Study On Gas Phase Oxidation-liquid Phase Absorption Process For Removal Of No_x From Industrial Waste Gases

Liquid absorption and NO catalytic oxidation were systematically investigated to remove NO_x in the waste gases from the fine chemical,pharmaceutical and nitric acid industries. These waste gases were emited under room temperature and normal pressure and contained much oxygen and vapor,while the oxidation degree of the NOx was very low.The NO_x removal efficiencies of the liquid absorption were studied in the NaOH solution and the NaOH solutions which contained oxidant or reducer.The influences of the relative humidity,the reaction temperature and the contact time on the NO oxidation behavior over the modified activated carbon(MAC)were also investigated. Some conclusions were drawn as follows:The NO_x removal efficiency increased with the increasing of NO_x oxidation degree in(NH₄)₂SO₃-NaOH liquid and H₂O₂-NaOH solution,while there was an optimal oxidation degree 50-60%for the NaOH solution and urea-NaOH absorption liquid,thus the optimum oxidation degree for the solution removal efficiency was different from each other.The removal efficiency of NO_x increased with the NO_x concentration increase, and the contact time was favorable for the NO₂ removal when contact time rose.During the NO catalytic oxidation over the MAC,the NO conversion increased with the reaction time,while it was severely inhibited by the water vapor content.The maximum NO conversion was obtained at 50-70℃in humid gas,while decreased with the temperature increase in the dry gas.Under the conditions of the saturated water vapor at 20℃,NO concentration 650 ppmv,contact time 4 s,and temperature 50℃, the NO conversion was gotten to be 51%.By the above investigation,two new multi-stage processes were proposed for the NO_x removal of the industry waste gas. One is for the nitric acid industry,which was made up of the catalytic oxidation-caustic alkali absorption,and another for the fine chemical and pharmaceutical industries,which contained catalytic oxidation-ammonium sulfite alkali absorption.The processes could decrease the NO_x content to be lower than 100 ppmv and 120 ppmv respectively.