Catalytic Oxidation of Phenol over MnO₂in Supercritical Water

Abstract

Bulk MnO2 was used as a catalyst for phenol oxidation in supercritical water at 380−420 °C and 219−300 atm in a flow reactor. The bulk MnO2 catalyst enhances both the phenol disappearance and CO2 formation rates during supercritical water oxidation (SCWO), but it does not affect the selectivity to CO2 or to the phenol dimers at a given phenol conversion. The role of the catalyst appears to be accelerating the rate of formation of phenoxy radicals, which then react in the fluid phase by the same mechanism operative for noncatalytic SCWO of phenol. The rates of phenol disappearance and CO2 formation are sensitive to the phenol and O2 concentrations but independent of the water density. Both power-law and dual site Langmuir−Hinshelwood−Hougen−Watson (LHHW) rate laws were developed to correlate the catalytic kinetics. Our results show that SCWO reactor volumes can be reduced by an order of magnitude if bulk MnO2 is used as the catalyst and by yet another order of magnitude if a supported oxidation catalyst is used.

Recent Advances in Catalytic Oxidation in Supercritical Water

“…Other metal oxide catalysts have also been shown to experience chemical and morphological changes during SCWO processing (Yu and Savage, 2001b). Yu and Savage (1999) and Oshima et al (1999) reported independently but nearly simultaneously on catalytic SCWO of phenol over MnO 2 . The former report covers a much larger parameter space, but both groups found the kinetics to be about first order in phenol and 0.5 order in oxygen.…”

“…Table 4 gives the best-fit parameters for the Mars-van Krevelen model for phenol SCWO over different transition metal oxides. Yu and Savage (1999). 2 Yu and Savage (2001a).…”

Coal Conversion Wastewater Treatment by Catalytic Oxidation in Supercritical Water

“…The catalyst was pretreated overnight by flowing a supercritical water stream carrying just oxygen through the reactor. Yu and Savage (1999) provide additional details.…”

“…Our investigation of catalytic SCWO using bulk MnO 2 has very recently been published (Yu and Savage, 1999). We provide an overview of this work in this section.…”

On-line monitoring of the hydrolysis of acetonitrile in near-critical water using Raman spectroscopy

“…Vibrational Spectroscopy 35 (2004) 103-109 scH 2 O has been previously used for the total oxidation and destruction of various chemical compounds [17][18][19][20][21][22][23]. Recently, we have reported how scH 2 O can be used as an effective solvent for the selective partial oxidation of paraxylene to terephthalic acid [24], a key reaction in the manufacture of bulk chemicals for the polyester industries [25].…”