Isotherm slope factors influencing

It was stated, that macroporous carbons of plant origin show better properties in dynamic than in static conditions. It is cormected with relationship of quantity of macropores and diffusion rate. Greater differences in classsification are observed at lower equilibrium concentrations (0,1 and 0,01 mg/dm ) in static adsorption. Therefore direct factors of Freundlich s isotherms influencing adsorption capacities at different concentrations should be considered. It was stated that angle of slope, adsorption rate in static conditions, shape of breaktrough curves in dynamic conditions... 

In ideal chromatography, we assume that the column efficiency is infinite, or in other words, that the axial dispersion is negligibly small and the rate of the mass transfer kinetics is infinite. In ideal chromatography, the surface inside the particles is constantly at equilibrium with the solution that percolates through the particle bed. Under such conditions, the band profiles are controlled only by the thermodynamics of phase equilibria. In linear, ideal chromatography, all the elution band profiles are identical to the injection profiles, with a time or volume delay that depends only on the retention factor, or slope of the linear isotherm, and on the mobile phase velocity. This situation is unrealistic, and is usually of little importance or practical interest (except in SMB, see Chapter 17). By contrast, nonlinear, ideal chromatography is an important model, because the profiles of high-concentration bands is essentially controlled by equilibrium thermodynamics and this model permits the detailed study of the influence of thermodynamics on these profiles, independently of the influence of the kinetics of mass transfer... 

From this, it js apparent that the reservoir principle is more apt to have economic utility when the isotherm has a steep slope. As of now, we know but little of ways and means to control the slope of the isotherm. Some of the factors that influence the slope of the isotherm of solutes are ... 

The porous structure of active carbons is the defining factor of their adsorption performance The pore diameter distribution determines the adsorption energy and therefore, the slope of adsorption isotherm, whereas in mainly microporous carbons the micropore volume limits the adsorption capacity at the higher end of t.he adsorptive concentration. Furthermore, the chemical compositor of the carbon surface influences the selectivity of adsorption, e.g. the competition of the water adsorption when working in aqueous solution. However, here only the structural properties of carbons are taken into account. 

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