Membrane reactors oxygen permeability

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... 

One example of membrane reactors is oxidation, in which oxygen from one phase diffuses from one side of an oxygen-permeable membrane to react with a fuel on the other side of the membrane. This avoids a high concentration of O2 on the fuel side, which would be flammable. A catalyst on the fuel side of the membrane oxidizes the fuel to partial oxidation products. One important process using a membrane reactor is the reaction to oxidize methane to form syngas,... 

Silver membranes are permeable to oxygen. Metal membranes have been extensively studied in the countries of the former Soviet Union (Gryaznov and co-workers are world pioneers in the field of dense-membrane reactors), the United States, and Japan, but, except in the former Soviet countries, they have not been widely used in industry (although fine chemistry processes were reported). This is due to their low permeability, as compared to microporous metal or ceramic membranes, and their easy clogging. Bend Research, Inc. reported the use of Pd-composite membranes for the water-gas shift reaction. Those membranes are resistant to H2S poisoning. The properties and performance characteristics of metal membranes are presented in Chapter 16 of this book. 

Wang H, Cong Y, and Yang W. Partial oxidation of ethane to syngas in an oxygen-permeable membrane reactor. J. Membr. Sci. 2002 209 143-152. 

The only other metal that has received some serious attention for membrane reactor applications is Ag [14,38] which is permeable to oxygen. Ag has similar thermal/mechanical stability problem as Pd and in addition its oxygen permeability is orders of magnitude lower. 

The vanadium pentoxide cataKtic membrane reactor was prepared by coating its sol inside the Vycor tube membrane. After heat treatment of the prepared membrane, the [010] planes of vanadium pentoxide layer were grown largely which contributes to partial oxidation reaction of 1-butene to maleic anhydride. The partial oxidation of 1-butene to maleic anhydride was carried out in the catalytic membrane reactor. The maximum selectivity of 95% was obtained at 350 °C when the surface velocity was 500cm/h. And at this condition, oxygen permeability was almost four times higher than the reaction had not occured. 

The consideration of thermal effects and non-isothermal conditions is particularly important for reactions for which mass transport through the membrane is activated and, therefore, depends strongly on temperature. This is, typically, the case for dense membranes like, for example, solid oxide membranes, where the molecular transport is due to ionic diffusion. A theoretical study of the partial oxidation of CH4 to synthesis gas in a membrane reactor utilizing a dense solid oxide membrane has been reported by Tsai et al. [5.22, 5.36]. These authors considered the catalytic membrane to consist of three layers a macroporous support layer and a dense perovskite film (Lai.xSrxCoi.yFeyOs.s) permeable only to oxygen on the top of which a porous catalytic layer is placed. To model such a reactor Tsai et al. [5.22, 5.36] developed a two-dimensional model considering the appropriate mass balance equations for the three membrane layers and the two reactor compartments. For the tubeside and shellside the equations were similar to equations (5.1) and... 

Figure 17 Reactor configurations for conversion of methane to syngas using a dense oxygen-permeable disk membrane (a) no catalyst (b) catalyst loaded downstream from membrane (c) catalyst loaded directly on to membrane...

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