2CH4--(t)-> C2H2 + 3H2 C2H2---( C, t)---> C6H6 C6H6 + Cl2 ---> C6H5Cl + HCl C6H5Cl+ Cl2---> C6H4Cl2 + HCl C6H4Cl2+ Cl2--->C6H3Cl3 + HCl