Treatment and valorisation of wastewater through aqueous phase reforming

• Autores: Adriana Catarina De Souza Oliveira
• Directores de la Tesis: Luisa Calvo Hernández (dir. tes.), Miguel Angel Gilarranz Redondo (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2020
• Idioma: inglés
• Número de páginas: 279
• Tribunal Calificador de la Tesis: Juan José Rodríguez Jiménez (presid.), Carolina Belver Coldeira (secret.), Ana Paula Baptista (voc.), Tomás Cordero Alcántara (voc.), Alicia Carrero Fernández (voc.)
• Programa de doctorado: Programa de Doctorado en Química Aplicada por la Universidad Autónoma de Madrid
• Materias:
  • Ciencias tecnológicas
    • Ingeniería y tecnología químicas
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Aqueous phase reforming (APR) is an attractive alternative for H2 and alkanes production from biomass-derived compounds. Good results have been reported in the literature for a variety of model compounds, although some studies have shown that the cost of the feedstock may be an important burden for the application of APR. In this sense, the use of APR could be extended to biomass-derived wastewater treatment, thus integrating wastewater treatment and valorisation of effluents. This new potential application could be of special interest in the case of wastewater that are difficult to treat by conventional technologies and for industries producing large volumes of wastewater with high loads of biomass-derived organic compounds. Accordingly, the main aim of this thesis is to evaluate the application of APR process to the simultaneous treatment and valorisation of wastewaters.

    In order to evaluate the flexibility of the process, different types of industrial wastewater were treated by APR, mainly for H2 production. Pt and Pt based bimetallic catalysts (PtRe and PtPd) supported on different carbons materials were used in the APR experiments and the influence of different variables that could affect the catalytic performance was investigated. Likewise, the catalysts stability was evaluated and two processes were coupled to APR (hydrogenation and catalytic wet air oxidation (CWAO)) in order to improve valorisation and/or reduce catalyst deactivation.

    In the APR of tuna-cooking wastewater at 200 ºC using Pt catalysts supported on different carbon materials, high TOC and COD removal values (45 – 60 %) were achieved due to a combination of adsorption on the supports, hydrothermal carbonization (HTC) and APR. The gas production was low and CO2 was the main gas component (82 – 99 %), due to the presence of components, such as chloride, that lead to catalyst deactivation. The use of a basic support significantly increased the gas production and the H2 percentage in the gas fraction. In addition, gas production increased in semi-continuous compared to batch operation.

    In the APR of brewery wastewater, HTC was observed as a main contribution in the experiments without catalyst. In batch APR experiments with catalysts, the best catalytic performance was observed at higher temperature (225 ºC) and using highly mesoporous carbon black support with virtually no microporosity and high pH slurry ( 50 % of H2 and 12.2 mmol H2 / g CODi). The removal of organic matter increased up to ca. 99 % decreasing organic load of the wastewater. The addition of KOH or NaOH to wastewater also resulted in a slightly lower TOC and COD removal, however higher H2 yield was obtained in those cases where KOH was added. Increasing the KOH concentration led to CO2-free H2 without significant changes in H2 yield and the results with real and synthetic brewery wastewater were relatively similar. In continuous APR experiments at 225 ºC, PtRe/C catalyst exhibited higher catalytic activity and H2 production than Pt/C, which was attributed to an increase in the water-gas shift (WGS) activity. A longer residence time and a higher carrier gas flow also increased the H2 production. At low time-on-stream (TOS) values, Pt catalysts supported on different modified carbons, whose microporosity was gradually decreased by impregnation and carbonization of resol resin, showed higher H2 production than the reference Pt catalyst and an indirectly effect of the Pt nanoparticles (NPs) size was observed. All the catalysts tested showed an important deactivation with TOS and the characterization of used catalysts revealed that the main cause of the pronounced catalysts deactivation in the first hours of reaction was the coke deposition on the catalyst surface. Finally, a higher H2 selectivity and yield were achieved after pretreatment of the feedstock by hydrogenation, and the coupled hydrogenation-APR was considered efficient since H2 production compensated for the need for hydrogenation. The durability of the catalyst was also increased, due to the reducing of the formation of carbonaceous deposits.

    In the APR of fruit juice wastewater using Pt/C catalyst at 220 ºC, H2 production was little affected by pH, yielding around 6.6 mmol H2 / g CODi, in the pH range tested. The organic carbon removal declined slightly at the highest loads tested and the highest H2 yield value was observed with low-medium organic load. Finally, a decreased of H2 yield from 7.8 to 4.2 mmol H2 / g CODi was observed at high salinity, due to catalyst deactivation.

    In the APR of wastewater with phenolic compounds, a high range of TOC and COD removal (74 – 90 %) was observed for feedstocks with compounds representative of phenol oxidation pathway, with higher values for long chain acids. H2 production was low in all cases, due to competing direct conversion of long and short chain acids into CH4. In the APR of mixtures of feedstocks, the highest yield to CH4 (11.0 mmol CH4 / g TOCi) was achieved for mixtures rich in acids. CWAO-APR resulted in a similar TOC and COD removal and higher gas production and CH4 yield than direct APR, indicating that coupled CWAO-APR can overcome the low conversion and gas production observed in direct APR of phenol.