Spiral wound membrane thin-film composite

The membranes currently used for seawater desalination are aromatic polyamide membrane (hollow fiber, Du Pont), cellulose acetate membranes (hollow fiber, Toyobo), thin-flim composite membranes (spiral-wound, UOP). thin-film composite membranes (spiral-wound. Dow), and thln-fllm composite membranes (spiral-wound. Toray). 

The geometries for asymmetric mixed-matrix membranes include flat sheets, hollow fibers and thin-fihn composites. The flat sheet asymmetric mixed-matrix membranes are formed into spirally wound modules and the hollow fiber asymmetric mixed-matrix membranes are formed into hollow fiber modules. The thin-film composite mixed-matrix membranes can be fabricated into either spirally wound or hollow fiber modules. The thin-film composite geometry of mixed-matrix membranes enables selection of different membrane materials for the support layer and low-cost production of asymmetric mixed-matrix membranes utilizing a relatively high-cost zeolite/polymer separating layer on the support layer. 

FT-30 Membrane. FT-30 is a new thin-film-composite membrane discovered and developed by FilmTec. Initial data on FT-30 membranes were presented elsewhere (23). It was recently introduced in the form of spiral-wound elements 12 inches long and 2 to 4 inches in diameter (24). The barrier layer of FT-30 is of proprietary composition and cannot be revealed at this time pending resolution of patentability matters. The membrane shares some of the properties of the previously described "NS series of membranes, exhibiting high flux, excellent salt rejection, and nonbiodegradability. However, the response of the FT-30 membrane differs significantly from other noncellulosic thin-film-composite membranes in regard to various feedwater conditions such as pH, temperature, and the effect of chlorine. 

R.L. Riley, R.L. Fox, C.R. Lyons, C.E. Milstead, M.W. Seroy and M. Tagami, Spiral-wound Poly(ether/amide) Thin-film Composite Membrane System, Desalination 19, 113 (1976). 

Y. Kamiyama, N. Yoshioka, K. Matsui and E. Nakagome, New Thin-film Composite Reverse Osmosis Membranes and Spiral Wound Modules, Desalination 51, 79... 

Salts rejected by the membrane stay in the concentrating stream but are continuously disposed from the membrane module by fresh feed to maintain the separation. Continuous removal of the permeate product enables the production of freshwater. RO membrane-building materials are usually polymers, such as cellulose acetates, polyamides or polyimides. The membranes are semipermeable, made of thin 30-200 nanometer thick layers adhering to a thicker porous support layer. Several types exist, such as symmetric, asymmetric, and thin-film composite membranes, depending on the membrane structure. They are usually built as envelopes made of pairs of long sheets separated by spacers, and are spirally wound around the product tube. In some cases, tubular, capillary, and even hollow-fiber membranes are used. 

Fig. 12. A spkal-wound reverse osmosis membrane element (a) schematic depiction (b) cross section of a spiral-wound thin-film composite RO Fikntec...

Typical membranes in NF are thin film composite membranes and their surface layers are mostly proprietary and not very easily identified by the user. Some industrial use of sulfonated polyethersulfone membranes has also been seen (see Section 35.6.2. Linpac recycle paper mill in Cowpens, South Carolina). Tubular and spiral wound modules are the dominating module type in NF and RO. Both membrane processes are used in industrial-scale applications in the pulp and paper industry (Table 35.1). When the membranes are installed in spiral wound modules, water pretreatment is often important to prevent plugging of the modules and fouling of the membranes. 

Among others, spiral-wound and hollow-fiber modules are two commonly available RO membrane products on the market. Currently, spiral-wound modules have approximately 80 /o of the total RO membrane market. Thin film composite membrane... 

Kawada I., Inoue K., Kazuse Y., Ito H., Shintani T., Kamiyama Y. (1987), New thin-film composite low pressure reverse osmosis membranes and spiral wound modules. Desalination, 64, 387-401. 

Dechlorinated and softened water flows to the RO skid through a 5.0-nm (nominal pore size) cartridge filter. The cartridge filter removes resin fines, particles and complexed colloids necessary to protect the RO membranes from particulate fouling. The RO membranes are thin-film composite (TFC) polyamide RO membranes (20 cm diameter X 100 cm long spiral wound elements) with rejection 99%. 

The whole membrane module is composed of six racks, each of them consisting of eleven pressure vessels, operated in parallel, designed to house one spiral wound membrane each. The pressure vessels were originally equipped with cellulose acetate membranes specifically developed for PRO. During the first period, the plant operation has been optimized and the performance has been monitored, resulting in a power density lower than 0.5 W/m. Next, thin film composite membranes developed for PRO were installed in early 2011. So far the measured power density has reached nearly 1 W/m, which is a major improvement compared to the cellulose acetate membranes originally installed. Based on this preliminary experience, Statkraft plans to build a full-scale 25 MW osmotic power plant by 2015 [20]. 

Hollow-fiber designs are being displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. Also, thin-film interfacial composite membranes, the best reverse osmosis membranes available, have not been fabricated in the form of hoUow-fine fibers. 

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