Mass transfer analysis on air stripping of VOCs from water in microporous hollow fibers

The air stripping removal of VOCs such as toluene and phenol from water in microporous PP hollow fibers was studied. The VOC stream passed through the lumen side of the module, while air (stripping gas) flowed across the shell side. Experiments were performed at different liquid flow rates (8-16 cm3/min), gas flow rates (60-180 cm3/min), feed VOC levels (100-1000 ppm), and temperatures (24-35 °C). It was shown that the removal was more effective when feed VOC level, liquid or gas flow rate increased. The applicability of a mass transfer model that considers diffusion in the liquid layer, membrane, and gas layer under steady state was checked. Unlike phenol with a very small dimensionless Henry's law constant (equilibrium gas concentration divided by liquid concentration) and a relatively low amount of sorption on PP fibers, the measured overall mass transfer coefficients for toluene reasonably agreed with those predicted from the model. The large deviation observed for phenol indicated unsteady state nature, likely due to its small concentration difference between air and liquid phase/fiber matrix. The air stripping removal and separation of binary VOCs including o-xylene and chloroform from water was finally examined.