Beatriz Valle

Compositional Insights and Valorization Pathways for Carbonaceous Material Deposited During Bio-Oil Thermal Treatment

This work analyses the composition, morphology, and thermal behavior of the carbonaceous materials deposited during the thermal treatment of bio-oil (thermal pyrolytic lignin-TPL). The bio-oil was obtained by flash pyrolysis of lignocellulosic biomass (pine sawdust), and the TPLs were obtained in the 400-700 °C range. The TPLs were characterized by performing elemental analysis; (13)C NMR, Raman, FTIR, and X-ray photoelectron spectroscopy; SEM; and temperature-programmed oxidation analyzed by differential thermogravimetry and differential scanning calorimetry. The results are compared to a commercial lignin (CL). The TPLs have lower oxygen and hydrogen contents and a greater aromaticity and structural order than the CL material. Based on these features, different valorization routes are proposed: the TPL obtained at 500 °C is suitable for use as a fuel, and the TPL obtained at 700 °C has a suitable morphology and composition for use as an adsorbent or catalyst support.

Role of oxygenates and effect of operating conditions in the deactivation of a Ni supported catalyst during the steam reforming of bio-oil

This work investigates the correlation of the reaction conditions (temperature and steam-to-carbon ratio (S/C)) and the reaction medium composition with the deactivation behavior of a Ni/La2O3-αAl2O3 catalyst used in steam reforming of bio-oil, aiming at sustainable hydrogen production from lignocellulosic biomass. The reaction was performed in an in-line two-step system consisting of thermal treatment of bio-oil at 500 °C for retaining the thermal pyrolytic lignin and in-line steam reforming of the remaining oxygenates in a fluidized bed catalytic reactor. The reforming step was conducted at 550 and 700 °C and S/C ratios of 1.5 and 6. Fresh and deactivated catalyst samples were characterized using XRD, SEM, TEM, TPO, XPS, Raman and FTIR spectroscopy. The catalyst deactivation was mainly due to the amorphous and encapsulating coke deposition whose formation is attenuated when both the temperature and S/C ratio are increased. Although the highest catalyst stability is attained at 700 °C and/or an S/C ratio of 6, Ni sintering is noticeable under these conditions. The encapsulating coke is highly oxygenated, in contrast with the more aromatic and condensed nature of filamentous coke. Based on the correlation between the composition of the coke and the reaction medium, it was established that bio-oil oxygenates are the precursors of the encapsulating coke, particularly phenols and alcohols, whereas CO and CH4 are the possible precursors of the coke fraction made of filaments whose contribution to catalyst deactivation is hardly significant.

Development of Alternative Catalysts Based on HZSM-5 Zeolite for the BTO Process

The catalytic behaviour of a commercial HZSM-5 zeolite (Si/Al=30) for the selective transformation of bio-ethanol into olefins (BTO process) has been improved by two alternative methods: a) treatment with 0.2M alkali solution for a short time; and b) impregnation with Ni. By means of experimentation in an isothermal fixed bed reactor connected on-line to a GC for the analysis of the reaction products, it has been proven that moderate alkali treatment (10 min) slightly modifies the superficial structure and acidity of the HZSM-5 zeolite, which provokes a significant increase in the concentration of C2-C4 olefins, whereas deactivation rate and hydrothermal stability are similar. Moreover, 1 wt% nickel content in the catalyst is the optimum in order to obtain the better compromise concerning hydrothermal stability of the catalyst, coke deactivation, total yield of olefins and selectivity to C3-C4 olefins in the 400-500 °C range. In fact, the average production rate of C3-C4 olefins is twice as high as that of the parent zeolite in 8 h time on-stream experiments at 450 °C and 75wt% water content in the feed. Both methods are highly interesting because of the simplicity and reproducibility for obtaining economic and selective catalysts for the BTO process at moderate temperatures (catalysts modified by alkali treatment) and high temperatures (nickel based catalysts).

Temperature Programmed Oxidation Coupled with In Situ Techniques Reveal the Nature and Location of Coke Deposited on a Ni/La2O3-αAl2O3 Catalyst in the Steam Reforming of Bio-oil

The characterization of coke deposited on a Ni/La2O3‐αAl2O3 catalyst used in the steam reforming of bio‐oil has been studied by temperature programmed oxidation (TPO) coupled with different in situ techniques: thermogravimetry (TG), modulated thermogravimetry (MTG), FTIR spectroscopy with mass spectrometry (MS), Raman spectroscopy, and differential scanning calorimetry (DSC). The steam reforming of bio‐oil was carried out in a reactor equipment with two steps in series, comprising bio‐oil thermal treatment (500 °C) and subsequent reforming in a fluidized bed reactor (550–700 °C; and steam‐to‐carbon ratio, 1.5–6). TG/MS‐TPO experiments identify encapsulating and filamentous coke, and a more detailed analysis using other in situ techniques enable to characterize the nature and location of 4 types of coke: (i) an encapsulating coke with aliphatic nature placed in the most superficial layers; (ii) an encapsulating coke with higher aromatic nature in inner layers; (iii) the most superficial layers of a filamentous coke, further from active sites and with a more carbonized structure compared to encapsulating coke; and (iv) an innermost and mainly polyaromatic filamentous coke with a low oxygenates content.