Vacuum Membrane Distillation For Removal Of Voc In The Aqueous Solution

Membrane distillation(MD), which has the advantages of low operating temperature and high efficiency, is an innovative membrane separation technology developed in recent years. In this paper, an experimental investigation of the removal of volatile organic compounds (VOC) from dilute aqueous solutions was presented by vacuum membrane distillation (VMD). Experiments were carried out using aqueous mixtures of ethanol with hollow fiber module. The influences of operating variables such as feed concentration, flow rate, temperature and downstream pressure on the flux and separation factor were investigated. The mechanism of heat and mass transfer for VMD were also investigated . This study was supported by the Zhejiang Natural Science Foundation.The influences of membrane distillation conditions on the flux and separation factor were studied with the installation set up by ourselves. It was founded that the flux increases as the feed temperature, concentration and flow rate increase, and increases as the downstream pressure decreases. The separation factor increases as the feed flow rate and downstream pressure increase, and decreases as the feed temperature increases. Ethanol separation factor of 6.0 was achieved by VMD, which demonstrates that VMD is a promising separation technology.The mechanism of heat and mass transfer for VMD was also investigated. The heat transfer coefficient within the hollow fiber module was studied by the VMD experiments using pure water. The result shows that the heat transfer coefficient within the hollow fiber module with laminar flow can be calculated based on thecorrelation . By analyzing the equation, itwas founded that the heat transfer coefficient under laminar flow is almost independent of the feed flow rate. Numerical simulation of temperature distribution in hollow fiber membrane module with laminar flow was carried out. The simulation result shows that temperature drops more slowly when the flow rate is higher, which demonstrates the flow rate influences the flux by influencing the temperaturedistribution - The VMD experiments were carried out using aqueous binary mixtures of ethanol. Knudsen diffusion model and the mixed flow model were solved numerically for the ethanol-water system. Good agreement between experimental and theoretical values was found. But the mixed flow model is better.Finally, by studying the heat transfer coefficient and the mechanism of mass transfer through the membrane pores, a complete mathematical model was proposed for the removal of VOC from dilute aqueous solutions by VMD.