FilmTec

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

Fig. 12. A spinal-wound leveise osmosis membrane element (a) schematic depiction (b) cross section of a spinal-wound thin-film composite RO Filmtec...

The predominant RO membranes used in water applications include cellulose polymers, thin film oomposites (TFCs) consisting of aromatic polyamides, and crosslinked polyetherurea. Cellulosic membranes are formed by immersion casting of 30 to 40 percent polymer lacquers on a web immersed in water. These lacquers include cellulose acetate, triacetate, and acetate-butyrate. TFCs are formed by interfacial polymerization that involves coating a microporous membrane substrate with an aqueous prepolymer solution and immersing in a water-immiscible solvent containing a reactant [Petersen, J. Memhr. Sol., 83, 81 (1993)]. The Dow FilmTec FT-30 membrane developed by Cadotte uses 1-3 diaminobenzene prepolymer crosslinked with 1-3 and 1-4 benzenedicarboxylic acid chlorides. These membranes have NaCl retention and water permeability claims. 

X-2 FilmTec FT-30 Composition unknown (thin film composite)... 

In 1977 the North Star membrane research group was spun off by Midwest Research Institute, forming FilmTec Corporation. Two new thin-film-composite reverse osmosis membranes have been under development at FilmTec Corporation since that time, the NS-300 and the FT-30 membranes. 

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. 

Fig. 1. Water flux and NaCl rejection of several membrane types (10), where (D) represents seawater membranes, which operate at 5.5 MPa and 25°C ( ), brackish water membranes, which operate at 1500 mg/L NaCl feed, 1.5 MPa, and 25°C and (SSI) nanofiltration membranes, which operate at 500 mg/L NaCl feed, 0.74 MPa, and 25°C. A represents cellulose acetate—cellulose triacetate B, linear aromatic polyamide C, cross-linked polyether D, cross-linked fully aromatic polyamide E, other thin-film composite membranes F, asymmetric membranes G, BW-30 (FilmTec) H, SU-700 (Toray) I, A-15 (Du Pont) J, NTR-739HF (Nitto-Denko) K, NTR-729HF (Nitto-Denko) L, NTR-7250 (Nitto-Denko) M, NF40 (FilmTec) N, NF40HF (FilmTec) O, UTC-40HF (Toray) P, NF70 (FilmTec) Q, UTC-60 (Toray) R, UTC-20HF (Toray) and S, NF50 (FilmTec). To convert MPa to psi,...

RO membrane modules are available from many manufacturers including, for hollow-fiber modules, DuPont and Dow/FilmTec Corporation, and for spiral-wound modules, UOP Inc., Millipore Corporation, Nitto-Denko America, Inc., Toray Industries Inc., Dow/FilmTec Corporation, and DuPont. 

Figure 2.9 Flux and rejection data for a model seawater solution (3.5 % sodium chloride) in a good quality reverse osmosis membrane (FilmTec Corp. FT 30 membrane) as a function of pressure [10]. The salt flux, in accordance with Equation (2.44), is essentially constant and independent of pressure. The water flux, in accordance with Equation (2.43), increases with pressure, and, at zero flux, meets the pressure axis at the osmotic pressure of seawater 350 psi...

Table 2.6 Rejection of microsolutes by nanofiltration membranes (FilmTec data) [73], Reprinted from Desalination, 70,...

NF40 and NTR7250 Cadotte FilmTec [10] The first all-monomeric... 

The permeate of the MF units is fed to two SWRO units equipped with high-pressure pumps with an energy-recovery system (Pelton wheel). The SWRO units comprise 44 pressure vessels loaded with 6 Dow/FilmTec SW30 membranes each. The designed permeate capacity of each unit is 210 m3/h per unit with a recovery of 50-5 5%. Antisealant is dosed to the feed stream of the SWRO with a concentration of 3 to 4 ppm [15]. 

The first BWRO unit consists of 16 pressure vessels the second BWRO unit consists of 6 pressure vessels. Each vessel contains 6 Dow/FilmTec BW30 membranes. The designed permeate capacity of each BWRO unit is 175 m3/h with a recovery of 85% [15]. 

The membranes under study are thin-film composite membranes composed of two layers as illustrated in Fig. 3 a thin polyamide film as active layer and a large mesoporous polysulphone as the support layer. The three studied membranes are 2 NF membranes, noted NF90, NF270 and a low-polarization reverse osmosis (LPRO) membrane, noted BW30. All membranes were purchased from Filmtec (DOW, USA) the specifications of the membranes are given in Table 2. The chemical structures of the support and active layer materials are reported in Fig. 4 [86], Polyamide material is the more used but some authors have reported results... 

Table 2. NF and LPRO membrane characteristics from Filmtec (DOW)...

FT-30 membrane patented and assigned to FilmTec (now owned by Dow Chemical Company, Midland, MI). 

Figure 4.1 Flux and rejection data for a seawater FilmTec FT-30 membranes operating on 35,000 ppm (350 psi osmotic pressure) sodium chloride solution.2...

Figure 4.20 Dow Water Solutions-FilmTec iLEC ATDs with integral Oring. Courtesy of Dow Water and Process Solutions.

Dow Water Process Solutions Edina, MN FilmTec PA Standard... 

Low-differential-pressure membrane modules can be considered a subset of low-fouling membranes. These low-differential-pressure membrane modules typically have a thicker feed spacer. Instead of the standard 28-mil thick spacer, these low-differential-pressure membranes have 31- or 34-mil thick spacers. There is less resistance to flow through the feed channels, resulting in lower pressure drops through the membrane modules. Furthermore, the feed channels will not plug as quickly with suspended solids, foulants, or scale. Examples of low-differential-pressure membrane modules are the FilmTec BW30-400-34i (with a 34-mil feed spacer) and the Hydranautics CPA3-LD (with a 31-mil feed spacer). 

Dow Liquid Separations, FilmTec Reverse Osmosis Membranes Technical Manual, The Dow Chemical Company, form no. 609-00071-0705, 2007. 

Craig Granlund, Dow Water Soluhons-FilmTec, personal communication, February 6,2009. 

Modules should also be removed from pressure vessel in the same direction as the flow. Hence, the first module into the vessel, which is the last one in the series, is the first module out. Figures 6.10 a, b, and c show the removal sequence for a FilmTec iLEC membrane module (see Chapter 4.3.3). 

Figure 6.10 Sequence of module removal for Dow Water and Process Solutions-FilmTec iLEC membrane modules, a) module removal device, b) pulling module out of pressure vessel, c) disconnecting 2 modules. Courtesy of Nalco-Crossbow Water UC.

Chloramines also pose a risk to polyamide, composite membranes (see Chapter 8.2.1.1). Chloramines are virtually always in equilibrium with free chlorine. Although the tolerance of the FilmTec FT30 membrane to chloramines is 300,000 ppm-hrs, FilmTec still recommends that influent water with chloramines be dechlorinated prior... 

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