Determination of calcium oxide in calcined phosphate ores

It has been shown that an existing procedure to differentiate calcium oxide from the carbonate and silicate of calcium can be used in the presence of the phosphate, fluoride and sulphate of calcium, and of the carbonate and oxide of magnesium. It is based on the reaction in aqueous solution of calcium oxide with sucrose to form calcium saccharate, and subsequent titration with oxalic acid solution. The method has application for a direct chemical determination of calcium oxide in phosphate rock where calcination of accompanying carbonate is necessary in beneficiation processes.     

Enhancement of CO2 sorption uptake on hydrotalcite by impregnation with K2CO3

The awareness of symptoms of global warming and its seriousness urges the development of technologies to reduce greenhouse gas emissions. Carbon dioxide (CO(2)) is a representative greenhouse gas, and numerous methods to capture and storage CO(2) have been considered. Recently, the technology to remove high-temperature CO(2) by sorption has received lots of attention. In this study, hydrotalcite, which has been known to have CO(2) sorption capability at high temperature, was impregnated with K(2)CO(3) to enhance CO(2) sorption uptake, and the mechanism of CO(2) sorption enhancement on K(2)CO(3)-promoted hydrotalcite was investigated. Thermogravimetric analysis was used to measure equilibrium CO(2) sorption uptake and to estimate CO(2) sorption kinetics. The analyses based on N(2) gas physisorption, X-ray diffractometry, Fourier transform infrared spectrometry, Raman spectrometry, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of enhanced CO(2) sorption. The equilibrium CO(2) sorption uptake on hydrotalcite could be increased up to 10 times by impregnation with K(2)CO(3), and there was an optimal amount of K(2)CO(3) for a maximum equilibrium CO(2) sorption uptake. In the K(2)CO(3)-promoted hydrotalcite, K(2)CO(3) was incorporated without changing the structure of hydrotalcite and it was thermally stabilized, resulting in the enhanced equilibrium CO(2) sorption uptake and fast CO(2) sorption kinetics.     

CO2 sorption in wet ordered mesoporous silica kit-6: effects of water content and mechanism on enhanced sorption capacity

The sorption isotherms of CO₂ in wet ordered mesoporous silica KIT-6 with different amounts of pre-adsorbed water were firstly collected experimentally using a volumetric method in the temperature range of 275–281 K. The isotherms show an inflection point indicating CO₂ hydrates form in the pore spaces which is proofed by the enthalpy change calculated at the inflection pressure, and the quantity of water content shows considerable effect on the sorption capacity of CO₂. The highest enhancement of sorption capacity in the presence of water is observed in wet KIT-6 sample with water loadings of 2.48, which is about 12.80 mmol/g and 1.86 times than that on dry sample. However, the saturation capacity is still far less than that what can be stored merely in the form of hydrates due to the low ratio of water utilization because of the large pore and the polar surface of KIT-6.     

Effect of lithium oxide dopants on electrophysical and sorption properties of zinc oxide

The effects of lithium oxide dopants (0.5–0.8 at. % Li) on the electrophysical and sorption properties of ZnO were studied in the temperature range from 150 °C to 410 °C. The introduction of lithium increases the activation energy of the conductivity of ZnO, decreases its conductivity, and increases the amount of S0₂ sorbed. Two forms of chemisorbed SO₂ (donor and acceptor) are observed on the surface.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1096–1100, May, 1996.     

Effect of gallium oxide dopants on electrophysical and sorption properties of zinc oxide

The effect of gallium oxide dopants (0.1–0.3 at.% Ga) on the electrophysical and sorption properties of ZnO was studied in the temperature range from 19 to 350 °C. The introduction of the dopant increasing the conductivity of ZnO is accompanied by a change in the amounts of SO₂ and Cl₂ sorbed and the reactivity of zinc oxide. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 266–270, February, 1999.     

Sequestration of supercritical CO2 by mercury oxide

HgCO₃·2HgO (mercury oxide carbonate), along with partly unreacted reactants, was obtained by exploring the behaviour of the Hg₂Cl₂/HgO binary system in supercritical CO₂ (scCO₂) at 200°C, 22000 kPa in the presence and absence of water, using a self-made laboratory-scale system. The reaction of pure HgO with scCO₂ aimed at the synthesis of HgCO₃ (mercury carbonate), also yielded the same product. Meanwhile, with a small amount of water present in the Hg₂Cl₂/HgO-scCO₂ system, at 200°C, 22000 kPa, the mineral terlinguaite (Hg₄O₂Cl₂) was obtained instead of mercury oxide carbonate. Repeating this reaction under the same conditions, but in the absence of CO₂, again resulted in the synthesis of terlinguaite, leading to the assumption that the scCO₂ had no influence on the synthesis of terlinguaite. This study reveals a new moisture-free laboratory method and conditions for the permanent fixation of CO₂ by HgO. This method bears two benefits: 1) it can be introduced to reduce the Hg content in flue gas and fly ash emitted from coal-burning power plants and municipal waste incinerators; 2) it can contribute to CO₂ mineralisation in montroydite (HgO) geological formations as mercury oxide carbonate.     

Effect of physical and chemical modification on the sorption capacity of hydrolyzed lignin

Processes of thermal and chemical treatment of hydrolyzed lignins by fluorination are described. The thus treated product is suggested to be used as a sorbent in organic and inorganic media.     

Effect of surfactants on the structure and texture characteristics of aluminum oxide

The effect of surfactants (polyvinyl alcohol and cetyltrimethylammonium bromide), which were introduced at the aluminum hydroxide synthesis stage, on the structure and texture characteristics of aluminum oxide was studied by a set of physicochemical techniques. The introduction of the above surfactants did not cause considerable changes in the thermal transformations of aluminum hydroxides, but it affected the genesis of the formed carbon. An analysis of the diffuse reflectance spectra and electron micrographs indicated that the aluminum oxide obtained in the presence of polyvinyl alcohol and calcined at 300°C was covered with polyene-type coke. An increase in the treatment temperature to 550°C led to the formation of condensed aromatic coke; in this case, the specific surface area of the sample increased from 125 to 500 m²/g. The samples calcined at 550°C were γ-Al₂O₃ with a unit cell parameter of 7.933 Å and a crystallite size of no more than 30–40 Å. The pore size distribution was bimodal, with maximums at 35–65 and 380–415 Å, regardless of treatment temperature.     

Effect of water sorption on the dielectric behavior of calcium chondroitin-4-sulfate

The dielectric properties of calcium chondroitin-4-sulfate were studied as a function of frequency, temperature, and water content. The dielectric constant changes very little with water content below “monolayer” coverage, and after that the dielectric constant follows the shape of the adsorption isotherm. The dielectric behavior is discussed as affected by interfacial polarization and by the increase in the rotational freedom of the polymer side chains.     

SO2 removal performances of Al- and Mg-modified carbide slags from CO2 capture cycles at calcium looping conditions

Journal of Thermal Analysis and Calorimetry - In this work, the SO2 removal performances of the aluminum- and the magnesium-modified carbide slags fabricated by the combustion synthesis from CO2...     

High capacity CO2 adsorption in a Mg(II)-based phosphine oxide coordination material

The new porous phosphine coordination material, PCM-11, is an unusual 8,4-connected coordination polymer with an open 3-D pore structure, formed by reaction of Mg(II) with tris(para-carboxylato)triphenylphosphine oxide. The highly ionic nature of the metal-ligand bonding results in excellent thermal stability upon desolvation (>460 °C). PCM-11 is easily activated for small molecule sorption at low temperature without the requirement for solvent pre-exchange. It adsorbs 47.5 wt% CO(2) at 11.6 bar and 30 °C.     

Effect of phase behavior and pressure on the constant-volume heat capacity and intermolecular interaction of CO2-ethanol and CO2-n-pentane mixtures in the critical region

Study on the properties of the fluids near the critical point of mixed systems is a key for the development of supercritical (SC) technology and for the further understanding of the features of supercritical fluids (SCFs). The constant-volume molar heat capacity (Cv) of a solution is directly related to the internal energy, intermolecular interaction, and the microstructure of the solution. In this work, the Cv of CO2-n-pentane and CO2-ethanol systems was determined at 308.15 K in different phase regions. This work focuses on how the properties of the mixtures change with pressure, composition, and the structure of the components near the critical point of the mixtures. It was found that at fixed composition, a maximum in Cv versus pressure curve exists (Cv(max)) that occurs at the pressure at which the isothermal compressibility (K(T)) is the largest. We deduced that breaking the "clusters" in the SC mixtures is an endothermic process. It is very interesting that Cv increases sharply as the pressure approaches the critical point (CP) or bubble point (BP), while Cv is nearly independent of pressure and composition at the pressures well above the CP or BP pressure, and that the Cv at CP or BP can be several times larger than that at the high pressures. It can be deduced that at fixed composition the degree of "clustering" changes significantly with pressure near the CP or BP, and is the largest at CP and BP.     

Effect of gamma-ray irradiation on the sorption property of hydrous ferric oxide and ferric phosphate

The equilibirum sorption capacity of hydrous ferric oxide and ferric phosphate has been observed to increase on irradiation with γ-rays by 5.2 and 6.6%, respectively. The rate of sorption increases differently in the irradiated exchanger materials depending upon their characteristics nature; e.g., when the concentration of the Zn(ammine) solution is 0.10M, increase in the F-values, caused by irradiation is significantly more striking in the case of hydrous ferric oxide than in ferric phosphate. On the other hand, at lower external concentration of the Zn(ammine) ion (0.01M), the increase in F-values is more significant in the case of ferric phosphate.     

Effect of dopant addition on oxygen sorption properties of La-Sr-Co-Fe-O perovskite type oxide

The paper reports on effect of doping Ag⁺, Ni²⁺, Ca²⁺, Ba²⁺ or Zr⁴⁺ in La_0.1Sr_0.9Co_0.9Fe_0.1O_3−δ (LSCF1991) on its oxygen sorption capacity and desorption rate. The dopant can be incorporated into LSCF1991 matrix causing lattice expansion. The oxygen sorption capacity and tendency for the disordered perovskite to ordered brownmillerite phase transition for these samples decrease in the order: LSCF1991 > LSCF-Ag > LSCF-Ni > LSCF-Ca > LSCF-Ba > LSCF-Zr. The oxygen desorption rate also decreases in the same order for the doped samples. Doping increases the tendency of the disorder to order phase transition and enhances oxygen desorption rate during oxygen desorption step. Doping Ag and Ni provides more pronounced enhancement in oxygen desorption rate. The results suggest that Ag and Ni doped LSCF1991 samples are promising sorbents for use in a high temperature sorption process for air separation.     

Raman spectroscopic study of CO2 sorption process in poly methyl methacrylate

Raman spectra of poly methyl methacrylate (PMMA) in contact with compressed CO₂ were measured, to investigate effects of CO₂ sorption on structure of the PMMA chain. The solubility and diffusivity of CO₂ in PMMA were estimated from temporal variations of intensities of CO₂ peaks. The PMMA structure was analyzed from temporal variations of vibrational energies of PMMA peaks. The results show that the vibration energies of C H stretching modes of PMMA increase with CO₂ sorption, whereas those for skeletal vibration modes decrease. These energy shifts are attributed to elongational deformation of PMMA. The PMMA structure is deformed with stretching of the chains as a bundle. From energy shifts of the CO₂ peaks, the size of the CO₂ accommodated space between the bundles is estimated to be 1.6–1.9 nm. Furthermore, it was observed that the vibrational energies of the PMMA modes in foamed glassy PMMA differ from the values in glassy PMMA without foams. This result suggests that the local structure of the PMMA chain changes with the process of the CO₂ sorption and/or foaming. The local structure of the PMMA chain might be one of the dominant factors governing the properties of cellular materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 831–842, 2008