Synthesis of vinylidene chloride

vinylidene chloride, also known as 1,1-dichloroethylene (VDC). According to the process characteristics, there are three production methods of vinylidene chloride: 1,1,2-trichloroethane alkali dehydrochlorination method, methyl chloroform hot cracking dehydrochlorination method and 1,1-dichloroethane hot chlorination method; according to the raw material route, there are four methods: vinyl chloride chlorination method, vinyl chloride hydrochlorination method, 1,2-dichloroethane chlorination method and ethane chlorination method.

1．1 1, 1, Alkaline hydrolysis of 2-trichloroethane

Using vinyl chloride as starting material, 1,1,2-trichloroethane was synthesized by the reaction of vinyl chloride with chlorine. The catalyst used in the reaction was iron. In fact, the reaction can be carried out without catalyst, with high yield, simple equipment, less investment and low cost. Vinylidene chloride can be obtained by the reaction of 1,1,2-trichloroethane with alkali or pyrolysis.

1,1,2-trichloroethane was obtained by substituting 1,2-dichloroethane for chlorination, and then 1,1,2-trichloroethane was hydrolyzed with 1,1,2-trichloroethane to prepare vinylidene chloride. Using 1,2-dichloroethane as raw material, this method is one of the main methods used in the world to produce vinylidene chloride. This method is connected with the production of 1,1,1-trichloroethane, and is also one of the industrial methods to produce 1,1,1-trichloroethane. In this method, 1,2-dichloroethane and chlorine gas are chlorinated at 100 and 110 ℃, and the proportion of 1,2-dichloroethane is required to be greatly excessive. The reaction produces a mixture of 1,1,2-trichloroethane,1,2-dichloroethane and polychloride. After separation, 1,2-dichloroethane can be recycled and polychloride can be separated to obtain pure chlorine
1,1,2-trichloroethane. 1,1,1-trichloroethane was synthesized from the hydrogen chloride and vinylidene chloride. The reaction of 1,1,2-trichloroethane with lye was carried out at 70-80 ~ C under normal pressure. Because of the high price of 1,2-dichloroethane in China, it is not suitable to use this method at present.

The process is simple, but it needs to consume a lot of alkali liquor, and a lot of waste brine needs to be treated.

1.2 thermal dehydrochlorination of 1,1,1-trichloroethane

1,1-dichloroethane was synthesized from vinyl chloride and hydrogen chloride. 1,1-dichloroethane was chlorinated to obtain 1,1,1-trichloroethane. Vinylidene chloride was obtained by high temperature pyrolysis. This method is the latest method to synthesize vinylidene chloride. There are few by-products in the cracking process, and the product purity is high. However, 1,1-trichloroethane is expensive, the production cost is high, and the process is complex. Domestic development is difficult.

1.3 ethane chlorination

Vinylidene chloride was obtained from ethane by chlorination, distillation, separation and pyrolysis. The process of this method is complex. High equipment requirements and difficult process control, but the price of raw materials is cheap, less waste discharge.

In this paper, vinylidene chloride was synthesized from 1,1,2-trichloroethane by alkali hydrolysis and saponification in sodium hydroxide solution. Through a simple column distillation separation device, the boiling point of vinylidene chloride is very low, and the product is cooled and collected by flash evaporation method, so that the vinylidene chloride generated by the reaction immediately leaves the reaction system, so that the equilibrium is conducive to the direction of the product movement, and the long residence time of vinylidene chloride is avoided, and the by-product chloroacetylene is generated by the deep reaction of vinylidene chloride with alkali liquor.