Vapor pressures: The saturated Aliphatic Hydrocarbons

Sondak, Norman E.; Thodos, George

doi:10.1002/aic.690020311

Cited by 23 publications

(18 citation statements)

References 40 publications

(4 reference statements)

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“…This approach considers a detailed analysis of existing vapor-pressure data found in the literature as proposed by Sondak and Thodos (9), in which the calculated critical values are considered in order to see whether they actually represent the vapor-pressure behavior of each respective hydrocarbon. This analysis considers the resolution of the complicated vaporpressure function represented by the expression (9) For the saturated aliphatic hydrocarbons, Sondak and Thodos (9) have shown that a plot of the moduli Y vs. X on rectilinear coordinates produces straight-line relationships for vaporpressure data included between the triple and critical points. Through the use of this scheme, the accuracy of vaporpressure data can be critically reviewed once the pressure van der Waals' constant, a, of the substance becomes available.…”

Section: Comparison Of Resultsmentioning

confidence: 99%

Critical constants of the naphthenic hydrocarbons

Thodos¹

1956

AIChE Journal

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Group-contribution values are presented and, together with those already developed for the aliphatic hydrocarbons (10, ZZ), make possibfe the evaluation of both van der Waals' constants for the naphthenic hydrocarbons. These constants can be used to produce the critical temperatures, pressures, and volumes of these compounds entirely from a knowledge of their chemical structure.Critical constants have been calculated for several naphthenes, and from a comparison of them with the constants resulting from the methods of Riedel (5, 6 ) and Lydersen (3) it was found that the critical constants calculated by these three methods were in fair agreement for naphthenes having short alkyl side chains and progressively deviated from each other as the chains were permitted to lengthen. An appraisal has been made on five naphthenes along the lines proposed by Sondak and Thodos (9) in order to see whether these calculated critical constants properly represent the vapor-pressure function resulting from vapor-pressure data found in the literature for these hydrocarbons.Critical constants have been produced for more than 6fty naphthenes, for which vaporpressure data are available in the literature, and w i l l be used in a separate, comprehensive vapor-pressure study for hydrocarbons of this type.

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Section: Comparison Of Resultsmentioning

confidence: 99%

Critical constants of the naphthenic hydrocarbons

Thodos¹

1956

AIChE Journal

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“…When these assumptions are introduced into the Clapeyron equation (Equation 8 Coefficient Z I has been found by Reynes and Thodos (1962a,b) and Thompson to be the same for all substances; its value can be determined by recalling Frost Bond and Thodos (1960), Pasek and Thodos (1962), Perry and Thodos (1952), Reynes and Thodos (1962a,b), Smith and Thodos (1960), and Sondak and Thodos (1956) have published tables of the values of B and C obtained by direct fit of vapor pressure data, but Table I1 is the most comprehensive list available. Two values each are listed for B and E in Table 11; the column labeled "best" refers to the values obtained by fitting vapor pressure data to Equation 22, whereas the "predicted" values are obtained from Equations 26 and 27.…”

Section: Vapor Pressurementioning

confidence: 98%

A Four-Parameter Extension of the Theorem of Corresponding States

Harlacher¹,

Braun²

1970

Ind. Eng. Chem. Proc. Des. Dev.

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The usefulness of the theorem of corresponding states has been extended to include polar substances. The parachor is used as a fourth parameter to characterize molecular size-shape; the acentric factor, used as the third parameter, is a measure of molecular size-shape, polarity, quantum influence, and hydrogen bonding. These two parameters were combined empirically in a polynomial expansion to separate molecular size-shape effects from the association effects. The effectiveness of this separation was demonstrated by using this four-parameter theorem to generalize the Frost-Kalkwarf vapor pressure equation. Vapor pressures may be predicted from a knowledge of only the critical temperature, critical pressure, acentric factor, and parachor. An average deviation of 4.92% was obtained for 5952 vapor pressure data points representing 242 substances.CHEMICAL ENGINEERS must deal with many types of fluids in the development, design, and operation of chemical plants. I t is essential to know the physical and thermodynamic properties of these fluids as accurately as possible in order to determine equipment sizes, energy requirements, equilibrium yields, and separation ratios. Furthermore, this information can be best utilized in the areas of optimization and process control if it is represented as an analytical function of a process variable. For these reasons accurate correlations of these properties are becoming increasingly important.Although many correlations are available, there is very little uniformity among them. Different correlating parameters are required depending on the property being correlated and, in some instances, the temperature or pressure range represented. Many of these correlations were developed specifically for one substance by empirically determining specific coefficients for a given substance. The generalized correlations which use the same characterizing parameters for all properties and conditions are based on the theorem of corresponding states. Corresponding State ExtensionsThe early work of van der Waals used the critical temperature and pressure to characterize a substance. According to the simple theorem of corresponding states, two substances a t equal reduced conditions should behave identically. This has been shown to be valid only for spherical, noninteracting (simple) substances; however, Riedel (1954), Pitzer et al. (1955), Su (1946), and Lydersen et al. (1955) added a third parameter to the theorem I Present address, Research and Development Department, Continental Oil Co., Ponca City, Okla. 74601to correct it for nonidealities due to molecular size-shape. The result was a considerable improvement in the theorem for nonpolar substances. The most popular third parameter was the Pitzer et al. acentric factor, W . The acentric factor is used to correct the value of a physical property for a simple fluid:where G is any correlatable property, G o is a simple fluid property, and G Basically, the acentric factor is a measure of vapor pressure deviations from the simple fluid, caused by size...

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“…Calculate the vapor pressures of aheptane at 273.2", 298.9", 345.1", 371.6", 423.2", 463.2", and 523.2"K. from its molecular structure and Equation ( 6 ) . The van der Waals' constants for nheptane have been estimated by Thodos (8) (2) Thus the critical temperatures of those substances for which some reliable vapor-pressure data are available can be obtained from Equation (7).…”

Section: Examplementioning

confidence: 99%

“…data are available for a hydrocarbon, values of @, but not y, can be estimated from the methods available (1,3,4,6,7,8,9,10,11) for the prediction of B and T , from the molecular structure of the substance. Therefore it would be advantageous to relate , 8 and y so that vapor pressures can be calculated for substances for which no experimental data are reported.…”

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A reduced state vapor‐pressure relationship and its application to hydrocarbons

Reynes

Thodos

1962

AIChE Journal

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The Frost-Kalkwarf vapor-pressure equation has been modified to include as variables the reduced temperature and pressure of the substance. The resulting relationship was found to contain a universal constant 6 = 0.1832 and three other constants 01, (3, and 7, which are characteristic of the substance. Relationships between a, p, and y were found to exist, and thus a vapor-pressure equation was produced which contains only one characteristic constant f3 and which is capable of predicting vapor pressures o f pure substances up to the critical point.This vapor-pressure relationship has been applied to hydrocarbons of all types, including normal paraffins, isoparaffins, olefins, diolefins, acetylenes, naphthenes, and aromatics. In these calculations values of (3 were estimated from the molecular structure of the hydrocarbons. For hydrocarbons the approach developed in this study was found to reproduce experimental vapor pressures with an average deviation of 2.7% for 456 experimental points representing fifty four hydrocarbons.This study indicates that i f reliable vapor-pressure data, however meager, are available for a hydrocarbon, these data can be used to obtain constants which enable the prediction of the critical temperature and the critical pressure of the substance. The Frost-Kalkwarf equation (2) REDUCED VAPOR-PRESSURE E Q U A T I O Nhas been found to be of considerable utility for the calculation of vapor pressures of individual substances. This equation can be expressed as Equation (1) can be expressed in the alternate form containing reduced variables:where 01 = A -log P , + C log T<.,c, andThe constants A, B, and C result from Thus a unique linear relationship exists reference point ( P B , To), to determine the constants A, B, and C for the satti-between a and for all substances. rated showed that the 'Onstant If vapor-pressure data are available, values of both B and C can be deteris the mined from Equation ( 2 ) . From these values and the critical temperature of slope, and the constant C the inter-

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Vapor pressures: The saturated Aliphatic Hydrocarbons

Cited by 23 publications

References 40 publications

Critical constants of the naphthenic hydrocarbons

Critical constants of the naphthenic hydrocarbons

A Four-Parameter Extension of the Theorem of Corresponding States

A reduced state vapor‐pressure relationship and its application to hydrocarbons

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