Finger-like configuration

Both single- and multitube Pd-membrane reactors adopting the finger-like configuration were developed at ENEA laboratories [74,75]. Reaction tests verified the... 

A single-tube module used in both permeation and reaction tests consists of a Pd-Ag permeator tube assembled in a finger-like configuration inside a shell made of Pyrex glass. The membrane is heated through a Pt wire coil surrounding the permeator tube see Figure 13.34 [87]. The temperature is measured by a thermocouple above the surface of the membrane tube. 

For PERMCAT reactors, several design configurations of Pd-Ag membrane tubes of wall thickness 100 om were proposed [99], as described in Figure 13.39. The first reactor (a) uses a typical finger-like configuration the tritiated gases are fed in the shell side whereas the hydrogen is sent inside the membrane lumen. In the second reactor (b), a preloaded bellows is joined to the Pd-Ag membrane tube in order to compensate for expansion/contraction. In a third reactor (c), the permeator... 

In laboratory applications, the scale-up of membrane devices used multitube modules. At ENEA Frascati laboratories, a bundle of 19 Pd-Ag tubes in finger-like configuration was realized for separating up to 6 NL min of ultrapure hydrogen. Scheme and picture of the multitube reactor are shown in Figure 13.44 [12],... 

Tosti et al. tested Pd-Ag membrane reactor for 12 months for H2 permeation [14]. Excellent stability was observed for 12 months of operation. In fact, the complete hydrogen selectivity and none failure (formation of cracks, holes) were observed. They proposed that the reliability is a result of both the tube manufacturing procedure and the reactor design configuration (finger-like). Figure 6.11 shows the picture of membrane reactor before and after the 12 months of operation. 

This chapter also discusses how the stability of self-supported Pd membranes needs an appropriate design of the membrane module. The finger-like design of membrane modnles in both single- and multitube configuration avoids any mechanical stress of the thin-walled permeators, thus ensuring the durability of the membranes. 

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