A measurement of the average kinetic energy released during the unimolecular decomposition of CO2 ion clusters

A combined molecular beam—mass spectrometer apparatus has been used to measure the average kinetic energy E_t released during the unimolecular decomposition of CO₂ ion clusters in the field-free region of the mass spectrometer. For the reaction (CO₂), _n→ (CO_2n?1+CO₂, the measured value for E_t is found to increase as n increases from 3 to 13.     

Determination of formal charge transfer coefficients in adsorption processes in the system Hg,Tl, Tl+, H2O: II. Electrocapillary curves of the second kind

The determination of the dependence of the formal charge transfer coefficient n₂ on the amalgam solution potential difference ψ from the equilibrium electrocapillary curves of the 2nd kind (taken under the condition μ_Tl=const) shows that there exists a discontinuity on the n₂, ψ curve, i.e. a transition from n₂=∞ to n₂=?∞ with increasing ?ψ. The cause of this anomaly is the existence of a minimum on the surface tension of an uncharged amalgam surface vs. μ_Tl curve, which is observed in the case of the Tl-amalgam/vacuum interface as well.     

Production and properties of CO2 cluster anions

Stoichiometric and non-stoichiometric negatively charged CO₂ cluster ions have been produced in a crossed neutral cluster/electron beam ion source. The abundance and stability of these ions have been studied with a double focussing sector field mass spectrometer. The observed abundance anomalies (“magic numbers”) in the mass spectra of (CO₂) _n ^? and (CO₂) _n O^? ions correlate with corresponding small and large metastable fractions of these ions (for loss of one CO₂ unit). Variation of the measured metastable fractions as a function ofn are related to corresponding changes in the monomer binding energies. In addition, we have observed for the first time (CO₂) _n O ₂ ^? ions (i.e. at electron energies above 8 eV with an energy resonance at about 14 eV) and we discuss possible production mechanisms for these ions. Relative electron attachment cross sections have been determined in the energy regime O<E≦20 eV for (CO₂) _n ^? , (CO₂) _n O^? and (CO₂) _n O ₂ ^? withn=1 to 20. The shape of the cross section function for (CO₂) _n O^? is strongly dependent on the cluster sizen.     

Thermo-osmosis of sorbable gases in porous media. Part IV. Mixture separation by two procedures

High internal area carbon compacts have been used to measure thermo-osmotic separation factors for the mixtures C₃H₈+CO₂, n-C₄H₁₀+CO₂ and n-C₄H₁₀+CH₄ over ranges of initial pressures and compositions. Two procedures were employed: in the first, two vessels were connected by the thermo-osmosis membrane only; in the second, in addition to the membrane, a return capillary was provided in which isothermal flow was at least partly viscous in character.In all three gas mixtures, using either method, the more strongly adsorbed components (n-C₄H₁₀ or C₃H₈) were enriched at the hot side and the more weakly sorbed (CO₂ or CH₄) at the cold side of the membrane. In the second method the separation factors obtained with a long narrow return capillary were comparable with or larger than those measured without the return capillary. Separation factors increased the richer the mixture in the more strongly adsorbed component and the higher the initial pressure. For both methods separation factors were often large enough to indicate good potential for thermo-osmosis as a separation strategy. Heats of transport of the components in mixtures differed significantly, sometimes even in sign, from these heats for the pure components. Thus separation factors cannot be predicted from heats of transport of each pure gas or vapour. Rates of approach of separation factors to their steady state values were sensitive to the cross-sectional area of the membrane and also to stirring the gas mixtures during their un-mixing.     

Path dependence of surface–tension scaling in binary mixtures

A mean-field free-energy functional for an n-component mixture with an integral non-local interaction is introduced and then written explicitly for a binary mixture. We use this functional to calculate the liquid–vapor surface tension with parameters chosen to model CO₂/n–C₄H₁₀ and CO₂/n–C₁₀H₂₂, and we examine the scaling of the surface tension as a function of the difference in density between the liquid and vapor phases as various critical points are approached. Each critical point is approached on either a constant-temperature or constant-pressure path; we investigate the path dependence of the scaling behavior. For the constant-temperature paths in the CO₂/n–C₄H₁₀ mixture, we compare our calculated results with experimental data. We find no significant dependence of the scaling on the path to the critical point. We note that the asymptotic scaling holds for a larger range of densities the higher the temperature of the critical point.     

Monte Carlo simulation for pVT relationship of CO2+n-C4H10 and CO2+i-C4H10 systems

Monte Carlo simulation has been applied to calculate the pVT relationship of CO₂+butane (n-C₄H₁₀ and i-C₄H₁₀) systems at 310.93 K and up to 9.5 MPa. CO₂ is treated as a single-site molecule and butanes are treated as four-site molecules. The Lennard–Jones (12–6) potential is used as the site–site potentials and the combining rules proposed by Jorgensen et al. [W.L. Jorgensen, J.D. Madura, C.J. Swenson, J. Am. Chem. Soc. 106 (1984) 6638.] are adopted for unlike site pairs. The calculated results of the pVT relationship show good agreement with the experimental data [T. Tsuji, S. Honda, T. Hiaki, M. Hongo, J. Supercrit. Fluids 13 (1998) 15.] by introducing an intersite interaction parameter between unlike molecules. Furthermore, the radial distribution functions and the number of CO₂ and butanes around butanes are calculated as a fundamental information on the microscopic structures. It is found that the radial distribution functions and the number of CO₂ and n-C₄H₁₀ around n-C₄H₁₀ are different from those of CO₂ and i-C₄H₁₀ around i-C₄H₁₀.     

Electronic spectra and electrochemistry of disubstituted 2,2′-bipyridinetetracarbonylmolybdenum complexes. Solvent and substituent effects

Electronic absorption spectra of cis-[Mo(CO)₄(n,n′-X₂-bipy)] (n = 4, X = NMe₂, NH₂, OMe, CMe₃, Me, H, Ph, CH:CHPh, CO₂H, Cl, CO₂Me, NO; n=5, X = Me, CO₂H) have been measured at ambient temperature in a variety of solvents of different polarity. Emission spectra from glasses containing the complexes at 77 K have also been measured. The influence of the substituent X on the spectroscopic properties is correlated with the Hammett parameters, σ_p (X) and σ_p⁺ (X). The effect of solvent is correlated with the Taft-Kamlet parameter, π^★, indicating charge redistribution along the permanent dipole axis of the complex. The oxidation and reduction potentials in solution are simply related to the electronic effect of the substituent group, X, and are relatively independent of the solvent. The influence of the metal on these properties is not significant.     

Formate dehydrogenase–viologen-immobilized electrode for CO2 conversion,for development of an artificial photosynthesis system

Formate dehydrogenase (FDH)–viologen with a long alkyl chain (CH₃V(CH₂) _n COOH) immobilized on an indium–tin oxide (ITO) electrode, with the function of reduction of CO₂ to formic acid, was investigated as an artificial photosynthesis device based on CO₂ reduction. The amount of formic acid produced by use of FDH–CH₃V(CH₂) _n COOH immobilized on ITO in CO₂-saturated buffer solution, on application of a potential, as a result of one-electron reduction of viologen, depends on the carbon chain length of CH₃V(CH₂) _n COOH. When a CH₃V(CH₂)₉COOH–FDH/ITO electrode was used, production of formic acid was estimated to be 23 μmol after 3 h.     

Parameters estimation and VLE calculation in asymmetric binary mixtures containing carbon dioxide + n-alkanols

In the present work, the estimation of the parameters for asymmetric binary mixtures of carbon dioxide + n-alkanols has been developed. The binary interaction parameter k₁₂ of the second virial coefficient and non-random two liquid model parameters τ₁₂ and τ₂₁ were obtained using Peng–Robinson equation of state coupled with the Wong–Sandler mixing rules. In all cases, Levenberg–Marquardt minimization algorithm was used for the parameters optimization employing an objective function based on the calculation of the distribution coefficients for each component. Vapor–liquid equilibrium for binary asymmetric mixtures (CO₂ + n-alkanol, from methanol to 1-decanol) was calculated using the obtained values of the mentioned parameters. The agreement between calculated and experimental values was satisfactory.     

IR Emission Spectra of Carbonate-Chloride Melts 2CsCl-NaCl-Cs2CO3 Containing Lithium and Beryllium Ions

The IR emission spectra of the molten systems NaCl-CsCl-Cs₂CO₃-MCl _n (M = Li, Be) have been obtained. Spectral data shows that, at a definite limiting molar ratio n _lim = [CO₃]/[Mⁿ⁺] characteristic for each Mⁿ⁺, carbonate-chloride melts based on the NaCl-CsCl eutectic contain carbonate complexes [Li(CO₃)₃]^5? and [Be(CO₃)₃]^4? and, if n < n _lim, carbonato chloro complexes [M(CO₃) _m Cl_4?m ], where m = 1–2.     

Adsorption-Induced Deformation of Adsorbents

Adsorption-induced deformation of AR-V and AUK carbon adsorbents and NaX zeolite has been studied upon adsorption of n-С₅Н₁₂, n-С₆Н₁₈, n-С₇Н₁₆, and CO₂ at temperatures of 193?423 K. It has been shown that adsorption-induced deformation is positive upon the physical adsorption of gases and vapors on the surface of a nonporous (macroporous) solid when the excess adsorption is positive. When calculating the adsorption-induced deformation in the region of the capillary-condensation filling of mesopores, the additional pressure in capillaries, which is negative (contraction of an adsorbent), must be taken into account in the case of wetting a solid surface with a liquid adsorbate. The compressibility of AUK microporous carbon adsorbent as a porous solid is almost independent of the temperature and the properties of an adsorbate, and, for adsorption of n-C₅H₁₀ and n-C₇H₁₆ hydrocarbons and CO₂, it is γ_а = (5.6 ± 0.6) × 10^?6 bar^?1. The compressibility of AUK adsorbent appears to be 87% higher than that of nonporous graphite.     

The atomistic simulation of the gas permeability of poly(organophosphazenes). Part 1. Poly(dibutoxyphosphazenes)

Self-diffusion and solubility coefficients of six gas molecules (He, Ne, O₂, N₂, CH₄, and CO₂) in two poly(dibutoxyphosphazenes)—poly[bis(n-butoxy)phosphazene] (PnBuP) and poly[bis(sec-butoxy)phosphazene] (PsBuP)—have been investigated by means of molecular simulation using the COMPASS molecular mechanics force field. Diffusion coefficients were obtained from molecular dynamics (NVT ensemble) using up to 3 ns simulation time. Solubility coefficients were obtained by means of a Grand Canonical Monte Carlo (GCMC) method. Results of both simulations were in generally good agreement with experimental data with the exception of the simulation results for gas solubility in PsBuP where differences from the data may be attributed to microcrystallinity of the experimental sample. In the case of diffusivity, diffusion coefficients correlated well with the square of the effective diameter of the diffusing gas. Similarly a good correlation was found between the solubility coefficients obtained by GCMC simulation of sorption isotherms and the Lennard-Jones potential well depth parameter, ϵ/k.The transition-state model of Gusev and Suter was used to determine free volume and free volume distribution for PnBuP, PsBuP, and poly[bis(iso-butoxy)phosphazene] (PiBuP). The diffusion coefficient for a given gas in each polyphosphazene was found to correlate exponentially with its accessible free volume fraction. A model for the distribution of accessible free volume, derived from the Cohen–Turnbull theory for the self diffusion of a liquid of hard spheres, was found to provide excellent fit with the simulation results.     

Diffusion of linear paraffins in silicalite studied by the ZLC method in the presence of CO2

The diffusion behavior of C₄–C₁₀ n-alkanes in silicalite-1 has been investigated by using the Zero Length Column method. The diffusivities derived from measurements at different purge rates with different purge gases confirming intracrystalline diffusion control. Data are compared with results reported in the literature for MFI zeolites. The diffusivities were found to be consistent and agree well with data previous obtained by ZLC. However, these data showed a remarkable disagreement with other reported techniques (PFG-NMR, QENS and Permeation). The eventual influence of carbon dioxide (CO₂) adsorption on diffusion properties of n-alkanes in silicalite was also investigated. For this purpose, a series of experiments was performed involving hydrocarbons mixed with CO₂. Data were obtained at 303 K and flow rates between 20 and 80 mL/min. The presence of CO₂ does not seem to influence the intracrystalline transport rate of the investigated light hydrocarbons (n-C₄ and n-C₆). On the other hand, the situation for n-C₈ and n-C₁₀ is more complex. The diffusivity values are higher compared to the previously reported values.     

High-pressure vapor–liquid equilibria for CO2 + alkanol systems and densities of n-dodecane and n-tridecane

An apparatus based on the static-analytic method was used to measure the vapor–liquid equilibria (VLE) for CO₂ + alkanol systems. Equilibrium measurements for the CO₂ + 1-propanol system were performed from 344 to 426 K. For the case of the CO₂ + 2-propanol system, measurements were made from 334 to 443 K, and for the CO₂ + 1-butanol were obtained from 354 to 430 K. VLE data were correlated with the Peng–Robinson equation of state using the classical and the Wong–Sandler mixing rules. Moreover, compressed liquid densities for the n-dodecane and n-tridecane were obtained via a vibrating tube densitometer at temperatures from 313 to 363 K and pressures up to 25 MPa. The Starling and Han (BWRS), and The five-parameter Modified Toscani-Swarcz (MTS) equations were used to correlate them. The experimental density data were compared with those from literature, and with the calculated values obtained from available equations for these n-alkanes.     

Kinetics of electrochromic process in thin films of cathodically deposited nickel hydroxide

Ni(OH)₂ films have been obtained by cathodic deposition from 1 M Ni(NO₃)₂ on a glass with a current-conducting SnO₂ layer. The films have a porous structure and consist of chaotically joined formations of 100–150 nm in size. They contain a considerable amount of adsorbed water, because of which their refraction index was n?=?~1.5, whereas for crystalline nickel hydroxide, it was n?=?2.37. It has been shown that in the course of discoloration of films through a shift of their potential towards more negative values, an electric field is formed in the bulk of film, which accelerates the entry of cations into it (protons as [H₃O]⁺) from the electrolyte and electrons from ohmic contact. In this case, the initial dependence i(t), where i?~?t ^?1/4, is bound up with gradual increase in proton surface concentration. It is proposed to determine separately the dependence of the effective codiffusion coefficient of charge carriers (protons and electrons) on decoloration potential by the analysis of plots of current, injected charge, and luminous transmittance of films against time. This procedure involves a series of periodic stops of potential during the recording of current–potential curves for an electrochromic electrode and allows one to monitor the ratio of the film forms NiOOH and Ni(OH)₂ in the course of film reduction.     

Synthesis of EPA- and DHA-Enriched Structured Acylglycerols at the sn-2 Position Starting from Commercial Salmon Oil by Enzymatic Lipase Catalysis under Supercritical Conditions

There is consistent evidence that long-chain polyunsaturated fatty acids (LCPUFA) belonging to the n-3 series, i.e., eicosapentaenoic (20:5n-3, EPA) and docosahexaenoic (22:6n-3, DHA) acids, decrease the risk of heart, circulatory and inflammatory diseases. Furthermore, the bioavailability of such fatty acids has been shown to depend on their location in triacylglycerol (TG) molecules at the sn-2 position. Consequently, great attention has been accorded to the synthesis of structured acylglycerols (sAG), which include EPA or DHA at the sn-2 position. The aim of this work was to synthesize sAG starting from deodorized refined commercial salmon oil. For this, immobilized lipase B from Candida antarctica (nonspecific) was used as a catalyst for the intra–interesterification process under CO₂ supercritical conditions (CO₂SC). According to the CO₂SC reaction time, three different fractions including sAG compounds were obtained. The location of EPA and DHA at the sn-2 position in the resulting glycerol backbone was identified by mass spectrometry (MALDI-TOF) analysis. In all fractions obtained, a marked decrease in the starting TG content was observed, while an increase in the DHA content at the sn-2 position was detected. The fraction obtained after the longest reaction time period (2 h) led to the highest yield of sn-2 position DHA in the resulting sAG molecule.     

Measurements and modeling of cloud point behavior for polypropylene/n-pentane and polypropylene/n-pentane/carbon dioxide mixtures at high pressure

The phase behavior of polypropylene (PP) in n-pentane and n-pentane/carbon dioxide solvent mixtures has been studied using a high-pressure variable volume view cell. Cloud point pressures for polypropylene (M_w=50,400) in near-critical n-pentane were studied at temperatures ranging from 432 to 470 K for polymer concentrations of 1 to 15 mass%. Furthermore, cloud point pressures for polypropylene (M_w=95,400) in near-critical n-pentane were studied at temperatures ranging from 450 to 465 K for polymer concentrations of 1 to 8 mass%. Cloud point pressures were also measured for PP (M_w=200,000, 3 mass%) in n-pentane at temperatures ranging from 450 K to 465 K. The cloud point pressures for PP (M_w=50,400) in n-pentane/CO₂ mixtures were determined for PP concentrations of 3.0 mass% and 9.7 mass% with CO₂ solvent concentrations ranging from 12.6 mass% to 42.0 mass% at temperatures ranging from 405 K to 450 K. All of the experimental cloud point isopleths were relatively linear with approximately the same positive slope indicating LCST behavior. The experimental cloud point pressures were relatively insensitive to the concentration and molecular weight of polypropylene. At a given temperature, the cloud point pressure of the PP/n-pentane/carbon dioxide system increased almost linearly with increasing carbon dioxide solvent concentration (for carbon dioxide concentrations less than 30 mass%). The Sanchez–Lacombe (SL) equation of state was used to model the experimental data.     

Size effects in the CO-oxidation over supported Pd particles

Low pressure CO oxidation was studied over small supported Pd particles by means of static secondary ion mass spectrometry (SSIMS). The SSIMS spectra of adsorbed layers on Pd particles with diameters below ～7nm contained, besides other species, Pd _n X⁺ ions (X=C, O, CO;n=1–3). In experiments with Pd films, Pd _n C⁺ species were much less abundant or even absent from the mass spectra. We conclude that CO decomposed in appreciable amounts only on Pd particles. No significant influence of the support material (mica, MgO,α-Al₂O₃) was seen and posthumous TEM analysis revealed well defined particle morphologies with largely (111) and (100) facets. At total pressures below 10^?4 Pa, the relative carbidic intensities Pd _n C⁺/Pd _n ⁺ , which were taken as proportional to the carbon surface concentrations, first increased with increasing temperatures and then decreased after they passed a maximum at T=400–440 K. The smaller the particle size, the more intense were the maxima. For T ?440 K, carbon was removed from the surface via reaction with oxygen. Strong hysteresis effects in the C_ad and CO_ad concentrations occurred during temperature variation measurements. The Pd _n C⁺/Pd _n ⁺ ratios displayed maxima during heating but not during cooling. While the Pd _n CO⁺/Pd _n ⁺ ratios were always high at 300 K and always low at T>550 K, they were more intense in the medium temperature range when subjecting the samples to heating. These hysteresis effects are discussed in terms of asymmetric adsorption and reaction behaviour of CO/O₂ mixtures, involving inhibition of CO₂ formation by adsorbed carbon and carbon monoxide.