Heat capacity of liquids: database of recommended values and estimation by a group contribution method.
Advancing the chemical engineering fundamentals
Thermodynamics: General (T2-1e)
Keywords: heat capacity, database, estimation, group contribution methods
Heat capacity of liquids: database of recommended values and estimation by a group contribution method.
1Kolská Z., 2Zábranský M., 3Kukal J., 2Růžička V.
1Department of Chemistry, Faculty of Science, J. E. Purkyne University, České mládeže 8, 40096 Ústí nad Labem, Czech Republic, +420475283382, kolska@sci.ujep.cz;
2Department of Physical Chemistry, Institute of Chemical Technology, Technická 5, 16628 Prague, Czech Republic, +420220444068, milan.zabransky@vscht.cz, vlastimil.ruzicka@vscht.cz;
3Department Department of Computing and Control Engineering, Institute of Chemical Technology, Technická 5,16628 Prague 6, Czech Republic, jaromir.kukal@vscht.cz;
This work was aimed at updating and extending databases that contain recommended data on liquid heat capacities Cpl for almost 2000 mostly organic compounds [1,2]. Experimental data on heat capacities of 411 pure liquid organic and some inorganic compounds that have melting temperature below 573 K, as well as of 50 ionic liquids, published in the primary literature between 2000 and 2006, were compiled and critically evaluated. Recommended values supplemented with an assessment of their uncertainty and presented in terms of parameters of correlating equations for temperature dependence of heat capacities will be provided at the end of 2007 as a report to the IUPAC project.
Current database of recommended values [1,2] was used to extend the three-level group contribution method [3] to predict heat capacity of liquids as a function of temperature. The original method by Marrero and Gani [4] has so far been developed to estimate heat capacity at one temperature of 298 K only and was not capable of predicting heat capacities over a temperature range. We modified this method to estimate Cpl at some selected temperatures (298 K and some reduced temperatures Tr = 0.3, 0.4, 0.5 and 0.6). Although results obtained for heat capacity at individual temperatures were satisfactory, an analysis of values of individual groups revealed some discrepancies. Values of groups were not in accordance with expected monotonic increase with temperature. A further model development entailed a combination of the method by Marrero and Gani and a relation for the temperature dependence of heat capacity:
We tested this model for 549 compounds from the current database for three cases: a) for the so-called hierarchic approach consisting in the parameter calculation in three subsequent steps for the first, second and third level parameters, resp. (and with calculation of additional adjustable parameter in the first level only); b) for the similar approach similar as in the previous case with the additional adjustable parameter cp° being improved also at higher levels; c) and for the so-called non-hierarchic approach consisting in the parameter calculation in a single step.
This work was carried out within the IUPAC project number No. 2004-010-3-100 and within the Institutional Research Plan No. MSM 6046137307.
References:
1. Zábranský, M.; Růžička, V.; Majer, V.; Domalski, E. S., Heat Capacity of Liquids. Critical Review and Recommended Values, J. Phys. Chem. Ref. Data Monograph No. 6, American Chemical Society: Washington, D.C., 1996.
2. Zábranský, M.; Růžička, V.; Domalski, E. S., Heat Capacity of Liquids: Critical Review and Recommended Values. Supplement I, J. Phys. Chem. Ref. Data 30, 1199-1689 (2001).
3. Kolská, Z.; Růžička, V.; Gani, R. Estimation of the Enthalpy of Vaporization and the Entropy of Vaporization for Pure Organic Compounds at 298.15 K and at Normal Boiling Temperature by a Group Contribution Method. Ind. Eng. Chem. Res. 44, 8436-8454 (2005).
4. Marrero J., Gani R. Group-Contribution Based Estimation of Pure Component Properties. Fluid Phase Equilib. 183-184, 183-208 (2001).
Presented Tuesday 18, 15:40 to 16:00, in session Thermodynamics: General (T2-1e).
