Membrane Reactor Experiments and Modeling

The Vycor glass tube used in the membrane reactor experiments was filled with 3.2 g of catalyst. As the accessible area was ca. 30 cm2, the ratio of membrane area to catalyst mass is in the range specified by Eq. (35). Consequently, there should be sufficient membrane area available to remove significant amounts of hydrogen and, therefore, to have an effect on the reaction process. 

The experiments were performed at a temperature of 473 K, with three different feed compositions being investigated. For each composition the ratio between the sweep flow rate, Vs, and the feed flow rate, Vf, was altered over a wide range. This sweep (or dilution) ratio, y, was defined as  

The results of the experimental investigation are summarized in Fig. 12.10. Given is the achieved conversion defined as follows  

It is clear that the cyclohexane conversion increases with an increasing sweep ratio y- that is, with increasing driving forces for mass transfer through the membrane. In addition, the introduction of a more diluted feed leads to an enhanced conversion. Proof of an effect of the realized product removal via the Vycor glass membrane was the fact that the achieved conversions exceeded the equilibrium conversions (shown as dotted fines in Fig. 12.10). 

In addition to these experiments, a simplified isothermal 1-D dispersed plug-flow reactor model of the membrane reactor was used to carry out theoretical studies [47]. The model used consisted of the following mass balance equations for the feed and sweep sides  

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Al-Juaied, M.A., Lafarga, D. and Varma, A., 2001. Ethylene Epoxidation in a Catalytic Packed-Bed Membrane Reactor Experiments and Model. Chemical Engineering Science, 56(2) 395-402. 

Israni S H, Nair B K R and Harold M P (2009), Hydrogen generation and purification in a composite Pd hoUow fiber membrane reactor Experiments and modeling , Catal Today, 139,299-311. 

Israni, S., Harold, M. P. (2011). Methanol steam reforming in single-fiber bed Pd-Ag membrane reactor experiments and modeling. Journal of Membrane Science, 369,... 

Szegner J., Yueng A.K.L., Varma A. Effect of catalyst distribution in a membrane reactor experiments and model. AIChE J. 1997 43(8) 2059-2072... 

Diakov, V., Blackwell, B. and Varma, A. (2002) Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor Experiments and model. Chemical Engineering Science, 57, 1563—1569. 

Israni S H, Harold M P (2011) Methanol steam reforming in single-fiber packed bed Pd-Ag membrane reactor Experiments and modeling. J Membrane Sci, 369, 375-387. 

Based on the experimental data of the C02-selective facUitated transport membranes described earlier in this chapter, we proposed the concept of C02-selective WGS membrane reactor and developed a one-dimensional nonisothermal model to simulate the reaction and transport process (Huang et al., 2005a). The modeling results have shown that H2 enhancement and CO reduction to 10 ppm or lower are achievable for autothermal reforming synthesis gas via CO2 removal. With this model, we have elucidated the effects of system parameters on the membrane reactor performance. Using the membrane synthesized and the commercial WGS catalyst, we have obtained a CO concentration of less than 10 ppm in the H2 product in WGS membrane reactor experiments and verified the model developed (Huang et al., 2005b Zou et al., 2007). 

An interesting point regarding OCM is that the membrane material itself may act as a total oxidation catalyst, thus unintentionally turning the PBMR into a PBCMR. Lu et pre-treated their dense membrane with an OCM catalyst to prevent contact between hydrocarbons and the membrane oxide material. Coronas et al. carried out experiments to estimate the contribution from the membrane and used it to modify their model of OCM in a porous membrane. They found that the predicted advantage of the membrane reactor was decreased if the catalytic activity of the membrane was taken into account, and suggested the development of inert membrane reactor materials, and more active OCM catalysts, as possible remedies. 

Sopajaree, K., Qasim, S. A., Basak, S., and Rajeshwar, K., 1999a, Integrated flow-reactor membrane filtration system for heterogeneous photocatalysis. Part I. Experiments and modeling of a batch - recirculated photoreactor, J. App. Electrochem., 29(5) 533-539. 

Sopajaree K, Qasim S A, Basak S and Rajeshwar K (1999a), An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part I Experiments and modelling of a batch-recirculated photoreactor , / Appl Electrochem, 29,533-539. 

Diakov, V. and Varma, A. (2003). Methanol Oxidative Dehydrogenation in a Packed-Bed Membrane Reactor Yield Optimization Experiments and Model, Chem. Eng. Sci, 58, pp. 801-807. 

In the literature several experiments and some modelling results are presented about the possibilities of membrane reactors in the dehydrogenation of ethylbenzene. The results vary from a small increase in yield and selectivity [39,44] to very large increases in yield up to 20% [45-49]. 

The results found in this study are less promising then those reported in literature [45-49]. There are several reasons for this difference. In some publications experiments have been reported in which process conditions and/or feed compositions have been used that are not realistic or feasible on an industrial scale but do have a large impact on the performance of the membrane reactor. Also, when results are reported from modelling this process, incorrect assumptions were sometimes made, e.g. side-reactions which have a large influence on the performance of this process have been neglected [47]. In other publications a very large heat input is taken, which leads to a more or less isothermal reactor, and as a consequence to higher conversions [45,46,48]. 

B. Park, Models and Experiments with Pervaporation Membrane Reactors Integrated with a Water Adsorbent System, Ph.D Thesis, University of Southern California, Los Angeles USA, 2001. 

Both experimental and modelling studies have been carried out. It should be noted that in a membrane reactor, pb may be much lower than in a conventional co-feed reactor (PFR) of the type usually used for kinetics studies. It is possible that the reaction order could change, since most kinetics reflect a redox mechanism. Thus, kinetics taken from the literature that appear favorable could in fact be unfavorable at the lower partial pressures of B present in a membrane reactor. This may account for the fact that fewer instances of good agreement between theory and experiment have been reported for reactant feed situations than for product removal. 

A dynamic model was defined considering the kinetic equation and the hydraulics of the enzymatic membrane reactor. This model was validated comparing experimental data with model predictions at different experiments in steady-state conditions. Even when some modifications were performed, as changes in the Orange II concentration in the feed, the control system was able to predict the Orange II concentration in the reactor (Fig. 6.6.8). 

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