Recently, Tianjin Langxing launched an acid alkali resistant dynamic mixer for the organic silicon industry, which accurately connects the concentrated acid hydrolysis process of dimethyl dichlorosilane (Me ₂ SiCl ₂) and saturated hydrochloric acid. The equipment adopts PVDF integral processing, which has excellent chemical inertness and is specially designed for the working conditions of chlorosilanes and high-temperature hydrochloric acid. It solves the four core pain points of “heat release, corrosion, phase change, and mass transfer” in the hydrolysis section.
[Process Background]
The hydrolysis of dimethyldichlorosilane is the core reaction for preparing polydimethylsiloxane (PDMS) and also the “heart” section of the organic silicon industry chain. Me ₂ SiCl ₂ reacts with concentrated hydrochloric acid under strong exothermic conditions, instantly releasing a large amount of heat energy, generating a ring and linear hydrolysate, and producing hydrogen chloride gas as a byproduct – the latter is treated and sent back to chloromethane synthesis, forming an industrial closed-loop cycle. The hydrolyzed product is further cracked and rearranged to form basic cyclic compounds represented by D4 and D5, and ultimately enters the entire industrial chain of silicone oil, silicone rubber, silicone resin, and functional silane.
Six major engineering features of hydrolysis section
1、 Strong heat release and rapid cooling control result in intense heat release during the hydrolysis of Si Cl bonds. Uncontrolled temperature control triggered the excessive condensation of hydroxyl groups in silicon, which led to the imbalance of the proportion of gel and ring. The reactor must be equipped with an efficient heat exchange system to precisely lock the reaction temperature within the range of 30-50 ℃, achieving a process window of “reaction while cooling”.
2、 The full cycle utilization of hydrogen chloride results in a theoretical by-product of approximately 0.55 tons of hydrogen chloride gas per ton of dimethyl hydrolysis. After defogging and drying, it is sent back to the chloromethane synthesis process and reused as production raw materials. This is the key to closed-loop industrial circulation and the core of cost control.
3、 The hydrolysis product of extreme phase separation operation – oily polysiloxane and hydrochloric acid water phase are immiscible. In continuous production, it is necessary to maintain a clear phase interface: the upper oil phase (hydrolysate) and the lower acid phase (dilute hydrochloric acid) must be accurately separated. If the separation is not clear, acid will corrode the equipment and oil will block the pipeline.
4、 The composition of the hydrolyzed product with molecular structure determined by residence time (ring ratio, oligomer content, terminal hydroxyl density) is highly sensitive to the reaction residence time. Short stay → Multiple ring structures and high hydroxyl groups; Long residence → linear molecule with long length and high viscosity. In industry, viscosity and molecular weight distribution are locked within a narrow window through precise adjustment of feed ratio and overflow position.
5、 The medium with extremely high corrosion level is high-temperature hydrochloric acid and chlorosilane, with extremely high corrosion level. Equipment, pipelines, and valves often use PTFE lined, glass lined, special duplex stainless steel, or graphite heat exchangers. A gasket selection error may cause splashing of acidic materials.
6、 The pure multiphase mass transfer process initially involves an oil like monomer that is insoluble in the acid phase, essentially a liquid-liquid heterogeneous reaction. The mixing shear strength and dispersion effect determine the degree of hydrolysis completion and product quality. The blade design and speed control are the core process secrets of this section.