SOLUBILITIES AND MASS TRANSFER COEFFICIENTS OF GASES IN HEAVY SYNTHETIC HYDROCARBON LIQUIDS

Rakymkul, Yeldos SOLUBILITIES AND MASS TRANSFER COEFFICIENTS OF GASES IN HEAVY SYNTHETIC HYDROCARBON LIQUIDS. Master's Thesis, University of Pittsburgh.

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Abstract

The equilibrium gas solubility (C*) and the volumetric liquid-side mass transfer coefficient (kLa) of N2, He, H2 and CO and their mixtures were measured in two liquids (C12-C13 paraffins mixture and Sasol molten reactor wax) using a 4-liter agitated reactor operating in the gas-inducing mode under typical Fischer-Tropsch conditions. The experimental C* and kLa values were obtained in wide ranges of pressure (4-45 bar), temperature (300-500 K), mixing speed (800-1400 RPM), alumina particles concentration (0-20 vol%) and gas composition (0.25, 0.5, 0.75 mole fraction of He in N2 and H2 in CO). Within these experimental conditions, the following results were obtained: • The solubilities of the four gases in the two liquids at constant temperature followed the order C*CO > C*N2 > C*H2 > C*He and obeyed Henry’s Law as their values linearly increased with pressure up to 30 bar. The solubilities of the four gases in both liquids at constant pressure increased with temperature; and an Arrhenius-type equation was used to model the dependency of their Henry’s Law constants on the temperature. The solubilities of the four gases were greater in the paraffins mixture than those in the molten reactor wax. The solubility and diffusivity values showed that He and N2 could be used as surrogates for H2 and CO, respectively. • The mass transfer coefficients of the four gases each as a single-component or in gaseous mixtures in the two liquids increased with mixing speed, pressure and temperature at constant solid concentration. At constant mixing speed, pressure and temperature, kLa values of the four gases in the two liquids decreased with increasing solid concentration above 10 vol%. Also, kLa values for H2 were greater than those of CO and kLa values for He were greater than of N2 in the two liquids. Again, kLa values showed that He and N2 could be used as surrogates for H2 and CO, respectively. • A new empirical relationship was developed to predict kLa of each individual component in a gaseous mixture in liquids/slurries, if the overall kLa of this gas mixture and the diffusivities and solubilities of its components in those liquids/slurries were known.

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