Thermophysical properties of hexapropyl and hexabutyl phosphoramides in n-dodecane

Abstract

Hexapropyl phosphoramide (HPPA) and Hexabutyl phosphoramide (HBPA), which are structural analogs of Tributyl phosphate, are the novel extractants developed for the processing of spent nuclear fuel. For the commercial use of the above extractants in reprocessing plants, data on the thermophysical properties such as density, viscosity, interfacial tension (IFT) and radiation stability are needed to develop engineering-level flow sheets for liquid-liquid extraction process. In this work, we estimated the density, viscosity and IFT of binary mixtures of HPPA and HBPA in n-dodecane pre-equilibrated with 3.5 mol.kg−1 HNO3 and also without pre-equilibration. In addition, the effect of concentration and temperature on the thermophysical properties of these solvent systems was also investigated. Both the density and viscosity of HPPA and HBPA decrease with an increase in temperature and dilution with n-dodecane. The thermal expansion coefficients of neat extractants were lower than their diluted counterpart. From the variation of viscosities with temperature, the activation energy for viscous flow was calculated and increased with extractant concentration. The IFT of HBPA and HPPA systems was higher and the zirconium retention capacities of the irradiated phosphoramides were lower than the TBP system, indicating the feasibility of HPPA and HBPA for actinide separation processes.