Membranes modules

The membrane modules, which are commonly used in organic vapor separation, are spiral-wound modules or the envelope-type GKSS GS modules. Gapillary or hollow-fiber modules are only used in small-scale laboratory applications. The spiral-wound module and the envelope module are based on flat-sheet membranes. Spiral-wound modules are compact and cheaper in comparison to installed membrane area, but there are limitations in mass transfer on both sides of the membrane. The packing density - the ratio of installed membrane area over pressure vessel housing volume - of a spiral-wound module varies from approx. 300 to 1000 m /m (Fig. 1.3). 

The envelope-type GS module offers advantages in flow distribution and a minimized pressure drop at the permeate side. 

The membrane envelope consists of two membranes fleeces and spacers between the membranes to provide an open space for an unrestrained permeate drainage. Thermal welding at the outer cutting edges seals the membrane sandwich (Fig. 1.4). 

The membrane module consists of a pressure vessel, a central permeate tube and a stack of membrane envelopes. The stack of envelopes is divided into asymmetric arranged compartments by means of baffle plates. The design of a 

Reverse osmosis membranes for industrial applications are typically modularized using configurations that pack a large amount of membrane area into a relatively small volume. This makes the RO system more economical to use in that the system requires a smaller footprint, and membranes can be replaced in smaller modules rather than system wide. 

There are four basic forms for RO membrane modules Plate and frame, tubular, spiral wound, and hollow fine fiber. These four configurations are summarized in Table 4.3 and discussed below. Additionally, some manufacturers have developed other module configurations that are briefly discussed in Chapter 4.3.5. 

Property Plate-and- Frame Tubular Spiral Wound Hollow Fine Fiber 

Potential for Fouling Moderate Low High Very High 

Ease of Cleaning Good Excellent Poor Poor 

Shear-sensitive hiological materials require gentle operating conditions hence, turbulent flow conditions are not desirable. In contrast to TM modules, SW modules offer gender flow fields above the membrane surface. Plastic mesh spacers are used in SW modules to promote locahsed turbulence above the surface of the membrane. The SW modules come in standard sizes of 6, 10 and 20 cm diameter X 100 cm long. The elements fit in a pressure vessel connected in series by O-rings up to eight elements per vessel (see F ure 2.18). 

Tubular Hollow-fibre Submerged High shear 

Good Moderate—good Moderate- Very good 

In the production of high-purity water for pharmaceutical and beverage applications, full-fit modules are now used. Full fit means there is no brine seal that provide dead 

Short flow path disc-tube (DT) RO membrane modules developed by Rochem for treating highly turbid waters and folding feeds are now used extensively to minimise concentration polarisation, seating and fording. Typically, for RO systems the Silt Density Index (SDI) of feed water must be less than 5 to prevent premature fouling. 

To meet the requirements of the catalyst, additional steam is introduced before the second reactor lowering the stream temperature. 

The coupling of membrane separation modules and the conventional WGSR reactors through this kind of architecture results in a better overall efficiencies (97.5% as compared to 91% for the reference case). By this configuration, the fuel stream is enriched in H2 by the membrane reactor and requires only polishing by PSA. 

In this application, the separated hydrogen is fed to a gas turbine and to a post-combustion chamber using its exhausts to supply the dehydrogenation reactor thermal duty. The plant is designed for a propylene capacity of 

Palladium-based Selective Membranes for Hydrogen Production 

Successful experiences dealing with membrane applications are reported in literature, such as Galuszka et al. who observed considerable enhancement of 

Reverse osmosis is widely used for the desalination of sea or saline water, in obtaining pure water for clinical, pharmaceutical and industrial uses, and also in the food processing industries. 

Calculate the osmolar concentration and the osmotic pressure of the physiological sodium chloride solution (9 g I 1 NaCl aqueous solution). Note The osmotic pressure should be almost equal to that of human body fluids (ca. 6.7 atm). 

As NaCl dissociates completely into Na+ and Cl-, and the ions exert osmotic pressures independently, the total osmolar concentration is 

Although many types of membrane modules are used for various membrane processes, they can be categorized as follows. (It should be mentioned here that such membrane modules are occasionally used for gas-liquid systems.) 

A number of flat membranes are stacked with appropriate supporters (spacers) between the membranes, making alternate channels for the feed (retentate) and the permeate. Meshes, corrugated spacers, porous plates, grooved plates, and so on, can be used as supporters. The channels for feed distribution and permeate collection are built into the device. Rectangular or square membrane sheets are common, but some modules use round membrane sheets. 

Since the molecular weight of NaCl is 58.5, the molar concentration is 

Perforated permeate collection pipe Residue flow 

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Membrane filtration Membrane module Membrane permeability Membrane process Membrane processes Membrane reactor Membrane roofing Membranes... 

Membrane modules have found extensive commercial appHcation in areas where medium purity hydrogen is required, as in ammonia purge streams (191). The first polymer membrane system was developed by Du Pont in the early 1970s. The membranes are typically made of aromatic polyaramide, polyimide, polysulfone, and cellulose acetate supported as spiral-wound hoUow-ftber modules (see Hollow-FIBERMEMBRANEs). 

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. 

HoUow fibers are usuaUy on the order of 25 p.m to 2 mm in diameter. They can be made with a homogeneous dense stmcture, or preferably with a microporous stmcture having a dense permselective layer on the outside or inside surface. The dense surface layer can be integral, or separately coated onto a support fiber. The fibers are packed into bundles and potted into tubes to form a membrane module. More than a kilometer of fibers may be requited to... 

Module Selection. The choice of the appropriate membrane module for a particular membrane separation balances a number of factors. The principal factors that enter into this decision are Hsted in Table 2. 

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). 

Membralox Ceramic Multichannel Membrane Modules, Technical Brochure, Alcoa/SCT, Aluminum Company of America, Pittsburgh, Pa., 1987. 

Measurable Process Parameters. The RO process is relatively simple ia design. It consists of a feed water source, feed pretreatment, high pressure pump, RO membrane modules, and ia some cases, post-treatment steps. A schematic of the RO process is shown ia Figure 2a. 

Prediction of reverse osmosis performance is usefiil to the design of RO processes. Simulation of RO processes can be separated iato two categories. The first is the predictioa of membrane module performance. The second is the simulation of a network of RO processes, ie, flow sheet simulations, which can be used to determine the optimum placement of RO modules to obtain the overaH process objective. 

Owiag to the variety of situations encountered ia RO appHcatioas, there is ao single analytical technique to predict membrane module performance. The module and the feed stream, along with the operatiag parameters, determine system performance. To predict module performance, a model that... 

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

A foulinghke problem may occur when condensable vapors are left in the residiie. Condensation may result which in the best case results in blinding of the membrane, and in the usual case, destruction of the membrane module. Dew-point considerations must be part of any gas-membrane design exercise. 

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

If the pressure drop across a tubular membrane is 2.8 bars, determine the permeat velocity across the membrane module. The thickness and the porosity of the deposit are 2 mm and 40 %, respectively. The average diameter of the partices is 5 microns. The initial membrane resistance is estimated to be 1.7 X 10 1/m. 

To demonstrate the potential of the process in obtaining both enantiomers at a high purity, experiments were performed using racemic norephedrine as the compound to be separated. Two columns of seven small membrane modules were used. The enantiomer ratios in the outflows during start-up are shown in Fig. 5-15. It can be concluded that the system reaches equilibrium within approximately 24 h, and that both enantiomers are recovered at 99.3-99.8 % purity. 

In this case study, an enzymatic hydrolysis reaction, the racemic ibuprofen ester, i.e. (R)-and (S)-ibuprofen esters in equimolar mixture, undergoes a kinetic resolution in a biphasic enzymatic membrane reactor (EMR). In kinetic resolution, the two enantiomers react at different rates lipase originated from Candida rugosa shows a greater stereopreference towards the (S)-enantiomer. The membrane module consisted of multiple bundles of polymeric hydrophilic hollow fibre. The membrane separated the two immiscible phases, i.e. organic in the shell side and aqueous in the lumen. Racemic substrate in the organic phase reacted with immobilised enzyme on the membrane where the hydrolysis reaction took place, and the product (S)-ibuprofen acid was extracted into the aqueous phase. 

The concept of cross-flow microfiltration is shown in Figure 16.11, which represents a cross-section through a rectangular or tubular membrane module. The particle-containing fluid to be filtered is pumped at a velocity in the range 1-8 m/s parallel to the face of the membrane and with a pressure difference of 0.1-0.5 MN/m2 (MPa) across the membrane. The liquid penneates through the membrane and the feed emerges in a more concentrated form at the exit of the module.1617 All of the membrane processes are listed in Table 16.2. Membrane processes are operated with such a cross-flow of the process feed. 

Industrial membrane plants often require hundreds of thousands of square metres of membrane to perform the separation required on a useful scale. Before a membrane separation can be used industrially, therefore, methods of economically and efficiently packaging large areas of membrane are required. These packages are called membrane modules. The areas of membrane contained in these basic modules are in the range 1-20 m2. The modules may be connected together in series or in parallel to form a plant of the required performance. The four most common types of membrane module are tubular, spiral, wound and hollow fibre. 

Membrane modules can be configured in various ways to produce a plant of the required separation capability. A simple batch recirculation system has already been described in cross-flow filtration. Such an arrangement is most suitable for small-scale batch operation, but larger scale plants will operate as feed and bleed or continuous single pass operation (Figure 16.20). 

The choice of the most suitable membrane module type for a particular membrane separation must balance several factors. The principal module design parameters that enter into the decision are summarised in Table 16.3. 

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