Clean process for preparing chloroformyl-substituted benzene

A process for preparing a chloroformyl-substituted benzene, comprising (1) reacting a methyl aromatic hydrocarbon of formula (X)aC6H6−a−b(CH3)b or a pendant alkyl chloride thereof with chlorine gas under illumination conditions to prepare a trichloromethyl-substituted benzene and obtain hydrogen chloride as a byproduct, wherein X is a chlorine, bromine, or fluorine atom, a is an integer of 0, 1, 2, 3, 4, or 5, b is an integer of 1, 2, 3, or 4, and a+b≦6, and the pendant alkyl chloride is a compound where hydrogen atoms of the pendant alkyl group in the methyl aromatic compound are not completely substituted by chlorine atoms;

• (2) reacting the trichloromethyl-substituted benzene with water or a corresponding aromatic acid of formula (X)aC6H6−a−b(COOH)b to prepare the chloroformyl-substituted benzene and to obtain hydrogen chloride as a byproduct, wherein the corresponding aromatic acid is a substituent on a parent nucleus of the aromatic acid and a substituent on a parent nucleus of the methyl aromatic hydrocarbon or pendant alkyl chloride thereof are located at the same substitution position or corresponding substitution positions, and wherein X is a chlorine, bromine, or fluorine atom, a is an integer selected from 0, 1, 2, 3, 4 and 5, b is an integer selected from 1, 2, 3 and 4, and a+b≦6;
• (3) subjecting a gas stream containing the hydrogen chloride as the byproducts from steps (1) and (2) to catalytic oxidation in one or more reactors to form a product gas stream;
• (4) separating the product gas steam to obtain a gas stream containing chlorine, a gas stream containing oxygen, and optionally, a gas stream containing hydrogen chloride;
• and
• (5) introducing the gas stream containing chlorine as raw material into chlorination reaction in step (1).