Study on the antioxidant property of calixarene in high density hydrocarbon fuel JP-10

Since the 21st century, hypersonic flight technology has attracted much attention. When the aircraft is flying at a high Mach number, a large amount of aerodynamic heat is generated between the air and the aircraft due to friction, resulting in a rapid increase in the temperature of the aircraft subsystem, exceeding the range that the material can withstand, affecting the flight safety of the aircraft. In order to meet the thermal management needs, an integrated cooling approach combining heat transfer and combustion has been introduced. This method utilizes hydrocarbon fuels both as propellants and coolants to absorb the excess heat from the aircraft’s high-temperature components, thereby enhancing energy efficiency and managing the thermal conditions of high-speed aircraft. Fuels that satisfy this concept are called endothermic hydrocarbon fuels. However, these fuels are prone to oxidation due to heat, oxygen, and catalysis during storage and use, leading to the formation of insoluble gums and degraded performance, which may even clog the fuel system, endangering flight safety. Thus, suppressing the oxidation process of high-density endothermic hydrocarbon fuels is crucial for fuel storage and usage. Common methods to improve the oxidation stability of fuels include surface treatment, fuel deoxidation, and the addition of antioxidants to the fuel. Among these methods, adding antioxidants is one of the most commonly used methods. Hindered phenolic antioxidants are favored for their cost-effectiveness, but small molecule antioxidants like tert-butylhydroquinone (TBHQ) and butylated hydroxytoluene (BHT) suffer from sublimation at high temperatures, resulting in poor oxidation resistance. Conversely, commercial macromolecular antioxidants, such as L-1010 and L-1076, fall short of the antioxidant needs of hydrocarbon fuels due to their limited properties. In order to make up for the shortage of commercial hindered phenolic antioxidants, researchers have focused on the development of new antioxidants with high temperature resistance and significant antioxidant effect. Calixarenes, with their structural features of hindered phenols, are seen as potential antioxidants, Especially, the calixarene synthesized with resorcinol as monomer has high phenolic hydroxyl content, which can quench the oxygen free radicals produced in the process of fuel oxidation by providing more abundant hydrogen free radicals, thus has better oxidation resistance. However, reports on using calixarenes for enhancing the oxidation resistance of high-density hydrocarbon fuels remain scarce. In this paper, C-undecylcalix4resorcinarene(C₁₁-C4R) was synthesized by using resorcinol and dodecanal, and its oxidation resistance in high-density hydrocarbon fuel JP-10 was investigated.and compared with several commercial antioxidants:2,6-di-tert-butyl-4-methylphenol, tetra β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid pentaerythritol ester and β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid octadecyl ester. The results of high pressure differential scanning calorimeter (PDSC) showed that the effect of four antioxidants ranked as follows: C₁₁-C4R > BHT > L-1010 > L-1076. In addition, the oxidation consumption process of four hindered phenolic antioxidants in JP-10 was analyzed from the perspective of kinetics, and the oxidation consumption rate constant was calculated. The results showed that the reaction rate constant of C₁₁-C 4 was the smallest and the consumption rate in JP-10 was the slowest. Besides, the oxidation reaction process of JP-10 was also studied using the static kettle accelerated oxidation method. Based on these findings, a potential antioxidant mechanism of C₁₁-C4R in JP-10 was proposed.