Membrane Dense

Symmetrical dialkyl peroxides, 75 436, 446 Symmetrical dyes, substituent effects in heterocyclic nuclei of, 20 509-510 Symmetrical membranes dense, 75 800-801 microporous, 75 801-804 Symmetrical polymethine dyes,... 

The type of equipment used by Riley et al. is shown in Figure 3.18. The casting solution is cast onto a moving stainless steel belt. The cast him then passes through a series of environmental chambers. Warm, humid air is usually circulated through the first chamber, where the him loses the volatile solvent by evaporation and simultaneously absorbs water. A key issue is to avoid formation of a dense surface skin on the air side of the membrane. Dense skin formation is... 

Membranes can be divided into two categories according to their structural characteristics which can have significant impacts on their performance as separators and/or reactors (membrane reactors or membrane catalysts) dense and porous membranes. Dense membranes are free of discrete, well-defined pores or voids. The difference between the two types can be conveniently detected by the presence of any pore structure under electron microscopy. The effectiveness of a dense membrane strongly depends on its material, the species to be separated and their interactions with the membrane. 

Catalysts such as the platinum group metals can be used in dispersed or monolithic solid form. The catalyst can be deposited on the surface of a membrane (dense or porous) or, in the cases of catalyst particles, dispersed in the sub>surface layer or throughout the matrix of a porous membrane. 

For convenience of discussion, modeling studies of packed-bed inert membrane tubular reactors will be divided into two categories depending on the type of inorganic membranes dense or porous. 

There are essentially four different types of membranes, or semipermeable barriers, which have either been commercialized for hydrogen separations or are being proposed for development and commercialization. They are polymeric membranes, porous (ceramic, carbon, metal) membranes, dense metal membranes, and ion-conductive membranes (see Table 8.1). Of these, only the polymeric membranes have seen significant commercialization, although dense metal membranes have been used for commercial applications in selected niche markets. Commercial polymeric membranes may be further classified as either asymmetric (a single polymer composition in which the thin, dense permselective layer covers a porous, but thick, layer) or composite (a thick, porous layer covered by a thin, dense permselective layer composed of a different polymer composition).2... 

In principal, the membranes used in the various separation processes can be roughly divided into two groups, namely the porous membranes and dense membranes. However, there are some cases where it is not clear whether the membrane can be classified as porous or dense. According to the definition of the International Union for Pure and Applied Chemistry (lUPAC) porous membranes are those, having static transport channels or capillaries (pores) with a mean diameter larger than 2 nm. Porous membranes can simply be treated as very fine sieves, which grade particles on a molecular level of size. Corresponding to the above definition for porous membranes, dense membranes are those with a mean pore diameter less than 2 nm [3]. In dense membranes the pores are treated as nonstatic. 

As discussed elsewhere in this text, there are two types of dense, hydrogen-permeable metal membranes to consider from the perspective of module scale-up and design thin metal foils and permselective metal layers formed on a porous support. Another class of hydrogen-permeable inorganic membranes - dense proton-conducting ceramic membranes - are still under development and are addressed in Chapter 2. 

Porous catalytic polymeric membranes dense catalytic pervaporative membranes... 

Membrane Dense dividing wall between two compartments. 

Unlike porous membranes, dense membranes based on perovskites or other MIEC materials offer in theory infinite selectivities to O2, H2, and CO2. Any... 

This chapter reviews the possibilities that the application of a membrane in a catalytic reactor can improve the selectivity of a catalytic oxidation process to achieve a more compact system or to otherwise increase competitiveness. Classification differentiates between those reactors using dense membranes and those using porous membranes. Dense membranes provide high selectivity towards oxygen or hydrogen and the selective separation of one of these compounds under the reaction conditions is the key element in membrane reactors using such membranes. Porous membranes may have many different operation strategies and the contribution to the reaction can be based on a variety of approaches reactant distribution, controlled contact of reactants or improved flow. Difficulties for the application of membrane reactors in industrial operation are also discussed. 

Moreover, when two-layer membranes (asymmetric or composite) are studied, the total system is electrode/solution (c)/membrane (dense/porous layers)/solution (c)/ electrode and the impedance plots can then present three relaxation processes (two at the lowest frequencies which are associated with the membrane itself plus the contribution of the electrolyte solution at high frequencies with fmax 10 Hz), as can observed in Figure 9.4. Note, equivalent circuit (ReCe)-(RiQi)-(R2C2). 

The pretreatment was made by soaking the membrane (dense membrane) into liquid alcohols by Tin and co-workers [82], Dense membranes were prepared from two kinds of polyimide (PI), i.e. Matrimid 5218 (3,3 4,4 -benzophenone tetracar-boxilic dianhydride and 5(6)-amino-l-(4 -aminophenyl)-l,3-trimethylindane), and P84 (copolymer of 3,3, 4,4 -benzophenone tetracarboxylic anhydride and 80% methylphenylene-diamine+20% methylenediamine). The membranes were then immersed into nonsolvent for 1 day at room temperature, followed by drying naturally for 24 h. Then the membrane was subjeeted to the heating scheme given in Fig. 4.30 for carbonization. 

Membranes. Dense membranes of the polymers were cast onto glass plates from 7% solution in CHCI3/CH2CICHCI2 (4 6 vol.), dried 24 h at room temp., then dried for 6 h at 60 C, lifted fi om the glass plate in water, dried at 100 C for 4 h and finally dried for one week in a vacuum oven at 10 torr and 120 C. For polymers insoluble in the mixed solvent, membranes were cast from 7% DMF solution. 

---