Treatment of olefin plant spent caustic by combination of neutralization and Fenton reaction.
Spent caustic from olefin plants contains much H2S and some mercaptans, phenols and oil. A new treatment process of spent caustic by neutralization followed by oxidation with Fenton's reagent (Fe2+/H2O2) was successfully developed. Over 90% of dissolved H2S were converted to gas phase by neutralization at pH = 5 and T = 70 degrees, and the vent gas stream could be introduced to sulfur recovery plant. The neutralized liquid was oxidized with OH. free radical, which was provided by a Fenton's reagent. The residual sulfides in the neutralized spent caustic were oxidized to less than 0.1 mg/L. The total COD removal of spent caustic is over 99.5% and the final COD value of the effluent can be lower than 100 mg/L under the following oxidation conditions: reaction time = 50 min, T = 90 degrees, Fe2+ = 100 mg/L, and a stoichiometric H2O2/COD = 1.1. The value is better than the 800 mg/L value obtained by common WAO process. The optimum pH of the Fenton reaction is around 2 for this process, and the oxidation step can maintain a pH value in the range of 1.8-2.4. Moreover, the iron catalyst can be recycled without affecting process effectiveness thus preventing secondary pollution.
Sheu
S H
SH
Department of Chemical Engineering, National Cheng Kung University, Tainan, 70101, Taiwan, ROC.
Weng
H S
HS
D000475:Alkenes; D002424:Caustics; D004867:Equipment Design; D006861:Hydrogen Peroxide; D006862:Hydrogen Sulfide; D007220:Industrial Waste; D007501:Iron; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
D000475:Alkenes; D002424:Caustics; C045076:Fenton's reagent; D007220:Industrial Waste; D014874:Water Pollutants, Chemical; D006861:Hydrogen Peroxide; D007501:Iron; D006862:Hydrogen Sulfide