Novel homogeneous catalyst system for the oxidation of concentrated ammonium sulfite

A homogeneous catalyst system made up of [Co(NH3)6]2+/I− has been put forward to catalyze the oxidation of concentrated ammonium sulfite. The experiments were performed in a packed column with sulfite concentrations above 2.5 mol l−1, temperature range 20–65 °C, and oxygen partial pressure 0.052–0.21 atm. The experimental results indicate that the Co(NH3)62+/I− homogeneous catalyst system can obviously accelerate the concentrated ammonium sulfite oxidation rate. After 2 h reaction, the sulfite conversion is only 12.5% with no catalysts while 72.1% sulfite conversion can be obtained with 0.02 mol l−1 Co(NH3)62+ and 0.005 mol l−1 I− in the ammonium sulfite solution. The sulfite oxidation rate increases 284% as Co(NH3)62+ concentration increases from 0.01 to 0.02 mol l−1. But there is little use increasing the Co(NH3)62+ concentration above 0.04 mol l−1. The sulfite oxidation rate may increase 229% as the temperature increases from 20 to 65 °C. Sulfite oxidation rate is independent of the initial sulfite concentration. Increasing the oxygen partial pressure can increase the sulfite conversion. The reaction order with respect to oxygen is 1.2 and sulfite is zero. The apparent activation energy determined is 23.5 kJ mol−1.