Saturated Liquid Densities of n-Butane-Isobutane, n-Butane-Propane, Isobutane-Propane and n-Butane-Isobutane-Propane Mixtures

Saturated liquid density data were obtained for binary and ternary mixtures containing n-butane, isobutane and propane from 273.15 to 323.15 K using a pyrex glass pycnometer. To validate the mixture densities, data on pure components were also obtained from 273.15 to 323.15 K. The detail of the pycnometer is shown in Fig. 1. The volume of the pycnometer was determined by calibration with mercury. The volume up to the marked line is 10.9644±0.0008 cm³, and capillary part is 1.4535 cm³ at 293.15 K. The pycnometer was pressure tested and proved to be reliable up to a pressure of approximately 10 MPa. The saturated liquid densities were determined by measuring the height of the liquid level in capillary part with a cathetometer to 0.05 mm. Maximum error in measured densities was estimated as 0.2%. The presents results for the saturated liquid densities of n-butane, isobutane and propane are listed in Table 1. Graphical comparison of measured densities for n-butane, isobutane and propane with literature values were shown in Fig. 2. The present results agree within 0.1% with recommended density values by Das et al. The results for the n-butane-isobutane mixtures are shown in Table 2. The saturated liquid densities for the 7i-butane-isobutane mixtures were plotted as a function of composition in Fig. 3. From Fig. 3 this mixture should be considered as an ideal solution. The results for the n-butane-propane, isobutane-propane and n-butane-isobutane-propane mixtures are listed in Tables 3,4,5. The saturated liquid densities for these binary mixture were plotted as a function of composition in Figs. 4,5. It was found that the liquid densities of these binary and ternary mixtures show positive deviations from those obtained from an additive law by mole fraction, while those obtained from an additive law by weight fraction are almost in agreement with the measured density. The present results were compared with the calculated values by 1) Modified Redlich Kwong (MRK) equation, 2) Hankinson's liquid density equation, Eq.(4), 3) Teja's liquid density equation, Eq.(9). Mixing rules of each equation are as follows: 1) Eqs.(l)—(3), where k_ij=0, 2) Eqs. (5)—(8), 3) Eqs. (8), (10)—(14), where ξ_ij, η_ij=0. The comparison between calculated and the experimental saturated liquid density are given in Table 6. It can be seen that the methods proposed by Hankinson and Thomson and by Teja give results almost as good as those obtained by calculation of liquid density of light hydrocarbon mixture, while MRK equation gives slightly less accurate results.