Showing papers on "Hexane published in 1991"

Enzymatic esterification in organic media: role of water and organic solvent in kinetics and yield of butyl butyrate synthesis

Abstract: The respective roles of organic solvent and of water in butyl butyrate synthesis from n-butanol and n-butyric acid in n-hexane by Mucor miehei lipase have been investigated by analysis of the kinetics and the reaction balances. Esterificaton was found to take place in both low water systems containing solid enzyme in hexane and in biphasic aqueous enzyme solution/hexane systems. In the solid enzyme system, the enzyme adsorbed the water produced, thus delaying the appearance of a discrete aqueous phase. As expected, the presence of some water was indispensable for this system, as its removal or exclusion by various means (adsorption, distillation) affected enzyme activity. However, water removal had little effect on the final yield of esterification. Reaction velocities were quite similar for the solid enzyme/hexane system and for the biphasic aqueous enzyme solution/hexane system. In the latter case, the butyl butyrate formed was almost exclusively found in the organic phase. Ethyl butyrate, a more polar compound, was synthesized with a lower yield. These results allow the conclusion that the reaction took place in a phase consisting of either solid hydrated enzyme with no discrete aqueous phase or of an aqueous enzyme solution by basically similar mechanisms according to the amount of water available to the system, the esterification being driven to completion by transfer of the ester into the organic phase because of a favourable partition coefficient.

Deacidification of sulfur olive oil. I. Single-stage liquid-liquid extraction of miscella with ethyl alcohol.

Abstract: In this study, a systematic and detailed investigation on liquid-liquid extraction of sulfur olive oil miscella in hexane with aqueous ethanol solutions was performed. Optimal extraction conditions for recovery of free fatty acids (FFA) with a minor loss of neutral oil were determined in bench-scale single-stage extractions. It was concluded that, to ensure deacidification with a low triglycerides loss, it is appropriate to extract the miscella with 30% or more dilute ethanol solutions. It was also noted that under these circumstances the free fatty acid percentage extracted is not affected by increases in contents of FFA and partial glycerides of sulfur olive oil, and the solvent must be saturated with hexane before extraction. Changing the oil:hexane ratio in miscella from 1:2 to 2:1 by weight did not have any significant effect on extraction results.

Model for alkanol + alkane mixtures: Extension and experimental verification

Abstract: A recently developed model for 1-alkanol+alkane mixtures is extended to methanol mixtures and to the non-polar mixing partners tetrachloromethane and benzene. The model contains chemical and physical terms, which are combined in a thermodynamically consistent way. For our calculations on methanol mixtures, we have measured g E of methanol+ hexane via static vapor pressure measurements. In order to check the model predictions for systems with higher alkanols and alkanes, we have also determined g E of 1-octanol+tetradecane by measuring the melting curve. The reproduction of the excess properties of methanol+hexane, the agreement between predicted and measured values of g E for 1-octanol+ tetradecane, and the capability to deal also with other non-polar mixing partners demonstrate the power and reliability of the model.

Multicomponent solubilization in aqueous micelles of dodecyl- and tetradecyltrimethylammonium bromide: Solubilization equilibria

Abstract: Solubilization equilibria for hexane and a series of polycyclic aromatic compounds (dyes) in aqueous cationic micelles of dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) were studied experimentally. Solubilizates were compared first individually, for effects of molecular shape and structure, and then as mixtures, in a search for interactive effects. Hexane solutions of solid dyes, in binary mixtures of relative mole fraction 0 to 1 for each dye, were partitioned into the aqueous micellar phase, which was analyzed by ultraviolet-visible spectrophotometry for the dyes and gas chromatography for hexane. Solubilization ratios (SRs), expressed as the ratio of solubilizate to surfactant molecules in a micelle, were obtained from the experimental data. In our experiments, the micelles contained more solubilized hexane than dye. For cases of three-component solubilization (two dyes and hexane), compounds of similar molecular shape and chemical structure performed alike as solubilizates, possibly occupying sites in the micelle interchangeably. However, when a large molecule with three or four fused rings and a smaller two-ring molecule were contained in the micelle, solubilization of the smaller molecule was always enhanced.

Solubility of n-docosane in n-hexane and cyclohexane

Abstract: The solubility of docosane (n-alkane C 22 ) in cyclohexane and n-hexane has been measured over a wide range of temperature. The eutectic point has been determined for the system n-docosane-cyclohexane. In both solvents a transition point crystal-rotator of solute has been observed. Three methods of solubility prediction have been applied in calculations: the Flory-Huggins theory, the Kikic-Alessi improved Flory expression, and the Haulait-Pirson formula for combinatorial entropy

Infrared Study of Tetraalkylurea in Carbon Tetrachloride and/or Hexane and in Chloroform and/or Hexane 1% Solutions

Abstract: This study indicates that intermolecular complexes exist between tetraal-kylurea and carbon tetrachloride and between tetraalkylurea and chloroform. The type of complex or complexes formed is dependent upon the mole % CCl4/C6H14 or mole % CHCl3/C6H14. Intermolecular hydrogen-bonded complexes between tetraalkylurea and chloroform (such as I; I and II; II and III; and III) are formed as the mole % CHCl3/C6H14 increases. The steady decrease in the vC=O frequency is attributed in part to the bulk dielectric effects of the solvent system.

Association of Cycloalkanes with Cyclodextrins in Aqueous Medium

Abstract: The complex formation of α-, β-, and γ-cyclodextrins (CyDs, hosts) with five cycloalkanes (guests), cyclo(pentane, hexane, heptane, octane, and decane), has been studied in aqueous media at 25°C by making use of the volatilization rate of guest molecules from the aqueous into gas phase. In the excess of the host, α-CyD forms both 1 : 1 and 2 : 1 (host: guest) complexes, while β- and γ-CyDs form 1 : 1 complexes with an exception that β-CyD forms a 2 : 1 complex with cylodecane. The 2 : 1 complex formation constants of α-CyD with cyclo(hexane, heptane, octane, and decane), particularly with cyclooctane, are extremely large compared with their 1 : 1 formation constants. The host–guest spatial fitting models are proposed.

The effect of solutes on the orientational ordering of liquid-crystalline solvents

Abstract: The effect of solutes on the orientational ordering of the liquid-crystalline solvents 4-n-heptyl-4′-cyanobiphenyl (7CB) and 4-n-octyl-4′-cyanobiphenyl (8CB) has been studied by 13C NMR. The technique used was a combination of variable-angle spinning (VAS) and a two dimensional method called separated local field (SLF) spectroscopy. 7CB exhibits only a nematic phase. The effects of four different solutes (carbon tetrachloride, cyclohexane, benzene, hexane) with mole fractions of c. 0·08 as well as different mole fractions of hexane were studied. 8CB has a nematic phase and a smectic A phase, and the effect of hexane with mole fraction of c. 07middot;07 was investigated. It was found that the effect of solutes in reducing the nematic to isotropic temperature (T NI) has the order CCl4 ≈ cyclohexane > benzene > hexane. The incorporation of hexane in 8CB reduce T NI more significantly than T SN, the smectic to nematic transition temperature. On the other hand, at the same reduced temperature (T/T NI ...

Superacidic FSO3H/HF catalyzed butane isomerization [1]

Abstract: Superacid catalyzed isomerization of butane was studied. Highly efficient isomerization of butane to 2-methylpropane (isobutane) was achieved using fluorosulfuric acid containing up to 5% of hydrogen fluoride acting as a protic co-acid. The isomerization when carried out in excess FSO3H at 21 ° C in a flow system gave ∼70% conversion to 2-methylpropane with generally less than 3% cracking. When 2-methylpropane was isomerized under similar conditions about 12% butane was formed. Attempted isomerization of pentane and hexane with prolonged reaction times in a static system results in predominant protolytic cleavage (cracking).

Recovery of high octane components from isomerates

Abstract: An adsorption process for separating the high octane components, including multi-branched paraffins and isopentane of a C5 -C6 isomerate from lower octane monobranched and normal paraffin components by contacting the isomerate with an X zeolite exchanged with a mixture of at least two cations from Group II-A. The adsorbed low octane components are preferably desorbed with a desorbent selected from the group consisting essentially of isooctane, 2,2,3-trimethyl pentane, 2,2,4-trimethyl pentane, 2,3,4-trimethyl pentane, 1,2-dimethyl cyclohexane, 2,2-dimethyl hexane, 2,2-dimethyl octane, 3-ethyl hexane, 2,2,4-trimethyl hexane and mixtures thereof.

The Viscosity of cottonseed oil, fractionation solvents and their solutions

Abstract: Cold fractionation of cottonseed oil is made difficult by the high viscosity of the oil. This study was aimed at demonstrating the effect of solvents on the viscosity of mixtures between 0°C and 25°C with a view to facilitating the fractionation of refined cottonseed oil. The solvents used were acetone, methylethylketone, methylisobutylketone, hexane and heptane. Measurements of viscosity were carried out by means of a capillary viscometer. The ratio of the viscosity of cottonseed oil to that of pure solvents is of the order of 300. The viscosities of solutions of various ratios of solvent to oil (1/3, 1/1, 3/1) are between those of cottonseed oil and the pure solvents. The effect of the solvent/oil ratio overrides that of solvent nature. The effect of solvent in reducing the viscosity of cottonseed oil is by descending order: acetone, hexane, methylethylketone, heptane, methylisobutylketone.

Oil extraction from olive foot cake with acidic hexane

Abstract: The use of acidic hexane as a solvent increases the extracted oil yield from olive foot cake. Two extraction procedures are studied: open air extraction at room temperature and Soxhlet exhaustive extraction. The additional yield is about 5% for a 2.5% acetic acid content in case of open air extraction and turns out to be 9% for 7.5% acetic acid content in the Soxhlet procedure. An analysis of the extracted oil shows a light increase of the acidity of oil. The improved yield may be attributed to the action of acetic acid on the decomposition of intercellular structures and binding of some polar lipids. The phospholipids content of oil extracted with 7.5% acidic hexane is found to be 25 times more than with pure hexane.

Phospholipase D activity in hexane

Abstract: Phospholipase D converts phosphatidylcholine (PC) to phosphatidic acid (PA) at 65° C in water-saturated hexane. Presumably, the active site of the enzyme remains hydrated in the interior of a lipid micelle. Enzyme activity at elevated temperatures in a nonaqueous medium contrasts sharply with inactivation at high temperature in aqueous solution. Results demonstrate that nonhydratable phospholipids can be produced enzyma-tically under conditions comparable to those during oil extraction in commercial soybean processing.

Reverse osmosis process for recovery of C3-C6 aliphatic hydrocarbon from oil

Abstract: Solvents comprising C 3 , C 4 , C 5 and C 6 aliphatic hydrocarbons (i.e. propane, propylene, butane, butylene, pentane, cyclopentane, pentene, hexane, cyclohexane, hexene and their isomers) and mixtures thereof, preferably C 3 and C 4 hydrocarbons and mixtures thereof are recovered from hydrocarbon oils in the liquid phase by the reverse osmosis permeation of said solvent through a polyimide reverse osmosis membrane at low temperature.

Reaction of 1,2-borylphosphinoethene with phenyl isocyanate and the structure of the reaction products

Abstract: The reaction of 1-butyl-1-dibutylboryl-2-phenyl-2-phenylphosphinoethene with phenyl isocyanate gave two structural isomers, which were identified as 1-aza-5-phosphonia-2-borata-3-cyclohexene and 2-aza-4-phosphonia-1-boratabicyclo-[3.1.0]hexane by31P NMR and IR spectroscopy and x-ray diffraction structural analysis. The reversibility of the interconversion of these isomers was demonstrated. The reversible migration of a butyl anion from a carbon atom to the boron atom during this process was found.

Photochemical reaction of 1-(o-methylphenyl)-2,2-dimethyl 1,3-diketones

Abstract: The photochemistry of 1-(o-methylphenyl)-2,2-dimethylpropane-1,3-diones 4 has been investigated. Compounds 4a–h underwent photocyclization to give benzocyclobutenols 11a–h and naphthalenones 12a–h in hexane or methanol. Compound 4i gave the naphthalenone 12i in methanol. The product ratio 11:12 was greater in hexane than in methanol. This ratio increases with chain branching of the C-3 substituent R and with increasing size of R. Compounds 4a, b and d gave isobutyrophenones 13a, b and d along with products 11 and 12 in hexane.

NETWORK OF n-HEXANE ISOMERIZATION OVER Pt/Al2O3 AND Pd/HM CATALYSTS

Abstract: Products from alkane isomerization over various types of catalysts were examined. Rate constants were calculated by a new method called “two point method”. Network of this reaction has been quantitatively given. Experimental results could be well predicted with this method.