电催化氧化技术中传质系数的测试与验证

Measurement and Verification of Mass Transfer Coefficients in Electrocatalytic Oxidation

为通过电催化氧化体系中的极限电流密度(j lim)确定电催化氧化过程的传质/传荷界限,分别采用传统测试方法铁氰化钾-亚铁氰化钾体系和反向推导法,评价了两种方法用于测定电催化体系传质系数(k m)以确定j lim的适用性。通过对酸性红G和愈创木酚的电催化降解实验对传统测试方法进行了验证,测定了不同本体溶液浓度下同一体系k m;通过对愈创木酚的电催化氧化降解结果进行反向推导,考察了不同电流密度下同一体系的k m,分析了传质和传荷两种控制阶段下的电解效果和能耗。实验结果表明:使用传统测试方法测定同一体系k m,其测定结果受本体溶液浓度影响较大;反向推导法相比传统方法更适于测定电催化体系k m以确定j lim;施加不同电流密度,同一体系k m差异较大,对应j lim无法定量确定;当传荷控制阶段电流密度为50 A/m 2时电解愈创木酚,5 h内能耗为0.018 kW·h/g,远低于传质控制阶段500 A/m 2时的能耗0.135 kW·h/g,但是电解速率较低,愈创木酚的降解需要更长的电解时间。动态电流调控机制可改善长电解时间和高能耗两大缺陷,为电催化氧化技术的进一步工程应用提供参考。

The traditional test method“potassium ferricyanide-potassium ferrocyanide”system and the reverse derivation method are respectively used to determine the mass transfer/transport limits of the electrocatalytic oxidation process by the limiting current density(j lim)in the electrocatalytic oxidation system.The applicability of the two methods for measuring the mass transfer coefficient(k m)in an electrocatalytic system to determine the j lim is evaluated.The traditional test method is verified by electrocatalytic degradation experiments of acid red G and guaiacol,and values of k m in the same system under different bulk solution concentrations are determined.The results of electrocatalytic oxidation degradation of guaiacol are reversed,and the values of k m in the same system at different current densities are investigated.The electrolysis effect and energy consumption in the mass transfer/transfer control stage are analyzed.The results show that when the value of k m in the same system is determined by the traditional test method,the value of k m is greatly affected by the concentration of the bulk solution.The reverse derivation method is more suitable for determination of the k m in the electrocatalytic system to determine the j lim than the traditional method.When different current densities are applied,the values of k m in the same system are quite different and the j lim cannot be quantitatively determined;When guaiacol is electrolyzed at 50 A/m 2(transfer process),the energy consumption in 5 h is 0.018 kW·h/g,which is much lower than the energy consumption 0.135 kW·h/g under 500 A/m 2(mass transfer process),but the electrolysis rate is lower.Dynamic current regulation mechanism can be adopted to improve the long electrolysis time and high energy consumption.This mechanism will lay a better foundation for further engineering application of electrocatalytic oxidation technology.