Etude structurale et chimique de la lignine d'Alfa et sa valorisation comme macromonomère et/ou précurseur du charbon actif

Abstract : Lignin precipitated from black liquor of alfa (Stipa tenacissima) soda cooking before being carefully characterized and valorized following two different approaches: (i) its utilization after chemical modification in view of preparing rigid polyurethane foams; and (ii) its simple pyrolysis simple, in order to prepare charcoal. In fact, a comparative study concerning the careful characterization of the hydroxyl functions was realized using several methods and techniques, namely: the conductimetric titration and 13C-NMR spectroscopy. In the first approach, the precipitated lignin was converted in liquid polyols thanks to a chain-extension reaction with propylene oxide. These formulations were optimized by inspecting the effect of different parameters: lignin/propylene oxide ratio, the amount of catalyst, the molecular weight of the prepared polyols, the hydroxyl index and the glass transition temperature. The hydroxyl indexes and the viscosity of the prepared polyols were determined. The rigid polyurethane foams were studied in terms of their density, morphology and mechanical properties. The lignin was then used as a precursor for the preparation of charcoal without any activation treatment and compared with commercial homologue. The kinetic of the adsorption was performed and showed that the adsorption equilibrium is reached at about 50 min, and followed a pseudo-first order kinetic model. The adsorption isotherms revealed that lignin-based charcoal retained efficiently the metallic ions and presented a maximum adsorption capacity varying from 200 to 400 µmol/g. This is true even for concentrations much lower than 20 ppm. Le saturated lignin-based charcoal was efficiently regenerated by washing with solutions of EDTA or a nitric acid.The two approaches of the valorization of lignin precipitated from black liquor gave materials with promising properties. Thus, in the majority of cases, materials with properties similar to conventional ones were obtained, which presents a viable option of rational valorization of this industrial abundant and renewable by-product.
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Besma Berrima. Etude structurale et chimique de la lignine d'Alfa et sa valorisation comme macromonomère et/ou précurseur du charbon actif. Génie des procédés. Université Grenoble Alpes, 2015. Français. ⟨NNT : 2015GREAI071⟩. ⟨tel-01259480⟩

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