Hydrodynamics And Mass Transfer Characteristics Of Molybdenum In Peg-sodium Sulfate Aqueous Two-phase Systems

Hydrodynamics and mass transfer characteristics of molybdenum(?)were studied by aqueous two-phase systems composed of polyethylene glycol(PEG1000,2000,4000)and sodium sulfate in a packed column.Firstly,the liquid-liquid phase equilibrium data,physical parameters of two phases and the extracting isotherm of molybdenum(?)were measured for polyethylene glycol-sodium sulfate aqueous two-phase systems.The effect of system composition,temperature and PEG molecular weight on phase equilibrium,and of temperature and composition in two phases on physical parameters,and of temperature and PEG molecular weight on extracting isotherm was investigated,respectively.The experimental results showed that the tie-line length increases,the composition difference in two phases increases and the ability of phase separation strengthens with increasing tie-line length,temperature and PEG molecular weight.The tie-line data was correlated with the empirical model of Othmer-Tobias and Bancroft and the reliability of tie-line data was verified.It was obtained about the empirical equations among density,viscosity and interfacial tension in two phases and concentration in two phases and temperature.The extracting isotherm and the effect of temperature and PEG molecular weight on extracting isotherm were acquired by response surface experimental method.Secondly,the hydrodynamic properties were carried out for polyethylene glycol polymer-sodium sulfate aqueous two-phase systems in a specific packed column.The effect of four parameters on the liquid holdup and residence time distribution of the dispersed phase was investigated.The four parameters are the flow of the dispersed phase,the composition of two phases,the packing type and PEG molecular weight.It was found that the liquid holdup of dispersed phase increases as increasing the flow of dispersed phase,tie-line length,PEG molecular weight and the voidage of packing bed.The mean residence time of dispersed phase decreases with increasing the flow of dispersed phase and tie-line length,and increases with the increase of the voidage of packing bed.The back-mixing degree of dispersed phase in packed column is larger,and the flow pattern of dispersed phase is closer to the full mixed flow.Finally,the mass transfer characteristics of molybdenum(?)were studied with polyethylene glycol-sodium sulfate aqueous two-phase systems in a specific packed column by response surface experimental method,and the effect of the flow in two phases,tie-line length,PEG molecular weight and the packing type on the mass transfer of molybdenum(?)was investigated.The experimental results indicated that total volumetric mass transfer coefficient of the dispersed phase increases with increasing the flow of two phases,showing that the mass transfer resistance of two phases couldn't be neglected.The total volumetric mass transfer coefficient of the dispersed phase decreases when tie-line length increases,resulting from increasing viscosity of PEG phase.The viscosity of PEG phase and the distribution coefficient of molybdenum(?)increase with the increase of PEG molecular weight,leading to increasing the mass transfer coefficient of the dispersed phase under both combined effect.The mass transfer coefficient of dispersed phase increases with the increase of the voidage of packing bed,the reason is that the liquid holdup of dispersed phase increases,resulting in increasing the mass transfer area when the voidage increases.The mass transfer unit height,mass transfer unit number and packing layer height required under specified separation requirements were determined according to the research results and two-film model.