Nafion-PTFE hollow fiber composite membranes for ammonia removal and recovery using an aqueous-organic membrane contactor

Abstract

• A novel aqueous-organic membrane contactor process was applied. • The novel membrane contactor process was more favorable to treat low-ammonia-content feeds. • Accompanying water transport was avoided. Nafion-PTFE hollow fiber composite membranes were applied in the ammonia removal and recovery with a novel aqueous-organic membrane contactor (AOMC) process, in which an aqueous solution and an organic solution were separated by the composite membrane. A kerosene-diluted di-(2-ethylhexyl) phosphoric acid (D2EHPA) solution was used to receive the ammonia, which could be recycled and reused after regeneration by the stripping agent (a dilute solution of H 2 SO 4 , HNO 3 , or H 3 PO 4 ). The new-type membrane contactor can avoid the accompanying water transport in conventional membrane contactors. The effects of experimental factors including the pH, the velocity and the initial ammonia concentration of the feed on the overall mass transfer of the ammonia were investigated. Meanwhile, how the regeneration experiment parameters influenced the stripping ratio was also studied. The results showed that the AOMC process was more favorable to treat ammonia feed with low ammonia concentrations. The ammonia removal could be over 99% under certain conditions. Additionally, the ammonia was concentrated 26.4 times after four cycles. It was found that the accompanying water transport was non-negligible in the traditional aqueous-aqueous membrane contactor (AAMC) process when treating ammonia feed of low concentrations, with the maximum water flux two orders of magnitude higher than ammonia.