Development of a Kinetic Model for the Photodegradation of 4-Chlorophenol using a XeBr Excilamp

Excilamps are new UV sources with great potential for application in wastewater treatment. In the present work, a XeBr excilamp emitting radiation at 283 nm has been used for the photodegradation of 4-chlorophenol within a range of concentrations from 50 to 500 mg L. Total removal of 4-chlorophenol was achieved for all concentrations assayed. The two main photoproduct intermediates formed along the photodegradation process, benzoquinone and hydroquinone, although not being completely removed, remain at very low residual concentrations. Such concentrations are insignificant compared to the 4-chlorophenol initial ones and non-toxic. In order to simulate the process and scaleup, a kinetic model has been developed and validated from the experimental data. Keywords—4-chlorophenol, excilamps, kinetic model, photodegradation. NOMENCLATURE a1 = model parameter defined in (47), dimensionless a2 = model parameter defined in (61), dimensionless b1 = model parameter defined in (47), dimensionless b2 = model parameter defined in (61), dimensionless BQ = benzoquinone c1 = model parameter defined in (47), dimensionless c2 = model parameter defined in (61), dimensionless 4CP = 4-chlorophenol HQ = hydroquinone k = pseudo-first order rate constant for 4-chlorophenol M. Gomez was with the Department of Chemical Engineering, Murcia University, 30071 Murcia, Spain (corresponding author, phone: 0034968367351, Fax: 0034968-364148; e-mail: [email protected]). She is currently with the Pollution Research Unit, School of Life Sciences, Edinburgh Napier University, Merchiston Campus, Edinburgh EH10 5DT, Scotland UK. M. D. Murcia was with the Department of Chemical Engineering, Murcia University, 30071 Murcia, Spain (e-mail: [email protected]). She is currently with the Pollution Research Unit, School of Life Sciences, Edinburgh Napier University, Merchiston Campus, Edinburgh EH10 5DT, Scotland UK. E. Gomez is with the Department of Chemical Engineering, Murcia University, 30071 Murcia, Spain (e-mail: [email protected]). J. L. Gomez is with the Department of Chemical Engineering, Murcia University, 30071 Murcia, Spain (e-mail: [email protected]). N. Christofi is with the Pollution Research Unit, School of Life Sciences, Edinburgh Napier University, Merchiston Campus, Edinburgh EH10 5DT, Scotland UK (e-mail: [email protected]). photodegradation, min k1 = kinetic constant for HQ formation from 4CP, min k2 = kinetic constant for BQ formation from 4CP, min k3 = kinetic constant for HQ decomposition to final products, min k-3 = kinetic constant for final products partial conversion to HQ, min k4 = kinetic constant for BQ decomposition to final products, min k-4 = kinetic constant for final products partial conversion to BQ, min s = Laplace variable t = reaction time, min XBQ = benzoquinone conversion, dimensionless X4CP = 4-chlorophenol conversion, dimensionless XHQ = hydroquinone conversion, dimensionless [BQ] = concentration of benzoquinone at time t, mM [BQ]0 = initial concentration of benzoquinone, mM [4CP] = concentration of 4-chlorophenol at time t, mM [4CP]0 = initial concentration of 4-chlorophenol at time t, mM [HQ] = concentration of hydroquinone at time t, mM [HQ]0 = initial concentration of hydroquinone, mM