Kinetics of the autoxidation of sodium dodecyl sulfate catalyzed by alumina-supported Co-Zn composite

Sodium dodecyl (lauryl) sulfate (SDS), an important anionic surfactant used in a variety of textile and biotechnology operations, frequently ends up i n stationary water bodies where it promotes the formation of blue-green alg ae, an environmentally offensive species. The catalytic wet oxidation of SD S has been studied over alumina-supported cobalt-zinc oxide catalysts under relatively mild conditions of pressure (<1.3 MPa) and temperature (403-448 K). Five catalyst compositions examined showed a decreasing total (BET) su rface area with increasing ZnO loading suggesting possible loss of surface area as a result of the formation of a zinc aluminate phase during calcinat ion at 923 K. Catalytic activity also decreased with addition of ZnO; howev er, a 15 Co/5 Zn/80 delta -alumina catalyst exhibited the most superior per formance. Total degradation of the organic substrate could be achieved in a bout 5 h. The kinetics of SDS autoxidation on this catalyst revealed a firs t-order dependency on both the dodecyl sulfate concentration and the O-2 pa rtial pressure. The observed increase in acidity of the reaction medium wit h SDS conversion paralleled the production of SO42- or (HSO4-) species. Ind eed, the rate of sulfate production followed the same kinetics with SIDS de gradation albeit with different estimates of the pseudo-first-order rate co nstants. Independent measurement of the total organic carbon (TOC) oxidatio n rate also showed a linear correlation with SDS concentration but attained a plateau at high O-2 partial pressure (> 900 kPa). A temperature-dependen t expression for the degree (extent) of mineralization, alpha, in terms of the activation energy for SDS degradation and TOC oxidation was derived as alpha = 1.43 X 10(-2) e(1503.8/T) valid between 403 and 473 K. A mechanism was also proposed to explain the oxidative degradation of SDS.