• Département Génie des Procédés et Énergétique (GPE)
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Item SOLAR ENERGY TO GREEN HYDROGEN: EXPLORATION OF THE ELECTRO- SONOLYTIC PATHWAY IN A PERSPECTIVE OF SUSTAINABLE DEVELOPMENT(National Higher School of Technology and Engineering. Annaba, 2024-05-19) MERABET Nour Hane; KERBOUA Kaouther (Directeur de Thèse)The aim of the present thesis is to develop an innovative process for the production of green hydrogen from treated wastewater sono-electrolysis, using photovoltaic solar energy and low-cost materials. The thesis combines theoretical and experimental approaches, which focus on membraneless and membrane sono-electrolysis, with a transition from blue to green hydrogen by integrating PV supply. In addition, the project investigates the membrane bioreactor treatment of domestic wastewater for its reuse in hydrogen production and evaluates the purity of the produced gas. Finally, a comparative analysis is carried out to provide insights for scaling up the research results. At the very beginning, a preliminary parametric study was performed using two configurations, Hoffmann and H-cell, by varying the concentration and the nature of the salt, the solution and bath temperatures and the electrode’s material. The parametric study revealed that the integration of continuous sonication prevents high temperature operation. The H-cell experiments highlighted the significant influence of cell geometry on ion transport phenomena, while the sono-electrolytic configuration showed a dependency on the electrolyte type, with NaOH facilitating bubble formation and degassing. Continuous sonication offered the highest improvement in kinetics and energy efficiency, with the greatest reduction in bubble resistance observed with nickel foam electrodes and KOH electrolyte. Then, the investigation of the membraneless sonoelectrolytic process using an H-cell configuration and indirect continuous sonication demonstrated experimentally a 3.93% improvement in H2 rate and a 2.76% gain in energy conversion efficiency with sonication. Polarisation curves showed quasi-linear evolution, indicating an ohmic overpotential zone, with a 7.2% reduction in average ohmic resistance under sonication. At the microscopic scale, numerical simulations proved that small bubbles primarily contribute to shockwave-induced turbulence, which facilitated hydrogen bubble detachment, while large bubbles are more involved in microjetting, both phenomena reduced electrode coverage by bubbles from 76% to 42%, and decreased bubble resistance by 62.35%. Meanwhile, the contribution of the sonochemical activity was negligible. In terms of membrane sono-electrolysis, the results showed that the Zirfon® separator outperformed other diaphragms/membranes in terms of energy efficiency, hydrogen production kinetics and stability under high alkaline conditions. However, sonication integration didn't improve energy efficiency, yet it enhanced hydrogen production kinetics due to desorption and stirring effects in the electrolyte. Regarding the coupled PV-sono-electrolysis, Indirect continuous sono-electrolysis had the lowest electrode coverage (37%) and reduced bubble resistance by 76% compared to silent mode and 52% compared to pulsed sonication. The influence of ultrasound on the diffusion coefficient suggested a limited effect on mass transport properties, while the Faraday efficiency remained constant regardless of the presence of ultrasounds. This was confirmed by numerical simulations. Dynamic conditions showed higher hydrogen production in summer, with a notable reduction of ohmic and cell voltages with increased radiation. The substitution of fresh water by membrane bioreactor permeate passed through the pretreatment process. The membrane bioreactor treatment achieved high COD and TOC removal rates of 96% each. However, additional steps are required to meet ASTM Type II limits for H2 production. Despite achieving an overall hydrogen purity of 85%, traces of nitrogen and oxygen gases were present within safe limits of the O2/H2 ratio. When using a current source with permeate instead of distilled water, the integration of ultrasound didn't improve energy efficiency, but improved hydrogen flow rate due to enhanced desorption, leading to better electrochemical hydrogen production. Finally, the comparative study made in the last chapter showed that the integration of continuous ultrasound leads to higher improvement in hydrogen flow rate when a voltage source is used, due to reduced ohmic resistance and accelerated kinetics. Hydrogen purity from distilled water was 5% higher than from permeate.