Our project focuses on the study of the purification of 2G biofuels derived from lignocellulosic biomass. After pyrolysis of the biomass and catalytic cracking, the obtained 2G biofuels contain phenolic impurities (0.5 – 7 wt.%) that can impact the engine efficiency and the toxicity of the exhaust gases, which require their elimination. The selective adsorption elimination of these phenolic products has been studied on different solids: zeolites with different counter cation types (H + and Na +) and different Si/Al ratios (2.5 – 40), silic based solids (ASA, SiO2 and MCM-41), alumina (Al2O3) and activated carbon. The adsorptive properties were compared with the textural characteristics, the acidic properties determined by IR spectroscopy, the phenol adsorption modes studied in the liquid phase by IR-ATR spectroscopy, and the geometries and interaction energies determined by theoretical calculations (GCMC and DFT).
We have shown that in the zeolites micropores, phenol condenses in supercages (3-4 phenol/SC) without entering to the sodalite cages. In the mesopores (zeolites and silica based solids) phenol interacts with the silanol groups present on the mesoporous surface. The addition of variable toluene contents in the mixture has shown that the presence of strong acidic OH groups in high concentration is required to maintain the selectivity towards phenol adsorption. Regarding regeneration, a parallel between the experimental results and the DFT calculations, showed that highly adsorbed species are formed on both acid zeolitic OH (-90 kJ.mol-1) and Lewis acid sites (-154 kJ.mol-1).
This work was also an opportunity to develop at the LCS, a spectroscopic studies of the solid-liquid interfaces using IR-ATR spectroscopy. We have thus been able to directly characterize the adsorption modes of phenol on different solids and their selectivity in presence of toluene. In addition, this technological development in IR-ATR has also led us to study the inhibitory effect (adsorption and/or protonation) that nitrogen molecules with very low vapor pressure (indole) can present on acidic materials (zeolites Y) during the hydrocracking type reactions. Thus, IR-ATR is a methodology that can be applied to many fields of catalysis and adsorption.