| Bromine is an important chemical raw material. Currently the major methods of bromine extraction from brine in China are air blowing-out technique and steam stripping. However both of them have the shortcomings of high energy consumption and low utilization rate of resources. Therefore, developing a bromine extraction technique with the merits of low energy consumption and high bromine recovery rate, can not only save the cost and improve yield of bromine production, but also has great significance in rational utilization of concentrated seawater and brine resources.Hollow fiber gas membrane-absorption apparatus can be used for rapidly striping and recovering volatile components from dilute aqueous solutions, which feature huge specific surface area, high mass transfer efficiency, simple device, easy operation, low energy consumption, environmental benign, and so on. Due to the acidity and strong oxidation capacity of feed solution containing bromine and chlorine, the gas membrane modules used for bromine extraction must be resistant to acid, alkaline, and oxidation. Polypropylene(PP) membrane commonly used in the other field has a poor oxidation resistance, and polyvinylidene fluoride(PVDF) membrane can not withstand the corrosion of acid, alkaline, and oxidation of bromine and chlorine. Polytetrafluoroethylene(PTFE), with excellent hydrophobicity, oxidative resistance, acidic and alkali resistance, is the most perfect membrane material for bromine extraction.In this study, gas membrane process for bromine extraction with PTFE hollow fiber membrane modules made in China was investigated. First of all, the performances of PP, PVDF and PTFE porous hollow fiber membrane modules for bromine extraction and their oxidative resistance to bromine were studied and compared under the same conditions to demonstrate the superiority of PTFE membrane modules. Then, PTFE modules were further employed, by using the simulated concentrated seawater containing bromine as feed and using NaOH as absorbent, to test the influence of the operating conditions on overall mass transfer coefficient K and Bromine extraction rate ?. Experiment results showed that K significantly increased with the increase of feed temperature, and decreased with the increase of salt content of feed slightly,while feed-in flow rate, feed-in bromine concentration, absorbent concentration and flow rate of absorbing solution had little influence on K. At last, the long-term operation stability performance of PTFE modules were demonstrated on the operation condition that real concentrated seawater of pH=3.10, bromine concentration of 170 mg/L as feed, feed-in temperature of 25 oC, feed-in flow rate of 21.38 L/h, absorbent concentration of 0.4 mol/L and flow rate of 75.00 L/h. The experimental result showed that the overall mass transfer coefficient kept at about 1.64×10-5 m/s and no leakage occurred for the test period of 3 months at this operation condition, which showed excellent long-term operation stability.PTFE hollow fiber membrane modules overcome the backwards of poor resistance to acid, alkaline, and oxidation of chlorine and bromine of traditional PP and PVDF membrane modules, which shows excellent performance in both bromine extraction capacity and operational stability. This study offered a technical basis for the industrialized application of the gas membrane process for bromine extraction from brines. |
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