Nanofiltration of partial oxidation products from CWPO of phenol

N. INCHAURRONDO; J. FONT; P. HAURE

Salta

Congreso; VIII Congreso Ibero-Americano en Ciencia y Tecnología de Membranas; 2012

Industrial effluents can contain refractory pollutants negatively impacting ecosystems due to their toxicity and refractoriness to most traditional treatments. Catalytic Wet Peroxide Oxidation (CWPO) has emerged as a clean and effective alternative among other catalytic oxidation processes. Heterogeneous catalysts based on low-valence transition metals appear as a promising way for CWPO since oxidation efficiencies are relatively high and pH sensitivity is lower compared with homogeneous catalysts at similar operating conditions. Heterogenization of homogeneous catalysts by sorption onto materials of biological origin is an emerging technique to produce environmentally friendly catalysts. In this study, a home-made Cu chitosan composite catalyst, obtained by coating Cu-chitosan complexes onto  alumina, was used for CWPO of aqueous phenol solutions. In these cases, catalyst deactivation by leaching of the active phase, due to the acidic and oxidative conditions, is a serious drawback. In addition, the CWPO of phenol solutions generates intermediates with different levels of toxicity and recalcitrance against oxidation. Hence, the toxicity of partially oxidized organic intermediates as well as that resulting from copper loss by leaching must still be eliminated before the effluent is discharged into a municipal Wastewater Treatment Plant. Some partially oxidized intermediates and copper leached could be recovered, concentrated and recirculated to the oxidation reactor by the coupling of a nanofiltration system to the CWPO process. This could enhance mineralization giving more biodegradable final products, and the most important, the retention of the copper leached. Several authors studied the coupling of Advance Oxidation Processes with filtration [1-3]. Nanofiltration (NF) with membranes, which is in the transition between ultrafiltration (UF) and reverse osmosis (RO) processes, has properties of high retention of multivalent ions and organic matter with molecular weights (MW) larger than 200 Da. The rejection of different compounds depends on a complex interaction between operational conditions, steric hindrance, adsorption, hydrophobic and electrostatic interactions, solution effects on the membrane and the solute/membrane properties [3]. The scope of this study has been to determine the final distribution of intermediates from the CWPO of phenol solutions, using a Cu-chitosan/Al2O3 catalyst, and to investigate the retention of phenol, the main final intermediates (succinic, malonic, maleic and oxalic acid) and copper leached from the catalyst on a nanofiltration process with a NF90 membrane.