Application of ED and EDI Processes in NaOH recovery from Merox spent caustic waste

In this research work recovery of sodium hydroxide from waste stream of Merox process by two different processes of electrodialysis (ED) and electrodeionization (EDI) was studied. Effects of applied voltage and feed flow rate on NaOH recovery were investigated. The separation performance was evaluated in terms of sodium ion transport and electricity consumption. The obtained results showed that the percentage recovery of sodium hydroxide increased with the enhancement of the applied voltage and simultaneously the economy of processes decreased. Also, comparison between results of two processes showed that electrodeionization was more successful for recovery of NaOH from waste stream of mercaptan removal unit at suitable condition. High NaOH recovery was obtained by the electrodeionization at about 85%.