Reynaldo C. Castells

Gas chromatographic study of the adsorption of insoluble vapors on water

Abstract The use of gas chromatography for the study of the adsorption of insoluble vapors on water surfaces is described. The method involves using water coated on a porous support as packing material and presaturation of the carrier gas with water to prevent bleeding from the column. For saturated hydrocarbons it is found that the mechanism of retention is adsorption at the gas-liquid interface, whereas for aromatic hydrocarbons a mixed mechanism of adsorption and solution occurs. Contrary to results in recent literature, the differential heats of adsorption for the insoluble vapors are found to be 1 to 1.5 kcal/mol smaller than the heats of liquefaction. Possible causes for the discrepancy are examined in detail. The question of bulk water in the pores is explored via the partition coefficients of aromatic hydrocarbons. The solubilities and heats of solution are found to be close to the literature values, indicating the possibility of bulk water under the conditions of these experiments. A discussion of the advantages and disadvantages of the gas chromatographic method relative to static methods is presented.

Possibility and consequences of using different concentration scales in the study of solution thermodynamics by gas-liquid chromatography

Abstract Several concentration scales may be used to express the solute concentration, both in the condensed and in the vapour phase. Each choice of concentration units gives rise to a set of thermodynamic properties: distribution coefficient, activity coefficient, free energy, enthalpy and entropy of solution. The definitions and relationships between the different forms of activity coefficient are first reviewed. The standard states to which the thermodynamic properties obtainable from chromatographic data are referred are then unambiguously identified. Finally, some consequences on the correlation of the retention behaviour of members of homologous series are discussed.

Solution and adsorption thermodynamics in propylene glycol by gas chromatography : A comparative study with other polyhydroxylated solvents

Abstract The retention volumes of eighteen hydrocarbons representative of different families and of acetone, diisopropyl ether and three chloromethanes were measured at four temperatures within the range 12–22°C on columns containing five different percentages of propylene glycol (PG) as the stationary phase. The relative magnitudes of the adsorption on PG, on formamide and on four glycols are compared and discussed in terms of the thermodynamic properties of the bulk mixtures with hydrocarbons, From this comparison, PG is found to possess the weakest adsorption effects, and some of the solutes studied exhibit no adsorption within experimental error. The thermodynamic properties of solution in PG are calculated and compared to those in formamide and in the glycols. Recent extensions of the regular solutions model are inefficient for calculating infinite dilution activity coefficients, but yield a very acceptable correlation between heats of solution and solute solubility parameters.

Thermodynamics of the molecular association of tri-n-octylphosphine oxide and haloalkanes using gas-liquid chromatography

The gas chromatographic retention behavior of nineteen halogenated hydrocarbons and of seven saturated hydrocarbons was measured at four temperatures from 55 to 65°C in tri-n-octylphosphine oxide (TOPO) and at 60°C in squalane (SQ). Thermodynamic functions of solution in TOPO were computed from these data. Strongly negative deviations from the ideal behavior were interpreted in terms of halogenated hydrocarbon+TOPO association, and the equilibrium constants were calculated by reference to the inert solvent SQ. The larger equilibrium constants correspond to solutes with a definite proton donor capability. The substitution of Cl for Br, however, produces an increase in the association constants suggesting the existence of other interaction mechanisms. Complexing of halogenated hydrocarbons with TOPO is markedly greater than with ethers, thioethers or tertiary amines.

Determination of activity coefficients in gas chromatographic systems in the presence of mixed retention mechanisms: alkanols (C3–C5) at infinite dilution in squalane and in n-octadecane

Symmetrical peaks, with sample size independent retention times, are obtained when alkanols are chromatographed in columns packed with alkane stationary phases coated on a deactivated solid obtained by coating Chromosorb W with Carbowax 20M, followed by thermal treatment in inert atmosphere and exhaustive extraction with methanol. Adsorption on the solid support/alkane interface is precluded by this deactivation method, but adsorption on the gas/alkane interface persists as a non-negligible contribution to solute retention. Retention volumes of ten alkanols with three to five carbon atoms were measured at five temperatures within the 30–50°C interval in columns containing between 2 and 12 wt.% of squalane or of n-octadecane on the deactivated support. Partition and adsorption coefficients were obtained from the dependence of retention volumes on wt.% of stationary phase. Alkanols infinite dilution activity coefficients were calculated from partition coefficients; it is demonstrated that important errors are introduced on neglecting adsorption contributions. An indirect proof of consistency between calculated adsorption and partition parameters is given by comparing results obtained with both stationary phases. It is furthermore demonstrated that non-combinatorial contributions to the activity coefficients are independent of the alkane solvent.

Infinite dilution activity coefficents of hydrocarbons in tetra-n-alkyltin solvents between 40 and 60°C measured by gas-liquid chromatography

Infinite dilution activity coefficients for twenty-three hydrocarbons in tetra-n-amyltin (TAT) and in tetra-n-lauryltin (TLT) at several temperatures between 40 and 60°C were measured by gas liquid chromatography. The results, together with those obtained in an earlier paper in tetra-n-octyltin (TOT), are compared and discussed in terms of the equation of state theory of Flory and of the lattice fluid theory of Sanchez and Lacombe.

Activity coefficients of hydrocarbons at infinite dilution in di-n-octyltin dichloride. Comparison with results obtained in other alkyltin solvents

The gas chromatographic method was employed to measure the infinite dilution activity coefficients of twenty-eight hydrocarbons of different types in di-n-octyltin dichloride between 50 and 80°C, and of seven branched alkanes in tri-n-octyltin chloride between 40 and 60°C. A comparison is made between the results obtained for all the solutes in both solvents and in tetra-n-octyltin.