Estimation of Pure-Component Properties of Biodiesel-Related Components: Fatty Acid Methyl Esters, Fatty Acids, and Triglycerides

Common group-contribution and corresponding-state models for the estimation of normal boiling points, vapor pressures, liquid densities, and dynamic viscosities are reviewed in view of their application to fatty acid methyl esters, related fatty acids and triglycerides. Because of the limited representation of measured data for triglycerides, three previously published group-contribution models for normal boiling points, vapor pressures, and dynamic viscosities are extended through the introduction of a new group, representing the backbone structure common to all triglycerides and improving the performance of these models significantly. Conclusions are drawn in view of further refinement of the group-contribution approach for application to complex branched molecules

Comparison of the a Priori COSMO-RS Models and Group Contribution Methods: Original UNIFAC, Modified UNIFAC(Do), and Modified UNIFAC(Do) Consortium

A comparison of the performances of the COSMO-SAC, COSMO-RS­(Ol), original UNIFAC, modified UNIFAC­(Do), and modified UNIFAC­(Do) Consortium for activity coefficients at infinite dilution and binary VLE data is presented. The σ-profiles used in performing COSMO-SAC and COSMO-RS­(Ol) calculations were taken from the published σ-profile database VT 2005. The predicted results were compared with the experimental data stored in the Dortmund Data Bank and analyzed with respect to the types of components in the mixture. The results show that the UNIFAC models based on experimental data are superior to the a priori COSMO-RS models

Extension of the VTPR Group Contribution Equation of State: Group Interaction Parameters for Additional 192 Group Combinations and Typical Results

Today development, design, and optimization of the various processes is carried out with the help of process simulators. The reliability of the results mainly depends on the quality of the thermodynamic model and the model parameters used. While <i>g</i>^E models can be applied for calculation of the phase equilibrium behavior of multicomponent systems using only binary experimental data, group contribution methods like UNIFAC or modified UNIFAC Dortmund allow prediction of the required thermophysical properties using only a limited number of group interaction parameters. For systems containing supercritical components equations of state like Soave–Redlich–Kwong or Peng–Robinson or group contribution equations of state (GCEOS) like the predictive Soave–Redlich–Kwong (PSRK) or the volume-translated Peng–Robinson group contribution equations of state (VTPR) can be applied. In different papers it was already shown that VTPR is a very powerful thermodynamic model. In this paper new group interaction parameters for 192 group combinations are presented, so that the actual matrix now contains group interaction parameters for 252 group combinations. In this paper predicted results of the VTPR group contribution equation of state are compared with the results obtained using modified UNIFAC Dortmund or the PSRK method

Experimental and Theoretical Study of Chemical Equilibria in the Reactive Systems of Acetals Synthesis

The chemical equilibria of acetals of acetaldehyde reactive systems (with methanol, ethanol, and <i>n</i>-butanol to form 1,1-dimethoxyethane, 1,1-diethoxyethane, and 1,1-dibuthoxyethane, respectively) were studied in the temperature range (293–333 K) in the liquid phase. The three reactive systems exhibit a strong nonideal behavior in the liquid phase. The knowledge of the activity coefficients is required to obtain the thermodynamic equilibrium constants <i>K</i>_a. The activity coefficients were estimated by the modified UNIFAC method, which already includes the parameters for the acetal group. The reaction enthalpies for the three acetalizations in the liquid phase were obtained from the temperature dependences of the corresponding thermodynamic equilibrium constants. These values were compared to those obtained by high-level ab initio calculations of the reaction participants using the Gaussian 03 program package. Absolute electronic energy values of the molecules have been obtained using G3­(MP2) level. Using these results, calculated equilibrium constants and enthalpies of reaction of the acetals synthesis in the liquid phase based on the principles of statistical thermodynamics are found to be in acceptable agreement with the data obtained from the thermochemical measurements