An Experimental Investigation Into the Use of high-Pressure Liquid Chromatography for the Determination of Petroleum Sulfonates

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Abstract
The separation of petroleum mono- and disulfonates on an anion-exchange column using high-pressure liquid chromatography (HPLC) was investigated as a method /or the determination of sulfonate concentrations in aqueous or hydrocarbon solutions. Quantitative analysis o/ brine (3,000 ppm) or hexane solutions containing 500 to 5,000 ppm ppm) or hexane solutions containing 500 to 5,000 ppm of unfractionated Witco TRS 10-80 Petronate was possible to a precision of 2 percent. Extending the possible to a precision of 2 percent. Extending the method to solutions containing TRS 10-80 sulfonates with altered mono- and di-ratios was accomplished by deriving ultraviolet (UV) response factors /or the average mono- and disulfonates present in the original TRS 10-80. Application of the HPLC technique with monoand disulfonate response factors was demonstrated by analysis of sulfonate concentrations in both phases in a series of two-phase hexane-brine phases in a series of two-phase hexane-brine systems. Trends in the distribution coefficients were identified readily. Preferential partitioning of the mono- and disulfonates between the hydrocarbon and brine phases was indicated by changes in the ratio of the mono- and disulfonate areas on the chromatographs. The HPLC technique gave information on the sulfonate composition that was not obtained by traditional wet-lab methods. Introduction Surfactant concentration is an important parameter in the evaluation of surfactants used in oil recovery processes. Unfortunately, quantative analysis of processes. Unfortunately, quantative analysis of surfactants commonly used in enhanced oil recovery processes is difficult because these often are processes is difficult because these often are complex mixtures of anionic surfactant molecules. Commercially available petroleum sulfonates not only contain a range of molecular weights but also vary in percentage of mono-, di- and polysulfonated molecules. Numerous analytical techniques have been presented in the literature to determine anionic presented in the literature to determine anionic surfactants in water and oil. The two-phase titration technique, introduced by Epton in 1946, was modified and used to determine petroleum sulfonates. Disadvantages of the Epton titration method includethe average equivalent weight of the anionic surfactant must be known;it cannot differentiate between mono-, di-, and polysulfonated molecules;experimental evidence polysulfonated molecules; (3) experimental evidence indicates the method is not stoichiometric for low molecular-weight sulfonates and there is limited knowledge of be stoichiometry for polysulfonated molecules; andit is not automated easily. The Epton titration method has been used because no other good analytical techniques exist. Recent developments in HPLC and in ion-exchange resin offer the possibility of improved analytical techniques to determine petroleum sulfonates. Traditionally, the chromatographic separation of aromatic sulfonates by ion-exchange has been difficult because of excessive noncoulombic adsorption on polystyrene-type, anion-exchange resins. Successful separation of low molecular-weight aromatic sulfonates on a quaternized polyalkeneamine, anion-exchange resin was reported by Stehl. Development of pellicular anion-exchange resins with a quaternary alkylamine bonded to an inert nonpermeable core further reduced the anionic adsorption of aromatic sulfonate molecules and extended the range of application. Schmit and Singh reposed separations of naphthalene-sulfonic-acid dye intermediates on pellicular anion-exchange resin. Suffridge reported pellicular anion-exchange resin. Suffridge reported separation of a petroleum sulfonate into its monoand disulfonate constituents on a pellicular anion-exchange resin using a linear ionic-strength gradient. SPEJ P. 207

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