A study of the catalytic dehydrochlorination of 2-chloropropane in oxidizing conditions

The conversion of 2-chloropropane (2-CP) in the presence of oxygen has been investigated over a number of catalysts including alumina and alumina-supp orted copper chloride, manganese tungstate, mixed manganese-aluminum oxide, silica-alumina, and ZSM5 zeolite. Dehydrochlorination to propene + HCl is predominant, but other reactions such as oxychlorination to deeper chloride d compounds, cracking, oligomerization and aromatization can occur. On sili ca alumina, a selectivity to propene approaching 100% is found and very hig h conversion can be obtained above 400 K. Over this catalyst the reaction k inetics is found to be zero order in 2-CP with an activation energy near 14 .5 kcal/mol. 2-CP converts definitely faster than 1-chloropropane. FT-IR sp ectroscopy shows that the molecular adsorption of 2-CP is fast and reversib le at low temperature, while a nucleophilic substitution occurs to give str ongly adsorbed 2-propoxide species starting from near 373 K. The eliminatio n reaction of 2-propoxide to gas-phase propene occurs slowly just near 400 K. The desorption of HCl is also observed to be quite fast in this low-temp erature range. FT-IR and kinetic data suggest that the rate-determining ste p is associated with the elimination reaction from 2-propoxides to propene occurring via an E1-type mechanism through a secondary carbenium ion.