David A. Pacheco Tanaka

ADSORPTION CHARACTERISTICS AND REMOVAL OF OXO-ANIONS OF ARSENIC AND SELENIUM ON THE POROUS POLYMERS LOADED WITH MONOCLINIC HYDROUS ZIRCONIUM OXIDE

Adsorption properties for oxoanions of Se(IV), Se(VI), As(III), As(V), and methyl derivatives of As(V) have been examined by the porous polymer beads loaded with monoclinic hydrous zirconium oxide (Zr-resin). The retention of these ions on the Zr-resin has been analyzed using Langmuir model of adsorption. The equilibrium constants and the capacities for above ions have been determined. The equilibrium constants for monomethyl arsinic acid and dimethyl arsinic acid are similar to that of As(V) but the adsorption capacity depends on the number of methyl groups. As(V) and Se(IV) are effectively retained on the Zr-resin from an aqueous solution of acidic to neutral pH region, whereas As(III) is removed from neutral to alkaline solution. The column system packed with the present Zr-resin can quantitatively remove low levels of As(V) and Se(IV) from aqueous solution.

Adsorption and removal of oxo-anions of arsenic and selenium on the zirconium(IV) loaded polymer resin functionalized with diethylenetriamine-N,N,N′,N′-polyacetic acid

A polymer adsorbent in which a Zr(IV)-edta complex analogue is immobilized has been prepared and applied to the removal of oxo-anions of As(III), As(V) and Se(IV). Effective retention of these anions has been demonstrated with the proposed polymer complex system. The adsorption mechanism of oxo-anions onto the Zr(IV)-chelated polymer complex has been investigated using Zr(IV)-edta as the model compound. The formation of mixed complexes with oxo-anions has been exemplified by the isolation of the carbonato complex K2[Zr(CO3)edta].3H2O, the structure of which has been confirmed by X-ray crystallography. NMR study suggests that oxo-anions that form weak or moderate conjugate acids, including those of As(III), As(V) and Se(IV), can form mixed complexes with Zr(IV)-edta using the unsaturated coordination site. However, oxo-anions of strong conjugate acids did not show any appreciable interaction with this complex. According to these observations, retention of oxo-anions on the Zr(IV)-chelated polymer complex has been interpreted by a ligand substitution reaction. The adsorption characteristics of As(III), As(V) and Se(IV) on the Zr(IV)-loaded resin have been examined with respect to the equilibrium adsorption, percentage extraction and the effect of co-existing ions. The adsorption and desorption cycles of the oxo-anions have been demonstrated using a column packed with the proposed resin without any loss of column performance, which indicates the possibility for repeated use.

Preparation of porous chelating resin containing linear polymer ligand and the adsorption characteristics for harmful metal ions

Abstract A linear copolymer consisting of maleic anhydride and methylvinylether has been immobilized on the interior surface of porous polymer beads. The modified polymer beads thus obtained have formed the starting material for the preparation of metal selective chelating resins by the reaction of the maleic anhydride moiety with appropriate ligands. Cysteamine has been grafted as the pendant ligand and the resulting chelating resin (cysteamine resin) maintains a high porosity and large specific surface area. On the basis of scanning electron microscopy (SEM) and electron dispersion X-ray (EDX) analyses, the linear polymer is distributed from the outer layer to the inner pores of the resin beads. The adsorption characteristics of the cysteamine resin for Cd 2+ and Pb 2+ have been examined with respect to the percentage extraction, adsorption isotherm and reproducibility upon adsorption–regeneration cycles. The chelating resin shows a remarkably high adsorption rate, which has been attributed to the porous nature of the resin and geometrical flexibility of the ligand. Quantitative removal of Cd 2+ and Pb 2+ from aqueous solution has been demonstrated by the column procedure packed with the cysteamine resin.

Adsorption of fluoride ion on the zirconium(IV) complexes of the chelating resins functionalized with amine-N-acetate ligands

The reaction of fluoride ion with Zr(IV)-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complexes has been examined by 19F and 1H NMR spectroscopies and potentiometry using [Zr(H2O)2EDTA] and K2[Zr(CO3)EDTA] as the model compounds. Ternary complex formation has been suggested as the most plausible mechanism for the retention of fluoride ion on the Zr(IV) complexes. Removal of fluoride ion has been attempted by the use of polymer homologues of Zr(IV)–EDTA complexes. Adsorption characteristics of fluoride ion on Zr(IV) complexes of the chelating resins [CMA (carboxymethylamine) and IDA (iminodiacetic acid) resins] have been investigated. The adsorption capacities and the binding constants for fluoride ion on the Zr(IV) loaded resins have been analyzed using Langmuir model of adsorption. Common anions including chloride, nitrate, acetate, and sulfate ions did not interfere significantly with the adsorption of fluoride ion, whereas the presence of phosphate ion reduced the fluoride capacity markedly. The adsorption rate of fluoride ion uptake by Zr-CMA resin is much faster than that of the Zr-IDA resin. A column process including adsorption, desorption, and regeneration cycles has been demonstrated for the removal of fluoride ion to depict a practical application.

From neutral to ionic species: amine–p-tert-butylcalix(n)arene (n= 6, 8) interaction. Electrochemical, thermodynamic and structural studies in benzonitrile

Solubilities and derived Gibbs energies, enthalpies and entropies of solution of p-tert-butylcalix(n)arenes (n= 4, 6, 8) in benzonitrile at 298.15 K are reported. An important consequence of amine–calixarene interactions in solution is the generation of new electrolytes. Thus, using two different calixarenes (cyclic hexamer and octamer) and various amines, conductance measurements are performed in order to derive equilibria data for the process involving two neutral species to give an electrolyte, as a result of a proton-transfer reaction from the calixarene to the amine. The results obtained by conductivity are checked by using a combination of pKa values for p-tert-butylcalix(n)arene and various amines in benzonitrile calculated from potentiometric data. Thermodynamic parameters for these processes obtained from titration calorimetry reflect the distinctive properties of cryptands relative to other cyclic and aliphatic amines, suggesting that cryptand 222 is likely to host the proton released by the cyclic octamer in its cavity. 13C NMR studies on these systems revealed that the charge on the calixarene anion is delocalised as a result of a dynamic interchange of the remaining protons among the oxygen atoms present in the oligomeric molecule. Finally, the extraction of amines from aqueous solutions by calixarenes is analysed by taking into account the individual parameters that contribute to the overall process. It is shown that the transfer of amines from water to benzonitrile is favoured in the presence of calixarenes. Although the main contribution to the extraction process results from ion-pair formation in solution, the selective extraction of these amines by calixarenes is largely controlled by the transfer Gibbs energy of the amine from water to the non-aqueous phase.

Fluidized Bed Membrane Reactors for Ultra Pure H2 Production—A Step forward towards Commercialization

In this research the performance of a fluidized bed membrane reactor for high temperature water gas shift and its long term stability was investigated to provide a proof-of-concept of the new system at lab scale. A demonstration unit with a capacity of 1 Nm3/h of ultra-pure H2 was designed, built and operated over 900 h of continuous work. Firstly, the performance of the membranes were investigated at different inlet gas compositions and at different temperatures and H2 partial pressure differences. The membranes showed very high H2 fluxes (3.89 × 10−6 mol·m−2·Pa−1·s−1 at 400 °C and 1 atm pressure difference) with a H2/N2 ideal perm-selectivity (up to 21,000 when integrating five membranes in the module) beyond the DOE 2015 targets. Monitoring the performance of the membranes and the reactor confirmed a very stable performance of the unit for continuous high temperature water gas shift under bubbling fluidization conditions. Several experiments were carried out at different temperatures, pressures and various inlet compositions to determine the optimum operating window for the reactor. The obtained results showed high hydrogen recovery factors, and very low CO concentrations at the permeate side (in average <10 ppm), so that the produced hydrogen can be directly fed to a low temperature PEM fuel cell.

Recent Advances in Pd-Based Membranes for Membrane Reactors

Palladium-based membranes for hydrogen separation have been studied by several research groups during the last 40 years. Much effort has been dedicated to improving the hydrogen flux of these membranes employing different alloys, supports, deposition/production techniques, etc. High flux and cheap membranes, yet stable at different operating conditions are required for their exploitation at industrial scale. The integration of membranes in multifunctional reactors (membrane reactors) poses additional demands on the membranes as interactions at different levels between the catalyst and the membrane surface can occur. Particularly, when employing the membranes in fluidized bed reactors, the selective layer should be resistant to or protected against erosion. In this review we will also describe a novel kind of membranes, the pore-filled type membranes prepared by Pacheco Tanaka and coworkers that represent a possible solution to integrate thin selective membranes into membrane reactors while protecting the selective layer. This work is focused on recent advances on metallic supports, materials used as an intermetallic diffusion layer when metallic supports are used and the most recent advances on Pd-based composite membranes. Particular attention is paid to improvements on sulfur resistance of Pd based membranes, resistance to hydrogen embrittlement and stability at high temperature.

Simple hydrothermal synthesis method for tailoring the physicochemical properties of ZnO: morphology, surface area and polarity

A simple urea-assisted hydrothermal synthesis method was used to tailor the physicochemical properties of ZnO materials. The role of Pluronic P123 block copolymer in the crystal growth, morphology and specific surface area of the as-prepared ZnO was studied. When Pluronic P123 is used, well-dispersed hierarchical microspheres, with a flower-like morphology, are obtained, but in its absence large spherical agglomerated clusters are formed. The polarity of the ZnO, measured as the ratio between plane (002) and plane (100), is also significantly higher for the Pluronic P123 sample. The influence of zinc salt precursors was also analysed. The use of zinc nitrate led to the formation of urchin-like ZnO structures, instead of the microflowers that result from zinc acetate salt. Despite having similar surface areas, the polarity of the zinc nitrate sample was much smaller. The decomposition of methylene blue corroborated the higher photocatalytic activity of the ZnO materials with a higher proportion of polar planes (higher polarity). The formation mechanism of the crystals is also suggested based on the observed gradual growth and assembly of the hydrozincite during the initial steps of the synthesis for the samples with and without Pluronic P123.

Fluorometric detection of fluoride ion by ligand exchange reaction with 3-hydroxyflavone coordinated to a zirconium(IV)–EDTA complex

An aqueous solution composed of [Zr(H2O)2edta]·2H2O and 3-hydroxyflavone (flavonol) exhibits an intense blue fluorescence (λmax = 460 nm) upon excitation at 400 nm and the signal intensity decreases with the addition of fluoride ion. This observation has been interpreted by the ligand exchange of flavonol coordinated to Zr(IV) with fluoride ion. Based on this phenomenon, we have fabricated a simple fluorescent detection system of fluoride ion available in aqueous media. The present signaling system provides a simple, rapid and selective detection method of fluoride ion, which covers the concentration range from 1 × 10−3 to 3 × 10−6 M without any significant interference from common anions.

Thermodynamics of protonation and complexation of EDTA derivatives and metal cations in water

Two EDTA derivatives, ethylenedinitrilo-N,N′-diacetic-N,N′-bis(1-phenylethylacetamido) acid (EDTAMBA) and ethylenedinitrilo-N,N′-diacetic-N,N′-bis(2-pyridylacetamido) acid (EDTAPA) have been synthesised and characterised by IR anH NMR spectroscopy. The pKa values for the dissociation of the tertiary amino groups are lower by about three units relative to EDTA. Enthalpies of protonation of EDTAMBA and EDTAPA in water have been determined by titration calorimetry. Thermodynamic parameters of protonation show that the differences observed between the first protonation constants of these derivatives in water is of entropic origin. For EDTAPA, the enthalpy term is dominant in the differences found between the first and second protonation constants of this ligand. Stability constants (determined by potentiometry) and derived Gibbs energies, enthalpy (derived from calorimetry) and entropy data for these ligands and metal cations in water are reported. These data show that, unlike EDTA, there is hardly any variation in the Gibbs energies of complexation (or stability constants) of EDTAMBA and EDTAPA with metal cations in water, as a result of an almost complete compensation between enthalpy and entropy.