Gabriela de la Puente

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.

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.

Influence of dealumination on the micropore adsorption in FCC catalysts

The adsorption of nitrogen and argon on laboratory steam dealuminated and equilibrium commercial FCC catalysts (Y zeolite plus matrix) of various types, covering a wide range of catalyst properties, was studied. Different approaches were used to estimate micropore volumes. Micropore size distributions were assessed based on the area-averaged cylindrical micropore model. With both nitrogen and argon adsorption isotherms, it was possible to locate the peak indicating the pore size in the fresh catalysts at the expected value of 0.74 nm if proper values for the physical parameters in the model were adopted. On the dealuminated samples, nitrogen and argon yielded significantly different results. Ar-based micropore size distributions suggested that the physical parameters involved in the model change with the variations in the chemical composition accompanying dealumination. N2-based pore size distributions are more sensitive to variations in the overall adsorption energy due to the growing influence of specific contributions (quadrupolar interactions). The magnitude of the minimum of potential energy in the nitrogen adsorption process decreases with dealumination up to a stable value for Si/Al ratios over about 8.

Valorization of Polyolefin/LCO Blend over HZSM-5 Zeolites

The cracking of low density polyethylene (PE) and of polypropylene (PP) dissolved in LCO (light cycle oil, product of a commercial FCC unit) is studied in the 450-550 ºC range, by using a reactor simulating a FCC riser. The reaction was carried out on catalysts prepared based on HZSM-5 zeolites with different Si/Al ratio The results are explained by the shape selectivity of the HZSM-5 zeolite and by the total acidity, which decreases as the Si/Al ratio of the zeolite is increased. A feed with polyolefin content higher than 5 wt% limits the conversion of LCO. The cracking on HZSM-5 zeolite catalysts of PE/LCO and PP/LCO blends produces a yield of C5-C12 fraction, which is highly aromatic and with a high content of styrene, and a low yield of C1 and C2 gases and of coke. A feed made up of polyolefins and LCO contributes to increasing the yield of light olefins, of which the concentration of ethylene increases with temperature. When compared to the coke selectivity of LCO cracking, a feed with PP contributes to increasing it, whereas PE decreases it.

Adsorption of Thiophenic Compounds in the Gasoline Boiling Range over FCC Catalysts under Process Conditions

Experiments on commercial FCC equilibrium catalysts with different hydrogen transfer properties and content of Ni and V contaminant metals were performed in a CREC Riser Simulator reactor to study the behavior of thiophenic compounds in the gasoline boiling range. Thiophene and alkylthiophenes were used as test reactants dissolved in aromatic and paraffinic solvents in usual concentrations of the process, from about 150 to 400 ppm of each compound. The experiments were performed under conditions similar to those of the industrial operation (510 º C, contact time 5 to 20 s). The reaction effluents were analyzed by on-line gas chromatography using two detectors simultaneously: FID (hydrocarbons) and PFPD (sulfur). The results showed that a higher hydrogen transfer capacity in a catalyst favors the decrease of the concentration of sulfur compounds in gasoline by adsorption and / or coke formation. These results were more pronounced as the molecular weight of the alkylthiophene increased. Reductions in total sulfur concentration in the gas phase as high as 65 % were observed. Among contaminant metals, Ni seemed to have an important contribution to this effect.