鼠李糖脂液-固界面润湿改性机制

Interaction Mechanism between Rhamnolipid Biosurfactant and Hydrophobic Glass Surface

生物表面活性剂为一种特定微生物代谢产生的具有表面活性的物质,通过在岩石表面的吸附来达到改变其润湿性的目的,而润湿改性机制对油藏提高采收率至关重要。通过接触角的测定、洗油砂评价、液-固界面自由能计算及分子动力学模拟等方法,研究了鼠李糖脂表面活性剂与疏水Si O_(2)表面间的相互作用,并对其吸附特性和润湿改性机制进行了阐释。结果表明,鼠李糖脂可快速改善亲油玻片表面的润湿性。经10%鼠李糖脂溶液浸泡12 h后,亲油玻片的接触角从111.6°降至32.7°。鼠李糖脂溶液对油砂的最佳洗油有效加量为30%,洗油效率可达84.83%,原油黏附功降低了98.4%。通过液-固界面自由能计算得到去离子水与鼠李糖脂溶液作用后的亲油玻片间的自由能为-140.2 m J/m^(2),远低于去离子水与原始亲油玻片间的自由能(-52.1 m J/m^(2))。分子模拟计算结果表明,鼠李糖脂分子主要通过氢键这一强作用力吸附在亲水Si O_(2)表面,其与亲水界面的吸附结合能达到29.7 e V;而鼠李糖脂分子与疏水Si O_(2)表面的作用力为静电力和范德华力等弱作用力,导致其与疏水界面的吸附结合能仅为12.2 e V。结合液-固界面自由能和分子模拟计算结果推测,鼠李糖脂分子相较于原油极性分子具有更强的界面竞争吸附能力,从而使其易于锚定到亲水表面、最终替换油性分子,达到提高洗油效率的目的。研究结果可为构建以鼠李糖脂为主的生物润湿调控驱油体系提供理论支撑。

Biosurfactant is a specific natural surfactant produced by the microorganism.Its adsorption on rock surface has a great impact on the change of reservoir wettability.The mechanism of wettability alteration is crucial to the oil recovery.In this paper,the interaction between rhamnolipid biosurfactant and hydrophobic glass surface was studied by contact angle experiment,oil displacement experiment,free energy of liquid-solid interface measurement and molecular dynamics simulation,explaining the adsorption effect of rhamnolipid biosurfactant on the hydrophobic glass surface’s wettability.The results showed that the wettability of hydrophobic slide could be rapidly altered by rhamnolipid biosurfactant.Once the rhamnolipid biosurfactant adsorbed on the hydrophobic glass surface lasting for 12 h,the contact angle could be dramatically decreased from 111.6°to 32.7°.The optimum dosage of rhamnolipid biosurfactant to extract oil from oilsands was 30%,resulting in the better oil displacement efficiency(i.e.,84.83%)and the lower adhesion force(0.2 mN/m).Furthermore,the free energy between deionized water and hydrophobic glass slide treated by rhamnolipid solution using the liquid-solid interface free energy formula was-140.2 mJ/m^(2),which was much lower than that between deionized water and original hydrophobic glass slide(-52.1 mJ/m^(2)).On the other hand,based on the molecular simulation,the rhamnolipid molecules could quickly adsorb on the hydrophilic surface via hydrogen bonds(strong interaction force),while both the electrostatic force and van der Waals force(weak interaction force)were the main interaction forces between rhamnolipid molecules and hydrophobic surface.Therefore,the adsorption binding energy between rhamnolipid molecules and hydrophilic surface(29.7 eV)was much higher than that between molecule and hydrophobic surface(12.2 eV),leading to the stronger interfacial competitive adsorption capacity of rhamnolipid molecules compared to asphaltenes.In other words,according to the free energy calculation and molecular simulation results,rhamnolipid molecules would easily anchor to the hydrophilic surface and“sweep off”the oil molecule,resulting in higher oil displacement efficiency.This paper provided an insight to construct an effective wetting control flooding system based on rhamnolipid biosurfactants.