Célio L. Cavalcante

Evaluation of the main diffusion path in zeolites from ZLC desorption curves

A simple method of distinguishing between one-dimensional and three-dimensional diffusion in zeolite crystals is suggested based on the difference in the expressions obtained for the zerolength column (ZLC) desorption curve for “slab” and “spherical” diffusion models. The application of this approach is illustrated by experimental data for diffusion in erionite (threedimensional channel system) and offretite (one-dimensional channels).

Adsorption Equilibria of C8 Aromatic Liquid Mixtures on Y Zeolites Using Headspace Chromatography

Abstract Liquid phase adsorptive separations are found in several industrial applications such as the recovery of p‐xylene from its isomers. In this study, the headspace experimental technique was used to measure pure and multicomponent adsorption equilibria of liquid xylenes in Y zeolite. Data for pure‐component equilibrium were determined at temperatures between 80 and 120°C and correlated using the Extended Langmuir model. The parameters for pure components estimated from the correlated data showed good agreement with data reported in previous studies and relatively low deviations when compared to the experimental data dispersion. Using the pure‐component data, two models were tested for multicomponent (binary and quaternary) equilibrium correlation: Ideal Adsorbed Solution (IAS) model and Extended Langmuir Multicomponent model. The results from the IAS model did not conform well to the experimental results, indicating the existence of significant nonidealities in the system. The Extended Langmuir model predicted values generally in good agreement with the binary and quaternary experimental data measured using the Headspace technique.

Purification and Characterization of Microbial Hyaluronic Acid by Solvent Precipitation and Size-Exclusion Chromatography

Abstract Samples of hyaluronic acid (HA) produced by submerged fermentation using a synthetic culture medium were recovered, purified, fractioned, and characterized using solvent precipitation and size-exclusion chromatography (SEC). The samples showed a wide molar mass distribution in the range 103–107 Da, most of which had an average molar mass between 104 and 105 Da after purification by sequential precipitations. Fractions of HA with molar mass above 105 Da were purified by SEC in a semi-preparative scale with nearly no protein contamination. Characterization and fractionation of the HA was carried out by SEC in a analytical and semi-preparative scale using Shodex OHPak SB806M HQ and Superose 6 columns, respectively.

Sensitivity to guest–host force fields in adsorption equilibrium of cyclic hydrocarbons in one-dimensional molecular sieve

We have investigated the effect of different guest–host force fields (united atom, UA; all-atom, AA; and anisotropic united atom, AUA) on the adsorption of cyclic hydrocarbon molecules in AlPO4-5 molecular sieve. Grand canonical Monte Carlo (GCMC) simulations of benzene, xylene and cyclohexane adsorption and positioning are carried out. The results suggest that the force field choice affects considerably the positioning of benzene and cyclohexane molecules while xylenes presented a smaller sensibility. The force fields difference of sensibilities among cyclical molecules seems to be associated with the critical geometric condition identified by Yashonath and Santikary denominated levitation effect. In this condition, the net forces on the guest due to the host is at a minimum, the levitation ratio (γ) is close to unity and we have a weakly bound guest that can be easily moved from its balance position. Unlike xylene, that is only slightly affected by the choice of the force field, benzene and cyclohexane molecules in AlPO4-5 have such dimensions that result in levitation ratio (γ) close to unity. These results point out to the care that should be taken in the choice of the force field when the guest–host size ratio is near the value defined for the levitation effect.

Reclamation of Used Transformer Oil by Adsorption

This study presents an evaluation of the removal of degradation products from used transformer oil using a commercial activated clay in batch experiments, at temperatures between 60° and 100°C. Experimental data were correlated by means of Total Acid Number Analysis, ASTM D 3339. As qualitative measurements of the efficiency of the treatment, ASTM color methodology and infrared spectroscopy analysis were employed. Equilibrium isotherms showed a type I behavior and were correlated by both Langmuir and Freundlich equations. Pore diffusion coefficients were also obtained in the order of 10−12 m2/s and showed typical Arrhenius dependence with temperature, Infrared spectroscopy indicated that carbonyl groups present in the used oil were not present after treatment with the clay, thus proving this to be an efficient method for recovery and possible commercial reutilization of used lubricant oils.