Experimental study of the isochoric heat capacity of tert-butanol in the critical and supercritical regions

Abstract

The one- and two-phase isochoric heat capacities ( C V ) of tert-butanol in the critical and supercritical regions have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were made in the temperature range from 296 K to 524 K for 21 liquid and 7 vapor isochores from 70.56 kg m −3 to 763.98 kg m −3. The isochoric heat capacity jump (quasi-static thermograms supplemented by the sensor of adiabatic control) technique was used to accurately measure of the phase transition parameters ( ρ S , T S ) in the critical region. The total experimental uncertainty of density ( ρ S ), temperature ( T S ), and isochoric heat capacity ( C V ) measurements were estimated to be 0.02%, 15 mK, and 2–3%, respectively. The critical temperature ( T C = 506.35 ± 0.2 K) and the critical density ( ρ C = 268.1 ± 2 kg m −3) for tret-butanol were extracted from the measured saturated properties ( C VS , T S , ρ S ) near the critical point. The measured C V and saturated density ( ρ S , T S ) data near the critical point have been analyzed and interpreted in terms of extended scaling equations for the selected thermodynamic paths (critical isochore and coexistence curve) to accurately calculate the values of the asymptotical critical amplitude ( A 0 ± and B 0). The experimentally derived value of the critical amplitude ratio A 0 + / A 0 − = 0.525 is in good agreement with the value predicted by various scaling theories. The measured thermodynamic properties of tert-butanol near the critical point were also interpreted in terms of the “complete scaling” theory of critical phenomena. In particularly, the contributions of the “complete” and “incomplete scaling” terms on the coexistence-curve singular diameter were estimated. The Yang–Yang anomaly of strength parameter R μ = −0.036 for tert-butanol was estimated using derived second temperature derivatives of pressure and chemical potential. The measured values of saturated one- ( C ′ V 1 and C ″ V 1 ) and two-phase ( C ′ V 2 and C ″ V 2 ) liquid and vapor isochoric heat capacities and saturated thermal properties ( ρ S , T S ) together with reported vapor–pressure ( P S , T S ) data were used to calculate other derived thermodynamic properties such as K T , Δ H vap, C P , C S , W, ( ∂ P / ∂ T ) ′ V , ( ∂ V / ∂ T ) ′ P , ( d 2 P S / dT 2), and ( d 2 μ/ dT 2) of tert-butanol at saturation near the critical point.