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LGP2, a center of innovative research
LGP2, a center of innovative research

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Study & valorization of Alfa lignin

Published on February 1, 2016
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PhD Defense September 28, 2015

Besma Berrima, LGP2's Ph.D. student, defended her thesis: "Structural and chemical study of lignin and its recovery as Alfa macromonomer and/or activated charcoal precursor".

This Université Grenoble Alpes doctoral thesis was prepared under the supervision of Prof. Naceur Belgacem (Grenoble INP-Pagora / LGP2), of Prof. Sami Boufi, (University of Sfax, Tunisia) and the co-supervision of Prof. Gérard Mortha (Grenoble INP-Pagora / LGP2).

Lignin precipitated from black soda cooking liquor of Alfa (Stipa tenacissima) was carefully characterized and valorized following two different approaches: its utilization after chemical modification in view of preparing rigid polyurethane foams and its simple pyrolysis, 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, among which: the conductometric titration differential UV 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, amount of catalyst, molecular weight of the prepared polyols, hydroxyl index and 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 a commercial homologue. The kinetic of the adsorption was performed and showed that the adsorption equilibrium was reached at about 50 min, and followed a pseudo-first order kinetic model. The adsorption isotherms revealed that lignin-based charcoal retained efficiently metal ions and presented a maximum adsorption capacity varying from 200 to 400 µmol/g. This was true even for concentrations much lower than 20 ppm. The saturated lignin-based charcoal was efficiently regenerated by washing with solutions of EDTA and nitric acid.

These two approaches for the valorization of precipitated lignin from black liquor of alfa cooking gave materials with promising properties. Most 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.

LGP2' Ph.D. thesis (2015)

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Date of update February 2, 2016

Université Grenoble Alpes