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Vasiliadou E.S.,Greek Chemical Process Engineering Research Institute | Eggenhuisen T.M.,University Utrecht | Munnik P.,University Utrecht | de Jongh P.E.,University Utrecht | And 3 more authors.
Applied Catalysis B: Environmental | Year: 2014

The performance of Cu/SiO2 (commercial silica gel, SBA-15 and SBA-15 treated at 900°C) catalysts for the hydrogenolysis of glycerol to propylene glycol is investigated with emphasis on the stability characteristics. Cu catalysts with large crystals, small monodisperse crystallites or a highly dispersed XRD amorphous copper phase were obtained after calcination in stagnant air, in a flow of NO/N2 or a flow of air, respectively. Analysis by XRD, N2O surface oxidation and TEM confirmed the variation of the Cu specific surface area by the calcination conditions and the type of silica support used. The different dispersion characteristics resulted in different activities (20-50% glycerol conversion), while all the catalysts proved to be highly selective towards propylene glycol (92-97%). Present results indicate that glycerol hydrogenolysis over Cu-based catalysts is a structure sensitive reaction as significant variations in initial TOF were observed as a function of varying Cu crystallites. It is shown here that the presence of a solvent greatly influences the intrinsic reaction rate and the nature of structure sensitivity. The deactivation behaviour of all catalysts was studied, and based on detailed characterization of the spent samples it was attributed to Cu sintering and the presence of strongly adsorbed species on the catalytic surface. The 18wt%Cu/silica gel (air) catalyst presented only moderate deactivation (~20%) while the catalyst supported on SBA-15 calcined at 900°C (SBA900C) proved to be the most stable with negligible deactivation after three consecutive runs. © 2013 Elsevier B.V. Source

Iliopoulou E.F.,Greek Chemical Process Engineering Research Institute | Stefanidis S.D.,Greek Chemical Process Engineering Research Institute | Stefanidis S.D.,University of Western Macedonia | Kalogiannis K.G.,Greek Chemical Process Engineering Research Institute | And 3 more authors.
Applied Catalysis B: Environmental | Year: 2012

The main objective of the present work was the study of different ZSM-5 catalytic formulations for the in situ upgrading of biomass pyrolysis vapors. An equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading (1-10wt.%). The product yields and the composition of the produced bio-oil were significantly affected by the use of all ZSM-5 catalytic materials, compared to the non-catalytic flash pyrolysis, producing less bio-oil but of better quality. Incorporation of transition metals (Ni or Co) in the commercial equilibrium/diluted ZSM-5 catalyst had an additional effect on the performance of the parent ZSM-5 catalyst, with respect to product yields and bio-oil composition, with the NiO modified catalysts being more reactive towards decreasing the organic phase and increasing the gaseous products, compared to the Co 3O 4 supported catalysts. However, all the metal-modified catalysts exhibited limited reactivity towards water production, while simultaneously enhancing the production of aromatics and phenols. An interesting observation was the in situ reduction of the supported metal oxides during the pyrolysis reaction that eventually led to the formation of metallic Ni and Co species on the catalysts after reaction, which was verified by detailed XRD and HRTEM analysis of the used catalysts. The Co 3O 4 supported ZSM-5 catalysts exhibited also a promising performance in lowering the oxygen content of the organic phase of bio-oil. © 2012 Elsevier B.V. Source

Zacharopoulou V.,Aristotle University of Thessaloniki | Vasiliadou E.S.,Aristotle University of Thessaloniki | Lemonidou A.A.,Aristotle University of Thessaloniki | Lemonidou A.A.,Greek Chemical Process Engineering Research Institute
Green Chemistry | Year: 2015

This work presents a novel, one-step catalytic process, enabling highly selective propylene formation via glycerol hydro-deoxygenation (HDO) reactions. Fe-Mo catalysts, supported on black and activated carbons, are selective towards C-O bond cleavage, thus converting glycerol to propylene with high yields. BET, XRD, TPD-NH3 and TPD-He methods have been employed for the characterization of the samples. Molybdenum oxide, at its reduced state, is essential for driving selectively the reaction towards complete deoxygenation. The only product of glycerol HDO is propene, in the gas phase, while 2-propenol, propanols and propylene glycol have been detected, among others, in the liquid phase. Under the standard reaction conditions (300°C temperature, 8.0 MPa hydrogen pressure), glycerol conversion exceeds 88% and selectivity to propene reaches 76% after 6 hours of reaction. This study includes the investigation of the operating conditions effect (i.e. reaction time, reaction temperature, catalyst loading and H2 pressure) regarding glycerol HDO towards propene formation. This journal is © The Royal Society of Chemistry. The Royal Society of Chemistry 2015. Source

Triantafyllidis K.S.,Aristotle University of Thessaloniki | Peleka E.N.,Aristotle University of Thessaloniki | Komvokis V.G.,Greek Chemical Process Engineering Research Institute | Mavros P.P.,Aristotle University of Thessaloniki
Journal of Colloid and Interface Science | Year: 2010

Highly efficient sorbents for phosphate removal from aqueous solutions based on the calcined forms of Fe(III)-substituted Layered Double Hydroxides (LDH) materials have been developed in this study. Hydrotalcite-like materials with Mg/M3+ ∼3 (where M = Al3+, Fe3+ or combined) have been synthesized following simple co-precipitation method and were subsequently calcined in air at 450 °C. Both as-synthesized and calcined materials were characterized by means of X-ray Diffraction (XRD), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), elemental (C) analysis, N2 porosimetry, Scanning Electron Microscopy (SEM). All the materials were evaluated for the sorption of phosphates by batch equilibrium sorption experiments and kinetic measurements (effect of contact time). It was shown that chlorides or nitrates, being the charge-balancing anions in the LDH structure, are more easily exchanged by phosphates compared to carbonates. In the Fe(III)-modified LDHs, an increase of the Fe loading led to the decrease of the sorption efficiency. The maximum uptake of phosphates for both the Mg-Al LDH and Mg-Fe LDH samples containing mainly carbonates as charge-balancing anions was relatively low (ca. ≤25 mg P/g sorbent) while it was higher for the LDH samples containing mainly chlorides (∼80 mg P/g). On the other hand, the maximum sorption capacity for the calcined Mg-Al LDHs and the calcined Fe(III)-substituted sorbents were very high, ca. ∼250 and ∼350 mg P/g, respectively. The sorption data of both the as-synthesized and calcined LDHs was best fitted by the Freundlich model. Both the Mg-Al and Fe-substituted LDH sorbents were regenerated with mixed aqueous solution of NaCl and NaOH and were reused with a small loss of removal efficiency. © 2009 Elsevier Inc. All rights reserved. Source

Tzanetis K.F.,Aristotle University of Thessaloniki | Martavaltzi C.S.,Aristotle University of Thessaloniki | Lemonidou A.A.,Aristotle University of Thessaloniki | Lemonidou A.A.,Greek Chemical Process Engineering Research Institute
International Journal of Hydrogen Energy | Year: 2012

Exergy efficiency analysis tool is used to evaluate sorption enhanced steam reforming in comparison with the industrial hydrogen production route, steam reforming. The study focuses on hydrogen production for use in high pressure processes. Thermodynamic sensitivity analysis (effect of reforming temperature on hydrogen yield and reforming enthalpy) was performed to indicate the optimum temperature (650 °C) for the sorption enhanced reforming. The pressure was selected to be, for both cases, 25 bar, a typical pressure used in the industrial (conventional) process. Atmospheric pressure, 1000 °C and CO 2 as inert gas were specified as the optimum operating parameters for the regeneration of the sorbent after performing exergy efficiency analysis of three realistic case scenarios. Aspen Plus simulation process schemes were built for conventional and sorption enhanced steam reforming processes to attain the mass and energy balances required to assess comparatively exergy analysis. Simulation results showed that sorption enhanced reforming can lead to a hydrogen purity increase by 17.3%, along with the recovery of pure and sequestration-ready carbon dioxide. The exergy benefit of sorption enhanced reforming was calculated equal to 3.2%. Analysis was extended by adding a CO 2 separation stage in conventional reforming to reach the hydrogen purity of sorption enhanced reforming and enable a more effective exergy efficiency comparison. Following that analysis, sorption enhanced reforming gained 10.8% in exergy efficiency. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

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