Showing papers by "F. Javier Benitez published in 1998"

Kinetics of the direct reaction between ozone and phenolic aldehydes

Abstract: The kinetics of the ozonation of four phenolic aldehydes is investigated from ozone absorption experiments in a semi-continuous reactor. After the evaluation of the stoichiometric ratios for the individual reactions between ozone and each aldehyde, the single oxidation of vanillin aldehyde (4-hydroxy-3-methoxy benzaldehyde) by ozone is performed in a first stage. The influence of the operating variables on the degradation process is established, and the application of a mass transfer with chemical reaction model based on the film theory leads to the determination of the reaction orders and kinetic rate constants. The experimental absorption rates obtained agree well with those calculated theoretically. In a second stage, a mixture of protocatechuic aldehyde (3,4-dihydroxybenzaldehyde), p-hydroxybenzaldehyde, vanillin aldehyde and syringaldehyde (4-hydroxy-3,5-dimethoxy benzaldehyde) is ozonated under different experimental conditions. The kinetic study is performed by means of a competitive method that takes vanillin aldehyde as reference compound. The application of that model allows the determination of the kinetic rate constants for each aldehyde, which are correlated as a function of pH and temperature. The results obtained support the fact that the kinetic regime of absorption is fast and pseudo-first order with respect to ozone, a condition required by the competitive method to be used. © 1998 SCI

Ozonation and photodegradation kinetics of pollutant acids in wastewaters

Abstract: The kinetics of the degradation of four phenolic acids by ozonation and polychromatic UV radiation were investigated. The acids: p-hydroxyphenylacetic, homoprotocatechuic (3,4-dihydroxyphenylacetic acid), gentisic (2,5-dihydroxybenzoic acid) and 2,3-dihydroxybenzoic, have been selected because of they constitute major pollutants present in some agro-industrial wastewaters. The p-hydroxyphenylacetic acid was initially ozonated and UV irradiated alone. Its kinetic constants and reaction orders in the ozonation process were deduced by using a model based in the film theory which takes into account the mass transfer with the chemical reaction. The quantum yields in the photodegradation process were evaluated from a simple reaction mechanism with the help of an emission model to determine the radiation flow rate absorbed. Later, in the simultaneous ozonation and UV photodegradation of the mixtures of the four acids, competitive kinetic methods were developed to determine the individual rate constants between ozone and each acid in the ozonation process, and the individual quantum yields for every acid in the photodegradation process. On etudie les cinetiques de la degradation de quatre acides phenoliques par ozonisation et radiation polychromatique aux UV. On a choisi les acides p-hydroxyphenylacetique, homoprotocatechnique (acide 3,4-dihydroxyphenylacetique), gentisique (acide 2,5-dihydroxybenzoique) et 2,3-dihydroxybenzoique parce qu'ils constituent les principaux polluants presents dans certaines eaux usees agro-industrielles. L'acide p-hydroxyphenylacetique a ete initialement ozonise et irradiee aux UV seul. Ses constantes cinetiques et ses ordres de reaction dans le procede d'ozonisation ont ete deduites au moyen d'un modele s'appuyant sur la theorie du film qui tient compte du transfert de matiere avec la reaction chimique. Les rendements quantiques du procede de photodegradation ont ete evalues a partir d'un mecanisme de reaction simple allie a un modele d'emission afin de determiner le debit de radiation absorbe. Par la suite, dans l'ozonisation et la photodegradation aux UV simultanees des melanges des quatre acides, on a mis au point des methodes cinetiques concurrentes pour determiner les constantes de vitesse individuelles entre l'ozone et chaque acide dans le procede d'ozonisation ainsi que les rendements quantiques de chacun des acides dans le procede de photodegradation.

UV photodegradation of phenolic aldehydes present in industrial wastewaters. II. Simultaneous degradation of a mixture

Abstract: The simultaneous photodegradation of four phenolic aldehydes by a polychromatic UV radiation was studied in a batch reactor These phenolic substances, protocatechuic aldehyde (3,4‐dihydroxybenzaldehyde), p‐hydroxybenzaldehyde, syringaldehyde (4‐hydroxy‐3,5‐dimethoxybenzaldehyde) and vanillin aldehyde (4‐hydroxy‐3‐methoxy benzaldehyde), were selected because of they are major pollutants contained in wastewaters produced in some agro‐industrial plants The degradation levels obtained are reported and the influences of the operating variables, temperature and pH, are established Also, the quantum yields for the photoreaction of each individual aldehyde are evaluated by means of a competitive kinetic method, and correlated as a function of the temperature