Anti-Agglomerants Performance in Hydrates Management: Fundamental Insights

天然气水合物既代表了甲烷气体形式的一种可能的能源，也可以为长期的二氧化碳储存提供一种策略。在石油和天然气的管道运输过程中，天然气水合物也是一个麻烦，它们的形成会阻塞甚至有时会破坏管道，造成巨大的环境破坏。包括BP和E-ON在内的行业每年投资约5亿美元在管道中注入甲醇。不幸的是，要想有效，甲醇的含量必须超过重量的20%，有时高达输送流体的50%。随着生产油井越来越多地从陆上炼油设施中移除，随着生产油井的老化，导致出水量增加，迫切需要新的策略。目前的项目侧重于替代化学品，这些化学品应该是有效的(1)在低重量部分，以减少通过管道输送和泵送的流体量；(2)在低温和长时间下，要有效地通过全程管道到达远离海岸的油井；(3)在含有大量水的系统中，允许开采老化井，这些井会产生大量的水和石油和天然气。在这个项目中，这些化学物质被称为抗凝聚剂（AAs），它们在低至5%体积比的浓度下可以有效。巴斯夫，斯伦贝谢，壳牌，冠军和哈里伯顿生产和配制抗团聚剂。虽然人们认为AAs允许小的水合物颗粒形成，然后阻止它们聚集成大的塞，但它们的作用机制尚不清楚。因此，他们的发现是基于对从给定油气井中提取的流体的系统进行的长时间的试错协议。为了能够系统地发现新的有效原子吸收剂，本文提出的基础研究重点是其分子作用机制。分子模型和大规模计算机模拟将与详细的微观和宏观实验协同作用，用于特定类别的抗团聚剂。这些化合物含有三个疏水尾部和一个延伸的亲水头部，包括羧基和季铵离子。之所以选择这些分子，是因为宏观实验观察表明，在保持分子其余部分完整的情况下，只要改变其中一条疏水尾部的2-6个碳原子的长度，它们的性能就会从优异变差。我们的假设是在水合物颗粒上形成的原子吸收膜的分子结构影响其生长机制。通过初步模拟确定了两种可能的机制：(1)水合物的聚集；(2)水通过AAs膜的渗透。在不同的实验条件下（例如，不同的盐浓度），两种机制中的一种可能起主导作用。提出的研究旨在首先了解和量化各种实验条件下原子吸收剂的分子作用机制，然后了解可以调整哪些原子吸收剂的分子特征以最大化其性能。预期的基本结果不仅与更好地理解水合物管理有关，而且与更好地理解所有结晶过程中涉及的分子机制有关。这些过程发生在许多行业（例如，制药，特种化学品，涂料，食品）中，这些行业代表了英国高科技制造业的支柱。将受到拟议研究积极影响的部门包括能源、制造、化工和环境。

Gas hydrates represent both a possible energy source in the form of methane gas, and could provide a strategy for long-term CO2 repository. Gas hydrates are also a nuisance during the transport of oil and gas via pipelines, where their formation can block and sometimes break the pipeline, causing large environmental damages. The industry, including BP and E-ON, invests ~$500 million per year injecting methanol in pipelines. Unfortunately, methanol, to be effective, needs to be present in amounts exceeding 20% by weight, sometimes up to 50% of the transported fluid.As the productive oil wells become more and more removed from onshore refining facilities, and as productive oil wells age, leading to increased amount of water produced, new strategies are desperately needed. The present project focuses on alternative chemicals that should be effective (1) at low weight fraction to reduce the amount of fluids transported and pumped through the pipelines; (2) at low temperature and for long time, to be effective through the entire length of the pipelines needed to reach the wells far from shore; and (3) in systems that contain large amounts of water, to allow the exploitation of ageing wells, which produce large amounts of water together with oil and gas.These chemicals, considered in this project, are known as anti agglomerants (AAs), and they can be effective at concentrations as low as 5% by volume. BASF, Schlumberger, Shell, Champion and Halliburton manufacture and formulate anti-agglomerants. Although it is believed that AAs allow small hydrate particles to form, and then prevent their agglomeration into large plugs, their mechanism of action is not well understood. Consequently, their discovery is based on lengthy trial-and-error protocols conducted on systems representative of the fluids extracted from given oil and gas wells.To enable the systematic discovery of new effective AAs, the fundamental research proposed here focuses on their molecular mechanism of action. Molecular modelling and massive computer simulations will be implemented, in synergism with detailed micro- and macro-scopic experiments, for a specific class of anti-agglomerants. These compounds contain three hydrophobic tails, and one extended hydrate-philic head that comprises both carboxylic and quaternary ammonium ions. These molecules have been chosen because macroscopic experimental observations show that by changing the length of one of the hydrophobic tails by just 2-6 carbon atoms, while maintaining the rest of the molecule intact, changes their performance from excellent to poor. Our hypothesis is that the molecular structure of a film of AAs formed on a hydrate particle affects the growth mechanism. Two possible mechanisms have been identified by preliminary simulations: (1) aggregation of hydrates, and (2) penetration of water through the AAs film. It is possible that one of the two mechanisms acts as the dominant one at different experimental conditions (e.g., varying salt concentration). The proposed research is designed to first understand and quantify the molecular mechanisms of action of the AAs under various experimental conditions, and then to understand which AAs molecular features can be tuned to maximise their performance.The fundamental results expected are relevant not only for better understanding hydrates management, but also for better understanding the molecular mechanisms involved in all crystallisation processes. Such processes occur in a number of industries (e.g., pharmaceuticals, specialty chemicals, coatings, foodstuff) that represent the backbone of UK high tech manufacturing. The sectors that will be positively impacted by the proposed research include energy, manufacturing, chemicals and environment.