自稳定CO2开关智能泡沫的研究

The biggest step evidenced from foam research community is the emerging of ultrastable foams and smart aqueous foams which respond to the environmental stimuli. The triggers used are limited within traditional ones such as thermo, UV/Vis, magnetic field, pH; only one-way response other than switchability; the dispersing phase is composed of air or nitrogen, and the formulation is rather complex. Based on such a background, we proposed the concept of “self-stabilized CO2-switchable foams” which will be formulated by dispersing CO2 in water, along with CO2-sensitive ultra-long chain tertiary amines as a foam stabilizer. When reacting with CO2 in the wet environment, these tertiary amines will be protonated into cationic ammonium surfactants, which will further self-assemble into wormlike micelles, showing macroscopically viscoelasticity of the aqueous solution. Such viscoelastic micelles will adsorb at the CO2/water interface to prevent the coalescence from neighboring bubbles, the coarsening resulted from gas diffusion between different bubbles, as well as the fast gravity drainage of the liquid inside the foam channels. As a consequence, the as-prepared foams will be stabilized, and CO2 plays dual roles as both dispersing phase and a trigger. When CO2 is depleted by air or neutralized by ammonia, the quarternized surfactant will be deprotonated back to tertiary amines, thus diminish the viscosity, and finally rupture the formed foams. By this way, these foams are expected to show unique switchability. Moreover, if the foams are closed under high pressure and high temperature, the tertiary amines will be always protonated and the self-assembled wormlike micelles will continuously function as foam stabilizers, thus indefinitely stable foams may be obtained. Great efforts will be devoted to uncover the stabilizing mechanism from such ultra-long chain tertiary amines, to correlate molecular structural parameters, temperature, and pressure with foam stability and switchability. The results can diversify the smart foams and to further enrich the foam stabilization mechanism. As for practical end use, the developed CO2 foams may find potential applications in enhanced oil recovery process and volumetric fracturing for producing unconventional oil and gas, particularly shale gas.

超稳泡沫和智能泡沫一直是胶体分散体系研究的重点，但智能泡沫仍局限于传统刺激因子，多为单向响应，需要额外的刺激源，研究多在常温、常压下进行。为此，拟以CO2同时作为分散相和刺激因子，以超长链叔胺为起泡剂和稳定剂构筑自稳定CO2开关泡沫：叔胺被CO2水溶液质子化后自组装成蠕虫状胶束，可在液膜中形成粘弹性网络结构，维持泡沫的稳定性；在高温、高压密闭环境中，表面活性剂一直处于质子化状态和蠕虫状胶束组装体，可望得到超稳泡沫；循环通入和排出CO2可改变超长链叔胺的表面活性和自组装行为，预期能实现CO2泡沫的可逆开关。将从微观—介观—宏观三个层次建立表面活性剂分子结构、气—液界面性质、环境因素与泡沫性能的内在关系，从微观角度揭示超长链叔胺表面活性剂的稳泡和开关机理。研究结果在理论上可丰富智能泡沫种类和发展稳泡机理，在实践上有望为CO2泡沫用于三次采油、页岩气等非常规油气开采提供理论支持。

智能水基泡沫是软物质的发展方向之一，过去十年得到了快速发展部，但其种类较少、寿命较短，高温高压环境下的性能鲜见报道。本项目以长链表面活性剂为起泡剂，CO2为起泡气体，系统开展了如下工作。第一，设计、合成了长链脂肪叔胺（UC22AMPM），以其为起泡剂分别在常温常温（25oC，0.1 MPa）和高温高压（100 oC，100 MPa）环境下构建了稳定的CO2水基泡沫。第二，多维度阐明了UC22AMPM的稳泡机理。CO2存在下，UC22AMPM在水溶液中被质子化并转变为阳离子表面活性剂（UC22AMPMH+），降低了溶液的表面张力，促进泡沫产生。同时，UC22AMPM.H+在泡沫液膜中自组装形成蠕虫状胶束，提高了泡沫液膜的粘弹性，增强泡沫的稳定性。在此体系中UC22AMPM.H+同时扮演了起泡剂和稳泡剂的角色，而CO2则充当了起泡气体和刺激因子。第三，利用高温高压泡沫仪、高温高压流变仪以及高温高压小角中子散射仪揭示了UC22AMPM-CO2泡沫在高温高压环境下的演变过程：温度升高，泡沫体相溶液黏度下降，排液加快，液膜变薄，导致气泡间粗化和聚并加速，泡沫稳定性降低；压力增加，气泡间粗化速率减慢，液膜厚度保持不变，抑制液膜的破裂，泡沫寿命延长。第四，设计并构建具有温度可逆开关特性的泡沫体系。设计、合成了具有温度响应性的表面活性剂分子ESAB，以其为起泡剂制备水基泡沫，发现其在25 oC时仅有少量泡沫生成且迅速消失。随着温度升至80 oC，ESAB泡沫的高度及寿命也相应的增加，具有“高温起泡，低温消泡”的温度开关性能。将改性的纤维素纳米晶与ESAB结合，构建了一种能耐120 oC且仍保持温度响应特性的泡沫体系。第五，模拟新疆油田储层条件，考察了十二烷基苯磺酸钠（SDBS）和重烷基苯磺酸盐对原油的增溶能力，明确了油相在胶束中的增溶位置。还通过微流控技术，对表面活性剂驱油过程中的原位乳化进行系统性研究，揭示了原位乳化对提高采收率的内在机制。.基于本项目的研究，发表SCI论文16篇；专著1章，国内外学术会议邀请报告6次；获得中国发明专利3件；PCT国际专利1件；培养博士研究生、硕士研究生各1名。