A new calorimeter for simultaneous measurement of isotherms and heats of adsorption

Zimmermann, Wolfgang; Keller, J. U.

doi:10.1016/s0040-6031(03)00133-3

Cited by 38 publications

(41 citation statements)

References 13 publications

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“…10,11 The isostere method can lead to ambiguous results 1,2,12 particularly if the number of isotherms obtained is low, if the isotherms are widely spaced, or where the uncertainty in the isotherm measurement is high. Moreover even at moderate pressure (p < 1 MPa) the ideal gas assumption inherent in Clausius−Clapeyron can lead to large errors in predicting the heat of adsorption.…”

Section: ■ Introductionmentioning

confidence: 99%

Predicting the Integral Heat of Adsorption for Gas Physisorption on Microporous and Mesoporous Adsorbents

Whittaker

Wang

Zimmermann³

et al. 2014

J. Phys. Chem. C

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We have developed two predictive methods for the heats of adsorption that stem from isotherm models and benchmarked them against the Clausius−Clapeyron equation. These are the Toth potential function model and the modified Clapeyron equation. Three adsorbate/adsorbent working pairs are used as examples: n-butane/BAX 1500 activated carbon, isobutane/BAX 1500 activated carbon, and ammonia/Fuji Davison type RD silica gel, all of which are examples of gas physisorption on adsorbents with both micro-and mesopores. Isotherms and corresponding integral heats of adsorption were measured in the range 298−348 K. For n-butane and isobutane, the pressures were up to 235 kPa, and for ammonia, the pressures were up to 835 kPa. Our two predictive methods consistently offer significant improvements over the Clausius−Clapeyron equation. Between the two predictive methods, the Toth model is more robust across all three working pairs studied with predictions generally falling within 10−15% of the values of the measured heats. ■ INTRODUCTIONMost gas adsorption data in the literature are presented as experimentally obtained isotherm measurements without measured heats of adsorption. This is presumably because adsorption experiments that incorporate calorimetry are more expensive and more complicated to both set up and operate than experiments based upon volumetric or gravimetric measurements alone. 1,2 However knowledge of the heat of adsorption can lend insight into surface phenomena. 3 Additionally thermal management is an integral part of the design and operation of systems which make use of adsorption phenomena such as adsorption chillers, 4,5 adsorbed gas storage tanks, 6 and adsorption separation units, 7 all of which require knowledge of the heat of adsorption.Conventionally experimentalists circumvent the dearth of calorimetric data by invoking the Clausius−Clapeyron equation, either through measuring many closely spaced isotherms and applying the equation directly to the data (to wit, the isostere method) 8,9 or by fitting the isotherm data with an isotherm model and then applying the Clausius−Clapeyron equation to the model. 10,11 The isostere method can lead to ambiguous results 1,2,12 particularly if the number of isotherms obtained is low, if the isotherms are widely spaced, or where the uncertainty in the isotherm measurement is high. Moreover even at moderate pressure (p < 1 MPa) the ideal gas assumption inherent in Clausius−Clapeyron can lead to large errors in predicting the heat of adsorption. 13 Theoretical models (e.g., refs 14−17) have been developed for this problem by using numerous isotherm models consistent with statistical mechanics and specific to various different adsorbate/adsorbent modes of interaction. However it remains a challenge to know which model to apply to get a correct prediction of the surface interactions and heat of adsorption without significant prior knowledge of the behavior of the adsorbate/adsorbent system. Savara et al. 18 developed a rigorous method for selecting between a number of 2...

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Section: ■ Introductionmentioning

confidence: 99%

Predicting the Integral Heat of Adsorption for Gas Physisorption on Microporous and Mesoporous Adsorbents

Whittaker

Wang

Zimmermann³

et al. 2014

J. Phys. Chem. C

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“…To minimize the high experimental effort required for Tian‐Calvet microcalorimeters, Zimmermann and Keller designed a sensor gas calorimeter consisting of a volumetric measuring device and a calorimetric measuring setup with a newly developed sample vessel .…”

Section: Characterization Of Activated Carbonsmentioning

confidence: 99%

Characterization of Activated Carbon Adsorbents – State of the Art and Novel Approaches

et al. 2019

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Activated carbons are widely used as commercial adsorbents. Thermal or chemical activation creates a pore system and functional groups on the inner surface which may significantly change adsorption properties. Therefore, in addition to knowledge of the structural properties, a sound understanding of surface chemistry is indispensable. This paper summarizes the state of art as well as new developments in both fields. Standardized methods for characterizing structural properties are volumetric measurements and mercury porosimetry. To get a more detailed insight into the region of micropores, a probe molecule method was developed. For characterization of surface chemistry, methods such as IR spectroscopy, temperature-programmed desorption, and Boehm titration are subject of research. Novel methods were developed such as measuring of excess isotherms and calorimetric measurement of heat of adsorption, which are presented and discussed in greater detail in this paper. As each single method can only provide limited information, a better description of surface chemistry requires combination and careful interpretation of complementary information from different methods. Property Standard Limitation Apparent density ASTM D 2854-09 Total ash content ASTM D 2866-11 Moisture ASTM D 2867-17 Ball-pan hardness ASTM D 3802-16 pH-value ASTM D 3838-05 Electrical conductivity ASTM D 1125-14 Water soluble components ASTM D 5029-98 Volatile matter content ASTM D 5832-98 Acid extractable content ASTM D 6385-99 Particle size distribution ASTM D 2862-16 granular activated carbon ASTM D 5158-98 powdered activated carbon Ignition temperature ASTM D 3466-06 granular activated carbon Dusting attrition ASTM D 5159-04 granular activated carbon www.ChemBioEngRev.de

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“…Different reasons have been presented by the authors: some proposed that direct determination of heat effects is often complicated and more costly, particularly in non-environmental conditions [5]. While it is assumed that the approaches of direct and indirect methods should give identical results, often ambiguity is generated, mainly due to the definitions of the isotherms and the choice of different thermodynamic models to adjust the corresponding adsorption isotherms [5,[8][9][10][11]. The experimental results of the isosteric heat are very sensitive to the conditions of the adsorption isotherms, particularly if the analysis of the data is available only for a limited number of temperatures [5].…”

Section: Introductionmentioning

confidence: 99%

Isosteric Heat: Comparative Study between Clausius–Clapeyron, CSK and Adsorption Calorimetry Methods

2019

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This work presents the calorimetric study of five adsorbents with different chemical and textural characteristics: MOF-199, MCM-41, SBA-15, activated carbon prepared from corn cob (GACKP) and graphite. These solids were used to establish the differences between isosteric heats evaluated by three different methods: Clausius–Clapeyron (C-C), Chakraborty, Saha and Koyama (CSK) and Adsorption Calorimetry (A-Cal). The textural characterization results show solids that have values of specific surface area between 2271 m2·g−1 for the MOF-199 and 5.2 m2·g−1 for the graphite. According to the results obtained for the isosteric heats for each sample, the magnitude varies depending on the coverage of the adsorbate and the textural characteristics of each adsorbent. Solids with an organized structure have isosteric heat values that are coincident among the three methods. Meanwhile, heterogeneous solids such as activated carbon values evaluated by the CKS and C-C have a high dispersion method regarding the adsorption calorimetry method. The results obtained show that the adsorption calorimetry, being a direct experimental measurement method, presents less dispersed data. At low quantities, the isosteric heat of nitrogen adsorption decreased in the order MOF-199, GACKP, MCM-41, SBA-15 and Graphite. The order for the isosteric heats values was coherent with the surface characteristics of each of the solids, especially with the pore size distribution. Finally, throughout the coverage examined in this work, the isosteric heats for nitrogen adsorption determined by adsorption calorimetry (A-Cal) were larger than the evaluated by C-C and CSK indirect methods of vaporization. According to the results, it is shown that the adsorption calorimetry allows values of the isosteric heats of adsorption with an error of less than 2% to be established and also reveals the complex nature of the heterogeneity or homogeneity of the adsorbent.

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A new calorimeter for simultaneous measurement of isotherms and heats of adsorption

Cited by 38 publications

References 13 publications

Predicting the Integral Heat of Adsorption for Gas Physisorption on Microporous and Mesoporous Adsorbents

Predicting the Integral Heat of Adsorption for Gas Physisorption on Microporous and Mesoporous Adsorbents

Characterization of Activated Carbon Adsorbents – State of the Art and Novel Approaches

Isosteric Heat: Comparative Study between Clausius–Clapeyron, CSK and Adsorption Calorimetry Methods

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