Reverse Osmosis Systems

Spira.1- Wound Modules. Spiral-wound modules were used originally for artificial kidneys, but were fuUy developed for reverse osmosis systems. This work, carried out by UOP under sponsorship of the Office of Saline Water (later the Office of Water Research and Technology) resulted in a number of spiral-wound designs (63—65). The design shown in Figure 21 is the simplest and most common, and consists of a membrane envelope wound around a perforated central coUection tube. The wound module is placed inside a tubular pressure vessel, and feed gas is circulated axiaUy down the module across the membrane envelope. A portion of the feed permeates into the membrane envelope, where it spirals toward the center and exits through the coUection tube. 

Fig. 6. High pressure reverse osmosis system for alcohol reduction.

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

Hydrocomponents Technologies, Inc. Site describes products supplied for commercial, industrial and residential applications membrane production equipment components for manufacturers of reverse osmosis systems. http //www.hcti.com... 

Cordonna Associates, inc. Site provides online shopping for reverse osmosis systems, http //caitechnologies.com/water.htm... 

TDS affects taste also, and waters over 500 - 600 ppm can taste poor. When the levels top 1500 ppm, most people will report the water tastes very similar to weak alka-seltzer. TDS is removed by distillation, reverse-osmosis or electrodialysis. In our area, most desalination projects, both large and small are accomplished with reverse-osmosis. Depending on the water chemistry, reverse osmosis systems are the most popular, given their low cost and ease of use. Distillers work very well also, and produce very high quality water, but require electricity and higher... 

Gupta, S. K. (1987). Design and analysis of a radial-flow hollow-fiber reverse-osmosis system. Ind. Eng. Chem. Res. 26, 2319-2323,... 

Orofino, T. A. (1977). Technology of hollow fiber reverse osmosis systems. In Reverse Osmosis and Synthetic Membranes (S. Sourirajan, eds.), pp. 313-341 National Research Council, Ottawa, Canada. 

Soltanieh, M., and Gill, W. N. (1982). Analysis and design of hollow fiber reverse osmosis systems. Chem. Eng. Commun., 18, 311-330. 

Amjad, Zahid Zibrida, John F. Zuhl, Robert W. Silica Control Technology for Reverse Osmosis Systems. Ultrapure Water, Tall Oaks Publishing, Inc., USA, February 1999. 

Arlington, California, brackish reverse osmosis system, 26 82-83 Armor, silicon carbide in, 22 538 Army Corps of Engineers aquaculture regulation, 3 185 ARNITE, 20 33, 59... 

Nanofiltration membranes, 15 825 acid resistant, 21 635t in nonaqueous media, 21 654—656 organic rejections by, 21 656-657 Nanofiltration reverse osmosis systems, 26 80-83... 

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... 

Seawater pretreatment, 16 25 Seawater reverse osmosis systems,... 

To reduce the water usage of the BDS system to the lowest possible level, reverse osmosis (RO) can be used to reclaim up to 75% of the water from the BDS waste. The electrical and maintenance costs required to operate the RO system are more than balanced by the savings in water. In fact, several cases have shown that where water is in short supply, the savings can offset the additional capital cost of the reverse-osmosis system within three years. 

For purposes of illustration, the following discussion, unless otherwise specified, is limited to single-solute aqueous feed solutions, cellulose acetate membranes, and reverse osmosis systems for which osmotic pressure effects are essentially negligible. 

Figure 2a. Experimental data on the effect of operating pressure, average pore size on membrane surface, and feed concentration on solute separation and product rate for the reverse osmosis system cellulose acetate membrane-sodium chloride-...

Using these potential functions, one can then calculate (19) solute separation, product rate, and (PR)/(PWP) ratio obtainable for the reverse osmosis systems corresponding to data given In Figures 2(a) to 2(d). The results of such calculations are given In Figures 4(a) to 4(d) where the Indicated values of pore radius R represent only relative values. 

The solute-solvent-polymer (membrane material) interactions, similar to those governing the effect of structure on reactivity of molecules (20,21,22,23,24) arise in general from polar-, sterlc-, nonpolar-, and/or ionic-character of each one of the three components In the reverse osmosis system. The overall result of such interactions determines whether solvent, or solute, or neither is preferentially sorbed at the membrane-solution Interface. 

With particular reference to reverse osmosis systems involving cellulose acetate membranes and aqueous solutions, the membrane material has both polar and nonpolar character, and the solvent, of course, is polar. When these two components of the reverse osmosis system are kept constant, preferential sorption at the membrane-solution interface, and, in turn, solute separation in reverse osmosis, may be expected to be controlled by the chemical nature of the solute. If the latter can be expressed by appropriate quantitative physicochemical parameters representing polar-, steric-, nonpolar-, and/or ionic-character of the solutes, then one can expect unique correlations to exist between such parameters and reverse osmosis data on solute separations for each membrane. Experimental results confirm that such is indeed the case (18). 

The parameters AVg (acidity), AVg (basicity), pK, and Zo represent properties of solute in the bulk solution phase. If reverse osmosis separation is governed by the property of solute in the membrane-solution interface, the existence of unique correlations between data on reverse osmosis separations and those on the above parameters, means that the property of solute in the bulk solution phase and the corresponding property of solute in the membrane-solution interface are also uniquely related. This leads one to the development of interfacial free energy parameters (-AAG/RT) for both nonionized solute molecules and dissociated ions in solution for reverse osmosis systems where water is preferentially sorbed at the membrane-solution interface. 

Nonpolar Parameters. In a reverse osmosis system involving cellulose acetate membranes and aqueous solutions of hydrocarbon solutes, the adsorption of water and that of solute on the polar and nonpolar sites of the membrane surface respectively may be expected to take place essentially independently. Further, since the polymer-solute interaction forces are attractive in nature for the above case, the mobility of the solute molecules through the membrane pore is retarded, and they also tend to agglomerate... 

---