A Comparative Study on theNMR Relaxation of Methanol in Sub-and Super-Critical Mixtures of CO₂ and Methanol

Abstract

1 H NMR longitudinal relaxation times (T1,exp of the hydroxyl and methyl group) of methanol in supercritical and subcritical gas-like and liquid-like CO2 + methanol mixtures were obtained as a function of pressure up to 25 MPa and at 293.15 and 308.15 K, respectively. This study was designed to investigate the mechanism of the spin-lattice relaxation (SLR) time T1 in different phase regions of CO2 + methanol as homogenous gas-like, and liquid-like mixtures, and the influence of pressure, temperature, and composition on the relaxation rate was examined. Moreover, the density dependent isotherms of the SLR rates 1/T1,exp were comparatively studied between gas-like and liquid-like binary mixtures. There exists an obvious phase dependent SLR mechanism within the temperature and pressure range carried out herein, that is, the SLR process is dominated by the dipole-dipole (DD) interaction mechanism for both liquid-like mixture and methanol, whereas by the spin-rotation (SR) mechanism for gas-like mixture. Measurement of nuclear magnetic relaxation times can offer micro-dynamic and micro-structural information and are very useful for the study of fluids of strongly