Estimation of enthalpies: Multicomponent hydrocarbon mixtures at their saturated vapor and liquid states

Abstract

Based on the data reported by Rossini e t al. (9) analytical expressions have been developed for the calculation of enthalpies at zero pressure as functions of temperature for normal paraffins ranging from methane through octane. The coefficients of these equations have been found to correlate linearly with molecular weight, thus allowing the enthalpy relationships for hydrocarbons heavier than octane to be determined by extrapolation. The enthalpy of mixtures at zero pressure can then be obtained by combining the enthalpies of the individual components on an additive basis, weighted by the mole fractions.Corrections due to nonideal gaseous behavior have been developed in equation form from the work of Lydersen, Greenkorn, and Hougen (7) in terms of the reduced temperature TR and the critical compressibility factor zo of the substance. These corrections have been developed for both the saturated vapor and saturated liquid states and can be applied to the determination of the enthalpy of mixtures at these conditions. The results of this method have been compared with the experimental enthalpy data available for in excellent ogreement.

On the use of departure function correlations for hydrocarbon isobaric liquid phase heat capacity calculation

“…Tyagi [4] observed that saturated liquid heat capacities can be better estimated if the term (H 0 À H sg ) in the Reid and Sobel expressions is defined as a function of reduced temperature and reduced pressure. He then suggested analytical procedures, using the enthalpy departure from the ideal gas state, proposed by Lee and Edmister [17] and Stevens and Thodos [18] to estimate the values for functions dH sL /dT and (dQ/dT) sL . Among the three methods introduced, Method 1, preferred from the perspective of the current work, is discussed.…”

“…To explore the potential of using accurate and predictive universal constant pressure heat capacity correlations for ideal gases and for liquids to predict departure functions, correlations developed for liquids [9] (Eq. (18)) and ideal gases [3] (Eq. (19)) are used: …”

“…(21)) are presented in Table 3 where compounds present in the training sets for correlation development (Eqs. (18) and (19)) are distinguished from compounds that are part of the test data sets. Computed values for individual data points are presented as Supplemental data - Table S1.…”

Fugacity Coefficients and Isothermal Enthalpy Differences for Pure Hydrocarbon Liquids

“…Ln Pc is then subtracted from each side to make both sides dimensionless and the expression is rearranged to give ß = Zc( 1 -0.89 1/2) exp( 6 Integrating Equation 2with respect to pressure between the vapor pressure and system pressure gives (1967). 6 Stevens and Thodos (1963). ' Yen and Alexander (1965); Yen (1968).…”

Phase equilibria for chain‐fluid mixtures near to and far from the critical region

“…Although extensive experimental studies have been reported (for a review, see Dohrn and Brunner, 1995), it has been difficult to develop a universal model to describe the thermodynamic properties and phase behavior of fluid mixtures at high pressures over a wide range of conditions, including the critical region. Most previous studies are concerned with empirical or phenomenological correlations for vapor-liquid equilibria (VLE) (such as Chao and Seader, 1961;Dastur and Thodos, 1963;Stevens and Thodos, 1963;Van Horn and Kobayashi, 1968;Reid et al, 1987); these studies use any one of several popular EOSs, such as RK (Redlich and Kwong, 1949), SRK (Soave, 19721, and PR (Peng and Robinson, 1976). These cubic EOSs provide improvement over the original van der Waals EOS (van der Waals, 1873) through modifications of the attraction terms as reviewed by Yelash and Kraska (1999).…”