Synthesis And Interfacial Properties Of Pure Alkylbenzenesulfonates

Heavyalkylbenzenesulfonate (HABS) is one of the surfactants with good properties and cheap price, and it was empoldered in China recently. At present, many Oil Fields in China entered into high water-content stage. Daqing Oil Field is going to use HABS in enhanced oil recovery in 2007. But HABS is a mixture;it is difficult to satisfy the request for stable and high efficient enhanced oil recovery, now that these products are extremely uncertain. In order to understand which component of HABS plays important role in the EOR, and how to separate the fractions and obtain optimum synergistic proportion of HABS, a series of pure compounds with clear structures should be synthesized, this is useful for using value and realistic significance.In this paper, a series of alkylbenzenesulfonates and dialkylbenzensulfonates with high purity have been synthesized on the basis of "tailoring technology". Alkyl phenones, prepared by acylation of benzene and acid chlorides with the reaction of fatty acids and SOCl₂, reacted with Grinard reagents to give carbinols (phenyl and hydroxy were attached to the same carbon) that were reduced to alkylbenzene, alkylbenzene were then sulfonated and neutralized to produce alkylbenenesulfonates with unique structure. Furthermore, the reaction route of dialkylbenzenesulfonates has been improved, and polymer phosphorus acid (PPA) is used as a milder catalyst in place of AlCl₃, carboxylic acid is used in place of acyl chloride as a milder acylating reagent. Many side reactions were avoided using PPA instead of AlCl₃. Good results were also obtained by choosing the iodine modified by red phosphorus as the reducing agent. Pure compounds were achieved by methods designed in this paper. All synthesized surfactants, show over 95% of purity through two phase titration, True structures were proved by H NMR and GC/MS, MS gave right molecular weight. GC and GC/MS analyzed the structures and purities of some intermediates.The surface tensions of a series of pure samples aqueous solutions are measured with a ring method. From the surface tension curves, the properties such as CMC, γ cmc, Γ_max, and A_m of different alkylbenzenesulfonates could be gotten, and the following rules were found. When the length of carbonic chain holds, as the phenyl ring shifting to the middle of the carbonic chain, the volume of the hydrophobic group in surfactant molecules became bigger;this was disadvantageous to form micelle so as to the CMC will increase. At the same time A_m augmented while Γ_max decreased. When the total of carbon number increased, the hydrophobicity of surfactants increased, the CMC decreased, Γ_max increased, A_m decrease and Y cmc increased. The change of the position of the benzene ring has little effect on γ cmc-The interfacial tension behavior of this series of alkylbenzenesulfonates with carbon number 14,16,18 was investigated in alkane/aqueous system, it is found that alkylbenzenesulfonates of 16 total alkyl carbon number is the best. Effects of the position of benzene ring on the carbon chain were also studied. When the length of carbonic chain holds, as the phenyl ring shifting to the middle of the carbonic chain, the interfacial tension decrease and the optimal alkalinity is low. The addition of these extra groups causes the interfacial tensions to decrease and the optimal alkalinity to reduce compared to the parent linear alkylbenzenesulfonates. From the studies on alkane preference and alkalinity dependence of interfacial tension, it is found that alkylbenzenesulfonate of 16 total alkyl carbon number with an additional group and benzene ring located near the center of the alkyl chain is possible the most ideal structure for enhanced oil recovery because it can reduce the interfacial tension to ultra-low at low alkalinity and be applicable to a wide range of oils.The interfacial tension behavior of these products is investigated in crude oil/alkali system. The interfacial tension goes through a minimum, then came up again and it reached a very high value at last. Alkylbenzenesulfonates have the same dependence in alkane/aqueous system and crude oil/alkali system except the 7-isomers of dialkylbenzenesulfonates. 7Φ C16S and M5ΦC16S can show good results at low alkalinity in both systems. The results strongly confirmed that alkylbenzenesulfonate of 16 total alkyl carbon number with benzene ring located near the center of the alkyl chain is the most ideal structure for enhanced oil recovery. Furthermore, a series of mixed sodium hexadecylbenzene sulphonate, p-methyl sodium hexadecylbenzene sulphonate and p-ethyl sodium hexadecylbenzene sulphonate were synthesized and their interfacial tensions were compared. All these surfactant can give super-low interfacial tensions (10^-4-10^-3mN/m) from low alkalinity to high alkalinity. In addition, a series of sodium dodecylbenzene sulphonate, such as sodium pentadecylbenzene sulphonate and sodium octodecylbenzene sulphonate with cheap price and easy industrialization, were synthesized and blended with alkylbenzenesulfonates. The low interfacial tensions could be obtained and not changed when the ratio was 7:3. Therefore, if all the economy and capability are considered, sodium hexadecylbenzene sulphonate is the essential component in heavyalkylbenzenesulfonates, and some sodium dodecylbenzene sulphonates can be added in it.The configurations of organized assemblies of these compounds in aqueous solution are characterized by transmission electron microscopy and polarizing microscopy and it is found that the 5-isomers can form monolamellar vesicles spontaneously, whereas the 7-isomers form lamellar liquid crystalline structures but can be converted into monolamellar vesicles afterprolonged sonication. All these researches indicate that with benzene ring moves to the center of alkyl chain, the packing parameter of the alkylbenzenesulfonate surfactant increases and the molecular geometry transforms from taper to frustum then to column, resulting in the transformation of the assemblies from micelles to vesicles then to lamellar liquid crystals. But the pure surfactants with additional group can't form monolamellar vesicles.