Membrane reactor performances

Figure 2. Effect of permselectivity of HCHO, Shcho membrane reactor performance at 873K.

In order for a membrane reactor to produce yields of HCHO greater than in a plug flow reactor, the membrane must be permselective for this species. The more permselective the membrane is to formaldehyde the better the membrane reactor performs until the formaldehyde is approximately one thousand times more permeable than methane. At this limit, the concentration of HCHO is essentially equal on both sides of the membrane at all times. No further improvement is possible by increasing the diffusivity of the formaldehyde further because there is... 

More discussions on the membrane microstructure affecting the membrane reactor performance will be made in (Chapter 10 and 11. 

The flow patterns of the feed, permeate and retentate streams can greatly influence the membrane reactor performance. First of all, the crossflow configuration distinctly differs from the flow>through membrane reactor. In addition, among the commonly employed crossflow arrangements, the relative flow direction and mixing technique of the feed and the permeate have significant impacts on the reactor behavior as well. Some of these effects are the results of the contact time of the reactant(s) or produces) with the membrane pore surface. 

Over a wide range of conditions, especially those at moderate to high 7, the adiabatic membrane reactor performs better than the isothermal membrane reactor. 

Effects of space time under nonisothermal conditions. The above discussions around the effects of space time on a membrane reactor performance are limited to isothermal conditions. The behavior of the reaction conversion in response to space time can be further complicated under nonisothermal conditions. 

While inorganic membrane reactors perform more efficiemly than conventional reactors in most cases, there are situations calling for the combined usage of these two types of reactors for reasons to be discussed. The conventional reactors in these special cases serve as either the pre-processing or post-processing step for the inorganic membrane reactor system to derive a maximum overall reaction conversion. These hybrid types of reactors consist of conventional reactors at the front end or tail end or both of the membrane reactor. 

In order to study the impact of inlet feed temperature on the membrane reactor performance, Tm = 80,100,120,140,160,180, and 200 °C were applied in the model... 

Several other recent modelling membrane reactor studies are also worth discussing, Varma and coworkers [127] have analyzed the effect that nonuniform catalyst distribution on the membrane itself (for CMR and PBCMR applications) and in the catalyst bed (for PBMR applications) has on membrane reactor performance. Conventional membrane reactor models were utilized by a number of groups to model their experimental data. Shu and co-workers [33]... 

The effect of reactant loss on membrane reactor performance was explained nicely in a study by Harold et al [5.25], who compared conversion during the cyclohexane dehydrogenation reaction in a PBMR equipped with different types of membranes. The results are shown in Fig. 5.4, which shows the cyclohexane conversion in the reactor as a function of the ratio of permeation to reaction rates (proportional to the ratio of a characteristic time for reaction in the packed bed to a characteristic time for transport through the membrane). Curves 1 and 2 correspond to mesoporous membranes with a Knudsen (H2/cyclohexane) separation factor. Curves 3 and 4 are for microporous membranes with a separation factor of 100, and curves 5 and 6 correspond to dense metal membranes with an infinite separation factor. The odd numbered curves correspond to using an inert sweep gas flow rate equal to the cyclohexane flow, whereas for the even numbered curves the sweep to cyclohexane flow ratio is 10. 

Generally, membrane materials with high selectivities and permeabilities are required in order to achieve good membrane reactor performance. Furthermore, for applications in chemical industry, membranes resistant to aggressive chemical environments and able to withstand high temperatures and pressures are required. 

Then they investigated the influence of system parameters on the CO2 membrane reactor performance [41]. They investigated WGS reaction with auto-thermal reforming and steam reforming feeds. The required membrane... 

FIGURE 6.26 Effect of H2/CO2 and H2CO perm-selectivity on membrane reactor performance (a) CO conversion and (b) H2 recovery. (Taken from Figure 6 of p. Boutikosa, V. Nikolakisb, J. Membr. Sci. 350 (2010) 378.)... 

Theoretical Study of Staged Membrane Reactor Performance... 

Gallucci F, De Falco M, Tosti S, Marrelli L, Basile A (2007) The effect of the hydrogen flux pressure and temperature dependence factors on the membrane reactor performances. Int J Hydrogen Energy 32 4052-4058... 

Koukou MK, Papayannakos N, Markatos NC (1996) Dispersion effects on membrane reactor performance. AIChE J 42 2607-2615... 

Obviously, membrane reactor performance is strongly dependent on selective membrane behavior in terms of permeability, selectivity, and stability. Chapter 2 reports several data about hydrogen permeation performance of different metal-based and particularly of Pd-based membranes. 

Table 11.1 Membrane reactor performance for various chemical processes...

Hasanoglu et al. (2009) used cross-linked hydrophobic PDMS membranes, which were permselective to EA, for the esterification reaction of acetic acid and EtOH to produce EA and water, in a batch PV reactor. Temperature has a strong influence on the membrane reactor performance because it acts in kinetics of both esterification and PV. 

Porous metal membranes are commercially available in stainless steel and some other alloys (e.g.. Inconel, Hastelloy) and they are characterized by a macroporous structure. On the other hand, porous ceramic membranes can be found commercially in various oxides and combination of oxides (e.g., Al203,li02,Zr02, Si02) and pore size families in the mesopore and macropore ranges (e.g., from 1 nm to several microns). Most of the literature studies on three-phase catalytic membrane reactors have been carried out by developing catalytic ceramic membranes. The deposition techniques for the preparation of catalytic ceramic membranes involve methods widely used for the preparation of traditional supported catalysts (Pinna, 1998), and methods specifically developed for the preparation of structured catalysts (Cybulski and Moulijn, 2006). Other methods to introduce a catalytic species on a porous support include the chemical vapour deposition and physical vapour deposition (Daub et al, 2001). The catalyst deposition method has a strong influence on the catalytic membrane reactor performance. 

Zeng Y, Lin Y S and Swartz S L (1998), Perovskite-type ceramic membrane synthesis, oxygen permeation and membrane reactor performance for oxidative coupling of methane , Membrane Sci, 150,87-98. 

Effect of catalyst effectiveness factor on WGS membrane reactor performance in closed architecture (a) CO conversion and (b) temperature. 

Key words photocatalytic membrane reactors, photocatolytic membrane reactor performance, water/wastewater treatment, photocatalytic synthesis. 

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