Mathematical Modeling of Multicomponent Nonisothermal Adsorption in Sorbent Particles Under Pressure Swing Conditions

A detailed model for nonisothermal sorption of multicomponent mixtures in a single sorbent particle (monodisperse or bidisperse with negligible intracrystalline mass transport limitations) under pressure swing conditions is developed in this study. The dusty-gas model is used to describe the coupling of the molar fluxes, the temperature, the partial pressures and the partial pressure gradients of the components in the pore space of the particle. The variations of the temperature are described by an energy equation in which both convective and conductive modes of heat transport are accounted for. No limitations are imposed on the number of the components in the mixture and on the type of the adsorption isotherm. The model is applied in the investigation of the industrially important air-zeolite 5A system. Two cases with respect to the surrounding gas phase are examined: infinite environment, which is representative for single particle experiments, and finite environment, which is representative for the situation in packed bed adsorbers. It is found that in an infinite environment the external and internal temperature gradients are equally important while in a finite environment the external heat transport limitations are negligible. It is concluded that in modeling the nonisothermal operation of adsorption processes occurring in packed beds it is not necessary to allow for the temperature differences between the gas phase and the surface of the adsorbing particles. Furthermore, if the temperature gradients within the particles can be neglected, only a single temperature equation is needed to describe the energy transport in the bed.     

Flame AAS and UV-VIS determination of cobalt, nickel and palladium using the synergetic effect of 2-benzoylpyridine-2-pyridylhydrazone and thiocyanate ions

A quantitative synergetic extraction procedure for cobalt, nickel and palladium from thiocyanate aqueous solutions into methyl isobutyl ketone (MIBK), containing 2-benzoylpyridine-2-pyridylhydrazone (BPPH), was studied by flame atomic absorption spectrometry (FAAS) and molecular absorption spectrometry (UV-VIS). Using FAAS, linear calibration graphs were obtained from 0.0-0.5 mg l(-1) Co(II), 0.0-1.5 mg l(-1) Ni(II) and 0.0-2.0 mg l(-1) Pd(II). The reproducibilities were s(r,Co(II))=2.0%, s(r,Ni(II))=1.0% and s(r,Pd(II))=1.3% and the limits of detection were c(L,Co(II))=0.004 mg l(-1), c(L,Ni(II))=0.009 mg l(-1) and c(L,Pd(II))=0.012 mg l(-1). Using UV-VIS method the linear calibration graphs were 0.0-0.5 mg l(-1) for Co(II), 0.0-1.0 mg l(-1) for Ni(II) and 0.0-2.0 mg l(-1) for Pd(II). The reproducibilities were s(r,Co(II))=1.3%, s(r,Ni(II))=1.7% and s(r,Pd(II))=1.0% and the limits of detection were c(L,Co(II))=0.001 mg l(-1), c(L,Ni(II))=0.004 mg l(-1) and c(L,Pd(II))=0.002 mg l(-1). The extraction method is almost free from interferences and has been successfully applied to the determination of cobalt, nickel and palladium in dental alloys.     

Chemometrical approaches to evaluate analytical data from aquatic macrophytes and marine algae

The possibility of using aquatic macrophytes and algae as bioindicators of water pollution is investigated. The use of cluster analysis enables the treatment of the analytical data in a global way, revealing hidden clusters of similar behaviour between various biological species or sampling sites. A great number of species was collected from four rivers and fourteen coastal sites in Greece and were analysed for zinc, copper, cadmium, lead and manganese. The analytical data obtained were treated by hierarchical clustering, for marine algae and aquatic macrophytes separately.     

Development and validation of routine analysis methods for the determination of essential, nonessential, and toxic minor and trace elements in cereal and cereal flour samples by inductively coupled plasma-atomic emission spectrometry

Various digestion procedures were carefully investigated and accurately evaluated with respect to their effect on the analysis of cereals and cereal flours. Multielement methods were selected and well developed for the determination of essential (Cr, Cu, Fe, Mg, Mn, and Zn), nonessential (Ag, Al, Ba, Bi, In, and Ga), and toxic (Cd and Pb) minor and trace elements by inductively coupled plasma-atomic emission spectrometry. Only Ag could be determined, either with aqueous standard or standard addition calibration methods, while the standard addition methods were more accurate for the determination of other elements. The recoveries were mostly within the range of 84.1-113% for the expected values of all analytes with respect to certified reference material NIST SRM 1586a (rice flour). The results proved that, for cereals and cereal flours, the use of H2O2 for wet digestion and HNO3 for dry ashing were not necessary. Linear regression analysis and Student's paired t-test were applied to evaluate the significant differences between different procedures and type of samples.     

On-line liquid-liquid extraction system using a new phase separator for flame atomic absorption spectrometric determination of ultra-trace cadmium in natural waters

A robust flow injection (FI) on-line liquid-liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the μg l⁻¹ level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 μl loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h⁻¹, the enhancement factor was 155, the detection limit was 0.02 μg l⁻¹, the relative standard deviation was 3.2% at 2.0 μg l⁻¹ Cd concentration level and the calibration curve was linear over the concentration range 0.06-6.0 μg l⁻¹. The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples.     

Determination of arsenic(III) and total inorganic arsenic in water samples using an on-line sequential insertion system and hydride generation atomic absorption spectrometry

A simple and robust on-line sequential insertion system coupled with hydride generation atomic absorption spectrometry (HG-AAS) was developed, for selective As(III) and total inorganic arsenic determination without pre-reduction step. The proposed manifold, which is employing an integrated reaction chamber/gas-liquid separator (RC-GLS), is characterized by the ability of the successful managing of variable sample volumes (up to 25 ml), in order to achieve high sensitivity. Arsine is able to be selectively generated either from inorganic As(III) or from total arsenic, using different concentrations of HCl and NaBH₄ solutions. For 8 ml sample volume consumption, the sampling frequency is 40 h⁻¹. The detection limit is c_L = 0.1 and 0.06 μg l⁻¹ for As(III) and total arsenic, respectively. The precision (relative standard deviation) at 2.0 μg l⁻¹ (n = 10) level is s_r = 2.9 and 3.1% for As(III) and total arsenic, respectively. The performance of the proposed method was evaluated by analyzing the certified reference material NIST CRM 1643d and spiked water samples with various concentration ratios of As(III) to As(V). The method was applied for arsenic speciation in natural waters samples.     

Classification of byzantine glass samples by the use of different chemical component features

Summary An attempt is made to perform a classification of a small data set (nine unique Byzantine glass samples) by the use of different chemical component features (all components, major components, minor metallic components and colouring components). The strategy applied was cluster analysis (average and single linkage, centroid linkage). The classification using different variables has indicated that some samples have a more special position in the sample set than required by the traditional approaches of determination of similarities or dissimilarities between samples.

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Klassifizierung von byzantinischen Glasproben mit Hilfe verschiedenartiger chemischer Komponenten

     

A time domain analysis of wave motions in chiral materials

A time domain analysis of the equations governing wave propagation in an unbounded chiral medium is presented by a spectral family approach and by a direct eigenfunction expansion using Beltrami–Moses fields.     

Thermal,chemical, and mineralogical characterization of ceramic tobacco pipes from Cyprus

This study is focused on simultaneous thermoanalytical investigations by TG/DTG-DTA technique applied for characterization of samples collected from archaeological site of Nicosia, Cyprus, dating to seventeenth century and gave new information on the firing technology. The ceramic samples derived from Ottomanic tobacco pipes were characterized by the related techniques such as X-ray powder diffraction for the mineralogical composition, and inductively coupled plasma-atomic emission spectrometry and micro-X-ray fluorescence spectroscopic analysis for the chemical content. It was found that they consisted mainly of quartz, calcite, feldspars, and micas. For the majority of the investigated ceramic samples, the thermal behavior investigation collaborates with their mineralogical findings, and resulted to the firing temperature at ~700 °C, due to the existence of calcite. Only in two samples with very high content in quartz, absence of calcite, low amounts of adsorbed water and of total mass loss, and absence of micas, the firing process resulted up to 1000 °C.