The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Shivaji Sircar - One of the best experts on this subject based on the ideXlab platform.
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Removal of Heat of Adsorption from adsorbent by forced convection
Adsorption, 2006Co-Authors: Shivaji SircarAbstract:An analytical mathematical model is used to investigate the effectiveness of forced convection for removal of the Heat of Adsorption from an adsorbent mass undergoing a differential Adsorption process in a flow system. An example of such a process is measurement of gas Adsorption kinetics using a differential Adsorption bed. Isothermal operation may not be achieved even when a high gas flow rate is used, particularly if the sorption kinetics is relatively fast. Very small changes in the adsorbent temperature can cause significant departure from the isothermal uptake behavior when the Heat of Adsorption is moderately large. A criterion for validity of isothermal data analysis is given.
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Heat of Adsorption on heterogeneous adsorbents
Applied Surface Science, 2005Co-Authors: Shivaji SircarAbstract:Abstract The isosteric Heat of Adsorption is a critical design variable in estimating the performance of an adsorptive gas separation process. The Heats can be strong and complex functions of adsorbate loadings when the adsorbent is energetically heterogeneous. Ignoring these characterisitics in process design can lead to serious errors. Only calorimetric Heat measurements (pure and multi-component gas) can reveal the complex nature of the adsorbent heterogeneity. Examples of calorimetrically measured Heats for Adsorption of pure SF 6 and CO 2 on a silicalite sample bonded with alumina, and those for binary CO 2 –C 2 H 6 mixtures on NaX zeolite are cited to demonstrate the complexity of the subject. The loading dependence of the binary Heats is found to be counter-intuitive. A simple analytic thermodynamic model of patchwise heterogeneity is proposed to describe the isosteric Heat of Adsorption of a single gas and those for the components of a binary gas mixture.
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Heat of Adsorption
Chemical Engineering & Technology, 2002Co-Authors: Shivaji Sircar, D.v. CaoAbstract:Separation of gas mixtures by pressure swing and thermal swing Adsorption processes is an established unit operation in the chemical industry. Mathematical simulations of these processes require precise knowledge of multicomponent gas Adsorption equilibria, kinetics, and Heats for the system of interest over all conditions of pressure, temperature, gas composition and adsorbate loading encountered by the adsorber during the separation process. Unfortunately, the published data on Heats of Adsorption are often not adequate. Limited Heat data are generally available for pure gas Adsorption, Heat data for binary gas mixtures are rare, and Heat data for mixtures containing three or more components are nonexistent.
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Heat of Adsorption of Pure Sulfur Hexafluoride on Micro-Mesoporous Adsorbents
Adsorption, 2001Co-Authors: D.v. Cao, Shivaji SircarAbstract:The isotherms and the isosteric Heats of Adsorption of pure SF6 were measured on two microporous zeolites (NaX and Silicalite), one mesoporous alumina, and two activated carbons (BPL and PCB) at 305 K. The Adsorption isotherms were Type I by Brunauer classification. The PCB carbon adsorbed SF6 most strongly and the alumina adsorbed SF6 most weakly. The Adsorption of SF6 on the other three materials were comparable in the low pressure region despite their drastic differences in the physicochemical properties. The Heat of Adsorption of SF6 on the silicalite and the alumina remained practically constant over a large range of coverage. The Heat of Adsorption of SF6 increased with increasing adsorbate loading on the NaX zeolite in the high coverage region. The Heat of Adsorption of SF6 on the activated carbons decreased with increasing adsorbate loading before leveling off in the high coverage region.
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Isosteric Heat of Adsorption: Theory and Experiment
The journal of physical chemistry. B, 1999Co-Authors: Shivaji Sircar, R. Mohr, C. Ristic, M. B. RaoAbstract:The isosteric Heats of Adsorption of the components of a gas mixture are critical variables for design of adsorbers for gas separation. They can be unambiguously defined by the Gibbsian Surface Excess (GSE) model of multicomponent Adsorption. These variables can be experimentally measured by multicomponent differential calorimetry (MDC) and directly used to describe nonisothermal behavior of practical adsorbers. There is no need to make simplified assumptions about the nature and size of the adsorbed phase, as required by conventional Adsorption thermodynamic models, to define the isosteric Heats. Pure gas isosteric Heats of Adsorption of N2 and CO2 on a pelletized silicalite sample were measured using a MDC and a data analysis algorithm based on the GSE model. The silicalite sample behaved like a homogeneous adsorbent for weakly polar N2 Adsorption. The presence of polar alumina binder in the silicalite sample introduced significant heterogeneity for more polar CO2 Adsorption.
Abdouelilah Hachimi - One of the best experts on this subject based on the ideXlab platform.
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Adsorption models and Heat of Adsorption of adsorbed ortho di-methyl benzene and 1-propanol species in competitive Adsorption on silica by using temperature programmed Adsorption equilibrium methods
Journal of environmental chemical engineering, 2014Co-Authors: Abdouelilah HachimiAbstract:Abstract Single and binary Adsorptions of ortho di-methyl benzene and 1-propanol on silica at 300 K and at various Adsorption pressures were studied using temperature programmed Adsorption equilibrium (TPAE) procedure. The evolutions of the surface coverage with the Adsorption temperature ( θ e = f ( T a )) were compared to the Temkin and Langmuir models in order to determine the Heats of Adsorption and to reveal the presence of mutual interactions between adspecies. It has been shown that in single Adsorption equilibrium of 1-propanol on silica, the Heats of Adsorption were found to be dependent to the surface coverage. In contrast, of single Adsorption equilibrium of ortho di-methyl benzene on silica, the Heat of Adsorption was found independent to the surface coverage. However, in the competitive Adsorption, the Heats of Adsorption of the adsorbates were found varied with the surface coverage. The variation of Heats in single and in binary Adsorption characterizes the mutual interactions between the adspecies.
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Adsorption models and Heat of Adsorption of adsorbed ortho di-methyl benzene species on silica by using Temperature Programmed Adsorption Equilibrium methods
Applied Catalysis A : General, 2008Co-Authors: Abdouelilah Hachimi, T. Chafik, D. BianchiAbstract:The Adsorption of ortho dimethyl benzene (o-DMB) at different Adsorption temperatures T-a (T-a > 300 K) on a SiO2 solid pretreated at 723 K is studied by the Temperature Programmed Adsorption Equilibrium methods developed previously. These methods provide the evolutions of the Adsorption equilibrium coverage of the adsorbed species theta(e) (theta(e) < 0.7) with the Adsorption temperature Ta in quasi isobar conditions. These experimental curves theta(e) =f(T-a) are compared to theoretical curves associated to Adsorption models developed with the statistical thermodynamics formalism. These models assume either localized or mobile adsorbed species without and with interactions. It is shown that the Langmuir model (localized species without interaction) provides theoretical isobars overlapped with the experimental data for different Adsorption pressures P-a considering a Heat of Adsorption of 61 kJ/mol consistent with the isosteric Heat of Adsorption. FTIR data show that the Adsorption sites are mainly the free OH groups of SiO2 with a small contribution of superficial oxygen species. In line with the development of the experimental microkinetic approach of heterogeneous catalytic processes, and considering previous works dedicated to the Adsorption of diatomic molecules such as CO, H-2, NO on metal supported particles and metal oxides, it is concluded that Adsorption models assuming localized adsorbed species without (Langmuir model) and with (Temkin model) interactions provide robust mathematical expressions, for (a) the Adsorption coefficient and (b) the Adsorption equilibrium coverage theta(e) =f(T-a, P-a)(,) consistent with the experimental data for T-a > 300 K. (c) 2007 Elsevier B.V. All rights reserved.
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Adsorption models and Heat of Adsorption of adsorbed ortho di-methyl benzene species on silica by using Temperature Programmed Adsorption Equilibrium methods
Applied Catalysis A : General, 2008Co-Authors: Abdouelilah Hachimi, T. Chafik, D. BianchiAbstract:The Adsorption of ortho dimethyl benzene (o-DMB) at different Adsorption temperatures T-a (T-a > 300 K) on a SiO2 solid pretreated at 723 K is studied by the Temperature Programmed Adsorption Equilibrium methods developed previously. These methods provide the evolutions of the Adsorption equilibrium coverage of the adsorbed species theta(e) (theta(e) < 0.7) with the Adsorption temperature Ta in quasi isobar conditions. These experimental curves theta(e) =f(T-a) are compared to theoretical curves associated to Adsorption models developed with the statistical thermodynamics formalism. These models assume either localized or mobile adsorbed species without and with interactions. It is shown that the Langmuir model (localized species without interaction) provides theoretical isobars overlapped with the experimental data for different Adsorption pressures P-a considering a Heat of Adsorption of 61 kJ/mol consistent with the isosteric Heat of Adsorption. FTIR data show that the Adsorption sites are mainly the free OH groups of SiO2 with a small contribution of superficial oxygen species. In line with the development of the experimental microkinetic approach of heterogeneous catalytic processes, and considering previous works dedicated to the Adsorption of diatomic molecules such as CO, H-2, NO on metal supported particles and metal oxides, it is concluded that Adsorption models assuming localized adsorbed species without (Langmuir model) and with (Temkin model) interactions provide robust mathematical expressions, for (a) the Adsorption coefficient and (b) the Adsorption equilibrium coverage theta(e) =f(T-a, P-a)(,) consistent with the experimental data for T-a > 300 K. (c) 2007 Elsevier B.V. All rights reserved.
Charles T. Campbell - One of the best experts on this subject based on the ideXlab platform.
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Heat of Adsorption of naphthalene on Pt(111) measured by Adsorption calorimetry.
The journal of physical chemistry. B, 2006Co-Authors: J. Michael Gottfried, Ebbe K. Vestergaard, Parthasarathi Bera, Charles T. CampbellAbstract:The Heat of Adsorption of naphthalene on Pt(111) at 300 K was measured with single-crystal Adsorption calorimetry. The Heat of Adsorption on the ideal, defect-free surface is estimated to be (300 - 34 - 199(2)) kJ/mol. From this, a C-Pt bond energy for aromatic hydrocarbons on Pt(111) of approximately 30 kJ/mol is estimated, consistent with earlier results for benzene on Pt(111). There is higher Heat of Adsorption at very low coverage, attributed to step sites where the Adsorption Heat is >/=330 kJ/mol. Saturation coverage, = 1 ML, corresponds to 1.55 x 10(14) molecules/cm(2). Sticking probability measurements of naphthalene on Pt(111) give a high initial value of 1.0 and a Kisliuk-type coverage dependence that implies precursor-mediated sticking. The ratio of the hopping rate to the desorption rate of this precursor is approximately 51. Naphthalene adsorbs transiently on top of chemisorbed naphthalene molecules with a Heat of Adsorption of 83-87 kJ/mol.
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Calorimetric Measurement of the Heat of Adsorption of Benzene on Pt(111)
The Journal of Physical Chemistry B, 2004Co-Authors: Hyeran Ihm, J. Michael Gottfried, Parthasarathi Bera, Henry M. Ajo, Charles T. CampbellAbstract:The Heat of Adsorption of benzene on clean Pt(111) at 300 K is measured calorimetrically and found to decrease with coverage (θ) as (197 − 48θ − 83θ2) kJ/mol. Saturation coverage (θ = 1.0) is 2.3 × 1014 molecules/cm2. Sticking probabilities of benzene on Pt(111) were measured by mass spectrometry, giving an initial value of 0.97 and showing Kisliuk-type behavior with increasing coverage that implies there is a precursor to sticking with a ratio of its hopping rate to its desorption rate of ∼28. Benzene adsorbs transiently on the benzene-saturated surface at 300 K with a trapping probability of 0.90 and a Heat of Adsorption of 63−73 kJ/mol.
D. Bianchi - One of the best experts on this subject based on the ideXlab platform.
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Adsorption models and Heat of Adsorption of adsorbed ortho di-methyl benzene species on silica by using Temperature Programmed Adsorption Equilibrium methods
Applied Catalysis A : General, 2008Co-Authors: Abdouelilah Hachimi, T. Chafik, D. BianchiAbstract:The Adsorption of ortho dimethyl benzene (o-DMB) at different Adsorption temperatures T-a (T-a > 300 K) on a SiO2 solid pretreated at 723 K is studied by the Temperature Programmed Adsorption Equilibrium methods developed previously. These methods provide the evolutions of the Adsorption equilibrium coverage of the adsorbed species theta(e) (theta(e) < 0.7) with the Adsorption temperature Ta in quasi isobar conditions. These experimental curves theta(e) =f(T-a) are compared to theoretical curves associated to Adsorption models developed with the statistical thermodynamics formalism. These models assume either localized or mobile adsorbed species without and with interactions. It is shown that the Langmuir model (localized species without interaction) provides theoretical isobars overlapped with the experimental data for different Adsorption pressures P-a considering a Heat of Adsorption of 61 kJ/mol consistent with the isosteric Heat of Adsorption. FTIR data show that the Adsorption sites are mainly the free OH groups of SiO2 with a small contribution of superficial oxygen species. In line with the development of the experimental microkinetic approach of heterogeneous catalytic processes, and considering previous works dedicated to the Adsorption of diatomic molecules such as CO, H-2, NO on metal supported particles and metal oxides, it is concluded that Adsorption models assuming localized adsorbed species without (Langmuir model) and with (Temkin model) interactions provide robust mathematical expressions, for (a) the Adsorption coefficient and (b) the Adsorption equilibrium coverage theta(e) =f(T-a, P-a)(,) consistent with the experimental data for T-a > 300 K. (c) 2007 Elsevier B.V. All rights reserved.
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Adsorption models and Heat of Adsorption of adsorbed ortho di-methyl benzene species on silica by using Temperature Programmed Adsorption Equilibrium methods
Applied Catalysis A : General, 2008Co-Authors: Abdouelilah Hachimi, T. Chafik, D. BianchiAbstract:The Adsorption of ortho dimethyl benzene (o-DMB) at different Adsorption temperatures T-a (T-a > 300 K) on a SiO2 solid pretreated at 723 K is studied by the Temperature Programmed Adsorption Equilibrium methods developed previously. These methods provide the evolutions of the Adsorption equilibrium coverage of the adsorbed species theta(e) (theta(e) < 0.7) with the Adsorption temperature Ta in quasi isobar conditions. These experimental curves theta(e) =f(T-a) are compared to theoretical curves associated to Adsorption models developed with the statistical thermodynamics formalism. These models assume either localized or mobile adsorbed species without and with interactions. It is shown that the Langmuir model (localized species without interaction) provides theoretical isobars overlapped with the experimental data for different Adsorption pressures P-a considering a Heat of Adsorption of 61 kJ/mol consistent with the isosteric Heat of Adsorption. FTIR data show that the Adsorption sites are mainly the free OH groups of SiO2 with a small contribution of superficial oxygen species. In line with the development of the experimental microkinetic approach of heterogeneous catalytic processes, and considering previous works dedicated to the Adsorption of diatomic molecules such as CO, H-2, NO on metal supported particles and metal oxides, it is concluded that Adsorption models assuming localized adsorbed species without (Langmuir model) and with (Temkin model) interactions provide robust mathematical expressions, for (a) the Adsorption coefficient and (b) the Adsorption equilibrium coverage theta(e) =f(T-a, P-a)(,) consistent with the experimental data for T-a > 300 K. (c) 2007 Elsevier B.V. All rights reserved.
J. Michael Gottfried - One of the best experts on this subject based on the ideXlab platform.
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Heat of Adsorption of naphthalene on Pt(111) measured by Adsorption calorimetry.
The journal of physical chemistry. B, 2006Co-Authors: J. Michael Gottfried, Ebbe K. Vestergaard, Parthasarathi Bera, Charles T. CampbellAbstract:The Heat of Adsorption of naphthalene on Pt(111) at 300 K was measured with single-crystal Adsorption calorimetry. The Heat of Adsorption on the ideal, defect-free surface is estimated to be (300 - 34 - 199(2)) kJ/mol. From this, a C-Pt bond energy for aromatic hydrocarbons on Pt(111) of approximately 30 kJ/mol is estimated, consistent with earlier results for benzene on Pt(111). There is higher Heat of Adsorption at very low coverage, attributed to step sites where the Adsorption Heat is >/=330 kJ/mol. Saturation coverage, = 1 ML, corresponds to 1.55 x 10(14) molecules/cm(2). Sticking probability measurements of naphthalene on Pt(111) give a high initial value of 1.0 and a Kisliuk-type coverage dependence that implies precursor-mediated sticking. The ratio of the hopping rate to the desorption rate of this precursor is approximately 51. Naphthalene adsorbs transiently on top of chemisorbed naphthalene molecules with a Heat of Adsorption of 83-87 kJ/mol.
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Calorimetric Measurement of the Heat of Adsorption of Benzene on Pt(111)
The Journal of Physical Chemistry B, 2004Co-Authors: Hyeran Ihm, J. Michael Gottfried, Parthasarathi Bera, Henry M. Ajo, Charles T. CampbellAbstract:The Heat of Adsorption of benzene on clean Pt(111) at 300 K is measured calorimetrically and found to decrease with coverage (θ) as (197 − 48θ − 83θ2) kJ/mol. Saturation coverage (θ = 1.0) is 2.3 × 1014 molecules/cm2. Sticking probabilities of benzene on Pt(111) were measured by mass spectrometry, giving an initial value of 0.97 and showing Kisliuk-type behavior with increasing coverage that implies there is a precursor to sticking with a ratio of its hopping rate to its desorption rate of ∼28. Benzene adsorbs transiently on the benzene-saturated surface at 300 K with a trapping probability of 0.90 and a Heat of Adsorption of 63−73 kJ/mol.
