The pressure dependence of diffusion coefficients of naphthalene in supercritical C02 and naphthalene-¿8 in supercritical ethylene has been measured by using the NMR fixed field gradient spin-echo Bessel function analysis technique. The pressure dependence of the reorientational motion of naphthalene-if8 in C02 and ethylene has been studied by measuring the deuteron spin-lattice relaxation time, 7), as a function of pressure at several isotherms. The temperatures were chosen to cover two regions of the naphthalene-supercritical solvent phase diagram. The experimental data allowed the molecular level test of the applicability of the Stokes-Einstein and Debye equations in the binary systems studied. The expression D(ij/7')0,75 = constant represents the experimental diffusion data well, and the modified Debye equation describes the reorientational motion of naphthalene in supercritical C02 and ethylene solvents.

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The self-diffusion coefficients of supercritical toluene-d, were measured by using the NMR spin-echo technique for temperatures from 300 to 450 °C at constant pressures of 100, 500, and 1000 bar. The results at 100 bar are compared to the predictions for toluene diffusion by using various empirical correlation methods for estimation of the diffusion coefficients In the supercritical region.

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