Aurelio Vega

Effect of carbon nanofiber functionalization on the adsorption properties of volatile organic compounds.

The effect of the chemical activation, using HNO3, of a commercial carbon nanofiber (CNF) on its surface chemistry and adsorption properties is studied in this work. The adsorption of different alkanes (linear and cyclic), aromatic compounds and chlorohydrocarbons on both the parent and the oxidized CNF were compared. Temperature-programmed desorption results, in agreement with X-ray photoelectron spectroscopy experiments, reveal the existence of oxygen groups on the surface of the treated CNF. Capacity of adsorption was derived from the adsorption isotherms, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. Both the capacity and the strength of adsorption decrease after the oxidant treatment of the carbon nanofibers, although in the case of chlorinated compounds the specific component of the surface energy shows an important increase. For n-alkanes and cyclic compounds, it was demonstrated that the presence of oxygen surface groups does not affect their interaction, the morphology of the surface being the key parameter. The oxidation of the nanofiber leads to steric limitations of the adsorption. In the adsorption of aromatic compounds, these limitations are compensated by the nucleophilic interactions between the aromatic ring and surface oxygenated groups, leading to similar performances of both materials. The absence of nucleophilic groups in the chlorinated compounds hinders their adsorption on the activated nanofibers.

CORRELATION FOR THE ESTIMATION OF GAS-LIQUID DIFFUSIVITY

An empirical correlation for estimating diffusivities of gases in non-electrolytes at 25°C has been developed. The solute-solvent diffusivity has been correlated as a function of the solute and solvent molar volumes at their normal boiling point and the solvent viscosity. The temperature dependence is expressed by a second equation of the Arrhenius type. The proposed expression, in spite of its simplicity, predicts diffusivities with similar or better accuracy than the equations used for comparison. A nomograph based on the two proposed equations has been constructed.

Characterization of polyarylamide fibers by inverse gas chromatography

Two types of commercial polyaramide fibers have been characterized by inverse gas chromatography. Using the fibers as stationary phases, adsorption isotherms for nonane, decane and undecane were obtained. Specific surface areas and isosteric heats of adsorption were also obtained by this method. Experimental results have been discussed as a function of hydrocarbon--fiber interaction and fiber crystallinity.

Consequences of cavity size and chemical environment on the adsorption properties of isoreticular metal-organic frameworks: An inverse gas chromatography study

The role of the structure of three isoreticular metal-organic frameworks (IRMOFs) on their adsorption behavior has been studied in this work, selecting different kinds of volatile organic compounds (VOCs) as adsorbates (alkanes, alkenes, cycloalkanes, aromatics and chlorinated). For this purpose, three samples (IRMOF-1, IRMOF-8 and IRMOF-10) with cubic structure and without functionalities on the organic linkers were synthesized. Adsorption capacities at infinite dilution were derived from the adsorption isotherms, whereas thermodynamic properties have been determined from chromatographic retention volume. The capacity and the strength of adsorption were strongly influenced by the adsorbate size. This effect is especially relevant for n-alkanes adsorption, indicating the key role of the cavity size on this phenomenon, and hence the importance of the IRMOF structural properties. A different behavior has been observed for the polar compounds, where an enhancement on the specificity of the adsorption with the π-electron rich regions was observed. This fact suggests the specific interaction of these molecules with the organic linkers of the IRMOFs.

Programmed cooling control of a batch crystallizer

Abstract A dynamic model of the evolution of the temperature of a batch cooling crystallizer has been used for the development of a Generic Model Control (GMC) system: for the crystallizer. This servo-control system has been found experimentally to work adequately. The crystallizer has also been controlled with a conventional PI controller, and the process has been simulated with the model. Simulations are accurate enough to allow the model to be used for the design of control strategies for programmed cooling crystallizers. The methodology described can be adapted to the study of other systems or control algorithms.

Characterization of nanocarbons (nanotubes and nanofibers) by Inverse Gas Chromatography

The adsorption of different alkanes (linear and cyclic), aromatics and chlorohydrocarbons on non-microporous carbons-carbon nanotubes (CNTs) and carbon nanofibres (CNFs)- was studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. CNTs present the highest adsorption capacity. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene and chloroform) with the surfaces are mainly dispersive over all the carbons tested, being CNTs the material with the highest dispersive contribution. Adsorption parameters were correlated with morphological and chemical properties of the materials.

Activity Coefficients at Infinite Dilution of Organic Compounds in Acetonitrile and Methanol by Liquid Chromatography

Abstract Activity coefficients at infinite dilution of series of n-alkanes, n-alcohols, n-alkylbenzenes, cresols, α- and β-toluidine and γ -picoline in acetonitrile and methanol were determined at 25 °C by liquid-liquid chromatography. Apiezon L and Porapak Q were used as the stationary phases. For those components for which activity coefficients were available in the literature, there is reasonably good agreement with the data reported in this work, though in some cases the literature data were obtained by other techniques.

Activity coefficients at infinite dilution determined by gas-liquid chromatography. Organic solvents in Apiezon L

Abstract Activity coefficients at infinite dilution were determined by gas—liquid chromatography for a variety of solutes using Apiezon L as the solvent (liquid phase). Two temperature ranges (60–90 and 150–190°C) were used depending on the boiling points of the solutes. Solubility parameters were determined from retention data for Apiezon L at 90 and 150°C using regular solution theory and Flory-Huggins interaction parameters.

Determination of solubility parameters and thermodynamic properties in hydrocarbon-solvent systems by gas chromatography

Gas chromatography used to calculate the specific retention volume of several hydrocarbons in different chromatographic liquid phases (Squalane, Carbowax-400, Carbowax-1500, Carbowax-4000, Amine-220, Dinonyl phthalate, Tributyl phosphate and Trixylenyl phosphate). Some thermodynamic parameters, such as enthalpy of sorption and Flory-Huggins parameters relating the interaction between liquid phases and solutes, were also calculated from the determined retention volumes. Liquid phase solubility parameters of Squalane, Carbowax-400, Carbowax-1500 and Carbowax-4000 at 80 oC as well as the polar and apolar components were calculated too. A new model was proposed to correlate polar contribution to the solubility parameter of a liquid phase with the specific retention volume of a solute in this liquid phase.

An IGC Study of the Role of Washing Procedures on the Adsorption Properties of Activated Carbons

Inverse gas chromatography (IGC) was used to study the influence of different washing treatments (acid, basic and combined washings) on the adsorption properties of two different activated carbons (steam- and chemically-activated). Chemical and textural characterization was carried out by the use of nitrogen adsorption, ICP-MS and temperature programmed desorption methods. The adsorption capacity and the interaction strength (sub-divided into dispersive and specific components) were determined by IGC. Washing procedures (especially those involving acid washing) removed mineral ash almost completely from the carbon samples studied. The steam-activated carbon exhibited the best adsorptive behaviour. The removal of mineral ash enhanced the adsorption of the compounds studied, especially alkanes. Washing procedures also modified the chemical structures of the organic functionalities, but this did not appear to be relevant as far as the adsorption properties of these materials were concerned.