In the paper applicability of BET approach to modeling of adsorption of small nearly spherical molecules in submicro-and microporous sorbents is discussed. The BET assumptions are analyzed from physical point of view, and properly generalized to handle geometrical as well as energetic conditions for multilayer adsorption in microporous structures. A formal description of multilayer adsorption is derived, by using the thermodynamic approach, with any energy profile across the layers being admitted. To get an analytical formula describing the process one proposes to assume an exponential distribution of pore capacity, and apply the BET equation with limited number of layers. Formal properties of the obtained formula, referred to as LBET model, are carefully examined and compared with those of Dubinin-Radushkievith and BET equations. The examination showed that the LBET model describes adequately adsorption process on materials of submicroporous and microporous structure with dominant fraction of small micropores. It provides reliable information on the porous surface capacity and on the first layer adsorption energy. It gives also a semiquantitative characterization of pore volume distribution. Application of the LBET model to interpretation of sorption isotherms of water and methanol on a hard coal and of carbon dioxide on activated carbon is presented.

The paper shows what can be deduced on sorption mechanisms in hard coals and active carbon by using a theoretical model of sorption of small molecules in elastic submicroporous materials. This model (referred to as the multiple sorption modelsMSM) describes both adsorption and absorption phenomena. Basic assumptions and formulas of the MSM are presented. The computations were performed for isotherms of CO2 and CH4 at elevated pressures on three coal samples of different rank and on an active carbon. Nonideality of the sorbates is handled by an original state equation providing consistent information on fugacity and cohesion energy corresponding to a given molar volume of sorbate molecules in the sorption system. Surface structure of the studied coals and energetic parameters of the systems determined with MSM are compared to those obtained by using BET and Dubinin-Radushkievitch equations. It was stated that MSM provides more information on surface structure (including submicropores) and clearly explains sorption properties of hard coals (together with expansion phenomena). It is also applicable to examination and prediction of adsorption on microporous materials (like active carbon).

A kinetic model has been proposed for high-temperature oxidative degradation of lubricants under boundary lubrication conditions. This model incorporates primary oxidation reactions as well as subsequent condensation polymerization reactions that result in viscosity increase and sludge formation. Evaporation of the oil and its volatile primary oxidation products has also been considered. The model has been examined by conducting oxidation and evaporation studies on a commonly used neopentyl polyol ester, trimethylolpropane trlheptanoate, in the Penn State microoxidation test. This thin-film laboratory test simulates lubricant behavior in bearings under elastohydrodynamic and boundary lubrication conditions. The kinetic rate constants for the primary oxidation and the subsequent polymerization reactions have been determined. The rates of reaction appear to be first order. This information coupled with evaporation rates has been used to examine the ability of the model to correctly predict the oxidative behavior of the lubricant. Klaus, , 1983 suggests that the primary reaction is associated with the C-C chain and not the heteroatoms in these molecules.This study treats the oxidation of a polyolester, trimethylolpropane triheptanoate (TMPTH), as a simple reaction with no oxygen diffusion limitations. The basic data are used to model the primary oxidation reaction and subsequent reactions, thereby providing a relationship that can be used to predict the behavior of lubricants given the 0196-4321/86/1225-0596S01.50/0 environments in which they function.

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