Phenol Photoconversion in Photo CREC Water-II Reactor

PHENOL PHOTOCONVERSION IN PHOTO CREC WATER-II REACTOR 

Targeted experiments can be developed to investigate the phenol photocatalytic conversion mechanism (Salaices et al., 2004). In this context, four main intermediates of phenol photo-degradation are identified para-dihydroxybenzene (p — DHB), ortho-dihydroxybenzene (o — DHB), 1,2,4-trihydroxybenzene (1,2,4 — 77/6), and 1,4-Benzoquinone (I, 4 — BQ). 

The p-DHB is observed as the most abundant intermediate species in all the experiments. This species is, in many cases, followed in abundance by the o-DHB. When phenol is photoconverted over Degussa P25 at an initial pH of 7, maximum concentrations of p-DHB and o-DHB account for 15% and 7% of the initial concentration of phenol. The o-DHB, however, cannot be detected when the initial pH changes from 4 to 7 or when the catalyst changes from Degussa P25 to Hombikat I/V-100. This indicates that both the pH and the catalyst type have important influence on the reaction path. Furthermore, the concentrations of 1,2,4-77/6 and l,4-6g remain below 3% of the initial phenol concentration for most of the operating conditions. 

At the beginning of the reaction, the curve representing the chemical species mass addition matches well the TOC curve. This indicates that most of the species remaining in the liquid phase are determined and quantified. At reaction times beyond 5 hours the species mass addition (-I-) curve consistently lays below the TOC curve. Greater separation between the two curves can be observed with increasing reaction times. In the worst case scenario, this difference is close to 10% of the initial phenol concentration and can be the result of two contributing factors carbon-containing intermediate species 

FIGURE 5.1. Concentiation profiles of (o) phenol, ( ) TOC,(A, , -) inteiTnediate species, and (+) species 

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