FROM LIGNIN TO GRAPHENE: A LOW-TEMPERATURE CATALYTIC APPROACH

COVINICH L.G.; AREA, M.C.; HANKE, L.E. ; FELISSIA, F.E.

Lisboa

Congreso; XXIV TECNICELPA 2021 | XI CIADICYP 2021; 2021

TECNICELPA-RIADICYP

Lignin is the second most abundant organic molecule in nature after cellulose, and it is the most abundant aromatic organic compound. It can be valorized through thermochemical processes such as pyrolysis, and one of the most promising alternatives within this platform is the production of graphene nanomaterials. Graphene has attracted great attention since the first obtaining of a monolayer of graphene using the mechanical exfoliation of graphite in 2004. However, the chemical nature of the selected organic precursor conditions its subsequent evolution at high temperatures and the final graphene structure. The chemical structure of lignin is composed of aromatic rings with branches. The activity of its chemical bonds covers a wide range of temperatures, and thus thermal decomposition of lignin also covers a wide range of temperature, of 100-900°C. Lignin is characterized by its isotropic nature and low hydrogen/ high oxygen content. This type of precursor is known as a non-graphitizable material. The resulting materials after thermal treatment of this type of precursor do not evolve towards true graphitic structures, so a strategy to produce ordered structures from lignin consists of the use of fine metallic particles that act as a catalyst during the annealing. Therefore, this work aimed to study the role of several metallic salts as catalysts (that are going to be reduced to the metallic phase during heat treatment) in the pyrolysis of Kraft lignin as a highly oxygenated precursor. Kraft lignin, obtained from the acid precipitation of an industrial black liquor, was used as a nongraphitizable carbon precursor. The lignin/catalyst blend was prepared as follows: lignin impregnation was carried out with ethanol at 450 rpm during 2 h at room temperature, and then metallic salts aqueous solutions were added, drop by drop, and kept under magnetic stirring during 24 h at room temperature to complete the filling of the lignin pores. Overnight impregnation was made with NiCl2, MnCl, Fe(NO3)3, and Co(NO3)2 at metal range concentration of 8 e-3 to 5 mmol of metal/g of C. Subsequently, the blend samples were heated until complete ethanol evaporation. Thermal treatment was carried out in a muffle under exclusion of oxygen, in a self-generated atmosphere at 350°C during 3 h, followed by 2 h at 700 and 900°C, both stages with a mean heating ramp of 2 °C/min. Finally, the material was slowly cooling down to room temperature. Final structure characterization and crystalline phase identification were performed trough Powder Xray diffra tion (Rigaku Smartlab SE) measurements using Cu Kα radiation. Lc002 (crystallite thickness) and d002 (interplanar spacing) were determined according to Bragg?s equation and Scherrer?s equation respectively.