Multi-Scale Investigation of the Role of Surface-Active Agents in Gas Hydrate Formation Kinetics

自然产生的甲烷水合物引起了公众的极大关注，因为它们提供了作为未来能源的巨大潜力。人工包合物形式的气体存储是一种安全和经济的选择，安全是因为气体从水合物容器中缓慢释放减少了爆炸危险，并且经济是因为40bar的气体存储密度与200bar的压缩气体相当。另一方面，在加工生产线内形成的水合物堵塞对天然气和石油行业来说是一种滋扰。加速或减缓水合物形成的一个关键障碍是缺乏对水合物形成过程中气体水合物颗粒和表面活性物质之间多尺度相互作用的了解。为了对比这些相互作用，将研究甲烷(CH4)和二氧化碳(CO2)水合物体系，因为表面活性剂通常会加速CH4水合物的形成，但不影响甚至阻碍二氧化碳水合物的形成。水合物形成的三个连续阶段将在不同的长度尺度上进行分析：成核(100 Nm)、初始生长(1？m)和层状和团聚生长(1 Mm)。差示扫描量热法将通过相变的统计测量来量化表面活性剂对天然气水合物成核的影响。水合物生长的不同阶段将通过共聚焦和透射电子显微镜进行研究，以了解表面活性剂如何在水合物晶体尺寸和孔隙率方面对CH4和CO2水合物产生不同的影响。智力价值：有待检验的一个重要假设是，表面活性分子在水合物表面的吸附而不是它们在体相中的胶束化是加速和抑制天然气水合物形成的主要原因。作为拟议研究的一部分，将对吸附机理进行研究，这将有助于从微观观察的角度从根本上理解表面活性剂在实现不同形态和天然气水合物形成速率方面的作用。对微观界面结构的新型中子散射研究将阐明油-水合物-水界面上表面活性剂的结构和功能。这些关于水合物形态和界面现象的知识将与体相反应的宏观放大实验相联系。更广泛的影响：对表面活性剂和水合物抑制剂的积极作用的基本了解，使液态水分子能够受控地自组装成固态气体水合物。这一认识可用于安全储存天然气和封存二氧化碳所需的快速天然气水合物的形成，同时也可用于研究一种经济的替代方案，以替代每年花费10亿美元在甲醇上作为水合物抑制剂。这项研究将由两个机构密切合作进行，一所授予博士学位的学校(CCNY)和一所本科生文科学院(汉密尔顿)。PIs将通过现有的项目吸引代表不足的高中生，并将通过两所机构之间的暑期研究交流项目积极吸引本科生和研究生。他们将研究气体水合物辅助从废气中分离二氧化碳，以将该过程的热力学、动力学、界面科学/工程和设计方面纳入汉密尔顿大学和CCNY的本科生和研究生课程。该项目得到了两个CBET项目的支持：界面过程和热力学；过程和反应工程

0854210LeeNaturally-occurring methane hydrates have attracted a lot of public attention because they provide enormous potential as a future energy source. Gas storage in the artificial clathrate form is a safe and economical option, safe because the slow release of gas from a container of hydrate reduces explosion hazards, and economical because the gas storage density at 40 bar is comparable to a compressed gas at 200 bar. On the other hand, hydrate plugs formed inside processing lines are a nuisance to gas and oil industries. A critical obstacle to accelerating or retarding hydrate formation is a lack of understanding of the multi-scale interactions between gas hydrate particles and surface-active agents during hydrate formation. To contrast these interactions, methane (CH4) and carbon dioxide (CO2) hydrate systems will be investigated because surface-active agents generally accelerate CH4 hydrate formation but do not affect or even hinder CO2 hydrate formation. Three sequential stages of hydrate formation will be analyzed at different length scales: nucleation (100 nm), initial growth ( 1 ìm), and layered & agglomerated growth ( 1 mm). Differential scanning calorimetry will be used to quantify the effect of surface-active agents on gas hydrate nucleation by statistical measurements of phase-transitions. The different stages of hydrate growth will be investigated by confocal and transmission electron microscopes to understand how surface-active agents differently affect CH4 and CO2 hydrates in terms of hydrate crystal sizes and porosities. Intellectual Merit: An important hypothesis to be tested is that the adsorption of surface-active molecules onto the hydrate surface rather than their micellization in bulk phase is the main reason for accelerating and inhibiting gas hydrate formation. The adsorption mechanisms to be studied as part of the proposed research will lead to a fundamental understanding of the role of surface-active agents in achieving different morphologies and formation rates of gas hydrates in terms of the microscopic observations. Novel neutron scattering studies of the microscopic, interfacial structure will clarify the configuration and functionality of surface-active agents at the oil-hydrate-water interface. This knowledge on hydrate morphologies and interfacial phenomena will be connected to the macroscopic, scale-up experiments of bulk-phase reaction. Broader Impact: The fundamental understanding of the active role of surfactants and hydrate inhibitors enables controlled self-assembly of liquid-phase water molecules into solid gas hydrates. This understanding can be utilized for fast gas hydrate formation needed for safe natural gas storage and CO2 sequestration, while it can also be used for the investigation of an economical alternative to the 1 billion dollars per year spent on methanol as a hydrate inhibitor. This research will be performed by a close collaboration of two institutions, a Ph.D. granting school (CCNY) and an undergraduate liberal-arts college (Hamilton). The PIs will engage underrepresented high school students via existing programs and will actively involve undergraduate students and graduate students via a summer research exchange program between the two institutions. They will investigate gas hydrate-aided CO2 separation from flue gas to incorporate the thermodynamic, kinetic, interfacial science/engineering, and design aspects of this process into the undergraduate and graduate classes at Hamilton and CCNY.This project is supported by two CBET programs: Interfacial Processes and Thermodynamics; Process and Reaction Engineering