Chemical Engineering Journal 93 (2003) 23–30 Pd–Ag membrane reactors for water gas shift reaction S. Tosti a,∗ , A. Basile b , G. Chiappetta b , C. Rizzello c , V. Violante a a Associazione Euratom-ENEA sulla Fusione, Centro Ricerche Frascati, C.P. 65, 00044 Frascati (RM), Italy b CNR-IRMERC, c/o Calabria University, Via P. Bucci 17/C, 87030 Rende (CS), Italy c Tesi Sas, Rome, Italy Abstract Pd–Ag thin wall permeators have been obtained by coating ceramic porous tubes with thin Pd–Ag metal foils (50 m). A procedure of cold rolling and annealing has been used for producing thin metal foils. These membranes and membrane reactors have been proposed to recover hydrogen (and its isotopes) from tritiated water by using the water gas shift reaction, and by the reverse reaction (CO 2 conversion) for applications in the fusion reactor fuel cycle. The rolled membranes have been tested at 135–360 ◦ C with a hydrogen transmembrane pressure in the range 130–180 kPa and hydrogen flow rates up to 1.02 × 10 -4 mol s -1 . Both a complete hydrogen selectivity and a good chemical and physical stability have been observed through long-term tests. The tests on the membrane reactors have been carried out at the temperature of 325–330 ◦ C with a feed pressure of 100 kPa; in particular, reaction conversion values close to 100% (well above the equilibrium value, about 80%) have been attained with the water gas shift reaction. These tests have demonstrated their applicability to the fusion fuel cycle as well as to the hydrogenation or dehydrogenation processes involving the use or the production of highly pure hydrogen. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Pd–Ag membrane reactors; Water gas shift reaction; Hydrogenation and dehydrogenation processes; Tritiated water; Permeation; Permselectivity 1. Introduction Palladium and palladium alloy membranes show very high performances in terms of hydrogen permeability because of the high solubility and diffusivity of the hydrogen and its isotopes in their lattice [1–5]. In particular, by adding silver to palladium, we can ensure a reduced metal embrittlement as well as a higher hydrogen permeability values, than pure palladium alone. Therefore, Pd–Ag alloys are used to pre- pare commercial permeator tubes of thickness 100–150 m for hydrogen purification and separation. For the past few years, interesting developments have been raised around the membrane reactors; they have been obtained by filling the lumen of these Pd–Ag membranes with a catalyst bed, where a dehydrogenation reaction is promoted: the gain in terms of hydrogen permeation turns into an increase in the reaction conversion (equilibrium shifting). In fact, the hydrogen produced in the dehydrogena- tion reactions permeates the membrane, and the reaction is moved towards the products beyond the thermodynamic equilibrium [6]. ∗ Corresponding author. Tel.: +39-069-400-5160; fax: +39-069-400-5314. E-mail address: tosti@frascati.enea.it (S. Tosti). A general issue in the palladium membrane and mem- brane reactor technology is the achievement of high selec- tivity (or permselectivity) and high permeability [7–9]: both these properties contribute to reduce sizes and costs. Mainly, a complete hydrogen selectivity, besides the high permeabil- ity, is required for the palladium-based membranes used in applications with high pure hydrogen production. Examples of this procedure are found in nuclear processes, such as separation of hydrogen and its isotopes [10–13], and in re- cent energy applications, like pure hydrogen production by steam reforming of hydrocarbons [14–16]. Furthermore, the use of the membrane technologies has been proposed for ap- plications in the fusion reactor fuel cycle. In this particular case, a mandatory requirement for the membranes to avoid any tritium loss, is the achievement of a complete hydrogen selectivity, in order to both reduce the number of process units and be able to operate in a continuous mode. The development and creation of thin palladium mem- branes have been carried out to separate tritium (the mass-3 hydrogen isotope) from tritiated water by means of the water gas shift reaction [17]: CO + H 2 O ⇔ CO 2 + H 2 (1) Furthermore, a “closed loop process”, based on a batch mode operation by one membrane reactor for both the water gas 1385-8947/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1385-8947(02)00113-4