The adsorption of tri-n-butylphosphate at the n-dodecane–water interface

The adsorption of tri-n-butylphosphate (TBP) from n-dodecane to the n-dodecane–water interface has been studied as a function of TBP mole fraction up to 2.7 × 10−4 in the n-dodecane, and as a function of temperature from 293.15 K to 308.15 K. Free energies of adsorption were calculated from the results at low TBP mole fractions, where the surface pressures were linear with mole fraction. They were in the range −36.1 to −35.6 kJ/mol. The enthalpy of adsorption, determined from the variation of the free energies of adsorption with temperature, was −45.4 kJ/mol.Several equations of state based on two-dimensional gas laws were applied to the results. The Schofield–Rideal equation described the results adequately but the simpler Volmer equation was inadequate especially at lower temperatures. Deviations from the Volmer equation were in the direction of higher surface pressure. A simple version of the two-dimensional solution model equation of state was not helpful.

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The adsorption of lower trialkylphosphates at the dodecane – water interface

Canadian Journal of Chemistry ◽

10.1139/v80-446 ◽

1980 ◽

Vol 58 (24) ◽

pp. 2789-2795 ◽

Cited By ~ 6

Author(s):

Norman H. Sagert ◽

Woon Lee

Keyword(s):

Equation Of State ◽

Chain Length ◽

Water Interface ◽

Two Dimensional ◽

Free Energies ◽

Dimensional Solution ◽

Interfacial Tensions ◽

Enthalpy Of Adsorption ◽

Solution Models ◽

Methylene Group

The adsorption of tripropylphosphate, triethylphosphate, and trimethylphosphate at the dodecane–water interface has been studied at temperatures from 293 to 313 K. Standard free energies of adsorption were obtained from the lowering of interfacial tensions in the low (< 10−4) solute mole fraction region. Standard enthalpies and entropies of adsorption were then obtained from the temperature variation of the standard free energies of adsorption.Standard free energies of adsorption from dodecane showed little variation with solute chain length, with the exception of trimethylphosphate. On the other hand, free energies of adsorption from water decreased by 3.45 kJ/mol for each methylene group added, again with the exception of trimethylphosphate. Enthalpies of adsorption increased linearly with increasing solute chain length for adsorption from either phase. For each methylene group added, the enthalpy of adsorption from dodecane increased by 2.9 kJ/mol, while that from water increased by 2.4 kJ/mol.Results for tripropylphosphate adsorption and for triethylphosphate adsorption at higher temperatures could be adequately described by the Schofield–Rideal equation of state, but not by simple two-dimensional solution models. Results for trimethylphosphate adsorption and for triethylphosphate adsorption at lower temperatures could not be fitted adequately by either type of equation of state.

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Adsorption of Polar Organic Molecules at Oil/Water and Air/Water Interfaces

Canadian Journal of Chemistry ◽

10.1139/v75-129 ◽

1975 ◽

Vol 53 (6) ◽

pp. 916-925 ◽

Cited By ~ 13

Author(s):

Robert Aveyard ◽

John Chapman

Keyword(s):

Dicarboxylic Acid ◽

Water Surface ◽

Equations Of State ◽

Good Description ◽

Dicarboxylic Acids ◽

Solution Model ◽

Two Dimensional ◽

Free Energies ◽

Dimensional Solution ◽

Oil Water

A study has been made of the adsorption of several esters of dicarboxylic acids both at the alkane/water and the air/water interface. The adsorption of n-butanol and n-heptanol at the air/water surface has also been investigated. The surface pressure (π) – surface area (A) isotherms are compared for the various films, and standard free energies of adsorption have been determined.Attempts have been made to fit the π, A isotherms using surface equations of state based on the models of both a two-dimensional gas and a two-dimensional solution. The solution model has proved reasonably successful for fairly dilute films at the air/water surface. At higher coverages, an equation derived by Smith for liquid expanded monolayers gives a moderately good description of films of heptanol on water. A simple application of the solution model to adsorbed monolayers at the liquid/liquid interface met with little success. It is found however that two-dimensional gas equations describe such systems surprisingly well for fairly low surface concentrations.As part of the study, the activity coefficients of methyl dodecanoate, and the diethyl esters of pentan-1,5-dicarboxylic acid and decan-1,10-dicarboxylic acid, all in dilute solution in n-octane at 30 °C, have been determined.

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The adsorption of tri-N-butylphosphate at the benzene–water interface

Canadian Journal of Chemistry ◽

10.1139/v82-183 ◽

1982 ◽

Vol 60 (10) ◽

pp. 1244-1249 ◽

Cited By ~ 6

Author(s):

Norman H. Sagert ◽

Woon Lee ◽

Michael J. Quinn

Keyword(s):

Gas Chromatography ◽

Equations Of State ◽

Adsorbed Layer ◽

Distribution Coefficients ◽

Vapor Pressure Osmometry ◽

Water Interface ◽

Free Energies ◽

Drop Volume ◽

Enthalpy Of Adsorption ◽

Strong Adsorption

Adsorption of tri-n-butylphosphate (TBP) at the benzene–water interface was studied as a function of the TBP mole fraction in benzene up to 0.018 and at temperatures from 9 to 29 °C. The extent of adsorption was calculated from interfacial tension data obtained by the drop-volume technique. Standard free energies of adsorption from benzene ranged from −20.9 kJ/mol at 9 °C to −22.5 kJ/mol at 29 °C, giving a standard enthalpy of adsorption of +2.5 kJ/mol. Thus the strong adsorption occurs because of entropy changes. Distribution coefficients for the partition of TBP between benzene and water were measured by gas chromatography, and standard free energies of adsorption from water were derived. They ranged from −44.8 kJ/mol at 9 °C to −51.1 kJ/mol at 29 °C, with standard enthalpies of adsorption ranging from 74 to 15 kJ/mol over the same temperature range.Results at higher mole fractions were fitted to various equations of state, after using vapor pressure osmometry (at 37 °C) to determine that activity corrections were small. The Schofield–Rideal equation described the results adequately, with A0 close to 1.0 nm2 and/close to 1.0 at lower temperatures. These values imply that lateral repulsion between TBP molecules in the adsorbed layer is minimal.

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