Abstract
The present work is aimed at the understanding of the condensation by-products role in wet peroxide oxidation processes. This study has been carried out in absence of catalyst to isolate the (positive or negative) effect of the condensation by-products on the kinetics of the process, and in presence of oxygen, to enhance the oxidation performance. This process was denoted as oxygen-assisted wet peroxide oxidation (WPO-O2) and was applied to the treatment of phenol. First, the influence of the reaction operating conditions (i.e., temperature, pH0, initial phenol concentration, H2O2 dose and O2 pressure) was evaluated. The initial phenol concentration and, overall, the H2O2 dose, were identified as the most critical variables for the formation of condensation by-products and thus, for the oxidation performance. Afterwards, a flow reactor packed with inert quartz beads was used to facilitate the deposition of such species and thus, to evaluate their impact on the kinetics of the process. It was found that as the quartz beads were covered by condensation by-products along reaction, the disappearance rates of phenol, total organic carbon (TOC) and H2O2 were increased. Consequently, an autocatalytic kinetic model, accounting for the catalytic role of the condensation by products, provides a well description of wet peroxide oxidation performance.
Highlights
The decline of water quality is a global concern issue as it is crucial to the environment and human health, and to our social and economic development
The first set of experiments was focused on the comparison between wet air oxidation (WAO), wet peroxide oxidation (WPO) and oxygen-assisted wet peroxide oxidation (WPO-O2 ) in the degradation of phenol ([Phenol]0 = 1000 mg L−1 ) under moderate operating conditions ([H2 O2 ]0 = 5000 mg L−1, T = 127 ◦ C, PO 2 = 8 bar, QO2 = 92 NmL min−1, natural pH0 )
The results obtained in this work allowed us to demonstrate that the condensation by-products formed along wet peroxide oxidation can act as catalytic promoters
Summary
The decline of water quality is a global concern issue as it is crucial to the environment and human health, and to our social and economic development. Over the last hundred years, the use of water grew by a factor of seven and it is expected to increase by around 55% by 2050, including a 400% rise in industry water demand [1] This sector is one of the major water consumers and the main group responsible for its pollution by a wide variety of hazardous substances, persistent organic pollutants. These effluents must be treated prior to discharge, or involve recycling in the process. Adsorption is a non-destructive process and requires dealing with the resulting saturated adsorbent Compared to these technologies, catalytic wet air oxidation (CWAO) represents an interesting alternative for Catalysts 2019, 9, 516; doi:10.3390/catal9060516 www.mdpi.com/journal/catalysts
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