Regeneration of spent caustic of olefin unit in a bubble column reactor: Treatment and recovery optimization

Abstract

In this work, regeneration of spent caustic of olefin unit was investigated. Sulfur compounds in the petrochemical products lead to environmental issues, so they should be eliminated. The strong alkaline media such as caustic is used to remove these compounds. Spent caustic contains noxious components such as phenol, mercaptans, mercaptide, sulfide and high chemical oxygen demand (COD) value of up to 30,000 mg/L. The main purposes are treatment of wastewater and recovery of caustic. The process was carried out in a batch bubble column reactor, and then effluent was treated in a precipitation stirred tank reactor. The catalytic air oxidation was used for treating this waste via IVKAZ catalyst, and lime was applied to sedimentary reactions in second reactor. The full factorial method was used for experimental design along with the RSM method for optimization of experiment results. Three independent variables of temperature, reaction time, and air flow were considered. The results indicate that this method is able to use two different processes (catalytic oxidation and chemical precipitation), due to the fact that the amount of caustic can be increased up to six times of initial value and also could treat solution more than 50%. The optimum conditions are 90°C, 7 L/min, and 30 min, which can be reached by 6% wt caustic, around 5000 mg/L concentration of COD, and 360 mg/L amount of S2− with this newly developed process. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 341–347, 2017