Study On Oxidation Degradation Of DNT In Supercritical Water

Supercritical water oxidation (SCWO) was a promising technology for treatment organic-containing wastewater. When exceeding critical point of water (Tc=374.3oC,Pc=22.05MPa), the values of density, dielectric constant, surface tension, viscosity, ionic product and hydrogenous bond drop down, the upper diffusion modulus, so supercritical water acts as a non-polar solvent of high diffusivity and excellent transport properties. Consequently, even non-polar organic compounds and gases become completely miscible with the supercritical water. The process of SCWO that is based on the special physical properties of supercritical water has a great many of advantages. The oxidation reactions to occur rapidly without any interphase mass transport limitations. The organic compounds in wastewater were completely oxidation in several seconds to several minutes. DNT is a major component of"redwater"wastes. Redwaters are produced by detonator or TNT washing in industrial nitration plants, and ammoniumdinitrophenolate in particular is the major byproduct of nitrobenzene plants using ammonia washes. The DNT wastewater can badly pollute environment and organism, which is difficult to be decomposited by other solutions.The homogeneous and non-catalytic SCWO of DNT was performed in an intermittent flow reactor and a continuous flow reactor. The oxidation efficiency, reaction mechanism, kinetics and influence factor of DNT in supercritical water were investigated.The results indicate that DNT was easily oxidized in supercritical water. 99% COD removal was obtained in several seconds during 550 oC～600 oC, 21 MPa～24MPa with O2 in excess. Gas products were analyzed with qualitative anslysis. The results indicate that gas products were no NO2. The COD elimination efficiency was significantly improved as reaction temperature, pressure, residence time or oxidant dosage was increased. The main influential factors of COD elimination efficiency were temperature and residence time with O2 in excess. Pressure was only above critical point.The liquid products and gas products of SCWO of DNT were analyzed and identified systematically by GC-MS and qualitative anslysis. The reaction path and mechanism of DNT in SCWO processes were obtained. The oxidation of DNT in supercritical water was following to rules of free radical reaction. Free radicals HO·and ROO·began the reactions. Under these reaction conditions, DNT can be converted to coupling and quinine compounds, which to organic carboxylate and saturated alkanes, finally to N2, CO2 and H2O.The kinetics of oxidative degradation of DNT in SCW was investigated systematically. The global power-law rate equation during 425 oC～550 oC and at 24MPa with 300% excess oxygen as follows:The reaction order of DNT is 3.630, Ea is 2.419×104J·mol-1,A is 7.109×105. The reaction orders of O2 and H2O approach 0 because they are enough in SCWO processes.The application prospect and engineering problems were discussed deeply in this paper. Selecting materials of reactor, special reactor design and optimized of processing system and using appropriate catalysts will be bottleneck in supercritical water oxidation technology (SCWOT) industrialization adhibition processes.