Concentration Pulse Chromatography Research Articles

Nanodisperse gold catalysts in oxidation of benzyl alcohol: comparison of various supports under different conditions

Monodisperse gold particles (ca. 2 nm) were prepared and deposited on various supports (SiO2, Al2O3, HAP, MgAl2O4 and MgO). The acid/base properties of supports were characterized by NH3 and CO2 sorption. The size of the gold nanoparticles spans in the 1.7–6.5 nm mean diameter range after calcination as determined from TEM measurements. The amounts of accessible surface sites were estimated by binary concentration pulse chromatography of CO with Kr adsorption. The data are in agreement with the results of CO adsorption obtained by DRIFT spectroscopy. The activities of the catalysts were compared in the oxidation of benzyl alcohol in stirred batch reactors under two different conditions: in xylene solvent with atmospheric oxygen at 60 °C (in presence and in absence of K2CO3), and in a solvent-free mixture at elevated pressure and temperature (5 bar O2, 150 °C, 5 h). The activities of catalysts in benzyl alcohol conversion are described in two variants, namely related to (i) active catalytic sites (ASNA), and (ii) number of Au atoms on the geometric surface of particles (GSNA). The activities of catalysts in xylene solvent at 60 °C were excellent, with 0.28–1.11 s−1 characteristic GSNAini values (initial reaction rates related to surface Au atoms, Ausurf) in presence of K2CO3. The observed order of activities under these conditions is Au/SiO2 < Au/Al2O3 < Au/HAP < Au/MgAl2O4 < Au/MgO. In the experiments performed at 150 °C under solvent-free conditions, the reaction partners are depleted in greater extents (with the exception of Au/Al2O3), thus the obtained average GSNAave (average reaction rate during 5 h reaction related to Ausurf) values are less reliable, however selectivity data provide useful information as well. These estimated average GSNAave values (0.14–0.83 s−1) attest still good activities. For the interpretation of the obtained data, the roles of active sites on gold nanoparticles of various dispersion and the accessibility of their surfaces as well as the acid–base properties and surface hydroxyl concentration of supports, water ad- and desorption phenomena are considered simultaneously.

Adsorption of NO in clinoptilolite-rich zeolitic mineral by concentration pulse chromatography method

The equilibrium and kinetic parameters for NO adsorption in a clinoptilolite-rich natural zeolitic material from Turkey were determined using the concentration pulse chromatography method. Under the experimental conditions (carrier gas velocities and adsorption temperatures) the micropore diffusion resistance was found to be the mass transfer controlling step. Matching the first moment of the response peaks to the mathematical model the Henry’s Law constants and heat of adsorption at zero loading were determined. The axial dispersion, external film, macropore and micropore diffusion coefficients, and activation energy for diffusion of NO in the micropores were calculated from the analysis of the second moments of the response peaks. For successive NO pulses without regeneration between the pulses, the retention times of the response peaks decreased and peak areas increased with the injection number indicating irreversible adsorption. The reversibly adsorbed NO could be desorbed by purging with an inert gas at the adsorption pressure and temperature. Temperature programmed desorption profile obtained by heating the NO saturated adsorbent to 400 °C under inert flow revealed presence of multiple irreversibly adsorbed species in NZ with different thermal stabilities. Desorption of these species was not achieved during the heating up to 400 °C which makes the natural zeolitic materıal suitable for NO storage rather than for cyclic adsorptive separation processes.

Adsorption separation performance of H2/CH4 on ETS-4 by concentration pulse chromatography

To exploit an effective adsorbent to separate hydrogen and methane, microporous titanium silicate molecular sieve NaETS-4 was synthesized and modified by strontium. The adsorption characteristics and diffusion behaviors of the prepared titanosilicate molecular sieve were studied by concentration pulse chromatography. And the effects of ion-exchange and dehydration temperature on adsorbent structure and gas diffusion were also discussed. The results showed that the thermal stability and Henry's Law constants were enhanced and micropore diffusivity decreased after exchanging Na+ with Sr2+. With the increase of dehydration temperature, Henry's Law constant and micropore diffusivity of CH4 decreased in both NaETS-4 and SrETS-4. While for H2 in SrETS-4, the increase of Henry's Law constant and the decrease of diffusion rate can be attributed to the shrinks of pore diameter resulting from the relocation of Sr2+. Correspondingly, the kinetic selectivity of H2/CH4 reached 8.91 indicating its potentiality in separating H2 and CH4.

Improved method for determining binary adsorption isotherms by using concentration pulse chromatography: adsorption of CO2 and N2 by silicalite at different pressures

Adsorption separation of carbon dioxide from nitrogen at different system total pressures with silicalite as the adsorbent was studied by using concentration pulse chromatography. Improving the methodology for determining binary adsorption isotherms by concentration pulse method (CPM) was also the goal of this study. Binary adsorption isotherms, x–y phase diagrams and separation factor plots have been determined at 26 °C to look at the influence of pressure on the separation using concentration pulse chromatography. Available methods for determining binary adsorption isotherms using CPM have been reviewed and shown to be incapable of interpreting this particular binary system. An improved novel model has been proposed to interpret the data in this study. It has been referred to as the Kennedy-Tezel concentration pulse method (KT-CPM) and has been shown to be superior to other methods used in the literature. Results using this data were found to be consistent with the previous results in the literature. The binary isotherms for the CO2–N2 system show a decrease in CO2 selectivity as total system pressure increases. The optimal separation factor for silicalite was found to increase with decreasing system pressure and decreasing mole fraction of CO2 in the feed mixture.

Comparison of Concentration Pulse and Tracer Pulse Chromatography: Experimental Determination of Eluent Uptake by Bridged-Ethylene Hybrid Ultra High Performance Liquid Chromatography Packings

Abstract Excess volume isotherms of acetonitrile and methanol sorbed on a C 18 BEH UHPLC packing were determined over a range of pressure, temperature, flow rate and eluent composition. The isotherm measurements were carried out by two independent experimental methods, viz. , concentration pulse and tracer pulse chromatographies. Isotherms were measured with both experimental techniques at 30, 45 and 60 °C. The excess isotherms increased with decreasing temperature although the variations were relatively small. Direct comparison of the two experimental techniques showed that the measured void volumes were identical within experimental error. The measured excess volumes by both techniques were comparable with the concentration pulse experiments producing slightly higher excess volume data with highly aqueous eluents. Both experimental techniques show some variations of the retention volumes with sample volume, sample composition, flow rate and column inlet pressure. The results confirmed the validity of both concentration and tracer pulse chromatographies for the determination of column void volumes and the excess volume of eluent taken up by UHPLC packings.

Comparison of concentration pulse and tracer pulse chromatography: Experimental determination of eluent uptake by bridged-ethylene hybrid ultra-high performance liquid chromatography packings

Excess volume isotherms of acetonitrile and methanol sorbed on a C(18) BEH UHPLC packing were determined over a range of pressure, temperature, flow rate and eluent composition. The isotherm measurements were carried out by two independent experimental methods, viz., concentration pulse and tracer pulse chromatographies. Isotherms were measured with both experimental techniques at 30, 45 and 60 °C. The excess isotherms increased with decreasing temperature although the variations were relatively small. Direct comparison of the two experimental techniques showed that the measured void volumes were identical within experimental error. The measured excess volumes by both techniques were comparable with the concentration pulse experiments producing slightly higher excess volume data with highly aqueous eluents. Both experimental techniques show some variations of the retention volumes with sample volume, sample composition, flow rate and column inlet pressure. The results confirmed the validity of both concentration and tracer pulse chromatographies for the determination of column void volumes and the excess volume of eluent taken up by UHPLC packings.

Hybrid method of solution applied to simulation of pulse chromatography

In this communication, the method proposed by Cremasco et al. (2003) is applied to predict single and low concentration pulse chromatography. In previous work, a general rate model was presented to describe the breakthrough curve, where a hybrid solution was proposed for the linear adsorption. The liquid phase concentration inside the particle was found analytically and related with the bed liquid phase through Duhamel's Theorem, while the bulk-phase equation was solved by a numerical method. In this paper, this method is applied to describe pulse chromatography of solutes that present linear adsorption isotherms. The simulated results of pulse chromatography are compared with experimental ones for aromatic amino acid experiments from literature.

Pure and Binary Adsorption of Methane and Nitrogen by Silicalite

Methane is the most important non-CO2 greenhouse gas (GHG) responsible for global warming with more than 10 % of total GHG emissions. The greenhouse warming potential (GWP) of this gas is much higher than carbon dioxide. Therefore, any reduction in methane emissions is really important in atmosphere reconstruction. Nitrogen is needed to be removed from landfill gas to obtain low grade natural gas as a renewable source of energy from garbage, but the separation is really difficult. Adsorption was considered as a possibility for this separation, and silicalite was studied as the adsorbent. The adsorption behavior of methane and nitrogen with this adsorbent was studied by concentration pulse chromatography and constant volume techniques. Ideal separation factors were obtained from the experimental pure adsorption isotherms by using the temperature independent Toth isotherm model. Mixture adsorption isotherms for the binary system of methane and nitrogen at (40, 70, and 100) °C at 1 bar total pressure were determined experimentally. Corresponding x−y diagrams and separation factors were obtained from these data. The thermodynamic consistency tests between pure and binary gas adsorption systems were also carried out. The separation factors obtained with silicalite for the separation applications of methane and nitrogen gases in this work are much better than those obtained for other systems in the literature.

Equilibrium and kinetic analysis of CO 2–N 2 adsorption separation by concentration pulse chromatography

CO 2 and N 2 adsorption kinetics and equilibrium behaviours have been studied with silicalite, NaY and 13X by using concentration pulse chromatography for the separation of these gases in the present study. Adsorption Henry's Law constants, the heat of adsorption values, micropore diffusion coefficients and corresponding activation energies are determined experimentally and the three different mass transfer mechanisms are discussed. From the equilibrium data, the corresponding separation factors are obtained for the adsorption separation processes. The heat of adsorption values as well as the Henry's Law adsorption equilibrium constants of CO 2 are much higher than those of N 2 for all the adsorbents studied. 13X, NaY and silicalite all have good separation factors for CO 2/N 2 system based on equilibrium processes. The order of the equilibrium separation factors is 13X (Ceca) > 13X (Zeochem) > NaY (UOP) ≫ silicalite (UOP). Equilibrium selectivity favours CO 2 over N 2. Micropore diffusion resistance is the definite dominant mass transfer mechanism for CO 2 with silicalite and NaY.

Adsorption separation of N 2, O 2, CO 2 and CH 4 gases by β-zeolite

In the present study, adsorption equilibrium and kinetic separation potential of β-zeolite is investigated for N 2, O 2, CO 2 and CH 4 gases by using concentration pulse chromatography. Adsorption equilibrium and kinetic parameters have been studied. Henry’s Law constants, heat of adsorption values, micro-pore diffusion coefficients and adsorption activation energies are determined experimentally. The three different mass transfer mechanisms, that have to take place for adsorption to occur, are discussed. From the equilibrium and kinetic data, the equilibrium and kinetic selectivities are determined for the separation of the gases studied. With β-zeolite, carbon dioxide has the highest adsorption Henry’s Law constant at all the temperatures studied, followed by methane, nitrogen and oxygen. Carbon dioxide separation from oxygen, nitrogen and methane has good equilibrium separation factors. This factor is not very high for methane/nitrogen and methane/oxygen systems and is the lowest for nitrogen/oxygen system. Micro-pore diffusion is the dominant mass transfer mechanism for all the systems studied, except CH 4, with β-zeolite. The kinetic separation factors are very small at high temperatures for all the systems studied. Nitrogen/carbon dioxide and oxygen/carbon dioxide can be separated in kinetic processes with reasonable separation factors at low temperatures. Both equilibrium and kinetic separation factors decrease as column temperature increases. Considering all the observations from this study, it was concluded that β-zeolite is a good candidate for applications in flue gas separations, as well as natural gas and landfill gas purifications.

Moments method applied to the in-situ characterisation of normal butane mass transfer in MFI zeolite membranes

In most of the literature the performances of zeolite membranes are studied under steady state permeation conditions. With this type of experiments, extracting mass transfer parameters is often complex due to the non linearity of the studied phenomena. As a consequence, we propose in the present paper an original membrane transient characterisation method, derived from the concentration pulse chromatography (CPC) technique, applied in the linear response domain. With this method, short concentration pulses are injected at the membrane inlet and the concentration evolution as a function of time is measured at the outlet of the membrane. These data were analysed with the moments method, which allowed the estimation of two groups of mass transfer parameters. This approach has been validated with a first series of preliminary tests which gave promising results.

A CHROMATOGRAPHIC STUDY OF CARBON MONOXIDE ADSORPTION ON A CLINOPTILOLITE-CONTAINING NATURAL ZEOLITIC MATERIAL

In this study, the equilibrium and kinetic parameters for CO adsorption on clinoptilolite-rich natural zeolitic material were determined by the concentration pulse chromatography technique. Experiments were carried out at different column temperatures (60–120°C) and interstitial carrier gas velocities (3.1–16.3 cm/s) using a clinoptilolite-rich natural zeolitic material packed column. The equilibrium and kinetic parameters were determined by matching the moments of the experimentally obtained response curves to the parameters in the mathematical model. The Henry's Law constants were found to decrease from 700 to 49 with increasing temperature. The heat of adsorption at low coverage was found to be 50.73 kJ/molK. The contributions from external film, macropore, and micropore diffusion resistances to mass transfer were determined, and the micropore diffusion resistance was found to be the major contributor. The micropore diffusivity as a function of crystal radius (Dc/rc 2) was determined and found to change between 5.72 × 10−4 and 1.34 × 10−2 s−1 in the temperature range studied.

Adsorption of carbon dioxide, methane and nitrogen: pure and binary mixture adsorption for ZSM-5 with SiO2/Al2O3 ratio of 280

The adsorption of binary gas mixtures of CO2–N2, CO2–CH4 and CH4–N2 were studied by using H-ZSM-5 as the adsorbent with a SiO2/Al2O3 ratio of 280. Pure isotherms for N2 and CH4 at 40 °C and CH4–N2 binary isotherms at 40 °C and 1.0 atm total pressure have been determined using concentration pulse chromatography. For CO2–N2 and CO2–CH4 pure and binary systems, previously published data were used. The applicability of the binary adsorption prediction models, Extended Langmuir (EL), ideal adsorbed solution theory (IAST), and the Flory–Huggins form of the vacancy solution theory (FH-VST) have been studied. The CH4–N2 binary isotherms exhibit behavior similar to the pure component isotherms, with CH4 as the dominant adsorbate. The CH4 binary isotherm did not change from the pure component isotherm. The N2 binary isotherm decreased relative to the pure component N2 isotherm. The theoretical models reasonably predict the binary behavior for the strongly adsorbed component in the binary system, whereas the weakly adsorbed component was not predicted well. The models are able to predict systems where the adsorption capacities of each component are relatively similar. However, none of the models were able to predict the behavior resulting from the initial competing or dominant electrostatic interaction of the adsorbates with the heterogeneous nature of the adsorbent surface.

Use of Concentration Pulse Chromatography for Determining Binary Isotherms: Comparison with Statically Determined Binary Isotherms

The characterization of adsorption properties of binary gas mixtures is an important factor in the design of cyclic periodic adsorption processes. Presently, there are a few methods for determining the binary adsorption behaviour. However, most of these methods are very time demanding (static approaches). One dynamic approach for determining the binary adsorption behaviour is by employing the concentration pulse method. Although this experimental method has been shown to reliably reproduce the data obtained with static approaches, the application has been limited to systems where the adsorption capacities are similar. In our previous work, a novel method (HT-CPM) was shown to be capable of handling systems where the adsorption capacity of the heavy component is much greater than the light component.

Adsorption of carbon dioxide, methane, and nitrogen: pure and binary mixture adsorption by ZSM-5 with SiO2/Al2O3 ratio of 30

The adsorption of binary gas mixtures of CO2–N2, CO2–CH4, and CH4–N2 were studied by using H-ZSM-5 as the adsorbent with a SiO2/Al2O3 ratio of 30. Pure isotherms for N2 and CH4 at 40°C and CH4–N2 binary isotherms at 40°C and 1.0 atm total pressure have been determined using concentration pulse chromatography. For CO2–N2 and CO2–CH4 pure and binary systems, previously published data were used. The applicability of the binary adsorption prediction models, Extended Langmuir, Extended Nitta, Ideal Adsorbed Solution Theory, and the Flory–Huggins form of the Vacancy Solution Theory have been studied. The CH4–N2 binary isotherms exhibit behavior similar to the pure component isotherms, with CH4 as the dominant adsorbate. The separation factor steadily declines as the mole fraction of CH4 in the gas phase is increased. All the theoretical models used reasonably predict the binary systems for CH4–N2. The CO2–N2 system was not predicted well. CO2–CH4 behavior was predicted reasonably well by all the models, except by the Extended Nitta. The models appear to be able to predict systems where the adsorption capacities of each component are relatively similar.

A Novel Solution Method for Interpreting Binary Adsorption Isotherms from Concentration Pulse Chromatography Data

Adsorption separation of carbon dioxide from nitrogen (N2, which represents air) was investigated by using H-ZSM-5 as the adsorbent with SiO2/Al2O3 ratios of 30 and 280. Pure and binary isotherms at 40°C have been determined experimentally using concentration pulse chromatography. Presently available methods for determining binary isotherms from concentration pulse chromatography data have been reviewed and shown incapable of interpreting this particular binary system. A novel solution method is presented and shown to be superior to the other methods. The binary isotherms for the CO2-N2 system show an increase in CO2 selectivity with increase in surface heterogeneity. The optimal separation factor for H-ZSM-5-30 was found to be 215 at 0.7% CO2 in the feed, whereas, H-ZSM-5-280 has an optimal separation factor of 48 at 2.7% CO2 in the feed.

Gas adsorption isotherms from composition and flow-rate transient times in chromatographic columns. II. Effect of pressure changes

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Mason Geoffrey and Buffham Bryan A. 1996Gas adsorption isotherms from composition and flow-rate transient times in chromatographic columns. II. Effect of pressure changesProc. R. Soc. Lond. A.4521287–1300http://doi.org/10.1098/rspa.1996.0066SectionRestricted accessArticleGas adsorption isotherms from composition and flow-rate transient times in chromatographic columns. II. Effect of pressure changes Geoffrey Mason Google Scholar Find this author on PubMed Search for more papers by this author and Bryan A. Buffham Google Scholar Find this author on PubMed Search for more papers by this author Geoffrey Mason Google Scholar Find this author on PubMed Search for more papers by this author and Bryan A. Buffham Google Scholar Find this author on PubMed Search for more papers by this author Published:08 June 1996https://doi.org/10.1098/rspa.1996.0066AbstractIn the previous paper a method was described for measuring binary adsorption isotherms by a chromatographic method. The method involved making simultaneous small perturbations to the concentration and flow-rate of the stream entering a packed column and observing the changes with time of the composition and flow-rate of the gas leaving the column. The perturbation to the inlet flow was made by adding a small extra stream of gas of known composition to the main flow passing through the columns. The present paper describes the effect of the increased mean pressure in the column caused by the small increase in flow. The effect is surprisingly large. A correction term is derived to compensate for the effect of increased pressure. By reanalysing the results for argon-nitrogen reported in Paper I it is shown that instead of two different isotherms being obtained by making the perturbation with the addition of argon or nitrogen, a single isotherm for each component is obtained.FootnotesThis text was harvested from a scanned image of the original document using optical character recognition (OCR) software. As such, it may contain errors. Please contact the Royal Society if you find an error you would like to see corrected. Mathematical notations produced through Infty OCR. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Kennedy D and Handan Tezel F (2013) Improved method for determining binary adsorption isotherms by using concentration pulse chromatography: adsorption of CO2 and N2 by silicalite at different pressures, Adsorption, 10.1007/s10450-013-9562-z, 20:1, (189-199), Online publication date: 1-Jan-2014. Heslop M, Buffham B and Mason G (2007) Binary chromatographic retention times from perturbations in flowrate and composition, Adsorption, 10.1007/s10450-007-9082-9, 14:1, (143-155), Online publication date: 1-Feb-2008. Li P and Handan Tezel F (2007) Adsorption separation of N2, O2, CO2 and CH4 gases by β-zeolite, Microporous and Mesoporous Materials, 10.1016/j.micromeso.2006.08.016, 98:1-3, (94-101), Online publication date: 1-Jan-2007. Brandani S (2005) On the Chromatographic Measurement of Equilibrium Isotherms Using Large Concentration Steps, Adsorption, 10.1007/s10450-005-5929-0, 11:S1, (231-235), Online publication date: 1-Jul-2005. Matuszak D, Gaddy G, Aranovich G and Donohue M (2005) Cosorption effect in gas chromatography: flow fluctuations caused by adsorbing carrier gases, Journal of Chromatography A, 10.1016/j.chroma.2004.11.064, 1063:1-2, (171-180), Online publication date: 1-Jan-2005. Buffham B, Hellgardt K, Heslop M, Mason G and Richardson D (2002) Modelling and simulation of the flux responses of a gas–solid catalytic micro-reactor, Chemical Engineering Science, 10.1016/S0009-2509(01)00436-5, 57:6, (953-966), Online publication date: 1-Mar-2002. Buffham B, Hellgardt K, Heslop M and Mason G (2000) Remote sensing of the flux responses of a gas–solid catalytic micro-reactor, Chemical Engineering Science, 10.1016/S0009-2509(99)00413-3, 55:9, (1621-1632), Online publication date: 1-May-2000. Mason G, Buffham B, Heslop M and Zhang B (1998) Capillary viscometry by perturbation of flow and composition, Chemical Engineering Science, 10.1016/S0009-2509(98)00106-7, 53:15, (2665-2674), Online publication date: 1-Aug-1998. Mason G, Buffham B and Heslop M (1997) Gas adsorption isotherms from composition and flow–rate transient times in chromatographic columns. III. Effect of gas viscosity changes, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 453:1963, (1569-1592), Online publication date: 8-Aug-1997.Mason G and Buffham B (1997) Gas adsorption isotherms from composition and flow-rate transient times in chromatographic columns I. Basic theory and a binary experimental test, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 452:1949, (1263-1285), Online publication date: 8-Jun-1996. This Issue08 June 1996Volume 452Issue 1949 Article InformationDOI:https://doi.org/10.1098/rspa.1996.0066Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Manuscript received22/02/1995Manuscript accepted07/06/1995Published online01/01/1997Published in print08/06/1996 License:Scanned images copyright © 2017, Royal Society Citations and impact

Determination of competitive adsorption isotherms of enantiomers on a dual-site adsorbent

The competitive adsorption isotherms of praziquantel enantiomers on microcrystalline cellulose triacetate were determined by concentration pulse chromatography. A model comprising a non-selective linear term and a selective first order improved Langmuir term was found to fit the data excellently. It is postulated that this chiral stationary phase consists of two types of binding sites: one responsible for the chiral, selective interactions and one responsible for the achiral, non-selective interactions of the enantiomers with the stationary phase. The selective sites are easily saturated compared to the non-selective sites, accounting for the experimental observation of lower separation efficiency at higher enantiomer concentrations.

Adsorption and diffusion of hydrocarbons in silicalite at very low concentration: effect of defect sites

Adsorption and diffusion of benzene, p-xylene, ethylbenzene, toluene, isobutene, cis-but-2-ene, trans-but-2-ene, isobutane and n-butane has been studied in large silicalite crystals, at very low sorbate concentration, by non-isobaric concentration pulse chromatography. At these low concentrations the heats of adsorption and Henry constants for the aromatic and olefinic hydrocarbons are substantially greater than previously reported values, which were derived from measurements at higher loading levels, while the intracrystalline diffusivities of these species are substantially smaller with higher activation energies. In contrast, the results for saturated hydrocarbons are similar to the values obtained at higher loadings. This behaviour parallels the previously reported results of detailed calorimetric measurements which, for olefins and aromatics, show a rapid increase in heat of adsorption at very low loadings, suggesting the presence of a small fraction of highly favourable adsorption sites. Such sites are probably associated with defects in the crystal structure and, although the precise nature of these sites is not established, it seems plausible to suggest that they may be associated with the presence of silanol groups.