Study On Liquidliquid Interfacial Mass Transfer Process

Interphase mass transfer plays an important role in chemical engineering process. Because of the special property of interface phase, the conventional theories of interphase mass transfer have not yet reached full development therefore it is vitally necessary to deeply study the theories in the micro-scale level. The study on gas-liquid interfacial mass transfer mechanism has been reported considerably, but few about liquid-liquid interfacial mass transfer. By use of the real-time holographic technique, the interfacial phenomena and the characteristic of mass transfer during the liquid-liquid mass transfer process were investigated.A real-time laser holographic interferometer and a liquid-liquid mass transfer modeling cell were specially designed and established to observe the phenomena and characteristic of interfacial mass transfer, and the principle and method of measurements were also introduced respectively. The holographic diagrams of mass transfer through the interface of oil and water were obtained using a CCD camera and the computer picture collection and treatment technique. The programming language Visual C++ was used to deal with the holographic diagrams, thus the shift and interval of interference fringes were attained, according to the correlation between refractive index and solute concentration measured, the concentration distribution profile was obtained, furthermore, the concentration near the interface and the mass transfer coefficient, as well as the thickness of concentration boundary layer were attained.The liquid-liquid interfacial mass transfer across the interface between oil and water phases without or with surfactant on aqueous solution was also studied. On the oil side, interfacial turbulence was observed in real-time, and it was found that the concentration near the interface linearly increased and mass transfer enhanced exponentially, which could be attributed to the interfacial turbulence during the mass transfer process. However, no interfacial turbulence was observed on the aqueous side. As shown in the concentration distribution profiles on aqueous side, the solute concentration varies approximately in linear within the interfacial region, whereas non-linearly varied far away from the interface. The concentration near the interface on aqueous side increases exponential with the increase of bulk concentration on oil side. The influence of surfactant on mass transfer process was investigated, an approach of interfacial energy with concentration of surfactant was established, and a correlation of concentration near the interface to the bulk concentration of the solute on the oil side and concentration of surfactant was proposed to predict the concentration near interface, and the calculated results are at good agreement with the experimental data. The variation of concentration near the interface of mass transfer process under three different solutes appear the same tendency, declining to a lowest point at 0.2,0.3,0.6×10^-3mol·L^-1 and then increasing with the addition of surfactant, however, the turning point is not the critical micelle concentration.The main conclusions of this thesis are as follows: the interfacial turbulence enhance mass transfer obviously, the interfacial resistance exists in liquid-liquid mass transfer process and the interface of liquid-liquid is non-equilibrium thermodynamically, in the presence of a small amount of surfactant, the interfacial resistance occurs and blocks the mass transfer, but as the concentration of surfactant is higher than a certain point, the surfactant can enhance mass transfer, the turning point depends on the surfactant itself and is effected comprehensively by properties of the solute and the oil phase.