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

Abstract

Tetra-n-butyl ammonium chloride (TBAC) is an organic salt known to form semiclathrate complexes in the presence of water. Previous studies using differential scanning calorimetry have shown that the addition of either NaCl or KCl can affect these semiclathrate structures. In this work, the effect of adding LiCl to aqueous TBAC solutions on the melting points of these semiclathrate structures was determined and compared to the effects of adding either NaCl or KCl. Ternary TBAC–LiCl–H2O systems were created by adding LiCl to 1, 1.5, 2, 3, and 4 m TBAC–H2O solutions to give ionic strength fractions of TBAC (YTBAC) from 0.25 to 1. It was found that the melting points of TBAC–H2O semiclathrate were unaffected with the addition of LiCl as long as there were sufficient amounts of free, bulk water present to solvate the salt at concentrations less than 2 m TBAC where free, bulk water can exist. However, at lower ionic strength fractions of TBAC, when the system runs out of free, bulk water, LiCl was found to disrupt the TBAC–H2O semiclathrate structures. At concentrations above 2 m TBAC, the situation is more complex as there is no free, bulk water in the TBAC–H2O system. Adding LiCl disrupted the normal TBAC–H2O semiclathrate complex, forming new TBAC–LiCl–H2O semiclathrate structures at high ionic strength fraction of TBAC that were disrupted upon increasing the relative concentration of LiCl.