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Continual catalytic wet oxidation of phenol and its derivatives as a suitable chemical pretreatment before a biological treatment process was investigated. The evaluation of (i) the inÑuence of amino-, carboxy-and sulfo-phenol substituents on the course of the oxidation of hydroxyl-aromatics, (ii) the catalytic ability of an active carbon, and (iii) the inÑuence of reaction conditions, viz. temperature (120È160¡C) and oxygen partial pressure (2È5 MPa) in the continuous trickle bed reactor, is presented. The active carbon type catalyst seems to be active enough for phenol oxidation, but it is not so e †ective for aromatic acids. The results of trickle bed operation were strongly inÑuenced by hydrodynamics, viz. wetting efficiency. An insufficient catalyst wetting compensates for an e †ect of residence time in the bed and undesirable Ñuctuation of conversion appears at the low liquid velocities which are typical for waste water treatment processes. It is possible to achieve an optimal value of reactor productivity. ( 1998 SCI

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Periodic operation of three phase reactors has been explored for more than two decades. This type of forcing changes selectivity and can increase either conversion or throughput. Experiments and simulation demonstrate periodic flow interruption or variation enhances reaction rates for concurrent trickle beds provided reactants are in the gas phase or can be volatilized under bed operating conditions. Temperature excursions in trickle beds can be controlled by either flow variation or switching the feed between an inert and a reactant. Several approaches to increasing rate through faster mass transfer using flow pulsing have been studied. Pulsing flow can be induced by low amplitude modulation. Periodic switching of flow direction in airlift reactors increases gas hold up and thereby the mass transfer rate. Periodic operation of three phase reactors, thus, appears to be a fertile area for engineering research.