters the secondary reactor to carry out the secondary reaction. Here, the siloxane and dilute hydrochloric acid carry out a two-step reaction.

[0009] (3) After the secondary reaction is completed, the mixture of hydrolysis product and dilute acid enters the secondary reaction phase separator for oil-water separation. The dilute acid is refluxed to the primary reaction system as makeup water, while the hydrolysate enters the washing section to obtain the final product.

[0010] Further, in step (1), the mass ratio of saturated hydrochloric acid to dimethyldichlorosilane is ≥2; the concentration of hydrochloric acid is 37%; 155 kg of water is added for every 1 ton of dimethyldichlorosilane; the auxiliary agent is n-octylamine, and when the ring ratio is less than 45%, the amount added is 20-50 kg, and the addition cycle is 3-5 days; the conditions for the first-order reaction are: reaction temperature 30-60℃, pressure 0.07-0.15 MPa, and reaction time 1.5-3 min.

[0011] Furthermore, in step (1), the dimethyl hydrolysis reactor is a plug flow reactor with bulk packing inside; the bulk packing is graphite ring or plastic flower ring type; the inlet diameter of the dimethyl hydrolysis reactor is DN250 and the outlet diameter is DN600.

[0012] Furthermore, in step (1), both dimethyl hydrochloric acid and saturated hydrochloric acid enter from the bottom and overflow from the top, operating in a full-liquid state, flowing turbulently and mixing as they flow upward through the reactor packing section.

[0013] The hydrogen chloride purification tower provided by this invention consists of two towers, upper and lower, with two-stage washing. In the lower tower, unreacted dimethyldichlorosilane monomer vapor undergoes further hydrolysis to generate hydrolysis products siloxane and hydrogen chloride gas. Simultaneously, droplets entrained in the gas are dissolved in acid. The gas enters the upper tower, where it undergoes secondary washing and cooling purification with cold acid. Acid oil droplets are absorbed by the cold acid solution. The dried and cooled hydrogen chloride gas then enters a demister from the top of the tower to further remove droplets carried in the hydrogen chloride gas. The collected droplets enter a primary phase separator for reuse in the system.

[0014] Furthermore, the lower column acid washing uses saturated hydrochloric acid at 50℃-60℃; the cold acid uses saturated hydrochloric acid at -9℃ to -4℃; the hydrogen chloride purification tower is a packed tower; the packing material is graphite rings or plastic rosettes. Preferably, the outlet temperature of the upper column of the hydrogen chloride purification tower does not exceed 0℃; the internal components of the demister use fiber demisting.

[0015] Furthermore, in step (2), the secondary reactor is a continuously stirred tank reactor with baffles to form turbulence; the operating temperature of the secondary reactor is 30-75℃, the pressure is 0.08~0.2Mpa, and the reaction time is 20-25min; the concentration of the secondary reaction acid in the secondary reactor is controlled at 15-25%; the concentration of the dilute hydrochloric acid is 17%.

[0016] Furthermore, in step (2), the two-step reaction specifically includes:

[0017] The first step involves mixing a siloxane with a dilute acid solution. Under the catalysis of the dilute acid, the siloxane reacts to remove the Cl-terminated ends of the wire, generating HCl- and OH-terminated wires. The reaction formula is as follows:

[0018]

[0019] In Formula 1, x≤4;

[0020] In the second step, the dilute acid concentration and suitable temperature conditions in the secondary reactor promote the condensation of the OH-terminated filament, thereby producing a longer OH-terminated filament or ring. The following reaction equations represent the condensation reaction of two filaments of lengths x and y:

[0021]

[0022] In Equation 2, x ≤ 4, and y can be any value.

[0023] The two-stage reaction process for dimethyl acid hydrolysis provided by this invention includes equipment and pipeline connections such as a dimethyl acid hydrolysis reactor, a hydrogen chloride purification tower, a circulating acid heater, a hydrogen chloride demister, a hydrogen chloride buffer tank, a primary phase separator, a secondary reactor, and a secondary phase separator.

[0024] The beneficial effects of the present invention are:

[0025] (1) The dimethyldichlorosilane provided by the present invention undergoes a two-stage hydrolysis reaction, resulting in a significant reduction in the chlorine-terminated content and low acid content in the hydrolysate, and high quality of the hydrolysate.

[0026] (2) The new process provided by the present invention adopts a two-stage reaction system, which solves the problems of high chlorine end cap content and dimethyl and hydrolysate in hydrogen chloride gas, obtains high-quality hydrolysate, and the reaction system maintains a slight positive pressure, which does not inhibit the dimethyl hydrolysis reaction. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the two-stage hydrolysis reaction of dimethyl acid;

[0028] Among them, 1 is the primary reactor, 2 is the lower tower of the hydrogen chloride purification tower, 3 is the upper tower of the hydrogen chloride purification tower, 4 is the demister, 5 is the circulating acid heater, 6 is the cold acid cooler, 7 is the primary reaction phase separator, 8 is the secondary reactor, and 9 is the secondary reaction phase separator. Detailed Implementation

[0029] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0030] The specific process for the two-stage hydrolysis reaction of dimethyl acid provided by this invention is as follows: Figure 1 As shown: The system provided by the present invention includes a primary reactor 1, a lower column of a hydrogen chloride purification tower 2, an upper column of a hydrogen chloride purification tower 3, a demister 4, a circulating acid heater 5, a cold acid cooler 6, a primary reaction phase separator 7, a secondary reactor 8, and a secondary reaction phase separator 9.

[0031] Example 1

[0032] A two-stage process for the hydrolysis of dimethyl dichlorosilane includes the following steps: Dimethyl dichlorosilane is fed at a rate of 20 t / h, with the ratio of dimethyl to saturated acid controlled at 1:3. The first-stage reaction is carried out in a hydrolysis reactor at a temperature of 60℃ and a pressure of 0.2 MPa for 2 minutes. Periodic monitoring is performed; when the ring ratio is below 45%, 30 kg of n-octylamine is added at once. The reaction product enters a hydrogen chloride purification tower in a liquid-gas mixture. The hydrogen chloride purification tower consists of upper and lower towers: the lower tower is for warm acid washing, and the upper tower is for cold acid washing, cooled by a cold acid cooler. In the lower tower, unreacted dimethyl dichlorosilane is washed away... The methyldichlorosilane monomer vapor undergoes further hydrolysis to produce hydrolysis products siloxane and hydrogen chloride gas. Simultaneously, droplets entrained in the gas are dissolved in a hot washing acid solution. The gas enters the upper column, where it undergoes secondary washing with cold acid and cooling purification, absorbing acid oil droplets. The dried and cooled hydrogen chloride gas then enters a demister from the top of the column to further remove droplets. The collected droplets enter a primary phase separator and are returned to the system for reuse. The hydrogen chloride purification tower is divided into upper and lower columns; the lower column undergoes warm acid washing, and the upper column undergoes cold acid washing. Both columns are packed towers; the packing material is graphite rings or plastic rosettes. The hydrolysis products and saturated acid obtained from the reaction enter the primary phase separator, while the generated HCl gas (30°C, 0.15 MPa) undergoes warm acid countercurrent washing in the lower column of the hydrogen chloride purification tower before entering the upper column for further purification and drying. After passing through a demister, it is delivered to the user. The hydrolysate separated by the primary phase separator is pumped to the secondary reactor for a secondary reaction. The secondary reaction temperature is controlled at 70℃ and the pressure at 0.08 MPa for 20 minutes, with an acid concentration of 15%. The reaction product then enters the secondary phase separator for acid-oil separation. The acid phase is pumped back to the reaction acid heater as makeup water. The oil phase undergoes subsequent washing and purification to obtain high-quality hydrolysate.

[0033] After undergoing a two-stage hydrolysis reaction and a two-stage phase separator, the oil phase hydrolysis product polysiloxane contains 55% cyclic phase and 45% linear phase, with an acid content of 0.1% and a viscosity of 20 mPa·s. The yield of the hydrolysis product is 99.6%, the purity is higher than 99%, and the quality meets the process requirements.

[0034] Comparative Example 1

[0035] This embodiment includes the following steps: Dimethyldichlorosilane is fed at a rate of 20 t / h, with the ratio of dimethyl to saturated acid controlled at 1:3. A first-stage reaction is carried out in a hydrolysis reactor under the same conditions as in Example 1. The hydrolysis products and saturated acid obtained from the reaction enter a first-stage phase separator. The generated HCl gas, at a temperature of 30°C and a pressure of 0.15 MPa, undergoes warm acid countercurrent washing in the lower column of a hydrogen chloride purification tower, and then enters the upper column of the hydrogen chloride purification tower for further purification and drying. After passing through a demister, it is sent to the user. The hydrolysate separated by the first-stage phase separator is pumped to a second-stage reactor for a second-stage reaction. The reaction conditions for the second-stage reaction are a temperature of 70°C, a pressure of 0.08 MPa, and a reaction acid concentration of 17%. The reaction products enter the second-stage phase separator for acid-oil separation. The acid phase is pumped to the reaction acid heater as makeup water. The oil phase undergoes subsequent washing and purification treatment to obtain high-quality hydrolysis products.

[0036] After undergoing a two-stage hydrolysis reaction and a two-stage phase separator, the oil phase hydrolysis product polysiloxane contains 45% cyclic phases and 55% linear phases, with an acid content of 0.1% and a viscosity of 33 mPa·s. The yield of the hydrolysis product is 99.2%, the purity is higher than 99%, and the quality meets the process requirements.

[0037] Comparative Example 2

[0038] This embodiment includes the following steps: Dimethyldichlorosilane is fed at a rate of 20 t / h, with the ratio of dimethyl to saturated acid controlled at 1:3. A first-stage reaction is carried out in a hydrolysis reactor at a temperature of 50°C and a pressure of 0.07 MPa. 40 kg of n-octylamine is added to the hydrolysis reactor as an auxiliary agent. The hydrolysis products and saturated acid obtained from the reaction enter a first-stage phase separator, while the generated HCl gas, at a temperature of 30°C and a pressure of 0.15 MPa, undergoes warm acid countercurrent washing in the lower column of a hydrogen chloride purification tower, and then enters the upper column of the hydrogen chloride purification tower for further purification and drying. After passing through a demister, it is sent to the user. This comparative example only includes the first-stage hydrolysis reaction.

[0039] After passing through the primary phase separator, the oil phase hydrolysis product polysiloxane contains 50% cyclic and 50% linear components, with an acid content of 1.0%. The hydrolysis is incomplete, with high end-group chlorine content and a viscosity of 25 mPa·s. The yield of the hydrolysis product is 98.2%, and the purity is less than 99%, which does not meet the process requirements.

[0040] Compared with the above examples, Example 1 has the highest ring ratio, the lowest acid content, the lowest viscosity, and the highest yield of hydrolysate.

Claims

1. A two-stage hydrolysis reaction process of dimethyldichlorosilane concentrated acid, characterized in that, It comprises the following steps: (1) The feeding amount of dimethyldichlorosilane is 20 t / h, the ratio of dimethyldichlorosilane to saturated hydrochloric acid is controlled to be 1:3, the first-stage reaction is carried out in a hydrolysis reactor, the temperature is 60℃, the pressure is 0.2 Mpa, and the reaction time is 2 min; the reaction product enters a hydrogen chloride purification tower in a liquid-gas mixed form, the hydrogen chloride purification tower is divided into an upper tower and a lower tower, the lower tower is used for warm acid washing, and the upper tower is used for cold acid washing; in the lower tower, the unreacted dimethyldichlorosilane monomer steam continues to be hydrolyzed to generate hydrolysis products siloxane and hydrogen chloride gas, meanwhile, the liquid drops entrained in the gas are dissolved in hot washing acid liquid; the gas enters the upper tower, is washed and cooled by the cold acid for the second time, and the acid oil drops are absorbed by the cold acid solution; the dry and cooled hydrogen chloride gas enters a mist eliminator from the top of the tower, the liquid drops carried by the hydrogen chloride gas are removed, and the collected liquid drops enter a first-stage phase separator to be reused in the system; the hydrogen chloride purification tower is divided into an upper tower and a lower tower, the lower tower is used for warm acid washing, and the upper tower is used for cold acid washing; both the towers are packed towers; the packing is graphite ring or plastic flower ring type; (2) The hydrolysis products obtained in the reaction and saturated acid enter the first-stage phase separator, the generated HCl gas has a temperature of 30℃ and a pressure of 0.15 MPa, is first washed by warm acid countercurrently in the lower tower of the hydrogen chloride purification tower, then enters the upper tower of the hydrogen chloride purification tower, is further purified and dried, and is sent to a user after passing through a mist eliminator; the hydrolysis products separated from the first-stage phase separator are pumped to a second-stage reactor to carry out second-stage reaction, the second-stage reaction temperature is controlled to be 70℃, the second-stage reaction pressure is controlled to be 0.08 Mpa, the reaction time is 20 min, the reaction acid concentration is 15%, and the reaction product enters a second-stage phase separator to carry out acid oil separation; the acid phase is sent to a reaction acid heater by a circulating pump to be used as make-up water; the oil phase is subjected to subsequent washing and purification treatment to obtain high-quality hydrolysis products.

2. The reaction process according to claim 1, characterized in that, In step (1), the hydrolysis reactor is a plug flow reactor, and the inside is bulk packing; the bulk packing is graphite ring or plastic flower ring type; the inlet diameter of the hydrolysis reactor is DN250, and the outlet diameter is DN600.

3. The reaction process of claim 1, wherein, In step (1), the dimethyldichlorosilane and the saturated hydrochloric acid both enter from the bottom and overflow from the top, full-liquid operation, and turbulent mixing is carried out in the process of flowing upward through the packing section of the reactor.

4. The reaction process of claim 1, wherein, The warm acid of the lower tower is 50℃-60℃ saturated hydrochloric acid; the cold acid is -9℃~-4℃ saturated hydrochloric acid; the hydrogen chloride purification tower is a packed tower; and the packing is graphite ring or plastic flower ring type.

5. The reaction process according to claim 1 or 4, characterized in that, The outlet gas temperature of the upper tower of the hydrogen chloride purification tower is not higher than 0℃; and the inner part of the mist eliminator uses fiber mist removal.

6. The reaction process of claim 1, wherein, In step (2), the second-stage reactor is a continuously stirred tank reactor, and there is a baffle plate in the reactor to form turbulent flow.

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