An experimental study was carried out on regeneration sodium hydroxide (NaOH) from the spent caustic by bipolar membrane electrodialysis (BMED). The effects of operation parameters, such as concentration of electrolyte, current density and initial base concentration, on regeneration were investigated. The results indicate that low energy consumption and high current efficiency can be achieved with the concentration of electrolyte in the range of 0.20–0.30 mol/L, initial concentration of the base in range of 0.10–0.25 mol/L and current density in the range of 30–60 mA/cm2. The process cost is estimated to be USD 0.97 for regenerating 1 kg NaOH with the laboratory-scale equipment, showing economically competitive.Highlights► Regenerating NaOH from spent caustic by bipolar membrane electrodialysis was firstly reported. ► The operation parameters on the process were fully investigated and optimized. ► The process cost was estimated.

•Regenerating NaOH from the spent caustic using two kinds of ED was firstly compared.•The influences of operation parameters on the performance were fully investigated.•The economics were analyzed and commented.Sodium hydroxide has been widely used in removing acidic compounds from crude oil and natural gas or their fractions during the production of petrochemical industry. This must leads to the generation of a large amount of spent caustic. In previous paper, BMED was used to regenerate sodium hydroxide (NaOH) from spent caustic. To find the variety of that regeneration process, the reclamation of sodium hydroxide by using electro-electrodialysis (EED) were performed. The influences of current density and initial base concentration on regeneration process were analyzed. In comparison, BMED has higher base yield and current efficiency. However, its process cost is higher than that of EED due to the extra expenditure for its tank, pumps and bipolar membrane. The process cost is estimated to be 0.97 $/kg NaOH for BMED and 0.86 $/kg NaOH for EED. However, BMED will be more economically attractive as the price of bipolar membrane decreases, and has more environmental benefits by prevention secondary pollution.