Method for recycling of reflow condensate in a liquid silicone rubber based adhesive preparation

Abstract

The application discloses a recycling method of reflux condensate in liquid silicone rubber base glue preparation, and water in the reflux condensate generated in the liquid silicone rubber base glue preparation process is removed first; the reflux condensate after water removal can be used for base glue preparation instead of part of silazane, and can also be added into an enamel reaction kettle, concentrated sulfuric acid is added, the temperature is increased to 50-100 DEG C, and after 1-5 hours of reaction, the sulfuric acid is removed by layering, the sulfuric acid can be reused to base glue tail gas absorption, and the remaining reflux condensate is washed to neutral, and hexamethyldisiloxane can be obtained by rectification. The effective recycling of the reflux condensate is solved, and cost reduction and benefit increase are realized.

Description

Technical Field

[0001] This invention relates to the technical field of liquid silicone rubber-based adhesive preparation, and more particularly to a method for recycling reflux condensate during the preparation of liquid silicone rubber-based adhesive. Background Technology

[0002] The preparation process of liquid silicone rubber is mainly a physicochemical mixing process of silicone oil and silica. Silica treatment agents need to be added during the process, most commonly silazane and water. Small molecules are generated during the treatment, such as trimethylsilanol or hexamethyldisiloxane after hydrolysis of silazane. Some of these react with the hydroxyl groups on the silica during the treatment, while others do not participate in the reaction and either evaporate directly into the air or are collected to form reflux condensate.

[0003] Over the past few decades, especially in the last 20 years, the preparation of liquid silicone rubber base has evolved from the initial open and semi-open processes to the current fully closed process. Initially, due to limitations in technology, the preparation of liquid silicone rubber base was primarily carried out in an open or semi-open manner. In this way, small molecules that did not participate in the reaction would evaporate into the air, thus virtually eliminating the formation of reflux condensate. This method caused significant environmental damage and also posed substantial safety hazards.

[0004] With the increasing emphasis placed on human health, environmental protection, and safety by the nation, the base rubber preparation technology is constantly being innovated and equipment is continuously being improved. The base rubber preparation process has also evolved to a fully enclosed and automated mode. In this mode, the ammonia tail gas generated during base rubber production can be treated through a tail gas absorption tower, and the resulting reflux condensate is collected and further treated.

[0005] Currently, reflux condensate is treated as hazardous waste, requiring significant costs for disposal. Recycling and reusing reflux condensate could not only save costs but also eliminate the safety and environmental hazards associated with hazardous waste. However, there are currently no reports or data on the recycling and reuse of reflux condensate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive, so as to reuse the compounds in the reflux condensate and achieve cost reduction and efficiency improvement.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for recycling reflux condensate during the preparation of liquid silicone rubber-based adhesive includes the following steps:

[0009] (1) The reflux condensate generated during the preparation of liquid silicone rubber base is allowed to stand and separate into layers. After separating the lower layer of water, the remaining reflux condensate is passed through a dryer to obtain reflux condensate with water removed.

[0010] (2) The reflux condensate after removing water is used for the preparation of base adhesive or is treated to obtain hexamethyldisiloxane.

[0011] The reflux condensate generated during the preparation of the base adhesive mainly consists of a small amount of water-soluble ammonia, water, trimethylsilanol, hexamethyldisiloxane, a small amount of unreacted silazane, and a small amount of low molecular weight siloxane, as shown in Table 1.

[0012] Table 1 Main components of reflux condensate

[0013] Compound Name mass percentage Trimethylsilyl alcohol 52.0-54.0 hexamethyldisiloxane 20.0-22.0 Octamethylcyclotetrasiloxane 3.0-5.0 other 0.5-2.0 water 19.0-21.0

[0014] In this invention, the reflux condensate generated during the preparation of liquid silicone rubber base is first dehydrated. The dehydrated reflux condensate can replace part of the silazane in the preparation of the base, or it can be put into an enamel-lined reactor, concentrated sulfuric acid is added, the temperature is raised to 50-100℃, and after reacting for 1-5 hours, the sulfuric acid is removed by separation. The sulfuric acid can be reused for the base gas absorption. The remaining reflux condensate is washed with water until neutral, and then distilled to obtain hexamethyldisiloxane.

[0015] Preferably, the specific method for preparing the base adhesive is as follows:

[0016] (a1) Add vinyl-terminated silicone oil, silazane, reflux condensate with water removed, water, and fumed silica to a kneader, heat and reflux and vacuum treatment to obtain base glue 1.

[0017] (b1) Add vinyl-terminated silicone oil, silazane, water, and fumed silica to a kneader, heat and reflux and vacuum treatment to obtain base glue 2;

[0018] Base Gel 1 uses silanol produced by the hydrolysis of silazane and silanol in the reflux liquid to react with the hydroxyl groups of fumed silica to treat silica; Base Gel 2 uses silanol produced entirely by the hydrolysis of silazane to react with the hydroxyl groups of fumed silica to treat silica.

[0019] The reflux condensate after removing moisture contains silanols, silazanes, etc., and can still be used as a treatment agent for fumed silica (white carbon black), but the effect is not as good as that of silazanes. Therefore, it can only replace a small portion of silazanes, and the appearance and other properties of the resulting base adhesive will be affected to some extent. Therefore, only a small portion of the reflux condensate can be reused in the preparation of base adhesives, and most of the reflux condensate needs to be treated in other ways.

[0020] Preferably, the reflux condensate with moisture removed replaces a portion of the silazane in the treatment of fumed silica, with a replacement ratio of less than 30 wt%, preferably less than 20 wt%. The replacement ratio is the mass ratio of the reflux condensate to the silazane.

[0021] Preferably, the amount of reflux liquid used is 100-200 wt% of the amount of silazane replaced.

[0022] Preferably, in step (a1), the mass fraction ratio of terminal vinyl silicone oil, silazane, reflux condensate after water removal, water, and fumed silica is 100:5~6.5:2~4:1.5~2.5:40.

[0023] Preferably, in step (b1), the mass fraction ratio of terminal vinyl silicone oil, silazane, water, and fumed silica is 100:6-9:1.5-2.5:40.

[0024] The preferred method for obtaining hexamethyldisiloxane is as follows:

[0025] (a2) Add the dehydrated reflux condensate to the reactor and add concentrated sulfuric acid to react at a constant temperature. Let it stand and separate into two layers. The lower layer is acid and water. Take out the lower layer liquid for the absorption of tail gas generated during the production of base rubber.

[0026] (b2) Wash the upper liquid with pure water 3-5 times until it is neutral, and then distill it under normal pressure to obtain hexamethyldisiloxane.

[0027] The small amounts of ammonia, silanol, and unreacted silazane in the reflux condensate after removing moisture can be reacted with concentrated sulfuric acid. Ammonia can generate ammonium sulfate, and silanol can be dehydrated by concentrated sulfuric acid to form hexamethyldisiloxane. The unreacted silazane reacts with sulfuric acid to form ammonium sulfate and hexamethyldisiloxane.

[0028] Preferably, in step (a2), the specific method for absorbing the tail gas generated during the production of the base rubber is as follows: the tail gas contains ammonia, protective nitrogen, etc., which are absorbed by an absorption tower containing dilute sulfuric acid to generate an ammonium sulfate solution. After the ammonium sulfate solution is concentrated, it is centrifuged to obtain solid ammonium sulfate.

[0029] Preferably, in step (a2), the amount of concentrated sulfuric acid added is 1-6 wt% of the total amount, the constant temperature reaction temperature is 50-100℃, and the reaction time is 1-5 hours.

[0030] The concentrated sulfuric acid used is 98% or higher, which serves to neutralize and catalyze dehydration. The water content in the reflux condensate is kept as low as possible to prevent water from diluting the concentrated sulfuric acid and affecting its catalytic dehydration effect.

[0031] Preferably, in step (b2), during atmospheric distillation, when the temperature reaches 100°C, a substance is distilled off. The temperature is then raised to 200°C until no more distillate flows out, at which point the distillation is stopped and the fraction at 100°C-200°C is collected.

[0032] Preferably, the reflux condensate is obtained by collecting low-molecular-weight liquids generated during the silica treatment process in the preparation of base adhesive 1 and base adhesive 2 through reflux condensation.

[0033] By adopting the above technical solution, the present invention has the following beneficial effects:

[0034] 1. Solved the problem of effective recycling of reflux condensate in the preparation of liquid silicone rubber base, achieving cost reduction and efficiency improvement.

[0035] 2. The obtained hexamethyldisiloxane can be sold directly or used in the synthesis of MQ silicone resin, MDM, MD2M, and methyl silicone oil, achieving internal recycling. Attached Figure Description

[0036] The embodiments will be further described below with reference to the accompanying drawings.

[0037] Figure 1 This is a schematic diagram of the equipment used for producing base adhesive. Detailed Implementation

[0038] Example 1

[0039] like Figure 1 As shown, the reflux condensate generated by the reflux condenser 2 in the base rubber production process enters the reflux condensate storage tank 4 through the reflux condensate discharge pipe 3. After the reflux condensate in the reflux condensate storage tank 4 separates into layers, the water in the lower layer is separated, and the remaining reflux condensate passes through a dryer to obtain reflux condensate with water removed.

[0040] In kneader 1, 815 kg of 20,000 mPas end-vinyl silicone oil, 45 kg of silazane, 25 kg of dehydrated reflux condensate, 16 kg of water, and 330 kg of fumed silica were added. After heating, reflux, and vacuum treatment, base rubber 1 was obtained. In kneader 1, 815 kg of 20,000 mPas end-vinyl silicone oil, 60 kg of silazane, 16 kg of water, and 330 kg of fumed silica were added. After heating, reflux, and vacuum treatment, base rubber 2 was obtained. Base rubber 1: viscosity 3.5 million mPas, hardness 52 degrees, light transmittance 78%; Base rubber 2: viscosity 3 million mPas, hardness 51 degrees, light transmittance 80%.

[0041] Example 2

[0042] Add the dehydrated reflux condensate to the reactor, along with 3 wt% concentrated sulfuric acid. Heat to 50-55°C and react at this temperature for 3 hours. Allow to stand and separate into two layers. The lower layer consists of acid and water, which can be used to absorb the tail gas generated during base rubber production. Wash the upper liquid 3-5 times with pure water until neutral. Then, perform atmospheric distillation. When the temperature reaches 100°C, substances will distill off. Continue heating to 200°C until no more distillate flows out, at which point distillation is stopped. Collect the fraction obtained at 100-200°C for GC-MS analysis. Analysis results: Hexamethyldisiloxane (MM) content: 75%, Trimethylsilanol content: 19%, MDM content: 4%, Octamethylcyclotetrasiloxane content: 2%.

[0043] Example 3

[0044] Add the dehydrated reflux condensate to the reactor, along with 5 wt% concentrated sulfuric acid. Heat to 50-55°C and react at this temperature for 3 hours. Allow to stand and separate into two layers. The lower layer consists of acid and water, which can be used to absorb the tail gas generated during base rubber production. Wash the upper liquid 3-5 times with pure water until neutral. Then, perform atmospheric distillation. When the temperature reaches 100°C, substances will distill off. Continue heating to 200°C until no more distillate flows out, at which point distillation is stopped. Collect the fraction obtained at 100-200°C for GC-MS analysis. Analysis results: Hexamethyldisiloxane (MM) content: 80%, Trimethylsilanol content: 14%, MDM content: 4%, Octamethylcyclotetrasiloxane content: 2%.

[0045] Example 4

[0046] The dehydrated reflux condensate was added to the reactor, along with 5 wt% concentrated sulfuric acid. A water separator was installed, and the reaction was initiated by heating. When the temperature reached 90°C, droplets began to distill and flow into the water separator. The temperature was maintained between 90°C and 100°C, and droplets continued to flow into the water separator. The reaction continued for 3 hours. The liquid in the reactor was allowed to settle and separate into layers. The lower layer of acidic water was removed, and the upper layer was washed 3-5 times with pure water until neutral. Distillation was then carried out, with the temperature further increased to 200°C until no more distillate flowed out. Distillation was then stopped. The fraction collected between 100°C and 200°C was analyzed by GC-MS. Analysis results: Hexamethyldisiloxane (MM) content: 92%, MDM content: 8%.

[0047] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive, characterized in that, Includes the following steps: (1) The reflux condensate generated during the preparation of liquid silicone rubber base is allowed to stand and separate into layers. After separating the lower layer of water, the remaining reflux condensate is passed through a dryer to obtain reflux condensate with water removed. (2) The reflux condensate after removing water is used for the preparation of the base adhesive or treated to obtain hexamethyldisiloxane, wherein, The specific method for preparing the base adhesive is as follows: (a1) Vinyl end silicone oil, hexamethyldisilazane, dehydrated reflux condensate, water, and fumed silica are added to a kneader. After heating, reflux, and vacuum treatment, base adhesive 1 is obtained. The dehydrated reflux condensate replaces part of the hexamethyldisilazane in the treatment of fumed silica, with a replacement ratio of less than 30 wt%. (b1) Add vinyl-terminated silicone oil, hexamethyldisilazane, water, and fumed silica to a kneader, heat to reflux and vacuum process to obtain base glue 2; The specific method for obtaining hexamethyldisiloxane is as follows: (a2) Add the dehydrated reflux condensate to the reactor and add concentrated sulfuric acid to react at a constant temperature. Let it stand and separate into two layers. The lower layer is acid and water. Take out the lower layer liquid for the absorption of tail gas generated during the production of base rubber. (b2) Wash the upper liquid with pure water 3-5 times until it is neutral, and then distill it under normal pressure to obtain hexamethyldisiloxane.

2. The method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive according to claim 1, characterized in that: In step (a1), the mass fraction ratio of vinyl-terminated silicone oil, hexamethyldisilazane, reflux condensate with water removed, water, and fumed silica is 100:5~6.5:2~4:1.5~2.5:

40.

3. The method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive according to claim 1, characterized in that: In step (b1), the mass fraction ratio of terminal vinyl silicone oil, hexamethyldisilazane, water, and fumed silica is 100:6~9:1.5~2.5:

40.

4. The method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive according to claim 1, characterized in that: In step (a2), the specific method for absorbing the tail gas generated during the production of the base rubber is as follows: the tail gas contains ammonia and nitrogen, which are absorbed by an absorption tower containing dilute sulfuric acid to generate ammonium sulfate solution. After the ammonium sulfate solution is concentrated, it is centrifuged to obtain solid ammonium sulfate.

5. The method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive according to claim 1, characterized in that: In step (a2), the amount of concentrated sulfuric acid added is 1-6 wt% of the total amount, the constant temperature reaction temperature is 50-100℃, and the reaction time is 1-5 hours.

6. The method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive according to claim 1, characterized in that: In step (b2), during atmospheric distillation, substances distill out when the temperature reaches 100°C. Continue heating to raise the temperature to 200°C until no more fractions flow out, then stop distillation and collect the fractions at 100°C-200°C.

7. The method for recycling reflux condensate in the preparation of liquid silicone rubber-based adhesive according to claim 1, characterized in that: The reflux condensate is obtained by collecting low-molecular-weight liquids generated during the silica treatment process in the preparation of the base adhesive through reflux condensation.

Images