Molecular dynamics simulation of nanobubble evolution characteristics during synthesis of methane-doped hydrogen storage hydrate

doi:10.11949/0438-1157.20250480

Abstract

Abstract:

Hydrogen storage in hydrates offers advantages of environmental friendliness and high economic efficiency, and has broad application prospects in energy storage. In the early stages of hydrate synthesis, gas molecules tend to form supersaturated states, which in turn induce the formation of nanobubbles and affect the hydrogen storage efficiency of hydrates. Therefore, this paper takes nanobubbles as the research object and adopts the molecular dynamics method to analyze the evolution law of nanobubbles and explore the influence of nanobubble evolution process on gas molecular diffusion, water molecular order and gas interaction during the synthesis of hydrogen-storage hydrates using a mixture of methane and hydrogen gases. The results show that the formation of nanobubbles undergoes an expansion phase and a stabilization phase, effectively promoting gas molecule diffusion. However, the promoting effect of nanobubbles on methane molecules is stronger than that on hydrogen molecules, which affects the hydrogen-storage density of hydrates. Nanobubbles improve the order of water molecules during the expansion phase, and the order of water molecules gradually tends to be constant during the stabilization phase. Hydrogen molecules tend to accumulate in the central region of the nanobubble, while methane molecules are enriched at the gas-liquid interface. Although this distribution is conducive to hydrate nucleation, it may affect the hydrogen content in hydrate structures.

Key words: hydrogen, hydrate, methane, molecular simulation, nanobubbles

摘要：

水合物储氢具有环境友好、经济性高的优点，在储能领域具有广阔的应用前景。水合物合成前期易形成气体分子的过饱和状态，进而诱导生成纳米气泡，这会对水合物储氢效率产生影响。因此，本文以纳米气泡为研究对象，采用分子动力学数值模拟方法，围绕甲烷与氢气混合气体合成储氢水合物阶段，分析纳米气泡的演化规律，探究纳米气泡演化过程对气体分子扩散、水分子有序度和气体相互作用的影响。结果表明，纳米气泡的生成经历膨胀期与稳定期，可有效促进气体分子扩散。但纳米气泡对甲烷分子的促进作用强于对氢气分子，进而影响水合物的储氢密度。纳米气泡在膨胀期会提升水分子的有序度，在稳定期水分子的有序度逐渐趋于恒定。气泡内部的氢气分子倾向于在中心区域聚集分布，甲烷分子则富集于气液界面，该分布特征虽利于水合物成核，却可能影响水合物结构内的氢气含量。

关键词: 氢, 水合物, 甲烷, 分子模拟, 纳米气泡

CLC Number:

O 643.1

Yufei ZENG, Tianqi TANG, Yurong HE. Molecular dynamics simulation of nanobubble evolution characteristics during synthesis of methane-doped hydrogen storage hydrate[J]. CIESC Journal, 2025, 76(11): 5617-5629.

曾宇飞, 唐天琪, 何玉荣. 掺甲烷储氢水合物合成过程纳米气泡演化特性分子动力学模拟研究[J]. 化工学报, 2025, 76(11): 5617-5629.

Figures/Tables 19

Fig.1 Molecular models

Fig.2 Conformation of the simulation system at the initial moment

Table 1 Interaction parameters and atomic charges of simulation systems［26.28-31］

原子	摩尔质量/(g/mol)	势能参数ε/(kJ/mol)	势能参数σ/nm	电荷量q/e
H₂O
O	16.000	0.882	0.317	0
H	1.008	0	0	0.590
M（virtual site）	0	0	0	-1.178
CH₄
C	12.011	0.276	0.035	-0.240
H	1.008	0.125	0.250	0.060
H₂
H	1.008	0	0	0.590

Fig.3 Characteristic peaks radial distribution function curves and schematic diagrams

Table 2 Comparison of the positions of characteristic wave peaks

波峰	$r i'$ /Å	文献^[36]		文献^[37]
波峰	$r i'$ /Å	r_i /Å	φ/%	r_i /Å	φ/%
第一波峰	2.76	2.71	1.8	2.76	0
第二波峰	4.52	4.43	1.9	4.54	0.4
第三波峰	6.46	6.33	2.0	6.34	1.9

Table 2 Comparison of the positions of characteristic wave peaks

波峰	$r i'$ /Å	文献^[36]		文献^[37]
波峰	$r i'$ /Å	r_i /Å	φ/%	r_i /Å	φ/%
第一波峰	2.76	2.71	1.8	2.76	0
第二波峰	4.52	4.43	1.9	4.54	0.4
第三波峰	6.46	6.33	2.0	6.34	1.9

Fig.4 Initial and 400 ps molecular conformation of hydrogen storage hydrate crystals

Fig.5 Mean square displacement curves of propane, hydrogen and water molecules in the simulation system

Fig.6 Normalized density curves of water molecules in the reaction system at different moments

Fig.7 Temporal evolution of nanobubble radius and relative radius increment

Fig.8 Molecular conformation of the mixed system at different moments

Fig.9 Mean squared displacement of methane molecules at characteristic moments

Fig.10 Mean squared displacement of hydrogen molecules at characteristic moments

Table 3 Diffusion coefficients of hydrogen molecules and methane molecules at characteristic moments

气体分子	D₀/(10³ cm²/s)	D₁/(10³ cm²/s)	μ₁	D₁₀₀/(10³ cm²/s)	μ₁₀₀	D₂₀₀/(10³ cm²/s)	μ₂₀₀
氢气	1.14	1.72	0.509	2.12	0.860	1.91	0.675
甲烷	0.488	1.08	1.21	1.55	2.18	1.49	2.05

Fig.11 Radial distribution function curves of gas molecules and water molecules at characteristic moments

Fig.12 Change curve of the four-body order parameter

Fig.13 F4 function at characteristic moments under different bubble states

Fig.14 Normalized density curves at different distances from nanobubbles

Fig.15 Radial distribution function curves between gas molecules

Fig.16 Radial distribution function curves between gas molecules and water molecules

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