Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Adsorption: Journal of the International Adsorption Society (v.18, #1)
FTIR studies of butane, toluene and nitric oxide adsorption on Ag exchanged NaMordenite by Soledad G. Aspromonte; Eduardo E. Miró; Alicia V. Boix (pp. 1-12).
In this work, we studied the adsorption of butane, toluene and nitric oxide on NaMordenite exchanged with different amounts of silver. The reactions that occurred when the adsorbed hydrocarbons interacted with NO and the effect of water adsorption were also addressed. Different silver species were formed after ion exchange and they were detected by TPR analysis. Highly dispersed Ag2O particles were reduced at temperatures lower than 300 °C whereas Ag+ exchanged ions showed two TPR peaks, which can be ascribed to species exchanged at different mordenite sites. The TPD experiments after adsorption of NO at 25 °C showed that the only desorbed species was NO2 which was formed by the total reduction of Ag2O particles. When the adsorbed butane was exposed to NO (1000 ppm), isocyanate species were formed on Ag+ ionic sites as well as Ag+–(NOx)–CO species. Toluene adsorption was stronger than butane since adsorbed toluene molecules were held even at 400 °C. The characteristic bands of the aromatic ring C=C bond was observed as well as that of methyl groups interacting with Ag+ and Na+ ions. However, the appearance of carboxylic groups at temperatures above 300 °C in inert flow indicated the partial oxidation of toluene due to Ag2O species present in the samples. After contacting adsorbed toluene with NO, different FTIR bands correspond to organic nitro-compounds, isocyanate, cyanide and isocyanide species adsorbed on Ag+ ions, were detected. The presence of water inhibited the formation of NO2 species and the hydrocarbon adsorption on Na+ sites but did not affect the toluene-Ag+ interaction.
Keywords: Hydrocarbon adsorption; Ag-Mordenite; FTIR spectroscopy; NOx selective reduction
Investigation of hydrogen and methane adsorption/separation on silicon nanotubes: a hierarchical multiscale method from quantum mechanics to molecular simulation by Sahra Balilehvand; Seyed Majid Hashemianzadeh; SeyedehSaleheh Razavi; Hedayat Karimi (pp. 13-22).
A combination of ab initio quantum mechanical (QM) calculations and canonical Monte Carlo (CMC) simulations are employed to investigate possible usage of single-walled silicon nanotubes (SWSiNTs) as a novel media for hydrogen and methane adsorption as well as their separation from each other. By fitting the force field, a Morse potential model is selected as an efficient potential to describe the binding energies between both hydrogen-SiNTs and methane-SiNTs obtained from ab initio calculations. Then CMC simulations are performed to evaluate the adsorption and separation behaviors of H2 and CH4 on the three different sizes of SiNTs including (5, 5), (7, 7), and (9, 9) SiNTs at ambient temperatures and pressures from 1 up to 10 MPa. As a comparison, the adsorption and separation of H2 and CH4 on the (8, 8) CNTs which are isodiameter with (5, 5) SiNTs are also simulated. Results are indicative of remarkable enhancement of H2 and CH4 adsorption capacity on the SiNTs compared to the CNTs, which arise from stronger van der Waals (VDW) attractions. In the case of methane adsorption on SiNTs, the stored volumetric energy exceeds the goal of the US Freedom CAR Partnership by 2010, which can not be achieved by methane compression at such low pressures. Moreover, simulation results indicate that SiNTs preferentially adsorb methane relative to hydrogen in their equimolar mixture, which results in efficient separation of these gases from each other at 293 K.
Keywords: Silicon nanotube (SiNT); Canonical Monte Carlo simulation; Morse potential; Gas adsorption; Gas separation
Silane modification and characterization of activated carbon by Qing He; Yingbo Xu; Chenghui Wang; Shike She; Shun Zhou; Ran Wang (pp. 23-29).
Activated carbons have been wildly used as adsorbents for various purpose. When used in a cigarette filter activated carbon can selectively remove a number of the vapor phase compounds to varying degrees of efficiency. To improve the wet-feeling of cigarette smoke with AC in the filter, a new method is developed to chemically functionalize a coal-based activated carbon (AC) based on silanization reaction. Silanization using 3-glycidoxypropyltrimethoxy silane was performed after the oxidized AC was reduced by lithium aluminum hydride.N2 and water adsorption, FTIR, and XPS were employed to characterize the changes in the surface morphology, chemistry and physical conditions at different processing stages. Water content analysis in cigarette mainstream smoke (MSS) showed a positive result in the application of modified AC.
Keywords: Activated carbon; Silanization; Functional groups; Modification
Adsorption of benzene and propene in zeolite MCM-22: a grand canonical Monte Carlo study by Peng He; Hui Liu; Yanfeng Li; Jiqin Zhu; Shiping Huang; Zhigang Lei; Peng Wang; Huiping Tian (pp. 31-42).
The GCMC (grand canonical Monte Carlo) simulation technique was used to predict the competition adsorption characteristics of benzene and propene in different pore systems of MCM-22. The nine-site model of benzene was used, which proved to be effective and efficient. The zeolite was divided into three adsorption sites following a simulated annealing method. It is found that benzene and propene have the same preferential adsorption site and a similar adsorption order in different sites. Moreover, the pure and mixture isotherms of the three sites are drawn. From the isotherms, we obtained a selectivity reversal of the mixture isotherms of benzene and propene in different sites. It is also noted that the competition adsorption in the three adsorption sites for the two adsorbates can fall into three successive steps and the adsorption order of propene in mixture in these three sites is S3→S1→S2. A new model is presented to predict the benzene and propene adsorption equilibrium in MCM-22. This approach yields better multicomponent equilibrium predictions than ideal adsorbed solution theory (IAST). Isotherms at different mole fraction of benzene in gas phase indicate an advantage to increase the feed radio of benzene and propene. Thus, this work is helpful for a better understanding of the adsorption mechanism of benzene and propene in MCM-22 and hence the relation of the catalytic properties of the zeolite to its structure.
Keywords: MCM-22 zeolite; Benzene alkylation; Selectivity reversal
The Pickett equation analytical continuation by Valdemar V. Kutarov; Erich Robens (pp. 43-47).
Usually gas adsorption isotherms are evaluated by means of the classic two-parameter equation of Brunauer, Emmett and Teller (BET II). This equation however fails when multilayer adsorption or capillary condensation occurs. The present work suggests the use of the three-parameter Pickett equation in the range of high adsorptive pressure of the gaseous phase. An analytical continuation of the Pickett equation allows for the description of the whole isotherm. Adsorption isotherms of krypton, water vapor, and n-heptane at Lunar regolith samples are evaluated using both, BET II and continued Pickett equation.
Keywords: Adsorption; BET-equation; Moon; Pickett-equation; Regolith; Surface
Pure and binary adsorption of CO2, H2, and N2 on activated carbon by Johanna Schell; Nathalie Casas; Ronny Pini; Marco Mazzotti (pp. 49-65).
A new developing field of application for pressure swing adsorption (PSA) processes is the capture of CO2 to mitigate climate change, especially the separation of CO2 and H2 in a pre-combustion context. In this process scheme the conditions of the feed to the separation step, namely a pressure of 3.5 to 4.5 MPa and a CO2 fraction of around 40% are favorable for an adsorption based separation process and make PSA a promising technology. Among the commercial adsorbent materials, activated carbon is most suitable for this application. To evaluate the potential, to benchmark new materials, and for process development a sound basis of the activated carbon thermodynamic data is required, namely equilibrium adsorption isotherms of the relevant pure components and mixtures, Henry’s constants and isosteric heats.In this work pure adsorption equilibria of CO2, H2 and N2 on commercial activated carbon (AP3-60 from Chemviron, Germany) are measured using a Rubotherm Magnetic Suspension Balance (MSB) (Bochum, Germany) in a wide temperature and pressure range. The data is used to fit the temperature dependent parameters of Langmuir and Sips (Langmuir-Freundlich) isotherms and to determine the Henry’s constants as well as isosteric heats. Based on this evaluation different methods to evaluate the data are compared and discussed. With the pure isotherm parameters of the Sips isotherm binary adsorption is predicted using an empirical binary Sips equation and ideal adsorbed solution theory (IAST). The results are compared to binary measurements in the same MSB applying a gravimetric-chromatographic method.
Keywords: Pre-combustion CO2 capture; Activated carbon; PSA; Multicomponent adsorption equilibria; CO2 ; H2 ; N2