Thermophysical properties of 1-butyl-3-methylimidazolium acetate over a wide range of temperatures and pressures

(p,ρ,T) data of ionic liquid 1-butyl-3-methylimidazolium acetate [BMIM][AC] at T = (273.15–413.15) K and pressures up to p = 140 MPa are reported with an estimated experimental relative combined standard uncertainty of Δρ/ρ = ±(0.01–0.08)% in density. The density at different temperatures and under high pressures, ρ(p,T), was determined by means of high pressure–high temperature Anton-Paar DMA HMP vibrating tube densimeter. The viscosity correction (ρHPM − ρ)/ρHPM is included in the density measurements according to literature suggestion. Density ρ, at ambient pressure was additionally measured using Anton Paar densimeter DMA 5000. Dynamic viscosity, η, was measured using Anton Paar SVM 3000 Stabinger viscometer with the reproducibility in 0.35%. The isobaric heat capacity cp, was measured using Pyris 1 diamond differential scanning calorimeter. The standard uncertainty is around 1% for temperatures excluding lower values (around T = 273.15 K), where δcp/cp reaches 3%. Surface tension, σ, was measured using pendant drop method with drop shape analysis system DSA 100 (Krüss GmbH). The uncertainty of the surface tension measurements was Δσ = ±0.1 mN m−1. iric equation of state for fitting of the (p,ρ,T) data of [BMIM][AC] has been developed as a function of pressure and temperature. This equation is used for fitting of the experimental results and also for the calculation of the thermophysical properties of IL, such as isothermal compressibility, isobaric thermal expansibility, thermal pressure coefficient, internal pressure, isobaric and isochoric heat capacities, speed of sound and is entropic exponent.