Pore population kinetics

The kinetics of the pore population are quantitatively described by Smoluchowskfs equation (14, 42) ... 

N diffuses into the structural pores of clinoptilolite 10 to 10 times faster than does CH4. Thus internal surfaces are kinetically selective for adsorption. Some clino samples are more effective at N2/CH4 separation than others and this property was correlated with the zeolite surface cation population. An incompletely exchanged clino containing doubly charged cations appears to be the most selective for N2. Using a computer-controlled pressure swing adsorption apparatus, several process variables were studied in multiple cycle experiments. These included feed composition and rates, and adsorber temperature, pressure and regeneration conditions. N2 diffusive flux reverses after about 60 seconds, but CH4 adsorption continues. This causes a decay in the observed N2/CH4 separation. Therefore, optimum process conditions include rapid adsorber pressurization and short adsorption/desorp-tion/regeneration cycles. 

The Hill coefficient n obtained from the curve fit of the Cm profile of Class I channels and pores (Fig. 11.7a) corresponds to the number of monomers in the active supramolecule (if self-assembly indeed occurs from an excess monomer in solution. With self-assembly from excess dimer, the number of monomers per active supramolecule is 2n, and so on). The compatibility with the Hill equation further demonstrates the presence of excess monomer besides a small population of active supramolecule. The presence of excess monomer, in turn, reveals that the self-assembly of the channel or pore is an endergonic process. Structural studies of unstable n > 1 supramolecules at concentrations near the EC o by conventional methods are therefore meaningless. For example, NMR or IR measurements will report on the inactive monomers, whereas the unstable active structure of Class I channels and pores is invisible (see Section 11.4 for methods to selectively detect and study minority populations of active supramolecules). In BLMs, the thermodynamic instability of Class I channels and pores is expressed in low open probabilities Po (Fig. 11.4). The n > 1 of Class I channels and pores is unrelated to the kinetic stability expressed in short lifetimes for labile Class lA and long lifetimes for inert Class IB supramolecules. 

The presence of iron oxyhydroxide coatings (i.e., Fe plaque, often dominated by ferrihydrite) on the surface of wetland plant roots is visual evidence that subsurface iron oxidation is occurring in otherwise anoxic wetland soils and sediments. Oxygen delivered via radial O2 loss may react with reduced iron in soil pore spaces to form oxidized iron that can be deposited on the plant roots as Fe plaque. Despite a long history of observing Fe plaque on wetland plant roots and understanding the basics of plaque formation [i.e., reaction of plant-transported O2 with Fe(II) in soils and sediments], it was largely assumed that plaque formation is predominately an abiotic (i.e., chemical) process because the kinetics of chemical oxidation can be extremely rapid (Mendelssohn et al., 1995). However, recent evidence has demonstrated that populations of lithotrophic FeOB are associated with Fe plaque and may play a role in plaque deposition. 

Another possible explanation of the low GORs in the Field is the imperfect seal over the reservoir. Shows of petroleum resembling the Snorre population have been found several hundreds of metres over the reservoir interval (Caillet 1993 Leith et al. 1993 Leith Fallick 1995), even though the field probably has never reached fracture pressure. It is clear that the poor cap rock quality on the relatively shallow and underfilled Snorre structure makes this a perfect candidate for a Type 3 trap as explicitly classified by Sales (1997), i.e. the GOR of the Snorre petroleum charge is determined more by the cap rock properties than by SR quality and its kinetic properties. The oil inferred by Leith et al. (1993) may have leaked from the reservoir as the cap rock section has very low pore entry pressures and micro fracturing is also observed in the cap rock section. One can therefore speculate that the leakage may be a prerequisite to maintain black oil in the Snorre Field. 

Batycky et al. (1997) adopted population balances along with a pseudo-first order degradation kinetics to describe the behavior of eroding microparticles. The kinetic mechanism includes both random chain scission and chain-end scission. The change in matrix porosity is accounted for by considering the coalescence of small pores caused by the breakage of polymer chains. 

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