Gas-liquid mass transfer parameters in benzoic acid oxidation process.

摘要

Benzoic acid oxidation process is an intermediate step in the commercial production of phenol through toluene oxidation using air. In this process, phenol can be easily oxidized to undesirable by-products; and the overall reaction rate can be controlled by gas-liquid mass transfer.; In this study, the solubility (C*) volumetric mass transfer coefficients (k_La) and gas-liquid interfacial area (a) for oxygen and nitrogen in molten benzoic acid and mixtures were measured in one-liter agitated reactor operating in gas-inducing (GIR) and surface-aeration (SAR) modes under typical industrial conditions. The effects of mixing speed, temperature, pressure, and magnesium and copper benzoate concentrations on the mass transfer parameters in both reactor types were statistically investigated.; The C* values for both gases were found to increase with temperature and pressure while the effect of MgBz and CuBz concentrations on C* values for both gases was insignificant. The k_La values obtained for both gases in both reactor types using the transient physical gas absorption technique were statistically correlated with a confidence level >95%. The diameter of gas bubbles, mass transfer coefficients, and gas holdup were also calculated. The k_La values were found to significantly increase with mixing speed and slightly increase with pressure and temperature. The k_La values appeared to slightly increase with Mg benzoate concentration in the GIR while the values increased and then decreased in the SAR. The k_L a values for both gases in the GIR were always higher than those in the SAR; and under similar operating conditions, k_La values for N₂ were higher than or equal to those of O₂.; The gas-liquid interfacial areas for O₂ and N₂ in benzoic acid containing copper and magnesium benzoates were obtained using a physical and a chemical method. The addition of CuBz and MgBz to benzoic acid significantly affected the gas-liquid interfacial areas due to the changes of the liquid phase properties. Also, the gas-liquid interfacial areas obtained using the chemical method were consistently smaller than those obtained with the physical method.