Studies in wet air oxidation of aqueous morpholine over Ru/TiO2 catalyst: an insight into the fate of the ‘N’ atom

Abstract

AbstractBACKGROUND: Wet air oxidation (WAO) is a very attractive process for the treatment of aqueous streams containing amino compounds. During WAO, it is important to ensure that the ‘N’ atom in various ‘N’ bearing organic compounds is converted into N2. Morpholine is selected as model pollutant for the present study. In order to reduce the severity of operating conditions and to maximize N2 formation, the suitability of a heterogeneous catalyst namely 5% (w/w) Ru/TiO2, was studied.RESULTS: The studies were carried out at a morpholine concentration of 500 mg L−1. Among the various catalysts studied 5% (w/w) Ru/TiO2 was found to be an effective catalyst. The selectivity towards N2 varied between 47 and 56% in the temperature range 473–483 K at 0.66 kg m−3 catalyst loading and 0.69 MPa oxygen partial pressure. Below 473 K more NH4+ ions were formed and at higher temperatures (>483 K) more NO3− ions were generated. It was also observed that under the influence of diffusional resistance, selectivity towards N2 formation was enhanced considerably (80%) when compared with the kinetically controlled regime at 483 K. The experimental data can be well correlated by assuming dissociative adsorption of oxygen followed by surface reaction.CONCLUSIONS: The heterogeneous catalyst 5% (w/w) Ru/TiO2 was found to be very effective in the complete (100%) degradation of morpholine. The highest selectivity for conversion of NH group in morpholine to N2 gas was obtained at 483 K. Under a partial mass transfer controlled regime, selectivity towards N2 formation was enhanced considerably relative to the kinetically controlled regime. Copyright © 2008 Society of Chemical Industry