Valorisation hydrothermales de la liqueur noire à des fins énergétiques et de chimie verte

Abstract : This thesis aims to study sulfur free black liquor valorization through two hydrothermal processes: supercritical water gasification and hydrothermal liquefaction. These processes will be compared to the industrial process (evaporation and Tomlinson boiler) with 3 mains criteria: energetic yield, sodium recovery and phenolic molecules production.In supercritical conditions, gas formation is competitive with char formation. Fast heating and high temperature permit to increase gas yield, thus energetic yield. However, conversion of phenolic compounds from lignin is low below 500°C, leading to a lower energetic yield than reference. In a continuous process, at high temperatures (700°C) and fast heating, energetic yield should be 2 times higher than industrial process (simulation at thermodynamic equilibrium). Wood prehydrolysis and softwood lead to a lower conversion of black liquor.Hydrothermal liquefaction produces a biocrude which can be burnt and phenolic platform compounds. Indeed, lignin is depolymerized into reactive fragments which can be degraded into platform phenolic molecules. Moreover, the recombination of these fragments, leading to biocrude formation, is favored by the carbohydrates derivatives in black liquor. Wood prehydrolysis and hardwood lead to better energetic and phenolic molecules yields.Sodium recovery is satisfactory for both processes. Substitution of Tomlinson recovery by a hydrothermal process is then possible.
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Marion Huet. Valorisation hydrothermales de la liqueur noire à des fins énergétiques et de chimie verte. Génie des procédés. Université Grenoble Alpes, 2015. Français. ⟨NNT : 2015GREAI085⟩. ⟨tel-01268144⟩

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