As the main components of synthetic hydrocarbons obtained using gas to liquid conversion technologies, long-chain alkanes and alcohols play an important role in the Fischer–Tropsch process. So the reliable surface tension data of these fluids are significant for the understanding and eventual improvement of synthesis efficiency. In the present study, a new high temperature and high pressure pendant drop apparatus was developed and tested with n-heptane at temperatures from (303.15 to 473.15) K, and a good agreement between the experimental data and the literature data could be found. With the new apparatus, the experimental surface tension measurements of n-dodecane, n-hexadecane, 2,2,4,4,6,8,8-heptamethylnonane, n-octacosane, squalane, 1-dodecanol, 1,12-dodecandiol, 2-butyl-1-octanol, 1-hexadecanol and 2-hexyl-1-decanol were performed under saturation conditions over the temperature range from 303.15 K (348.15 K for n-octacosane and 1-hexadecanol, 373.15 K for 1,12-dodecandiol) to 573.15 K. The combined expanded uncertainties of temperature and surface tension with a level of confidence of 0.95 (k = 2) are estimated to be 20 mK and less than 1.5% over the entire temperature, respectively. Furthermore, the surface tension data were correlated with the modified van der Waals equation, and the average absolute deviations are within 0.65%. On the basis of the correlations, the comparisons of our experimental data with the available literature data were discussed, and the satisfactory agreement revealed that the experimental results of this work were reliable and reasonable.
This work contributes to the experimental measurements and modelling of the surface tension for the medium- to long-chained hydrocarbon mixtures involved in the Fischer-Tropsch process under the high-temperature conditions. For this purpose, the experimental surface tension measurements for the four investigated binary mixtures of n -Hexadecane with n -Dodecane, 2,2,4,4,6,8,8-Heptamethylnonane, n -Octacosane and Squalane were performed by pendant drop method at temperatures up to 573.15 K covering the mass fractions of w n -Hexadecane = (0.25, 0.50 and 0.75). The combined expanded uncertainties of temperature, mole fraction and surface tension with a level of confidence of 0.95 ( k = 2) are estimated to be 20 mK, within 0.6% and less than 2.2% over the entire temperature, respectively. On the basis of the surface tension correlations of pure substances in our previous study, the experimental surface tension data of the four investigated binary mixtures were correlated with the three-parameter Jouyban − Acree model and two-parameter Fu-Li-Wang (FLW) model. However, the experimental results show increasing negative deviations from Jouyban − Acree model with maximum values up to −2.66% and increasing positive deviations from FLW model with maximum values up to 9.93% in the high temperature zone. Therefore, we proposed a new model for correlating the surface tension of multicomponent mixtures with excellent reproducibility. The relative deviations of the experimental data from the present model are distributed evenly on both sides of the zero line and the relative absolute deviations are within 0.6%.
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