Ceramic membrane design

Figure 8.6 Figures 6 (A) and 7 (B) from Hazbun, U.S. Patent 4 791 079 [17] showing some of the first concepts for a monoiithic ceramic membrane design for the partiai oxidation of hydrocarbons.

Ceramic Ceramic membranes are made generally by the sol-gel process, the successive deposition of ever smmler ceramic precursor sph eres, followed by firing to form multitube monoliths. The diameter of the individual channels is commonly about 2 to 6 mm. Monoliths come in a variety of shapes and sizes. A 19-channel design is common. One manufacturer makes large monoliths with square channels. 

It is well known that dense ceramic membranes made of the mixture of ionic and electron conductors are permeable to oxygen at elevated temperatures. For example, perovskite-type oxides (e.g., La-Sr-Fe-Co, Sr-Fe-Co, and Ba-Sr-Co-Fe-based mixed oxide systems) are good oxygen-permeable ceramics. Figure 2.11 depicts a conceptual design of an oxygen membrane reactor equipped with an OPM. A detail of the ceramic membrane wall... 

The membrane areas needed in these plants are not huge, but the technical challenges are substantial. Defect-free, anisotropic composite ceramic membranes that are 1-5 pm thick, able to operate continuously at 800-1000 °C, nonpoisoning, nonfouling and low-cost are required—not impossible, but difficult. Conceptual designs of the type of reactor required are beginning to appear. 

New reactor designs and immobilisation methods have been used to extend the lifetime of lipases in scCC>2 (Lozano et al., 2004). Ceramic membranes have been coated with hydrophilic polymers and the enzyme covalently attached to these. In SCCO2, activities and selectivities were excellent and the half-life of the catalyst was enhanced. It is thought the hydrophilic layer of the membrane protected the enzyme. Operational stability of enzymes has also been increased by using ionic liquid/scC02 biphasic systems (Lozano et al., 2002 Reetz et al., 2003). 

P.M. Biesheuvel, H. Verweij, Design of Ceramic Membrane Supports Permeability, Tensile Strength and Stress ,J. Membrane Sci. 156 [1] 141-52 (1999). 

Mechanical stability against thermal cycling between ambient temperature and Top requires matching of thermal-expansion coefficients of the electrolyte and electrodes, the interconnects, and the seals. Note Ceramic strength is improved where cell design retains the ceramic membrane under a compressive stress. 

It has been suggested that the design and operational practices for cracking furnace reactors can be put to use for heat supply to inorganic membrane reactors [Tsotsis et al., 19931. Having sufficient electrical conductivity at typical reaction temperatures for dehydrogenation reactions, ceramic membranes allow the use of electric current through... 

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. 

Ceramic Membrane Processing New Approaches in Design and Applications... 

Due to their remarkable intrinsic properties, ceramic membranes have enjoyed rapid development over the two last decades. In order to update the previous overview on ceramic membrane processing, this chapter is devoted to the new approaches in their design and applications. This description is preceded by background information for better understanding of current research in the ceramic membrane area. 

FIGURE 6.2 Evolution of the geometiy of ceramic membrane elements, (a) Conventional cyhndrical-shaped channels (b) flower-like designed channels and (c) honeycomb-t5fpe stmcture. 

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... 

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... 

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