Fractionation of deuterium and protium between water and methanol

Abstract

The overall deuterium-protium separation factor, ..cap alpha.., between hydrogen gas and aqueous methanol mixtures has been measured over the full composition range at temperatures between 25 and 55/sup 0/C. At each temperature ..cap alpha.. increases smoothly with increasing mole fraction of methanol but the values fall significantly below the straight line joining the separation factors for the methanol-hydrogen and water-hydrogen systems. The equilibrium constant, K/sub 1/(1), for exchange of a deuterium atom tracer between the hydroxyl groups of methanol and liquid water, calculated from the values of ..cap alpha.. for each solution, is independent of composition within experimental error. The value of K/sub 1/(1) at 25/sup 0/C is 0.54 +/- 0.02, so that deuterium favors the methanol environment rather than water. The dependence of k/sub 1/(1) on absolute temperature, T, is given by the expression 1n K/sub 1/(1) = -0.776 + 52.6/T, which corresponds to a reaction enthalpy of -0.43 kJ mol/sup -1/. 24 references, 2 figures, 2 tables.