Palladium composite membranes conversion

Because Pd-based metal membranes, commonly used for hydrogen separation [11] are not resistant towards sulphur, not much research has been performed on the use of such membranes in H2S dehydrogenation reactors. Some success has, however, been reported by Edlund and Pledger [12], They developed a platinum-based layered metal membrane that could resist irreversible attack by H2S at 700°C. At this temperature a conversion of 99.4% was achieved in the membrane reactor. Without hydrogen removal the conversion was only 13%. No permeance data is provided, but platinum-based metal membranes are known for their low hydrogen permeance [14], Johnson-Matthey developed palladium composite membranes with a hydrogen permeance of about 1 10 mol/m sPa [14], but these are most probably not resis-... 

BasUe et aL [116] studied the WGS reaction using a MR consisting of a composite palladium-based membrane realized with an ultrathin palladium film ( 0.1 pm) coated on the inner surface of a porous ceramic support (y-Al203) by the co-condensation technique. The authors pointed out the benefit of applying a palladium MR, taking into account that, at 320°C and 1.1 bar, the thermodynamic equilibrium of CO conversion is around 70%, while the authors obtained with the MR CO conversion of around 100%. Moreover, the same authors illustrated that a complete CO conversion could be reached by using a composite membrane with a thinner palladium layer (10 pm Pd film coated on a ceramic support) [117]. 

Paturzo, L., Basile, A. (2002). Methane conversion to syngas in a composite palladium membrane reactor with increasing number of Pd layers. Industrial Engineering Chemistry, 41, 1703. 

Kikuchi [111] described a natural gas MR, which had been developed and operated by Tokyo Gas and Mitsubishi Heavy Industries to supply PEM fuel cells with hydrogen. It was composed of a central burner surrounded by a catalyst bed filled with commercial nickel catalyst. Into the catalyst bed 24 supported palladium membrane tubes were inserted. The membranes had been prepared by electroless plating and were 20 pm thick. Steam was used as sweep gas for the permeate. The reactor carried 14.5 kg catalyst. It was operated at 6.2 bar pressure, S/C ratio of 2.4, and 550°C reaction temperature. The conversion of the natural gas was close to 100%, wdiile the equilibrium conversion was only 30% under the operating conditions. The retentate composition was 6 vol.% hydrogen, 1 vol.% carbon monoxide, 91 vol.% carbon dioxide, and 2 vol.% methane. 

Paturzo, L. and Basile, A. (2002). Methane Conversion to Syngas in a Composite Palladium Membrane Reactor with Increasing Number of Pd Layers, Ind Eng. Chem. Res., 41, pp. 1703-1710. 

As an example. Fig. 3.13 shows the results of WGS tests carried out at 410°C in a Pd membrane reactor with gas mixtures simulating a syngas produced in IGCC plants (Pinacci et al., 2010). A composite palladium-porous stainless steel membrane, 29 pm thick, obtained by electroless plating on a porous stainless steel support, has been used for this purpose. The reactor was fed with a shift gas mixture with a 7.6% CO concentration and HjO/CO ratio of 2.7 and 3.6,respectively. CO conversions up to the 85.0% and 78%,respectively, have been reached, while operating at a feed pressure of 6 bar. These values can be compared with the corresponding conversions obtained with a... 

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