Selective recovery of carboxylic acid through PVDF blended anion exchange membranes using electrodialysis

Selective transport of carboxylic acids (acetic, AA; malic, MA; and citric, CA) from their equimolar (0.1 mol.L-1) ternary mixture was investigated through electrodialysis (ED) using three different anion exchange membranes [(i) Fumatech, FAB-PK-130, and two indigenous membranes made by solution blend of polyvinylidene fluoride (PVDF): copolymer of polymethyl methacrylate-co-polychloromethyl styrene (PMMA-co-PCMSt) at (ii) 50:50 wt % (BM-1), and (iii) 30:70 wt% (BM-2) followed by aminating them using tetramethyl 1,6 diamino hexane]. Recovery ratio (RR) for AA/MA and AA/CA mixtures were 1.97 and 2.71 respectively, indicating higher selectivity for AA through BM-2 and the same was explained based on highest ion exchange capacity (2.10 meq.g(-1)) and ion conductivity (2.3 mS.cm(-1)) data. Selective transport of AA was further endorsed by ED performance separately done with AA, MA and CA (0.1 mol.L-1 each) and equimolar binary (AA/MA) mixture at pH 7.5. Increasing trend in AA recovery: FAB-PK-130 < BM-1 < BM-2 at pH 7.5 was further supported by physical properties of the electrolyte (transport number from binary/ternary mixture) and membrane (water uptake, fractional adsorption, and ion conductivity) separately with each membrane. Highest current efficiency of 63.7% (energy consumption 5.13 kWh.kg(-1)) could be achieved with AA during ED analysis of ternary mixture through BM-2.

Automated summary

Selective transport of carboxylic acids (acetic, AA; malic, MA; and citric, CA) from their equimolar ternary mixture was investigated through electrodialysis. The study found that BM-2 membrane exhibited higher selectivity for AA, which was attributed to its highest ion exchange capacity and ion conductivity.