Seawater reverse osmosis membrane

R.E. Larson, J.E. Cadotte and R.J. Petersen, The FT-30 Seawater Reverse Osmosis Membrane-element Test Results, Desalination 38, 473 (1981). 

S. Ebrahim and H. El-Dessouky, Evaluation of commercial cleaning agents for seawater reverse osmosis membranes. Desalination 99, 169-188 (1994). 

V. Murugan, K. Rajanbabu, S.A. Tiwari, C. Balasubramanian, M.K. Yadav, A.Y. Dangore, S. Prabhakar, P.K.Tewari, Fouling and cleaning of seawater reverse osmosis membranes in Kalpakkam nuclear desalination plant, Int. J. Nucl. Desal. 2,2006,172-178. 

J.E. Cadotte, R.J. Petersen, R.E. Larson, E. E. Erickson, A new thin-film composite seawater reverse osmosis membrane. Desalination 32 (1980) 25. 

B. Hofs, R. Schurer, D.J.H. Harmsen, C. Ceccarelli, E.F. Beerendonk, E.R. Cornelissen. Characterization and performance of a commercial thin film nanocomposite seawater reverse osmosis membrane and comparison with a thin film composite. Journal of Membrane Science 446 (2013) 68-78. 

In other areas, POD has been used to improve the wear resistance of a mbber latex binder by incorporation of 25% of Oksalon fibers. Heat-resistant laminate films, made by coating a polyester film with POD, have been used as electrical insulators and show good resistance to abrasion and are capable of 126% elongation. In some instances, thin sheets of PODs have been used as mold release agents. For this appHcation a resin is placed between the two sheets of POD, which is then pressed in a mold, and the sheets simply peel off from the object and mold after the resin has cured. POD-based membranes exhibit salt rejection properties and hence find potential as reverse osmosis membranes in the purification of seawater. PODs have also been used in the manufacturing of electrophotographic plates as binders between the toner and plate. These improved binders produce sharper images than were possible before. 

In reverse osmosis membranes, the pores are so smaH, in the range 0.5— 2 nm in diameter, that they ate within the range of the thermal motion of the polymer chains. The most widely accepted theory of reverse osmosis transport considers the membrane to have no permanent pores at aH. Reverse osmosis membranes are used to separate dissolved microsolutes, such as salt, from water. The principal appHcation of reverse osmosis is the production of drinking water from brackish groundwater or seawater. Figure 25 shows the range of appHcabHity of reverse osmosis, ultrafiltration, microfiltration, and conventional filtration. 

Although the principal appHcation of reverse osmosis membranes is still desalination of brackish water or seawater to provide drinking water, a significant market is production of ultrapure water. Such water is used in steam boilers or in the electronics industry, where huge amounts of extremely pure water with a total salt concentration significantly below 1 ppm are required to wash siUcon wafers. 

Reverse osmosis membrane process, 27 637 Reverse osmosis membrane cleaning citric acid application, 6 647 Reverse-osmosis membranes, 75 811, 825 development of, 75 797 Reverse osmosis models, 27 638-639 Reverse osmosis permeators, 76 19 Reverse osmosis seawater desalination process, 26 85 Reverse osmosis systems blending in, 26 80-81 brackish and nanofiltration, 26 80-83 Reverse osmosis technology... 

Figure 16. Decrease of separation (or increase of solute permeabilities) of seawater reverse osmosis desalination at several concentration levels of NaOCl. Initial membrane constants pure water permeability constant = 97.0 nmol m Pa s and the solute permeability constant for NaCl = 0.9 X 10 cm s . Operational conditions k = 7.(97 X 10 cm s Ap = 6.0 MPa, and T = 25°C.

Figure 2. Exposure of FT-30 membranes to 100 ppm chlorine in water at different pH levels. Effect on salt refection in simulated. seawater reverse osmosis tests (0) pH 1 Cn pH 5 (O) pH 8 (A) pH 12.

Albany International Research Co. has developed an advanced hollow fiber composite reverse osmosis membrane and module under the name of Quantro II . This composite membrane is comprised of a porous hollow fiber substrate on which has been deposited a rejection barrier capable of fluxes of commercial importance at high rejection of dissolved salts at elevated temperatures. Resistance to active chlorine has been demonstrated. Proprietary processes have been developed for spinning of the fiber, establishment of the rejection barrier and processing of the fiber to prepare modules of commercial size. Prototype modules are currently in field trials against brackish and seawater feed solutions. Applications under consideration for this membrane include brackish and seawater desalination as well as selected industrial concentration processes. 

Figure 2.9 Flux and rejection data for a model seawater solution (3.5 % sodium chloride) in a good quality reverse osmosis membrane (FilmTec Corp. FT 30 membrane) as a function of pressure [10]. The salt flux, in accordance with Equation (2.44), is essentially constant and independent of pressure. The water flux, in accordance with Equation (2.43), increases with pressure, and, at zero flux, meets the pressure axis at the osmotic pressure of seawater 350 psi...

A number of membrane materials and membrane preparation techniques have been used to make reverse osmosis membranes. The target of much of the early work was seawater desalination (approximately 3.5 wt% salt), which requires membranes with salt rejections of greater than 99.3 % to produce an acceptable permeate containing less than 500 ppm salt. Early membranes could only meet... 

Since the discovery by Cadotte and his co-workers that high-flux, high-rejection reverse osmosis membranes can be made by interfacial polymerization [7,9,10], this method has become the new industry standard. Interfacial composite membranes have significantly higher salt rejections and fluxes than cellulose acetate membranes. The first membranes made by Cadotte had salt rejections in tests with 3.5 % sodium chloride solutions (synthetic seawater) of greater than 99 % and fluxes of 18 gal/ft2 day at a pressure of 1500 psi. The membranes could also be operated at temperatures above 35 °C, the temperature ceiling for Loeb-Sourirajan cellulose acetate membranes. Today s interfacial composite membranes are significantly better. Typical membranes, tested with 3.5 % sodium chloride solutions,... 

The approximate operating costs for brackish and seawater reverse osmosis plants are given in Table 5.3. These numbers are old, but improvements in membrane technology have kept pace with inflation so the costs remain reasonably current. 

The reverse-osmosis membrane process is considered universally as the most promising technology for brackish and seawater desalination [18]. Potential directions for reducing desalination costs may be deduced by analyzing the cost of the components. 

An UF system utilizing hollow-fiber (FIF) membranes has been successfully used as pretreatment prior to seawater reverse osmosis (SWRO) desalination without any chemical treatments [8]. The quality of UF permeate was good and satisfied the need of SWRO feed water [8]. 

Some of the largest plants for seawater desalination, wastewater treatment and gas separation are already based on membrane engineering. For example, the Ashkelon Desalination Plant for seawater reverse osmosis (SWRO), in Israel, has been fully operational since December 2005 and produces more than 100 million m3 of desalinated water per year. One of the largest submerged membrane bioreactor unit in the world was recently built in Porto Marghera (Italy) to treat tertiary water. The growth in membrane installations for water treatment in the past decade has resulted in a decreased cost of desalination facilities, with the consequence that the cost of the reclaimed water for membrane plants has also been reduced. 

Reverse osmosis membranes can be divided into subclasses according to their solute/water selectivity and operating pressure regimes. Figure 30 shows a number of commercial membranes developed for seawater and brackish desalination, and for nanofiltration. These include cellulose ester and polyamide asymmetric membranes available since the 1960s, and high-performance composite membranes developed in the 1970s. Collectively, they make it possible to produce potable water from virtually all saline water sources. 

FIGURE 30 Performance of some commercial reverse osmosis membranes for (a) seawater desalination (test conditions 56 bar 25°C 3.5% NaCI feed) (b) low-pressure desalination (15 bar 25°C 1500 mg/liter NaCI feed) and (c) ultralow-pressure nanofiltration applications (7.5 bar, 25°C 500 mg/liter NaCI feed). 

Goosen M.F.A., Sablani S., Dal Cin M., Wilf M., Jackson D., Al-Belushki R., and AlMaskri S., Effect of high temperature and pressure on permeation properties of composite polyamide seawater reverse osmosis and brackish water nanofiltration membranes. Journal of Membrane Science (Submitted 2008). 

Reverse osmosis membrane is widely used in seawater and brackish water desalination processes. Compared to traditional distillation, there is no energy-intensive phase change involved in membrane processes. Therefore, desalination with RO membrane is more energy efficient. In addition to the traditional desalination processes, RO membranes have also found wide application in industrial and municipal wastewater treatment, in pure water production for the electronic and pharmaceutical industries, and in the food industries. 

Generally, the salt rejections observed for these membranes in seawater reverse osmosis tests did not exceed 80 percent. This process was applied at Albany International to form composite membranes on hollow polysulfone fibers (25). Salt rejections on the hollow fiber membranes were above 98 percent at an average flux of about 1.5 gfd (2.5 L/sq m/hr) in a 12 000-hour test using 30 000 ppm seawater at 1000 psi. In other 5000-hour tests using 3500 ppm brackish water at 400 psi with addition of 100 ppm chlorine at pH 8 flux and salt rejection remained constant at 1 gfd and 98 percent respectively (Figures 8 and 12 in Reference 25 a). 

Properties of FT-30. The properties of FT-30 membranes have been reviewed in several publications. Therefore, only the salient features that relate to the chemistry of the barrier layer will be considered here. Reverse osmosis performance of FT-30 under seawater and brackish water test conditions was described by Cadotte et al (48) and by Larson et al (51). In commercially produced spiral-wound elements the FT-30 membrane typically gives 99.0 to 99.2 percent salt rejection at 24 gfd (40 L/sq m/hr) flux in seawater reverse osmosis tests with 3.5 percent synthetic seawater at 800 psi (5516 kPascaJJand 25°C. 

Graefe, A.F. "Development of a Composite Reverse Osmosis Membrane for Single Pass Seawater Desalting" NTIS Report No. PB-80 124852... 

As of the end of 1984, the desalination of brackish water accounted for 82% of capacity. This is due to the fact that early reverse osmosis membranes were incapable of single stage seawater desalination and, thus, they were limited to brackish water desalination. Within the last 10 years, significant advances have been made in both the flux and rejection capability of membranes and reverse osmosis is technically able to desalt seawater in a single stage. In the recent past, it has been an effective competitor to the distillation process in seawater desalination. In fact, reverse osmosis is now beginning to replace existing distillation capacity in the Middle East.4... 

The PA-300 membrane was the first composite reverse osmosis membrane to be used successfully in a major seawater desalination facility-the 3.2 MGD plant at Jeddah, Saudi Arabia.35 Much of the original membrane in this plant, as well as replacement membrane, is believed to be RC-100 (the TDI-based analog) because of its greater stability and retention of salt rejection. The Jeddah plant was truly a pioneer installation for spiral-wound composite membranes. Even though it was attended by a variety of start-up and operating problems, mostly unrelated to the membranes,36 it continues to operate successfully at this date. 

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