Measurement of high pressure densities and atmospheric pressure viscosities of alkyl phosphate anion ionic liquids and correlation with the ε^∗-modified Sanchez-Lacombe equation of state

Highlights: • Experimental densities for phosphate anion ionic liquids at pressures up to 200 MPa. • Atmospheric densities and viscosities of phosphate anion ionic liquids. • Data correlation with ε^∗-modified Sanchez-Lacombe equation of state. • Close-packed volume value important for reliable correlation with lattice equations. • Low close-packed volume of ε^∗-mod SL EoS allows reliable correlation of PVT data. - Abstract: High pressure densities up to 200 MPa from 313 to 393 K and atmospheric pressure viscosities from 293 to 373 K for two alkyl phosphate anion ionic liquids, 1-ethyl-3-methylimidazolium dimethylphosphate ([emim][DMP]) and 1-butyl-3-methylimidazolium dimethylphosphate ([bmim][DMP]), are reported. Several forms of the Tait equation were applied and all forms could correlate the data to within 0.03% average relative deviation (ARD). The derivative properties calculated had specific trends for the ionic liquids. The ε^∗-modified Sanchez-Lacombe equation of state could correlate the data to within an ARD of 0.07%, and the deviations were lower than those of the original Sanchez-Lacombe equation of state (0.19%). The improvement by ε^∗-modified Sanchez-Lacombe equation of state can be attributed its assumed close-packed density structure at low temperature.