Interfacial Properties Of Alkylbenzene Sulfonate Surfactants

Alkylbenzene sulfonate surfactant is widely used chemical product in detergents,medical drugs,etc,and it is the mail agent of ASP flooding.The oil recovery can be greatly improve by ASP flooding(Alkaline-Surfactant-Polymer),which is higher of 10% recovery rate compared to polymer flooding.The advantages of ASP flooding increase surfactants and alkali,which can improve the displacement efficiency.The interface performance of Surfactants is the most important guarantee for ASP flooding.The key founction of surfactant is the interface performance,which can be affected by many factors such as surfactant structure,concentration,salinity,and chain length of the oil phase.In this paper,dimethyl-alkylbenzene sulfonate isomers and homologues are synthesized.Spinning drop tensiometer is used to evaluate the interfacial tension(IFT).The mechanisms of IFT changed by ABS under different conditions are clarified.The more details are as follows:1.Six isomers and eight homologues of sodium para-dimethyl-dodecyl benzene sulfonates(PDDBS)are synthesized.The structure and purity of the product are characterized by 1H-NMR and UPLC-MS.2.The surface tension of the PDDBS is determined by the maxium bubble method.The results show that the critical micelle concentration(CMC)of PDDBS increases with the moving of the benzene carrying a hydrophilic group sulfonic acid group towards to the intermediate position of the oleophilic alky chain,the surface tension under the corresponding CMC decreases,and the occupation area(Amin)of the PDDBS molecular in the interface layer becomes larger,and the saturated adsorption amount ?max becomes smaller.The n-alkane is used as the oil phase,and the oil-water IFT of the PDDBS isomer is determined by spinning drop tensiometer.The results show that the dynamic IFT exhibits a maximum value via from low to high,then reduces to a stable value gradually.By measuring the corresponding minimum alkane carbon number to the PDDBS,The IFTmin presents lower and then higher with the position of the benzene moving to the center of the alky chain,caused by hydrophilic-lipophilic properties and structurre of the PDDBS isomer.When the forces between the lipophilic and hydrophilic groups of PDDBS are at balance,the minimum value of the IFT is obtained.3.The crude oil is used as the oil phase,the effect of Na OH concentration on the IFT of the homolog of PDABS was studied.The results show that electric double layer is compressed,weakened electrostatic interactions with increasing the Na OH concentration,the interfacial concentration improved.The electrical double layer was further compressed by a continuous increase,and water molecules incorporate into the interface,the interficial tension decreased firstly and then increased.However,PDABS are driven into oil phase by salting out effect at higher Na OH concentrations,resulting in the decreasing of IFT for water-soluble p-S12-5 and p-S14-5.The effect of Na OH concentrations is weak in oil phase.The effective distribution of PDABS in the oil phase plays an important role on stabilizing the interface and reducing IFT.4.The effects of different electrolytes on the IFT of PDABS surfactant are discussed in detail.The results showed that the electrolyte can reduce the IFT by changing the ionic strength of the aqueous solution,compressing the electric double layer of hydrophilic group of the surfactant,and increasing the adsorption concentration of surfactant at the interface.With the increase of electrolyte concentration,IFT decreases rapidly at first and then decreased slowly.The surfactant is continuously distributed into the oil phase with the increase of electrolyte concentration.When the oil-water partition coefficient amounts to 1,IFT obtains a minimum value.Due to the differences in electrolyte anions,the polarity and structure of water molecules near the interface layer were changed,resulting in the different degree decreased of IFT.Water is polarized and produced OH-by the hydrolysis of CO32-,the forces between molecules are weaken for the large ionic radius,leading to differences between the two sides of the interface layer,which decrease the IFTs at a slower rate.Na Cl had no ability to produce OH-,decrease the IFTs fastly.While,the decreasing rate of IFTs for Na OH and Na HCO3 is situated between Na2CO3 and Na Cl.With the increase of long-chain alkyl group of PDABS,the solubility of PDABS in water is greatly affected by the electrolyte concentration,and the IFTmin of oil-water interface moved to lower electrolyte concentration.5.The theoretical model in cylindrical coordinates is established by using Fick's diffusion equation,lumped parameter method in heat conduction,combined with gibbs equation,the dynamic interfacial tension equation of rotating droplet method is derived to describe the dynamic characteristics of oil-water interfacial tension.The results shows the experimental curve is in good agreement with the theoretical calculation curve.The DIFTs of alkylbenzene sulfonate surfactants are a function of time and show an exponential decreasing trend.Meanwhile,the curve of the calculable variable r/2·ln [1-e-(?-??)/RT?] as a function of the diffusion time t is linear.The slope of the curve depends on the interphase diffusion coefficient K.The average value and range of interphase diffusion coefficient K of surfactants at different concentrations were calculated by using the slope of linear part.The equations of DIFT can be applied for the interface of cylindrical drop,spherical drop,flat surface and irregular interfaces when the surface curvature parameter is modified.