Durability membrane material properties

It can be concluded that there is a potential for membrane separation of almost any gas from a mixture of gases if physical and chemical properties are carefully considered as well as material properties and durability, possible transport mechanisms, and optimum process conditions evaluated. Creative reflection and advanced research will be able to develop this environmental friendly separation technique for applications within many areas in the future, and hopefully be able to displace old, energyconsuming (and not so clean) technology or combine with them in hybrid process solutions. The costs of the final solution will always be a major issue for commercialization. 

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. 

Several publications on the processing of membranes based on these materials could be found in the literature [5-28]. The selection of membrane material for a given application could be divided in to two parts Screening of materials based on bulk properties and screening based on thin film properties. In the former case, intrinsic material properties such as stability and conductivity will decide the outcome of the research work. In the latter case, the defect free formability of thin film will be the deciding part. The method of film formation as well as the quality of the support substrates could become important in this respect. In supported membranes, material stability and membrane performance are very much related. The most important issue - the application of membranes in high temperature environments - is therefore the study of the stmcture of the membrane/material and its correlation with the stability/durability. 

Membrane materials usually get selected for building construction on the basis of properties such as mechanical strength, cost, flexibility, process-ability, cleaning behaviour, durability and resistance to UV light, fire, humidity and chemical attacks or other fouling behaviour, besides their ecological and environmental effects. 

Polymeric roofing membranes are evaluated using various test methods developed for assessment of durability. Mechanical properties of polymeric materials have two facets one is related to the macroscopic behavior and the other to the molecular behavior. PI Engineers are concerned only with the description of the mechanical behavior (physical properties) under the design conditions. Evaluation of the mechanical properties of roofing membranes (tensile properties at different temperatures, load at break, elongation at break, and energy to break) provides information about the material structural failures and how it can be improved, but does not offer an explanation. If the failure is related to molecular activity, additional information is necessary to comprehend the problem fully. 

In addition to the intrinsic properties of the polymer, the film-forming capabilities are important. When selecting a membrane material, two main properties are targeted, namely, stability and formability. Stability refiects on the durability of the membrane and its ability to perform under harsh operation conditions. This includes flexibility, which is important for membrane installation and handling. Formability is related to the fihn-forming capabilities of the material with control over porosity, pore size, and pore size distribution. Material hydrophobicity is also an important factor depending on the intended application. Selection of membrane fabrication technique depends on the choice of the polymer and the desired structure of the membrane. The most commonly used techniques for the preparation of... 

Due to the environmental focus on CO2 emissions around the world, there are numerous CO2 selective materials under development—several hundred polymers are reported (articles and patents). The main challenge for bringing these membranes into commercialization is to document durability over time (maintaining separation properties) during real operating conditions. 

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