Effect of Adding Potassium Chloride on Tetra-n-butyl Ammonium Chloride Semiclathrate Thermal Stability at Atmospheric Pressure

Abstract

Tetra-n-butyl ammonium chloride (TBAC) is known to form semiclathrate complexes with water. In this work, the melting points and latent heats of fusion of these semiclathrate structures were determined using Differential Scanning Calorimetry (DSC). A phase diagram was created for binary TBAC-H2O from 0 to 7.775 molal TBAC at atmospheric pressure. Below 2 molal TBAC, the semiclathrate is in equilibrium with free, bulk water. At approximately 2 molal TBAC a congruent melting point at 286.96 K is observed in this phase diagram. Beyond this composition, there is no free, bulk water present, and there are multiple forms of the TBAC-H2O semiclathrate complexes with varying amounts of water. Ternary TBAC-KCl-H2O systems were created by adding KCl to 1, 1.5, 2, 3, and 4 molal TBAC solutions to give ionic strength fractions of TBAC (YTBAC) from 0.25 to 1. It was found that the melting points of the TBAC-H2O semiclathrate were unaffected as long as there was a sufficient amount of free, bulk water at concentrations less than 2 molal TBAC. However, at greater concentrations, adding KCl disrupted the normal TBAC-H2O semiclathrate complex, and KCl was incorporated into new, TBAC-KCl-H2O complexes that melted at higher temperatures than previously reported for similar TBAC-NaCl-H2O complexes.