Production process of deacidified silane crosslinker
---【CAFSI】
Overview of the acetic anhydride process The reaction of carboxylic anhydride with chlorosilane to produce organic acyloxysilane is one of the commonly used production processes for obtaining deacidified silane crosslinkers in industry. This method can use solvents to remove the byproduct acetyl chloride in time, accelerate the forward movement of the reaction and increase the reaction rate. It can also remove acetyl chloride in time by increasing the reaction temperature without using solvents. At present, the industry usually uses monomethyltrichlorosilane and acetic anhydride as raw materials for acylation reaction to synthesize methyltriacetoxysilane products, whose content can reach more than 95%, and the total chlorine is ≤100ppm. The reaction formula is as follows: CH3SiCl3 + 3C4H6O3 → (CH3CO2)3SiCH3 + 3C2H3ClO. The production process is briefly described as follows: Using monomethyltrichlorosilane and acetic anhydride as raw materials, the materials are put into the synthesis reactor at a certain ratio for acylation reaction. The temperature is first raised to 80℃ for normal pressure reflux reaction, and acetyl chloride is collected while reflux at 80~95℃ until the flow is cut off. The semi-finished product of methyltriacetoxysilane in the synthesis reactor is put into the synthetic crude product tank. The semi-finished product is pumped to the acetyl chloride vacuum film evaporator. The material temperature is controlled at 100℃ to evaporate acetic anhydride and acetyl chloride. The material is then pumped to the acetic anhydride vacuum film evaporator. The material temperature is controlled at 105-115℃ to obtain the finished product of methyltriacetoxysilane. The materials containing a large amount of acetic anhydride extracted from the two sets of vacuum film evaporators are returned to the synthesis reactor. The finished product of methyltriacetoxysilane is decolorized at 70℃ using activated carbon in the decolorization kettle. After the decolorization is completed, the material is filtered through a candle filter to the modification kettle to obtain pure methyltriacetoxysilane. The acetyl chloride collected from the synthesis reactor is further distilled and purified in the distillation reactor to obtain high-content acetyl chloride.
Overview of the acetic acid process Using acetic acid as the acyl oxidant, the reaction of organochlorosilane and acetic acid is a reversible process:
RnSiCl4-n + (4-n)AcOH ⇌RnSi(OAc)4-n + (4-n)HCl, n=0,1,2 In order to shift the equilibrium to the right and obtain a higher yield of the target product, effective measures must be taken to remove the by-product HCI from the reaction system in time, or add HCI absorbent. In order to remove HCI in time, there are three methods: 1. Add a low-boiling inert organic solvent to the reaction system and react at reflux temperature to discharge the by-product HCI from the reaction system in time; 2. Pass inert gas to drive out HCI; 3. Use a tower reactor to enhance the mass transfer and heat transfer efficiency to accelerate the separation rate of HCI and reduce the occurrence of side reactions. In addition, the raw materials, solvents, water and other harmful impurities in the system must be strictly controlled. It is well known that methyltriacetoxysilane is a commonly used crosslinking agent for deacetic acid-type one-component room temperature vulcanized silicone rubber. When the acetic acid method is used for preparation, acetic acid and petroleum ether used as a solvent can be added to the reactor together, and then the temperature is raised to reflux and monomethyltrichlorosilane is added dropwise. After the addition is completed, the temperature is kept to reflux for 4 hours, so that the by-product HCI is promptly expelled from the reaction system and absorbed. After the liquid product is neutralized and fractionated, methyltriacetoxysilane with a yield of 90% (mass fraction) can be obtained. At the same time, the solvent petroleum ether can also be recycled and reused.