Development of an electrodialysis–distillation integrated process for separation of hazardous sodium azide to recover valuable DMSO solvent from pharmaceutical effluent

Recovery of solvents from aqueous industrial effluents containing hazardous compounds is not directly feasible by conventional methods due to the complex nature of such wastewaters. An effluent from a pharmaceutical industry contains 2–3 wt% explosive sodium azide + corrosive ammonium chloride salts, 15–20% dimethylsulfoxide (DMSO) solvent and water. The focus of this work is to establish a hybrid process to facilitate removal of salts by electrodialysis (ED) followed by distillation to recover DMSO. An indigenously constructed ED system of 1.05 m2 membrane area was used to process 10 L batch size. Pure DMSO was recovered from desalted liquor by vacuum distillation in two stages to obtain DMSO concentration up to 60–70% in the first stage and subsequent recovery of pure DMSO in the second. Effect of operating parameters such as flow rate, limiting current density and voltage was evaluated. Distillation was carried out at 20–30 mmHg at reboiler temperature below 150 °C. Drug prepared using the recycled DMSO (>99.5%) was found to meet desired specifications. Detailed design of the ED–distillation process scheme to treat 7500 L/day of the effluent revealed that it was technically and economically feasible, since 30 Metric Tonnes of solvent has been recovered by the industry.

► Membrane-based hybrid process for DMSO solvent recovery has been developed.
► Separation of hazardous sodium azide by electrodialysis is established.
► Commercial plant for treating 7500 L/batch of effluent is designed.