Partial Oxidation permeator

It is expected that the conclusions reached in the analysis of the series reaction will also be valid for methane partial oxidation. The first objective of this study was to verify this expectation. The second objective of the study was to determine how much faster than methane formaldehyde must permeate for the membrane reactor to begin to outperform a plug-flow reactor. 

The conditions are substantially more favorable for the microporous catalytic membrane reactor concept. In this case the membrane wall consists of catalyti-cally active, microporous material. If a simple reaction A -> B takes place and no permeate is withdrawn, the concentration profiles are identical to those in a catalyst slab (Fig. 29a). By purging the permeate side with an inert gas or by applying a small total pressure difference, a permeate with a composition similar to that in the center of the catalyst pellet can be obtained (Fig. 29b). In this case almost 100% conversion over a reaction length of only a few millimeters is possible. The advantages are even more pronounced, if a selectivity-limited reaction is considered. This is shown with the simple consecutive reaction A- B- C where B is the desired product. Pore diffusion reduces the yield of B since in a catalyst slab B has to diffuse backwards from the place where it was formed, thereby being partly converted to C (Fig. 29c). This is the reason why in practice rapid consecutive reactions like partial oxidations are often run in pellets composed of a thin shell of active catalyst on an inert support [30],... 

The process of catalytic partial oxidation of methanol with air in a fuel-rich mixture has been commercialized to produce formaldehyde since about 1890. Various catalysts have been used but silver catalyst is by far most widely used. Song and Hwang [1991] used a packed-bed porous membrane tubular reactor wi the catalyst packed on the shell side. They used a model consmicted essentially from Equations (10-36) and (10-44) with the permeation terms replaced by some terms similar to Equation (10-56) and k- =0. The partial oxidation of methanol can be conveniently described by... 

Permeate side as above, without reaction terms. Cocurrent flow. Heat balances only in case of 0-xylcnc partial oxidation. 

Bilayer membranes have been successfully operated under partial oxidation conditions for several hundred hours without any significant deterioration of the permeation flux. ... 

The fraction of CH4 feed is fed through the bottom section in such a way that the permeating O2 is able to generate CPO (catalytic partial oxidation) equilibrium conditions in the bottom section, the temperature of which is in turn favorable for the permselective O2 transport. The steam is also added to avoid coke formation in the bottom section. The top section is then fed with the remaining CH 4 and steam feed so that overall autothermal process is achieved when both sections are considered together. The endothermic heat demand of the top section is thus catered by the equilibrium mixture corning from the bottom section and the side feed of additional CH4 and steam. 

The permeabilities of oxygen through the Vycor were constant with the pressure difference and decreased with the square root of the temperature (figure not included). So the main mechanism for gas permeation is Knudsen diffusion. However, the permeabilities of oxygen through the V20s-coated catalytic membrane were deviated from Knudsen diffusion. As the partial oxidation proceeded, the... 

Dixon et al. simulated the partial oxidation of o-xylene to phthalic anhydride over a vanadium pentoxide catalyst supported on alumina, in a dense perovskite membrane tube. A non-isothermal model was used, which included the effect of temperature on the permeation rate. The competing reaction, complete oxidation to combustion products, is favored at higher temperatures. Comparisons were made to fixed bed reactors operated under the same conditions. For the fixed bed with inlet temperature 630 K, the usual hotspot near the front of the bed was seen, as shown in Figure 11. 

Use of the Reaction to Modify the Membrane and Improve Driving Force -The use of dense oxide membranes to feed O2 to partial oxidation reactions is limited by the need for high temperatures to obtain reasonable permeation rates. The potential exists for selectivity gains and the control of heat effects. One application where dense membranes have a clear role to play is in methane activation. In particular, the partial oxidation of methane to syngas. 

Systems with partial oxidation in the membrane reactor at the permeate side. 

These estimates give only an upper limit of oxygen permeation rate because surface exchange reactions may result in some suppression of the overall transport. For the conditions typical for syngas generation (pO2=0.21 atm, pOj = 10 atm, 950°C), the results for the membranes with L = 0.1cm and different chromium contents are shown in Fig. 3. In the calculations at high pressures the ion conductivity values were assumed to be nearly equal to those at low pressures. Fig. 2. It is seen that the permeation rate in chromium doped samples is smaller than in the parent ferrite. Nonetheless, it may achieve a value of about 4 ml cm min in the sample with y = 1, which corresponds to the syngas production rate of about 20-25 ml-cm -min in the methane partial oxidation process. In combination... 

In the oxidation section, CH4 is partially oxidized in order to achieve the high temperatures required for O2 permeation through the perovskite membranes and to simultaneously preheat part of the CH4/steam feed. 

Santos, L.C., Moraes, C. and Hughes, R. (2011) Characterization of hollow fibre membranes for oxygen permeation and partial oxidation reactions. Brazilian Journal... 

Ikeguchi M,MimiuaT, Sekine Y, Kikuchi E and Matsukata M (2005), Reaction and oxygen permeation studies in Smo,4Bao.6Coo,2Feo,803.5 membrane reactor for partial oxidation of methane to syngas, Appl CatalA-Gen, 290,212-220. 

IshiharaT and Takita Y (2000), Partial oxidation of methane into syngas with oxygen permeating ceramic membrane reactors , Catal Surveys Japan, 4,125-133. 

Zhu X, Li Q, He Y, Cong Y and Yang W (2010), Oxygen permeation and partial oxidation of methane in dual-phase membrane reactors , J Membr Sci, 360, 454-460. 

Layout of a coal gasification plant integrated with an OTM permeator for syngas oxy-combustion. (PO refers to partial oxidizer.)... 

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