Technical and Materials Challenges

Recently, the fluidized bed membrane reactor (FBMR) has also been examined from the scale-up and practical points of view. Key factors affecting the performance of a commercial FBMR were analysed and compared to corresponding factors in the PBMR. Challenges to the commercial viability of the FBMR were identified. A very important design parameter was determined to be the distribution of membrane area between the dense bed and the dilute phase. Key areas for commercial viability were mechanical stability of reactor internals, the durability of the membrane material, and the effect of gas withdrawal on fluidization. Thermal uniformity was identified as an advantageous property of the FBMR. 

A timely review paper focusing on the hurdles to inorganic membrane use was presented by Saracco et They listed the main drawbacks as the high cost of membranes, low permeability, defects in permselective layers, instability of membranes and catalysts, and sealing. They were not optimistic for the future of the CNMR or CMR, and considered circumventing equilibrium in a PBMR to be most promising, if membranes with good characteristics become available. 

Saracco et broke their challenges into three groups materials, catalysis and chemical engineering. This is a useful classification and we will follow it. The 

The need for thin, high permeability membranes has been confirmed by a technology assessment by Ward et al. Their goal was to determine what thickness of membrane is needed for petrochemical applications. They considered only high-selectivity materials, both dense and porous, and calculated the approximate membrane thickness to provide sufficient gas flux to have a substantial impact on the process. Both H2- and 02-transporting membranes were considered, and the conditions and typical space velocities of the process. A sample of their results is presented here in Table 2. 

These numbers show that for Ci-utilization, quite thick membranes ca. 1 mm) can be used, which can be self-supporting. For dehydrogenation reactions very thin films are needed, which will be a difficult challenge for materials scientists to obtain phase and mechanical stability under process conditions. Further evidence of the need for highly selective materials for dehydrogenation is presented by Harold et al. and Sheintuch.  

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There are a number of reasons for the absence of CBRN attacks including the technical and material challenges. In addition, while al Qaeda is set to destroy the West, few other groups have the motivation to kill large numbers of people. Other factors include terrorists prefer the certainty of conventional weapons to the uncertainty of CBRN the weapons can be hazardous to the terrorists themselves the response to a CBRN terrorist attack may result in further degradation of terrorist capabilities and finally political support of the terrorist organization s base may be turned away by the use of unconventional tactics. 

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