The substitution reaction of chlorine gas with the free radicals of active hydrogen in the reaction raw materials is an important means of functionalizing carbon-hydrogen bonds. For example, chlorination at the benzyl position can yield mono- and poly-chlorinated intermediates, which can then be converted into other intermediates. The chlorination of the active methylene in ethyl acetoacetate is an effective way to obtain a variety of heterocycles.

Traditional chlorination processes are usually carried out in a kettle-type bubble-through-chlorine system, where the utilization rate of chlorine gas is very low and selective control is difficult. Although the falling film reactor can reduce backmixing, it still requires the recycling of a large excess of chlorine gas.

Microreactors provide another option for continuous chlorination. Chlorine gas and raw materials enter the reactor in a co-current manner, and the raw material equivalents can be accurately controlled. Ideal plug flow operation is achieved at a certain temperature, thereby improving the selectivity of the reaction.

Chlorination reactions require accurate control of the flow rate of chlorine gas, therefore the design and performance of the chlorine gas feed system is one of the key factors for success.