Selective oxidative degradation of toluene for the recovery of surfactant by an electro/Fe2+/persulfate process
2015
Long, Anhua | Zhang, Hui
An electro/Fe²⁺/persulfate process has been conducted for toluene removal from surfactant (SDS) flushing solution, and the pseudo-second-order reaction rate constant (k ₂ value) of toluene removal has been optimized by a response surface methodology (RSM). The results indicated that in this process, the reaction between persulfate and externally added Fe²⁺ generates sulfate-free radicals, and at the same time, Fe²⁺ is electro-regenerated at the cathode by the reduction of Fe³⁺. RSM based on Box–Behnken design (BBD) has been applied to analyze the experimental variables, of which the concentrations of persulfate and Fe²⁺ showed a positive effect on the rate constant of toluene removal, whereas the concentration of SDS showed a negative effect. The interactions between pairs of variables proved to be significant, such as between SDS, persulfate, and Fe²⁺ concentrations. ANOVA results confirmed that the proposed models were accurate and reliable for analysis of the variables of the electro/Fe²⁺/persulfate process. The shapes of the 3D response surfaces and contour plots showed that the SDS, persulfate, and Fe²⁺ concentrations substantially affected the k ₂ value of toluene removal. The results indicated that increasing persulfate or Fe²⁺ concentration increased the k ₂ value, whereas increasing SDS concentration decreased the k ₂ value. The reaction intermediates have been identified by GC-MS, and a plausible degradation pathway for toluene degradation is proposed.
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