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Sofia Calero

Publications and source records attributed to Sofia Calero.

4 recordsLinked to original sources
PubMed2006

Evaluation of a new force field for describing the adsorption behavior of alkanes in various pure silica zeolites.

The recently proposed united atom force field by Dubbeldam et al. (Phys. Rev. Lett. 2004, 93, 088302) for the adsorption of alkanes in MFI-type zeolites was extended to other zeolites in this work. Its applicability to FER-type zeolites was evaluated in detail, for which the Henry coefficients, the isosteric heat of adsorption, the adsorption isotherms, as well as the locations of alkanes in the FER-type zeolites were computed and compared to experimental values. The results show that the new force field works well for FER zeolites. Furthermore, its applicability to MWW-, MTW-, CFI-, LTA-, and STF-type zeolites was investigated, and we found that the experimental isotherms could be accurately predicted except for STF-type zeolites. This work shows that the new united atom force field proposed by Dubbeldam et al. is applicable to most pure silica zeolites.

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PubMed2005

A new insight on the structural changes of linear quadrupole liquids.

Molecular-dynamics simulations for linear quadrupole liquids are presented. The study is carried out for two different molecular lengths at constant density and a number of temperatures and quadrupole moments. All the simulated thermodynamic states correspond to the condensed phases and some of them show typical features of a solid structure. Furthermore, a change on the preferred intermolecular orientation in the liquid phase is observed from a shifted parallel molecular arrangement to a perpendicular orientation as the quadrupole raises. This change depends on the quadrupole moment as well as on the molecular length and is put in relation with the solid structure of different "diatomic" molecules such as nitrogen, ethane, and acetylene. The appearance of a plastic solid phase at low quadrupole moment and density is also justified. A thoroughly discussion about the availability of classical perturbation theories for this kind of systems is presented.

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PubMed2002

Entropy effects during sorption of alkanes in zeolites.

Recent developments in Configurational-Bias Monte Carlo (CBMC) techniques allow the accurate calculation of the sorption isotherms for alkanes, and their mixtures, in various zeolites. The CBMC simulations give new insights into subtle entropy effects affecting mixture adsorption. Three types of entropy effects can be distinguished. (1) Size entropy effects favour the component with the smaller number of C atoms because the smaller molecule finds it easier to fill in the 'gaps' within the zeolite matrix at high molecular loadings. (2) Configurational entropy effects come into play for mixtures of alkanes that differ in the degree of branching. For a mixture of linear and branched alkanes with the same number of C atoms, configurational entropy effects favour the linear isomer because such molecules 'pack' more efficiently within, say, the intersecting channel topology of MFI zeolite. (3) Length entropy effects comes into force for sorption of linear and branched alkanes within the cylindrical channels of say AFI and MOR zeolites; here the double branched alkane has the shortest length and can be packed more efficiently within the channels. We demonstrate that CBMC simulations allow the efficient screening of zeolite structures for a given separation duty and aid the development of novel separation processes exploiting entropy effects.

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