Hollow fibers, geometries spiral-wound

Membranes are manufactured in a diverse range of geometries they include flat, tubular, and multi-tubular, hollow-fiber, and spiral-wound membranes. The type of geometry the membrane is manufactured into depends on the material the membrane is made from. Ceramic membranes, generally, come in tubular, multi-tubular and flat geometries, whereas spiral-wound and hollow-fiber membranes seem, for the most part (with a few notable examples), to be made from polymers. 

An ILM can be made in at least three different geometries. A planar or flat geometry is very useful for laboratory purposes. For industrial purposes a planar geometry is not very effective since the ratio of surface area to volume is too low. Hollow fiber and spiral wound modules can be used to provide high surface area to volume ratios. Surface area to volume ratios can approach 10,000 m /m for hollow fiber and 1000 m /m for spiral wound modules (2). Way et al. (.3) discuss the criteria for selecting supports for ILMs. 

In all these endeavors, rigorous or approximate, transport parameters play a key role and must be addressed first. They are dependent on a number of variables, including flow conditions, membrane and module geometry, and the specific membrane process being addressed. Thus, the flow can be laminar or turbulent, involve gases or liquids, or take place in hollow-fiber or spiral-wound geometries. We listed some of these features and the resulting transport parameters in Table 8.8. 

A next-future application of MOFs is predicted for MOF-oiganic polymer-based mixed matrix membranes in hollow fiber or spiral wound geometry. Established membrane production technologies such as hollow fiber spinning or foil casting can be used for the preparation of mixed matrix membranes. Further, MOFs match much better with organic polymers than zeolites, for example, even if the latter have been hydrophobized, such as by silylation. 

Supported Liquid Membranes. A SLM can be fabricated in at least three different geometries. Planar or flat sheet SLMs are very useful for laboratory research and development purposes, but the surface area to volume ratio of flat sheets is too low for industrial applications. Spiral wound and hollow fiber geometries can... 

Common types of membrane materials used are listed in Table 3. This gets us into the concept of geometry. There are three types of modules generally used, namely Tubular, Spiral wound, and Hollow fiber. A comparison of the various geometries is given in Table 4. 

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. 

Design of the membrane module system involves selection of the membrane material the module geometry, eg, spiral-wound or hollow-fiber product flow rate and concentration solvent recovery operating pressure and the minimum tolerable flux (9,11). The effects of these variables can be obtained from laboratory or pilot experiments using different membranes and modules. The membrane module as well as the solvent recovery can be chosen to minimize fouling. Spiral-wound modules are widely used because these offer both high surface area as well as a lower fouling potential. 

Hollow fiber refers to a membrane tube of very small diameter (e.g., 200 pm). Such small diameters enable a large membrane area per unit volume of device, as well as operation at somewhat elevated pressures. Hollow-fiber modules are widely used in medical devices such as blood oxygenators and hemodialyzers. The general geometry of the most commonly used hollow-fiber module is similar to that of the tubular membrane, but hollow fibers are used instead of tubular membranes. Both ends of the hollow fibers are supported by header plates and are connected to the header rooms, one of which serves as the feed entrance and the other as the retentate exit. Another type of hollow-fiber module uses a bundle of hollow fibers wound spirally around a core. 

A further generality of the MDPE is that knowledge of the actual shape and geometry of the membrane within the MCS is not necessary. The equation is not restricted, and can be applied to any chosen shape (plate module, hollow fiber, spiral wound, and so on). 

Depending on their geometry, the membranes can be subdivided in tubular, hollow fiber, spiral wound and flat sheettubular membranes are the most common solution, even if they require relatively high volume per membrane area unit and present high costs. 

Membranes can be subdivided into four categories according to their geometry tubular, hollow fiber, spiral wound and flat sheet (Basile et al, 2011). Tubular membranes are used most frequently, even though they require relatively high volumes and involve high costs. 

The second type of membrane module, which is the hardest to visualize, is the spiral-wound element. This module essentially consists of a large membrane envelope loosely rolled like a jelly roll. The feed stays outside the envelope and products are harvested from the inside via a central tube. In some more sophisticated designs, many envelopes may come out from the central tube, so that a cross-section of the module would look like a daisy with petals twisted in a circular direction. This type of module has become the dominant geometry for reverse osmosis. While it has less membrane area per volume than a hollow-fiber module, it plugs less easily. However, even if only part of the membrane fails, the entire module must be discarded. 

---