R-3 Repository :: Browsing by Author "Kobayashi, Riki"

Browsing by Author "Kobayashi, Riki"

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A classical approach to the critical equilibrium in a binary sustem
(1976) Kwon, O'Dae; Kobayashi, Riki; Kim, Dae M.
Recently extensive investigations have been directed toward the critical phenomena occurring in the liquid column of binary mixtures in a manner similar to the case of a pure component. This thesis presents a self-consistent analytic theory concerning these phenomena for "simple" binary systems. In particular, this thesis discusses, (1) a detailed derivation of the equation of state concerning the gravity-induced inhomogeneity (2) power law dependence of the coexistence curve (3) geometrical realization of the coexistence curve in a miscibility gap (4) thermodynamic stabilities in a binary system. In addition, the possibility of applying the present theory to thermodynamic measurements and the analogy between unitary and binary critical equilibria are discussed.
Analysis of low temperature chromatographic separation of methane-propane mixtures with N-decane on celite
(1957) Rangel, Enrique Trevino; Kobayashi, Riki
An outline of the history of chromatography is presented, reviewing briefly the existing theories. The theory of Jame sand Martin for gas liquid partition chromatography and the extension to their theory by Litlewood and porter are Derived. The equipment to investigate the variables involved in gas-liquid partition chromatography (GLPC) was built and a large number of experiments were performed to study these variables. An analysis of the data results in the verification of the conclusions of other investigators. Investigations at temperature below the freezing point of the fixed phase suggests the concurrent action of absorption and adsorption chromatography on solid surfaces. Data were taken to permit the calculation of equilibrium vaporization constants (K values) from GLPC measurements. The constants so obtained follow closely the predicted values taken from the charts. A column with spherical beads from 0.07 to 0.028 mm in diameter indicated that the Klinkenberg effect did not contribute to the separation of methane from propane and probably has no effect on the separation in practical columns. Preliminary investigations suggest the application of partition chromatographic principles to gas hydrate studies.
Correlations of NMR relaxation time with viscosity/temperature, diffusion coefficient and gas/oil ratio of methane-hydrocarbon mixtures
(2000) Lo, Sho-Wei; Hirasaki, George J.; Kobayashi, Riki
A 90 MHz NMR Spectrometer equipped with a high pressure probe was used to study relationship between NMR relaxation time and temperature, viscosity, diffusivity and gas/oil ratio of methane-hydrocarbon mixtures. This research project involves three parts: (1) modifications of the existing NMR apparatus. (2) Measurements of relaxation times and diffusion coefficients of methane-hydrocarbon mixtures. (3) Development of generalized correlations between transport properties and temperature and relaxation times. The NMR apparatus was modified in order to make elevated temperature and pressure measurements. The modifications included calibration of pressure transducers, addition of temperature measuring devices, connection to the high pressure sample probe of a sapphire sample cell and leak detection of the system. After the modifications, the apparatus was capable of measurements from 20 to 60°C at pressure up to 6000 psia. NMR relaxation measurements of three mixtures, methane-n-hexane, methane-n-decane and methane-n-hexadecane, were made. The log mean relaxation times were plotted against viscosity/temperature and it was found that unlike stock tank oils, they do not depend linearly on viscosity/temperature on a log-log scale. Each of the mixtures forms a different curve on the plot of relaxation time vs. viscosity/temperature. Diffusivity measurements were also made for these three mixtures, as well as pure hexane, decane and hexadecane. The log mean diffusion coefficients were calculated. The relationship between diffusion coefficients and relaxation times were studied, and it was found that diffusion coefficients depend linearly on T1 for pure hydrocarbons, but the dependence does not hold for methane-hydrocarbon mixtures. Correlations between transport properties and NMR relaxation times were developed. First, a relaxation time mixing rule was developed by studying the theory of NMR relaxation mechanism. From the mixing rule, it was found that departure of relaxation times of methane-n-alkane mixtures from linear correlation on a log-log scale can be correlated with proton fractions of methane, which can be expressed as gas/oil ratio. Thus, correlation between relaxation time, viscosity/temperature and gas/oil ratio was developed. Correlation between relaxation time, diffusivity and gas/oil ratio was also developed. From these correlations, viscosity and gas/oil ratio can be estimated just from NMR relaxation time and diffusion coefficient.
Corresponding states correlations relating proton spin-lattice relaxation rates of hydrocarbons to viscosities at advanced pressures
(1994) Beznik, Frantz; Kobayashi, Riki
A new five-parameter corresponding states model has been developed for viscosity and proton spin-lattice relaxation rate applicable to a variety of hydrocarbons in the dense fluid phase region. This model is the key to the development of unprecedented, accurate correlations between the proton spin-lattice relaxation rate, R$\sb1$, and the viscosity, $\eta$, of pure hydrocarbons, with an observed root-mean-square deviations of less than 8.0%. For hydrocarbon mixtures, the notion of "effective" spin-lattice relaxation rate, introduced by Zega et al$\sp{1,2}$, is pursued. Then, simple mixing rules are successfully applied to extend the model to mixtures. The four-parameter corresponding states treatment, utilizing the shape factors as proposed by Leach and Leland$\sp3$, yields correlations of comparable accuracy, when confined to long-chain alkanes.
Demonstration of the Gibbs definition of dew point conditions of methane-n-butane mixtures on an organic surface
(1977) Everett, Armgard Koehler; Kobayashi, Riki
An extended form of Gibbs’ definition of the dew point is experimentally demonstrated to be valid. The adsorption K-values of methane-n-butane mixtures on a porous, hydrocarbon-like polymer substrate are shown to coincide With the known vapor-liquid K-values at five different dew point conditions. It is thereby shown that a chromatographic column packed with that substrate provides a new method to determine the dew point of a hydrocarbon gas mixture with greater precision than conventional methods. Five adsorption isotherms are presented. From the total number of moles adsorbed at the dew point, the adsorption layer thickness is shown to be less than 5 A or 1 layers of butane molecules at the higher pressures.
Derivation of an infinite-dilution activity coefficient model and application to two-component vapor-liquid equilibria data
(1988) Roper, Vaughan Phillip; Kobayashi, Riki
Infinite-dilution fugacity coefficients were obtained for the binary system fluorene/phenanthrene at thirteen temperatures by fitting total pressure across the entire mole fraction range by a computer routine. A thermodynamically consistent routine, that allowed for both positive and negative pressure derivations from the ideal values, was used to correlate data over the full mole fraction range from 0 to 1. The four-suffix Margules activity coefficient model without modification essentially served this purpose since total pressures and total pressure derivatives with respect to mole fraction were negligible compared to pressure measurement precision. The water/ethanol system studied by Kolbe and Gmehling and binary systems studied by Maher, Srivastava and Smith comprised of aniline, chlorobenzene, acetonitrile and other polar compounds were fit for total pressure across the entire mole fraction range for binary Vapor-Liquid-Equilibria (VLE) using the rigorous, thermodynamically consistent expression derived by Ibl and Dodge from the Gibbs-Duhen Relation. Data correlation was performed using a computer least squares procedure. Infinite-dilution fugacity coefficients were obtained using a modified Margules activity coefficient model which gives residual values of x$\sb1$ dly$\gamma\sb1$ + x$\sb2$ dln$\gamma\sb2$ across the mole fraction range that lie between the value of vd$\Pi$/dx$\sb1$/RT at x$\sb1$ = 0 and x$\sb1$ = 1. x$\sb1$ and $\gamma\sb1$ and x$\sb2$ and $\gamma\sb2$ are the mole fraction and activity coefficient of components 1 and 2 respectively. v is the mixture liquid molar volume, $\Pi$ is total pressure, R is the ideal gas constant, and T is temperature in absolute units. This correlational procedure, a modified Margules model, yielded infinite-dilution fugacity coefficients differing from the non-rigorous Margules model (derived for a binary at constant pressure) by a few percent but in some cases by as much as ten percent. The modified version is necessary in fitting binary total pressure versus mole fraction data to an expression totally consistent with Gibb's Phase Rule. Its application implies that the derivative of pressure with respect to mole fraction may affect the values of activity coefficients determined, especially at either infinite-dilution axis where the absolute value of this derivative is greatest.
Development of a Burnett-Isochoric apparatus for the study of the volumetric behavior of pure components and mixtures at high reduced temperature and high pressure, and development of a method for the analysis of PVT isochores
(1981) Magee, Joe Wilton; Kobayashi, Riki; Leland, Thomas W.; Kilpatrick, John E.
A Burnett-isochoric apparatus was used to obtain six PVT isochores for a 79.95 mol% methane-hydrogen mixture, from 273.15 K to 5 K, and 13 to 55 bar . The Burnett method was selected since no direct measurements of mass or volume are necessary for density determinations. Densities for each isochore, obtained by intersection with a Burnett isotherm at 273.15 K , are believed to have an accuracy approaching .1% at high pressures. Pressures were measured with calibrated dead weight gages to within .1 % of the true pressure. Temperatures registered with a platinum resistance thermometer have accuracies that approach ±.1°C of the International Practical Temperature Scale of 1968. System design refinements have reduced the error contributions from elastic distortion and thermal expansion of the cells and from vertical temperature gradients. The system consists of three thick-walled spherical cells, each fabricated of the same material with equal outside to inside diameter ratios. Their centerlines lie in a single horizontal plane. Temperature gradients were .1°C or less as determined by thermopiles. As a second part of this work an empirical equation for isochoric P-T was derived and applied to a set of seventeen 5.31 mol% propane-methane isochores recently measured by Kunio Arai in this laboratory. The equation for isochores is explicit in pressure and features a linear temperature dependence augmented by terms which depend on exponentials of temperature and inverse temperature. The nonlinear terms were designed to reflect deviations from linearity and the first and second derivatives of pressure with temperature at fixed density. Among the results of a regression analysis, were the estimates of eight isochoric inflection temperatures.
Development of an augmented hard sphere equation of state
(1980) Casas, Alvaro, Jr.; Leland, Thomas W.; Kobayashi, Riki; Rowley, Richard L.
A new three-parameter generalized equation of state for application to mixtures and multicomponent equilibrium systems has been developed. The equation of state is developed from isothermal and isochoric behavior of pure fluids. This equation of state is based on the hard sphere equation of state and is made to favor vapor-liquid equilibrium computations, and also gives satisfactory prediction of other properties. It models the second order perturbation theory expansion in powers of 1/KT for which there is a theoretical base for the mixing rules. This is much more effective than a completely empirically derived set of mixing rules. Methane, Ethane, and Propane were selected for testing this approach. Satisfactory results in the calculation of densities, compressibility factors, vapor pressure and fugacity over a wide range of temperature and pressure demonstrates the applicability of this equation of state. The possibility of a completely analytical expression of the methods previously developed, such as the van der Waals' one-fluid theory and the original Hard Sphere Expansion theory on vapor-liquid equilibrium is in sight.
Effective molecular diameters for a conformal solution theory of hard sphere mixture
(1981) Kajiyama, Yohki; Leland, Thomas W.; Rowley, Richard L.; Kobayashi, Riki
The hard sphere expansion conformal solution theory is a very useful technique to predict the thermodynamic properties of a mixture. When we apply this theory, an important problem is the method of determining the effective diameters. Hwu developed a diameter evaluation method using pure component P-V-T data represented by accurate equation of state. This method requires a very time consuming iterative process. Consequently, if it is possible to obtain an analytical equation that expresses accurate diameter values in terms of known variables, we can shorten the computation time. In addition, one can simplify the prediction of derived thermodynamic properties from a single correlation of the optimal diameters for compressibility factor computation. Hard sphere diameters for light hydrocarbons (i.e., methane, ethane, and propane) were calculated using the hard sphere expansion conformal solution theory. The diameter correlation is presented in generalized form as a reduced temperature, reduced density, and acentric factor. Thermodynamic properties for methane-propane mixtures were calculated using the diameters from this diameter equation. The calculated results showed a good agreement with experimental values. The diameters for simple fluids were calculated and compared with those values reported by Bienkowski and Chao. Other than the same trend of temperature dependence, there was no agreement between them, indicating that the optimal values to accompany a particular method of determining the attractive contributions are not closely related to an actual hard molecular core.
Elucidation of the formation and decomposition of clathrate hydrates of natural gases through gas solubility measurements
(1996) Feneyrou, Guillaume; Kobayashi, Riki
Through isobaric temperature ramping experiments, the solubility of pure methane, ethane, propane, carbon dioxide gases and a methane-propane gas mixture in pure liquid water has been measured. The experiments are conducted at low temperatures and pressures corresponding to the clathrate hydrate formation and decomposition region. The inhibitory effect of a 10 weight percent methanol aqueous solution and a 0.5 weight percent polyvinylpyrrolidone aqueous solution on the hydrate formation and decomposition conditions has been estimated. A study of the pH-induced change in the hydrate stability has also been performed. The isobaric solubility data obtained show a significant divergence from Henry's law prior to and during hydrate formation. A molecular mechanism of hydrate nucleation is hypothesized, based on an analysis of the gas supersaturation observed and the current knowledge on the structure of liquid water.
Estimation of the heat of solution in hydrogen sulfide-monoethanolamine-water system
(1955) Yorizane, Masahiro; Kobayashi, Riki
An hypothetical chemical reaction between hydrogen sulfide and monoethanolamine is set up to permit thermodynamic calculations of the partial heats of solution of hydrogen sulfide in aqueous monoethanolamine solutions. The solubility data of hydrogen sulfide in various concentrations of monoethanolamine and water were used to make the calculations. The partial heats of solution of hydrogen sulfide were calculated for 0.6, 1.0, 1.5, 2.0, 3.0, 4.0, and 5.0 normal monoethanolamine solution at 15, 25, 35, 45, 55, and 60 deg. C. at partial pressures of hydrogen sulfide ranging from 25 mm of mercury to 700 mm of mercury. The partial heat cf solution calculate( for the 100 deg. C. isotherms are to be considered a extrapolated values since no experimental solubility data is available at 100 deg. C. The accuracy with which the derived equation represent the solubility data is determined by tabular comparison of the calculated values with the original experimental data. Over the range of conditions studied, the partial heat of solution of hydrogen sulfide is found to vary from -4,000 to -13,000 calories per gram mol of dissolved hydrogen sulfide. The pronounced effect of partial pressure, ethanolamine concentration, and temperature on partial heats of solution of hydrogen sulfide are presented graphically.
Extension of Pitzer corresponding states correlations using new vapor pressure measurements of then-alkanes C(10) to C(28)
(1990) Morgan, David Lee; Kobayashi, Riki
Pitzer et al. (1955) three-parameter (T$\sb{\rm c}$, P$\sb{\rm c}$,$\omega$) corresponding states principle (CSP) correlations for saturated properties are extended to long-chain n-alkanes and to other classes of compounds by use of n-alkane reference fluid properties. New vapor pressure measurements, a critical review of the n-alkane literature, and numerous correlational studies are described. Direct vapor pressure measurements of zone-refined n-alkanes (decane, dodecane, tetradecane, hexadecane, octadecane, nonadecane, eicosane, docosane, tetracosane, and octacosane) are reported in the 0.1 to 1400 kPa and 323 to 588$\sp\circ$K pressure and temperature ranges. These results allow the evaluation of existent data and the subsequent development of accurate correlations for vapor pressures and heats of vaporization. Wagner equation fits, which are scaled using the T$\sb{\rm c}$ and P$\sb{\rm c}$ correlations of Twu (1984) for the longer n-alkanes, are given for representing vapor pressures of n-alkanes over the liquid-vapor coexistence range. The scarcity of low-pressure data in the vicinity of the triple point is addressed by use of two-real-fluid CSP techniques (Ambrose & Patel, 1984) to extrapolate data available at higher pressures. Observations of triple point corresponding states in the long-chain n-alkanes suggest an alternative approach for fitting vapor pressure equations at low-pressures. Extensions of Pitzer-type CSP correlations to long-chain n-alkanes (C$\sb{36+}$) are achieved in two ways. First, a second-order perturbation term in Pitzer's acentric factor expansion of In(P$\sb{\rm r}$) is included. This approach is referred to as the PERT2 model. In a second method, parameters (P$\sb{\rm c}$, $\omega$) for a two-fluid CSP model based on methane and n-octane, C$\sb1$/C$\sb8$, are determined by regression of vapor pressures. The two models are compared with experimental data and literature correlations. Applications of the n-alkane-based correlations to other classes of compounds, such as model compounds derived from coals, are given. Extensions of Pitzer-type CSP correlations to associated fluids are briefly considered by applying two- and three-fluid CSP models.
High pressure NMR study of carbon dioxide and supercritical carbon dioxide-n-hexadecane mixtures
(1992) Etesse, Patrick; Kobayashi, Riki
For the first time, an NMR spectrometer equipped with a high pressure probe has been interfaced with a Vapor-Liquid-Equilibrium apparatus to study solvent-solute interactions in supercritical fluids. The following three paragraphs detail the sequential progress of the work where we focused on the pure solvent, the pure solvent near its critical point and then the mixtures. Spin-lattice relaxation time T$\sb1$ and self-diffusion coefficient D in $\rm\sp{13}CO\sb2$ have been measured from 0 to 75$\sp\circ$C at pressures up to 500 bar. The governing relaxation mechanism in this range is shown to be spin-rotation relaxation. For both T$\sb1$ and D data, a kinetic theory based model describes well the low density values, whereas a hydrodynamics based model works adequately at high densities. Using recent molecular dynamics calculations, we found that the smooth hard-sphere theory predicts surprisingly well the self-diffusion of CO$\sb2$ at densities above critical. T$\sb1$ and D have then been measured near the critical point of CO$\sb2$. T$\sb1$ values are unprecedented and this is the third D determination in the critical region. The two previous D determinations are in serious disagreement. One reported the presence of a strong critical anomaly whereas the other observed that D behaves normally in the critical region. No critical anomaly was found for either T$\sb1$ or D. Finally, T$\sb1$ and D of $\rm\sp{13}CO\sb2$ and $\rm C\sb{16}\sp1H\sb{34}$ have been measured on relevant isotherms from atmospheric pressure up to the critical point of the mixture in the coexisting vapor and liquid phases. The data have been correlated with phase compositions determined earlier in this laboratory and with calculated viscosities. $\rm\sp{13}CT\sb1$ data indicate that the reorientational correlation time of the CO$\sb2$ molecule is constant in the liquid phase up to the critical region. $\rm\sp1HT\sb1$ data are in qualitative agreement with theory. The ratios of the self-diffusion coefficients in each phase is closely related to the ratios of the partial molar volumes, in agreement with arguments from statistical mechanics and irreversible thermodynamics. Calculated mutual diffusivities are found to be in excellent agreement with available experimental diffusivities.
Improvement of the effective hard sphere diameter and the intermolecular potential of lighter paraffin hydrocarbons, carbon dioxide and hydrogen sulfide
(1979) Jones, Lawley; Leland, Thomas W.; Kobayashi, Riki; Rowley, Richard L.
Effective hard sphere diameters for non-spherical molecules were obtained through use of the corresponding states principle and hard sphere expansion theory. The Weeks Chandler Andersen "blip" function technique, with an expanded form of the Verlet and Weis equation, was utilized to fit potential parameters for several models. In this manner, an equation was developed to predict effective hard sphere diameters. Intermolecular potential functions were developed with a three parameter Mie model and second virial coefficients. The numerical values of the Mie intermolecular potential model were compared to the more commonly used Lennard-Jones intermolecular potential model. Effective hard sphere diameters were evaluated from P-V-T data. Dimensionless plots of the effective hard sphere diameters were prepared.
Isochoric PVT studies of binary fluid mixtures: The hydrogen-methane and methane-methanol systems
(1991) Jett, Maurice David; Kobayashi, Riki
The isochoric PVT behavior of two binary fluid mixtures has been studied over extensive ranges of temperature and pressure. Emphasis in both experimental investigations was on definition of single-phase compressed liquid behavior, as indicated by isochoric curvatures and isochoric inflection loci, although PVT behavior in the virial region was also determined with comparable accuracy. In the first study, a mixture of 4.65 mole % hydrogen and 95.35 mole % methane was studied at temperatures from 140 to 273.15 K, densities from 2.2 to 23.6 moles/liter, and pressures to 700 bar. Densities of the nine isochores were determined by coupling to a reference isotherm at 273.15 K, where isothermal Burnett experiments were conducted to determine the dependence of density on pressure. Results of this hydrogen-methane study showed that the mixture isochoric inflection locus is "open". This is surprising, as it qualitatively resembles the inflection locus of hydrogen more than that of methane, even though hydrogen is the minority constituent of the mixture. This has significant implications for prediction of hydrogen-methane mixture properties by corresponding states and equation of state methods. Conventional mixing rules cannot predict the quantitative and qualitative dominance of hydrogen at such low concentrations. The second isochoric study consisted of measurements on a mixture of 20.19 mole % methane and 79.81 mole % methanol. Thirteen isochores were measured at temperatures from 350 to 550 K, densities from 1.7 to 21.8 moles/liter, and pressures to 700 bar. A reference isotherm at 510 K was used to determine isochore densities. A gravimetric technique was used to characterize this isotherm. Methanol decomposition at the high temperatures of this study was modeled as a pseudohomogeneous zeroth-order reaction. Each isochoric data point was density-corrected using the model parameters. Results of the methane-methanol investigation show the mixture isochoric inflection locus is "open", like pure methanol. The exact shape of the locus could not be determined because points on the locus were outside the operating range of the apparatus and/or methanol's stability region. Strong positive curvature near the bubble point line at high densities indicates the "open" nature of the locus.
Low temperature vapor - liquid equilibrium. Ternary system: Methane - Ethane - Propane
(1953) Harvey, Phillip D; Kobayashi, Riki
A vapor recycle type apparatus for obtaining vapor-liquid equilibrium data at low temperatures and high pressures was constructed. Its description and testing are presented. A method of analysis for light hydrocarbons using the infrared spectrophotometer was developed. Curves for the analysis of methane-ethane-propane mixtures are included. Equilibrium data for methane-ethane-propane mixtures at -100°F and at both 215 psia and 365 psia were obtained. Comparisons between the phase compositions predicted from the Kellogg fugacity data and those obtained in this work and in the experimental Methane-Propane and Methane-Ethane systems are shown.
New methods for activity coefficients correlations based on an improved prediction of pair distribution functions in mixtures
(1982) Zhang, Lingling (b. 1936); Leland, Thomas W.; Rowley, Richard L.; Kobayashi, Riki
Two new methods are examined for computing liquid phase activity coefficients at low pressures. The first is the Modified Regular Solution Theory (MRST), the second is a new group contribution method. These two methods are based entirely on the mean density approximation (MDA) to evaluate pair distribution functions in mixtures. The mean density approximation assumes that a pair distribution function in a mixture is the same as for this pair in a pure component at a composition dependent average density which is different from the mixture density. The original Regular Solution Theory of Scatchard and Hildebrand made some assumptions. The first is that the probability of finding a particular pair having a specified center-to-center separation distance in a mixture is independent of composition and is the same as the probability for the pair in the pure component. The second assumption is that the entropy change is the same as the ideal solution entropy change. In this work,we incorporate the mean density approximation and the Flory-Huggins entropy change into the Regular Solution Theory of Scatchard and Hildebrand instead of the unrealistic assumptions about pair distribution functions and the entropy change made in the original theory. The result is called the Modified Regular Solution Theory (MRST). In 197, Funk and Prausnitz have proposed the incorporation of an unlike pair coefficient in the original Regular Solution Theory to derive the Funic version of the Regular Solution Theory(RST). The unlike pair coefficient is used to relate the interactions between unlike molecules to those between like molecules. This work likewise incorporates an unlike pair coefficient in the MRST. In Chapter II,we predict excess thermodynamic functions and activity coefficients from the MRST, the incorporation of the ideal solution entropy change to the RST, the incorporation of the Flory - Huggins entropy change to the RST respectively. Each of these are compared with experimental data. Prom the predicted values, we observe that the results from the MRST is the best and results using the ideal solution entropy change with the RST are poorer. Unlike pair coefficients are necessary in all the theories test. With unlike pair coefficients the MRST is better in predicting excess thermodynamic functions and activity coefficients in mixtures with large differences in molecular size and shape. We also calculate activity coefficients for the MRST by a new analytical differentiation developed in this work and compare with a numerical differentiation.We find the results from these two differentiation methods are almost same. The mean density approximation is also used in this work to develop a new theory of group contributions. This new theory was tested by studying the effect of different molecular species on the inter-group parameters. The group contribution method results from an expansion of a mixture property about this property of a pure reference component conformal with the constituents of the mixture. The expansion is developed in terms of the deviations of the interaction parameters for the individual molecules of the mixture from those of the reference. These deviations constitute effective group contributions for liquid phase activity coefficients. In Chapter III, we predict activity coefficients based on this group contribution method in binary mixtures of acetone-methanol, methanol-ethanol, acetone-ethanol and ternary mixtures of acetone-methanol-ethanol and compare with experimental data. The predicted values are generally good but the errors from the binary mixtures are usually smaller than those from the ternary mixtures.
Spin lattice relaxation in pure and mixed alkanes and their correlation with thermodynamic and macroscopic transport properties
(1988) Zega, James Alexander; Kobayashi, Riki
Spin-lattice, T$\sb1$, and spin-spin, T$\sb2$, relaxation times of the alkanes from n-pentane to n-hexadecane were measured at 25$\sp\circ$C. The T$\sb1$ values agree well with those of previous investigators. The values of T$\sb1$ and T$\sb2$ were equal for each alkane studied. Empirical correlations were found between T$\sb1$ and two parameters: the acentric factor and the rotational coupling coefficient. The product $\eta$T$\sb1$ was constant for all the alkanes except n-pentane. The spin-lattice relaxation time was dedimensionalized and a three parameter corresponding states correlation was developed following the treatment of Tham and Gubbins (42) for transport coefficients. Excellent correspondence was found for the saturated alkanes over the temperature range 22 to 90$\sp\circ$C and for benzene from 12 to 63$\sp\circ$C. Spin-lattice relaxation times of mixtures of n-hexane and n-hexadecane were measured at 25$\sp\circ$C. The decay of magnetization could not be described by a single exponential curve. The results were analyzed using three methods. (Abstract shortened with permission of author.)
Spin-lattice relaxation in normal alkanes at elevated pressures
(1991) Zega, James Alexander; Kobayashi, Riki
A high pressure, variable temperature NMR probe for low signal to noise relaxation time and self-diffusion coefficient measurements was constructed and tested. The probe has a high pressure limit of 10,000 psia and a current temperature range of 10 to 250 C. Since the magnetic field gradient coils are inside the pressure vessel, the diffusion measurements may be performed with either pulsed or constant gradients. Spin-lattice relaxation times of octane, decane, dodecane, and hexadecane were measured at temperatures between 10 and 85 C and pressures between atmospheric and 6000 psia. These data are the first for these fluids at elevated pressures and represent a significant expansion of the data base. The relaxation rate at constant temperature is proportional to the ratio of the viscosity divided by the temperature, thus being in qualitative agreement with the Bloembergen, Pound, and Purcell (1948) theory. The corresponding states treatment of spin relaxation has been extended to fluids at arbitrary temperature and pressure. Using decane as a reference fluid, the calculated relaxation times of octane, dodecane, and, hexadecane were in good agreement with the experimental values. The low signal to noise capability of the probe was tested by measuring T$\sb1$ of $\sp{13}$CO$\sb2$ at 504 psia and 25 C. Agreement with the literature value (Smith, 1986) was excellent. The gradient coils were calibrated using benzene. Measurements of benzene at various temperatures, and water at 25 C, gave reliable diffusion coefficients when either the pulsed gradient or the constant gradient method was used.
The comparison of experimental and theoretical hydrate numbers
(1968) Galloway, Travis J; Kobayashi, Riki
Experimental apparatus and an effective technique for a more precise determination of the hydrate numbers of gas hydrates were developed. Hydrate numbers (the ratio of the moles of water to moles of gas in the gas hydrate) were determined for pure component ethane and methane hydrates at several equilibrium decomposition conditions and compared with hydrate numbers calculated from the solid solution theory of van der Waals and Platteeuw as extended by Saito et al. and Nagata et al. Two methods were used for each experimental determination. Method I involved calculation of the difference in the number of moles of free gas in a closed system (as determined by pressure-volume-temperature changes) before and after complete conversion of gas and liquid water to gas hydrate. In Method II the number of moles of gas in the hydrate were determined by direct measurement of the volume of gas evolved during hydrate decomposition at constant pressure. The experimental hydrate numbers for ethane hydrate were determined at equilibrium decomposition conditions of 118.0 PSIA, 40.0°F; 119.4 PSIA, 40.2°F; and 225.0 PSIA, 48.9°F. The results essentially confirmed the hydrate numbers calculated from the solid solution theory. The maximum discrepancy from the theoretical values for ethane hydrate was a hydrate number of 8.01 (Method II at 119.4 PSIA, 40.2°F) compared to a theoretical hydrate number of 8.25. The experimental results supported the contention that only the larger cavities of Structure I are occupied for ethane hydrate, since the lowest hydrate number obtained experimentally was 7.89, whereas the limiting hydrate number assuming complete occupancy of only the larger cavities of Structure I is 7-2/3. The experimental hydrate numbers for methane hydrate were determined at equilibrium decomposition conditions of 1030 PSIA, 50.0°F; 1032 PSIA, 50.1°F; 1902 PSIA, 60.0°F; and 1901 PSIA, 59.9°F. The experimental hydrate numbers for methane hydrate were generally lower than the theoretical values. The maximum discrepancy was an experimental hydrate number of 5.93 (Method II at 1030 PSIA, 50.0°F) compared to a theoretical hydrate number of 6.30. No experimental hydrate number for methane hydrate, however, was less than the limiting value of 5-3/4, which represents complete occupancy of large and small cavities in Structure I.

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