A Master of Science thesis in Chemical Engineering by Muhammad Ashraf Sabri entitled, "Treatment of Spent Caustic Using Ionic Liquids," submitted in April 2017. Thesis advisor is Dr. Taleb Hassan Ibrahim. Soft and hard copy available.
Treatment of spent caustic (SC) wastes from downstream of refineries and petrochemical industries is not only complex but also highly expensive due to its content of high concentration of hazardous compounds, high pH, variations in the waste composition and the need to comply with the environmental regulations. Owing to the presence of pollutants such as sulfides, mercaptans and phenols, SC is known to be among the most difficult class of wastes to be treated and disposed. Several existing technologies have been applied to treat SC; however, they require extreme operation conditions of pressure and temperature. These methods are neither environment friendly nor cost effective. Thus, efforts are directed toward removal of specific pollutants particularly phenols, sulfides and mercaptans from SC streams in simple and environment-friendly manner. In this work, two hydrophobic ionic liquids (IL), tetrahexylammoniumdihexyl-sulfosuccinate (IL1) and trioctylmethylammonium salicylate (IL2), were used to treat industrial SC at room temperature using both bench scale batch contactor and sequential batch contactor modes. UVVis spectroscopy, gas chromatography coupled with mass spectrometry (GC-MS) and chemical oxygen demand (COD) analysis were employed for SC characterization. The chemical composition and the COD values of SC were determined before and after treatment with IL1 and IL2. The operating conditions for extraction were optimized. The results reveal that both ionic liquids have the same optimum phase ratio and initial pH of 1.0 and 1.7, respectively. The optimum contact time for IL1 and IL2 is less than 6.0 minutes and 1.0 minute, respectively. Under these optimum conditions, IL1 and IL2 are able to reduce the COD level from 6.4x104 mg/L to 63 mg/L and the phenol level from 3.2x102 mg/L to 0.032 mg/L in SC. Thiol and benzaldehyde concentrations after treatment are brought below the detection limit of the GC-MS. Thus, this work highlights the high potential of ILs as an alternative SC treatment solution compared tothe current complex industrial processes that require drastic operation conditions, use of hazardous chemicals and long contact times for SC treatment. The results of this work assure that the use of ILS for SC treatment is highly efficient, environmentally friendly, simple and novel.