Calculation of the Standard Molal Thermodynamic Properties of Crystalline, Liquid, and Gas Organic Molecules at High Temperatures and Pressures

Abstract Calculation of the thermodynamic properties of organic solids, liquids, and gases at high temperatures and pressures is a requisite for characterizing hydrothermal metastable equilibrium states involving these species and quantifying the chemical affinities of irreversible reactions of organic molecules in natural gas, crude oil, kerogen, and coal with minerals and organic, inorganic, and biomolecular aqueous species in interstitial waters in sedimentary basins. To facilitate calculations of this kind, coefficients for the Parameters From Group Contributions (PFGC) equation of state have been compiled for a variety of groups in organic liquids and gases. In addition, molecular weights, critical temperatures and pressures, densities at 25°C and 1 bar, transition, melting, and boiling temperatures (Tt,Pr, Tm,Pr, and Tv,Pr, respectively) and standard molal enthalpies of transition (ΔH°t,Pr), melting (ΔH°m,Pr), and vaporization (ΔH°v,Pr) of organic species at 1 bar (Pr) have been tabulated, together with an internally consistent and comprehensive set of standard molal Gibbs free energies and enthalpies of formation from the elements in their stable state at 298.15 K (Tr) and Pr (ΔG°f and ΔH°f, respectively). The critical compilation also includes standard molal entropies (S°) and volumes (V°) at Tr and Pr, and standard molal heat capacity power function coefficients to compute the standard molal thermodynamic properties of organic solids, liquids, and gases as a function of temperature at 1 bar. These properties and coefficients have been tabulated for more than 500 crystalline solids, liquids, and gases, and those for many more can be computed from the equations of state group additivity algorithms. The crystalline species correspond to normal alkanes (CnH2(n+1)) with carbon numbers (n, which is equal to the number of moles of carbon atoms in one mole of the species) ranging from 5 to 100, and 23 amino acids including glycine (C2H5NO2), alanine (C3H7NO2), valine (C5H11NO2), leucine (C6H13NO2), isoleucine (C6H13NO2), aspartic acid (C4H7NO4), glutamic acid (C5H9NO4), asparagine (C4H8N2O3), glutamine (C5H10N2O3), proline (C5H9NO2), phenylalanine (C9H11NO2), tryptophan (C11H12N2O2), methionine (C5H11SNO2), serine (C3H7NO3), threonine (C4H9NO3), cysteine (C3H7SNO2), tyrosine (C9H11NO3), lysine (C6H14N2O2), lysine:HCl (C6H15N2O2Cl), arginine (C6H14N4O2), arginine:HCl (C6H15N4O2Cl), histidine (C6H9N3O2), and histidine:HCl (C6H10N3O2Cl). 1 The data for the latter compounds permit calculation of the standard molal thermodynamic properties of protein unfolding in biogeochemical processes (Helgeson et al 1998). The liquids and gases considered in the present study include normal alkanes (CnH2(n+1)) for carbon numbers ranging from 1 to 100, 2- and 3-methylalkanes (CnH2(n+1)) for 4 ≤ n ≤ 20 and 6 ≤ n ≤ 20, respectively, 2,3-dimethylpentane (C7H16), 4-methylheptane (C8H18), cycloalkanes (CnH2n) for 3 ≤ n ≤ 8, methylated benzenes (CnH2(n−3)) for 7 ≤ n ≤ 12, normal alkylbenzenes (CnH2(n−3)) for 6 ≤ n ≤ 20, normal 1-alcohols (CnH2(n+1)O) for 1 ≤ n ≤ 20, ethylene glycol (C2H6O2), glycerol (C3H8O3), normal 1-alkanethiols (CnH2(n+1)S) for 1 ≤ n ≤ 20, normal carboxylic acids (CnH2nO2) for 2 ≤ n ≤ 20, and the following miscellaneous species: 2-thiabutane (C3H8S), thiophene (C4H4S), thiophenol (C6H6S), acetone (C3H6O), 2-butanone (C4H8O), ethyl acetate (C4H8O2), pyridine (C5H5N), 3-methylpyridine (C6H7N), and quinoline (C9H7N). One additional liquid (2-methylthiacyclopentane (C5H10S)) was also considered along with crystalline and gaseous carbazole (C12H9N). The thermodynamic data and equations summarized below can be used together with the standard molal thermodynamic properties of high molecular weight organic compounds ( Richard and Helgeson 1995 , Richard and Helgeson 1998a , Richard and Helgeson 1998b ) and minerals, inorganic gases, and aqueous species, including biomolecules ( Johnson et al 1992 ; Shock 1992a , Shock 1994 , Shock 1995 ; Shock et al 1997 ; Shock and Koretsky 1993 , Shock and Koretsky 1995 ; Sassani and Shock 1992 , Sassani and Shock 1994 ; Schulte and Shock 1993 , Schulte and Shock 1995 ; Oelkers et al 1995 ; Amend and Helgeson 1997a , Amend and Helgeson 1997b , Amend and Helgeson 1997c , Amend and Helgeson 1998 ; Sverjensky et al 1997 ) to compute equilibrium constants and chemical affinities for a wide variety of organic-inorganic reactions in geochemical and biochemical processes at both high and low temperatures and pressures.