Membrane reactor performance metrics and design parameters

4 Membrane reactor performance metrics and design parameters 

The performance of a membrane reactor is then a combination of the reactor performance and the membrane performance. The product of Da and Pe numbers, the DaPe number, gives the ratio of the maximum reaction rate per reactor volume over the maximum permeation per reactor volume. The DaPe number is defined as  

A silica membrane reactor will be efficient and effective therefore, when the membrane, working at full capacity, is able to process all the H2 produced by the reaction. This situation arises when the DaPe = 1 and simulations for silica membrane reactors for the water gas shift (WGS) reaction have indeed demonstrated that maximum CO conversion was achieved at DaPe close to 1 (Battersby et al., 2006 Ikuhara et al, 2007). Thus the DaPe number is a valuable metric to evaluate the potential performance of a membrane reactor and a valuable, yet simple, design tool to ensure that both the reactor and membrane components work together for maximum efficacy. However, the DaPe number does not take into account the selectivity of the membrane which obviously does affect the membrane reactor performance. Both experimental and simulation studies have shown that higher permeation results in higher conversion and product yield enhancements (Battersby et al., 2006 Boutikos and Nikolakis, 2010 Lim et al., 2010).That is not to say that a membrane with a low selectivity cannot be successfully utilized in a membrane reactor set-up. Provided the membrane has nominal selectivity for the desired products over reactants, the conversion of equilibrium-limited reactions will be enhanced in a membrane reactor system. However, the product purity will remain dilute and thus additional operational and capital expenditure will be required for further downstream processing. If the membrane is unable to separate gases then the system behaves as a packed bed reactor. 

Additional metrics for assessment of the performance of a catalytic membrane reactor, specifically to generate H2 from liquid hydrocarbon fuels, are provided in Equations [9.6][9.8j. Similar equations can be applied to processes other than H2 generation as well. The liquid hydrocarbon feed conversion is given by  

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