Computer Simulation of the Absorption of CO<Subscript>2</Subscript> Molecules by Water Cluster: 2. The Microstructure

The simulation of the absorption of CO₂ molecules by the (H₂O)₁₀ cluster is performed by the molecular dynamics method using the modified TIP4P model of water. The detailed structure of (CO₂)_i(H₂O)₁₀ clusters (0≤i≤11) is analyzed by the statistic geometry method based on the construction of the Voronoi polyhedra. The obtained distributions of the geometric elements of polyhedra indicate the significant changes in the structure of a cluster after the absorption of one CO₂ molecule. Only polyhedra characterizing the structure of unstable water clusters that absorbed six or seven CO₂ molecules demonstrate a nonsphericity close to the ideal tetrahedron. Linear CO₂ molecule tends to be oriented in a cluster so that the average angle formed by this molecule and permanent dipole moments of water molecules would be equal to about 30°.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 315–321.Original Russian Text Copyright © 2005 by Galashev, Rakhmanova, Chukanov.     

Computer Simulation of the Absorption of CO<Subscript>2</Subscript> Molecules by Water Cluster: 3. Dynamic and Dielectric Properties

Autocorrelation functions of translational and angular velocities of H₂O and CO₂ molecules in (CO₂)_i(H₂O)₁₀ clusters that are generated by the molecular dynamics method, as well as their frequency spectra, are calculated. Self-diffusion coefficients of molecules in clusters are determined. The IR spectra thus obtained and frequency-dependent dielectric permittivity of the clusters indicate the enhancement of absorption of Earth’ thermal radiation by these aggregates with an increase in the number of CO₂ molecules in the aggregates. Dielectric losses also increase with the i number.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 322–327.Original Russian Text Copyright © 2005 by Galashev, Rakhmanova, Chukanov.     

FT-IR study on CO<Subscript>2</Subscript> adsorbed species of CO<Subscript>2</Subscript> sorbents

The stability of amine-functionalized silica sorbents prepared through the incipient wetness technique with primary, secondary, and tertiary amino organosilanes was investigated. The prepared sorbents were exposed to different gaseous streams including CO₂/N₂, dry CO₂/air with varying concentration, and humid CO₂/air mixtures to demonstrate the effect of the gas conditions on the CO₂ adsorption capacity and the stability of the different amine structures. The primary and secondary amine-functionalized adsorbents exhibited CO₂ sorption capacity, while tertiary amine adsorbent hardly adsorbed any CO₂. The secondary amine adsorbent showed better stability than the primary amine sorbent in all the gas conditions, especially dry conditions. Deactivation species were evaluated using FT-IR spectra, and the presence of urea was confirmed to be the main deactivation product of the primary amine adsorbent under dry condition. Furthermore, it was found that the CO₂ concentration can affect the CO₂ sorption capacity as well as the extent of degradation of sorbents.     

Thermal behavior of LDH 2CuAl.CO<Subscript>3</Subscript> and 2CuAl.CO<Subscript>3</Subscript>/Pd

Cu/Al layered double hydroxide (LDH) can be used as a catalyst for important processes such as cross-coupling reactions. This property may be improved by adding palladium by either impregnation or intercalation. Therefore, the LDH matrix and its composites with Pd⁰ or [PdCl₄]^2? have been prepared. By powder X-ray diffraction, FT-infrared spectroscopy, thermogravimetric and elemental analysis it was determined the LDH formula Cu₄Al₂(OH)₁₂CO₃.4H₂O, with malachite as the second phase. The LDH thermal decomposition occurs between 120 and 600 °C, having as intermediates the double oxi-hydroxide and the mixed oxide phases. At 800 °C the residue is composed of CuO and CuAl₂O₄. The composites were obtained employing [PdCl₄]^2? and Pd₂(dba)₃ as precursors, and the solvent choice for this process was shown to be of significant importance: the materials obtained using DMF had Pd impregnated in the surface, while the usage of water promoted the intercalation of [PdCl₄]^2? in the LDH matrix. The thermogravimetric analysis was able to distinguish the mode of supporting palladium between the composites being a reliable characterization for such task.     

CO<Subscript>2</Subscript> and SO<Subscript>2</Subscript> uptake by oil shale ashes

In the present research, CO₂ and SO₂ binding ability of different oil shale ashes and the effect of pre-treatment (grinding, preceding calcination) of these ashes on their binding properties and kinetics was studied using thermogravimetric, SEM, X-ray, and energy dispersive X-ray analysis methods. It was shown that at 700 °C, 0.03–0.28 mmol of CO₂ or 0.16–0.47 mmol of SO₂ was bound by 100 mg of ash in 30 min. Pre-treatment conditions influenced remarkably binding parameters. Grinding decreased CO₂ binding capacities, but enhanced SO₂ binding in the case of fluidized bed ashes. Grinding of pulverized firing ashes increased binding parameters with both gases. Calcination at higher temperatures decreased binding parameters of both types of ashes with both gases studied. Clarification of this phenomenon was given. Kinetic analysis of the binding process was carried out, mechanism of the reactions and respective kinetic constants were determined. It was shown that the binding process with both gases was controlled by diffusion. Activation energies in the temperature interval of 500–700 °C for CO₂ binding with circulating fluidized bed combustion ashes were in the range of 48–82 kJ mol⁻¹, for SO₂ binding 43–107 kJ mol⁻¹. The effect of pre-treatment on the kinetic parameters was estimated.     

Fast CO<Subscript>2</Subscript> sequestration by aerogel composites

The increasingly evident impact of anthropogenic CO₂ emissions on climate change and associated environmental effects is stimulating the search for viable methods to remove this gas. One of the most promising strategies is the long-term storage of CO₂ in inert, insoluble and thermodynamically-stable materials. This strategy mimics the natural reactions that transform silicates into carbonates regulating the cycle of CO₂ on the surface of the Earth, operating on a geological time-scale. Consequently, the aim is to accelerate these reactions to be applicable on the timescale of human lives. We present the various technologies developed or proposed to date, based on this particular approach. The principal limiting factor is that high pressures and temperatures are required to produce appropriate materials capable of CO₂ sequestration and storage. Nevertheless, the synthetic materials known as aerogels can be modified in shape, size and chemical functionality so as to catalyse the process of CO₂ elimination through silicates (of Ca or Mg), considerably reducing the reaction time and working at atmospheric pressure and temperature.     

Mechanochemical interaction of alkali metal metasilicates with carbon dioxide: 1. Absorption of CO<Subscript>2</Subscript> and phase formation

Processes proceeding during the mechanochemical activation of alkali metal metasilicates M₂SiO₃ (where M is Li, Na, K) are studied in the air and in an atmosphere of carbon dioxide. At the initial stage of activation in a centrifugal planetary mill in an atmosphere of carbon dioxide, the main portion of supplied mechanical energy is expended for grinding and the mechanosorption of CO₂ occurs in the regime of cleavage, i.e., on the freshly formed surfaces of particles. As the time of activation increases, the specific surface area becomes constant, which, however, does not substantially affect the rate of interaction between carbon dioxide and silicates. The absorption of CO₂ occurs in the regime of friction on the active sites of already formed surfaces and is accompanied by the tribodiffusion of gas molecules into structurally disordered layers of particles. With identical amounts of supplied energy, the CO₂/M₂SiO₃ molar ratio in the samples activated in the medium of carbon dioxide increases in the Li < Na < K series. The main product of mechanically induced interactions between Li₂SiO₃ and CO₂ is the X-ray amorphous carbonate-silicate phase. In the case of sodium and potassium metasilicates, the reaction of mechanochemical substitution occurs to form corresponding carbonates, hydrocarbonates, and amorphous silica. It is shown that the character of mechanochemical interaction between M₂SiO₃ and CO₂ depends on the change in the Gibbs energy of the transformation of silicate into corresponding carbonate, as well as on the melting temperature and the hygroscopicity of silicate.     

Hybrid catalytic effects of K<Subscript>2</Subscript>CO<Subscript>3</Subscript> on the synthesis of salicylic acid from carboxylation of phenol with CO<Subscript>2</Subscript>

As a base-promoted Kolbe–Schmitt carboxylation reaction, the mechanism of synthesis of salicylic acid derivatives from phenols with CO₂ in the industry is still unclear, even up to now. In this paper, synthesis of 3,6-dichloro salicylic acid (3,6-DCSA) from 2,5-dichloro phenoxide and CO₂ was investigated in the presence of K₂CO₃. We show the reaction can proceed by itself, but it goes at a slower rate as well as a lower yield, compared to the case with the addition of K₂CO₃. However, the yield of 3,6-DCSA is only minorly affected by the size of K₂CO₃, which cannot be explained from the view of catalytic effect. Therefore, K₂CO₃ may on one hand act as a catalyst for the activation of CO₂ so that the reaction can be accelerated, while on the other hand, it also acts as a co-reactant in deprotonating the phenol formed by the side reaction to phenoxide, which is further converted to salicylate.     

Photocatalytic reduction of CO<Subscript>2</Subscript> over TiO<Subscript>2</Subscript> based catalysts

At present, carbon dioxide is considered the largest contributor among greenhouse gases. This review covers the current state of problem of carbon dioxide emissions from industrial and combustion processes, the principle of photocatalysis, existing literature related to photocatalytic CO₂ reduction over TiO₂ based catalysts and the effects of important parameters on the process performance including light wavelength and intensity, type of reductant, metal-modified surface, temperature and pressure. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Organometallic coordination polymers based on silver carboxylates: [AgCF<Subscript>3</Subscript>CO<Subscript>2</Subscript>(2,3-Et<Subscript>2</Subscript>Pyz)] and [AgCF<Subscript>3</Subscript>CO<Subscript>2</Subscript>(Bpeta)]

Coordination polymers [AgCF₃CO₂(2,3-Et₂Pyz)](I)(2,3-Et₂Pyz-C₈H₁₂N₂) and [AgCF₃CO₂(Bpeta)] (II) (Bpeta is 4′4-bipyridylethane, C₁₂H₁₂N₂) are synthesized. Their structures are determined. The crystals of compound I are monoclinic, space group P2(1)/n, a = 7.185(1), b = 14.754(1), c = 12.317(1)Å, β = 97.09(1)°, V = 1295.7(2) ų, ρ_calcd = 1.831 g/cm³, Z = 4. Structure I consists of infinite chains of doubled polymeric chains joined by silver carboxylate dimers [[Ag₂(CF₃CO₂)₂(Et₂Pyz)₂]_∞. The coordination polyhedron of Ag⁺ is a distorted tetrahedron. The crystals of compound II are orthorhombic, space group Pbca, a = 13.555(3), b = 13.991(3), c = 16.449(3) Å, V = 3119.5(11) ų, ρ_calcd = 1.725 g/cm³, Z = 8. Doubled polymeric chains with the Ag…Ag bond (3.16 Å) are also formed in structure II. Supramolecular layers are formed in the structure due to the weak π-π-stacking interaction between the aromatic groups of chains. The CF₃CO ₂ ^? anion is weakly bound to Ag⁺ (Ag-O_avg 2.790 Å).     

NaBO<Subscript>2</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>WO<Subscript>4</Subscript> quaternary system

This is the first study of the NaBO₂-Na₂CO₃-Na₂MoO₄-Na₂WO₄ quaternary system by differential thermal analysis. Na₂[MoO_4(x)WO_{4(1 − x)}] solid solutions in the quaternary system are found to not decompose.     

Adsorption of CO<Subscript>2</Subscript>-containing gas mixtures over amine-bearing pore-expanded MCM-41 silica: application for CO<Subscript>2</Subscript> separation

Adsorption of CO₂, N₂, CH₄ and H₂ on triamine-grafted pore-expanded MCM-41 mesoporous silica (TRI-PE-MCM-41) was investigated at room temperature in a wide range of pressure (up to 25 bar) using gravimetric measurements. The material was found to exhibit high affinity toward CO₂ in comparison to the other species over the whole range of pressure. Column-breakthrough dynamic measurements of CO₂-containing mixtures showed very high selectivity toward CO₂ over N₂, CH₄ and H₂ at CO₂ concentrations within the range of 5 to 50%. These conditions are suitable for effective removal of CO₂ at room temperature from syngas, flue gas and biogas using temperature swing (TS) or temperature-pressure swing (TPS) regeneration mode. Moreover, TRI-PE-MCM-41 was found to be highly stable over hundreds of adsorption-desorption cycles using TPS as regeneration mode.     

On the history and prehistory of CO<Subscript>2</Subscript>

I will trace the little known prehistory and parts of the better known history of CO₂ by investigating some of the names it has been given from Antiquity to the present day. In Antiquity, the words pneuma or spiritus letalis designated both a supernatural force and an exhalation that emanated from certain caves. We will see how CO₂ gradually came to be regarded as something natural, a gas and then substance.     

Molecular Mechanisms of the Effect of Water on CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> Mixture Adsorption in Slitlike Carbon Pores

The grand canonical ensemble Monte Carlo method has been used to study adsorption of carbon dioxide, methane, and their mixtures with different compositions in slitlike carbon pores at a temperature of 318 K and pressures below 60 atm. The data obtained have been used to show the effect of fixed amounts of pre-adsorbed water (19, 37, and 70 vol %) on the adsorption capacity and selectivity of carbon micro- and mesopores. The presence of water reduces the adsorption capacity throughout the studied pressure range upon adsorption of gaseous mixtures containing less than 50% CO₂, as well as in narrow micropores (with widths of 8?12 Å). Upon adsorption of mixtures with CO₂ contents higher than 50%, the adsorption capacity of pores with low water contents appears, in some region of the isotherm, to be higher than that in dry pores. In the case of wide pores (16 and 20 Å), this region is located at low and moderate pressures, while for mesopores it is located at high pressures. The analysis of the calculated data has shown that the molecular mechanism of the influence of preadsorbed water on the adsorption capacity is based on the competition between the volume accessible for adsorption (decreases the capacity) and the strength of the interaction between carbon dioxide molecules and water molecules (increases the capacity). Therewith, the larger the surface area of the water–gas contact, the stronger the H₂O–CO₂ interactions.     

No-Glycerol rapid heterogeneous biodiesel production on K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by coupling process

Biodiesel containing almost no glycerol has been produced by coupling reaction carried out over K₂CO₃ supported by calcium oxide as solid base catalysts. The solid base catalysts synthesized by wet impregnation exhibit an exceedingly high activity in biodiesel production. It was found that the reaction time required for the highest yield of biodiesel, 99.2%, can be shortened to 30 min over K₂CO₃/Al₂O₃ under the optimum reaction conditions: 8: 1: 1 molar ratio of methanol/DMC/oil, 30 wt % K₂CO₃/Al₂O₃ catalyst, and 65°C reaction temperature. Solid basic catalysts examined in the study were characterized by BET surface area, XRD, CO₂-TPD, and SEM techniques. The strong interaction between K₂CO₃ and the support yields a new basic active site, which can be probably responsible for the high activity of K₂CO₃/Al₂O₃.     

Oxidation of Aromatic Compounds: XIII. Oxidation of Unsymmetrically Substituted 1,3-Diarylpropynones in a System CF<Subscript>3</Subscript>CO<Subscript>2</Subscript>H-CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>-PbO<Subscript>2</Subscript>

Oxidation of unsymmetrically sunstituted 1,3-diarylpropynones in a system trifluoroacetic acid-dichloromethane-lead(IV) oxide proceeds through intermediate formation of cation radicals and occurs regio- and stereoselectively affording E-1,1,2,2-tetraaroylethenes. The highest yield of these compounds was obtained from 1,3-diarylpropynones containing electron-donor methoxy and methyl groups in the aromatic ring conjugated with the triple bond.     

Pressurized CO<Subscript>2</Subscript>-enhanced gasification of coal

Carbon dioxide was considered as a co-gasifying agent in a coal gasification reactor. The work presented herein describes the simulation results for the process and the experimental data on coal char gasification with CO₂ addition as the rate-controlling step for the entire process. To study the potentially beneficial effect of the introduction of CO₂ into the gasification system, several simulations were conducted using the commercial process simulation software ChemCAD 6.3^®. The results of a Gibbs equilibrium reactor were evaluated. The Boudouard reaction is a critical path for the development of this process, and the kinetics were studied experimentally. Four chars derived from the pyrolysis of Polish coals of different origins were selected for the experiments. The kinetic characteristics of this system were examined using a custom-designed pressurized fixed-bed reactor. To determine the effect of pressure on the gasification rate, several preliminary studies on the gasification of coal chars were performed isothermally at the temperature of 950 °C and pressures of 1, 10, and 20 bars. In contrast to the thermodynamic calculations, the experimental data revealed that increasing the CO₂ pressure leads to a higher reaction rate for medium-rank coal chars and low-rank lignite coal char, resulting in higher efficiency for carbon monoxide production. The pressure influences the reactivity more strongly when varied from 1 to 10 bars; a further increase in pressure affects the rate almost insignificantly. The observed behavior representing the changes in carbon conversion degree during gasification is satisfactorily described by the grain model.     

Oxidation of aromatic compounds: XII. Regio- and stereoselective oxidative dimerization of alkyl 3-arylpropynoates in the system CF<Subscript>3</Subscript>CO<Subscript>2</Subscript>H-CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>-PbO<Subscript>2</Subscript>

Regio- and stereoselective oxidative dimerization of alkyl 3-arylpropynoates in the system CF₃CO₂H-CH₂Cl₂-PbO₂ (1–30 h, 0–20°C) leads to dialkyl (E)-2,3-bis(arylcarbonyl)-2-butene-1,4-dioates with trans arrangement of the substituents at the double bond.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 9, 2004, pp. 1329–1333.Original Russian Text Copyright © 2004 by Savechenkov, Vasilev, Rudenko.For communication XI, see [1].