Palladium composite membranes development

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-... 

PagUeri SN, BirdseU SA, Snow RC, Springer RW, Smith FM. Development of palladium composite membranes for hydrogen separation. AlChE - Advances in Gas Separation Membranes and Applications II. Los Alamos Los Alamos National Laboratory 2003. 

The cost of Pd-alloy membranes used for hydrogen separation may be reduced by depositing a thin Pd-alloy film on a suitable porous substrate to form a composite membrane. Almost all of the Pd-alloy membrane development efforts are, thus, focused on preparing thin yet defect-free Pd-alloy composite membranes (e.g., Hopkins, 2007 Coulter, 2007 Delft et al., 2005 Damle et al., 2005 Mardilovich et al., 2002). A detailed review of the Pd-alloy membrane research has been prepared by Paglieri and Way (2002) with an extensive bibliography of the palladium membrane research to date. An updated review has been recently prepared by Collot (2003) and Paglieri (2006). 

Gryaznov ct al. [30-32] have done pioneering work in the study of differently designed palladium-alloy membrane reactors for reactions in both gas phase and liquid phase. Most interest was directed to the composition and properties of the membranes, which were decisive questions at this stage of the development, and still are. Selectivity problems in various organic chemical reactions were also of importance to study. 

Metal membranes that are composed principally of palladium alloys are used to purify hydrogen. Although tubular and foil membrane units are commercially available, several types of composite membranes are currently under development to minimize the use of palladium, a precious, platinum-group metal. 

To ensure high permeabilities, it is important to work with low membrane thickness without compromising membrane integrity. For this purpose, several techniques for the production of composite membranes, in which thin palladium alloy layers are deposited onto porous supports have been developed (Fig. 9.8) and are summarized by Drioli et al. [11]. The main problems related to composite membranes concern the achievement of defect-free deposited layers which maintain performance both with time, and also with thermal cycling. Usually, the dif-... 

Yoon et al. used Palladium (Pd) to modify Nafion membranes by coating them with a different thickness of Pd film, using as puttering method (Yoon et al. 2002). The scanning electron microscopy (SEM) micrographs showed that the 10 and 30 nm Pd films were dense and appeared to be well attached to the membrane. However, some cracks were found on the surface of the 100 nm Pd film. It was believed that the cracks were caused by the difference between the Nafion membrane and the Pd film in the expansion that took place when the composite membrane was immersed in water. The Nafion membrane swells more than the Pd film, which eventually develops cracks in the Pd film. Therefore, the sputtering procedures for a membrane thicker than 100 nm apparently need to be improved. From this research, a trade-off between proton conductivity and methanol crossover was noted similar to the results... 

These composite membranes are the only feasible solution for the development of a large-scale process that is incompatible with the high costs of a thick layer of palladium. 

Tubular composite (X-AI2O3 -based supports for Pd-containing metal membrane have been developed. Their distinction consists in using metal nickel for the modification of the porous structure of ceramic supports. Nickel is analog of palladium in many respects it is also effective catalyst for molecular hydrogen... 

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