Please use this identifier to cite or link to this item: http://hdl.handle.net/10889/9232
Title: Σχεδιασμός προηγμένων χημικών αντιδραστήρων θερμικής ολοκλήρωσης για αντιδράσεις παραγωγής υδρογόνου
Other Titles: Advanced heat integrated wall chemical reactor design for hydrogen production reactions
Authors: Σταύρακας, Ανδρέας
Keywords: Υδρογόνο
Αντιδραστήρες
Αναμόρφωση
Keywords (translated): Hydrogen
Reactors
Reforming
Abstract: Τo υδρογόνο αποτελεί τον πιο ελπιδοφόρο φορέα ενέργειας σε μεσοπρόθεσμο χρονικό ορίζοντα. Η καταλυτική αναμόρφωση με ατμό διαφόρων καυσίμων είναι από τις αποδοτικότερες διεργασίες που μπορούν να χρησιμοποιηθούν. Η χρήση μεταλλικών μορφοποιημένων δομών για την εναπόθεση των καταλυτών στις αντιδράσεις αναμόρφωσης παρουσιάζει σημαντικά πλεονεκτήματα σε σχέση με τη χρήση των συνήθων κεραμικών υλικών, όπως επίτευξη υψηλότερων ρυθμών μεταφοράς θερμότητας, εξισορρόπηση των θερμοκρασιακών προφίλ, αυξημένη αντοχή σε μηχανικές καταπονήσεις και ευελιξία στο σχεδιασμό αντιδραστήρων. Η χρήση μεταλλικών δομών για την παρασκευή καταλυτών αναμόρφωσης με ατμό του προπανίου και της αιθανόλης μελετήθηκε με τη χρήση κραμάτων Σιδήρου- Χρωμίου- Αλουμινίου με επιπλέον προσθήκη Ύττριου. Μελετήθηκε επίσης η εναπόθεση σε αυτά με διάφορους πιθανούς τρόπους κεραμικού υποστρώματος υψηλής επιφάνειας και ακολούθως η εναπόθεση της ενεργού καταλυτικής φάσης. Διεξήχθησαν πειράματα αναμόρφωσης με ατμό τόσο με χρήση προπανίου όσο και με χρήση αιθανόλης με ιδιαίτερα ικανοποιητικά αποτελέσματα. Ακολούθως διεξήχθηκαν πειράματα καταλυτικής καύσης- αναμόρφωσης σε σχεδιαστικά καινοτόμους αντιδραστήρες θερμικά εξαρτημένης αναμόρφωσης.
Abstract (translated): In the present study, the use of catalysts deposited on metal structures (metal sheets, metal monoliths, metal foams) for the production of hydrogen via steam reforming of propane and bio-ethanol has been investigated. For this purpose, metal alloys containing aluminum, known as Fecralloys®, have been used. Following proper thermal treatment, aluminum from the bulk of the above alloys diffuses towards the surface of the material and after a second thermal treatment in the presence of air, aluminum is being oxidized producing a thin layer of alumina. Plain sheets and corrugated formed sheets of these alloys have been etched and thermally treated in various conditions in order to optimize the produced alumina layer. Optimization was achieved by maximizing alumina layer thickness and producing “whisker” type structures on the surface of the layer, aiming to success a stronger bond between the metal structure and the catalyst. For the deposition of adequate quantity and consequently high performance of the catalyst it was necessary to create an intermediate layer of γ-alumina, over the superficial aluminum oxide layer, which would offer the desired surface area, thickness and porosity for the diffusion of the catalytically active compounds. This intermediate layer was deposited via various methods in order to study the effect of each procedure to the performance of the produced catalyst. Impregnation of the specimens in aqueous alumina solutions and thin film spraying of alumina solution were the methods studied. In addition, the effect of parameters such as density of the solutions used and temperature of the specimens during application of each method were studied in order to find the optimal preparation conditions. In a further step, deposition of the catalytically active phase was studied over the above metal sheets. The same methods of application of the intermediate layer of γ-Al2O3 were also followed for the deposition of the active material. The reforming catalyst used was the 5% Ru/γ-Al2O3 catalyst, which was found in earlier studies to exhibit high activity and stability during steam reforming of various fuels. The produced samples were tested in steam reforming experiments using propane or ethanol as fuels. Catalytic performance measurements were obtained and it was found that the samples prepared by the above mentioned method present similar behavior with catalysts in the form of pellets used in conventional fixed bed reactors. Furthermore, the samples presented remarkable stability with time-on-stream. Finally, the preparation method of the catalysts was optimized by examining various factors employed in the production methods such as deposition procedure, the nature of the corresponding impregnation/deposition solution, the quantity of the intermediate adherent alumina layer as well as the quantity of the active phase.
Appears in Collections:Τμήμα Χημικών Μηχανικών (ΜΔΕ)

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