Showing papers on "Hexane published in 1996"

Comparison of isopropanol and hexane for extraction of vitamin E and oryzanols from stabilized rice bran

Abstract: The effects of solvent-to-bran ratio (2∶1 and 3∶1, w/w), extraction temperature (40 and 60°C), and time (5, 10, 15, 20, and 30 min) were studied for hexane and isopropanol extraction. Increasing the solvent-to-bran ratios and extraction temperature increased the amounts of crude oil, vitamin E and oryzanol recovered for both solvents. An extraction time of 15 min was sufficient for optimum crude oil, vitamin E, and oryzanol extraction. Preheated isopropanol (3∶1 solvent/bran ratio and 60°C) extracted less crude oil (P .05) relative to preheated hexane. The data suggest that isopropanol is a promising alternative solvent to hexane for extraction of oil from stabilized rice bran.

Analysis of Polar Cholesterol Oxidation Products: Evaluation of a New Method Involving Transesterification, Solid Phase Extraction, and Gas Chromatography

Abstract: Monitoring cholesterol oxidation products is important in the evaluation of the potential health risks associated with lipid oxidation. In the present study, a method allowing quick and reliable analysis of polar cholesterol oxidation products was evaluated. After Soxhlet-lipid extraction, the fat was transesterified under mild conditions, thereby minimizing degradation and allowing determination of the free and esterified cholesterol oxides. Sample fractionation was achieved with aminopropyl solid phase extraction cartridges and a stepwise elution with hexane, hexane/methyl tert-butyl ether, and acetone to separate polar cholesterol oxides from cholesterol and other lipid products. Further analysis of the trimethylsilyl derivatives was performed by gas chromatography with detection by flame ionization or mass spectrometry. A phytosterol oxide such as sitosterol α-epoxide (24α-ethyl-5α,6α-epoxycholestan-3β-ol) was employed for the first time as an internal standard for the quantification of cholesterol ox...

Ambient‐temperature extraction of rice bran oil with hexane and isopropanol

Abstract: Hexane and isopropanol were compared as solvents for use in ambient-temperature equilibrium extraction of rice bran oil (RBO). Isopropanol was as effective as hexane in extracting RBO when 20 mL of solvent was used to extract 2 g of bran. Free fatty acid levels were 2–3% in both solvents and similar to that previously reported for hexane extraction of RBO hexane extraction by this method. Larger-scale extractions with 30 g of bran and 150 mL of solvent produced oil with a similar free fatty acid content and a phosphorus level of approximately 500 ppm. The oil extracted with isopropanol was significantly more stable to heat-induced oxidation than hexane-extracted oil. Antioxidants that are more easily extracted by isopropanol than hexane may be responsible for the increased stability.

Solute–solvent and solvent–solvent interactions in binary solvent mixtures. Part 5. Preferential solvation of solvatochromic indicators in mixtures of propan-2-ol with hexane, benzene, ethanol and methanol

Abstract: The solvatochromic shifts of several indicators {2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-1-phenolate [Reichardt’s ET(30) betaine dye], 4-nitroanisole, 4-nitroaniline and N,N-diethyl-4-nitroaniline} have been measured in binary mixtures of propan-2-ol with hexane, benzene, ethanol and methanol at 25 °C over the whole range of solvent composition. From the UV–VIS spectroscopic data the preferential solvation of the indicators has been studied. The solvatochromic parameters ET(30), π*, α and β of the binary solvent mixtures studied have been calculated from the solvatochromic shifts.

Control of Subtilisin Substrate Specificity by Solvent Engineering in Organic Solvents and Supercritical Fluoroform

Abstract: We have investigated the effect of physical properties of 30 nonaqueous solvents on the specificity of Subtilisin Carlsberg for nucleophiles in the transesterification of N-acetyl-l-phenylalanine ethyl ester by methanol, 1-propanol, and 1-butanol at fixed thermodynamic water activity In organic solvents, enzyme activity and nucleophile specificity are solvent-dependent, while in supercritical fluoroform, the activity and specificity are pressure-dependent Losses in catalytic efficiency and substrate specificity are observed when subtilisin is exposed to hydrophilic organic solvents such as dioxane, tetrahydrofuran, and acetonitrile as compared to hydrophobic solvents (hexane and heptane) Log P is an important descriptor for correlating both the rate and the specificity of deacylation with solvent properties A linear model of log initial rate against both log P and nonpolar unsaturated area provides the best two-variable fit to the data for solvents of high log P A nonlinear model of specificity again

Acidity and cracking activity changes during coke deactivation of ultrastable Y zeolite

Abstract: Changes in acidic ultrastable Y zeolite (H-USY) due to coke deactivation during hexane cracking were determined by ammonia TPD, microcalorimetry, IR spectroscopy of adsorbed pyridine, 13C NMR, powder XRD, TGA of hexane adsorption, and nitrogen and argon adsorption. Small amounts of coke produced a large decrease in activity; however, few acid sites were poisoned. Compared to a fresh USY zeolite, coke deactivated H-USY did not show significant changes in the acid strength distribution, number of acid sites, fraction of Bronsted and Lewis acid sites, pore size distribution, or hexane diffusivity that could account for the large decrease in the cracking activity. It is proposed that the rapid loss in activity resulting from a small decrease in the number of acid sites is consistent with a site poisoning deactivation model for a diffusion-limited reaction, i.e., the rate of hexane reaction is greater than the rate of diffusion. For a diffusion limited reaction, the initial hexane cracking and coke deposition occurs primarily at active sites near the external surface of the crystal with little reaction at the particle interior. As deactivation proceeds, the thickness of coked region grows and hexane diffuses further into the zeolite particle before reaction.

Self-diffusion coefficients of methane or ethane mixtures with hydrocarbons at high pressure by NMR

Abstract: Self-diffusion coefficients have been measured in homogeneous mixtures of methane + hexane, ethane + hexane, methane + octane, ethane + octan, methane + decane, ethane + decane, and methane + hexane + benzene over the whole concentration range, at 303.2 K and 333.2 K and 30 MPa, 40 MPa, and 50 MPa. The experiments were performed in a glass cell by application of the NMR−PGSE technique. The estimated accuracy of the measurements is ±5%. Experimental self-diffusion coefficients were compared to the Sigmund correlation, which was found not to fit the experimental data.

Resonant-surface second-harmonic generation studies of phenol derivatives at air/water and hexane/water interfaces

Abstract: Resonant-surface second-harmonic generation and surface tension measurements have been used to study the adsorption of p-nitrophenol, phenol and p-propylphenol at the air/water and hexane/water interfaces at full monolayer coverage. The determining forces defining the angle of orientation of the moieties are the solute–solvent interactions at both interfaces. In particular, we observed the screening effect of the hexane phase on the solute–water interactions. Surface tension measurements performed on these interfaces showed that the number of molecules per unit surface at full coverage follows from the angle of orientation. From a wavelength analysis of the SH response of the monolayers, we are led to the conclusion that partial hydration of the aromatic rings of phenol and p-propylphenol occurs at both the air/water and the hexane/water interfaces, whereas p-nitrophenol remains largely within the water phase at both interfaces.

Separation of branched hexane isomers using zeolite molecular sieves

Abstract: A range of small, medium and large pore zeolite, and their modified forms are studied for their ability to separate di- from monobranched isomers of hexane. The separation studies are carried out using high-temperature (250--350 C) gas chromatography. Beta(H,Ba) is found to be the most effective separator of 2,3-dimethylbutane and 3-methyl-pentane and is therefore studied for its sorption capacities toward the two hexane isomers. This work is directed to the improvement of the quality of petrol by separating hydrocarbon mixtures using zeolites. Since maximum hydrocarbon branching is desirable in petrol (hydrocarbons with a branching structure burn more efficiently and thus have a higher octane rating), catalytic isomerization is used to isomerize straight-chain hydrocarbons to their mono- or dibranched isomers.

Solvation and Dynamics of Chymotrypsin in Hexane

Abstract: We have investigated the serine protease γ-chymotrypsin (γ-CT) in three different solvation environments using molecular dynamics simulations. These solvation environments include the following: (1) γ-CT taken from the crystal structure of Yennawar et al. (Biochemistry 1994, 33, 7326−7336) with seven surface bound hexane molecules and 50 bound “essential” water molecules all immersed in 1109 hexane molecules (simulation labeled CT); (2) γ-CT taken from Yennawar et al. and solvated with 50 “essential” water molecules and immersed in 1107 hexane molecules (simulation labeled CTWAT); and (3) γ-CT taken from Yennawar et al. and solvated with a monolayer of 444 water molecules and immersed in 931 hexane molecules (simulation labeled CTMONO). From these trajectories we found that the placement of bound water molecules and the amount of hydration of the protein in the simulated structure had an effect on the protein flexibility as indicated by changes in the RMS deviation. The radius of gyration value was simil...

Densities of Mixtures Containing n-Alkanes with Sunflower Seed Oil at Different Temperatures

Abstract: Densities for mixtures containing sunflower seed oil with pentane, hexane, heptane, and octane have been determined at various temperatures between 29815 K and 31315 K using a vibrating tube densimeter The derived excess volumes have been correlated by the Redlich−Kister equation All the systems showed negative deviations from ideality The excess volumes increased with an increase in temperature

Allium Chemistry: Structure, Synthesis, Natural Occurrence in Onion (Allium cepa), and Reactions of 2,3-Dimethyl-5,6-dithiabicyclo[2.1.1]hexane S-Oxides

Abstract: Peracetic acid oxidation of di-1-propenyl disulfide (8) gives (±)-(1α,2α,3β,4α,5β)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5-oxide (10a; 10%) and (1α,2α,3α,4α,5β)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5-oxide (11a; 11%), both also isolated from extracts of homogenized onion. Compound 10a could be converted into bissulfoxides (±)-(1α,2α,3β,4α,5α,6α)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5,6-dioxide (16) and (±)-(1α,2α,3β,4α,5β,6α)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5,6-dioxide (17a); these could be oxidized further to (±)-(1α,2α,3β,4α,5α,5β,6α)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5,5,6-trioxide (18a) and (±)-(1α,2α,3β,4α,5α,5β,6β)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5,5,6-trioxide (18b) from 16 and 18a from 17a. Extended oxidation of 10a gave (±)-trans-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5,5,6,6-tetraoxide (19). Oxidation of 11a gave (1α,2α,3α,4α,5β,6β)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5,6-dioxide (21a) which was further oxidized to trioxides (1α,...

Catalytic hydrogenation of aromatic aldehydes and ketones over ruthenium catalysts

Abstract: Catalytic hydrogenations of acetophenone, benzaldehyde, and cinnamaldehyde using a catalyst of 5% wt. Ru/activ. carbon in hexane and/or 2-propanol were studied. Basic kinetic parameters were evaluated. The influence of the reactants’ structure and the kind of solvent used on the course of the reaction were also discussed.

Separation of hexane isomers on zeolites mordenite and beta

Abstract: A gas chromatographic technique has been used to study the separation properties of mordenite and beta zeolites towards 3-methylpentane and 2,3-dimethylbutane at elevated temperatures (300–350 °C). Mordenite(Na, K) and beta(H, Ba) were found to be successful at separating these two hexane isomers. To establish the cause for the obtained separation of the hexane isomers, the heats of adsorption and the diffusion coefficients of the hexane isomers on the modified zeolites were studied using pulse gas chromatography. The results showed that the separation of 2,3-dimethylbutane and 3-methylpentane on mordenite(Na, K) and beta(H, Ba) zeolites is based on differences in the heats of adsorption of these two hexane isomers on the above-mentioned zeolites and that it is also diffusion controlled.

Simultaneous Vapor−Liquid−Liquid Equilibria and Phase Molar Densities of a Quaternary System of Propane + Pentane + Octane + Water

Abstract: This paper presents a new procedure to measure simultaneously equilibrium phase compositions and phase densities of multicomponent fluid mixtures. This is accomplished using a uniquely designed pressure/volume/temperature-vapor/liquid/liquid equilibrium apparatus (PVT-VLLE) connected to a modified sampling system for gas chromatographic analysis (GC) at high pressures and temperatures. The data reported in this paper include (1) three-phase equilibrium compositions and pressures of hexane + water and (2) three-phase equilibrium compositions and phase molar densities for a quaternary system of propane + pentane + octane + water. The equilibrium compositions and three-phase equilibrium pressures for hexane and water compare well with the published data of Tsonopolous and Wilson, which are considered as a calibration test to validate our procedure. Thus we conclude that this methodology is suitable for determining volumetric and phase equilibria properties of multiphase systems.

Separation and quantitation of mono-, di-, and triglycerides and free oleic acid using thin-layer chromatography with flame-ionization detection.

Abstract: α-Monoolein was prepared from glycidol and oleic acid by the regioselective opening of glycidol in the presence of an anionic resin. During the reaction, the lipochemical synthesis medium becomes enriched in monoolein, the effective emulsifying agent. This mixture can be analyzed by thinlayer chromatography coupled with flame-ionization detection (FID). The products and reagents do not need to be derivatized. Diglyceride and triglyceride by-products affecting the selectivity of the reaction also could be detected using this technique. Cholesterol was used as an internal standard. The factors influencing the separation, including the hydrogen flow rate, scan speed, and the composition of the developing solvent, were investigated. The degree of separation is highly sensitive to the hexane/diethyl ether ratio of the developing solvent. Good separation of triglyceride, oleic acid, the two diglycerides, cholesterol, α-monoolein, and glycidol was obtained with the mixture hexane/diethyl ether/formic acid (65:35:0.04, by vol). Detector response, detection limits, and rod-to-rod variations also were examined. A range of rod loads giving a straightforward relationship between FID response and amount of compound loaded (relative to oleic acid and α-monoolein) was defined. The accuracy of the quantification was illustrated by analysis of a mixture of oleic acid and α-monoolein standards of known composition.

Composition and oil-retaining capacity of jet-cooked starch-oil composites

Abstract: Jet-cooked starch-oil composites were evaluated to determine whether the cooking procedure resulted in alteration of the chemical composition of either the starch or oil. Although these composites, both in dry form and in aqueous solution, were highly resistant to separation of starch and oil, there was no evidence of covalent bonding of the components, and composition of the starch moiety was unchanged. Extraction of oil from dried composites with a variety of organic solvents was not effective for complete recovery of oil ; an amount of oil representing approximately 5% of the starting weight of the composite could be recovered only after hydrolytic degradation of the starch. Extraction of oil from aqueous solutions of composites was also inefficient for complete oil recovery. The extent of extraction varied with concentration of both starch and oil. Typically, extraction repeated eight times with hexane recovered less than 80% of the oil from solutions with starch concentrations above 0.6%.

Evaluation of the diffusion coefficient of rapeseed oil during solvent extraction with hexane

Abstract: The diffusion coefficient of rapeseed oil was determined from data obtained during time-varied solvent extraction experiments. The experiments were carried out in a Gulbaran extractor-diffuser with hexane as the solvent. A relationship was found between the slope of the diffusion line and the shape and size of the rapeseed particles. This relation can be used to calculate the diffusion coefficient. A diffusion coefficient of 3.4×10−8 cm2/s was determined from the experimental data.