Malic acid photocatalytic degradation using a TiO2-coated optical fiber reactor

A photoreactor containing a bundle of TiO2-coated optical fibers was employed for the photocatalytic degradation of malic acid, a polycarboxylic acid found in fermentation processes and in biomass. TiO2 film was coated on optical fiber using a dip-coating method. The kinetic behavior of malic acid conversion in this study was found to follow a first-order kinetics with a degradation rate of 6.8 x 10(-2) h(-1). Laboratory experiments enabled one to detect six intermediates presented in five degradation pathways. Their evolution during the photocatalytic reaction was also investigated. The major one, malonic acid, is initiated by a decarboxylation (photo-Kolbe) reaction in the a-position with respect to the OH group followed by an OH addition. The others intermediates come from the same process or from H-abstraction or oxidation. The total organic carbon removal after 20 h of treatment was 21%. A high photonic efficiency of 6% was achieved for experiments operated in the optical fiber photoreactor due to the optimized light utilization. (c) 2007 Elsevier B.V. All rights reserved.