Fabrication of asymmetrical diffusion dialysis membranes for rapid acid recovery with high purity

Anion exchange membranes with fast acid permeation and high retention of salts are urgently needed to increase the process efficiency of acid recovery from various industrial processes via diffusion dialysis, thereby greatly reducing their energy consumption and environmental impact. In this work, we have developed a novel one-step method of simultaneous crosslinking and quaternization for the fabrication of high-performance diffusion dialysis membranes. As an example, porous brominated poly(phenyleneoxide) (BPPO) ultrafiltration membranes with a thin active layer (<1 μm thick) were prepared and then converted to diffusion dialysis membranes by simple immersion in N,N,N′,N′-tetramethylethylenediamine (TEMED) aqueous solution. Manipulation of crosslinking and quaternization degrees by control of the reaction time enabled the optimisation of the membrane performance. Apart from outstanding thermal stability and chemical resistance in an acidic environment, our membranes had remarkably improved performance due to the thin skin layer (<1 μm thick) and porous support, as compared to conventional dense membranes. The optimal membrane (TPPO-4h) showed a high proton dialysis coefficient (U_H⁺) of 0.043 m h^-1 and a high separation factor (S) of 73.8 for HCl recovery from HCl/FeCl₂ solution, which are a 5.1 and 4 times increase of the corresponding values of the commercial DF-120 membrane. In other words, the process capacity for acid recovery from the acidic waste solution can be increased from 11.3 to 57.8 L m^-2 d^-1, with 3 times increase in acid purity, by replacing DF-120 with the TPPO-4h membrane. The strategy developed in this work is very promising for developing high-performance anion exchange membranes for the rapid recovery of acid with high purity in many industrial processes.