Reverse osmosis applications

Two other major factors determining module selection are concentration polarisation control and resistance to fouling. Concentration polarisation control is a particularly important issue in liquid separations such as reverse osmosis and ultrafiltration. Hollow-fine-fibre modules are notoriously prone to fouling and concentration polarisation and can be used in reverse osmosis applications only when extensive, costly feed solution pretreatment removes all particulates. These fibres cannot be used in ultrafiltration applications at all. 

Amine sulfide terminal moieties can be imparted into vinyl polymers by using aminethiols as chain transfer agents in aqueous radical polymerization [1182]. The polymers are useful as mineral dispersants. Other uses are as water-treatment additives for boiler waters, cooling towers, reverse osmosis applications, and geothermal processes and oil wells and as detergent additives... 

The synthesis of 5 lan thick Ti02 Si02 layers on a porous support can be performed using the procedure given below. First a mixed Ti[(OMe)3]4 alkoxide is synthesized by reacting partially hydrolyzed Si(OMe)4 with Ti-isopropoxide. This inorganic polymer is hydrolyzed at pH 11.0 and treated with 2-methyl-2-4-pentanediol and a binder. This solution is then slip-cast onto a porous support, dried and calcined at 700°C. The membrane can be useful in reverse osmosis applications. 

Plate and frame systems offer a great deal of flexibility in obtaining smaller channel dimensions. Equations 4 and 5 show that the Increased hydrodynamic shear associated with relatively thin channels Improves the mass-transfer coefficient. Membrane replacement costs are low but the labor involved is high. For the most-part, plate and frame systems have been troublesome in high-pressure reverse osmosis applications due to the propensity to leak. The most successful plate and frame unit from a commercial standpoint is that manufactured by The Danish Sugar Corporation Ltd. (DDS) (Figure 15). 

Approximately one-half of the reverse osmosis systems currently installed are desalinating brackish or seawater. Another 40 % are producing ultrapure water for the electronics, pharmaceutical, and power generation industries. The remainder are used in small niche applications such as pollution control and food processing. A review of reverse osmosis applications has been done by Williams et al. [52],... 

The development of high-flux anisotropic membranes and large-surface-area membrane modules for reverse osmosis applications in the late 1960s and early 1970s provided the basis for modem membrane gas separation technology. The first company to establish a commercial presence was Monsanto, which... 

RO occurs when a solution is pressurized against a solvent-selective membrane, and the applied pressure exceeds the osmotic pressure difference across the membrane. Water is the solvent in most existing reverse osmosis applications the solutes may be salts or organic compounds. 

Some of those developments at Oak Ridge were believed to spin off in some form at Union Carbide and some aspects of the efforts led to the commercialization of dyiuunically formed membranes primarily for ultrafiltration and hypeiTiltration (reverse osmosis) applications. In these dynamic membranes, a mixture of zirconium hydroxide and polyacrylic acid deposited on a porous support which provides the necessary mechanical strength. The support is mostly made of porous carbon although porous ceramic and stainless steel are also used. These non-sintered membranes, in great contrast to most of the membranes discussed in this book, are formed in situ and require periodic regeneration with new zirconium hydroxide and polyacrylic acid. 

Table 32.3 shows the values of feed and permeate activity evolution in one of the experiments, representative of a typical treatment process. It can be seen how it is possible to obtain a permeate with a level of activity below the legal discharge limits by means of successive reverse osmosis applications. 

These developments result from the introduction of composite membranes, originally developed in the 1970s primarily, for desalination by reverse osmosis. Application of the same membrane fabrication techniques to pervaporation membranes radically improved their performance and spurred commercial utilization. Today, pervaporation and vapor permeation plants are widely used to dehydrate volatile organics and separate other mixtures, primarily in the pharmaceutical and fine chemical industries. 

We want to obtain an expression to relate the solvent flux (typically water) to measurable quantities. In general, we need to include the effect of osmotic pressure, especially for reverse osmosis applications. 

FIGURE 20.1-8 Schematic representation or ihin-filin composite-type films pioneered by Cadone for reverse osmosis application. Typical monomers might include Tor A, mesyl chloride for B, piperazine or 1,4 phenyldiamine. 

Typical data for asymmetric fibers for reverse osmosis applications are reported in Table 20.5-1. The ranges of these variables for as-spun and post reared cellulose acetate and polysulfone membranes currently used in gas separation are proprietary. Nevertheless, the surfnee porosity for such membranes is undoubtedly lower than for those described in Table 20,5-1, since, as indicated in Table 20,1-2, in their posttreated forms such membranes have seleclivities approaching the values or dense films. Porosities as high as those shown in Table 20.5-1 weuld produce unacceptably low seleclivities as a result of nondiscrirafimat pore flow,... 

R.W. Okey and P.L. Stavenger, Reverse Osmosis Applications in Industrial Wastewater Treatmenf, in Membrane Processes for Industry Proceedings of the Symposium, Southern Research Institute, (May 19-20 1966). 

Once the feed water source has been determined, analysis of the feed water composition is necessary before a treatment system can be designed. Feed water constituents that must be analysed prior to designing a RO/NF membrane system as per ASTM Designation D4195-88 Standard Guide for Water Analysis for Reverse-Osmosis Applications are discussed in Chapter 6. Typical water treatment methods are summarised in Table 2.2. 

High performance thin-film composite membranes for reverse osmosis applications were fabricated by coating solutions of a highly chlorine-tolerant disulfonated PAES [92,93]. As base monomers, 4,4 -dichlorodiphenyl sulfone and 4,4 -biphenol are used. 4,4 -dichlorodiphenyl sulfone is then directly sulfonated to get a disulfonated monomer, 3,3 -disutfonate-4,4 -dichlorodiphenyl sulfone. These monomers can be directly copolymerized on a commercially available porous polysulfone support. 

Lee CH, McCloskey BD, Cook J, Lane O, Xie W, Freeman BD, et al. Disulfonated poly(arylene ether sulfone) random copolymer thin film composite membrane fabricated using a benign solvent for reverse osmosis applications. J Membr Sci 2012 389 363-71. 

Polysulfone is used in applications requiring good high-temperature resistance such as coffee carafes, piping, sterilizing equipment, and microwave oven cookware. Polysulfone is also used in electrical applications for connectors, switches, and circuit boards and in reverse osmosis applications as a membrane support. 

However, this certainly does not imply that all such membranes are suitable for every reverse osmosis application because the material constants A and B must have optimal values for a given application. Thus for aqueous applications, e.g. the desalination of seawater and brackish water, hydrophilic materials should be used (high A value) with a low solute permeability. 

Applications -182 MW(e) of electricity plus 102 000 m7day of potable water by reverse osmosis - Applicable to district heating Electricity production oidy... 

---