Eduardo Falabella Sousa-Aguiar

Isobutane/2-butene alkylation on zeolite beta: Influence of post-synthesis treatments

The influence of the framework and extraframework composition of zeolite beta on its activity, selectivity, and deactivation behavior during the alkylation of isobutane with 2-butene has been studied by submitting a H-beta sample to different post-synthesis treatments. The parent Hβ sample was prepared by calcination, conventional NH4+ exchange, and further calcination of a commercial TEA-beta. These treatments were seen to produce some framework dealumination with formation of dispersed cationic extraframework aluminum (EFAL) species. The Hβ was then dealuminated by two chemical treatments (hydrochloric acid and ammonium hexafluorosilicate) and by steam calcination, the former procedures leading to almost EFAL-free catalysts. Furthermore, Hβ was also treated with the required amount of ammonium hexafluorosilicate (HFS) in order to remove EFAL species generated during the activation of the parent TEA-beta sample. The catalysts were characterized by XRD, N2 adsorption-desorption isotherms,27Al and29Si MAS-NMR, XPS, and IR spectroscopy with adsorption-desorption of pyridine. In general, dealumination of Hβ leads to less active, selective, and stable catalysts for isobutane/butene alkylation. The chemically dealuminated EFAL-free catalysts were much more active than the steamed sample, which was attributed to the presence of both cationic EFAL compensating framework charge and condensed type EFAL blocking acid sites in the latter catalyst. Furthermore, elimination of EFAL in Hβ by HFS treatment also decreased the alkylation activity of the zeolite, suggesting a synergistic effect of dispersed cationic EFAL species with framework hydroxyls of Hβ to form Bronsted acid sites of enhanced acid strength.

The main catalytic challenges in GTL (gas-to-liquids) processes

In the present review the main catalytic challenges for GTL processes are discussed. It is considered that GTL comprises three main catalytic areas, namely synthesis gas generation, Fischer–Tropsch synthesis and upgrade. Each one is analysed and the main characteristics of traditional and innovative catalysts are presented. For syngas generation, steam methane reforming, non-catalytic partial oxidation, two-step reforming, autothermal reforming and catalytic partial oxidation of methane are discussed. For Fischer–Tropsch, we highlight the role of nanocatalysis, hybrid zeolite-containing catalysts, diffusion limitations and selectivity to high molecular weight hydrocarbons. Also, new reactors technologies such as micro reactors are presented. Finally, special attention is paid to the main upgrade steps (Hydrocracking and Hydroisomerisation/Dewaxing), the new mechanisms of isomerisation being discussed for bifunctional zeolitic catalysts.

Influence of the external surface area of small crystallite zeolites on the micropore volume determination

Abstract The micropore volumes of zeolites displaying different external surface areas were determined with the help of two classical methods: the Dubinin–Radushkevich (DR) and t-plot. The results were compared with a new approach, in which adsorption isotherms are decomposed into two adsorption areas: one corresponding to the micropore filling and described by the DR equation, and the other ascribed to adsorption on the external surface and ruled by the classical BET equation. The results indicate that the proposed model fits the experimental data very well. Furthermore, the DR-plot seems to overestimate micropore volume, whereas the t-plot, in the range 6

Aldol condensation of acetone over alkali cation exchanged zeolites

The aldol condensation of acetone was studied over faujasite type zeolites with different silica/alumina ratios (X and Y) both in the original Na form and Cs and K exchanged. The pore volume and specific surface of cesium exchanged zeolites were smaller than that of the parent sodium form, since cesium is a more volumous cation. The increase in the zeolite basicity is related to the decrease of the silica/alumina ratio and to the electronegativity of the counter cation. This increase has favoured the mesityl oxide (MO) hydrogenation to methylisobuthylketone (MTBK) and has decreased the selectivity to isobutene (IB).

Rietveld refinement and solid state NMR study of Nd-, Sm-, Gd-, and Dy-containing Y zeolites

Abstract Na-Y zeolites ion exchanged with rare earth cations (Nd3+, Sm3+, Gd3+, Dy3+) were studied by X-ray diffraction in order to locate the rare earth cations in the zeolite framework and the resulting changes in its structural properties. The results indicate that the rare earth cations dealuminate the framework differently. This is observed as a decrease in the values of the unit cell parameters, a0. This systematic decrease in a0 is related to the rare earth ionic radius and its coordination to the oxygen framework. The correlation between the Si/Al ratio obtained from the Fichtner-Schmittler equation and the ionic radius of the rare earth cations reveals that smaller ionic radii gives higher dealumination and smaller a0. This is related to hydrolysis constant cation. Samples treated with Dy3+ cations show a higher level of dealumination than those treated with the other cations (Sm3+, Gd3+, Nd3+). In order to characterize the dealumination process 29 Si and 27 Al magic angle spinning NMR measurements were attempted. Except for the Sm3+ treated sample, the Nd3+, Gd3+, Dy3+ samples could not have their tetrahedral and octahedral aluminum signal detected due to the high concentration of the paramagnetic ions with large effective number of Bohr magnetons.

The luminescent behavior of the steamed EuY zeolite incorporated with vanadium and rare earth passivators

Abstract In the present work, the use of rare earth ions as passivating agents to prevent vanadium poisoning of Y zeolite-based cracking catalysts during typical hydrothermal operating conditions of FCC units was studied to establish the capability of each RE 3+ passivator used here (RE=La, Gd or Lu) to interact with vanadium in order to protect the zeolite from structural collapse by exploring the photoluminescent properties of the Eu 3+ ion as local probe in the zeolitic lattice environment. The Ω λ intensity parameters ( λ =2 and 4) were determined from the emission spectra which showed that Eu 3+ ion assumes a stronger covalent character in relation to V attack. In another approach, the formation of orthovanadate ion was determined by means of excitation spectra and related with the intraconfigurational transitions from the Eu 3+ ion. It was suggested that the interaction with vanadium could be associated to REVO 4 intrinsic thermodynamic values.

Mathematical modeling and simulation of catalytic cracking of gasoil in a fixed bed: Coke formation

Abstract In the present work a 12-lump model for the catalytic cracking of gasoil in a fixed bed microreactor was solved, with the differential-algebraic approach, using previously published kinetic constants. The influence of different feedstocks and injection times were studied. Taking into account the sequential design of experiments, this model was used as a virtual data generator to validate a simplified 5-lump model. The 5-lump model was also validated with real microactivity test (MAT) data. Although the naphthenic feed yielded more gasoline, the aromatic feed was responsible for more coke on catalyst than were the other feeds. Simulation results for the 5-lump model are in agreement with experimental and virtual data.

Reactivity of USY extraframework alumina in alkaline medium

Two ultrastable Y zeolites with different degrees of dealumination were treated with NaOH solution at various temperatures and contact times. Filtrate analysis showed the transference of the solubilized nonframework aluminum species to the solid phase, at a rate that increases with both increasing temperature and dealumination degree. The reinsertion of this aluminum in the lattice was verified by the reduction in the structural silica-to-alumina ratios (SAR) determined by 29Si n.m.r. and FTi.r. The mesoporosity reduction points to a reinsertion in the structural defects. An estimate of the activation energy for the reinsertion process was obtained from the data fitting to a basic zeolite crystallization model.

Three-Dimensional Gas-Liquid CFD Simulations in Cylindrical Bubble Columns

Results from CFD simulations in a laboratory scale cylindrical bubble column with an internal diameter of 0.44 m under different operation conditions are presented. The effects of the continuous phase viscosity, bubble diameter and drag model were evaluated and the results were compared with experimental data found in the literature in three different gas inlet velocities. It was found that the approach used in this work provided physically consistent results, showing the transient effects in the column and good agreement with experimental data found in the literature for a homogeneous flow regime. Also, a case for a column with internals was simulated and a flow behavior qualitatively different from the column without internals was found.

Short chain paraffins isomerization on Pt/beta catalysts. Influence of framework and extraframework zeolite composition

Zeolite beta samples with different framework and extraframework composition have been prepared by submitting the acid form of a commercial TEA-beta sample to different post-synthesis treatments, i.e. steam calcination, acid (HCl) leaching, and ammoniums hexafluorosilicate (HFS) treatment. The samples were characterized by XRD, adsorption of N 2 at 77 K. i.r. spectroscopy with adsorbed pyridine, 29 Si and 27 Al MAS-NMR and XPS. Bifunctional catalysts were obtained by impregnation with 0.3 wt% Pt, and the catalytic activity for the isomerization of a simulated LSR feed (n-C 5 /n-C 6 , 60/40 wt%) was measured under different reaction conditions. The dealuminated beta catalysts were less active than the parent Hβ sample, but the activity strongly depended on the procedure of dealumination used. Thus, the chemically treated EFAL-free catalysts were much more active than the steam dealuminated EFAL-containing sample. The latter sample contained a reduced number of Bronsted acid sites, mainly due to a charge compensation effect and pore blockage by the EFAL generated during the steam treatment. Furthermore, elimination of the EFAL present in the parent Hβ sample by ammonium hexafluorosilicate treatment produced an increase of the concentration of Bronsted acid sites owing to the mentioned charge compensation effect, but the activity for isomerization of the C 5 fraction of the feed decreased. Then, it is suggested that some of the EFAL in Hβ was interacting with the OH groups of framework Al producing Bronsted sites of enhanced activity.