Investigation of low-temperature regeneration of activated carbon

Granular activated carbon loaded with aniline,o-nitroaniline oro-nitrophenol, regenerated at relatively low temperature (450° in N₂ atmosphere), shows losses of cyclic adsorption performances (about 5 % per cycle) comparable to those occurring with standard thermal regeneration (950° in controlled atmosphere). Adsorbate build-ups and related surface modifications have been determined.

---

Zusammenfassung Mit Anilin,o-Nitroanilin undo-Nitrophenol beladene, bei relativ niedriger Temperatur (450° in N₂-Atmosphäre) regenerierte granulierte Aktivkohle, zeigt zyklische Verluste der Adsorptionsleistung (etwa 5 % je Zyklus), welche mit den bei thermischer Standard-Regenerierung (950° in gesteuerter Atmosphäre) vorkommenden vergleichbar sind. Der Aufbau der Adsorbate und die damit verbundenen Oberflächenänderungen wurden bestimmt.

---

Résumé Le charbon actif en granulés, chargé d'aniline, d'o-nitroaniline et d'o-nitrophénol, régénéré à une température relativement faible (450° dans une atmosphère d'azote) montre des pertes de rendement d'adsorption cyclique (environ 5 p.c. par cycle) comparables à celles qui ont lieu lors de la régénération thermique standard (950° en atmosphère contrôlée). On a déterminé la constitution des adsorbats et les modifications relatives de surface.

---

, , -, - – 450° . , ( 5% ) – 950° . .

---

---

Work supported by IRSA-CNR, contract no. 77.01823.11.

---

Thanks are due to Mr. L. Pace for skilful contribution to the experimental work.     

Fractionation of nitrogen stable isotopes by ion exchange chromatography

The ion exchange chromatography displacement technique was used for the enrichment of ¹⁵N. The runs were conducted in laboratory and bench scales using two systems of columns filled with Wofatit KPS ion exchange resin (medium porosity type). Ammonia NH₄ ⁺/NH₃ aq. was chosen as the isotopic exchange system. The ammonium bands formed in the columns were eluted by means of sodium hydroxide solution. Hydrodynamic patterns in the column beds was evaluated in terms of dimensionless Reynolds number. The results show that separation process can be performed in the turbulent or laminar flow regime.     

The linear electro-optic effect in CdS0.75Se0.25

The electro-optic coefficient of CdS_0.75 Se_0.25 is measured at the frequency of the He-Ne laser light and the application of this crystal in light modulators is discussed. The figure of merit is found to be |³_or_c| = 7 × 10^-9 cm/V at room temperature. The voltage required to achieve one half wave retardation is 9 kV.     

InSe electrical characterization by means of transport parameters

SCLC measurements in single crystals of the layered semiconductor n-type InSe are reported. The measurements were carried out at various temperatures and on samples grown with indium added in excess (from 5 to 10%). The experimental results suggest that the trapping levels location and the charge transport are dependent on the indium excess. Only the samples grown with an indium excess of about 5% show the features typical of intrinsic semiconductors. The anomalous behaviour of samples grown with indium excess between 6 and 10 is explained by means of scattering mechanisms between charge carriers and ionized impurity centers.     

Low-temperature regeneration of activated carbon

Activated granular carbon samples, routinely equilibrated with synthetic aqueous solutions of o-NO₂-phenol, were regenerated by heating up to 500 °C in a dynamic N₂ atmosphere. Kinetic evaluation of five subsequent thermodesorption cycles was accomplished by two different non-isothermal computation methods. Quantitative estimation of adsorbent-adsorbate interactions was carried out by means of the thermal coefficient of the massive adsorbate release.

---

Zusammenfassung Routinemäßig mit synthetischen wässrigen Lösungen von o-Nitrophenol äquilibrierte, granulierte Aktivkohle-Proben wurden durch Aufheizen auf 500 °C in einer dynamischen N₂-Atmosphäre regeneriert. Fünf aufeinanderfolgende Thermodesorptionszyklen wurden nach zwei verschiedenen nicht-isothermen Berechnungsmethoden kinetisch ausgewertet. Die quantitative Bestimmung der Adsorbent-Adsorbat-Wechselwirkungen wurde mittels der thermischen Koeffizienten der massiven Adsorbatdesorption ausgeführt.

---

, - , 500 ° . . — .

     

Interaction of monochlorinated phenols with granular activated carbon

The validity of an empirical model to estimate the adsorption affinity of a solute from its acidity constant (pKa) was confirmed through study of the adsorption of monochlorinated phenols on granular activated carbon.Neglecting possible adsorbate fragmentation, simplified desorption kinetic data were obtained for the massive thermal release of the investigated solutes. The resulting non-isothermal kinetic parameters confirm that thermal cleaning of the adsorbent surface is a phase-boundary controlled process involving the interruption of physical interactions according to the calculated activation energy values.

---

Zusammenfassung Die Gültigkeit eines empirischen Modells zur Abschätzung der Adsorptionsaffinität eines gelösten Stoffes auf Grund der Aciditätskonstante (pKa) wurde durch Untersuchung der Adsorption von monochlorierten Phenolen an granulierter Aktivkohle bestätigt. Unter Vernachlässigung einer möglichen Adsorbatfragmentierung wurden vereinfachte kinetische Daten für die thermische Desorption der untersuchten gelösten Stoffe erhalten. Die erhaltenen, nichtisothermen kinetischen Parameter zeigen, daß die thermische Säuberung der Adsorbentoberfläche ein phasengrenzflächenkontrollierter Prozeß ist, bei dem physikalische Wechselwirkungen entsprechend den berechneten Werten der Aktivierungsenergie aufgehoben werden.

---

, K_a. , . , , , « », .

     

Infrared study of pressure-induced insulator to metal transitions in vanadium oxide compounds at the SISSI@Elettra beamline

Vanadium oxides display insulator to metal transitions with conductivity jumps up to seven orders of magnitude which makes them very attractive both for technological applications and for the several fundamental issues they raise. We present here an optical study of pressure-induced insulator to metal transitions in VO₂ and V₃O₅, performed at the infrared synchrotron source SISSI@Elettra.     

Thermoanalytical study of activated carbon regeneration. I. Desorption of phenol and aniline

During a thermoanalytical investigation to determine the mechanism and desorption energies of common pollutants, a complex pattern has been demonstrated when activated carbon loaded with phenol or aniline is heated up to 950°C in a dynamic nitrogen atmosphere. Water is completely removed before 150°C. Four and three consecutive steps appear when phenol and aniline are released, respectively.     

Pressure dependence of the charge-density-wave gap in rare-earth tritellurides

We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the midinfrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3.