| Mass transfer in gas-liquid-liquid three-phase system ofoxygen-benzaldehyde-NaOH aqueous solution has been studied in this paper. Theprocess involved the oxidation of benzaldehyde without any catalyst in toluene byoxygen to produce benzoic acid, and benzoic acid is in-situ extracted by theneutralization with sodium hydroxide to produce sodium benzoate. This researchwill provide a theoretical basis for the novel oxidation-extraction integrated process.Firstly, Oxygen absorption by aqueous phase and organic phase wasmeasured in a 500 mL, three-necked flask equipped with a stirrer, condenser andthermometer. Comparing oxygen absorption in aqueous phase and organic phase,the absorption rate of oxygen by the organic phase is 40 times higher than that byaqueous phase, oxygen in organic phase will firstly approach saturation. Becauseof its smaller saturated value in aqueous phase, the absorption of oxygen by theaqueous phase can be neglected as long as the amount of organic phase is largerthan or equal to that of aqueous phase.Secondly, Reaction mechanism and kinetics of benzaldehyde oxidition byoxygen without any catalyst and mass transfer in gas-liquid-liquid three-phasesystem were studied. The effects of reaction temperature, agitated speed andreactant concentration on the oxidation were experimentally investigated, andfound that 70℃ is the optimum reaction temperature and reaction rate increasedwith reactant concentration. A mechanism for oxidation of benzaldehyde withoutany catalyst was proposed in this investigation, the reaction orders are 1 forbenzaldehyde concentration and 0.5 for oxygen concentration, so the reaction ratecan be expressed r=CRCHOCO21/2Third, the mass transfer in gas-liquid-liquid three-phase system was studiedemphatically. It was found that oxygen consumption increased obviously with theincrease of stirring speed, and the higher of stirring speed, the more of benzoic acidin aqueous phase. So did the reaction temperature and reactant concentration, andthe increasing trend of benzoic acid in aqueous phase is linear. Combiningtwo-film theory with eddy diffusion, a mathematic model of mass transfer hadbeen built. The mass transfer and eddy coefficients were calculated by this model,they are k 2a2=0.054 min-1 and k t=0.6379 min-1 respectively. |
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