Dissertation/Thesis Abstract

Determination of Thermodynamic Characterizations of Semi-Clathrates Formed in TBAC-H2O Binary and TBAC-NaCl-H2O Ternary Electrolyte Mixture Systems
by Siddiq, Miad Ali, Ph.D., University of the Sciences in Philadelphia, 2019, 350; 22622129
Abstract (Summary)

Tetra-n-butyl ammonium chloride (TBAC) is known to form semi-clathrate cages when dissolved in water. Melting points determined using Differential Scanning Calorimetry (DSC) were used to create a phase diagram for the binary TBAC-H2O semi-clathrate system from 0 to 8 molal TBAC at atmospheric pressure. Further, NaCl was added to this binary system to create ternary solutions of various ionic strength fractions of TBAC (YTBAC). The results of DSC scans were used to create a phase diagram for the TBAC-NaCl-H2O system.

The thermodynamic properties, including osmotic and activity coefficients and free energies, enthalpies and entropies, of the non-ideal portion of binary systems of NaCl-H2O and TBAC-H2O at temperatures ranging from 20 to 45 °C were determined. These were determined by measuring water activity (aw). The concentration dependence of the osmotic and activity coefficients of TBAC-H2O system are found to exhibit maxima around 2 molal TBAC due to semi-clathrate formation at lower temperatures. However, the maxima are then found to gradually disappear with increasing temperature. The free energy, enthalpy and entropy of non-ideal portion of both systems were calculated and broken down due to solvent and solute to find the significant contribution of each component.

A similar study using the same methods was performed for the ternary TBAC-NaCl-H2O system as a function of concentration at temperatures ranging from 20 to 45 °C. A new methodology developed by Wigent allowed for the fitted values of the contribution of the osmotic coefficients due to the ternary components of the solution (ΦTernary) as a function of TBAC concentration at various concentrations of NaCl for the ternary system to determine interaction parameters (BMNX). In the new methodology, these interaction parameters can provide a precise discerption for the interactions that are occurring at various temperatures in the mixed TBAC-NaCl-H2O system that are not occurring within either of the binary solutions more than other models. These parameters were used to calculate the excess free energies of mixing due to the total solution, and those due to the water, TBAC and NaCl components as a function of TBAC concentration and various ionic strength fractions of TBAC. Using this new methodology with proper fitting techniques suggested that only interaction parameters (BMNX) with a net ionic charge of either zero or +1 can be used to fit the concentration dependence of the osmotic coefficients for the TBAC-NaCl-H2O system at the temperatures studied. Further, the excess free energy, enthalpy and entropy of mixing were determined at 2 molal total ionic strength and at 0.25, 0.5 and 0.75 ionic strength fraction of TBAC.

Indexing (document details)
Advisor: Wigent, Rodney J.
Commitee: Moore, Preston, Liu, Zhiwei, Neau, Steven, Sidorenko, Alexander
School: University of the Sciences in Philadelphia
Department: Chemistry
School Location: United States -- Pennsylvania
Source: DAI-B 81/4(E), Dissertation Abstracts International
Subjects: Physical chemistry, Chemistry
Keywords: Electrolytes mixtures, Excess free energy of mixing, Ionic interaction parameters, Semi-clathrates, TBAC, Thermodynamic properties
Publication Number: 22622129
ISBN: 9781687922687
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