Reactions of Hydrazines, Reactions of the MMH Radical Cation, and Statistical Analysis of a Two-Dimensional Gas Chromatography Method as Compared to the ASTM Method D2425-19 for the Analysis of Aviation Fuels

Hypergolic propellants contain a fuel and an oxidizer that ignite on contact without the need for an external ignition source. Hydrazines are often used as the fuel, despite health and environmental safely concerns. Monomethylhydrazine (MMH) is a commonly used fuel in conjunction with dinitrogen tetroxide as the oxidizer for in-space maneuvering, although the mechanisms for the reactions of these two compounds are not fully understood. Based on the spontaneous generation of product ions in liquid phase experiments, quantum chemical calculations using the SMD model of implicit solvation were used to probe proposed reaction mechanisms. The reactions of hydrazine and MMH with the nitrosonium cation and the nitronium cation, which included the formation of the corresponding fuel radical cation, were explored. The reactions of hydrazines with the nitronium cation in model solvents were found to be highly exergonic, by as much as 70 kcal mol^-1. Further reactions of the MMH radical cation were also explored, including the formation of tetrazanes. Developing a complete mechanism to explain the formation of the most abundant product ions can further the understanding of hypergolicity and aid in the development of safer fuels.

The ASTM D2425 method was originally developed in 1965 and updated in 2019 for analyzing aviation fuels. However, a method using two dimensional gas chromatography coupled to a flame ionization detector (GCxGC/FID) was previously developed at Purdue University for the analysis of aviation fuels, including those derived from traditional sources and those derived from sustainable feedstocks. The established ASTM D2425 method was compared to the GCxGC/FID method for the analysis of Jet A-1, a sustainable aviation fuel, and a model compound mixture. The peak areas of eleven compound classes were compared across the three different samples by using a Pearson coefficient to determine skewness, an Anderson-Darling test for normality, Levene’s test and F-test for equal variances (depending on the normality of the data), and a 2-sample t-test. The results of these statistical analyses were somewhat vague and further studies should be done to fully compare the ASTM D2425 method with the GCxGC/FID method.