Modelling electro-scrubbers for removal of VOCs

This work focuses on the development and testing of simple phenomenological models for understanding the behaviour of processes happening at the same time in the electro-scrubbers during the electrochemically assisted absorption of two relevant volatile organic compounds: perchloroethylene and toluene. Formulation of the model considers physical absorption of the organics into the electrolyte and reactivity according to experimental observations. Different experimental case studies have been used to validate the model obtaining regression coefficients higher than 0.9 and 0.85 for perchloroethylene and toluene, respectively. The model points out the high relevance of the absorption technology and of the presence of cobalt. In the case of perchloroethylene, the model also highlighted the important contribution of the wet decomposition of this chlorinated hydrocarbon. Results obtained clearly evidence the industrial application of the electro-scrubbers technologies

Continuous electro-scrubbers for the removal of perchloroethylene: Keys for selection

In this work, the removal of perchloroethylene (PCE) using continuous-operation electro-scrubbers is evaluated. Two types of electro-scrubbers were made by combining a jet mixer or a packed absorption column with a single flow-cell. The absorbent/electrolyte is recirculated between both devices, being electrolyzed in the cell and retaining the pollutant in the scrubber. In both scrubber’s system, an important amount of PCE was absorbed into the electrolyte and the application of electric current significantly improved the results, highlighting the efficiency of the integration of technologies. Tests in the absence of absorbent/electrolyte confirmed the reactivity of the PCE in the wet gas phase. The jet-mixer system turned out to be more efficient than the packed column, yielding better results both in absorption and electro-absorption modes, and reaching a PCE removal greater than 90%. Meanwhile, the addition of cobalt mediators did not improve the electro-scrubbing efficiency as initially expected: in the case of the packed column electro-scrubber there were no changes while in the case of the jet mixer surprisingly it is generated a negative effect

Cobalt mediated electro-scrubbers for the degradation of gaseous perchloroethylene

This work focuses on the treatment of gaseous perchloroethylene (PCE) using electro-scrubbing with diamond electrodes and cobalt mediators. PCE was obtained by direct desorption from an aqueous solution containing 150 mg L−1, trying to a real pollution case. The electro-scrubber consisted of a packed absorption column connected with an undivided electrochemical cell. Diamond anodes supported on two different substrates (tantalum and silicon) were used and the results indicated that Ta/BDD was more successful in the production of Co (III) species and in the degradation of PCE. Three experimental systems were studied for comparison purposes: absorbent free of Co (III) precursors, absorbent containing Co (III) precursors, and absorbent containing Co (III) precursors undergoing previous electrolysis to the electro-scrubbing to facilitate the accumulation of oxidants. The most successful option was the last, confirming the important role of mediated electrochemical processes in the degradation of PCE. Trichloroacetic acid (TCA) and carbon tetrachloride (CCl4) were found as the primary reaction products and ethyl chloroacetate esters were also identified. A comprehensive mechanism of the processes happening inside electro-scrubber is proposed.Este trabajo se centra en el tratamiento del percloroetileno gaseoso (PCE) mediante electro-fregado con electrodos de diamante y mediadores de cobalto. El PCE se obtuvo por desorción directa de una solución acuosa que contenía 150 mg L -1 , tratando de un caso de contaminación real. El electrodepurador constaba de una columna de absorción empaquetada conectada con una celda electroquímica no dividida. Se utilizaron ánodos de diamante soportados sobre dos sustratos diferentes (tantalio y silicio) y los resultados indicaron que Ta / BDD tuvo más éxito en la producción de especies de Co (III) y en la degradación de PCE. Se estudiaron tres sistemas experimentales con fines comparativos: absorbente libre de precursores de Co (III), absorbente que contiene precursores de Co (III) y absorbente que contiene precursores de Co (III) sometidos a electrólisis previa.al electro-fregado para facilitar la acumulación de oxidantes. La opción más exitosa fue la última, lo que confirma el importante papel de los procesos electroquímicos mediados en la degradación del PCE. Se encontraron ácido tricloroacético (TCA) y tetracloruro de carbono (CCl 4 ) como productos de reacción primarios y también se identificaron ésteres de cloroacetato de etilo. Se propone un mecanismo integral de los procesos que ocurren dentro del electrodepurador

Treatment of toluene gaseous streams using packed column electro-scrubbers and cobalt mediators

An absorption system has been combined with an electrochemical cell to treat a gaseous stream polluted with toluene. Toluene retention in 3 h operation tests was higher than 87.0% in the case of treating the gaseous stream with single scrubbing, 97.0% in the case of using electro-scrubbing and over 99.0% in using cobalt-mediated electro-scrubbing. It was found that the amount of toluene that escapes from the electro-scrubber does not only depend on the flow rate but also on the current density and the presence of the metallic mediator. The higher the current densities are, the higher the amount of electrochemically degraded toluene is. In addition to the mediating effect of the metal catalyst, the results also suggest an important participation of the redox sulfate/persulfate pair in the degradation of toluene. Only methyl-cyclohexane (at very low concentrations) is observed as intermediate, despite carboxylic acids were also initially expected. The formation of this compound can be explained in terms of the hydrogenation of toluene. The very low concentrations absorbed, and the very high current densities, support the occurrence of an electrochemical cold combustion in the electro-scrubber.Se ha combinado un sistema de absorción con una celda electroquímica para tratar una corriente gaseosa contaminada con tolueno. La retención de tolueno en las pruebas de funcionamiento de 3 h fue superior al 87,0% en el caso del tratamiento de la corriente gaseosa con lavado simple, al 97,0% en el caso de electro-fregado y superior al 99,0% con electro-fregado con cobalto. Se encontró que la cantidad de tolueno que escapa del electrodepurador no solo depende del caudal sino también de la densidad de la corriente y de la presencia del mediador metálico. Cuanto mayores sean las densidades de corriente, mayor será la cantidad de tolueno degradado electroquímicamente. Además del efecto mediador del catalizador metálico, los resultados también sugieren una participación importante del par redox sulfato / persulfato en la degradación del tolueno. Sólo metilciclohexano (a concentraciones muy bajas) se observa como intermedio, a pesar de que inicialmente también se esperaban ácidos carboxílicos. La formación de este compuesto se puede explicar en términos de hidrogenación de tolueno. Las muy bajas concentraciones absorbidas y las altísimas densidades de corriente favorecen la aparición de una combustión electroquímica en frío en el electrodepurador