Degradation Kinetics and Solvent Effects of Various Long-Chain Quaternary Ammonium Salts

Surfactants such as quaternary ammonium salts (QAS) have been in increasing demand, for emerging new applications. Recent attempts at process intensification of their production, have disclosed the need for a better understanding of QAS thermal stability. This work aims to determine degradation kinetics of various QASs, and the associated solvent effects. Degradation kinetics of four methyl carbonate QASs were determined in various polar solvents in stainless steel batch autoclaves. 1 H NMR spectrometry was employed for online analysis of the reaction mixtures. The kinetic parameters were then used to compare the thermal stability of the four compounds in the polar solvents. Water showed not degradation, and methanol (MeOH) was the solvent that provided the second-best stability. Water-MeOH mixtures may provide an overall optimum. More, and longer long-chain substituents increased the degradation rate. Thermogravimetric Analysis was used to obtain the thermal stability in a solid- state, i.e. solventless environment. Isoconversional analysis showed that no reliable kinetic parameters could be determined. Nevertheless, the data did allow for a compar- ison of the thermal stability of 14 different QASs. Furthermore, the relative instability of the compounds in solid-state demonstrated the challenges of solventless QAS production.