ESEL Paper Review_20140508
By Hong Guo
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1, Title and Author
Title: Application of thin film composite membrane with forward osmosis technology for separation of emulsified oil-water
Journal: Journal of Membrane Science
Phuoc H.H. Duonga,Tai-Shung Chunga,b,*
a Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore
b Water Desalination & Reuse (WDR) Center, King Abdullah University of Science and Technology, 23955-6900 Saudi Arabia
2. Summary of Paper
? The aim of the paper is to investigate the effectiveness of forward osmosis(FO) processes to treat the stable oil-water emulsions.
? The FO techniques has been demonstrated successfully for the treatment of a wide range of oil-water emulsions from a low to a very high concentration up to 200,000 ppm
? Water can be separated from oily feeds containing 500 ppm or 200,000 ppm emulsified oil at relatively high flux of 16.5 ± 1.2 LMH or 11.8 ± 1.6 LMH respectively by using a thin fim composite membrane PAN-TFC and 1M NaCl as the draw solution. This membrane can achieve an oil rejection of 99.88% to produce water with a negligible oil level.
? Performance of PAN-TFC membranes towards various emulsified oil-water concentrations
? All FO experiments in this study were conducted for 30 min using a 1 M NaCl draw solution and fresh PAN-TFC membranes. Five feed concentrations were employed; namely, 0 ppm (DI water), 500 ppm, 5000 ppm, 50,000 ppm and 200,000 ppm (20 wt %).
? The water flux drops from 19.6 7 1.0 LMH using DI water as the feed to 16.5 71.2 LMH using a feed containing 500 ppm oil. The decrease in water flux is probably due to the presence of emulsified oil particles in the feed which causes viscosity increase and additional water transportation resistance across the membrane because of the presence of emulsified oil particles.
? The water flux further decreases with an increase in emulsified oil particle concentration from 500 ppm to 200,000 ppm. In addition to viscosity increase, the more precipitation and adsorption of emulsified oil particles on the membrane surface may be the other causes.
? Effect of feed flow rate to water flux for oil-water separation
? The effect of feed flow rate to water flux was studied using 1 M NaCl as the draw solution and oil?water emulsions with concentrations ranging from 0 ppm to 200,000 ppm as feeds under the FO mode.
? Each experiment was conducted in 30 min by using a fresh PAN-TFC membrane. The system was operated under the laminar flow with a fixed draw flow rate but various feed flow rates. As shown in Fig. 9, water flux does not vary much by changing the feed flow rate from 0.15 L/min to 1 L/min when oil?water emulsions of 0 ppm or 500 ppm are used.
? However, water flux is a function of feed flow rate when the feed contains oil particles equal to or greater than 5000 ppm possibly due to colloidal fouling.
? To understand more the effect of the feed flow rate to water flux, additional experiments were conducted to investigate the fouling behavior of the emulsified oil particles onto the membrane surfaces under various feed conditions
? The higher feed flow rate (i.e., larger Re Number) can reduce the fouling tendency of the emulsified oil particles onto the membrane surface. The water flux is increased under higher feed flow rate operations because of less fouling occurred
? The higher the oil particle concentration, the higher the feed flow rate and Re number are required to reach the plateau. This phenomenon is probably due to the thicker and more compact cake layer of oil particles formed on the membrane surface when the oil concentration increases. And as soon as the cake layer forms, the fouling is less sensitive to the change in feed flow rate.
? For the function between the normalized water flux and water recovery for the emulsified oily water with an extremely high concentration of 200,000 ppm, the water recovery rate is more than 60% while the water flux still maintains half of the initial water flux
? The water recovery rate of treatment process mainly depends on the feed conditions, membrane properties and the osmotic efficiency of the draw solution.
? A comparison of PAN-TFC and the HTI-FO membranes
? Compared to the HTI-FO membrane, the PAN-TFC membrane shows a faster decline in water flux overtime. This is due to the fact that the latter has greater fouling of emulsified oil particles on the membrane surface. Interestingly, no
severe fouling was observed for the HTI-FO membrane under a similar feed condition.
? From the view of the molecular structure of two membranes, the CTA active layer of HTI-FO membrane only contains the hydroxyl (OH) groups which generate weak hydrogen bonds between water/ emulsified oil particles and the membrane surface, while the active layer of the PAN-TFC membrane is an aromatic polyamide layer that contains a cross-linked portion of amide linkages (?NH?CO?) and a linear portion of carboxylic groups (?COOH). Although both groups (?NH?CO? and ?COOH) help lower the contact angle and assist water permeation by the formation of hydrogen bonds between these functional groups and water molecules, they also facilitate the hydrogen bonds between the OH groups around the emulsified oil particles and the TFC layer. This would result in fast fouling of oil particles onto the PAN-TFC membrane surface
This research give the guideline of research for the produced water treatment by using the desalination technology. Detail information from the pater would be greatly helpful for the future study.
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