Diesel Oil Removal by Froth Flotation Under Low Interfacial Tension Conditions II: Continuous Mode of Operation

Abstract

The objective of this study was to investigate the relationship between interfacial tension (IFT) and foam characteristics and the efficiency of diesel oil removal from water in a continuous froth flotation column. The effects of operational parameters, including surfactant concentration, salinity, oil-to-water ratio, foam height, air flow rate, and hydraulic retention time (HRT) on the oil removal were investigated in the continuous mode of a froth flotation operation and compared to batch operation results. Unlike the batch system, for the continuous system used in the present study, having only branched alcohol propoxylate sulfate sodium salt surfactant (C_14–15(PO)₅SO₄Na) and NaCl present in the solution yielded such poor foam characteristics that a stable froth which overflowed the flotation column could not be produced, so the addition of sodium dodecyl sulfate (SDS) as a froth promoter was used to improve the foam stability. Unlike the batch froth flotation system with only C_14–15(PO)₅SO₄Na, the continuous froth flotation with the mixture of C_14–15(PO)₅SO₄Na and SDS, it was not possible to find a SDS and a NaCl concentration at which both ultralow IFT and good foaming were both achieved. Foam formation, stability, and production rate were found to be crucial parameters to the froth flotation efficiency. The continuous froth flotation system offers a high diesel oil removal of 96% in the single stage unit. Demonstration of efficient operation in the continuous mode in this work is important to the practical application of froth flotation in large scale processing.

Keywords:

• Continuous froth flotation
• Diesel oil removal
• Foam formation
• Foam stability
• Microemulsion

ACKNOWLEDGEMENTS

The Thailand Research Fund is acknowledged for providing a Royal Golden Jubilee Ph.D. fellowship for Ms. Sunisa Watcharasing. The expenses for this research were mainly supported by The Advanced Research Scholar Grant from the Thailand Research Fund and the Research Unit of Applied Surfactants for Separation and Pollution Control under The Ratchadapisek Somphot Fund, Chulalongkorn University. The National Excellence Center for Petroleum, Petrochemicals and Advanced Materials under The Ministry of Education is also acknowledged for providing all research facilities. Sasol North America Inc., Texas, USA, is acknowledged for providing the extended surfactant used in this research. Moreover, support was also received from the industrial sponsors of The Institute for Applied Surfactant Research, University of Oklahoma including Akzo Nobel, Clorox, Conoco/Phillips, Church and Dwight, Dow, Ecolab, Halliburton, Huntsman, Oxiteno, Procter & Gamble, Sasol North America, Shell Chemical, and Unilever.