Membrane modules ceramic

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. 

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

Adamson, A. W. 1982. Physical Chemistry of Surfaces. 4th ed. John Wiley Sons, New York. Alcoa. 1987. Mcmbralox ceramic multichannel membrane modules. Product brochure. 

Goldsmith, R. L. 1990. Low-cost ceramic membrane modules. Paper read at 1990 Eighth Annual Membrane Technology Planning Conference, October 16, Newton, MA. 

Cabral and coworkers [253] have investigated the batch mode synthesis of a dipeptide acetyl phenylalanine leucinamide (AcPhe-Leu-NH2) catalyzed by a-chymotrypsin in a ceramic ultrafiltration membrane reactor using a TTAB/oc-tanol/heptane reverse micellar system. Separation of the dipeptide was achieved by selective precipitation. Later on the same group successfully synthesized the same dipeptide in the same reactor system in a continuous mode [254] with high yields (70-80%) and recovery (75-90%). The volumetric production was as high as 4.3 mmol peptide/l/day with a purity of 92%. The reactor was operated for seven days continuously without any loss of enzyme activity. Hakoda et al. [255] proposed an electro-ultrafiltration bioreactor for separation of RMs containing enzyme from the product stream. A ceramic membrane module was used to separate AOT-RMs containing lipase from isooctane. Application of an electric field enhanced the ultrafiltration efficiency (flux) and it further improved when the anode and cathode were placed in the permeate and the reten-tate side respectively. 

Backflushing is another way of cleaning heavily fouled membranes. The method is widely used to clean capillary and ceramic membrane modules that can withstand a flow of solution from permeate to feed without damaging the... 

Both Mitsui [26] and Sulzer [27] have commercialized these membranes for dehydration of alcohols by pervaporation or vapor/vapor permeation. The membranes are made in tubular form. Extraordinarily high selectivities have been reported for these membranes, and their ceramic nature allows operation at high temperatures, so fluxes are high. These advantages are, however, offset by the costs of the membrane modules, currently in excess of US 3000/m2 of membrane. 

To the best of our knowledge this possibility has not yet been shown to work. The two major challenges are the relatively high Reynolds numbers necessary inside the membrane module and the need to find selective membranes suitable for ionic liquids. Ceramic membranes show great potential for this application but so far there are only a few choices available on the market. 

Membranes are used to separate gaseous mixtures or liquid mixtures. Membrane modules can be tubular, spiral-wound, or plate and frame configurations. Membrane materials are usually proprietary plastic films, ceramic or metal tubes, or gels with hole size, thickness, chemical properties, ion potential, and so on appropriate for the separation. Examples of the kinds of separation that can be accomplished are separation of one gas from a gas mixture, separation of proteins from a solution, dialysis of blood of patients with kidney disease, and separation of electrolytes from non electrolytes. 

There are also techniques involving the use of nonporous, solid or liquid membranes that separate the donor phase from the receiving phase by an evident phase boundary. Most often used are three-phase systems (donor phase, membrane, and acceptor phase) or two-phase systems, in which one of the surrounding phases is the same as the membrane. Solid membranes are made of chemically resistant, hydrophobic polymers (PTFE, PVDF, PS, PP, silicates), metals (Pd alloys), or ceramic materials. Channels of membrane modules have a volume ranging from 10 to 1000 pL and, according to their geometry, can be classified as planar or fibrous. For setting up a membrane system, two modes can be used the membrane can be immersed in a sample (membrane in sample, MIS) or the sample can be introduced into a membrane (sample in membrane, SIM). In both systems, only a small amount of sample is in direct contact with membrane, because ratio of the membrane surface area to the sample volume is small. 

In the fabrication of ceramic membrane modules, several processing steps must be acconplished sol preparation, gelation, coating of supports, and firing at elevated tenperatures. Within each step, several independent variables can be used to tailor the properties of the ultimate product for the specific application of interest. Although discussion of the influence of these variables is beyond the scope of the present paper, a cursory treatment of each step and the most important variables will be given here. 

A membrane system consists of many membrane modules which, in turn, are made of several membrane elements. Both ends of a membrane element are sealed with such materials as enamels or ceramic materials. The connections between elements and between elements and the housing or pipings are typically made from plastics or elastomers for liquid phase applications. 

An example of this configuration is filtration of the methane fermentation broth from a sewage sludge liquor [Kayawake et al., 1991]. The liquor is u eated anaerobically in a fermentor. The broth is pumped to a ceramic membrane module which is contained in the fermentor. The retentate is returned to the fermentor while the permeate is discharged to the environment This is schematically shown in Figure 8.2. Although the membrane module is enclosed in the bioreactor for compactness and process simplification, the membrane step in essence follows the fermentation step. 

The objective in membrane design is to pack as much permeation surface area into as small a space as possible to minimize operation requirements. Depending on the application, various membrane designs are used, such as flat sheet, disc tube, hollow fiber, spiral wound, and ceramic (17). Module design has a measurable effect on the hydrodynamic performance of the cross-flow membrane device. The advantages and disadvantages of different membrane modules are summarized in Table 1. 

Compared to modules based on cylindrical elements, flat ceramic membrane modules are not developed in a large extent and are limited to date to small liquid volume treatment [27]. Flat ceramic membranes are generally implemented as disks in laboratory scaled cells, offering a limited filtration surface area. Indeed a diameter of 90 mm that is one of the largest available dimensions for these membrane disks results in a filtration surface of -56 cm. Anopore alumina membranes supplied by Whatman or ATZ ceramic membrane disks with zirconia or titania top-layers from Sterlitech are typical examples of these commercially available flat ceramic membranes. Sterlitech ATZ ceramic membrane disks and the corresponding membrane holder are shown in Figure 6.16. 

Interestingly, an innovative design has been described recently by the Fraunhofer IGB, Germany [27], allowing the production of flat membrane modules with an effective filtration area of 1 m (Figure 6.17a). This concept is based on novel flat ceramic supports specially processed to produce corrugated channels and able to receive micro- and ultrafiltration membranes (Figure 6.17b). 

In a general way, most of ceramic membrane modules operate in a cross-flow filtration mode [28] as shown in Figure 6.18. However, as discussed hereafter, a dead-end filtration mode may be used in some specific applications. Membrane modules constitute basic units from which all sorts of filtration plants can be designed not only for current liquid applications but also for gas and vapor separation, membrane reactors, and contactors, which represent the future applications of ceramic membranes. In liquid filtration, hydrodynamics in each module can be described as one incoming flow on the feed side gf, which results in two... 

FIGURE 6.1S Examples of ceramic membrane modules, (a) Multi-elements module from Orelis and (b) single-element module from CeraMem. 

In industrial plants, ceramic membrane modules are arranged in different ways based on the general principles used for the design of membrane processes. The simplest module implementation is the dead-end operation mode. Here, the feed is forced through the membrane, which implies that the concentration of rejected components on the feed side of the membrane increases continuously and consequently the quality and the flux of permeate decrease with time. The main advantage of the dead-end... 

FIGURE 6.17 Flat membrane module with an effective membrane area of 1 m (a), obtained by assembling channel corrugated porous ceramic supports (b), from (IGB, 26). 

Aside from membrane morphology, various membrane module geometries were also studied to determine their appropriateness in various dairy processes. Operation of tubular ceramic membranes usually involves high TMP and pressure drop... 

The apparams equipped with Sunflower CeRam Inside (23-8-1178), characterized in Table 30.10, was used in pilot plant tests. The plant consisted of feed tank (1) equipped with cooler (2) membrane module housing (3) pretreatment filters (4) pressrue pump TONKAFLO (5) circulating pump Grandfos (6) non-return valve (7) two needle valves and four ball valves (Figure 30.14). 

In contrast, if the membrane is an inorganic composition (e.g., a dense metal membrane or a nanoporous ceramic membrane), the membrane module may be operated at the elevated temperature of 450 °C. In this case, there is no need for optional HEX 2 as the fuel gas stream will exit the membrane module at 450 °C and pass to the burner without further cooling. In addition to a net increase in overall process energy efficiency, the elimination of HEX 2 also represents a reduction in capital cost for the system. 

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