Study On The Synthesis And Properties Of Double Long-alkyl Polyoxyethylene Ether Betaines

Alkali-Surfactant-Polymer(ASP) flooding is a major chemical flooding technique for enhanced oil recovery in China. However, the field tests in recent years indicated that the use of alkali, especially the caustic alkali may have some side effects, and it has been a new tendency to replace ASP flooding by SP flooding. It has been shown that a new carboxyl betaine with double dodecyl chains(di C12B) displays very good properties in reduce crude oil/connate water interfacial tension(IFT). But due to with double long alkyl chains, it has a poor water solubility and large adsorption at sandstone/water interface. Whereas another new carboxyl betaine in which the double dodecyl were replaced by double coconut alcohol polyoxyethylene(2) ether(C12-14EO2OH) not only keeps the excellent properties of di C12 B, but also possesses improved water solubility and reduced adsorption at sandstone/water interface. Since the industrial alcohol ethers are normally mixtures of homologues with wide EO distribution, the effect of EO number on the properties of the products as well as the optimum EO number is not clear. This research is thus aimed to synthesize a series of double dodecyl polyoxyethylene(n) ether methyl carboxyl betaines with mono distributed EO number(n=2, 3, 4) and to examine the effect of n value on properties.Firstly, dodecanol polyoxyethylene ether, C12EOnOH(n=2, 3, 4), were synthesized using bromododecane and diethylene glycol/triethylene glycol/tetraethylene glycol as starting materials. Then the intermediate didodecyl polyoxyethylene(n) ether methyl amines, di C12EOnA(n=2, 3, 4) were synthesized by chlorination and condensation with monomethyl amine. Finally the target products, di C12EOnB(n=2, 3, 4), were obtained by reaction with lithium chloroacetate. The molecular structure of synthesized products was confirmed to be in good agreement with that of the target molecules by Mass spectra and 1HNMR.The water solubility, basic surface activity, ability in reducing n-alkane/water IFT and Daqing crude oil/connate water IFT, as well as the adsorption at quartz/water interface of the synthesized products were systematically evaluated. The results show that the solubility of di C12EOnB(n=2, 3, 4) in aqueous solution at 25 °C increases with increasing EO number, and the di C12EO4 B gives a solubility of 1.5′10-4 mol/L, about three times that of di C12 B. di C12EOnB(n=2, 3, 4) in general keep the high surface activities of di C12 B, with the cmc being(1.15~2.0)′10-5 mol/L, gcmc being 27.0~29.5 m N/m, saturated adsorption at air/water interface being(6.2~5.7)′10-10mol/cm2, respectively. The cmc, gcmc, as well as a￥, the cross section area at air/water interface, increases with increasing EO number in general. For reducing n-alkane/water ITF, di C12EOnB(n=2, 3, 4) solely are better than di C12 B, where di C12EO2 B and di C12EO4 B solely can reduce C13~C15 alkane/water IFT and C7~C9 alkane/water to 10-3 m N/m magnitude, respectively, and di C12EO3 B solely can reduce C7~C16 alkane/water IFT to 10-2 m N/m magnitude. Di C12EOnB(n=2, 3, 4) solely can reduce Daqing crude oil/connate water IFT to 10-2 m N/m magnitude. For obtaining ultralow IFT, di C12EO2 B is still too hydrophobic, but can reduce Daqing crude oil/connate water IFT to ultralow by mixing with hydrophilic homologues, hexadecyl dimethyl carboxyl betaine(C16B), at a wide(1.25~7.5 mmol/L) total concentration range; di C12EO3 B is slightly too hydrophobic, although it can reduce Daqing crude oil/connate water IFT to ultralow by mixing with C16 B, the total working concentration is relatively narrow(5~7.5 mmol/L); whereas di C12EO4 B is slightly too hydrophilic, which can reduce Daqing crude oil/connate water IFT to ultralow by mixing with di C12 B and C16 B at a wide(0.625~5.0 mmol/L) total concentration range. Di C12EO2 B is the best among the three products in this respect. The adsorption of di C12EOnB(n=2, 3, 4) at quartz/water interface at 45 °C displays a saturated adsorption, which decreases with increasing EO number, where di C12EO4 B gives lowest adsorption, about 35% that of di C12 B. The effect in reducing adsorption at quartz/water interface by introducing EO group into surfactant molecules with double long alkyl chains seems to be not significant.