Showing papers on "Hexane published in 2007"

Separation of benzene and hexane by solvent extraction with 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ionic liquids: effect of the alkyl-substituent length.

Abstract: The influence of the alkyl-substituent chain in 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ionic liquids ([Cnmim][NTf2], where n is the length of a linear alkyl chain) as solvents for the separation of benzene and hexane by liquid extraction was investigated. The liquid−liquid equilibrium (LLE) at 25 °C for the ternary systems ([Cnmim][NTf2] + hexane + benzene), with n taking the values 4, 8, 10, and 12, were determined. These data were analyzed and compared to those previously reported for the system ([C2mim][NTf2] + hexane + benzene). The results show that short alkyl chains on the imidazolium cation of the ionic liquid lead to a better extractive separation of benzene and hexane, and reveal the influence of the relative degree of ordering in the ionic liquids on the extraction parameters.

Kinetic separation of hexane isomers by fixed-bed adsorption with a microporous metal-organic framework.

Abstract: A three-dimensional microporous metal−organic framework Zn(BDC)(Dabco)0.5 (BDC = 1,4-benzenedicarboxylate, Dabco = 1,4-diazabicyclo [2,2,2]octane), having two types of intersecting pores to encapsulate linear hexane and to block branched hexanes, and thus exhibiting highly selective sorption with respect to n-hexane, has been successfully applied to the kinetic separation of hexane isomers by fixed-bed adsorption.

On the importance of the supporting material for activity of immobilized Candida antarctica lipase B in ionic liquid/hexane and ionic liquid/supercritical carbon dioxide biphasic media

Abstract: A commercial solution of free Candida antarctica lipase B (Novozyme 525L) has been immobilized by adsorption onto 12 different silica supports modified with specific side chains (e.g. alkyl, amino, carboxylic, nitrile, etc.). The immobilized derivatives were assayed for the kinetic resolution of rac -1-phenylethanol in both ionic liquid/hexane and ionic liquid/supercritical carbon dioxide biphasic media. The best results were obtained for the supports modified with non-functionalized alkyl chains and when the in water activity increased from 0.33 to 0.90 (e.g. the CALB/butyl-silica activity was enhanced up to five times). Coating immobilized enzyme particles with ionic liquids (butyltrimethylammonium bistriflimide or trioctylmethylammoniun bistriflimide) resulted in a decrease in activity (10 times), although half-life times were enhanced (up to six times) in hexane media at 95 °C. However, immobilized derivatives coated with ionic liquids clearly improved their synthetic activity in supercritical CO 2 by up to six times with respect to the hexane medium, which agrees with the “philicity” between alkyl chain lengths of both the silica support and the cation of ionic liquid.

Ab initio evaluation of primary cyclo-hexane oxidation reaction rates

Abstract: Naphthenes are chemical species that are always present in liquid hydrocarbon fuels and their pyrolysis and oxidation can play an important role in real liquid fuel combustion. In spite of its practical relevance, the chemical kinetics of naphthene pyrolysis and oxidation is not yet thoroughly investigated and there is not a general agreement on the role and rate of several elementary reactions involved. In this paper, the kinetics of the pyrolysis and oxidation of a simple naphthene, namely cyclo -hexane, has been investigated through detailed kinetic modeling. Ab initio calculations were performed to estimate the kinetic parameters of some primary reactions following the oxygen attack to the cyclo -hexane radical. In fact, due to the complex behavior induced by the ring structure of cyclo -hexane, such data were difficult to determine through thermo-chemical methods. Density functional theory (B3LYP/6-31g(d, p)) was adopted to determine structure and vibrational frequencies of transition states and reaction intermediates, while energies were evaluated using the G2MP2 approach. The kinetic parameters of the investigated primary reactions were then introduced in a general detailed kinetic model consisting of elementary reactions whose kinetic constants were taken from the literature. The so obtained kinetic model was used to simulate ignition delay times and species concentrations measured in various experiments reported in the literature. The agreement between experimental data and theoretical predictions shows the validity of the chosen approach and supports the correctness of the proposed kinetic model.

Liquid−Liquid Equilibria for Systems Composed by 1-Methyl-3-octylimidazolium Tetrafluoroborate Ionic Liquid, Thiophene, and n-Hexane or Cyclohexane

Abstract: Liquid−liquid equilibrium data have been determined experimentally for {1-methyl-3-octylimidazolium tetrafluoroborate + thiophene + hexane} and {1-methyl-3-octylimidazolium tetrafluoroborate + thiophene + cyclohexane} ternary systems at 298.15 K. The compositions of the ends of the tie-lines were obtained by gas chromatographic analysis of phases at equilibrium. Data have been adequately correlated using the nonrandom two-liquid (NRTL) activity coefficient model despite this being an equation intended for nonelectrolyte solutions.

Lipase-catalyzed long chain fatty ester synthesis in dense carbon dioxide: Kinetics and thermodynamics

Abstract: Catalytic synthesis of n -octyl oleate by esterification of free fatty acid (FFA) with 1-octanol over immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) was successfully performed using dense carbon dioxide as reaction medium. Process conditions (pressure, temperature, stirrer speed, water concentration, substrates molar ratio and incubation time) were optimised performing experiments in a high-pressure batch stirred tank reactor (BSTR). Experiments were carried out in the operative pressure and temperature ranges 8–30 MPa and 308.15–383.15 K, respectively. Pressure of 10 MPa, temperature of 323.15 K, stirring rate of 300 rpm, fatty acid/alcohol concentration molar ratio 40/60, water concentration of 166.7 μL/g reaction bulk , enzyme concentration of 25 mg/cm 3 and incubation time of 5 h were found to be the optimum reaction conditions. Operating at these conditions a maximum FFA conversion of 88% was attained. A comparison with reactions performed at atmospheric pressure in almost non-aqueous solvent-free medium and in n -hexane was also proposed. It resulted that CO 2 expanded reaction mixture required lower enzyme concentrations, desired at commercial industrial scales, and enhanced the reaction kinetics with respect to the solvent-free system due to decrease of the interphase transport limitations. Higher fatty acid ester (FAE) concentration was also obtained in SC-CO 2 when compared with those attained over n -hexane under identical reaction conditions.

Densities and viscosities of binary mixtures of tributyl phosphate with hexane and dodecane from (298.15 to 328.15) K

Abstract: Densities and viscosities of the binary mixtures of the tributyl phosphate + hexane and tributyl phosphate + dodecane systems have been experimentally determined at different temperatures and atmospheric pressure, over the entire composition range. Other mixing properties such as the excess molar volumes and the viscosity deviations have been also obtained for each of the systems. The excess molar volumes (V (E)) and viscosity deviations (Delta eta) have been fitted to the Redlich-Kister equation, and the coefficients and estimate of the standard error values are presented. A discussion on these quantities in terms of molecular interactions is reported.

Thermodynamic Phase Behavior of Ionic Liquids

Abstract: The phase diagrams of the following imidazolium ionic liquids, {1-ethyl-3-methylimidazolium tosylate [EMIM][TOS] + hexane or cycloheptane} and {1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4] + hexane or benzene}, have been measured. The (solid + liquid) (SLE) and (liquid + liquid) (LLE) phase equilibria of binary mixtures containing {hexyl(2-hydroxyethyl)dimethylammonium bromide (C6Br) + hexane or benzene or an alcohol (ethanol or dodecan-1-ol)} and the salt with a different anion {hexyl(2-hydroxyethyl)dimethylammonium tetrafluoroborate (C6BF4) + hexane or benzene or dodecan-1-ol} have been measured. The effect of anion type (Br- vs BF4-) on the thermophysical properties of the IL and on the phase behavior is dependent on the strength of the cation−anion interaction in the investigated ILs and is noticeable. The phase diagrams for some novel ammonium ionic liquids, (2-decanoyloxyethyl)dimethylpentyloxymethylammonium trifluoro-acetate [C10OOEtC5OMMMN][CF3COO] or (2-methyloyoxyethyl)dimethylpentylox...

GC/MS characterization of mate tea leaves extracts obtained from high-pressure CO2 extraction

Abstract: This work presents a study concerning the chemical characteristics and analytical separation process of the essential oil obtained from high-pressure carbon dioxide extraction of Ilex paraguariensis. The experiments were performed in a laboratory-scale unit in the temperature range of 20–40 °C, from 100 to 250 bar. A blend of the I. paraguariensis extracts was percolated through a preparative chromatographic column, containing silica gel, and successively eluted with 150 mL of each of the following solvents: hexane, toluene, dichloromethane, ethyl acetate, acetone and methanol. The raw extract and its fractions were analyzed by gas chromatography coupled to mass spectrometry detection (GC/MS). The fractionation procedure showed to be a good clean up technique due to the isolation of different classes of compounds in each fraction. Chromatographic analyses allowed the identification of caffeine, fatty acids and esters, phytol, squalene, Vitamin E, stigmasterol derivatives and saturated hydrocarbons.

Effect of fruit ripeness and method of fruit drying on the extractability of avocado oil with hexane and supercritical carbon dioxide

Abstract: BACKGROUND: Oil yield from avocado fruit may be influenced by fruit pre-treatment and extraction method. Unripe and ripe avocado fruit pieces were deep-frozen at − 20 °C and either freeze-dried or oven-dried (80 °C). Oil yield from these samples was determined after extraction with hexane and supercritical carbon dioxide (SC-CO2). The fruit samples were examined using scanning electron microscopy before and after oil extraction. RESULTS: Average oil yield from ripe fruit (freeze-dried and oven-dried combined) was 72 g kg−1 higher than from unripe fruit for SC-CO2 extracts and 61 g kg−1 higher for hexane extracts. This may be due to enzymatic degradation of parenchyma cell walls during ripening, thus making the oil more available for extraction. Freeze-dried samples had a mean oil yield 55 g kg−1 greater than oven-dried samples for SC-CO2 extracts and 31 g kg−1 higher for hexane extracts. However, oil yields from ripe fruit (freeze-dried and oven-dried) subjected to hexane extraction were not significantly different. All hexane extracts combined had a mean oil yield 93 g kg−1 higher than SC-CO2 extracts. CONCLUSION: SC-CO2 may be more selective and may create paths of least resistance through the plant material. Hexane, on the other hand, is less selective and permeates the whole plant material, leading to more complete extraction and higher oil yields under the experimental conditions. Copyright © 2007 Society of Chemical Industry

Effect of solvent exchanging process on the preparation of the hydrophobic silica aerogels by ambient pressure drying method using sodium silicate precursor

Abstract: Experimental results obtained on the preparation of hydrophobic silica aerogels by ambient pressure drying method using the sodium silicate precursor with the variation of solvent exchanging process, are reported The silica hydrogel was prepared by passing the 112 specific gravity sodium silicate through the Amberlite (TM) 120 Na+ resin and addition of 1 M ammonium hydroxide to silicic acid The gel was kept in an oven for 3 h to strengthen the gel Solvent exchange was carried out with ethanol and hexane for 36 h each followed by 24 h silylation using 20% hexamethyldisilazane (HMDZ) in hexane Unreacted HMDZ was washed with hexane by keeping the gel in hexane for 24 h Solvent was decanted and the gel was dried for 24 h by keeping the gel at 50 °C for 6 h, at 150 °C for 12 h and at 200 °C for 6 h The low density (006 g/cm3), highly porous (969%), highly hydrophobic (contact angle of 160°), low thermal conductivity (007 W/m K) aerogels were obtained for the process of three times exchange with ethanol and three times exchange with hexane in 36 h each, followed by silylation with 20% HMDZ in hexane and two times washing with hexane in 24 h FTIR studies showed the increase in the intensity of the Si–H and C–H bands of the aerogels with the increase of solvent exchanging times because of increase in silylation for more times of solvent exchange processes It was found from the TG–DTA studies that the hydrophobicity of the aerogels retained up to the temperature of 325 °C Water absorption studies show that the aerogels were remained hydrophobic up to 4 months when the aerogels were placed over the water as well as for up to 60 h in a 90% humid atmosphere SEMs of the aerogels reveal that the pore sizes of the silica network increased, so the percentage of optical transparency decreased with the increase in exchange times with ethanol and hexane

Lipase-catalyzed synthesis of phenolic lipids from fish liver oil and dihydrocaffeic acid

Abstract: The enzymatic synthesis of phenolic lipids by lipase-catalyzed transesterification of dihydrocaffeic acid (DHCA) with fish liver oil was investigated in a selected organic solvent medium. These synthesized phenolic lipids have potential use as nutraceutical products. Using a molar ratio of 1:8 DHCA to fish liver oil in hexane:2-butanone mixtures of 75:25 and 85:15 (v/v), the lipase-catalyzed reaction resulted in maximum conversion of 55.8 and 65.4%, respectively. The maximum conversion of phenolic monoacylglycerols in hexane:2-butanone mixture of 75:25 and 85:15 (v/v) was 40.3 and 37.7%, respectively; using the same solvent mixtures, the conversions of the phenolic diacylglycerol were 15.8 and 36.8%, respectively. Hexane:2-butanone mixture of 75:25 (v/v) was, therefore, the best organic solvent mixture for the production of phenolic monoacylglycerols, while that of 85:15 (v/v) was best for the production of phenolic diacylglycerols. The phenolic lipids produced from the fish liver oil and DHCA demonstrate...

Multicomponent sorption of hexane isomers in zeolite BETA

Abstract: Breakthrough curves of single, binary, ternary, and quaternary mixtures of hexane (C6) isomers n-hexane (nHEX), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB), and 2,2-dimethylbutane (22DMB) were performed in commercial pellets of zeolite BETA (BEA structure), covering the temperature range between 423 and 523 K and partial pressures up to 30 kPa. From these data, single and multicomponent adsorption equilibrium isotherms were collected. A tri-site Langmuir model (TSL) was developed to interpret the equilibrium data based on considerations about zeolite structure, and a dynamic adsorption model was tested predicting with a good accuracy the behavior of multicomponent fixed-bed experiments. At the partial pressures studied, the sorption hierarchy in the zeolite BETA is nHEX >>> 3MP > 23DMB >> 22DMB. BEA structure demonstrates a significant selectivity between C6 isomers, especially at low coverage, giving a good perspective regarding their separation by adsorption processes. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Can alkane isomers be separated? Adsorption equilibrium and kinetic data for hexane isomers and their binary mixtures on MFI

Abstract: In this study we present a global overview of the adsorption behavior of hexane isomers on MFI. With an experimental approach that couples a manometric technique with Near Infrared (NIR) spectroscopy, which has been recently developed, we did address adsorption kinetic properties of n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane, and their binary mixtures. The adsorption equilibrium properties of the binary mixtures were also assessed using the same technique. Whereas the adsorption isotherms and heats of adsorption for single components have been studied by a manometric technique coupled with a micro calorimeter. The differential heats of adsorption of n-hexane increase slightly with loading, on the other hand the heat of adsorption of branched hexanes exhibits a decrease with loading. The diffusion rates on MFI of n-hexane, 2-methylpentane and 2,3-dimethylbutane are in the same order of magnitude. However, the diffusion rate of 2,2-dimethylbutane is two orders of magnitude lower than rates of the other isomers. In the binary mixtures the components interact and the difference between the diffusion rates of the components decreases. The MFI zeolite presents equilibrium selectivity towards the less branched isomers. In conclusion, a separation process for linear/mono-branched alkanes + double-branched alkanes, has to be based on its equilibrium properties and not based on adsorption kinetics.

Infrared spectroscopy of acetone-hexane liquid mixtures.

Abstract: Acetone and hexane mixtures covering the whole solubility range were studied by Fourier transform infrared attenuated total reflectance spectroscopy. Factor analysis separates the spectra into four principal factor spectra and multiplying factors. Those containing negative factors are abstract, but the spectra are real. A statistical distribution model of the molecules in the solutions rendered the factors real. From these we define the intermediate species that occur in a 1:2 molar ratio of acetone in hexane, present principally in the low acetone concentration regions, and in a 2:1 molar ratio of acetone in hexane, present principally in the higher acetone concentration region. However, except at the concentration range limits where only pure acetone and pure hexane are present, the four species are present over the whole solubility range. The IR spectra of the species indicated very little displacement of the CH stretch bands, HCH deformation bands, and CC stretch bands, although there are some small intensity variations. Most of the modifications are observed on the acetone C=O stretch band. From the gas phase position, a strong bathochromic shift of 19 cm(-1) of the pure liquid is assigned to dipole-dipole interactions. In the 2:1 groupings, the shift that decreases to 15 cm(-1) is due to the diminished dipole-dipole interactions. In the 1:2 groupings, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. In the one acetone to two hexanes grouping, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. From the statistical distribution of the molecules, we determine that mixtures of hexane and acetone form a random organization with no preferred association or complex.

Study of Mechanism for Hexane Decomposition with Gliding Arc Gas Discharge

Abstract: The mechanism of hexane decomposition under gliding arc gas discharge conditions is studied from both qualitative and quantitative analyses of its products for various hexane initial concentrations and different background atmospheres : nitrogen, argon, air (O2 21% N2 79% vol.) and N2–O2 mixtures. The decomposition rate, which decreases with increasing hexane initial concentration, can reach 94% when the carrier gas is air. Due to the electron energy consumed by the dissociation of nitrogen, the decomposition rate of hexane in nitrogen is lower than in argon. The radical channel plays a predominant role in the hexane decomposition process. With increasing oxygen concentration in the carrier gas, the hexane decomposition rate increases and promotes the conversion of CO– CO2, but it also leads to the formation of NO2.