Article pubs.acs.org/EF
Mechanistic Insights into Thermal Stability Improvement of exoTetrahydrodicyclopentadiene by a New Hydrogen Donor: 5,6,7,8Tetrafluoro-1,2,3,4-tetrahydroquinoxaline Sun Hee Park,†,‡,§ Yumi Park,§,∥ Jeong Sik Han,⊥ Byung Hun Jeong,⊥ Hogyu Han,*,∥ and Sung Hyun Kim*,† †
Department of Chemical and Biological Engineering, and ∥Department of Chemistry, Korea University, Seoul 136-701, Korea ‡ Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353, Korea ⊥ Agency for Defense Development, 111 Sunam-dong, Yuseong-gu, Daejeon 305-152, Korea S Supporting Information *
ABSTRACT: We investigated the thermal stability of exo-tetrahydrodicyclopentadiene (exo-THDCP, C10H16) in the absence and presence of 5,6,7,8-tetrafluoro-1,2,3,4-tetrahydroquinoxaline (TFQox), a new hydrogen donor (H donor). Conversion of exo-THDCP was slowed in the presence of TFQox but less effectively compared to its analogues, 1,2,3,4-tetrahydroquinoxaline (THQox) and 1,2,3,4-tetrahydroquinoline (THQ). We analyzed the H-donor effects on the thermal decomposition kinetics of exo-THDCP, which explains the relative effect of the H donors on the thermal stability improvement of exo-THDCP. effectively improved by THQox compared to THQ. 23 Previously, THQ was known to be the best thermal stabilizer for various fuels, including exo-THDCP.5,8,9,16,18,19,21 It was found that THQox performs faster H donation than THQ, which accounts for the more effective thermal stability improvement of exo-THDCP by THQox compared to THQ.23 This result suggests that the faster H donor can act as the more effective thermal stabilizer. To test this possibility, it is necessary to examine more H donors for their effect on the thermal stability of exo-THDCP. Here, we report the study on the thermal stability of exoTHDCP in the absence and presence of 5,6,7,8-tetrafluoro1,2,3,4-tetrahydroquinoxaline (TFQox), a fluorinated analogue of THQox (Figure 1). The thermal stability of exo-THDCP was improved by TFQox but less effectively compared to THQox and THQ. We analyzed the H-donor effects on the thermal decomposition kinetics of exo-THDCP, which explains the relative effect of the H donors on the thermal stability improvement of exo-THDCP.
1. INTRODUCTION Fuel is subjected to high temperatures prior to combustion when it is a primary coolant for the engine and subsystem in aircraft.1−4 Upon exposure to high precombustion temperatures, fuel undergoes thermal and oxidative decomposition to form coke and gum. Because fuel coking and fouling can cause many problems for the engine and subsystem, the thermal and oxidative stability of fuel need to be improved for their proper functioning. To improve the thermal and oxidative stability of fuel, additives, such as hydrogen donors (H donors), are used.5−19 H donors terminate the propagation of radicals, which are produced upon thermal and oxidative decomposition of fuel mainly at high (>400 °C) and moderate (
