Representation for binary mixtures of n-alcohols + sub and supercritical CO2 by a group-contribution method

In order to represent vapour–liquid equilibria of binary n-alcohol–carbon dioxide mixtures the excess function-equation of state method is used in which carbon dioxide is described by the IUPAC equation of state and alcohols by a Peng–Robinson type equation where the attractive parameter is estimated by a group-contribution method. The excess function is of the Van Laar type in which the interaction parameters are calculated by a group-contribution method. This approach allows to correlate and predict with quite good accuracy VLE of binary systems of alcohols and CO₂, even for heavier alcohols.     

Zeolites modified by CuCl for separating CO from gas mixtures containing CO2

Although zeolites such as NaY and 13X adsorb CO₂ much more than CO, the adsorption amount of CO₂ and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO₂. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO₂ adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO₂, N₂, H₂ and CH₄. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO₂. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.     

A cross-association model for CO2-methanol and CO2-ethanol mixtures

A cross-association model was proposed for CO₂-alcohol mixtures based on the statistical associating fluid theory (SAFT). CO₂ was treated as a pseudo-associating molecule and both the self-association between alcohol hydroxyls and the cross-association between CO₂ and alcohol hydroxyls were considered. The equilibrium properties from low temperature-pressure to high temperature-pressure were investigated using this model. The calculated p-x and p-ρ diagrams of CO₂-methanol and CO₂-ethanol mixtures agreed with the experimental data. The results showed that when the cross-association was taken into account for Helmholtz free energy, the calculated equilibrium properties could be significantly improved, and the error prediction of the three phase equilibria and triple points in low temperature regions could be avoided.     

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.     

Copper-cerium oxide catalysts prepared by the Pechini method for CO removal from hydrogen-containing mixtures

A series of copper-cerium oxide catalysts was prepared by the Pechini method, and their physicochemical and catalytic properties in CO oxidation in hydrogen-containing gas mixtures were studied. The method chosen for catalyst preparation yields finely dispersed copper and cerium oxides in the catalyst.     

CO2 sequestration by high initial strength Portland cement pastes

During the formation of pastes, mortar and concretes have been used to capture CO₂. This work presents a methodology to estimate the carbon dioxide (CO₂) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO₂ amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO₂ content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO₂ sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)₂, important for CO₂ fixation.     

CO2 storage in cement and concrete by mineral carbonation

The production of cement is responsible for about 8% of man-made CO₂ emissions. CO₂ fixation by mineral carbonation in Ca- and Mg-rich raw materials such as cement-based concrete in various stages of its lifetime and magnesium silicate-based rocks (e.g. olivine) can provide a significant and long-lasting sink of CO₂. Carbonated material can be used in novel construction materials, which potentially could even be CO₂ negative. Despite first applications beyond pilot stage, further research is needed to reach economically and environmentally friendly processes. The properties of the novel construction materials, their reaction mechanisms, suitable mix designs, mechanical properties, and durability need to be explored further.     

Supercritical CO2-ionic liquid mixtures for modification of organoclays

The use of supercritical CO(2) as solvent in the modification of montmorillonite by imidazolium and phosphonium ionic liquids bearing long alkyl chains (C(18)) known for their excellent thermal stability is described. The objective is to combine the environmentally friendly character of ionic liquids and supercritical carbon dioxide for the organophilic treatment of lamellar silicates. Dialkyl imidazolium and alkyl phosphonium salts were synthesized to be used as new surfactants for cationic exchange of layered silicates. Then, the synthesized phosphonium (MMT-P) or imidazolium (MMT-I) modified montmorillonites, cationically exchanged under supercritical carbon dioxide with or without co-solvent, have been analyzed by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) and compared to montmorillonites treated by conventional cationic exchange.     

An in situ radiotracer method for the characterization of a corrosion protective coating by sorption

A new approach for the characterization of coatings with respect to their corrosion protection is presented. The applicability of a simple in situ radiotracer method and some information which can be gained from sorption measurement of corrosive ions are demonstrated based on the results obtained in case of HSO₄ ^–/SO₄ ^2– accumulation on a coating chosen. The technique used has low detection limit and the measurements can be performed without disturbing the primary experimental conditions.     

Raman investigation of the CO2 complex formation in CO2-acetone mixtures

Polarized and depolarized Raman spectra of CO2-acetone mixtures have been measured along the isotherm 313 K as a function of CO2 concentration (0.1-0.9 molar fractions in CO2) by varying the pressure from 0.2 up to 8 MPa. Upon CO2 addition, a new band appears at about 655 cm(-1) and is assigned to the lower frequency nu 2(1) component of the bending mode after degeneracy removal due to the formation of a 1:1 electron donor acceptor (EDA) CO2 complex. The equilibrium constant associated with the complex formation was estimated and found close to those of contact charge transfer complexes. The main modifications of the Fermi dyad of CO2 in the mixtures compared with that of pure CO2 at equivalent density have been assessed. The band-shape analysis revealed that each dyad component is described by two Lorentzian profiles, showing that a tagged CO2 molecule probes two kinds of environment in its first shell of neighbors. The first one involves nonspecific interactions of CO2 with surrounding acetone whereas the second is assigned to the signature of 'transient' CO2 complexes formed with acetone. An upper bound life time of the complex has been estimated to be 8 ps. In addition, a broad band has been detected between the Fermi dyad peaks at about 1320 cm(-1) and its origin interpreted as a further evidence of the CO2-acetone heterodimer formation. Finally, the values of the equilibrium concentration of the heterodimer versus the total concentration of CO2 deduced from the analysis of the nu 2(1) band and from the Fermi dyad have been compared, and the difference is interpreted as due to a lack of theoretical approach of Fermi resonance transitions associated with species existing in different environments.     

High CO2 uptake and selectivity by triptycene-derived benzimidazole-linked polymers

Successful incorporation of triptycene into benzimidazole-linked polymers leads to the highest CO(2) uptake (5.12 mmol g(-1), 273 K and 1 bar) by porous organic polymers and results in high CO(2)/N(2) (63) and CO(2)/CH(4) (8.4) selectivities.     

Serine-based homochiral nanoporous frameworks for selective CO2 uptake

Presented here are two serine-based homochiral materials that show isostructural nanoporous three-dimensional frameworks with high selectivity and storage capacity for CO(2) over N(2) and CO at ambient conditions.     

咪唑类离子液体混合物吸收CO2性能研究

结合常规离子液体和功能型离子液体在吸收CO₂方面的优势,将两类咪唑类离子液体进行混合,对其吸收CO₂的效果和再生性能进行了实验研究。结果表明,两类咪唑类离子液体混合后流动性明显改善,与CO₂接触气液传质顺畅;常规离子液体[bmim][BF₄]和[bmim][Tf₂N]与胺功能型离子液体[NH₂e-mim][BF₄]混合物较单一的离子液体吸收CO₂的量大,[bmim][CH₃CO₂]与[NH₂e-mim][BF₄]混合后较单一的[bmim][CH₃CO₂]吸收量有明显的减低;随着常规咪唑类离子液体阳离子碳链增长,混合离子液体吸收CO₂的效果变强;与胺乙基功能型离子液体混合吸收CO₂时,阴离子为[Tf₂N]的常规咪唑类离子液体要比阴离子为[BF₄]的吸收效果好;离子液体混合物吸收CO₂后经再生循环利用10次,混合物质量基本不变,循环使用后吸收CO₂性能为初始吸收性能的75%~85%。     

Synthesis of amine-modified mesoporous materials for CO2 capture by a one-pot template-free method

A one-pot template-free route was developed for the synthesis of novel tetraethylenepentamine modified porous silica as CO₂ adsorbents, the obtained materials were characterized by N₂ adsorption/desorption, thermogravimetry, elemental analysis, Fourier transform infrared spectrometry,scanning electron microscopy and transmission electron microscopy. It was found that the amine species were inserted into the silica skeleton, which considerably enhanced their dispersion. Compared with similar materials derived from impregnation, the porous structure of the silica can be better reserved, leading to a promising CO₂ adsorption capacity of 3.98 mmol CO₂/g-adsorbent and a fast adsorption kinetic in simulated flue gas at 348 K. The resulted adsorbents could also be easily regenerated and showed a good durability in multiple adsorption–desorption cycles. All these features make this method a promising option for the preparation of CO₂ adsorbents.     

CO(2) as a separation switch for ionic liquid/organic mixtures

A novel technique to separate ionic liquids from organic compounds is introduced which uses carbon dioxide to induce the formation of an ionic liquid-rich phase and an organic-rich liquid phase in mixtures of methanol and 3-butyl-1-methyl-imidazolium hexafluorophosphate ([C4mim][PF6]). If the temperature is above the critical temperature of CO2 then the methanol-rich phase can become completely miscible with the CO2-rich phase, and this new phase is completely ionic liquid-free. Since CO2 is nonpolar, it is not equipped to solvate ions. As the CO2 dissolves in the methanol/[C4mim][PF6] mixture, the solvent power of the CO2-expanded liquid is significantly reduced, inducing the formation of the second liquid phase that is rich in ionic liquid. This presents a new way to recover products from ionic liquid mixtures and purify organic phases that have been contaminated with ionic liquid. Moreover, these results have important implications for reactions done in CO2/ionic liquid biphasic mixtures.     

Application of autoradiography and a radiotracer method for the isolation of iodine-accumulating bacteria

Summary An efficient method for the isolation of iodine-accumulating bacteria was established. A total number of 138 bacterial strains were grown on agar media containing ¹²⁵I, and the strains having strong radioactivity were chosen by autoradiography. They were then grown in liquid media containing ¹²⁵I, and the radioactivity of the cells and the supernatants was determined after centrifugation through silicone oil. Eight strains were found to remove 78 to 90% of iodine from the media within 24 hours, and corresponding amount of iodine was detected in their cells. The advantage of this method is in its simplicity and the low detection limit.     

Evaluation of the precision in the dentifrice abrasivity measurements obtained by a radiotracer method

The radiotracer method was applied to evaluate the precision of themeasurements of abrasivity data obtained for dentifrice samples and for abrasiveagents (silica and calcium carbonate). This method consists of measuring 32P transferred to a dentifrice or abrasive slurry when an irradiated dentinis submitted to a brushing simulation. Results obtained for abrasivity indiceshad good precision with relative standard deviations lower than 11.8%. Comparisonsmade between our abrasivity index data with those obtained at the Oral HealthResearch Institute of Indiana University also showed a good agreement.     

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2 + ethanol and CO2 + methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.