Supercritical water oxidation kinetics and pathways for ethylphenols, hydroxyacetophenones, and other monosubstituted phenols

We examined the decomposition of o-, m-, and p-ethylphenol and o-, m-, and p-hydroxyacetophenone in dilute aqueous solutions at 460 degrees C and 25.3 MPa, both in the presence and absence of added oxygen. In the absence of o xygen, the ethylphenols produced vinylphenols as the major product and the hydroxyacetophenones produced phenol, benzendiols, and hydroxybenzaldehydes . In the presence of oxygen, ethylphenols and hydroxyacetophenones reacted through two major parallel paths and one minor path. The major primary path s for ethylphenols were to vinylphenols and to ring-opening products and ul timately CO2. The minor path was to phenol. For hydroxyacetophenones, the m ajor primary paths were to phenol and to ring-opening pro ducts and ultimat ely CO2. The minor path was to hydroxybenzaldehydes. The relative rates of these parallel paths were sensitive to the location of the substituent. Alt hough reactions did occur in the absence of oxygen, the disappearance rates were much slower than those observed during oxidation. Power-law global ra te expressions were developed for reactant disappearance during oxidation. These rate laws were used along with rate laws previously reported for othe r monosubstituted phenols to examine the relative oxidation rates for diffe rent phenols. All of the substituted phenols oxidized more quickly than phe nol itself. The oxidation rates for the substituted phenols were functions of both the identity and location of the substituent. For a given substitue nt, the reactivity was always in the order ortho > para > meta for all of t he substituted phenols examined.