天然气水合物纳米促进剂的制备及作用机理研究

As a clean energy, natural gas has aroused more and more attention and efficient storage and transportation methods are critical for utilizing natural gas. Natural gas hydrates have been viewed as a potential technique for natural gas storage and transportation due to the high storage capacity and mild storage condition; and how to achieve the rapid formation of gas hydrates together with high storage capacity is the key to utilize this technique. Surfactants have been confirmed with efficient promotion to gas hydrate formation, however, the existence of surfactants will cause lots of foam generated during hydrate dissociation, which not only impacts the application of gas hydrates, but also leads to the loss of surfactants. In this program, we would firstly prepare functional group-coated nano-promoters by grafting the hydrophilic groups of surfactants on the surface of polymer nanospheres through soap-free emulsion polymerization. Afterwards, we would graft nano-metal particles on the surface of the functional group-coated nanospheres through electrostatic adsorption and in-situ reduce to prepare functional group & nano-metal coated nanopromoters. Moreover, we could achieve the property control during the preparation of the nanopromoters. Whereafter, the novel nano-promoters would be applied for methane hydrates to study the effects and mechanisms during hydrate formation and dissociation. Moreover, the dynamic models of methane hydrate formation-dissociation under the existence of nano-promoters would also be developed based on the numerical simulation. This program would be carried out with the expectation of improving the promotion efficiency and avoiding the defects of surfactants, such as, foam generation and poor recycling performance, which would be of great significance to the hydrate-based natural gas storage and transportation.

天然气作为清洁能源受到越来越多关注，合理有效的储运手段是利用天然气的关键；天然气水合物因储气量高、存储条件温和而被视为极具潜力的天然气储运技术，如何实现水合物的快速生成和高储气量是利用该技术的关键；尽管表面活性剂可以有效促进水合物的生成，但导致水合物分解过程产生大量泡沫，不利于水合物技术的应用，且导致表面活性剂的流失。本项目通过无皂乳液聚合将表面活性剂亲水基团以共价键连接在聚合物纳米球表面制备功能基团包覆的纳米促进剂，通过静电吸附-原位还原将金属粒子接枝在聚合物纳米球表面制备功能基团&金属粒子包覆的纳米促进剂，并通过实验手段实现纳米促进剂性能可控；然后将纳米促进剂应用于甲烷水合物，研究其对水合物生成分解过程的作用及作用机理，并通过数值模拟建立纳米促进剂存在时甲烷水合物动力学模型，在提高促进效果的同时改善表面活性剂易产生泡沫、循环利用差等缺陷，对水合物储运天然气技术的发展和应用具有重要意义.

天然气水合物因储气量高（150-170 v/v）、存储条件温和（-15~-20 ℃、常压）而被视为极具应用潜力的天然气储运技术，而如何实现水合物的快速生成和高储气量是利用该技术的关键。本项目立足于-SO3-/-SO4-型表面活性剂优异的水合物促进效果，通过分子组装技术构建了基于纳米球载体的-SO3-型高效水合物纳米促进剂。. 首先，通过调控-SO3-型十二烷基苯磺酸钠SDBS浓度以及无皂乳液聚合实现了-SO3-型水合物促进剂形态结构可控，包括：分子游离态、胶束态、无定型大分子聚集态、单分散纳米球态，探究了-SO3-的聚集形态对其促进效果的作用，结果表明当-SO3-固载于纳米球表面时（-SO3-@PSNS）可达到最佳促进效果，在浓度为1 mmol/L、静止条件下，甲烷水合物生成诱导期为6.5±3.7 min，生长过程在35-40 min完成，储气量可达146±5.1 v/v，但是生成的水合物结构松散、表观密度较低。. 然后，通过无皂乳液聚合制备了基于纳米球固载不同活性基团（-SO3-、-COO-、-N(CH3)3+）的水合物纳米促进剂，-SO3-@PSNS可以有效促进水合物的生成，但水合物结构疏松、表观密度较低，而-COO-@PSNS和-N(CH3)3+@PSNS可以明显提高水合物的致密度，但水合物的生成速率大大降低。因此，本研究中将-COO-和-SO3-同时固载于纳米球表面（-SO3-&-COO-@PSNS），通过调控-COO-和-SO3-的比例实现了甲烷水合物生成速率及表观密度的协同可控，当-SO3-和-COO-比例为2:1、300 rpm磁子搅拌下，甲烷水合物诱导期为6.3±2.4 min、生长过程在45 min完成、结构致密且储气量可达143±2.6 v/v。. 最后，将纳米金属粒子（Ag）亦固载于纳米球表面成功构建了基于纳米球同时固载活性基团及纳米金属粒子的新型水合物纳米促进剂（Ag&-SO3-@PSNS），固载于纳米球表面的-SO3-和银粒子可以在液相中更稳定的存在、且与水分子有更好的接触，从而导致更优异的促进效果。在0.5 mmol/L、300 rpm磁子搅拌条件下，甲烷水合物生成过程在1 h完成、储气量可达150 v/v，并且在10次水合物生成-分解实验中表现出优异循环使用性能，对水合物技术的产业化应用具有重要价值。