| Membrane contactor is a device that achieves gas/liquid or liquid/liquid mass transfer without mixing or dispersion of one phase within another. This is usually accomplished by using non-selective micoporous membrane as a barrier to separate two fluids on opposite sides. In this study, polyethersulphone (PES), polysulphone (PS) and polypropylene (PP) hollow fiber membranes were chosen to separate isopropanol-water binary mixture. Due to the advantages of hollow fiber membrane contactors such as inherent huge interfacial area and independent two fluids flow, they performed very well in separation efficiency and operation flexibility. The physical chemical properties of membrane material played an important role in separation. Based on our previous work, the process operated under total reflux. The condensate flowed down along the inner wall of hollow fibers while the vapor flowed countercurrent in shell side. We have investigated the effects of membrane structure and compatibility between ploymers and IPA on distillation efficiency and operation stability. It is represented that a hydrophobic asymmetric microporous membrane coating thin dense layer on the liquid side with good compatibility might be more suitable in our process. To be specific, the PES hollow fiber module performed best in the height of transfer unit (HTU), product concentration, operation stability and the overall mass transfer coefficients (K) when the parameters differences among various modules were ignored. Furthermore, the effect of membrane wetting on mass transfer was also discussed here. It was found that even a slight wetting (<20%) could result in a sharp decrease (about 70%) of the mass transfer across membrane. For the deviation of K_L and K'_L, it was probably related with individual mass transfer resistance contributions, membrane wetting and fluids characteristics. In the experiment, all hollow fiber membrane contactors got a high separation efficiency with HTU < 0.1m when these modules operated stably. |
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