Liquid phase PVTx properties of {water (1) + 1,3-dimethylurea (2)} mixtures at temperatures from 278.15 to 323.15 K and pressures to 100 MPa

Abstract

In this study, the compression coefficients k=ΔV/Vo of the binary mixture {water (1) + 1,3-dimethylurea (2)} were measured within the temperature range from 278.15 K to 323.15 K (278.15, 288.15, 288.15, 308.15, 323.15), the pressure range from 10 to 100 MPa (10, 25, 50, 75 and 100) and the composition range up to x2 = 0.19364 (1,3-dimethylurea mole fraction). The molar isothermal compression, KT,m, molar isobaric thermal expansion, EP,m, isochoric coefficient of thermal pressure, βV, and the internal pressure of the mixture, Pint, were calculated. It was demonstrated that the concentration dependences (on the mole fraction of 1,3-dimethylurea (1,3-DMU)) of the molar isothermal compressions of the mixture at low pressures and low temperatures are characterized by a minimum at x2≈0.06 ÷ 0.07, which levels out both with increase in pressure and with increase in temperature. The molar isobaric thermal expansion of the mixture increases with an increase in the 1,3-DMU concentration for all state parameters. At low temperatures, the concentration dependences of the molar expansion are characterized by the presence of a pressure inversion zone. The concentration dependences of the isochoric coefficient of thermal pressure of the mixture indicate the hydrophobic properties of the 1,3-DMU molecule become stronger at high pressures. The obtained results are discussed in terms of solute–solvent and solute–solute interactions.