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What are the preparation methods of silicone oil

Mar 05, 2020

1. Co-hydrolytic condensation method


The traditional method is to add a fixed amount of a mixed solution of methylhydrodichlorosilane and trimethylchlorosilane to a reaction kettle containing a solvent and water. After the hydrolysis is completed, acid water is separated, and then concentrated sulfuric acid is added to telomerize the reaction; After the layers are separated, the upper layer is washed with water to neutrality, and the low-boiler is removed, filtered, and decolorized to obtain the finished product. The solvent is generally a derivative of hydrocarbon or benzene. The solvents currently used are mostly heptane and toluene. In the above method, the acidic water separated after the reaction is a mixed solution of sulfuric acid and hydrochloric acid, which has a lot of impurities and cannot be recycled, and multiple washings waste resources and pollute the environment. Bo Fengdeng improved the process, using the reverse hydrolysis method, that is, adding water droplets to the reaction kettle containing the monomer mixed solution, because the solubility of HC organic solvents is much less than water, so the residual acid in the hydrolysate will be much less , Easy to wash. Zhou Anan proposed a method for continuous production of silicone oil: methylhydrodichlorosilane, trimethylchlorosilane, and water were introduced into the reaction kettle from the bottom of the kettle in a certain proportion, and the hydrogen chloride gas generated was processed by an absorption device to generate The material is separated by a layerer. The separated lower acid water enters the concentrated hydrochloric acid storage tank for recycling. The upper hydrolyzed material enters the alkaline washing and neutralization tank for neutralization. The neutralizing agent can be sodium sulfate or sodium bicarbonate. After layering in a layerer, a neutral hydrolyzate is obtained; the neutral hydrolyzate is telomerized with a catalyst in a telomerization reactor, and the product is filtered and the low-boiling matter is removed in a thin-film evaporator to obtain a hydrogen-containing silicone oil . This method avoids the disadvantages of inefficiency and unstable product batches caused by indirect production, and can be automatically controlled, reducing labor costs. T. Lindner et al. Introduced an improved continuous production process. For each mole of hydrolyzable chlorine, the monomer reacts with a maximum of 0.5 mol of water to form a part of the hydrolysate. The HC produced is recycled and used directly in other processes. Excess water reacts, and the separated hydrochloric acid can be used as the water source in the previous step, and the volatile methyl hydrogen siloxane ring body obtained after hydrolysis is separated; the distillate in the final distillation stage is added to the equilibrium reactor for purification. The equilibrium reaction is performed under the action of a strongly acidic ion exchange resin to obtain a low-volatility, straight-chain, fully hydrogenated silicone oil. In order to improve the yield, the ring produced in this process can be mixed with a hydrochloric acid aqueous solution and a quaternary ammonium salt and heated to convert it into a linear product. Because the silicon-hydrogen bond is relatively active, the hydrolysis rate is fast, and gel is easy to be produced; therefore, the solvent is usually diluted during the hydrolysis of the organochlorosilane to reduce the reaction rate, but the solvent odor in the product prepared by the solvent method is difficult to remove and the product quality is poor. Not as a high-end product.


The solvent-free method was used to react the monomer mixed solution with the hydrochloric acid mixed solution, and the temperature was controlled at 5 to 45 ° C. After the reaction, the layers were separated, washed with water, dried, and neutralized; the temperature was controlled at 20 to 60 ° C, and the product was mixed with strong The acidic cation exchange resin undergoes an equilibrium reaction, and is filtered and distilled to obtain a completely hydrogenated silicone oil with good appearance and no odor]. At present, some domestic manufacturers, such as Jilin Changjie Silicon Chemical Co., Ltd., use solvent-free methods for mass production.


The molar mass of the products produced by the co-hydrolysis condensation method is wide, and the hydrolysis reaction is difficult to control. During the reaction, hydroxyl groups will be formed on the main chain to a certain extent, causing cross-linking, which will cause changes in product properties, such as shortening the shelf life; However, due to the simple operation and mature process of this method, most domestic manufacturers still produce fully hydrogenated silicone oil by this method.


2. Silicone catalytic equilibrium method


This method is similar to the principle of co-hydrolysis condensation method, but the capping agent uses hexamethyldisiloxane (MM). That is, first add methyl hydrodichlorosilane and MM to the reaction kettle to prepare a mixture, then add concentrated sulfuric acid and stir for a while, slowly add water for catalytic equilibrium reaction, and then stand still to separate the layers, and wash the upper product to neutrality. The target product was obtained by distillation under reduced pressure and filtration. Lu Qi et al. Slowly mixed a certain amount of water after uniformly mixing methyl hydrodichlorosilane and MM, and controlled the decolorization and filtration of the water to obtain an active hydrogen mass fraction ≥58% after filtration. The viscosity was 25clC. 00 ~ 40.00 mm / s finished product. This method can save energy and improve product quality.


3. Alcoholysis followed by hydrolysis and condensation


There are fewer reports on the law. Dissolve methyl hydrogen dichlorosilane in an organic solvent, add anhydrous ethanol for alcoholysis reaction, and heat up the acid h; add 2 times solvent and 4 times water to the alcoholysis product to carry out the hydrolysis reaction. After the reaction, The acidic water was separated and the upper product was washed with water to neutrality, and the hydrolysate was distilled under reduced pressure. The hydrolysate was mixed with MM and catalyst for equilibrium reaction, and the sulfate was separated. The product was washed with water to neutrality, dried and filtered. The target product was obtained. Since the reaction of silane in an ethanol solution is slower than that of an aqueous solution, the reaction is mild and the gelation is not easy, so the yield is high. However, because this method uses a large amount of ethanol, the production cost is relatively high, and the reaction steps are cumbersome, which limits the application of this method to mass production.


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