Study On Catalytic Supercritical Water Oxidation Process For Treating The Perfume Wastewater

In order to resolve problems of high cost and low destruction efficiency faced to high concentration refractory organic wastewater, supercritical water oxidation was used to treat this kind of wastewater. The non-catalytic SCWO and homogeneous catalyzed SCWO of practical spice wastewater were performed in transpiring wall reactor with hydrogen peroxide as oxidant. Effects of reaction temperature, reaction pressure,reaction time,catalyst type, and catalyst concentration on destruction efficiency of organic pollutants in practical spice wastewatewas studied. Kinetics foi practical spice wastewater oxidized in supercritical water were regressed from experimental data. Destruction pathway of organic matter in perfume wastewater in supercritical water was proposed. Corrosion and inorganic salt deposition, which obstruct the industrialization of transpiring wall reactor, was investigated during the period of reaction.In supercritical water,the efficiency of removing organic is much better after adding metal ions such as Mn2+ or Cu2+ catalysts. The higher removal of COD, TN were obtained at higher concentration of the catalyst. The temperature, pressure and residence time have important influence on the removal of organic matter. The higher removal of COD, TN were obtained at higher concentration of higher temperature, higher pressure and longer residence time. With Mn2+ as catalyst,in proper reaction conditions(T=440℃, t=50s),the removal of COD could reach 99.5%, meeting the first grade of Comprehensive Wastewater Discharge Standard,(GB9878-1996 China).The removal of TN is not so ideal under all of the conditions we take,it is smaller than the COD. the nitrogen element of TN does not have all directly convert N2 and N2O, part of them convert NH3-N. The concentrations of ammonia nitrogen in water rises with the enhancement of reaction temperature because it is difficult to be degradated.The emissions containsC02,CO,N2,NOx gas after SCWOand CSCWO organic wastewater of spice, and most is CO2 and N2 , NOx and SO2 is little.In order to investigate destruction pathway of organic pollutants in practical spice wastewatewas in supercritical water, reaction products of practical spice wastewater oxidized under supercritical condition was examined by GC-MS method. The results indicated that 4-amino-1-hydroxybenzene and 2,3,5-Trimethyl pyrazine were decomposed to monocyclic intermediate hydrocarbons by means of opening-ring reaction, then destructed to short-chain carboxylates, finally oxidized to CO2 and H2O. Simultaneous, reactions such as coupling, hydrolyzing and substitution between intermediates and radicals were also existed. But, those by-products were oxidized to benzoic acid, phenol and final products such as H2O, CO2.The kinetics of oxidative degradation of organic pollutants in practical spice wastewaterinSCWOwereinvestigatedsystematieally.A modified first-order rate expression was regressed from experimental data, Kinetic equation, reaction activation energy and the reaction order of practical spice wastewateroxidized in supercritical water were achieved.The resulting activation energy Ea were 52.36 kJ.mol-1(without catalyst),30.12 kJ.mol-1 (Cu2+ catalyst) and 27.47 kJ.mol-1 (Mn2+ catalyst); the Arrhenius pre-exponential factors were 6.72s-1(without catalyst),4.61 (Cu2+ catalyst)and3.92 (Mn2+ catalyst); The reaction order for feed wastewater (based on COD)were1.21 (without catalyst),0.92 (Cu2+ catalyst) and 0.89 (Mn2+ catalyst); The reaction order for oxidant1.21 (without catalyst),0.92 (Cu2+ catalyst) and 0.89 (Mn2+ catalyst).The reaetion order of organic compound apparoach 1, and reaction order of oxygen less than 1 and approach to zero. The organic pollutants in CSCWO exhibited lower reaction active energy than the organic pollutants in SCWO,it showed that the catalyst had significant effect.Aiming at present situation of supercritical water oxidation, several problems such as equipment corrosion, inorganic salt precipitation and exploitation for highly effective catalyst for further development of this technology were put forward in this paper.