Abstract
Multiple-effect membrane distillation (MEMD) using a hollow fiber-based air-gap membrane distillation module was experimentally examined for concentrating dilute aqueous hydrochloric acid. The effects of the hot and cold feed-in temperatures, and the feed-in volumetric flow rates on the performance of the MEMD process were studied. The performance was evaluated using the performance ratio ( ), the average selectivity of water over HCl ( ) and the permeation flux ( ). Two types of porous fibers made from polypropylene were used to fabricate the MEMD modules. The experimental data indicated that hollow fibers with high porosity were preferred for the MEMD process. The , and all decreased as the feed concentration increased. When the feed concentration was below 12 wt-%, the was 6.0 – 9.6 and was 10 – 190. When the concentration of HCl reached 18 wt-%, the and were about 4.4 and 2.3, respectively. However, sharply decreased to around 1.0 when the feed was further concentrated. During an operational stability test that lasted for 30 days, the performance of the MEMD modules remained good.
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