Sonochemical treatment of effluent originating from desulfurization process; validation of predictive models

Ultrasound has been shown to have desirable effects on reactions in liquid medium. Enhancement in the reaction rates and the rates of mass transfer due to ultrasound may be attributed to its chemical and/or mechanical effects; generation of free radicals occurs with a great propensity for reaction. In this work, the degradation of specific pollutants (dibenzothiophene sulfone, carboxylic acids and acetonitrile) in the effluent originating from desulfurization process of fuel loaded with dibenzothiophene was studied by the means of ultrasonic enhanced Fenton process. Operating parameters were obtained ([Fe2+] = 1.98 mmol dm−3, [H2O2] = 20.03 mmol dm−3, pH 3.15) using experimental design technique coupled with numerical optimization. Special emphasis was put on sonochemical process modeling. Experimental data were compared with the values obtained by the previously published model, whereas the sonochemical effectiveness factor (eUS) was introduced in the kinetic models to incorporate cavitational phenomena and its influence on conversions. Intrinsic rate constants for the reaction between OH radicals and organic compounds (k2) and other kinetic parameters of Fenton process were treated as independent of ultrasound, since eUS presents a simplification of complex cavitation steps responsible for the mineralization and degradation rate enhancement. The study resulted in the model applicable for degradation of volatile compounds as well, since pyrolysis in the cavitation bubble was included in the model as a first-order rate constant, kP. Finally, three-frequency ultrasonic pilot reactor was utilized for the treatment of the effluent. Developed kinetic model was validated accordingly.