Production process of dealcoholization silane crosslinker
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Overview of the reaction process of chlorosilane and methanol The most commonly used method for synthesizing alkoxysilane is to react CH3SiCl3 or silicon tetrachloride SiCl4 with ROH (mainly MeOH and EtOH) for alcoholysis (esterification). For example, the reaction of CH3SiCl3 or SiCl4 with MeOH can be expressed as follows:
CH3SiCl3+ 3MeOH → CH3Si(OMe)3+3HCl(1)SiCl4+ 4MeOH → Si(OMe)4+4HCl(2)In addition to the main reaction, there are the following side reactions:MeOH+HCl → MeCl+H2O(3)CH3Si(OMe)3+ H2O→ polymer + MeOH (4)CH3Si(OMe)2Cl+ MeOH → ClSi(OMe)3 + CH4↑(5)From the above, it can be seen that preventing or reducing the occurrence of side reactions is crucial to improving the yield of CH3Si(OMe)3 and the utilization rate of raw materials. In order to inhibit the occurrence of side reactions, methods such as controlling the reaction temperature in stages, lowering the alcoholysis temperature, alcoholysis in steps, adding solvents, and blowing nitrogen can be adopted. The purpose is to make HCl leave the reaction system as soon as possible and reduce the probability of contact reaction between HCl and MeOH. Since ferric chloride has a catalytic effect on (3), iron impurities should be prevented from mixing into the raw materials CH3SiCl and MeOH. At the same time, iron equipment should not be used in the alcoholysis system. At present, the most common process is the single-tower alcoholysis process: methanol and monomethyltrichlorosilane enter the pre-reactor according to a certain ratio, and after the pre-reaction, they enter the esterification tower for esterification reaction to obtain the reaction crude product. The reaction crude product is neutralized and then sent to the distillation system. The distillation tower collects the 103.5±1℃ fraction, which is the colorless and transparent liquid product methyltrimethoxysilane, with a product content of ≥99% and a Cl content of ≤50ppm.
Overview of the direct process Based on the great achievements in the synthesis of organochlorosilanes, the direct method has made gratifying achievements in the synthesis of organoalkoxysilanes in the 1990s, pushing organosilicon into a new era. The direct method for synthesizing organic alkoxysilanes is to make solid silicon powder react directly with methanol (or ethanol) under the combined action of heating, catalyst and solvent to obtain the target product organic alkoxysilane. In industry, silicon powder, solvent and copper catalyst (cuprous chloride) are often put into the reactor in a certain proportion for heating and activation to obtain silicon-copper active contacts. The activation temperature is generally controlled at above 180°C. Then methanol is introduced into the mixture that meets the activation conditions for reaction to obtain crude alkoxysilane. The rate of passing alcohol is adjusted with the temperature, pressure and product composition of the system. The crude alkoxysilane is separated by distillation to obtain high-content trimethoxyhydrogensilane, tetramethoxysilane and other organic alkoxysilanes. The trimethoxyhydrogensilane generated by the reaction can be dehydrogenated by methanol reflux, adding organic base and other methods to further obtain tetramethoxysilane.
Transesterification process overview The transesterification reaction between alkoxysilane and alcohol is a reversible equilibrium process: ≡Si—OR +R＇OH ⇌ ≡Si—OR＇+ROH Starting from low alkoxysilane, it reacts with high alcohol under the action of catalyst to obtain partially substituted mixed alkoxysilane or fully substituted high alkoxysilane. This method has been widely used to synthesize new organic alkoxysilanes. In addition to monohydric alcohols, polyols, polyols and phenol can also be used as raw alcohols to participate in the reaction. If no catalyst is used in the transesterification reaction, the reaction rate is very slow, but it will quickly reach equilibrium under the catalysis of acid and base. In addition, timely removal of the by-product ROH is also conducive to the shift of equilibrium to the right. Since low alcohols are easily evaporated from the reaction system, this method is particularly suitable for converting ≡SiOMe or ≡SiOEt into higher alkoxysilanes. Common process operations, such as reacting Si(OMe)4 with ethanol under N2 at 100-150°C for 24 hours, can produce products with different substitutions, including MeOSi(OEt)3, (MeO)2Si(OEt)2, (MeO)3SiOEt and Si(OEt)4. At present, the ester exchange method can be used to conveniently prepare silane coupling agents and organic alkoxysilanes, especially silanes with the general formula RSi(OR')a(OR")3-a. In the formula, R is an alkyl, aryl, cycloalkyl, alkenyl, etc.; R' is Me, Et; R" is i-Pr, i-Bu, t-Bu, t-C5H11, etc.