Experimental study of the isochoric heat capacity and coexistence-curve singular diameter of sec-butanol near the critical point and Yang-Yang anomaly strength

Abstract

One-and two-phase isochoric heat capacities (C V ) and saturated liquid and vapour densities (T S , 0 S and 00 S ) of sec-butanol near the critical point have been measured with a high-temperature and high-pressure nearly constantvolume adiabatic calorimeter. The measurements were made in the temperature range from 307 K to 551 K for 22 liquid and vapour isochores from 76.44 to 794.06 kg m À3 . The isochoric heat capacity jump (quasi-static thermograms supplemented by the sensor of adiabatic control) technique have been used to accurately measure of the phase transition parameters (T S , S ) near the critical point. The total experimental uncertainty of density (), temperature (T) and isochoric heat capacity (C V ) measurements were estimated to be 0.06%, 15 mK and 2-3%, respectively. The critical temperature (T C ¼ 535.95 AE 0.02 K) and the critical density ( C ¼ 276.40 AE 2 kg m À3 ) for sec-butanol were determined from the measured saturated properties (C VS , T S , S ) near the critical point. The measured C V and saturated density (T S , S ) data near the critical point have been analysed and interpreted in terms of extended scaling theory for the selected thermodynamic paths (critical isochore and coexistence curve) to accurately calculate the values of the asymptotical critical amplitudes of heat capacity (A AE 0 ) and coexistence curve (B 0 ). The measured thermodynamic properties (C V , T S , S ) of sec-butanol near the critical point were also interpreted in terms of the 'complete scaling' theory of critical phenomena and the theory of logarithmic singularity of C V . In particular, the contributions of the 'incomplete' (B 2 t 1À ) and 'complete' (B 4 t 2 ) scaling terms on the coexistence-curve singular diameter were estimated. We determined the values of the asymmetry parameters a 3 and b 2 of the 'complete' scaling theory of coexistence curve singular diameter. The strength of the Yang-Yang anomaly R for sec-butanol was estimated using asymmetry parameters a 3 and the contribution of the second temperature derivative of vapour-pressure and chemical potential in the singularity of two-phase isochoric heat capacity, C V2 , at the critical point.

Experimental determination of critical data of multi-component mixtures containing potential gasoline additives 2-butanol by a flow-type apparatus

“…The experimental values of critical temperatures (T c ) and critical pressures (p c ) were listed in Tables 2 and 3. They agree well with the data from literatures [26][27][28][29][30][31][32][33][34][35]. Six binary systems of 2-butanol + hydrocarbon (hexane, cyclohexane, heptane, octane, nonane and decane) were measured over the whole range of composition with mass fraction intervals of 0.1.…”