Showing papers on "Hexane published in 2002"

A Study of the Ionic Liquid Mediated Microwave Heating of Organic Solvents

Abstract: The use of ionic liquids as aids for microwave heating of nonpolar solvents has been investigated. We show that hexane and toluene together with solvents such as THF and dioxane can be heated way above their boiling point in sealed vessels using a small quantity of an ionic liquid, thereby allowing them to be used as media for microwave-assisted chemistry. Using the appropriate ionic liquid, the heating can be performed with no contamination of the solvent. To show the applicability of the system, two test reactions have been successfully performed.

Kinetics of the deep oxidation of benzene, toluene, n-hexane and their binary mixtures over a platinum on γ-alumina catalyst

Abstract: In this work, the catalytic oxidation of benzene, toluene and n -hexane in air, both alone and in binary mixtures, over a commercial Pt on γ-alumina catalyst was studied. Studies have been carried out at concentrations of up to 4200 ppmV, in a laboratory fixed-bed catalytic reactor. Results for single compounds show that temperature at which 50% conversion is attained ( T 50 ) increases as concentration increases for benzene and toluene, while the opposite behaviour is observed for n -hexane. Results for mixtures show that, while the presence of n -hexane does not affect the conversion of benzene and toluene, the presence of benzene or toluene inhibits the combustion of hexane, and the aromatic compounds inhibits each other when are reacted together. Results obtained in absence of mass transfer limitations were fit to kinetic expressions: simple Mars–Van Krevelen kinetic expressions for single compounds, and a modified Mars–Van Krevelen mechanism, considering competitive adsorption of the hydrocarbons, for binary mixtures.

Detailed chemical kinetic reaction mechanisms for autoignition of isomers of heptane under rapid compression

Abstract: Detailed chemical kinetic reaction mechanisms are developed for combustion of all nine isomers of heptane (C 7 H 16 ), and these mechanisms are tested by simulating autoignition of each isomer under rapid compression machine conditions. The reaction mechanisms focus on the manner in which the molecular structure of each isomer determines the rates and product distributions of possible classes of reactions. The reaction pathways emphasize the importance of alkylperoxy radical isomerizations and addition reactions of molecular oxygen to alkyl and hydroperoxyalkyl radicals. A new reaction group has been added to past models, in which hydroperoxyalkyl radicals that originated with abstraction of an H atom from a tertiary site in the parent heptane molecule are assigned new reaction sequences involving additional internal H atom abstractions not previously allowed. This process accelerates autoignition in fuels with tertiary C−H bonds in the parent fuel. In addition, the rates of hydroperoxyalkylperoxy radical isomerization reactions have all been reduced so that they are now equal to rates of analogous alkylperoxy radical isomerizations, significantly improving agreement between computed and experimental ignition delay times in the rapid compression machine. Computed ignition delay times agree well with experimental results in the few cases where experiments have been carried out for specific heptane isomers, and predictive model calculations are reported for the remaining isomers. The computed results fall into three general groups: the first consists of the most reactive isomers, including n -heptane, 2-methyl hexane, and 3-methyl hexane. The second group consists of the least reactive isomers, including 2,2-dimethyl pentane, 3,3-dimethyl pentane, 2,3-dimethyl pentane, 2,4-dimethyl pentane, and 2,2,3-trimethyl butane. The remaining isomer, 3-ethyl pentane, was observed computationally to have an intermediate level of reactivity. These observations are generally consistent with knocking tendencies of these isomers, as measured by octane ratings, although the correlations are only approximate.

Vapor-Phase Adsorption of Hexane and Benzene on Activated Carbon Fabric Cloth: Equilibria and Rate Studies†

Abstract: Volatile organic compounds (VOCs) comprise more than 60% of total hazardous air pollutants that are emitted by major industrial point sources. Adsorption by an activated carbon fiber has been recognized as one of the feasible regenerative control processes to separate and recover VOCs for reuse. The adsorption behavior of hexane and benzene in a single-component and in a mixture system onto activated carbon fabric cloth was studied. The adsorption capacities were evaluated using the Langmuir adsorption isotherm model. Depending upon the design of the experiment, we have concluded that internal diffusion controls the adsorption of benzene and n-hexane on activated carbon cloth.

Supercritical fluid extraction and characterisation of oil from hazelnut

Abstract: Hazelnut (Corylus avellana L.) oil was extracted with compressed carbon dioxide in the temperature range of 308—321 K and in the pressure range of 18—23.4 MPa. In addition the influence of the superficial velocity, within a tubular extractor was studied. Physical and chemical characteristics of the oil were obtained. The results including contents of free fatty acids, sterols, triacylglycerols and tocopherols were compared with those obtained when n-hexane was used as solvent. No significant differences were found when the oils extracted by both methods were analysed. The main fatty acid was the oleic acid (83—85%), followed by linoleic acid (6—8%) and palmitic acid (5—6%). The main triglyceride found in hazelnut oils was the trioleylglycerol (OOO) (63.4—69.6%), followed by the linoleyl-dioleylglycerol (LOO) (11.6—15.5%) and palmitoyl-dioleylglycerol (POO) (9.9—10.4%). In terms of sterols, the main component was β-sitos-terol (∼83%) followed by campesterol (∼6%). The amount of cholesterol was very low (∼0.2%). The CO2 extracted oil contained about 17% more tocopherols (458.7 μg/g oil) than the oil extracted by n-hexane (382.8 μg/g). Oxidative stability was studied by using the induction time determined by the Rancimat method. The oil obtained by supercritical fluid extraction (SFE) was slightly more protected against oxidation (8.7 h for SFE extracted oil and 6.7 h for the hazelnut oil extracted with n-hexane). Both oils presented high stability index values (7.81 for the oil extracted by n-hexane and 8.7 for the oil extracted with supercritical CO2). Oil extracted by supercritical CO2 was clearer than the one extracted by n-hexane, showing some refining. Besides, the acidity index was 1.6 for the n-hexane extracted oil and 0.9 for the oil extracted with supercritical carbon dioxide. The central composite non-factorial design was used to optimise the extraction conditions, using the Statistica, version 5 software (Statsoft). The best results, in terms of recoveries of hazelnut oil by SFE, were found at 22.5 MPa, 308 K and superficial velocity of 6.0 × 10—4 ms—1.

Direct cryogenic-temperature transmission electron microscopy imaging of phospholipid aggregates in soybean oil.

Abstract: Cryogenic-temperature transmission electron microscopy (cryo-TEM) was fine-tuned to make it applicable to the study of a natural oil-based system. While liquid ethane, the cryogen of choice for specimen preparation, was found to dissolve the oil, we observed that the triglycerides found in many natural oils serve as cryoprotectants that allow vitrification of such oil systems in liquid nitrogen, a cryogen that provides relatively low cooling rates. Using the modified technique combined with digital imaging by a cooled CCD camera, we were able to directly visualize inverse micellar and liquid-crystalline aggregates formed in the soybean oil/soybean phospholipids/water/hexane system, which is commercially important in soybean oil processing. The method developed here should be widely applicable to other organic solvent-based systems.

Characterisation and Process Development of Supercritical Fluid Extraction of Soybean Oil

Abstract: This work describes and analyses the extraction of soybean oil using supercritical carbon dioxide as a solvent from the point of view of both operative method and pre-treatment of the raw material. The best conditions for soybean oil extraction were obtained at a pressure of 300 bar, a temperature of 40 � C and a solvent flow rate of 1.8 L/min at STP. The yields obtained using the supercritical fluid under the best operating conditions were similar to those obtained byconventional extraction methods using hexane as the solvent (19.9 %w/w.); furthermore, the qualityof oil extracted bythe supercritical fluid was higher (acidity, 0.8). The fatty acid composition of the soybean seed oil extracted by supercritical fluid was particularlyrich in unsaturated fattyacids, particularlylinoleic acid (51.8%). For these reasons, the soy bean seed oil extracted using supercritical carbon dioxide could compete with that obtained bythe conventional process, since the oil refinement stages are simplified significantlyand the solvent distillation stage is completelyremoved, which are the two most costlyprocessing stages in terms of energyconsumption.

Impact of Extraction Method on Yield of Lipid Oxidation Products from Oxidized and Unoxidized Walnuts

Abstract: The objective of this study was to measure and compare differences in oxidized products of oil extracted from unoxidized and oxidized walnuts using five different extraction methods: (i) mechanical pressing, or solvent extraction with (ii) hexane, (iii) methylene chloride, (iv) chloroform/methanol, or (v) supercritical carbon dioxide (SC−CO2). Of the extraction methods evaluated, only chloroform/methanol and methylene chloride provided reasonable results for all parameters measured (total lipid yield, FA profile, PV, conjugated dienes, FFA content, and volatile content); however, chloroform/methanol extracted significantly greater levels of volatile compounds. The SC−CO2 extraction with purified gas was simple and accurate for all data except collection of volatile compounds, as these materials are lost during the lipid extraction. Pressing was neither quantitative nor qualitative, and hexane extraction retrieved significantly lower levels of volatiles than the other methods, except for SC−CO2.

Effect of Organic Additives on the Onset of Asphaltene Precipitation

Abstract: Onset of solid precipitation from oils was determined by identifying the minimum in near-infrared absorbance. Solvent-induced precipitation typically causes asphaltene precipitation, but is also known to cause high-molecular-weight waxes to come out of solution. The effects of the addition of solid saturated and unsaturated compounds on the onset of solvent-induced precipitation from a crude oil were examined. Crude oil from Rangely, an oil field in northwestern Colorado was used. The solvent-induced precipitation was brought about using pentane, hexane, and heptane. On the basis of limited solvent carbon number investigated (5−7), less solvent was required for precipitation onset as the carbon number of alkanes decreased. As the flow rate of the precipitant increased, the onset was delayed. Addition of solid n-alkanes, such as eicosane and tetracosane to the oil initially, accelerated the onset of precipitation. When solid polyaromatic compounds (naphthalene and phenanthrene) were dissolved in the oil, m...

Electrokinetic Study of Hexane Droplets in Surfactant Solutions and Process Water of Bitumen Extraction Systems

Abstract: The effect of surfactant and inorganic salts on the electrokinetics of bitumen and model oil (hexane) in aqueous solution was studied. The zeta potentials of the hexane droplets became less negativ...

Separation of oil constituents in organic solvents using polymeric membranes.

Abstract: Different types of commercial nonporous (reverse osmosis and gas separation) polymeric membranes were screened for their abilities to separate FFA, MG, DG, and TG from a lipase hydrolysate of high-oleic sunflower oil after diluting it with organic solvents (ethanol and hexane). Cellulose acetate (CA) (NIR-1698) membrane gave the largest difference in rejection between FFA and glycerides and high flux in oil/ethanol mixtures. In the hexane system, the values of permeate flux and rejection were generally lower than those in the ethanol system. The silicone-polyimide composite membrane (NTGS-2100) gave the highest flux and rejections of solutes (70.2% for FFA, 94.4% for TG) in oil/hexane mixtures. In the ethanol system with the CA membrane, TG had the highest rejection (98%) followed by DG (90%) and MG and FFA (50–70%) when the oil concentration was varied from 6.3 to 45.8%. A discontinuous diafiltration process (16 batches) using the CA membrane with ethanol changed the composition of the oil from 31∶28∶9∶32 TG/DG/MG/FFA to 65∶30∶1∶4. The results of this study showed that oil constituents can be separated in suitable solvents using appropriate nonporous membranes.

Vapor−Liquid Equilibrium of the Ternary System Ethyl Acetate + Hexane + Acetone at 101.32 kPa

Abstract: Experimental isobaric vapor−liquid equilibrium data at 101.32 kPa for the ternary system ethyl acetate + hexane + acetone and for its constituent binary systems are reported. These data were found to be thermodynamically consistent and were satisfactorily correlated with the Wilson, NRTL, and UNIQUAC equations. They were also compared with predictions of the ASOG and UNIFAC group contribution methods.

Influence of operating variables on yield and quality parameters of olive husk oil extracted with Supercritical carbon dioxide

Abstract: Supercritical fluid extraction is a viable alternative process for extracting oil from olive husk, a residue obtained in the olive oil production. We analyzed the effects of pressure (P) (100–300 bar), temperature (T) (40–60°C), solvent flow (1–1.5 L/min), and particle size (D) (0.30–0.55 mm) on extraction yield, and three oil-quality parameters: acidity (OA), PV, and phosphorus content (PC). A response surface methodology based on the statistical analysis of the experimental data permitted us to obtain mathematical expressions relating the operational variables and parameters studied. At the best extraction condition of the experimental range analyzed (P=300 bar, T=60°C, D=0.30 mm, and solvent flow=1.25 L/min at standard conditions), the oil yield was 80% (w/w) with respect to hexane extraction, whereas the quality parameters OA, PV, and PC were 14% (w/w), 8 meq/kg, and 2.3·10−3% (w/w), respectively. These results were compared to those obtained by hexane Soxhlet extraction. The quality of the supercritical extract was superior, requiring only simple refining. This advantage may result in improved economics of the supercritical process in relation to the conventional extraction with hexane.

Estrogenic Activities of Chemicals in Diesel Exhaust Particles

Abstract: In a previous study, we focused on estrogenic activity of the hexane extract of diesel exhaust particles (DEP) The extract of hexane was first fractionated to acidic, phenolic and neutral portions according to their chemical properties, of which the neutral fraction was fractionated by column chromatography on silica gel The chemical structures of compounds in these fractions were then analyzed It was found that the neutral fraction of the hexane extract of DEP contains dibenzothiophene derivatives, one of which, 4,6-dimethyldibenzothiophene, possesses estrogenic activity

Isopropyl alcohol extraction of cottonseed collets: efficiency and performance

Abstract: Isopropyl alcohol (IPA) is one of the most favorable alternatives to hexane for oil extraction. Compared to hexane and other solvents such as ethanol, IPA is less flammable and less toxic and is free of restrictive governmental regulations. Thus, the effects of collets versus flake with hexane and IPA as extraction solvents at various alcohol concentrations (88, 93, 95 and 97% IPA levels) were examined. Cottonseed meats were flaked and cooked before they were processed using a Hivex expander. The solvent extractions were carried out using a seven-stage countercurrent laboratory extraction unit. Extractability of collets with 95% IPA was better than that of flakes. The residual oil content and solvent hold-up of the collets were 1.6 and 33.0% compared 4.5; and 53.2% for the flakes, respectively. The aqueous IPA extraction proceeded more slowly and showed a lower oil carrying capacity than that of hexane. The residual oil content of the cottonseed collets extracted with hexane was 1.2% while the solvents containing 97, 93, and 88% IPA resulted in 1.5, 1.9, and 2.4%, respectively. Reduction in water content improved the extraction efficiency of IPA.

Liquid−Liquid Equilibria for Methanol + Water + Hexane Ternary Mixtures

Abstract: Liquid−liquid equilibria for methanol + water + hexane ternary mixtures were measured at (298.15, 308.15, and 318.15) K under atmospheric pressure. The reliability of the experimental tie-line data was determined through the Othmer−Tobias plots. Such data were essential for the product separation and solvent recycling in the process of methanol synthesis under supercritical conditions using hexane as the solvent.

Destruction of carbon tetrachloride in the presence of hydrogen-supplying compounds with ionisation and catalytic oxidation

Abstract: Catalytic combustion with and without pre-catalytic actions (i.d., ionisation/ozonisation (I/O)) of tetracloromethane (CCl 4 ) over alumina-supported copper-chromite (Cu-Cr) and manganese (Mn) dioxide catalysts with and without the presence of hydrogen-rich compounds, i.e. n -hexane and toluene, was evaluated. Experiments were performed at conditions of lean carbon tetrachloride (CCl 4 ) concentration (from 500 to 3000 ppm V) in excess air, between 100 and 500 °C in a continuous reaction line at laboratory scale. n -Hexane and toluene were added to the feedstream in variable concentration, between 100 and 500 ppm V. Ionisation/ozonisation of pure CCl 4 streams and of streams of hexane or toluene admixtures showed the efficiency of the hydrogen donor role of the hydrocarbons on CCl 4 conversion. The tests of ionisation/ozonisation were performed at different residence times in the ionisation reactor and a rate equation with second-order in CCl 4 concentration was found to represent the ionisation process. Over Cu-Cr and Mn catalysts, both n -hexane and toluene improved the CCl 4 combustion when added at low concentration (ca. 300 °C) but inhibited it when they were present at high concentration (ca. 350 °C). Catalytic combustion assisted with ionisation process enhanced CCl 4 conversion at low temperatures in comparison with conventional catalytic combustion (e.g. 90% of 1000 ppm V of CCl 4 –hexane mixture was converted on Cu-Cr at 250 °C and 5000 h −1 by the combined actions of catalytic and ionisation processes). Selectivity to CO 2 was controlled on the two catalysts. Mn was more active but less selective than Cu-Cr catalyst. Various oxygenated and chlorinated by-products, in particular COCl 2 , were formed during ionisation of CCl 4 streams. By-products were greatly reduced and COCl 2 disappeared at 250 °C on catalysts.

Liquid-liquid equilibria for acetic anhydride + selected alkanes

Abstract: Liquid−liquid equilibria (LLE) temperatures for systems of acetic anhydride with hexane, heptane, octane, decane, cyclohexane, and methylcyclohexane have been measured between 314 K and the upper c...

Liquid-liquid equilibria for binary systems containing N-formylmorpholine

Abstract: Liquid−liquid equlilibrium (LLE) data were measured for four binary systems containing N-formylmorpholine and alkanes (i.e. pentane, hexane, heptane, and octane) over the temperature range 298 K to 413 K using circulation type equipment with an equilibrium view cell. The compositions of both light and heavy phases were analyzed by on-line gas chromatography. The mutual solubility increased as the temperature increased for all these systems. The binary liquid−liquid equilibrium data were correlated with the NRTL and UNIQUAC equations using temperature-dependent parameters. Both models correlate the experimental data well. The solubility in N-formylmorpholine increased in the following order at the same temperature: pentane, hexane, heptane, and octane.

Liquid-liquid equilibrium of the castor oil + soybean oil + hexane ternary system

Abstract: Liquid−liquid equilibria for the ternary system castor oil + soybean oil + hexane are studied at 298.15 K. Mixtures are equilibrated in a temperature-controlled water bath. After evaporation of hexane, the oil compositions of each phase are determined by a combination of gravimetric measurements and the analysis of fatty acid methyl esters (FAMEs) using gas chromatography. Since castor and soybean triglycerides are a mixture of five or six fatty acids, the castor and soybean fractions are characterized by the relative concentration of ricinoleic acid. Fitting the K-ratios for castor oil, soybean oil, and hexane smoothed the liquid−liquid equilibrium data. A computational cross-flow extraction is designed on the basis of the smoothed phase diagram and is experimentally validated.

Limiting Activity Coefficients of Lower 1-Alkanols in n-Alkanes: Variation with Chain Length of Solvent Alkane and Temperature

Abstract: Limiting activity coefficients ( ) of lower 1-alkanols (methanol, ethanol, 1-propanol, 1-butanol) in n-alkanes (hexane, heptane, octane, decane, dodecane, tetradecane, hexadecane) were systematically determined to obtain reliable information about their variation with the chain length of solvent alkane and temperature. Using the inert gas stripping technique, values were determined at 293.15 K and for methanol and ethanol in hexane, heptane, and octane at 5 K increments between 288 K and 323 K. The present data appear to be of higher accuracy than most previous measurements and are shown to be consistent with the solution-of-groups concept, the modified Flory−Huggins combinatorial of Kikic et al., and the calorimetric information on limiting partial molar excess enthalpies.

Sorption kinetics of selected volatile organic compounds in humin

Abstract: Each component of the chemically heterogeneous soil exhibits a unique sorption behavior toward organic sorbates. The sorption kinetics of some volatile organic compounds (VOCs) in pressed humin disks was investigated by tracking the weight change of the disks with a microbalance. Higher sorbing capacity for more polar VOCs as well as C13 nuclear magnetic resonance data indicates that humin was more hydrophilic than Aldrich humic acid (Milwaukee, WI, USA). The apparent diffusivity of acetone, toluene, and hexane in the disks ranged from 10−8 to 10−10 cm2/s. The sorbed toluene in humin does not seem persistent to desorption; however, acetone and hexane, either as polar or linear compounds in humin, show persistence against desorption. On completion of the desorption experiments, there were approximately 35 and 20% sorbate residue for acetone and hexane, respectively.

Oil fractionation as a preliminary step in the characterization of vegetable oils by high-resolution 13C NMR spectroscopy

Abstract: One hundred nine oil samples were separated chromatographically to obtain oil fractions with a decreased TAG content but with enhanced levels of the minor components that define oil genuineness and quality. The oils, which included virgin olive oils from different cultivars and regions of Europe and north Africa and refined olive, “lampante” olive, refined olive pomace, hazelnut, rapeseed, high-oleic sunflower, corn, grapeseed, soybean, and sunflower oils, were fractionated on a silica gel column with hexane/diethyl ether as the mobile phase eluent. The method was highly reproducible, and the fraction obtained contained about 15% unmodified TAG and 85% polar compounds, which included polymeric TAG, oxidized TAG, DAG, MAG, and FFA, in addition to other minor polar components of the oils. The presence of these compounds, in an enriched fraction, should provide information about the thermal, oxidative, and hydrolytic alterations of the oils, as well as many compounds of interest in determining oil genuineness. The results indicate that these fractions can provide more information than the original oils for NMR or other spectroscopic studies used in the determination of oil quality.