Permselectivity infinite

Table 4.3 Infinite dilution permselectivity characteristics of semicrystalline polyethylene oxide) at 35°C [76],...

In the case of dense membranes, where only hydrogen can permeate (permselectivity for H2 is infinite), the permeation rate is generally much lower than the reaction rate (especially when a fixed bed is added to the membrane). Experimental conditions and/or a reactor design which diminishes this gap will have positive effects on the yield. An increase of the sweep gas flow rate (increase of the driving force for H2 permeation) leads to an increase in conversion and, if low reactant flow rates are used (to limit the H2 production), conversions of up to 100% can be predicted [55]. These models of dense membrane reactors explain why large membrane surfaces are needed and why research is directed towards decreasing the thickness of Pd membranes (subsection 9.3.2.2.A.a). 

The single palladium membrane tube reactor used is shown in Fig. 13.1, where the shell tube is stainless-steel with a length of 250 mm and an inside diameter (ID) of 21 nun. A palladium membrane tube was inserted into the centre of the reactor and was covered with a stainless-steel mesh tube to prevent contact with the catalyst pellets, such that the clearance between the membrane tube and stainless-steel mesh was 1.2 mm. The 5 am-thick palladium membrane supported on a porous a-AljOs tube was 100 mm long and 3 mm in outer diameter (OD), and showed almost infinite selectivity to hydrogen that is, the ideal permselectivity for Hj/Nj observed was more than 10 000 (Itoh et al., 2007). 0.5 wt% Pt/AljOj cylindrical pellets (3.2 mm diameter and 3.6 mm height) were packed around... 

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