Membrane reactors decomposition

Figure 11.8 Comparison of co-current and counter-current porous membrane reactors decomposition of ammonia with a high hydrogen/nitrogen separation factor (= 50 627 C[ColUns etal., 1993)...

Decomposition of methane to H2 and carbon over Ni/Si02 was carried out in a membrane reactor (membrane 90Pd-10Ag) [106]. The use of the membrane reactor allowed increasing the H2 yield by shifting the reaction equilibrium toward the products. An excellent review of the literature data on nonoxidative methane activation over the surface of transition metals was recently published by Choudhary et al. [107]. 

Ishihara, T. et al., Decomposition of methane over Ni/Si02 catalysts with membrane reactor for the production of hydrogen, Chem. Lett., 93, 1995. 

Edlund, D., A Membrane Reactor for H2S Decomposition, Proceedings of the U.S. DOE Advanced Coal Fired Power Systems Review Meeting, Morgantown, WV, July 1996. 

Moziaa S, Morawskia AW, Toyodab M et al (2009) Application of anatase-phase Ti02 for decomposition of azo dye in a photocatalytic membrane reactor. Desalination 24 97-105... 

The research group of Van Leeuwen reported the use of carbosilane de-ndrimers appended with peripherial diphenylphosphino end groups (i.e. 25, Scheme 26) [37]. After in situ complexation with allylpalladium chloride, the resultant metallodendrimer 25 was used as catalyst in the allylic alkylation of sodium diethyl malonate with allyl trifluoroacetate in a continuous flow reactor. Unlike in the batch reaction, in which a very high activity of the dendrimer catalyst and quantitative conversion of the substrate was observed, a rapid decrease in space time yield of the product was noted inside the membrane reactor. The authors concluded that this can most probably be ascribed to catalyst decomposition. The product flow (i.e. outside the membrane reactor)... 

Table 7.1. Membrane Reactor Studies on Decomposition Reactions...

Table 7.2. Summarized Results on Inorganic Membrane Reactors Used for Decomposition Reactions... 

Ozone decomposition in airplanes Selective catalytic reduction of NOx Arrays of corrugated plates Arrays of fibers Gauzes Ag Methanol -> formaldehyde Pt/Rh NO production from ammonia HCN production from methane Foams Catalytic membranes reactors... 

Another important issue evolves if the dendritic catalyst will be used in a continuous-flow membrane reactor. Generally, two forms of leaching have to be considered when dendritic transition metal catalysts are used in such reactors depletion of the dendritic catalyst through the membrane and metal dissociation (possibly after decomposition) from the dendrimer resulting... 

H. Ohya, M. Yatabe, M. Aihara, Y. Negishi, and T. Takeuchi, Feasibility of hydrogen production above 2500 K by direct thermal decomposition reaction in membrane reactor using solar energy, Int. J. Hydrogen Energy, 27 369-376 (2002). 

Hwang, G.J. and Onuki, K., Simulation study ou the catalytic decomposition of hydrogen iodide in a membrane reactor with a silica membrane for the thermochemical water splitting IS process. Journal of Membrane Science, 194, 207, 2001. 

Some dense inorganic membranes made of metals and metal oxides are oxygen specific. Notable ones include silver, zirconia stabilized by yttria or calcia, lead oxide, perovskite-type oxides and some mixed oxides such as yttria stabilized titania-zirconia. Their usage as a membrane reactor is profiled in Table 8.4 for a number of reactions decomposition of carbon dioxide to form carbon monoxide and oxygen, oxidation of ammonia to nitrogen and nitrous oxide, oxidation of methane to syngas and oxidative coupling of methane to form C2 hydrocarbons, and oxidation of other hydrocarbons such as ethylene, methanol, ethanol, propylene and butene. 

Similar to the case of dehydrogenation or other hydrogen-generating reactions, the use of a dense membrane reactor to remove oxygen from an oxygen-generating reaction such as decomposition of carbon dioxide displaces the reaction equilibrium and increases the conversion from 1.2% (limited by the equilibrium) to 22% [Nigara and Cales, 1986]. This has been confumed by Itoh et al. [1993]. 

Figure 9.3 Conversion of thermal decomposition of carbon dioxide in a dense yttria-stabilized zirconia membrane reactor as a function of membrane thickness when a sweep gas is used (top) and when vacuum is applied (bottom) [Itoh et al., 1993]...

Whether and how much a component in the entering reactant stream has any effects depend on its role in the reaction. In a study of ammonia decomposition in a counter-current microporous packed-bed membrane reactor, the inlet concentration of hydrogen greatly influences the decomposition rate. As expected from Figure 11.15, ammonia conversion increases as the hydrogen concentration in the feed stream decreases at a given temperature [Collins et al., 1993). On the contrary, the inlet nitrogen concentration... 

First of all, the space time defined in Eq. (11-5) or (11-6) depends on the volume of the reactor and the total volumetric feed rate. Thus, for a given reactor volume, space time is inversely proportional to the total feed rate. Itoh et al. [1993] studied the use of a dense yttria-stabilized zirconia membrane reactor for thermal decomposition of carbon dioxide. The reactor temperature was not kept constant everywhere in the reactor but varying with the reactor length instead. The resulting temperature profile is parabolic with the maximum temperature at the midpoint of the reactor length. This nonisothermal... 

Itoh et al. [1984] modeled a 1.5-m long packed-bed membrane reactor for catalytic decomposition of HI. The reactor consists of a large number of microporous hollow fiber... 

---