Wet Oxidation of Phenol and Naphthalene in Aqueous and Sludge Solutions: Applicability for the Treatment of Phenolics and PAHs Found in Coal Conversion Wastewater and Biological Sludge

摘要

The wastewaters produced during direct coal liquefaction and fixed bed gasification typically contain significant quantities of phenolic and polyaromatic compounds. Wet oxidation processing is under consideration for use both as a primary treatment process for removing dissolved organics and as a technique for destroying bioligical sludge produced during biotreatment. Phenol and naphthalene were selected as surrogate compounds from each of these chemical classes for wet-oxidation kinetic studies. Experiments were performed on both aqueous solutions of the compounds and combinations of aqueous solution with biological sludge from municipal wastewater treatment. The studies were carried out in a 1-L stirred autoclave batch reaction system at temperatures from 130 to 250 exp 0 C and oxygen overpressures of 55 to 110 atm. To minimize heatup effects, the feed charge was introduced to the autoclave after it had been heated to temperature. Initial concentrations ranged from 10 mg/L to 50 g/L for phenol and 10 to 420 mg/L for naphthalene. The kinetic data were adequately modeled as a pseudo-first-order system in the absence of oxygen mass transfer effects. The oxidation of both phenol and naphthalene was found to be rapid at temperatures above 170 exp 0 C; typically, 95% conversion occurred in less than 15 min. Mass transfer effects were appreciable for initial phenol concentrations greater than 2.5 g/L and for both phenol and naphthalene when combined with municipal sludge at a solids concentration of approx. 40 g/L. in the absence of oxygen mass transfer limitation, activation energies of exp - 22.3 and exp - 29.9 kcal/mol were obtained for phenol and naphthalene, respectively. The autoclave system and experimental techniques are described. kinetic analysis and mass transfer limitations are discussed. (ERA citation 08:040007)