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Desorption Cycles (desorption + cycle)
Selected AbstractsHydrogen Adsorption and Diffusion in p - tert -Butylcalix[4]arene: An Experimental and Molecular Simulation StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2010Dr. Saman Alavi Abstract Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H2 gas uptake in the low-density p - tert -butylcalix[4]arene (tBC) phase. 1H,NMR peak intensity measurements for pressures up to 175,bar were used to determine the H2 adsorption isotherm. Weak surface adsorption (up to ,2,mass,% H2) and stronger adsorption (not exceeding 0.25,mass,% or one H2 per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H2 molecule has restricted motion and shows a reversible gas adsorption/desorption cycle. Pulsed field gradient (PFG) NMR pressurization/depressurization measurements were performed to study the diffusion of H2 in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H2 gas to ,60,bar are also presented, and show a maximum H2 adsorption of 0.4,H2 per calixarene bowl. Adsorption isotherms of H2 in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ,1,H2 per calixarene bowl at saturation. Classical molecular dynamics simulations with a fully flexible calixarene molecular force field are used to determine the guest distribution and inclusion energy of the H2 in the solid with different loadings. [source] Sorption kinetics of ethanol/water solution by dimethacrylate-based dental resins and resin compositesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Irini D. Sideridou Abstract In the present investigation the sorption,desorption kinetics of 75 vol % ethanol/water solution by dimethacrylate-based dental resins and resin composites was studied in detail. The resins examined were made by light-curing of bisphenol A glycol dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), bisphenol A ethoxylated dimethacrylate (Bis-EMA), and mixtures of these monomers. The resin composites were prepared from two commercial light-cured restorative materials (Z100 MP and Filtek Z250), the resin matrix of which is based on copolymers of the above-mentioned monomers. Ethanol/water sorption/desorption was examined in both equilibrium and dynamic conditions in two adjacent sorption,desorption cycles. For all the materials studied, it was found that the amount of ethanol/water sorbed or desorbed was always larger than the corresponding one reported in literature in case of water immersion. It was also observed that the chemical structure of the monomers used for the preparation of the resins directly affects the amount of solvent sorbed or desorbed, as well as sorption kinetics, while desorption rate was nearly unaffected. In the case of composites studied, it seems that the sorption/desorption process is not influenced much by the presence of filler. Furthermore, diffusion coefficients calculated for the resins were larger than those of the composites and were always higher during desorption than during sorption. Finally, an interesting finding concerning the rate of ethanol/water sorption was that all resins and composites followed Fickian diffusion kinetics during almost the whole sorption curve; however, during desorption the experimental data were overestimated by the theoretical model. Instead, it was found that a dual diffusion,relaxation model was able to accurately predict experimental data during the whole desorption curve. Kinetic relaxation parameters, together with diffusion coefficients, are reported for all resins and composites. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Fiber introduction mass spectrometry: determination of pesticides in herbal infusions using a novel sol,gel PDMS/PVA fiber for solid-phase microextractionJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2007Rogério Cesar da Silva Abstract An application of the direct coupling of solid-phase microextraction (SPME) with mass spectrometry (MS), a technique known as fiber introduction mass spectrometry (FIMS), is described to determine organochlorine (OCP) and organophosphorus (OPP) pesticides in herbal infusions of Passiflora L. A new fiber coated with a composite of poly(dimethylsiloxane) and poly(vinyl alcohol) (PDMS/PVA) was used. Sensitive, selective, simple and simultaneous quantification of several OCP and OPP was achieved by monitoring diagnostic fragment ions of m/z 266 (chlorothalonil), m/z 195 (,-endosulfan), m/z 278 (fenthion), m/z 263 (methyl parathion) and m/z 173 (malathion). Simple headspace SPME extraction (25 min) and fast FIMS detection (less than 40 s) of OCP and OPP from a highly complex herbal matrix provided good linearity with correlation coefficients of 0.991,0.999 for concentrations ranging from 10 to 140 ng ml,1 of each compound. Good accuracy (80 to 110%), precision (0.6,14.9%) and low limits of detection (0.3,3.9 ng ml,1) were also obtained. Even after 400 desorption cycles inside the ionization source of the mass spectrometer, no visible degradation of the novel PDMS/PVA fiber was detected, confirming its suitability for FIMS. Fast (ca 20 s) pesticide desorption occurs for the PDMS/PVA fiber owing to the small thickness of the film and its reduced water sorption. Copyright © 2007 John Wiley & Sons, Ltd. [source] Recovery of transition metal complex by reverse flow adsorptionAICHE JOURNAL, Issue 1 2008Jeroen Dunnewijk Abstract Reverse flow adsorption (RFA) is a technique with a definite potential to prevent the leaching of a homogenous catalyst. In this work, we model an RFA-process for a continuous ideally stirred tank reactor with an adsorption bed upstream and another one downstream from the reactor. The model parameters concerning adsorption equilibrium and kinetics are taken from previous experimental studies on CoCl2 adsorption on polymer-bound trifenylfosfine. We use this model to study the concentration profiles of CoCl2 in the adsorption beds during consecutive adsorption,desorption cycles. The model calculations show that the concentration profile eventually reaches a fixed position after a number of adsorption,desorption cycles, even though internal mass transfer was a limiting factor. Hence, the transition metal is kept within the system boundaries, which is an essential requirement for the application of RFA. © 2007 American Institute of Chemical Engineers AIChE J, 2008 [source] Biosorption of heavy metal using brown seaweed in a regenerable continuous columnASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2008N. Rajamohan Abstract This paper deals with the experimental investigation on removal of cadmium [Cd(II)] ions from an aqueous solution using a marine alga, Sargassum tenerrimum, in a fixed-bed column. The effects of the inlet flow rate and the sorbent bed height on the biosorption of Cd(II) ions were studied. The dynamics of column biosorption was modeled by the bed depth service time (BDST) model and the Thomas model. The BDST model was used to study the dynamic sorption behavior at different bed heights, whereas the Thomas model was used to fit the column biosorption data at different flow rates. The uptake capacity and the breakthrough time increase with an increase in the bed height. The sorption capacities of the bed per unit volume and the rate constant Ka were found to be 3819.42 mg/l and 0.0353 mg/h respectively. In flow rate experiments, the results confirmed that the metal uptake capacity and the metal removal efficiency of S. tenerrimum decreased with increasing flow rate. The Thomas model was used to fit the column biosorption data at different flow rates and model constants were evaluated. After five sorption,desorption cycles, the selected marine alga exhibited a high cadmium uptake of 63.43 mg/g. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||