Abstract:

Two heteropoly zinc salts of Zn_1.2H_1.8PW₁₂O₄₀ and  Zn_1.1H_1.9PMo₁₂O₄₀ are prepared by template impregnation. They are used as catalyst to oxidative degradation of 4,4′-dibromobiphenyl (4,4′-DBB) in subcritical water. Zn_1.2H_1.8PW₁₂O₄₀ pays better role on accelerating degradation rate and shows enough stability. Thus oxidative degradation and the kinetics of 4,4′-DBB in subcritical water are investigated using Zn_1.2H_1.8PW₁₂O₄₀ as catalyst. The optimal experiment conditions are obtained as follows: m(H₂O₂)∶m(4,4′-DBB)= 200∶1, temperature of 320 ℃, pressure of 11.9 MPa, and reaction time of 15 min. Under the optimal condition, chemical oxygen demand （COD） of water sample after reaction can be down to 55.9 mg/L, which meets the Chinese National Standard GB 8978—1996. The order of catalytic oxidation degradation kinetic of 4,4′-DBB in subcritical water is 1.70, and the apparent activation energy is 44.04 kJ/mol. 

Key words: heteropoly zinc salt; 4,4′-dibromobiphenyl; subcritical water oxidation; catalysis; chemical oxygen demand (COD)