Thermal Stability and Decomposition Kinetics of 1,3-Dimethyladamantane

Abstract

For a comprehensive understanding of the properties of 1,3-dimethyladamantane (1,3-DMA) as a candidate of high energy-density hydrocarbon fuels, thermal stability of 1,3-DMA under different conditions is investigated. The thermal decomposition kinetics in the batch reactor between 693 and 743 K has been determined, with the rate constants ranging from 4.00 × 10^–7 s^–1 at 693 K to 35.19 × 10^–7 s^–1 at 743 K, along with the Arrhenius parameters of <i>A</i> = 2.39 × 10⁷ s^–1 and activation energy <i>E</i>_a = 183 kJ·mol^–1. The rate constants for the thermal decomposition of 1,3-DMA are observed to be smaller than those of some typical model fuels, decalin, propylcyclohexane, butylcylohexane, and <i>n</i>-dodecane, demonstrating that the thermal stability of 1,3-DMA is satisfactory. The thermal decomposition of 1,3-DMA in the flowing reactor at temperatures from 873 to 973 K and pressures from 0.1 to 5.0 MPa is further performed. It can be observed that the conversion of 1,3-DMA and the yield of gaseous products increase clearly with the rise of temperature or pressure. The residence time is the main factor for the change of decomposition depth. Methane and hydrogen are the major gaseous products that are produced through demethylation and dehydrogenation. In the liquid residues, toluene and xylene are observed and quantified by GC-MS, HPLC, and NMR as the main aromatics produced. On the basis of component analysis, a hypothetical mechanism of thermal decomposition of 1,3-DMA is proposed to explain the product distribution. It is shown that the different products are mainly obtained through a combination of isomerization, hydrogen transfer, β-scission, and dehydrogenation. The results are expected to provide experimental information for the search of new high energy-density hydrocarbon fuels