Susana Curbelo

Modelling of Ethane/Ethylene Separation Using Microporous

Grand Canonical Monte Carlo simulations of the adsorption of a mixture of ethane and ethylene on microporous slit graphite pores are reported. A two-centre Lennard-Jones with point quadrupole potential and a Steele potential with embedded quadrupoles for the carbon were used to model the fluids and solids, respectively. Under conditions of moderate temperature (260–400 K) and pressure (0.1–1.0 MPa), ethane was preferentially adsorbed over ethylene for the pore widths studied. For micropores less than 2 nm wide, the selectivity towards ethane varied markedly with small changes in the pore structure, whilst for the mesopores with widths greater than 2 nm the selectivity was remarkably insensitive towards the pore size. The results provide qualitative guidelines for the synthesis and design of carbons for lower olefin/paraffin separations.

Selective hydrogenation of 1,3-butadiene in presence of 1-butene under liquid phase conditions with NiPd/Al2O3 catalysts

The catalytic performance of Al2O3-supported monometallic and bimetallic catalysts in selective hydrogenation of 1,3-butadiene in the presence of 1-butene under liquid phase conditions was studied. Bimetallic catalysts were prepared by the coimpregnation method with the required amounts of the precursors salts [Ni(NO3)2·6H2O and Pd(NH3)4Cl2·H2O] over pellet-form γ-Al2O3 with a constant content of Pd (0.5 wt%) and varying Ni/Pd atomic ratio (0.25, 0.5, 0.75, and 1) obtaining egg-shell profiles of the active components. The catalysts were characterized by X-ray diffraction, temperature-programmed techniques, such as reduction in hydrogen and desorption of ammonia, N2 physisorption, and transmission electron microscopy. The catalytic test showed that the 1,3-butadiene was selectively hydrogenated when bimetallic catalysts were used. The addition of Ni to the Pd-based catalysts suppressed n-butane formation and increased recovery of 1-butene at medium conversion. Therefore, it was observed an improved catalytic performance of the bimetallic catalysts being highest in the case of the 1NiPd/Al2O3.

Selective hydrogenation of 1,3-butadiene. Effect of the operating conditions

A three-phase fixed-bed reactor for selective hydrogenation of butadiene in liquid phase with toluene as solvent is modeled using published kinetics. Thermodynamic and transport properties are estimated from models and correlations available in the literature. The model incorporates momentum and energy balances and mass transfer resistances. The results show that use of toluene increases the yield of cis-butane and trans-butane isomers by comparison with a previous study by Bressa et al. where a solvent was not included. The effects of temperature, pressure, hydrogen/butadiene ratio and toluene/feed ratio on the reactor performance are studied. A temperature rise of 37.8 K and a pressure drop of 100 kPa are predicted for a reactor 1 m in length and 0.58 m in diameter using a typical feed composition. Greater reactor lengths result in complete vaporization of the reacting mixture. This vaporization effect can be controlled by increasing the inlet pressure and toluene/feed ratio, and by decreasing the inlet temperature and hydrogen/butadiene ratio. The effect of inlet hydrogen/butadiene ratio is found to be negligible, whereas a rise in inlet temperature rise has a significant effect on the conversions and yields for the same reactor length. Finally, it was found that the yield of 1-butene increases with increasing inlet solvent/feed ratio and pressure.

Promoting effect of ceria on the performance of NiPd/CeO2–Al2O3 catalysts for the selective hydrogenation of 1,3-butadiene in the presence of 1-butene

The removal of traces of highly unsaturated compounds, such as 1,3-butadiene, from olefin feedstocks via selective hydrogenation is of particular importance because the oligomerization of these impurities produces deactivation and an increased pressure drop across the catalytic beds used in the polymerization processes. The present work focuses on the selective hydrogenation of 1,3-butadiene in the presence of 1-butene using (xCeO2-)Al2O3-supported NiPd catalysts (x = 0, 1, 2, and 3 wt% CeO2) in both liquid and gas conditions. The samples were characterized by XRD, N2 physisorption, Zeta potential, H2-TPR, NH3-TPD, HRTEM and STEM-HAADF. Modifying the catalysts with CeO2 resulted in an increase of 1,3-butadiene conversion, an enhancement of 1-butene selectivity and a decrease of butane production under liquid phase conditions. In contrast, in the gas phase both the Ce-modified and unmodified catalysts behaved similarly: while the fresh catalysts showed similar reactivity to that found in liquid phase conditions, the reacted and thermally pretreated catalysts showed increased reactivity, leading to full hydrogenation up to butane. The improvements observed under liquid phase conditions may be related to modification of the acid strength with increasing CeO2 loading, which would increase the adsorption of 1,3-butadiene and diminish the further hydrogenation of 1-butene. Optimal activity and selectivity were observed for the catalyst with an Ni/Pd atomic ratio of 1, and loadings of 0.5 wt% Pd and 3.0 wt% CeO2.