NMR investigation of Fischer-Tropsch waxes. II. Hard wax

Abstract

For pt.I see J.A.J. Lourens and E.C. Reynhardt, ibid., vol.12, p.1963 (1970). The proton spin-lattice relaxation time and the liquid content of polycrystalline hard wax, average chain length m=50 carbon atoms and chain length disorder Delta m=15.7, were determined as a function of temperature (385>T>118K). In the low-temperature phase (T<308K) the activation energy and pre-exponential factor of threefold reorientations of methyl groups are 7.9+or-0.4 kJ mole-1 and 1.46*10-12 s respectively. All methyl groups have the same correlation time. The motional parameters associated with this motion in waxes are independent of chain length or chain length disorder. In the high-temperature region of the low-temperature phase, T1 is dominated by reorientational-translational (RET) motions. The activation energy is 21.3+or-0.8 kJ mole-1. A linear relationship exists between ( Delta m/m)1/2 and the activation energies for RET motions in waxes. The high-temperature phase (T>308K) is dominated by the gradual melting of the crystalline phase of the wax. Linear relationships exist between the percentage liquid in the wax and the specific volume and thermal conductivity of the wax. The thermogram of the wax is discussed in terms of the melting process of the wax and the effect of this process on the average chain length and chain length disorder.