Reverse osmosis membrane modules development

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

Spiral-wound modules were used in a number of early artificial kidney designs, but were fully developed for industrial membrane separations by Gulf General Atomic (a predecessor of Fluid Systems, Inc.). This work, directed at reverse osmosis membrane modules, was carried out under the sponsorship of the Office of Saline Water [112-114], The design shown in Figure 3.42 is the simplest, consisting of a membrane envelope of spacers and membrane wound around a perforated central collection tube the module is placed inside a tubular pressure vessel. Feed passes axially down the module across the membrane envelope. A portion of the feed permeates into the membrane envelope, where it spirals towards the center and exits through the collection tube. 

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. 

First multi-leaf spiral wound membrane module developed by Don Bray and others at Gulf General Atomic, under US Patent no. 3,417,870, "Reverse Osmosis Purification Apparatus," December, 1968. A multi-leaf spiral configuration improves the flow characteristics of the RO module by minimizing the pressure drop encountered by permeate as it spirals into the central collection tube. 

The separation of water from soluble dissolved species in water using membrane processes is often referred to as reverse osmosis, as pressiue must be applied to overcome the osmotic pressiue. This is particularly relevant for water desalination but is also important for itrilk and whey concentration, fruit juice concentration, maple syrup concentration, and suaose and dextrose concentration. The membranes employed for these processes are similar, and the membrane module con-straction is usually in the spiral woimd configuration. Early desalination membranes were based on cellulose acetate as an asymmetric membrane produced by the phase inversion process. Another early reverse osmosis membrane involved extraded thin hollow fibers of polyamides (both aliphatic and aromatic). The rntetfadal polymerization of polyamides on a pororrs polysirlfone support developed in the 1970s (FihnTec) became one of the preferred membranes and... 

The first reverse osmosis modules made from cellulose diacetate had a salt rejection of approximately 97—98%. This was enough to produce potable water (ie, water containing less than 500 ppm salt) from brackish water sources, but was not enough to desalinate seawater efficiently. In the 1970s, interfacial composite membranes with salt rejections greater than 99.5% were developed, making seawater desalination possible (29,30) a number of large plants are in operation worldwide. 

Developments and advances in both membrane materials and reverse osmosis modules have increased the range of appHcations to which RO can be apphed. Whereas the RO industry has developed around water desalination (9,53,73,74), RO has become a significant cornerstone in other industries. 

Research effort at Albany International Research Co. has developed unit processes necessary for pilot scale production of several species of reverse osmosis hollow fiber composite membranes. These processes include spin-dope preparation, a proprietary apparatus for dry-jet wet-spinning of microporous polysul-fone hollow fibers, coating of these fibers with a variety of permselective materials, bundle winding using multifilament yarns and module assembly. Modules of the membrane identified as Quantro II are in field trial against brackish and seawater feeds. Brackish water rejections of 94+% at a flux of 5-7 gfd at 400 psi have been measured. Seawater rejections of 99+% at 1-2 gfd at 1000 psi have been measured. Membrane use requires sealing of some portion of the fiber bundle for installation in a pressure shell. Much effort has been devoted to identification of potting materials which exhibit satisfactory adhesion to the fiber while... 

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... 

Membrane research and development started in Du Pont in 1962 and culminated in the introduction of the first B-9 Permasep permeator for desalination of brackish water by reverse osmosis (RO) in 1969. The membrane in this B-9 Permasep module consisted of aramid hollow fibers. In 1969, proponents of RO technology had ambitious dreams and hopes. Today, RO is a major desalination process used worldwide to provide potable water from brackish and seawater feeds. Du Font s membrane modules for RO are sold under the trademark Permasep permeators. The RO business is a virtually autonomous profit center that resides in the Polymer Products Department. The growth and success of the Permasep products business is a direct result of Du Font s sustained research and development commitment to polyamides, a commitment that dates back to the 1930 s and the classic polymer researches of Wallace H. Carothers. Since 1969, improved and new Permasep permeators have been introduced six times, as shown in Table I. 

Membrane Process for Recovery of Alkanesulfonates. Many attempts have been made over the years to reduce the wastewater load—which represents a loss of product—by a number of different methods. These include evaporation, extraction, reverse osmosis, and ultrafiltration. All of these processes have the disadvantage of high equipment cost and high energy requirements, and the space-time yield is low. The first breakthrough came with the development of new types of membrane with a definite separating efficiency and a large surface area, so-called spiral-wound modules. 

Nanofiltration will continue to be a rapidly growing segment of the membrane industry. To sustain this growth, a better understanding of transport is needed, in particular the differences between aqueous and organic systems. Additionally, tremendous opportunities exist in membrane and module development for separations that fall in the gap between reverse osmosis and ultrafiltration. 

A reverse osmosis process developed by Mobil for this separation is illustrated in Fig. 7.4(b). Polyimide membranes formed into spiral-wound modules are used to separate up to 50% of the solvent from the dewaxed oil. The membranes have a flux of 10-20 gal/ft day at a pressure of 450 to 650 psi. The solvent filtrate bypasses the distillation step and is recycled directly to the incom-... 

In addition, the ability to work in a wide range of operative conditions is another key aspect for the development of advanced membranes. Chemical stability is of particular importance when the membrane interfaces are exposed to aggressive solvents, such as in several organic solvent nanofiltration (OSN) applications [21]. Resistance to fouling is also important in water filtration because this phenomenon can threaten the continuous operability of the membrane module [22]. In high-temperature (eg, precombustion CO2 capture from syngas [23] or polymer electrolyte membranes for fuel cells [24]) and high-pressure (eg, reverse osmosis and nanofiltration membranes for... 

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