Thermodynamic properties of compressed 1,4- and 2,3-butanediol calculated from the high-pressure speed of sound measurements


M. Dzida1, E. Zorebski1 and M. Zorebski1

1Silesian University, Katowice, Poland

Keywords: speed of sound; thermodynamic properties; elevated pressures
property: density; compressibility; heat capacity; thermal expansion
material: 1,4-butanediol; 2,3-butanediol

The data on the thermodynamic properties at elevated pressures are still rather scarce. This refers, in particular, to associating liquids that are key substances in the chemical industry. We report the thermodynamic properties of compressed 1,4- and 2,3-butanediol calculated from the high-pressure speed of sound measurements. The speeds of sound in 1,4- and 2,3-butanediol were measured within temperature range from (293/298 to 318) K and at pressures up to 101 MPa by means of two measuring sets operate on the principle of the pulse-echo-overlap method [1,2]. The densities at atmospheric pressure and temperatures T ranging from (293/298 to 363) K were measured by means of a vibrating-tube densimeter DMA 5000 (Anton Paar). 1,4- and 2,3-Butanediol (mass fraction > 0.995 and > 0.990, respectively) were supplied by Fluka and used without further purification. For a given pressure p, the speed of sound in the diols is decreasing almost linearly with increasing T, while the pressure dependencies at constant T are evidently non-linear. Moreover, with increasing pressure its effect on the speed of sound becomes smaller. Based on the speeds of sound measured as function of T and p as well as on the isobaric heat capacity (the literature values were used) and density determined as functions of T at atmospheric pressure (so-called reference isobars) the thermodynamic quantities of interest were calculated over the same T and p ranges as in the case the measured speed of sound. The densities of both diols increase monotonically with increasing p and decreasing T. A maximum change of the density with changing p occurs near the atmospheric pressure (i.e., with increasing p the changes of the density are smaller). The heat capacities (isobaric and isochoric) for the diols increase with increasing T (at constant p) and decrease with increasing p (at constant T). However, the effect of p on the heat capacity is much smaller than that of T. The isentropic compressibility increases almost linearly with increasing T at constant p and decreases evidently non-linearly with increasing p at constant T. The shape of the isobars and isotherms of the isothermal compressibility is identical to that observed for the isentropic compressibility. The curves are translated only by the almost temperature independent term (its contribution falls as the p increases). Simultaneously, both compressibilities depend significantly on the p for pressures close to the atmospheric one, while the pressure effect on the compressibility is gradually decreasing with increasing p. The isobaric coefficient of thermal expansion changes with p and T in a similar way. The results are compared with those for 1,2- and 1,3-butanediols [3].

References
  1. A.Żak, M.Dzida, M.Zorebski, S.Ernst, Rev.Sci.Instrum. 71, 1756 (2000)

  2. M.Dzida, M.Chorążewski, M.Zorębski, R.Mańka, J.Physique IV, 137, 203 (2006)

  3. E.Zorebski, M.Dzida, J.Chem.Eng.Data, 53, 1010 (2007)

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