Adsorption of Alkyltrimethylammonium Bromides at Water/Alkane Interfaces: Competitive Adsorption of Alkanes and Surfactants
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Abstract:
The adsorption of members of the homologous series of alkyl trimethylammonium bromides (CnTAB) is studied at water/alkane interfaces by drop profile analysis tensiometry. The results are discussed in terms of a competitive adsorption process of alkane and surfactant molecules. A thermodynamic model, derived originally for the adsorption of surfactant mixtures, is adapted such that it describes a competitive adsorption of the surfactant molecules from the aqueous phase and alkane molecules from the oil phase. This new model involves the interspecies attraction coefficient, which mutually increases the adsorption activities of the alkane and CnTAB. The effects of the alkyl chain length n of CnTABs and the influence of the number of C atoms in the alkane chain are discussed, and the physical quantities are compared to those determined at the aqueous solution/air interface. The new theoretical model for aqueous solution/oil interfaces is also compared to a theory that does not consider the adsorption of alkane. The proposed new model demonstrates good agreement with the experimental data.Keywords:
Alkane
Aqueous two-phase system
Homologous series
Methylcyclohexane
UNIFAC
Hydrocarbon mixtures
Aromatic hydrocarbon
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Hydrocarbon contained in leaf waxes of 30 species was isolated chromatographically. Branched and saturated hydrocarbons were found little in them. Most of hydrocarbon was confirmed to be n-alkane. Component of maximum content ofn-alkane and pattern of the component in each species are different expect the case thatn-nonacosane (C29) contained 80% ofn-alkane of Cruciferae species. Pattern of the component ofCoix ma-yuenis similar to that ofC.lachryma-jobi.It is found that there are some plant species, which contain a good deal of even-numberedn-alkane.
Alkane
Carbon number
Component (thermodynamics)
Carbon fibers
Hydrocarbon mixtures
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Squalane
Homologous series
Alkane
Kovats retention index
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Homologous series
Alkane
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The separation and determination of alkane and cycloparaffinic hydrocarbon in heavy oil is the difficult problem in hydrocarbons analysis.The alkane and the cycloparaffinic hydrocarbon in Daqing VGO are separated by combining ultrasonic wave with the adductions of urea and thiourea.The obtained alkane and cycloparaffinic hydrocarbon are determined by GC/MS and NMR.When the mass ratio of isopropanol to oil sample is 7.5 and the temperature of reaction is 38～43 ℃,the average mass fractions of alkane and cycloparaffin in Daqing VGO are 46.56% and 41.88% and the RSD are 0.7% and 0.51% respectively according to 5 determination results.The carbon number distribution of normal paraffin in alkane is C_ 20 —C_ 38 .Cycloparaffinic hydrocarbon in alkane is less than the detection limit of NMR,and the total ion chromatogram of cycloparaffinic hydrocarbon shows that the content of alkane in cycloparaffinic hydrocarbon is very little.These indicate that ultrasonic wave can accelerate the adduction of urea and thiourea and improve the separation result of alkane and cycloparaffinic hydrocarbon in heavy oil.This method has high accuracy and good repeatability in the separation and analysis of alkane and cycloparaffin in heavy oil.
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Dilution
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Abstract The interfacial tension and solubilisation characteristics of the alkane/water interfaces of a series of alkyl aryl sulphonates synthesised with 1‐butanol as a co‐surfactant have been studied. It was observed that there is a narrow range of carbon numbers of these sulphonates at which maximum solubilisation of a particular alkane occurred. This range shifted progressively to a higher value, with a corresponding increase in the carbon number of the n‐alkane. The extent of solubilisation of the alkane is highly dependent on the structure of the hydrocarbon portion of the sulphonate. Unexpectedly, an ultra‐low interfacial tension seems not to be an important prerequisite for the solubilisation of hydrocarbon in the aqueous surfactant phase. The free energy decrease required for solubilisation seems to be far more dependent on the energetic interactions connected with entropy parameters. The conformational aspects of the hydrocarbon portion of sulphonate molecules, as a consequence, seem to play a decisive role in molecular interactions, leading to solubilisation of a large quantity of a particular hydrocarbon in aqueous solution of a given sulphonate. The present work aims at understanding the selection criteria for sulphonates in applications involving solubilisation and ultra‐low interfacial tension at the hydrocarbon/water interface, such as those in insecticidal/pharmaceutical formulations, fire‐resistant hydraulic fluids and enhanced oil recovery.
Alkane
Homologous series
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An infinite-dilution activity coefficient model for predicting the SLE of a binary system consisting of a long-carbon-chain alkane solute (j) and a short-carbon-chain alkane solvent (i) has been investigated using SLE data satisfying the Gibbs−Duhem equation. It has been demonstrated that the temperature dependency of heat capacities of a solute alkane has a strong effect on the infinite-dilution activity coefficient of the solute, ln γj∞. The criteria for the establishment of infinite-dilution for the alkane/alkane SLE have been proposed. Infinite-dilution Wilson parameters introduced in the residual term of ln γj∞ have been determined from the regression using the SLE data. The Wohl equation combined with the present model accurately predicts the solubilities of the solute alkanes, while conventional models less satisfactorily predict the solubility. The ordered structure formed in a short-chain carbon solvent alkane liquid is partly destroyed, leaving the strength of molecular interactions unchanged when a molecule of an alkane having a longer carbon chain is introduced into the solvent alkane.
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Alkane
Homologous series
Atmospheric temperature range
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Alkane
Decane
Hexane
Heptane
Dilution
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