Crossflow microfiltration of oily water |
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| Institution: | 1. School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore;2. Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore 637141, Singapore;1. Gas Processing Centre, Qatar University, Doha, Qatar;2. Department of Chemical Engineering, Qatar University, Doha, Qatar;3. Maersk Oil Research and Technical Centre, Doha, Qatar;4. Maersk Oil Qatar, Doha, Qatar;1. CAS Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, PR China;2. Ningbo Urban Environment Observation and Research Station-NUEORS, Chinese Academy of Sciences, PR China;3. Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong;4. Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, PR China;5. School of Chemistry and Chemical Engineering, South China University of Technology, PR China;1. Department of Energy Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran;2. Department of Chemical & Petroleum Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran;1. Key Laboratory of Hydraulic Machinery Transients (Wuhan University), Ministry of Education, School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei 430072, China;2. Key Laboratory of Green Chemical Process of Ministry of Education, Key Laboratory of Novel Reactor and Green Chemical Technology of Hubei Province, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430205, China;3. Key Laboratory of Processing and Testing Technology of Glass & Functional Ceramics of Shandong Province, School of Materials Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan, Shandong 250353, China |
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| Abstract: | Two α-alumina ceramic membranes (0.2 and 0.8 μm pore sizes) and a surface-modified polyacrylonitrile membrane (0.1 μm pore size) were tested with an oily water, containing various concentrations (250–1000 ppm) of heavy crude oil droplets of 1–10 μm diameter. Significant fouling and flux decline were observed. Typical final flux values (at the end of experiments with 2 h of filtration) for membranes at 250 ppm oil in the feed are ≈30–40 kg m?2 h?1. Increased oil concentrations in the feed decreased the final flux, whereas the crossflow rate, transmembrane pressure, and temperature appeared to have relatively little effect on the final flux. In all cases, the permeate was of very high quality, containing <6 ppm total hydrocarbons. The addition of suspended solids increased the final membrane flux by one order of magnitude. It is thought that the suspended solids adsorb the oil, break up the oil layer, and act as a dynamic or secondary membrane which reduces fouling of the underlying primary membrane. Resistance models were used to characterize the type of fouling that occurs. Both the 0.2 μm and the 0.8 μm ceramic membranes appeared to exhibit internal fouling followed by external fouling, whereas external fouling characterized the behavior of the 0.1 μm polymer membrane from the beginning of filtration. Examination of the external fouling layer showed a very thin hydrophobic oil layer adsorbed to the membrane surface. This oil layer made the membrane surface hydrophobic, as demonstrated by increased water-contact angles. The oil layer proved resistant to removal by hydrodynamic (shear) methods. By extracting the oil layer with tetrachloroethylene, followed by IR analysis, its average thickness at the end of a 2 h experiment under typical conditions was determined to be 60 μm for the 0.2 μm ceramic membrane and 30 μm for the 0.1 μm polymer membrane. These measured amounts of oil associated with the membrane at the end of the experiments are in good agreement with those determined from a simple mass balance, in which it is assumed that all of the oil associated with the permeate collected is retained on or in the membrane, indicating that the tangential flow did not sweep the rejected oil layer to the filter exit. |
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