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

[0854210]天然存在的甲烷水合物吸引了大量公众的关注，因为它们作为未来的能源提供了巨大的潜力。人工包合物形式的气体储存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，经济是因为40 bar的气体储存密度与200 bar的压缩气体相当。另一方面，在加工线内形成的水合物堵塞对天然气和石油工业来说是一个麻烦。加速或延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天然气水合物颗粒与表面活性剂之间多尺度相互作用的理解。为了对比这些相互作用，我们将研究甲烷（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，但不会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纳米），初始生长（1 ìm）和层状和凝聚生长（1毫米）。差示扫描量热法将通过对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。通过共聚焦和透射电子显微镜研究水合物生长的不同阶段，了解表面活性剂对CH4和CO2水合物晶体大小和孔隙率的不同影响。智力优势：需要验证的一个重要假设是，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，所研究的吸附机制将导致对表面活性剂在微观观察中实现不同形态和天然气水合物形成速率的作用的基本理解。新的微观界面结构中子散射研究将阐明油-水合物-水界面表面活性剂的构型和功能。这些关于水合物形态和界面现象的知识将与宏观的、体积相反应的放大实验联系起来。更广泛的影响：对表面活性剂和水合物抑制剂的活性作用的基本理解使液相水分子能够控制自组装成固体气体水合物。这种理解可以用于安全天然气储存和二氧化碳封存所需的快速天然气水合物形成，同时也可以用于研究每年花费10亿美元用于甲醇作为水合物抑制剂的经济替代品。这项研究将由两个机构密切合作进行，一个是博士学位授予学校（CCNY），一个是本科文理学院（Hamilton）。pi将通过现有项目吸引代表性不足的高中学生，并通过两所大学之间的夏季研究交流项目积极吸引本科生和研究生。他们将研究天然气水合物辅助二氧化碳从烟道气中分离，将这一过程的热力学、动力学、界面科学/工程和设计方面纳入汉密尔顿大学和纽约大学的本科生和研究生课程。本课题由两个CBET项目资助：界面过程和热力学；过程与反应工程

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