The unimolecular character of the classical Brunauer, Emmett and Teller adsorption equation and moisture adsorption

Abstract

A reformulation of the classical Brunauer, Emmett and Teller multimolecular adsorption equation resulted in a unimolecular equation in which a third parameter was introduced into general statements. The third parameter represented adsorption centres on the unimolecular surface. This parameter modified the constant C in the BET equation to C 1/n which, on analysis, was found to measure the density of the most strongly adsorbed molecules. The new equation, which was shown to apply to all isotherm shapes, delineated limits between which three states of unimolecularly adsorbed molecules could be identified along the isotherm. It also provided a new method for calculating the net heat of adsorption, which is identical with the Clausius-Clapeyron equation at low values of Aw. The equation also explained the phenomenon of adsorption compression in sorption studies and this was because of the increased density of primary adsorbate molecules at low values of Aw.

Thermodynamic properties of moisture adsorption of whole wheat flour. Calculation of net isosteric heat

“…This fraction contains polar groups of high binding energy to hydrophilic components (crude fibre, starches, proteins, etc.) These values were similar to those obtained by Caurie (2005). The high-moisture end of the first stage, which is known as the 'BET monolayer', corresponds to the amount of water needed to form a monolayer and is the most accessible part of this first stage.…”

“…The relationships between water vapour adsorption capacities and equilibrium-relative humidities were described using two-three-parameter models: the GAB and the Caurie (2005) equation. The first is:…”

“…Nevertheless, Caurie (2005) proposes an alternative and more recent method to calculate this parameter. Thus, if the moisture content remains constant, we can use the equation:…”

“…However, the Guggenheim-Anderson-de Boer (GAB) equation has been recognised as the most versatile sorption model (Furmaniak et al, 2009) as it provides the best description of sorption behaviour over a wide range of water activities. Likewise, and considering that the hydration of a food can be explained by the number of adsorption centres rather than an infinite number of layers of water as in the original Brunauer-Emmett-Teller (BET) model, we tested a second three-parameter model that was reformulated from this equation, and whose new form is of unimolecular character (Caurie, 2005). Likewise, and considering that the hydration of a food can be explained by the number of adsorption centres rather than an infinite number of layers of water as in the original Brunauer-Emmett-Teller (BET) model, we tested a second three-parameter model that was reformulated from this equation, and whose new form is of unimolecular character (Caurie, 2005).…”

Water Sorption Isotherms and Crispness of Fried Yam Chips in the Temperature Range from 293K to 313K

“…[4] The graphical relationship between the amount of water adsorbed and the corresponding environmental humidity, expressed as water activity at constant temperature is called a sorption isotherm. [6] The relationship between water activity and equilibrium moisture content is fundamental to the design of dehydration operations (optimal moisture content and energy requirements) and also, to determine suitable storage and packaging conditions (to improve several characteristics such as texture or stability related to the quality) [7] of fried food material. Moisture sorption isotherms are usefull thermodynamic tools for determining the interactions between water and the products dry surface and provide information useful for assessing food processing operation such as frying (drying), mixing, and storage.…”