Element and Module Assembling Joining

In addition to the end seal issue just described, there is another critical material engineering issue facing membrane reactors. It concerns the connection between the membrane element and module housing or piping. In fact, this is considered to be one of the most critical issues to be addressed to make inorganic membrane reactors technically feasible and economically viable. 

There are several possible ways of accomplishing this. These include localized cooling at the joining area, mechanical seal (such as Swagelok), ceramic-to-ceramic, ceramic-to-metal seals (cermets), gland packing, and special types of seals. 

Nourbakhsh et al. [1989] employed a compressible Knudsen flow-type seal for flat membrane reactors. To avoid membrane cracking due to the difference in the thermal expansion coefficients of the membrane and the reactor wall, the membrane reactor is equipped with a pneumatic system which compresses the membrane after the desired operating temperature has been established and all reactor parts have reached steady state temperauires. This type of sealing is also limited to laboratory applications and not practical for production environments. 

Similar to the end sealing issues mentioned above, some module packing considerations are mismatching of the thermal expansion coefficients and chemical compatibility. Shown in Table 9.5 is the comparison of the values of the thermal expansion coefficient 

A simpler (one-step) and more economical joining process is direct brazing in a furnace under a vacuum or inert gas atmosphere through the use of active filler metals [Mizuhara Cl al., 1989]. An active element such as the commonly used Ti in the filler metal forms a true alloy with the base metal. The difference in the thermal expansion coefficients between the ceramic membrane and the metal housing can lead to high stress at the 

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