Metal supported hydrotalcite catalytic depolymerization of lignin: Effects of reaction parameter on compounds distribution

In this study different metal (Ni, Co and Fe) supported hydrotalcite catalysts were synthesis and it was used for lignin depolymerization. Catalytic pyrolysis reactions have been carried out at reaction temperature range of 400 to 550 °C, reaction time 30 to 120 min. with the presence of different amount of metal supported catalysts. From product distribution, it has been found that reaction temperature 500 °C was the optimal temperature for the production of maximum bio-oil yield of 32.4 wt% at reaction time of 60 min reaction. With the addition of the catalysts in pyrolysis, bio-oil significantly increased and maximum bio-oil (47.4 wt%) was found with cobalt supported hydrotalcite catalyst (Co/MgAl2O4). Other catalysts for example Ni/MgAl2O4 and Fe/MgAl2O4 catalyst exhibited bio-oil yield of 42.1 and 43.2 wt%. Different metals on MgAl2O4 showed different properties, which is affecting the lignin depolymerization during the pyrolysis. Catalytic pyrolysis produced higher amount of G-types phenolic monomer with higher bio-oil yield. This is suggesting that Co supported MgAl2O4 catalyst effectively breakdown the ether bond (COC) in the lignin. Elemental analysis and GPC of bio-oil was specified that the macromolecules structure of lignin depolymerized effectively with the using of catalysts. breaking of lignin macromolecule into small monomers phenolic compounds. Co/MgAl2O4 and Fe/MgAl2O4 was effectively encouraged the breaking of raw lignin into low molecular weight monomers as compared to others catalyst. Higher Mw and PDI were obtained for the Fe/MgAl2O4 catalytic pyrolysis reactions due to the repolymerization of monomers are promoted during pyrolysis.