Gas-liquid mass transfer in cyclohexane oxidation process using gas-inducing and surface-aeration agitated reactors

Abstract

The equilibrium solubilities, C ∗ , and volumetric liquid-side mass transfer coefficients ( k L a) for gaseous nitrogen and oxygen in liquid cyclohexane were obtained in wide ranges of pressures (1–40 bar), temperatures (380–480 K) and mixing speeds (13.3–20 Hz) in gas-inducing (GIR) and surface-aeration (SAR) agitated reactors. The C ∗ values were calculated using a modified Peng-Robinson equation of state and the transient physical gas absorption technique was employed to obtain the mass transfer coefficients. The C ∗ values for both N 2 and O 2 were found to increase with the solute gas equilibrium partial pressure and temperature. Under the same operating conditions, O 2 appeared to be more soluble in cyclohexane than N 2. The k L a values for the two gases were found to increase strongly with mixing speed and slightly increase with pressure in both reactor types. k L a values for both gases appeared to slightly increase with temperature in the SAR while an opposite trend was observed in the GIR. k L a values for both gases in the GIR were higher than those in the SAR at higher mixing speeds (16.6 and 20.0 Hz). It appeared that k L a values in the SAR were controlled by the mass transfer coefficient, k L , whereas those in the GIR were controlled by the gas-liquid interfacial area. a. The effect of gas nature on k L a values in both reactors was insignificant. Two empirical correlations to predict k L a and gas holdup values for N 2 and O 2 in liquid cyclohexane in both reactor types with ±30% accuracy were developed.