Desenvolvimento e otimização de reatores com eletrodos tridimensionais para eletrogeração de H2O2

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

This work reports a study on a process for the electrogeneration of hydrogen peroxide. Two types of electrochemical reactors. using three-dimensional porous electrodes. with a reticulated structure. were used. In both systems the performance the reactors. during the hydrogen peroxide production was investigated. as a function of applied potential. flow rate and the use of different types of turbulence promoters. Initially. a kinetic study of oxygen dissolution in some aqueous solutions. which can be used as support electrolyte. Was carried out. A solution of 0.5M Na2 804. pH 10, was chosen as electrolyte. In this case, the rate constant for mass transfer to liquid phase (kL ae) was 0,0037 m-I S-I, which corresponds to a oxygen dissolution rate of 0.116 J.Ullol L-I S.I. In view of the low solubility of oxygen, the hydrogen peroxide electrogeneration process showed to be a mass transport controlled process which exhibits low values of limiting cürrents. Then, a threedimensional reticulated vitreous carbon electrode was used to become viable the oxygen electroredution processo Results showed that the hydrogen peroxide formation and its decomposition to water are separated by 1 V on the vitreous carbon surface. The potential of 1,3V vS. Agi AgI was the more appropriated potential for constant potential experiments. Hydrogen peroxide electrogeneration process was carried out for two reactor configurations: flow-through and flow-by. Mass transfer coefficients were greater for the flow hrough configuration than for the flow-by configuration. However, with an introduction of turbulence promoters, an increasing of the mass transport coefficient, for flow-by mo de, was observed. In this case, 20% increasing was observed and then the flow-by mode became more efficient than the flow-through mode. The characteristics of the best configuration for flow-through mode for the generation of hydrogen peroxide were: a) applied potential of -1,3 V vs. A/AgI, b) anode/cathode distance of 1,5 cm, c) linear velocity of 9,3 10-3 m S-I, which corresponds to flow rate of 750 L h-I, and d) the use of turbulence promoter of type C. In this condition, the mass transport efficient was 3,4 10-5 m S.I, the constant of hydrogen peroxide electrogeneration rate was 26 J.Lg L-I S.I, the energetic consumption was approximately 5,0 kWh kg-I and the current efficient was 80%. For the flow-by mode, the best operation condition were: a) applied potential of -1,3 V vs. A/AgI, b) anode/cathode distance of 0,5 cm, c) linear velocity of 6,79 10-2 m S-I, which corresponds to flow rate of 550 L h-I, and d) the use of turbulence promoter of type B. In this condition, the mass transport efficient was 5,0 10-5 m S.I, the constant of hydrogen peroxide electrogeneration rate was 40 J.Lg L-I S-I, the energetic consumption was approximately 4,5 kyvh kg-I and the current efficient was 82%. In a series of final experiments the efficiency of the cell reactors was followed during textile dye solution degradation. During the experiments using remazol black, at the optimized conditions, the flow-by configuration showed better performance. A textile dye degradation greater than 90% was observed for 240 min of treatment time. The discoloration process, when UV irradiation was used, showed to be considerably faster. In this case 100% of dye degradation was observed in 45 minutes. During these experiments, hydrogen peroxide remaining in the solution was also followed

ASSUNTO(S)

celulas eletroliticas agua oxigenada tecnologia quimica reações quimicas eletrodo de carbono eletrolise agua - oxigenio dissolvido

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