Aromatic chemicals by iron-catalysed hydrotreatment of lignin pyrolysis vapours
Résumé
Lignin is fond of iron! This poster will give an overview of the works conducted at CNRS Nancy on lignin hydrotreatment by iron-based catalysts. Iron/silica and iron/activated carbon were first assessed on guaiacol gas-phase hydrodeoxygenatation [1, 2]. The effect of gas composition was carefully investigated especially for iron speciation by Mössbauer spectroscopy [2]. Iron-based catalyst shows very good selectivity for the production of benzene, toluene or phenol. A kinetic study and a model of the lignin to benzene process have been also developed [3]. The hydrotreatment of real lignin pyrolysis vapours, before any condensation, was then studied [4]. Lignin pyrolysis was conducted in a tubular reactor and vapours were injected in a fixed bed of catalysts (673K, 1 atm) with stacks to investigate the profile of coke deposit. More than 170 GC-analysable compounds were identified by GC*GC (heart cutting)/FID-MS. Lignin oligomers (analysed by petroleomic) were trapped by the catalytic fixed bed and especially by the activated carbon. The catalysts showed a good selectivity for the hydrodeoxygenation (HDO) of real lignin vapours to benzene, toluene, xylenes (BTX), phenol, cresols and alkyl phenols. The spent catalysts were characterised by temperature programmed oxidation (TPO), Transmission Electron Microscopy (TEM) and N2 sorption. Micropores in the Fe/AC catalyst are completely plugged by coke deposit whereas the mesoporous structure of Fe/SiO2 is not affected by coke deposit. TEM reveals two different types of coke deposit: (1) catalytic coke deposited in the vicinity of iron particles and (2) thermal coke (carbonaceous particles of ~ 1µm diameter) formed from the gas-phase growth of lignin oligomers [4]. [1] Applied Catalysis B: Environmental, 115- 116, 63- 73, 2012. [2] Applied Catalysis B: Environmental 129, 528-538, 2013. [3] Energy Fuels 27(2), 975-984, 2013. [4] ChemSusChem, 6 (8) , 1490-1499, 2013.