Membrane scientists challenges

US DOE (Department of Energy) has set technical targets in PEMs for transportation apphcations (Table 7.1) [1]. The targets are for gas crossover (permeability), area-specific resistance, operating temperature, cost, and durability. In 2015, car companies will make a decision whether they continue their endeavor to commercialize fuel cell vehicles. The membrane scientists are facing a big challenge in order to help them go further with fuel cells. 

There are several challenges which remain for the membrane scientists and membrane manufacturers. The material related technical challenges of the membrane separation systems have been widely reported in the literature. The gas separation membranes need to maintain a stable performance over a long period of time, generally 5 years or longer. The life and replacement frequency of the membrane modules influence the overall capital cost of the equipment. The membranes must be able to withstand the process upsets, operate over a broad range of temperature and, most importantly, not have eatastrophic failure. In spite of great advancement of materials in the field of gas separation membranes, we still lack commercially viable materials which are more solvent/ chemical resistant and can operate at elevated temperatures. 

There are two major challenges for membrane scientists with regard to proton exchange membrane fuel cells (1) PEMEC membranes that conduct protons under high-temperature and low-humidity conditions and (2) DMFC membranes that are highly conductive but act as barriers to methanol. 

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. ... 

Challenges to catalysis scientists set out by Saracco et aO include catalyst activation and reproducibility in CMRs, the assessment of catalysts i.e. kinetics and selectivity), avoiding deactivation, and the distribution of the catalyst in the membrane as desired, without changing structure or permeability. The question of location and loading of the catalyst in a membrane is one that continues to be addressed (see Section 4.3.2). It has been determined that loading a membrane with a catalyst does usually reduce permeability, and, unfortunately, does not usually improve permselectivity. Some studies of CMRs have not measured the permeability of the membrane before deposition, after deposition, and after use as a reactor. These measurements are essential to discover if permeability has changed, and to interpret results properly. 

Selective layer deposition methods. Depositing the Pd-based layer on selected substrates is not an easy task. Finding and applying reliable and cost-competitive deposition methods is the main challenge that scientists and technicians have to stiU overcome. Deposition method has to assure a proper membrane stability within the operative range in which the membrane has to work. 

More down-to-earth challenges do get attention from thermodynamics scientists such as supercritical polymerizations, energy storage via organic solar cells, copolymeric compatibilizers in the interphase of compressed heterogeneous polymer blends, membranes and monolayers. 

The development of new high-performance materials that offer a better balance between permeability and selectivity is a greater challenge ahead of the materials scientist. Many glassy materials with improved gas separation efficiency have been investigated for this purpose. Recently, polyazoles have emerged as suitable membrane materials due to their combination of high gas permeability and selectivity. 

Permeation temperature. Many important catalytic reactions, such as the selective oxidation of alkanes, are operated at relatively low temperatures (<500°C), but the operation temperatures to obtain acceptable oxygen fluxes for the ITMs are usually high (>600°C). The development of such membranes operating at moderate temperatures poses a key challenge to material scientists in this area. 

Both porous ceramic and metallic tubes or plates can be used as the support for Pd and Pd-alloy membrane layers. Porous ceramic supports have the advantages of small pore sizes, uniform pore size distributions, and excellent chemical stability. The small pore size and uniform pore size distribution allow the formation of thinner and uniform membrane layers. However, ceramic supports are brittle and prone to cracking. In addition, connecting ceramic material to metallic elements in a process presents a considerable challenge to both material scientists and process engineers. On the other hand, porous metallic supports, such as porous stainless steel and other porous specialty alloys, can... 

Combinations of penetration enhancers have given limited success in the delivery of insulin through the vagina. However, the subject of insulin delivery across the vaginal membrane is still a challenge for future researchers and scientists in the field of vaginal delivery. 

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