The stability study of myristyl dimethyl amine oxide as an amphoteric surfactant in strong oxidant media containing 5 % m/m sodium hypochlorite through measurement of decomposing rate using high performance liquid chromatography and two phase titration
Myristyl dimethyl amine oxide is a surface-active agent (surfactant) that has been used in recent years widely in detergent industry as the foaming agent and a viscousing agent. Although this type of surfactants are very stable, however, in some specific chemical media such as strong acid and alkaline cleaners, oxidant media containing sodium hypochlorite may not have sufficient stability. In this study, we will study the effective variables on the decomposition of mirystyl dimethyl amine oxide surfactant with trading name of "Ammonyx" and obtain the rate constant and reaction order of decomposition reaction of the surfactant in specific chemical media for each of these variables and finally the rate law of decomposition. The results of this study show that the decomposition rate of the Ammonyx surfactant to the concentration of NaOH is first-order and the rate constants at three temperatures to 4, 20 and 47 degrees of Celsius are 1.8655×10-4, 2.7548×10-4 and 4.3294×10-4 hr-1 respectively. The Ammonyx surfactants decomposition rate relative to the NaClO concentration is first-order and the rate constant in the three mentioned temperatures is 3.4682×10-4, 4.9251×10-4 and 7.2582×10-4 hr-1 respectively.
Finally, the decomposition rate of Ammonyx relative to surfactant concentration (like other two variables) is first-order and the rate constant at above temperatures equal to 1.6892×10-4, 3.2205×10-4 and 5.8045×10-4 hr-1 respectively.
The activation energy for the decomposition of Ammonyx in collision with NaOH, NaClO and the surfactant molecules equals to 14.3, 12.55, 20.85 kJ mol and Arrhenius constants for these molecules equals to 0.0975 hr-1, 0.0823 hr-1 and 0.6542 hr-1 respectively.
In addition, for comparing the accuracy of the two-phase titration results, high performance liquid chromatography HPLC method has also been used. For this purpose, surfactant concentrations in some samples under study were also measured by using analytical HPLC system. The results showed that two-phase titration data have good agreement with HPLC data but chromatography has less accuracy and precision from two phase titration method.
Keywords: Myristyl dimethyl amine oxide, Two-phase titration, Reaction rate, Reaction order, surfactant analysis, Bleaching agents