Nuclear magnetic resonance measurement of spin-lattice relaxation and self-diffusion in supercritical CO₂-<i>n</i>-hexadecane mixtures

Abstract

Spin-lattice relaxation time and self-diffusion coefficient of 13CO2 and C16 1H34 have been measured on the four isotherms 35, 40, 50 and 60°C from atmospheric pressure up to the critical point of the mixture in both the coexisting vapour and liquid phases. The data have been correlated with phase compositions determined earlier in this laboratory and with calculated viscosities. 13CT 1 data indicate a peculiar behaviour of carbon dioxide in the liquid phase, namely that the reorientational correlation time of the CO2 molecule is constant in the liquid phase up to the critical region. 1HT 1 data are in qualitative agreement with theory. The ratio of the self-diffusion coefficients in each phase is closely related to the ratios of the partial molar volumes, in agreement with arguments from statistical mechanics and irreversible thermodynamics. Calculated mutual diffusivities are found to be in excellent agreement with available experimental diffusivities. Unfortunately, because of the scarcity of experimental mutual diffusivities, no conclusions can be drawn at this point concerning the relationship between self and mutual diffusivities for this type of system.