Gas-liquid mass-transfer and hydrodynamic parameters in a soybean oil hydrogenation process under industrial conditions

This paper presents some experimental data on the volumetric gas-liquid mass-transfer coefficient (k(L)a), liquid-side mass-transfer coefficient (k(L)), gas-liquid interfacial area (a), bubble Sauter mean diameter (d(S)), gas holdup (epsilon(G)), and solubility (C*) for N-2 and H-2 in soybean oil obtained in a 4 x 10(-3) m(3) agitated reactor operating under typical industrial conditions as a surface aeration reactor (SAR) and a gas-inducing reactor (GIR). The data were measured in wide ranges of temperature (373-473 K), pressure (0.1-0.5 MPa), mixing speed (10-23.3 Hz), and liquid height (0.171-0.268 m). The central composite statistical design approach was used to distribute the experiments and correlate the k(L)a and d(S) results. The solubility values for both gases were found to increase with pressure and temperature and to obey Henry's law. The effect of temperature on Henry's law constants was modeled using an Arrhenius-type equation. The mass-transfer and hydrodynamic parameters were significantly affected by the mixing speed and liquid height. At high mixing speeds and low liquid levels, bubbles coalescence was found to control the behavior of the gas-liquid interfacial area for H-2 in the GIR, whereas the gas holdup dictated the behavior of a(GIR) at high mixing speeds and high liquid heights. For both gases, k(L)a and k(L) in the SAR increased with temperature. k(L)a, a(GIR), d(S), and epsilon(G) in the GIR decreased with temperature because of the decrease of the induced gas bubbles in the liquid. Under the operating conditions investigated, the mass-transfer and hydrodynamic parameters for both gases in soybean oil were independent of pressure. Also, under similar operating conditions, hydrogen mass-transfer and hydrodynamic parameters in the oil were higher than those of nitrogen because of its higher diffusivity and lower momentum.