Study Of Liquid-Liquid Two-Phase Dispersed Flow Induced Mass Transfer Enhancement In A Hollow Fiber Membrane Contactor

Hollow fiber membrane contactor (HFMC) has been widely used in areas of chemical engineering, environmental engineering and bioengineering. The aim of this work is to provide experimental and theoretical supports for the industrial applications of HFMC, and enhance the mass transfer performance of HFMC. In this work, the mechanism of liquid-liquid two-phase dispersed flow induced mass transfer enhancement in HFMC is investigated.Visualization experiments are used to investigate the liquid-liquid two-phase dispersed flow, and the experimental parameters of dispersed flow are determined. The droplet size distribution (DSD) along2D axis (flow and radial directions) is obtained. A visualization system to simultaneously monitor the inlet and outlet of hollow fiber is established. The effect of various parameters including organic-to-feed volume ratio, flow velocity and inner diameter of hollow fiber on liquid-liquid two-phase dispersed flow are studied. The influences of the various factors on DSDs are also investigated.Based on the visualization experiment, the DSDs of inlet and outlet of the hollow fiber lumen side are obtained by using the TBP/deionized water system. Effects of various parameters including feed-to-organic volume ratio, stirrer rate, flow velocity, and inner diameter of hollow fiber on DSDs are obtained and analyzed. According to the multiphase flow theories, the reasons of DSD formed under various experimental conditions are clarified.In order to obtain the evolution of DSD along the axial direction, a population balance model (PBM) with1D spatial coordinate is derived. A ID spatial-discretized high-order moment conservation method is proposed. The simulation results fit well with the experimental results, demonstrating that the present model is accurate and have good predict capability. For the liquid-liquid two phase dispersed flow in a hollow fiber, the factors which represent the coalescence and breakage of droplets are obtained.Based on the surface renewal model and hidden markov model (HMM), a mass transfer model for liquid-liquid two-phase dispersed flow of HFMC are proposed and demonstrated. This model uses the simulation results obtained from PBM, and can be used to clarify the mechanism of mass transfer enhancement in hollow fiber renewal liquid membrane (HFRLM). A series of HFRLM experiments are conducted to verify the effectiveness of the model. Effects of stirrer rate, organic-to-feed volume ratio, pH value of feed and strip phases, carrier concentration, initial solute concentration in the feed phase, and lumen and shell sides flow rates on the mass transfer performance are investigated. For the mass transfer enhancement on shell side of HFMC, a Residence Time Distribution-multi Continuous Stirrer Tank Reactor (RTD-mCSTR) model is established. The mechanism of vibration-induced mass transfer enhancement for membrane gas absorption process is investigated, and the relationship between the momentum and mass transports on the shell side of HFMC is established. The mass transfer coefficient of membrane gas absorption process is predicted by the RTD-mCSTR model, and the agreement with experimental results is reasonably good.According to the Hollow fiber renewal liquid membrane (HFRLM) technique and Supported Liquid Membranes with Strip Dispersion (SLM-SD), two novel liquid membrane techniques, supported liquid membrane with feed dispersion (SLM-FD) and supported liquid membrane with organic dispersion (SLM-OD) are proposed and demonstrated, by using a Cephalexin-Aliquat336system. For SLM-FD, by dispersing the feed aqueous solution in the bulk organic solution, the mass transfer area can be significantly enlarged, and the mass transfer resistance is therefore reduced. On the other hand, the small droplets enhance the micro-mixing in the shell side of HFMC, which is also benefit to the mass transfer performance. Compared with supported liquid membrane with strip dispersion, the mass transfer coefficient of SLM-FD increases by70%; for SLM-OD, using a small amount of organic solution can also enhance the mass transfer performance.