Benito Serrano

Experimental evaluation of photon absorption in an aqueous TiO2 slurry reactor

This study presents an experimental evaluation of photon absorption in a TiO2 slurry medium using an annular photoreactor. This photoreactor was equipped with several windows placed at equidistant axial positions. Tubular black collimators and inner polished-aluminum collimators were attached to these windows to measure the total transmitted radiation and the transmitted non-scattered radiation. Experiments were developed with six TiO2 commercial powders having differences in particle size, agglomerate particle size in water suspension, and specific surface area. Modeling allowed to establish that the forward-transmitted radiation can be represented by the difference of two exponential decay functions accounting respectively for the total transmitted radiation and the transmitted non-scattered radiation. These two exponentials are functions of particle concentration and extinction coefficients, with the extinction coefficient for the transmitted radiation being strongly affected by the particle agglomerate size.

Photocatalytic degradation of water organic pollutants : Pollutant reactivity and kinetic modeling

Photocatalytic reactors can play an increasing role in novel technologies for the purification of water polluted with organic chemicals. These organic pollutants may strongly adsorb on the TiO 2 -mesh system leading to an overall process influenced by the combined adsorption/reaction phenomena. In the present study, chlorinated aromatics frequently found as water contaminants (2-chlorophenol and 2-4-dichlorophenol) are selected as model pollutants. It is demonstrated, developing experiments in a novel photocatalytic reactor (Photo-CREC unit) that addition of chlorine atoms to the phenol molecule has a significant impact on both adsorption and photoreaction. Due to catalyst deactivation and drop in lamp power, kinetic constants are corrected to conditions of new lamp and fresh catalyst. It is foreseen that using these corrected kinetic constants, high-energy efficiencies (PTEF) can be achieved in Photo-CREC.

Production of chemicals from cellulose and biomass-derived compounds through catalytic sub-critical water oxidation in a monolith reactor

Abstract Selective conversion of cellulose to small organic molecules, including carboxylic acids, represents a potential route for upgrading biomass resources to value-added chemical precursors. However, since biomass resources such as cellulose are not soluble in water, the use of a catalyzed system requires a novel reactor design that facilitates slurry flow. As demonstrated herein, the monolith froth reactor is uniquely suited for the conversion of solid materials in a four-phase (solid catalyst, solid reactant, gaseous reactant, and aqueous solution) reaction system. Reactions were performed using a palladium catalyst and 1000 ppm ( w ) cellulose, and results were compared with previous experiments conducted over platinum. At 150°C, nearly 100% conversion of the cellulose was achieved in approximately 5 h , which compares favorably with results obtained using a platinum catalyst. The palladium catalyst gave a different distribution of intermediate products compared to platinum. For example, acetic acid and malic acid achieved yields of 40 and 80 ppm ( w ) , respectively, using the palladium catalyst. The product selectivity was evaluated under pH control, through the addition of acetic or carbonic acid, and shown to have only a minor effect on the performance of the system.

Novel Photocatalytic Reactors for Water and Air Treatment

The development of water and air treatment systems based on heterogeneous photocatalysis is an area of major technical importance (Blanco and Malato, 1993; Matthews, 1993; Ollis et al., 1989; Pelizzetti et al., 1992). Harada et al., (1999) have stated, “... the design of highly efficient photocatalytic systems is of vital interest and one of the most desirable yet challenging goals in the research of environmentally friendly catalysts”. There is general agreement that an important obstacle in the development of highly efficient photocatalytic reactors is the establishment of effective reactor designs for intermediate and large-scale use, as demanded by industrial and commercial applications. To achieve a successful commercial implementation, several reactor design parameters must be optimized, such as the photoreactor geometry, the type of photocatalyst and the utilization of radiated energy. A fundamental issue regarding the successful implementation of photocatalytic reactors is the transmission of irradiation in a highly scattering and absorbing medium composed of water and fine TiO2 particles.

The Irradiation Field in Photocatalytic Reactors

The evaluation of absorption photon rates in slurry reactors is a rather challenging task since light can experience a combination of reflection, scattering and absorption in the TiO2 particle suspension.

Establishing Photocatalytic Kinetic Rate Equations: Basic Principles and Parameters

Heterogeneous photocatalysis is a promising new alternative method for the removal of organic pollutants in water (Carey, 1976). The degradation of organic pollutants in water, using irradiated dispersions of titanium dioxide, is a growing area of both fundamental and applied research.

Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway

Abstract High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO2 and water by photocatalysis with TiO2, UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.

Kinetic Modeling of the Photocatalytic Reaction Network: The Parallel-Series Approximation

Photocatalytic oxidation of phenol has been studied at a laboratory scale by several researchers (Al-Ekabi and Serpone, 1988; Matthews and McEvoy, 1992; Okamoto et al., 1985b; Tseng and Huang, 1990; Wei and Wan, 1992; Winterbottom et al., 1997). Phenol is a chemical species difficult to convert in conventional bio-treatment processes. Phenol is also a very useful model contaminant in photocatalytic research for ranking reactor performance.

Photocatalytic Degradation of Air Borne Pollutants

Heterogeneous photocatalytic oxidation of organic air contaminants is a promising technology that offers distinct advantages. These advantages include potential lower operating costs, the elimination of treatment reagents or electron acceptors, the possible recovery, regeneration and reuse of the photocatalyst and finally its widespread applicability for the complete mineralization of organic compounds (Miller and Fox, 1993; Suri et al., 1993). Cabrera et al., (1994) indicated that almost any organic pollutant, and many inorganic ones, could be completely mineralized or separated by means of heterogeneous photocatalysis. Additionally, photocatalytic technology can be used in conjunction with solar radiation (Suri et al., 1993) at close to ambient temperature (Cassano et al., 1995; Falconer and Magrini-Bair, 1998; Miller and Fox, 1993). Photocatalysis also shows important prospects for certain air treatment applications, given that the observed apparent quantum efficiencies can be in excess of 100% (Ibrahim and de Lasa, 2003).

The Energy Efficiency Factors in Photocatalytic Processes

Heterogeneous photocatalysis on metal oxide semi-conductors has been shown to be effective in degrading organic pollutants in gaseous and aqueous streams (Fox and Dulay, 1993; Hoffmann, et al., 1995). In photocatalysis, the definition of energy yield parameters describing the light utilization efficiency is very critical (Fox, 1988).