Adsorption and porosity properties of carbon-covered alumina surfaces

Uniformly carbon-covered alumina (CCA) was prepared via the carbonisation of sucrose highly dispersed on the alumina surface. Using special thermogravimetry and sorptometry methods physicochemical properties of carbon-covered alumina surfaces were investigated. A numerical and analytical procedure for the evaluation of total heterogeneous properties (desorption energy distribution and pore-size distribution functions) on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented. The desorption energy distribution was derived from the mass loss Q-TG and the differential mass loss Q-DTG curves of thermodesorption of pre-adsorbed polar and apolar liquid films. For the first time, the evaluation of the fractal dimensions of carbon-covered alumina using the sorptometry, thermogravimetry and AFM data is presented.     

Studies of surface properties of pure and modified by Mn<Superscript>2+</Superscript> and Ni<Superscript>2+</Superscript> ions of aluminium oxide samples using complex methods

Complex studies of physicochemical properties of pure and modified of aluminia oxides samples are presented. The presence of Mn²⁺ and Ni²⁺ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and decrease in benzene and n-octane adsorption. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystal formation during modification with manganese and nickel chlorides. Microcrystal formation on the surface and porosity decrease as confirmed by AFM, EDX and powder diffraction studies using automated diffractometer by step scanning. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface in aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the complex measuring methods (thermal analysis, sorptometry, porosimetry, AFM and EDX).     

The influence of Mn2+ and Ni2+ ions on the surface properties of the aluminium oxide samples using Q-TG and Q-DTG data

The paper presents the complex studies of adsorption and porosity of pure and modified–aluminium oxides samples. The presence of Mn²⁺ and Ni²⁺ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and its decrease in the case of benzene and n-octane. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystals formation during modification with manganese and nickel chlorides. Microcrystals formation on the surface and porosity decrease where confirmed by the AFM and SEM studies. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the run of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface of aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the measuring methods (thermal analysis, sorptomate, porosimetry, AFM).     

Study on a novel oil-in-water-type microemulsion system of water/Triton X-100/Tween80/n-hexyl alcohol/n-octane

A novel oil-in-water-type microemulsion system (water/Triton X-100/Tween80/n-hexyl alcohol/n-octane) has been studied. The results of investigations of the mechanism of formation of this system have indicated that the mixture of Triton X-100, Tween80 and n-hexyl alcohol acts as a surface layer. Further studies have shown that by controlling the n-octane content of this system, it is possible to change its cloud point. Furthermore, variation of the environmental temperature has been shown to affect the maximum n-octane content of this system, the maximum n-octane content increases with increasing environmental temperature.     

Chemical ionization mass spectrometry—XIX: n-hexane and n-octane as reactants

The suitability of n-hexane and n-octane as reactant gases in chemical ionization mass spectrometry has been investigated. The mass spectra of these substances have been investigated as a function of pressure up to 2·4 Torr for n-hexane and 1·7 Torr for n-octane. The major ion present in n-hexane at 0·8 Torr is [C₆H₁₃]⁺ (m/e 85) with a relative intensity of 0·65. In n-octane at 0·8 Torr the major ions are [C₈H₁₇]⁺ (m/e 113), [C₆H₁₃]⁺ (m/e 85) and [C₅H₁₁]⁺ (m/e 71). The relative intensities of these ions are 0·38, 0·12 and 0·19, respectively. These alkyl ions in both n-hexane and n-octane are thought to have tertiary structures. Rate constants for the rates of reaction of the primary ions in the two compounds have been determined. The n-hexane chemical ionization spectra of 26 compounds were determined. The spectra of polar compounds are dominated by proton transfer, whereas those of nonpolar compounds exhibit proton transfer and in addition often surprisingly large amounts of electron transfer. The n-octane chemical ionization spectra of 15 compounds were determined and the spectra in general are quite similar to those obtained with n-hexane. n-Hexane and n-octane can be used as reagents in analytical chemical ionization mass spectrometry, but except in certain specialized uses they would probably have no advantage over i-butane.     

Determination of total heterogeneity and fractal dimensions of high-temperature superconductors

Using thermo-analytical and sorptometric methods physicochemical properties and especially surface heterogeneity of HgBa₂Ca₂Cu₃O₈₊, (Hg-1223) was investigated. The desorption energy distribution was derived from mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption in quasi-isothermal conditions of pre-adsorbed n-octane and water vapour. It is shown that the superconducting Hg-1223 phase is highly sensitive to water vapours. The mechanism of water adsorption depends largely on the activation time. By water vapour saturation in a period of 90 min, physisorption takes place. Prolonged periods result in a chemical decomposition. From nitrogen ad- and desorption isotherms the fractal dimension of superconductors were calculated. A new approach is proposed to calculate fractal dimension from Q-TG curves.This revised version was published online in November 2005 with corrections to the Cover Date.     

Study of Gaseous Sample Ionization by Excited Particles Formed in Glow Discharge Using High-Resolution Orthogonal Acceleration Time-of-Flight Mass Spectrometer

The experimental results of a mass spectral analysis of volatile organic compounds in a gaseous sample, obtained using an original design of an ion source based on the Penning ionization of a gas sample by excited metastable inert gas atoms, are presented. Using ANSYS software, a gas-dynamic simulation of reagent gas flow from discharge zone to ionization region was carried out to analyze the effect of gas flow profile on the transport of metastable atoms and ionization efficiency. The n-octane and toluene samples diluted with helium at 100 ppb mole concentrations were used for our experiments. The resulting mass spectra of n-octane and toluene samples containe far more intensive molecular ions in comparison to n-octane and toluene electron ionization mass spectra from the NIST database. The sensitivity of 5 ions per 1 pg and 130 ions per 1 pg was achieved for n-octane and toluene molecular ions using the developed ion source combined with our mass spectrometer. The corresponding detection limits are 2.3 pg s^–1 for n-octane molecular ions and 0.08 pg s^–1 for toluene molecular ions. The detection limit for the reported ion source was considered theoretically.     

Thermodynamics of binary mixtures of aliphatic linear alkanes (C6–C12) at 298.15 K

This article reports experimental values of speeds of sound, densities and refractive indices on mixing of the binary mixtures n-hexane + (n-heptane, n-octane, n-nonane, n-decane, n-undecane, or n-dodecane) at 298.15?K and atmospheric pressure, over the whole concentration range. The corresponding excess and derived properties were computed from the experimental data. The results were fitted by means of the Redlich–Kister equation, such parameters being gathered. Different estimation methods (equations of state, mixing rules, Collision Factor and Free Length Theory) were applied, qualitative agreement between the experimental and theoretical values both in magnitude and sign being obtained.     

(Liquid + liquid) equilibria for ternary mixtures of (ethylene glycol + toluene + n-octane)

Tie-line data for ternary systems of (ethylene glycol + toluene + n-octane) at three temperatures (295.15, 301.15, and 307.15) K are reported. The compositions of liquid phases at equilibrium were determined and the results were correlated with the UNIQUAC and NRTL activity coefficient models. The partition coefficients and the selectivity factor of ethylene glycol are calculated and compared to suggest which ethylene glycol is more suitable for extracting of toluene from n-octane. The phase diagrams for the studied ternary mixtures including both the experimental and correlated tie lines are presented. From the phase diagrams and the selectivity factors, it is concluded that ethylene glycol may be used as a suitable solvent in extraction of toluene from n-octane mixtures.     

Viscosity of the Systems Methanol-n-Octane and Ethanol-n-Octane

The kinematic viscosity of binary solutions methanol-n-octane at 293.15-313.15 K and ethanol-n-octane at 263.15-298.15 K in the miscibility range (low concentrations of n-octane) was measured. In the methanol-octane system, the viscosity shows an abnormal behavior. As shown by molecular-dynamic calculations, this effect is due to formation of a specific type of associates, which results in a decrease in the molecular mobility as the n-octane concentration is increased (up to the phase separation point).     

Thermodynamics of Adsorption ofn-Alkanes on Maleated Wood Fibers by Inverse Gas Chromatography

The adsorption ofn-heptane,n-octane,n-nonane, andn-decane on untreated wood fiber and wood fiber treated with maleated polypropylene was studied by inverse gas chromatography (IGC) at infinite dilution or zero surface coverage. The specific retention volume increased with increasing probe chain length, decreased with increasing column temperature, and increased with increasing maleated polypropylene concentration. The enthalpy of adsorption increased with increasing chain length of the probe vapors. The enthalpy of adsorption remained constant after the treatment of wood fiber. The London dispersive component of the surface free energy decreased with the column temperature and showed no dependency with either the type of wood fiber or the maleated polypropylene concentration.     

Decomposition of perfluoropolyether lubricants

Decomposition has been studied in the chemistry of perfluoropolyethers (PFPE), thus far no molecular structure information is reported. TG-MS is a tool to follow the off gassing of decomposition for clues. We selected two PFPEs that have different properties: Krytox® XHT-1000 and Fomblin Z60 heating to normal decomposition and catalytic decomposition in the presence of alumina powder. Comparing the decomposition fragment intensities, the molecular structure of the branched Krytox® XHT-1000 oil is more stable than the blocky Fomblin Z60. We see aluminum-containing fluorine fragments in the rapid decomposition of oils in contact with alumina powder. It has been suggested the formation of Al(O_6?n F _n ), where n = 1, 2, and 3, in which the fluorine atoms are selectively associated with aluminum atom. The major decomposition products are small and large fragments of fluorocarbons and perfluoroalkoxy. In the absence of alumina powder, Krytox XHT-1000 shows only a loss of 13 mass/% after several hours at 330 °C, whereas in the presence of 1 mass/% alumina powder the oil has rapidly decomposed to 67 mass/% of its original mass within 15 min. Fomblin Z60, a product might not be designed for high temperature, exposing to the same conditions at 330 °C for several hours and shows a loss of 98 mass/% alone, but in the presence of 1 mass/% alumina powder shows a loss of 98 mass/% in 3.6 min. When 3 mass/% of two new developmental additives were added to the both oils, the catalytic decomposition in the presence of 1 mass/% alumina powder was significantly reduced in Krytox® XHT-1000, showing only a loss of 23 mass/% in 4 h, but nearly all weight for Z60 in 60 min. In the oil grades that contain the new additives, we see the fragments of Al–O–S, and F–Al–O–S. The sulfur-containing compound has been reported ionically bonded to oxide in a tripod configuration of alumina surface, which shields the formation of Al–F.     

Studies of physico-chemical properties of mixed adsorbent in the zeolite/SiO2 system

The paper presents physico-chemical properties of mixed adsorbents in the clinoptylolite (mordenite)/SiO₂ system containing 30, 50, 80 mass% zeolite. Adsorption capacity towards polar (water, butanol) and non-polar (n-octane) substances as well as total surface heterogeneity (energetic and geometrical) were determined. Desorption energy distribution functions as well as fractal dimensions were also determined and compared with the low-temperature nitrogen adsorption data. Irregular shapes of the curves q=f(E _d) as well as large values of volumetric fractal dimensions (D _f~2.6) revealed heterogeneous properties of the zeolite/SiO2 system surfaces. Addition of zeolite increases total heterogeneity of the material.     

Effect of phosphomolybdic acid on the catalytic behavior of bifunctional Pt-Cr/nanocrystalline Y zeolite in hydroisomerization of n-octane

In this study, Y zeolite nanocrystals were synthesized without an organic template and were used as a support for bifunctional nanocatalysts in the hydroisomerization of n-octane. Different types of catalysts were synthesized by loading Pt, Cr, and phosphomolybdic acid (HPMo) on Y zeolite nanocrystal supports and were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) analysis. The Cr-Pt/HPMo-Y nanocatalyst with a surface area of approx. 600 m²/g showed the best performance in the hydroisomerization of n-octane. The optimization of n-octane hydroisomerization over bifunctional nanocatalysts supported on nanocrystalline Y zeolite, in the presence of H₂ gas, was applied based on the response surface methodology (RSM) and Box–Behnken design (BBD) template. The effect of three different process variables on the yield of iso-alkanes as the purpose process was determined. Experiments were carried out using a fixed-bed microreactor under different ranges of weight hourly space velocity (WHSV) (A = 0.5–1.5 hr⁻¹), H₂ to n-C₈ molar ratio (B = 1:1–3:1), and reaction temperature (C = 200–300°C). The RSM proved that the temperature variable had the greatest impact on the hydroisomerization reaction yield.     

Thermodynamics of Organic Mixtures Containing Amines. II. Excess Molar Volumes at 25°C for Methylbutylamine + Alkane Systems and Eras Characterization of Linear Secondary Amine + Alkane Mixtures

Excess molar volumes, at 25°C and atmospheric pressure for methylbutyl amine + n-hexane; + cyclohexane; + n-octane; n-decane; + n-dodecane; + n-tetradecane, or + n-hexadecane systems are reported from densities measured with a vibrating-tube densimeter. The excess functions, molar enthalpy, and volume, for linear secondary amine + n-alkane systems are discussed in terms of interactional and structural effects. In addition, these solutions, which include amines from dimethyl to dioctylamine, are studied in the framework of the ERAS model. The corresponding ERAS parameters are reported. The agreement between experimental data and ERAS results is good for excess enthalpies, excess Gibbs energies, and excess molar volumes. The larger discrepancies are found for the excess volumes when strong free-volume effects are present in the investigated mixtures. The variation with temperature of the thermodynamic properties is well described by ERAS.     

Temperature dependence of the derived properties of mixtures containing chlorobenzene and aliphatic linear alkanes (C6–C12)

This article reports experimental densities, refractive indices and speeds of sound of the binary mixtures chlorobenzene?+?(n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane or n-dodecane) and speeds of sound of the ternary mixtures chlorobenzene?+?n-hexane?+?(n-undecane or n-dodecane) at 298.15?K and atmospheric pressure, over the whole concentration range. The corresponding derived properties were computed from the experimental data. The results were fitted by means of the Redlich–Kister equation for binary mixtures and the Nagata equation for ternary mixtures. A set of estimation methods were applied, and an interpretation in terms of structure and length of molecular chain of the n-alkane molecules was made.     

Limited Solubility and Critical Exponents for Some Indole + Hydrocarbon Systems

Abstract

The solubility of indole n-octane, n-decane and n-dodecane has been measured at several temperatures. The three systems exhibit limited solubilities with upper critical solution temperatures. The critical exponents of the three systems, evaluated from the experimental data, are found to be the same within the limits of experimental error: β = 0.50 ± 0.4.     

The partition of ethoxylated non-ionic surfactants between two non-miscible phases

The partition of a polydispersed ethoxylated non-ionic surfactant in equilibrated oil–water systems has been studied at 25 °C. The model surfactant used was a commercial sample of nonylphenol ethoxylated with 10 moles of ethylene oxide (NPEO₁₀). The partition isotherms over the range of surfactant concentration including the critical micelle concentration (CMC) were made with n-hexane, i-octane and n-decane as oil phases. Each partition isotherm exhibits a change of slope that matched the CMC value of surfactant determined by surface tension measurements on aqueous solutions. During the partition of NPEO₁₀ in the oil–water systems, the oligomer distribution in the oil and water phases changed because of fractionation. Below CMC, the mean ethoxylation degree in the oil phase was smaller, whereas in water it was higher than the mean initial value of the surfactant. Moreover, the mean ethoxylation degree in both oil and water phase was practically independent of surfactant concentration. Above CMC, the mean distribution of ethoxymers decreased in both phases. This was ascribed to the competition between micelles from water and the oil phase for the more hydrophobic species of the surfactant. The mean distribution of ethoxymers in the aqueous phase asymptoted to a value that was the mean of the surfactant itself, whereas it steeply decreased in the organic phase.     

Evaluation of the Thermodynamic Parameters for the Adsorption of Some Hydrocarbons on Chemically Treated-Bentonites by Inverse Gas Chromatography

Inverse gas chromatography has been used to evaluate the adsorption parameters (ΔH_a, ΔH_st, ΔS_a and ΔG_a) of some probe molecules, each representing a class of organic (n-hexane, cyclohexane, benzene, n-octane, 1-octene and isooctane) on bentonite and chemically treated-bentonites. The adsorption parameters of the probes on the bentonite samples were determined in infinite dilution region. Adsorption of the organic species was investigated in the temperature range of 200–275^∘C, using a flame ionization detector, and nitrogen as a carrier gas. The net retention volumes (V_n) of the probes were determined by the help of the retention times (t_R) observed on gas chromatograms for each probe. Injection was made at least three times for each probe, obtaining reproducible results of ± 0.5%. It was found that benzene exhibits more negative ΔH than for n-hexane and cyclohexane on all of the adsorbents. In addition, it was found that 1-octene exhibits more negative ΔH than for n-octane and isooctane on the chemically treated-bentonites, whereas n-octane exhibits more negative ΔH than for 1-octene and isooctane on the natural bentonite. Also, interactions of benzene with the natural- and chemically treated-bentonites were found to be stronger than those of n-hexane and cyclohexane with the same carbon number. Again, interactions of the 1-octene with the chemically treated-bentonites were found to be stronger those of n-octane and isooctane with the same carbon number. On the contrary, interactions of n-octane with the untreated-bentonite were found to be stronger than those of 1-octene and isooctane.