Recovery of Iodine in the Gaseous Phase Using the Silicone Hollow Fiber Membrane Module.

Iodine, being an important resource, must be recovered and reused. Iodine is not only attracted to the hydrophobic silicone membrane but also easily vaporized. In this study, we explored the use of five types of silicone hollow fiber membrane modules (SFMMs) for separating iodine in the gaseous phase. In the SFMM, iodine gas and the recovery solution (sodium sulfite and sodium carbonate at a concentration of 10 mM each) were flowed outside and inside the silicone hollow fiber, respectively, in a co-current-flow manner. At an iodine gas flow rate of 0.2 L/min (8.4 × 10 mmol-I/L), the capture efficiency of iodine into the SFMM was approximately 100% for all five SFMMs. With increasing feed gas flow rates, the capture efficiency of iodine decreased, reducing to approximately 50% at 0.8 L/min. However, the recovery efficiency of iodine in the recovery solution was 60-30% at 0.2-0.8 L/min. This decrease in capture efficiency with increasing flow rates was because iodine could not spread and diffuse successfully in the SFMM, resulting in a low recovery efficiency of iodine. Thus, we next improved the structure of the SFMM by placing a perforated pipe in the center of the module. The perforated pipe effectively directs the iodine feed gas from the holes in the pipe to the hollow fiber membrane bundle wrapped around the pipe. With the improved SFMM, the capture efficiency markedly increased to approximately 100% in the range of the flow rates tested in our experiments. The recovery efficiency also increased to ≥70%. These data illustrate the potential application of the improved SFMM for recovering iodine in the gaseous phase.