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Excess molar enthalpiesHEmand excess molar volumesVEmhave been determined for {xC2H6+ (1 −x)CH3(CH2)2OH} atT= (298.15, 323.15, and 348.15) K andp= (5, 10, 12.5, and 15) MPa. TheHEms were measured with a high-temperature high-pressure flow calorimeter. TheVEms were measured simultaneously with a vibrating-tube densitometer inserted in the flow line of the calorimeter past the mixing chamber. (Vapor + liquid) equilibrium is present atp= 5 MPa andT= (323.15 K and 348.15 K). The value of the pressure coefficient (∂HEm/∂p)T, which is large at all three temperatures, is calculated fromVEmand (∂VEm/∂T)p. The results are in good agreement with the values obtained directly from the change inHEmwith pressure.

Excess molar enthalpiesHEmand excess molar volumesVEmhave been determined for {xCH3(CH2)2CH3+ (1 −x)CH3CH2OH} at the temperatures (298.15, 323.15, and 348.15) K and at the pressures (5, 10, and 15) MPa. Large and positiveHEmandCEp, mare explained in terms of chemical, physical, and structural effects. The small (∂HEm/∂p)T, which changes sign from positive to negative with increasingx, is explained by a smallVEm, which changes from negative to positive asxincreases.

Excess molar enthalpies are reported over the composition range from x ≈ 0.02 to x ≈ 0.96 for {xCH₃(CH₂)₃CH₃ + (1 - x)CH₃OH} at the temperatures (283.15, 298.15, and 363.15) K and the pressures (0.4, 5, and 15) MPa. The excess molar enthalpies obtained at the pressure and temperature conditions where both components are liquid are positive and have a small pressure coefficient, but a large temperature coefficient C^E_p,m. These results are typical of those obtained when a liquid alkane is mixed with a liquid alkanol at temperatures well below the critical temperature of the alkane. (Liquid + liquid) equilibrium is present at T = 283.15 K. The resulting H^E_m(x) curves show a linear region where incomplete mixing occurs. At p = 0.4 MPa and T = 363.15 K, pentane is gaseous and methanol is liquid, and H^E_m(x) changes from a small negative value at low x to a large positive value at higher x with a linear H^E_m(x) between, resulting from (vapor + liquid) equilibrium. The negative H^E_m(x) is due principally to a contribution resulting from the condensation of the gaseous pentane into the liquid methanol, while the large positive region results principally from the vaporization of the liquid methanol into the gaseous pentane. Copyright 1994, 1999 Academic Press

This paper describes the application of calorimetry to the measurement of the excess molar enthalpies %@scp@%%@ital@%H%@rsf@%%@sx@%m%@be@%E%@sxx@%%@mx@% for binary mixtures of nonelectrolytes. Batch, displacement, and flow calorimeters are described, using as examples the batch calorimeter of McGlashan;, the displacement calorimeters of Van Ness and of Marsh and Stokes, and the flow calorimeters of Christensen, Wormald, and Picker. Applications are described using calorimeters to measure %@scp@%%@ital@%H%@rsf@%%@sx@%m%@be@%E%@sxx@%%@mx@% for {(nonpolar + nonpolar), (polar + nonpolar), and (polar + polar)} mixtures. Excess enthalpies for liquid mixtures containing charge-transfer complexes and hydrogen bonds are used to help in understanding the nature of the molecular interactions in these systems. Applications involving measurements on liquid, gas, and supercritical fluid mixtures, including measurements in the near-critical region, are also described. The use of calorimetric measurements to determine {(liquid + liquid) and (vapor + liquid)} phase equilibria is discussed. Finally, equations used to represent %@scp@%%@ital@%H%@rsf@%%@sx@%m%@be@%E%@sxx@%%@mx@% (x) measurements are summarized.

Excess molar enthalpies for (propane + ethanol) have measured at the temperatures (298.15, 323.15, 348.15, and 363.15) K and pressures (5, 10, and 15) MPa. The results are compared with the measurements reported previously for (propane + methanol or propane-1-ol or butan-1-ol). Copyright 1993, 1999 Academic Press

Excess molar enthalpiesHEmfor {xC2H6+ (1 −x)C2H4} have been measured over the entire composition range at the temperaturesT= (273.15, 298.15, 323.15, 348.15, and 363.15) K and the pressuresp= (5, 7.5, 10, 12.5, and 15) MPa. Thus, measurements were made at a temperature where both components are liquid (T= 273.15 K), at a temperature where one component (C2H6) is a liquid while the other (C2H4) is a supercritical fluid (T= 298.15 K), and at three temperatures where both components are supercritical fluids {T= (323.15, 348.15, and 363.15) K}. AtT= 273.15 K, a temperature near the critical temperature of ethene,HEm(x) is positive with a large positive pressure coefficient. AtT= 298.15 K andp= 5 MPa, a temperature and pressure near, but below, the critical locus,HEm(x) is S shaped, changing from large positive values at lowxto negative values at highx. At each of the three higher temperatures, maxima and minima inHEmare obtained at intermediate pressures. A corresponding-states method correctly predicts the pressure and temperature effects onHEmin both the subcritical and supercritical (p, T) regions. At high pressures,HEm(x= 0.5) converges at all the temperatures to a value of approximately 100 J mol−1. A (quadrupole + quadrupole) interaction is probably a major contribution toHEmfor this system, since ethane and ethene have quadrupole moments of opposite sign.

Excess molar enthalpies H^E_m for (propane + chloromethane) have been measured using a flow calorimeter at the temperatures (298.15, 323.15, and 348.15) K and pressures (5 and 15) MPa and at the temperature 363.15 K and pressures (5, 10, and 15) MPa. The comparison with earlier measurements reported in the literature at the temperatures (193.15, 203.25, 213.15, and 223.15) K indicates that the change of H^E_m with temperature is small over a wide range of temperatures. Copyright 1993, 1999 Academic Press

Measurements of the excess molar enthalpiesHmEas a function of pressure and temperature have now been completed for all of the binary mixtures of ethane, propane, and butane with methanol, ethanol, propan-1-ol, and butan-1-ol. Excess molar volumesVmEwere also obtained for selected systems. This paper summarizes the results obtained and compares the effect of molar mass temperature, and pressure onHmE,VmE, (∂HmE/∂p)T, andCp,mE. The effect of (fluid + fluid) equilibria onHmEis described. The UNIFAC-II prediction ofHmEis also compared with the experimental results. The effects of molar mass of the alkane and the alkanol, temperature, and pressure are qualitatively explained by a model that includes contributions toHmEandVmEby a positive hydrogen bonding term and a negative packing term. The hydrogen bonding term is most important at high mole fraction of alkane and is dependent on temperature and the molar mass of the alkane. The packing term is most important at low mole fraction of alkane and is dependent on the molar masses of the alkane and the alkanol, temperature, and pressure. The packing term increases in importance in liquid (alkane + alkanol) mixtures as the temperature approaches the critical temperature of the alkane, and becomes large and at temperatures where the alkane is a supercritical fluid.