Methane sorption mechanism

The system methane-krypton 5A was selected for study because previous pure component studies for each of these sorbates on Linde 5A zeolite indicate that the sorption mechanisms are significantly different. 

The description of CO transient is the same for the models with a buffer step or a parallel route, since the sorption mechanism of CO is identical for all these models. The CH transient description allowed the homogeneous model and one of the models with reversible reaction between C ads and Cp,ads to be excluded from consideration. The discrimination of other undistinguishable models was possible since the steps that describe higher hydrocarbon (i.e., ethane) formation could be incorporated into the methanation models. 

The epoxy resin formed by tetraglycidyl 4,4 -diamino diphenyl methane and 4,4 -diamino diphenyl sulfone was characterized by dynamic mechanical analysis. Epoxy specimens were exposed to varying dose levels of ionizing radiation (0.5 MeV electrons) up to 10,000 Hrads to assess their endurance in long-term space applications. Ionizing radiation has a limited effect on the mechanical properties of the epoxy. The most notable difference was a decrease of approximately 40°C in Tg after an absorbed dose of 10,000 Mrads. Sorption/desorption studies revealed that plasticization by degradation products was responsible for a portion of the decrease in Tg. 

Teppen et al. [89] have used a flexible model for clay minerals that allows full movement of the M-O-M bonds in the clay structure, where M represents Si, Al, or other cations in the octahedral sheet. This model was used in MD simulations of interactions of hydrated clay minerals with trichloroethene [90, 91]. The simulations suggest that at least three distinct mechanisms coexist for trichloroethene sorption on clay minerals [90], The most stable interactions of trichloroethene with clay surfaces are by full molecular contact, coplanar with the basal surface. The second type more reversible, less stable is adsorption through single-atom contact between one chlorine atom and the surface. In a third mechanism, trichloroethene interacts with the first water layer and does not interact with clay surface directly. Using MC and MD simulation the structure and dynamics of methane in hydrated Na-smectite were studied [92], Methane particles are solvated by approximately 12-13 water molecules, with six oxygen atoms from the clay surface completing the coordination shell. 

Many computational studies of the permeation of small gas molecules through polymers have appeared, which were designed to analyze, on an atomic scale, diffusion mechanisms or to calculate the diffusion coefficient and the solubility parameters. Most of these studies have dealt with flexible polymer chains of relatively simple structure such as polyethylene, polypropylene, and poly-(isobutylene) [49,50,51,52,53], There are, however, a few reports on polymers consisting of stiff chains. For example, Mooney and MacElroy [54] studied the diffusion of small molecules in semicrystalline aromatic polymers and Cuthbert et al. [55] have calculated the Henry s law constant for a number of small molecules in polystyrene and studied the effect of box size on the calculated Henry s law constants. Most of these reports are limited to the calculation of solubility coefficients at a single temperature and in the zero-pressure limit. However, there are few reports on the calculation of solubilities at higher pressures, for example the reports by de Pablo et al. [56] on the calculation of solubilities of alkanes in polyethylene, by Abu-Shargh [53] on the calculation of solubility of propene in polypropylene, and by Lim et al. [47] on the sorption of methane and carbon dioxide in amorphous polyetherimide. In the former two cases, the authors have used Gibbs ensemble Monte Carlo method [41,57] to do the calculations, and in the latter case, the authors have used an equation-of-state method to describe the gas phase. 

Independent of the concrete mechanism of the sorption processes the maximum character of the isobars prove that the uptake of methane in coal takes place at two energy levels. The first is the normal physical adsorption in (on) the surface-(micro)pores and the second sorption takes place in the lattice structure... 

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