Showing papers on "Hexane published in 2003"

Critical properties of binary and ternary mixtures of hexane+methanol, hexane+carbon dioxide, methanol+carbon dioxide and hexane+carbon dioxide+methanol

Abstract: Critical properties of both binary mixtures (hexane + methanol, hexane + carbon dioxide, and methanol + carbon dioxide) and a ternary mixture (hexane + carbon dioxide + methanol) were measured by using a high-pressure view cell with visual observation. The critical lines of the binary mixtures are continuous over the whole composition range between the critical points of the two pure components. The critical pressure of the binary mixtures of hexane + carbon dioxide and methanol + carbon dioxide shows a maximum, while the critical temperature of the binary mixture of hexane + methanol shows a minimum with the composition.

Comparison between ethanol and hexane for oil extraction from Quercus suber L. fruits

Abstract: The aim of this study was to (i) evaluate the feasibility of replacing n -hexane with ethanol for the extraction of oil from Quercus suber fruits and (ii) optimize, at lab scale, sample preparation and extraction time for both solvents used ( n -hexane vs . anhydrous ethanol). For both solvents, the effect of the conditioning process on extraction yield was evaluated. Therefore, a full factorial design was used as a function of four variables: dehulling (with vs . without husks), and thermal treatment of the crushed material (40oC vs . 75oC), at different times (5 min vs . 120 min) and pressures (10 kPa vs. 100 kPa). Higher oil yields were obtained with n -hexane when dehulled fruits were conditioned under atmospheric pressure. Better yields were obtained with n -hexane, when dehulled material was treated at 75oC for 90 min. Ethanol was not adequate for oil extraction from Quercus fruits, since other materials rather than oil were also extracted.

Electron spectroscopy of sulfated zirconia, its activity in n-hexane conversion and possible reasons of its deactivation

Abstract: Sulfated zirconia catalysts were prepared and characterized by X-ray photoelectron spectroscopy taken in the dried state (fresh) and after calcination at 900 K (calc.). A maximum activity was observed as a function of the calcination temperature. The Zr 3d region showed that any Zr hydroxide in the dried catalyst transformed into zirconium oxide upon calcination. The O 1s peak could be fitted by two components corresponding to ZrO 2 and sulfate, respectively. Sulfur was present as sulfate. Both catalysts showed activity in n -hexane conversion (including isomerization) between 300 and 473 K. The activity of the calcined catalyst was much higher. The main products were isopentane and isobutane, along with 2-methyl- and 3-methylpentane. The activity was not stable and only a limited amount of n -hexane transformed before final deactivation. This observation pointed to a limited amount of active sites able to start the reaction. The activity could be fully regenerated by oxygen treatment. Thus, the “oxidative” start of the reaction [ A. Ghenciu, D. Farcasiu, Catal. Lett. 44 (1997) 29] may have also played a role apart from those on strong acid sites. Deactivation may have been due to a partial reduction of sulfate groups rather than to carbon accumulation, as shown also by the minor amounts of S 4+ detected by XPS. Parallel isomerization and splitting of hexane into two C 3 units may occur, followed by the formation of surface C 9 units, the latter being intermediate of larger fragments.

The effects of dense carbon dioxide on nickel plating using emulsion of carbon dioxide in electroplating solution

Abstract: This paper discusses the effects of dense carbon dioxide (CO 2 ) on the nickel film obtained in an agitated ternary system of dense CO 2 and an electroplating solution with a non-ionic surfactant. On the basis of the transport properties of dense CO 2 and hexane discussed within, it was found that both the low viscosity of dense CO 2 and its good miscibility with hydrogen play an important role for achieving the higher uniformity and a smoother surface formation of nickel film.

Viscosities and densities of binary mixtures of hexane with 1-chlorohexane between 293.15 K and 333.15 K

Abstract: The density and viscosity values of binary mixtures of hexane with 1-chlorohexane have been measured as a function of composition and temperatures between 293.15 K and 333.15 K. The estimated uncertainties are less than ±1 × 10-4 g·cm-3 for density and ±0.5% for viscosity. Viscosity deviations Δη were fitted by the Redlich−Kister equation.

A Comparison Between the Oil, Hexane Extract and Supercritical Carbon Dioxide Extract of Juniperus communis L.

Abstract: Volatile compounds from the berries of common juniper (Juniperus communis L.) were isolated by hydrodistillation, hexane extraction and supercritical CO2 extraction. The hydrodistillation yield was 2.17%, the hexane extraction yield 5.31 % and supercritical CO2 extraction yield 0.96%. Their compositions were compared using GC/M S as the method of analysis. Analyses reveal that samples differ quantitatively and qualitatively. The concentrations of monoterpene hydrocarbons (α-pinene, sabinene, myrcene) were higher in the hydrodistilled oil, while some less volatile compounds were present in extracts, especially in the hexane extract.

Solubilities of n-Alkanes (C6 to C8) in Water from 30 °C to 180 °C

Abstract: A solid-phase extraction method has been developed for measuring low solubilities of hydrocarbon in water. The solubilities of hexane, heptane, and octane in water were determined at temperatures ranging from (30 to 180) °C. The solubilities of alkanes in water at 30 °C decrease with increasing carbon number. At 30 °C, the mole fraction solubility is (2.06 ± 0.01) × 10-6 for hexane and (0.120 ± 0.002) × 10-6 for octane. The temperature effect on solubility in water is much more important for octane than for hexane. Increasing the temperature from (30 to 180) °C increases the solubilities by a factor of 23 for hexane and 110 for octane.

Speed of Sound of Hexane + 1-Chlorohexane, Hexane + 1-Iodohexane, and 1-Chlorohexane + 1-Iodohexane at Saturation Condition

Abstract: Speed of sound for the binary mixtures hexane + 1-chlorohexane, hexane + 1-iodohexane, and 1-chlorohexane + 1-iodohexane has been measured as a function of composition and temperature along the saturation line between 293.15 K and 373.15 K. Nonlinear behavior is observed with temperature and concentration. The experimental results are correlated with polynomial equations of the second power.

Surface Characterization of PBO Fibers

Abstract: We report on the surface characterization of commercial poly(p-phenylene benzobisoxazole) (PBO) fibers. Several solvents (hexane, acetone, and ethanol) were employed to remove the sizing present on the fiber surfaces. The surface properties of the different samples were studied by means of inverse gas chromatography (IGC) at infinite dilution using nonpolar n-alkanes and molecules with different acid−base characteristics (benzene, pyridine, acetonitrile, nitromethane, tert-butyl alcohol). Complementary information was obtained by using thermogravimetric/differential thermal analysis (TG/DTA) and atomic force microscopy (AFM). Results showed that, whereas the sizing of high-modulus (HM) fibers can be gradually washed off as the polarity of the solvent increases, only ethanol washing allowed to detect changes in the surface characteristics of PBO as-spun (AS) fibers, with hexane and acetone having little or no effect. In fact, it is believed that the effect of any coating applied eventually to the PBO AS fi...

Continuous monitoring the oxyfunctionalization of hexane by aqueous H2O2 over TS-1 related catalysts

Abstract: The title reaction was studied over three TS-1 type catalysts at atmospheric pressure and at temperatures from 40 to 60 °C. By monitoring the consumption of H 2 O 2 continuously we found that the selective oxidation of n -hexane to 2- and 3-hexanols and -hexanones proceeds usually faster than previous experiments suggest, but the reaction stops before reaching total hydrocarbon conversion despite ample H 2 O 2 supply. One of our catalysts permitted >99% H 2 O 2 utilization even in the absence of any homogenizing co-solvent. This material has an MFI structure but does not show significant UV absorption near 48,000 cm −1 , which is a benchmark of the isomorphously substituted TS-1. Our other TS-1 catalyst, with a strong UV band near 48,000 cm −1 , promoted the oxidation of n -hexane by aqueous H 2 O 2 best in the presence of methanol. The hydroxyl content of catalysts and their Ti 4+ coordination were compared by dispersive Raman and Fourier transform (FT) mid-infrared (MIR), near infrared (NIR), and UV spectroscopy. Spectra of hydrated and dehydrated samples were scanned from 900 to 52,000 cm −1 in a single DRIFT cell before and after in situ dehydration at ∼10 −3 Pa pressure at temperatures from 25 to 400 °C. High-resolution FT-UV measurements indicated an array of charge transfer transitions for Ti 4+ ions in every sample.

Reactivity of GaX3 with silylamines and thermal decomposition of the compounds [Cl2Ga{NH(SiMe3)}]2 and [Cl3Ga{NH(SiMe3)2}]

Abstract: The Lewis acid/base adducts [X3Ga{NH(R)(R′)}] (X = Cl, R = R′ = SiMe3 (1), SiMe2Ph (2) and R = But, R′ = SiMe3 (3); X = Br, R = R′ = SiMe3 (4) or SiMe2Ph (5)) were synthesised by the 1 ∶ 1 reaction of GaX3 with NH(R)(R′) in hexane solution at room temperature. Dimeric complexes, of the type [X2Ga{NH(R)}]2 (X = Cl, R = SiMe3 (6), R = SiMe2Ph (7) and R = But (8); X = Br, R = SiMe3 (9)) were prepared by the 1 ∶ 1 reaction of GaX3 with NH(R)(R′) in CH2Cl2 solution. Compounds 1 and 8 have been structurally characterised. Polycrystalline GaN was obtained from the pyrolysis of compounds 1 and 6 under inert conditions (N2, vacuum) above 500 °C, as shown by the X-ray powder diffraction patterns.

Direct sampling of orujo oil for determining residual hexane by using a chemsensor

Abstract: Hexane is used to extract edible oils from oleaginous seeds. The detection of hexane in orujo oil is mandatory, as its presence in the final product may negatively affect human health. Headspace-GC is the technique of choice for determining residual solvent in foods. In the present work, a new instrument based on the headspace principle and mass spectrometric detection without chromatographic separation, ChemSensor, is proposed for the direct screening of orujo oil to determine residual hexane. This instrument provided an overall response, corresponding to the volatiles profile, including that of hexane, which could not be directly discriminated. By selecting the m/z values corresponding to n-hexane (major component of commercial hexane), the selectivity of the method was good enough to determine residual hexane in the range of 2.0–65 μg mL−1 (corresponding to 2.3–75.6 mg of hexane per kg of oil) with high precision. The detection limit achieved (0.7 mg per kg of oil) was lower than the maximum residual limit established by the European Union (5 mg per kg of oil). Two multivariate techniques, partial least squares and principal components regression (PCR), were compared with univariate regression; PCR provided the best results.

Synthesis of butyl rubber in hexane using a mixture of Et2AlCl and EtAlCl2 in the initiating system

Abstract: A method was studied to obtain butyl rubber in hexane at −75 and −60°C using a mixture of a major amount of diethylaluminum chloride and a minor amount of ethylaluminum dichloride in the initiating system. The Jaacks method was used to determine the monomer reactivity ratio of isobutylene in copolymerization with isoprene in hexane at −75°C with the above initiating system; rIB = 1.54 ± 0.06. This value was different from a literature value rIB = 1.08 when just EtAlCl2 was used in hexane at −80°C. The mixture of both alkylaluminum chlorides in the initiating solution was subsequently directly activated with minute amounts of water or methylaluminoxane (MAO). The use of the modified initiators resulted in higher molecular weights, higher degrees of conversion, and higher isoprene contents in the butyl rubber. At the same time, temperature control was good during polymerizations. With modified alkylaluminum halides, the monomer reactivity ratio of isobutylene in copolymerization with isoprene in hexane at −75°C was close to unity, similar to the reported case with just EtAlCl2. The system activated with MAO made it possible to synthesize butyl rubber in hexane at −60°C having main characteristics typical of commercial butyl rubber manufactured in methyl chloride at −95°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2360–2364, 2003

1 H-NMR Spectroscopy Study of Oleic Acid and Methyl Oleate Ozonation in different reaction conditions

Abstract: Reactions of ozone with oleic acid or methyl oleate were carried out in presence of hexane, carbon tetrachloride, ethanol or water. All the reaction mixtures were studied by 1 H - Nuclear Magnetic Resonance Spectroscopy ( 1 H-NMR). Differences in the composition of the reaction mixture of the samples by 1 H-NMR analysis were found. During the ozonation of oleic acid, the acyl-oxy-alquil-hydroperoxides were formed as major products in all the studied conditions. Nevertheless, during ozonation of methyl oleate, a striking dependence of reaction products with the solvent or additive used was found. In hexane, the corresponding ozonides/oligomers were obtained, whereas when ethanol is present, the ethoxy-hydroperoxides were the major products. The analysis in the presence of water only reveals the aldehyde and ozonides/oligomers signals. These results are discussed taking into account the Criegee mechanism, the characteristic of the bubbling reactor employed, and some properties of the solvents or additives used.

Modifications of fullerenes extractions and chromatographies with different solvents

Abstract: In the Bucky System II, based on electrical arc method, carbon soot was produced. Fullerenes C60 and C70 were Soxhlet extracted from the collected soot samples with toluene, chlorobenzene and with both of them successively, modifying the original methods. The yields of the both obtained toluene extracts were 5.4%. Chlorobenzene extract yield was 5.8%. After extraction of toluene insoluble soot with chlorobenzene, the entire extract yield was increased from 5.4% to 5.8%, due to modification of the existing methods. The difference of fullerenes solubilities in these solvents has been concluded. In the second part of our work toluene and chlorobenzene fullerenes extracts were separated by column chromatographies on active Al2O3, modifying the existing methods, by elution with hexane and mixtures of benzene, toluene, or xylene with hexane in determined ratios and orders. Identifications of buckminsterfullerene C60 in the first chromatographically purified fractions were achieved by electron impact io...

A method for the separation of the letrozole precursor 4-‘1-(1,2,4-triazolyl) methyl!benzonitrile from its 1,3,4-triazolyl isomer

Abstract: A chemical method for the separation of letrozole precursor 4-[1-1,2,4-triazolyl)methyl]benzonitrile of formula (I) from the isomeric unwanted byproduct 4-[1-(1,3,4-triazolyl)methyl]benzonitrile of formula (II) of the reaction in which it is produced, which comprises (a) Preparing an isomeric mixtures of the compounds of formula (I) and (II) by conventional methods. (b) Dissolving the resultant crude isomeric mixture in dichloro methane (or) chloroform. (c) Adding 10-14% isopropylalcohol hydrochloride (IPACHI) to the resulting solution. (d) Adding isopropyl ether to precipitate undesired isomer is hydrochloride form. (e) Filtering off the undesired isomer hydrochloride. (f) Distilling off the filtrate completely. (g) Adding dilute sodium hydroxide solution and dichloromethane to the residue to liberate required isomer base of the formula (I). (h) Evaporating the separated dichloromethane layer and charging hexane or petroleum ether. (i) Centrifuging the resultant product of the formula (I) and washing with hexane or petroleum ether.

Extraction of Europium(III) into W/O Microemulsion Containing Aerosol OT and a Bulky Diamide. I. Cooperative Effect

Abstract: The extraction of Eu(III) from aqueous HNO3 solution into a water‐in‐oil (W/O) microemulsion occurring in hexane was studied. Aerosol OT (AOT−) was used as an anionic surfactant, and a bulky diamide (DA), N,N ′‐dioctyl‐N,N ′‐dimethyl‐2‐(3′‐oxapentadecyl)propane‐1,3‐diamide, was employed as an electrically neutral extractant. The combination of AOT− and the DA shows a very strong cooperative effect on the metal extraction. The microemulsion containing AOT− alone in hexane, equilibrated with the acidic solution, is unstable. However, in the presence of the electrically neutral extractant acting as a “masking” ligand to H+, the microemulsion in the hexane phase is dramatically stabilized, which enhances the distribution of Eu(III) to the organic phase. The distribution of the metal in the micellar extraction system is also greatly affected by the concentration of an electrolyte, such as HNO3 or NaNO3, playing two important roles, i.e., the formation of the microemulsion, “promoting” the metal extrac...

Dissociation equilibrium of dinitrogen tetroxide in organic solvents: An electron paramagnetic resonance measurement

Abstract: The dissociation equilibrium of N2O4−NO2 has been measured in hexane, carbon tetrachloride and chloroform at different temperatures. The equilibrium constants at 298.15 K (25°C),K m (molality basis), are 3.5·10−5 in hexane, 5.9·10−6 in carbon tetrachloride and 5.3·10−6 in chloroform. The EPR technique has been used to quantify the NO2 radical. These data are compared with gas-phase and solution data of previous reports. The applicability of Hildebrand and Scatchard theory of solutions is also discussed and some thermodynamic properties are deduced, such as Henry’s N2O4 and NO2 constants in different solvents.

In-house validation of an improved sample extraction and clean-up method for GC determination of isomers of nervonic acid in meat products

Abstract: An improved extraction and clean-up method for determination of brain-specific fatty acids, in particular lignoceric acid (C24:0) and the cis / trans isomers of nervonic acid (15 c-t C24:1), in meat products has been developed. The method is based on isolation of the polar lipids of interest from the bulk lipids by solid-phase extraction. The fatty acids, derivatised to their fatty acid methyl esters, are quantified by GC in a DB5 column. Fresh meat samples were extracted by using a mixture of n -butanol:hexane (1:9) as solvent. The extract was loaded in a silica gel cartridge column previously equilibrated with hexane. The first fraction containing the major part of the fat was eluted with hexane while acetone and methanol allowed the elution of fatty acids bound to polar moieties such as nervonic and lignoceric acids. This second fraction containing the analyte was methylated and injected into the GC for quantification after addition octacosane (C28) as internal standard.