Model based analysis of the effect of 2-ethylphenol addition to n-decane in fluid catalytic cracking over a series of zeolites

The catalytic cracking of n-decane (C10) purely, representing the conventional gasoil feed, and in admixture with 2-ethylphenol (EP), as a model component for HDO bio-oil, is investigated in a fixed-bed reactor over three faujasites. It was observed that EP induces faster deactivation with time-on-stream (TOS), which was more pronounced when materials with low mesoporous surface area were employed. The gasoline selectivity was also shown to increase more steeply with TOS for an EP containing feed. A 5-lump FCC kinetic model, including selective deactivation functions, was developed and incorporated into a transient reactor model to assess the obtained data and account for the observed effects. With the aid of the model, the above trends were rationalized by an increase in the value of the frequency factors, related to the feed conversion into coke and gasoline. The FCC kinetic model was subsequently integrated into a riser reactor model for pilot level simulations, via the extrapolation of the results obtained based on the transient model for the fixed-bed reactor to the steady-state behavior of a riser reactor. In particular, a unique deactivation factor Phi, reflecting catalyst condition, was introduced in the model for the latter reactor to adequately account for the deactivation functions determined making use of the data acquired in the former. Simulation results demonstrate the significance of the first meters of the riser, as well as the effect of operation parameters, i.e, Phi, EP addition in the feed, inlet catalyst-to-oil ratio, on conversion and selectivities

Effect of composition and preparation of supported MoO3 catalysts for anisole hydrodeoxygenation

A series of zirconia supported molybdenum oxide materials with Mo loadings of 7, 12, and 19 wt% were synthesized using incipient wetness impregnation. The as synthesized oxide materials were further modified under H-2/CH4 (80/20%, v/v) at 550 and 700 degrees C. The obtained catalysts were characterized by ICP-OES, XRD, Raman spectroscopy, H-2-TPR, NH3-TPD, XPS, (S) TEM-EDX, BET, CHNS and CO chemisorption. While the Mo species, i.e., MoO3 and Zr(MoO4)(2), in the 7 wt% Mo loaded material were found to be of rather amorphous nature, their crystallinity increased significantly with Mo loading. The anisole hydrodeoxygenation performance of the catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. A predominant selectivity towards hydrodeoxygenation and methyl transfer reactions rather than to hydrogenation was observed, irrespective of the Mo loading and further treatment, yet interesting differences in activity were observed. The highest anisole conversion was obtained on the catalyst(s) with 12% Mo loading, while the 7% Mo loaded one(s) exhibited the highest turnover frequency (TOFanisole) of 0.15 s(-1). CO chemisorption, XPS analysis and kinetic measurements indicate that treatment under H-2/CH4 slightly reduced the initial anisole conversion, yet enhanced catalyst stability as well as TOF, probably due to the increased amounts of Mo5+ species. The importance of appropriate tuning of the reduction and/or preparation procedures has been addressed to improve the catalysts' performance during anisole HDO

Μελέτη νανοσωλήνων άνθρακα ως καταλυτικών υποστρωμάτων: βελτιστοποίηση της παραγωγής νανοσωλήνων άνθρακα με τη μέθοδο της χημικής εναπόθεσης ατμών

The main goal of this research was the investigation of the influence of catalytic and operational parameters on the rate of growth and quality of carbon nanotubes via chemical vapor deposition of ethylene. Deposition experiments were carried out in a thermogravimetric reactor, while the products of the reaction were characterized by different methods. Controlled explosive burning of precursor compounds was found to be the most effective technique of preparation of the monometallic catalyst Fe₂O₃/Al₂O₃. Moreover, the optimal loading of Fe₂O₃ was proven to be 75% wt. During the study of bimetallic catalysts M- Fe₂O₃/Al₂O₃ (M, Ru, Ni, Co, Mo), it was found that the nature of the metal (M) and the preparation technique affect significantly the rate of growth and quality of the multi-walled carbon nanotubes. In particular, co-precipitation technique is preferred when M-Mo or M=Ru, while burning technique for M=Co and M-Ni. Especially, in the case of M=Ni, the prepare catalyst exhibits the highest yield of nanotubes, approximately 36 times the weight of the catalyst. Finally, the optimal reaction temperature and the optimal concentration of C₂H₄ in the gas feed, were 650°C and 20% respectively.Ο βασικός στόχος της παρούσας διατριβής ήταν να εξερευνηθεί η επίδραση καταλυτικών και λειτουργικών παραμέτρων στο ρυθμό της ανάπτυξης και την ποιότητα των παραγόμενων νανοσωλήνων άνθρακα μέσω της χημικής εναπόθεσης ατμών αιθυλενίου. Τα πειράματα εναπόθεση διεξήχθησαν σε θερμοβαρυμετρικό αντιδραστήρα, ενώ τα προϊόντα της αντίδρασης χαρακτηρίστηκαν με διάφορες μεθόδους. Η ελεγχόμενη εκρηκτική καύση των πρόδρομων ενώσεων βρέθηκε ότι είναι η πιο αποδοτική τεχνική για την Παρασκευή του μονομεταλλικού καταλύτη Fe₂O₃/Al₂O₃. Επίσης, η βέλτιστη φόρτιση σε Fe₂O₃ αποδείχθηκε ότι είναι η 75% κβ. Κατά την εξέταση των διμεταλλικών καταλυτών M- Fe₂O₃/Al₂O₃ (M, Ru, Ni, Co, Mo), βρέθηκε ότι η φύση του μετάλλυ (Μ) και η τεχνική παρασκευής τους, επηρεάζει σημαντικά το ρυθμό ανάπτυξης και την ποιότητα των πολυφλοιϊκών νανοσωλήνων άνθρακα. Συγκεκριμένα, η μέθοδος της συγκαθίζησης ενδείκνυται όταν M=Mo ή M=Ru, ενώ αυτή της καύσης για M=Co ή M=Ni. Ειδικά για M=Ni, ο παραγόμενος καταλύτης παρουσιάζει την υψηλότερη απόδοση σε νανοσωλήνες, ίση περίπου με 36 φορές το βάρος του. Τέλος, η βέλτιστη θερμοκρασία αντίδρασης και η βέλτιστη συγκέντρωση του C₂H₄ στη τροφοδοσία ήταν οι 650°C και η 20% αντίστοιχα

Effect of Co incorporation and support selection on deoxygenation selectivity and stability of (Co)Mo catalysts in anisole HDO

A series of supported Co modified Mo catalysts was prepared by varying the Co/Mo ratio in the range from 0 to 1 while maintaining the Mo loading at ca. 10 wt%. A sequential incipient wetness impregnation method, with Mo being introduced first, using aqueous solutions of the corresponding precursor salts was employed during the synthesis procedure. Three supports, i.e., Al2O3, ZrO2, and TiO2 differing in textural and acidic properties were investigated. Material physicochemical characteristics were evaluated through ICP-OES, N2-sorption, XRD, H2-TPR, NH3-TPD, O2-TPO, STEM-EDX and XPS techniques. The anisole HDO performance of these CoMo catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. The catalysts performance is correlated with properties such as reducibility, acidity, and metal-support interactions. Cobalt addition enhanced the total HDO selectivity by 45% as compared to Mo catalysts. Alumina catalysts displayed higher initial activity (Xanisole≈97%) relative to titania and zirconia supported variants (Xanisole <40%) at identical operating conditions. Titania supported catalysts exhibited rather higher stability compared to zirconia and alumina catalysts over 50 h time on stream (TOS), while zirconia catalysts displayed the highest HDO selectivity (up to 86%). Characterization studies of pre and post-reaction catalysts indicate Mo5+ to be the main active phase while over-reduction to lower Mo states (Mo4+ and Mo3+) as well as carbon deposition are identified as the cause for catalyst activity decrease with TOS.publishedVersio

Analysis of volume‐to‐surface ratio effects on methane oxidative coupling using microkinetic modeling

The effect of the volume‐to‐surface (V/S) ratio on the catalytic performance of a La–Sr/CaO catalyst in a fixed bed reactor under oxidative coupling of methane (OCM) conditions is investigated by adjusting the amount of diluent in the catalyst bed. It was observed experimentally that the catalyst activity, C2 selectivity, and C2H4/C2H6 ratio are all favored at high V/S ratios. The total void volume, available in the intraparticle and the interstitial phase, was considered. A comprehensive OCM microkinetic model, explicitly distinguishing between these two phases, allowed accounting for the observed dependence of catalytic performance on V/S ratio. The major experimentally implemented variation in interstitial volume available for reaction, provoked also changes in radical concentration profiles in intraparticle phase. Given the high reaction rates occurring at this location, the experimentally observed effects with varying the V/S ratio, are attributed to concentration and, hence, reaction rate changes occurring mainly in the intraparticle phase. © 2018 American Institute of Chemical Engineers AIChE J, 201