Black liquor valorization by hydrothermal processes
Published on March 7, 2016
A+Augmenter la taille du texteA-Réduire la taille du texteImprimer le documentEnvoyer cette page par mailPartagez cet articleFacebookTwitterLinked InGoogle+Viadeo
November 24, 2015
Marion Huet, LGP2's Ph.D. student, defended her doctoral thesis: "Black liquor valorization by hydrothermal processes for energetic and green chemistry purposes".
This Grenoble Alpes University doctoral thesis was prepared under the supervision of Dominique Lachenal, Professor (Grenoble INP-Pagora / LGP2) et de Anne Roubaud, Research Engineer (CEA).
This thesis aims at studying 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 combustion in Tomlinson boiler) with three mains criteria: energetic yield, sodium recovery and phenolic molecules production.
In supercritical conditions, gas formation is in competition with char formation. Fast heating and high temperature permit to increase the gas yield, thus the 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 higher temperatures (700°C) and fast heating, energetic yield should be two times higher than for the industrial process (simulation at thermodynamic equilibrium). Wood prehydrolysis prior to cooking and use of softwood instead of hardwood lead to a lower conversion of black liquor.
Hydrothermal liquefaction produces both a biocrude which can be burnt and phenolic platform molecules. 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 present in black liquor. Wood prehydrolysis and hardwood lead to better energetic and phenolic molecules yields. Sodium recovery is satisfactory in both processes. Substitution of Tomlinson recovery by a hydrothermal process is then possible.