Heats of Adsorption. II

Smith, R. Nelson; Pierce, Conway

doi:10.1021/j150463a002

Cited by 20 publications

(18 citation statements)

References 17 publications

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“…Micro‐cracks and fissures, which may form as Aw increases have been observed radiographically by Milner & Shellenberger (1953) and these may expose deeper‐seated energetic sites not previously available to the adsorbate molecules. With these additional exposed sites Smith & Pierce (1948) have stated that at any Aw active sites would adsorb moisture or vapour appropriate to their surface energies. This means that not all the additional sites exposed inside micro‐cracks and fissures will adsorb moisture or vapour at Aws at which they were exposed on the way up to higher Aws, because they may not have appropriate surface energies.…”

Section: Discussionmentioning

confidence: 99%

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Hysteresis phenomenon in foods

Caurie

2006

Int J of Food Sci Tech

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It has been explained that hysteresis is a sorption phenomenon, which rests on temperature, Aw, moisture content and on surface energy Q. As temperature and Aw as environmental variables have opposite effects on moisture content the isobar and isotherm methods are bound to have opposite effects on the hysteresis loop. Using Caurie's equation it has been shown that the desorption isotherm of the hysteresis loop is always at a higher energy level than the adsorption isotherm. This energy difference is stated to arise from physical changes in the adsorbent matrix which expose new energetic sites which adsorb moisture on return to lower Aws rather than desorb moisture and this is indicated to be responsible for the hysteresis phenomenon. It has also been argued that hysteresis may be used as an index of food quality.

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Section: Discussionmentioning

confidence: 99%

“…Smith & Pierce (1948) have stated that at any Aw, active sites adsorb moisture appropriate to their surface energies. These surface energies have been explained to be higher on the desorption arm of the hysteresis loop than on the adsorption arm of the loop (Chung & Pfost, 1967; Caurie, 1981).…”

Section: Methodsmentioning

confidence: 99%

Hysteresis phenomenon in foods

Caurie

2006

Int J of Food Sci Tech

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“…This inference is in disagreement with the essential assumption of the multilayer adsorption theories as given by Hiittig [6], Brunauer, Emmett and Teller [7] and modifications of the BET theory [8][9][10][11][12]. According to these authors multilayer formation should be impossible in our pressure and temperature range, which is above the boiling point of methanol.…”

Section: Discussion and Interpretationmentioning

confidence: 74%

Methanol adsorption by amorphous silica alumina in the critical temperature range

Kuczynski

Ooteghem

Westerterp

1986

Colloid & Polymer Sci

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Abstract:The methanol adsorption capacity of an amorphous silica-alumina was measured using an equilibrium technique. The experimental temperature range was of 140 to 260 ~ and the pure methanol pressure range was 0.1 to 1.2 MPa. A multilayer adsorption was found, also for temperatures above the critical temperature of the adsorbate. Based on the Jovanovic adsorption model, the mean residence times of the adsorbed molecules were calculated. Surprisingly, the heat of adsorption was found to be independent of the temperature in the multilayer adsorption range.Key words: , high temperature adsorption, silica-alumina, multilayers, adsorption heat. NotationSymbols a = parameter defined by Equation (7) a' = parameter defined by Equation ( = parameter defined by Equation (11) fi (

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“…The earliest report is from Smith and Pierce (1948) and Pierce et al (1949) Like methanol, the heat curve has a steep initial decrease with loading, denoting the presence of strong sites. Also in common with methanol, there is a constant heat plateau in the submonolayer region.…”

Section: Ammonia Adsorptionmentioning

confidence: 99%

The interplay between molecular layering and clustering in adsorption of gases on graphitized thermal carbon black – Spill-over phenomenon and the important role of strong sites

Tan

Zeng

et al. 2015

Journal of Colloid and Interface Science

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We analyse in detail our experimental data, our simulation results and data from the literature, for the adsorption of argon, nitrogen, carbon dioxide, methanol, ammonia and water on graphitized carbon black (GTCB), and show that there are two mechanisms of adsorption at play, and that their interplay governs how different gases adsorb on the surface by either: (1) molecular layering on the basal plane or (2) clustering around very strong sites on the adsorbate whose affinity is much greater than that of the basal plane or the functional groups. Depending on the concentration of the very strong sites or the functional groups, the temperature and the relative strength of the three interactions, (a) fluid-strong sites (fine crevices and functional group) (F-SS), (b) fluid-basal plane (FB) and (c) fluid-fluid (FF), the uptake of adsorbate tends to be dominated by one mechanism. However, there are conditions (temperature and adsorbate) where two mechanisms can both govern the uptake. For simple gases, like argon, nitrogen and carbon dioxide, adsorption proceeds by molecular layering on the basal plane of graphene, but for water which represents an extreme case of a polar molecule, clustering around the strong sites or the functional groups at the edges of the graphene layers is the major mechanism of adsorption and there is little or no adsorption on the basal planes because the F-SS and FF interactions are far stronger than the FB interaction. For adsorptives with lower polarity, exemplified by methanol or ammonia, the adsorption mechanism switches from clustering to layering in the order: ammonia, methanol; and we suggest that the bridging between these two mechanisms is a molecular spill-over phenomenon, which has not been previously proposed in the literature in the context of physical adsorption.

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Heats of Adsorption. II

Cited by 20 publications

References 17 publications

Hysteresis phenomenon in foods

Hysteresis phenomenon in foods

Methanol adsorption by amorphous silica alumina in the critical temperature range

The interplay between molecular layering and clustering in adsorption of gases on graphitized thermal carbon black – Spill-over phenomenon and the important role of strong sites

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