Study On Synthesis And Properties Ofalcohol Ethoxy Carboxylates For EOR

The synthesis and properties of a kind of new surfactant with anionic-nonionic mixed hydropilic group, fatty alcohol polyoxyethylene ether carboxylates, were investigated. To render the surfactant good hydrophobocity, fatty alcohol polyoxyethylene ether with short EO chain, or coconut alcohol polyoxyethylene (2) ether (C12EO2), and cetyl alcohol polyoxyethylene (3) ether (C16EO3), were used as materials, which are transformed to corresponding fatty alcohol polyoxyethylene ether caoboxylates, C12AEC and C16AEC by reaction with chloroacetic acid in the presence of NaOH. The results show that the yield is strongly affected by the chloroacetic acid/alcohol polyoxyethylene ether molar ratio, temperature and reaction time. A yeald as high as 80% can be achieved at appropriate conditions, or at a molar ratio=1.1, reacted for 7 h at 60°C.The taget products, C12AEC and C16AEC, can be purified by removing salts as an insoluble precipitate in ethanol by filtration, followed by re-crystallization from ethanol, and a purity as high as 99% can be achieved as certificated by chemical analysis. The chemical structure and composition of the target products was proved by IR and HPLC-mass spectra. C12AEC is a mixture of homologues with both C12 and C14 alkyls and a EO number between 0 to 5, which is in good agreement with the composition of the raw material used, whereas C16AEC is a mixture of homologues with only C16 alkyl and a EO number between 0 to 3.It is found that C16AEC is highly surface active, as indicated by its low cmc (6.0×10-5 mol/L) and lowγcmc (28.3 mN/m) at 25℃. Similarly C12AEC is also highly surface active as indicated by its lowγcmc (<30mN/m), although its cmc is relatively higher (1.0×10-3 mol/L) at 25℃. However both products have relatively larger cross section area at saturated adsorption at air/water interface at 25℃, or 0.70nm2å'Œ0.84nm2 compared with that of SDS (0.5nm2). At 45℃, the cross section areas increase a little but both the cmc andγcmc values keep unchanged.It is also found that at 45℃C12AEC and C16AEC has a high tolerance to Na+ ion, as indicated by its salt tolerance, 122 g/L and 135g/L, to NaCl in aqueous solution, and by the high optimum salinity (NaCl), 103 g/L and 108g/L, of the C12AEC and C16AEC microemulsion, which are all similar to that of AES, a typical surfactant with excellent salt tolerance. However, C12AEC and C16AEC has a poor tolerance to Ca2+ and Mg2+ ions, as indicated by its low tolerance, 0.41 g /L and 0.5 g /L, to CaCl2, 1.4 g /L and 1.8 g /L, to MgSO4, respectively. Nevertheless, with suitable hydrophobicity, C12AEC and C16AEC can reduce Daqing crude oil/connate water interfacial tension to an order of 10-3 mN/m, by mixing with alkylbetaines, or alkylbetaine/nonionic surfactants, in a total surfactant concentration, 0.05%-0.3%, at 45℃without adding any alkaline agent or neutral electrolyte.However, due to relatively larger cross section areas at saturated adsorption, C12AEC and C16AEC are not appropriate to be used as main surfactants in surfactant flooding for Daqing crude oil/connate water system, and their molar fraction in total surfactants can not be larger than 0.2 when mixed with other main surfactants such as alkylbetaines or alkylbetaines/nonionic surfactants.