Solid extractants pore characteristics

In addition to having high ligand density, the solid extractant should have accessible pores and good mechanical strength. The mechanical strength of the solid extractants can be easily measured by standard methods usually used for polymer resins. Hence, only pore characteristics of the solid extractants are discussed in this section. 

Planar faults are common in zeolites and related crystalline microporous solids. These can influence the sorptive characteristics in any one of several ways (i) they can have little influence on the overall accessibility or capacity, but alter the pore architecture, accessibility or difiusional constraints (ii) they can reduce the limiting dimensions of pore windows while leaving the tot pore volume unaffected (iii) they can block channels. Pores or pore access can also be blocked by detrital material such as alumina extracted from the framework, coke or sintered metal catalyst particles, immobile organic molecules or non-framework cations in blocking positions. 

In an effective properties model, the porous microstructures of the SOFC electrodes are treated as continua and microstructural properties such as porosity, tortuosity, grain size, and composition are used to calculate the effective transport and reaction parameters for the model. The microstmctural properties are determined by a number of methods, including fabrication data such as composition and mass fractions of the solid species, characteristic features extracted from micrographs such as particle sizes, pore size, and porosity, experimental measurements, and smaller meso- and nanoscale modeling. Effective transport and reaction parameters are calculated from the measured properties of the porous electrodes and used in the governing equations of the ceU-level model. For example, the effective diffusion coefficients of the porous electrodes are typically calculated from the diffusion coefficient of Eq. (26.4), and the porosity ( gas) and tortuosity I of the electrode ... 

The wettability must also be accounted for. This is explained if one considers that oil, water, and gas are accommodated in a rock reservoir. It is expected that water preferably wets the solid surfaces, as depicted in Figure 15.18a. Since gas is the least likely fluid to wet the solid surface, it is stored in the cores of the pores, with oil occupying intermediary positions. This is the case in the majority of oil reservoirs, but in some cases, where the formation characteristics are changed during prospection, the rock surface is coated with oil, as shown in Figure 15.18b. This situation requires more attention from engineers and operation personnel in the extraction activities [29,30]. 

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