Fenton’s Oxidation Kinetics, Pathway, and Toxicity Evaluation of Diethyl Phthalate in Aqueous Solution

Abstract

Abstract:A comprehensive study of the chemical oxidation degradation of diethyl phthalate (DEP) was conducted through Fenton processes. Effects of various operating parameters that considerably affect DEP decomposition were investigated, including solution pH, H 2 O 2 , Fe 2+ , and DEP concentration. The removal efficiency of DEP achieved 98% under reaction conditions of pH value of 3.0, concentration of 0.3 mM of Fe 2+ , and 6.0 mM of H 2 O 2 after 170 min. In general, DEP degradation in Fenton process was found to occur in two stages, with an extremely fast stage and then a slow one, as a result of change of H 2 O 2 and Fe 2+ initial concentration. Based on the pseudo-steady-state hypothesis of hydroxyl radical formed by the Fenton reaction, a kinetic model for DEP degradation has been proposed which describes the effect of decomposition byproducts on the oxidation reaction. The experiment results also were in good agreement with Behnajady-Modirshahla-Ghanbery (BMG) kinetic model. During the degradation process, seven degradation intermediates of DEP were detected out by means of GC/MS, including ethyl 2-hydroxybenzoate, ethyl 3-hydroxybenzoate, phthalic anhydride, benzoic acid ethyl ester, malonic acid, oxalic acid, and acetic acid. Probable degradation pathway of DEP by the Fenton reaction was also proposed. Inhibitory effects of DEP and intermediate products were investigated in aqueous solution with Photobacterium phosphoreum. Findings indicated that the solution was not completely detoxified even if DEP completely disappeared, further post-treatment was recommended. All these observations have significant potential applications and require further investigation.

Decreasing COD in Sugarcane Vinasse Using the Fenton Reaction: The Effect of Processing Parameters

“…At a pH > 4, generation of hydroxyl radical in solution is inhibited due to precipitation of Fe(OH)3, and thus the concentration of dissolved Fe 3+ decreased. As the amount of catalysts in the Fenton reaction decreased, the oxidation efficiency of the Fenton process was also reduced [20,21]. An acidic condition is needed for the Fenton reaction to produce the hydroxyl radicals.…”

“…• which had a weaker ability than hydroxyl radical. It also caused H 2 O 2 , as the provider of • OH, to be depleted [16,20]. Therefore, the production of • OH was ceased and the degradation rate of organics gradually decreased.…”

“…However, an excessive amount of Fe 2+ could bring a negative impact because this ion also reacts with hydroxyl radical based on Equation (4), causing hydroxyl radicals to be scavenged and reducing the degradation rate of the COD [29]. as the provider of • OH, to be depleted [16,20]. Therefore, the production of • OH was ceased and the degradation rate of organics gradually decreased.…”

“…Data obtained from the experiment were tested using three kinetic models, first order, second order, and BMG kinetic model. Some researchers have reported that the BMG model has effectively predicted degradation of the Fenton process [20,24,34]. By applying the equations in Table 1 below, the three kinetic models at different [H 2 O 2 ] to [COD] ratios during the 15 min Fenton reaction were calculated.…”

“…For Equations (10)-(12), C 0 and Ct are showing COD concentration (mg/L) of sugarcane vinasse at initial (t = 0) and time t (min), respectively; k 1 is first order kinetic parameter (min −1 ); k 2 is second order kinetic parameter (L·mg −1 ·min −1 ); m (min) and b are two characteristic constants of BMG kinetic model which represent the relation between oxidation capacity and reaction kinetics. predicted degradation of the Fenton process [20,24,34]. By applying the equations in Table 1 below, the three kinetic models at different [H2O2] to [COD] ratios during the 15 min Fenton reaction were calculated.…”