Optimisation of the Fischer-Tropsch process using zeolites for tail gas separation.

This work is aimed at optimizing a Fischer-Tropsch Gas To Liquid (GTL) process by recycling compounds of the expelled gas mixture using zeolites for the separation. To that end, we have performed a computational study on four structures widely used in industry. A range of Si/Al ratios have been explored and the effects of their distribution assessed. The ability of the considered force fields and molecular models to reproduce experimental results has been widely proved in previously reported studies. Since this tail gas is formed by a five-component mixture, namely carbon dioxide, methane, carbon monoxide, nitrogen and hydrogen, molecular simulations present clear advantages over experiments. In addition, the viability of the Ideal Adsorption Solution Theory (IAST) has been evaluated to easily handle further separation steps. On the basis of the obtained results, we provide a separation scheme to perform sequentially the separation of CO2, CH4, CO, N2 and H2.

Influence of the displacement out of the center of mass and nonaxiality of the dipole on the thermodynamics of liquids composed of linear dipole molecules.

We present results for organic liquids modeled as linear rods with an embedded point dipole shifted from the geometrical center. Previously, we have obtained results for the vapor-liquid equilibrium (VLE) of similar systems with centered point dipoles. Our results included both models and applications to real systems. Results presented here are based on a previous work ( Phys. Rev. E 2003, 68, 021201) on the structural properties of these systems where relevant results about the appearance of dimers were found. Now, we have also performed systematic simulations on these systems to calculate the VLE of models with different aspect ratios, dipole shifts, and dipole strengths using the Gibbs ensemble Monte Carlo (GEMC) to calculate equilibrium densities and vapor pressure at each temperature. The applications considered here include some important substances such as 1-amines, acetonitrile, and 1-alcohols whose intermolecular parameters were fitted from our model simulations. Furthermore, we have used quantum chemistry calculations to obtain a reliable charge distribution, and we have applied our model to predict the vapor pressure of alpha,omega-diols where experimental results are rather scarce. Our results show a general improvement of the agreement between experiment and models compared to centered dipole models previously used. Results for amines are particularly remarkable.

N-2-(azol-1(2)-yl)ethyliminodiacetic acids: a novel series of Gd(III) chelators as T2 relaxation agents for magnetic resonance imaging.

The synthesis, physicochemical properties, and toxicological implications of a novel series of N-2-(azol-1(2)-yl)ethyliminodiacetic acids, useful as contrast agents for magnetic resonance imaging are reported. Compounds were prepared by alkylation of methyl iminodiacetate with N-2-bromoethylazoles and subsequent hydrolysis. Stability constants of the corresponding Gd(III) complexes and T1 and T2 relaxivities were determined and interpreted in terms of optimized geometries obtained by semiempirical PM3 calculations. Compounds show increased T2 relaxivity and decreased toxicity in vitro as compared to EDTA-Gd(III) complexes.