1,721,040 research outputs found
High temperature characterization of Y-zeolite loaded with chlorobenzene
No full textDue to their widespread use in many industrial sectors, low solubility in water and their bioaccumulation tendency,
Volatile Organic Compounds (VOCs) are hazardous organic chemicals commonly present in water. Among this class of
pollutants, chlorobenzene (CB) is included as benzene (i.e., BTEX species) halogenated compound. Therefore, due to
its toxic effects on both human health and environmental systems, the removal of CB from water is a primary issue.
Recently, it has been highlighted that organophylic and hydrophobic zeolites are efficient as sorbent materials and
completely regenerable without showing remarkable changes in adsorption capacity and structural properties.
Nowadays, these zeolites features, combined with their high thermal stability, are exploited in regeneration processes
through thermal treatment in order to reuse regenerated zeolites in new adsorption processes (Rodeghero et al., 2016).
Therefore, the aim of the project is to investigate the desorption process of chlorobenzene (purchased by Sigma Aldrich
with a purity of 99.8%) Y (HSZ-390HUA code; 200 SiO2/Al2O3 ratio) system to: 1) determine the desorption
temperature of extraframework content; 2) characterize the structural modifications induced by high temperature
treatment and 3) highlight the temperature effects on the interactions between organic molecules and framework oxygen
atoms. With this purpose, Y-CB sample was prepared and characterized by chromatographic (via Headspace Solid
Phase Microextraction-GC) and thermal (TG and DTA) analysis. Desorption process was constantly monitored, through
synchrotron X-ray powder diffraction, at the high resolution Beamline ID22 (ESRF, Grenoble) from room temperature
to 590°C with a heating rate of 8°C/min. Rietveld refinements showed that chlorobenzene molecules are desorbed at
about 210°C. These results are in good agreement with thermal analysis, which suggest that all the extraframework
(H2O and CB molecules) content is completely released between 190 and 210°C. Hence, the detected desorption
temperature reveals an acceleration of desorption kinetics compared to that reported on a patent previously published
(Vignola et al., 2008). Moreover, structural refinements highlighted that both only slight memory effects in terms of
structural deformations are registered in 12MR channel geometry after regeneration process and the reactivated zeolite
regain the unit-cell parameters of the bare material almost perfectly. Furthermore, any significant crystallinity loss is
observed. Based on these results, the High Silica Y zeolite is potentially reusable in a new adsorption/desorption cycle.
Rodeghero, E., Martucci, A., Cruciani, G., Bagatin, R., Sarti, E., Bosi, V., Pasti, L. (2016): Kinetics and dynamic behaviour of
toluene desorption from ZSM-5 using in situ high-temperature Synchrotron X-ray diffraction and chromatographic techniques.
Catalysis Today, 277, 118-125.
Vignola, R. (2008): WO 2009/000429 A1, Eni S.p.A
Toluene and n-hexane competitive adsorption on high-silica ZSM-5 zeolite
No full textFuel-based compounds, such as toluene and n-hexane, are common pollutants present in water and wastewater. Due
to their tendency to persist in air, water and soil and to bioaccumulate through the food chain, they are included among
the most hazardous compounds for human health and environment. Acquatic ecosystems are especially vulnerable
because of the frequent use of water bodies as recipients of potentially toxic liquids and solids from domestic,
agricultural and industrial wastes. Hence, the removal of fuel-based compounds, through adsorption onto inorganic
sorbents is of considerable interest. Due to their selectivity towards organic contaminant and fast adsorption kinetics, it
has been recently highlighted that High Silica Zeolites are hydrophobic sorbent materials suitable for adsorption
processes (Martucci et al., 2015; Pasti et al., 2016). The aim of this work is to determine the ZSM-5 zeolite degree of
selectivity and its structural changes when a competitive adsorption of toluene and n-hexane occurs. A sample of ZSM-
5 zeolite (MFI topology, SiO2/Al2O3 ratio=280), was provided by Tosoh Corporation and loaded with a binary mixture
of toluene and n-hexane. Kinetics and adsorption isotherm data were obtained via Headspace Solid Phase
Microextraction-GC. Powders patterns were collected before and after adsorption on a Bruker D8 Advance
diffractometer equipped with SOL-X detector. Thermal (TG and DTA) analysis were performed in air up to 900°C at
10°C/min. This multidisciplinary approach allowed us to: 1) measure the sorption capacity of zeolite materials weighed
against organic pollutants dissolved in water; 2) characterise the sorbent structure after pollutant adsorption; 3) localise
the organic species in the zeolite channel systems; 4) probe the interaction between the adsorbate and zeolite framework.
Rietveld refinements provide information about the relative position of molecules inside the structure after toluene, nhexane
and their mixture adsorption. Data reveal that 1) n-hexane and toluene are preferentially adsorbed whether as
single components than as binary mixture; 2) zeolite selectivity is higher towards the n-hexane than toluene. Differences
Fourier maps analysis shows that n-hexane, water, and toluene have been adsorbed at about 8.95%, 2.2%, and 1.59%,
respectively, in good agreement with both adsorption data and thermal analysis. As a matter of fact, ZSM-5 zeolite
preferably adsorbs n-hexane, even in presence of a competitor, such as toluene.
Martucci, A., Braschi, I., Bisio, C., Sarti, E., Rodeghero, E., Bagatin, R., Pasti, L. (2015): Influence of water on the retention of
methyl tertiary-butyl ether by high silica ZSM-5 and Y zeolites: a multidisciplinary study on the adsorption from liquid and gas
phase. RSC Adv., 5, 86997-87006.
Pasti, L., Rodeghero, E., Sarti, E., Bosi, V., Cavazzini, A., Bagatin, R., Martucci, A. (2016): Competitive adsorption of VOCs from
binary aqueous mixtures on zeolite ZSM-5. RSC Adv., 6, 54544-54552
Chromatography as Lévy Stochastic Process
No full textThe Stochastic Theory of Chromatography has been revised in light of some of the most relevant Lévy's findings in Theory of Probability, including the so-called Lévy's distance, the characteristic function and the theory of infinitesimally divisible distributions. These concepts represent the key to exploit and understand, at a molecular basis, phenomena typical of chromatographic separations under linear conditions, such as peak tailing and splitting. In particular, Lévy's distance has been used to quantify the degree of convergence of real peaks towards an ideal Gaussian shape; the characteristic function properties, introduced by Lévy to deal with the problem of the addition of independent random variables, have been employed to solve a wide variety of chromatographic models (including adsorption on heterogeneous surfaces) and to interpret mobile phase dispersion from a probabilistic point of view. Finally, Lévy's studies concerning infinitesimally divisible distributions have allowed to introduce in the stochastic description of chromatography, effects associated to dispersion in mobile phase. It has been demonstrated that, according to Lévy's canonical representation of stochastic processes, the basis of chromatography is a mobile phase Poisson Process. Represented as a Lévy's process, the microscopic-probabilistic model of chromatography permits the establishment of a connection between single-molecule properties and their statistical fluctuations and shapes of real chromatographic peaks allowing, at the same time, for the constitution of a link between different branches of physical sciences
Thermal Field-Flow Fractionation of Charged Submicrometer Particles in Aqueous Media
No full textThermal field-flow fractionation (ThFFF) of various types of submicrometer silica particles in aqueous media is experimentally investigated under an extended range of medium ionic strengths with and without the presence of surfactant. The experiments were designed to examine the applicability to submicrometer particles of the theory of charged nanoparticles thermodiffusion recently proposed by Parola and Piazza (Parola, A.; Piazza, R. Eur. Phys. J. E. 2004, 15, 255-263). In particular, the expression for the calibration function in terms of particle radius and channel temperature is derived and experimentally verified. Moreover, retention is expected to be dependent on particle surface potential and charge, and on ionic strength. These dependences are experimentally investigated and the pertinent relationships and correlations derived. The effect of heavy metal adsorption on the silica surface was investigated, and significant ThFFF retention changes were measured. Independent measurements of the zeta potential (-potential) indicated that a decrease in the surface charge of a silica particle is a consequence of heavy metal adsorption, which is, in turn, correlated to the observed decrease in ThFFF retention
Qualità dell'aria nella Pianura Padana. Dal Rapporto CAFE e dalla Nuova Proposta di Direttiva Europea un ineludibile obbligo di Studio e di Governance
No full textViene presa in considerazione la situazione della qualità dell'aria nella pianura padana alla luce del Rapporto CAFE della Comunità Europea e gli obblighi di Governance conseguent
A new approach to cellular Ca2+ determination by the photoprotein aequorine
No full textWe here present a novel method for measuring the concentration of Ca2+ ions in defined subcompartments of living cells. The method is based on the recombinant expression of the Ca2+-sensitive photoprotein aequorin, modified in order to include specific targeting signals. The article will focus on the description of the 'mitochondrial' aequorin as the prototype of this class of indicators. A chimeric cDNA was constructed, which encoded a mitochondrial targeting signal fused to the photoprotein. The cDNA was cloned in the expression vector pMT2 and co-transfected into mammalian cells together with the selectable marker pSV2neo. After selection, stable clones were isolated and analyzed for aequorin production. The high producers were further tested. Biochemical analysis showed that the targeted photoprotein was indeed localized in mitochondria. This allowed the first specific measurement of mitochondrial Ca2+ concentration ([Ca2+](m)) in living cells, that showed that [Ca2+](m) is low at rest (< 0.5 μmoles/L), but rapidly rises to the micromolar range upon cell stimulation
Competitive adsorption of 4-hydroxybenzaldheyde (p-HBA) and toluene (TOL) by Y and ZSM-5 high-silica zeolites
No full textProgrammed field decay thermal field flow fractionation of polymers: A calibration method
No full textThe universal calibration procedure typical of thermal field
flow fractionation (ThFFF) under constant thermal field
operation was extended to thermal field programming
(TFP) operation. The method requires knowledge of the
following: (a) the programming function, which only
depends on the thermal field decay function, (b) the
physicochemical properties of the solvent, and (c) the
calibration plot under varying channel cold wall temperatures
(Tc). Two field flow fractionation field programming
conditions, with either a constant or a variable in time
carrier flow velocity, are exploited. The method is based
on determination, for each retention time position, of the
average ì retention value typical of TFP ThFFF. This
parameter is then used to obtain the calibration plot (i.e.,
the molecular weight of the species as a function of the
retention time position) by using the programming function
and the calibration plot under varying Tc values. The
procedure approximation errors are also derived as a
function of the programming type and solute-solvent
system. To properly test the procedure, the calibration
plot for the system constituted by polystyrene (PS) in cistrans
Decalin was determined, under varying conditions
Tc and thermal gradients, by using a set of monodisperse
PS standards of different molecular weights (M). The
procedure was first validated by simulation under two
typical cases of TFP ThFFF operation. The approximation
errors were found acceptable (in the worse cases, the
accuracy in M prediction was 3%) and are in agreement
with the theory. The procedure was then experimentally
validated under varying programming decay function
conditions. The reproducibility and accuracy of the M
determination are both better than 2%
Determination of calibration function in thermal field flow fractionation under thermal field programming
No full textA new procedure for determining the calibration function able to relate retention and operative parameters to molecular weight of the species in Thermal Field Flow (ThFFF) under Thermal Field Programming (TFP) conditions is presented. The procedure involves determining the average values of retention parameters under TFP and determining a numerical function related to the temperature variations that occur during TFP. The calibration parameters are obtained by a procedure fitting the retention and operative parameters that hold true at the beginning of the TFP. The procedure is closely related to the one previously developed to calibrate the retention time axis under TFP ThFFF and, together, they constitute a full calibration procedure. Experimental validation was performed with reference to Polystyrene (PS) -decalin and PS-tetrahydrofurane (THF) systems. The calibration functions here obtained were compared to those derived by the classical procedure at constant thermal field ThFFF to obtain the calibration function at variable cold wall temperatures. Excellent agreement was found in all cases proving “universality” of the ThFFF calibration concept, i.e. it is independent of the particular system on which it was determined and can thus be extended to ThFFF operating under TFP. The new procedure is simpler than the classical one since it requires less precision in setting the instrumentation and can be obtained with a fewer experiments. The potential applications for the method are discussed
TRATTAMENTO DI ACQUE CONTAMINATE DA MISCELE DI IDROCARBURI: SELETTIVITA’ DI ADSORBIMENTO SU MATERIALI MICRO E MESOPOROSI DA SISTEMI MODELLO RAPPRESENTATIVI DI ACQUE DI FALDA E DI PRODUZIONE
No full textObiettivo del programma di ricerca è lo studio dell’adsorbimento e della mobilità/diffusione di miscele complesse di composti organici in soluzioni acquose mediante l’impiego di materiali micro e mesoporosi (zeoliti e silico-allumine mesostrutturate). Nel presente progetto lo studio viene condotto considerando, con particolare riferimento alla fase acquosa, sistemi modello rappresentativi delle acque di falda e di produzione
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