A Thermodynamic Study of the Ternary System, Triethylamine, Water and Heavy Water, with Special Reference to Isotope Separation Problems.

An experimental isotope separation and solubility study in the two-phase region of the system, water (D/sub 2/O + H/sup 2/O)triethylamine (TEA) was carried out. Concentrations of D/sup 2/O and H/sup 2/O in TEA were determined by their absorption at 4.0 and 6.1 mu , respectively. Diethylamine and ethylamine as impurities in the triethylamine used, were determined by quantitative paper chromatography using a modified Levyprocedure. Fundamental thermodynamic equations pertinent to the calculation of hydrogen isotope separation effects in the system at equilibrium were developed. The total water concentration, x/sub w/ , of a phase and the isotopic composition, y/sub D/, of the water (both in mole fractions) were chosen as independent variables. It was presumed that changes in activity coefficients, f, when y/sub D/ is varied at constant x/sub w/ were small compared to changes when x/sub w/ is varied at constant y/sub D/. On this basis it was postulated that reasonable first-order or second-order approximate relations are obtained when it is assumed that ( partial delta lnf/ partial delta y/sub D/)/sub x/sub w/, T = 0 or ( partial delta l nf/ partial delta y/sub D/)/ sub xw,/T = a constant (independent of y/sub D/), respectively. The relations were introducedmore » into the fundamental equations and it is shown that in both cases a numerical calculation of the isotope separation effect can be carried through with reasonable accuracy, using available enthalpy data and/or vapor pressure data for pure H/sub 2/O-TEA together with twophase equilibrium data for the binary systems, H/sub 2/O-TEA and D/sub 2/O-TEA. The numerical calculation indicated that partial delta lnf/ partial delta y/sub D/ is less than 0.01 x ( partial delta lnf/ partial delta x/sub w/). The relativbbility change of water in TEA, when H/sub 2/O is replaced by D/sub 2/O at constant temperature, (dlnx'/ sub w//dy'/sub D/)/sub eq,t/ multip lied by a factor, Q = 1 + x'/sub w/( partial delta lnf'/sub w// partial delta x/sub w/), expressing the degre e of ideality in the triethylamine phase, was found to be a simple and convenient measure of the isotope separation effect. It is shown that the large dlnx'/sub w/ /dy'/sub D/ found in this system and in other similar systems must be compensated to a great extent by a small Q, so the absence of any high isotope separation effect is easily understood. (auth)« less