Simo Liukkonen

An improved correlation for compressed liquid densities of hydrocarbons. Part 1. Pure compounds

A new model for calculating compressed liquid densities is proposed. In the new model, the Hankinson-Thomson correlation (Hankinson and Thomson, 1979) is used to calculate saturated liquid densities, and a slightly modified Chang-Zhao equation (Chang and Zhao, 1990) is used in the compressed liquid region. Parameters of the new model are fitted from a data base consisting of 4426 density points for 29 pure alkanes and alkenes. The new model is compared with HBT (Thomson et al., 1982) and Chang-Zhao (Chang and Zhao, 1990) models, and it is found to be the most accurate of the three models. With the new model, densities of compressed liquids can also be calculated in the near critical region with good accuracy. The average absolute deviation was 0.38% for the region Tr < 0.95 and 0.44% for the whole region Tr < 1.0. The new model is also tested against compressed liquid density data for several other organic substances and inorganic light compounds, that were not included in the data set used to fit the parameters. The average absolute deviation was 0.72% for the region Tr < 0.95 and 0.86% for the whole region Tr < 1.0 indicating that though fitted from alkane and alkene data, the new model can be applied to many other compounds.

An improved correlation for compressed liquid densities of hydrocarbons. Part 2. Mixtures

Abstract A recently presented model for compressed liquid densities of pure hydrocarbons (Aalto et al., 1995) is extended to mixtures. Mixing rules for the parameters V ∗ , Tc. HBT, ωSRK and Pc are given. A collection of mixing rules was compiled. 75 combinations of the mixing rules were evaluated using a compressed liquid density data base. The data base was collected during this work and it contained 4223 density data points for 49 binary and ternary hydrocarbon systems. The set of mixing rules recommended in this work gave an average absolute deviation (AAD) of 0.45%. The new model was compared to the original HBT correlation (Thomson et al., 1982), which gave an AAD of 0.57%. Based on the comparison done, it was found that the new model is more accurate than HBT and it can be used at higher temperatures near the vapor-liquid critical point. No binary interaction parameters are needed.

Combination of overall reaction rate with Gibbs energy minimization

A method to calculate multi-component chemical reaction mixtures as a sequence of time-dependent, intermediate thermochemical states is presented. The method combines the overall reaction kinetics with thermodynamic Gibbs energy minimization. The overall reaction is assumed to proceed according to the Arrhenius rate law. During the time-course of the reaction, the temperature and composition of the reaction mixture are calculated by a thermodynamic subroutine, which minimizes the Gibbs energy of the system. The extent of the overall reaction is algorithmically constrained in the Gibbs energy minimization procedure. During the sequential calculation, the kinetic condition is removed by finite differences. The temperature of each intermediate state is reached by an iterative procedure, which takes into account the heat transfer between the system and its surroundings and the enthalpy changes due to the chemical reactions. Thus, the method allows for the effect of temperature on the reaction kinetics as the reaction evolves. The chemical species present in each intermediate state are virtually independent and there is a chemical potential assigned to each of these species. The gradual chemical change in the thermodynamic system proceeds from the initial state of mixed reactants to the final state of product mixture. Both stationary and transient phenomena may be calculated. The method has been applied to some well-known industrial multi-component reaction systems and a fair agreement between the calculated and measured values has been obtained. The application of the thermochemical algorithm in reaction calorimetry is discussed.