Reverse osmosis performance

Prediction of reverse osmosis performance is usefiil to the design of RO processes. Simulation of RO processes can be separated iato two categories. The first is the predictioa of membrane module performance. The second is the simulation of a network of RO processes, ie, flow sheet simulations, which can be used to determine the optimum placement of RO modules to obtain the overaH process objective. 

The reverse osmosis performance of the two membranes under typical brackish water conditions is shown in Figure 2 (I, reference membrane III, with bentonite). At a rejection of 85 % the flux is almost doubled (from 2000 to nearly 4000 l/m d), the effect becoming smaller when going to higher rejections. Maximum brackish water rejection of the bentonite membrane is 97 % as against 98 % for the reference membrane. 

Figure 2. Effect of hydrophilic bentonite incorporation on the reverse osmosis performance of asymmetric cellulose diacetate membranes I, reference membrane III, with hydrophilic bentonite.

Figure 6. Low-pressure reverse osmosis performance of ammonia-modified cellulose diacetate membranes (IV) compared with formamide-modified reference membranes (I)...

Membrane Properties. The reverse osmosis performance of the bentonite-doped membrane under brackish water conditions is compared to that of the reference membrane in Figure 5 (I, reference membrane II, with organophilic bentonite). At low salt rejection the bentonite membrane again shows a higher initial flux than the reference membrane, the performance of the two becoming identical at the high rejection limit. 

In light of the discussion above, it is desirable to alter the chemical nature of these polymers to induce a measure of hydrophilicity while maintaining the excellent physical character. Sulfonation has been known to dramatically alter a number of characteristics of poljmeric materials (for example, dyeabllity (17), tensile strength (18), and, of particular interest to the present studies, hydrophilicity (19)). In fact, sulfonation has been used to improve the reverse osmosis performance of poly(phenylene oxide)... 

Effect of Cosolvent Composition and Gelation Medium on Reverse Osmosis Performance... 

Reverse osmosis performs a separation without a phase change. Thus, the energy requirements are low. Typical energy consumption is 6 to 7 kWh/m2 of product water in seawater desalination. Reverse osmosis, of course, is not only used in desalination, but also for producing high-pressure boiler feedwater, bacteria-free water, and ultrapure water for rinsing electronic components—because of its properties for rejecting colloidal matter, particle and bacteria. 

Table 5.5 Advances in spiral-wound module reverse osmosis performance...

Fleming, S. The Reverse Osmosis Performance of a Polyelectrolyte Complex Membrane, Academic Press, New York (1970)... 

Adapted from "Reverse Osmosis Performance Data Collection and Interpretation," originally presented at the 28th Annual Electric Utility Chemistry Workshop, Champaign, IL, May 2008, and published in "UltraPure Water Journal, www.ultrapurewater.com, April, 2009. 

Standard Practice for Standardizing Reverse Osmosis Performance Data," ASTM D4516-00, Jan. 10,2000. 

Reverse Osmosis Performance in the Treatment of Cs Liquid Wastes.927... 

Ultrafiltration membranes are suitable for the treatment of radioactive liquid wastes, especially as reverse osmosis pretreatment [6]. Therefore, ultrafiltration is used for the removal of the radioactivity associated with the proteins and high-molecular-weight organic compounds, as these species can reduce reverse osmosis performance. 

S. 1. Graham, R. L. Reitz, and C. E. Hickman, Improving reverse osmosis performance by periodic cleaning. Desalination 74, 113-124 (1989). 

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. 

Figure 6. Average Reverse-Osmosis Performance of Membranes Evaluated...

Figure 8. Effect of Ethanol Feed Concentration on the Reverse-Osmosis Performance of Triplicate TFC-801 Membranes (800 psi, ambient temperature)...

Reverse-Osmosis Performance of 3N8 Membranes at Different Operating Pressures [Basis 1000 gal/hr of 50-volZ ethanol product output. ]... 

It was also shown that the change of reverse osmosis performance data of a particular solute with the change in pore size of the membrane and the experimental operating condition such as operating pressure depends significantly on the relative magnitude of the distance associated with the steric repulsion at the interface and the quantity representing the affinity of the solute molecule to the polymer surface. 

Reverse osmosis memhraaes. The exceptionally high moisture regain observed with polybenzimidazole fibers prompted a team at Celanese Research Co to investigate the utility of polybenzimidazole films as semipermeable membranes for reverse osmosis processes, such as sea water desalination66,94). A continuous process was devised in which films were cast from solution into a water precipitation bath. The films were tested for reverse osmosis performance with a saline solution (0.5% Nad) as feed stream at a pressure of 4.14 MN m-2 and a flow rate of 19.8 m min-1. Salt rejection was ca. 95% throughout. A cellulose acetate film of the type commonly used as a reverse osmosis standard was tested under the same conditions for comparison. Table 8 shows the results. 

Table 5.1 Reverse Osmosis Performance of the PA-300 Composite Membrane Toward Various Organic Solutes...

Table 5.2 Reverse Osmosis Performence of Membranes from Various Diamines or Polyamines Reacted with Terephthaloyl Chloride...

Cadotte discovered that aromatic diamines, interfacially reacted with triacyl halides, gave membranes with dramatically different reverse osmosis performance characteristics than membranes based on aliphatic diamines. 56 Before that time, the area of aromatic amines in interfacial membrane formation had been neglected because of two factors (a) the emphasis on chlorine-resistant compositions, which favored use of secondary aliphatic amines such as piperazine, and (b) poor results that had been observed in early work on interfacial aromatic polyamides. The extensive patent network in aromatic polyamide (aramid) technology may also have been a limiting factor. 

The properties of FT-30 membranes have been reviewed in several publications, including reverse osmosis performance under seawater and brackish water test conditions.60"62 In commercially produced spiral-wound elements, the FT-30 membrane typically gives 99.1 to 99.3% salt rejection at 24 gfd flux in seawater desalination at 800 psi and 25°C. In brackish water applications, FT-30 spiral elements can be operated at system pressures of as low as 225 psi while producing water at 22 to 24 gfd. Similar flux levels are possible with the TFC-202 and LP-300 membranes, as mentioned earlier. But it is notable that those membranes achieve such high fluxes through use of extremely thin surface barrier layers about only one-tenth the thickness of the FT-30 barrier layer. 

Table 5.6 Reverse Osmosis Performance of PEC-1000 Membrene for Various Organic Solutes in Aqueous Solutions...

Early work by Buck and Davar89 examined the plasma polymerization of several monomer systems. Best results in terms of reverse osmosis performance were achieved with vinylene carbonate/acrylonitrile and vinyl acetate/acrylo-nitrile. 

Wydeven and his coworkers examined the plasma polymerization of several amine monomers and obtained the best reverse osmosis membranes using allyl-amine.90/91 Reverse osmosis performances of 98 to 99% salt rejection and 4 to 8 gfd flux were achieved at test conditions of 1.0% sodium chloride, 600 psi, 20 C. ESCA spectra showed the nitrogen groups in the plasma-formed polymer to be nitrile or imine groups, but not amine groups. Oxygen was also present in the ESCA analysis. Elemental analysis showed a membrane stoichiometry of C3H 3 8N 0.9O0.1. 

Second, insoluble crosslinked barrier layer compositions are possible, and, in fact, are almost universal in the composite membrane approach. Optimum reverse osmosis performance and chemical stability can be achieved, in part, due to preparation of crosslinked compositions. This is readily possible by the composite membrane approach, but not so simple by the asymmetric membrane approach. The PA-300, FT-30, and PEC-1000 barrier layer compositions, for example, are simply not feasible to prepare by asymmetric film casting techniques. The composite approach, therefore, is far more versatile. 

Liu, M., Wu, D., Yu, S., and Gao, C. 2009. Influence of the polyacyl chloride structure on the reverse osmosis performance, surface properties and chlorine stability of the thin-fihn composite polyamide membranes. Journal of Membrane Science 326 205-214. 

M. Sancho, J.M. Amal, G. Verdu, J. Lora, J.I. Vfllaescusa, Ultrafiltration and reverse osmosis performance in the treatment of radioimmunoassay liquid wastes. Desalination 201, 2006, 207-215. 

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