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

A correlation for the constant pressure specific heat capacity, cp, 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 cp 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.