Ulises Sedran

Catalytic combustion of diesel soot particles. Activity and characterization of Co/MgO and Co,K/MgO catalysts

Abstract The catalytic combustion of diesel soot particles was studied on Co/MgO (12 wt% Co) and potassium-promoted Co/MgO (1.5 wt% K) that were calcined at different temperatures in the 300 to 700°C range. Catalyst samples were characterized by various techniques including nitrogen adsorption (BET), temperature programmed reduction (TPR),X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electron spin resonance (ESR),X-ray photoelectron spectroscopy (XPS) and temperature programmed oxidation (TPO). As observed by TPO experiments, the catalyst activity depends strongly on the calcination temperature: calcination at 300 and 400°C produced samples that were much more active than those calcined at higher temperatures, on which an inactive Mg Co mixed oxide is formed, as suggested by TPR, ESR and XRD results. FTIR shows carbonate species on the surface. Unpromoted samples seem to correlate their activity with the amount of reducible Co species present. Potassium not only increased the sample activity, probably due to the improvement in surface mobility, but also enhanced stability at high temperatures. Experiments with different soot to catalyst ratios showed no significant variation in combustion temperature. TheK-promoted catalyst burns off soot at a temperature lower than the one needed for calcination, thus proving to be a promising catalyst.

Laboratory testing of FCC catalysts and hydrogen transfer properties evaluation

Abstract The importance of fluid catalytic cracking of hydrocarbons (FCC) as a leading process in the chemical industry has been acknowledged for a long time. Present data on feedstock processing and its overall economical impact confirm such a role [1, 21. Technical, economic, and environmental concerns have played significant roles as driving forces in the research conducted on FCC matters, leading to developments that are identifiable along catalytic cracking chronology (e.g., fluid bed technology, zeolite catalyst introduction, promotor addition, octane boosting).

Synthesis of acetal (1,1-diethoxyethane) from ethanol and acetaldehyde over acidic catalysts

Various acidic catalysts (zeolitic and amorphous FCC catalysts, mordenite, montmorillonite, and sulfonic ion exchange resin) were tested for the synthesis of acetal from ethanol and acetaldehyde, at 4 and 20°C and atmospheric pressure in batch stirred reactors. All the catalysts were active, but the exchange resin showed a much better performance than the other catalysts, since it quickly reached equilibrium ethanol conversion values. The resin was also tested under different pressures and catalyst to reactants ratios. Clear relationships between the catalyst activity, the amount of acidity and the physical properties of the catalysts were not apparent. A possible reaction mechanism suggests that protonic acid sites are necessary. Water, a reaction product, seems to have an inhibitory effect on the reaction rate.

ZnOCr2O3 + ZSM-5 catalyst with very low Zn/Cr ratio for the transformation of synthesis gas to hydrocarbons

Abstract Three Zn Cr mixed oxide plus ZSM-5 compound catalysts with different compositions covering a wide range of Zn/Cr atomic ratios (0.064 to 1.913), aimed at the direct conversion of synthesis gas into hydrocarbons, were tested under different experimental conditions: temperature ranged from 356 to 410°C, pressure from 3.60 to 4.49 MPa and space velocity from 0.2 to 3.0 mmol reactants/(g cat min). Reaction products included carbon dioxide, water and hydrocarbons with methanol conversion (through which hydrocarbons are formed) being complete. The catalyst with the least content of zinc gave the highest yields of liquid hydrocarbons (up to 74% of total hydrocarbons). Different crystalline phases (ZnO, ZnCr 2 O 4 and Cr 2 O 3 ) were found in the methanol synthesis component as a function of Zn/Cr ratio. The low Zn/Cr catalyst was characterized by X-ray diffraction, differential thermal analysis, nitrogen adsorption, temperature-programmed reduction, Infrared and X-ray photoelectron spectroscopy. The only phases observed in this catalyst were ZnCr 2 O 4 and Cr 2 O 3 . Calcination temperature had an influence in both physical and chemical catalyst properties. After calcination, Cr VI and Cr III species could be seen on the catalyst surface, but only Cr III species were observed after reaction or reduction. The evidences gathered suggest that Cr 2 O 3 is mainly responsible for methanol synthesis, while ZnCr 2 O 4 contributes to increase the specific surface area of the catalyst and influences gas product distributions. Compound catalysts with the mixed oxide (Zn Cr) as the methanol synthesis component showed to be more active than those with the individual (Cr or Zn) oxides.

Conversion of methylcyclopentane on rare earth exchanged Y zeolite FCC catalysts

Methylcyclopentane was reacted under low conversion conditions on various plant equilibrated and laboratory steam dealuminated commercial, rare earth exchanged, Y zeolite FCC catalysts at reaction temperatures of 450 to 510°C. Reaction products included mainly C5− compounds as well as methylcyclopentene, saturated open chain C6 isomers, C6 alkenes, C5 to C8 cyclic, and aromatic compounds. The reaction is sensitive to catalyst properties, as well as a good probe to evaluate various reactions typical of FCC, like cracking, isomerization and hydrogen transfer, both total catalyst acidity and zeolite unit cell size being necessary to ascertain catalyst performance. The same trends were observed on all the samples. The extension of the reactions following single active site mechanisms (cracking and isomerization) correlated with total catalyst acidity. Reactions obeying mechanisms that demand paired active sites (hydrogen transfer) can be accounted for more properly on a zeolite unit cell size basis. Hydrogen transfer decreases significantly at unit cell sizes lower than 24.30A. Lower temperatures favored both isomerization and hydrogen transfer against cracking. The reaction could be used as a test to provide complementary information for commercial catalyst evaluation procedures.

Influence of different rare earth ions on hydrogen transfer over Y zeolite

A base NaY zeolite was exchanged to similar extension for various rare earth elements (La, Nd, Sm, Gd and Dy), and the resulting catalysts were evaluated with reference to hydrogen transfer properties by means of the conversion of cyclohexene at 300°C in a fluidized bed batch reactor. An index was defined using the corresponding kinetic constants of a simple lumped model to show that the relative importance of the hydrogen transfer reactions increased linearly as a function of both Bronsted acidity of the catalysts and ionic radius of the rare earth element considered. The differences observed in the effect of the various rare earth elements on hydrogen transfer were moderate, but they suggested that a certain degree of catalytic control can be exerted on these reactions through the selection of the rare earth elements to be loaded into commercial catalysts.

Modelling methanol conversion to hydrocarbons: revision and testing of a simple kinetic model

Abstract A simple lumped kinetic model for methanol conversion to hydrocarbons on a ZSM-5 catalyst over the 302–370°C temperature range is revised and tested, provingthe model to be satisfactory at different conversion levels and catalyst deactivation degrees.

Modelling methanol conversion to hydrocarbons: Alternative kinetic models

Abstract Three different lumped Kinetic models for methanol conversion to hydrocarbons on a ZSM-5 catalyst over the 302–370 °C temperature range were develo

Conversion of pine sawdust bio-oil (raw and thermally processed) over equilibrium FCC catalysts

A raw bio-oil from pine sawdust, the liquid product from its thermal conditioning and a synthetic bio-oil composed by eight model compounds representing the main chemical groups in bio-oils, were converted thermally and over a commercial equilibrium FCC catalyst. The experiments were performed in a fixed bed reactor at 500 °C. The highest hydrocarbon yield (53.5 wt.%) was obtained with the conditioned liquid. The coke yields were significant in all the cases, from 9 to 14 wt.%. The synthetic bio-oil produced lesser hydrocarbons and more oxygenated compounds and coke than the authentic feedstocks from biomass. The previous thermal treatment of the raw bio-oil had the positive effects of increasing 25% the yield of hydrocarbons, decreasing 55% the yield of oxygenated compounds and decreasing 20% the yield of coke, particularly the more condensed coke.

Operation of FCC with mixtures of regenerated and deactivated catalyst

Abstract The operation of FCC with mixtures of coked and regenerated catalyst was studied with a riser simulator reactor on two equilibrium catalysts at 550°C. The coked catalysts maintain an activity level that enables them to be used in the mixtures. The catalytic performances of the regenerated catalysts were used as references against which the behaviors of 25:75 and 50:50 (coked:regenerated) mixtures were compared. It was observed that overall catoil has to be increased to maintain conversion. While the yields of gases, gasoline and LCO showed to be independent of the operative mode, changes were observed in the selectivity to light olefins C4–C6 that are mainly due to changes in the yields of the isoparaffins in the groups. In turn, these changes could be the consequence of the resulting density of paired acid sites in the zeolite components on hydrogen transfer reactions, due to the contributions by the coked and regenerated portions of catalysts. Coke yields in mixtures of coked and regenerated catalysts are not higher, which would allow increasing catalyst circulation without impacting on heat balance. The particularities of this new operation of FCC are very dependent on catalyst properties.