Pd membrane reactor

The design of the Pd-membrane reactor was based on the chip design of reactor [R 10]. The membrane is a composite of three layers, silicon nitride, silicon oxide and palladium. The first two layers are perforated and function as structural support for the latter. They serve also for electrical insulation of the Pd film from the integrated temperature-sensing and heater element. The latter is needed to set the temperature as one parameter that determines the hydrogen flow. 

GP 11] ]R 20] Investigations with a Pd membrane reactor relied on reaction of streams separated via a membrane (to prevent complete mixing of reactants, not to enhance conversion) [11]. A hydrogen/nitrogen stream is guided parallel to an oxygen stream, both separated by the membrane and water is thereby formed. The membranes, made by thin-film processes, can sustain a pressure up to 5 bar. 

She, Y., Dardas, Z., Gummalla, M., Vanderspurt, T. and Emerson, S. (2005) Integrated water gas shift (WGS) Pd membrane reactors for compact hydrogen production systems from reforming of fossil fuels. ACS Division of Fuel Chemistry, Preprints, 50 (2), 561. 

Barbieri, G. DiMaio, F. Simulation of the Methane Steam reforming Process in a Catalytic Pd-Membrane Reactor Ind. Eng. Chem. Res. 36 (1997) 2121-2127. 

Figure 10.4 Methane conversion from steam reforming in a packed-bed Pd membrane reactor (Oertel et al., 19S7]...

Figure 11.10. Comparison of conversions in a dense Pd membrane reactor with five different ideal flow pauems [Itoh et al., 1990]...

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]...

Itoh [1990] simulated a Pd membrane reactor coupling the cyclohexane dehydrogenation reaction on the feed side with oxidation of hydrogen on the permeate side. Given in Figure 11.35 is the predicted conversion of the dehydrogenation reaction as a function of the total flow rate of the sweep gas with the Damkbhler number for the permeate side as a parameter... 

Fig. 11.2. Various types of Pd membrane reactors. Reproduced from Shu et al. [19] with permission.

Fig. 11.4. Top figure shows the effect of pressure on the reaction side of the membrane cm methane conversion in the Pd membrane reactor bottom figure shows the effect of temperature. The solid line and the sjmtibols (o) are for the Pd membrane reactor. The dotted line is the calculated equilibrium conversion and the symbols ( ) are for a membrane reactor using a porous Vycor glass membrane. Reproduced from Uemiya et al. [29] with permission.

Catalytic Oxidative Dehydrogenation of Isobutane in a Pd Membrane Reactor... 

Typically, this reaction is conducted at high temperature to achieve appreciable conversion in a reasonably short reaction time. However, under these conditions where the reaction kinetics are fast, this reaction tends to be thermodynamically limited. Therefore, it has been studied in a Pd membrane reactor [1, 3, 4] where the H2 is continuously removed. Since the rate of the dehydrogenation reaction is slow relative to the rate of hydrogen removal through the Pd membrane, these membrane systems remove the thermodynamic limitation and are instead kinetically limited [5]. 

Figure 2 Schematic of the radial flow Pd membrane reactor used for these studies. A circular Pd foil (.075 mm thick) separates the reaction side from the sweep side. The reaction side is loaded with 18.5 grams of 0.5 wt. % Pt/a-Al203 1/8 inch pellets.

Figure 3 Selectivity, iC4H o conversion, and reaction temperature for the oxidative dehydrogenation of 1C4H10 over Pt/o-Al203 in a Pd membrane reactor as pictured in Figure 2 as a function of the iC4H o 02 ratio. The reaction side contained 30% N2 dilution, had a total flow rate of 1 sipm, and was maintained at a pressure of 2 psig. The sweep side (N2) had a total flow rate of 4 slpm and was maintained at a pressure of 1 psig.

Light alkane (C2-C4) dehydrogenation was the reaction studied by Gryaznov and coworkers in their pioneering studies [2.1, 2.2]. In their dehydrogenation reaction studies, they used Pd or Pd-alloy dense membranes, which were 100 % selective towards hydrogen permeation. The choice of these membranes in many of the early studies is because they were commercially available at that time in a variety of compositions, and their metallic nature allows the construction of multitubular and other complex-shaped membrane reactor systems. Comprehensive review papers on Pd membrane reactors have been published by the same group [2.1, 2.2], and also by Shu et al [2.3]. 

The general behavior of product-removal membrane reactors has been well studied. More details on porous ceramic membrane reactors can be found in the series of publications by Mohan and Govind. An analysis of different flow configurations and the limits of each has been provided for dense Pd membrane reactors by Itoh. ... 

Feed Pd membrane separator Pd membrane reactor Outlet stream... 

For both membrane systems investigated (Pd membrane reactor, and Pd membrane separator plus Pd membrane reactor), the design was carried out by operating at the same reactant molar ratio used in the industrial plant (Pd Reactor 1) as well as lower values (Pd Reactor 2). The feed stream is available in the plant at 16 atm (16.2 bar) and, therefore, no further compression of the feed was considered for the membrane units. Furthermore, no sweep gas or vacuum was applied at the permeate side, and the hydrogen coming from the membrane units was pure, without any need for separation devices downstream. However, the hydrogen pressure was too low to be directly used and, therefore, a compression step has been taken into account. 

Then Uemiya et al. [2] reported another Pd membrane reactor for WGS reaction using Fe-Cr oxide catalysts. The model of flow in the palladium membrane reactor is illustrated in Figure 6.3. They proposed that hydrogen is permeated through palladium membrane via a solution diffusion transport mechanism, and the rate of hydrogen permeation, /, per unit area of membrane, is written in terms of Fick s first law as follows ... 

Criscuoli et al. compared Pd membrane reactor with mesoporous membrane reactor and fixed-bed reactor [5]. Figure 6.5 shows the effect of space velocity on the CO conversion for the three reaction systems. As expected both membrane reactors exhibit better CO conversion than traditional reactor. Between the two membrane reactors Pd membrane reactor exhibits much better CO conversion compared to mesoporous membrane reactor. At the highest time factor, Pd membrane reactor exhibits 100% CO conversion. By increasing the Pd membrane thickness, the hydrogen permeation rate decreases and lower conversions of carbon monoxide are achieved. When they compared experimental results with simulation results the model fits well with the experimental points. 

Basile et al. compared Pd membrane reactor with Pd/Ag membrane reactor. In this study, they used thin rolled membranes [6]. In rolled membranes, the main function of the ceramic support was to separate the Pd or Pd/Ag membrane from the catalyst bed of the MR. The catalyst is inside the ceramic support, while the permeating tubes are outside the ceramic support. Both the membranes exhibit excellent hydrogen permeation selectivity. The experimental data have shown that both membranes work well in terms of CO conversion. The maximum conversion of CO exceeds the value of 96.80%. 

Then Hwang et al. [21] prepared plat type Pd membrane reactor using the magnetron sputtering method over a nickel metal support. They conducted WGS reaction using nickel catalyst. The nickel metal catalyst with a disc shape was placed on a membrane without a metal cage or mesh to hold the catalyst in the reactor. However the membrane did not work very well. 

Bi et al. [23] reported WGS reaction in Pd membrane reactor using Pt/Ce-Zr catalyst. They prepared Pd membrane on outer surface of porous ceramic tubes. Figure 6.13 shows WGS CO conversion and H2 recovery in the Pd membrane reactor charged with the Pt/Ceo.6Zro.402 catalyst as a function of reaction pressure at 623 K, GHSV=4050 kg h and steam/CO = 3. In the Pd membrane... 

Pinaccia et al. [25] investigated the tubular Pd membrane reactor at higher temperatures, i.e., above 400 °C and higher pressures (100-800 kPa). They did permeation tests for 1200 h at 400 °C and the membrane exhibits excellent stability. After permeation they evaluated membrane reactor for WGS reaction using commercial Fe-Cr catalyst in the syngas mixture. They are able to achieve 85% CO conversion and 82% H2 recovery with 97% purity. 

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