Membranes temperature profile

Tosti et /., 2002). Due to stability-related problems, it generally has to operate at a temperature below 500°C (Bredesen, 2008). Considering that in a catalytic reactor the temperature profiles are usually steep (De Falco et al., 2008), if a 2D model is implemented, the reactor zone temperature is calculated in every point inside the reactor, and both axial and radial profiles are available, giving the reactor designer a much more reliable assessment of the membrane temperature profile. 

Temperature profiles, methane conversion, HRF and permeated flow are shown in Fig. 14.6. Figure 14.7 shows the membrane temperature profile and the permeation driving force along the reactor. Table 14.4 shows the permeation results and the product outcome, outlining that total hydrogen permeated is lower (26%) for the counter-current configuration. The calculated HRF and methane conversion ( CH4 ) in the counter-current flow... 

Figure 2.37 Temperature profiles across the membrane covering the reaction channel of the T micro reactor for a silicon and a silicon nitride membrane and two different heater designs, as discussed by Quiram et al. [128].

Figure 2. Shrinkage temperature profiles and membrane performances in relation to the additive composition...

These results are consistent with the reverse osmosis data shown In Figure 4. The shrinking temperature profiles of the membranes regularly shift toward higher temperatures with an Increased additive content. The corresponding membrane performances show a typical optimum at 14 wt.% of additive (513-type films) and a sudden drop of the performance at higher additive content. 

To elucidate this effect a series of membranes was prepared from the most promising casting dope (Batch 513) that has been cooled down to 0°C. The results presented In Figure 5 show that In this way a shift of the shrinkage temperature profile toward lower temperatures followed by the better membrane performance has been obtained. Such a result seems to be rather vmexpected, and It will be discussed later. 

At first sight, adsorption and reaction are well-matched functionalities for integrated chemical processes. Their compatibility extends over a wide temperature range, and their respective kinetics are usually rapid enough so as not to constrain either process, whereas the permeation rate in membrane reactors commonly lags behind that of the catalytic reaction [9]. The phase slippage observed in extractive processes [10], for example, is absent and the choice of the adsorbent offers a powerful degree of freedom in the selective manipulation of concentration profiles that lies at the heart of all multifunctional reactor operation [11]. Furthermore, in contrast to reactive distillation, the effective independence of concentration and temperature profiles... 

Live and deproteinated plasma membranes of Acholeplasma laUawii were investigated by FTIR (Casal et al., 1980 Cameron et al., 1985). The temperature profiles of the gel to liquid crystalline phase transition of intact and deproteinated membranes, monitored by z/as(CD2), differ considerably. In intact membranes, the transition is broad and at temperatures within the range of the phase transition the live mycoplasma is able to keep the fluidity of its plasma membranes at a much higher level than that of the isolated plasma membrane. Native and reconstituted sarcoplasmic recticulum were investigated by Mendelsohn et al. (Mendelsohn et al., 1984). It appears that the protein Ca -ATPase interacts preferentially with the DOPC component of the membrane. A survey of these studies is available (Mantsch and McElhaney, 1991). 

It is relevant at this point to stress the importance of preserving the nonisothermal condition of the reactor. Most of the modeling studies of membrane reactors assume an isothermal operation. However, as it has been demonstrated experimentally [Becker et al., 1993], this assumption is incorrect and, more often than not, a temperature profile exists along the membrane reactor length. 

Figure 11.26 Temperature profiles on the reaction and permeate sides and conversion of the endothermic cyclohexane dehydrogenation in a packed-bed dense Pd membrane reactor (Itoh, 1990]...

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... 

Controlling temperature and humidity of process air or ambient air is another unique application of membrane contactors. Membranes are used to humidify or dehumidify air by bringing air in contact with water or a hygroscopic liquid. Mass transfer in such processes is very fast since mass transfer resistance in the liquid phase is negligible. Heat transfer and mass transfer are directly related to these processes, since latent heat of evaporation (or condensation) creates temperature profiles inside the contactor. Some of the references in Literature are shown in Refs. [78-79]. Application of such processes has been proposed for conditioning air in aircraft cabins [80], in buildings or vehicles [81], or in containers to store perishable goods [82]. 

Figure 9.13. Feed-side and sweep-side temperature profiles along the length of the membrane reactor for autothermal reforming syngas. (Reprinted with permission from Huang et al.,6 Copyright...

The temperature profiles for both feed and sweep sides are shown in Figure 9.13 with a maximum for each profile. Since the overall module was adiabatic, the feed gas was heated by the exothermic WGS reaction. The highest feed-side temperature was 158 °C at about z = 15 cm. Beyond that, the feed-side temperature reduced, and it became very close to the sweep-side temperature at the end of membrane reactor. This was due to the efficient heat transfer provided by the hollow-fiber configuration. 

Figure 9.18. Feed-side temperature profiles along the length of membrane reactor for autothermal...

The membrane areas required for the exit feed CO concentration of <10 ppm in the H2 product were calculated with seven different inlet sweep temperatures ranging from 80 to 200 °C, while the other parameters for the reference case were kept constant. As demonstrated in Figure 9.19, the required membrane area or hollow-fiber number dropped rapidly as the inlet sweep temperature increased from 80 to 160 °C. Beyond 160 °C, it increased slightly. Figure 9.20 depicts the feed-side temperature profiles along the membrane reactor with different inlet sweep temperatures. Increasing the inlet sweep temperature increased the feed-side temperature... 

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