Separation of Oxygen and Nitrogen by Porous Cyanometallates

The adsorption-based separation in porous solids takes place through steric, kinetic, or equilibrium effect selectivity. In this contribution the oxygen-nitrogen separation by four porous frameworks representative of cyanometallates was studied by inverse gas chromatography. The following materials were considered: Cd3[Co(CN)6]2 (cubic), Zn3[Co(CN)6]2 (rhombohedral), Zn3K2 [Fe(CN)6]2 (rhombohedral) and Co[Fe(CN)5NO] (cubic). Chromatographic separation profiles from gases mixtures using columns of these materials were recorded. For columns prepared from rhombohedral zinc hexacyanocolbaltate(III) excellent separation of O2 and N2 was observed. Such behavior was attributed to a kinetic-based selectivity related to the size and shape for the pore windows of this material. The porous framework of this zinc phase is formed by ellipsoidal cavities (12.5 9 8A˚ ) communicated by elliptical windows of 5A˚ . For Cd3[Co(CN)6]2 and Co[Fe(CN)5 NO] also kinetic-based selectivity was observed while for Zn3K2[Fe(CN)6]2 the Kþ ion located close to the cavity windows hinders the porous windows accessibility for nitrogen and oxygen molecules. All the samples to be studied were characterized from X-ray diffraction, infrared spectroscopy, termogravimetric and adsorption data

Adsorption and separation of propane and propylene by porous hexacyanometallates

The separation capability for mixtures of propane and propylene by porous frameworks representatives of transition metal hexacyanometallates was studied from adsorption data under equilibrium conditions at 273.15K and from inverse gas chromatography profiles at different column temperatures. Samples of two porous solids were considered; Cd3[Co(CN)6]2, which is representative of Prussian blue analogues (cubic structure) with a porous framework related to vacancies for building block, and Zn3[Co(CN)6]2 (rhombohedral phase) where the porous framework results from the tetrahedral coordination for the Zn atoms. The two materials were found to be able for the mixtures separation, with the highest separation ability for the rhombohedral phase under equilibrium conditions but, in dynamic conditions the cubic one shown a better separation, which was ascribed to a kinetic contribution related to a smaller windows size. © 2010 Elsevier B.V. All rights reserved

Evaluation of cadmium hexacianoferrate(III) as a microporous material

The properties of cadmium hexacyanoferrate(III), Cd3[Fe(CN)6]2, as a microporous material were evaluated from adsorption data of CO2, N2 and water vapor. The adsorption isotherms were interpreted according to the Dubinin– Radushkevich and Dubinin–Astakhov models. The adsorbate–adsorbent interactions during the activation and the adsorption processes were monitored by XRD, IR and M€ossbauer techniques where the adsorption of propanol, ethanol and diethyl ether was also considered. As a measure of the adsorbate–adsorbent interactions, calculations of the adsorption isosteric heats were also carried out. 2002 Published by Elsevier Science Inc

Behavior of transition metals ferricyanides as microporous materials

The properties of divalent transition metal ferricyanides as microporous materials remain poorly documented. This family of compounds crystallizes with a cubic cell (Mn, Co, Ni, Cu, Zn, Cd) and also in a rhombohedral (R-3c) modification (Zn). The porous nature of the cubic complexes is related to the occurrence of systematic vacancies of the octahedral building unit [Fe(CN)6]. The system of vacancies forms a porous framework with polar surface. The rhombohedral modification for the zinc complex salt also has a porous structure but free of vacancy and with a practically non-polar surface. Such structural information was complemented with adsorption isotherms of H2O, N2 and CO2, which were evaluated according to Dubinin model for the volume pore filling. For CO2 the maximum adsorbed amount was calculated using the Langmuir–Freundlich isotherm. From these adsorption data, a characterization of the studied ferricyanides according to pore volume, pore accessibility and guest–host interactions is given. Information on the guest–host interaction was also derived from Mo¨ssbauer spectra recorded on samples with N2, CO2, ethanol, methanol and water as adsorbed species. The quadrupole splitting (D) of the Mo¨ssbauer spectrum appears as an excellent sensor for the interaction between the adsorbed species and the metal at the pore surface. The Mo¨ssbauer spectra were also used as sensor for the pore accessibility to light hydrocarbons. The surface properties of the studied ferricyanides result modulated by the metal used to form the 3D structure from the octahedral block. In this sense, the studied materials behave as tunable zeolites. The materials behavior during the dehydration process and their thermal stability were evaluated from X-ray powder patterns, thermogravimetric and spectroscopic (IR and Mo¨ssbauer) data. For all the studied compositions the crystal structure was refined from the corresponding X-ray powder patterns using the Rietveld method. 2006 Elsevier Inc. All rights reserved

On the Microporous Nature of Transition Metal Nitroprussides

Nitroprussides of divalent transition metals form a family of microporous molecular materials. Their properties in this sense depend on the transition metal cation involved and also on the preparative method, which determine their crystal structures. The stable phases of this family of materials belong to one of the following crystal structures: orthorhombic (Pnma) (Mn2+, Fe2+, Cu2+, Zn2+, and Cd2+), cubic (Fm3m) (Co2+ and Ni2+), and orthorhombic (Amm2) (Cu2+). These materials are stable up to above 160 °C, while their dehydration takes place around 100 °C. On dehydration, Amm2 copper complex changes into a tetragonal (I4mm) phase. The microporous nature of these materials is discussed according to their crystal structure and correlating structural and adsorption data. The accessibility to the pore system was evaluated through adsorption of H2O, CO2, and N2. Pores of both orthorhombic and cubic structures are accessible to H2O and CO2 in experiments carried out at 23 and 0 °C, respectively; however, they are inaccessible to N2 at -196 °C. This behavior is discussed as related to the large polarizing power of the nitrosyl (NO) ligand which distorts the local environment of the iron atom and reduces the effective window cross section. The small pores of tetragonal copper nitroprusside were inaccessible to the adsorbates used

Separation of Light Liquid Paraffin C5–C9 with Cuban Volcanic Glass Previously Used in Copper Elimination from Water Solutions

Featured Application: In this work, an inexpensive and available material, as volcanic glass, is used to absorb metals from wastewater and then it is used to the separation of light liquid-olefins.Abstract: Raw porous volcanic glass from Cuba was used as an adsorbent for Cu2+ removal from dyes after activation with an acid solution. After Cu2+ adsorption, it was also evaluated its capacity to separate n-paraffins from a mixture by inverse gas chromatography (IGC), and the results were compared with those obtained with bare volcanic glass without copper. The main goal of this work is to highlight the great applicability of natural volcanic glass, which can be reused without pretreatment as an adsorbent. The results from copper adsorption were quite promising, considering the availability and low cost of this material; the sample without acid treatment turned out to be the most adequate to remove copper. Moreover, the results from IGC revealed that the separation of paraffins from the mixture was achieved with both bare volcanic glass and glass containing Cu, although greater heat adsorption values were obtained when copper was present in the sample due to the stronger interaction between paraffin and copper. The high availability and low cost of this porous material make it a potential and attractive candidate to be used in both heavy metal removal and paraffin separation for industrial purposes

Separation of N–C₅H₁₂–C₉H₂₀ Paraffins Using Boehmite by Inverse Gas Chromatography

The separation of a mixture of C5−C9 n-paraffins was achieved by Inverse Gas Chromatography (IGC) by using boehmite; AlO(OH), in a packed column with short exposure times and temperatures; from 45 °C to 52 °C. The boehmite was characterized by XRD; ATG; SEM; IR spectroscopy and N2 adsorption. The material exhibited a low crystalline boehmite (AlOOH) structure and presented high hydration (pseudoboehmite). The reverse gas chromatography measurements showed that the elution temperatures of the C5−C9 n-paraffins were low compared with those obtained for other adsorbents. The differential heat of adsorption values ensures the satisfactory separation of the components in the C5−C9 mixture under suitable chromatographic conditions

CHARACTERIZATION AND USE OF A CUBAN MINERAL IN ELIM INATION OF CRYSTAL VIOLET FROM AQUEOUS SOLUTION

ABSTRACT: A Cuban mineral was used to evaluate its adsorption capacity of crystal violet (CV) from aqueous solutions. The mineral was characterized by several physicochemical techniques. Both N2 adsorption-desorption isotherm at 77K, fitted with the Brunnauer-Emmet-Teller model, and the results of the average pore distribution revealed that the Cuban mineral used in this study is a mesoporous material. The FTIR spectrum indicated a high content of carbonate species; however, the XPS spectrum also revealed the presence of silicon species on the surface of the adsorbent, which suggests the coexistence both carbonate and silicate species in the raw material. The efficiency for CV removal, the role of the contact time and of the initial concentrations of the adsorbate was evaluated in this study. The adsorption kinetic was fitted with the pseudo second order model. This result indicated that the adsorption mechanism was through chemisorption process between CV and Cuban mineral. The results showed that CV adsorption isotherm was best described by the Langmuir model. The adsorption capacity for CV was 55.63 mg/g. The abundant deposits, low cost and easy access make of mineral SAN1 a good natural adsorbent to treat large volumes of dye polluted waters