Effect of complex inhibitors containing ionic liquids and PVP K90 on formation of methane hydrate

doi:10.11949/0438-1157.20200342

Abstract

Abstract:

Injecting inhibitors is the most commonly used method in the oil and gas industry to solve the problem of blockage caused by hydrate formation during pipeline transportation. However, most of the kinetic hydrate inhibitors (KHIs) are strictly limited by weak inhibition performance and low subcooling. Ionic liquids, a kind of green solvent, have been recognized to act as excellent thermodynamic inhibitors on methane hydrate formation. So, it is proposed to add the ionic liquids into KHIs to improve their overall performance. In this paper, the kinetic effects of an ionic liquid N-butyl-N-methylpyrrolidine tetrafluoroborate ([BMP][BF₄]), a commercial kinetic inhibitor polyvinyl pyrrolidone (PVP K90) and their mixtures with different mass ratios on the methane hydrate formation were experimentally studied at 8.0 K subcooling and two concentrations [1.0%(mass) and 2.0%(mass)]. The best mass ratio of the compound inhibitor was determined. Moreover, the crystal structures and cage occupancy characteristics of methane hydrates formed without and with inhibitors at different mass concentrations and composition ratios were measured by using powder X-ray diffraction (PXRD) and low-temperature Laser Raman spectrometers. It was found that the addition of inhibitors did not change the crystal structure of methane hydrate, but affected the cage occupancies and hydration numbers. Based on the results from macroscopic kinetics and microscopic structure tests, the inhibition mechanism of compound inhibitors was proposed.

Key words: hydrate, ionic liquids, kinetics, Raman spectroscopy, microscopic test

摘要：

注入抑制剂是油气行业解决管道输送过程因水合物生成而引发的堵塞问题最常用的方法。但现有大多数动力学抑制剂（KHIs）存在抑制性能不足、高过冷度条件下会失效等问题，可应用场合大大受限。离子液体作为绿色溶剂对甲烷水合物具有良好的热力学抑制作用。为改进KHIs的性能，提出将离子液体与KHIs复合。本文实验考察8.0 K过冷度、两种浓度下[1.0%(质量)、2.0%(质量)]离子液体N-丁基-N-甲基吡咯烷四氟硼酸盐([BMP][BF₄])、聚乙烯基吡咯烷酮（PVP K90）以及二者复配构成的复合型抑制剂对甲烷水合物抑制规律，得到了最佳组分配比。利用粉末X射线衍射（PXRD）和低温激光拉曼光谱测量了不同抑制剂体系中形成的甲烷水合物晶体微观结构和晶穴占有率，发现添加抑制剂不会改变sI型甲烷水合物晶体结构，但会影响水合物晶体的大、小笼占有率和水合数。结合宏观动力学实验和微观结构测试结果，揭示离子液体与PVP K90复合抑制剂的抑制机理。

关键词: 水合物, 离子液体, 动力学, 拉曼光谱, 微观测试

CLC Number:

TK 123

Junjie REN,Zhen LONG,Deqing LIANG. Effect of complex inhibitors containing ionic liquids and PVP K90 on formation of methane hydrate[J]. CIESC Journal, 2020, 71(11): 5256-5264.

任俊杰,龙臻,梁德青. 离子液体与PVP K90复合抑制剂对甲烷水合物的生成影响[J]. 化工学报, 2020, 71(11): 5256-5264.

Figures/Tables 12

Fig.1 Schematic of the experimental apparatus

Table 1 List of the materials used for the experiments

试剂	缩写	摩尔质量/(g·mol^-1)	纯度/%	供应商
N-丁基-N-甲基吡咯烷四氟硼酸盐	[BMP][BF₄]	229.07	≥ 99	中科院兰州化学物理研究所
聚乙烯基吡咯烷酮 K90	PVP K90	360000		梯希爱（上海）化成工业发展有限公司
甲烷气体	CH₄	16	≥ 99.99	佛山市科的气体有限公司
去离子水	H₂O	18		实验室自制

Fig.2 Chemical structure of [BMP][BF4] and PVP K90

Fig.3 Changes of pressures versus time for methane hydrates with solutions containing different inhibitors at 1.0%(mass) and 2.0%(mass)

Fig.4 Induction time of methane hydrate formation in the presence of 1.0%(mass) and 2.0%(mass) [BMP][BF4] and the mixture of [BMP][BF4] with PVP (ratio of 1∶1)

Fig.5 Changes of pressures varying with time for methane hydrate formed with 2.0%(mass) composite inhibitors at different ratios

Fig.6 Gas consumption curves with time under different ratio of composite inhibitors within the first 200 minutes

Fig.7 PXRD patterns for hydrate samples formed from CH4 with different systems

Fig.8 Raman spectra of the C—H stretching mode for CH4 incorporated into hydrate formed with different systems

Table 2 Hydrate numbers and cage occupancies of methane hydrate formed in the presence of various inhibitors

反应体系	小笼占有率θ_S	大笼占有率θ_L	水合数n
无 (纯水)	0.936±0.080	0.946±0.041	6.095±0.124
IL	0.832±0.011	0.977±0.004	6.125±0.015
PVP	0.896±0.051	0.971±0.007	6.036±0.048
[PVP+IL](1∶4)	0.947±0.043	0.963±0.011	5.994±0.015
[PVP+IL](1∶2)	0.924±0.035	0.969±0.005	6.003±0.033
[PVP+IL](1∶1)	0.819±0.159	0.944±0.063	6.300±0.072
[PVP+IL](2∶1)	0.905±0.086	0.948±0.048	6.136±0.111
[PVP+IL](4∶1)	0.930±0.098	0.925±0.072	6.211±0.196

Fig.9 Relationship of occupancy of large and small cages by CH4 gas in hydrate and hydration number between different ratio of the compound inhibitor

Fig.10 Schematic diagram of the effect of compound inhibitor on CH4 hydrate formation

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