Sulfonated poly (ether ether ketone) composite cation exchange membrane for NaOH production by electro-electrodialysis using agro-based paper mill green liquor

Causticizing process of pulp and paper mills, is highly energy intensive and environmentally unsafe. We report environmental friendly electro-electrodialysis (EED) process using in-house prepared cation exchange membranes (CEMs) for NaOH production from green liquor solution (GLS) of agro-based paper mills. Different composite CEMs with varied composition of sulfonated graphene oxide (SGO) incorporated sulfonated poly (ether ether ketone) (SPK) were synthesized. Best optimized CEM (SPK-3 with 3.0 wt% SGO loading) exhibited 1.75 mmol.g(-1) cation exchange capacity, 32.01% water uptake, 11.41% swelling ratio, conductivity 0.037 S.cm(-1), and 0.97 counter-ion transport number with high alkaline and thermo-mechanical stabilities. Industrial GLS was used for NaOH production by EED at 60 mA.cm(-2) current density. Optimized SPK-3 membrane produced 1.17 mol.L-1 of NaOH with 61.4% current efficiency (eta), and 2.58 kW.h.kg(-1) energy consumption (EC) during 4 h of EED process. Under similar operating conditions, pristine (SPK), and commercial CEM (FKB-PK-130), showed inferior performance. Longevity of SPK-3 CEM was assessed with industrial GLS for fifty cycles of EED experiments 4 h duration each. Reported results are promising for sustainable NaOH production from industrial GLS of pulp and paper mills, and provide a resourceful alternate for industrial waste.