DIPPER project 871 determination of ideal-gas enthalpies of formation for key compounds, The 1991 project results

Abstract

This report describes the results obtained in the fifth year of a project whose goal is the improvement of group-contribution methodology for esti'nation of thermodynamic data. It has long been recognized that it is impractical to carry out experimental measurements of the thermodynamic properties of the multitude of organic substances that are of importance in an area such as the processing of alternate fuel sources, or for those chemicals which are of major importance in modern industry. Experimental measurements on a restricted number of carefully selected molecules can be used to relate thermodynamic properties to molecular structure and serve as the foundation for estimation of properties for great numbers of related molecules. The most successful methodology used for this structure/property correlation is the "group-contribution" approach as applied by numerous researchers. The empirical nature of this approach requires data of unassailable quality for the foundation of the correlation. The need for such high-quality data is the basis for this project. Representatives of the Department of Energy (Bartlesville Project Office), the Design Institute for Physical Property Data (DIPPR), and the National Institute for Petroleum and Energy Research (NIPER) agreed on a list of compounds for which the determination of the enthalpy of formation in the ideal-gas state would be of benefit to all the participants. Nine compounds were selected for study in the fifth year of the project, and the ideal-gas enthalpies of formation of cyclohexene, phthalan (2,5-dihydrobenzo-3,4-furan), isoxazole, phenyl isocyanate, 1,4,5,6-tetrahydropyrimidine, n-octylamine, din -octylamine, and tri-n-octylamine are reported here. Liquid-phase densities along the saturation line were measured for phthalan and isoxazole in the temperature range 298 K to 523 K. Values for the group-additivity parameters N-(C)(H)2, N-(C)2(H), and N-(C)3, were confirmed. A value for the N-(Cb)(CO) group-additivity parameter was defined. Ring correction terms were derived for cyclohexene and phthalan ring systems. An estimate for the ideal-gas enthalpy of formation of 2,3-dihydrofuran was derived. Also, the results of isoxazole and 1,4,5,6-tetrahydropyrimidine were used to estimate ideal gas enthalpies of formation for substituted compounds. The results reported continue to establish the validity of the group-contribution approach for the accurate estimation of the enthalpies of formation of organic compounds. They will extend the range of applicability of group-contribution methods open to the chemical engineer concerned with estimation of the energy hazard potential of new chemical processes. Pcs = density calculated using extended corresponding states Ig = IOglo = acentric factor = [-Ig (Px/Pc)-1.000] where Px is the vapor pressure at Tr = 0.700. To avoid listing units in the heat-capacity measurement tables, the heat capacities are reported as divided by the gas constant R. Units of time are s (seconds) or h (hours).

Thermochemistry of organic azides revisited

“…Using archival experimental enthalpies of formation for gaseous benzene and its cyano and nitro derivatives [23][24][25][26], we calculated values of D r H m according to the reaction:…”

“…a Calculated using the G4 energies from Table 7 for the reaction: phenyl azide + nitro-benzene = x-nitro-phenyl azide + benzene. b Calculated using the experimental data [22][23][24][25][26] for the reaction: benzonitrile + nitro-benzene = x-nitro-benzonitrile + benzene.…”

Vapor Pressures and Thermophysical Properties of Dimethoxymethane, 1,2-Dimethoxyethane, 2-Methoxyethanol, and 2-Ethoxyethanol: Data Reconciliation and Perturbed-Chain Statistical Associating Fluid Theory Modeling

“…Brown open circles, Pick et al; forest green inverted triangles, Quitzsch et al; blue diamonds, Chandak et al; red hexagonal stars, Kuus et al. ; green left-pointing triangles, Jonasson et al; orange solid circles, Steele et al; navy stars, Krishnaiah et al; purple triangles, Carmona et al; forest green cross marks, Lladosa et al; magenta right-pointing triangles, Marrufo et al. ; brown plus signs, Bejarano et al; olive asterisks, Reddy et al; red squares, this work (STAT6); red solid line, data obtained by the SimCor method (see Section ).…”

“…2-Methoxyethanol: relative deviations ( p – p calc )/ p calc of vapor pressures p from the recommended values p calc calculated using the Cox equation, eq , with parameters listed in Table . Brown open circles, Pick et al; forest green inverted triangles, Quitzsch et al; blue diamonds, Chandak et al (partially displayed); red hexagonal stars, Kuus et al; green left-pointing triangles, Jonasson et al; orange solid circles, Steele et al; navy stars, Krishnaiah et al; purple triangles, Carmona et al. ; forest green cross marks, Lladosa et al; magenta right-pointing triangles, Marrufo et al; brown plus signs, Bejarano et al; olive asterisks, Reddy et al (partially displayed); red squares, this work (static); dotted lines, absolute deviations.…”

“…Similarly, for dimethoxymethane and 2-ethoxyethanol, the DIPPR database (as well as its predecessors , ) contains only fragmentary data or data rejected in this work, which is reflected in relatively higher AARD­( p ) values achieved by the existing PC-SAFT parameters (2.14% and 4.08%, respectively) when compared to those of this work (0.60% and 0.04%, respectively). In the case of 2-methoxyethanol, correlation in the DIPPR database is based on reliable vapor pressures published by Steele et al; however, the same weight was given to many other datasets rejected in this work (e.g., Pick et al and Marrufo et al; see Figure for comparison of these datasets).…”