Research Of Solid-phase Catalysts Acting On The Ammonium Sulfite Heterogeneous Catalytic Oxidation In Ammonia Desulphurization

China’s energy structure is dominated by coal, sulfur dioxide emissions from the burning of coal has caused serious air pollution problems. The flue gas desulfurization is the main method to reduce the emission of SO2, At present, the commonly methods include limestone-gypsum desulphurization technology, spray drying method flue gas desulfurization technology, seawater flue gas desulfurization technology, ammonia desulphurization technology, etc. At the same time ammonia desulphurization technology has been widely applied in recent years because of so many advantages, such as high desulfurization efficiency, no secondary pollution, the byproduct of ammonium sulfate can be produced in resource recovery, and low operating cost. Through the process, it uses the ammonia water or liquid ammonia to absorb the sulfur dioxide existed in industrial waste gas and generates ammonium sulfite, recyclable ammonium sulfate can be generated by forced oxidation. Meanwhile, how to transform ammonium sulfite to ammonium sulfate steadily and economically is the key to realize the ammonia desulphurization’s industrialization.In this paper, we have used self-made solid catalysts loading with cobalt ion to study its promoting effect and mechanism on ammonium sulfite oxidation reaction. The cobalt salt is the main active component of solid-phase catalysts loading with cobalt ion, and it has been made by impregnation method. In terms of preparation, the 4A molecular sieves have been screened as the raw materials. Through the orthogonal experiment, we have changed the conditions of preprocessing method(including the washing and drying), the quantity of cobalt ion, the way of pre-roasting, the roasting temperature and roasting time, explored the preparation process of solid-phase catalysts loading with cobalt ion. The best preparation conditions of catalysts are as follows: no pretreatment, 1.2% loading with cobalt ion, pre-roasting for 2 h at 250 ℃, roasting for 3 hours at 400 ℃.Taking advantage of a stirred tank reactor with bubbling, by comparing the reaction rate of the different concentrations of ammonium sulfite non-catalytic oxidation, the catalytic oxidation kinetics of ammonium sulfite has been studied. Results show that under the condition of no catalyst, the catalytic oxidation rate of different concentrations of sulfite has no obvious difference and the reaction of ammonium sulfite is 0 magnitude response. Catalytic reaction dynamics of low concentration and high concentration of ammonium sulfite have been studied. At low concentration of ammonium sulfite(< 1.0 mol/L) conditions, the kinetics properties of ammonium sulfite of catalytic oxidation have been studied by changing the concentration of ammonium sulfite, the concentration of catalysts, oxygen partial pressure, temperature, pH and so on. The results confirmed that the solid-phase catalysts loading with cobalt ion has obvious catalytic effect on the low concentration of ammonium sulfate. The oxidation rate under catalytic conditions is up to 1.7 to 6 times of the rate under non-catalytic conditions. The general reaction orders with respect to catalyst and oxygen are 0.47 and 0.35 respectively. The apparent activity energy is 16.83 KJ.mol-1, and the catalytic oxidation of ammonium sulfite optimum pH value is 7.0.The high concentration of ammonium sulfite(> 1.0 mol/L) of catalytic oxidation experiment shows: with the increase of the concentration of ammonium sulfite, the effect of solid-phase catalysts loading with cobalt ion reduced gradually. Although the oxidation rate with catalysts is up to 2 to 4 times of the rate in the absence of catalyst under the same conditions, but overall, the effect of high concentration of ammonium sulfite catalytic is still not ideal. On the basis of the previous experience, we have tried to improve its catalytic efficiency by adding 0.1 ml of hydrogen peroxide. However, the results show that the solid-phase catalysts loading with cobalt ion and hydrogen peroxide have no synergy catalysis under the condition in this experiment.