Influence mechanism of free guest molecules in liquid phase on decomposition kinetics of CO₂-CH₄ hydrates

doi:10.11949/0438-1157.20250409

CIESC Journal ›› 2025, Vol. 76 ›› Issue (10): 5336-5350.DOI: 10.11949/0438-1157.20250409

• Energy and environmental engineering • Previous Articles Next Articles

Influence mechanism of free guest molecules in liquid phase on decomposition kinetics of CO₂-CH₄ hydrates

Shangfei SONG¹(), Yunchao LI¹, Wenyu WU¹, Yumo ZHU¹, Qingyun LIAO², Najia LIAO³, Bohui SHI¹(), Jing GONG¹

^1.National Engineering Research Center for Safe Oil & Gas Pipeline Transportation, Beijing Key Laboratory of Urban Gas Distribution Technology, Key Laboratory of Petroleum Engineering of the Ministry of Education, College of Mechanical and Storage & Transportation Engineering, China University of Petroleum, Beijing 102249, China
^2.Tianfu Yongxing Laboratory, Research Center for New Principles and Technology of Carbon Capture, Chengdu 610213, Sichuan, China
^3.Sinopec Engineering Incorporation, Beijing 100101, China

Received:2025-04-17 Revised:2025-07-22 Online:2025-11-25 Published:2025-10-25
Contact: Bohui SHI

液相游离客体分子对CO₂-CH₄水合物分解动力学的影响机理

宋尚飞¹(), 李匀超¹, 吴文宇¹, 朱羽墨¹, 廖清云², 廖那伽³, 史博会¹(), 宫敬¹

^1.中国石油大学（北京）机械与储运工程学院，油气管道输送安全国家工程研究中心，城市燃气输配技术北京市重点实验室，石油工程教育部重点实验室，北京 102249
^2.CO2捕集新原理与技术研究中心，天府永兴实验室，四川成都 610213
^3.中国石化工程建设公司，北京 100101

通讯作者: 史博会
作者简介:宋尚飞（1993—），男，博士，副教授，song.sf@cup.edu.cn
基金资助:
国家自然科学基金项目(52104069);北京市自然科学基金项目(3232030);国家重点研发计划项目(2022YFC2806200);中国博士后科学基金项目(2022M713460);中国石油大学(北京)科学基金项目(2462023BJRC018);中国石油大学(北京)科学基金项目(2462020YXZZ045)

Abstract

Abstract:

During the development of combustible ice, timely decomposition and removal of hydrates in the drainage and production system is an important task to ensure flow safety during offshore combustible ice development. To address the unclear mechanisms of synergistic effects between free guest molecules and nanobubble formation in the liquid phase on CO₂-CH₄ hydrate decomposition kinetics, this study employed molecular dynamics simulations to construct a CO₂-CH₄ hydrate system with a 1∶1 guest molecule ratio and 100% cage occupancy. Under varying temperature conditions, controlled quantities of CO₂ or CH₄ molecules were introduced into the liquid phase to simulate and analyze the effects of mole fraction variations and nanobubble formation on hydrate decomposition rates. The results demonstrate that elevated concentrations of free guest molecules in the liquid phase accelerate CO₂-CH₄ hydrate decomposition. In particular, free guest molecules form larger-scale bubbles that dramatically enhance decomposition kinetics.

Key words: molecular simulation, gas hydrates, nanobubbles, methane, carbon dioxide

摘要：

在可燃冰开发过程中，及时分解、清除排采系统中的水合物，是海域可燃冰开发过程中流动安全保障的重要工作。针对液相中游离客体分子及纳米气泡对CO₂-CH₄水合物分解动力学的协同作用机制尚未明晰、亟待系统探究的问题，本研究采用分子动力学方法构建了CO₂与CH₄分子比例为1∶1且孔穴占有率为100%的CO₂-CH₄水合物体系，在不同温度条件下，通过在液相中加入不同数量的CO₂或CH₄分子，模拟并观察其摩尔分数变化以及纳米气泡的出现对水合物分解速率的影响。研究结果表明，液相中存在的高浓度游离客体分子促进了CO₂-CH₄水合物的分解。游离客体分子在液相中形成较大尺寸的气泡，显著加快了水合物的分解速率。

关键词: 分子模拟, 水合物, 纳米气泡, 甲烷, 二氧化碳

CLC Number:

TE 31

Shangfei SONG, Yunchao LI, Wenyu WU, Yumo ZHU, Qingyun LIAO, Najia LIAO, Bohui SHI, Jing GONG. Influence mechanism of free guest molecules in liquid phase on decomposition kinetics of CO₂-CH₄ hydrates[J]. CIESC Journal, 2025, 76(10): 5336-5350.

宋尚飞, 李匀超, 吴文宇, 朱羽墨, 廖清云, 廖那伽, 史博会, 宫敬. 液相游离客体分子对CO₂-CH₄水合物分解动力学的影响机理[J]. 化工学报, 2025, 76(10): 5336-5350.

Figures/Tables 20

Fig.1 Schematic diagram of the process of CO2 substitution and depressurization method for mining combustible ice (adapted from Ref.[3] )

Fig.2 CO2-CH4 hydrate system with a molecular quantity ratio of 1∶1 (red spheres represent O atom, cyan spheres represent C atom, and white spheres represent H atom)

Table 1 Parameters of simulation systems for CO₂-CH₄ hydrate decomposition kinetic at 280 K

编号	模拟编号	液相中客体分子种类	液相中客体分子摩尔分数/%	液相中客体分子数量
1	1-0	—	0	0
2	M1-1	CH₄	1	15
3	M1-5	CH₄	5	75
4	M1-10	CH₄	10	150
5	M1-12	CH₄	12	180
6	M1-15	CH₄	15	225
7	C1-1	CO₂	1	15
8	C1-5	CO₂	5	75
9	C1-10	CO₂	10	150
10	C1-12	CO₂	12	180
11	C1-15	CO₂	15	225

Fig.3 Simulated snapshot of hydrate decomposition process at different time points (10—500 ps) of M2-12(blue spheres represent methane molecules, yellow spheres represent carbon dioxide molecules, bold solid red lines indicate the structural framework formed by water molecules in the hydrate, and dashed red lines denote hydrogen bonds formed by water molecules in the liquid phase，the blue circle is a nanobubble，all simulation snapshots adopt the same representation scheme )

Fig.4 Simulated snapshot of hydrate decomposition process at different time points (10—500 ps) of M2-15

Fig.5 Simulated snapshot of hydrate decomposition process at different time points (600—800 ps) of M2-12

Fig. 6 Simulated snapshot of hydrate decomposition process at different time points (600—2000 ps) of M2-1

Fig.7 Simulated snapshot of hydrate decomposition process at different time points (600—2000 ps) of M2-5

Fig.8 Simulated snapshot of hydrate decomposition process at different time points (600—2000 ps) of M2-10

Fig.9 The F4φ of different systems containing different amounts of guest molecules in the liquid phase at 280 K and 0.5 MPa

Fig.10 The F4φ of different systems containing different amounts of guest molecules in the liquid phase at 290 K and 0.5 MPa

Fig.11 The F4φ of different systems containing different amounts of guest molecules in the liquid phase at 300 K and 0.5 MPa

Fig.12 Total number of fixed guest molecules in the decomposition process of CO2-CH4 hydrate at 280 K and 0.5 MPa

Fig.13 Total number of fixed guest molecules in the decomposition process of CO2-CH4 hydrate at 290 K and 0.5 MPa

Fig.14 Total number of fixed guest molecules in the decomposition process of CO2-CH4 hydrate at 300 K and 0.5 MPa

Fig.15 RDF of M2-1：(a) RDF between CH4 molecules; (b) RDF between CO2 molecules; (c) RDF between CH4 molecules and H2O molecules; (d) RDF between CO2 molecules and H2O molecules

Fig.16 RDF of M2-5：(a) RDF between CH4 molecules; (b) RDF between CO2 molecules; (c) RDF between CH4 molecules and H2O molecules; (d) RDF between CO2 molecules and H2O molecules

Fig.17 RDF of M2-10：(a) RDF between CH4 molecules; (b) RDF between CO2 molecules; (c) RDF between CH4 molecules and H2O molecules; (d) RDF between CO2 molecules and H2O molecules

Fig.18 (a) F4φ value during the decomposition of CO2-CH4 hydrate at 290 K and 0.5 MPa; (b) The decomposition rate of CO2-CH4 hydrate characterized by the decreasing rate of F4φ value; (c) MSD during the decomposition of CO2-CH4 hydrate at 290 K and 0.5 MPa

Table 2 The nucleation time of nanobubbles and the time required for the accumulation of guest molecules to 50 and 100

模拟编号	液相中客体分子摩尔分数/%	纳米气泡形成时间/ps	纳米气泡内分子数达到50个的时刻/ps	纳米气泡内分子数达到100个的时刻/ps
M2-1	1	5750	7075	7335
M2-5	5	1245	3210	4225
M2-10	10	215	740	1405
M2-12	12	0	270	640
M2-15	15	0	55	325

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