Fiber-optic bundled array cable reactors for heterogeneous photocatalysis and waste stream remediation (2008)

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Application of semiconductor photocatalysis in a fixed-bed fiber-optic bundled array cable reactor (OFR) for the purification of contaminated water is investigated in this thesis. An optical fiber cable is employed as a means of light transmission and distribution to solid-supported TiO2. The system is designed for remote delivery of light to the photocatalyst, to allow for measurement of light fluxes for direct determination of quantum yields and for reuse of the reactor to test various coatings and light input angles, and to minimize possible heat build-up and delamination problems. Experiments are carried out to determine the operational factors affecting the chemical efficiency of the OFR system. The uniformity and extent of light propagation down the fiber, the degree of light absorption by the TiO2 coating, the fiber diameter, the input light intensity, and the ability of the chemical substrates to diffuse into the TiO2 coating are determined to be important parameters. In addition, a TiO2 coating that minimizes the interfacial surface area of the quartz core and TiO2 particles and operation with incident irradiation angles near 90° enhance light propagation down the fibers. Relative quantum efficiencies in the OFR are found to be comparable to slurry-phase photochemical reaction systems. The OFR is shown to effectively degrade several model chemical contaminants such as pentachlorophenol (PCP), 4-chlorophenol (4CP), dichloroacetate (DCA), and oxalate (OX) under varying reaction conditions. Relatively high quantum efficiencies of [...] = 0.010, 0.015, 0.08, and 0.17, respectively, and complete mineralization to CO2, H2O and HCl are observed. When iron(III)-doped quantum-sized (Q) TiO2 (Fe/Q-TiO2) is used as a photocatalytic coating, the extent of linear light transmission in a single fiber is doubled relative to Degussa P25. However, the Fe/Q-TiO2 coating is found to have inferior light absorption properties and chemical reactivity leading to lower relative quantum efficiencies. A concentrating, solar powered prototype OFR is designed and tested. Photoefficiencies with sunlight were comparable to that achieved with a Xe-arc source. Lower light intensity-to-photocatalytic surface area ratios result in increased relative quantum efficiencies. A mathematical model of a fiber-optic bundled array reactor system is developed using Langmuir-Hinshelwood kinetics and compared to experimental data. A global quantum efficiency, [...], is defined and used as a model fitting parameter. It incorporates reaction parameters such as the absorbed light intensity, the intrinsic rate constant, and the effects of other adsorbed reactants and reaction intermediates. An empirical term to describe the radiation field within the coated fiber is derived and normalized by the coating photocatalyst particle concentration to account for the inverse relationship between the absorbed light intensity and the reaction quantum efficiency. The [...] is determined to be independent of the absorbed light intensity and calculated values are in excellent agreement with experimental values. An analysis of conventional and advanced remediation technologies is performed (Appendix). The chemistry and engineering behind advanced oxidation systems is reviewed, and a means of technical evaluation and comparison is presented. The "electrical energy per order," or EEO is defined as the electrical energy required to reduce the concentration of a given pollutant by one order of magnitude in 1000 gal of water. The EEO can be used to compare the efficacy of remediation technologies with other AOT's and conventional systems for a particular cleanup application.