A similarity variable for estimating the heat capacity of solid organic compounds: Part II. Application: Heat capacity calculation for ill-defined organic solids

Abstract

A correlation for the constant pressure specific heat capacity, c p , valid from 50 K to the fusion temperature for pure crystalline organic solids was presented recently [V. Laštovka, J.M. Shaw, J. Chem. Eng. Data 52 (2007) 1160–1164]. The predictive correlation includes seven universal coefficients. The variables are temperature and a similarity variable, α, which possesses a value proportional to the number of atoms in a molecule divided by molecular mass. This similarity variable, identified in the first paper of this series [V. Laštovka, N. Sallamie, J.M. Shaw, Fluid Phase Equilib. 268 (2008) 51–60] is more robust than molecular structure or composition as a descriptor for heat capacity for solid hydrocarbons. In this contribution the correlation is applied to the estimation of solid-state heat capacities, identification of temperature ranges where phase transitions arise, and the enthalpy associated with such phase transitions for poorly defined mixed organic solids. Agreement between predicted and measured c p values is within anticipated error bounds [V. Laštovka, J.M. Shaw, J. Chem. Eng. Data 52 (2007) 1160–1164]. Illustrative examples include polymers, charge transfer complexes, and hydrocarbon resource fractions such as asphaltenes, where the role of the correlation as a baseline for solid behavior was found to be particularly useful. This general purpose correlation can also be used as a basis for the development of high precision predictive equations tailored to specific compounds or mixtures where limited experimental heat capacity data are available.