Condensation By-Products in Wet Peroxide Oxidation: Fouling or Catalytic Promotion? Part II: Activity, Nature and Stability

• Main Authors: Asunción Quintanilla, Jose L. Diaz de Tuesta, Cristina Figueruelo, Macarena Munoz, Jose A. Casas
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Catalysts
• Subjects: wet peroxide oxidation; wet air oxidation; condensation by-products nature; fouling; autocatalytic kinetics
• Online Access: https://www.mdpi.com/2073-4344/9/6/518

The deposition of condensation by-products onto the catalyst surface upon wet peroxide and wet air oxidation processes has usually been associated with catalyst deactivation. However, in Part I of this paper, it was demonstrated that these carbonaceous deposits actually act as catalytic promoters in the oxygen-assisted wet peroxide oxidation (WPO-O₂) of phenol. Herein, the intrinsic activity, nature and stability of these species have been investigated. To achieve this goal, an up-flow fixed bed reactor packed with porous Al₂O₃ spheres was used to facilitate the deposition of the condensation by-products formed in the liquid phase. It was demonstrated that the condensation by-products catalyzed the decomposition of H₂O₂ and a higher amount of these species leads to a higher degree of oxidation degree The reaction rates, conversion values and intermediates’ distribution were analyzed. The characterization of the carbonaceous deposits on the Al₂O₃ spheres showed a significant amount of condensation by-products (~6 wt.%) after 650 h of time on stream. They are of aromatic nature and present oxygen functional groups consisting of quinones, phenols, aldehydes, carboxylics and ketones. The initial phenol concentration and H₂O₂ dose were found to be crucial variables for the generation and consumption of such species, respectively.